Isolation, Structure, and Reactivity of an Arylnickel(II) Pivalate Complex in Catalytic C–H/C–O Biaryl Coupling

We describe mechanistic studies of a C–H/C–O biaryl coupling of 1,3-azoles and aryl pivalates catalyzed by Ni­(cod)2/dcype. This study not only supports a catalytic cycle consisting of C–O oxidative addition, C–H nickelation, and reductive elimination but also provides insight into the dramatic ligand effect in C–H/C–O coupling. We have achieved the first synthesis, isolation and structure elucidation of an arylnickel­(II) pivalate, which is an intermediate in the catalytic cycle after oxidative addition of a C–O bond. Furthermore, kinetic studies and kinetic isotope effect investigations reveal that the C–H nickelation is the turnover-limiting step in the catalytic cycle.本研究针对Ni(cod)2/dcype催化的1,3-唑类与芳基新戊酸酯的C-H/C-O联芳基偶联（C–H/C–O biaryl coupling）反应开展机理研究。本研究不仅证实了包含C-O氧化加成（C–O oxidative addition）、C-H镍化（C–H nickelation）与还原消除（reductive elimination）的催化循环路径，还阐明了配体在该偶联反应中的显著调控效应。我们首次实现了催化循环中C-O键氧化加成步骤后生成的芳基镍(II)新戊酸酯（arylnickel(II) pivalate）中间体的合成、分离与结构解析。此外，动力学研究与动力学同位素效应（kinetic isotope effect）实验证实，C-H镍化步骤为该催化循环的限速步骤（turnover-limiting step）。