Kenneth G. Caulton

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Name: Caulton, Kenneth

Organization: Indiana University , USA

Department: Department of Chemistry

Title: (PhD)

TOPICS

Inorganic Chemistry

Chemicals
References

Ligand Design toward Multifunctional Substrate Reductive Transformations

Co-reporter:Alexander V. Polezhaev, Chun-Hsing Chen, Adam S. Kinne, Alyssa C. Cabelof, Richard L. Lord, and Kenneth G. Caulton

Inorganic Chemistry August 21, 2017 Volume 56(Issue 16) pp:9505-9505

Publication Date(Web):August 1, 2017

DOI:10.1021/acs.inorgchem.7b00785

The synthesis of bis(N1-phenyl-5-hydroxypyrazol-3-yl)pyridines (“L”) is described, and these are silylated to achieve analogues (“Si2L”) without the variable of the hydroxyl proton mobility. One hydroxyl example is characterized in its bis-pincer iron(II) complex, which shows every OH proton involved in hydrogen bonding. The steric bulk of the silylated N-phenyl-substituted ligands allows the synthesis and characterization of paramagnetic (Si2L)FeCl2 complexes, and one of these is reduced, under CO, to give the diamagnetic (Si2L)Fe(CO)2 species. Structural comparison and density functional theory calculations of the dichloride and dicarbonyl species show that much, but not all, of the reduction occurs at both the ligand pyridine and pyrazole rings, and thus this ligand type is more resistant to reduction than the simpler bis(iminopyridines). The OSiR3 substituent offers a useful diagnostic of reduction at pyrazole via the degree of π-donation to pyrazole by the oxygen lone pairs, and the stereoelectronic features of the NPh moiety are analyzed. The X-ray photoelectron spectroscopy binding energies of both iron and nitrogen are analyzed to show details of the locus of reduction.

Deprotonation, Chloride Abstraction, and Dehydrohalogenation as Synthetic Routes to Bis-Pyrazolate Pyridyl Iron(II) Complexes

Co-reporter:Brian J. Cook;Alexer V. Polezhaev;Chun-Hsing Chen;Maren Pink

European Journal of Inorganic Chemistry 2017 Volume 2017(Issue 34) pp:3999-4012

Publication Date(Web):2017/09/15

DOI:10.1002/ejic.201700558

The process of removal of protons and chloride, dehydrohalogenation, from [(H2L)FeCl2] is investigated systematically, to understand the reactivity of the implied transient LFeII. Reaction of [(H2L)FeCl2] with 2 equiv. of LiN(SiMe3)2 yields the “-ate” complex LiClFe2L2, as its dimer with every iron five-coordinate in an FeN4Cl environment. To avoid Li+ cation derived from LiN(SiMe3)2, reaction of Na2L with FeCl2 gives a product from addition of water, paramagnetic Na2[NaFe(HL)(L)]2(LFeO), which reveals Na/pyrazolate Nβ interactions and a five coordinate oxo group in the OFe3Na2 core of this aggregate. Abstraction of chloride in [(H2L)FeCl2] with NaBArF4 in THF gives paramagnetic [(H2L)Fe(THF)3]2+, which fails to react with CO. Dehydrohalogenation in the presence of Ph2PC2H4PPh2, dppe, gives both [LFe(κ2-dppe)]2(µ-dppe)] and [LFe(κ2-dppe)(κ1-dppe)], diamagnetic saturated species, which can be separated by pentane extraction. Dehydrohalogenation in the presence of tBuNC gives diamagnetic [LFe(CNtBu)3]. This is selectively methylated at both pyrazolate β-nitrogen atom to give [LMeFe(tBuNC)3]2+ which shows rich cyclic voltammetry, and which is reduced, with KC8, to diamagnetic [LMeFe(tBuNC)2]. Structure determination of some of these, together with IR data on isocyanide stretching frequencies, show L2– to be a stronger donor than LMe. First installing triflate (to avoid the more persistent chloride ligand) facilitates access to [LFe(Lewis base)3]2+ complexes, but this cation still shows relatively weak binding of CO to LFeII, which implicates weak π basicity of that d6 species. Production of paramagnetic bis-pincer complexes [(H2L)2Fe]2+ and [(LMe)2Fe]2+ in the presence of abundant Lewis base in polar medium is demonstrated, which illustrates a pincer ligand redistribution challenge to be kept in mind when trying to maintain a 1:1 Fe:pincer ratio, for highest reactivity.

Coordination and electronic characteristics of a nitrogen heterocycle pincer ligand

Co-reporter:Brian J. Cook, Chun-Hsing Chen, Maren Pink, Richard L. Lord, Kenneth G. Caulton

Inorganica Chimica Acta 2016 Volume 451() pp:82-91

Publication Date(Web):1 September 2016

DOI:10.1016/j.ica.2016.07.011

•Pincer featuring pyridine and two alkylated pyrazole is evaluated for redox activity.•Two new Fe(II) complexes of this ligand are synthesized and full characterized.•CV shows Fe(II) complexes are reducible, DFT predict electrons go to the ligand.•Free ligand reduction gives an EPR signal which shows radical on the pyridyl ring.The Fe(II) coordination chemistry of bis(pyrazole-3-yl)pyridine ligands with both proton or methyl substituents on pyrazole nitrogen are investigated, including the willingness of the ligand to undergo redox change. Protons on the pyrazole nitrogen promote intermolecular hydrogen bonding and lead to redox irreversibility; N methylation of those nitrogens eliminates those intermolecular interactions and leads to reversible outer-sphere reducibility. The resulting anion radical of the N-methylated ligand has more spin in the pyridine moiety than in the pyrazolyl pincer ligand arms, but also detectably delocalized into the electron withdrawing pyrazolyl pincer ligand arms; EPR and density functional calculations assist in characterizing the ligand radical anion, as its potassium complex.An electroactive pincer ligand.

Two- and Three-Electron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design

Co-reporter:Daniel Skomski; Christopher D. Tempas; Brian J. Cook; Alexander V. Polezhaev; Kevin A. Smith; Kenneth G. Caulton;Steven L. Tait

Journal of the American Chemical Society 2015 Volume 137(Issue 24) pp:7898-7902

Publication Date(Web):June 1, 2015

DOI:10.1021/jacs.5b03706

Rational, systematic tuning of single-site metal centers on surfaces offers a new approach to increase selectivity in heterogeneous catalysis reactions. Although such metal centers of uniform oxidation states have been achieved, the ability to control their oxidation states through the use of carefully designed ligands had not been shown. To this end, tetrazine ligands functionalized by two pyridinyl or pyrimidinyl substituents were deposited, along with vanadium metal, on the Au(100) surface. The greater oxidizing power of the bis-pyrimidinyltetrazine facilitates the on-surface redox formation of V3+, compared to V2+ when paired with the bis-pyridinyltetrazine, as determined by X-ray photoelectron spectroscopy. This demonstrates the ability to control metal oxidation states in surface coordination architectures by altering the redox properties of organic ligands. The metal–ligand complexes take the form of one-dimensional polymeric chains, resolved by scanning tunneling microscopy. The chain structures in the first layer are very uniform and are based on the same quasi-square-planar coordination geometry around single-site V with either ligand. Formation of a different, dimer structure is observed in the early stages of the second layer formation. These systems offer new opportunities in controlling the oxidation state of single-site transition metal atoms at a surface for new advances in heterogeneous catalysts.

Probing the Steric and Electronic Characteristics of a New Bis-Pyrrolide Pincer Ligand

Co-reporter:Nobuyuki Komine, René W. Buell, Chun-Hsing Chen, Alice K. Hui, Maren Pink, and Kenneth G. Caulton

Inorganic Chemistry 2014 Volume 53(Issue 3) pp:1361-1369

Publication Date(Web):January 10, 2014

DOI:10.1021/ic402120r

A new pincer ligand is synthesized to be dianionic, with the potential to be redox active. It has pyrrrole rings attached to both ortho sites of a pyridine, as the linking element. This H2L can be doubly deprotonated and then used to replace two chloride ligands in MCl2(NCPh)2, to form LM(NCPh) for M = Pd, Pt. The acid form H2L reacts with ZnEt2 with elimination of only 1 mol of ethane to yield (HL)ZnEt, a three-coordinate species with one pendant pyrrole NH functionality. This molecule binds the Lewis base p-dimethylaminopyridine (DMAP) to give first a simple 1:1 adduct that eliminates ethane on heating to form four-coordinate LZn(DMAP), which has an unusual structure due to the strong preference of the pincer ligand to bind in a mer (planar) geometry. A molecule with two HL– ligands each bonded in a bidentate manner to FeCl2 is synthesized and shown to contain four-coordinate iron with a flattened-tetrahedral structure. The electrochemistry of LM(NCPh) and (L)Zn(DMAP) shows three oxidation processes, which is interpreted to involve at least two oxidations of the pyrrolide arms.

Transition Metal Chlorides Are Lewis Acids toward Terminal Chloride Attached to Late Transition Metals

Co-reporter:Alice K. Hui, Brian J. Cook, Daniel J. Mindiola, and Kenneth G. Caulton

Inorganic Chemistry 2014 Volume 53(Issue 7) pp:3307-3310

Publication Date(Web):March 10, 2014

DOI:10.1021/ic402107z

Two different neutral tridentate imine-donor pincer ligands interact with excess MCl2 (M = Co or Cu) to form compounds of the same stoichiometry, (LMCl2)2·MCl2, where the assembling force is the electron richness of the terminal chlorides on the LMCl2 unit. Finite aggregation occurs for M = Co, but for M = Cu, an infinite polymeric structure is adopted, all because MCl2 is bifunctional, which thus bridges multiple MCl units. The bis-pyrazolylpyridine ligand has two acidic NH protons, and both of these are involved in intramolecular hydrogen bonds. The generality of this Lewis acid aggregation is discussed.

Chemical Implications of Incompatible Ligand versus Metal Coordination Geometry Preferences

Co-reporter:Alice K. Hui, Yaroslav Losovyj, Richard L. Lord, and Kenneth G. Caulton

Inorganic Chemistry 2014 Volume 53(Issue 6) pp:3039-3047

Publication Date(Web):March 6, 2014

DOI:10.1021/ic402866e

Binding an electron deficient pincer ligand which strongly dictates planar, mer stereochemistry, to a metal which prefers tetrahedral structure, e.g., d10 CuCl, is explored for possible intramolecular redox chemistry. Experiment shows that the pincer ligand 2,2′-bis-tetrazinyl pyridine, btzp, forms a complex (btzp)CuCl which is a chloride-bridged polymer in the solid state, hence with 20 valence electrons around copper. DFT calculations show that even the monomer has nonplanar copper with the tetrazinyl nitrogen lone pairs somewhat misdirected away from copper, with long Cu/N bonds, in a singlet ground state; 13.9 kcal/mol less stable is a triplet, whose electronic structure shows one electron from the ground state Cu(I) has been transferred to a pincer π* orbital. Outer sphere electron transfer to (btzp)CuCl yields (btzp)Cu where the added electron has gone into the pincer, to leave a ligand-centered radical, characterized by EPR, chemical reactivity, and X-ray photoelectron spectroscopy.

Multiplying the electron storage capacity of a bis-tetrazine pincer ligand

Co-reporter:Christopher R. Benson, Alice K. Hui, Kumar Parimal, Brian J. Cook, Chun-Hsing Chen, Richard L. Lord, Amar H. Flood and Kenneth G. Caulton

Dalton Transactions 2014 vol. 43(Issue 17) pp:6513-6524

Publication Date(Web):13 Feb 2014

DOI:10.1039/C4DT00341A

An unexpected doubling in redox storage emerging from a new pincer ligand upon bis-ligation of iron(II) is described. When tetrazine arms are present at the two ortho positions of pyridine, the resulting bis-tetrazinyl pyridine (btzp) pincer ligand displays a single one-electron reduction at ca. −0.85 V vs. Ag/AgCl. Complexation to iron, giving the cation Fe(btzp)22+, shows no oxidation but four reduction waves in cyclic voltammetry instead of the two expected for the two constituent ligands. Mossbauer, X-ray diffraction and NMR studies show the iron species to contain low spin Fe(II), but with evidence of back donation from iron to the pincer ligands. CV and UV-Vis spectroelectrochemistry, as well as titration studies as monitored by CV, electronic spectra and EPR reveal the chemical reversibility of forming the reduced species. DFT and EPR studies show varying degrees of delocalization of unpaired spin in different species, including that of a btzp−1 radical anion, partnered with various cations.

In search of redox non-innocence between a tetrazine pincer ligand and monovalent copper

Co-reporter:Alice K. Hui, Richard L. Lord and Kenneth G. Caulton

Dalton Transactions 2014 vol. 43(Issue 21) pp:7958-7963

Publication Date(Web):17 Mar 2014

DOI:10.1039/C3DT52490F

The synthesis and characterization of a “super-saturated” six-coordinate complex of monovalent copper (PF6− salt) and the potentially oxidizing pincer ligand 2,6, bis-(methyl tetrazinyl)pyridine, btzp, are described. This cation has a structure with the two pincers symmetry related, but each btzp having one short and one long Cu–N(tetrazine) bond; facile exchange is observed between short and long tetrazine donors. The structure shows no evidence of full electron transfer from Cu+ to tetrazine, and DFT calculations not only confirm this conclusion, but also show that the lowest energy triplet state, an excited state relative to the singlet ground state, has the MLCT character where the electron lost by copper now resides in both tetrazine rings of only one pincer ligand; the two pincers in this excited state are inequivalent, having charged btzp0 and btzp−1. The unusual orientation of the distinct tetrazines in the ground state structure of Cu(btzp)2+ is attributed to charge/dipole attraction unhindered by significant entropy cost.

A tale of hydrogen abstraction, initially detected via X-ray diffraction

Co-reporter:Alice K. Hui;Chun-Hsing Chen;Adam M. Terwilliger;Richard L. Lord

Acta Crystallographica Section C 2014 Volume 70( Issue 3) pp:250-255

Publication Date(Web):

DOI:10.1107/S2053229614003234

Reaction of a bis-tetrazinyl pyridine pincer ligand, btzp, with a vanadium(III) reagent gives not a simple adduct but dichlorido{3-methyl-6-[6-(6-methyl-1,2,4,5-tetrazin-3-yl-κN²)pyridin-2-yl-κN]-1,4-dihydro-1,2,4,5-tetrazin-1-yl-κN¹}oxidovanadium(IV) acetonitrile 2.5-solvate, [V(C₁₁H₁₀N₉)Cl₂O]·2.5CH₃CN, a species which X-ray diffraction reveals to have one H atom added to one of the two tetrazinyl rings. This H atom was first revealed by a short intermolecular N...Cl contact in the unit cell and subsequently established, from difference maps, to be associated with a hydrogen bond. One chloride ligand has also been replaced by an oxide ligand in this synthetic reaction. This formula for the complex, [V(Hbtzp)Cl₂O], leaves open the question of both ligand oxidation state and spin state. A computational study of all isomeric locations of the H atom shows the similarity of their energies, which is subject to perturbation by intermolecular hydrogen bonding found in X-ray work on the solid state. These density functional calculations reveal that the isomer with the H atom located as found in the solid state contains a neutral radical Hbtzp ligand and tetravalent d¹ V center, but that these two unpaired electrons are more stable as an open-shell singlet and hence antiferromagnetically coupled.

A cis-Divacant Octahedral and Mononuclear Iron(IV) Imide

Co-reporter:Keith Searles;Dr. Skye Fortier;Dr. Marat M. Khusniyarov;Dr. Patrick J. Carroll;Dr. Jörg Sutter;Dr. Karsten Meyer;Dr. Daniel J. Mindiola;Dr. Kenneth G. Caulton

Angewandte Chemie International Edition 2014 Volume 53( Issue 51) pp:14139-14143

Publication Date(Web):

DOI:10.1002/anie.201407156

Abstract

A rare, low-spin Fe^IV imide complex [(pyrr₂py)FeNAd] (pyrr₂py²⁻=bis(pyrrolyl)pyridine; Ad=1-adamantyl) confined to a cis-divacant octahedral geometry, was prepared by reduction of N₃Ad by the Fe^II precursor [(pyrr₂py)Fe(OEt₂)]. The imide complex is low-spin with temperature-independent paramagnetism. In comparison to an authentic Fe^III complex, such as [(pyrr₂py)FeCl], the pyrr₂py²⁻ ligand is virtually redox innocent.

Mechanistic Understanding of a Silver Pyridylpyrrolide as a Catalyst for 3 + 2 Cyclization of a Nitrile with Diazo Ester

Co-reporter:Jaime A. Flores, Kuntal Pal, Maria E. Carroll, Maren Pink, Jonathan A. Karty, Daniel J. Mindiola, and Kenneth G. Caulton

Organometallics 2014 Volume 33(Issue 7) pp:1544-1552

Publication Date(Web):March 24, 2014

DOI:10.1021/om400756t

The trinuclear argentate complex Ag3(μ2-3,5-(CF3)2PyrPy)3 (PyrPy = 2,2′-pyridylpyrrolide) catalyzes the 3 + 2 cycloaddition of several NCR (R = Me, Ph, tBu) and N2CHCO2Et to disubstituted oxazoles, even in the presence of light and air. Structural and theoretical studies imply a three-coordinate silver carbene complex, (3,5-(CF3)2PyrPy)Ag(CHCO2Et), to be responsible in a stepwise nitrile addition and cyclization step to form the heterocycle.

A Dinuclear Cobalt Complex Featuring Unprecedented Anodic and Cathodic Redox Switches for Single-Molecule Magnet Activity

Co-reporter:Skye Fortier ; Jennifer J. Le Roy ; Chun-Hsing Chen ; Veacheslav Vieru ; Muralee Murugesu ; Liviu F. Chibotaru ; Daniel J. Mindiola

Journal of the American Chemical Society 2013 Volume 135(Issue 39) pp:14670-14678

Publication Date(Web):August 30, 2013

DOI:10.1021/ja405284t

One-electron oxidation or reduction of the paramagnetic dinuclear Co(II) complex dmp2Nin{Co[N(SiMe3)2]}2 (1; dmp2Nin2– = bis(2,6-dimethylphenyl)nindigo), by fully reversible chemical or electrochemical methods, generates the radical salts [1(OEt2)]+ and [1]−, respectively. Full structural and magnetic analyses reveal the locus of the redox changes to be nindigo-based, thus giving rise to ligand-centered radicals sandwiched between two paramagnetic and low-coordinate Co(II) centers. The presence of these sandwiched radicals mediates magnetic coupling between the high-spin (S = 3/2) cobalt ions, which gives rise to single-molecule magnet (SMM) activity in both the oxidized ([1(OEt2)]+) and reduced ([1]−) states. This feature represents the first example of a SMM exhibiting fully reversible, dual “ON/OFF” switchability in both the cathodic and anodic states.

Synthesis and Oxidative Reactivity of 2,2′-Pyridylpyrrolide Complexes of Ni(II)

Co-reporter:Nikolay P. Tsvetkov, Chun-Hsing Chen, José G. Andino, Richard L. Lord, Maren Pink, René W. Buell, and Kenneth G. Caulton

Inorganic Chemistry 2013 Volume 52(Issue 16) pp:9511-9521

Publication Date(Web):August 2, 2013

DOI:10.1021/ic4011746

Synthesis and characterization of divalent nickel complexed by 2-pyridylpyrrolide bidentate ligands are reported, as possible precursors to complexes with redox active ligands. Varied substituents on the pyrrolide, two CF3 (L2), two tBu (L0), and one of each type (L1) are employed and the resulting Ni(Ln)2 complexes show different Lewis acidity toward CO, H2O, tetrahydrofuran (THF), or MeCN, the L2 case being the most acidic. Density functional theory calculations show that the frontier orbitals of all three Ni(Ln)2 species are localized at the pyrrolide groups of both ligands and Ni(Ln)2+ can be detected by mass spectrometry and in cyclic voltammograms (CVs). Following cyclic voltammetry studies, which show electroactivity primarily in the oxidative direction, reactions with pyridine N-oxide or Br2 are reported. The former yield simple bis adducts, Ni(L2)2(pyNO)2 and the latter effects electrophilic aromatic substitution of the one pyrrolide ring hydrogen for both chelates, leaving it brominated.

2,2′-Pyridylpyrrolide Ligand Redistribution Following Reduction

Co-reporter:Keith Searles, Atanu K. Das, René W. Buell, Maren Pink, Chun-Hsing Chen, Kuntal Pal, David Gene Morgan, Daniel J. Mindiola, and Kenneth G. Caulton

Inorganic Chemistry 2013 Volume 52(Issue 9) pp:5611-5619

Publication Date(Web):April 19, 2013

DOI:10.1021/ic400803e

The potential redox activity of the 2,2′-pyridylpyrrolide ligand carrying two CF3 substituents (L2) is investigated. Synthesis and characterization of d6 and d7 species M(L2)2 for M = Fe and Co are described (both are nonplanar, but not tetrahedral), as are the Lewis acidity of each. In spite of CV evidence for quasireversible reductions to form M(L2)2q– where q = 1 and 2, chemical reductants instead yield divalent metal complexes KM(L2)3, which show attractive interactions of K+ to pyrrolide, to F, and to lattice toluene π cloud. The collected evidence on these products indicates that pyridylpyrrolide is a weak field ligand here, but CO can force spin pairing in Fe(L2)2(CO)2. Evidence is presented that the overall reductive reaction yields 33 mol % of bulk metal, which is the fate of the reducing equivalents, and a mechanism for this ligand redistribution is proposed. Analogous ligand redistribution behavior is also seen for nickel and for trimeric monovalent copper analogues; reduction of Cu(L2)2 simply forms Cu(L2)2–.

Reactivity of the terminal oxo species ((tBu2PCH2SiMe2)2N)RhO

Co-reporter:Nikolay P. Tsvetkov, José G. Andino, Hongjun Fan, Alexander Y. Verat and Kenneth G. Caulton

Dalton Transactions 2013 vol. 42(Issue 19) pp:6745-6755

Publication Date(Web):13 Mar 2013

DOI:10.1039/C3DT31972E

Reactivity of the 4-coordinate molecule (PNP)RhO (PNP is (tBu2PCH2SiMe2)2N) towards CO proceeds stepwise, first forming an η2-CO2 complex, by a mechanism which involves a preliminary adduct of CO on Rh, then a second CO displaces CO2. Reaction of the oxo complex with CO2 occurs in time of mixing even at low temperature to form (PNP)Rh(η2-CO3), with no intermediate detectable. DFT calculations indicate an initial bond formation between the oxo center and the CO2 carbon. Reaction of (PNP)RhO with H2 occurs only at a 1:2 molar stoichiometry, to ultimately form (PNP)Rh(H)2 and free H2O. No intermediate reaches detectable population even at −60 °C, but DFT mapping of various possible mechanisms on the singlet energy surface shows that the nearly equi-energetic (PNP)Rh(H2O) and (PNP)RhH(OH) are formed, but only the latter readily adds the second molecule of H2 to proceed to the observed products; these reactions thus both involve heterolytic splitting of H2.

New Approaches to Functionalizing Metal-Coordinated N2

Co-reporter:Dr. José G. Andino;Shivnath Mazumder;Dr. Kuntal Pal ; Kenneth G. Caulton

Angewandte Chemie International Edition 2013 Volume 52( Issue 18) pp:4726-4732

Publication Date(Web):

DOI:10.1002/anie.201209168

Neue Anstze zur Funktionalisierung von metallkoordiniertem N2

Co-reporter:Dr. José G. Andino;Shivnath Mazumder;Dr. Kuntal Pal ; Kenneth G. Caulton

Angewandte Chemie 2013 Volume 125( Issue 18) pp:4824-4831

Publication Date(Web):

DOI:10.1002/ange.201209168

Büchner Reactions Catalyzed by a Silver(I) Pyridylpyrrolide: Understanding Arene C═C Insertion Selectivity

Co-reporter:Nobuyuki Komine, Jaime A. Flores, Kuntal Pal, Kenneth G. Caulton, and Daniel J. Mindiola

Organometallics 2013 Volume 32(Issue 11) pp:3185-3191

Publication Date(Web):May 30, 2013

DOI:10.1021/om301240d

The complex Ag3(μ2-3,5-(CF3)2PyrPy)3 (3,5-(CF3)2PyrPy = 2,2′-pyridylpyrrolide(1−) ligand) catalytically promotes the insertion of the carbene of ethyl diazoacetate (EDA), at room temperature, into the C═C bond of a series of arenes to ultimately ring-open them and form the corresponding cycloheptatrienes. In one case, the norcaradiene intermediate can be isolated, while regioselective C═C insertion can be promoted with certain arene substrates. The mechanism of C═C insertion, preference over C–H insertion, and origin of C═C regioselectivity has been probed by a combination of experimental and theoretical studies.

Silver(I)-Catalyzed Insertion of Carbene into Alkane C–H Bonds and the Origin of the Special Challenge of Methane Activation Using DFT as a Mechanistic Probe

Co-reporter:Jaime A. Flores, Nobuyuki Komine, Kuntal Pal, Balazs Pinter, Maren Pink, Chun-Hsing Chen, Kenneth G. Caulton, and Daniel J. Mindiola

ACS Catalysis 2012 Volume 2(Issue 10) pp:2066

Publication Date(Web):August 6, 2012

DOI:10.1021/cs300256b

The argentate trinuclear cluster Ag3(μ2-3,5-(CF3)2PyrPy)3 (3,5-(CF3)2PyrPy = 2,2′-pyridylpyrrolide– ligand) catalytically promotes the insertion of the carbene of ethyl diazoacetate at room temperature into the C–H bond of a series of alkanes ranging from ethane to hexane, as well as branched and cyclic hydrocarbons. In addition to experimental studies, we also present theoretical studies elucidating the mechanism to C–H activation and functionalization by the transient silver carbene monomer (3,5-(CF3)2PyrPy)Ag(CHCO2Et). On the basis of DFT studies, formation of the silver carbene complex was found to be rate-determining for alkane substrates such as ethane and propane. On the other hand, DFT studies on methane, a substrate that we failed to activate, revealed that carbene insertion into the C–H bond was overall rate-determining. Theoretical analysis of charge flow also shows that the change from separated reagents to the TS involves charge flow from alkane to the silver carbene carbon with the bridging H behaving as a conduit. KIE studies using cyclohexane as a substrate suggest that the product-determining step involves only modest C–H bond lengthening, which can be also represented as a very early transition state with respect to C–H insertion of the carbene.Keywords: carbene; catalysis; pyridylpyrrolide; silver

Probing the redox non-innocence of dinuclear, three-coordinate Co(II) nindigo complexes: not simply β-diketiminate variants

Co-reporter:Skye Fortier, Octavio González-del Moral, Chun-Hsing Chen, Maren Pink, Jennifer J. Le Roy, Muralee Murugesu, Daniel J. Mindiola and Kenneth G. Caulton

Chemical Communications 2012 vol. 48(Issue 90) pp:11082-11084

Publication Date(Web):21 Sep 2012

DOI:10.1039/C2CC34560A

Reduction of the dinuclear Co(II) nindigo complex dmp2Nin[Co(N{SiMe3}2)]2, with 1 or 2 equiv. of K0 (or KC8), affords the reduced complexes [dmp2Nin{Co(N{SiMe3}2)}2]− and [dmp2Nin{Co(N{SiMe3}2)}2]2−, respectively. Inspection of these reduced species reveals ligand-centered reduction, with each cobalt ion retaining a formal 2+ oxidation state.

Systematics and Future Projections Concerning Redox-Noninnocent Amide/Imine Ligands

Co-reporter:Kenneth G. Caulton

European Journal of Inorganic Chemistry 2012 Volume 2012( Issue 3) pp:435-443

Publication Date(Web):

DOI:10.1002/ejic.201100623

Abstract

An analysis of the conjugative possibilities of dienes carrying two terminal heteroatom donors shows some generalizations of these as possible redox-active (redox “noninnocent”) ligands. If the two E=C functionalities (E = O,S, NR, CHR) are connected by an odd number of sp²-hybridized atoms, full conjugation between the two terminal E donors is not possible, a situation which is found both in 2,6-bis(imino)pyridine (BIMPY) and beta-diketiminate ligands; the character of their redox noninnocence is thus altered, compared to 1,4-diheterodienes. Some insight into the BIMPY ligand comes from the analog where one imino arm is absent. The traditional stereochemical relationships which govern conjugation in arenes are analyzed for their implications for different bis(imino)pyridine isomers, and also for 2,6-dipyrimidyl- and dipyridazinyl-pyridines, as generalizations of the classic terpyridyl ligands. Factors which favor oxidized vs. reduced ligand forms are discussed.

Mechanism of N/O Bond Scission of N2O by an Unsaturated Rhodium Transient

Co-reporter:José G. Andino

Journal of the American Chemical Society 2011 Volume 133(Issue 32) pp:12576-12583

Publication Date(Web):June 22, 2011

DOI:10.1021/ja202439g

The mechanism of formation of triplet (PNP)RhO and (PNP)Rh(N2) (PNP = N(SiMe2CH2PtBu2)2) from reaction of two molecules of (PNP)Rh with N2O has been studied by DFT, evaluating mechanisms which (1) involve free N2, and (2) which effect N/O bond scission in linearly coordinated (PNP)RhNNO. This work shows the variety of modes of binding N2O to this reducing, unsaturated metal fragment and also evaluates why a mechanism avoiding free N2 is preferred. Comparisons are made to isoelectronic CO2 in its reaction with (PNP)Rh.

Three-Coordinate NiII: Tracing the Origin of an Unusual, Facile Si−C(sp3) Bond Cleavage in [(tBu2PCH2SiMe2)2N]Ni+

Co-reporter:Benjamin C. Fullmer ; Hongjun Fan ; Maren Pink ; John C. Huffman ; Nikolay P. Tsvetkov

Journal of the American Chemical Society 2011 Volume 133(Issue 8) pp:2571-2582

Publication Date(Web):February 9, 2011

DOI:10.1021/ja108426f

All attempts to synthesize (PNP)Ni(OTf) form instead (tBu2PCH2SiMe2NSiMe2OTf)Ni(CH2PtBu2). Abstraction of F− from (PNP)NiF by even a catalytic amount of BF3 causes rearrangement of the (transient) (PNP)Ni+ to analogous ring-opened [(tBu2PCH2SiMe2NSiMe2F)]Ni(CH2PtBu2). Abstraction of Cl− from (PNP)NiCl with NaB(C6H3(CF3)2)4 in CH2Cl2 or C6H5F gives (PNP)NiB(C6H3(CF3)2)4, the key intermediate in these reactions is (PNP)Ni+, [(PNP)Ni]+, in which one Si−C bond (together with N and two P) donates to Ni. This makes this Si−C bond subject to nucleophilic attack by F−, triflate, and alkoxide/ether (from THF). This σSi−C complex binds CO in the time of mixing and also binds chloride, both at nickel. Evidence is offered of a “self-healing” process, where the broken Si−C bond can be reformed in an equilibrium process. (PNP)Ni+ reacts rapidly with H2 to give (PN(H)P)NiH+, which can be deprotonated to form (PNP)NiH. A variety of nucleophilic attacks (and THF polymerization) on the coordinated Si−C bond are envisioned to occur perpendicular to the Si−C bond, based on the character of the LUMO of (PNP)Ni+.

Assessment of the Electronic Structure of 2,2′-Pyridylpyrrolides as Ligands

Co-reporter:Jaime A. Flores, José G. Andino, Nikolay P. Tsvetkov, Maren Pink, Robert J. Wolfe, Ashley R. Head, Dennis L. Lichtenberger, Joseph Massa, and Kenneth G. Caulton

Inorganic Chemistry 2011 Volume 50(Issue 17) pp:8121-8131

Publication Date(Web):July 21, 2011

DOI:10.1021/ic2005503

The ligand class 2,2′-pyridylpyrrolide is surveyed, both for its structural features and its electronic structure, when attached to monovalent K, Cu, Ag, Au, and Rh. The influence of pyrrolide ring substituents is studied, as well as the question of push/pull interaction between the pyridyl and pyrrolide halves. The π donor ability of the pyrrolide is found to be less than that of an analogous phenyl. However, in contrast to the phenyl analog, the HOMO is pyrrolide π in character for pyridylpyrrolide complexes of copper and rhodium, while it is conventionally metal localized for planar, d8 rhodium pyridylphenyl. Monovalent three-coordinate copper complexes show great deviations from Y-shaped toward T-shaped structures, including cases where the pyridyl ligand bonds only weakly.

An evaluation of monovalent osmium supported by the PNP ligand environment

Co-reporter:Nikolay Tsvetkov, Hongjun Fan and Kenneth G. Caulton

Dalton Transactions 2011 vol. 40(Issue 5) pp:1105-1110

Publication Date(Web):16 Dec 2010

DOI:10.1039/C0DT00989J

Nitrogen is essential to reaction of (PNP)OsI (PNP is N(SiMe2CH2PtBu2)2) and Mg powder in THF, to give equimolar (PNP)OsH(N2) and hydrido carbene [(tBu2PCH2SiMe2)N(SiMe2CH2PtBu(CMe2CH)]OsH. This reaction is attributed to H2 evolution from solid magnesium, rather than high energy H atom transfer between molecules, but relies also on the strong π-basicity of Os in favoring α-H migration from the metallated tBu group on Os to form the second product, the hydrido carbene species. The path to two different products begins because the simple N2 adduct of (PNP)OsI undergoes spontaneous heterolytic H–C splitting of the tBu methyl group, to produce a secondary amine intermediate [(tBu2PCH2SiMe2)N(H)(SiMe2CH2PtBu(CMe2CH2)]OsI(N2) which can then be dehydrohalogenated by Mg. The analogous reaction for (PNP)RuCl shows production of only (PNP)RuH(N2), with none of the hydride carbene dehydrogenation product. Comparative (Ruvs. Os) DFT calculations reveal the reaction steps where the Os analog is much more exothermic, accounting for certain reaction selectivities.

Evaluating the reducing power of 3-coordinate T-shaped NiI

Co-reporter:Benjamin C. Fullmer, Hongjun Fan, Maren Pink, Kenneth G. Caulton

Inorganica Chimica Acta 2011 Volume 369(Issue 1) pp:49-54

Publication Date(Web):15 April 2011

DOI:10.1016/j.ica.2010.12.059

The reactivity of (PNP)NiI, where PNP = (tBu2PCH2SiMe2)2N, with oxidants was evaluated. Towards the nitroxyl TEMPO, a 1:1 adduct is formed which was shown to have η2-TEMPO bound through both N and O, with the consequence that one P of the PNP ligand is displaced, leaving the pincer ligand bidentate to NiII. DFT calculations show that the bidentate character of TEMPO is due to steric clash between tBu and TEMPO ring methyl groups. Reaction of (PNP)Ni with I2, Br2, C2Cl6 and even CH2Cl2 all yield (PNP)NiIIX, but never (PNP)NiIIIX2. Excess Br2 instead oxidizes one phosphorus, yielding the zwitterion [(BrtBu2PCH2SiMe2)N(SiMe2CH2PtBu2)]NiBr2, whose structure is determined. DFT calculation of the species (PNP)NiIII(Br)2 yields reaction thermodynamics which show the reason for its absence, and also shows the low BDE of its Ni–Br bond. (PNP)Ni slowly catalyzes the polymerization of HCCR (R = H or Ph), but gives no detectable conversion to a new alkyne-derived nickel complex.Graphical abstractOxidation of a monovalent nickel pincer complex shows arm displacement, and limitations of reaching Ni(III).Research highlights► Coordination of N2 initiates higher reactivity of a C–H bond. ► Mg next reacts with 4-coordinate Os(II) to dehalogenate. ► Transient intermediate then undergoes H migration.

Selectivity of attack on a Si–C(sp3) sigma bond coordinated to NiII

Co-reporter:Matthew F. Laird, Nikolay P. Tsvetkov, Maren Pink, Tao He, René W. Buell, Kenneth G. Caulton

Inorganica Chimica Acta 2011 Volume 374(Issue 1) pp:79-87

Publication Date(Web):1 August 2011

DOI:10.1016/j.ica.2010.12.061

(PNP)Ni+ (as its (BArF4- salt) adds PhCN to Ni, but HX cleaves the Si–CH2 bond to form Ni[η2−(tBu2PCH2SiMe2)N(H)(SiMe2X)][η2–CH2tBu2P]+, for X = OMe, piperidyl, N(H)CH2Ph, N(H)Ph, morpholinyl. The diprotic reagent H2O gives (η2–tBu2PCH2SiMe2OSiMe2NH2)(η2–tBu2CH2P)Ni+. RCCH (R = Ph, SiMe3, tBu) reacts, through three detected intermediates, to form (tBu2PCH2SiMe2)N(H)(SiMe2CH2tBu2PCCR)Ni+, a product where one P has been oxidized and Ni reduced, each by two electrons. This shows the dominant influence on reactivity of Si–C bond activation by its unconventional donation to nickel in the structure of (PNP)Ni+.Graphical abstract(PNP)Ni+ reacts with RCCH by P/C coupling, which is a 2-electron change at phosphorus, and at nickel, (PNP) = N[(SiMe2)CH2PtBu2]2.Research highlights► Pincer ligand backbone is subject to Si/C bond cleavage. ► Nickel coordinates this Si/C bond. ► Acetylide carbon couples to phosphorus to effect net redox at Ni.

Ligand Influence on Metal Aggregation: a Unique Bonding Mode for Pyridylpyrrolides

Co-reporter:José G. Andino, Jaime A. Flores, Jonathan A. Karty, Joseph P. Massa, Hyunsoo Park, Nikolay P. Tsvetkov, Robert J. Wolfe and Kenneth G. Caulton

Inorganic Chemistry 2010 Volume 49(Issue 17) pp:7626-7628

Publication Date(Web):August 5, 2010

DOI:10.1021/ic100878s

The synthesis and characterization of a CuI complex with a cis-bidentate monoanionic nitrogenous ligand, 2-pyridylpyrrolide, L, is reported. This shows binding of one base B = MeCN or CO per copper in a species LCu(B), but this readily releases the volatile ligand under vacuum with aggregation of transient LCu to a mixture of two enantiomers of a chiral trimer: a zwitterion containing inequivalent CuI centers, possible via a new bonding mode of pyridylpyrrolide, and one with nitrogen lone pairs donating to two different metals. Density functional theory calculations show the energetics of both ligand binding and aggregation (including dimer and monomer alternatives), as well as the ability of this ligand to rotate away from planarity to accommodate a bridging structural role. The trimer serves as a synthon for the simple fragment LCu.

Redox and Lewis Acid Reactivity of Unsaturated OsII

Co-reporter:Nikolay Tsvetkov;Maren Pink;Hongjun Fan;Joo-Ho Lee

European Journal of Inorganic Chemistry 2010 Volume 2010( Issue 30) pp:4790-4800

Publication Date(Web):

DOI:10.1002/ejic.201000503

Abstract

A synthesis of [(PNP)OsI] {PNP = (tBu₂PCH₂SiMe₂)₂N} permits evaluation of its reactivity, both Lewis acidity and reducing power (i.e., ability to be oxidized). It binds two molecules of PhCN, into trans sites, but only one of ethylene, and, upon binding of one N₂, there is heterolytic splitting of one tBu C–H bond to put the proton on amide N and the carbon on Os, leaving divalent metal in [{PN(H)P*}Os(N₂)(I)]. Two moles of H₂ add, forming [{PN(H)P}OsH(H₂)I], via H–H bond heterolysis. Thermolysis of [(PNP)OsI] gives the product of adding a tBu methyl C–H bond across the Os/N bond, and also net dehydrogenation of this intermediate, forming a carbene complex; the released H₂ forms [(PNP)OsH₂I], and the chemistry of [(PNP)Os] hydridohalides is described. Reaction with O₂ occurs with no detectable intermediate, to completely split the O=O bond, and form trans-[(PNP)Os(O)₂I], a product of four electron redox change. Attempted two electron oxidation by oxygen atom transfer with pyridine N-oxide or Me₃NO or N₂O surprisingly effect transposition of N from its silyl substituents onto the metal, and replace N by O, forming a nitride complex of a bis(silyl ether, phosphane) chelate whose oxygen fails to bind to Os. The product is thus four-coordinate, tetrahedral [(POP)Os(N)I], with an Os/N triple bond.

Unexpected selectivity in electrophilic attack on (PNP)RuN

Co-reporter:Amy Walstrom, Hongjun Fan, Maren Pink, Kenneth G. Caulton

Inorganica Chimica Acta 2010 Volume 363(Issue 3) pp:633-636

Publication Date(Web):15 February 2010

DOI:10.1016/j.ica.2008.11.010

Protonation of (PNP)RuN, where PNP is (tBu2PCH2SiMe2)2N, with HCl occurs at the amide nitrogen, with coordination of chloride to RuIV, while triflic acid protonates the same nitrogen, but has triflate anion hydrogen-bonded to the proton on the PNP amide nitrogen, not triflate coordinated to the metal. Methyl triflate however alkylates the nitride nitrogen, to give a C2v symmetric product. DFT calculations show that the thermodyamic preference is for proton on amide nitrogen while alkyl favors nitride alkylation, even without the need for a hydrogen bond to reverse the H vs. alkyl preference. Alkylation at the amide nitrogen leads to nearly complete loss of the PN(R)P Ru/N bond in this unobserved isomer. These preferences among nucleophilic sites on (PNP)RuN are rationalized based on the frontier orbitals of this molecule.In (PNP)RuN, protonation occurs at the amide nitrogen, but methylation is at the nitride nitrogen, the latter selectivity influenced by steric factors.

Mechanism of Heterolysis of H2 by an Unsaturated d8 Nickel Center: via Tetravalent Nickel?

Co-reporter:Tao He ; Nikolay P. Tsvetkov ; José G. Andino ; Xinfeng Gao ; Benjamin C. Fullmer

Journal of the American Chemical Society 2009 Volume 132(Issue 3) pp:910-911

Publication Date(Web):December 31, 2009

DOI:10.1021/ja908674x

Collision of H2 with the unusual nickel complex, (PNP)Ni+, where PNP = (tBu2PCH2SiMe2)2N, forms a rare dihydrogen complex of the d8 configuration which then rearranges to heterolytically cleave the H−H bond. Experimental studies support a short H/H distance in the coordinated diatomic, and DFT calculations show that the transition state for heterolysis, in spite of the fact that this involves an amide nitrogen located trans to the H2, has the H/H bond fully split, and has all the geometric features of Ni(IV), but this is a local maximum, not a minimum.

Surprising isomer preference on IrIII, favoring facile H–C(sp3) bond cleavage

Co-reporter:Nikolai P. Tsvetkov, Matthew F. Laird, Hongjun Fan, Maren Pink and Kenneth G. Caulton

Chemical Communications 2009 (Issue 30) pp:4578-4580

Publication Date(Web):29 Jun 2009

DOI:10.1039/B908954C

Species (PNP)Ir(X)(Y), where PNP = N(SiMe2CH2PtBu2)2−1 with X and Y halide, have a tBu group C–H bond heterolytically split by addition across the Ir–N bond.

Unusual selectivity of a (pincer)Ni-hydride reacting with CO2

Co-reporter:Matthew F. Laird, Maren Pink, Nikolay P. Tsvetkov, Hongjun Fan and Kenneth G. Caulton

Dalton Transactions 2009 (Issue 8) pp:1283-1285

Publication Date(Web):07 Jan 2009

DOI:10.1039/B822677F

The reaction of (PNP)NiH, where PNP is (tBu2PCH2SiMe2)2N−1, with CO2 occurs over a period of hours at 25 °C to form (POP)NiH(NCO), which involves transposition of the initial amide nitrogen and one oxygen of CO2.

Influence of the Metal Orbital Occupancy and Principal Quantum Number on Organoazide (RN3) Conversion to Transition-Metal Imide Complexes

Co-reporter:Amy N. Walstrom ; Benjamin C. Fullmer ; Hongjun Fan ; Maren Pink ; Drew T. Buschhorn

Inorganic Chemistry 2008 Volume 47(Issue 19) pp:9002-9009

Publication Date(Web):August 30, 2008

DOI:10.1021/ic801035z

The reaction of phenyl azide with (PNP)Ni, where PNP = (tBu2PCH2SiMe2)2N−, promptly evolves N2 and forms a P═N bond in the product (PNP═NPh)NiI. A similar reaction with (PNP)FeCl proceeds to form a P═N bond but without N2 evolution, to furnish (PNP═N—N═NPh)FeCl. An analogous reaction with (PNP)RuCl occurs with a more dramatic redox change at the metal (and N2 evolution), to give the salt composed of (PNP)Ru(NPh)+ and (PNP)RuCl3−, together with equimolar (PNP)Ru(NPh). The contrast among these results is used to deduce what conditions favor N2 loss and oxidative incorporation of the NPh fragment from PhN3 into a metal complex.

Nitrogen-Ligated Iron Complexes: Photolytic Approach to the FeN+ Moiety

Co-reporter:Drew Buschhorn, Maren Pink, Hongjun Fan and Kenneth G. Caulton

Inorganic Chemistry 2008 Volume 47(Issue 12) pp:5129-5135

Publication Date(Web):May 15, 2008

DOI:10.1021/ic702279b

The synthesis of (PNP)FeCl, (PNP)Fe[NH(xylyl)], and (PNP)FeN3 are reported(PNP = (tBu2PCH2SiMe2)2N−). While the azide is thermally stable, it is photosensitive to lose N2 and form [(PNP═N)Fe]2,in which the nitride ligand has formed a double bond to one phosphorus, and this N bridges to a second iron to form a 2-fold symmetric dimer. The reaction energy to form the (undetected) monomeric [η3-tBu2PCH2SiMe2NSiMe2CH2PtBu2═N]Fe is −15.9 kcal/mol, so this PIII → PV oxidation is favorable. The η2 version of this same species is less stable by 23.7 kcal/mol, which shows that the loss of one P→ Fe bond is caused by dimerization, and therefore, it does not precede and cause dimerization. A comparison is made to Ru analogs.

The Effect of One Valence Electron: Contrasting (PNP)Ni(CO) with (PNP)Ni(NO) to Understand the Half-Bent NiNO Unit

Co-reporter:Benjamin C. Fullmer ; Maren Pink ; Hongjun Fan ; Xiaofan Yang ; Mu-Hyun Baik

Inorganic Chemistry 2008 Volume 47(Issue 9) pp:3888-3892

Publication Date(Web):March 21, 2008

DOI:10.1021/ic702503m

Reaction of a (PNP)Ni radical with NO finishes in the time of mixing to form a 1:1 adduct with a NO stretching frequency of 1654 cm−1. NMR data of this diamagnetic product indicate C2v symmetry, which is contradicted by the X-ray structure, which shows it to be nonplanar at Ni, with a geometry intermediate between planar and tetrahedral; the planar geometry is thus the transition state for fluxionality giving time-averaged C2v symmetry. The X-ray structure, together with DFT calculations, reveals that the “half-bent” NiNO unit and the intermediate coordination geometry result from a Ni → NO charge transfer, which has a nonintegral value, resulting in a continuum between NO+ (hence Ni0) and NO− (hence NiII). This is related to the nonaxially symmetric character of the Ni → NO back-donation caused by the (PNP) environment on Ni. Steric effects of tBu and even chelate constraints are ruled out as the cause of the unusual electronic and structural features.

O/C Bond Cleavage of CO2 by NiI

Co-reporter:Benjamin C. Fullmer ; Hongjun Fan ; Maren Pink

Inorganic Chemistry 2008 Volume 47(Issue 6) pp:1865-1867

Publication Date(Web):February 20, 2008

DOI:10.1021/ic701843u

Reaction of (PNP)Ni, where PNP is [(tBu2PCH2SiMe2)2N]−1, with CO2 occurs rapidly even at −60 °C to form exclusively the product of transposition of the amide N and one CO2 oxygen: [(tBu2PCH2SiMe2)2O]Ni(NCO). DFT(B3LYP) evaluation of several candidate intermediates for breaking two Si/N and one C/O bond and forming two Si/O and one N/C bond reveal species at and below the energy of the separated particles, and establish the location of the spin densities in each.

Reactivity of the Radical NO with a Masked Form of 14 Valence Electron (PNP)Rh: Forming Rh(0, I or II)?

Co-reporter:Alexer Y. Verat;Maren Pink;Hongjun Fan;Benjamin C. Fullmer;Joshua Telser

European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 30) pp:4704-4709

Publication Date(Web):

DOI:10.1002/ejic.200800256

Abstract

The reaction of NO with [(tBu₂PCH₂SiMe₂)NSiMe₂CH₂PtBu(CMe₂CH₂)]RhH, a functional equivalent of “(PNP)Rh,” rapidly forms (PNP)Rh(N₂) and (PNP)Rh(NO)(NO₂). Detected intermediates include (PNP)Rh(NO), characterized by its NMR, EPR and IR spectra as well as by DFT calculation, as having the neutral NO-centered radical Lewis base donating to Rh^I. One other intermediate is detected, using a combination of spectroscopic and DFT methods, as containing a nitrite (O–N=O) ligand that is O-bound to Rh, giving an overall C_s symmetry. The overall reaction is thus the disproportionation of NO catalyzed by Rh^I, and the reaction serves to produce nonradical products from radical NO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

[Ni{N(SiMe2CH2PtBu2)2}]+: Direct Observation of Transannular SiC(sp3) Bond Coordination

Co-reporter:Hongjun Fan Dr.;BenjaminC. Fullmer;Maren Pink Dr. ;KennethG. Caulton

Angewandte Chemie International Edition 2008 Volume 47( Issue 47) pp:9112-9114

Publication Date(Web):

DOI:10.1002/anie.200802654

[Ni{N(SiMe2CH2PtBu2)2}]+: Direct Observation of Transannular SiC(sp3) Bond Coordination

Co-reporter:Hongjun Fan Dr.;BenjaminC. Fullmer;Maren Pink Dr. ;KennethG. Caulton

Angewandte Chemie 2008 Volume 120( Issue 47) pp:9252-9254

Publication Date(Web):

DOI:10.1002/ange.200802654

[(tBu2PCH2SiMe2)2N]RhI? Rapidly Reversible H−C(sp3) and H−C(sp2) Bond Cleavage by Rhodium(I)

Co-reporter:Alexander Y. Verat, Maren Pink, Hongjun Fan, John Tomaszewski and Kenneth G. Caulton

Organometallics 2008 Volume 27(Issue 2) pp:166-168

Publication Date(Web):December 29, 2007

DOI:10.1021/om701165n

The product of the reaction of (tBu2PCH2SiMe2)2N− (MgCl+ salt) with [RhCl(cyclooctene)2]2 is a RhIII complex where one tBu methyl C−H bond has oxidatively added to Rh: (PNP*)RhH. This is in rapid exchange among all 9 × 4 C−H bonds of the four tBu groups. (PNP*)RhH undergoes oxidative addition equilibrium with the C−H bonds of benzene at ∼103 s−1 at 25 °C and oxidatively adds the ring C−H of other arenes. (PNP*)RhH forms η2-olefin complexes with several olefins and dehydrogenates allylic C−H bonds to form (PNP)Rh(H)2.

Spin State, Structure, and Reactivity of Terminal Oxo and Dioxygen Complexes of the (PNP)Rh Moiety

Co-reporter:AlexerY. Verat;Hongjun Fan;Maren Pink;Y.-S. Chen ;KennethG. Caulton

Chemistry - A European Journal 2008 Volume 14( Issue 25) pp:7680-7686

Publication Date(Web):

DOI:10.1002/chem.200800573

Abstract

[Rh^IIIH{(tBu₂PCH₂SiMe₂NSiMe₂CH₂PtBu{CMe₂CH₂})}], ([RhH(PNP*)]), reacts with O₂ in the time taken to mix the reagents to form a 1:1 η²-O₂ adduct, for which OO bond length is discussed with reference to the reducing power of [RhH(PNP*)]; DFT calculations faithfully replicate the observed O–O distance, and are used to understand the oxidation state of this coordinated O₂. The reactivity of [Rh(O₂)(PNP)] towards H₂, CO, N₂, and O₂ is tested and compared to the associated DFT reaction energies. Three different reagents effect single oxygen atom transfer to [RhH(PNP*)]. The resulting [RhO(PNP)], characterized at and above −60 °C and by DFT calculations, is a ground-state triplet, is nonplanar, and reacts, above about +15 °C, with its own tBu CH bond, to cleanly form a diamagnetic complex, [Rh(OH){N(SiMe₂CH₂PtBu₂)(SiMe₂CH₂PtBu{CMe₂CH₂})}].

Reactivity of ˙NO with an osmium polyhydride: Reductive elimination and reductive nitrosylation on the path from odd- to even-electron molecules

Co-reporter:Joo-Ho Lee, Hongjun Fan, Maren Pink and Kenneth G. Caulton

New Journal of Chemistry 2007 vol. 31(Issue 6) pp:838-840

Publication Date(Web):17 May 2007

DOI:10.1039/B702078C

The reaction of ˙NO with (PNP)Os(H)3, where PNP is N(SiMe2CH2PtBu2)2, involves H2 loss from a 1 : 1 adduct to form the intermediate (PNP)OsH(NO)2, which then forms coordinated HNO; loss of this triatomic molecule forms the final metal complex product in high yield: (PNP)Os(NO). Under a different concentration of gaseous reagents, a second path leads to the same products. These results are supported by spectroscopic observations at various temperatures, as well as by DFT calculations of the energies of alternative transition states and intermediates.

New d4 dihydrides of Ru(IV) and Os(IV) with π-donor ligands: M(H)2(chelate)(PiPr3)2 with chelate = ortho-XYC6H4 with X, Y = O, NR; R = H or CH3

Co-reporter:German Ferrando-Miguel, Peng Wu, John C. Huffman and Kenneth G. Caulton

New Journal of Chemistry 2005 vol. 29(Issue 1) pp:193-204

Publication Date(Web):15 Dec 2004

DOI:10.1039/B411487F

The synthesis and characterization of Ru(H)2(ortho-OC6H4E)L2 (L = PiPr3, E = NH, O) show these to be dihydrides with a nonoctahedral structure. The former compound reacts with H2 to give Ru(H)3(OC6H4NH2)L2, which has the ability to hydrogenate tBuHCCH2. Osmium analogs are available from Os(H)3ClL2, and the mono-N-methyl example Os(H)2[N(Me)C6H4NH]L2 shows inequivalent hydrides by 1H NMR at 20 °C. It exchanges with D2 faster into the NH site than into the OsH sites. Triflic acid protonates Os(H)2[N(Me)C6H4NH]L2 at the metal to give a trihydride. Catechol protonates Os(H)2[N(Me)C6H4NH]L2 to displace the ortho-diamine to give Os(H)2(OC6H4O)L2. The collective evidence is consistent with a dianionic, not a quinoid oxidation state for the chelate ligands and a d4, six-coordinate potential energy surface, often with low barriers between alternative non-octahedral structures.

Amido/phosphine pincer hydrides of ruthenium

Co-reporter:Lori A. Watson, Joseph N. Coalter III, Oleg Ozerov, Maren Pink, John C. Huffman and Kenneth G. Caulton

New Journal of Chemistry 2003 vol. 27(Issue 2) pp:263-273

Publication Date(Web):17 Dec 2002

DOI:10.1039/B206202J

The chemistry of the ligand (R2PCH2SiMe2)2N− (R=cyclohexyl and tBu), “PNP-R”, on ruthenium is developed, including RuH(PNP-Cy)(PPh3) and (HPNP-R)RuH3Cl. The latter contains a protonated nitrogen (i.e., amine as a donor to Ru) and one H2 ligand (X-ray structure for R=tBu). This compound can be dehydrohalogenated to give (PNP-Cy)RuH3, which undergoes H/D exchange of D2 into its cyclohexyl rings, and is itself dehydrogenated by excess H2CCHR to give [Cy2PCH2SiMe2NSiMe2CH2PCy(C6H8)] Ru, which contains a triply dehydrogenated cyclohexyl ring π-allyl bonded to Ru. (PNP-Cy)RuH3 reacts with dihydrofurans to give the heteroatom-stabilized carbene complex (PNP-Cy)RuH[CO(CH2)3].

Evaluation of energies of isomeric SO2 complexes

Co-reporter:Alexei V. Marchenko, Andrei N. Vedernikov, John C. Huffman and Kenneth G. Caulton

New Journal of Chemistry 2003 vol. 27(Issue 4) pp:680-683

Publication Date(Web):26 Feb 2003

DOI:10.1039/B212025A

SO2 binds to MHCl(CO)L2 (M=Ru, Os; L=PiPr3) to give a product in which SO2 binds trans to hydride, and with an η1-SO2 binding mode, planar around sulfur, as shown in part by an X-ray diffraction study for M=Ru. We have investigated the structures and energies of various isomers and insertion (of SO2 into the Ru–H bond) products of the observed product to evaluate, in a fixed molecular environment, their stabilities relative to the observed product, in which SO2 functions as a Lewis base. In contrast to CH2 insertion into the analogous Os–H bond, insertion of SO2 into Ru–H here is not strongly favored. A search of the potential energy surface shows that η1-SO2 with pyramidal sulfur is not a stationary state.

Facile C(sp2)/O2CR bond cleavage by Ru or Os

Co-reporter:German Ferrando, Joseph N. Coalter, III, Hélène Gérard, Dejian Huang, Odile Eisenstein and Kenneth G. Caulton

New Journal of Chemistry 2003 vol. 27(Issue 10) pp:1451-1462

Publication Date(Web):09 Sep 2003

DOI:10.1039/B306111F

[RuHClL2]2, L=PiPr3, reacts with H2CCH(O2CR) (R=CH3, CF3, C6H5) during mixing at 20°C, via two observable intermediates, to give RuCl(O2CR)(CHMe)L2; this carbene complex then redistributes the Cl and O2CR groups. Vinyl tosylate gives RuCl(OTs)(CHMe)L2 already at −60°C. Vinyl chloroformate, H2CCH(O2CCl) reacts rapidly with [RuHClL2]2 to give the olefin metathesis catalyst RuCl2(CHMe)L2 and CO2. Os(H)3ClL2 (L=PiPr3 or PtBu2Me) reacts with vinyl esters H2CCHE (E=O2CR) to form first an η2-olefin adduct. This is followed by C/O bond cleavage, giving the carbyne OsHCl(O2CCF3)(CMe)L2. Vinyl chloroformate and Os(H)3ClL2 gives OsHCl2(CMe)L2 and CO2. RuHCl(PPh3)3 reacts with vinyl chloroformate, via RuCl(O2CCl)(CHMe)(PPh3)2, to give RuCl2(CHMe)(PPh3)2 while OsHCl(PPh3)3 reacts analogously, through observable OsCl2(CHMe)(PPh3)2, to form OsHCl2(CMe)(PPh3)2. Vinyl trifluoroacetate converts OsHCl(PPh3)3, to OsHCl(O2CCF3)(CMe)(PPh3)2. The less π-basic metal in OsH(CO)(PtBu2Me)2+ reacts with vinyl esters to give only an olefin adduct; detectable binding of the ester oxygen to Os in this adduct suggests a mechanism for carboxylate migration from carbene carbon to metal. The mechanisms of these reactions are explored, and the thermodynamic disparity between Ru and Os is discussed. DFT (B3PW91) calculations have been carried out to establish the energy pattern of possible products. The thermodynamic preference for cleaving the C–O2CR bond is shown to have a thermodynamic origin associated with the energy of the formed Ru–O2CR bond. The calculations also indicate the very large thermodynamic driving force for loss of CO2 in the case of H2CCH(O2CCl). The corresponding loss of CO2 is shown to be thermodynamically unfavorable in the case of H2CCH(O2CR). The energy of the Ru-R bond is a key factor.

π-Donor olefin substituents alter olefin binding to CpFe(CO)2+

Co-reporter:Lori A. Watson, Bethany Franzman, John C. Bollinger and Kenneth G. Caulton

New Journal of Chemistry 2003 vol. 27(Issue 12) pp:1769-1774

Publication Date(Web):06 Oct 2003

DOI:10.1039/B305252D

The X-ray diffraction structures of the olefin complexes [CpFe(CO)2(H2CCHDo)]PF6 (Do=OEt and NMe2) have been determined to further evaluate the previous report that the distance from Fe to the olefin carbon substituted by Do (referred to as Cβ) is long or even nonbonding. These Fe–C distances are determined here to be long [2.402(10) Å for Do=OEt] or nonbonding [2.823(11) Å for Do=NMe2]. DFT optimization of the geometries of these, together with CpFe(CO)2−n(PH3)n(H2CCHDo])+ for n=1 and 2, show (a) agreement with experiment for n=0, (b) a progression of Fe–Cβ distances to shorter values with increasing n for Do=OEt, (c) persistence of the Fe–Cβ distance at a nonbonding value for all n when Do=NMe2 and (d) the shortest Fe–Cβ distances for the weakest π-donor substituent, Do=F. These results are rationalized in terms of increased localization of nucleophilicity on the olefin Cα as the π-donor ability of Do strengthens. Therefore, not all olefins will show η2-binding.

Geminal dehydrogenation of ether and amine C(sp3)H2 groups by electron-rich Ru(II) and Os

Co-reporter:German Ferrando-Miguel, Joseph N. Coalter III, Hélène Gérard, John C. Huffman, Odile Eisenstein and Kenneth G. Caulton

New Journal of Chemistry 2002 vol. 26(Issue 6) pp:687-700

Publication Date(Web):07 Jun 2002

DOI:10.1039/B200168N

Reaction of [RuHCl(PiPr3)2]2 with THF or dioxolane doubly dehydrogenates the carbon α to the oxygen to yield RuHCl(H2)(PiPr3)2, together with the coordinated cyclic carbene, RuHCl[CO(CH2)2E](PiPr3)2, where E=CH2 or O. In the presence of CH2CHtBu as hydrogen acceptor, all Ru is converted to its carbene complex. The cyclic amines RN(CH2)4 (R=H, Me) react analogously, to produce N-substituted carbene complexes by geminal dehydrogenation; a crystal structure is presented for the carbene complex with R=H, which reveals intermolecular NH⋯Cl hydrogen bonding. Similar chemistry is established for Os(H)3Cl(PiPr3)2, at 25°C, in the presence of H2CCHtBu, to give OsHCl[CO(CH2)3](PiPr3)2. Pyrrolidine reacts rapidly at 25°C to give first a 1∶1 amine adduct, then slowly the trihydride carbene Os(H)3Cl[C(NH)(CH2)3](PiPr3)2, together with H2. Os(H)2Cl2(PiPr3)2 is first dehydrochlorinated by one mole of pyrrolidine, then a second mole of pyrrolidine is geminally dehydrogenated to form Os(H)3Cl[C(NH)(CH2)3](PiPr3)2. The five-coordinated carbene OsHCl[CO(CH2)3](PiPr3)2 will add H2, and the resulting product exists as two isomers, a trihydride with Cl cis to the carbene and a species with Cl trans to carbene and H and “2H” mutually trans. Isomer preferences, strength of H2 binding, and carbene plane orientation are discussed, together with DFT calculations on the thermodynamics of ether dehydrogenation by ruthenium. The latter reveal that coordination of removed H2 to Ru is essential to achieving favorable thermodynamics.

Evolving approaches to integration of computational with experimental chemistry: an example from osmium hydrido (η1/η2-)nitrosyl/nitroxyl chemistry

Co-reporter:Andrei N. Vedernikov and Kenneth G. Caulton

New Journal of Chemistry 2002 vol. 26(Issue 10) pp:1267-1269

Publication Date(Web):27 Aug 2002

DOI:10.1039/B205506F

The energies and structures of less stable isomers of metal-ligand systems need to be analyzed to learn about general trends in stability; the example of H–M–NO is considered.

Control of HC(sp3) Bond Cleavage Stoichiometry: Clean Reversible Alkyl Ligand Exchange with Alkane in [LPt(Alk)(H)2]+ (L=[2.1.1]-(2,6)-Pyridinophane)

Co-reporter:Andrei N. Vedernikov Dr.

Angewandte Chemie International Edition 2002 Volume 41(Issue 21) pp:

Publication Date(Web):31 OCT 2002

DOI:10.1002/1521-3773(20021104)41:21<4102::AID-ANIE4102>3.0.CO;2-#

Reversible alkane oxidative addition occurs to transient [LPtH]⁺ (L=[2.1.1]-(2,6)-pyridinophane; see scheme), which is generated at 86 °C from [LPtMe(H)₂]⁺ in 1:1 hydrocarbon/CD₂Cl₂ mixtures. DFT calculations reveal why [LPtMe(H)₂]⁺ eliminates methane, not dihydrogen, and why, in contrast to [LPtMe₂H]⁺, no alkane dehydrogenation occurs.

Control of HC(sp3) Bond Cleavage Stoichiometry: Clean Reversible Alkyl Ligand Exchange with Alkane in [LPt(Alk)(H)2]+ (L=[2.1.1]-(2,6)-Pyridinophane)

Co-reporter:Andrei N. Vedernikov Dr.

Angewandte Chemie 2002 Volume 114(Issue 21) pp:

Publication Date(Web):4 NOV 2002

DOI:10.1002/1521-3757(20021104)114:21<4276::AID-ANGE4276>3.0.CO;2-8

Alkane addieren reversibel an eine [LPtH]⁺-Zwischenstufe (L=[2.1.1]-(2,6)-Pyridinophan; siehe Schema), die bei 86 °C aus [LPtMe(H)₂]⁺ in Kohlenwasserstoff/CD₂Cl₂ (1:1) erzeugt wird. DFT-Rechnungen beantworten die Fragen, warum das [LPtMe(H)₂]⁺-Kation Methan eliminiert (anstelle von Wasserstoff) und warum anders als im Fall von [LPtMe₂H]⁺ keine Alkandehydrierung auftritt.

Carbene transposition involving double dehydrogenation of an sp3 carbon

Co-reporter:Joseph N. Coalter III, John C. Huffman and Kenneth G. Caulton

Chemical Communications 2001 (Issue 13) pp:1158-1159

Publication Date(Web):07 Jun 2001

DOI:10.1039/B102422C

Two benzylic hydrogens of 2,6-Me2C6H3O− coordinated to RuCl(PCy3)2(CHPh)+ are transferred to the benzylidene ligand, liberating toluene to form a new carbene which is covalently linked to the aryloxide ligand.

A comprehensive view of M–H addition across the RCCH bond: frustration culminating in ultimate union

Co-reporter:Alexei V. Marchenko, Hélène Gérard, Odile Eisenstein and Kenneth G. Caulton

New Journal of Chemistry 2001 vol. 25(Issue 10) pp:1244-1255

Publication Date(Web):18 Sep 2001

DOI:10.1039/B103815J

The reaction of MHCl(CO)L2 (L = PiPr3; M = Ru or Os) with more than a dozen terminal alkynes RCCH has been studied at variable temperatures and for a variety of R groups representing a wide range of steric and electronic effects. This sometimes reveals (for the slower osmium examples) formation of an η2-alkyne adduct, then the vinylidene OsHCl(CCHR)(CO)L2 and finally the η1-vinyl complex OsCl(CHCHR)(CO)L2. The rate of formation of the vinyl complex decreases with R according to the series primary > tertiary > secondary and electron-withdrawing > electron-donating. Deuterium labeling of OsHCl(CO)L2 at either Os or the alkyne sp carbons shows that isotope exchange between these two sites can be competitive with vinylidene and vinyl product formation, and thus can confuse some attempts to trace the fate of the hydride. When this complication is absent, conventional syn addition of Os–D to HCCR is established, to give Os(E-CHCDR). The rate of conversion to the vinyl product is not suppressed by added free PiPr3 . Taken together, these results are consistent with a mechanism of vinyl complex formation involving neither the adduct with H trans to RCCH, nor the vinylidene, but rather with direct alkyne attack cis to the hydride, which is also consistent with the considerable steric influence on the rate of vinyl formation. DFT (B3PW91) calculations show that the vinyl complex is the thermodynamically most stable product and thus is always the final observed product. The calculations also show that the “direct” addition of the alkyne occurs ia approach of the alkyne cis to M–H inside the H–M–Cl quadrant. This direct route is in fact calculated to be a multistep process with an alkyne intermediate that is not in a deep well and thus cannot be observed experimentally. Calculations also agree with the fact that the vinylidene and the vinyl complexes are obtained through two independent routes.

A comparative study of olefin or acetylene insertion into Ru–H or Os–H of MHCl(CO)(phosphine)2

Co-reporter:Alexei V. Marchenko, Hélène Gérard, Odile Eisenstein and Kenneth G. Caulton

New Journal of Chemistry 2001 vol. 25(Issue 11) pp:1382-1388

Publication Date(Web):19 Oct 2001

DOI:10.1039/B103113A

The adduct OsHCl(C2D4)(CO)L2 (L = PiPr3) shows only very slow H/D exchange at 25 °C, but this is easily detectable at 65 °C; no ethyl species is formed in detectable concentration. RuHCl(CO)L2 shows no detectable C2D4 adduct, but Ru–H/C–D exchange at 60 °C is actually faster than for Os. DFT (B3PW91) calculations have been carried out to analyze the relative energies of the isomeric forms that would result from the addition of an alkene or an alkyne to MH(Cl)(CO)(PH3)2 (M = Os, Ru). Thus, 18-electron alkyne adducts are compared to the 18-electron vinylidene isomer and to the 16-electron vinyl complex. Similarly, the 18-electron alkene adduct is compared to the 18-electron carbene isomer and to the 16-electron ethyl complex. Two factors are found to control the products formed: (i) the Os complex favors unsaturated π-bonded ligands and an 18-electron count while Ru favors saturated ligands and an unsaturated metal center; (ii) the weaker π bond in the alkyne than in the alkene makes insertion or isomerization of an alkyne thermodynamically more favored than that of an alkene. This results in ethyl complexes being less favored than vinyl complexes in similar experimental conditions. For RuHCl(CO)L2′, where L′ is PiPr2[3,5-(CF3)2C6H3], 1 atm ethylene gives a detectable, colorless ethylene adduct, then also a detectable ethyl complex, all in facile equilibrium.

Factors governing the equilibrium between metalalkyl, alkylidene and alkylidyne: MCX2R, XMCXR and X2MCR

Co-reporter:Kenneth G. Caulton

Journal of Organometallic Chemistry 2001 Volumes 617–618() pp:56-64

Publication Date(Web):15 January 2001

DOI:10.1016/S0022-328X(00)00706-3

The reactions of vinyl ethers, H2CCH(OR), with RuHClL2 (L=PiPr3) furnish the carbene complexes RuHCl[C(CH3)(OR)]L2 by H migration. Os(H)3ClL2 serves as a surrogate for unknown OsHClL2, to give the analogous carbene, but this transforms further for RPh to give the carbyne OsHCl(OPh)(CCH3)L2. DFT calculations furnish insight into the relative thermodynamic stability of the various isomeric species, and are consistent with the major influence of π-donation by OR, as well as the preference of Os (versus Ru) for saturation and higher oxidation state. Comparison of the reactivity of H2CCHD0 (D0=π-donor) towards MHClL2 versus Cp2ZrHCl shows the dominant influence of metal π-donor power. Ruthenium and osmium complexes containing an MCF3 subunit show remarkably facile isomerization to FMCF2 carbenes.

R-Group reversal of isomer stability for RuH(X)L2(CCHR) s. Ru(X)L2(CCH2R): access to four-coordinate ruthenium carbenes and carbynes

Co-reporter:Joseph N. Coalter, III, John C. Bollinger, Odile Eisenstein and Kenneth G. Caulton

New Journal of Chemistry 2000 vol. 24(Issue 12) pp:925-927

Publication Date(Web):06 Nov 2000

DOI:10.1039/B006971J

NaOPh converts equimolar RuHClL2(CCHR) (L = PPr3i and PCy3) first to RuH(OPh)L2(CCHR), but then, only for R = H, these isomerize to the more stable carbynes Ru(OPh)L2(C–CH3); the rate of isomerization is slowed considerably by THF. RuH(OPh)L2(CCHR) can also be synthesized by reaction of RuCl2L2[CH(CH2R)] with 2 NaOPh; again, only when R = H does the hydrido vinylidene isomerize to the carbyne. While phenoxide converts RuCl2L2(CHPh) to Ru(OPh)L2(CPh), ia the observable intermediates RuCl2−n(OPh)nL2(CHPh), alkoxides OBut and OAdamantyl cause phosphine displacement to give the four-coordinate carbenes Ru(OR)2L(CHPh). DFT (B3PW91) calculations show these d6 species have a traditional cis-divacant octahedral structure with trans OR groups.

Synthetic approaches to Fe(II) complexes of the bulky phosphine PtBu2Me

Co-reporter:Kenton B Renkema, Masamichi Ogasawara, William E Streib, John C Huffman, Kenneth G Caulton

Inorganica Chimica Acta 1999 Volume 291(1–2) pp:226-230

Publication Date(Web):August 1999

DOI:10.1016/S0020-1693(99)00104-8

Reaction of anhydrous FeCl3 with PtBu2Me in alcohol gives [HPtBu2Me][FeCl3(PtBu2Me)], a salt with a tetrahedral Fe(II) anion hydrogen bonded (via Cl) to the P–H proton of the cation. Reaction of FeCl2(CO)4 with PtBu2Me in benzene, followed by workup gives FeCl2(PtBu2Me)2, a tetrahedral molecule with a crystallographic C2 axis and Fe–Cl=2.260(1) Å and Fe–P=2.506(1) Å and an unusually small P–Fe–P angle of 106.38(3)°.

[Ru(Ph)(CO)(PtBu2Me)2]+, ein einzigartiger 14-Elektronen-RuII-Komplex mit zwei agostischen Wechselwirkungen

Co-reporter:Dejian Huang;William E. Streib; Odile Eisenstein; Kenneth G. Caulton

Angewandte Chemie 1997 Volume 109(Issue 18) pp:

Publication Date(Web):31 JAN 2006

DOI:10.1002/ange.19971091826

Probing the redox non-innocence of dinuclear, three-coordinate Co(II) nindigo complexes: not simply β-diketiminate variants

Co-reporter:Skye Fortier, Octavio González-del Moral, Chun-Hsing Chen, Maren Pink, Jennifer J. Le Roy, Muralee Murugesu, Daniel J. Mindiola and Kenneth G. Caulton

Chemical Communications 2012 - vol. 48(Issue 90) pp:NaN11084-11084

Publication Date(Web):2012/09/21

DOI:10.1039/C2CC34560A

Surprising isomer preference on IrIII, favoring facile H–C(sp3) bond cleavage

Co-reporter:Nikolai P. Tsvetkov, Matthew F. Laird, Hongjun Fan, Maren Pink and Kenneth G. Caulton

Chemical Communications 2009(Issue 30) pp:NaN4580-4580

Publication Date(Web):2009/06/29

DOI:10.1039/B908954C

Species (PNP)Ir(X)(Y), where PNP = N(SiMe2CH2PtBu2)2−1 with X and Y halide, have a tBu group C–H bond heterolytically split by addition across the Ir–N bond.

In search of redox non-innocence between a tetrazine pincer ligand and monovalent copper

Co-reporter:Alice K. Hui, Richard L. Lord and Kenneth G. Caulton

Dalton Transactions 2014 - vol. 43(Issue 21) pp:NaN7963-7963

Publication Date(Web):2014/03/17

DOI:10.1039/C3DT52490F

Multiplying the electron storage capacity of a bis-tetrazine pincer ligand

Co-reporter:Christopher R. Benson, Alice K. Hui, Kumar Parimal, Brian J. Cook, Chun-Hsing Chen, Richard L. Lord, Amar H. Flood and Kenneth G. Caulton

Dalton Transactions 2014 - vol. 43(Issue 17) pp:NaN6524-6524

Publication Date(Web):2014/02/13

DOI:10.1039/C4DT00341A

Reactivity of the terminal oxo species ((tBu2PCH2SiMe2)2N)RhO

Co-reporter:Nikolay P. Tsvetkov, José G. Andino, Hongjun Fan, Alexander Y. Verat and Kenneth G. Caulton