Peroxidative bromination and oxygenation of organic compounds: Synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands

Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H₂L¹) in methanol with aqueous NH₄VO₃ solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex VOL¹(MeOH)]·ClO₄ (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H₂L¹) with aqueous solution of VOSO₄ leads to the formation of di-(μ-oxo) bridged vanadium(V) complex VO₂L²]₂ (2) as green solid where HL² = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL² is generated in situ by the hydrolysis of one of the imine bonds of HL¹ ligand during the course of formation of complex VO₂L²]₂ (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H₂O₂ and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by ¹H NMR spectroscopic studies.