Formal Deoxygenative Hydrogenation of Lactams Using PNHP-Pincer Ruthenium Complexes under Nonacidic Conditions

A formal deoxygenative hydrogenation of amides to amines with RuC12(NHC)(PNHP) (NHC = 1,3-dimethylimizadol-2-ylidene, PNHP = bis(2-diphenylphosphinoethyl)amine) is described. Various secondary amides, especially NHlactams, are reduced with H2 (3.0-5.0 MPa) to amines at a temperature range of 120-150 C with 1.0-2.0 mol % of PNHP Ru catalysts in the presence of Cs2CO3. This process consists of (1) deaminative hydrogenation of secondary amides to generate primary amines and alcohols, (2) dehydrogenative coupling of the transient amines with alcohols to generate imines, and (3) hydrogenation of imines to give the formally deoxygenated secondary amine products.