Catalytic Roles of Metal Centers in the Selective Oxidation of Cyclohexanol by Cr(salten) Complexes Immobilized on MCM-41

A series of transition metal complexes of 3-[N,N′-bis-3-(salicylidenamino)ethyltriamine] (salten) immobilized on MCM-41 were prepared for the solvent and additive-free selective oxidation of cyclohexanol with 30 % hydrogen peroxide (H2O2). The immobilized complexes were effective catalysts and exhibited much higher catalytic performance than their homogeneous analogues. Moreover, the metal centers were found to play important roles in the catalytic performance of immobilized complexes. When the immobilized chromium complex was used as catalyst, the optimal cyclohexanol conversion could reach 90.5 % with 100 % of the selectivity to cyclohexanone. In addition, the catalytic performance remained after being recycled five times. Owing to the different 3d electronic numbers of metal centers, eight kinds of immobilized Schiff base complexes exhibited significantly different catalytic performance in the selective oxidation of cyclohexanol with 30 % H2O2. The optimal cyclohexanol conversion could reach 90.5 % with 100 % of the selectivity to cyclohexanone over immobilized chromium complex.