Imido Alkylidene Research Articles

Cationic Imido Alkylidene Complexes of Molybdenum Supported by β-Diketonate and β-Diketiminate Ligands

Reaction of Mo(NAr)(CHCMe2Ph)(OTf)2(DME) (Ar = 2,6-i-Pr2C6H3) with the lithium salt of various β-diketonates and β-diketiminates leads to complexes of the type Mo(NAr)(CHCMe2Ph)(L)(OTf) (L = β-diketonate or β-diketiminate). Treatment of these compounds with NaB[3,5-(CF3)2C6H3]4 in dichloromethane affords rare examples of cationic imido alkylidene complexes. The solid-state structures of two of these compounds, {Mo(NAr)(CHCMe2Ph)(TMHD)(THF)}{B[3,5-(CF3)2C6H3]4} and {Mo(NAr)(CHCMe2Ph)(ArCl-Nacnac)}{B[3,5-(CF3)2C6H3]4} (TMHD = tetramethylheptanedionato, ArCl-Nacnac = [2,6-Cl2C6H3NC(Me)]2CH), have been determined by X-ray diffraction, and their reactivity with ethylene and other simple olefins has been explored.

Dimers that Contain Unbridged W(IV)/W(IV) Double Bonds

Compounds that contain an unbridged WW bond can be prepared through bimolecular decomposition of various imido alkylidene complexes. One type of WW species is [W(NR)(CH2-t-Bu)(OR‘)]2 (R = 2,6-dimethylphenyl (Ar‘) or 2,6-diisopropylphenyl (Ar); R‘ = pentafluorophenyl or hexafluoroisopropyl), which is found in both heterochiral and homochiral forms. The other type is [W(NR)(OR‘)2]2 (R‘ = trifluoro-tert-butyl or hexafluoro-tert-butyl). All species contain an unbridged W(IV)/W(IV) double bond with a WW bond distance of 2.4−2.5 A, a 90° angle between the imido ligands and the WW bond, and an anti relationship of the imido ligands. There is no indication that WW bonds are broken spontaneously; for example, heterochiral and homochiral [W(NR)(CH2-t-Bu)(OR‘)]2 species do not interconvert.

Investigations of Reactions between Chiral Molybdenum Imido Alkylidene Complexes and Ethylene: Observation of Unsolvated Base-Free Methylene Complexes, Metalacyclobutane and Metalacyclopentane Complexes, and Molybdenum(IV) Olefin Complexes

In this paper we explore reactions between 13CH213CH2 and the imido alkylidene complexes, Mo(NAr)(CHCMe2Ph)[(S)-Biphen] (3a; NAr = N-2,6-i-Pr2C6H3), Mo(NArCl)(CHCMe3)[(S)-Biphen] (3b; NArCl = N-2,6-Cl2C6H3), Mo(NAd)(CHCMe2Ph)[(S)-Biphen] (3c; NAd = N-1-adamantyl), Mo(NAr)(CHCMe2Ph)[(R)-Benz2Bitet] (3d), and Mo(NArCl)(CHCMe2Ph)[(R)-Benz2Bitet] (3e). (See text for a description of Biphen and Benz2Bitet.) Under a variety of conditions and for various combinations of imido, alkylidene, and diolate ligands, we have observed α-substituted molybdacyclobutanes Mo(NR)(*CH2*CH2CHCMe2Ph)[diolate] (*C = 13C), unsubstituted molybdacyclobutanes Mo(NR)(*CH2*CH2*CH2)[diolate], olefin complexes Mo(NR)(*CH2CHR)[diolate] (R = H or CMe2Ph), molybdacyclopentane complexes Mo(NR)(*CH2*CH2*CH2*CH2)[diolate], and base-free methylene complexes Mo(NR)(*CH2)[diolate]. We also have crystallographically characterized a molybdenum ethylene complex derived from a biphenolate complex, Mo(N-2,6-Cl2C6H3)(CH2CH2)[rac-Biphen](Et2O).

Recent advances in olefin metathesis by molybdenum and tungsten imido alkylidene complexes

Abstract Recent advances in olefin metathesis studies include the preparation of catalysts “in situ,” supported catalysts, and tungsten-based catalysts, and observation of molybdacyclobutane complexes, molybdacyclopentane complexes, base-free methylene complexes, and ethylene complexes such as Mo(N-2,6-Cl2C6H3)(CH2CH2)[rac-Biphen](Et2O).

Molybdenum and Tungsten Imido Alkylidene Complexes as Efficient Olefin‐Metathesis Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Molybdenum and tungsten imido alkylidene complexes as efficient olefin-metathesis catalysts.

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.

Synthesis and reactivity of hydridotris(1-pyrazolyl)borate tungsten(VI) amido alkylidyne complexes

The synthesis of a series of tungsten(VI) amido alkylidyne complexes containing the chelating ligands Tp (hydridotris(1-pyrazolyl)borate) and Tp′ (hydridotris(3,5-dimethyl-1-pyrazolyl)borate) is described. Complexes of general formula, TpW(CC(CH 3) 3)(Cl)(NHR) [R=C 6H 5, 4-BrC 6H 4, 3,5-(CF 3) 2C 6H 3, H], ( 3– 6), were formed by reaction of TpW(CC(CH 3) 3)(Cl) 2 with the appropriate amide [M][NHR] (M=Li, K). In presence of excess [Li][NHPh], TpW(CC(CH 3) 3)(NHPh) 2 ( 7) was isolated. Sub-stoichiometric quantities of H 2O or HCl were found to catalyze the tautomerization of 3 to the corresponding imido alkylidene. Reaction of excess H 2O with 3 produced significant amounts of TpW(O)(CHC(CH 3) 3)(Cl) ( 10) and TpW(O)(CC(CH 3) 3)(Cl) ( 11) along with tautomerization. Attempted acid catalyzed tautomerizations of 4 and 5 with HCl resulted in loss of the amido ligands and recovery of TpW(CC(CH 3) 3)(Cl) 2. The complex Tp′W(CC(CH 3) 3)(Cl)(NHPh) ( 8), was synthesized by reaction of (CH 3) 3SiN(H)Ph with (DME)W(CC(CH 3) 3)(Cl) 3 followed by addition of KTp′. X-ray crystal structures have been obtained for compounds 7 and 8 and show that the amido groups are syn with respect to the neopentylidyne ligand probably due to the steric demands of the chelating Tp and Tp′ ligands.

Evaluation of Enantiomerically Pure Binaphthol-Based Molybdenum Catalysts for Asymmetric Olefin Metathesis Reactions that Contain 3,3‘-Diphenyl- or 3,3‘-Dimesityl-Substituted Binaphtholate Ligands. Generation and Decomposition of Unsubstituted Molybdacyclobutane Complexes

Enantiomerically pure molybdenum imido alkylidene complexes were prepared that contain binaphtholate ligands substituted in the 3 and 3‘ positions with either phenyl (4; Mo(NAr)(CHCMe2Ph)[Ph](THF)) or 2,4,6-trimethylphenyl groups (5; Mo(NAr)(CHCMe2Ph)[Mes](THF); Ar = 2,6-i-Pr2C6H3). Compound 5 was found to be an anti trigonal bipyramidal complex in an X-ray study. Asymmetric metatheses employing complex 5 were found to proceed to high conversion and to give high product % ee, while reactions that employed complex 4 were found to give lower conversion and lower % ee. One ring-closing reaction with 5 was shown to take place at a rate that was proportional to catalyst and substrate. Molybdacyclobutane complexes were observed in solution during ring-closing reactions. The molybdacyclobutane complex generated by treating 5 with ethylene was found to be a trigonal bipyramidal species which decomposed to yield some propylene; the metal-containing product or products of decomposition could not be identified. Moly...

Molybdenum Imido Alkylidene Complexes Containing Biphen Ligands that Have Silyl Groups Attached through the 6 and 6‘ Methyl Group Carbon Atoms

Two new biphenolate ligands were prepared starting from 3,3‘-di-tert-butyl-5,5‘,6,6‘-tetramethyl-2,2‘-dimethoxy-1,1‘-biphenyl via deprotonation of the 6 and 6‘ methyl group with KO-t-Bu/n-BuLi, reaction with dichlorodimethylsilane or chlorotrimethylsilane, and deprotection with boron tribromide. Molybdenum imido alkylidene complexes were prepared by treating Mo(NAr)(CHCMe2Ph)(OTf)2(DME) with the dipotassium salt of each biphenolate. X-ray crystallographic studies of syn-Mo(NAr)(CHCMe2Ph)[(rac)-Me2SiBiphen] and syn-Mo(NAr)(CHCMe2Ph)[(rac)-TMS2Biphen] revealed a significantly different geometry of the biphenolate ligands compared to previously structurally characterized four-coordinate biphenolate molybdenum imido alkylidene complexes. The enantiopure complexes were shown to catalyze asymmetric olefin metathesis with an enantioselectivity comparable to that of Mo(NAr)(CHCMe2Ph)[(S)-Biphen].

ChemInform Abstract: Olefin Metathesis by Molybdenum Imido Alkylidene Catalysts

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Olefin metathesis by molybdenum imido alkylidene catalysts

A “well-defined” alkylidene complex of the type Mo(CHCMe 2Ph)(N-2,6-i-Pr 2C 6H 3)[OCMe(CF 3) 2] 2 has proven to be a useful initiator in catalytic olefin metathesis reactions of interest to organic chemists. A variety of related molybdenum imido alkylidene complexes can be prepared readily from a common precursor. This article is a summary of what is known about the details of the steps in a metathesis reaction catalyzed by complexes of the type Mo(CHR′)(NAr)(OR) 2, and how the activity and stability of complexes of this type change upon altering each of the ligands in the pseudo-tetrahedral species. Some recent asymmetric ring-closing metathesis reactions are also discussed briefly.

Bent versus linear imido ligands in five-co-ordinate molybdenum complexes

A comparison of the molecular structures of the five-co-ordinate bis(imido) and imido alkylidene molybdenum complexes [Mo(NC6H3Pri2-2,6)(L)(L′)], where L is a tridentate pyridinediolato ligand and L′ is either NC6H3Pri2-2,6 or CHCMe2Ph, strongly supports the notion that the nitrogen of the bent imido ligand in the bis(imido) complex is sp2-hybridised.

Preparation of Biscarboxylato Imido Alkylidene Complexes of Molybdenum and Cyclopolymerization of Diethyldipropargylmalonate To Give a Polyene Containing only Six-Membered Rings

We wanted to prepare a catalyst that would yield polymers having exclusively one ring size and therefore began a search for new initiators containing `ancillary` ligands other than alkoxides. We report here that a new class of catalysts containing bulky carboxylate ligands can be prepared which encourage regioselective addition of the first triple bond to an alkylidene to give only a {beta}-subsituted metallacyclobutene and therefore polyenes that contain only six-membered rings in the polymer backbone as a consequence of specific head-to-tail cyclopolymerization. 14 refs., 1 fig., 2 tabs.

A Chelate-Stabilized Molybdenum–Imido–Alkylidene Complex, [TpMo{CHC(Me)2Ph}(NAr)(OTf)

The title compound, (2,6-diisopropylphenylimido)[hydrotris(1-pyrazolyl-N 3 )borato](2-methyl-2-phenylpropylidene) (trifluoromethanesulfonato) molybdenum(VI), [MO(CF 3 O 3 S)(C 10 H 12 )(C 12 H 17 N)(C 9 H 10 BN 6 )], has been synthesized and its crystal structure determined. The geometry around the Mo atom, imposed by the tridentate tris(pyrazolyl)borate ligand, is that of a distorted octahedron. There appears to be significant interaction between the ligands and the transition metal center. Principal distances include Mo-N(imido) 1.753(8), Mo-C(propylidene) 1.949(10), Mo-O(trifluoromethanesulfonate) 2.121(7) and Mo-N(pyrazolyl) 2.167 (8)2.311(9) A.

Synthesis and Reactivity of Tris(pyrazolyl)borate-Stabilized Molybdenum Imido Alkylidene Complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and Reactivity of Tris(pyrazolyl)borate-Stabilized Molybdenum Imido Alkylidene ComplexesWilliam M. Vaughan, Khalil A. Abboud, and James M. BoncellaCite this: Organometallics 1995, 14, 4, 1567–1577Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/om00004a009RIGHTS & PERMISSIONSArticle Views249Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Synthesis of a tris(pyrazolyl) borate-stabilized molybdenum alkylidene and its hydrolysis products. Crystal structures of TpMo(CH2C(Me)2Ph) (NAr)(O) and [TpMo(NAr)(O)]2O

The synthesis of a tris(pyrazolyl)borate-stabilized molybdenum (VI) imido alkylidene complex, TpMo(CHC(Me)2Ph)(NAr) (OTf) (1) [Ar= 2,6-i-Pr2-C6H3,Ph=C6H5,OTf=OSO2CF3], has been achieved by addition of potassium hydridotris(1-pyrazolyl)borate (KTp) to Mo(CHC(CH3)2Ph)(NAr)(OTf)2(DME). Stirring compound1 over alumina in the presence of H2O gave TpMo(CH2C(Me)2Ph)(NAr)(O) (2). Alternatively, compound1 was converted to2 by the addition of CsOH·H2O in THF. A single crystal of [TpMo(NAr)(O)]2O (4) was isolated from a solution of2. Compounds2 and4 have been characterized by X-ray crystallography and the bonding considerations about the molybdenum atoms are discussed.

Coupling of Terminal Olefins by Molybdenum(VI) Imido Alkylidene Complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCoupling of Terminal Olefins by Molybdenum(VI) Imido Alkylidene ComplexesHarold H. Fox, Richard R. Schrock, and Rick O'DellCite this: Organometallics 1994, 13, 2, 635–639Publication Date (Print):February 1, 1994Publication History Published online1 May 2002Published inissue 1 February 1994https://doi.org/10.1021/om00014a039RIGHTS & PERMISSIONSArticle Views377Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (677 KB) Get e-Alerts Get e-Alerts

Synthesis of stable tungsten(VI) imido alkylidene complexes: crystal structure of an air-stable cationic alkylidene complex

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of stable tungsten(VI) imido alkylidene complexes: crystal structure of an air-stable cationic alkylidene complexLaura L. Blosch, A. Scott Gamble, Khalil Abboud, and James M. BoncellaCite this: Organometallics 1992, 11, 7, 2342–2344Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/om00043a010RIGHTS & PERMISSIONSArticle Views172Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (408 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Further studies of imido alkylidene complexes of tungsten, well-characterized olefin metathesis catalysts with controllable activity [Erratum to document cited in CA113(17):152665k

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFurther studies of imido alkylidene complexes of tungsten, well-characterized olefin metathesis catalysts with controllable activity [Erratum to document cited in CA113(17):152665k]Richard R. Schrock, R. T. DePue, J. Feldman, K. B. Yap, D. C. Yang, W. M. Davis, L. Park, M. DiMare, M. Schofield, and Cite this: Organometallics 1990, 9, 10, 2850Publication Date (Print):October 1, 1990Publication History Published online1 May 2002Published inissue 1 October 1990https://doi.org/10.1021/om00160a040RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (80 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Synthesis of Molybdenum Imido Alkylidene Complexes and Some Reactions Involving Acyclic Olefins.

AbstractThe imido neopentylidene‐Mo complex (IV) is obtained as shown and converted into the olate derivatives (VI).