Rhodium-Catalyzed Hydrocarboxylation of Olefins with Carbon Dioxide

The catalytic hydrocarboxylation of styrenes derivatives and alpha,beta-unsaturated carbonyl compounds with CO2 (101.3 kPa) in the presence of an air-stable rhodium catalyst was explored. The combination of [RhCl(cod)](2) (cod = cyclooctadiene) as a catalyst and diethylzinc as a hydride source allowed for effective hydrocarboxylation and provided the corresponding a-aryl carboxylic acids in moderate to excellent yields. In this catalytic process with carbon dioxide, intervention of the Rh-I-H species, which could be generated from the Rh-I catalyst and diethylzinc, was clarified. Significantly, the catalytic asymmetric hydrocarboxylation of alpha,beta-unsaturated esters with carbon dioxide was also performed by employing a cationic rhodium complex possessing (S)-(-)-4,4'-bi-1,3-benzodioxole-5,5'-diylbis(diphenylphosphine) [(S)-SEGPHOS] as a chiral diphosphine ligand. A plausible model for asymmetric induction was proposed by determination of the absolute configuration of the product.