Reusable Cobalt(III)-Salen Complex Immobilized on Activated Carbon

Significance

The activated carbon-immobilized cobalt(III)-salen complex [CoxO-Co(salen)] was prepared with the intention to use it for the preparation of 2-arylbenzimidazole derivatives 4. Thus, an air-oxidized activated carbon (CoxOH) was treated with aq NaOH under reflux for one hour to give CoxONa. Then, CoxONa reacted with cobalt(III)-salen complex 1 in refluxing EtOH to afford the CoxO-Co(salen) catalyst. The reaction of o-phenylenediamines 2 with aryl aldehydes 3 was carried out in the presence of CoxO-Co(salen) at room temperature under air as a reoxidant to give the corresponding 2-arylbenzimidazoles 4 (17 examples, 90-96% yield).