Department of Chemistry, Georgetown University, Box 571227-1227, Washington, DC 20057, United States.
J Am Chem Soc. 2013 Jun 26;135(25):9399-406. doi: 10.1021/ja400879m. Epub 2013 Jun 13.
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-N(t)Bu) (3) demonstrate that the terminal nitrene [Cl2NN]Cu═N(t)Bu 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, rendering 1° and 2° alkylnitrene complexes unsuitable for C-H amination.
我们通过可分离的β-二酮亚胺二铜烷基氮烯中间体{[Cl2NN]Cu}2(μ-NR)来研究与化学计量和催化 C-H 胺化有关的重要反应途径。涉及{[Cl2NN]Cu}2(μ-N(t)Bu)（3）对乙基苯的化学计量胺化的动力学研究表明，末端氮烯[Cl2NN]Cu═N(t)Bu 是 C-H 胺化中的活性中间体。初始速率在高乙基苯负载下表现出饱和行为，并且对铜物种[Cl2NN]Cu 呈逆依赖性，这两者都与 3 中[Cl2NN]Cu 片段在 C-H 胺化之前解离一致。使用 1,4-二甲基环己烷和苄基自由基时钟底物进行的 C-H 胺化实验支持逐步 H 原子攫取/自由基回弹途径。由 1°和 2°烷基叠氮化物衍生的二铜氮烯[Cu]2(μ-NCHRR')对互变异构为铜（I）亚胺配合物Cu不稳定，使得 1°和 2°烷基氮烯配合物不适合 C-H 胺化。
