Nickel in Photocatalysis

Robust methods to forge C-C bonds selectively are treasured by the chemical community because of the inherent value of such processes in the convergent construction of complex molecules and the notorious challenges associated with creating such linkages. The advent of cross-coupling technologies (e.g., Suzuki, Negishi, and Heck processes) has revolutionized how synthetic chemists establish C(sp2)-C(sp2) bonds. However, the mechanistic features that make these transition-metal-catalyzed processes ideal for this type of transformation are the same ones that limit their abilities to involve C(sp3)-hybridized species. In this chapter, a recently developed solution to the underlying challenge of engaging C(sp3)-hybridized nucleophiles in cross coupling is outlined: nickel/photoredox dual catalysis. By proceeding through radical intermediates, the enthalpic penalty for two-electron transmetalation can be side-stepped, and cross coupling can proceed under mild, functional-group-tolerant conditions. Several variants of this dual catalytic process are presented which, taken together, demonstrate the breadth and scope of this new cross-coupling paradigm.