Manganese-Mediated Formic Acid Dehydrogenation

A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand (PNNOP)-P-tBu ((PNNOP)-P-tBu=2,6-(di-tert-butylphosphinito)(di-tert-butylphosphinamine)pyridine) (1) and the catalyst is readily prepared with MnBrCO5 to form [((PNNOP)-P-tBu)Mn(CO)(2)][Br] (2). Dehydrohalogenation of 2 generated the neutral five coordinate complex ((PNNOP)-P-tBu)Mn(CO)(2) (3). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h(-1), rivaling many noble metal systems. The parent chelate, (PONOP)-P-tBu ((PONOP)-P-tBu=2,6-bis(di-tert-butylphosphinito)pyridine) or (PNNNP)-P-tBu ((PNNNP)-P-tBu=2,6-bis (di-tert-butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [((PONOP)-P-tBu)Mn(CO)(2)][Br] (4) and [((PNNNP)-P-tBu)Mn(CO)(2)][Br] (5). FA dehydrogenation with the hybrid-ligand supported 2 exhibits superior catalysis to 4 and 5.