Phosphine oxides as ligands in the hydroformylation reaction

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. R(2)N(CH2)(n)P(O)R(2)', R' = Ph, Cy; n = 0, 1, 2, 3; R = Me, Et, Pr-i, or NR(2) = 2-pyridyl) were found to be better ligands than the phosphine analogues (i.e. R(2)N(CH)(2)PR(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-H-2 and only by the amino group under 600 Ibf in(-2) of CO-H-2.