C−H Bond Activation of Benzene by Unsaturated η2-Cyclopropene and η2-Benzyne Complexes of Niobium

We report the synthesis of a niobium cyclopropyl complex, TpMe2NbMe(c-C3H5)(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C−H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η2-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C−H activation chemistry of this type represents a rather unusual reactivity pattern for η2-alkene complexes but is favored in this case by the strain in the C3 ring which prevents the decomposition of the key intermediate via loss of cyclopropene.

本报告阐述了钽基环丙基复合物TpMe2NbMe(c-C3H5)(MeCCMe)的合成过程，并揭示了该化合物中甲烷的热解释放能够产生一种中间体，该中间体具有激活脂肪族和芳香族C-H键的能力。同位素标记、捕获实验、详细的动力学分析和密度泛函理论研究表明，该活性中间体是通过β-氢原子提取形成的一种η2-环丙烯复合物，而非同分异构的环丙基亚甲基物种。此类C-H激活化学在η2-烯烃复合物中呈现出较为罕见的反应模式，但在此例中，由于C3环上的张力阻碍了关键中间体的分解，因此该反应模式得到了青睐。