Preparation and properties of rhodium(I) complexes of phosphinated poly(methylsiloxanes)

Abstract

A series of poly(methylsiloxanes) that contain carbon-functional diphenylphosphine groups were prepared and subsequently treated with RhCl(CO)(PPh 3) 2 to produce polymer-attached chlorocarbonylrhodium(I) complexes. The materials are soluble in a variety of organic solvents, and are easily precipitated from solution by the addition of excess methanol. The polymer complex A derived from a phosphinated silicone polymer containing one PPh2 group per 60 siloxy units has a molecular weight of 21000 daltons and contains 0.8% Rh. In accord with its formulation, the polymer shows a ν(CO) at 1970 cm -1 and an ultraviolet absorption at 3625 Å. Similar rhodium(I) complexes derived from phosphinated silicones containing one PPh 2 group per 20 (complex B) and 8 (complex C) siloxy units were also investigated. Complexes A and B catalyze the hydroformylation of hex-1-ene at 100°C, 1000 psi CO/H 2 pressure yielding the linear/branched heptaldehyde in a ratio of 0.9 with 95% selectivity and an overall conversion of 97% to products in 3 h. Although the hydroformylation conditions do not lead to depolymerization, both Rh and P are lost from the polymers and the actual catalyst appears to be a free rhodium carbonyl species. Complex C is a less active hydroformylation catalyst (14% aldehyde conversion, normal/branched ratio 1.7) and the polymer undergoes extensive degradation in the reaction.