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(η²‐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‐η²‐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‐η²‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] (D₂]‐ 4 ) to give the partially deuterated complex D_n]‐ 4 . In addition, 4 undergoes β‐H abstraction between a hydride and an NMe₂ ligand and forms a new complex (Me₂N){(Me₃Si)₂N}Ta(μ‐H)(μ‐N‐η²‐C,N‐CH₂NMe)(μ‐C‐η²‐C,N‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ( 5 ) with a cyclometalated, η²‐imine ligand. These results indicate that there are two simultaneous processes in D_n]‐ 4 : 1) H–D exchange through σ‐bond metathesis, and 2) H?D elimination through β‐H abstraction (to give D_n]‐ 5 ). Both 4 and 5 have been characterized by single‐crystal X‐ray diffraction studies.