Hydroformylation of 1-Octene under Atmospheric Pressure Catalyzed by Rhodium Carbonyl Thiolate Complexes Tethered to Silica

The silica-tethered rhodium thiolate complex catalysts Rh−S/SiO 2 and Rh−S−P/SiO 2 were prepared by the condensation of SiO 2 with Rh 2 [μ-S(CH 2 ) 3 Si(OCH 3 ) 3 ] 2 (CO) 4 (Rh−S) or Rh 2 [μ-S(CH 2 ) 3 Si(OCH 3 ) 3 ] 2 [Ph 2 P(CH 2 ) 3 Si(OC 2 H 5 ) 3 ] 2 (CO) 2 (Rh−S−P). These tethered complex catalysts exhibit high activity for the hydroformylation of 1-octene in the presence of phosphine donor ligands under the mild conditions of 60 °C and 1 atm. IR (DRIFT) spectral studies of the catalysts used indicate that tethered monorhodium dicarbonyl thiolate complexes of the type Rh(SR)(CO) 2 (PR‘ 3 ) are the predominant species on the surface for the catalysts that have the highest hydroformylation activity. The catalysts are easily separated from the reaction mixtures, and the Rh−S/SiO 2 catalyst maintains its activity through at least three cycles over a total period of 69 h, during which time there are 1273 (mol of aldehyde/mol of Rh) turnovers. Effects of the phosphine ligand and PR‘ 3 /Rh mole ratio on the hydroformylation rate, conversion, and chemo- and regioselectivity for aldehyde products were also investigated.