Synthesis of novel N4O4 type bis(diazoimine)-metal complexes supported on mesoporous silica: Microwave assisted catalytic oxidation of cyclohexane, cyclooctane, cyclohexene and styrene

Cu(II), Co(II), Mn(II) and Ni(II) complexes of silica-supported N4O4 type bis(diazoimine) ligands were synthesized and characterized by using FT-MIR/FAR, TG/DTA, elemental analysis, ICP-OES, SEM and EDX techniques. Catalytic activities of the complexes were investigated on the selective oxidation of cyclohexane, cyclohexene, cyclooctane and styrene under microwave power. In cyclohexane oxidation, L1-Cu(II) catalyst showed the best catalytic activity with the conversion of 7331% and 46.05% cyclohexanol and 34.87% cyclohexanone selectivity. L1-Cu(II) and L2-Cu(II) catalyst were selective for 2-cyclohexen-l-ol (40.54% and 65.01%) in the cyclohexene oxidation with high conversions (66.77% and 54.59%). Cycloctanone selective Ll-Cu(II), L2-Cu(II), L2-Cu(II) and L1-Ni(II) (75-80%) complexes showed very selective catalytic properties in the catalytic oxidation of cyclooctane. L1-Ni(II), L2-Ni(II) and L3-Ni(II) catalysts have had 81.28%, 73.70% and 81.39% selectivities respectively in styrene oxidation. Generally, it can be said that Cu(II) complexes are highly active and selective catalysts on the oxidation of cyclohexane, cyclohexene and cyclooctane. Nevertheless, Ni(II) complexes of L1 and L2 showed important selective catalytic performances towards the epoxidation of styrene. (C) 2016 Elsevier B.V. All rights reserved.