Zeolite-encapsulated manganese(III)salen complexes

Abstract

Manganese(III) complexes of [N,N'-ethylenebis(salicylidene-aminato)] (salen), [N,N'-ethylenebis(5-chloro-salicylidene-aminato)] (Cl₂Salen), [N,N'-ethylenebis(5-bromo-salicylidene-aminato)] (Br₂Salen) and [N,N'-ethylenebis(5-nitro-salicylidene-aminato)] [(NO₂)₂Salen] have been encapsulated in the supercages of zeolite X by the zeolite synthesis method. The catalysts have been characterized by FTIR, UV-Vis and EPR spectroscopic techniques, XRD, SEM, thermal and elemental analysis, as well as nitrogen adsorption and cyclic voltammetric studies. The extent of encapsulation of the Mn(III)Salen complexes in zeolite X varies with the nature of the substituent group on the aromatic ring. While bromo groups enhance encapsulation, substitution with -NO₂ groups decreases the amounts of Mn(III) complexes encapsulated in the cavities of the zeolites. Cyclic voltammetric data indicate that the zeolite matrix facilitates the reduction of Mn(III) to Mn(II), suggesting that it behaves like an electron-withdrawing substituent. The aerobic oxidation of styrene to benzaldehyde, styrene oxide and phenylacetaldehyde over these catalysts is also reported.