Molecular Engineering in Homogeneous Catalysis: One-Phase Catalysis Coupled with Biphase Catalyst Separation. The Fluorous-Soluble HRh(CO){P[CH2CH2(CF2)5CF3]3}3 Hydroformylation System

Abstract

The hydroformylation of decene-1 was studied in the presence of the fluorous-soluble P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 modified rhodium catalyst at 100 °C and 1.1 MPa of CO/H 2 (1:1) in a 50/50 vol % toluene/C 6 F 11 CF 3 solvent mixture, which forms a homogeneous liquid phase at and above 100 °C. P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 was selected on the basis of a semiempirical calculation of the electronic properties of P[(CH 2 ) x (CF 2 ) y CF 3 ] 3 ( x = 0, y = 2, 4 and x = 0−5, y = 2) and prepared by the reaction of PH 3 with CH 2 CH(CF 2 ) 5 CF 3 . The solution structure of HRh(CO){P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 } 3 ( 1 ) in C 6 F 11 CF 3 is similar to that of HRh(CO)(PPh 3 ) 3 ( 2 ) in toluene and HRh(CO){P( m -C 6 H 4 SO 3 Na) 3 } 3 ( 3 ) in water. High-pressure NMR of 1 under 2.1−8.3 MPa of CO/H 2 (1:1) revealed that 1 is in equilibrium with HRh(CO) 2 {P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 } 2 ( 4 ). Kinetic studies show that the reaction is first order in both rhodium and decene-1. While the reaction is inhibited by P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3, the normal/iso (n/i) ratio of the aldehyde increases with increasing phosphine concentration. The catalytic activity of the Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 catalyst is similar to that of the nonfluorous analogue Rh/P[(CH 2 ) 7 CH 3 ] 3 catalyst and is an order of magnitude lower than that of the Rh/PPh 3 catalyst. Surprisingly, the n/i product selectivity of Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 is closer to the selectivity of the Rh/PPh 3 catalyst than that of the Rh/P[(CH 2 ) 7 CH 3 ] 3 catalyst. The fluorous biphase catalyst recovery concept was tested in a semicontinuous hydroformylation of decene-1 with the Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 catalyst. During 9 consecutive reaction/separation cycles, a total turnover of more than 35 000 was achieved with a loss of 1.18 ppm of Rh/mol of undecanals. The fluorous-soluble Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 catalyst was also tested for the continuous hydroformylation of ethylene using the high-boiling fluorous solvent FC-70, which allows continuous removal of propanal at the reaction temperature of 110 °C. The long-term stability of the Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 catalyst is better than that of the Rh/PPh 3 catalyst. Thus, the Rh/P[CH 2 CH 2 (CF 2 ) 5 CF 3 ] 3 catalyst is the first catalyst system which can be used for the hydroformylation of both low and high molecular weight olefins and provides facile catalyst separation for both low and high molecular weight aldehydes.