Liu Yuan, Yu Zhunzhun, Luo Zhoujie, Zhang John Zenghui, Liu Lu, Xia Fei
Department of Physics and State Key Laboratory of Precision Spectroscopy, ‡School of Chemistry and Molecular Engineering, and §NYU-ECNU Center for Computational Chemistry at New York University Shanghai, East China Normal University , Shanghai 200062, China.
J Phys Chem A. 2016 Mar 24;120(11):1925-32. doi: 10.1021/acs.jpca.6b00636. Epub 2016 Mar 8.
It was recently reported that the gold-carbenes have an unprecedented catalysis toward the functionalization of C(sp(2))-H bonds of aromatic compounds. However, the associated mechanisms of C(sp(2))-H bonds inserted by gold-carbenes have not been comprehensively understood. We carried out a detailed mechanistic investigation of gold-carbene insertion into the C(sp(2))-H bond of anisole by means of theoretical calculations and control experiments. It significantly reveals that the aromatic C(sp(2))-H bond activation starts with the electrophilic addition of aromatic carbon toward the carbene carbon and subsequently followed the [1,3]-proton shift to form an enol intermediate. The rearrangement of enol proceeds through the mechanisms of proton transfer assisted by water molecules or enol intermediates, which are supported by our control experiments. It was also found that the C(sp(3))-H insertions of alkanes by gold-carbenes proceed through a concerted process via a three-centered transition state. The further comparison of different mechanisms provides a clear theoretical scheme to account for the difference in aromatic C(sp(2))-H and alkyl C(sp(3))-H bond activation, which is instructive for the further experimental functionalization of C-H bonds by gold-carbenes.
最近有报道称，金卡宾对芳香族化合物的C(sp(2))-H键官能团化具有前所未有的催化作用。然而，金卡宾插入C(sp(2))-H键的相关机制尚未得到全面理解。我们通过理论计算和对照实验，对金卡宾插入苯甲醚的C(sp(2))-H键进行了详细的机理研究。结果显著表明，芳香族C(sp(2))-H键的活化始于芳香族碳对卡宾碳的亲电加成，随后发生[1,3]-质子转移形成烯醇中间体。烯醇的重排通过水分子或烯醇中间体辅助的质子转移机制进行，这得到了我们对照实验的支持。还发现金卡宾对烷烃的C(sp(3))-H插入通过三中心过渡态的协同过程进行。对不同机制的进一步比较提供了一个清晰的理论方案，以解释芳香族C(sp(2))-H键和烷基C(sp(3))-H键活化的差异，这对金卡宾进一步实现C-H键的实验官能团化具有指导意义。
