Mechanistic Insights into C-H Amination via Dicopper Nitrenes

We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable beta-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]Cu}(2)(mu-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]Cu}(2)(mu-(NBu)-Bu-t) (3) demonstrate that the terminal nitrene [Cl2NN]Cu=(NaBu)-Bu-t 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 [Cl2NN]Cu, both consistent with dissociation of a [Cl2NN]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)(mu-NCHRR') derived from 1 degrees and 2 degrees alkylazides are unstable toward tautomerization to copper(I) imine complexes [Cu](HN=CRR'), rendering 1 degrees and 2 degrees alkylnitrene complexes unsuitable for C-H amination.