Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
J Am Chem Soc. 2021 Oct 13;143(40):16663-16672. doi: 10.1021/jacs.1c07613. Epub 2021 Sep 29.
This paper describes a detailed mechanistic study of the silver-catalyzed Z-selective hydroalkylation of terminal alkynes. Considering the established mechanistic paradigms for -selective hydroalkylation of alkynes, we explored a mechanism based on the radical carbometalation of alkynes. Experimental results have provided strong evidence against the initially proposed radical mechanism and have led us to propose a new mechanism for the -selective hydroalkylation of alkynes based on boronate formation and a 1,2-metalate shift. The new mechanism provides a rationale for the excellent Z-selectivity observed in the reaction. A series of stoichiometric experiments has probed the feasibility of the proposed elementary steps and revealed an additional role of the silver catalyst in the protodeboration of an intermediate. Finally, a series of kinetic measurements, KIE experiments, and competition experiments allowed us to identify the turnover limiting step and the resting state of the catalyst. We believe that the results of this study will be useful in the further exploration and development of related transformations of alkynes.
本文对银催化的末端炔烃 Z-选择性氢烷基化反应进行了详细的机理研究。鉴于炔烃的 -选择性氢烷基化反应的既定机理范例，我们探索了一种基于炔烃自由基碳金属化的机理。实验结果有力地否定了最初提出的自由基机理，并促使我们提出了一种新的基于硼酸酯形成和 1,2-金属迁移的炔烃 -选择性氢烷基化反应机理。新的机理为反应中观察到的优异 Z-选择性提供了依据。一系列的计量实验探究了所提出的基元步骤的可行性，并揭示了银催化剂在中间体的脱硼作用中的额外作用。最后，一系列的动力学测量、KIE 实验和竞争实验使我们能够确定周转限制步骤和催化剂的静止状态。我们相信，这项研究的结果将有助于进一步探索和开发相关的炔烃转化反应。
