Hydroformylation of mixture of isomeric octenes to C₉-aldehydes catalyzed by Rh-phosphine oxide complexes

The hydroformylation of mixture of isomeric octenes to C₉-aldehydes has been studied using rhodium complex catalysts in an autoclave (100 ml). Phosphine oxide ligands showed high activities in the hydroformylation. The yield of C₉-aldehydes was about 90% by using [Rh(CH₃COO)₂]₂-Ph₃PO as the catalyst at 140°C and 10.5 MPa. Triphenyl phosphine ligand was found to be inactive in the synthesis of C₉-aldehydes from mixture of isomeric octenes. Different rhodium precursors ([Rh(CH₃COO)₂]₂, Rh₆(CO)₁₆, and Rh(CO)(PPh₃)(acac)) showed similar performance in the Rh-Ph₃PO system. The yield of C₉-aldehydes was influenced by the reaction conditions. The suitable reaction temperatures were in the range of 120-140°C for the Rh-phosphine oxide systems. High pressures were favorable for the formation C₉-aldehydes. The yield of C₉-aldehydes increased with the increase of P/Rh ratio when the ratio of P/Rh was below 20, while no significant changes were found in the yield of C₉-aldehydes when P/Rh ratio was larger than 20. In situ IR spectroscopy demonstrated the presence of Rh-H bond in the intermediate species in Rh-Ph₃PO catalyzed hydroformylation.