FINE-TUNING OF BULKY-PHOSPHITE MODIFIED RHODIUM CATALYSTS BY BINDING THEM TO COPOLYMERS

The influence of the chain loading on the activity and complex formation of a copolymer-bound rhodium hydroformylation catalyst in comparison with its low molecular weight analogue has been studied in detail. As polymer support a perfectly random copolymer of styrene and 2,2'-bis(4,6-di-t-butylphenyl)-p-styryl phosphite (2) was used. The chain loading, alpha, of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis-phosphite catalysts are formed. Low chain loadings give active, easily accessible, mono-phosphite complexes. Study of the copolymer-bound catalysts yielded mechanistic information about the catalytic species involved in the hydroformylation of styrene and cyclooctene. The active species in the hydroformylation of sterically hindered alkenes is a mono-phosphite rhodium complex. The activity of the catalyst can be enhanced if excess phosphite is used. This effect was ascribed to faster reaction with hydrogen of bis-phosphite rhodium intermediate(s). The activity of the copolymer-bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. The hydroformylation of styrene proceeds more slowly.