In situ mechanistic studies in rhodium catalyzed hydroformylation of alkenes

Abstract

A new in situ high-pressure IR (HP-IR) autoclave is presented that is especially suited for mechanistic studies of fast catalytic reactions. This review summarizes several applications of the HP-IR cell in the rhodium catalyzed hydroformylation of alkenes. The most abundant species during the very fast hydroformylation of 1-alkenes using tris(2- tert-butyl-4-methylphenyl) phosphite was identified as the Rh acyl complex RhC(O)R(CO) 3L. A detailed kinetic study and (in situ) spectroscopic techniques revealed that when a monodentate biuret-based phosphorus diamide ligand is used several of the elementary reaction steps are involved in the hydroformylation rate control. Depending on the reaction conditions, the rate-determining step is early or late in the catalytic cycle. The rates of single steps of the catalytic hydroformylation cycle could be determined using labeling experiments. The use of 13CO labeling in rapid-scan IR experiments to determine the rate of CO dissociation in the (diphosphine)Rh(CO) 2H complexes is described. Furthermore, the H/D exchange rate of DRh(L–L)(CO) 2 with H 2 was measured using rapid-scan high-pressure IR spectroscopy. Finally, the HP IR cell was used to identify the reaction between the most likely impurities in alkene feeds and the rhodium catalyst.