Dendritic effects in catalysis by Pd complexes of bidentate phosphines on a dendronized support: Heck vs. carbonylation reactions.

Bidentate phosphine ligands have been prepared on polystyrene beads modified with polyether dendron spacers. When complexed to Pd(0), these systems exhibited a negative dendritic effect on Heck catalysis (contrary to the analogous monodentate phosphine systems), but mostly a positive influence on carbonylation. This opposite influence of the dendronization falls into line with other differences in the optimal ligand structure for the two reactions. The negative effect on the Heck catalysis with bidentate phosphines may indicate that dendrimer-induced reduction in the cross-linking upon Pd complexation is responsible for the positive effect in the corresponding monodentate phosphine systems.