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Mechanistic Insights into C–H Amination via Dicopper Nitrenes

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posted on 26.06.2013, 00:00 by Mae Joanne B. Aguila, Yosra M. Badiei, Timothy H. Warren
We examine important reactivity pathways relevant to stoichiometric and catalytic C–H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]­Cu}2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]­Cu}2(μ-NtBu) (3) demonstrate that the terminal nitrene [Cl2NN]­CuNtBu 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(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.