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

Abstract

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, 29Si CP–MAS-NMR, TGA, ICP-AES and nitrogen adsorption–desorption. Both two were active in the catalytic epoxidation of cyclohexene at 80°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.