Au^I‑Catalyzed Hydroalkynylation of Haloalkynes

The AuI-catalyzed reaction between terminal alkynes and aromatic haloalkynes proceeds through divergent pathways depending on the nature of the catalyst counteranion. Thus, cationic complexes containing strongly basic NHC ligands and noncoordinating anions such as BArF4 catalyze the cis haloalkynylation of the terminal alkyne, whereas introduction of a weakly basic triflate counteranion results in the stereoselective hydroalkynylation of the haloalkyne, yielding haloenyne products in good yields and complete trans selectivity. Experimental and computational studies suggest that the hydroalkynylation reaction takes place via nucleophilic attack of the terminal alkyne to the C2 carbon of the activated haloalkyne, assisted by a concerted proton abstraction by the triflate, and that the protodeauration is the turnover-limiting step, in agreement with an observed primary kinetic isotope effect.一价金（Au(I)）催化的端炔与芳香卤代炔烃之间的反应，其反应路径会因催化剂抗衡阴离子的性质不同而出现分化。具体而言，搭载强碱性氮杂环卡宾（N-Heterocyclic Carbene, NHC）配体与非配位阴离子（如BArF4）的阳离子配合物，可催化端炔的顺式卤代炔基化反应；而当引入弱碱性三氟甲磺酸根（triflate）抗衡阴离子后，则可实现卤代炔烃的立体选择性氢炔基化反应，以良好收率得到具有完全反式选择性的卤代烯炔产物。实验与计算研究显示，该氢炔基化反应通过端炔对活化态卤代炔烃的C2位发生亲核进攻完成，此过程由三氟甲磺酸根协同夺取质子辅助完成；其中脱金质子化反应（protodeauration）为反应的决速步，这与观测到的一级动力学同位素效应（primary kinetic isotope effect）结果一致。