Ship-in-a-bottle synthesis, characterization and catalytic oxidation of styrene by host (nanopores of zeolite-Y)/guest ([bis(2-hydroxyanil)acetylacetonato manganese(III)]) nanocomposite materials (HGNM)

A series of manganese(III) complexes with Schiff-base tetradentate ligands, [bis(2-hydroxyanil)acetylacetone], [Mn(X2-haacac)Cl] (X = H, CH3, Cl and NO2) have been synthesized and characterized as homogeneous and encapsulated into the nanopores of zeolite-Y by the flexible ligand method (FLM). The new materials were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET and DRS). The analytical data indicated a composition corresponding to the mononuclear complex of Schiff-base ligand ([Mn(X2-haacac)Cl]). The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Substitution of the aromatic hydrogen atoms of the Schiff-base ligand by electron withdrawing groups like –Cl, and –NO2 has two major effects: (1) retention and concentration of the Mn(III) complex in the zeolite cavities is enhanced (due to the larger size of the substituents) and (2) the electronic and spectral properties of the encapsulated complex are modified. The aerobic oxidation of styrene to benzaldehyde, styrene oxide and phenylacetaldehyde over these catalysts is also reported. Reaction conditions have been optimized by considering the amount of catalyst, effect of time and temperature. Under the optimized reaction conditions, [Mn((NO2)2-haacac)Cl]-NaY has shown the highest conversion of 95.8% after 12 h. Encapsulated Mn(III) complex is catalytically very efficient as compared to other neat complexes for the oxidation of styrene and is stable to be recycled without much deterioration.