Iron-Catalyzed C-H Borylation of Arenes

Well-defined iron bis(diphosphine) complexes are active catalysts for the dehydrogenative CH borylation of aromatic and heteroaromatic derivatives with pinacolborane. The corresponding borylated compounds were isolated in moderate to good yields (25-73%) with a 5 mol% catalyst loading under UV irradiation (350 nm) at room temperature. Stoichiometric reactivity studies and isolation of an original trans-hydrido(boryl)iron complex, Fe(H)(Bpin)(dmpe)(2), allowed us to propose a mechanism showing the role of some key catalytic species.