RHODIUM(I)-CATALYZED ALTERNATING COOLIGOMERIZATION OF CARBON-MONOXIDE WITH OLEFINS - SYNTHETIC AND MECHANISTIC STUDIES

Rhodium(I) phosphine complexes were found to catalyze the alternating co-oligomerization of ethylene and carbon monoxide in appropriate solvents. In a mixture of alcohol (ROH) and acetic acid, the products were H-(CH2CH2CO)n-CH2CH3 and H-(CH2CH2CO)n-OR (n = 1-4). Only the oligomeric polyketones were formed when a mixture of alcohol and water was used as the solvent. The effect of solvent composition and additives on the product distribution was studied extensively. The reactions were initiated by a rhodium-hydride species formed through the water-gas shift reaction. The chain growth involved the alternate insertions of ethylene and carbon monoxide into the initial rhodium-hydride bond. The oligomeric polyketoesters were formed by the alcoholysis of the intermediate rhodium-acyl species, whereas the oligomeric polyketones were generated through a bimolecular reductive elimination from the intermediate rhodium alkyls and a rhodium hydride. The catalyst system was also found to effect the carbonylation of propylene and butene.