Hybrid organic -: inorganic catalysts:: a cooperative effect between support, and palladium and nickel salen complexes on catalytic hydrogenation of imines

A method for immobilizing chiral salen palladium and nickel complexes (salen = (R,R)-N',N-bis-(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) on ordered mesoporous silica supports (MCM-41), delaminated ITQ-2 and ITQ-6 zeolites, and amorphous silica has been developed. Hydrogenation, of imines was studied with the homogeneous as well as with the heterogenized counterpart catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs of 200 x 10(3) h(-1). A moderate acidity in the support increases the catalytic activity by stabilizing the charged transition state and can duplicate the activity of the homogeneous analogues. No deactivation of the catalysts was observed after repeated recycling. (C) 2004 Elsevier Inc. All rights reserved.