Co(II) Schiff Base Complex Supported on Nano-Silica for the Aerobic Oxidation of Cyclohexene: Reaction Pathways and Overoxidation on the Experimental and Calculated Mechanism

摘要

A heterogeneous, recoverable catalyst of Co(II)-L@nano-SiO2 (where L=N-(3-trioxysilyl-propyl)-o-vanillin imine) was synthesized, and it was thoroughly characterized by EA, ICP, FT-IR, UV-vis, TGA, XPS and BET techniques. The catalytic performance of Co(II)-L@nano-SiO2 was investigated in cyclohexene(CyH) oxidation under mild conditions with oxygen as the sole oxidant. The results showed that Co(II)-L@nano-SiO2 exhibited better catalytic activity with the CyH conversion of 61 %, and a total selectivity of 55-60 % for the major products (2-cyclohexen-1-one (CyO) and 2-cyclohexen-1-ol (CyOH)), and there was no significant decrease in activity after five times reused. Furthermore, the overoxidation process was performed by epoxidation of CyO and CyOH. The mechanism involved allylic oxidation and overoxidation was confirmed by DFT calculations in the gas phase and the acetonitrile solvent.