An improved catalytic system was developed for the Rh complex-catalyzed hydroxycarbonylation of alkenes using formic acid (HCOOH). Ligand screening revealed DPEphos, a bidentate phosphine ligand, to be effective, and the corresponding rhodium(III) hydride diiodide complex, RhHI2(CO)(DPEphos) (2), was applied as a catalyst. Complex 2 showed high activity and selectivity in the hydroxycarbonylation of alkenes using HCOOH without any additives and was applicable to a variety of alkene substrates. Analysis of the catalytic cycle using density functional theory calculations was used to elucidate the reaction steps. Initially, an alkyl group was formed by the insertion of an alkene into Rh-H with subsequent acyl group formation via the insertion of a CO ligand, similar to the reaction steps suggested for Rh-catalyzed alkene hydroformylation. The latter part of the catalytic cycle involved the reductive elimination of acyl iodide and subsequent hydrolysis to form a carboxylic acid, analogous to the reaction steps suggested for the synthesis of acetic acid from methanol and CO using a rhodium complex catalyst with hydroiodic acid as an auxiliary catalyst. These results indicate that the iodine atom in complex 2 acts as an auxiliary catalyst during the additive-free hydroxycarbonylation of alkenes using HCOOH.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry