Shin-ichiroKeywords: Hydroformylation / Rhodium / Dialdehyde / Fluorinated ligand / Supercritical carbon dioxideRhodium-catalyzed hydroformylation of 1,5-hexadiene to dialdehydes was investigated in compressed CO 2 and in toluene using different fluorinated phosphane compounds as ligands at a temperature of 60°C. Product yields depend greatly on the ligand used and, of the ligands examined, tris[3,5-bis(trifluoromethyl)phenyl]phosphane is the most effective for the production of dialdehydes both in supercritical CO 2 (scCO 2 ) and in toluene. The total yield of the dialde-
IntroductionSupercritical carbon dioxide (scCO 2 ) is gaining considerable interest as an ecologically benign and economically feasible new generation reaction medium that could replace conventional toxic, flammable organic solvents. [1,2] Various chemical substances are soluble in scCO 2 and they can be easily separated by depressurization; scCO 2 is also nonflammable, nontoxic and has no gas/liquid phase boundary. The physicochemical properties of scCO 2 can be tuned within a certain range by adjusting the pressure and temperature, these also being the parameters for optimization of reactions in this solvent.Organometallic complexes are effective catalysts for various chemical transformations in conventional solvents. [3] Although homogeneous organometallic catalysis in scCO 2 is attractive, the organometallic complexes must be soluble in scCO 2 . Phosphane ligands, such as triphenylphosphane (TPP), that are often used in these complexes are less sol- [a]