Synthetic and mechanistic investigations of trimethylsilyl-substituted triamidoamine complexes of tantalum that contain metal-ligand multiple bonds

Joel S. Freundlich, Richard R. Schrock, William M. Davis

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123 Scopus citations

Abstract

[N3N]Ta=PPh ([N3N]3- = [(Me3SiNCH2CH2)3N]3-) reacts with excess lithium metal in tetrahydrofuran to give '[N3N]Ta=PLi', as judged by NMR studies and by reactions with RX at -35°C to afford the phosphinidene complexes [N3N]Ta=PR (R = Me, n-Bu, SiMe3, SiMe2Ph). [N3N]TaCl2 reacts with 2 equiv of LiN(H)R (R = H, CMe3, Ph) to produce 1 equiv of RNH2 and imido complexes [N3N]Ta=NR and with 2 equiv of benzylmagnesium chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N3N]Ta=CHR (R = Ph or SiMe3). The ethylene complex [N3N]Ta(C2H4) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride to [N3N]TaCl2. [N3N]Ta(C2H4) decomposes in a first-order manner in solution over a period of days at room temperature to give a complex in which a C-N bond in the TREN backbone has been cleaved. Alkylation of [N3N]TaCl2 with 2 equiv of RCH2CH2MgX (R = CH3, CH2CH3, CH(CH3)2, C(CH3)3; X = Cl or Br) produces a mixture of alkylidene and products derived from decomposition of the incipient olefin complex. When R = t-Bu, only an alkylidene complex is formed as a consequence of a sterically disfavored β abstraction process. [N3N]TaCl2 reacts with 2 equiv of vinylmagnesium bromide to afford white crystalline [N3N]Ta(C2H2). An analogous benzyne complex can be prepared by refluxing [N3N]TaCl2 with 2 equiv of phenyllithium in toluene. [N3N]Ta(C2H4) reacts with a catalytic amount of phenylphosphine to afford [N3N]Ta=CHMe, while reactions with ammonia, aniline, or pentafluoroaniline yield [N3N]Ta=NR complexes. In contrast, excess Me3SiAsH2 reacts with [N3N]Ta(C2H4) to afford [N3N]Ta=CHMe first, and then what is proposed to be [N3N]Ta=AsSiMe3. [N3N]Ta(C2H4) reacts with dihydrogen to give [N3N]Ta(H)(C2H5) reversibly. [N3N]Ta(C6H4) reacts with ArNH2 (Ar = Ph, C6F5) to give [N3N]Ta=NAr complexes, but [N3N]Ta(C2H2) is relatively unreactive. X-ray structures of [N3N]Ta(Me)Et and [N3N]Ta(C2H2) are included.

Original languageEnglish (US)
Pages (from-to)3643-3655
Number of pages13
JournalJournal of the American Chemical Society
Volume118
Issue number15
DOIs
StatePublished - Apr 17 1996
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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