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

Abstract

Treatment of of ( R, R)-N,N-salicylidene cyclohexane 1,2-diamine(H 2L 1) in methanol with aqueous NH 4VO 3 solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL 1(MeOH)]·ClO 4 ( 1) as deep blue solid while the treatment of same solution of ( R, R)-N,N-salicylidene cyclohexane 1,2-diamine(H 2L 1) with aqueous solution of VOSO 4 leads to the formation of di-(μ-oxo) bridged vanadium(V) complex [VO 2L 2] 2 ( 2) as green solid where HL 2 = ( R, R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL 2 is generated in situ by the hydrolysis of one of the imine bonds of HL 1 ligand during the course of formation of complex [VO 2L 2] 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 H 2O 2 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.