Dinuclear Magnesium-Catalyzed Hydroboration: Unveiling Metal-Ligand Cooperative Activation of Polar Unsaturated Bonds

Metal-ligand cooperation (MLC) has emerged as a cornerstone strategy for catalytic small molecule activation across both synthetic and biological chemistry. While MLC has driven significant progress in catalytic hydroboration, most known systems rely on MLC-mediated activation of the H-B bond to generate metal hydride intermediates. In contrast, catalytic hydroboration via direct MLC activation of polar unsaturated bonds remains largely unexplored, despite its potential for expanding substrate scope and achieving novel selectivity. Here, we report a dinuclear magnesium complex [Mg]-1, supported by dianionic ligands capable of dearomatization-rearomatization MLC at each metal center. This complex exhibits unconventional MLC behavior, preferentially activating ketones over HBpin to form a magnesium-ketone adduct [Mg]-2. This selectivity diverges from that of analogous Ruthenium(II) complexes bearing the same ligand framework, which preferentially activate HBpin over ketones to yield ruthenium hydride species. These findings underscore the distinctive MLC reactivity of main-group metal systems compared to transition metal analogues. Kinetic studies and DFT calculations reveal that the rate-determining step involves hydride transfer from HBpin to the ketone within the magnesium-ketone adduct, enabled by synergistic activation across both Mg centers. The catalyst demonstrates broad utility, enabling the hydroboration of over 70 polar unsaturated substrates, including challenging classes such as nitro compounds. Notably, it also mediates selective 1,4-hydroboration of quinoline derivatives, a transformation rarely achieved with main-group catalysts.