Oxidation of cyclic hydrocarbons with hydrogen peroxide over iron complexes encapsulated in cation-exchanged zeolite

Fe-bipyridine complexes were encapsulated into cation-exchanged Y-type zeolites (M-Na-Y: M = K+, Cs+, Mg2+, Ca2+, NH4+, TMA+, and TBA+) and their catalytic activities for oxidation of benzene with hydrogen peroxide (H2O2) to phenol were investigated in three types of solvents (CH3CN, H2O, and CH3CN + H2O(1:1)). Regardless of the kind of solvent, the counter cation in [Fe(bpy)3]2+@M-Na-Y did not affect the selectivity to phenol. No significant difference in catalytic activity of [Fe(bpy)3]2+@M-Na-Y appeared in CH3CN + H2O (1:1), while a difference on catalytic activity appeared in each CH3CN and H2O solvent. It was suggested that the catalytic activity is related with the accessibility of benzene to [Fe(bpy)3]2+ site in [Fe(bpy)3]2+@M-Na-Y, controlled by the hydrated ionic radius of the counter cation introduced. The effect of ligand coordinated with Fe ion was investigated by comparing the catalytic activities for oxidation of cyclic hydrocarbons (benzene, cyclohexane, and cyclohexene) over [Fe(bpy)3]2+@Na-Y, [Fe(phen)3]2+@Na-Y, and [Fe(terpy)2]2+@Na-Y (phen = 1,10-phenanthroline and terpy = 2,2′;6′,2″-terpyridine). It was suggested that the expansion of π-electron over the ligands such as phen and terpy improves the uptake ability of substrates having π-electron such as benzene.