[N3N]Ta=PPh ([N3N](3-) = [(Me(3)SiNCH(2)CH(2))(3)N](3-)) reacts with excess lithium metal in tetrahydrofuran to give "[N3N]Ta=PLi", as judged by NMR studies and by reactions with RX at -35 degrees C to afford the phosphinidene complexes [N3N]Ta=PR (R = Me, n-Bu, SiMe(3), SiMe(2)Ph). [N3N]TaCl2 reacts with 2 equiv of LiN(H)R (R = H, CMe(3), Ph) to produce 1 equiv of RNH(2) and imido complexes [N3N]Ta=NR and with 2 equiv of benzylmagnesium chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N3N]Ta=CHR (R = Ph or SiMe(3)). The ethylene complex [N3N]Ta(C2H4) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride to [N3N]TaCl2. [N3N]Ta(C2H4) 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 [N3N]TaCl2 with 2 equiv of RCH(2)CH(2)MgX (R = CH3, CH2CH3, CH(CH3)(2), C(CH3)(3); X = Cl or Pr) 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 beta abstraction process. [N3N]TaCl2 reacts with 2 equiv of vinylmagnesium bromide to afford white crystalline [N3N]Ta(C2H2). An analogous benzyne complex can be prepared by refluxing [N3N]TaCl2 with 2 equiv of phenyllithium in toluene. [N3N]Ta(C2H4) reacts with a catalytic amount of phenylphosphine to afford [N3N]Ta=CHMe, while reactions with ammonia, aniline, or pentafluoroaniline yield [N3N]Ta=NR complexes. In contrast, excess Me(3)SiAsH(2) reacts with [N3N]Ta(C2H4) to afford [N3N]Ta=CHMe first, and then what is proposed to be [N3N]Ta=AsSiMe(3). [N3N]Ta(C2H4) reacts with dihydrogen to give [N3N]Ta(H)(C2H5) reversibly. [N3N]Ta(C6H4) reacts with ArNH2 (Ar = Ph, C6F5) to give [N3N]Ta=NAr complexes, but [N3N]Ta(C2H2) is relatively unreactive. X-ray structures of [N3N]Ta(Me)Et and [N3N]Ta(C2H2) are included.