Phosphite modified cobalt complexes for olefin hydroformylation

Several dinuclear complexes of the form [Co2(CO)6L2] with L being an aromatic phosphite ligand were varied as follows: L = P(OPh)3, P(O-4-tBuC6H4)3, P(O-2- tBuC6H4)3, P(O-2-EtC6H4)3, P(O-2-iPrC6H4)3. These dinuclear complexes have been synthesised and characterized by IR and NMR. The dinuclear complexes which were successful in being characterized by X ray crystallography were the ones with L = P(O-4-tBuC6H4)3 and P(O-2-EtC6H4)3. These two dinuclear complexes including the complex with P(OPh)3 as a ligand were used as precursors as active catalysts in the hydroformylation of 1-octene. High pressure spectroscopy was used to detect hydride intermediates. High pressure infra red (HP-IR) studies revealed the formation the monophosphite hydrides ([HCo(CO)3L]) for all the studied ligands, as well as the formation of bisphosphite hydrides [HCo(CO)2L2] and the unmodified hydride [HCo(CO)4]. At 140 °C both the unmodified and the bisphosphite had disappeared and the only specie present was the monophosphite hydride which is the active hydride catalyst in hydroformylation reactions. This study has proven the importance of the stability of the hydride in the hydroformylation reaction along with the selectivity and conversion rate of the 1- octene to the aldehyde. The stability of the hydride was tested in the presence of 1- octene and in the absence of 1-octene. Catalytic activity of the studied cobalt phosphite complexes was tested at the end of the stability runs.