Transfer Hydrogenation of Aldehydes, Allylic Alcohols, Ketones, and Imines Using Molybdenum Cyclopentadienone Complexes

The molybdenum tetraphenylcyclopentadienone complex (C₅Ph₄O)­Mo­(CO)₃­(CH₃CN) 1a is an effective precatalyst for the transfer hydrogenation of aldehydes, allylic alcohols, ketones, and imines under mild conditions with either 2-propanol or formic acid as reducing reagent. Mechanistic studies suggest that these molybdenum cyclopentadienone complexes can be reduced to the corresponding hydroxycyclopentadienyl Mo hydrides. These complexes, by virtue of the hydroxyl group on the cyclopentadienyl ligand, are more reactive and chemoselective than the analogous cyclopentadienyl molybdenum complexes for the reduction of ketones, aldehydes, and imines.