Noninnocent Spectator Ligands Facilitate CO Ligand-Stabilized Mn(I) Metal-Catalyzed Hydrogenation of Urea Derivatives or Carbamates to the More Reactive Formamides

The carbonyl ligands that stabilize the Mn(I) center in the Mn(CO)₅Br metal precursor are usually retained upon complexation with the tridentate ligand; however, their presence limits the hydrogenation performance of the Mn complex. Herein, we report the highly selective semihydrogenation of urea derivatives or carbamates, two of the most challenging carbonyl compounds, and polyurethanes to more active formamides using a catalyst system containing earth-abundant metal Mn under mild reaction conditions, which has been previously achieved using precious metal Ru or Ir catalysts. This catalytic activity stems from the fact that the Mn complex bears a noninnocent ligand, which facilitates the simultaneous transfer of both hydrogen atoms from a dihydrogen molecule, thereby avoiding the energetically demanding dihydrogen coordination step observed in systems with exclusively innocent ligands. Additionally, DFT calculations provide insights into the reason for the selective hydrogenation of urea or carbamates to more reactive formamides.