Rhodium(I) complex catalysts immobilized on polyamides having a pyridine moiety: Effect of the polymer structure

Abstract

A series of polyamides 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, where n=2 and 6, and used as the model supports for immobilization of the Rh(I) complex catalyst. Physical characterization of these materials has involved the measurements of the structural parameters in the dry and swollen states by WAXS, SAXS, DSC, the nitrogen BET adsorption method, ISEC and pycnometry. From these results it can be concluded that the original polymer structure has been changed during the complex attachment giving rise to materials of higher porosity. The relation between the support structure and catalyst activity and selectivity was studied in the model reactions, namely, hydrosilylation of alkenes, dienes and alkynes. It was found that the catalyst activity decreased with increasing polymer crystallinity. A strong impact of support structure on the catalyst selectivity was also revealed. A high regioselectivity of the catalyst in the hydrosilylation of alkenes toward formation of the linear products was achieved due to the favorable microporous structure of the polyamide supports with pore sizes between 10 and 20 Å. It was also demonstrated that the stereoselectivity of the reaction can be reversed to the opposite direction by a proper choice of the donor functions in a polymer support, e.g. the traditional cis-selectivity of the rhodium (Rh) catalysts in the hydrosilylation of phenylacetylene was changed to trans-selectivity by use of the 2,5-py instead of 2,6-py moiety. The results of the 6–9 times repeated catalytic runs indicated high stability of the polyamide-supported catalysts.