Synthetic and Mechanistic Investigations of Trimethylsilyl-Substituted Triamidoamine Complexes of Tantalum That Contain Metal−Ligand Multiple Bonds

Abstract

[N 3 N]Ta PPh ([N 3 N] 3 - = [(Me 3 SiNCH 2 CH 2 ) 3 N] 3 - ) reacts with excess lithium metal in tetrahydrofuran to give “[N 3 N]Ta PLi”, as judged by NMR studies and by reactions with RX at −35 °C to afford the phosphinidene complexes [N 3 N]Ta PR (R = Me, n -Bu, SiMe 3, SiMe 2 Ph). [N 3 N]TaCl 2 reacts with 2 equiv of LiN(H)R (R = H, CMe 3, Ph) to produce 1 equiv of RNH 2 and imido complexes [N 3 N]Ta NR and with 2 equiv of benzylmagnesium chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N 3 N]Ta CHR (R = Ph or SiMe 3 ). The ethylene complex [N 3 N]Ta(C 2 H 4 ) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride to [N 3 N]TaCl 2 . [N 3 N]Ta(C 2 H 4 ) 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 [N 3 N]TaCl 2 with 2 equiv of RCH 2 CH 2 MgX (R = CH 3, CH 2 CH 3, CH(CH 3 ) 2, C(CH 3 ) 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. [N 3 N]TaCl 2 reacts with 2 equiv of vinylmagnesium bromide to afford white crystalline [N 3 N]Ta(C 2 H 2 ). An analogous benzyne complex can be prepared by refluxing [N 3 N]TaCl 2 with 2 equiv of phenyllithium in toluene. [N 3 N]Ta(C 2 H 4 ) reacts with a catalytic amount of phenylphosphine to afford [N 3 N]Ta CHMe, while reactions with ammonia, aniline, or pentafluoroaniline yield [N 3 N]Ta NR complexes. In contrast, excess Me 3 SiAsH 2 reacts with [N 3 N]Ta(C 2 H 4 ) to afford [N 3 N]Ta CHMe first, and then what is proposed to be [N 3 N]Ta AsSiMe 3 . [N 3 N]Ta(C 2 H 4 ) reacts with dihydrogen to give [N 3 N]Ta(H)(C 2 H 5 ) reversibly. [N 3 N]Ta(C 6 H 4 ) reacts with ArNH 2 (Ar = Ph, C 6 F 5 ) to give [N 3 N]Ta NAr complexes, but [N 3 N]Ta(C 2 H 2 ) is relatively unreactive. X-ray structures of [N 3 N]Ta(Me)Et and [N 3 N]Ta(C 2 H 2 ) are included.