The iron-catalysed Suzuki coupling of aryl chlorides

The very widely exploited Suzuki biaryl coupling reaction typically requires catalysts based on palladium, but there is an increasing desire to replace this metal with a more sustainable, less expensive alternative, with catalysts based on iron being a particularly attractive target. Here we show that a simple iron-based catalyst with an N-heterocyclic carbene ligand can be used to excellent effect in the 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 lead to a renaissance of iron-catalysed carbon-carbon bond-forming transformations with soft nucleophilic coupling partners. The replacement of palladium with other metal catalysts in C-C bond-forming reactions is attractive in terms of costs and sustainability. Now an iron-based catalyst is successfully employed in the Suzuki cross-coupling of aryl chlorides with aryl boronic esters activated with tert-butyl lithium.