Molybdenum(VI) complex with a tridentate Schiff base ligand immobilized on SBA-15 as effective catalysts in epoxidation of alkenes

Two novel molybdenum(VI) tridentate Schiff base complexes supported onto modified mesoporous SBA-15 were prepared by a covalent grafting method, one of which involved the postsynthesis trimethylsilylation of Mo-FSAP-Cl-SBA-15 to remove the residual surface silanol groups. The prepared complex materials were characterized by FT-IR, XRD, SEM, TEM, Si-29 CP-MAS-NMR, TGA, ICP-AES and nitrogen adsorption-desorption. Both two were active in the catalytic epoxidation of cyclohexene at 80 degrees C using tert-butylhydroperoxide (TBHP) as oxidant and 1,2-dichloroethane as solvent. The catalytic activity of the heterogenized organo catalyst can be further enhanced by silylation of the residual Si-OH groups using Me3SiCl, due to the higher content of Mo active sites and better surface hydrophobicity. As a result, using the more efficient catalyst Mo-FSAP-CH3-Cl-SBA-15 for catalytic reaction, the conversion and selectivity were 94.38% and 91.63%, respectively, under the optimized condition. After being used five times, the conversion and selectivity of Mo-FSAP-CH3-Cl-SBA-15 were still above 80.00% and 90.00% indicating the good reusability of Mo-FSAP-CH3-Cl-SBA-15. (C) 2014 Elsevier Inc. All rights reserved.