Chemoselective Hydrogenation and Transfer Hydrogenation of Aldehydes Catalyzed by Iron(II) PONOP Pincer Complexes

Iron-catalyzed hydrogenation has drawn much attention, yet the scope and chemoselectivity of iron catalysis warrant further improvement. Here we report new iron pincer complexes as chemoselective hydrogenation and transfer hydrogenation catalysts. Several Fe(II) complexes supported by a 2,6-bis(phosphinito)pyridine ligand (PONOP) have been synthesized. Fe(II) hydride complexes [((PrPONOP)-Pr-i)Fe(CO)(H)Br] (2) and ((PrPONOP)-Pr-i)Fe(CO)(H)(CH3CN) (3) can activate H-2 at room temperature. Complexes 2 and 3 are hydrogenation catalysts at room temperature, and the hydrogenation is selective for aldehyde in the presence of ketone and alkene groups. 2 and 3 are also chemoselective transfer hydrogenation catalysts using sodium formate as the hydride source.