Hydrocarboxylation and stepwise alternating oligomerization of carbon monoxide and ethylene catalyzed by cis-[Rh(CO)2(amine)2](PF6) complexes in a wet liquid tetrabutylammonium hydrogensulfate

In aqueous solution with tetrabutylammonium hydrogensulfate cocatalyst, rhodium complexes like cis-[Rh(CO)2(amine)2](PF6) (amine¼4-picoline, 3-picoline, 2-picoline, pyridine, or 2,6-lutidine) promote the oligomerization and, to a lesser extent, the hydrocarboxylation of CO/ethylene. Higher rates for both the production of alternating polyketones and propionic acid are observed in wet tetrabutylammonium hydrogensulfate medium. An in situ FT-IR spectroscopy study confirms that five coordinated rhodium species of the type trans-[Rh(CO)3(amine)2]þ are formed under catalytic conditions. The data are discussed in terms of a potential catalytic cycle, and the formation of propionic acid and ketones is determined to come from the hydrolysis and hydrogenolysis of the Rh-acyl intermediates formed under the catalytic conditions.