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

Cobalt(II) halides in combination with phenoxy-imine (FI) ligands generated efficient precatalysts for the C(sp)-C(sp) 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 diamine-type ligands. Studies of the phenoxy(imine)-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.