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.

Graphical abstractNew mononuclear complex of oxovandium(V) [VOL1(MeOH)]·ClO4 (1) of tetradentate chiral Schiffbase ligand (R,R)-N,N-di-salicylidene cyclohexane 1,2-diamine(H2L1) and binuclear di-(μ-oxo) bridged vanadium(V) complex [VO2L2]2 (2) with tridentate chiral Schiffbase (R,R)-N-salicylidene cyclohexane 1,2-diamine(HL2) have been synthesized and characterized by Spectroscopic and X-ray diffraction studies. Both the compounds are used as catalyst for the peroxidative bromination of organic compounds as well as oxofunctionalisation of hydrocarbons in presence of H2O2 as terminal oxidant.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis and structure of mononuclear [VOL1(MeOH)]·ClO4 and dinuclear [VO2L2]2. ► H2L1 = (R,R)-N,N-disalicylidene cyclohexane 1,2-diamine. ► HL2 = (R,R)-N-salicylidene cyclohexane 1,2-diamine. ► Catalytic bromination of organic compounds using the above complexes as catalyst. ► Oxidative activation of aliphatic and aromatic C–H bond using H2O2 as terminal oxidant.