Alkyl and Alkylidene Tantalum−Lithium Complexes Supported by an Anionic Triazacyclononane Ligand

A new iPr2-tacn--supported alkyl tantalum species, (Me3SiCH2)2(RN)Ta(μ-CH2SiMe3)(μ-η1:η3-iPr2-tacn)Li (R = 2,6-iPr2C6H3; 2), was synthesized and found to undergo α-H abstraction under gentle heating to form the alkylidene (Me3SiCH2)(RN)Ta(μ-CHSiMe3)(μ-η1:η3-iPr2-tacn)Li (3). The syntheses and crystal structures of 2 and 3 and their precursor ((iPr2-tacn)TaCl2(NR) (1)) are described, as well as kinetic data for the first-order thermolysis reaction producing 3.