Dioxovanadium( V ) Complexes of ONO Donor Ligands Derived from Pyridoxal and Hydrazides: Models of Vanadate‐Dependent Haloperoxidases

Autor: Dieter Rehder, Mannar R. Maurya, Cerstin Bader, Shalu Agarwal
Rok vydání: 2005
Předmět:
Zdroj: European Journal of Inorganic Chemistry. 2005:981-981
ISSN: 1099-0682
1434-1948
DOI: 10.1002/ejic.200500051
Popis: [VO(acac)2] reacts with H2L [H2L are the hydrazones H2pydx-inh (I), H2pydx-nh (II), or H2pydx-bhz (III); pydx = pyridoxal, inh = isonicotinohydrazide, nh = nicotinohydrazide, bhz = benzohydrazide] in dry methanol to yield the oxovanadium(IV) complexes [VOL] (H2L = I: 1; H2L = II: 4) or [VO(pydx-bhz)]. These complexes, when exposed to air, convert into the corresponding dioxovanadium(V) complexes [VO2HL] (H2L = I: 2; H2L = II: 5; H2L = III: 7). Aqueous solutions of vanadate and the ligands at pH = 7.5 give rise to the formation of [K(H2O)3][VO2(pydx-inh)] (3), [K(H2O)2][VO2(pydx-nh)] (6) and [K(H2O)2][VO2(pydx-bhz)] (8). Treatment of 6 and 8 with H2O2 generates the oxo(peroxo)vanadium complexes [VO(O2)L] (H2L = II: 9; H2L = III: 10). Complexes 9 and 10 are capable of transferring an oxo group to PPh3. Acidification of 8 with HCl afforded a hydroxo(oxo) complex. The crystal and molecular structures of ligand I and complex 3 have been solved by single-crystal X-ray diffraction. In the anion 3, the vanadium atom is in a distorted tetragonal-pyramidal environment (τ = 0.23). The K+ ion is coordinated to four water molecules (two of which bridge to a neighbouring K+ ion), the pyridine nitrogen atom of an isonicotinic moiety, the equatorial oxo group of the VO2+ fragment, and the alcoholic group of the pyridoxal moiety, which links adjacent layers in the three-dimensional lattice network. In the presence of KBr/H2O2, the anionic complexes 3, 6 and 8 catalyse the oxidative bromination of salicylaldehyde in water to 5-bromosalicylaldehyde in ca. 40% yields with ca. 87% selectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Databáze: OpenAIRE
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