In situ spectroscopic investigations on BiPhePhos modified rhodium complexes in alkene hydroformylation†

Abstract

Structural and dynamic properties of BiPhePhos modified rhodium complexes under hydroformylation conditions have been investigated in detail by using high-pressure (HP) in situ transmission IR- and NMR-spectroscopy. An experiment design approach which combines component/reagent perturbations, in situ-FTIR measurements and chemometric peak group analysis (PGA) led to the identification of most relevant components. The ligand coordination in the structures of the hydrido and acyl 18-VE resting state complexes has been elucidated. The hydrido complex of the type e,e-[HRh(CO)₂(P∩P)] represents the dominant resting state after catalyst preformation and during the n-regioselective hydroformylation. Dimer formation only takes place to a minor extent under severe reaction conditions under hydrogen depletion. Mono- and dinuclear hydrido monocarbonyl complexes are formed at higher ligand-to-metal ratios and low partial pressures of carbon monoxide. Both stereoisomeric forms of the bisphosphite modified acyl complexes e,a-[RC(O)Rh(CO)₂(P∩P)] and e,e-[RC(O)Rh(CO)₂(P∩P)] are generated as an equilibrium mixture.