Ru- and Fe-based N,N′-bis(2-pyridylmethyl)-N-methyl-(1S,2S)-1,2-cyclohexanediamine complexes immobilised on mesoporous MCM-41: Synthesis, characterization and catalytic applications

Protected mesoporous MCM-41 phases were synthesized by grafting of the ligand, (1S,2S)-N,N′-bis-pyridin-2-ylmethyl-cyclohexane-1,2-diamine (L2Me), through the reactive 3-chloropropyltrimethoxysilane (3-CPTMS) group and designated as L2Me-MCM-41. Subsequently, RuCl3 and Fe(BF4)2 or Fe(CF3SO3)2 were added to the heterogenized L2Me-MCM-41 for complexation and designated as M-L2Me-MCM-41 (M = Ru and Fe). All samples were characterized in detail using XRD, N2 sorption isotherm, FT-IR, TGA-DTA, XPS, UV–vis, solid state 13C NMR, EPR and elemental analysis, etc. The XRD and sorption measurements of the catalyst confirmed the structural integrity of the mesoporous hosts and the spectroscopic characterization techniques proved the successful anchoring of the metal complexes over the modified mesoporous support. The screening of catalyst M-L2Me-MCM-41 was done for the oxidation reaction of thioanisole (methyl phenyl sulphide) using H2O2 as an oxidant. The Ru-L2Me-MCM-41 and Fe-L2Me-MCM-41 catalysts show higher activities and turnover numbers and exhibit enantiomeric excess comparable to the homogeneous catalysts, Ru-L2(Me)2 and Fe-L2(Me)2. Furthermore, Fe-L2Me-MCM-41 and Fe-L2(Me)2 were also found active in the epoxidation of styrene. These results indicate that metal complexes are confined into the pore of the material which play a major role in the reaction.

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