Manganese-Catalyzed C(sp2)-H Borylation of Furan and Thiophene Derivatives

Aryl boronic esters are bench-stable, platform building-blocks that can be accessed through metal-catalyzed aryl C(sp(2))-H borylation reactions. C(sp(2))-H bond functionalization reactions using rare- and precious-metal catalysts are well established, and while examples utilizing Earth-abundant alternatives have emerged, manganese catalysis remains lacking. The manganese-catalyzed C-H borylation of furan and thiophene derivatives is reported alongside an in situ activation method providing facile access to the active manganese hydride species. Mechanistic investigations showed that blue light irradiation directly affected catalysis by action at the metal center, that C(sp(2))-H bond borylation occurs through a C-H metallation pathway, and that the reversible coordination of pinacolborane to the catalyst gave a manganese borohydride complex, which was as an off-cycle resting state.