Tetranuclear Zn complex covalently immobilized on sulfopropylsilylated mesoporous silica: An efficient catalyst for ring opening reaction of epoxide with amine

Tetranuclear Zn complex, [Zn-4(L)(2)(LH)(2)((CH3)(2)SO)(2)]center dot 2CH(3)OH center dot(CH3)(2)SO center dot H2O (1) [where LH3 = 3-(E)-(2hydroxyphenylimino)methyl-4-hydroxy-5-hydroxymethylphenyl (LH3)] was prepared and characterized by single-crystal X-ray analysis. Then, it was incorporated to the sulfopropylsilylated MCM-48, MCM-41 and SBA-15 mesoporous silica materials. The prepared materials were thoroughly characterized by XRD, FT-IR, N-2 adsorption/desorption analysis, NH3-TPD, TGA, SEM-EDX and ICP-OES measurements. These catalysts were successfully used for the ring opening reaction of propylene oxide with morpholine producing the corresponding beta-aminoalcohols. An abrupt increase in catalytic activities was observed after anchoring of the tetranuclear Zn complex onto the inner surface of sulfopropylsilylated mesoporous materials. Among all the catalysts, the tetranuclear Zn complex incorporated MCM-48 was found to be most active in this reaction system and gave maximum 95% conversion. Catalysis by the tetranuclear Zn complex immobilized on MCM-48 was totally heterogeneous and the catalyst was recyclable up to 4 times without leaching.