Synthesis, characterization and liquid-phase hydroxylation of phenol with hydrogen peroxide over host (nanopores of zeolite-Y)/guest (oxovanadium(IV) complexes of tetraaza macrocyclic ligands) nanocatalyst

Oxovanadium(IV) tetraaza complexes of [14]aneN₄: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane; [16]aneN₄: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane; Bzo₂[14]aneN₄: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and Bzo₂[16]aneN₄: dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane have been encapsulated in the nanopores of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)VO(IV)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [VO(N-N)₂]²⁺-NaY; in the nanopores of the zeolite-Y and (ii) in situ condensation of the oxovanadium(IV) precursor complex with ethylcinnamate. The new host-guest nanocatalysts were characterized by several techniques: chemical analysis and spectroscopic methods (FT-infrared (FT-IR), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), nitrogen adsorption and diffuse reflectance spectra (DRS)) technique. The analytical data indicated a composition corresponding to the mononuclear complex of tetraaza ligand. The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN have been reported using oxovanadium(IV) tetraaza complexes encapsulated in zeolite-Y as catalysts. All these catalysts are more selective toward catechol formation.