The iron-catalysed Suzuki coupling of aryl chlorides

A simple iron-based catalyst with an N-heterocyclic carbene ligand can be used to excellent effect in the previously unknown Suzuki biaryl coupling of aryl chloride substrates with aryl boronic esters activated by an organolithium reagent. Mechanistic studies suggest the possible involvement of Fe(I) as the lowest oxidation state on the catalytic manifold and show that the challenging step is not activation of the aryl chloride substrate, but rather the transmetallation step. These findings are likely to pave the way for a renaissance of iron-catalysed carbon-carbon bond-forming transformations with ‘soft’ nucleophilic coupling partners.