Combined homogeneous and heterogeneous catalysts.: Rhodium carbonyl thiolate complexes tethered on silica-supported metal heterogeneous catalysts: olefin hydroformylation and arene hydrogenation

Abstract

The rhodium carbonyl thiolate complex, Rh 2[μ-S(CH 2) 3Si(OCH 3) 3] 2(CO) 4 (Rh–S) was tethered to phosphine-modified Pd–SiO 2 (P–(Pd–SiO 2)), which was prepared by tethering the phosphine ligand Ph 2P(CH 2) 3Si(OC 2H 5) 3 to Pd–SiO 2, to give the tethered complex catalyst Rh–S/P–(Pd–SiO 2). Also, the phosphine-substituted Rh 2[μ-S(CH 2) 3Si(OCH 3) 3] 2[Ph 2P(CH 2) 3Si(OC 2H 5) 3] 2(CO) 2 (Rh–S–P) was tethered to several silica-supported metal heterogeneous catalysts M–SiO 2 (M=Pd, Pt, Ru, Ir) to give Rh–S–P/M–SiO 2. These complex catalysts, consisting of a tethered complex on a supported-metal (TCSM), were used to catalyze the hydroformylation of olefins and the hydrogenation of toluene under atmospheric pressure. In the presence of phosphorus donor-ligands, all the TCSM catalysts are active for the hydroformylation of olefins under the mild conditions of 60°C and 1 atm of H 2 and CO (1:1). The most active catalysts, Rh–S/P–(Pd–SiO 2) and Rh–S–P/Pd–SiO 2, give maximum TOF values of 1.04 and 0.88 (mol aldehyde/mol Rh min), respectively, and TO values of 905 and 703 (mol aldehyde/mol Rh) during 22.5 h and 23.5 h in the hydroformylation of 1-octene. The Rh–S–P/Pd–SiO 2∼PPh 3 catalyst system maintains its activity through three cycles and 68 h to give a total turnover of 2118 mol aldehyde/mol Rh. These activities are higher than those of the homogeneous rhodium thiolate complex catalyst (Rh–S–P) and the rhodium thiolate complex catalysts tethered on just SiO 2(Rh–S/P–SiO 2 and Rh–S–P/SiO 2). The effects of the phosphorus ligand and PR 3/Rh mole ratio on the hydroformylation rates, conversions, and chemo- and regioselectivities for aldehyde were also investigated. The Rh–S/P–(Pd–SiO 2) and Rh–S–P/Pd–SiO 2 catalysts are also active for the hydrogenation of toluene under the mild conditions of 40°C and 1 atm of H 2; they are much more active than the homogeneous rhodium thiolate complex catalyst Rh–S–P, the simple silica-supported heterogeneous palladium catalyst (Pd–SiO 2) and the rhodium thiolate complex catalysts tethered on just SiO 2(Rh–S/P–SiO 2 and Rh–S–P/SiO 2). The synergistic advantages of the two components (tethered complex and supported metal) of the TCSM catalysts are greater for the hydrogenation of toluene than for the hydroformylation of 1-octene.