Zeolite-Y entrapped metallo-pyrazolone complexes as heterogeneous catalysts: Synthesis, catalytic aptitude and computational investigation

Abstract

Transition metal [M = VO(IV) and/or Co(II)] complexes with Schiff base ligand (Z)-3-methyl-1-phenyl-4-(2,2,2-trifluoro-1-(2-hydroxyphenyl)imino)ethyl)-1H-pyrazol-5-ol (H2L) have been entrapped in the super cages of zeolite-Y by Flexible Ligand Method. These nanohybrid materials have been characterized by preferential physico-chemical techniques such as ICP-OES, elemental analyses, (FT-IR, 1H and 13C-NMR and electronic) spectral studies, BET, scanning electron micrographs (SEMs), AAS, X-ray diffraction patterns (XRD) and thermogravimetric analysis. The density functional theory calculations are performed to find optimized structures together with the bond angles, bond lengths, dihedral angles and electronic properties of ligand and neat complexes. The catalytic competence of zeolite-Y entrapped metallo-pyrazole complexes was examined by the oxidation of olefins viz. limonene, cyclohexene, styrene, and α-pinene using H2O2 as an oxidant. So as to ensure the shielding effect of the nanohybrid over the active center on the catalytic properties, the performance of the entrapped complexes (heterogeneous system) was weighing up against the neat complexes (homogeneous system). The effect of experimental variables (such as solvents, mole ratio of substrate and oxidant, the amount of catalyst and reaction time) with their probable justification on the conversion of limonene was discussed. Under the optimized reaction conditions, [VO(L)·H2O]-Y was found to be potential candidate, achieving 87.44%, 90.01%, 82.01%, and 85.44% conversions of limonene, cyclohexene, styrene, and α-pinene oxidation reactions, respectively.