Microwave assisted catalytic oxidation of cyclohexene, cyclohexane, cyclooctane and styrene with metal complexes of bis(azo-imine) ligands supported on mesoporous silica

Abstract

Novel multifunctional bis(azo-Schiff base) ligands supported on mesoporous silica and their Cu(II), Co(II), Mn(II) and Ni(II) complexes were synthesized and characterized with the techniques of FT-IR, TGA, SEM, EDX, ICP-OES (metal content) and C, H, N content analyses. The synthesized complexes were tried as catalysts in the oxidation of cyclohexene, cyclohexane, cyclooctane and styrene substrates under microwave power. The Co(II) complex of silica-supported bis(azo-Schiff base) ligand derivatized from m-xylylenediamine and 2,4-dihydroxybenzaldehyde (L2) behaved as the best catalyst in cyclohexane oxidation to cyclohexanol with 73.84% selectivity. The complexes of Cu(II) were very selective to the yield of 2-cyclohexen-1-ol synthesis from the oxidation of cyclohexene under microwave power especially L2-Cu(II) with 64.29% selectivity. According to the calculated selectivities of the complexes in the catalytic reactions, it can be said that the complexes were not active in cycloctane and styrene oxidation.

Graphical Abstract

Keywords:

• Azo
• Schiff base
• imine
• oxidation
• silica
• microwave
• catalysis

Acknowledgements

I would like to thank The Scientific & Technological Research Council of Turkey (TÜBİTAK) (Project No: 111T211) and Kahramanmaraş Sütçü İmam University for their financial supports. Besides, I thank Prof. Dr. Mehmet Tümer, Prof. Dr. Ferhan Tümer, Mahmut İncesu, Hamza Adıgüzel and Seda Köşker Akkaya.