Synthesis and physicochemical characterization of polymeric supports and polymer-supported rhodium catalysts based on polyamides having a pyridine moiety

Abstract

A series of polyamide supports have been synthesized by low-temperature interfacial condensation of 2,5- and 2,6-pyridinedicarboxylic chlorides and aliphatic diamines H 2N(CH 2) n NH 2, where n=2 and 6. Rhodium catalysts have been prepared by treating the polyamides, PA py, with a solution of catalyst precursor, [RhCl(CO) 2] 2. Physical characterization of these materials has involved the measurements of the structural parameters in the dry state by the nitrogen BET adsorption method, and in the swollen state by pycnometry and inverse steric exclusion chromatography (ISEC). The swelling of polymer supports and supported catalysts in different solvents has also been examined. The results of these studies have revealed that the original structure of the polymer supports has been changed by metal complex attachment, i.e. porosity increased after the complexation process. This effect was ascribed to the formation of crosslinking between polymer chains and metal species through coordination bonds. The effect of the polymer structure on the catalytic properties of the polyamide-supported Rh(I) species was tested in the hydrosilylation of vinyl compounds. A significant increase in selectivity towards formation of the linear products was found to be greatly affected by the matrix microporous structure. The thermal behaviour of polyamide supports and supported catalysts has been evaluated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The DSC analysis for these polymer-supported rhodium species has shown the appearance of new endothermic transitions. This result was explained by structural rearrangements (crosslinking) of polymer chains that took place during complexation. TG measurements have shown high thermal stability for both the polyamide, PA py, supports and the supported catalysts. Incorporation of the rhodium slightly reduced the inherent stability of the polyamides.