Preparation and characterization of tantalum(III) olefin complexes and tantalum(V) metallacyclopentane complexes made from acyclic .alpha. olefins

McLain, Stephan J.; Wood, C. D.; Schrock, Richard R.

doi:10.1021/ja00510a022

Cited by 129 publications

(54 citation statements)

References 9 publications

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“…[86] It also was shown that the synthesis of drugs, such as tipranavir, an HIV protease inhibitor, could be shortened dramatically through the use of an asymmetric metathesis step to synthesize the problematic enantiomerically pure tertiary ether [Eq. (31)]. [87,88] These are but a few examples of what has been accomplished in the last several years.…”

Section: It Soon Became Clear That [W(nar)(ch-tbu)(or)mentioning

confidence: 99%

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

2006

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Its my great privilege to be here today, in a position I never thought possible. The story I will tell you I hope will give you some idea what I have contributed to the area for which the Nobel prize in chemistry was awarded this year.The story begins 32 years ago in 1973, the year the Nobel prize was shared by G. Wilkinson and E. O. Fischer. Wilkinsons Nobel lecture [1] concerned the nature of a single bond between a transition metal and a carbon atom in an alkyl group, and emphasized the fact that the metal-carbon bond is not inherently weak. E. O. Fischer in his Nobel Lecture [2] summarized the extensive chemistry of transitionmetal "carbene" complexes [3,4] that contain a metal-carbon double bond discovered by him and his group in 1964 (Scheme 1).[5] He also reported new "carbyne" complexes that contain a metal-carbon triple bond. [6] It was clear that metal-carbon single bonds were of great importance in the emerging area of homogeneous catalysis. However, no catalytic reactions involving species that contain metalcarbon double or triple bonds were known. When I went to the Central Research Department of E. I. DuPont de Nemours and Company in 1972, transition-metal organometallic chemistry and homogeneous catalysis were of great interest as a consequence of their huge potential in organic chemistry and therefore in industry.In the early 1970s inorganic chemists knew that many transition metal species containing a metal-carbon bond are subject to various modes of decomposition that are much more rapid than in a non-transition-metal species such as Zn(CH 2 CH 3 ) 2 or Al(CH 2 CH 3 ) 3 . The most common of these decomposition reactions involves transfer of a b hydrogen atom, from a metal-bound ethyl group (MÀCH 2 CH 3 ) for example, to the metal center (M) to yield a metal hydride and an alkene. The relative stabilities of high-oxidation-state "homoleptic" or "peralkyl" compounds such as [M{CH 2 Si-(CH 3 ) 3 } 4 ], [M(CH 2 C 6 H 5 ) 4 ], and [M{CH 2 C(CH 3 ) 3 } 4 ] (M = Ti, Zr, or Hf; Scheme 2), were rationalized on the basis of the fact that unlike a compound having an ethyl ligand, the alkyl ligands in these species lack b hydrogen atoms and so of course cannot undergo decomposition processes that involve b hydrogen atoms.[ 6 ] is stable at 22 8C. The methyl carbon is a with respect to the metal center; there is no b carbon atom and so no b hydrogens. However, methyl species are not

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Section: It Soon Became Clear That [W(nar)(ch-tbu)(or)mentioning

confidence: 99%

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

2006

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“…The 1 H NMR spectra of the mixed silylcyclopentadienyl niobium (2, 4, 7) and tantalum (8,9,13) complexes show an ABC spin system for the protons of the Cp ring, whereas the 13 C{ 1 H} NMR spectra show five resonances for the same group, in accordance with a C 1 symmetry. On the other hand, the 1 H NMR spectra of the bistrimethylsilylcyclopentadienyl niobium (3, 5, 6) and tantalum (10,11,12,14) complexes show an A 2 B spin system for the Cp ring protons and consistently, three ring carbon resonances appear in the 13 C{ 1 H} NMR spectra.…”

Section: Resultsmentioning

confidence: 95%

“…It is very well known that the overpopulation [4] of the coordination sphere of the metal is the basis for the formation of an alkylidene compound by a-hydrogen elimination and this process was observed in the reactions with trimethylsilylmethyl lithium in which dialkyl alkylidene complexes can be isolated with simultaneous elimination of tetramethylsilane [5]. Methyl monocyclopentadienyl complexes [MCp * Cl 4Àx Me x ] (Cp * = g 5 -C 5 Me 5 ; M = Nb [6], x = 2, 4; M = Ta, x = 1 [7], 2 [7], 3 [8], 4 [9]) were prepared by treatment of the corresponding tetrachloro derivatives with the appropriate amount of the alkylating reagent. On the other hand, the chemical behaviour of pseudooctahedral monocyclopentadienyl tantalum complexes containing anionic phosphorous ylide ligands [TaCp * Cl 3 (CH 2 ) 2 PRR 0 )] [10] (R = R 0 = Me, Ph; R = Me, R 0 = Ph) with alkylating reagents was studied [11] in order to isolate a trimethyl derivative [TaCp * Me 3 {(CH 2 ) 2 PPh 2 }] which pyrolysis takes place with evolution of methane and leads to the formation of a methylidyne complex [TaCp * Me 2 {(CH)(CH 2 )PPh 2 }].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of new chloro methyl niobium and tantalum complexes with silyl-cyclopentadienyl ligands: X-ray crystal structure of [Ta{η5-C5H3(SiMe3)2}Cl2Me2]

Gómez

Gómez‐Sal

Hernández

2007

Journal of Organometallic Chemistry

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“…First generation of 2a,b and then reduction to a transient Re(ethylene) 2 complex is suggested, which eventually converts into a metallacyclopentane structure with oxidative coupling of the two ethylene ligands. [10][11][12] Double β-hydride elimination and H 2 reductive elimination [2,13] is followed by the ethylene replacement of one phosphane ligand.…”

Section: Reactions Of [Re(ch 3 Cn)(no)(pr 3 ) 2 Br 2 ]mentioning

confidence: 99%