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.