Alkyl and alkylidene complexes of tantalum that contain a triethylsilyl-substituted triamido-amine ligand

Addition of Li-3[N3N*] ([N3Ni*](3-)=[N(CH(2)CH(2)NSiEt(3))(3)](3-)) to TaCl5 yields [N3N*]TaCl2, from which [N3N*]TaMe(2) is formed quantitatively upon adding 2 equiv of methylmagnesium chloride. Alkylation of [N3N*]TaCl2 with 2 equiv of ethylmagnesium chloride yields [N3N*]Ta(C2H4) along with similar to 10% [N3N*]Ta=CHMe, while dialkylation with Grignard or lithium reagents (alkyl=RCH(2)(-), in which R=CH2CH3, CH2CH2CH3, CH2CH(CH3)(2), SiMe(3), or Ph) yields the alkylidene complexes [N3N*]Ta=CHR. [N3N*]TaMe(2) decomposes upon thermolysis to afford MeTa[N(SiEt(3))(CH=CH2)][N(CH(2)CH(2)NSiEt(3))(2)] [N3N*]Ta(C2H4) decomposes in a first-order manner to afford EtTa[N(SiEt(3))(CH=CH2)][N(CH(2)CH(2)NSiEt(3))(2)]. An X-ray structure of the latter showed it to be a distorted trigonal bipyramid in which a C-N-ax bond in the original TREN backbone has been cleaved. An approximately equimolar mixture of [N3N*]Ta(C2H2) and {[N3N*]Ta=CHCH2}2 is formed upon treating [N3N*]TaCl2 with 2 equiv of vinylmagnesium bromide in refluxing toluene. An X-ray structure of {[N3N*]Ta=CHCH2}(2) showed it to contain two distorted trigonal bipyramidal [N3N*]Ta units bridged by a four carbon ''dialkylidene'' unit in which each alkylidene is severely distorted (average angle Tac-c=172 degrees).