Chemically Modified Silica-Gel With an Azo-Schiff Ligand and Its Metal Complexes With Cu(II), Co(II), Ni(II) and Mn(II): Applications as Catalysts on the Oxidation of Cyclohexane Under Microwave Power

Abstract

A novel 2-hydroxy-5-((2-hydroxyphenyl)diazenyl)benzal- dehyde (L¹: HPDB) ligand was synthesized and bound to silica gel, which was activated with 3-aminopropyltriethoxysilane. Cu(II), Co(II), Ni(II), and Mn(II) complexes of silica-supported ligand (L²: MDPMP) were synthesized. A buffer (pH = 12) was used for a coupling reaction of diazonium electrophile to salicylaldehyde. The ligand and its complexes were characterized by using NMR, FT-MIR/FAR, elemental analysis, ICP-OES, TGA, and scanning electron microscopy. Catalytic properties of the complexes were investigated for the selective oxidation of cyclohexane under microwave power. Silica-supported L²-Cu(II) complex showed well selective catalytic activity for the oxidation of cyclohexane to cyclohexanol and cyclohexanone with 8.40% and 3.77% yields with 48.43% conversion.