Transfer Hydrogenation Reactions Catalysed by Free or Silica-immobilized Complexes [RuCl2(ampy)(RN(CH2PPh2)2)]

The complexes cis-[RuCl2(ampy){(RN)-N-1(CH2PPh2)(2)}] [ampy = (2-aminomethyl)pyridine, R-1 = C6H5 or (CH3CH2O)(3)Si-(CH2)(3)] showed very high catalytic activity in the homogeneous transfer hydrogenation of acetophenone (TOF > 300000 h(-1)) with the use of 2-propanol as the hydrogen donor and in the presence of sodium isopropoxide. The ligand (CH3CH2O)(3)Si(CH2)(3)N(CH2PPh2)(2) (ATM) was prepared in high yield by reacting (3-aminopropyl)triethoxysilane, paraformaldehyde, and diphenylphosphane in toluene heated at 80 degrees C. The -N(CH2PPh2)(2) function was attached to the surface of three different kinds of silica by means of two alternative methods. Thus, MA-Si-150 and mesoporous MA-Si-MCM-41 were prepared by the reaction of the inorganic matrix with ATM, whereas MA-Si-60 was synthesized by reaction of the commercially available 3-aminopropyl-functionalized silica gel with HCHO and PHPh2 in refluxing toluene. The -(CH2)(3)N(CH2PPh2)(2) functionalized inorganic materials were used to anchor the RuCl2(ampy) moiety; thus, three different silica-immobilized versions of the cis-[RuCl2(ampy)-(ATM)] complex were obtained. The silica-anchored complexes were tested in the transfer hydrogenation of acetophenone, which was found to be fast and quantitative; the effect of the nature of the silica support on the activity of the catalyst was almost negligible. It was possible to reuse the catalytic system for a second cycle without a decrease in the activity, but the efficiency of the catalyst considerably diminished in successive reuses.