C-H bond activation during and after the reactions of a metallacyclic amide with silanes: formation of a μ-alkylidene hydride complex, its H-D exchange, and β-H abstraction by a hydride ligand.

Metallacyclic complex [(Me2N)3Ta(η(2)-CH2SiMe2NSiMe3)] (3) undergoes C-H activation in its reaction with H3SiPh to afford a Ta/μ-alkylidene/hydride complex, [(Me2N)2{(Me3Si)2N}Ta(μ-H)2(μ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] (4). Deuterium-labeling studies with [D3]SiPh show H-D exchange between the Ta-D-Ta unit and all methyl groups in [(Me2N)2{(Me3Si)2N}Ta(μ-D)2(μ-C-η(2)-CHSiMe2NSiMe3)Ta(NMe2)2] ([D2]-4) to give the partially deuterated complex [Dn]-4. In addition, 4 undergoes β-H abstraction between a hydride and an NMe2 ligand and forms a new complex [(Me2N){(Me3 Si)2N}Ta(μ-H)(μ-N-η(2)-C,N-CH2NMe)(μ-C-η(2)-C,N-CHSiMe2NSiMe3)Ta(NMe2)2] (5) with a cyclometalated, η(2)-imine ligand. These results indicate that there are two simultaneous processes in [Dn]-4:1) H-D exchange through σ-bond metathesis, and 2) H-D elimination through β-H abstraction (to give [Dn]-5). Both 4 and 5 have been characterized by single-crystal X-ray diffraction studies.