Dinuclear pincer-palladium(II) complexes and their use as homogeneous or heterogeneous catalyst for the aldol reaction of methyl isocyanoacetate

Two new bimetallic Pd complexes have been synthesized and characterized and their catalytic activity checked for the aldol reaction of aldehydes with methyl isocyanoacetate. Each palladium atom is coordinated to an SCS-type ligand and the two pincer units are linked by a chiral spacer. The catalytic aldol reaction of methyl isocyanoacetate with aldehydes proceeds quickly but no significant diastereoselectivity and enantioselectivity is found. The comparison with a homologous mononuclear Pd complex shows no differences with the bimetallic compounds, concluding that there is no cooperativity between the metal centers, Two silica-supported catalysts prepared with a bimetallic compound show catalytic activity with very minor enantioselectivity. (C) 2001 Elsevier Science B.V. All rights reserved.