New rhodium systems for biphasic hydrogenation and hydroformylation of 1-hexene

Abstract

The catalytic activity of rhodium complexes formed in reactions of catalyst precursor, [Rh(acac)(CO) 2] with water soluble phosphines: Ph 2PCH 2CH 2CONHC(CH 3) 2CH 2SO 3Li ( PNS), Ph 2PCH 2CH(COOLi)(CH 2COOLi) ( PC), Ph 2PCH 2CH(CH 3)(COOH) ( PH) or Ph 2PCH 2CH(CH 3)(COONa) ( PNa) in hydrogenation and hydroformylation of 1-hexene in mono- and biphasic systems have been studied. The yield of aldehydes obtained in hydroformylation of 1-hexene in the system [Rh(acac)(CO) 2]+PNS strongly depends on the kind of solvent: 24% in toluene, 53–86% ( n/ iso 2.9–4.6) in the toluene–water–ethanol mixture and 77–94% ( n/ iso 2.5–3.8) in water–ethanol solution. The mixture of water–ethanol as a solvent was also found to be the best for hydrogenation of 1-hexene (96% of hexane) with [Rh(acac)(CO) 2]+PNS system. Application of PH phosphine (in hydrogen form) produces ca. 2% of aldehydes in both solvents, toluene only and toluene–water mixture. However, conversion of PH phosphine into its sodium salt, PNa, increased the catalytic activity of rhodium catalyst up to 85% yield of aldehydes in toluene, 92% in toluene–water and 94% in toluene–water–ethanol mixture. Spectroscopic studies of the reaction mixture in situ (IR, 1 H -, 31 P -NMR) allowed to identify following rhodium complexes existing in hydroformylation reaction conditions in the system [Rh(acac)(CO) 2]+PH/PNa: [Rh(acac)(CO)(PH)], [Rh(OH)(CO)(PH) 2], [HRh(CO)(PNa) 3], [Rh 4(CO) 12− x (PH) x ]. [HRh(CO)(PNa) 3] was found to be stable only when sodium hydroxide was introduced to the system.