Mechanistic Insights into C-H Amination via Dicopper Nitrenes

摘要

We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl_2NN]Cu}_2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl_2NN]Cu}_2(μ-N~tBu) (3) demonstrate that the terminal nitrene [Cl_2NN]Cu=N~tBu is the active intermediate in C-H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [G_2NN]Cu, both consistent with dissociation of a [Cl_2NN]Cu fragment from 3 prior to C-H amination. C-H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]_2(μ-NCHRR') derived from 1° and 2° alkylazides are unstable toward tautomerization to copper(I) imine complexes [Cu](HN=CRR'), rendering 1° and 2° alkylnitrene complexes unsuitable for C-H amination.