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 [Dn]‐4. In addition, 4 undergoes β‐H ion 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 [Dn]‐4: 1) H–D exchange through σ‐bond metathesis, and 2) HD elimination through β‐H ion (to give [Dn]‐5). Both 4 and 5 have been characterized by single‐crystal X‐ray diffraction studies. A tantalum metallacyclic complex undergoes intramolecular CH activation upon reaction with H3SiPh to give a Ta/μ‐alkylidene/hydride complex, which then undergoes β‐H ion to form a complex with a bridging tantalaaziridine ligand (see scheme).