Cobalt-Catalyzed C(sp2)–C(sp3) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands

Cobalt­(II) halides in combination with phenoxyimine (FI) ligands generated efficient precatalysts in situ for the C­(sp2)–C­(sp3) Suzuki–Miyaura cross-coupling between alkyl bromides and neopentylglycol (hetero)­arylboronic esters. The protocol enabled efficient C–C bond formation with a host of nucleophiles and electrophiles (36 examples, 34–95%) with precatalyst loadings of 5 mol %. Studies with alkyl halide electrophiles that function as radical clocks support the intermediacy of alkyl radicals during the course of the catalytic reaction. The improved performance of the FI–cobalt catalyst was correlated with decreased lifetimes of cage-escaped radicals as compared to those of diamine-type ligands. Studies of the phenoxyimine–cobalt coordination chemistry validate the L,X interaction leading to the discovery of an optimal, well-defined, air-stable mono-FI–cobalt­(II) precatalyst structure.