Co-reporter:Konstantin V. Bukhryakov, Sudarsan VenkatRamani, Charlene Tsay, Amir Hoveyda, and Richard R. Schrock
Organometallics November 13, 2017 Volume 36(Issue 21) pp:4208-4208
Publication Date(Web):October 23, 2017
DOI:10.1021/acs.organomet.7b00647
Reactions between Mo(N-t-Bu)2(CH2-t-Bu)2 or Mo(NAdamantyl)2(CH2CMe2Ph)2 and 3 equiv of HCl in the presence of 1 equiv of PPh2Me yield Mo(NR)(CHR′)(PPh2Me)Cl2 complexes, from which Mo(NR)(CHR′)(PPh2Me)(OAr)Cl complexes (OAr = a 2,6-terphenoxide) can be prepared. The Mo(NR)(CHR′)(PPh2Me)(OAr)Cl complexes were evaluated as cross-metathesis catalysts between cyclooctene and Z-1,2-dichloroethylene. The efficiencies of the test reaction for complexes in which OAr = OTPP, OHMT, OHIPT, or OHTBT (where OTPP is 2,3,5,6-tetraphenylphenoxide, OHMT is hexamethylterphenoxide, OHIPT is hexaisopropylterphenoxide, and OHTBT is hexa-t-butylterphenoxide) maximize when OAr is OHMT or OHIPT. Mo(N-t-Bu)(CH-t-Bu)(PPh2Me)Cl2 is essentially inactive for the reaction between cyclooctene and Z-1,2-dichloroethylene. X-ray structural studies were carried out on Mo(NAd)(CHCMe2Ph)(PPh2Me)Cl2, Mo(N-t-Bu)(CH-t-Bu)(PPh2Me)(OHMT)Cl, Mo(NAd)(CHCMe2Ph)(Cl)(OHTBT)(PMe3), and [Mo(NAd)(CHCMe2Ph)(PMe3)(Cl)]2(μ-O), the product of the reaction between Mo(NAd)(CHCMe2Ph)(Cl)(OHTBT)(PMe3) and 0.5 equiv of water.
Synthesis of 2,6-Hexa-tert-butylterphenyl Derivatives, 2,6-(2,4,6-t-Bu3C6H2)2C6H3X, where X = I, Li, OH, SH, N3, or NH2
Co-reporter:Konstantin V. Bukhryakov, Richard R. Schrock, Amir H. Hoveyda, Peter Müller, and Jonathan Becker
Organic Letters May 19, 2017 Volume 19(Issue 10) pp:
Publication Date(Web):May 1, 2017
DOI:10.1021/acs.orglett.7b01062
A “double benzyne” reaction between 1,3-dichloro-2-iodobenzene and 2,4,6-t-Bu3C6H2MgBr followed by the addition of iodine led to 2,6-(2,4,6-t-Bu3C6H2)2C6H3I (HTBTI) in 65% yield. Lithiation of HTBTI with Li-t-Bu gave Li(Et2O)2HTBT from which HTBTSH, HTBTN3, HTBTNH2, and HTBTOH were prepared. An X-ray structure of W(OHTBT)2Cl4 shows that the two HTBTO ligands are trans to one another with the t-Bu3C6H2 groups on one HTBTO interdigitated with the t-Bu3C6H2 groups on the other HTBTO.
Co-reporter:Eun Sil Jang, Jeremy M. John, and Richard R. Schrock
Journal of the American Chemical Society April 12, 2017 Volume 139(Issue 14) pp:5043-5043
Publication Date(Web):March 29, 2017
DOI:10.1021/jacs.7b01747
Cis,syndiotactic A-alt-B copolymers, where A and B are two enantiomerically pure endo-2-substituted-5,6-norbornenes with “opposite” chiralities of the endo-2-substituted-5,6-norbornene skeleton, can be prepared using Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OHMT)(pyrrolide) (1) as the initiator (OHMT = O-2,6-Mesityl2C6H3). Formation of a high percentage of A-alt-B dyads is proposed to rely on an inversion of chirality at the metal with each propagating step and a kinetically preferred diastereomeric relationship between a given chirality at the metal in propagating species and the chirality of the endo-2-substituted-5,6-norbornene skeleton. We also demonstrate that A-alt-B copolymers can be modified to give new variations which may not be accessible through direct copolymerization.
Co-reporter:Jonathan K. Lam, Congqing Zhu, Konstantin V. Bukhryakov, Peter Müller, Amir Hoveyda, and Richard R. Schrock
Journal of the American Chemical Society 2016 Volume 138(Issue 48) pp:15774-15783
Publication Date(Web):November 10, 2016
DOI:10.1021/jacs.6b10499
Molybdenum complexes with the general formula Mo(NR)(CHR′)(OR″)(Cl)(MeCN) (R = t-Bu or 1-adamantyl; OR″ = a 2,6-terphenoxide) recently have been found to be highly active catalysts for cross-metathesis reactions between Z-internal olefins and Z-1,2-dichloroethylene or Z-(CF3)CH═CH(CF3). In this paper we report methods of synthesizing new potential catalysts with the general formula M(NR)(CHR′)(OR″)(Cl)(L) in which M = Mo or W, NR = N-2,6-diisopropylphenyl or NC6F5, and L is a phosphine, a pyridine, or a nitrile. We also test and compare all catalysts in the cross-metathesis of Z-1,2-dichloroethylene and cyclooctene. Our investigations indicate that tungsten complexes are inactive in the test reaction either because the donor is bound too strongly or because acetonitrile inserts into a W═C bond. The acetonitrile or pivalonitrile Mo(NR)(CHR′)(OR″)(Cl)(L) complexes are found to be especially reactive because the 14e Mo(NR)(CHR′)(OR″)Cl core is accessible through dissociation of the nitrile to a significant extent. Pivalonitrile can be removed (>95%) from Mo(NAr)(CHCMe2Ph)(OHMT)(Cl)(t-BuCN) (Ar = 2,6-diisopropylphenyl; OHMT = 2,6-dimesitylphenoxide) to give 14e Mo(NAr)(CHCMe2Ph)(OHMT)Cl in solution as a mixture of syn and anti (60:40 at 0.015 M) nitrile-free isomers, but these 14e complexes have not yet been isolated in pure form. The syn isomer of Mo(NAr)(CHCMe2Ph)(OHMT)Cl binds pivalonitrile most strongly. Other Mo(NR)(CHR′)(OR″)(Cl)(L) complexes can be activated through addition of B(C6F5)3. High stereoselectivities (>98% Z,Z) of ClCH═CH(CH2)6CH═CHCl are not restricted to tert-butylimido or adamantylimido complexes; 96.2% Z selectivity is observed with boron-activated Mo(NC6F5)(CHR′)(OHIPT)(Cl)(PPhMe2). So far no Mo═CHCl complexes, which are required intermediates in the test reaction, have been observed in NMR studies at room temperature.
Co-reporter:Sara Zahim, Lasantha A. Wickramasinghe, Gwilherm Evano, Ivan Jabin, Richard R. Schrock, and Peter Müller
Organic Letters 2016 Volume 18(Issue 7) pp:1570-1573
Publication Date(Web):March 21, 2016
DOI:10.1021/acs.orglett.6b00410
A new calix[6]azacryptand ligand has been prepared in six steps starting from 1,3,5-trismethoxycalix[6]arene. An X-ray study shows that this ligand has a sterically protected tren-based binding site at the bottom of a polyaromatic bowl and ether sites around its rim. It binds Zn2+ to give a complex in which zinc is in a trigonal bipyramidal geometry with a water bound in one apical position and two additional hydrogen-bonded waters that fill the calixarene cavity.
Co-reporter:Eun Sil Jang, Jeremy M. John, and Richard R. Schrock
ACS Central Science 2016 Volume 2(Issue 9) pp:631
Publication Date(Web):September 6, 2016
DOI:10.1021/acscentsci.6b00200
Cis,syndiotactic A-alt-B copolymers, where A and B are two enantiomerically pure trans-2,3-disubstituted-5,6-norbornenes with “opposite” chiralities, can be prepared with stereogenic-at-metal initiators of the type M(NR)(CHR′)(OR”)(pyrrolide). Formation of a high percentage of alternating AB copolymer linkages relies on an inversion of chirality at the metal with each propagating step and a relatively fast formation of an AB sequence as a consequence of a preferred diastereomeric relationship between the chirality at the metal and the chirality of the monomer. This approach to formation of an alternating AB copolymer contrasts dramatically with the principle of forming AB copolymers from achiral monomers and catalysts.
Co-reporter:Peter E. Sues, Jeremy M. John, Richard R. Schrock, and Peter Müller
Organometallics 2016 Volume 35(Issue 5) pp:758-761
Publication Date(Web):February 22, 2016
DOI:10.1021/acs.organomet.5b00976
Molybdenum imido alkylidene and tungsten oxo alkylidene complexes that contain a tridentate “pincer” [ONO]2– ligand have been prepared and treated with ethylene to give unsubstituted metallacyclobutane complexes that have a 16e count. Both Mo and W metallacyclobutane complexes exchange C2D4 into the metallacyclobutane ring at 22 °C at a rate that is first order in metal and zero order in C2D4. These metallacycles lose ethylene at least 104–105 times slower than reported 14e unsubstituted Mo and W metallacyclobutane complexes that have been explored in the literature that have a TBP geometry with the metallacyclobutane ring bound in the equatorial positions. Our studies suggest that breaking up the metallacyclobutane ring in these 16e d0 Mo or W complexes is slow because a 14e TBP metallacyclobutane complex cannot be accessed readily.
Co-reporter:Peter E. Sues, Jeremy M. John, Konstantin V. Bukhryakov, Richard R. Schrock, and Peter Müller
Organometallics 2016 Volume 35(Issue 20) pp:3587-3593
Publication Date(Web):October 4, 2016
DOI:10.1021/acs.organomet.6b00644
In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (∼150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3C6H2 (Trip) in the other ortho position ([MesON]− or [TripON]−, respectively). The alkylidene (neophylidene) complexes that were prepared include W(O)(CHCMe2Ph)(Me2Pyr)(RON) (R = Mes or Trip), Mo(NC6F5)(CHCMe2Ph)(RON)Cl, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(RON)Cl, Mo(N-t-Bu)(CHCMe2Ph)(RON)Cl, and M(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(TripON)(OTf) (M = Mo or W). The reaction between Mo(NAr)(CHCMe2Ph)(TripON)(OTf) and ethylene yielded an ethylene complex, Mo(NAr)(C2H4)(TripON)(OTf)(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W(O)(CHCMe2Ph)(Me2Pyr)(MesON) also stereoselectively polymerized several substituted norbornadienes at 100 °C.
Co-reporter:Hyangsoo Jeong; Jeremy M. John; Richard R. Schrock;Amir H. Hoveyda
Journal of the American Chemical Society 2015 Volume 137(Issue 6) pp:2239-2242
Publication Date(Web):February 2, 2015
DOI:10.1021/jacs.5b00221
Four alternating AB copolymers have been prepared through ring-opening metathesis polymerization (ROMP) with Mo(NR)(CHCMe2Ph)[OCMe(CF3)2]2 initiators (R = 2,6-Me2C6H3 (1) or 2,6-i-Pr2C6H3 (2)). The A:B monomer pairs copolymerized by 1 are cyclooctene (A):2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B), cycloheptene (A′):dimethylspiro[bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1′-cyclopropane] (B′), A:B′, and A′:B; A′:B′ and A:B′ are also copolymerized by 2. The >90% poly(A-alt-B) copolymers are formed with heterodyads (AB) that have the trans configuration. Evidence suggests that one trans hetero C═C bond is formed when A (A or A′) reacts with the syn form of the alkylidene made from B (syn-MB = syn-MB or syn-MB′) to give anti-MA, while the other trans C═C bond is formed when B reacts with anti-MA to give syn-MB. Cis and trans AA dyads are proposed to arise when A reacts with anti-MA in competition with B reacting with anti-MA.
Co-reporter:Hyangsoo Jeong, Victor W. L. Ng, Janna Börner, and Richard R. Schrock
Macromolecules 2015 Volume 48(Issue 7) pp:2006-2012
Publication Date(Web):March 17, 2015
DOI:10.1021/acs.macromol.5b00264
Ring-opening metathesis polymerization (ROMP) of methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate (PhEtNNBE; (S) and racemic) was investigated employing six molybdenum and tungsten imido alkylidene initiators and two tungsten oxo alkylidene initiators. Of the six initiators that we proposed should yield cis,syndiotactic-poly[(S)-PhEtNNBE], two molybdenum OHMT alkylidene initiators, Mo(NR)(CHMe2Ph)(pyr)(OHMT) (R = 1-adamantyl (Ad) or 2,6-Me2C6H3 (Ar′); OHMT = O-2,6-mesityl2C6H3; pyr = pyrrolide), and two tungsten oxo alkylidene initiators, W(O)(CHMe2Ph)(2,5-dimethylpyrrolide)(PMe2Ph)(OR) (OR = OHMT or (R)-OBr2Bitet where (R)-Br2BitetOH = (R)-3,3′-dibromo-2′-(tert-butyldimethylsilyloxy)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2-ol), produced essentially pure cis,syndiotactic-poly[(S)-PhEtNNBE]. Essentially pure cis,isotactic-poly[(S)-PhEtNNBE] was formed when (S)-PhEtNNBE was polymerized by Mo(NAr′)(CHCMe2Ph)(OBiphenCF3)(thf) or W(NAr′)(CHCMe2Ph)((S)-OBiphenMe) (OBiphenCF3 = 3,3′-di-tert-butyl-5,5′-bistrifluoromethyl-6,6′-dimethyl-1,1′-biphenyl-2,2′-diolate; (S)-OBiphenMe = 3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diolate). The best initiator for ROMP of rac-PhEtNNBE was Mo(NAd)(CHMe2Ph)(pyr)(OHMT) at 0 °C, which led to a polymer that is biased (∼80%) toward a cis,syndiotactic structure and that contains alternating enantiomers in the chain (cis,syndio,alt-poly[(rac)-PhEtNNBE]).
Co-reporter:Hyangsoo Jeong, Jeremy M. John, and Richard R. Schrock
Organometallics 2015 Volume 34(Issue 20) pp:5136-5145
Publication Date(Web):October 13, 2015
DOI:10.1021/acs.organomet.5b00709
Ring-opening metathesis polymerization (ROMP) is used to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A1) or cycloheptene (A2) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B1) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1′-cyclopropane (B2). The most successful initiators that were examined are of the type Mo(NR)(CHCMe2Ph)[OCMe(CF3)2]2 (R = 2,6-Me2C6H3 (1) or 2,6-i-Pr2C6H3 (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo═C bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with either A or B, and interconverts slowly with syn-MB through rotation about the Mo═C bond. Syn-MB does not readily react with B, but it does react slowly with A (rate constant ∼1 M–1 s–1) to give anti-MA and one trans-AB linkage. anti-MA then reacts with B (rate constant ∼300 M–1 s–1 or larger) to give syn-MB and the second trans-AB linkage. The reaction has been modeled using experimental data in order to obtain the estimated rate constants above. The reaction between anti-MA and A is proposed to give rise to AA linkages, but AA dyads can amount to <5%. Several other A and B monomers, initiators, and conditions were explored.
Co-reporter:Hyangsoo Jeong, Richard R. Schrock, and Peter Müller
Organometallics 2015 Volume 34(Issue 17) pp:4408-4418
Publication Date(Web):September 1, 2015
DOI:10.1021/acs.organomet.5b00633
A variety of molybdenum or tungsten complexes that contain a tert-butylimido ligand have been prepared. For example, the o-methoxybenzylidene complex W(N-t-Bu)(CH-o-MeOC6H4)(Cl)2(py) was prepared through addition of pyridinium chloride to W(N-t-Bu)2(CH2-o-MeOC6H4)2, while Mo(N-t-Bu)(CH-o-MeOC6H4)(ORF)2(t-BuNH2) complexes (ORF = OC6F5 or OC(CF3)3) were prepared through addition of two equivalents of RFOH to Mo(N-t-Bu)2(CH2-o-MeOC6H4)2. An X-ray crystallographic study of Mo(N-t-Bu)(CH-o-MeOC6H4)[OC(CF3)3]2(t-BuNH2) showed that the methoxy oxygen is bound to the metal and that two protons on the tert-butylamine ligand are only a short distance away from one of the CF3 groups on one of the perfluoro-tert-butoxide ligands (H···F = 2.456(17) and 2.467(17) Å). Other synthesized tungsten tert-butylimido complexes include W(N-t-Bu)(CH-o-MeOC6H4)(pyr)2(2,2′-bipyridine) (pyr = pyrrolide), W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (OHMT = O-2,6-(mesityl)2C6H3), W(N-t-Bu)(CH-t-Bu)(OHMT)(Cl)(py) (py = pyridine), W(N-t-Bu)(CH-t-Bu)(OHMT)(Cl), W(N-t-Bu)(CH-t-Bu)(pyr)(ODFT)(py), W(N-t-Bu)(CH-t-Bu)(OHMT)2, and W(N-t-Bu)(CH-t-Bu)(ODFT)2 (ODFT = O-2,6-(C6F5)2C6H3). Interestingly, W(N-t-Bu)(CH-t-Bu)(OHMT)2 does not react with ethylene or 2,3-dicarbomethoxynorbornadiene. Removal of pyridine from W(N-t-Bu)(CH-t-Bu)(BiphenCF3)(pyridine) (BiphenCF3 = 3,3′-di-tert-butyl-5,5′-bistrifluoromethyl-6,6′-dimethyl-1,1′-biphenyl-2,2′-diolate) with B(C6F5)3 led to formation of a five-coordinate 14e neopentyl complex as a consequence of CH activation in one of the methyl groups in one tert-butyl group of the BiphenCF3 ligand, as was proven in an X-ray study. An attempted synthesis of W(N-t-Bu)(CH-t-Bu)(BiphenMe) (BiphenMe = 3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diolate) led to formation of a 1:1 mixture of W(N-t-Bu)(CH-t-Bu)(BiphenMe) and a neopentyl complex analogous to the one characterized through an X-ray study. The metallacyclobutane complexes W(N-t-Bu)(C3H6)(pyrrolide)(ODFT) and W(N-t-Bu)(C3H6)(ODFT)2 were prepared in reactions involving W(N-t-Bu)(CH-t-Bu)(pyr)2(bipy), ZnCl2(dioxane), and one or two equivalents of DFTOH, respectively, under 1 atm of ethylene.
Co-reporter:Jonathan C. Axtell, Richard R. Schrock, Peter Müller, and Amir H. Hoveyda
Organometallics 2015 Volume 34(Issue 11) pp:2110-2113
Publication Date(Web):February 4, 2015
DOI:10.1021/om501213x
Molybdenum and tungsten alkylidene complexes that contain the sterically demanding hexaisopropylterphenylimido ligand, N-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (NHIPT), have been prepared from Mo(N-t-Bu)2Cl2(1,2-dimethoxyethane) or W(N-t-Bu)2Cl2(pyridine)2, employing tert-butylimido ligands as sacrificial proton acceptors. These complexes include M(NHIPT)(CH-t-Bu)Cl2 (M = Mo, W), Mo(NHIPT)(CH-t-Bu)(pyrrolide)2, and Mo(NHIPT)(CH-t-Bu)(pyrrolide)(OC6F5)(CH3CN). In all cases only anti alkylidene isomers are observed in solution, as a consequence of the steric demands of the NHIPT ligand. An X-ray structure of W(NHIPT)(CH-t-Bu)Cl2 showed it to be a monomer with a disordered alkylidene that is 86% in the anti configuration and 14% in the syn configuration.
Co-reporter:Jakub Hyvl, Benjamin Autenrieth, and Richard R. Schrock
Macromolecules 2015 Volume 48(Issue 9) pp:3148-3152
Publication Date(Web):April 23, 2015
DOI:10.1021/acs.macromol.5b00477
Co-reporter:Benjamin Autenrieth, Hyangsoo Jeong, William P. Forrest, Jonathan C. Axtell, Antje Ota, Thomas Lehr, Michael R. Buchmeiser, and Richard R. Schrock
Macromolecules 2015 Volume 48(Issue 8) pp:2480-2492
Publication Date(Web):April 17, 2015
DOI:10.1021/acs.macromol.5b00123
We report an examination of the ring-opening metathesis polymerization (ROMP) of endo-dicyclopentadiene (DCPD) by 10 well-defined molybdenum-based and 16 tungsten-based alkylidene initiators. Five tungsten-based MAP (monoaryloxide pyrrolide) initiators with the general formula W(X)(CHCMe2Ph)(Me2Pyr)(OAr) (X = arylimido, alkylimido, or oxo; Me2Pyr =2,5-dimethylpyrrolide; OAr = an aryloxide) were found to yield >98% cis, >98% syndiotactic poly(DCPD); they are W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (2, OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3, pyr = pyrrolide), W(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(pyr)(OHMT) (3), W(O)(CHCMe2Ph)(Me2Pyr)(OHMT)(PPh2Me) (7, Me2Pyr =2,5-dimethylpyrrolide), W(O)(CHCMe2Ph)(Me2Pyr)(ODFT)(PPh2Me) (9, ODFT = O-2,6-(C6F5)2C6H3), and W(O)(CHCMe2Ph)(Me2Pyr)(OTPP)(PMePh2) (10, OTPP = O-2,3,5,6-Ph4C6H). Two biphenolate alkylidene complexes, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-biphen) (17) and W(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-biphen) (22, biphen =3,3′-(t-Bu)2-5,5′-6,6′-(CH3)4-1,1′-biphenyl-2,2′-diolate), were found to yield >98% cis, >98% isotactic poly(DCPD). Cis, syndiotactic or cis, isotactic poly(DCPD)s (made with 50–1000 equiv of DCPD) are accessible within seconds to minutes in dichloromethane at room temperature. No isomerization or cross-linking reactions are observed, and addition of a chain transfer reagent (1-hexene) or the use of THF as a solvent does not decrease the stereospecificity of the polymerizations. Cis, syndiotactic and cis, isotactic poly(DCPD)s can be distinguished readily from each other by 13C NMR spectroscopy. Hydrogenation of each stereoregular poly(DCPD) produces H-poly(DCPD)s that have melting points near 270 °C (syndiotactic) or 290 °C (isotactic) and high crystallinities (wc = 0.83 for syndiotactic and wc = 0.74 for isotactic).
Co-reporter:Benjamin Autenrieth and Richard R. Schrock
Macromolecules 2015 Volume 48(Issue 8) pp:2493-2503
Publication Date(Web):April 7, 2015
DOI:10.1021/acs.macromol.5b00161
We report the synthesis of >98% cis,isotactic and cis,syndiotactic polynorbornene (poly(NBE)) and poly(endo,anti-tetracyclododecene) (poly(TCD)). Cis,isotactic poly(NBE) and poly(TCD) were prepared employing Mo-based biphenolate imido alkylidene initiators, Mo(NR)(CHCMe2Ph)(Biphen) (Biphen = e.g., 3,3′-(t-Bu)2-5,5′-6,6′-(CH3)4-1,1′-biphenyl-2,2′-diolate), while cis,syndiotactic poly(NBE) and poly(TCD) were prepared employing W-based imido or oxo monoaryloxide pyrrolide (MAP) initiators, W(X)(CHR′)(Pyrrolide)(OTer) (X = NR or O; OTer = a 2,6-terphenoxide). Addition of 1-hexene or coordinating solvents such as THF do not decrease the stereospecificity of the polymerization. Cis,iso and cis,syndio dyads can be distinguished through examination of 1H and 13C NMR spectra of the two polymers in a mixture. The polymers were hydrogenated to give isotactic and syndiotactic H-poly(NBE) and H-poly(TCD).
Co-reporter:Richard R. Schrock
Accounts of Chemical Research 2014 Volume 47(Issue 8) pp:2457-2466
Publication Date(Web):June 6, 2014
DOI:10.1021/ar500139s
Some of the most readily available and inexpensive monomers for ring-opening metathesis polymerization (ROMP) are norbornenes or substituted norbornadienes. Polymers made from them have tacticities (the stereochemical relationship between monomer units in the polymer chain) that remain after the C═C bonds in the polymer backbone are hydrogenated. Formation of polymers with exclusively a single structure (one tacticity) was rare until approximately 20 years ago, when well-defined ROMP catalysts based on molybdenum imido alkylidene complexes that contain a chiral biphenolate or binaphtholate ligand were shown to yield cis,isotactic-poly(2,3-dicarbomethoxynorbornadiene) and related polymers through addition of the monomer to the same side of the M═C bond in each step. Over the past few years, molybdenum and tungsten monoaryloxide pyrrolide (MAP) imido alkylidene initiators have been found to produce cis,syndiotactic polynorbornenes and substituted norbornadienes through addition of the monomer to one side of the M═C bond in one step followed by addition to the other side of the M═C bond in the next step. This “stereogenic metal control” is possible as a consequence of the fact that the configuration of the stereogenic metal center switches with each step in the polymerization. Stereogenic metal control also allows syndiotactic polymers to be prepared from racemic monomers in which enantiomers of the monomer are incorporated alternately into the main chain. Because pure trans polymers have not yet been prepared through some predictable mechanism of stereochemical control, it seems unlikely that all four basic polymer structures from a single given monomer can be prepared simply by choosing the right initiator. However, because tactic, and relatively oxygen-stable, hydrogenated polymers are often a desirable goal, the ability to form pure cis,isotactic polymers (through enantiomorphic site control) and cis,syndiotactic polymers (through stereogenic metal control) is sufficient for preparing hydrogenated polymers with a single structure. It is hoped that the principles of forming polymers that have a single structure through ring-opening metathesis polymerization will be general for a relatively large number of monomers and that some important problems in ROMP polymer chemistry can benefit from knowledge of polymer structure at a molecular level. With an increase in knowledge concerning the mechanistic details of polymerization by well-defined initiators, more elaborate ROMP polymers and copolymers with stereoregular structures may be possible.
Co-reporter:William P. Forrest ; Jonathan G. Weis ; Jeremy M. John ; Jonathan C. Axtell ; Jeffrey H. Simpson ; Timothy M. Swager
Journal of the American Chemical Society 2014 Volume 136(Issue 31) pp:10910-10913
Publication Date(Web):July 18, 2014
DOI:10.1021/ja506446n
We report here the polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, stereoregular polymers. The tacticities of the menthyl ester derivatives of two polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not polymerized stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, stereoregular polymer was formed in the presence of 1 equiv of B(C6F5)3.
Co-reporter:Graham E. Dobereiner, Gulin Erdogan, Casey R. Larsen, Douglas B. Grotjahn, and Richard R. Schrock
ACS Catalysis 2014 Volume 4(Issue 9) pp:3069
Publication Date(Web):July 25, 2014
DOI:10.1021/cs500889x
A tandem catalytic reaction has been developed as part of a process to discover tungsten-based olefin metathesis catalysts that have a strong preference for terminal olefins over cis or trans internal isomers in olefin metathesis. This tandem isomerization/terminal olefin metathesis reaction (ISOMET) converts Cn trans internal olefins into C2n–2 cis olefins and ethylene. This reaction is made possible with Ru-based “alkene zipper” catalysts, which selectively isomerize trans olefins to an equilibrium mixture of trans and terminal olefins, plus tungsten-based metathesis catalysts that react relatively selectively with terminal olefins to give Z homocoupled products. The most effective catalysts are W(NAr)(C3H6)(pyr)(OHIPT) (Ar = 2,6-diisopropylphenyl; pyr = pyrrolide; OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) and various [CpRu(P–N)(MeCN)]X (X– = [B(3,5-(CF3)2C6H3)4]–, PF6–, B(C6F5)4–) isomerization catalysts.Keywords: isomerization; metathesis; olefin; ruthenium; tandem catalysis; tungsten
Co-reporter:Erik M. Townsend, Jakub Hyvl, William P. Forrest, Richard R. Schrock, Peter Müller, and Amir H. Hoveyda
Organometallics 2014 Volume 33(Issue 19) pp:5334-5341
Publication Date(Web):September 22, 2014
DOI:10.1021/om500655n
Imido alkylidene complexes of Mo and W and oxo alkylidene complexes of W that contain thiophenoxide ligands of the type S-2,3,5,6-Ph4C6H (STPP) and S-2,6-(mesityl)2C6H3 (SHMT = S-hexamethylterphenyl) have been prepared in order to compare their metathesis activity with that of the analogous phenoxide complexes. All thiolate complexes were significantly slower (up to ∼10× slower) for the metathesis homocoupling of 1-octene or polymerization of 2,3-dicarbomethoxynorbornene, and none of them was Z-selective. The slower rates could be attributed to the greater σ-donating ability of a thiophenoxide versus the analogous phenoxide and consequently a higher electron density at the metal in the thiophenoxide complexes.
Co-reporter:Jonathan C. Axtell, Richard R. Schrock, Peter Müller, Stacey J. Smith, and Amir H. Hoveyda
Organometallics 2014 Volume 33(Issue 19) pp:5342-5348
Publication Date(Web):September 17, 2014
DOI:10.1021/om5006676
Tungsten NArR alkylidene complexes have been prepared that contain the electron-withdrawing ArR groups 2,4,6-X3C6H2 (ArX3, X = Cl, Br), 2,6-Cl2-4-CF3C6H2 (ArCl2CF3), and 3,5-(CF3)2C6H3 (Ar(CF3)2). Reported complexes include W(NArR)2Cl2(dme) (dme = 1,2-dimethoxyethane), W(NArR)2(CH2CMe3)2, W(NArR)(CHCMe3)(OTf)2(dme), and W(NArR)(CHCMe3)(ODBMP)2 (DBMP = 4-Me-2,6-(CHPh2)C6H2). The W(NArR)(CHCMe3)(ODBMP)2 complexes were explored as initiators for the polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD).
Co-reporter:William P. Forrest, Jonathan C. Axtell, and Richard R. Schrock
Organometallics 2014 Volume 33(Issue 9) pp:2313-2325
Publication Date(Web):April 30, 2014
DOI:10.1021/om5002364
We have employed 2,3-dicarbomethoxynorbornadiene (DCMNBD) as a monomer to explore new tungsten oxo alkylidene complexes as initiators for stereoregular ROMP (ring-opening metathesis polymerization). The initiators include MAP (monoaryloxide pyrrolide) oxo alkylidene complexes with the general formula W(O)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide, OAr = an aryloxide) and W(O)(CHCMe2Ph)(OR)2 (OR = an aryloxide or OC(CF3)3), or PPh2Me or CH3CN adducts thereof. We have found that MAP initiators yield cis,syndiotactic-poly(DCMNBD) as a consequence of stereogenic metal control. In contrast, W(O)(CHCMe2Ph)(OR)2(L) initiators (where L = PPh2Me or acetonitrile) are strongly biased toward formation of cis,isotactic structures, while W(O)(CHCMe2Ph)(OR)2 initiators are strongly biased toward formation of cis,syndiotactic structures. Addition of B(C6F5)3 to W(O)(CHCMe2Ph)(Me2Pyr)(OR) species leads to a dramatic increase in the rate of polymerization and to an increase in the cis,syndiotacticity of the polymer (if not already high), while addition of B(C6F5)3 to W(O)(CHCMe2Ph)(OR)2 initiators leads to a dramatic increase in the rate of polymerization and to the formation of highly cis,syndiotactic polymers. All evidence supports the proposal that 16e W(O)(CHCMe2Ph)(OR)2(L) complexes can operate either through loss of L to yield 14e W(O)(CHCMe2Ph)(OR)2 species (which yield largely cis,syndiotactic-poly(DCMNBD)) or by directly reacting with DCMNBD to yield an 18e intermediate and largely cis,isotactic-poly(DCMNBD). All polymerizations by W(O)(CHCMe2Ph)(OR)2(L) and W(O)(CHCMe2Ph)(OR)2 initiators are proposed to operate through some version of chain end control.
Co-reporter:Dr. Matthew P. Conley;Dr. William P. Forrest;Dr. Victor Mougel;Dr. Christophe Copéret;Dr. Richard R. Schrock
Angewandte Chemie International Edition 2014 Volume 53( Issue 51) pp:14221-14224
Publication Date(Web):
DOI:10.1002/anie.201408880
Abstract
The reaction of [W(O)(CHCMe2Ph)(dAdPO)2], containing bulky 2,6-diadamantyl aryloxide ligands, with partially dehydroxylated silica selectively yields a well-defined silica-supported alkylidene complex, [(SiO)W(O)(CHCMe2Ph)(dAdPO)]. This fully characterized material is a very active and stable alkene metathesis catalyst, thus allowing loadings as low as 50 ppm in the metathesis of internal alkenes. [(SiO)W(O)(CHCMe2Ph)(dAdPO)] also efficiently catalyzes the homocoupling of terminal alkenes, with turnover numbers exceeding 75 000 when ethylene is constantly removed to avoid the formation of the less reactive square-based pyramidal metallacycle resting state.
Co-reporter:Matthew P. Conley ; Victor Mougel ; Dmitry V. Peryshkov ; William P. Forrest ; Jr.; David Gajan ; Anne Lesage ; Lyndon Emsley ; Christophe Copéret
Journal of the American Chemical Society 2013 Volume 135(Issue 51) pp:19068-19070
Publication Date(Web):December 4, 2013
DOI:10.1021/ja410052u
Grafting (ArO)2W(═O)(═CHtBu) (ArO = 2,6-mesitylphenoxide) on partially dehydroxylated silica forms mostly [(≡SiO)W(═O)(═CHtBu)(OAr)] along with minor amounts of [(≡SiO)W(═O)(CH2tBu)(OAr)2] (20%), both fully characterized by elemental analysis and IR and NMR spectroscopies. The well-defined oxo alkylidene surface complex [(≡SiO)W(═O)(═CHtBu)OAr] is among the most active heterogeneous metathesis catalysts reported to date in the self-metathesis of cis-4-nonene and ethyl oleate, in sharp contrast to the classical heterogeneous catalysts based on WO3/SiO2.
Co-reporter:Matthew F. Cain ; William P. Forrest ; Jr.; Dmitry V. Peryshkov ; Richard R. Schrock ;Peter Müller
Journal of the American Chemical Society 2013 Volume 135(Issue 41) pp:15338-15341
Publication Date(Web):September 27, 2013
DOI:10.1021/ja408964g
A substituted TREN has been prepared in which the aryl groups in (ArylNHCH2CH2)3N are substituted at the 3- and 5-positions with a total of six OCH2(CH2)nCH═CH2 groups (n = 1, 2, 3). Molybdenum nitride complexes, [(ArylNCH2CH2)3N]Mo(N), have been isolated as adducts that contain B(C6F5)3 bound to the nitride. Two of these [(ArylNCH2CH2)3N]Mo(NB(C6F5)3) complexes (n = 1 and 3) were crystallographically characterized. After removal of the borane from [(ArylNCH2CH2)3N]Mo(NB(C6F5)3) with PMe3, ring-closing olefin metathesis (RCM) was employed to join the aryl rings with OCH2(CH2)nCH═CH(CH2)nCH2O links (n = 1–3) between them. RCM worked best with a W(O)(CHCMe3)(Me2Pyr)(OHMT)(PMe2Ph) catalyst (OHMT = hexamethylterphenoxide, Me2Pyr = 2,5-dimethylpyrrolide) and n = 3. The macrocyclic ligand was removed from the metal through hydrolysis and isolated in 70–75% yields relative to the borane adducts. Crystallographic characterization showed that the macrocyclic TREN ligand in which n = 3 contains three cis double bonds. Hydrogenation produced a TREN in which the three links are saturated, i.e., O(CH2)10O.
Co-reporter:Graham E. Dobereiner ; Jian Yuan ; Richard R. Schrock ; Alan S. Goldman ;Jason D. Hackenberg
Journal of the American Chemical Society 2013 Volume 135(Issue 34) pp:12572-12575
Publication Date(Web):August 2, 2013
DOI:10.1021/ja4066392
n-Alkyl arenes were prepared in a one-pot tandem dehydrogenation/olefin metathesis/hydrogenation sequence directly from alkanes and ethylbenzene. Excellent selectivity was observed when (tBuPCP)IrH2 was paired with tungsten monoaryloxide pyrrolide complexes such as W(NAr)(C3H6)(pyr)(OHIPT) (1a) [Ar = 2,6-i-Pr2C6H3; pyr = pyrrolide; OHIPT = 2,6-(2,4,6-i-Pr3C6H2)2C6H3O]. Complex 1a was also especially active in n-octane self-metathesis, providing the highest product concentrations reported to date. The thermal stability of selected olefin metathesis catalysts allowed elevated temperatures and extended reaction times to be employed.
Co-reporter:Richard R. Schrock
Chemical Communications 2013 vol. 49(Issue 49) pp:5529-5531
Publication Date(Web):03 May 2013
DOI:10.1039/C3CC42609B
Alkyne metathesis by molybdenum and tungsten alkylidyne complexes is now ∼45 years old. Progress in the practical aspects of alkyne metathesis reactions with well-defined complexes, as well as applications, in the last decade, guarantees that it is destined to become a useful method for the synthesis of organic molecules.
Co-reporter:Laura C. H. Gerber
Organometallics 2013 Volume 32(Issue 19) pp:5573-5580
Publication Date(Web):October 3, 2013
DOI:10.1021/om400844k
Monoalkoxide pyrrolide (MAP) complexes that contain a 2,6-dimesitylphenylimido (NAr*) ligand react with ethylene to yield unsubstituted metallacyclobutanes that are in equilibrium with methylidene complexes, W(NAr*)(CH2)(Me2Pyr)(OR) (R = t-Bu, OCMe(CF3)2, SiPh3, or 2,6-Me2C6H3). Polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) with M═CHCMe2Ph (M = Mo or W) initiators is slow as a consequence of a slow propagation step. However, W(NAr*)(CH2)(Me2Pyr)(OR) (R = SiPh3 or 2,6-dimethylphenyl) complexes react readily with 1 equiv of DCMNBD to give a monoinsertion product. The facile reaction between the monoinsertion product and ethylene then allows these complexes to be catalyts for the ring-opening cross-metathesis (ethenolysis) of DCMNBD and DCMNBE (2,3-dicarbomethoxynorbornene) with minimal formation of polymer.
Co-reporter:Hyangsoo Jeong, Daniel J. Kozera, Richard R. Schrock, Stacey J. Smith, Jihua Zhang, Ning Ren, and Marc A. Hillmyer
Organometallics 2013 Volume 32(Issue 17) pp:4843-4850
Publication Date(Web):August 23, 2013
DOI:10.1021/om400583t
Ring-opening metathesis polymerization of a series of 3-substituted cyclooctenes (3-MeCOE, 3-HexCOE, and 3-PhCOE) initiated by various Mo and W MAP complexes leads to cis,HT-poly(3-RCOE) polymers. The apparent rate of polymerization of 3-HexCOE by W(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1c; Pyr = pyrrolide; OHMT = O-2,6-Mesityl2C6H3) is greater than the rate of polymerization by Mo(N-t-Bu)(CH-t-Bu)(Pyr)(OHMT) (1b), but both gave the same cis,HT polymer structures. Formation of HT-poly(3-RCOE) employing 1c takes place via propagating species in which the R group (methyl, hexyl, or phenyl) is on C2 of the propagating alkylidene chain, a type of intermediate that has been modeled through the preparation of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT). The rate of ROMP is exceedingly sensitive to steric factors: e.g., W(N-t-Bu)(CH-t-Bu)(Me2Pyr)(OHMT), the dimethylpyrrolide analogue of 1c, essentially did not polymerize 3-HexCOE at 22 °C. When a sample of W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) and 3-methyl-1-pentene in CDCl3 is cooled to −20 °C, the alkylidene resonances for W(N-t-Bu)(CHCHMeEt)(Pyr)(OHMT) disappear and resonances that can be ascribed to protons in a synα/synα′ disubstituted trigonal bipyramidal metallacyclobutane complex appear. 3-Methyl-1-pentene is readily lost from this metallacycle on the NMR time scale at room temperature.
Co-reporter:Erik M. Townsend, Stefan M. Kilyanek, Richard R. Schrock, Peter Müller, Stacey J. Smith, and Amir H. Hoveyda
Organometallics 2013 Volume 32(Issue 16) pp:4612-4617
Publication Date(Web):August 7, 2013
DOI:10.1021/om400584f
Reactions between Mo(NAr)(CHR)(Me2Pyr)(OTPP) (Ar = 2,6-i-Pr2C6H3, R = H or CHCMe2Ph, Me2Pyr = 2,5-dimethylpyrrolide, OTPP = O-2,3,5,6-Ph4C6H) and CH2═CHX where X = B(pin), SiMe3, N-carbazolyl, N-pyrrolidinonyl, PPh2, OPr, or SPh lead to Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes in good yield. All have been characterized through X-ray studies (as an acetonitrile adduct in the case of X = PPh2). The efficiencies of metathesis reactions initiated by Mo(NAr)(CHX)(Me2Pyr)(OTPP) complexes can be rationalized on the basis of steric factors; electronic differences imposed as a consequence of X being bound to the alkylidene carbon do not seem to play a major role. Side reactions that promote catalyst decomposition do not appear to be a serious limitation for Mo═CHX species.
Co-reporter:Jian Yuan, Richard R. Schrock, Laura C. H. Gerber, Peter Müller, and Stacey Smith
Organometallics 2013 Volume 32(Issue 10) pp:2983-2992
Publication Date(Web):May 6, 2013
DOI:10.1021/om400199u
The bisDFTO alkylidene complexes of molybdenum Mo(NR)(CHCMe2Ph)(DFTO)2 (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, C6F5, 1-adamantyl; DFTO = 2,6-(C6F5)2C6H3O) and monoaryloxide monopyrrolide (MAP) complexes Mo(NR)(CHCMe2Ph)(Me2Pyr)(OAr) (Me2Pyr = 2,5-dimethylpyrrolide; R = C6F5, OAr = DFTO, 2,6-dimesitylphenoxide (HMTO); R = 2,6-Me2C6H3, OAr = DFTO) have been prepared in good yields. Addition of dicarbomethoxynorbornadiene (DCMNBD) to bisDFTO complexes yielded polymers that have a cis,isotactic structure. Polymerization of DCMNBD by Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)(HMTO) gives a polymer that contains the expected cis,syndiotactic structure, but polymerization of DCMNBD by Mo(NR)(CHCMe2Ph)(Me2Pyr)(DFTO) (R = C6F5, 2,6-Me2C6H3) generates a polymer that has a cis,isotactic structure, the first observation of a cis,isotactic polymer prepared employing a MAP initiator. Norbornene is polymerized to give what is proposed to be highly tactic cis-polyNBE. Addition of ethylene to Mo(NC6F5)(CHCMe2Ph)(DFTO)2 leads to formation of Mo(NC6F5)(CH2CH2)(DFTO)2, which also behaves as an initiator for polymerization of DCMNBD to cis,isotactic-polyDCMNBD and norbornene to cis highly tactic polyNBE. Mo(NC6F5)(CH2CH2)(DFTO)2 reacts with 3-methyl-3-phenylcyclopropene (MPCP) to give Mo(NC6F5)(CHCHCMePh)(DFTO)2 in ∼50% yield.
Co-reporter:Michael R. Reithofer, Graham E. Dobereiner, Richard R. Schrock, and Peter Müller
Organometallics 2013 Volume 32(Issue 9) pp:2489-2492
Publication Date(Web):May 2, 2013
DOI:10.1021/om400114h
We report the synthesis of Mo and W MAP complexes that contain O-2,6-(2,5-R2-pyrrolyl)2C6H3 (2,6-dipyrrolylphenoxide or ODPPR) ligands in which R = i-Pr, Ph. W(NAr)(CH-t-Bu)(Pyr)(ODPPPh) (4a; Ar = 2,6-disopropylphenyl, Pyr = pyrrolide) reacts readily with ethylene to yield a metallacyclobutane complex, W(NAr)(C3H6)(Pyr)(ODPPPh) (5). The structure of 5 in the solid state shows that it is approximately a square pyramid with the WC4 ring spanning apical and basal positions. This SP′ structure, which has never been observed as an actual intermediate, must now be regarded as an integral feature of the metathesis reaction.
Co-reporter:Laura C. H. Gerber, Richard R. Schrock, and Peter Müller
Organometallics 2013 Volume 32(Issue 8) pp:2373-2378
Publication Date(Web):April 4, 2013
DOI:10.1021/om4000693
Molybdenum and tungsten bispyrrolide alkylidene complexes that contain a 2,6-dimesitylphenylimido (NAr*) ligand have been prepared, in which the pyrrolide is the parent pyrrolide or 2,5-dimethylpyrrolide. Monoalkoxide pyrrolide (MAP) complexes were prepared through addition of 1 equiv of an alcohol to the bispyrrolide complexes. MAP compounds that contain the parent pyrrolide (NC4H4–) are pyridine adducts, while those that contain 2,5-dimethylpyrrolide are pyridine free. Molybdenum and tungsten MAP 2,5-dimethylpyrrolide complexes that contain O-t-Bu, OCMe(CF3)2, or O-2,6-Me2C6H3 ligands were found to have approximately equal amounts of syn and anti alkylidene isomers, which allowed a study of the interconversion of the two employing 1H–1H EXSY methods. The Keq values ([syn]/[anti]) are all 2–3 orders of magnitude smaller than those observed for a large number of Mo bisalkoxide imido alkylidene complexes, as a consequence of the destabilization of the syn isomer by the sterically demanding NAr* ligand. The rates of interconversion of syn and anti isomers were found to be 1–2 orders of magnitude faster for W MAP complexes than for Mo MAP complexes.
Co-reporter:Erik M. Townsend ; Richard R. Schrock ;Amir H. Hoveyda
Journal of the American Chemical Society 2012 Volume 134(Issue 28) pp:11334-11337
Publication Date(Web):June 26, 2012
DOI:10.1021/ja303220j
Molybdenum or tungsten monoaryloxide pyrrolide (MAP) complexes that contain OHIPT as the aryloxide (hexaisopropylterphenoxide) are effective catalysts for homocoupling of simple (E)-1,3-dienes to give (E,Z,E)-trienes in high yield and with high Z selectivities. A vinylalkylidene MAP species was shown to have the expected syn structure in an X-ray study. MAP catalysts that contain OHMT (hexamethylterphenoxide) are relatively inefficient.
Co-reporter:Travis J. Hebden, Richard R. Schrock, Michael K. Takase and Peter Müller
Chemical Communications 2012 vol. 48(Issue 13) pp:1851-1853
Publication Date(Web):12 Dec 2011
DOI:10.1039/C2CC17634C
(t-BuPOCOP)MoI2 (1; t-BuPOCOP = C6H3-1,3-[OP(t-Bu)2]2) has been synthesized from MoI3(THF)3. Upon reduction of 1 with Na/Hg under dinitrogen molecular nitrogen is cleaved to form [(t-BuPOCOP)Mo(I)(N)]−. The origin of the N atom was confirmed using 15N2. Protonation of [(t-BuPOCOP)Mo(I)(N)]− results in the formation of a neutral species in which it is proposed that the proton has added across the Mo–P bond.
Co-reporter:Dmitry V. Peryshkov and Richard R. Schrock
Organometallics 2012 Volume 31(Issue 20) pp:7278-7286
Publication Date(Web):October 2, 2012
DOI:10.1021/om3008579
Reaction of W(O)2(CH2-t-Bu)2(bipy) with a mixture of ZnCl2(dioxane), PMe2Ph, and trimethylsilyl chloride in toluene at 100 °C produced the known tungsten oxo alkylidene complex W(O)(CH-t-Bu)Cl2(PMe2Ph)2 (1a) in 45% isolated yield. The neophylidene analogue W(O)(CHCMe2Ph)Cl2(PMe2Ph)2 was prepared similarly in 39% yield. The reaction between 1a and LiOR (LiOR = LiOHIPT, LiOHMT) in benzene at 22 °C led to formation of the off-white W(O)(CH-t-Bu)Cl(OR)(PMe2Ph) complexes 4a (OR = OHMT = 2,6-dimesitylphenoxide) and 4b (OR = OHIPT = 2,6-(2,4,6-triisopropylphenyl)2phenoxide). Compound 4a serves as a starting material for the synthesis of W(O)(CH-t-Bu)(OHMT)(2,6-diphenylpyrrolide) (6), W(O)(CH-t-Bu)[N(C6F5)2](OHMT)(PMe2Ph) (7), W(O)(CH-t-Bu)[OSi(t-Bu)3](OHMT) (8), and W(O)(CH-t-Bu)(OHMT)2 (10). The reaction between 8 and ethylene was found to yield the square-pyramidal metallacyclobutane complex W(O)(C3H6)[OSi(t-Bu)3](OHMT) (9), while the reaction between 10 and ethylene was found to yield the square-pyramidal metallacyclobutane complex W(O)(C3H6)(OHMT)2 (11). Compound 11 loses ethylene to yield isolable W(O)(CH2)(OHMT)2 (12). X-ray structures were determined for 6, 7, 9, and 12.
Co-reporter:Hyangsoo Jeong, Jonathan C. Axtell, Béla Török, Richard R. Schrock, and Peter Müller
Organometallics 2012 Volume 31(Issue 18) pp:6522-6525
Publication Date(Web):August 30, 2012
DOI:10.1021/om300799q
Routes to new tungsten alkylidene complexes that contain tert-butylimido or adamantylimido ligands have been devised that begin with a reaction between WCl6 and 4 equivalents of HNR(TMS) to give [W(NR)2Cl(μ-Cl)(RNH2)]2 (R = t-Bu or 1-adamantyl). Alkylation leads to W(NR)2(CH2R′)2 (R′ = t-Bu or CMe2Ph), which upon treatment with pyridinium chloride yields W(NR)(CHR′)Cl2(py)2 complexes, from which W(NR)(CHR′)(pyrrolide)2 and two W(N-t-Bu)(CHR′)(pyrrolide)(OAr) complexes (OAr = hexamethyl- or hexaisopropylterphenoxide) have been prepared.
Co-reporter:Margaret M. Flook, Janna Börner, Stefan M. Kilyanek, Laura C. H. Gerber, and Richard R. Schrock
Organometallics 2012 Volume 31(Issue 17) pp:6231-6243
Publication Date(Web):August 14, 2012
DOI:10.1021/om300530p
Addition of rac-DCENBE (2,3-dicarboethoxynorbornene) or rac-DCBNBE (2,3-dicarbo-tert-butoxynorbornene) to Mo(NAd)(CHCMe2Ph)(Pyr)(OHMT) (1a) (Ad = 1-adamantyl, OHMT = 2,6-dimesitylphenoxide, Pyr– = NC4H4–) led to the formation of polymers that have a cis,syndiotactic,alt structure analogous to the structure observed for the polymer obtained from rac-DCMNBE (2,3-dicarbomethoxynorbornene). The PDI of cis,syndio,alt-poly(DCBNBE) is low and decreases as the polymer length increases, and there is a linear relationship between the number of equivalents of monomer employed and the molecular weight of the polymers measured in THF versus polystyrene standards. In contrast, polymerization of (+)-DCMNBE by 1a at 25, 0, −25, and −40 °C yields a polymer that contains ∼25% trans,isotactic dyads and 75% cis,syndiotactic dyads. A similar polymerization by Mo(NAd)(CHCMe2Ph)(Pyr)(OHIPT) (1b) (OHIPT = 2,6-(2,4,6-i-Pr3)2C6H3) gives a polymer that contains cis,syndiotactic and trans,isotactic dyads in a ratio of ∼8:92, respectively. This is the first report of synthesis of a norbornene polymer that has primarily a trans,isotactic structure. Addition of 100 equiv of (+)-DCMNBE, (−)-DCENBE, or (−)-DCBNBE to a toluene solution of W(O)(CH-t-Bu)(2,5-Me2NC4H2)(OHMT)(PMe2Ph) (5) led to formation of ∼99% cis,syndiotactic polymer. Cis,syndiotactic dyads arise through a mechanism that consists of a syn approach of the monomer to a syn alkylidene isomer followed by inversion of configuration at the metal center as a consequence of an exchange of aryloxide and pyrrolide ligands. The mechanism for formation of trans,isotactic dyads is one in which the monomer approaches in an anti fashion to the syn isomer followed by a “turnstile” rotation in the five-coordinate intermediate metallacyclobutane that allows the metallacylic ring to open productively with retention of configuration at the metal center. The metallacyclobutane intermediate that gives rise to trans,isotactic dyads in the copolymer could be regarded as a relatively high energy species with a “nonideal” structure compared to a trigonal bipyramidal or a square pyramidal structure.
Co-reporter:Jian Yuan, Richard R. Schrock, Peter Müller, Jonathan C. Axtell, and Graham E. Dobereiner
Organometallics 2012 Volume 31(Issue 13) pp:4650-4653
Publication Date(Web):June 20, 2012
DOI:10.1021/om300408n
Pentafluorophenylimido alkylidene complexes of molybdenum and tungsten have been prepared in good yields. Examples include Mo(NC6F5)(CHCMe2Ph)(Me2Pyr)2 (Me2Pyr = 2,5-dimethylpyrrolide), W(NC6F5)(CH-t-Bu)(DME)(Pyrrolide)2, Mo(NC6F5)(CHCMe2Ph)[OC(CF3)3]2, W(NC6F5)(CH-t-Bu)(DME)[OC(CF3)3]2, Mo(NC6F5)(CHCMe2Ph)[OC(C6F5)3]2, W(NC6F5)(CH-t-Bu)[OC(C6F5)3]2, Mo(NC6F5)(CHCMe2Ph)(ODFT)2 (ODFT = O-2,6-(C6F5)2C6H3), and W(NC6F5)(CH-t-Bu)(ODFT)2. Treatment of W(NC6F5)(CH-t-Bu)(DME)[OC(CF3)3]2 with ethylene led to formation of W(NC6F5)(CH2CH2CH2)[OC(CF3)3]2, which has a TBP structure in which the metallacyclobutane ring lies in the equatorial plane. 2,3-Dicarbomethoxynorbornadiene is polymerized by M(NC6F5)(CHR′)(ODFT)2 initiators to give cis,isotactic-poly(DCMNBD).
Co-reporter:Alejandro G. Lichtscheidl, Victor W. L. Ng, Peter Müller, Michael K. Takase, and Richard R. Schrock, Steven J. Malcolmson, Simon J. Meek, Bo Li, Elizabeth T. Kiesewetter, and Amir H. Hoveyda
Organometallics 2012 Volume 31(Issue 12) pp:4558-4564
Publication Date(Web):June 6, 2012
DOI:10.1021/om300353e
Seven bipyridine adducts of molybdenum imido alkylidene bispyrrolide complexes of the type Mo(NR)(CHCMe2R′)(Pyr)2(bipy) (1a–1g; R = 2,6-i-Pr2C6H3 (Ar), adamantyl (Ad), 2,6-Me2C6H3 (Ar′), 2-i-PrC6H4 (AriPr), 2-ClC6H4 (ArCl), 2-t-BuC6H4 (ArtBu), and 2-MesitylC6H4 (ArM), respectively; R′ = Me, Ph) have been prepared using three different methods. Up to three isomers of the adducts are observed that are proposed to be the trans- and two possible cis-pyrrolide isomers of syn-alkylidenes. Sonication of a mixture containing 1a–1g, HMTOH (2,6-dimesitylphenol), and ZnCl2(dioxane) led to the formation of MAP species of the type Mo(NR)(CHCMe2R′)(Pyr)(OHMT) (3a–3g). DCMNBD (2,3-dicarbomethoxynorbornadiene) is polymerized employing 3a–3g as initiators to yield >98% cis,syndiotactic poly(DCMNBD). Attempts to prepare bipy adducts of bisdimethylpyrrolide complexes led to the formation of imido alkylidyne complexes of the type Mo(NR)(CCMe2R′)(Me2Pyr)(bipy) (Me2Pyr = 2,5-dimethylpyrrolide; 4a–4g) through a ligand-induced migration of an alkylidene α proton to a dimethylpyrrolide ligand. X-ray structures of Mo(NAr)(CHCMe2Ph)(Pyr)2(bipy) (1a), Mo(NAriPr)(CHCMe2Ph)(Pyr)(OHMT) (3d), Mo(NAr)(CCMe2Ph)(Me2Pyr)(bipy) (4a), the NAr′ analog of 4a (4c), and Mo(NArT)(CCMe3)(Me2Pyr)(bipy) (ArT = 2-(2,4,6-i-Pr3C6H2)C6H4; 4g) showed normal bond lengths and angles.
Co-reporter:Alejandro G. Lichtscheidl, Victor W. L. Ng, Peter Müller, Michael K. Takase, and Richard R. Schrock
Organometallics 2012 Volume 31(Issue 6) pp:2388-2394
Publication Date(Web):March 5, 2012
DOI:10.1021/om3000289
Monaryloxide pyrrolide (MAP) molybdenum imido alkylidene complexes of the type Mo(NArX)(CHCMe2R)(Me2Pyr)(OR′) (Me2Pyr = 2,5-dimethylpyrrolide) have been prepared in which NArX is an ortho-substituted phenylimido group (X = Cl (NArCl), CF3 (NArCF3), i-Pr (NAriPr), t-Bu (NArtBu), mesityl (NArM), or TRIP (TRIP = triisopropylphenyl; NArT)) and OR′ = O-2,3,5,6-(C6H5)4C6H (OTPP), O-2,6-(2,4,6-Me3C6H2)2C6H3 (OHMT), or O-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (OHIPT). The object was to explore to what extent relatively “large” NArM or NArT ligands would alter the performance of MAP catalysts in reactions that have been proposed to depend upon the relative size of the imido and OR′ groups. Preliminary studies employing the ring-opening metathesis polymerization of 5,6-dicarbomethoxynorbornadiene as a measure of selectivity suggest that a single phenylimido ortho substituent, even in an NArM or NArT group, does not produce any unique behavior and that the outcome of the ROMP reaction correlates with the overall relative size of the imido and OR′ group. Single-crystal X-ray structures of six species that contain the new NArM or NArT groups are reported.
Co-reporter:Lei Zhu, Margaret M. Flook, Shern-Long Lee, Li-Wei Chan, Shou-Ling Huang, Ching-Wen Chiu, Chun-Hsien Chen, Richard R. Schrock, and Tien-Yau Luh
Macromolecules 2012 Volume 45(Issue 20) pp:8166-8171
Publication Date(Web):October 4, 2012
DOI:10.1021/ma301686f
Upon treatment with a molybdenum-carbene with bidentate substituted biaryl-o,o′-diphenoxide ligand 12, norbornene fused with N-aryl-endo-pyrrolidine 9a undergoes ROMP to give exclusively polynorbornene with cis, isotactic-selectivity. Bis(norbornenes) connected with ferrocene 18 or benzene 20 linkers yield the corresponding double-stranded ladderphanes 19 and 21, respectively with isotactic stereochemistry having all double bonds in Z-configuration. Like the corresponding ladderphanes with E-double bonds, ladderphane 19 also assembles on HOPG to give a highly ordered two-dimensional array as revealed by STM images.
Co-reporter:Smaranda C. Marinescu ; Daniel S. Levine ; Yu Zhao ; Richard R. Schrock ;Amir H. Hoveyda
Journal of the American Chemical Society 2011 Volume 133(Issue 30) pp:11512-11514
Publication Date(Web):June 30, 2011
DOI:10.1021/ja205002v
Monoaryloxide–pyrrolide (MAP) complexes of molybdenum were employed for the selective ethenolysis of 1,2-disubstituted Z olefins in the presence of the corresponding E olefins. Reactions were performed in the presence of 0.02–3.0 mol % catalyst at 22 °C under 20 atm ethylene. We have demonstrated that the Z isomer of an easily accessible E:Z mixture can be destroyed through ethenolysis and the E alkene thereby isolated readily in high yield and exceptional stereoisomeric purity.
Co-reporter:Margaret M. Flook ; Victor W. L. Ng
Journal of the American Chemical Society 2011 Volume 133(Issue 6) pp:1784-1786
Publication Date(Web):January 25, 2011
DOI:10.1021/ja110949f
Ring-opening metathesis polymerization (ROMP) of rac-endo,exo-5,6-dicarbomethoxynorbornene (inter alia) yields a cis,syndio,alt-polymer, one in which the sequential units in the cis,syndiotactic polymer consist of alternating enantiomers. Cis selectivity arises through addition of the monomer to produce an all-cis-metallacyclobutane intermediate, while syndioselectivity and alternating enantiomer structures arise as a consequence of inversion of configuration at the metal center with each metathesis step.
Co-reporter:Dmitry V. Peryshkov ; Richard R. Schrock ; Michael K. Takase ; Peter Müller ;Amir H. Hoveyda
Journal of the American Chemical Society 2011 Volume 133(Issue 51) pp:20754-20757
Publication Date(Web):November 22, 2011
DOI:10.1021/ja210349m
Addition of LiOHMT (OHMT = O-2,6-dimesitylphenoxide) to W(O)(CH-t-Bu)(PMe2Ph)2Cl2 led to WO(CH-t-Bu)Cl(OHMT)(PMe2Ph) (4). Subsequent addition of Li(2,5-Me2C4H2N) to 4 yielded yellow W(O)(CH-t-Bu)(OHMT)(Me2Pyr)(PMe2Ph) (5). Compound 5 is a highly effective catalyst for the Z-selective coupling of selected terminal olefins (at 0.2% loading) to give product in >75% yield with >99% Z configuration. Addition of 2 equiv of B(C6F5)3 to 5 afforded a catalyst activated at the oxo ligand by B(C6F5)3. 5·B(C6F5)3 is a highly active catalyst that produces thermodynamic products (∼20% Z).
Co-reporter:Laura C. H. Gerber ; Richard R. Schrock ; Peter Müller ;Michael K. Takase
Journal of the American Chemical Society 2011 Volume 133(Issue 45) pp:18142-18144
Publication Date(Web):October 14, 2011
DOI:10.1021/ja208936s
Compounds that have the formula M(NR)(CHR′)(OR″)(Pyrrolide), where OR″ is “large” relative to NR and M = Mo or W, have been shown to be Z-selective olefin metathesis catalysts. In this communication we report a new route to Mo complexes in which the relationship between NR and OR″ has been reversed; i.e., the imido ligand is the sterically demanding 2,6-dimesitylphenylimido ligand (NAr*).
Co-reporter:Yu Zhao, Amir H. Hoveyda, and Richard R. Schrock
Organic Letters 2011 Volume 13(Issue 4) pp:784-787
Publication Date(Web):January 20, 2011
DOI:10.1021/ol1030525
The utility of W-alkylidene complexes for enyne ring-closing metathesis is demonstrated in a direct comparison with Mo-based analogs. Tungsten complexes lead to less alkyne oligomerization and higher levels of endo-selectivity and enantioselectivity.
Co-reporter:Jian Yuan;Erik M. Townsend;Alan S. Goldman;Peter Müller;Michael K. Takase
Advanced Synthesis & Catalysis 2011 Volume 353( Issue 11-12) pp:1985-1992
Publication Date(Web):
DOI:10.1002/adsc.201100200
Abstract
A new tungsten alkylidene complex, W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) {Ar=2,6-(i-Pr)2C6H3; HIPT-NMe2=2,6-[2,4,6-(i-Pr)3C6H2]2-4-NMe2-C6H2}, has been synthesized and shown to be highly selective for Z homocoupling metathesis of selected terminal olefins in pentane, as is W(NAr)(CH2CH2CH2)(OHIPT)(pyrrolide) (5). Both 5 and W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) (6) are adsorbed onto calcined alumina. Control experiments and metathesis homocoupling of four substrates lead to the conclusions that 5 is largely adsorbed in a reaction that liberates HIPTOH, while 6 is adsorbed largely through an interaction between the dimethylamino group and an acidic site on the surface. There is no evidence that any adsorbed catalyst can give rise to Z selectivity of a magnitude equal to that found in a homogeneous reaction involving 5 or 6.
Co-reporter:R. Adam Kinney ; Rebecca L. McNaughton ; Jia Min Chin ; Richard R. Schrock ;Brian M. Hoffman
Inorganic Chemistry 2011 Volume 50(Issue 2) pp:418-420
Publication Date(Web):December 14, 2010
DOI:10.1021/ic102127v
Dinitrogen is reduced to ammonia by the molybdenum complex of L = [HIPTN3N]3− [Mo; HIPT = 3,5-(2,4,6-iPr3C6H2)2C6H3]. The mechanism by which this occurs involves the stepwise addition of proton/electron pairs, but how the first pair converts MoN2 to MoN═NH remains uncertain. The first proton of reduction might bind either at Nβ of N2 or at one of the three amido nitrogen (Nam) ligands. Treatment of MoCO with [2,4,6-Me3C5H3N]BAr′4 [Ar′ = 2,3-(CF3)2C6H3] in the absence of reductant generates HMoCO+, whose electron paramagnetic resonance spectrum has greatly reduced g anisotropy relative to MoCO. 2H Mims pulsed electron nuclear double-resonance spectroscopy of 2HMoCO+ shows a signal that simulations show to have a hyperfine tensor with an isotropic coupling, aiso(2H) = −0.22 MHz, and a roughly dipolar anisotropic interaction, T(2H) = [−0.48, −0.93, 1.42] MHz. The simulations show that the deuteron is bound to Nam, near the Mo equatorial plane, not along the normal, and at a distance of 2.6 Å from Mo, which is nearly identical with the (Nam)2H+−Mo distance predicted by density functional theory computations.
Co-reporter:Smaranda C. Marinescu, Richard R. Schrock, Peter Müller, Michael K. Takase, and Amir H. Hoveyda
Organometallics 2011 Volume 30(Issue 7) pp:1780-1782
Publication Date(Web):March 15, 2011
DOI:10.1021/om200150c
3,5-Dimethylphenylimido complexes of tungsten can be prepared using procedures analogous to those employed for other tungsten catalysts, as can bispyrrolide species and MonoAryloxide-Pyrrolide (MAP) species. Homocouplings of 1-hexene, 1-octene, and methyl 10-undecenoate are achieved in 45−89% yield and a Z selectivity of >99% with W(NAr′′)(C3H6)(pyr)(OHIPT) as a catalyst. Homocoupling of terminal olefins in the presence of (E)-olefins elsewhere in the molecule also was achieved with excellent selectivity.
Co-reporter:Michael R. Reithofer ; Richard R. Schrock ;Peter Müller
Journal of the American Chemical Society 2010 Volume 132(Issue 24) pp:8349-8358
Publication Date(Web):May 25, 2010
DOI:10.1021/ja1008213
Molybdenum complexes that contain a new TREN-based ligand [(3,5-(2,5-diisopropyl-pyrrolyl)2C6H3NCH2CH2)3N]3− ([DPPN3N]3−) that are relevant to the catalytic reduction of dinitrogen have been prepared. They are [Bu4N]{[DPPN3N]MoN2}, [DPPN3N]MoN2, [DPPN3N]MoN═NH, {[DPPN3N]MoN═NH2}[BArf4], [DPPN3N]Mo≡N, {[DPPN3N]Mo≡NH}[BArf4], and {[DPPN3N]MoNH3}[BArf4]. NMR and IR data for [Bu4N]{[DPPN3N]MoN2} and [DPPN3N]MoN2 are close to those reported for the analogous [HIPTN3N]3− compounds (HIPT = hexaisopropylterphenyl), which suggests that the degree of reduction of dinitrogen is virtually identical in the two systems. However, X-ray studies and several exchange studies support the conclusion that the apical pocket is less protected in [DPPN3N]Mo complexes than in [HIPTN3N]Mo complexes. For example, 15N/14N exchange studies showed that exchange in [DPPN3N]MoN2 is relatively facile (t1/2 ≈ 1 h at 1 atm) and depends upon dinitrogen pressure, in contrast to the exchange in [HIPTN3N]MoN2. Several of the [DPPN3N]Mo complexes, e.g., the [DPPN3N]MoN2 and [DPPN3N]MoNH3 species, are also less stable in solution than the analogous “parent” [HIPTN3N]Mo complexes. Four attempted catalytic reductions of dinitrogen with [DPPN3N]MoN yielded 2.53 ± 0.35 equiv of total ammonia. These studies reveal more than any other just how sensitive a successful catalytic reduction is to small changes in the triamidoamine supporting ligand.
Co-reporter:J. M. Chin, R. R. Schrock and P. Müller
Inorganic Chemistry 2010 Volume 49(Issue 17) pp:7904-7916
Publication Date(Web):July 27, 2010
DOI:10.1021/ic100856n
A potentially useful trianionic ligand for the reduction of dinitrogen catalytically by molybdenum complexes is one in which one of the arms in a [(RNCH2CH2)3N]3− ligand is replaced by a 2-mesitylpyrrolyl-α-methyl arm, that is, [(RNCH2CH2)2NCH2(2-MesitylPyrrolyl)]3− (R = C6F5, 3,5-Me2C6H3, or 3,5-t-Bu2C6H3). Compounds have been prepared that contain the ligand in which R = C6F5 ([C6F5N)2Pyr]3−); they include [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, [(C6F5N)2Pyr]MoOTf, and [(C6F5N)2Pyr]MoN. Compounds that contain the ligand in which R = 3,5-t-Bu2C6H3 ([Art-BuN)2Pyr]3−) include {[(Art-BuN)2Pyr]Mo(N2)}Na(15-crown-5), {[(Art-BuN)2Pyr]Mo(N2)}[NBu4], [(Art-BuN)2Pyr]Mo(N2) (νNN = 2012 cm−1 in C6D6), {[(Art-BuN)2Pyr]Mo(NH3)}BPh4, and [(Art-BuN)2Pyr]Mo(CO). X-ray studies are reported for [(C6F5N)2Pyr]Mo(NMe2), [(C6F5N)2Pyr]MoCl, and [(Art-BuN)2Pyr]MoN. The [(Art-BuN)2Pyr]Mo(N2)0/− reversible couple is found at −1.96 V (in PhF versus Cp2Fe+/0), but the [(Art-BuN)2Pyr]Mo(N2)+/0 couple is irreversible. Reduction of {[(Art-BuN)2Pyr]Mo(NH3)}BPh4 under Ar at approximately −1.68 V at a scan rate of 900 mV/s is not reversible. Ammonia in [(Art-BuN)2Pyr]Mo(NH3) can be substituted for dinitrogen in about 2 h if 10 equiv of BPh3 are present to trap the ammonia that is released. [(Art-BuN)2Pyr]Mo−N═NH is a key intermediate in the proposed catalytic reduction of dinitrogen that could not be prepared. Dinitrogen exchange studies in [(Art-BuN)2Pyr]Mo(N2) suggest that steric hindrance by the ligand may be insufficient to protect decomposition of [(Art-BuN)2Pyr]Mo−N═NH through a variety of pathways. Three attempts to reduce dinitrogen catalytically with [(Art-BuN)2Pyr]Mo(N) as a “catalyst” yielded an average of 1.02 ± 0.12 equiv of NH3.
Co-reporter:David Gajan, Nuria Rendón, Keith M. Wampler, Jean-Marie Basset, Christophe Copéret, Anne Lesage, Lyndon Emsley and Richard R. Schrock
Dalton Transactions 2010 vol. 39(Issue 36) pp:8547-8551
Publication Date(Web):19 Jul 2010
DOI:10.1039/C0DT00315H
Reaction of Li(3,5-R2-pyrazolide) (R = tBu or Ph, dXpz) with Mo(NAr)(CHCMe2Ph)(OTf)2(DME) yields Mo(NAr)(CHCMe2Ph)(dXpz)2 in good yield. These complexes react with alcohols or the surface silanols of silica, to yield bis-alkoxy and surface mono-siloxy alkene metathesis catalysts, respectively.
Co-reporter:Smaranda C. Marinescu, Annie J. King, Richard R. Schrock, Rojendra Singh, Peter Müller, and Michael K. Takase
Organometallics 2010 Volume 29(Issue 24) pp:6816-6828
Publication Date(Web):December 2, 2010
DOI:10.1021/om101003v
Exposure of heptane solutions of Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OAr) (1a; Ar = 2,6-diisopropylphenyl), Mo(NAr)(CHCMe3)(Me2Pyr)[OCMe(CF3)2] (1b), and Mo(NAr)(CHCMe2Ph)(Me2Pyr)(OSiPh3) (1c) to one atmosphere of ethylene for 12 h yields the ethylene complexes, Mo(NAr)(CH2CH2)(Me2Pyr)(OAr) (2a), Mo(NAr)(CH2CH2)(Me2Pyr)[OCMe(CF3)2] (2b), and Mo(NAr)(CH2CH2)(Me2Pyr)(OSiPh3) (2c). Addition of 1 equiv of triphenylsilanol to a solution of 2c gives Mo(NAr)(CH2CH2)(OSiPh3)2 (3) readily. Mo(NAr)(CHCMe2Ph)(OTf)2(dme) reacts slowly with ethylene (60 psi) in toluene at 80 °C to give cis and trans isomers of Mo(NAr)(CH2CH2)(OTf)2(dme) (4a) in the ratio of ∼2(cis):1. Addition of lithium 2,5-dimethylpyrrolide to 4a under 1 atm of ethylene produces Mo(NAr)(CH2CH2)(η1-Me2Pyr)(η5-Me2Pyr) (5a). Mo(NAr)(CHCMe2Ph)(η1-MesPyr)2 (MesPyr = 2-mesitylpyrrolide) reacts cleanly with ethylene in benzene at 60 °C over a period of four days to give exclusively Mo(NAr)(CH2CH2)(MesPyr)2 (5b). Treatment of 5b with 2 equiv of (CF3)2CHOH in ether yields Mo(NAr)(CH2CH2)[OCH(CF3)2]2(Et2O) (6). Neat styrene reacts with 2c and 3 to generate the styrene complexes, Mo(NAr)(CH2CHPh)(Me2Pyr)(OSiPh3) (7) and Mo(NAr)(CH2CHPh)(OSiPh3)2 (8), respectively. Similarly, the trans-3-hexene complex, Mo(NAr)(trans-3-hexene)(OSiPh3)2 (9a), can be prepared from 3 and neat trans-3-hexene. When 3 is exposed to 1 atm of ethylene, the molybdacyclopentane species, Mo(NAr)(C4H8)(OSiPh3)2 (10), is generated. X-ray structural studies were carried out on 2c, 5a, 6, 8, 9a, and 10. All evidence suggests that alkene exchange at the Mo(IV) center is facile, followed by cis,trans isomerization and isomerization via double bond migration. In addition, trace amounts of alkylidene complexes are formed that result in slow metathesis reactions of free olefins to give (e.g.) a distribution of all possible linear olefins from an initial olefin and its double bond isomers.
Co-reporter:Richard R. Schrock, Annie J. Jiang, Smaranda C. Marinescu, Jeffrey H. Simpson, and Peter Müller
Organometallics 2010 Volume 29(Issue 21) pp:5241-5251
Publication Date(Web):July 12, 2010
DOI:10.1021/om100363g
Addition of ethylene to Mo(NAr)(CHCMe2Ph)(OHIPT)(Pyr) (NAr = N-2,6-i-Pr2C6H3, OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3, Pyr = NC4H4) led to the trigonal-bipyramidal metallacyclobutane complex Mo(NAr)(C3H6)(OHIPT)(Pyr), in which the imido and aryloxide ligands occupy axial positions. Mo(NAr)(C3H6)(OHIPT)(Pyr) loses ethylene to give isolable Mo(NAr)(CH2)(OHIPT)(Pyr). W(NAr)(CH2)(OTPP)(Me2Pyr) (OTPP = O-2,3,5,6-Ph4C6H, Me2Pyr = 2,5-Me2NC4H2) was prepared similarly. Single-crystal X-ray studies of Mo(NAr)(CH2)(OHIPT)(Pyr) and W(NAr)(CH2)(OTPP)(Me2Pyr) show that they are monomers that contain an η1-pyrrolide ligand and a methylidene ligand in which the M−C−Hanti angle is smaller than the M−C−Hsyn angle, consistent with an agostic interaction between CHanti and the metal. Attempts to prepare analogous Mo(NAd)(CH2)(OHIPT)(Pyr) (Ad = 1-adamantyl) yielded only the ethylene complex Mo(NAd)(C2H4)(OHIPT)(Pyr). W(NArtBu)(CH2)(OTPP)(Me2Pyr) (ArtBu = 2-t-BuC6H4) was isolated upon loss of ethylene from W(NArtBu)(C3H6)(OTPP)(Me2Pyr), but decomposed in solution over a period of several hours at 22 °C. NMR studies of Mo(NAr)(C3H6)(OHIPT)(Pyr) and W(NAr)(C3H6)(OHIPT)(Pyr) species showed them both to be in equilibrium with ethylene/methylidene intermediates before losing ethylene to yield the respective methylidene complexes. Detailed NMR studies of Mo(NAr)(C3H6)(OBitet)(Me2Pyr) (OBitet is the anion derived from (R)-3,3′-dibromo-2′-(tert-butyldimethylsilyloxy)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2-ol) were carried out and compared with previous studies of W(NAr)(C3H6)(OBitet)(Me2Pyr). It could be shown that Mo(NAr)(C3H6)(OBitet)(Me2Pyr) forms an ethylene/methylidene intermediate at 20 °C at a rate that is 4500 times faster than the rate at which W(NAr)(C3H6)(OBitet)(Me2Pyr) forms an ethylene/methylidene intermediate. It is proposed that the stability of methylidene complexes coupled with their high reactivity accounts for the high efficiency of many olefin metathesis processes that employ monoaryloxidepyrrolide catalysts.
Co-reporter:Margaret M. Flook, Laura C. H. Gerber, Galia T. Debelouchina, and Richard R. Schrock
Macromolecules 2010 Volume 43(Issue 18) pp:7515-7522
Publication Date(Web):August 31, 2010
DOI:10.1021/ma101375v
We report the Z-selective and syndioselective polymerization of 2,3-bis(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene (NBDF6) and 3-methyl-3-phenylcyclopropene (MPCP) by monoaryloxide monopyrrolide imido alkylidene (MAP) catalysts of Mo. The mechanism of polymerization with syn-Mo(NAd)(CHCMe2Ph)(Pyr)(OHIPT) (1; Ad = 1-adamantyl, OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) as the initiator is proposed to consist of addition of monomer to the syn initiator to yield a syn first insertion product and propagation via syn insertion products. In contrast, the mechanism of polymerization with syn-Mo(NAr)(CHCMe2Ph)(Pyr)(OTPP) (4; Ar = 2,6-i-Pr2C6H3, OTPP = 2,3,5,6-Ph4C6H) as the initiator at −78 °C consists of addition of monomer to the syn initiator to yield an anti first insertion product and propagation via anti insertion products. Polymerizations of NBDF6 and MPCP at room temperature initiated by 4 led to polymers without a regular structure. We propose that the syndiotacticity of cis polymers is the consequence of the required inversion at the metal center with each insertion of monomer, i.e., stereogenic metal control of the polymer structure. We also propose that the two mechanisms for forming cis,syndiotactic polymers arise as a consequence of the relative steric bulk of the imido and phenoxide ligands.
Co-reporter:Richard R. Schrock
Chemical Reviews 2009 Volume 109(Issue 8) pp:3211
Publication Date(Web):March 13, 2009
DOI:10.1021/cr800502p
Co-reporter:Annie J. Jiang ; Yu Zhao ; Richard R. Schrock ;Amir H. Hoveyda
Journal of the American Chemical Society 2009 Volume 131(Issue 46) pp:16630-16631
Publication Date(Web):October 30, 2009
DOI:10.1021/ja908098t
Mo and W MonoAryloxide-Pyrrolide (MAP) olefin metathesis catalysts can couple terminal olefins to give as high as >98% Z-products in moderate to high yields with as little as 0.2% catalyst. Results are reported for 1-hexene, 1-octene, allylbenzene, allyltrimethylsilane, methyl-10-undecenoate, methyl-9-decenoate, allylB(pinacolate), allylOBenzyl, allylNHTosyl, and allylNHPh. It is proposed that high Z-selectivity is achieved because a large aryloxide only allows metallacyclobutanes to form that contain adjacent cis substituents and because isomerization of Z-product to E-product can be slow in that same steric environment.
Co-reporter:Corina Scriban ; Bryan S. Amagai ; Elizabeth A. Stemmler ; Ronald L. Christensen
Journal of the American Chemical Society 2009 Volume 131(Issue 37) pp:13441-13452
Publication Date(Web):August 28, 2009
DOI:10.1021/ja904541b
Linear oligoenes of 1,6-heptadiynes (derived from dialkyl dipropargylmalonates) with a single basic structure and up to 23 conjugated double bonds were synthesized through Wittig-like reactions between bimetallic Mo−alkylidene compounds and aldehyde-capped oligoenes. The relatively rigid and isomerically pure oligoenes have structures with alternating cis,trans conjugated double bonds in which the cis double bond is part of a cyclopentene ring. Molecular weights have been confirmed through MALDI-MS measurements of samples purified by HPLC. Optical spectra of the purified samples show significant vibronic resolution, even in room temperature samples, and are remarkably similar to those of simple polyenes and carotenoids. Therefore, a systematic investigation of the dependence of the allowed electronic transition energies (electronic origins) on conjugation lengths has become possible. Studies of seven allowed transitions for molecules with 5−23 double bonds (= N) indicate asymptotic convergence (with approximately a 1/N dependence) to a common long polyene limit at ∼16 000 cm−1. The convergence of these electronic transitions agrees with theoretical treatments of polyene excited-state energies and is consistent with the absorption spectra of analogous diethyl dipropargylmalonate polymers (1/N ≈ 0).
Co-reporter:Thomas Kupfer
Journal of the American Chemical Society 2009 Volume 131(Issue 35) pp:12829-12837
Publication Date(Web):August 12, 2009
DOI:10.1021/ja904535f
In this paper we explore the ethylation of dinitrogen (employing [Et3O][BArf4]; Arf = 3,5-(CF3)2C6H3) in [HIPTN3N]Mo (Mo) complexes ([HIPTN3N]3− = [N(CH2CH2NHIPT)3]3−; HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) with the objective of developing a catalytic cycle for the conversion of dinitrogen into triethylamine. A number of possible intermediates in a hypothetical catalytic cycle have been isolated and characterized: MoN═NEt, [Mo═NNEt2][BArf4], Mo═NNEt2, [Mo═NEt][BArf4], Mo═NEt, MoNEt2, and [Mo(NEt3)][BArf4]. Except for MoNEt2, all compounds were synthesized from other proposed intermediates in a hypothetical catalytic reaction. All alkylated species are significantly more stable than their protonated counterparts, especially the Mo(V) species, Mo═NNEt2 and Mo═NEt. The tendency for both Mo═NNEt2 and Mo═NEt to be readily oxidized by [Et3O][BArf4] (as well as by [H(Et2O)2][BArf4], [Mo═NNH2][BArf4], and [Mo═NH][BArf4]) suggests that their alkylation is unlikely to be part of a catalytic cycle. All efforts to generate NEt3 in several stoichiometric or catalytic runs employing MoN2 and Mo≡N as starting materials were unsuccessful, in part because of the slow speed of most alkylations relative to protonations. In related chemistry that employs a ligand containing 3,5-(4-t-BuC6H4)2C6H3 amido substituents alkylations were much faster, but a preliminary exploration revealed no evidence of catalytic formation of triethylamine.
Co-reporter:Smaranda C. Marinescu ; Richard R. Schrock ; Peter Müller ;Amir H. Hoveyda
Journal of the American Chemical Society 2009 Volume 131(Issue 31) pp:10840-10841
Publication Date(Web):July 20, 2009
DOI:10.1021/ja904786y
Monoaryloxide-pyrrolide (MAP) olefin metathesis catalysts of molybdenum that contain a chiral bitetralin-based aryloxide ligand are efficient for ethenolysis of methyl oleate, cyclooctene, and cyclopentene. Ethenolysis of 5000 equiv of methyl oleate produced 1-decene (1D) and methyl-9-decenoate (M9D) with a selectivity of >99%, yields up to 95%, and a TON (turnover number) of 4750 in 15 h. Tungstacyclobutane catalysts gave yields approximately half those of molybdenum catalysts, either at room temperature or at 50 °C, although selectivity was still >99%. Ethenolysis of 30 000 equiv of cyclooctene to 1,9-decadiene could be carried out with a TON of 22 500 at 20 atm (75% yield), while ethenolysis of 10 000 equiv of cyclopentene to 1,6-heptadiene could be carried out with a TON of 5800 at 20 atm (58% yield). There is no reason to propose that the efficiency of ethenolysis has been maximized with the most successful catalyst reported here.
Co-reporter:Margaret M. Flook ; Annie J. Jiang ; Richard R. Schrock ; Peter Müller ;Amir H. Hoveyda
Journal of the American Chemical Society 2009 Volume 131(Issue 23) pp:7962-7963
Publication Date(Web):May 22, 2009
DOI:10.1021/ja902738u
The molybdenum-based monoaryloxide monopyrrolide (MAP) species, Mo(NAd)(CHCMe2Ph)(C4H4N)(HIPTO) (2a), which contains “small” imido (Ad = 1-adamantyl) and “large” aryloxide (HIPTO = O-2,6(2,4,6-i-Pr3C6H2)C6H3) ligands, catalyzes Z-selective metathesis reactions as a consequence of intermediate metallacyclobutane species not being able to have an (anti) substituent pointing toward the HIPTO group. Ring-opening metathesis polymerization (ROMP) of dicarbomethoxynorbornadiene (DCMNBD) with 2% 2a in toluene leads to >99% cis and >99% syndiotactic poly(DCMNBD), while ROMP of cyclooctene and 1,5-cyclooctadiene (300 equiv) with initiator 2a leads to poly(cyclooctene) and poly(cyclooctadiene) that have cis contents of >99%; all are previously unknown microstructures. Z-Selectivity is also observed in the metathesis of cis-4-octene and cis-3-hexene by initiator 2a to give cis-3-heptene.
Co-reporter:Annie J. Jiang ; Jeffrey H. Simpson ; Peter Müller
Journal of the American Chemical Society 2009 Volume 131(Issue 22) pp:7770-7780
Publication Date(Web):May 12, 2009
DOI:10.1021/ja9012694
Two diastereomers of the monoalkoxidepyrrolide (MAP) species, W(NAr)(CH2)(Me2Pyr)(OR*) (1; Ar = 2,6-diisopropylphenyl, Me2Pyr = 2,5-dimethylpyrrolide, OR* = (R)-3,3′-dibromo-2′-(tert-butyldimethylsilyloxy)-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2-olate), were generated through addition of R*OH to W(NAr)(CH2)(Me2Pyr)2. The unsubstituted tungstacyclobutane species, W(NAr)(C3H6)(Me2Pyr)(OR*) (2), was isolated by treating the mixture of diastereomers of 1 with ethylene. An X-ray study revealed 2 to have a trigonal bipyramidal structure in which the imido and phenoxide ligands are in axial positions. A variety of NMR experiments were carried out on 1 and 2. The major findings are the following: (i) the methylidene ligands in the two diastereomers of 1 rotate readily about the W═C bond (k = 2−7 s−1 at 22 °C); (ii) NMR studies are consistent with 2 breaking up to give an intermediate alkylidene/ethylene complex, (R)- and (S)-W(CH2)(C2H4); and (iii) the ethylene in the (R)-W(CH2)(C2H4) intermediate can rotate about the W−ethylene bond axis at approximately the same rate as 2 re-forms or ethylene is lost to give 1. Compound 1 reacts with trimethylphosphine to yield (R)-1(PMe3). Two intermediate PMe3 adducts were observed and found to convert to (R)-1(PMe3) in an intramolecular fashion with an average rate constant at 5 °C of ∼1.4 × 10−4 s−1. Both neophylidene (4) and methylidene (5) MAP species containing 2,3,5,6-tetraphenylphenoxide ligand also were prepared. Compound 5 can be heated to 80 °C, where methylidene rotation about the W═C bond is facile and observable in a variable-temperature 1H NMR spectrum. A 1H−1H EXSY spectrum of 5 in benzene-d6 at 20 °C showed that the methylidene protons are exchanging with k = 90 s−1. A structure of 5(THF) showed it to be a square pyramid with the methylidene ligand in the apical position and THF coordinated trans to the imido ligand. Exposure of 5 to ethylene generated the tungstacyclobutane complex, W(NAr)(C3H6)(Me2Pyr)(OR) (6), whose structure is analogous to that of 2. Treatment of 5 with PMe3 yielded yellow 5(PMe3), an X-ray study of which revealed it to be a square pyramid with the methylidene ligand in the apical position and the phosphine trans to the pyrrolide. These studies suggest that metallacyclobutane intermediates in metathesis reactions with MAP species are likely to contain axial imido and phenoxide ligands, that metallacycles are formed when an olefin approaches the metal in a MAP species trans to the pyrrolide, and that the configuration at the metal inverts as a consequence of each forward metathesis step.
Co-reporter:Dennis G. H. Hetterscheid ; Brian S. Hanna
Inorganic Chemistry 2009 Volume 48(Issue 17) pp:8569-8577
Publication Date(Web):July 29, 2009
DOI:10.1021/ic900468n
[HIPTN3N]Mo(N2) (MoN2) ([HIPTN3N]3− = [(HIPTNCH2CH2)3N]3− where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3) reacts with dihydrogen slowly (days) at 22 °C to yield [HIPTN3N]MoH2 (MoH2), a compound whose properties are most consistent with it being a dihydrogen complex of Mo(III). The intermediate in the slow reaction between MoN2 and H2 is proposed to be [HIPTN3N]Mo (Mo). In contrast, MoN2, MoNH3, and MoH2 are interconverted rapidly in the presence of H2, N2, and NH3, and MoH2 is the lowest energy of the three Mo compounds. Catalytic runs with MoH2 as a catalyst suggest that it is competent for reduction of N2 with protons and electrons under standard conditions. [HIPTN3N]MoH2 reacts rapidly with HD to yield a mixture of [HIPTN3N]MoH2, [HIPTN3N]MoD2, and [HIPTN3N]MoHD, and rapidly catalyzes H/D exchange between H2 and D2. MoH2 reacts readily with ethylene, PMe3, and CO to yield monoadducts. Reduction of dinitrogen to ammonia in the presence of 32 equiv of added hydrogen (vs Mo) is not catalytic, consistent with dihydrogen being an inhibitor of dinitrogen reduction.
Co-reporter:Brad C. Bailey, Richard R. Schrock, Sabuj Kundu, Alan S. Goldman, Zheng Huang and Maurice Brookhart
Organometallics 2009 Volume 28(Issue 1) pp:355-360
Publication Date(Web):December 12, 2008
DOI:10.1021/om800877q
Over 40 molybdenum and tungsten imido alkylidene mono(alkoxide) mono(pyrrolide) (MAP) or bis(alkoxide) olefin metathesis catalysts were examined in combination with Ir-based pincer-type catalysts for the metathesis of n-octane. The imido group, alkoxide, and metal in the metathesis catalysts were all found to be important variables. The best catalyst was W(NAr)(CHR)(OSiPh3)2 (Ar = 2,6-diisopropylphenyl), which performed about twice as well as the only previously employed catalyst, Mo(NAr)(CHR)[OCMe(CF3)2]2. Product yields decreased at temperatures greater than 125 °C, most likely because of the instability of the metathesis catalysts at such temperatures. POCOP Ir catalysts gave higher yields than PCP Ir catalysts, although the latter exhibited some selectivity for formation of tetradecane. Eight catalysts were synthesized in situ through addition of alcohols to bis(2,5-dimethylpyrrolide) complexes; in situ catalysts were shown to perform approximately as well as the isolated complexes, which suggests that 2,5-dimethylpyrrole is not detrimental to the alkane metathesis process and that potential catalysts can be screened more conveniently in this way.
Co-reporter:Keith M. Wampler
Inorganic Chemistry 2008 Volume 47(Issue 22) pp:10226-10228
Publication Date(Web):October 16, 2008
DOI:10.1021/ic801695j
The monomeric, homoleptic molybdenum(III) complex molybdenum tris(2,5-dimethylpyrrolide) has been prepared. Reduction with KC8 in THF yields the molybdenum(II) complex potassium [molybdenum tris(2,5-dimethylpyrrolide)], while protonation with [H(OEt2)2][BArF4] yields a cationic species that contains an η1-3H-pyrrole ligand.
Co-reporter:Zachary J. Tonzetich ; Richard R. Schrock ; Keith M. Wampler ; Brad C. Bailey ; Christopher C. Cummins ;Peter Müller
Inorganic Chemistry 2008 Volume 47(Issue 5) pp:1560-1567
Publication Date(Web):February 8, 2008
DOI:10.1021/ic701913q
The tungsten nitrido species, [W(μ-N)(CH2-t-Bu)(OAr)2]2 (Ar = 2,6-diisopropylphenyl), has been prepared in a reaction between the alkylidyne species, W(C-t-Bu)(CH2-t-Bu)(OAr)2, and organonitriles. The dimeric nature of the nitride was established in the solid state through an X-ray study and in solution through a combination of 15N NMR spectroscopy and vibrational spectroscopy. Reaction of the nitride with trimethylsilyl trifluoromethanesulfonate afforded the monomeric trimethylsilyl imido species, W(NSiMe3)(CH2-t-Bu)(OAr)2(OSO2CF3), which was also characterized crystallographically. The W2N2 core can be reduced by one electron electrochemically or in bulk with metallocenes to afford the radical anion, {n-Bu4N}{[W(μ-N)(CH2-t-Bu)(OAr)2]2}. Density functional theory calculations suggest that the lowest-energy allowable transition in [W(μ-N)(CH2-t-Bu)(OAr)2]2 is from a highest occupied molecular orbital consisting largely of ligand-based lone pairs into what is largely a metal-based lowest unoccupied molecular orbital.
Co-reporter:AndreaJ. Gabert Dr.;RichardR. Schrock ;Peter Müller Dr.
Chemistry – An Asian Journal 2008 Volume 3( Issue 8-9) pp:1535-1543
Publication Date(Web):
DOI:10.1002/asia.200800076
Abstract
Addition of four equivalents of lithium 2,5-dimethylpyrrolide to a solution of [Mo(NAr)(ORF6)2(CHC5H4)]2Fe (ORF6=OCMe(CF3)2) in dichloromethane led to [Mo(NAr)(Me2Pyr)2(CHC5H4)]2Fe (2; Me2Pyr=2,5-dimethylpyrrolide) and lithium hexafluoro-tert-butoxide, which crystallizes out upon cooling the reaction mixture to −35 °C. Attempts to prepare parent pyrrolide complexes analogous to 2 resulted in the formation of a mixture of two products. The one that could be isolated contains one equivalent of lithium pyrrolide per molybdenum, that is [Mo(NAr)(Pyr)3(CHC5H4)]2FeLi2 (3). The X-ray structure obtained shows it to be a dimer of dimers in which each lithium atom is bound to three pyrrolides. Addition of four equivalents of lithium 2,5-dimethylpyrrolide to [Mo(NAr)(ORF6)2]2(DME)2(CH-1,4-C6H4CH) (1 b) in cold DME produced [Mo(NAr)(Me2Pyr)2]2(CH-1,4-C6H4CH) (4) in good yield, in which the bridging alkylidene is derived from 1,4-divinylbenzene. Three equivalents of (S)-H2[Biphen] are required for a clean reaction with 3 to form [Mo(NAr)(Biphen)(CHC5H4)]2Fe (5) (H2[Biphen]=3,3′-di-tert-butyl-5,5′,6,6′-tetramethyl-1,1′-biphenyl-2,2′-diol), Li2[Biphen], and two equivalents of pyrrole. Reactions involving 4 with the chiral diols are the best behaved. Brown [Mo(NAr)(Benz2Bitet)]2(CH-1,4-C6H4CH) (6) can be isolated upon addition of (R)-H2[Benz2Bitet] (H2[Benz2Bitet]=(3,3′-dibenzhydryl-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2,2′-diol) to 4, while addition of (R)-H2[Mes2Bitet] (H2[Mes2Bitet]=3,3′-dimesityl-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl-2,2′-diol) to 4 yields [Mo(NAr)(Mes2Bitet)]2(CH-1,4-C6H4CH) (7). Compounds 5, 6, and 7 were employed as initiators for the polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) and 2,3-bis(trifluoromethyl)norbornadiene (NBDF6).
Co-reporter:Smaranda C. Marinescu, Rojendra Singh, Adam S. Hock, Keith M. Wampler, Richard R. Schrock and Peter Müller
Organometallics 2008 Volume 27(Issue 24) pp:6570-6578
Publication Date(Web):November 12, 2008
DOI:10.1021/om800816q
An X-ray structural study of Mo(NAd)(CHCMe2Ph)(2,5-Me2NC4H2)2 (1; Ad = 1-adamantyl) reveals it to contain one η1-2,5-Me2NC4H2 ring and one η5-2,5-Me2NC4H2 ring. The structures of Mo(NAr)(CHCMe2Ph)(pyrrolide)2 (Ar = 2,6-i-Pr2C6H3) complexes that contain 2,3,4,5-tetramethylpyrrolides, 2,5-diisopropylpyrrolides, or 2,5-diphenylpyrrolides are analogous to that of 1. In contrast, Mo(NAr)(CH2CMe2Ph)(indolide)2 (6) was shown to contain two η1-bound indolides. Monohexafluoro-t-butoxide pyrrolide (MAP) species can be prepared, either through addition of one equiv of Me(CF3)2COH to a bispyrrolide or through reactions between the lithium pyrrolide and the bishexafluoro-t-butoxide. A trimethylphosphine adduct of a bispyrrolide, Mo(NAd)(CHCMe2Ph)(η1-NC4H4)2(PMe3), has been prepared and structurally characterized, while a PMe3 adduct of MAP hexafluoro-t-butoxide species was found to have PMe3 bound approximately trans to the pyrrolide. This adduct serves as a model for the structure of the initial olefin adduct in olefin metathesis.
Co-reporter:Corina Scriban, Richard R. Schrock and Peter Müller
Organometallics 2008 Volume 27(Issue 23) pp:6202-6214
Publication Date(Web):October 30, 2008
DOI:10.1021/om8007585
In this paper we demonstrate a method of synthesizing oligoenes of diisopropyldipropargylmalonate, [CH2][bx][CH2] (x = 2, 3, 4, 5), in which the “b” repeat unit is identical to the five-membered ring formed in a tail-to-tail cyclopolymerization of diisopropyldipropargylmalonate, and methylene groups are capping the ends. For example, a “degenerate” metathesis reaction between the “monomer”, [CH2][b][CH2], and 2 equiv of Mo(NAr′)(CHCMe2Ph)(ORF6)2 ([Mo][CHCMe2Ph] where Ar′ = 2,6-Me2C6H3 and ORF6 = OCMe(CF3)2) gives [Mo][b][Mo]. An “Mo-Wittig” reaction between [Mo][b][Mo] and 2 equiv of the aldehyde, [CH2][b][O], then gives the “trimer”, [CH2][b3][CH2]. Treatment of [CH2][b3][CH2] with 2 equiv of [Mo][CHCMe2Ph] gives [Mo][b3][Mo], which upon treatment with 2 equiv of [CH2][b][O] gives the “pentamer”, [CH2][b5][CH2], which contains 11 double bonds in conjugation in a molecule in which the repeat units are connected by trans C═C bonds. The oligoenes are not always obtained in high yield in pure form because (inter alia) C═C metathesis reactions compete with the Mo-Wittig reaction of the aldehyde (e.g., to give [CH2][b2][CH2] also in the synthesis of [CH2][b3][CH2]). These complications could be minimized by employing adducts (L)[Mo][bx][Mo](L), where L = PMe3 or quinuclidine, instead of base-free [Mo][bx][Mo] species in the Mo-Wittig reaction. X-ray structures are reported for [CH2][b2][CH2], [CH2][b3][CH2], (THF)[Mo][b2][Mo](THF), (Et2O)[Mo][b3][Mo](Et2O), and a mixture of homochiral and heterochiral [quin][Mo][b][Mo][quin].
Co-reporter:Annie J. Jiang, Richard R. Schrock and Peter Müller
Organometallics 2008 Volume 27(Issue 17) pp:4428-4438
Publication Date(Web):August 6, 2008
DOI:10.1021/om800209b
Addition of 1 equiv of [HNMe2Ph]BArF4 (ArF = 3,5-(CF3)2C6H3) to Mo(NAr)(CHCMe2Ph)(Pyrrolide)2 (Pyrrolide = parent pyrrolide (Pyr) or 2,5-dimethylpyrrolide (Me2Pyr)) species in THF produced [Mo(NAr)(CHCMe2Ph)(Pyrrolide)(THF)x]BArF4 species (x = 2 for Me2Pyr (1b) or 3 (1a) for Pyr; Ar = 2,6-diisopropylphenyl). [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(2,4-lutidine)]BArF4 (1c) was formed upon addition of 2,4-lutidine to [Mo(NAr)(CHCMe2Ph)(Me2Pyr)(THF)2]BArF4 (1b). Addition of 1 equiv of hexafluoro-tert-butanol to 1a produced {Mo(NAr)(CHCMe2Ph)[OC(CF3)2Me](THF)3}BArF4 (3a), while {Mo(NAr)(CHCMe2Ph)[OCMe(CF3)2](THF)2}BArF4 (3b) was obtained similarly through addition of hexafluoro-tert-butanol to 1b. Similar reactions produced unstable [Mo(NAr)(CHCMe2Ph)(O-2,6-i-Pr2C6H3)(THF)]BArF4 (3c) and [Mo(NAr)(CHCMe2Ph)(OAdamantyl)(THF)2]BArF4 (3d). Treatment of 1b with 2 equiv of 2,6-diisopropylphenol yielded [Mo(NAr)(CH2CMe2Ph)(O-2,6-i-Pr2C6H3)2]BArF4 (4). Compound 3a reacts with ethylene to yield {Mo(NAr)(CH2CH2)[OC(CF3)2Me](THF)3}BArF4 (6). The reaction between Mo(NAr)(CHCMe2Ph)(OTf)2(dme) and 2 equiv of Li(MesPyr) (MesPyr = 2-mesitylpyrrolide) gave Mo(NAr)(CHCMe2Ph)(MesPyr)2 (2), but no cationic species could be prepared that contain 2-mesitylpyrrolide. Compounds 1a, 1c, 2, 3a, 4, and 6 were characterized crystallographically.
Co-reporter:Florian J. Schattenmann
Organometallics 2008 Volume 27(Issue 15) pp:3986-3995
Publication Date(Web):July 19, 2008
DOI:10.1021/om800314y
The carboxylate species Mo(NR)(CHCMe2R′)(O2CCPh3)2 (R = various aryl groups or 1-adamantyl; R′ = Ph or Me) have been synthesized by salt metathesis between Mo(NR)(CHCMe2R′)(OTf)2(DME) (OTf = trifluoromethanesulfonate; DME = 1,2-dimethoxyethane) and sodium triphenylacetate. Other carboxylate compounds that have been prepared by this route include Mo(NAr)(CHCMe2Ph)(O2CR′′)2 (Ar = 2,6-i-Pr2C6H3; R′′ = CPh2Me, Si(SiMe3)3) and Na[Mo(NAd)(CHCMe2Ph)(O2CAr′)3] (Ar′ = 2,6-Me2C6H3). Terphenylcarboxylate species Mo(NR)(CHCMe2Ph)(O2CTer)2 (Ter = 2,6-diphenyl-4-methylphenyl or 2,6-diphenyl-4-methoxyphenyl) were prepared through protonolysis of Mo(NR)(CHCMe2R′)(Me2Pyr)2 with TerCO2H, and one of them was characterized through X-ray crystallography. Trimethylphosphine adducts of selected triphenylacetate complexes have been isolated, and the X-ray crystal structure of Mo(NAr′′)(CH-t-Bu)(O2CCPh3)2(PMe3) (Ar′′ = 2-t-BuC6H4) was obtained. Several of the triphenylacetate complexes are active initiators for the regioselective polymerization of diethyl dipropargylmalonate (DEPDM).
Co-reporter:RichardR. Schrock
Angewandte Chemie 2008 Volume 120( Issue 30) pp:5594-5605
Publication Date(Web):
DOI:10.1002/ange.200705246
Abstract
Molybdänkomplexe mit dem Triamidoamin-Liganden [(RNCH2CH2)3N]3− (R=3,5-(2,4,6-iPr3C6H2)2C6H3) katalysieren die Reduktion von Distickstoff unter Einwirkung von Protonen und Elektronen zu Ammoniak. Die Protonen stammen dabei aus 2,6-Dimethylpyridinium-Ionen, die Elektronen aus Decamethylchromocen, die Reaktion verläuft bei 22 °C und 1 atm Druck. Mögliche Intermediate dieser Reduktion und ihre Reaktionscharakteristik wurden in mehreren theoretischen Arbeiten untersucht. So wurden DFT-Rechnungen des Mo-Komplexes [(HIPTNCH2CH2)3N]Mo (HIPT=Hexaisopropylterphenyl=3,5-(2,4,6-iPr3C6H2)2C6H3) durchgeführt, der wie die katalytisch wirksamen Intermediate den Liganden Triamidoamin enthält. In diesem Kurzaufsatz vergleichen wir für jeden angenommenen Teilschritt der Katalysereaktion aktuelle theoretische Befunde und experimentelle Ergebnisse.
Co-reporter:RichardR. Schrock
Angewandte Chemie International Edition 2008 Volume 47( Issue 30) pp:5512-5522
Publication Date(Web):
DOI:10.1002/anie.200705246
Abstract
Molybdenum complexes that contain the triamidoamine ligand [(RNCH2CH2)3N]3− (R=3,5-(2,4,6-iPr3C6H2)2C6H3) catalyze the reduction of dinitrogen to ammonia at 22 °C and 1 atm with protons from 2,6-dimethylpyridinium and electrons from decamethylchromocene. Several theoretical studies have been published that bear on the proposed intermediates in the catalytic dinitrogen reduction reaction and their reaction characteristics, including DFT calculations on [(HIPTNCH2CH2)3N]Mo species (HIPT=hexaisopropylterphenyl=3,5-(2,4,6-iPr3C6H2)2C6H3), which contain the actual triamidoamine ligand that is present in catalytic intermediates. Recent theoretical findings are compared with experimental findings for each proposed step in the catalytic reaction.
Co-reporter:Richard R. Schrock;Constantin Czekelius
Advanced Synthesis & Catalysis 2007 Volume 349(Issue 1-2) pp:
Publication Date(Web):18 JAN 2007
DOI:10.1002/adsc.200600459
The last several years have produced some key advances in the area of alkene and alkyne metathesis by high oxidation state alkylidene and alkylidyne complexes along with new applications in organic and polymer chemistry. In this review we cover some of these developments and applications. The first part of this review concerns developments in catalyst synthesis and new catalysts. The second part concerns notable applications in organic and polymer chemistry. We discuss only high oxidation state alkylidene and alkylidyne chemistry of relevance to alkene or alkyne metathesis reactions and favor studies in the homogeneous phase.
Co-reporter:Richard R. Schrock
Advanced Synthesis & Catalysis 2007 Volume 349(Issue 1-2) pp:
Publication Date(Web):18 JAN 2007
DOI:10.1002/adsc.200600524
Co-reporter:Richard R. Schrock
Advanced Synthesis & Catalysis 2007 Volume 349(Issue 1-2) pp:
Publication Date(Web):18 JAN 2007
DOI:10.1002/adsc.200600619
Co-reporter:Adam S. Hock Dr.;Richard R. Schrock
Chemistry – An Asian Journal 2007 Volume 2(Issue 7) pp:867-874
Publication Date(Web):14 JUN 2007
DOI:10.1002/asia.200700093
The structure of [(CF3N2NMe)Mo(CH2SiMe3)2] (in which (CF3N2NMe)2− is [(3-CF3C6H4NCH2CH2)2NMe]2−) is approximately trigonal bipyramidal with one axial and one equatorial alkyl ligand. Heating of solutions of [(CF3N2NMe)Mo(CH2SiMe3)2] in [D6]benzene in the presence of five equivalents of 2-butyne led to diamagnetic [(CF3N2NMe)Mo(CHSiMe3)(η2-MeCCMe)], whose structure is approximately square pyramidal with the alkyne occupying the axial site. Addition of one equivalent of cyclohexene sulfide to [(CF3N2NMe)Mo(CH2SiMe3)2] at room temperature produced the diamagnetic, dimeric molybdenum(IV) sulfido complex, [{(CF3N2NMe)MoS}2]. This complex is composed of two approximately trigonal bipyramidal centers, each containing one axial and one equatorial sulfur atom. Oxidation of [(CF3N2NMe)Mo(CH2SiMe3)2] with hexachloroethane resulted in formation of tetramethylsilane, HCl, and the sparingly soluble, red alkylidyne complex, [{(CF3N2NMe)Mo(CSiMe3)Cl}2]. This complex forms a dimer through bridging chlorides. The oxidation reactions of [(CF3N2NMe)Mo(CH2SiMe3)2] with 2-butyne, cyclohexene sulfide, or C2Cl6 are all proposed to proceed by α-hydrogen abstraction in the MoVI species to yield (initially) the MoCHSiMe3 species and tetramethylsilane.
Co-reporter:Keith M. Wampler, Richard R. Schrock and Adam S. Hock
Organometallics 2007 Volume 26(Issue 26) pp:6674-6680
Publication Date(Web):November 27, 2007
DOI:10.1021/om700864u
Monosiloxide and disiloxide complexes have been prepared through the addition of silanols to Mo(NR)(CHCMe2Ph)(pyrrolyl)2 species [R = 1-adamantyl (Ad) or 2,6-i-Pr2C6H3 (Ar)]. The silanols employed include (t-Bu)3SiOH (HSilox), (i-Pr)3SiOH, (Me3Si)3SiOH, (t-Bu-O)3SiOH, Me2(t-Bu)SiOH, and Ph3SiOH. The monoSilox complex, Mo(NAr)(CHCMe2Ph)(Silox)(pyrrolyl) (2a), could be isolated, while Mo(NAd)(CHCMe2Ph)(Silox)(pyrrolyl) was observed in situ but could not be crystallized. Disiloxides that could be crystallized include Mo(NAd)(CHCMe2Ph)(Silox)2 (1b), Mo(NAd)(CHCMe2Ph)[OSi(SiMe3)3]2 (4), Mo(NAd)(CHCMe2Ph)[OSi(O-t-Bu)3]2 (5), and Mo(NAr)(CHCMe2Ph)[OSiMe2(t-Bu)]2 (6); other disiloxide examples could be observed in situ but could not be crystallized. Compound 2a reacts readily with (CF3)Me2COH, (CF3)2MeCOH, (CF3)2CHOH, ArOH, C6F5OH, (−)-menthol, and (−)-borneol to give compounds of the type Mo(NAr)(CHCMe2Ph)(Silox)(OR) (3a−g) in situ. No reaction was observed upon heating of 1b under 5 atm of ethylene at 120 °C in toluene-d8; only at 240 °C in o-dichlorobenzene-d4 did 1b react with ethylene to yield CH2═CHCMe2Ph, but the Mo-containing product could not be identified. Compound 2a reacts with ethylene at 120 °C to give Mo(NAr)(CH2)(Silox)(pyr), while 3a−e react with ethylene at ∼60 °C; methylene species could be observed in several cases but could not be isolated. X-ray studies were carried out for 1b and 2a.
Co-reporter:Lourdes Pia H. Lopez, Richard R. Schrock, Peter J. Bonitatebus Jr.
Inorganica Chimica Acta 2006 Volume 359(Issue 15) pp:4730-4740
Publication Date(Web):1 December 2006
DOI:10.1016/j.ica.2006.03.044
Several niobium and tantalum compounds were prepared that contain either the diamidoamine ligand, [(3,4,5-F3C6H2NCH2CH2)2NMe]2− ([F3N2NMe]2−), or the triamidoamine ligand, [(3,5-Cl2C6H3NCH2CH2)3N]3− ([Cl2N2NMe]3−). The former include [F3N2NMe]TaCl3, [F3N2NMe]NbCl3, [F3N2NMe]TaMe3, [F3N2NMe]NbMe3, [(F3N2NMe)TaMe2][MeB(C6F5)3], [F3N2NMe]Ta(CHSiMe3)(CH2SiMe3), [F3N2NMe]Ta(CH2-t-Bu)Cl2, [F3N2NMe]Ta(CH-t-Bu)(CH3), and [F3N2NMe]Ta(η2-C2H4)(CH2CH3). The latter include [Cl2N2NMe]TaCl2, [Cl2N2NMe]TaMe2, [Cl2N2NMe]Ta(η2-C2H4), and [Cl2N2NMe]Ta(η2-C2H2).X-ray diffraction studies were carried out on [F3N2NMe]Ta(CHSiMe3)(CH2SiMe3), [F3N2NMe]Ta(η2-C2H4)(CH2CH3), and [Cl2N2NMe]TaMe2..Several niobium and tantalum compounds were prepared that contain either the diamidoamine ligand, [(3,4,5-F3C6H2NCH2CH2)2NMe]2−, or the triamidoamine ligand, [(3,5-Cl2C6H3NCH2CH2)3N]3−. An example of the former is [(3,4,5-F3C6H2NCH2CH2)2NMe]Ta(CHSiMe3)(CH2SiMe3), which is prepared by treating [(3,4,5-F3C6H2NCH2CH2)2NMe]TaCl3 with 3 equiv. of Me3SiCH2MgCl.
Co-reporter:Richard R. Schrock
Angewandte Chemie International Edition 2006 Volume 45(Issue 23) pp:
Publication Date(Web):16 MAY 2006
DOI:10.1002/anie.200600085
Metathesis reactions are among the most important processes in organic synthesis. The decisive breakthrough in making these reactions practical for industrial purposes, which range from the synthesis of polymers to pharmaceuticals, came with the discovery of the reaction mechanism by Yves Chauvin and the targeted development of transition-metal-based metathesis catalysts by Richard Schrock and Robert Grubbs. The winners of the Chemistry Nobel Prize in 2005 present first-hand accounts of these developments.
Co-reporter:Frédéric Blanc;Christophe Copéret Dr.;Jean Thivolle-Cazat Dr.;Jean-Marie Basset Dr.;Anne Lesage Dr.;Lyndon Emsley Dr.;Amritanshu Sinha Dr.
Angewandte Chemie 2006 Volume 118(Issue 8) pp:
Publication Date(Web):16 JAN 2006
DOI:10.1002/ange.200503205
Oberflächenorganometallchemie: Struktur- und Festkörper-NMR-Spektroskopiestudien sowie eine Untersuchung der Reaktivität in der Olefinmetathese bescheinigen den molekularen und Oberflächen-Siloxyliganden in 1 m bzw. 1 ähnliche elektronische Eigenschaften. 1 m und 1 reagieren zunächst mit vergleichbaren Umsatzzahlen, der Trägerkatalysator 1 ist jedoch in Gegenwart von Olefinen beständiger, sodass höhere Umsätze möglich sind. Dies zeigt den Vorteil isolierter aktiver Zentren auf Oberflächen.
Co-reporter:Richard R. Schrock
Angewandte Chemie 2006 Volume 118(Issue 23) pp:
Publication Date(Web):16 MAY 2006
DOI:10.1002/ange.200600085
Die Metathesereaktion zählt zu den wichtigsten Prozessen in der organischen Synthese. Der entscheidende Durchbruch für ihre industrielle Anwendung, die von der Synthese von Kunststoffen bis hin zu Pharmazeutika reicht, kam mit der Aufklärung des Reaktionsmechanismus durch Yves Chauvin und der gezielten Entwicklung von Übergangsmetallkatalysatoren durch Richard Schrock und Robert Grubbs. Die drei Chemie-Nobelpreisträger 2005 berichten hier aus erster Hand über die Geschichte dieser Reaktion.
Co-reporter:Richard R. Schrock
PNAS 2006 Volume 103 (Issue 46 ) pp:17087
Publication Date(Web):2006-11-14
DOI:10.1073/pnas.0603633103
Co-reporter:Xuliang Dai;Matthew J. Byrnes;Peter Müller;Walter W. Weare;Jia Min Chin
PNAS 2006 Volume 103 (Issue 46 ) pp:17099-17106
Publication Date(Web):2006-11-14
DOI:10.1073/pnas.0602778103
Since our discovery of the catalytic reduction of dinitrogen to ammonia at a single molybdenum center, we have embarked on
a variety of studies designed to further understand this complex reaction cycle. These include studies of both individual
reaction steps and of ligand variations. An important step in the reaction sequence is exchange of ammonia for dinitrogen
in neutral molybdenum(III) compounds. We have found that this exchange reaction is first order in dinitrogen and relatively
fast (complete in <1 h) at 1 atm of dinitrogen. Variations of the terphenyl substituents in the triamidoamine ligand demonstrate
that the original ligand is not unique in its ability to yield successful catalysts. However, complexes that contain sterically
less demanding ligands fail to catalyze formation of ammonia from dinitrogen; it is proposed as a consequence of a base-catalyzed
decomposition of a diazenido (MoNNH) intermediate.
Co-reporter:Frédéric Blanc, Christophe Copéret, Jean Thivolle-Cazat, Jean-Marie Basset, Anne Lesage, Lyndon Emsley, Amritanshu Sinha,Richard R. Schrock
Angewandte Chemie International Edition 2006 45(8) pp:1216-1220
Publication Date(Web):
DOI:10.1002/anie.200503205
Co-reporter:Dmitry V. Yandulov
Science 2003 Vol 301(5629) pp:76-78
Publication Date(Web):04 Jul 2003
DOI:10.1126/science.1085326
Abstract
Dinitrogen (N2) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN3N]3– triamidoamine ligands {such as [HIPTN3N]Mo(N2), where [HIPTN3N]3– is [{3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2}3N]3–} in heptane. Slow addition of the proton source [{2,6-lutidinium}{BAr′4}, where Ar′ is 3,5-(CF3)2C6H3]and reductant (decamethyl chromocene) was critical for achieving high efficiency (∼66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.
Co-reporter:Richard R Schrock, Jennifer Y Jamieson, James P Araujo, Peter J Bonitatebus Jr., Amritanshu Sinha, L.Pia H Lopez
Journal of Organometallic Chemistry 2003 Volume 684(1–2) pp:56-67
Publication Date(Web):1 November 2003
DOI:10.1016/S0022-328X(03)00504-7
The reaction between K2[Biphen] ([Biphen]2−=3,3′-Di-t-butyl-5,5′,6,6′-tetramethyl-1,1′-Biphenyl-2,2′-diolate) and Mo(NArCl)(CH-t-Bu)(OTf)2(dme) (ArCl=2,6-Cl2C6H3) in the presence of ten equivalents of triethylamine gave Mo(NHArCl)(C-t-Bu)[Biphen] (4a) in 40–50% yield. Addition of K2[S-Biphen] to Mo(NArCl)(CHCMe2Ph)(OTf)2(THF) in THF led to the isolation of Mo(NHArCl)(CCMe2Ph)[S-Biphen] (4b) in ∼40% yield. An X-ray crystal study of 4b confirmed the proposed structure and also revealed that one ortho chloride approaches within 2.93 Å of the metal approximately trans to the alkylidyne ligand. Addition of one equivalent of H2[Biphen] to Mo(CCH2SiMe3)[N(i-Pr)Ar″)]3 (Ar″=3,5-dimethylphenyl) produced Mo(CCH2SiMe3)[Biphen][N(i-Pr)Ar″)] in situ, which when treated with one equivalent of 1-adamantanol gave a mixture of Mo(CCH2SiMe3)[Biphen](OAd) (9) and three equivalents of HN(i-Pr)Ar″, from which 9 could be isolated as a beige powder in 46% yield. An X-ray study of 9 confirmed that it is a pseudotetrahedral species in which the MoC bond length is 1.707(15) Å and the MoCC angle is 168.3(11)°. Addition of ten equivalents of 2-butyne or 3-hexyne to a pale yellow solution of 9 produced the molybdacyclobutadiene complexes Mo(C3R3)[Biphen](OAd) (R=Me or Et; 10a and 10b, respectively) in high yield. Both 10a and 10b decompose slowly in solution, even in the presence of added alkyne. An X-ray structure of the decomposition product of 10a revealed it to have the stoichiometry of 10a plus one additional equivalent of 2-butyne. The most unusual feature of the structure of this alkyne complex is a fusion of the C3Me3 portion of the metallacyclobutadiene ring to carbons in position 5 and 6 in the [Biphen]2− backbone to create a σ allyl linkage. These results suggest that Mo biphenolate alkylidyne complexes are not likely to be stable under conditions where alkynes are metathesized.The reaction between K2[Biphen] ([Biphen]2−=3,3′-Di-t-butyl-5,5′,6,6′-tetramethyl-1,1′-Biphenyl-2,2′-diolate) and Mo(NArCl)(CH-t-Bu)(OTf)2(dme) (ArCl=2,6-Cl2C6H3) in the presence of ten equivalents of triethylamine gave Mo(NHArCl)(C-t-Bu)[Biphen] (4a) in 40–50% yield.
Co-reporter:Richard R. Schrock Dr.;Amir H. Hoveyda Dr.
Angewandte Chemie International Edition 2003 Volume 42(Issue 38) pp:
Publication Date(Web):1 OCT 2003
DOI:10.1002/anie.200300576
Catalytic olefin metathesis has quickly emerged as one of the most often-used transformations in modern chemical synthesis. One class of catalysts that has led the way to this significant development are the high-oxidation-state alkylidene complexes of molybdenum. In this review key observations that resulted in the discovery and development of molybdenum- and tungsten-based metathesis catalysts are outlined. An account of the utility of molybdenum catalysts in the synthesis of biologically significant molecules is provided as well. Another focus of the review is the use of chiral molybdenum complexes for enantioselective synthesis. These highly efficient catalysts provide unique access to materials of exceptional enantiomeric purity and often without generating solvent waste.
Co-reporter:Richard R. Schrock Dr.;Amir H. Hoveyda Dr.
Angewandte Chemie International Edition 2003 Volume 42(Issue 38) pp:
Publication Date(Web):1 OCT 2003
DOI:10.1002/anie.200390586
Co-reporter:Richard R. Schrock Dr.;Amir H. Hoveyda Dr.
Angewandte Chemie 2003 Volume 115(Issue 38) pp:
Publication Date(Web):1 OCT 2003
DOI:10.1002/ange.200300576
Die katalytische Olefinmetathese hat sich schnell zu einer der am häufigsten eingesetzten Transformationen der modernen chemischen Synthese entwickelt. Ein Klasse von Katalysatoren, die den Weg zu dieser bedeutenden Entwicklung wiesen, sind die hochoxidierten Alkylidenkomplexe des Molybdäns. Dieser Aufsatz umreißt entscheidende Beobachtungen, die zur Entdeckung und Entwicklung von Molybdän- und Wolfram-Metathesekatalysatoren führten. Schwerpunktmäßig beschrieben wird der Einsatz von Molybdänkatalysatoren in der Synthese biologisch relevanter Verbindungen und die Verwendung von chiralen Molybdänkomplexen zur enantioselektiven Synthese. Derartige hocheffiziente Katalysatoren eröffnen einen einzigartigen Zugang zu Materialien von außergewöhnlicher Enantiomerenreinheit, häufig unter Vermeidung von Lösungsmittelabfällen.
Co-reporter:Richard R. Schrock Dr.;Amir H. Hoveyda Dr.
Angewandte Chemie 2003 Volume 115(Issue 38) pp:
Publication Date(Web):1 OCT 2003
DOI:10.1002/ange.200390613
Co-reporter:Kai C. Hultzsch Dr.;Jesper A. Jernelius;Amir H. Hoveyda
Angewandte Chemie 2002 Volume 114(Issue 4) pp:
Publication Date(Web):14 FEB 2002
DOI:10.1002/1521-3757(20020215)114:4<609::AID-ANGE609>3.0.CO;2-6
Deutlich weniger Verunreinigungen durch toxische Metalle als bei Verwendung nicht immobilisierter chiraler Komplexe fallen mit den ersten polymergebundenen chiralen Katalysatoren für die Olefinmetathese an. Diese ermöglichen die effiziente Synthese einer Reihe ungesättigter Carbo- und Heterocyclen in hoher Enantiomerenreinheit durch Ringöffnungs- (siehe Schema) und Ringschluss-Reaktionen.
Co-reporter:Kai C. Hultzsch Dr.;Jesper A. Jernelius;Amir H. Hoveyda
Angewandte Chemie International Edition 2002 Volume 41(Issue 4) pp:
Publication Date(Web):14 FEB 2002
DOI:10.1002/1521-3773(20020215)41:4<589::AID-ANIE589>3.0.CO;2-V
Substantially less toxic metal impurity than when unbound chiral complexes are used—this is achieved by the first polymer-supported chiral catalysts for olefin metathesis. These allow for efficient synthesis of various unsaturated carbo- and heterocycles in high optical purity through ring-opening (see scheme) and ring-closing reactions.
Co-reporter:R. R. Schrock
Advanced Synthesis & Catalysis 2001 Volume 343(Issue 1) pp:
Publication Date(Web):6 FEB 2001
DOI:10.1002/1615-4169(20010129)343:1<3::AID-ADSC3>3.0.CO;2-Q
Co-reporter:Amir H. Hoveyda
Chemistry - A European Journal 2001 Volume 7(Issue 5) pp:
Publication Date(Web):23 FEB 2001
DOI:10.1002/1521-3765(20010302)7:5<945::AID-CHEM945>3.0.CO;2-3
This paper provides a survey of the first examples of efficient catalytic enantioselective olefin metathesis reactions. Mo-catalyzed asymmetric ring-closing (ARCM) and ring-opening (AROM) reactions allow access to myriad optically enriched compounds that are otherwise difficult to access.
Co-reporter:Dr. Nadia C. Zanetti; Dr. Richard R. Schrock;Dr. William M. Davis
Angewandte Chemie 1995 Volume 107(Issue 18) pp:
Publication Date(Web):21 JAN 2006
DOI:10.1002/ange.19951071820
Co-reporter:Richard R. Schrock
Chemical Communications 2013 - vol. 49(Issue 49) pp:NaN5531-5531
Publication Date(Web):2013/05/03
DOI:10.1039/C3CC42609B
Alkyne metathesis by molybdenum and tungsten alkylidyne complexes is now ∼45 years old. Progress in the practical aspects of alkyne metathesis reactions with well-defined complexes, as well as applications, in the last decade, guarantees that it is destined to become a useful method for the synthesis of organic molecules.
Co-reporter:Travis J. Hebden, Richard R. Schrock, Michael K. Takase and Peter Müller
Chemical Communications 2012 - vol. 48(Issue 13) pp:NaN1853-1853
Publication Date(Web):2011/12/12
DOI:10.1039/C2CC17634C
(t-BuPOCOP)MoI2 (1; t-BuPOCOP = C6H3-1,3-[OP(t-Bu)2]2) has been synthesized from MoI3(THF)3. Upon reduction of 1 with Na/Hg under dinitrogen molecular nitrogen is cleaved to form [(t-BuPOCOP)Mo(I)(N)]−. The origin of the N atom was confirmed using 15N2. Protonation of [(t-BuPOCOP)Mo(I)(N)]− results in the formation of a neutral species in which it is proposed that the proton has added across the Mo–P bond.
Co-reporter:David Gajan, Nuria Rendón, Keith M. Wampler, Jean-Marie Basset, Christophe Copéret, Anne Lesage, Lyndon Emsley and Richard R. Schrock
Dalton Transactions 2010 - vol. 39(Issue 36) pp:NaN8551-8551
Publication Date(Web):2010/07/19
DOI:10.1039/C0DT00315H
Reaction of Li(3,5-R2-pyrazolide) (R = tBu or Ph, dXpz) with Mo(NAr)(CHCMe2Ph)(OTf)2(DME) yields Mo(NAr)(CHCMe2Ph)(dXpz)2 in good yield. These complexes react with alcohols or the surface silanols of silica, to yield bis-alkoxy and surface mono-siloxy alkene metathesis catalysts, respectively.
Co-reporter:Victor Polo, Richard R. Schrock and Luis A. Oro
Chemical Communications 2016 - vol. 52(Issue 96) pp:NaN13884-13884
Publication Date(Web):2016/11/08
DOI:10.1039/C6CC07875C
The positive effect of the addition of water to acetone hydrogenation by [RhH2(PR3)2S2]+ catalysts has been studied by DFT calculations. The studied energetic profiles reveal that the more favourable mechanistic path involves a hydride migration to the ketone followed by a reductive elimination that is assisted by two water molecules.
Co-reporter:Dmitry V. Peryshkov ; William P. Forrest ; Richard R. Schrock ; Stacey J. Smith ;Peter Müller
Organometallics () pp:
Publication Date(Web):September 23, 2013
DOI:10.1021/om4007906
We have found that coordination of B(C6F5)3 to an oxo ligand in tungsten oxo alkylidene bis(aryloxide) complexes, where the aryloxide is O-2,6-(mesityl)2C6H3 (HMTO) or 2,6-diadamantyl-4-methylphenoxide (dAdPO), accelerates the formation of metallacyclobutane complexes from alkylidenes as well as the rearrangement of metallacyclobutane complexes. In contrast, a tungstacyclopentane complex, W(O)(C4H8)(OHMT)2, is relatively stable toward rearrangement in the presence of B(C6F5)3. A careful balance of steric factors allows a single isomer of W(O)(trans-4,4-dimethylpent-2-ene)(dAdPO)2 to be formed from W(O)(CH-t-Bu)(dAdPO)2 in the presence of both ethylene and B(C6F5)3.
.jpg)
![(2R,3R)-bicyclo[2.2.1]hept-5-ene-2,3-diyldimethanol](http://img.cochemist.com/ccimg/79600/79516-58-8.png)
![(2R,3R)-bicyclo[2.2.1]hept-5-ene-2,3-diyldimethanol](http://img.cochemist.com/ccimg/79600/79516-58-8_b.png)
![BICYCLO[2.2.1]HEPT-5-ENE-2,3-DICARBOXYLIC ACID, (1R,2S,3S,4S)-](http://img.cochemist.com/ccimg/70200/70190-87-3.png)
![BICYCLO[2.2.1]HEPT-5-ENE-2,3-DICARBOXYLIC ACID, (1R,2S,3S,4S)-](http://img.cochemist.com/ccimg/70200/70190-87-3_b.png)
![Phenol, 3-[[bis(1,1-dimethylethyl)phosphino]methyl]-](http://img.cochemist.com/ccimg/646100/646069-73-0.png)
![Phenol, 3-[[bis(1,1-dimethylethyl)phosphino]methyl]-](http://img.cochemist.com/ccimg/646100/646069-73-0_b.png)
![[1,1':3',1''-Terphenyl]-2'-amine, 2,2'',4,4'',6,6''-hexamethyl-, lithium salt (1:1)](http://img.cochemist.com/data/images/450374-37-5.png)
![[1,1':3',1''-Terphenyl]-2'-amine, 2,2'',4,4'',6,6''-hexamethyl-, lithium salt (1:1)](http://img.cochemist.com/data/images/450374-37-5_b.png)
![Lithium, (2,2'',4,4'',6,6''-hexamethyl[1,1':3',1''-terphenyl]-2'-yl)-](http://img.cochemist.com/ccimg/164400/164356-88-1.png)
![Lithium, (2,2'',4,4'',6,6''-hexamethyl[1,1':3',1''-terphenyl]-2'-yl)-](http://img.cochemist.com/ccimg/164400/164356-88-1_b.png)
![Hexacosanamide,N-[(1S,2S,3R)-1-[(a-D-galactopyranosyloxy)methyl]-2,3-dihydroxyheptadecyl]-](http://img.cochemist.com/ccimg/158100/158021-47-7.png)
![Hexacosanamide,N-[(1S,2S,3R)-1-[(a-D-galactopyranosyloxy)methyl]-2,3-dihydroxyheptadecyl]-](http://img.cochemist.com/ccimg/158100/158021-47-7_b.png)
![Poly[[4,5-bis(methoxycarbonyl)-1,3-cyclopentanediyl]-1,2-ethenediyl]](http://img.cochemist.com/ccimg/82500/82441-77-8.png)
![Poly[[4,5-bis(methoxycarbonyl)-1,3-cyclopentanediyl]-1,2-ethenediyl]](http://img.cochemist.com/ccimg/82500/82441-77-8_b.png)
![BENZENE, 1,1'-[(2E)-2-BUTENE-1,4-DIYLBIS(OXYMETHYLENE)]BIS-](http://img.cochemist.com/ccimg/69000/68972-93-0.png)
![BENZENE, 1,1'-[(2E)-2-BUTENE-1,4-DIYLBIS(OXYMETHYLENE)]BIS-](http://img.cochemist.com/ccimg/69000/68972-93-0_b.png)
![Bicyclo[2.2.1]hepta-2,5-diene,7-(1-methylethylidene)-2,3-bis(trifluoromethyl)-](http://img.cochemist.com/ccimg/63800/63718-31-0.png)
![Bicyclo[2.2.1]hepta-2,5-diene,7-(1-methylethylidene)-2,3-bis(trifluoromethyl)-](http://img.cochemist.com/ccimg/63800/63718-31-0_b.png)
![Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, (1R,2R,3R,4S)-](http://img.cochemist.com/ccimg/32300/32216-02-7.png)
![Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, (1R,2R,3R,4S)-](http://img.cochemist.com/ccimg/32300/32216-02-7_b.png)
![Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylicacid, 2,3-diethyl ester, (1S,2S,3S,4R)-rel-](http://img.cochemist.com/ccimg/26300/26272-67-3.png)
![Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylicacid, 2,3-diethyl ester, (1S,2S,3S,4R)-rel-](http://img.cochemist.com/ccimg/26300/26272-67-3_b.png)
![[1,1'-Biphenyl]-2-amine, 2',4',6'-trimethyl-](http://img.cochemist.com/ccimg/25700/25627-20-7.png)
![[1,1'-Biphenyl]-2-amine, 2',4',6'-trimethyl-](http://img.cochemist.com/ccimg/25700/25627-20-7_b.png)
![dimethyl 1-methyl-7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate](http://img.cochemist.com/ccimg/18100/18064-04-5.png)
![dimethyl 1-methyl-7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate](http://img.cochemist.com/ccimg/18100/18064-04-5_b.png)
![(2S,3S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarbonitrile](http://img.cochemist.com/ccimg/6400/6343-16-4.png)
![(2S,3S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarbonitrile](http://img.cochemist.com/ccimg/6400/6343-16-4_b.png)
![[1,1':3',1''-Terphenyl]-2'-ol](http://img.cochemist.com/ccimg/2500/2432-11-3.png)
![[1,1':3',1''-Terphenyl]-2'-ol](http://img.cochemist.com/ccimg/2500/2432-11-3_b.png)
![[1,1':2',1''-Terphenyl]-3'-ol, 6'-bromo-4',5'-diphenyl-](http://img.cochemist.com/ccimg/2000/1974-42-1.png)
![[1,1':2',1''-Terphenyl]-3'-ol, 6'-bromo-4',5'-diphenyl-](http://img.cochemist.com/ccimg/2000/1974-42-1_b.png)
![Spiro[4.4]nona-1,3-diene](http://img.cochemist.com/ccimg/800/766-29-0.png)
![Spiro[4.4]nona-1,3-diene](http://img.cochemist.com/ccimg/800/766-29-0_b.png)
![POLY[(OCTAHYDRO-4,7-METHANO-1H-INDENE-1,3-DIYL)-1,2-ETHENEDIYL]](http://img.cochemist.com/ccimg/591300/591207-13-5.png)
![POLY[(OCTAHYDRO-4,7-METHANO-1H-INDENE-1,3-DIYL)-1,2-ETHENEDIYL]](http://img.cochemist.com/ccimg/591300/591207-13-5_b.png)
![Bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylic acid, 7-(1-methylethylidene)-, 2,3-dimethyl ester](/data/chemimg/1775400/19019-88-6.png)
![Bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylic acid, 7-(1-methylethylidene)-, 2,3-dimethyl ester](/data/chemimg/1775400/19019-88-6_b.png)
bis(2-methyl-2-propanolato)-,(T-4)-](http://img.cochemist.com/ccimg/127000/126949-65-3.png)
bis(2-methyl-2-propanolato)-,(T-4)-](http://img.cochemist.com/ccimg/127000/126949-65-3_b.png)
![1,2-DIMETHOXYETHANE;[2,6-DI(PROPAN-2-YL)PHENYL]IMINO-(2-METHYL-2-PHENYLPROPYLIDENE)MOLYBDENUM(2+);TRIFLUOROMETHANESULFONATE](http://img.cochemist.com/ccimg/127000/126949-63-1.png)
![1,2-DIMETHOXYETHANE;[2,6-DI(PROPAN-2-YL)PHENYL]IMINO-(2-METHYL-2-PHENYLPROPYLIDENE)MOLYBDENUM(2+);TRIFLUOROMETHANESULFONATE](http://img.cochemist.com/ccimg/127000/126949-63-1_b.png)
![Dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate](http://img.cochemist.com/ccimg/1000/947-57-9.png)
![Dimethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate](http://img.cochemist.com/ccimg/1000/947-57-9_b.png)