Manganese(I)-Catalyzed Transfer Hydrogenation and Acceptorless Dehydrogenative Condensation: Promotional Influence of the Uncoordinated N‑Heterocycle

The four bidentate manganese­(I) complexes [(C₅H₄N-C₅H₃N-OH)­Mn­(CO)₃Br] (1), [(C₉H₆N-C₅H₃N-OH)­Mn­(CO)₃Br] (2), [(C₈H₅N₂-C₅H₃N-OH)­Mn­(CO)₃Br] (3), and [(C₈H₅N₂-C₅H₃N-OCH₃)­Mn­(CO)₃Br] (4) were synthesized. These complexes were tested as catalysts for the transfer hydrogenation of ketones, and 3 showed the highest activity. The reactions proceeded well with 0.5 mol % of catalyst loading and 20 mol % of t-BuOK at 85 °C for 24 h. Furthermore, 3 was also used as a catalyst for the synthesis of primary alcohols via transfer hydrogenation of aldehydes and the synthesis of 1,2-disubstituted benzimidazoles and quinolines via acceptorless dehydrogenative condensations.