Catalytic acceptorless dehydrogenative borylation of styrenes enabled by a molecularly defined manganese complex

In this study, we employed a 3d metal complex as a catalyst to synthesize alkenyl boronate esters through the dehydrogenative coupling of styrenes and pinacolborane. The process generates hydrogen gas as the sole byproduct without requiring an acceptor, rendering it environmentally friendly and atom-efficient. This methodology demonstrated exceptional selectivity for dehydrogenative borylation over direct hydroboration. Additionally, it exhibited a preference for borylating aromatic alkenes over aliphatic ones. Notably, derivatives of natural products and bioactive molecules successfully underwent diversification using this approach. The alkenyl boronate esters served as precursors for the synthesis of various pharmaceuticals and potential anticancer agents. Our research involved comprehensive experimental and computational studies to elucidate the reaction pathway, highlighting the B-H bond cleavage as the rate-determining step. The catalyst's success was attributed to the hemilability and metal-ligand bifunctionality of the ligand backbone. A highly chemo- and regioselective acceptorless dehydrogenative borylation of alkenes is reported employing a molecularly defined Mn(i)-complex as a catalyst with a detailed study of different mechanistic parameters.