Pd(II)-Schiff base complexes heterogenised on MCM-41 and delaminated zeolites as efficient and recyclable catalysts for the Heck reaction

We present a widely applicable approach for the preparation of Pd-complexes supported on silica-based mesoporous and laminar inorganic solids (silica gel, purely siliceous and acidic MCM-41, and delaminated zeolites ITQ-2 and ITQ-6) which involves the use of the Schiff bases 2-tert-butyl-4-methyl-6{(E)-[(2S)-1-(1-arylmethyl)pyrrolidinyl]imino}methylphenol (aryl=phenyl, 1-naphthyl, 2-naphthyl) as anchored ligands. As an extension of our research in "recyclable catalytic systems" we report results demonstrating the reactivity and recyclability of these systems for the Heck reaction (in a biphasic mode using ethylene glycol and toluene) and Suzuki coupling under phosphine-free conditions. The complexes are insensitive to oxygen or moisture, and no change of their activity was observed when exposed to an open system during the usual operation. No palladium black was observed after an extended reaction time and no residual palladium was detected from the filtrate at the end of the reaction.