Alkyl and Alkylidene Complexes of Tantalum That Contain a Triethylsilyl-Substituted Triamido−Amine Ligand

Addition of Li 3 [N 3 N*] ([N 3 N*] 3 - = [N(CH 2 CH 2 NSiEt 3 ) 3 ] 3 - ) to TaCl 5 yields [N 3 N*]TaCl 2, from which [N 3 N*]TaMe 2 is formed quantitatively upon adding 2 equiv of methylmagnesium chloride. Alkylation of [N 3 N*]TaCl 2 with 2 equiv of ethylmagnesium chloride yields [N 3 N*]Ta(C 2 H 4 ) along with ∼10% [N 3 N*]Ta CHMe, while dialkylation with Grignard or lithium reagents (alkyl = RCH 2 -, in which R = CH 2 CH 3, CH 2 CH 2 CH 3, CH 2 CH(CH 3 ) 2, SiMe 3, or Ph) yields the alkylidene complexes [N 3 N*]Ta CHR. [N 3 N*]TaMe 2 decomposes upon thermolysis to afford MeTa[N(SiEt 3 )(CH CH 2 )][N(CH 2 CH 2 NSiEt 3 ) 2 ], while [N 3 N*]Ta(C 2 H 4 ) decomposes in a first-order manner to afford EtTa[N(SiEt 3 )(CH CH 2 )][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 [N 3 N*]Ta(C 2 H 2 ) and {[N 3 N*]Ta CHCH 2 } 2 is formed upon treating [N 3 N*]TaCl 2 with 2 equiv of vinylmagnesium bromide in refluxing toluene. An X-ray structure of {[N 3 N*]Ta CHCH 2 } 2 showed it to contain two distorted trigonal bipyramidal [N 3 N*]Ta units bridged by a four carbon “dialkylidene” unit in which each alkylidene is severely distorted (average ∠Ta−C−C = 172°).