Co(II) Schiff base complexes on silica by sol–gel method as heterogeneous catalysts for oxidative carbonylation of aniline

Two kinds of Co(II) Schiff base complexes, Co(salen)[N,N’-bis(salicylidene)-ethylene-diaminto cobalt (II)] and Co(salophen)[N,N′-bis(salicylidene)-o-phenyldiaminto cobalt (II)], were covalently bonded to silica matrix via a sol–gel process. Characterizations of the obtained silica materials with FTIR, UV–vis, TG and XPS spectroscopy clearly showed that the Co(II) complexes were successfully incorporated into the silica matrix. These two Co(II) complexes performed good catalytic activity in the oxidative carbonylation of aniline (AN) in the presence of methanol to methyl N-phenylcarbamate (MPC). When the reaction was carried out at 150 °C and 6 MPa (CO/O2 = 9:1) for 3 h in AN (11 mmol), 0.5 g catalyst and 0.365 g KI, the conversion of AN and selectivity of MPC were 62.6% and 87.2% for immobilized Co(salen), and 63.8% and 88.6% for immobilized Co(salophen), respectively. Furthermore, the immobilized Co(salen) could be recycled and there was no significant loss on the catalytic activity when it was reused for five times.