Effect of carboxylic acids on the yield and selectivity of the hydroformylation of hex-1-ene catalyzed by [Rh(acac)(CO)(PPh3)]

Article abstract of DOI:10.1016/0304-5102(93)85077-7

The effect of the carboxylic acids RCO₂H (R=C₂H₅, C₆H₅, m-ClC₆H₄, p-NO₂C₆H₄ and o-HOC₆H₄) on the hydroformylation of hex-1-ene catalyzed by Rh(acac) (CO) (PPh₃) (1) have been studied. The decrease of the rate of hydroformylation compared with a carboxylic acid-free systems was observed. The inhibiting influence of carboxylic acids is stronger in reactions proceeding in the presence of free phosphine (e.g. (1)/]RCO₂H + PPh₃]) where not only the reaction rate, but also hex-1-ene conversion decrease. The inhibiting effect of carboxylic acids may be explained by partial elimination of catalytically active forms of the general formula HRh(CO)_x(PPh₃)_y by the reaction of HRh(CO)_x(PPh₃)_y in the presence of RCO₂H/PPh₃ and H₂/CO to give Rh(RCO₂) (CO) (PPh₃)₂. The equilibrium of this reaction depends mainly on the concentrations of the H⁺ ions and that of free phosphine. Several new rhodium complexes were formed in the reaction of (1) with RCO₂H, e.g, [Rh(RCO₂) (CO) (PPh₃)]₂, [Rh(RCO₂) (CO)₂ (PPh₃], [Rh (RCO₂) (CO) (PPh₃)₂], [Rh (RCO₂) (CO)₂]₂, have been isolated and used as hydroformylation reaction catalysts. The structures of Rh(acac) (HOC₆H₄CO₂) (PPh₃) (H₂O) and [Rh(HOC₆H₄CO₂) (COD) ]₂ have been determined by X-ray diffraction studies.