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 quantita tively upon adding 2 equiv of methylmagnesium chloride. Alkylation of [N3N]TaCl2 with 2 equiv of ethylmagnesium chloride yields [N3N*]Ta(C2 H4) along with similar to 10% [N3N]Ta=CHMe, while dialkylation with G rignard or lithium reagents (alkyl=RCH(2)(-), in which R=CH2CH3, CH2CH 2CH3, 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) decompose s in a first-order manner to afford tTa[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 di storted 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 w ith 2 equiv of vinylmagnesium bromide in refluxing toluene. An X-ray s tructure of {[N3N]Ta=CHCH2}(2) showed it to contain two distorted tri gonal bipyramidal [N3N]Ta units bridged by a four carbon ''dialkylide ne'' unit in which each alkylidene is severely distorted (average angl e Tac-c=172 degrees).