Phosphine oxides as ligands in the hydroformylation reaction

Article abstract of DOI:10.1016/0022-328X(96)06137-2

A new rhodium-phosphine oxide system has been investigated in the hydroformylation reaction. Some of the phosphine oxide ligands of type 2-12 (i.e. R₂N(CH₂)_nP(O)R′₂, R′ = Ph, Cy; n = 0, 1, 2, 3; R = Me, Et, ⁱPr, or NR₂ = 2-pyridyl) were found to be better ligands than the phosphine analogues (i.e. R₂N(CH)₂PR′₂) in the hydroformylation of olefins catalyzed by rhodium complexes. Detailed examination of factors controlling the selectivity for aldehydes formation revealed the following characteristics of the reaction: (a) use of ligands having bulkier amino groups decrease the yield of the aldehydes slightly; (b) ligands having amino groups with low basicity decrease the rate of the hydroformylation dramatically; (c) the electronic properties of the phosphine oxide group have no influence on the hydroformylation reaction; (d) uncoordinating solvents of low polarity such as dichloromethane, chloroform and toluene gave the best reaction rate and selectivity; (e) spectroscopic investigation of the hydroformylation of styrene catalyzed by rhodium with ligand 2 shows that the ligand is coordinated by the amino and the phosphine oxide groups under 1 atm of CO-H₂ and only by the amino group under 600 lbf in^-2 of CO-H₂.