In the co-hydrogenation of deutero-acetonitrile (CD3CN) and butyronitrile (C3H7CN) over SiO2-supported Pt and Ru catalysts, H atoms are preferentially added to the C atom of the CN groups, but D atoms are added to the N atom. This shows that intermolecular hydrogen transfer from acetonitrile to the nitrogen atom of CN groups takes place. The methyl group of acetonitrile is a more effective donor of hydrons than the propyl group in butyronitrile. Hydrogen transfer is most efficient for breaking the strong N=M chemisorption bond, releasing an amine molecule to the gas phase. The cis-insertion of an alkyl group into an N=M bond leads to a secondary amine. (C) 2000 Academic Press.