New oxo-bridged dinuclear peroxotungsten(VI) complexes: Synthesis, stability and activity in bromoperoxidation
- 作者：Pankaj Hazarika ; Diganta Kalita ; Swapnalee Sarmah ; Ruli Borah ; Nashreen S. Islam
- 关键词：Oxobridged peroxotungstate ; Heteroligand diperoxotungsten(VI) ; Dinuclear peroxotungstate ; Peptide containing peroxotungstate ; Bromide oxidant ; Peroxidative bromination
- 刊名：Polyhedron
- 出版年：2006
- 期刊代码：87_02775387
- 类别：ch
- 出版时间：25 December 2006
- 卷：25
- 期：18
- 页码：3501-3508
- 文件大小：233 K
摘要
Two new dinuclear oxo-bridged peroxo complexes of tungsten with coordinated dipeptides of the type, Na2[W2O3(O2)4(glycyl-glycine)2] · 3H2O (1) and Na2[W2O3(O2)4(glycyl-leucine)2] · 3H2O (2) have been synthesized from the reaction of H2WO4, 30%H2O2 and the respective dipeptide at pH ca. 2.5. Synthesis of the compounds, in addition to pH, is sensitive to reaction temperature and concentrations of the components. The compounds were characterized by elemental analysis, spectral and physico-chemical methods including thermal analysis. In the dimeric complexes the two W(VI) centres with edge bound peroxo groups are bridged by an oxo group. The dipeptides occurring as zwitterions bind the metal centers through O (carboxylate) atoms leading to hepta co-ordination around each W(VI). Thermal stability of the compounds as well as their stability in solution were determined. The compounds are highly stable toward decomposition in solutions of acidic as well as physiological pH. These compounds, besides another similar dimeric compound Na2[W2O3(O2)4(cystine)] · 4H2O (3) efficiently oxidized bromide to a bromination competent intermediate in phosphate buffer at physiological pH, a reaction in which only two of the peroxide groups of the complex species were found to be active. The complexes could also mediate bromination of organic substrate in aqueous-organic media.