Cobalt-Catalyzed C(sp<sup>2</sup>)–C(sp<sup>3</sup>) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands
L. Reginald Mills, David Gygi, Jacob R. Ludwig, Eric M. Simmons, Steven R. Wisniewski, Junho Kim, Paul J. Chirik
Abstract
) 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.