Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States.
J Am Chem Soc. 2018 Sep 26;140(38):12056-12068. doi: 10.1021/jacs.8b06458. Epub 2018 Sep 18.
Cobalt/nickel-dual catalyzed hydroarylation of terminal olefins with iodoarenes builds complexity from readily available starting materials, with a high preference for the Markovnikov (branched) product. Here, we advance a mechanistic model of this reaction through the use of reaction progress kinetic analysis (RPKA), radical clock experiments, and stoichiometric studies. Through exclusion of competing hypotheses, we conclude that the reaction proceeds through an unprecedented alkylcobalt to nickel direct transmetalation. Demonstration of catalytic alkene prefunctionalization, via spectroscopic observation of an organocobalt species, distinguishes this Csp-Csp cross-coupling method from a conventional transmetalation process, which employs a stoichiometric organometallic nucleophile, and from a bimetallic oxidative addition of an organohalide across nickel, described by radical scission and subsequent alkyl radical capture at a second nickel center. A refined understanding of the reaction leads to an optimized hydroarylation procedure that excludes exogenous oxidant, demonstrating that the transmetalation is net redox neutral. Catalytic alkene prefunctionalization by cobalt and engagement with nickel catalytic cycles through direct transmetalation provides a new platform to merge these two rich areas of chemistry in preparatively useful ways.
钴/镍双催化末端烯烃与碘芳烃的氢芳基化反应从易得的起始原料构建复杂结构，对 Markovnikov（支链）产物具有高选择性。在这里，我们通过使用反应进度动力学分析（RPKA）、自由基时钟实验和计量研究来推进该反应的机理模型。通过排除竞争假说，我们得出结论，该反应通过前所未有的烷基钴到镍的直接转金属化进行。通过观察到有机钴物种的光谱，证明了催化烯烃预官能化，这将这种 Csp-Csp 交叉偶联方法与传统的转金属化过程区分开来，后者使用的是化学计量的有机金属亲核试剂，以及通过自由基断裂和随后在第二个镍中心捕获烷基自由基在镍上进行的双金属氧化加成反应。对反应的深入理解导致优化的氢芳基化程序排除了外源氧化剂，证明转金属化是净氧化还原中性的。钴的催化烯烃预官能化作用以及通过直接转金属化与镍催化循环的结合，为以实用方式融合这两个丰富的化学领域提供了一个新的平台。
