Addition of Li3[N3N*] ([N3N*]3- = [N(CH2CH2NSiEt3)3]3-) to TaCl5 yields [N3N*]TaCl2, from which [N3N*]TaMe2 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 ∼10% [N3N*]TaCHMe, while dialkylation with Grignard or lithium reagents (alkyl = RCH2-, in which R = CH2CH3, CH2CH2CH3, CH2CH(CH3)2, SiMe3, or Ph) yields the alkylidene complexes [N3N*]TaCHR. [N3N*]TaMe2 decomposes upon thermolysis to afford MeTa[N(SiEt3)(CHCH2)][N(CH2CH2NSiEt3)2], while [N3N*]Ta(C2H4) decomposes in a first-order manner to afford EtTa[N(SiEt3)(CHCH2)][N(CH2CH2NSiEt3)2]. An X-ray structure of the latter showed it to be a distorted trigonal bipyramid in which a C−Nax bond in the original TREN backbone has been cleaved. An approximately equimolar mixture of [N3N*]Ta(C2H2) and {[N3N*]TaCHCH2}2 is formed upon treating [N3N*]TaCl2 with 2 equiv of vinylmagnesium bromide in refluxing toluene. An X-ray structure of {[N3N*]TaCHCH2}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 ∠Ta−C−C = 172°).