TRANSITION-METAL COMPLEXES BOUND TO MACROPOROUS RESINS CARRYING NITRILE GROUPS - EFFECT OF MATRIX STRUCTURE ON THE ACTIVITY OF SUPPORTED CATALYSTS

Two groups of resins bearing nitrile (CN) groups based on macroporous copolymers of acrylonitrile and divinylbenzene (AN/DVB) and terpolymers of styrene, acrylonitrile and divinylbenzene (S/AN/DVB) have been used as polymer matrices for the immobilization of Rh(I), Pt(II) and Pd(II) complexes. A group of four S/DVB resins functionalized with the CN ligands have been prepared and used for comparison. The resins differ in their chemical and physical structure, local concentration of the CN groups and their availability. Characterization of the heterogeneous complexes by IR spectroscopy confirmed the coordination of the metal ions to the polymer-CN ligands. The catalytic behaviour of the immobilized complex catalysts was tested in the hydrosilylation of 1-hexene. The activity of the polymer-bound catalysts strongly depends on the structure of the support used. The largest effect of the chemical structure of the polymer was found for the catalysts immobilized on the AN/DVB resins, while the polymer morphology played the major role in the high activity of the catalysts attached to the S/AN/DVB resins. Lower activity was found for the systems bound to the functionalized S/DVB resins. Both polymer-supported Pt and Rh systems appeared to be highly effective for the hydrosilylation of the C = C double bonds, but the platinum catalysts proved to be considerably more active. The rhodium catalysts were found efficient in the hydrosilylation of ketones. The immobilized Pd(II) complex was reduced to the metallic Pd by hydrosilanes. The supported Pt catalyst remained active when recycled 5 times, while the activity of the rhodium systems gradually decreased. The results offer the possibility of choosing the most suitable polymer matrix for the immobilization of metal complex catalysts for use in hydrosilylation and other catalytic reactions.