Dioxidomolybdenum(VI) and dioxidouranium(VI) complexes as functional mimic of haloperoxidases catalytic activity in presence of H2O2–KBr–HClO4

The stable dibasic tetradentate ligand 1,4-bis-(2-hydroxy-3,5-dimethylbenzyl)piperazine (H2pip-2,4-dmp, I) prepared by reacting 2,4-dimethylphenol with piperazine in the presence of formaldehyde reacts with [MoVIO2(acac)2] and [UVIO2(CH3COO)2] in equimolar ratio to give neutral hexa-coordinated [MoVIO2(pip-2,4-dmp)] (1) and hepta-coordinated [UVIO2(pip-2,4-dmp)(MeOH)] (2), respectively. After characterizing these complexes by spectroscopic (IR, UV/Vis, 1H and 13C NMR) data, elemental and thermal analyses (and single crystal X-ray diffraction study of uranium complex), they are used as catalysts to study the oxidative bromination of thymol. Such catalytic reactions are observed by many model vanadium complexes and are considered as a functional mimic of haloperoxidases. The catalytic oxidation resulted in the formation of three products namely, 2-bromothymol, 4-bromothymol and 2,4-dibromothymol. The optimized reaction conditions are obtained considering concentration of KBr, HClO4, and oxidant for the maximum yield of brominated products. Under the optimized reaction conditions, the product selectivity for both the prepared complexes is investigated. They are found to be competent homogeneous catalysts to afford the products in good yield.