Dehydrogenation of secondary amines to imines catalyzed by an iridium PCP pincer complex: initial aliphatic or direct amino dehydrogenation?

The PCP pincer complex, IrH2(C6H3-2,6-(CH(2)PBut(2))(2)) catalyzes the transfer dehydrogenation of secondary amines to imines. The catalytic system is highly sensitive to both steric and electronic factors and greater than 99% regioselectivity are observed in the dehydrogenation of the asymmetric substrates, cyclohexyethylamine and benzylpropyl amine. Good to excellent yields are obtained when the reactions are carried out in toluene solution. The dehydrogenation of 2,2,2',2'-tetramethyldibutylamine leads exclusively to the production of the corresponding imine indicating that the catalytic reaction pathway involves direct amino rather than initial aliphatic dehydrogenation. (C) 2002 Elsevier Science B.V. All rights reserved.