Iridium-catalysed arylation of C–H bonds enabled by oxidatively induced reductive elimination

Direct arylation of C–H bonds is in principle a powerful way of preparing value-added molecules that contain carbon–aryl fragments. Unfortunately, currently available synthetic methods are not sufficiently effective to be practical alternatives to conventional cross-coupling reactions. We propose that the main problem lies in the late portion of the catalytic cycle where reductive elimination gives the desired carbon–aryl bond. Accordingly, we have developed a strategy where the Ir(III) centre of the key intermediate is first oxidized to Ir(IV). Density functional theory calculations indicate that the barrier to reductive elimination is reduced by nearly 19 kcal mol–1 for this oxidized complex compared with that of its Ir(III) counterpart. Various experiments confirm this prediction, affording a new methodology capable of directly arylating C–H bonds at room temperature with a broad substrate scope and in good yields. This work highlights how the oxidation states of intermediates can be targeted deliberately to catalyse an otherwise impossible reaction. The direct arylation of C–H bonds is an attractive synthetic step, but the reductive elimination of an organometallic catalyst carrying the desired C–H and aryl functionalities has remained challenging. Now, this step has been achieved by first oxidizing the iridium centre of the catalyst, which facilitates the arylation of arene C–H bonds of a range of substrates.