Dehydrogenation of Secondary Amines to Imines Catalyzed by an Iridium PCP Pincer Complex

Abstract

The PCP pincer complex, IrH2{C6H3-2,6-(PBut2)2}, catalyzes the transfer dehydrogenation of secondary amines. Dehydrogenation occurs across C-N bonds rather than C-C bonds to give imines that are obtained in good to excellent yields when the reactions are carried out in toluene solution. The regioselectivity of the dehydrogenation of aliphatic amines is stringently controlled by steric factors while dehydrogenation of aromatic amines leads to imine products favored thermodynamically by conjugated π bonds in the aromatic system. The dehydrogenation reaction has been successfully carried out in large scale (separable) with N-butylbenzylamine with acceptable separation yield. The dehydrogenation of 2,2,2',2'-tetramethyldibutylamine leads exclusively to production of the corresponding imine indicating that the catalytic reaction pathway involves the initial intermolecular oxidative addition of a N-H bond rather than a C-H bond.