Redox Chemistry in the Reaction of Oxovanadium(V) with Thiolate‐Containing Ligands: the Isolation and Characterization of Non‐Oxo Vanadium(IV) Complexes Containing Disulfide and Thioether Groups

Abstract

The reactions of VVO(O‐iPr)3 with [PS3′]H3 and [PS3]H3 {[PS3′]H3 = P(C6H3‐5‐Me‐2‐SH)3, [PS3]H3 = P(C6H4‐2‐SH)3} led to the formation of [VIV(L)] [L = P2S4′ (1a), P2S4 (1b)], where L was formed by the oxidative coupling of two PS3′ or PS3 ligands by a disulfide bond. When the reaction of VVO(O‐iPr)3 with [PS3′]H3 was conducted in the presence of methoxide followed by the addition of a cation, [VIV(PS3′)(PS2SMe′)]X [X = N(C2H5)4 (2a), N(C2H5)3(CH2Ph) (2b)] was isolated, where PS2SMe′ is a bis(benzenethiolato)phenylmethylthioetherphosphane ligand generated from the methylation of one thiolate group in PS3′. The structures of complexes 1a,b and 2a,b, determined by X‐ray crystallography, contain six‐ and seven‐coordinate non‐oxo vanadium(IV) centers, respectively, with an octahedral geometry for 1a,b and a pentagonal‐bipyramidal geometry for 2a,b. The electronic, magnetic, and electrochemical properties of these complexes were determined by UV/Vis and EPR spectroscopy, SQUID measurements, and cyclic voltammetry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Is Vanadate Reduced by Thiols under Biological Conditions? Changing the Redox Potential of V(V)/V(IV) by Complexation in Aqueous Solution

“…A detailed description of the vanadium(IV)- glutathione system confirms multiple species with a polydentate glutathione bound to the oxovanadium center 100. Isolation and structural characterization of a range of oxo and non oxo vanadium-sulfur complexes support the types of structures proposed in this system 2,5–11…”

“…A range of vanadium-sulfur complexes and their chemistries have demonstrated that vanadium-sulfur complexes have interest as models for nitrogenase chemistry,2 as the vanadium binding proteins,3,4 as anti-amoebic agents,5–7 as anti-diabetic agents,8 and as catalysts 9,10. The literature provides many examples that rapid reduction of vanadium(V) compounds takes place in the presence of biological thiols such as glutathione, cysteine, 2-mercaptoethanol and dithiothreitol (DTT) under physiological conditions 11–17.…”

“…Redox reactions of glutathione and cysteine have also been reported with chromium(VI) 18,19 iron(III)20,21 and ruthenium(III)22,23 compounds. Reports on formation and characterization of stable vanadium(V) complexes with thiol-containing ligands2,5–7,24–26 and their solution chemistry show26–28 that these complexes can be stable. Slow reduction of vanadium(V) by thiols in biological systems15,29 implies that vanadium(V) complexes can form, be characterized and possibly isolated 24–28,30,31.…”

Activation of O−H and C−O Bonds in Water and Methanol by a Vanadium‐Bound Thiyl Radical

“…The results were similar, indicating the observed reactions did not occur inside am ass spectrometer.I no ur earlier studies, we have reported an analogue of complex 3,[ V IV (PS3')(PS2'S CH3 )] À ,w here PS3' = [P(C 6 H 3 -5-Me-2-S) 3 ] 3À and PS2S' CH3 = [P(C 6 H 3 -5-Me-2-S) 2 (C 6 H 3 -5-Me-2-SCH 3 )] 2À . [18] The complex was obtained from the reactiono f[ V V O(OiPr) 3 ]w ith Li 3 [PS3']i nm ethanol. At that time, it was proposed that the reaction led to the formation of am etal thiyl radical intermediate that was likely involved in the cleavage of the CÀOb ondi nm ethanol.…”

“…At that time, it was proposed that the reaction led to the formation of am etal thiyl radical intermediate that was likely involved in the cleavage of the CÀOb ondi nm ethanol. [18] With this in mind, we began work to isolate the intermediate that could verify this hypothesis. [16] Consequently,c omplex 1 was isolated and characterizeda sametal thiyl radicals pecies.…”