Well-Defined Nickel Precatalysts: Form, Function, and Application.

Modern synthetic methods for the synthesis of pharmaceuticals, fine chemicals, and agrochemicals have been revolutionized by the advent of cross-coupling chemistry. Well-defined palladium precatalysts have often been the mainstay for such reactions; however, more investigators are increasingly turning to Earth-abundant metals (EAMs), in particular nickel precatalysts. Nickel precatalysts have shown to allow for a broad substrate scope, they provide active species in variable oxidation states and demonstrate reactions that often proceed by unique mechanisms. This review will provide guidance on which nickel precatalysts to choose for a given application or which properties to prioritize in reaction development. Discussion points will cover the ease of synthesis, stability, diversity, accessibility, modularity, and general applicability.