DFT study on Ir-quinoid catalyzed C–H functionalization: new radical reactivity or direct carbene transfer?

DFT methods are used to probe the mechanism of a newly developed Ir-quinoid catalyzed C(sp³)–H functionalization of 1,4 dienes. The lowest energy pathway proceeds via an old-school concerted C–H insertion as opposed to a unique hydrogen atom transfer process proposed previously. The concertedness of the reaction shows an intriguing dependence on sterics of the diene leading to either inserted or dehydrogenated products. We use these new insights to tune the axial ligand, and design a more efficient catalyst.