Reusable MCM-41 Immobilized Rh(I) Hydroformylation Catalysts Built on Binaphthyl-based Phosphoramidite and Phosphite Ligands

The immobilization of Rh/phosphorus complexes in MCM-41 was performed using two different methodologies. The first synthetic strategy was based on the covalent attachment of a new binaphthyl-based phosphoramidite ligand through a trimethoxysilyl linkage, followed by its complexation with the rhodium(I) precursor Rh(CO)2(acac). The resulting heterogeneized Rh(I)/phosphoramidite complex was characterized by FT-IR, N2 adsorption and TG-DSC techniques, which indicated its effective bonding to the mesoporous material. A second approach was based on the physical adsorption of Rh(CO)2(acac) in MCM-41, followed by addition of tris[(R)-2'-(benzyloxy)-1,1'-binaphthyl-2- yl]phosphite, to generate in situ a Rh(I)/phosphite complex, whose rhodium content was determined by chemical analysis (ICP). The two hybrid materials were applied as catalysts in styrene hydroformylation, where both achieved high conversions and regioselectivity for the branched aldehyde, under moderate reaction conditions. The covalent immobilization strategy allowed the reutilization of the Rh/phosphoramidite catalyst, without loss of activity after four runs, while the physically adsorbed Rh/phosphite catalyst lost most of its activity, with occurrence of rhodium leaching.