Co-reporter:David H. Woen, Guo P. Chen, Joseph W. Ziller, Timothy J. Boyle, Filipp Furche, and William J. Evans
Journal of the American Chemical Society October 25, 2017 Volume 139(Issue 42) pp:14861-14861
Publication Date(Web):September 28, 2017
DOI:10.1021/jacs.7b08456
The first (N═N)2– complex of a rare-earth metal with an end-on dinitrogen bridge, {K(crypt)}2{[(R2N)3Sc]2[μ-η1:η1-N2]} (crypt = 2.2.2-cryptand, R = SiMe3), has been isolated from the reduction of Sc(NR2)3 under dinitrogen at −35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically characterized rare-earth metal (N═N)2– complexes of formula [A2Ln(THF)x]2[μ-η2:η2-N2] (Ln = Sc, Y, and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide, and aryloxide). The 1.221(3) Å N—N distance and the 1644 cm–1 Raman stretch are consistent with the presence of an (N═N)2– bridge. The observed paramagnetism of the complex by Evans method measurements is consistent with DFT calculations that suggest a triplet (3A2) ground state in D3 symmetry involving two degenerate Sc—N2—Sc bonding orbitals. Upon brief exposure of the orange Sc3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc2+ complex, [K(crypt)][Sc(NR2)3], was observed. Conversion of the Sc2+ complex to the Sc3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)}2{[(R2N)3Sc]2[μ-η1:η1-N2]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system.
Co-reporter:Cory J. Windorff, Megan T. Dumas, Joseph W. Ziller, Andrew J. Gaunt, Stosh A. Kozimor, and William J. Evans
Inorganic Chemistry October 2, 2017 Volume 56(Issue 19) pp:11981-11981
Publication Date(Web):September 15, 2017
DOI:10.1021/acs.inorgchem.7b01968
Small-scale reactions of the Pu analogues La, Ce, and Nd have been explored in order to optimize reaction conditions for milligram scale reactions of radioactive plutonium starting from the metal. Oxidation of these lanthanide metals with iodine in ether and pyridine has been studied, and LnI3(Et2O)x (1-Ln; x = 0.75–1.9) and LnI3(py)4 (2-Ln; py = pyridine, NC5H5) have been synthesized on scales ranging from 15 mg to 2 g. The THF adducts LnI3(THF)4 (3-Ln) were synthesized by dissolving 1-Ln in THF. The viability of these small-scale samples as starting materials for amide and cyclopentadienyl f-element complexes was tested by reacting KN(SiMe3)2, KCp′ (Cp′ = C5H4SiMe3), KCp′′ (Cp′′ = C5H3(SiMe3)2-1,3), and KC5Me4H with 1-Ln generated in situ. These reactions produced Ln[N(SiMe3)2]3 (4-Ln), Cp′3Ln (5-Ln), Cp″3Ln (6-Ln), and (C5Me4H)3Ln (7-Ln), respectively. Small-scale samples of Cp′3Ce (5-Ce) and Cp′3Nd (5-Nd) were reduced with potassium graphite (KC8) in the presence of 2.2.2-cryptand to check the viability of generating the crystallographically characterizable Ln2+ complexes [K(2.2.2-cryptand)][Cp′3Ln] (8-Ln; Ln = Ce, Nd).
Co-reporter:Cory J. Windorff, Guo P. Chen, Justin N. Cross, William J. Evans, Filipp Furche, Andrew J. Gaunt, Michael T. Janicke, Stosh A. Kozimor, and Brian L. Scott
Journal of the American Chemical Society March 22, 2017 Volume 139(Issue 11) pp:3970-3970
Publication Date(Web):February 24, 2017
DOI:10.1021/jacs.7b00706
Over 70 years of chemical investigations have shown that plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0 and +3 to +7), and four different oxidation states can exist simultaneously in solution. We report a new formal oxidation state for plutonium, namely Pu2+ in [K(2.2.2-cryptand)][PuIICp″3], Cp″ = C5H3(SiMe3)2. The synthetic precursor PuIIICp″3 is also reported, comprising the first structural characterization of a Pu–C bond. Absorption spectroscopy and DFT calculations indicate that the Pu2+ ion has predominantly a 5f6 electron configuration with some 6d mixing.
Co-reporter:Selvan Demir, Monica D. Boshart, Jordan F. Corbey, David H. Woen, Miguel I. Gonzalez, Joseph W. Ziller, Katie R. Meihaus, Jeffrey R. Long, and William J. Evans
Inorganic Chemistry December 18, 2017 Volume 56(Issue 24) pp:15049-15049
Publication Date(Web):November 22, 2017
DOI:10.1021/acs.inorgchem.7b02390
We report the serendipitous discovery and magnetic characterization of a dysprosium bis(ammonia) metallocene complex, [(C5Me5)2Dy(NH3)2](BPh4) (1), isolated in the course of performing a well-established synthesis of the unsolvated cationic complex [(C5Me5)2Dy][(μ-Ph)2BPh2]. While side reactivity studies suggest that this bis(ammonia) species owes its initial incidence to impurities in the DyCl3(H2O)x starting material, we were able to independently prepare 1 and its tetrahydrofuran (THF) derivative, [(C5Me5)2Dy(NH3)(THF)](BPh4) (2), from the reaction of [(C5Me5)2Dy][(μ-Ph)2BPh2] with ammonia in THF. The low-symmetry complex 1 exhibits slow magnetic relaxation under zero applied direct-current (dc) field to temperatures as high as 46 K and notably exhibits an effective barrier to magnetic relaxation that is more than 150% greater than that previously reported for the [(C5Me5)2Ln][(μ-Ph)2BPh2] precursor. On the basis of fitting of the temperature-dependent relaxation data, magnetic relaxation is found to occur via Orbach, Raman, and quantum-tunneling relaxation processes, and the latter process can be suppressed by the application of a 1400 Oe dc field. Field-cooled and zero-field-cooled dc magnetic susceptibility measurements reveal a divergence at 4 K indicative of magnetic blocking, and magnetic hysteresis was observed up to 5.2 K. These results illustrate the surprises and advantages that the lanthanides continue to offer for synthetic chemists and magnetochemists alike.
Co-reporter:Megan E. Fieser;Maryline G. Ferrier;Jing Su;Enrique Batista;Samantha K. Cary;Jonathan W. Engle;Juan S. Lezama Pacheco;Stosh A. Kozimor;Angela C. Olson;Austin J. Ryan;Benjamin W. Stein;Gregory L. Wagner;David H. Woen;Tonya Vitova;Ping Yang
Chemical Science (2010-Present) 2017 vol. 8(Issue 9) pp:6076-6091
Publication Date(Web):2017/08/21
DOI:10.1039/C7SC00825B
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31− (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31− (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31− (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4fn 5d1 configurations (not 4fn+1 5d0). In these 4fn 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a′ symmetry that made the 4fn 5d1 electronic configurations lower in energy than the more typical 4fn+1 5d0 configuration.
Co-reporter:Daniel N. Huh;Christopher M. Kotyk;Milan Gembicky;Arnold L. Rheingold;Joseph W. Ziller
Chemical Communications 2017 vol. 53(Issue 62) pp:8664-8666
Publication Date(Web):2017/08/01
DOI:10.1039/C7CC04396A
Cp′2Ln(THF)2 metallocenes (Cp′ = C5H4SiMe3) react with 2.2.2-cryptand (crypt) to form Ln2+-in-crypt complexes, [Ln(crypt)(THF)][Cp′3Ln]2 (Ln = Sm, Eu) and [Yb(crypt)][Cp'3Yb]2, that contain Ln2+ ions surrounded only by neutral ligands. A bimetallic, mixed-ligand metallocene/opened-crypt complex of Sm2+, [Sm(C16H32N2O6-κ2O:κ2O′)SmCp′′2], was obtained by KC8 reduction of Cp′′2Sm(THF) [Cp′′ = C5H3(SiMe3)2] in the presence of crypt.
Co-reporter:Megan E. Fieser;Chad T. Palumbo;Henry S. La Pierre;Dominik P. Halter;Vamsee K. Voora;Joseph W. Ziller;Filipp Furche;Karsten Meyer
Chemical Science (2010-Present) 2017 vol. 8(Issue 11) pp:7424-7433
Publication Date(Web):2017/10/23
DOI:10.1039/C7SC02337E
A new series of Ln3+ and Ln2+ complexes has been synthesized using the tris(aryloxide)arene ligand system, ((Ad,MeArO)3mes)3−, recently used to isolate a complex of U2+. The triphenol precursor, (Ad,MeArOH)3mes, reacts with the Ln3+ amides, Ln(NR2)3 (R = SiMe3), to form a series of [((Ad,MeArO)3mes)Ln] complexes, 1-Ln. Crystallographic characterization was achieved for Ln = Nd, Gd, Dy, and Er. The complexes 1-Ln can be reduced with potassium graphite in the presence of 2.2.2-cryptand (crypt) to form highly absorbing solutions with properties consistent with Ln2+ complexes, [K(crypt)][((Ad,MeArO)3mes)Ln], 2-Ln. The synthesis of the Nd2+ complex [K(crypt)][((Ad,MeArO)3mes)Nd], 2-Nd, was unambiguously confirmed by X-ray crystallography. In the case of the other lanthanides, crystals were found to contain mixtures of 2-Ln co-crystallized with either a Ln3+ hydride complex, [K(crypt)][((Ad,MeArO)3mes)LnH], 3-Ln, for Ln = Gd, Dy, and Er, or a hydroxide complex, [K(crypt)][((Ad,MeArO)3mes)Ln(OH)], 4-Ln, for Ln = Dy. A Dy2+ complex with 18-crown-6 as the potassium chelator, [K(18-crown-6)(THF)2][((Ad,MeArO)3mes)Dy], 5-Dy, was isolated as a co-crystallized mixture with the Dy3+ hydride complex, [K(18-crown-6)(THF)2][((Ad,MeArO)3mes)DyH], 6-Dy. Structural comparisons of 1-Ln and 2-Ln are presented with respect to their uranium analogs and correlated with density functional theory calculations on their electronic structures.
Co-reporter:Megan T. Dumas, Guo P. Chen, Jasper Y. Hu, Mitchell A. Nascimento, Jeremy M. Rawson, Joseph W. Ziller, Filipp Furche, William J. Evans
Journal of Organometallic Chemistry 2017 Volumes 849–850(Volumes 849–850) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.jorganchem.2017.05.057
•Synthesis of bimetallic and trimetallic rare-earth metal hydrides.•Reduction of bimetallic yttrium, dysprosium, and terbium hydrides and chlorides.•DFT suggests reduction of bimetallics could lead to metal-metal bond character.•EPR evidence for a metal-based radical on yttrium.The reductive chemistry of [Cp'2Ln(μ–H)(THF)x]y [Ln = Y, Dy, Tb; Cp' = (C5H4SiMe3)1−; x = 2, 0 and y = 2, 3] was examined to determine if these hydrides would be viable precursors for 4fn5d1 Ln2+ ions that could form 5d1-5d1 metal–metal bonded complexes. The hydrides were prepared by reaction of the chlorides, [Cp'2Ln(μ–Cl)]2, 1-Ln, with allylmagnesium chloride to form the allyl complexes, [Cp'2Y(η3–C3H5)(THF)], 2-Ln, which were hydrogenolyzed. The solvent-free reaction of solid 2-Ln with 60 psi of H2 gas in a Fischer-Porter apparatus produced, in the Y case, the trimetallic species, [Cp'2Y(μ–H)]3, 3-Y, and in the Dy and Tb cases, the bimetallic complexes [Cp'2Ln(μ–H)(THF)]2, 4-Ln (Ln = Dy, Tb). The latter complexes could be converted to 3-Dy and 3-Tb by heating under vacuum. Isopiestic data indicate that 3-Y solvates to 4-Y in THF. Reductions of 4-Y, 4-Dy, and 4-Tb with KC8 in the presence of a chelate such as 2.2.2-cryptand or 18-crown-6 all gave reaction products with intense dark colors characteristic of Ln2+ ions. In the yttrium case, with either chelating agent, the dark green product gives a rhombic EPR spectrum (g1 = 2.01, g2 = 1.99, g3 = 1.98, A = 24.1 G) at 77 K. However, the only crystallographically-characterizable products obtainable from these solutions were Ln3+ polyhydride anion complexes of composition, [K(chelate)]{[Cp'2Ln(μ–H)]3(μ–H)}. Reduction of 1-Y with KC8 in the presence of 2.2.2-cryptand also yields an intensely colored product with an axial EPR spectrum (gx = gy = 2.05, Ax = Ay = 35.5 G; gz = 2.07, Az = 34.5) similar to that of (Cp'3Y)1− ion, but crystals were not obtained from this system.Download high-res image (129KB)Download full-size image
Co-reporter:Ryan R. Langeslay; Megan E. Fieser; Joseph W. Ziller; Filipp Furche
Journal of the American Chemical Society 2016 Volume 138(Issue 12) pp:4036-4045
Publication Date(Web):March 15, 2016
DOI:10.1021/jacs.5b11508
The reactivity of the recently discovered Th2+ complex [K(18-crown-6)(THF)2][Cp″3Th], 1 [Cp′′ = C5H3(SiMe3)2-1,3], with hydrogen reagents has been investigated and found to provide syntheses of new classes of thorium hydride compounds. Complex 1 reacts with [Et3NH][BPh4] to form the terminal Th4+ hydride complex Cp″3ThH, 2, a reaction that formally involves a net two-electron reduction. Complex 1 also reacts in the solid state and in solution with H2 to form a mixed-valent bimetallic product, [K(18-crown-6)(Et2O)][Cp″2ThH2]2, 3, which was analyzed by X-ray crystallography, electron paramagnetic resonance and optical spectroscopy, and density functional theory. The existence of 3, which formally contains Th3+ and Th4+, suggested that KC8 could reduce [(C5Me5)2ThH2]2. In the presence of 18-crown-6, this reaction forms an analogous mixed-valent product formulated as [K(18-crown-6)(THF)][(C5Me5)2ThH2]2, 4. A similar complex with (C5Me4H)1– ligands was not obtained, but reaction of (C5Me4H)3Th with H2 in the presence of KC8 and 2.2.2-cryptand at −45 °C produced two monometallic hydride products, namely, (C5Me4H)3ThH, 5, and [K(2.2.2-cryptand)]{(C5Me4H)2[η1:η5-C5Me3H(CH2)]ThH]}, 6. Complex 6 contains a metalated tetramethylcyclopentadienyl dianion, [C5Me3H(CH2)]2–, that binds in a tuck-in mode.
Co-reporter:William J. Evans
Organometallics 2016 Volume 35(Issue 18) pp:3088-3100
Publication Date(Web):September 15, 2016
DOI:10.1021/acs.organomet.6b00466
A fundamental aspect of any element is the range of oxidation states accessible for useful chemistry. This tutorial describes the recent expansion of the number of oxidation states available to the rare-earth and actinide metals in molecular complexes that has resulted through organometallic chemistry involving the cyclopentadienyl ligand. These discoveries demonstrate that the cyclopentadienyl ligand, which has been a key component in the development of organometallic chemistry since the seminal discovery of ferrocene in the 1950s, continues to contribute to the advancement of science. Background information on the rare-earth and actinide elements is presented, as well as the sequence of events that led to these unexpected developments in the oxidation state chemistry of these metals.
Co-reporter:Jordan F. Corbey, David H. Woen, Joseph W. Ziller, William J. Evans
Polyhedron 2016 Volume 103(Part A) pp:44-50
Publication Date(Web):8 January 2016
DOI:10.1016/j.poly.2015.09.002
The coordination chemistry of MeCN, tBuCN, and PhCN with the cationic rare earth metallocene complexes [(C5Me5)2Ln][(μ-Ph)2BPh2], 1-Ln (Ln = Y, La, Gd), has been examined to determine how nitrile coordination will affect the metallocene geometry. Crystallographic determination of geometry was possible for [(C5Me5)2Ln(NCMe)3][BPh4] (2-Y, 2-Gd), [(C5Me5)2Y(NCtBu)3][BPh4] (3-Y), and [(C5Me5)2Ln(NCPh)3][BPh4] (4-La, 4-Gd). In each case, only three nitriles are found to coordinate and the metallocenes are bent with (C5Me5 ring centroid)–metal–(C5Me5 ring centroid) angles of 137–140°. The THF adduct, [(C5Me5)2La(NCMe)2(THF)][BPh4], 5-La, was also crystallographically characterized. A similar result was observed with the yttrium metallocene of the trimethylsilyl-containing ligand (C5H4SiMe3)1−: coordination of only three nitriles is found in [(C5H4SiMe3)2Y(NCMe)3][BPh4], 6-Y, which has a 136.8° (C5Me5 ring centroid)–Y–(C5Me5 ring centroid) angle.In the presence of excess amounts of MeCN, tBuCN, and PhCN, the cationic rare earth tetraphenylborate complexes [(C5Me5)2Ln][(μ-Ph)2BPh2] form complexes containing just three nitriles [(C5Me5)2Ln(NCR)3][BPh4], which have bent metallocene geometries with 137–140° (C5Me5 ring centroid)–metal–(C5Me5 ring centroid) angles.
Co-reporter:Christopher L. Webster, Ryan R. Langeslay, Joseph W. Ziller, and William J. Evans
Organometallics 2016 Volume 35(Issue 4) pp:520-527
Publication Date(Web):February 9, 2016
DOI:10.1021/acs.organomet.5b00942
Tetrabutylammonium chloride and nitrate salts react with (C5Me5)2UCl2 to expand the coordination sphere of the metallocene to form the formal 9- and 10-coordinate complexes, [NBu4][(C5Me5)2UCl2(NO3)], 1, and [NBu4][(C5Me5)2UCl2(NO3)], 2, respectively. Complex 2 displays modified reactivity compared to that of (C5Me5)2UCl2 in substitution reactions with Khpp [hpp =1,3,4,6,7,8-hexahydro-2H-pyrimido(1,2-a)pyrimidine] and K(NC4Me4) in the synthesis of (C5Me5)2U(hpp)Cl, (C5Me5)U(hpp)3, and (C5Me5)2U(NC4Me4)Cl. The U3+ complex, [NBu4][(C5Me5)2UCl2], can be formed by reduction of 2 with K(Hg), as well as with KC5Me5, K2C8H8, and Li3N.
Co-reporter:Matthew R. MacDonald; Ryan R. Langeslay; Joseph W. Ziller
Journal of the American Chemical Society 2015 Volume 137(Issue 46) pp:14716-14725
Publication Date(Web):November 12, 2015
DOI:10.1021/jacs.5b08597
(C5Me5)2Y(μ-Ph)2BPh2, 1, reacted with ethyllithium at −15 °C to make (C5Me5)2Y(CH2CH3), 2, which is thermally unstable at room temperature and formed the C–H bond activation product, (C5Me5)2Y(μ-H)(μ-η1:η5-CH2C5Me4)Y(C5Me5), 3, containing a metalated (C5Me5)1– ligand. Spectroscopic evidence for 2 was obtained at low temperature, and trapping experiments with iPrNCNiPr and CO2 gave the Y–CH2CH3 insertion products, (C5Me5)2Y[iPrNC(Et)NiPr-κ2N,N′], 4, and [(C5Me5)2Y(μ-O2CEt)]2, 5. Although 2 is highly reactive, low temperature isolation methods allowed the isolation of single crystals which revealed an 82.6(2)° Y–CH2–CH3 bond angle consistent with an agostic structure in the solid state. Complex 2 reacted with benzene and toluene to make (C5Me5)2YPh, 7, and (C5Me5)2YCH2Ph, 8, respectively. The reaction of 2 with [(C5Me5)2YCl]2 formed (C5Me5)2Y(μ-Cl)(μ-η1:η5-CH2C5Me4)Y(C5Me5) in which a (C5Me5)1– ligand was metalated. C–H bond activation also occurred with methane which reacted with 2 to make [(C5Me5)2YMe]2, 9.
Co-reporter:Katie R. Meihaus; Megan E. Fieser; Jordan F. Corbey; William J. Evans;Jeffrey R. Long
Journal of the American Chemical Society 2015 Volume 137(Issue 31) pp:9855-9860
Publication Date(Web):July 13, 2015
DOI:10.1021/jacs.5b03710
The recently reported series of divalent lanthanide complex salts, namely [K(2.2.2-cryptand)][Cp′3Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp′ = C5H4SiMe3) and the analogous trivalent complexes, Cp′3Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp′3Dy]− and [Cp′3Ho]− exhibit magnetic moments of 11.3 and 11.4 μB, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4fn+1 configuration for Ln = Sm, Eu, Tm and a 4fn5d1 configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an LS coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets.
Co-reporter:Ryan R. Langeslay, Megan E. Fieser, Joseph W. Ziller, Filipp Furche and William J. Evans
Chemical Science 2015 vol. 6(Issue 1) pp:517-521
Publication Date(Web):03 Nov 2014
DOI:10.1039/C4SC03033H
Reduction of the Th3+ complex Cp′′3Th, 1 [Cp′′ = C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp′′3Th], 2, a complex containing thorium in the formal +2 oxidation state. Reaction of 1 with KC8 in the presence of 18-crown-6 generates the analogous Th2+ compound, [K(18-crown-6)(THF)2][Cp′′3Th], 3. Complexes 2 and 3 form dark green solutions in THF with ε = 23000 M−1 cm−1, but crystallize as dichroic dark blue/red crystals. X-ray crystallography revealed that the anions in 2 and 3 have trigonal planar coordination geometries, with 2.521 and 2.525 Å Th–(Cp′′ ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp′′3Th)1− is consistent with a 6d2 ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp′′2Th(C8H8), 4, and [K(18-crown-6)]Cp′′.
Co-reporter:Christopher M. Kotyk, Megan E. Fieser, Chad T. Palumbo, Joseph W. Ziller, Lucy E. Darago, Jeffrey R. Long, Filipp Furche and William J. Evans
Chemical Science 2015 vol. 6(Issue 12) pp:7267-7273
Publication Date(Web):21 Sep 2015
DOI:10.1039/C5SC02486B
A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp′′3Ln)1− and (Cp′3Ln)1− (Cp′′ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2− ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1−. The intensely colored (ε = ∼8000 M−1 cm−1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)].
Co-reporter:Jordan F. Corbey; Ming Fang; Joseph W. Ziller
Inorganic Chemistry 2015 Volume 54(Issue 3) pp:801-807
Publication Date(Web):August 28, 2014
DOI:10.1021/ic501753x
The reactivity of the (N2)2– complex {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2) (1) with sulfur and selenium has been studied to explore the special reductive chemistry of this complex and to expand the variety of bimetallic rare-earth amide complexes. Complex 1 reacts with elemental sulfur to form a mixture of compounds, 2, that is the first example of cocrystallized complexes of (S2)2– and S2– ligands. The crystals of 2 contain both the (μ-S2)2– complex {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-S2) (3) and the (μ-S)2– complex {[(Me3Si)2N]2Y(THF)}2(μ-S) (4), respectively. Modeling of the crystal data of 2 shows a 9:1 ratio of 3:4 in the crystals of 2 obtained from solutions that have 1:1 to 4:1 ratios of 3/4 by 1H NMR spectroscopy. The addition of KC8 to samples of 2 allows for the isolation of single crystals of 4. The [S3N(SiMe3)2]− ligand was isolated for the first time in crystals of [(Me3Si)2N]2Y[η2-S3N(SiMe3)2](THF) (5), obtained from the mother liquor of 2. In contrast to the sulfur chemistry, the (μ-Se2)2– analogue of 3, namely, {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-Se2) (6), can be cleanly synthesized in good yield by reacting 1, with elemental selenium. The (μ-Se)2– analogue of 4, namely, {[(Me3Si)2N]2Y(THF)}2(μ-Se) (7), was synthesized from Ph3PSe.
Co-reporter:Douglas R. Kindra, Jeffrey K. Peterson, Joseph W. Ziller, and William J. Evans
Organometallics 2015 Volume 34(Issue 1) pp:395-397
Publication Date(Web):December 23, 2014
DOI:10.1021/om5010786
The first crystallographic characterization of bismuth complexes containing benzyl ligands is reported. The NCN pincer ligand complex, Ar′BiCl2 [Ar′ = 2,6-(Me2NCH2)2C6H3], reacts with (PhCH2)MgCl to form Ar′Bi(η1-CH2Ph)2 in high yield. X-ray crystallography and spectroscopic studies confirm η1-bonding of the benzyl ligands in Ar′Bi(η1-CH2Ph)2 as well as in the homoleptic Bi(η1-CH2Ph)3.
Co-reporter:Linus Appel;Jennifer Leduc;Christopher L. Webster;Dr. Joseph W. Ziller;Dr. William J. Evans;Dr. Sanjay Mathur
Angewandte Chemie International Edition 2015 Volume 54( Issue 7) pp:2209-2213
Publication Date(Web):
DOI:10.1002/anie.201409606
Abstract
Four air-stable, volatile uranium heteroarylalkenolates have been synthesized and characterized by three synthetic approaches and their gas phase deposition to uranium oxide films has been examined.
Co-reporter:Megan E. Fieser, Casey W. Johnson, Jefferson E. Bates, Joseph W. Ziller, Filipp Furche, and William J. Evans
Organometallics 2015 Volume 34(Issue 17) pp:4387-4393
Publication Date(Web):August 26, 2015
DOI:10.1021/acs.organomet.5b00613
Dinitrogen can be reduced by photochemical activation of the trivalent rare-earth-metal bis(pentamethylcyclopentadienyl) allyl complexes (C5Me5)2Ln(η3-C3H4R) (Ln = Y, Lu; R = H, Me) to form the (N═N)2– complexes [(C5Me5)2Ln]2(μ-η2:η2-N2). This demonstrates that productive organolanthanide photochemistry is not limited to complexes of the unusual (η3-C5Me4H)− ligand in the heteroleptic complexes (C5Me5)2(C5Me4H)Ln and (C5Me5)(C5Me4H)2Ln. Photolytic activation of (C5Me5)2Ln(η3-C3H5) (Ln = Y, Lu) in the presence of isoprene provides a rare photopolymerization route to polyisoprene. Sulfur can also be reduced by photolysis of (C5Me5)2Ln(η3-C3H5) (Ln = Y, Lu) to generate the (S)2– complexes, [(C5Me5)2Ln]2(μ-S), which have variable Ln–S–Ln angles depending on crystallization conditions.
Co-reporter:Jordan F. Corbey, David H. Woen, Chad T. Palumbo, Megan E. Fieser, Joseph W. Ziller, Filipp Furche, and William J. Evans
Organometallics 2015 Volume 34(Issue 15) pp:3909-3921
Publication Date(Web):July 28, 2015
DOI:10.1021/acs.organomet.5b00500
The tris(cyclopentadienyl) yttrium complexes Cp3Y(THF), CpMe3Y(THF), Cp″3Y, Cp″2YCp, and Cp″2YCpMe [Cp = C5H5, CpMe = C5H4Me, Cp″ = C5H3(SiMe3)2] have been treated with potassium graphite in the presence of 2.2.2-cryptand to search for more stable examples of complexes featuring the recently discovered Y2+ ion first isolated in [K(18-crown-6)][Cp′3Y] and [K(2.2.2-cryptand)][Cp′3Y], 1-Y (Cp′ = C5H4SiMe3). Reduction of the tris(cyclopentadienyl) complexes generates dark solutions like that of 1-Y, and the EPR spectra contain doublets with g values between 1.990 and 1.991 and hyperfine coupling constants of 34–47 gauss that are consistent with the presence of Y2+. [K(2.2.2-cryptand)][Cp″2YCp], 2-Y, was characterizable by X-ray crystallography. Reduction of the Cp″3Gd, Cp″2GdCp, and Cp″2GdCpMe complexes containing the larger metal gadolinium were also examined. In each case, dark solutions and EPR spectra like that of [K(2.2.2-cryptand)][Cp′3Gd], 1-Gd, were obtained, and [K(2.2.2-cryptand)][Cp″2GdCp], 2-Gd, was crystallographically characterizable. None of the new yttrium and gadolinium complexes displayed greater stability than 1-Y and 1-Gd. Exploration of this reduction chemistry with indenyl ligands did not give evidence for +2 complexes. The only definitive information obtained from reductions of the CpIn3Ln (CpIn = C9H7, Ln = Y, Ho, Dy) complexes was the X-ray crystal structure of {K(2.2.2-cryptand)}2{[(C9H7)2Dy(μ–η5:η1-C9H6)]2}, a complex containing the first example of the indenyl dianion, (C9H6)2–, derived from C–H bond activation of the (C9H7)1– monoanion. Density functional theory analysis of these results provides an explanation for the observed hyperfine coupling constants in the yttrium complexes and for the C–H bond activation observed for the indenyl complex.
Co-reporter:Christopher M. Kotyk, Matthew R. MacDonald, Joseph W. Ziller, and William J. Evans
Organometallics 2015 Volume 34(Issue 11) pp:2287-2295
Publication Date(Web):January 12, 2015
DOI:10.1021/om501063h
The reductive capacity of the recently discovered Ln2+ complexes [K(2.2.2-cryptand)][Cp′3Ln], 1-Ln (Cp′ = C5H4SiMe3; Ln = Y, La, Ce, Dy), has been probed by examining their reactions with aromatic hydrocarbons. [K(2.2.2-cryptand)][Cp′3Y], 1-Y, is capable of reducing naphthalene and forms a mixture of the naphthalenide dianion complex [K(2.2.2-cryptand)][Cp′2Y(η4-C10H8)], 2-Y, as well as the ligand redistribution product [K(2.2.2-cryptand)][Cp′4Y], 3-Y, and the cyclopentadienyl ligand salt [K(2.2.2-cryptand)][Cp′], 4. Naphthalene is reduced analogously by 1-La, 1-Ce, and 1-Dy. Each complex in the yttrium reaction was synthesized independently to confirm its identity in the mixture. Complex 2-Y was prepared from [Cp′2Y(THF)2][BPh4], 5 (synthesized from [Et3NH][BPh4] and Cp′3Y), and K/naphthalene. Complex 3-Y was obtained by adding KCp′ to Cp′3Y in the presence of 2.2.2-cryptand. [K(2.2.2-cryptand)][Cp′] was synthesized from 2.2.2-cryptand and KCp′. Each C10 unit in the reduced naphthalene products, 2-Y, 2-La, 2-Ce, and 2-Dy, is bent with four carbon atoms of one ring oriented toward the metal, while the remaining six carbon atoms form a planar ring consistent with (η4-C10H8)2– coordination. In the solid state, 3-Y contains one η1-Cp′ ligand and three η5-Cp′ rings, whereas all four Cp′ rings in 3-La have η5-coordination. In the solid-state structure of 4, the (Cp′)− anion is not coordinated to potassium, which is encapsulated by the cryptand and located 7.063 Å from the ring centroid. Complex 1-Y also reduces biphenyl to form [K(2.2.2-cryptand)][Cp′2Y(η6-C6H5Ph)], 6-Y, which contains a dianion with a planar aromatic phenyl ring as a substituent on a nonplanar η6-C6 ring oriented toward the metal ion.
Co-reporter:Linus Appel;Jennifer Leduc;Christopher L. Webster;Dr. Joseph W. Ziller;Dr. William J. Evans;Dr. Sanjay Mathur
Angewandte Chemie 2015 Volume 127( Issue 7) pp:2237-2241
Publication Date(Web):
DOI:10.1002/ange.201409606
Abstract
Four air-stable, volatile uranium heteroarylalkenolates have been synthesized and characterized by three synthetic approaches and their gas phase deposition to uranium oxide films has been examined.
Co-reporter:Douglas R. Kindra and William J. Evans
Chemical Reviews 2014 Volume 114(Issue 18) pp:8865
Publication Date(Web):August 19, 2014
DOI:10.1021/cr500242w
Co-reporter:Megan E. Fieser; Matthew R. MacDonald; Brandon T. Krull; Jefferson E. Bates; Joseph W. Ziller; Filipp Furche
Journal of the American Chemical Society 2014 Volume 137(Issue 1) pp:369-382
Publication Date(Web):December 26, 2014
DOI:10.1021/ja510831n
The Ln3+ and Ln2+ complexes, Cp′3Ln, 1, (Cp′ = C5H4SiMe3) and [K(2.2.2-cryptand)][Cp′3Ln], 2, respectively, have been synthesized for the six lanthanides traditionally known in +2 oxidation states, i.e., Ln = Eu, Yb, Sm, Tm, Dy, and Nd, to allow direct structural and spectroscopic comparison with the recently discovered Ln2+ ions of Ln = Pr, Gd, Tb, Ho, Y, Er, and Lu in 2. 2-La and 2-Ce were also prepared to allow the first comparison of all the lanthanides in the same coordination environment in both +2 and +3 oxidation states. 2-La and 2-Ce show the same unusual structural feature of the recently discovered +2 complexes, that the Ln–(Cp′ ring centroid) distances are only about 0.03 Å longer than in the +3 analogs, 1. The Eu, Yb, Sm, Tm, Dy, and Nd complexes were expected to show much larger differences, but this was observed for only four of these traditional six lanthanides. 2-Dy and 2-Nd are like the new nine ions in this tris(cyclopentadienyl) coordination geometry. A DFT-based model explains the results and shows that a 4f n5d1 electron configuration is appropriate not only for the nine recently discovered Ln2+ ions in 2 but also for Dy2+ and Nd2+, which traditionally have 4f n+1 electron configurations like Eu2+, Yb2+, Sm2+, and Tm2+. These results indicate that the ground state of a lanthanide ion in a molecule can be changed by the ligand set, a previously unknown option with these metals due to the limited radial extension of the 4f orbitals.
Co-reporter:Shan-Shan Liu, Joseph W. Ziller, Yi-Quan Zhang, Bing-Wu Wang, William J. Evans and Song Gao
Chemical Communications 2014 vol. 50(Issue 77) pp:11418-11420
Publication Date(Web):06 Aug 2014
DOI:10.1039/C4CC04262J
A half-sandwich organolanthanide complex, [(C6Me6)Dy(AlCl4)3], in which Dy(III) is coordinated with a π-bonded arene was synthesized and magnetically characterized. This complex displays slow magnetic relaxation and a hysteresis loop associated with single-ion magnet behavior. The orientation of the magnetic anisotropy axis is analyzed using ab initio calculations.
Co-reporter:Katie R. Meihaus, Jordan F. Corbey, Ming Fang, Joseph W. Ziller, Jeffrey R. Long, and William J. Evans
Inorganic Chemistry 2014 Volume 53(Issue 6) pp:3099-3107
Publication Date(Web):February 28, 2014
DOI:10.1021/ic4030102
The synthesis and full magnetic characterization of a new series of N23– radical-bridged lanthanide complexes [{(R2N)2(THF)Ln}2(μ3-η2:η2:η2-N2)K] [1-Ln; Ln = Gd, Tb, Dy; NR2 = N(SiMe3)2] are described for comprehensive comparison with the previously reported series [K(18-crown-6)(THF)2]{[(R2N)2(THF)Ln]2(μ-η2:η2-N2)} (2-Ln; Ln = Gd, Tb, Dy). Structural characterization of 1-Ln crystals grown with the aid of a Nd2Fe13B magnet reveals inner-sphere coordination of the K+ counterion within 2.9 Å of the N23– bridge, leading to bending of the planar Ln–(N23–)–Ln unit present in 2-Ln. Direct current (dc) magnetic susceptibility measurements performed on 1-Gd reveal antiferromagnetic coupling between the GdIII centers and the N23– radical bridge, with a strength matching that obtained previously for 2-Gd at J ∼ −27 cm–1. Unexpectedly, however, a competing antiferromagnetic GdIII–GdIII exchange interaction with J ∼ −2 cm–1 also becomes prominent, dramatically changing the magnetic behavior at low temperatures. Alternating current (ac) magnetic susceptibility characterization of 1-Tb and 1-Dy demonstrates these complexes to be single-molecule magnets under zero applied dc field, albeit with relaxation barriers (Ueff = 41.13(4) and 14.95(8) cm–1, respectively) and blocking temperatures significantly reduced compared to 2-Tb and 2-Dy. These differences are also likely to be a result of the competing antiferromagnetic LnIII–LnIII exchange interactions of the type quantified in 1-Gd.
Co-reporter:Ryan R. Langeslay, Justin R. Walensky, Joseph W. Ziller, and William J. Evans
Inorganic Chemistry 2014 Volume 53(Issue 16) pp:8455-8463
Publication Date(Web):July 29, 2014
DOI:10.1021/ic501034b
Reactions of the 2,2,6,6-tetramethylpiperidin-1-oxyl radical (TEMPO) with thorium metallocenes have been examined to investigate both the radical reaction patterns for organothorium complexes and the coordination chemistry of TEMPO with thorium. (η5-C5Me5)2ThMe2 reacts with 2 equiv of TEMPO to generate 1-methoxy-2,2,6,6-tetramethylpiperidine (Me-TEMPO) and (η5-C5Me5)2ThMe(η1-TEMPO), which contains a TEMPO– anion coordinated to thorium through oxygen only. (η5-C5Me5)2Th(η1-C3H5)(η3-C3H5), synthesized from (η5-C5Me5)2ThBr2 and (C3H5)MgBr, reacts with 2 equiv of TEMPO to form 1-(2-propen-1-yloxy)-2,2,6,6-tetramethylpiperidine (allyl-TEMPO) and (η5-C5Me5)2Th(η1-C3H5)(η1-TEMPO). Although bis(TEMPO) metallocenes were not obtained in these reactions, the methyl group in (η5-C5Me5)2ThMe(η1-TEMPO) is reactive with 1 equiv of CuBr to form (η5-C5Me5)2ThBr(η1-TEMPO). The bis(TEMPO) metallocene (η5-C5Me5)2Th(η1-TEMPO)2 is accessible in the reaction of [(η5-C5Me5)2ThH2]2 with 4 equiv of TEMPO. In contrast, (η5-C5Me5)2ThBr2 reacts with 2 equiv of TEMPO by loss of C5Me5 to form (C5Me5)2 and (η2-TEMPO)2ThBr2, in which the TEMPO– anions bind through oxygen and nitrogen. The bromide ions in (η2-TEMPO)2ThBr2 can be replaced by an additional 2 equiv of TEMPO in the presence of 2 equiv of KC8 to form the per(TEMPO) complex Th(η1-TEMPO)2(η2-TEMPO)2. ThBr4(THF)4 reacts with TEMPO to form ThBr4(THF)2(η1-TEMPO), which contains an oxygen-bound TEMPO radical. The Th3+ complex (η5-C5Me4H)3Th is oxidized in the presence of TEMPO, without ligand loss, to afford the Th4+ species (η5-C5Me4H)3Th(η1-TEMPO). The reactions show that TEMPO can react with organothorium complexes in several ways including coordination, anion substitution, and cyclopentadienyl replacement.
Co-reporter:Douglas R. Kindra and William J. Evans
Dalton Transactions 2014 vol. 43(Issue 8) pp:3052-3054
Publication Date(Web):02 Dec 2013
DOI:10.1039/C3DT53187B
3,5-Di-tert-butyl-4-hydroxybenzoic acid can be made under mild conditions in a cyclic process from carbon dioxide and 3,5-di-tert-butyl-4-phenol using bismuth-based C–H bond activation and CO2 insertion chemistry starting with the Bi3+ complex, Ar′BiCl2, of the NCN pincer ligand, Ar′ = 2,6-(Me2NCH2)2C6H3. Complexes of the recently discovered oxyaryl dianion, (C6H2tBu2-3,5-O-4)2−, and the oxyarylcarboxy dianion, [O2C(C6H2tBu2-3,5-O-4)]2−, are intermediates in the process. Further studies of the oxyarylcarboxy dianion in Ar′Bi[O2C(C6H2tBu2-3,5-O-4)-κ2O,O′], show that it undergoes decarboxylation upon reaction with I2 and it reacts with trimethylsilyl chloride to produce the trimethylsilyl ether of the trimethylsilyl ester of 3,5-di-tert-butyl-4-hydroxybenzoic acid and the Ar′BiCl2 starting material.
Co-reporter:Cory J. Windorff and William J. Evans
Organometallics 2014 Volume 33(Issue 14) pp:3786-3791
Publication Date(Web):July 15, 2014
DOI:10.1021/om500512q
29Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that, although there is some overlap in the range of shifts of U4+ complexes versus U3+ complexes, in general U3+ species have shifts more negative than those of their U4+ analogues. The single U2+ example has the most negative shift of all at −322 ppm at 170 K. With only a few exceptions, U4+ complexes have shifts between 0 and −150 ppm (vs SiMe4), whereas U3+ complexes resonate between −120 and −250 ppm. The small data set on U5+ species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit chemical shifts less negative than those of other types of ligands.
Co-reporter:Christopher L. Webster, Joseph W. Ziller, and William J. Evans
Organometallics 2014 Volume 33(Issue 1) pp:433-436
Publication Date(Web):December 23, 2013
DOI:10.1021/om401122d
Gas/solid reactions involving H2 and CO2 with the metallocenes (C5Me5)2UMe2 and (C5Me5)2U(allyl)2 as solids in the absence of solvent provide an improved method to make organouranium hydride and carboxylate products. Decomposition products that can form in solution from the reactive hydrides can be avoided by this method, and this approach can also provide intermediates too reactive to isolate in some solution reactions. In contrast to the variable nature of the hydrogenolysis reaction of (C5Me5)2UMe2 in toluene that forms byproducts along with the mixture of [(C5Me5)2UH2]2 and [(C5Me5)2UH]2, a byproduct-free hydrogenolysis occurs when (C5Me5)2UMe2 in the solid state is treated with H2 gas to form predominantly [(C5Me5)2UH2]2. H2 reacts with solid (C5Me5)2U(C3H5)2 and (C5Me5)2U(C3H5) similarly. The reaction of CO2 (80 psi) with solid (C5Me5)2UMe2 forms the monocarboxylate (C5Me5)2U(O2CCH3-κ2O,O′)Me, in contrast to the solution reaction that forms the diacetate (C5Me5)2U(O2CCH3-κ2O,O′)2 in minutes. The reaction of H2 with solid (C5Me5)2Y(C3H5) provided (C5Me5)2Y(μ-H)YH(C5Me5)2 without the decomposition products that it forms in solution such that single crystals suitable for X-ray diffraction could be isolated for the first time.
Co-reporter:Dr. Douglas R. Kindra;Dr. Ian J. Casely;Dr. Joseph W. Ziller ; William J. Evans
Chemistry - A European Journal 2014 Volume 20( Issue 46) pp:15242-15247
Publication Date(Web):
DOI:10.1002/chem.201404910
Abstract
The first example of NO insertion into a BiC bond has been found in the direct reaction of NO with a Bi3+ complex of the unusual (C6H2tBu2-3,5-O-4)2− oxyaryl dianionic ligand, namely, Ar′Bi(C6H2tBu2-3,5-O-4) [Ar′=2,6-(Me2NCH2)2C6H3] (1). The oximate complexes [Ar′Bi(ONC6H2-3,5-tBu2-4-O)]2(μ-O) (3) and Ar′Bi(ONC6H2-3,5-tBu2-4-O)2 (4) were formed as a mixture, but can be isolated in pure form by reaction of NO with a Bi3+ complex of the [O2C(C6H2tBu2-3-5-O-4]2− oxyarylcarboxy dianion, namely, Ar′Bi[O2C(C6H2tBu2-3-5-O-4)-κ2O,O’]. Reaction of 1 with Ph3CSNO gave an oximate product with (Ph3CS)1− as an ancillary ligand, (Ph3CS)(Ar′)Bi(ONC6H2-3,5-tBu2-4-O) (5).
Co-reporter:Matthew R. MacDonald ; Megan E. Fieser ; Jefferson E. Bates ; Joseph W. Ziller ; Filipp Furche
Journal of the American Chemical Society 2013 Volume 135(Issue 36) pp:13310-13313
Publication Date(Web):August 28, 2013
DOI:10.1021/ja406791t
Flash reduction of Cp′3U (Cp′ = C5H4SiMe3) in a column of potassium graphite in the presence of 2.2.2-cryptand generates crystalline [K(2.2.2-cryptand)][Cp′3U], the first isolable molecular U2+ complex. To ensure that this was not the U3+ hydride, [K(2.2.2-cryptand)][Cp′3UH], which could be crystallographically similar, the hydride complex was synthesized by addition of KH to Cp′3U and by reduction of H2 by the U2+ complex and was confirmed to be a different compound. Density functional theory calculations indicate a 5f36d1 quintet ground state for the [Cp′3U]− anion and match the observed strong transitions in its optical spectrum.
Co-reporter:Douglas R. Kindra ; Ian J. Casely ; Megan E. Fieser ; Joseph W. Ziller ; Filipp Furche
Journal of the American Chemical Society 2013 Volume 135(Issue 20) pp:7777-7787
Publication Date(Web):April 26, 2013
DOI:10.1021/ja403133f
The reactivity of the unusual oxyaryl dianionic ligand, (C6H2tBu2-3,5-O-4)2–, in the Bi3+ NCN pincer complex Ar′Bi(C6H2tBu2-3,5-O-4), 1, [Ar′ = 2,6-(Me2NCH2)2C6H3] has been explored with small molecule substrates and electrophiles. The first insertion reactions of CO2 and COS into Bi–C bonds are observed with this oxyaryl dianionic ligand complex. These reactions generate new dianions that have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands were identified by X-ray crystallography in Ar′Bi[O2C(C6H2tBu2-3-5-O-4)-κ2O,O′], 2, and Ar′Bi[OSC(C6H2tBu2-3-5-O-4)-κ2O,S], 3, respectively. Silyl halides and pseudohalides, R3SiX (X = Cl, CN, N3; R = Me, Ph), react with 1 by attaching X to bismuth and R3Si to the oxyaryl oxygen to form Ar′Bi(X)(C6H2tBu2-3,5-OSiR3-4) complexes, a formal addition across five bonds. These react with additional R3SiX to generate Ar′BiX2 complexes and R3SiOC6H3tBu2-2,6. The reaction of 1 with I2 forms Ar′BiI2 and the coupled quinone, 3,3′,5,5′-tetra-tert-butyl-4,4′-diphenoquinone, by oxidative coupling.
Co-reporter:Matthew R. MacDonald, Jefferson E. Bates, Joseph W. Ziller, Filipp Furche, and William J. Evans
Journal of the American Chemical Society 2013 Volume 135(Issue 26) pp:9857-9868
Publication Date(Web):May 22, 2013
DOI:10.1021/ja403753j
The first examples of crystallographically characterizable complexes of Tb2+, Pr2+, Gd2+, and Lu2+ have been isolated, which demonstrate that Ln2+ ions are accessible in soluble molecules for all of the lanthanides except radioactive promethium. The first molecular Tb2+ complexes have been obtained from the reaction of Cp′3Ln (Cp′ = C5H4SiMe3, Ln = rare earth) with potassium in the presence of 18-crown-6 in Et2O at −35 °C under argon: [(18-crown-6)K][Cp′3Tb], {[(18-crown-6)K][Cp′3Tb]}n, and {[K(18-crown-6)]2(μ-Cp′)}{Cp′3Tb}. The first complex is analogous to previously isolated Y2+, Ho2+, and Er2+ complexes, the second complex shows an isomeric structural form of these Ln2+ complexes, and the third complex shows that [(18-crown-6)K]1+ alone is not the only cation that will stabilize these reactive Ln2+ species, a result that led to further exploration of cation variants. With 2.2.2-cryptand in place of 18-crown-6 in the Cp′3Ln/K reaction, a more stable complex of Tb2+ was produced as well as more stable Y2+, Ho2+, and Er2+ analogs: [K(2.2.2-cryptand)][Cp′3Ln]. Exploration of this 2.2.2-cryptand-based reaction with the remaining lanthanides for which Ln2+ had not been observed in molecular species provided crystalline Pr2+, Gd2+, and Lu2+ complexes. These Ln2+ complexes, [K(2.2.2-cryptand)][Cp′3Ln] (Ln = Y, Pr, Gd, Tb, Ho, Er, Lu), all have similar UV–vis spectra and exhibit Ln–C(Cp′) bond distances that are ∼0.03 Å longer than those in the Ln3+ precursors, Cp′3Ln. These data, as well as density functional theory calculations and EPR spectra, suggest that a 4fn5d1 description of the electron configuration in these Ln2+ ions is more appropriate than 4fn+1.
Co-reporter:Megan E. Fieser ; Jefferson E. Bates ; Joseph W. Ziller ; Filipp Furche
Journal of the American Chemical Society 2013 Volume 135(Issue 10) pp:3804-3807
Publication Date(Web):February 22, 2013
DOI:10.1021/ja400664s
Dinitrogen can be reduced by photochemical activation of the Ln3+ mixed-ligand tris(cyclopentadienyl) rare-earth complexes (η5-C5Me5)3–x(C5Me4H)xLn (Ln = Y, Lu, Dy; x = 1, 2). [(C5Me4R)2Ln]2(μ-η2:η2-N2) products (R = H, Me) are formed in reactions in which N2 is reduced to (N═N)2– and (C5Me4H)− is oxidized to (C5Me4H)2. Density functional theory indicates that this unusual example of rare-earth photochemistry can be rationalized by absorptions involving the (η3-C5Me4H)− ligands.
Co-reporter:Christopher L. Webster, Jefferson E. Bates, Ming Fang, Joseph W. Ziller, Filipp Furche, and William J. Evans
Inorganic Chemistry 2013 Volume 52(Issue 7) pp:3565-3572
Publication Date(Web):June 28, 2012
DOI:10.1021/ic300905r
(C5Me5)2M(NC4Me4) complexes (M = Y, Sm, Ce, U) were synthesized to act as structural models for the (η5-C5Me5)2M(η1-C5Me5) intermediate postulated to give pseudoalkyl reactivity to sterically crowded (C5Me5)3M complexes. This synthesis was accomplished through reaction of the tetraphenylborate complexes, [(C5Me5)2M][(μ-Ph)2BPh2], with potassium tetramethylpyrrolyl, KNC4Me4. X-ray crystallographic studies on the resulting (C5Me5)2M(NC4Me4) complexes showed that, although the two (C5Me5)− rings bind to the metal with η5 coordination and tetramethylpyrrolyl has a primary η1 coordination, the complexes are not symmetrical in the solid state, and disparate M–N–C(ring) angles within a complex orient a (NC4Me4)− ring carbon and methyl carbon near the metal in a pseudo-η3 binding mode. Moreover, these (C5Me5)2M(NC4Me4) complexes display unexpectedly large structural variations not only between metals but also between crystals grown from the same mother liquor. Large variations are observed in the M–N–C(ring) angles that lead to close metal ring carbon distances [105.6(1)–115.7(2)°] as well as in the M–N–(NC4Me4 ring centroid) angles (152.2–167.3°). The synthesis and structure of 4d, 4f, and 5f metal examples are described, and the results are compared to predictions from the density functional theory. The reasons for the variable structures displayed by the (C5Me5)2M(NC4Me4) complexes are discussed.
Co-reporter:Nathan A. Siladke, Christopher L. Webster, Justin R. Walensky, Michael K. Takase, Joseph W. Ziller, Daniel J. Grant, Laura Gagliardi, and William J. Evans
Organometallics 2013 Volume 32(Issue 21) pp:6522-6531
Publication Date(Web):October 23, 2013
DOI:10.1021/om4008482
Hydrogenolysis of the dimethyl actinide metallocenes (C5Me4SiMe3)2UMe2 and (C5Me4H)2AnMe2 (An = Th, U) was examined for comparison with the hydrogenolysis of (C5Me5)2AnMe2 that forms the hydrides [(C5Me5)2ThH2]2, [(C5Me5)2UH2]2, and [(C5Me5)2UH]2. Parallel reactivity is not found with the (C5Me4SiMe3)− and (C5Me4H)− complexes. Instead, this study led to the first example of a “tuck-over” [μ-η5-C5Me3H(CH2)-κC]2– dianion derived from (C5Me4H)− ligands by C–H bond activation and rare examples of a polymetallic thorium polyhydride compound and an organometallic Th3+ complex. (C5Me4SiMe3)2UMe2 reacts with H2 to form the bis(tethered alkyl) complex (η5-C5Me4SiMe2CH2-κC)2U, a product of C–H bond activation of the silylmethyl groups. The only identifiable product of hydrogenolysis of (C5Me4H)2UMe2 is (C5Me4H)3U. The first thorium complex of (C5Me4H)− was synthesized by reaction of 2 equiv of (C5Me4H)MgCl(THF) with ThBr4(THF)4 to produce (C5Me4H)2ThBr2. This complex reacts with MeLi to make (C5Me4H)2ThMe2. The latter complex reacts with H2 to form the ligand redistribution product (C5Me4H)3ThMe and the tetrametallic octahydride tuck-over complex (C5Me4H)4[μ-η5-C5Me3H(CH2)-κC]2Th4(μ-H)4(μ3-H)4. For comparison with the (C5Me4H)3U product, the thorium analogue, (C5Me4H)3Th, was synthesized by potassium reduction of a [(C5Me4H)3Th][BPh4] intermediate obtained in situ from (C5Me4H)3ThMe and [HNEt3][BPh4]. (C5Me4H)3Th can also be prepared from KC8 and (C5Me4H)3ThBr, obtained from KC5Me4H and ThBr4(THF)4.
Co-reporter:Christopher L. Webster, Joseph W. Ziller, and William J. Evans
Organometallics 2013 Volume 32(Issue 17) pp:4820-4827
Publication Date(Web):August 22, 2013
DOI:10.1021/om400526h
The U3+ allyl complexes (C5Me5)2U[CH2C(R)CH2] (R = H, Me) display three different types of reactivity, as exemplified by reactions with PhN═NPh, cyclooctatetraene, and CO2. Two equivalents of (C5Me5)2U[CH2C(R)CH2] effect a four-electron reduction of PhN═NPh to form the bis(imido) complex (C5Me5)2U(═NPh)2 and the bis(allyl) species (C5Me5)2U[CH2C(R)CH2]2. Two-electron reduction of C8H8 occurs to form (C5Me5)(C8H8)U[CH2C(R)CH2] products that contain only one cyclopentadienyl ring per metal. With CO2 at 80 psi, both reduction and insertion occur. A hexametallic uranium carbonate, [(C5Me5)2U]6(μ-κ1:κ2-CO3)6, is isolated as well as the bis(carboxylate) complexes (C5Me5)2U[κ2-O,O′-O2CCH2C(R)═CH2]2. The polymetallic carbonate complex can also be synthesized from [(C5Me5)2U]2(μ-η6:η6-C6H6) and [(C5Me5)2U][(μ-Ph)2BPh2] and CO2.
Co-reporter:Jeffrey K. Peterson, Matthew R. MacDonald, Joseph W. Ziller, and William J. Evans
Organometallics 2013 Volume 32(Issue 9) pp:2625-2631
Publication Date(Web):April 22, 2013
DOI:10.1021/om400116d
New analogues of Cp′3Ln (Cp′ = C5H4SiMe3, Ln = rare earth) complexes have been synthesized with the largest and smallest lanthanides, La and Lu. Due to the smaller size of Lu, the reaction of LuCl3 with 3 equiv of KCp′ produced only traces of Cp′3Lu, yielding [Cp′2Lu(μ-Cl)]2 as the major product. An alternative route was developed in which [Cp′2Lu(μ-Cl)]2 reacts with (C3H5)MgCl to form the tetrameric allyl complex [Cp′2Lu(μ-η1:η1-C3H5)]4. The allyl complex reacts with [HNEt3][BPh4] to generate [Cp′2Lu(THF)2][BPh4], which reacts with KCp′ to produce Cp′3Lu in good yield. The reaction of LaCl3 with 3 equiv of KCp′ in Et2O gave the unsolvated Cp′3La, while the same reaction in rigorously dry THF gave solvated Cp′3La(THF). The reaction of LaCl3 and KCp′ in improperly dried THF gave the mixed-ligand complex Cp′2CpLa(THF) (Cp = C5H5), rather than the expected hydrolysis product, [Cp′2La(μ-OH)]2.
Co-reporter:Matthew R. MacDonald ; Jefferson E. Bates ; Megan E. Fieser ; Joseph W. Ziller ; Filipp Furche
Journal of the American Chemical Society 2012 Volume 134(Issue 20) pp:8420-8423
Publication Date(Web):May 14, 2012
DOI:10.1021/ja303357w
The first molecular complexes of holmium and erbium in the +2 oxidation state have been generated by reducing Cp′3Ln [Cp′ = C5H4SiMe3; Ln = Ho (1), Er (2)] with KC8 in the presence of 18-crown-6 in Et2O at −35 °C under argon. Purification and crystallization below −35 °C gave isomorphous [(18-crown-6)K][Cp′3Ln] [Ln = Ho (3), Er (4)]. The three Cp′ ring centroids define a trigonal-planar geometry around each metal ion that is not perturbed by the location of the potassium crown cation near one ring with K–C(Cp′) distances of 3.053(8)–3.078(2) Å. The metrical parameters of the three rings are indistinguishable within the error limits. In contrast to Ln2+ complexes of Eu, Yb, Sm, Tm, Dy, and Nd, 3 and 4 have average Ln–(Cp′ ring centroid) distances only 0.029 and 0.021 Å longer than those of the Ln3+ analogues 1 and 2, a result similar to that previously reported for the 4d1 Y2+ complex [(18-crown-6)K][Cp′3Y] (5) and the 5d1 La2+ complex [K(18-crown-6)(Et2O)][Cp″3La] [Cp″ = 1,3-(Me3Si)2C5H3]. Surprisingly, the UV–vis spectra of 3 and 4 are also very similar to that of 5 with two broad absorptions in the visible region, suggesting that 3–5 have similar electron configurations. Density functional theory calculations on the Ho2+ and Er2+ species yielded HOMOs that are largely 5dz2 in character and supportive of 4f105d1 and 4f115d1 ground-state configurations, respectively.
Co-reporter:Ming Fang ; Joy H. Farnaby ; Joseph W. Ziller ; Jefferson E. Bates ; Filipp Furche
Journal of the American Chemical Society 2012 Volume 134(Issue 14) pp:6064-6067
Publication Date(Web):March 21, 2012
DOI:10.1021/ja211220r
Deep-blue solutions of Y2+ formed from Y(NR2)3 (R = SiMe3) and excess potassium in the presence of 18-crown-6 at −45 °C under vacuum in diethyl ether react with CO at −78 °C to form colorless crystals of the (CO)1– radical complex, {[(R2N)3Y(μ-CO)2][K2(18-crown-6)2]}n, 1. The polymeric structure contains trigonal bipyramidal [(R2N)3Y(μ-CO)2]2– units with axial (CO)1– ligands linked by [K2(18-crown-6)2]2+ dications. Byproducts such as the ynediolate, [(R2N)3Y]2(μ-OC≡CO){[K(18-crown-6)]2(18-crown-6)}, 2, in which two (CO)1– anions are coupled to form (OC≡CO)2–, and the insertion/rearrangement product, {(R2N)2Y[OC(═CH2)Si(Me2)NSiMe3]}[K(18-crown-6)], 3, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of 2, the ynediolate [(R2N)3Y]2(μ-OC≡CO)[K(18-crown-6)(THF)2]2, 2a. CO2 reacts analogously with Y2+ to form the (CO2)1– radical complex, {[(R2N)3Y(μ-CO2)2][K2(18-crown-6)2]}n, 4, that has a structure similar to that of 1. Analogous (CO)1– and (OC≡CO)2– complexes of lutetium were isolated using Lu(NR2)3/K/18-crown-6: {[(R2N)3Lu(μ-CO)2][K2(18-crown-6)2]}n, 5, [(R2N)3Lu]2(μ-OC≡CO){[K(18-crown-6)]2(18-crown-6)}, 6, and [(R2N)3Lu]2(μ-OC≡CO)[K(18-crown-6)(Et2O)2]2, 6a.
Co-reporter:Joy H. Farnaby, Ming Fang, Joseph W. Ziller, and William J. Evans
Inorganic Chemistry 2012 Volume 51(Issue 20) pp:11168-11176
Publication Date(Web):October 4, 2012
DOI:10.1021/ic301778q
The reaction chemistry of the side-on bound (N2)2–, (N2)3–, and (NO)2– complexes of the [(R2N)2Y]+ cation (R = SiMe3), namely, [(R2N)2(THF)Y]2(μ-η2:η2-N2), 1, [(R2N)2(THF)Y]2(μ-η2:η2-N2)K, 2, and [(R2N)2(THF)Y]2(μ-η2:η2-NO), 3, with oxidizing agents has been explored to search for other (E2)n−, (E = N, O), species that can be stabilized by this cation. This has led to the first examples for the [(R2N)2Y]+ cation of two fundamental classes of [(monoanion)2Ln]+ rare earth systems (Ln = Sc, Y, lanthanides), namely, oxide complexes and the tetraphenylborate salt. In addition, an unusually high yield reaction with dioxygen was found to give a peroxide complex that completes the (N2)2–, (NO)2–, (O2)2– series with 1 and 3. Specifically, the (μ-O)2– oxide-bridged bimetallic complex, [(R2N)2(THF)Y}2(μ-O), 4, is obtained as a byproduct from reactions of either the (N2)2– complex, 1, or the (N2)3– complex, 2, with NO, while the oxide formed from 2 with N2O is a polymeric species incorporating potassium, {[(R2N)2Y]2(μ-O)2K2(μ-C7H8)}n, 5. Reaction of 1 with 1 atm of O2 generates the (O2)2– bridging side-on peroxide [(R2N)2(THF)Y]2(μ-η2:η2-O2), 6. The O–O bond in 6 is cleaved by KC8 to provide an alternative synthetic route to 5. Attempts to oxidize the (NO)2– complex, 3, with AgBPh4 led to the isolation of the tetraphenylborate complex, [(R2N)2Y(THF)3][BPh4], 7, that was also synthesized from 1 and AgBPh4. Oxidation of the (N2)2– complex, 1, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO, generates the (TEMPO)− anion complex, (R2N)2(THF)Y(η2-ONC5H6Me4), 8.
Co-reporter:Jordan F. Corbey, Joy H. Farnaby, Jefferson E. Bates, Joseph W. Ziller, Filipp Furche, and William J. Evans
Inorganic Chemistry 2012 Volume 51(Issue 14) pp:7867-7874
Publication Date(Web):July 3, 2012
DOI:10.1021/ic300934g
The effect of the neutral donor ligand, L, on the Ln2N2 core in the (N═N)2– complexes, [A2(L)Ln]2(μ-η2:η2-N2) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2), 1, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine N-oxide were investigated. THF is displaced by all of these ligands to form {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) complexes (L = PhCN, 2; py, 3; DMAP, 4; Ph3PO, 5; Me3NO, 6) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y2N2 cores in 2–5 are similar to that in 1 with N–N bond distances between 1.255(3) Å and 1.274(3) Å, but X-ray analysis of the N–N distance in 6 shows it to be shorter: 1.198(3) Å.
Co-reporter:Daniel J. Grant, Timothy J. Stewart, Robert Bau, Kevin A. Miller, Sax A. Mason, Matthias Gutmann, Garry J. McIntyre, Laura Gagliardi, and William J. Evans
Inorganic Chemistry 2012 Volume 51(Issue 6) pp:3613-3624
Publication Date(Web):February 24, 2012
DOI:10.1021/ic202503h
The unusual uranium reaction system in which uranium(4+) and uranium(3+) hydrides interconvert by formal bimetallic reductive elimination and oxidative addition reactions, [(C5Me5)2UH2]2 (1) ⇌ [(C5Me5)2UH]2 (2) + H2, was studied by employing multiconfigurational quantum chemical and density functional theory methods. 1 can act as a formal four-electron reductant, releasing H2 gas as the byproduct of four H2/H– redox couples. The calculated structures for both reactants and products are in good agreement with the X-ray diffraction data on 2 and 1 and the neutron diffraction data on 1 obtained under H2 pressure as part of this study. The interconversion of the uranium(4+) and uranium(3+) hydride species was calculated to be near thermoneutral (∼−2 kcal/mol). Comparison with the unknown thorium analogue, [(C5Me5)2ThH]2, shows that the thorium(4+) to thorium(3+) hydride interconversion reaction is endothermic by 26 kcal/mol.
Co-reporter:Selvan Demir, Nathan A. Siladke, Joseph W. Ziller and William J. Evans
Dalton Transactions 2012 vol. 41(Issue 32) pp:9659-9666
Publication Date(Web):11 Jun 2012
DOI:10.1039/C2DT30861D
The synthetically accessible borohydride complexes (C5Me4H)2Ln(THF)(BH4) and (C5Me5)2Ln(THF)(BH4) (Ln = Sc, Y) were examined as precursors alternative to the heavily-used tetraphenylborate analogs, [(C5Me4H)2Ln][BPh4] and [(C5Me5)2Ln][BPh4], employed in LnA2A′/M reduction reactions (A = anion; M = alkali metal) that generate “LnA2” reactivity and form reduced dinitrogen complexes [(C5R5)2(THF)xLn]2(μ-η2:η2-N2) (x = 0, 1). The crystal structures of the yttrium borohydrides, (C5Me4H)2Y(THF)(μ-H)3BH, 1, and (C5Me5)2Y(THF)(μ-H)2BH2, 2, were determined for comparison with those of the yttrium tetraphenylborates, [(C5Me4H)2Y][(μ-Ph)2BPh2], 3, and [(C5Me5)2Y][(μ-Ph)2BPh2], 4. The complex (C5Me4H)2Sc(μ-H)2BH2, 5, was synthesized and structurally characterized for comparison with (C5Me5)2Sc(μ-H)2BH2, 6, [(C5Me4H)2Sc][(μ-Ph)BPh3], 7, and [(C5Me5)2Sc][(μ-Ph)BPh3], 8. Structural information was also obtained on the borohydride derivatives, (C5Me4H)2Sc(μ-H)2BC8H14, 9, and (C5Me5)2Sc(μ-H)2BC8H14, 10, obtained from 9-borabicyclo(3.3.1)nonane (9-BBN) and (C5Me4R)2Sc(η3-C3H5), where R = H, 11; Me, 12. The preference of the metals for borohydride over tetraphenylborate binding was shown by the facile displacement of (BPh4)1− in 3, 4, 7, and 8 by (BH4)1− to make the respective borohydride complexes 1, 2, 5, and 6. These results are consistent with the fact that the borohydrides are not as useful as precursors in A2LnA′/M reductions of N2. An unusual structural isomer of [(C5Me4H)2Sc]2(μ-η2:η2-N2), 13′, was isolated from this study that shows the variations in ligand orientation that can occur in the solid state.
Co-reporter:Nathan A. Siladke;Jennifer LeDuc;Dr. Joseph W. Ziller ; Dr. William J. Evans
Chemistry - A European Journal 2012 Volume 18( Issue 46) pp:14820-14827
Publication Date(Web):
DOI:10.1002/chem.201201908
Abstract
The synthesis of mixed tethered alkyl uranium metallocenes has been investigated by examining the reactivity of the bis(tethered alkyl) metallocene [(η5-C5Me4SiMe2CH2-κC)2U] (1) with substrates that react with only one of the UC linkages. The effect of these mixed tether coordination environments on the reactivity of the remaining UC bond has been studied by using CO insertion chemistry. One equivalent of azidoadamantane (AdN3) reacts with 1 to yield the mixed tethered alkyl triazenido complex [(η5-C5Me4SiMe2CH2-κC)U(η5-C5Me4SiMe2-CH2NNN-Ad-κ2N1,3)]. Similarly, a single equivalent of CS2 reacts with 1 to form the mixed tethered alkyl dithiocarboxylate complex [(η5-C5Me4SiMe2CH2-κC)U(η5-C5Me4SiMe2- CH2C(S)2-κ2S,S′)], a reaction that constitutes the first example of CS2 insertion into a U4+C bond. Complex 1 reacts with one equivalent of pyridine N-oxide by CH bond activation of the pyridine ring to form a mixed tethered alkyl cyclometalated pyridine N-oxide complex [(η5-C5Me4SiMe2CH2-κC)(η5-C5Me4SiMe3)U(C6H4NO-κ2C,O)]. The remaining (η5-C5Me4SiMe2CH2-κC)2− ligand in each of these mixed tethered species show reactivity towards CO and tethered enolate ligands form by insertion. Subsequent rearrangement have been identified in [(η5-C5Me4SiMe3)U(C5H4NO-κ2C,O)(η5-C5Me4SiMe2C(CH2)O-κO)] and [(η5-C5Me4SiMe2CH2NNN-Ad-κ2N1,3)U(η5-C5Me4SiMe2C(CH2)O-κO)].
Co-reporter:Christopher L. Webster, Joseph W. Ziller, and William J. Evans
Organometallics 2012 Volume 31(Issue 20) pp:7191-7197
Publication Date(Web):October 2, 2012
DOI:10.1021/om3007536
The U4+ metallocene allyl chloride complexes (C5Me5)2U[η3-CH2C(R)CH2]Cl (R = H, Me) can be synthesized by reaction of (C5Me5)2UCl2 with 1 equiv of the corresponding allyl Grignard reagents, [CH2C(R)CH2]MgCl, in hydrocarbon solvents. Bis(allyl)uranium complexes can also be obtained in this manner using 2 equiv of the corresponding allyl Grignard, and X-ray crystallographic studies reveal the presence of both η3- and η1-allyl ligands: (C5Me5)2U[η3-CH2C(R)CH2][η1-CH2C(R)═CH2]. Sodium amalgam reduction of (C5Me5)2U[η3-CH2C(R)CH2]Cl generates the U3+ metallocene allyl complexes (C5Me5)2U[η3-CH2C(R)CH2]. Carbon dioxide reacts with the U4+ allyl complexes to form the U–C insertion products (C5Me5)2U[κ2O,O′-O2CCH2CH═CH2]2–xClx (x = 0, 1). The dicarboxylate (C5Me5)2U[κ2O,O′-O2CCH2CH═CH2]2, which has a 171.98(5)° O–U–O angle, reacts with Me3SiCl to regenerate (C5Me5)2UCl2 and liberate Me3SiOC(O)CH2CH═CH2.
Co-reporter:Benjamin M. Schmiege ; Megan E. Fieser ; Joseph W. Ziller
Organometallics 2012 Volume 31(Issue 15) pp:5591-5598
Publication Date(Web):July 30, 2012
DOI:10.1021/om300546t
The trivalent yttrium tuck-over hydride complex, (C5Me5)2Y(μ-H)(μ-η1:η5-CH2C5Me4)Y(C5Me5), 1, acts as a reductant in reactions in which the (μ-H)− hydride ligand and the bridging Y–C alkyl anion linkage in the (μ-η1:η5-CH2C5Me4)2– ligand combine to form a C–H bond in (C5Me5)− and deliver two electrons to a substrate. Complex 1 reacts with PhSSPh, AgOTf (OTf = OSO2CF3), and Et3NHBPh4 to form [(C5Me5)2Y(μ-SPh)]2, [(C5Me5)2Y(μ-OTf)]2, and (C5Me5)2Y(μ-Ph)2BPh2, respectively. The reactivity of the Y–H and Y–CH2C5Me4 linkages in 1 was probed via carbodiimide insertion reactions. iPrN═C═NiPr inserts into both Y–H and Y–C bonds to yield (C5Me5)[iPrNC(H)NiPr]Y{μ-η5-C5Me4CH2[iPrNCNiPr]}Y(C5Me5)2. Carbodiimide insertion with [(C5Me5)2YH]2, 2, was also examined for comparison, and (C5Me5)2Y[iPrNC(H)NiPr-κ2N,N′] was isolated and structurally characterized. To examine the possibility of selective reactivity of the bridging ligands, μ-H versus μ-CH2C5Me4, trimethylsilylchloride was reacted with 1, and the tuck-over chloride complex, (C5Me5)2Y(μ-Cl)(μ-η1:η5-CH2C5Me4)Y(C5Me5), was isolated.
Co-reporter:Stéphanie Labouille, François Nief, Xavier-Frédéric Le Goff, Laurent Maron, Douglas R. Kindra, Heidi L. Houghton, Joseph W. Ziller, and William J. Evans
Organometallics 2012 Volume 31(Issue 14) pp:5196-5203
Publication Date(Web):July 3, 2012
DOI:10.1021/om300573z
The reactions of the samarium(II) complexes Tmp2Sm (Tmp = 2,3,4,5-tetramethyl-1H-phosphol-1-yl) and Cp*2Sm(THF)2 (Cp* = 1,2,3,4,5-tetramethyl-2,4-cyclopentadien-1-yl) with pyridine were found to be different, despite the fact that the Cp* and Tmp π-ligands are similar in size. With Tmp2Sm, a simple adduct, Tmp2Sm(pyridine)2 is isolated, while with Cp*2Sm(THF)2 pyridine is dimerized with concomitant oxidation of samarium to form [Cp*2Sm(C5H5N)]2[μ-(NC5H5–C5H5N)]. However, reaction of Tmp2Sm with acridine, a better π-acceptor than pyridine, did result in acridine dimerization and the isolation of [Tmp2Sm]2[μ-(NC13H9–C13H9N)]. DFT calculations on the model structures of Tmp2Sm and Cp*2Sm, and on the single electron transfer step from Sm to pyridine and acridine in these ligand environments, confirmed that, even though the Sm−π-ligand bonds are mostly ionic, the different electronic properties of the Tmp ligand versus that of Cp are responsible for the difference in reactivity of Tmp2Sm and Cp*2Sm.
Co-reporter:Jeffrey D. Rinehart ; Ming Fang ; William J. Evans ;Jeffrey R. Long
Journal of the American Chemical Society 2011 Volume 133(Issue 36) pp:14236-14239
Publication Date(Web):August 12, 2011
DOI:10.1021/ja206286h
The synthesis and magnetic properties of three new N23– radical-bridged dilanthanide complexes, {[(Me3Si)2N]2(THF)Ln}2(μ-η2:η2-N2)− (Ln = Tb, Ho, Er), are reported. All three display signatures of single-molecule-magnet behavior, with the terbium congener exhibiting magnetic hysteresis at 14 K and a 100 s blocking temperature of 13.9 K. The results show how synergizing the strong magnetic anisotropy of terbium(III) with the effective exchange-coupling ability of the N23– radical can create the hardest molecular magnet discovered to date. Through comparisons with non-radical-bridged ac magnetic susceptibility measurements, we show that the magnetic exchange coupling hinders zero-field fast relaxation pathways, forcing thermally activated relaxation behavior over a much broader temperature range.
Co-reporter:Ian J. Casely ; Joseph W. Ziller ; Ming Fang ; Filipp Furche
Journal of the American Chemical Society 2011 Volume 133(Issue 14) pp:5244-5247
Publication Date(Web):March 18, 2011
DOI:10.1021/ja201128d
The Bi3+ (N,C,N)-pincer complex Ar′BiCl2 (1) [Ar′ = 2,6-(Me2NCH2)2C6H3], reacts with 2 equiv of KOC6H3Me2-2,6 and KOC6H3iPr2-2,6 by ionic metathesis to form the anticipated bis(aryloxide) complexes Ar′Bi(OC6H3Me2-2,6)2 (2) and Ar′Bi(OC6H3iPr2-2,6)2 (3), respectively. However, the analogous reaction with 2 equiv of KOC6H3tBu2-2,6 forms HOC6H3tBu2-2,6 and a dark-orange complex containing only one aryloxide-derived ligand bound via a Bi−C and not a Bi−O linkage. This complex is formulated as Ar′Bi(C6H2tBu2-3,5-O-4) (4), a product of para C−H bond activation. Structural, spectroscopic, and DFT studies and a comparison with the protonated analogue [Ar′Bi(C6H2tBu2-3,5-OH-4)][BPh4] (5), which was obtained by treatment of 4 with [HNEt3][BPh4], suggest that 4 contains an oxyaryl dianion. Complex 4 represents a fully characterizable product of a bismuth-mediated C−H activation and rearrangement of the type postulated in catalytic SOHIO processes.
Co-reporter:Ming Fang ; David S. Lee ; Joseph W. Ziller ; Robert J. Doedens ; Jefferson E. Bates ; Filipp Furche
Journal of the American Chemical Society 2011 Volume 133(Issue 11) pp:3784-3787
Publication Date(Web):March 1, 2011
DOI:10.1021/ja1116827
Examination of the Y[N(SiMe3)2]3/KC8 reduction system that allowed isolation of the (N2)3− radical has led to the first evidence of Y2+ in solution. The deep-blue solutions obtained from Y[N(SiMe3)2]3 and KC8 in THF at −35 °C under argon have EPR spectra containing a doublet at giso = 1.976 with a 110 G hyperfine coupling constant. The solutions react with N2 to generate (N2)2− and (N2)3− complexes {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2) (1) and {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2)[K(THF)6] (2), respectively, and demonstrate that the Y[N(SiMe3)2]3/KC8 reaction can proceed through an Y2+ intermediate. The reactivity of (N2)3− radical with proton sources was probed for the first time for comparison with the (N2)2− and (N2)4− chemistry. Complex 2 reacts with [Et3NH][BPh4] to form {[(Me3Si)2N]2(THF)Y}2(μ-N2H2), the first lanthanide (N2H2)2− complex derived from dinitrogen, as well as 1 as a byproduct, consistent with radical disproportionation reactivity.
Co-reporter:Volker Lorenz ; Benjamin M. Schmiege ; Cristian G. Hrib ; Joseph W. Ziller ; Anja Edelmann ; Steffen Blaurock ; William J. Evans ;Frank T. Edelmann
Journal of the American Chemical Society 2011 Volume 133(Issue 5) pp:1257-1259
Publication Date(Web):January 7, 2011
DOI:10.1021/ja109604t
The use of the superbulky cyclooctatetraenide dianion ligand [C8H6(SiPh3)2]2− (= COTBIG) in organo-f-element chemistry leads to unprecedented effects such as the formation of a significantly bent anionic CeIII sandwich complex, a novel cerocene formed by sterically induced SiPh3 group migration, as well as the first example of a bent uranocene.
Co-reporter:Nathan A. Siladke a; Katie R. Meihaus b; Joseph W. Ziller a; Ming Fang a; Filipp Furche a; Jeffrey R. Long b a
Journal of the American Chemical Society 2011 Volume 134(Issue 2) pp:1243-1249
Publication Date(Web):December 2, 2011
DOI:10.1021/ja2096128
(C5Me4H)3U, 1, reacts with 1 equiv of NO to form the first f element nitrosyl complex (C5Me4H)3UNO, 2. X-ray crystallography revealed a 180° U–N–O bond angle, typical for (NO)1+ complexes. However, 2 has a 1.231(5) Å N═O distance in the range for (NO)1– complexes and a short 2.013(4) Å U–N bond like the U═N bond of uranium imido complexes. Structural, spectroscopic, and magnetic data as well as DFT calculations suggest that reduction of NO by U3+ has occurred to form a U4+ complex of (NO)1– that has π interactions between uranium 5f orbitals and NO π* orbitals. These bonding interactions account for the linear geometry and short U–N bond. The complex displays temperature-independent paramagnetism with a magnetic moment of 1.36 μB at room temperature. Complex 2 reacts with Al2Me6 to form the adduct (C5Me4H)3UNO(AlMe3), 3.
Co-reporter:Matthew R. MacDonald ; Joseph W. Ziller
Journal of the American Chemical Society 2011 Volume 133(Issue 40) pp:15914-15917
Publication Date(Web):September 16, 2011
DOI:10.1021/ja207151y
The La2+ complex [K(18-crown-6)(OEt2)][Cp″3La] (1) [Cp″ = C5H3(SiMe3)2-1,3], can be synthesized under N2, but in the presence of KC5Me5, 1 reduces N2 to the (N═N)2– product [(C5Me5)2(THF)La]2(μ-η2:η2-N2). This suggests a dichotomy in terms of ligands that optimize isolation of reduced dinitrogen complexes versus isolation of divalent complexes of the rare earths. To determine whether the first crystalline molecular Y2+ complex could be isolated using this logic, Cp′3Y (2) (Cp′ = C5H4SiMe3) was synthesized from YCl3 and KCp′ and reduced with KC8 in the presence of 18-crown-6 in Et2O at −45 °C under argon. EPR evidence was consistent with Y2+ and crystallization provided the first structurally characterizable molecular Y2+ complex, dark-maroon-purple [(18-crown-6)K][Cp′3Y] (3).
Co-reporter:Thomas J. Mueller, Megan E. Fieser, Joseph W. Ziller and William J. Evans
Chemical Science 2011 vol. 2(Issue 10) pp:1992-1996
Publication Date(Web):03 Aug 2011
DOI:10.1039/C1SC00139F
Synthesis of the mixed ligand complexes (C5Me5)(C5Me4H)2Ln (Ln = Lu, Y) for comparison with (C5Me5)2(C5Me4H)Ln to evaluate details of steric effects on reductive reactivity has revealed that (C5Me5)3−x(C5Me4H)xLn complexes can reduce dinitrogen to (NN)2−. (C5Me5)(C5Me4H)2Lu reacts with N2 to form [(C5Me5)(C5Me4H)Lu]2(μ-η2:η2-N2), (C5Me5)2(C5Me4H)Y reduces N2 to [(C5Me5)2Y]2(μ-η2:η2-N2), and (C5Me4H)3Sc converts N2 to [(C5Me4H)2Sc]2(μ-η2:η2-N2). Exclusive (C5Me4H)1− loss occurs in each case with formation of (C5Me4H)2 as the byproduct. (C5Me5)2, the signature byproduct of sterically induced reduction reactions, is not observed. Since these complexes do not exhibit unusual steric parameters and since the more crowded (C5Me5)2(C5Me4H)Lu and (C5Me5)3Y do not display analogous reactivity, these reactions do not appear to be sterically induced reductions and suggest a new type of ligand-based reduction pathway involving (C5Me4H)1−.
Co-reporter:Matthew R. MacDonald, Joseph W. Ziller, and William J. Evans
Inorganic Chemistry 2011 Volume 50(Issue 9) pp:4092-4106
Publication Date(Web):March 25, 2011
DOI:10.1021/ic2000409
The reactivity of the tetraphenylborate salts of the rare earth metallocene cations [(C5Me5)2Ln][(μ-Ph)2BPh2] (Ln = Y, 1; Sm, 2) has been investigated with substrates that undergo reduction with f element complexes to probe metal-substrate interactions prior to reduction. Results with NaN3, 1-adamantyl azide, acetone, benzophenone, phenanthroline, pyridine, azobenzene, and phenazine are described. Not only were coordination complexes isolated, but substrate reduction by (BPh4)− was also observed. Complex 1 reacts with NaN3 to form the azide [(C5Me5)2YN3]x, 3, which crystallizes as [(C5Me5)2Y(μ-N3)]3, 4, when obtained from 1 and 1-adamantyl azide. The samarium analogue [(C5Me5)2SmN3]x, 5, can be produced similarly from 2 and NaN3 and crystallized from MeCN as [(C5Me5)2Sm(NCMe)(μ-N3)]3, 6, and {[(C5Me5)2Sm(μ-N3)][(C5Me5)2Sm(NCMe)(μ-N3)]}n, 7. Complexes 1 and 2 react with stoichiometric amounts of acetone and benzophenone to form the ketone adducts [(C5Me5)2Ln(OCMe2)2][BPh4] (Ln = Y, 8; Sm, 9) and [(C5Me5)2Ln(OCPh2)2][BPh4] (Ln = Y, 10; Sm, 11), respectively. Phenanthroline (phen) coordinates to 1 to form [(C5Me5)2Y(phen)][BPh4], 12. Complexes 1 and 2 react with pyridine (py) to form [(C5Me5)2Ln(py)2][BPh4], (Ln = Y, 13; Sm, 14). Complexes 3, 8, 10, and 12 can also be made from the solvated cation [(C5Me5)2Y(THF)2][BPh4]. The reaction of 1 with PhNNPh yields the diamagnetic adduct [(C5Me5)2Y(PhNNPh)][BPh4], 15, which transforms in benzene to the radical anion complex (C5Me5)2Y(PhNNPh), 16, via a one electron reduction by (BPh4)−. Complex 1 similarly reacts with phenazine (phz) to produce the first rare earth phenazine radical anion complex {[(C5Me5)2Y]2(phz)}{BPh4}, 17. Further reduction of phenazine by (BPh4)− in 17 yields [(C5Me5)2Y]2(phz), 18, which contains the common (phz)2− dianion. The reduction of fluorenone by (BPh4)− is also reported.
Co-reporter:Ming Fang ; Jefferson E. Bates ; Sara E. Lorenz ; David S. Lee ; Daniel B. Rego ; Joseph W. Ziller ; Filipp Furche
Inorganic Chemistry 2011 Volume 50(Issue 4) pp:1459-1469
Publication Date(Web):January 4, 2011
DOI:10.1021/ic102016k
New syntheses of complexes containing the recently discovered (N2)3− radical trianion have been developed by examining variations on the LnA3/M reductive system that delivers “LnA2” reactivity when Ln = scandium, yttrium, or a lanthanide, M = an alkali metal, and A = N(SiMe3)2 and C5R5. The first examples of LnA3/M reduction of dinitrogen with aryloxide ligands (A = OC6R5) are reported: the combination of Dy(OAr)3 (OAr = OC6H3tBu2-2,6) with KC8 under dinitrogen was found to produce both (N2)2− and (N2)3− products, [(ArO)2Dy(THF)2]2(μ-η2:η2-N2), 1, and [(ArO)2Dy(THF)]2(μ-η2:η2-N2)[K(THF)6], 2a, respectively. The range of metals that form (N2)3− complexes with [N(SiMe3)2]− ancillary ligands has been expanded from Y to Lu, Er, and La. Ln[N(SiMe3)2]3/M reactions with M = Na as well as KC8 are reported. Reduction of the isolated (N2)2− complex {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2), 3, with KC8 forms the (N2)3− complex, {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2)[K(THF)6], 4a, in high yield. The reverse transformation, the conversion of 4a to 3 can be accomplished cleanly with elemental Hg. The crown ether derivative {[(Me3Si)2N]2Y(THF)}2(μ-η2:η2-N2)[K(18-crown-6)(THF)2] was isolated from reduction of 3 with KC8 in the presence of 18-crown-6 and found to be much less soluble in tetrahydrofuran (THF) than the [K(THF)6]+ salt, which facilitates its separation from 3. Evidence for ligand metalation in the Y[N(SiMe3)2]3/KC8 reaction was obtained through the crystal structure of the metallacyclic complex {[(Me3Si)2N]2Y[CH2Si(Me2)NSiMe3]}[K(18-crown-6)(THF)(toluene)]. Density functional theory previously used only with reduced dinitrogen complexes of closed shell Sc3+ and Y3+ was extended to Lu3+ as well as to open shell 4f9 Dy3+ complexes to allow the first comparison of bonding between these four metals.
Co-reporter:Ian J. Casely ; Joseph W. Ziller ; Bruce J. Mincher
Inorganic Chemistry 2011 Volume 50(Issue 4) pp:1513-1520
Publication Date(Web):December 30, 2010
DOI:10.1021/ic102119y
A series of bis(aryl) bismuth compounds containing (N,C,N)-pincer ligands, [2,6-(Me2NCH2)2C6H3]− (Ar′), have been synthesized and structurally characterized to compare the coordination chemistry of Bi3+ with similarly sized lanthanide ions, Ln3+. Treatment of Ar′2BiCl, 1, with ClMg(CH2CH═CH2) affords the allyl complex Ar′2Bi(η1-CH2CH═CH2), 2, in which only one allyl carbon atom coordinates to bismuth. Complex 1 reacts with KOtBu and KOC6H3Me2-2,6 to yield the alkoxide Ar′2Bi(OtBu), 3, and aryloxide Ar′2Bi(OC6H3Me2-2,6), 4, respectively, but the analogous reaction with the larger KOC6H3tBu2-2,6 forms [Ar′2Bi][OC6H3tBu2-2,6], 6, in which the aryloxide ligand acts as an outer sphere anion. Chloride is removed from 1 by NaBPh4 to form [Ar′2Bi][BPh4], 5, which crystallizes from THF in an unsolvated form with tetraphenylborate as an outer sphere counteranion.
Co-reporter:Dr. Michael K. Takase;Dr. Joseph W. Ziller ; William J. Evans
Chemistry - A European Journal 2011 Volume 17( Issue 17) pp:4871-4878
Publication Date(Web):
DOI:10.1002/chem.201002857
Abstract
The steric factors that allow trivalent [(C5Me5)3U] (1) to function as a three-electron reductant with C8H8 to form tetravalent [{(C5Me5)(C8H8)U}2(μ-C8H8)] (2) have been explored by examining the synthesis and reactivity of the intermediate, “[(C5Me5)2(C8H8)U]” (3), and the slightly less crowded analogues, [(C5Me5)(C5Me4H)(C8H8)U] and [(C5Me4H)2(C8H8)U], that have, successively one less methyl group. The reaction of [{(C5Me5)(C8H8)U(μ-OTf)}2] (4; OTf=OSO2CF3) with two equivalents of KC5Me5 in THF gave ring-opening to “[(C5Me5)(C8H8)U{O(CH2)4(C5Me5)}]” consistent with in situ formation of 3. Reaction of 4 with two and four equivalents of KC5Me4H generates two equivalents of [(C5Me5)(C5Me4H)(C8H8)U] (5) and [(C5Me4H)2(C8H8)U] (6), respectively, which in contrast to 3 were isolable. Tetravalent 5 reduces phenazine and PhEEPh (E=S, Se, and Te) to form the tetravalent uranium reduction products, [{(C5Me5)(C8H8)U}2(μ-C12H8N2)] (7), [{(C5Me5)(C8H8)U}2(μ-SPh)2] (8), [{(C5Me5)(C8H8)U}2(μ-SePh)2] (9), and [{(C5Me5)(C8H8)U}2(μ-TePh)2] (10), consistent with sterically induced reduction. In contrast, the less sterically crowded 6 does not react with these substrates.
Co-reporter:Selvan Demir;Thomas J. Mueller;Joseph W. Ziller ; William J. Evans
Angewandte Chemie International Edition 2011 Volume 50( Issue 2) pp:515-518
Publication Date(Web):
DOI:10.1002/anie.201005898
Co-reporter:Selvan Demir;Thomas J. Mueller;Joseph W. Ziller ; William J. Evans
Angewandte Chemie 2011 Volume 123( Issue 2) pp:535-538
Publication Date(Web):
DOI:10.1002/ange.201005898
Co-reporter:Ian J. Casely, Joseph W. Ziller, and William J. Evans
Organometallics 2011 Volume 30(Issue 18) pp:4873-4881
Publication Date(Web):August 23, 2011
DOI:10.1021/om200419k
The yttrium alkynide (C5Me5)2Y(C≡CPh)(THF), 1, and the related trienediyl [(C5Me5)2Y]2(μ-η2:η2-PhC═C═C═CPh), 2, can be isolated from the reaction of (C5Me5)2Y(η3-CH2CHCH2)(THF) with phenylacetylene in THF and hexane, respectively. Complex 1 reacts with tBuN═C═NtBu to afford the conventional amidinate insertion product (C5Me5)2Y[tBuNC(C≡CPh)NtBu-κ2N,N′], 3. However, the analogous reaction with iso-propyl and cyclohexyl carbodiimides involves C–H activation and forms the iminovinyl complexes (C5Me5)2Y[C(═CHPh)C(N═CMe2)═NiPr-κ2C,N], 4, and (C5Me5)2Y{C(═CHPh)C[N═C(CH2)5]═NCH(CH2)5-κ2C,N}, 5, respectively. The reaction is formally a variation of the Alder-ene reaction in which a C–H bond of the carbodiimide (ene) is activated and transferred to the alkynide ligand (enophile) bound to yttrium. The trienediyl 2 reacts with iso-propyl carbodiimide via conventional insertion to form a bis(amidinate) product with a trienediyl linker, namely, (C5Me5)2Y[μ-κ2-(iPrN)2C–C(Ph)═C═C═C(Ph)–C(NiPr)2]Y(C5Me5)2, 6. The alkynide ligand in 1 is also modified in the reaction with benzylcyanide that forms an unusual insertion product, the amidonitrile complex [(C5Me5)2Y{μ-N(H)C(CH2Ph)═C[C(Ph)═CHPh]C≡N}]2, 7.
Co-reporter:Selvan Demir, Thomas J. Mueller, Joseph W. Ziller, and William J. Evans
Organometallics 2011 Volume 30(Issue 11) pp:3083-3089
Publication Date(Web):May 9, 2011
DOI:10.1021/om2001876
The σ bond metathesis reactivity of (C5Me4H)3Sc, which has a (η5-C5Me4H)2Sc(η1-C5Me4H) structure in the solid state, has been investigated and compared with that of a conventional (C5Me4H)− metallocene complex, (C5Me4H)2Sc(η3-C3H5), 1. Complex 1 reacts with PhEEPh (E = S, Se, Te) in toluene to form the σ bond metathesis products (C3H5)EPh and [(C5Me4H)2Sc(SPh)]2, (C5Me4H)2Sc(SePh), and (C5Me4H)2Sc(TePh), respectively. Analogous reactions in toluene/THF generate the THF solvates (C5Me4H)2Sc(EPh)(THF). The monometallic sulfur derivative (C5Me4H)2Sc(Spy-κ2-S,N) forms from the reaction of 1 with 2,2′-dipyridyl disulfide, pySSpy. (C5Me4H)3Sc reacts similarly, showing that the (η1-C5Me4H)− solid-state structure yields Sc–C bond reactivity in solution.
Co-reporter:Thomas J. Mueller, Gregory W. Nyce, and William J. Evans
Organometallics 2011 Volume 30(Issue 5) pp:1231-1235
Publication Date(Web):February 22, 2011
DOI:10.1021/om101149z
Reactions between (η5-C5Me5)3M and (η5-C5Me5)2M′(μ-Ph)2BPh2 (M, M′ = La, Ce, Pr, Nd, Sm, and U; M radius < M′ radius) were examined to evaluate the relative steric crowding in the (C5Me5)3M series as a function of metal size and 4f vs 5f electron configuration. The sterically more crowded (C5Me5)3M complexes transfer (C5Me5)− to (C5Me5)2M′(μ-Ph)2BPh2 to generate less crowded (C5Me5)3M′ products and (C5Me5)2M(μ-Ph)2BPh2 in mixtures with equilibrium constants in the range that allows all four components to be observed by NMR spectroscopy. The (C5Me5)3M to (C5Me5)3M′ ratios depend on the difference in size of the two metals. Hence, (C5Me5)3Sm and (C5Me5)2La(μ-Ph)2BPh2 form a mixture with 99% (C5Me5)3La and 1% (C5Me5)3Sm, but the analogous reaction with (C5Me5)2Nd(μ-Ph)2BPh2 contains 90% (C5Me5)3Nd and 10% (C5Me5)3Sm. In analogous reactions with (C5Me5)2U(μ-Ph)2BPh2 and (C5Me5)3Ln lanthanide complexes, a size dependence is also observed, but the (C5Me5)3Ln complexes are favored over (C5Me5)3U to a greater extent than expected based on size differences.
Co-reporter:Michael K. Takase, Nathan A. Siladke, Joseph W. Ziller, and William J. Evans
Organometallics 2011 Volume 30(Issue 3) pp:458-465
Publication Date(Web):January 20, 2011
DOI:10.1021/om100700p
[(C5Me5)(C8H8)U(μ-OTf)]2, 1 (OTf = OSO2CF3), reacts with LiMe to form the metathesis product (C5Me5)(C8H8)UMe, 2, as well as the product of a methyl C−H activation, (C8H8)(C5Me4CH2)U, 3. Methane was observed in the 1H NMR spectrum of the reaction mixture, which is consistent with the metalation of a (C5Me5)− ligand by the uranium methyl group in 2. Complex 2 was identified in this reaction mixture by addition of iPrN═C═NiPr to form the previously reported (C5Me5)(C8H8)U[iPrNC(Me)NiPr-κ2N,N′], 4. The reactions of 1 with LiEt and LiCH2CMe3 similarly form mixtures at room temperature that contain 3 and compounds with 1H NMR spectra consistent with (C5Me5)(C8H8)UEt, 5, and (C5Me5)(C8H8)U(CH2CMe3), 6, respectively. Complexes 2, 5, and 6 convert to 3 after 24 h at 100 °C. Complex 3 can also be synthesized at 100 °C from (C5Me5)(C8H8)UPh, 7, and was characterized as the THF adduct of a “tuck-in” complex, (η8-C8H8)(η5:η1-C5Me4CH2)U(THF), 8, by X-ray crystallography. Complex 3 allowed the insertion chemistry of an isolable f element (η5:η1-C5Me4CH2)2− metallocene complex to be studied for the first time and provides access to new heteroleptic tethered metallocenes. iPrN═C═NiPr inserts into the U−C(η1-C5Me4CH2) bond of 3 to form the amidinate complex (C8H8)[C5Me4CH2C(NiPr)2]U, 9. tBuN≡C reacts in a series of steps through intermediates such as (C8H8)(C5Me4CH2C═NtBu)U, 10, and (C8H8)(C5Me4CH2C═NtBu)U(C≡NtBu) that leads to the isolation of the isocyanide double-insertion product, (η8-C8H8)[η5-C5Me4CH2C(═C═NtBu)NtBu-κN]U, 11.
Co-reporter:Selvan Demir ; Sara E. Lorenz ; Ming Fang ; Filipp Furche ; Gerd Meyer ; Joseph W. Ziller
Journal of the American Chemical Society 2010 Volume 132(Issue 32) pp:11151-11158
Publication Date(Web):July 21, 2010
DOI:10.1021/ja102681w
Investigation of the bis(tetramethylcyclopentadienyl) metallocene chemistry of scandium has revealed that the method involving reduction of trivalent salts with alkali metals used with lanthanides can also be applied to scandium to make a dinitrogen complex of the first member of the transition metal series. ScCl3 reacts with 2 equiv of KC5Me4H to form (C5Me4H)2ScCl(THF), 1, which reacts with allylmagnesium chloride to make (C5Me4H)2Sc(η3-C3H5), 2. Complex 2 reacts with [HNEt3][BPh4] to yield [(C5Me4H)2Sc][(μ-Ph)BPh3], 3, which has just one primary Sc−C(phenyl) contact connecting the tetraphenylborate anion and the metallocene cation. Treatment of 3 with KC8 in THF under N2 generates [(C5Me4H)2Sc]2(μ-η2:η2-N2), which has a coplanar arrangement of scandium and nitrogen atoms within a square planar array of tetramethylcyclopentadienyl rings. Density functional calculations explain the bonding that results in the 1.239(3) Å N−N bond distance in the (N═N)2− moiety.
Co-reporter:Tanya K. Todorova ; Laura Gagliardi ; Justin R. Walensky ; Kevin A. Miller
Journal of the American Chemical Society 2010 Volume 132(Issue 35) pp:12397-12403
Publication Date(Web):August 18, 2010
DOI:10.1021/ja103588w
Recent studies of organouranium chemistry have provided unusual pairs of similar polymetallic molecules containing (N)3− and (O)2− ligands, namely [(C5Me5)U(μ-I)2]3(μ3-N), 1, and [(C5Me5)U(μ-I)2]3(μ3-O), 2, and chair and boat conformations of [(C5Me5)2U(μ-N)U(μ-N3)(C5Me5)2]4, 3. These compounds were analyzed by density functional theory and multiconfigurational quantum chemical studies to differentiate nitride versus oxide in molecules for which the crystallographic data were not definitive and to provide insight into the electronic structure and unique chemical bonding of these polymetallic compounds. Calculations were also performed on [(C5Me5)2UN3(μ-N3)]3, 4, and [(C6F5)3BNU(N[Me]Ph)3], 5, for comparison with 1 and 3. On the basis of these results, the complex, [(C5Me5)U(μ3-E)]8, 6, for which only low-quality X-ray crystallographic data are available, was analyzed to predict if E is nitride or oxide.
Co-reporter:Benjamin M. Schmiege, Joseph W. Ziller, and William J. Evans
Inorganic Chemistry 2010 Volume 49(Issue 22) pp:10506-10511
Publication Date(Web):October 22, 2010
DOI:10.1021/ic101558e
Treatment of [(C5Me5)2YH]2, 1, with KC8 under N2 in methylcyclohexane generates the unsolvated reduced dinitrogen complex, [(C5Me5)2Y]2(μ-η2:η2-N2), 2, and extends the range of yttrium and lanthanide LnZ2Z′/M (Z = monoanion; M = alkali metal) dinitrogen reduction reactions to (Z′)− = (H)−. The hydride complex, 1, is unique in this reactivity compared to other alkane-soluble yttrium metallocenes, [(C5Me5)2YX]x {X = [N(SiMe3)2]−, (Me)−, (C3H5)−, and (C5Me5)−} which did not generate 2 when treated with KC8. [(C5Me5)2LnH]x/KC8/N2 reactions with Ln = La and Lu did not give isolable dinitrogen complexes. Complex 2 and the unsolvated lutetium analogue, [(C5Me5)2Lu]2(μ-η2:η2-N2), 3, were obtained using benzene as a solvent and [(C5Me5)2Ln][(μ-Ph)2BPh2] as precursors with excess KC8. Complex 2 functions as a reducing agent with PhSSPh to form [(C5Me5)2Y(μ-SPh)]2, 4, in high yield.
Co-reporter:Justin R. Walensky ; Richard L. Martin ; Joseph W. Ziller
Inorganic Chemistry 2010 Volume 49(Issue 21) pp:10007-10012
Publication Date(Web):September 30, 2010
DOI:10.1021/ic1013285
The synthesis of a rare trivalent Th3+ complex, (C5Me5)2[iPrNC(Me)NiPr]Th, initiated a density functional theory analysis on the electronic and molecular structures of trivalent actinide complexes of this type for An = Th, Pa, U, Np, Pu, and Am. While the 6d orbital is found to accommodate the unpaired spin in the Th3+ species, the next member of the series, Pa, is characterized by an f2 ground state, and later actinides successively fill the 5f shell. In this report, we principally examine the evolution of the bonding as one advances along the actinide row. We find that the early actinides (Pa−Np) are characterized by localized f orbitals and essentially ionic bonding, whereas the f orbitals in the later members of the series (Pu, Am) exhibit significant interaction and spin delocalization into the carbon- and nitrogen-based ligand orbitals. This is perhaps counter-intuitive since the f orbital radius and hence metal−ligand overlap decreases with increasing Z, but this trend is counter-acted by the fact that the actinide contraction also leads to a stabilization of the f orbital manifold that leads to a near degeneracy between the An 5f and cyclopentadienyl π-orbitals for Pu and Am, causing a significant orbital interaction.
Co-reporter:Sara E. Lorenz ; Benjamin M. Schmiege ; David S. Lee ; Joseph W. Ziller
Inorganic Chemistry 2010 Volume 49(Issue 14) pp:6655-6663
Publication Date(Web):June 14, 2010
DOI:10.1021/ic100682d
The metallocene precursors needed to provide the tetramethylcyclopentadienyl yttrium complexes (C5Me4H)3Y, [(C5Me4H)2Y(THF)]2(μ-η2:η2-N2), and [(C5Me4H)2Y(μ-H)]2 for reactivity studies have been synthesized and fully characterized, and their reaction chemistry has led to an unexpected conversion of an azide to an amide. (C5Me4H)2Y(μ-Cl)2K(THF)x, 1, synthesized from YCl3 and KC5Me4H reacts with allylmagnesium chloride to make (C5Me4H)2Y(η3-C3H5), 2, which is converted to [(C5Me4H)2Y][(μ-Ph)2BPh2], 3, with [Et3NH][BPh4]. Complex 3 reacts with KC5Me4H to form (C5Me4H)3Y, 4. The reduced dinitrogen complex, [(C5Me4H)2Y(THF)]2(μ-η2:η2-N2), 5, can be synthesized from either [(C5Me4H)2Y]2[(μ-Ph)2BPh2], 3, or (C5Me4H)3Y, 4, with potassium graphite under a dinitrogen atmosphere. The 15N labeled analogue, [(C5Me4H)2Y(THF)]2(μ-η2:η2-15N2), 5-15N, has also been prepared, and the 15N NMR data have been compared to previously characterized reduced dinitrogen complexes. Complex 2 reacts with H2 to form the corresponding hydride, [(C5Me4H)2Y(μ-H)]2, 6. Complex 5 displays similar reactivity to that of the analogous [(C5Me4H)2Ln(THF)]2(μ-η2:η2-N2) complexes (Ln = La, Lu), with substrates such as phenazine, anthracene, and CO2. In addition, 5 reduces Me3SiN3 to form (C5Me4H)2Y[N(SiMe3)2], 7.
Co-reporter:William J. Evans ; Justin R. Walensky ;Joseph W. Ziller
Inorganic Chemistry 2010 Volume 49(Issue 4) pp:1743-1749
Publication Date(Web):January 22, 2010
DOI:10.1021/ic902141f
The reductive chemistry of U3+ in the metallocene amidinate coordination environment of (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U, 1, has been explored. Two equivalents of 1 react with PhSSPh and 2,2′-dithiopyridine (pySSpy) to produce (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U(SPh), 2, and (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U(Spy), 3, respectively. Complexes 2 and 3 can also be synthesized through insertion of iPrN═C═NiPr into the methyl group in (C5Me5)2UMe(SPh) and (C5Me5)2UMe(Spy), 4, respectively. Complex 1 readily reduces the Cu1+ reagents, CuBr, CuI, and CuO2CMe, to produce the corresponding (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]UX complexes (X = Br, 5; I, 6; O2CMe, 7). X-ray crystallography established complex 7 as the first f element complex containing a monodentate acetate anion. Complex 7 can also be obtained by reaction of (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]UMe with CO2 at 80 psi. In contrast to the reactions above, 1 reduces TlC5H5 with the unusual loss of (C5Me5)− to form (C5Me5)(C5H5)2[iPrNC(Me)NiPr-κ2N,N′]U, 8.
Co-reporter:William J. Evans ; Elizabeth Montalvo ; Joseph W. Ziller ; Antonio G. DiPasquale ;Arnold L. Rheingold
Inorganic Chemistry 2010 Volume 49(Issue 1) pp:222-228
Publication Date(Web):December 3, 2009
DOI:10.1021/ic901790t
The utility of the 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato ligand, (hpp)−, in uranium chemistry has been probed by synthesizing metallocene complexes and studying their reactivity. (C5Me5)2UMe2 reacts with 1 equiv of Hhpp to form (C5Me5)2(hpp)UMe, 1, which does not react further with Hhpp. (C5Me5)2UCl2 reacts with Khpp to form (C5Me5)2(hpp)UCl, 2, which similarly does not react with additional Khpp. Complex 2 reacts with NaN3 to form the azide complex, (C5Me5)2(hpp)UN3, 3. The trivalent uranium (hpp)− metallocene complex, (C5Me5)2(hpp)U, 4, can be synthesized by the reaction of [(C5Me5)2U][BPh4] with Khpp and from 2 with KC8. Complex 4 can be oxidized with Ph3P═Se to produce the tetravalent product, [(C5Me5)2(hpp)U]2(μ-Se), 5. The reaction of 4 with Me3SiN3 provides the pentavalent uranium complex, (C5Me5)2(hpp)U(=NSiMe3), 6
Co-reporter:Thomas J. Mueller, Joseph W. Ziller and William J. Evans
Dalton Transactions 2010 vol. 39(Issue 29) pp:6767-6773
Publication Date(Web):13 May 2010
DOI:10.1039/C002654A
To further explore the reactivity of the (C5Me5)− ligand in the sterically crowded (C5Me5)3M complexes, reactions with PhEEPh (E = S, Se, Te) have been examined. With M = La, Pr, Nd, Sm, and Y, PhSSPh reacts to form the expected reduction products, [(C5Me5)2M(SPh)]2, but the major organic byproduct is not the sterically induced reduction product, (C5Me5)2. Instead, the sigma bond metathesis product, C5Me5SPh, is the major byproduct. In contrast, reactions with (C5Me5)3Ce and (C5Me5)3U gave a mixture of C5Me5SPh and (C5Me5)2 as byproducts. PhSSPh reactions with the lanthanide nitrile adducts, (C5Me5)3Ln(NCCMe3)2 (Ln = La, Ce) and (C5Me5)3Nd(NCCMe3), formed [(C5Me5)2Ln(SPh)(NCCMe3)]2 and only C5Me5SPh as the byproduct. PhSeSePh reactions paralleled the PhSSPh results, but reactions of PhTeTePh with (C5Me5)3La, (C5Me5)3Sm, and (C5Me5)3La(NCCMe3)2 gave only (C5Me5)2 as a byproduct.
Co-reporter:Michael K. Takase, Ming Fang, Joseph W. Ziller, Filipp Furche, William J. Evans
Inorganica Chimica Acta 2010 Volume 364(Issue 1) pp:167-171
Publication Date(Web):15 December 2010
DOI:10.1016/j.ica.2010.07.074
The U4+ cyclooctatetraenyl complex, [(C5Me5)(C8H8)U]2(μ-C8H8), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me2bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η5-C5Me5)(η8-C8H8)U(Me2bipy-κ2N,N′) and (η5-C5Me5)(η8-C8H8)U(bipy-κ2N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U4+ complexes of bipyridyl radical anions. Hence, only one of the (C8H8)2− ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C8H8)2−, Me2bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.The U4+ cyclooctatetraenyl complex, [(C5Me5)(C8H8)U]2(μ-C8H8), 1, reacts with 4,4′-dimethyl-2,2′-bipyridine (Me2bipy) and 2,2′-bipyridine (bipy) to form (η5-C5Me5)(η8-C8H8)U(Me2bipy-κ2N,N′) and (η5-C5Me5)(η8-C8H8)U(bipy-κ2N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that these complexes are best described as U4+ complexes of bipyridyl radical anions.
Co-reporter:Selvan Demir, Elizabeth Montalvo, Joseph W. Ziller, Gerd Meyer, and William J. Evans
Organometallics 2010 Volume 29(Issue 23) pp:6608-6611
Publication Date(Web):November 3, 2010
DOI:10.1021/om100917w
Attempts to generate a scandium metallocene oxide using N2O have revealed that N2O undergoes facile insertion into metal−carbon bonds of allyl metallocene complexes to form (RN2O)− ligands where R = C3H5. This has been demonstrated in reactions with the tetramethylcyclopentadienyl allyl complexes (C5Me4H)2M(η3-C3H5) (M = Sc, Y) and the pentamethylcyclopentadienyl allyl compounds (C5Me5)2M(η3-C3H5) (M = Y, Sm, La), which generate the insertion products [(C5Me4H)2M(μ-η1:η2-ON═NC3H5)]2 (M = Sc, 1; Y, 2) and [(C5Me5)2M(μ-η1:η2-ON═NC3H5)]2 (M = Y, 3; Sm, 4; La, 5), respectively.
Co-reporter:Ian J. Casely, YoungSung Suh, Joseph W. Ziller, and William J. Evans
Organometallics 2010 Volume 29(Issue 21) pp:5209-5214
Publication Date(Web):June 15, 2010
DOI:10.1021/om100364k
Nitric oxide (NO) reacts with (C5Me5)2Ln(η3-CH2CHCH2)(THF) to form the first crystallographically characterized group 3 and organolanthanide NO insertion products, namely, {(C5Me5)2Ln[μ-ONN(CH2CH═CH2)O]}2 (Ln = Y, La, Sm). The [ONN(allyl)O]− anions adopt an unusual trans geometry and presumably arise from insertion of NO into the Ln−C(allyl) bond followed by coupling of the (allyl-NO) radical anion with a second molecule of NO. Heating a solution of the yttrium product at 110 °C for 20 h affords (C5Me5)2Y[ONN(CH2CH═CH2)O-κ2O,O′], resulting from cleavage of the dimer and formation of the monomer as the thermodynamic product. The N═N, N−O, and Ln−O bond distances suggest that a zwitterionic (−)O−N═N(+)(R)−O(−) resonance structure is a main contributor to the bonding of these N-allyl-N-nitrosohydroxylaminato ligands.
Co-reporter:Elizabeth Montalvo, Kevin A. Miller, Joseph W. Ziller, and William J. Evans
Organometallics 2010 Volume 29(Issue 18) pp:4159-4170
Publication Date(Web):August 31, 2010
DOI:10.1021/om1007538
The reactivity of the uranium tuck-in and tuck-over cyclopentadienyl moieties {[η5:η1-C5Me4CH2]U}2+ and {U[μ-η5:η1-C5Me4CH2]U}6+, respectively, has been investigated by examining the reactivity of (C5Me5)U[μ-η5:η1:η1-C5Me3(CH2)2](μ-H)2U(C5Me5)2, 1, and (C5Me5)(η5:η1-C5Me4CH2)(hpp)U [(hpp)− = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato], 2, with hydrogen, silyl halide, sulfide, amine, and hydrocarbon reagents. The reactivity of 2, which has a single tuck-in reactive site, provides valuable comparisons with that of 1, where the presence of two hydride ligands as well as both tuck-in and tuck-over moieties leads to products in which multiple transformations have occurred. Both 1 and 2 react with H2 to form hydrides, namely, the [(C5Me5)2UH2]2/[(C5Me5)2UH]2 equilibrium mixture and (C5Me5)2(hpp)UH, 3, respectively. Attempts to make a simple chloride derivative of 1 with Me3SiCl yielded a new tethered metallocene, (C5Me5)ClU(η5-C5Me4CH2SiMe2CH2-κC), 4, which formally results from a silylmethyl C−H bond activation as well as insertion of the silyl group into the U−CH2 tuck-in linkage. The trivalent chloride [(C5Me5)2UCl]3, 5, is the byproduct of this reaction. This sequence of reactions is probably not initiated by the tuck-in functionality, since 2 does not react with Me3SiCl under comparable conditions. Hydride complex 3 reacts readily with Me3SiCl to form (C5Me5)2(hpp)UCl, but (C5Me5)2(hpp)UMe, 6, requires 100 °C to form the chloride. Complex 1 also displays complicated reactivity with HC≡CPh, whereas 2 and 3 react with this substrate to form (C5Me5)2(hpp)U(C≡CPh), 7, in high yield. Complex 1 converts PhSSPh cleanly to (C5Me5)2U(SPh)2, 8, in a reaction that involves S−S cleavage and C−H bond formation. Complex 1 reacts with a 1:1 mixture of PhSSPh and p-tolylSS-p-tolyl to form a 1:2:1 mixture of (C5Me5)2U(SPh)2, 8, (C5Me5)2U(SPh)(S-p-tolyl), 9, and (C5Me5)2U(S-p-tolyl)2, 10, but the mechanistic implications are compromised by exchange of 8 with 10 to make 9. PhSH, a possible intermediate in a σ-bond metathesis reaction pathway for the 1/PhSSPh reaction, reacts with 1 to form 8. Complex 2 forms a σ-bond metathesis product, (C5Me4CH2SPh)(C5Me5)(hpp)U(SPh), 11, from PhSSPh that contains a new peralkylated cyclopentadienyl ligand. The reaction of 2 and PhSH forms (C5Me5)2(hpp)U(SPh), 12. Complexes 1 and 2 react similarly with PhNH2 to generate amide products (C5Me5)2U(NHPh)2, 13, and (C5Me5)2(hpp)U(NHPh), 14, respectively. No reactions were observed between complex 1 or 2 and methane, benzene, or toluene, but 1 and 2 react with CuI to form (C5Me5)2UI2, 15, and (C5Me5)2(hpp)UI, 16, respectively, in which the CH2 tuck components have been converted to methyl groups.
Co-reporter:Elizabeth Montalvo, Joseph W. Ziller, Antonio G. DiPasquale, Arnold L. Rheingold and William J. Evans
Organometallics 2010 Volume 29(Issue 9) pp:2104-2110
Publication Date(Web):April 13, 2010
DOI:10.1021/om100076s
Monoalkyl uranium chemistry has been probed by reacting the metallocene chloride complex (C5Me5)2(hpp)UCl, 1, (hpp)− = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato, with alkyl lithium reagents. Complex 1 reacts with LiMe, LiC≡CPh, LiPh, and LiEt to generate (C5Me5)2(hpp)UMe, 2, (C5Me5)2(hpp)U(C≡CPh), 3, (C5Me5)2(hpp)UPh, 4, and (C5Me5)2(hpp)UEt, 5, respectively. Complexes 2−5 react with CuI to form the iodide complex (C5Me5)2(hpp)UI, 6, and methane, phenylacetylene, benzene, and ethane, respectively. Attempts to make a neopentyl analogue of 2−5 from the reaction of 1 with neopentyllithium yielded the “tuck-in” complex (C5Me5)(η5:η1-C5Me4CH2)(hpp)U, 7. Complex 7 can also be synthesized by heating 5 to 70 °C in a reaction that forms ethane as a byproduct.
Co-reporter:William J. Evans, Justin R. Walensky and Joseph W. Ziller
Organometallics 2010 Volume 29(Issue 4) pp:945-950
Publication Date(Web):January 22, 2010
DOI:10.1021/om901006t
The insertion reactivity of (C5Me5)2U(C≡CPh)2, 1, has been studied with CO2, PhNCO, Me3CC≡N, and Me3CN≡C. Insertion into both U−C≡CPh bonds of 1 occurs with the first three substrates to form (C5Me5)2U(O2CC≡CPh)2, 2, (C5Me5)2U[PhNC(C≡CPh)O-κ2N,O]2, 3, and (C5Me5)2U[N═C(CMe3)(C≡CPh)]2, 4, respectively. Only 1 equiv of Me3CN≡C reacts with 1 to form (C5Me5)2[(PhC≡C)C═N(CMe3)-η2C,N]U(C≡CPh), 5, a result similar to the iPrN═C═NiPr insertion that forms (C5Me5)2[iPrNC(C≡CPh)NiPr-κ2N,N′]U(C≡CPh), 6.
Co-reporter:William J. Evans, Justin R. Walensky and Joseph W. Ziller
Organometallics 2010 Volume 29(Issue 1) pp:101-107
Publication Date(Web):December 8, 2009
DOI:10.1021/om9008179
The effect of the heteroleptic ligand sets {(C5Me5)2[iPrNC(Me)NiPr]}3− and {(C5Me5)2[(Me)NNN(Ad)]}3− on actinide−carbon bond reactivity has been evaluated by examining the monomethyl actinide metallocene amidinate complexes (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]AnMe (An = U, 1; Th, 2) and the triazenido complex (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UMe, 3. This has led to a facile method to convert methyl groups in U4+ and Th4+ complexes to halide and pseudo-halide ligands. Complexes 1 and 3 react with AgOSO2CF3 (AgOTf) to produce (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U(OTf), 4, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(OTf), 5, respectively. The methyl complexes are also reactive with copper reagents, as demonstrated by the reactions of CuI with 1 and 2 to make (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]UI, 6, and (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]ThI, 7, respectively. Similarly, reactions of CuBr with 1 and 3 generate (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]UBr, 8, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]UBr, 9, respectively. These triflate and halide complexes are good precursors to other complexes with these ligand sets, as exemplified by their reactions with NaN3, which produce (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U(N3), 10, and (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(N3), 11, respectively. However, the reactions of 4 and 6 with LiCH2SiMe3 lead to reduction and the formation of the trivalent uranium heteroleptic metallocene (C5Me5)2[iPrNC(Me)NiPr-κ2N,N′]U, 12. LiCH2SiMe3 does not cause reduction with the triazenido ligand set, and the monoalkyl complex (C5Me5)2[(Me)NNN(Ad)-κ2N1,3]U(CH2SiMe3), 13, can be isolated.
Co-reporter:WilliamJ. Evans ;NathanA. Siladke ;JosephW. Ziller Dr.
Chemistry - A European Journal 2010 Volume 16( Issue 3) pp:796-800
Publication Date(Web):
DOI:10.1002/chem.200902428
Co-reporter:WilliamJ. Evans ;ThomasJ. Mueller ;JosephW. Ziller Dr.
Chemistry - A European Journal 2010 Volume 16( Issue 3) pp:964-975
Publication Date(Web):
DOI:10.1002/chem.200901990
Abstract
The limits of steric crowding in organometallic metallocene complexes have been examined by studying the synthesis of [(C5Me5)3MLn] complexes as a function of metal in which L=Me3CCN, Me3CNC, and Me3SiCN. The bis(tert-butyl nitrile) complexes [(C5Me5)3Ln(NCCMe3)2] (Ln=La, 1; Ce, 2; Pr, 3) can be isolated with the largest lanthanide metal ions, La3+, Ce3+, and Pr3+. The Pr3+ ion also forms an isolable mono-nitrile complex, [(C5Me5)3Pr(NCCMe3)] (4), whereas for Nd3+ only the mono-adduct [(C5Me5)3Nd(NCCMe3)] (5) was observed. With smaller metal ions, Sm3+ and Y3+, insertion of Me3CCN into the MC(C5Me5) bond was observed to form the cyclopentadiene-substituted ketimide complexes [(C5Me5)2Ln{NC(C5Me5)(CMe3)}(NCCMe3)] (Ln=Sm, 6; Y, 7). With tert-butyl isocyanide ligands, a bis-isocyanide product can be isolated with lanthanum, [(C5Me5)3La(CNCMe3)2] (8), and a mono-isocyanide product with neodymium, [(C5Me5)3Nd(CNCMe3)] (9). Silicon–carbon bond cleavage was observed in reactions between [(C5Me5)3Ln] complexes and trimethylsilyl cyanide, Me3SiCN, to produce the trimeric cyanide complexes [{(C5Me5)2Ln(μ-CN)(NCSiMe3)}3] (Ln=La, 10; Pr, 11). With uranium, a mono-nitrile reaction product, [(C5Me5)3U(NCCMe3)] (12), which is analogous to 5, was obtained from the reaction between [(C5Me5)3U] and Me3CCN, but [(C5Me5)3U] reacts with Me3CNC through CN bond cleavage to form a trimeric cyanide complex, [{(C5Me5)2U(μ-CN)(CNCMe3)}3] (13).
Co-reporter:William J. Evans ; Ming Fang ; Gaël Zucchi ; Filipp Furche ; Joseph W. Ziller ; Ryan M. Hoekstra ;Jeffrey I. Zink
Journal of the American Chemical Society 2009 Volume 131(Issue 31) pp:11195-11202
Publication Date(Web):July 17, 2009
DOI:10.1021/ja9036753
DyI2 reacts with 2 equiv of KOAr (OAr = OC6H3(CMe3)2-2,6) under nitrogen to form not only the (N2)2− complex, [(ArO)2(THF)2Dy]2(μ-η2:η2-N2), 1, but also complexes of similar formula with an added potassium ion, [(ArO)2(THF)Dy]2(μ-η2:η2-N2)[K(THF)6], 2, and [(ArO)2(THF)Dy]2(μ3-η2:η2:η2-N2)K(THF), 3. The 1.396(7) and 1.402(7) Å N−N bond distances in 2 and 3, respectively, are consistent with an (N2)3− ligand, but the high magnetic moment of 4f9 Dy3+ precluded definitive identification. The Y[N(SiMe3)2]3/K reduction system was used to synthesize yttrium analogues of 2 and 3, {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2)[K(THF)6] and {[(Me3Si)2N]2(THF)Y}2(μ3-η2:η2:η2-N2)K, that had similar N−N distances and allowed full characterization. EPR, Raman, and DFT studies are all consistent with the presence of (N2)3− in these complexes. 15N analogues were also prepared to confirm the spectroscopic assignments. The DFT studies suggest that the unpaired electron is localized primarily in a dinitrogen π orbital isolated spatially, energetically, and by symmetry from the metal orbitals.
Co-reporter:William J. Evans ; Christopher A. Traina ;Joseph W. Ziller
Journal of the American Chemical Society 2009 Volume 131(Issue 47) pp:17473-17481
Publication Date(Web):November 5, 2009
DOI:10.1021/ja9075259
Reactivity studies on the sterically crowded [(C5Me5)2U]2(μ−η6:η6-C6H6), 1, have revealed that η1-ligands can displace one of the normally inert (η5-C5Me5)1− ligands in each metallocene unit to form a series of heteroleptic bimetallic sandwich complexes of nonplanar (C6H6)2−, namely, [(C5Me5)(X)U]2(μ−η6:η6-C6H6), where X = N(SiMe3)2, OC6H2(CMe3)2-2,6-Me-4, and CH(SiMe3)2. Displacement by an amidinate is also possible, that is, X = iPrNC(Me)NiPr. This allows the multielectron reactivity of the (μ−η6:η6-C6H6)2− sandwich complexes to be studied as a function of ancillary ligands. Specifically, the reaction of 1 with K[N(SiMe3)2], previously found to form {(C5Me5)[(Me3Si)2N]U}2(C6H6), 2, also occurs with K[OC6H2(CMe3)2-2,6-Me-4], Li[CH(SiMe3)2], and Li[iPrNC(Me)NiPr] to form {(C5Me5)[4-Me-2,6-(Me3C)2C6H2O]U}2(C6H6), 3, {(C5Me5)[(Me3Si)2CH]U}2(C6H6), 4, and {(C5Me5)[iPrNC(Me)NiPr]U}2(C6H6), 5, respectively. The reactivity of 2−5 vis-à-vis 1 has been compared with the substrates 1,3,5,7-cyclooctatetraene (C8H8) and 1-azidoadamantane (AdN3). Complex 1 acts as a six electron reductant to convert three equiv of C8H8 to [(C5Me5)(C8H8)U]2(μ−η3-η3-C8H8), whereas the sterically less crowded 2−5 provide only four electrons to reduce two equiv of C8H8 generating U4+ products of formula (C5Me5)(X)U(C8H8). With AdN3, complexes 1, 2, and 5 react similarly to form bis(imido) U6+ complexes, (C5Me5)(X)U(═NAd)2. Complexes 2 and 5 also form the ligand redistribution product, (C5Me5)2U(═NAd)2. The reaction of 4 with AdN3 generates at least three imido complexes: (C5Me5)2U(═NAd)2 from reduction and ligand redistribution, (C5Me5)[AdN3CH(SiMe3)2-κ2N1,2]U(═NAd)2, from reduction and insertion, and (C5Me5)(η5:κΝ-C5Me4CH2NAd)U(═NAd), from reduction, ligand redistribution, metalation, and insertion.
Co-reporter:William J. Evans, Justin R. Walensky and Joseph W. Ziller
Chemical Communications 2009 (Issue 47) pp:7342-7344
Publication Date(Web):05 Nov 2009
DOI:10.1039/B912222B
A uranium complex containing an outer sphere aryloxide anion is formed by the proteolytic cleavage of the methyl group in the mono-methyl uranium metallocene, (C5Me5)2[iPrNC(Me)NiPr]UMe, by 2,6-di-tert-butyl-4-methyl phenol.
Co-reporter:William J. Evans, Sara E. Lorenz and Joseph W. Ziller
Inorganic Chemistry 2009 Volume 48(Issue 5) pp:2001-2009
Publication Date(Web):January 28, 2009
DOI:10.1021/ic801853d
Metal size effects in reductive chemistry using [(C5Me4H)2Ln(THF)]2(μ-η2:η2-N2) complexes have been evaluated using the extremes in ionic radii of the lanthanide series, Ln = La, 1, and Lu, 2. Comparisons have been made using 1,3,5,7-cyclooctatetraene, phenazine, carbon dioxide, and anthracene as substrates. Complexes 1 and 2 react similarly with 1,3,5,7-cyclooctatetraene to form (C5Me4H)3Ln and (C5Me4H)Ln(C8H8)(THF)x (Ln = La, x = 2, or Lu, x = 0) in a reaction analogous to the reduction of this substrate with divalent (C5Me5)2Sm. Complexes 1 and 2 differ in their reactions with phenazine in that 1 forms at least three products, including [(C5Me4H)2La](μ-η4:η2-C12H8N2)[La(THF)(C5Me4H)2], 3, and (C5Me4H)3La, whereas 2 forms a single product, [(C5Me4H)2Lu]2(μ-η3:η3-C12H8N2), 4, in quantitative yield. Complexes 3 and 4 are similar to the product obtained from the reaction of (C5Me5)2Sm and phenazine, [(C5Me5)2Sm]2(μ-η3:η3-C12H8N2), since all three complexes contain a reduced phenazine dianion, but the phenazine ligand displays structural variations depending on the size of the metal. With CO2, complex 1 forms multiple products, but 2 reacts cleanly to form the reductively coupled oxalate complex, [(C5Me4H)2Lu]2(μ-η2:η2-C2O4), 5, in high yield. With anthracene, 1 forms a complex product mixture from which only (C5Me4H)3La(THF), 9, characterized by X-ray crystallography, could be identified. In contrast, 2 is unreactive toward anthracene even upon heating to 75 °C after 24 h.
Co-reporter:WilliamJ. Evans Dr.;JustinR. Walensky ;JosephW. Ziller Dr.
Chemistry - A European Journal 2009 Volume 15( Issue 45) pp:12204-12207
Publication Date(Web):
DOI:10.1002/chem.200901942
Co-reporter:William J. Evans, Justin R. Walensky, Filipp Furche, Antonio G. DiPasquale and Arnold L. Rheingold
Organometallics 2009 Volume 28(Issue 20) pp:6073-6078
Publication Date(Web):October 2, 2009
DOI:10.1021/om9006104
To examine the difference between the trigonal-planar structure of the tris(ring) heteroleptic 4f14 Yb2+ complex (C5Me5)Yb(μ-η6:η1-Ph)2BPh2, 1, and the pyramidal geometry of the 4f6 Sm2+ analogue (C5Me5)Sm(μ-η6:η1-Ph)2BPh2, 2, the structure of the half-filled-shell 4f7 Eu2+ complex was of interest. (C5Me5)Eu(μ-η6:η1-Ph)2BPh2, 3, was synthesized by reaction of (C5Me5)2Eu with [Et3NH][BPh4] and characterized by X-ray crystallography. All three complexes were analyzed using density functional theory. In addition, (C5Me5)− exchange reactions were performed in order to examine the preference of the divalent lanthanide ions for ligand sets containing one or two (C5Me5)− groups.
Co-reporter:William J. Evans, Michael K. Takase, Joseph W. Ziller and Arnold L. Rheingold
Organometallics 2009 Volume 28(Issue 19) pp:5802-5808
Publication Date(Web):September 16, 2009
DOI:10.1021/om900620m
The utility of [(C5Me5)(C8H8)U]2(μ-η3:η3-C8H8), 1, as a precursor to monoalkyl and monoaryl heteroleptic pentamethylcyclopentadienyl cyclooctatetraenyl U4+ metallocene complexes, (C5Me5)(C8H8)UR (R = alkyl, aryl), has been explored. Complex 1 reacts with AgOTf (OTf = OSO2CF3) to form [(C5Me5)(C8H8)U(μ-OTf)]2, 2, which contains readily displaceable triflate ligands. Complex 2 reacts with KN(SiMe3)2, LiCH(SiMe3)2, LiPh, and Li[iPrNC(Me)NiPr] to form (C5Me5)(C8H8)U[N(SiMe3)2], 3, (C5Me5)(C8H8)U[CH(SiMe3)2], 4, (C5Me5)(C8H8)UPh, 5, and (C5Me5)(C8H8)U[iPrNC(Me)NiPr-κ2N,N′], respectively. The insertion reactivity of 5 with tert-butyl isocyanide and the carbodiimide iPrN═C═NiPr was investigated, and (C5Me5)(C8H8)U[η2-C(Ph)═NtBu], 6, and (C5Me5)(C8H8)U[iPrNC(Ph)NiPr], 7, were isolated, respectively.
Co-reporter:William J. Evans, Justin R. Walensky, Joseph W. Ziller and Arnold L. Rheingold
Organometallics 2009 Volume 28(Issue 12) pp:3350-3357
Publication Date(Web):May 13, 2009
DOI:10.1021/om900135e
Manipulation of steric crowding in organoactinide complexes has been explored by examining the insertion chemistry of carbodiimides, RN═C═NR, and organic azides, RN3, with actinide alkyl, alkynyl, and aryl complexes. iPrN═C═NiPr reacts with (C5Me5)2AnMe2 to produce the isomorphous methyl amidinates (C5Me5)2AnMe[(iPr)NC(Me)N(iPr)-κ2N,N′], An = Th, 1; U, 2, in high yield. The reaction of iPrN═C═NiPr with (C5Me5)2U(C≡CPh)2 forms a similar insertion product, (C5Me5)2U(C≡CPh)[(iPr)NC(C≡CPh)N(iPr)-κ2N,N′], 3. (C5Me5)2U(C6H5)2 does not generate an analogous product with iPrN═C═NiPr, but forms instead a complex formally derived from carbodiimide insertion into a “(C5Me5)2U(C6H4)” intermediate, (C5Me5)2U[(iPr)NC═N(iPr)(C6H4)-κN,κC], 4. Adamantyl azide, AdN3, inserts into the An−Me bonds in the (C5Me5)2AnMe2 complexes to make monomethyl actinide triazenido complexes that differ in the mode of triazenido coordination: (C5Me5)2ThMe[(Me)NN═N(Ad)-κ2N1,2], 5, and (C5Me5)2UMe[(Me)NNN(Ad)-κ2N1,3], 6. A κ2N1,3-triazenido complex of thorium was also isolated in a crystal comprised of a mixture of (C5Me5)2ThMe[(Me)NNN(Ad)-κ2N1,3] and (C5Me5)2Th(OH)[(Me)NNN(Ad)-κ2N1,3], 7.
Co-reporter:William J. Evans, Elizabeth Montalvo, Timothy M. Champagne, Joseph W. Ziller, Antonio G. DiPasquale and Arnold L. Rheingold
Organometallics 2009 Volume 28(Issue 9) pp:2897-2903
Publication Date(Web):April 6, 2009
DOI:10.1021/om8012103
Reactions of [(C5Me5)2Ln][(μ-Ph)2BPh2] complexes with Li[Me3SiCN2] form dimeric isocyanotrimethylsilyl amide complexes {(C5Me5)2Ln[μ-N(SiMe3)NC]}2, not only for Ln = Sm (1-Sm) and La (1-La) but also for the intermediate and small size metal ions Ln = Nd, Y, Yb, and Lu. Complexes 1-Y and 1-Yb were characterized by X-ray crystallography and are structurally similar to 1-Sm and 1-La. A more convenient synthesis of 1-Sm and 1-La from the corresponding (C5Me5)2LnCl2K(THF)2 “ate” salts with Li[Me3SiCN2] is also reported. Analogues of reactions of 1-Sm and 1-La with Me3CCN that form the 1,2,3-triazolato complexes (C5Me5)2Ln(NCCMe3)[NNC(SiMe3)C(CMe3)N] (2-Sm, 2-La) were examined with C6H5CH2CN and Me3SiCN to investigate the diversity of the triazoles accessible by this route. Complex 1-La reacts with C6H5CH2CN to make a 1,2,3-triazole complex, but in contrast to 2-La, the product is a base-free dimer in which each triazole is ligated by two metallocenes, {(C5Me5)2La[μ-η1:η2-NNC(SiMe3)C(CH2C6H5)N]}2, 3. The reaction of 1-La with Me3SiCN involves Si−C bond cleavage, and a nitrile-solvated cyanide trimer, [(C5Me5)2La(μ-CN)(NCSiMe3)]3, 4, was isolated. The reaction of 1-La with the isocyanide reagent Me3SiCH2NC also generated a cyanide trimer, this time via N−C bond cleavage as an isocyanide solvate, [(C5Me5)2La(μ-CN)(Me3SiCH2NC)]3, 5. Unsubstituted 1,2,3-triazoles {(C5Me5)2Ln[μ-η1:η2-NNC(SiMe3)C(H)N]}2 (6-Sm, 6-La) can be isolated directly from 1-Sm and 1-La in reactions that involve N−N bond cleavage.
Co-reporter:William J. Evans, Michael K. Takase, Joseph W. Ziller, Antonio G. DiPasquale and Arnold L. Rheingold
Organometallics 2009 Volume 28(Issue 1) pp:236-243
Publication Date(Web):November 20, 2008
DOI:10.1021/om800747s
The reductive reactivity of the cyclooctatetraenide ligands in [(η5-C5Me5)(η8-C8H8)U]2(μ-η3:η3-C8H8), 1, was examined with polycyclic hydrocarbons, phenazine, and the diphenyldichalcogenide compounds PhEEPh (E = S, Se, Te). Complex 1 does not reduce anthracene, acenaphthylene, or benzanthracene, but it acts as a two-electron reductant with phenazine to form 1 equiv of C8H8 and the bimetallic complex [(η5-C5Me5)(η8-C8H8)U]2(μ-η1:η1-C12H8N2), 2. X-ray crystallography showed that the heteroleptic metallocene unit [(C5Me5)(C8H8)U]1+ adopted an η1-coordination mode with the phenazine dianion rather than the η3-coordination previously found with the homoleptic f element metallocene cations [(C5Me5)2M]1+. Complex 1 also reacts as a two-electron reductant with PhEEPh (E = S, Se, Te) to form C8H8 and the heteroleptic complexes [(η5-C5Me5)(η8-C8H8)U]2(μ-EPh)2 (E = S, 3; Se, 4; Te, 5).
Co-reporter:William J. Evans, Justin R. Walensky, Timothy M. Champagne, Joseph W. Ziller, Antonio G. DiPasquale, Arnold L. Rheingold
Journal of Organometallic Chemistry 2009 694(7–8) pp: 1238-1243
Publication Date(Web):
DOI:10.1016/j.jorganchem.2008.11.038
Co-reporter:William J. Evans ; Elizabeth Montalvo ; Dustin J. Dixon ; Joseph W. Ziller ; Antonio G. DiPasquale ;Arnold L. Rheingold
Inorganic Chemistry 2008 Volume 47(Issue 23) pp:11376-11381
Publication Date(Web):November 5, 2008
DOI:10.1021/ic801029v
Reaction of the lanthanide metallocene allyl complexes, (C5Me5)2Ln(η3-CH2CHCH2)(THF) (Ln = Ce, Sm, Y) with 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, Hhpp, forms a series of metallocene complexes, (C5Me5)2Ln(hpp) (Ln = Ce, Sm, Y) in which the (hpp)1− anion coordinates as a terminal bidentate ligand. Isomorphous structures were observed by X-ray crystallography regardless of the size of the metal. The acetonitrile adduct, (C5Me5)2Sm(hpp)(MeCN), was also crystallographically characterized to provide an unusual pair of eight- and nine-coordinate complexes. The coordination mode of the (hpp)1− anion in these complexes is compared with that in other heteroallylic metallocenes like the caprolactamate (C5Me5)2Y(ONC6H10) and the dithiocarbamate (C5Me5)2Sm(S2CNEt2), which was also structurally characterized.
Co-reporter:William J. Evans ; Justin R. Walensky ; Filipp Furche ; Joseph W. Ziller ; Antonio G. DiPasquale ;Arnold L. Rheingold
Inorganic Chemistry 2008 Volume 47(Issue 21) pp:10169-10176
Publication Date(Web):October 9, 2008
DOI:10.1021/ic801232e
To probe the correlation of unusual (C5Me5)1− reactivity with steric crowding in complexes such as (C5Me5)3UMe and (C5Me5)3UCl, slightly less crowded (C5Me5)2(C5Me4H)UX analogues (X = Me, Cl) were synthesized and their reactivity was evaluated. The utility of the cationic precursors [(C5Me5)2UMe]1+, 1, and [(C5Me5)2UCl]1+, 2, in the synthesis of (C5Me5)2(C5Me4H)UMe, 3, and (C5Me5)2(C5Me4H)UCl, 4, was also explored. Since the use of precursor [(C5Me5)2UMe][MeBPh3], 1a, is complicated by the equilibrium between 1a and (C5Me5)2UMe2/BPh3, the reactivity of [(C5Me5)2UMe(OTf)]2, 1b, (OTf = O3SCF3) prepared from (C5Me5)2UMe2 and AgOTf, was also studied. Both 1a and 1b react with KC5Me4H to form 3. Complex 4 readily forms by addition of KC5Me4H to [(C5Me5)2UCl][MeBPh3], generated in situ from (C5Me5)2UMeCl and BPh3. Complex 1b was preferred to 1a for the synthesis of (C5Me5)2(C5H5)UMe, 5, and (C5Me5)2UMe[CH(SiMe3)2], 6, from KC5H5 and LiCH(SiMe3)2, respectively. Complex 6 is the first example of a mixed alkyl uranium metallocene complex. Sterically induced reduction (SIR) reactivity was not observed with 3−6 although the methyl displacements from the (C5Me5)1− ring plane for 3 are the closest observed to date to those of SIR-active complexes. The 1H NMR spectra of 3 and 4 are unusual in that all of the (C5Me4H)1− methyl groups are inequivalent. This structural rigidity is consistent with density-functional theory calculations.
Co-reporter:WilliamJ. Evans ;KevinA. Miller;AntonioG. DiPasquale Dr.;ArnoldL. Rheingold ;TimothyJ. Stewart;Robert Bau
Angewandte Chemie International Edition 2008 Volume 47( Issue 27) pp:5075-5078
Publication Date(Web):
DOI:10.1002/anie.200801062
Co-reporter:WilliamJ. Evans ;KevinA. Miller ;JosephW. Ziller
Angewandte Chemie International Edition 2008 Volume 47( Issue 3) pp:589-592
Publication Date(Web):
DOI:10.1002/anie.200703969
Co-reporter:WilliamJ. Evans ;KevinA. Miller ;JosephW. Ziller
Angewandte Chemie 2008 Volume 120( Issue 3) pp:599-602
Publication Date(Web):
DOI:10.1002/ange.200703969
Co-reporter:WilliamJ. Evans ;KevinA. Miller;AntonioG. DiPasquale Dr.;ArnoldL. Rheingold ;TimothyJ. Stewart;Robert Bau
Angewandte Chemie 2008 Volume 120( Issue 27) pp:5153-5156
Publication Date(Web):
DOI:10.1002/ange.200801062
Co-reporter:William J. Evans, Daniel B. Rego, Joseph W. Ziller
Inorganica Chimica Acta 2007 Volume 360(Issue 4) pp:1349-1353
Publication Date(Web):1 March 2007
DOI:10.1016/j.ica.2006.03.011
The synthesis of Bi[N(SiMe3)2]3 from BiCl3 and KN(SiMe3)2 generates an unusual amido bismuth imide by-product, {[(Me3Si)2N]Bi[μ-N(SiMe3)]}2, evidently formed via SiN bond cleavage. X-ray diffraction shows that the complex contains a planar Bi2N2 ring with tetrahedral bismuth and trigonal planar imido nitrogen atoms.The BiCl3/KN(SiMe3)2 reaction system produced a cyclic amido bismuth imido complex, {[(Me3Si)2N]Bi[μ-N(SiMe3)]}2, that was obtained via an unusual SiN cleavage.
Co-reporter:Joseph W. Ziller;Benjamin L. Davis;Timothy M. Champagne
PNAS 2006 Volume 103 (Issue 34 ) pp:12678-12683
Publication Date(Web):2006-08-22
DOI:10.1073/pnas.0602672103
Synthesis of the sterically crowded Tris(pentamethylcyclopentadienyl) lanthanide complexes, (C5Me5)3Ln, has demonstrated that organometallic complexes with unconventionally long metal ligand bond lengths can be isolated that
provide options to develop new types of ligand reactivity based on steric crowding. Previously, the (C5Me5)3M complexes were known only with the larger lanthanides, La–Sm. The synthesis of even more crowded complexes of the smaller
metals Gd and Y is reported here. These complexes allow an evaluation of the size/reactivity correlations previously limited
to the larger metals and demonstrate a previously undescribed type of C5Me5-based reaction, namely C–H bond activation. (C5Me5)3Gd, was prepared from GdCl3 through (C5Me5)2GdCl2K(THF)2, (C5Me5)2Gd(C3H5), and [(C5Me5)2Gd][BPh4] and structurally characterized by x-ray crystallography. Although Gd3+ is redox-inactive, (C5Me5)3Gd functions as a reducing agent in reactions with 1,3,5,7-cyclooctatetraene (COT) and triphenylphosphine selenide to make
(C5Me5)Gd(C8H8), [(C5Me5)2Gd]2Se2, and [(C5Me5)2Gd]2Se depending on the stoichiometry used. When the analogous synthetic method was attempted with yttrium in arene solvents,
the previously characterized (C5Me5)2YR complexes (R=C6H5, CH2C6H5) were isolated instead, i.e., C–H bond activation of solvent occurred. To avoid this problem, (C5Me5)3Y was synthesized in high yield from [(C5Me5)2YH]2 and tetramethylfulvene in aliphatic solvents. Isolated (C5Me5)3Y was found to metalate benzene and toluene with concomitant formation of C5Me5H, a reaction contrary to the normal pKa values of these hydrocarbons. In this case, the normally inert (C5Me5)1− ligand engages in C–H bond activation due to the extreme steric crowding.
Co-reporter:William J. Evans;Stosh A. Kozimor;Joseph W. Ziller
Science 2005 Vol 309(5742) pp:1835-1838
Publication Date(Web):16 Sep 2005
DOI:10.1126/science.1116452
Abstract
Uranium nitrides offer potential as future nuclear fuels and as probes of metal ligand multiple bonding involving the f-block actinide metals. However, few molecular examples are available for study owing to the difficulties in synthesis. Recent advances in organoactinide chemistry have provided a route to uranium nitride complexes that expands the options for developing UN chemistry. Several 24-membered uranium nitrogen rings, (UNUN3)4, have been synthesized by reduction of sodium azide with organometallic metallocene derivatives, [(C5Me4R)2U][(μ-Ph)2BPh2] (R = Me, H; Me = methyl, Ph = phenyl). The nanometer-sized rings contain unusual UNU nitride linkages that have short U-N distances within the double-bond range.
Co-reporter:William J. Evans, Stosh A. Kozimor and Joseph W. Ziller
Chemical Communications 2005 (Issue 37) pp:4681-4683
Publication Date(Web):25 Aug 2005
DOI:10.1039/B508612D
Examination of the reactivity of [(C5Me5)2U][(μ-Ph)2BPh2] as a “blank” for comparison with the four- and eight-electron reductive chemistry of the sterically crowded (C5Me5)3U and [(C5Me5)2U]2(C6H6) complexes revealed that the tetraphenylborate complex surprisingly functions as a four-electron reductant by combining [BPh4]1− and U(III) reduction; all three complexes cleave the NN bond in PhNNPh to form the bis(organoimido) U(VI) complex, (C5Me5)2U(NPh)2, and they also reduce PhCCPh to form (C5Me5)2U(C4Ph4).
Co-reporter:William J. Evans, Timothy M. Champagne and Joseph W. Ziller
Chemical Communications 2005 (Issue 47) pp:5925-5927
Publication Date(Web):21 Oct 2005
DOI:10.1039/B511714C
[(C5Me5)2Sm(μ-O2CPh)]2 reacts with iBu3Al to form a mixed bridge samarium aluminium complex [(C5Me5)2Sm(μ-O2CPh)(μ-iBu)Al(iBu)2], that displays two different carboxylate orientations toward the metals in a single crystal.
Co-reporter:William J. Evans ;David S. Lee;Charlie Lie;Joseph W. Ziller Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 41) pp:
Publication Date(Web):13 OCT 2004
DOI:10.1002/anie.200461170
Dinitrogen reduction with diamagnetic trivalent lanthanum complexes is possible for the first time using a combination of a trivalent metallocene and potassium graphite. Both [(C5Me4H)3La] and [(C5Me5)2La][BPh4] are viable starting materials and reduce dinitrogen in the presence of KC8 to give [NN]2− containing structures (see picture).
Co-reporter:William J. Evans ;David S. Lee;Charlie Lie;Joseph W. Ziller Dr.
Angewandte Chemie 2004 Volume 116(Issue 41) pp:
Publication Date(Web):13 OCT 2004
DOI:10.1002/ange.200461170
Die Distickstoffreduktion gelingt mit diamagnetischen dreiwertigen Lanthankomplexen, wenn ein dreiwertiges Metallocen mit Graphitkalium kombiniert wird. Sowohl [(C5Me4H)3La] als auch [(C5Me5)2La][BPh4] eignen sich als Ausgangsmaterialien und reduzieren Distickstoff in Gegenwart von KC8, wobei Strukturen mit dem anionischen Liganden [NN]2− gebildet werden (siehe Bild).
Co-reporter:William J Evans, Benjamin L Davis, Gregory W Nyce, Jeremy M Perotti, Joseph W Ziller
Journal of Organometallic Chemistry 2003 Volume 677(1–2) pp:89-95
Publication Date(Web):1 July 2003
DOI:10.1016/S0022-328X(03)00378-4
Examination of the chemistry of sterically crowded (C5Me4R)3Ln complexes has provided access to a series of [(C5Me4R)2Ln]2(μ-O) complexes: [(C5Me5)2La]2(μ-O), [(C5Me5)2Nd(NC5H4NC4H8)]2(μ-O), [(C5Me4iPr)2Sm]2(μ-O), [(C5Me4Et)2Gd]2(μ-O), and [(C5Me5)2Sm(NC5H5)]2(μ-O). X-ray crystallographic data on these complexes provide information on the effect of metal and cyclopentadienyl ring size on LnO bond distances and LnOLn angles, which vary between 173 and 180° in these complexes.The high reactivity of the sterically crowded (C5Me4R)3Ln complexes has provided five new [(C5Me4R)2Ln]2(μ-O) complexes that have LnOLn angles between 173 and 180°. The effect of metal and cyclopentadienyl ring size on LnO bond distances and LnOLn angles in this class of complexes is presented.
Co-reporter:William J Evans, Dimitrios G Giarikos, Joseph W Ziller
Journal of Organometallic Chemistry 2003 Volume 688(1–2) pp:200-205
Publication Date(Web):15 December 2003
DOI:10.1016/j.jorganchem.2003.09.013
(C5Me4H)SiMe2Cl reacts with (THF)KCH2CHCHCHCH2 to form (C5Me4H)SiMe2(CH2CHCHCHCH2) (1). Compound 1 reacts with KH and n-BuLi to make M(C5Me4)SiMe2(CH2CHCHCHCH2), M=K, 2; Li, 3, respectively. Carbon–silicon cleavage occurs when 1 reacts with K to form (C5Me4H)K, which crystallizes from dimethoxyethane as [(C5Me4H)K(DME)]x. This potassium salt has an extended structure which generates bent metallocene (C5Me4H)2K(DME) sub-structures which have 133.9° ring centroidKring centroid angles. Compound 1 reacts with TiCl4 to make (C5Me4H)TiCl3 (5), which has a piano stool structure.(C5Me4H)SiMe2Cl reacts with (THF)KCH2CHCHCHCH2 to form the title compound shown here, which can be deprotonated with KH. Reactions with K and TiCl4 involved C-Si clevage and isolation of [(C5Me4H)K(DME)]x and (C5Me4H)TiCl3.
Co-reporter:William J. Evans ;Nathan T. Allen;Joseph W. Ziller Dr.
Angewandte Chemie 2002 Volume 114(Issue 2) pp:
Publication Date(Web):17 JAN 2002
DOI:10.1002/1521-3757(20020118)114:2<369::AID-ANGE369>3.0.CO;2-V
Dank der richtigen Wahl der Lösungsmittel, des Liganden ([C5H3(SiMe3)2]−) und der Reaktionsbedingungen konnte das erste TmII-Metallocen isoliert und strukturell charakterisiert werden (siehe Bild). Am Beispiel des in situ gebildeten DyII-Ions, das N2 unter Bildung des DyIII-N2-Komplexes [{[C5H3(SiMe3)2]2Dy}2N2] reduziert, konnte bestätigt werden, dass sich derartige Reaktionen nicht unter Stickstoff durchführen lassen, sondern erst in einer noch „inerteren“ Atmosphäre gelingen.
Co-reporter:William J. Evans ;Nathan T. Allen;Joseph W. Ziller Dr.
Angewandte Chemie International Edition 2002 Volume 41(Issue 2) pp:
Publication Date(Web):18 JAN 2002
DOI:10.1002/1521-3773(20020118)41:2<359::AID-ANIE359>3.0.CO;2-A
The right choice of solvents, ligand ([C5H3(SiMe3)2]−), and reaction conditions has facilitated the isolation and structural characterization of the first TmII metallocene (see picture). In situ organometallic chemistry of the even more reducing DyII ion, namely a dinitrogen reduction to give the DyIII dinitrogen complex [{[C5H3(SiMe3)2]2Dy}2N2], reveals the importance of carrying out such reactions in an atmosphere more inert than nitrogen.
Co-reporter:William J. Evans, Jeremy M. Perotti, Robert J. Doedens and Joseph W. Ziller
Chemical Communications 2001 (Issue 22) pp:2326-2327
Publication Date(Web):25 Oct 2001
DOI:10.1039/B106869P
(C5Me5)3Sm reacts with the
free radical 2,2,6,6-tetramethylpiperidinyl-1-oxy (TMPO) to form
(C5Me5)2 and the per nitroxide
[(η1-ONC5H6Me4)2
Sm(μ-η1∶η2-ONC5H
6Me4)]2
Co-reporter:William J. Evans;Cy H. Fujimoto;Michael A. Greci;Joseph W. Ziller
European Journal of Inorganic Chemistry 2001 Volume 2001(Issue 3) pp:
Publication Date(Web):6 FEB 2001
DOI:10.1002/1099-0682(200103)2001:3<745::AID-EJIC745>3.0.CO;2-R
Examination of the coordination chemistry of ϵ-caprolactam with lanthanide trichlorides reveals that cationic ϵ-caprolactam-solvated complexes of two types can be obtained from acetonitrile depending on the size of the metal. The larger lanthanides Ce, Nd, Pr, and Sm form capped octahedral dications, [Ln(C6H11NO)6Cl]+2, with the chloride ligand in the capping position. The smaller metals Eu, Gd, and Ho form trans-octahedral monocations [Ln(C6H11NO)4Cl2]+. Chloride ions are the counteranions in both cases.
Co-reporter:William J. Evans ;Gregory W. Nyce;Joseph W. Ziller Dr.
Angewandte Chemie International Edition 2000 Volume 39(Issue 1) pp:
Publication Date(Web):12 JAN 2000
DOI:10.1002/(SICI)1521-3773(20000103)39:1<240::AID-ANIE240>3.0.CO;2-Z
Steric crowding can be coupled with a UIII reduction to make the complex [(C5Me5)3U] a formal three-electron reductant in its reaction with C8H8, which generates a product, 1, containing a bridging nonplanar C8H82− ligand [Eq. (1)].
Co-reporter:William J. Evans ;Gregory W. Nyce;Joseph W. Ziller Dr.
Angewandte Chemie 2000 Volume 112(Issue 1) pp:
Publication Date(Web):12 JAN 2000
DOI:10.1002/(SICI)1521-3757(20000103)112:1<246::AID-ANGE246>3.0.CO;2-V
Das Zusammenwirken von sterischer Hinderung und Reduktion durch das UIII-Zentrum macht den Komplex [(C5Me5)3U] zu einem formalen Dreielektronen-Reduktionsmittel in seiner Reaktion mit C8H8. Es entsteht 1 [Gl. (1)], das einen verbrückenden, nichtplanaren C8H82−-Liganden enthält.
Co-reporter:William J. Evans;Gregory W. Nyce;Robert D. Clark;Robert J. Doedens;Joseph W. Ziller
Angewandte Chemie 1999 Volume 111(Issue 12) pp:
Publication Date(Web):8 JUN 1999
DOI:10.1002/(SICI)1521-3757(19990614)111:12<1917::AID-ANGE1917>3.0.CO;2-T
Ein Se22−-Komplex entsteht bei der Reduktion von Se = PPh3 durch den NdIII-Komplex [(C5Me5)3Nd] zu Ph3P und (C5Me5)2 [Gl. (a)]. Er ähnelt hierin [(C5Me5)3Sm], das allerdings ein stärkeres Reduktionsmittel als [(C5Me5)3Nd] zu sein scheint, was darauf hindeutet, daß das Reduktionsvermögen von [(C5Me5)3Ln]-Komplexen durch Variation der Metallgröße eingestellt werden kann.
Co-reporter:William J. Evans;Gregory W. Nyce;Robert D. Clark;Robert J. Doedens;Joseph W. Ziller
Angewandte Chemie International Edition 1999 Volume 38(Issue 12) pp:
Publication Date(Web):8 JUN 1999
DOI:10.1002/(SICI)1521-3773(19990614)38:12<1801::AID-ANIE1801>3.0.CO;2-H
A Se22−complex, Ph3P, and (C5Me5)2 are formed in the reduction of Se=PPh3 by the NdIII complex [(C5Me5)3Nd] [Eq. (a)]. The latter is thus reminiscent of [(C5Me5)3Sm], which, however, appears to be a stronger reductant than [(C5Me5)3Nd]. This suggests that the reductive reactivity of [(C5Me5)3Ln] complexes can be tuned by varying the size of the metal atom.
Co-reporter:William J. Evans;Michael A. Greci;Matthew A. Johnston;Joseph W. Ziller
Chemistry - A European Journal 1999 Volume 5(Issue 12) pp:
Publication Date(Web):30 NOV 1999
DOI:10.1002/(SICI)1521-3765(19991203)5:12<3482::AID-CHEM3482>3.0.CO;2-Y
Enhanced solubility of the dizirconiumnonaisopropoxide (dzni) complexes [(dzni)Ln(C5H5)] and [{(dzni)Ln}2(C8H8)] (shown here for Ln=Sm; R=iPr), compared with their cyclopentadienyl analogues, was revealed by examining the reactions of [{(dzni)LnI}2] with NaC5H5 and K2C8H8 to probe the compatibility of the dzni ligand with organometallic reagents.
Co-reporter:Wim T. Klooster;Roy S. Lu;Reiner Anwer;Thomas F. Koetzle;Robert Bau
Angewandte Chemie International Edition 1998 Volume 37(Issue 9) pp:
Publication Date(Web):17 DEC 1998
DOI:10.1002/(SICI)1521-3773(19980518)37:9<1268::AID-ANIE1268>3.0.CO;2-Y
Weak agostic Nd⋅⋅⋅H interactions and Nd−C bonds are involved in the bonding of the bridging methyl groups in the title compound (see sketch on the right): Two of the three H atoms of the methyl group are directed at the Nd center. The C atoms have distorted trigonal-bipyramidal geometry with the Nd atom and one of the H atoms (HA) as axial ligands, and the Al atom and the other two H atoms (HB and HC) in equatorial positions. The Al2Me6 “solvate” molecule is disordered.
Co-reporter:Wim T. Klooster;Roy S. Lu;Reiner Anwer;William J. Evans;Thomas F. Koetzle;Robert Bau
Angewandte Chemie 1998 Volume 110(Issue 9) pp:
Publication Date(Web):12 MAR 1999
DOI:10.1002/(SICI)1521-3757(19980504)110:9<1326::AID-ANGE1326>3.0.CO;2-V
Schwache agostische Nd-H-Wechselwirkungen werden zusätzlich zu den Nd-C-Bindungen bei der Verbrückung durch die Methylgruppen in der Titelverbindung diskutiert (siehe rechts): Zwei der drei H-Atome der Methylgruppe weisen zum Nd-Zentrum hin. Die C-Atome sind mit dem Nd-Atom und einem der H-Atome (Ha) als axialen und dem Al-Atom sowie den anderen beiden H-Atomen (Hb und Hc) als äquatorialen Liganden verzerrt trigonal-bipyramidal koordiniert. Das „Solvat”-Molekül Al2Me6 ist fehlgeordnet.
Co-reporter:Daniel N. Huh, Christopher M. Kotyk, Milan Gembicky, Arnold L. Rheingold, Joseph W. Ziller and William J. Evans
Chemical Communications 2017 - vol. 53(Issue 62) pp:NaN8666-8666
Publication Date(Web):2017/07/12
DOI:10.1039/C7CC04396A
Cp′2Ln(THF)2 metallocenes (Cp′ = C5H4SiMe3) react with 2.2.2-cryptand (crypt) to form Ln2+-in-crypt complexes, [Ln(crypt)(THF)][Cp′3Ln]2 (Ln = Sm, Eu) and [Yb(crypt)][Cp'3Yb]2, that contain Ln2+ ions surrounded only by neutral ligands. A bimetallic, mixed-ligand metallocene/opened-crypt complex of Sm2+, [Sm(C16H32N2O6-κ2O:κ2O′)SmCp′′2], was obtained by KC8 reduction of Cp′′2Sm(THF) [Cp′′ = C5H3(SiMe3)2] in the presence of crypt.
Co-reporter:William J. Evans, Sara E. Lorenz and Joseph W. Ziller
Chemical Communications 2007(Issue 44) pp:NaN4664-4664
Publication Date(Web):2007/09/26
DOI:10.1039/B709841C
(C5Me5)2Y(η3-C3H5) reacts with 9-borabicyclo[3.3.1]nonane, 9-BBN, to form single crystals containing both a borane-substituted allyl complex, (C5Me5)2Y[η3-C3H4(BC8H14)], and a borohydride, (C5Me5)2Y(μ-H)2BC8H14, that can be synthesized directly from 9-BBN and the yttrium hydride, [(C5Me5)2YH]x.
Co-reporter:Megan E. Fieser, David H. Woen, Jordan F. Corbey, Thomas J. Mueller, Joseph W. Ziller and William J. Evans
Dalton Transactions 2016 - vol. 45(Issue 37) pp:NaN14644-14644
Publication Date(Web):2016/03/04
DOI:10.1039/C5DT04547A
Raman spectra have been collected on single crystals of over 20 different rare earth complexes containing reduced dinitrogen ligands to determine if these data will correlate with periodic properties or relative stability. Four types of complexes were examined: [(C5Me5)2Ln]2(μ–η2:η2-N2), 1-Ln, [(C5Me4H)2(THF)Ln]2(μ–η2:η2-N2), 2-Ln, [(C5H4Me)2Ln]2(μ–η2:η2-N2), 3-Ln, and {[(Me3Si)2N]2(THF)Ln}2(μ–η2:η2-N2), 4-Ln. Although each of the complexes contains a side-on bound dinitrogen ligand that is formally (N2)2−, the N–N bond distances determined by X-ray crystallography range from 1.088(12) to 1.305(6) Å. In the 4-Ln series (Ln = Gd, Tb, Dy, Ho, Er and Tm), the 1.26–1.31 Å N–N distances do not follow any periodic trends, but the Raman stretching frequencies for Gd–Tm were found to decrease regularly with decreasing atomic number and increasing Lewis acidity of the metal. Similar correlations can be seen with the late metals in complexes of the other series, 1-Ln, 2-Ln and 3-Ln, but exceptions exist, particularly for the larger metals. Comparisons between the several types of complexes as a function of ligand were more complicated and variations in stretching frequency as a function of L in the {[(Me3Si)2N]2Y(L)}2(μ–η2:η2-N2) substituted versions of 4-Y did not give trends consistent with bond distances or Gutmann donor numbers.
Co-reporter:Shan-Shan Liu, Song Gao, Joseph W. Ziller and William J. Evans
Dalton Transactions 2014 - vol. 43(Issue 41) pp:NaN15531-15531
Publication Date(Web):2014/08/15
DOI:10.1039/C4DT02194K
X-ray crystallographic data obtained on the metallocene hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, and Dy), of interest for their magnetic properties, have revealed unexpected structural variability in a closely related series of rare earth complexes that can complicate magnetic analysis. Crystals of the two larger metals, Gd and Tb, were structurally straightforward and isomorphous with crystals of [(C5Me5)2SmH]2. However, only for Tb were the locations of the hydride ligands in this structural type identified for the first time and found to be consistent with a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. In contrast, for Ln = Dy, the [(C5Me5)2H]3− ligand set does not appear to have one optimum crystal structure. Two different types of crystals and one other solid form of [(C5Me5)2DyH]2 were repeatedly isolated upon crystallization and demonstrated that the structure of any particular crystalline sample selected for magnetic analysis could be variable. Asymmetric structures with a single hydride bridge, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, were identifiable for the two crystalline forms. This demonstrated uncertainty in structure and highlights the importance of having a coordination environment with one preferred form for magnetically interesting complexes.
Co-reporter:Shan-Shan Liu, Joseph W. Ziller, Yi-Quan Zhang, Bing-Wu Wang, William J. Evans and Song Gao
Chemical Communications 2014 - vol. 50(Issue 77) pp:NaN11420-11420
Publication Date(Web):2014/08/06
DOI:10.1039/C4CC04262J
A half-sandwich organolanthanide complex, [(C6Me6)Dy(AlCl4)3], in which Dy(III) is coordinated with a π-bonded arene was synthesized and magnetically characterized. This complex displays slow magnetic relaxation and a hysteresis loop associated with single-ion magnet behavior. The orientation of the magnetic anisotropy axis is analyzed using ab initio calculations.
Co-reporter:William J. Evans, Justin R. Walensky and Joseph W. Ziller
Chemical Communications 2009(Issue 47) pp:NaN7344-7344
Publication Date(Web):2009/11/05
DOI:10.1039/B912222B
A uranium complex containing an outer sphere aryloxide anion is formed by the proteolytic cleavage of the methyl group in the mono-methyl uranium metallocene, (C5Me5)2[iPrNC(Me)NiPr]UMe, by 2,6-di-tert-butyl-4-methyl phenol.
Co-reporter:Ryan R. Langeslay, Megan E. Fieser, Joseph W. Ziller, Filipp Furche and William J. Evans
Chemical Science (2010-Present) 2015 - vol. 6(Issue 1) pp:NaN521-521
Publication Date(Web):2014/11/03
DOI:10.1039/C4SC03033H
Reduction of the Th3+ complex Cp′′3Th, 1 [Cp′′ = C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp′′3Th], 2, a complex containing thorium in the formal +2 oxidation state. Reaction of 1 with KC8 in the presence of 18-crown-6 generates the analogous Th2+ compound, [K(18-crown-6)(THF)2][Cp′′3Th], 3. Complexes 2 and 3 form dark green solutions in THF with ε = 23000 M−1 cm−1, but crystallize as dichroic dark blue/red crystals. X-ray crystallography revealed that the anions in 2 and 3 have trigonal planar coordination geometries, with 2.521 and 2.525 Å Th–(Cp′′ ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp′′3Th)1− is consistent with a 6d2 ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp′′2Th(C8H8), 4, and [K(18-crown-6)]Cp′′.
Co-reporter:Christopher M. Kotyk, Megan E. Fieser, Chad T. Palumbo, Joseph W. Ziller, Lucy E. Darago, Jeffrey R. Long, Filipp Furche and William J. Evans
Chemical Science (2010-Present) 2015 - vol. 6(Issue 12) pp:NaN7273-7273
Publication Date(Web):2015/09/21
DOI:10.1039/C5SC02486B
A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp′′3Ln)1− and (Cp′3Ln)1− (Cp′′ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2− ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1−. The intensely colored (ε = ∼8000 M−1 cm−1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)].
Co-reporter:Thomas J. Mueller, Megan E. Fieser, Joseph W. Ziller and William J. Evans
Chemical Science (2010-Present) 2011 - vol. 2(Issue 10) pp:NaN1996-1996
Publication Date(Web):2011/08/03
DOI:10.1039/C1SC00139F
Synthesis of the mixed ligand complexes (C5Me5)(C5Me4H)2Ln (Ln = Lu, Y) for comparison with (C5Me5)2(C5Me4H)Ln to evaluate details of steric effects on reductive reactivity has revealed that (C5Me5)3−x(C5Me4H)xLn complexes can reduce dinitrogen to (NN)2−. (C5Me5)(C5Me4H)2Lu reacts with N2 to form [(C5Me5)(C5Me4H)Lu]2(μ-η2:η2-N2), (C5Me5)2(C5Me4H)Y reduces N2 to [(C5Me5)2Y]2(μ-η2:η2-N2), and (C5Me4H)3Sc converts N2 to [(C5Me4H)2Sc]2(μ-η2:η2-N2). Exclusive (C5Me4H)1− loss occurs in each case with formation of (C5Me4H)2 as the byproduct. (C5Me5)2, the signature byproduct of sterically induced reduction reactions, is not observed. Since these complexes do not exhibit unusual steric parameters and since the more crowded (C5Me5)2(C5Me4H)Lu and (C5Me5)3Y do not display analogous reactivity, these reactions do not appear to be sterically induced reductions and suggest a new type of ligand-based reduction pathway involving (C5Me4H)1−.
Co-reporter:Douglas R. Kindra and William J. Evans
Dalton Transactions 2014 - vol. 43(Issue 8) pp:NaN3054-3054
Publication Date(Web):2013/12/02
DOI:10.1039/C3DT53187B
3,5-Di-tert-butyl-4-hydroxybenzoic acid can be made under mild conditions in a cyclic process from carbon dioxide and 3,5-di-tert-butyl-4-phenol using bismuth-based C–H bond activation and CO2 insertion chemistry starting with the Bi3+ complex, Ar′BiCl2, of the NCN pincer ligand, Ar′ = 2,6-(Me2NCH2)2C6H3. Complexes of the recently discovered oxyaryl dianion, (C6H2tBu2-3,5-O-4)2−, and the oxyarylcarboxy dianion, [O2C(C6H2tBu2-3,5-O-4)]2−, are intermediates in the process. Further studies of the oxyarylcarboxy dianion in Ar′Bi[O2C(C6H2tBu2-3,5-O-4)-κ2O,O′], show that it undergoes decarboxylation upon reaction with I2 and it reacts with trimethylsilyl chloride to produce the trimethylsilyl ether of the trimethylsilyl ester of 3,5-di-tert-butyl-4-hydroxybenzoic acid and the Ar′BiCl2 starting material.
Co-reporter:Selvan Demir, Nathan A. Siladke, Joseph W. Ziller and William J. Evans
Dalton Transactions 2012 - vol. 41(Issue 32) pp:NaN9666-9666
Publication Date(Web):2012/06/11
DOI:10.1039/C2DT30861D
The synthetically accessible borohydride complexes (C5Me4H)2Ln(THF)(BH4) and (C5Me5)2Ln(THF)(BH4) (Ln = Sc, Y) were examined as precursors alternative to the heavily-used tetraphenylborate analogs, [(C5Me4H)2Ln][BPh4] and [(C5Me5)2Ln][BPh4], employed in LnA2A′/M reduction reactions (A = anion; M = alkali metal) that generate “LnA2” reactivity and form reduced dinitrogen complexes [(C5R5)2(THF)xLn]2(μ-η2:η2-N2) (x = 0, 1). The crystal structures of the yttrium borohydrides, (C5Me4H)2Y(THF)(μ-H)3BH, 1, and (C5Me5)2Y(THF)(μ-H)2BH2, 2, were determined for comparison with those of the yttrium tetraphenylborates, [(C5Me4H)2Y][(μ-Ph)2BPh2], 3, and [(C5Me5)2Y][(μ-Ph)2BPh2], 4. The complex (C5Me4H)2Sc(μ-H)2BH2, 5, was synthesized and structurally characterized for comparison with (C5Me5)2Sc(μ-H)2BH2, 6, [(C5Me4H)2Sc][(μ-Ph)BPh3], 7, and [(C5Me5)2Sc][(μ-Ph)BPh3], 8. Structural information was also obtained on the borohydride derivatives, (C5Me4H)2Sc(μ-H)2BC8H14, 9, and (C5Me5)2Sc(μ-H)2BC8H14, 10, obtained from 9-borabicyclo(3.3.1)nonane (9-BBN) and (C5Me4R)2Sc(η3-C3H5), where R = H, 11; Me, 12. The preference of the metals for borohydride over tetraphenylborate binding was shown by the facile displacement of (BPh4)1− in 3, 4, 7, and 8 by (BH4)1− to make the respective borohydride complexes 1, 2, 5, and 6. These results are consistent with the fact that the borohydrides are not as useful as precursors in A2LnA′/M reductions of N2. An unusual structural isomer of [(C5Me4H)2Sc]2(μ-η2:η2-N2), 13′, was isolated from this study that shows the variations in ligand orientation that can occur in the solid state.
Co-reporter:Thomas J. Mueller, Joseph W. Ziller and William J. Evans
Dalton Transactions 2010 - vol. 39(Issue 29) pp:NaN6773-6773
Publication Date(Web):2010/05/13
DOI:10.1039/C002654A
To further explore the reactivity of the (C5Me5)− ligand in the sterically crowded (C5Me5)3M complexes, reactions with PhEEPh (E = S, Se, Te) have been examined. With M = La, Pr, Nd, Sm, and Y, PhSSPh reacts to form the expected reduction products, [(C5Me5)2M(SPh)]2, but the major organic byproduct is not the sterically induced reduction product, (C5Me5)2. Instead, the sigma bond metathesis product, C5Me5SPh, is the major byproduct. In contrast, reactions with (C5Me5)3Ce and (C5Me5)3U gave a mixture of C5Me5SPh and (C5Me5)2 as byproducts. PhSSPh reactions with the lanthanide nitrile adducts, (C5Me5)3Ln(NCCMe3)2 (Ln = La, Ce) and (C5Me5)3Nd(NCCMe3), formed [(C5Me5)2Ln(SPh)(NCCMe3)]2 and only C5Me5SPh as the byproduct. PhSeSePh reactions paralleled the PhSSPh results, but reactions of PhTeTePh with (C5Me5)3La, (C5Me5)3Sm, and (C5Me5)3La(NCCMe3)2 gave only (C5Me5)2 as a byproduct.
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