Synthesis, characterisation and catalytic potential of hydrazonato-vanadium(v) model complexes with [VO]3+ and [VO2]+ cores
| Autor: | Shalu Agarwal, Cerstin Bader, Mannar R. Maurya, Martin Ebel, Dieter Rehder |
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| Rok vydání: | 2005 |
| Předmět: |
Bromides
Vanadium Compounds Stereochemistry Catechols Molecular Conformation Vanadium chemistry.chemical_element Crystallography X-Ray Ligands Hydrazide Medicinal chemistry Catalysis Inorganic Chemistry chemistry.chemical_compound Nickel Benzene Nuclear Magnetic Resonance Biomolecular Aldehydes Catechol Aqueous solution Molecular Structure Phenol Electron Spin Resonance Spectroscopy Hydrazones Hydrogen Peroxide Oxygen Models Chemical chemistry Salicylaldehyde Methanol |
| Zdroj: | Dalton Transactions. :537 |
| ISSN: | 1477-9234 1477-9226 |
| DOI: | 10.1039/b416292g |
| Popis: | Reaction between [VO(acac)2] and H2L (H2L are the hydrazones H2sal-nah I or H2sal-fah II; sal = salicylaldehyde, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) in methanol leads to the formation of oxovanadium(IV) complexes [VOL·H2O] (H2L = I: 1, H2L = II: 4). Aerial oxidation of the methanolic solutions of 1 and 4 yields the dinuclear oxo-bridged monooxovanadium(V) complexes [{VOL}2µ-O] (H2L = I: 2, H2L = II: 5). These dinuclear complexes slowly convert, in excess methanol, to [VO(OMe)(MeOH)L] (H2L = I: 9, H2L = II: 10), the crystal and molecular structures of which have been determined, confirming the ONO binding mode of the dianionic ligands in their enolate form. Reaction of aqueous K[VO3] with the ligands at pH ca. 7.5 results in the formation of [K(H2O)][VO2L] (H2L = I: 3, H2L = II: 6). Treatment of 3 and 6 with H2O2 yields (unstable) oxoperoxovanadium(V) complexes K[VO(O2)L], the formation of which has been monitored spectrophotometrically. Acidification of methanolic solutions of 3 and 6 with HCl affords oxohydroxo complexes, while the neutral complexes [VO2(Hsal-nah)] 7 and [VO2(Hsal-fah)] 8 were isolated on treatment of aqueous solutions of 3 and 6 with HClO4. These complexes slowly transform into 9 and 10 in methanol, as confirmed by 1H, 13C and 51V NMR. The anionic complexes 3 and 6 catalyse the oxidative bromination of salicylaldehyde in water in the presence of H2O2/KBr to 5-bromosalicylaldehyde and 3,5-dibromosalicylaldehyde, a reaction similar to that exhibited by vanadate-dependent haloperoxidases. They are also catalytically active for the oxidation of benzene to phenol and phenol to catechol and p-hydroquinone. |
| Databáze: | OpenAIRE |
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