Kinetics of the Homogeneous Catalytic Hydroformylation of 1-Octene in Supercritical Carbon Dioxide with HRh(CO)[P(p-CF₃C₆H₄)₃]₃

The first kinetic study of the rhodium-catalyzed homogeneous hydroformylation of olefins in supercritical carbon dioxide (scCO2) is reported. The hydroformylation of 1-octene using HRh(CO)[P(p-CF3C6H4)3]3 (1) in scCO2 was investigated at 50 °C and 273 atm. A kinetic rate expression was developed to represent the experimental data, having the form r1-octene = kA0.48C0.84D0.50/(1 + KBB2.2), where A = [H2], B = [CO], C = [1], and D = [1-octene]. The observed kinetic behavior differs significantly from behavior of conventional systems employing the nonfluorinated analogue of 1, HRh(CO)(PPh3)3, in organic solvents. Most notable are the ∼0.5 order H2 dependence of the reaction rate, the lack of substrate inhibition, and the absence of a critical catalyst concentration. The altered kinetic behavior relative to conventional systems may be due to scCO2 solvent effects, the modified phosphine ligand, or the high concentrations of reactant gases in the system. This study also illustrates the usefulness of scCO2 as a mechanistic tool in homogeneous catalysis, especially for reactions involving gases such as H2 and CO.