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.