Triazole backbone ligand in an unprecedented efficient manganese catalyst for use in transfer hydrogenation

Noble metal catalysts are generally expensive,and thus,abundant 3d metals recently received significant attention as catalysts in catalytic hydrogenation.Mn catalysts are widely applied in transfer hydrogenations,but the reported catalyst loadings remain up to three orders of magnitude higher than noble metals.Thus,catalyst consumption should be overcome before 3d metal catalytic systems may be utilized practically in industry.Here,a catalytic system based on novel,scalable triazole N5-ligands coordinated to Mn is presented for use in transfer hydrogenations.Based on pre-activation via dehydrohalogenation,an unprecedented,efficient catalytic system operating via synergistic H-bond auxiliary activation was established.The Mn catalysts are practical at metal concentrations 0.0001 mol%,generating alcohol with turnover number(TON)up to 857,200,thus approaching loadings more conventionally observed in precious-metal-based systems.Notably,using this protocol,several pharmaceuticals may be easily synthesized in one pot.