Fluorinated rhodium-phosphine complexes as efficient homogeneous catalysts for the hydrogenation of styrene in supercritical carbon dioxide

A fluorinated trisphenylphosphine ligand was reacted with [(COD)CIRh]2 (COD = cyclooctadiene) and [(COD)2Rh]+BArF− {BArF = tetrakis[(3,5-bistrifluoromethyl)phenyl]borate} to synthesize new fluorinated derivatives of the well-known Wilkinson catalyst as {[P(Ph(CF3)2)3]3RhBArF}, {[P(Ph)3]3RhBArF} and {[P(Ph(CF3)2)3]3RhCl}. BArF anion was used to synthesize cationic complexes. All the synthesized complexes were tested and found to be soluble in supercritical carbon dioxide (scCO2) media. The catalytic activities of the rhodium complexes were examined for hydrogenation of styrene in scCO2. The catalysts showed different activities between 47.9–77.4%. The most effective result among the synthesized Rh-catalysts was obtained with a conversion of 77.4% corresponding to {[P(Ph(CF3)2)3]3RhBArF} under the reaction conditions of 343K temperature and 123 bar pressure after 8 h in scCO2 (molar ratio of substrate to catalyst = 500).