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 (scCO 2 ) is reported. The hydroformylation of 1-octene using HRh(CO)[P( p -CF 3 C 6 H 4 ) 3 ] 3 ( 1 ) in scCO 2 was investigated at 50 °C and 273 atm. A kinetic rate expression was developed to represent the experimental data, having the form r 1-octene = kA 0.48 C 0.84 D 0.50 /(1 + K B B 2.2 ), where A = [H 2 ], 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)(PPh 3 ) 3, in organic solvents. Most notable are the ∼0.5 order H 2 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 scCO 2 solvent effects, the modified phosphine ligand, or the high concentrations of reactant gases in the system. This study also illustrates the usefulness of scCO 2 as a mechanistic tool in homogeneous catalysis, especially for reactions involving gases such as H 2 and CO.