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 t Bu PNNOP ( t Bu PNNOP=2,6‐(di‐ tert ‐butylphosphinito)(di‐ tert ‐butylphosphinamine)pyridine) ( 1 ) and the catalyst is readily prepared with MnBrCO 5 to form [( t Bu PNNOP)Mn(CO) 2 ][Br] ( 2 ). Dehydrohalogenation of 2 generated the neutral five coordinate complex ( t Bu PNNOP)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, t Bu PONOP ( t Bu PONOP=2,6‐bis(di‐ tert ‐butylphosphinito)pyridine) or t Bu PNNNP ( t Bu PNNNP=2,6‐bis (di‐ tert ‐butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [( t Bu PONOP)Mn(CO) 2 ][Br] ( 4 ) and [( t Bu PNNNP)Mn(CO) 2 ][Br] ( 5 ). FA dehydrogenation with the hybrid‐ligand supported 2 exhibits superior catalysis to 4 and 5 .