The reactivity of an electronically unsaturated tantalum methylidene complex [TolC(NSiMe(3))(2)](2)Ta(CH(2))CH(3) supported by [TolC(NSiMe(3))(2)] amidinate ligands is described. Electrophilic addition and olefination reactions of the Ta=CH(2) functionality are reported. Alkylidene participates in group-transfer reactions not observed in sterically similar, but electronically saturated, analogues. Reactions with substrates containing unsaturated C-X (X = C, N, O) bonds yield [Ta]=X compounds and vinylated organic products; carbon-sulfur cleavage reactions to produce tantalum thioformaldehyde and tantalum sulfido complexes.