Search

Reactions of bis(acetylacetonato)oxovanadium(IV), [VO(acac)2], with biacetylmonoxime 4-R-benzoylhydrazones (H2L1 (R = Me) and H2L2 (R = OMe), where 2Hs represent the dissociable oxime and amide protons) in 1:1 mole ratio in methanol result in complexes [VO(OMe)(MeOH)(L1)] (1) and [VO(μ-OMe)(L2)]2 (2). When reactions were performed in the presence of two molar equivalents of KOH, K[VO2(L1)]·MeOH (3) and K[VO2(L2)]·2MeOH (4) were obtained. The complexes have been characterized using elemental analysis and mass spectrometry along with magnetic, solution electrical conductivity, thermogravimetric, various spectroscopic (IR, UV-Vis, and 1H NMR), and cyclic voltammetric measurements. The molecular structures of H2L1 and complexes 1-4 were determined by single-crystal X-ray crystallographic studies. In both 1 and the dimethoxo bridged centrosymmetric 2, the metal centers are in distorted octahedral NO5 environment, where (L1/2)2− meridionally coordinate the respective metal centers through the amidate-O, imine-N, and oximate-O and form fused 5,6-membered chelate rings. In 3 and 4, the metal centers have distorted trigonal bipyramidal N2O3 coordination spheres, where the fused 5,5-membered chelate rings forming amidate-O, imine-N, and oximate-N donors (L1/2)2− occupy the axial-equatorial-axial positions. The physical properties of all four complexes are consistent with their molecular formulas and structures. [ABSTRACT FROM AUTHOR]

The formation of vanadium complexes with synthesized enantio- and diastereomerically pure polydentate tetrahydrosalicylidene ligands of the diterpene series was studied using UV, visible, and 51V NMR spectroscopy. The obtained catalyst complexes were tested in the oxidation of prochiral sulfides with an aqueous 35% hydrogen peroxide solution. The studies on the oxidation of prochiral sulfides showed that chiral sulfoxides formed with yields of 28–90% and an enantiomeric excess (EE) of up to 96%. The nature of the solvent used was found to determine the configuration of sulfoxide. R-sulfoxides formed in ethanol, and S-sulfoxides, in methylene. [ABSTRACT FROM AUTHOR]

Four new vanadium complexes containing hydrazone and benzohydroxamate ligands with the general formula [VO(L n)(bzh)]·MeOH have been prepared and characterised. The complexes are active catalysts for epoxidation of cis -cyclooctene by tert -BuOOH, and for sulfoxidation of methyl- p -tolylsulfide by tert -BuOOH or H 2 O 2. [Display omitted] Four isostructural oxovanadium(V) complexes with hydrazone ligands have been synthesised, characterised, and evaluated as epoxidation and sulfoxidation catalysts. The reactions between [VO(acac) 2 ] (acac– = acetylacetonate) and H 2 L n (n = 1–4), precursors for monoanionic tridentate hydrazone ligands, afford complexes formulated as [VO(L n)(bzh)·MeOH] (1 – 4) when bidentate benzohydroxamic acid (Hbzh) is included as a co-ligand. Single crystal X-ray structure analyses showed that complexes 1 – 3 have a distorted octahedral coordination geometry with an O 5 N coordination environment. Cyclic voltammetry showed that all complexes undergo two quasi-irreversible reduction peaks and a single irreversible oxidation peak. The bonding in 1 has been investigated by electronic structure calculations, and these data are discussed with respect to the electrochemical results. Complexes 1 – 4 were tested as catalysts for the epoxidation of cis -cyclooctene at 50 °C and sulfoxidation of methyl- p -tolylsulfide at room temperature using tert -butyl hydroperoxide (t BuOOH) and aqueous H 2 O 2 as the terminal oxidants. [ABSTRACT FROM AUTHOR]

Condensation of 2,4‐dihydroxyacetophenone with isonicotinoyl hydrazide and nicotinoyl hydrazide in an equimolar ratio in methanol results in the formation of two stable ONO donor ligands, H2dhap‐inh (I) and H2dhap‐nah (II), respectively. These ligands react with [VIVO(acac)2] (Hacac=acetylacetone) in 1:1 molar ratio to give the corresponding neutral dioxidovanadium(V) complexes, [VVO2(Hdhap‐inh)] (1) and [VVO2(Hdhap‐nah)] (2), after overnight aerial oxidation in the presence of K2CO3. In the absence of K2CO3, they result in (μ‐O){bisoxidovanadium(V)} complexes, [{VVO(dhap‐inh)}2(μ‐O)] (3) and [{VVO(dhap‐nah)}2(μ‐O)] (4). Treatment of neutral dioxidovanadium(V) complexes, 1 and 2, with H2O2 yields oxidoperoxidovanadium(V) complexes K[VVO(O2)(dhap‐inh)(H2O)] (5) and K[VVO(O2)(dhap‐nah)(H2O)] (6). The ligands also react with [MoVIO2(acac)2] in 1:1 molar ratio to form [MoVIO2(dhap‐inh)]n (7) and [MoVIO2(dhap‐nah)]n (8). The reaction of oxidoperoxidomolybdenum(VI) species, generated in situ by the reaction of MoO3 with H2O2 with ligands I and II, gives the oxidoperoxidomolybdenum(VI) complexes, [MoVIO(O2)(dhap‐inh)(MeOH)] (9) and [MoVIO(O2)(dhap‐nah)(MeOH)] (10), respectively. All synthesized complexes are characterized by elemental analysis, thermogravimetric, electrochemical, spectroscopic (IR, UV–Vis, 1H, 13C and 51V NMR) and single crystal X‐ray diffraction (for 1, 2 and 8). Complexes are explored as catalysts for the oxidative bromination of phenol, a model oxidative halogenation reaction, in the presence of HClO4 and KBr, using 30% H2O2 as oxidant. Under optimized reaction conditions, the product selectivity follows the order: 4‐bromophenol>2‐bromophenol, both for molybdenum and vanadium complexes. Products characterized by GC analysis showed very good conversion of phenol. [ABSTRACT FROM AUTHOR]

Several vanadium(V) complexes have been investigated as possible antidiabetic and anticancer therapeutic agents. Among these, vanadium(V) complexes linked to tridentate ONO Schiff bases stand out for their potential in the treatment for cancer. However, further studies are necessary in order to learn about their specific action at the cellular level. We investigate structural and spectroscopic properties of these particular complexes, which are formed by a Schiff base linked to a [VO2]+ ion that contains different functional groups. Molecular structure optimizations of these vanadium-containing complexes were performed by the ONIOM (QM1:QM2) method, where the high layer (complexes) were described by density functional theory methods whereas the low layer (eight water molecules) were described by the HF approach. Various solvation models were utilized; however, the introduction of both implicit (using a solvation model based on density, SMD) and explicit (eight water molecules) solvation improves the stability of the systems. Interestingly, we found that the location of the explicit water molecules in the different octahydrated vanadium complexes was conserved surrounding the oxo-vanadate moiety. A detailed analysis of the chemical shift (δ) values for 1H, 13C and 51V is presented based on the ONIOM optimized geometries using the gauge-independent atomic orbital methodology. For obtaining accurately chemical shifts, the complete basis set using the correlation-consistent Dunning basis sets from double-ξ to quadruple-ξ and the Ahlrichs basis set were utilized. The results from the methodology presented here are consistent with those reported experimentally for 1H. Again, the inclusion of explicit water molecules in the inner solvation shell during the calculation of the chemical shifts was crucial. The analysis of solvation energies also indicates the relevance of including explicit water molecules as the main stabilization factor suggesting the central role of intermolecular interaction in the stability of the metallic complexes. From this analysis, a possible vanadium complex candidate for further evaluation in the cellular environment is suggested. This work not only provides evidence of a suitable methodology for studying the structural and spectroscopic properties of vanadium complexes but also highlights the relevance of explicitly including water molecules in their inner shell. [ABSTRACT FROM AUTHOR]

Graphical abstract Three new V(V) oxido complexes containing bis- or monophenolate ligands have been prepared and investigated as epoxidation and sulfoxidation catalysts. Highlights • Three new vanadium(V) oxo complexes have been synthesized and characterized. • Ligands used are potentially tetradentate amino bisphenols or amino bis-alcohol monophenols. • The V(V) complexes function as catalysts for oxidation of olefin and organic sulfides by H 2 O 2 or tBuOOH. Abstract The reactions between [VO(acac) 2 ] (acac– = acetylacetonate) and the tripodal amino bisphenols 6,6′-(((2-morpholinoethyl)azanediyl)bis(methylene))bis(2,4-di- tert -butylphenol) (H 2 L1) and 6,6′-(((thiophen-2-ylmethyl)azanediyl)bis(methylene))bis(2,4-di- tert -butylphenol) (H 2 L2) as well as the tetradentate amino phenol 2,2′-((3,5-di- tert -butyl-2-hydroxybenzyl)azanediyl)bis(ethan-1-ol) (H 3 L3) afford the complexes [VO(L1)(OMe)] (1), [VO(L2)(acac)] (2) and [VO(L3)] (3), correspondingly. Complexes 1 and 3 can also be prepared using VOSO 4 ·xH 2 O or [VO(OPr) 3 ] as vanadium precursors. When [VO(acac) 2 ] or VOSO 4 ·xH 2 O is used, mononuclear oxovanadium(V) complexes are formed upon oxidation of the metal precursor. Single crystal X-ray structure analysis show that complexes 1 and 2 have distorted octahedral coordination spheres, in which the amino bisphenolate coordinates in a tetradentate or tridentate manner, respectively, and the coordination spheres are completed by methoxy or acetylacetonato ligands. Complex 3 has a slightly distorted trigonal bipyramidal geometry with an NO 4 coordination environment. All three complexes can catalyze epoxidation of cis -cyclooctene at 50 °C with tert -butyl hydroperoxide (TBHP) or H 2 O 2 as an oxygen source, and sulfoxidation of thioanisole or methyl- p -tolylsulfide proceeds at 25 °C using the same oxidants. [ABSTRACT FROM AUTHOR]

The reaction between vanadyl sulfate and an NNO donor Schiff base (HL 1 or HL 2 ) in methanol resulted in the formation of two new binuclear vanadium(V) complexes, viz., [(L 1 )VO(μ-O) 2 VO(L 1 )]0.5H 2 O ( 1 ) and [(L 2 )VO(μ-O) 2 VO(L 2 )] ( 2 ) (L 1 = N ′-[( E )-phenyl(pyridin-2-yl)methylidene]benzohydrazide and L 2 = N ′-[( E )-phenyl(pyridin-2-yl)methylidene]furan-2-carbohydrazide). During the reaction, atmospheric oxygen spontaneously acted as an oxidizing agent and yielded new (V IV → V V ) vanadium(V) complexes. The electronic spectra of 1 and 2 shown the vanadium(V) centre is in a distorted octahedral environment in each case. The complexes were characterized by routine physico-chemical methods. The single crystal X-ray structures of 1 and 2 also revealed a distorted octahedral coordination around each of the vanadium(V) centres, confirming the NNO binding mode of the ligands L 1 and L 2 . In these binuclear complexes, the bridging functions are the μ-oxido bonds. The occurrence of weak CH⋯π interactions in 1 and π⋯π stacking interactions in 2 contribute extra stabilization in their solid state. The complexes catalyzed the dismutation of superoxide in an alkaline nitroblue tetrazolium chloride assay and the IC 50 values were estimated. [ABSTRACT FROM AUTHOR]

With the increasing development of metallopharmaceuticals, coordination compounds become viable alternatives for therapeutic uses. Despite the importance of platinum derivatives in this area, first-row transition metals complexes are welcome due to their characteristics. Vanadium is a promising metal in this context, as it has a range of compounds with different biological applications, including anticancer therapeutic effects. In this effort, the study of interactions between coordination compounds with deoxyribonucleic acid and with human serum albumin is fundamental. In this way, ten iminic ligands were synthesized by condensing p -substituted aromatic benzohydrazides (OH, CH 3 , H, NO 2 , and NH 2) with salicylaldehyde (L1As - L5As) or pyridoxal hydrochloride (L1P-L5P). These ligands have characteristics that allow the tridentate coordination of vanadium cations, leading to the formation of ten vanadium(V) complexes (C1As - C5As and C1P - C5P) with different structural features, all characterized by single-crystal X-ray diffraction, UV–Vis and infrared spectroscopies, and cyclic voltammetry. In addition, the complexes were tested for their interactions with calf thymus deoxyribonucleic acid and human serum albumin by spectroscopic assays and molecular docking calculations. These new results can contribute to further research and provide different ways to design new vanadium complexes with biological applications. [Display omitted] • Ten vanadium(V) complexes using benzohydrazides were synthesized. • Aromatic aldehydes such as pyridoxal and salicylic were used. • All complexes were characterized by single crystal X-ray diffraction. • The complexes were tested for interaction with macromolecules and molecular docking. [ABSTRACT FROM AUTHOR]

• Tow V(V) and V(IV) complexes have been prepared. • The prepared complexes characterized by different spectroscopic methods. • The ligands coordinated by nitrogen and oxygen atoms. • Insulin mimetic study has been designed and carried out. • The study of liver and kidney function parameters demonstrated the superiority of the C2 complex, so it could be promised as insulin-enhancing factor with low side effect. Two vanadium complexes in two oxidation states (IV) and (V) have were prepared with 3,4-diaminobenzoic acid and acetylacetone ligands. The chemical formula of the complexes is [VO(DABA)(acac)].3H 2 O (C1) and [VO 2 (DABA)(acac)].1/2H 2 O (C2). The complexes are characterized by using different tools such as; molar conductivity, magnetic susceptibility, spectroscopic techniques (FTIR, UV-Vis., mass, and 1H-NMR), and finally by the DFT calculations. The collected data showed that the ligands bound through two amines (NH 2) groups for (DABA) ligand and two carbonyls (C=O) groups for (acac) ligand. The spectroscopic data and the DFT calculations confirmed the mononuclear structure of both complexes. Distorted square pyramidal geometry for the C1 complex and distorted octahedral geometry for the C2 complex have been proposed. The calculations confirmed that the C2 complex is more stable than the C1 complex and the electronic energies are (-1098.98 and -1023.04 a.u.); respectively. The HOMO and the LUMO orbitals of the C2 complex (H = -0.385 and L = -0.228 a.u.) are more negative than that of the C1 complex (H = -0.248 and L = -0.206 a.u.). The bond angles in the two complexes have deviated from that of perfect octahedral and square planar (90° and 180°). The bond lengths between the vanadium atoms and the surrounded nitrogen and oxygen atoms are in the constituted range. The double bond between the vanadium atoms and the oxygen atoms (V=O) is 1.587 in the C1 complex and (1.60 and 1.62) in the C2 complex. The mimic insulin study showed that the C1 and the C2 complexes possess a good insulin-enhancing activity. The study of liver and kidney function parameters demonstrated the superiority of the C2 complex, so it promising result that as an insulin-enhancing factor with the low side effect. However, the C2 complex showed non-toxicity toward liver and kidney biochemical parameters, and that may be due to the oxidation state and the structure of the vanadium metal ion. The HOMO and LUMO molecular orbitals and energy gap of the [VO(DABA)(acac)].3H 2 O complex. [VO(DABA)(acac)].3H 2 O complex was prepared by the direct reaction of the (DABA) and (acac) ligands with the precursor of vanadium VOSO 4.5H 2 O. The complex was very stable and has a square pyramidal geometry. [Display omitted] [ABSTRACT FROM AUTHOR]

Structural and spectral properties of three complex anions of vanadium(V) with tartrato ligands were theoretically studied by all-electron DFT calculations employing various functionals, such as BP86, BLYP, B3LYP, BHHLYP, and the M06-family. Results were statistically evaluated, with the aim to find a reliable, fairly accurate, and yet computationally efficient combination of methods and basis sets to be used in computational chemistry of vanadium(V) complex anions at even larger scale. Subsequent vibrational analysis based upon BP86 and B3LYP data provided a fair agreement with the experimental vibrational spectra. Additionally, the absorption UV–Vis and the electronic circular dichroism spectra of studied compounds were simulated via time-dependent density functional theory calculations with the long-range corrected functionals (CAM-B3LYP, LC-ωPBE, and ωB97XD). Finally, the 51V NMR chemical shifts were calculated using the GIAO approach at the B3PW91 level. The solvent effect was simulated within the PCM model. Where available, the calculated spectral properties were compared with experimental data. [ABSTRACT FROM AUTHOR]

The tridentate ONN donor ligand, Hbzpy-fah ( I ) (Hbzpy-fah = Schiff base derived from 2-benzoylpyridine and 2-furoylhydrazide) upon reaction with [V IV O(acac) 2 ] in methanol followed by aerial oxidation give a dinuclear complex, [{V V O(bzpy-fah)} 2 (μ-O) 2 ] ( 1 ) having [{V V O} 2 (μ-O) 2 ] 2+ core. Treatment of 1 with H 2 O 2 in methanol results in the formation of dinuclear peroxido complex, [{V V O(bzpy-fah)} 2 (μ-O 2 ) 2 ] ( 2 ). The molecular structure of 2 was determined by single-crystal X-ray diffraction, confirming the ONN binding mode of I and μ-bis(peroxido) with side-on coordination. Reaction of 1 with imidazolomethylpolystyrene cross-linked with 5% divinylbenzene (PS-im) in DMF gives the polymer-supported complex 3 (abbreviated as PS-im[V V O 2 (bzpy-fah)]) which was characterized by field-emission scanning electron micrographs (FE-SEM) as well as energy dispersive X-ray (EDAX), atomic force microscopy (AFM) and thermal analysis along with usual spectroscopic techniques. Complexes 1 and 3 have been used as catalyst precursors for the oxidation of isoeugenol in the presence of aqueous H 2 O 2 as oxidant and gave vanillin, vanillic acid and dehydrodiisoeugenol. The polymer-supported complex showed higher conversion than its neat counterpart. This has also allowed for recyclable catalytic system with increased catalyst lifetime and thus proved to be better over the homogeneous counterpart. [ABSTRACT FROM AUTHOR]

A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO 2 (HL 5 )]·MeOH·H 2 O (H 2 L 5 = pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO 2 moiety. A DFT study of this molecule and of the related [VO 2 (H 2 L 5 )] complex of V IV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert -butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs . olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert -butoxido ( t BuOO – ) ligand, without the need to generate a peroxido (O 2 2– ) ligand. [ABSTRACT FROM AUTHOR]

The vanadium(V) complexes bearing the aroylhydrazone Schiff base 2-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide ligand [VO(OMe)L] (1) and [Et 3 NH][VO 2 L] (2) were synthesized, characterized and supported on porous MIL-100(Fe) forming the 1 @MIL-100(Fe) and 2 @MIL-100(Fe) composites. The outcome of such immobilizations was assessed by several characterization techniques, namely powder X-ray diffraction, UV/Vis, FTIR, SEM-EDS, ICP and BET surface area analysis, confirming the successful heterogenization of both vanadium complexes. They were screened as catalysts towards the oxidation of toluene, under homogenous (1 and 2) and heterogeneous (1 @MIL-100 and 2 @MIL-100) conditions. The influence of several parameters, namely the type and amount of catalyst or oxidant, reaction time, temperature, and radical trapping, was studied. The main products obtained were benzaldehyde, benzyl alcohol and benzoic acid. Under the optimized conditions, using 1 and 2 as homogeneous catalysts, total yields of 19 and 23%, respectively, were achieved at 80 °C after 6 h. Using 1 @MIL100(Fe) and 2 @MIL100(Fe) composites under heterogeneous conditions, total yields up to 11% after 24 h, were achieved. [Display omitted] • New oxidovanadium(V) complexes derived from 2-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide ligand. • The vanadium complexes were successfully supported on the porous MIL-100(Fe) framework. • Catalytic efficiency in homogeneous and heterogeneous conditions was screened for oxidation of toluene (VOC model substrate). • Benzaldehyde, benzyl alcohol and benzoic acid were obtained as main products. • The catalysts showed activity in toluene oxidation using eco-friendly oxidants with enhanced selectivity for benzaldehyde. [ABSTRACT FROM AUTHOR]

Abstract: 5-Tert-butyl-(3-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-2-hydroxybenzaldehyde (L1), (4-tert-butyl-2-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-6-(dimethoxymethyl) phenol (L2) and (2-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-6-methoxyphenol (L3), react with vanadyl acetylacetonate to give the vanadium(V) complexes [VO(L1-3H+)]2·dmso, [VO(L2-3H+)]2 and [VO(L3-3H+)]2·dmso. All complexes present the vanadium(V) center as the less common [VO]3+ cation. The structural features of the title compounds, specially the occurrence of supramolecular assemblies supported by bifurcated and trifurcated hydrogen bonding are discussed, as well as DFT studies and HOMO–LUMO energy gaps. Calculated spatial maps of the Fukui functions, f +(r) and f −(r), are also presented and discussed. [Copyright &y& Elsevier]

Two mononuclear cis-dioxovanadium(V) complexes of pyrazole-derived, Schiff-base ligands have been synthesized and characterized. Single crystal X-ray analyses were performed with N '-[(3-methyl-1H-pyrazole-5-yl)carbonyl]pyridine-2-carbohadrazonamido cis-dioxovanadium(V), {[VO2(PzOAP)] · H2O} (1), and 5-methyl-N-[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazonate cis-dioxovanadium(V), {[VO2(PzCAP)]} (2). Both complexes crystallize in monoclinic crystal systems with different space groups. Complex 1 crystallizes in the space group P21/c, 2 in space group C2/C. In each complex, the vanadium sits within a distorted square pyramidal geometry with an N2O3 chromophore. The τ parameters of the complexes (0.33 for 1, 0.22 for 2) support their square pyramidal geometry. The interesting finding in the work is that the alkoxide oxygen, imino nitrogen, and pyridine nitrogen take part in the coordination process leaving the pyrazole rings inactive in coordination. [ABSTRACT FROM AUTHOR]

Abstract: Two oxovanadium(V) salicylhydroximate complexes, [VO(SHA)(H2O)]·1.58H2O (1) and [V3O3(CSHA)3(H2O)3]·3CH3COCH3 (2) have been synthesized by reaction of VO4 3− with N-salicyl hydroxamic acid (SHAH3) and N-(5-chlorosalicyl) hydroxamic acid (CSHAH3), respectively, in methanol medium. Compound 1 on reaction with pyridine 2,6-dicarboxylic acid (PyDCH2) yields mononuclear complex [VO(SHAH2)(PyDC)] (3). Treatment of compound 3 with hydrogen peroxide at low pH (2-3) and low temperature (0–5°C) yields a stable oxoperoxovanadium(V) complex H[VO(O2)(PyDC)(H2O)]·2.5H2O (4). All four complexes (1–4) have been characterized by spectroscopic (IR, UV–Vis, 51V NMR) and single crystal X-ray analyses. Intermolecular hydrogen bonds link complex 1 into hexanuclear clusters consisting of six {VNO5} octahedra surrounded by twelve {VNO5} octahedra to form an annular ring. While the molecular packing in 2 generates a two-dimensional framework hydrogen bonds involving the solvent acetone molecules, the mononuclear complexes 3 and 4 exhibit three-dimensional supramolecular architecture. The compounds 1 and 2 behave as good catalysts for oxygenation of benzylic, aromatic, carbocyclic and aliphatic hydrocarbons to their corresponding hydroxylated and oxygenated products using H2O2 as terminal oxidant; the process affords very good yield and turnover number. The catalysis work shows that cyclohexane is a very easily oxidizable substrate giving the highest turnover number (TON) while n-hexane and n-heptane show limited yield, longer time involvement and lesser TON than other hydrocarbons. [Copyright &y& Elsevier]

Abstract: A family of complexes containing the {VO(OMe)}2+ motif with the O,N,S-donor Schiff bases (H2tbhsR) derived from thiobenzhydrazide and 5-substituted salicylaldehydes has been reported. Reactions of [VO(acac)2] with H2tbhsR in methanol provide the complexes having the general formula [VO(OMe)(tbhsR)] (R=H, OMe, Cl, Br and NO2) in 40–53% yields. Microanalytical, various spectroscopic (IR, UV–Vis and NMR) and electrochemical measurements have been used for the characterization of the complexes. All the complexes are redox active and display a near reversible metal centred reduction in the potential range 0.20–0.47V (versus Ag/AgCl). The trend in these potential values reflects the polar effect of the substituent on the salicylidene fragment of tbhsR2−. The X-ray crystal structures of all the complexes have been determined. In each of the complexes where R=H, OMe, Cl and Br, the metal ion is in a distorted square-pyramidal O3NS coordination sphere assembled by the O,N,S-donor tbhsR2−, the methoxo and the oxo groups. The complex where R=NO2, crystallizes as a hexacoordinated species due to coordination of a methanol O-atom at the vacant sixth site. The bond parameters associated with the metal ions and the physical properties of the complexes are consistent with the +5 oxidation state of the metal ion in all the complexes. Scrutiny of crystal packing reveals dimeric, one-dimensional and two-dimensional self-assembled structures via intermolecular C–H⋯O and O–H⋯O interactions. The two-dimensional network contains the cyclic tetramer of methanol. [Copyright &y& Elsevier]

In the reaction of tris(2,4-pentandionato)vanadium(III) with salicylaldehyde 4-phenyithiosemicarbazone (H2L1) and 3-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L2), two new mononuclear complexes of vanadium(V), [VOL1(OCH3)] (1) and [VOL2(OCH3)] (3), as well as thiazoline derivatives, {R-CHNN[CNC(C6H5)C(CH3)C(O)(CH3)S]}[ R = -C6H4(OH) (L1cycl, 2) or -C6H3(OCH3)(OH) (L2cycl, 4)] have been prepared. The isolation of the thiazoline deriatives is the first example of cyclization reactions of thiosemicarbazones with appropriate β-diketone involving vanadium. In vanadium(V) complexes 1 and 3, vanadium is coordinated by one doubly bonded oxygen atom, ONS atoms from the salicylaldehyde thiosemicarbazone ligand and by an oxygen atom from the methoxo ligand. All compounds have been characterized by means of chemical analyses and IR spectroscopy. The crystal and molecular structures of 1-4 have been determined by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

Abstract: Two vanadium(V) complexes, [VO(L1)](acac)] (1) and [VO(L2)(acac)] (2), where H2L1 = N,N-bis(2-hydroxy-3-5-di-tert-butylbenzyl)propylamine and H2L2 =2,2′-selenobis(4,6-di-tert-butylphenol), have been synthesized and characterized by elemental analyses, IR, 51V NMR, both in the solid and in solution, and cyclic voltammetric studies. Single crystal X-ray studies reveal that in complex 1 the vanadium atom is octahedrally coordinated with an O5N donor environment, where the oxygen atom of the VV and the N atom of the ONO ligand occupy the axial sites while two oxygen atoms (O1 and O2) from the bisphenolate ligand and two oxygen atoms (O3 and O4) from the acac ligand occupy the equatorial plane. A similar bonding pattern has also been encountered for 2 with the exception that a Se atom instead of N is involved in weak bonding to the metal center. Both complexes showed reversible cyclic voltammeric responses and E 1/2 appears at −0.18 and 0.10V versus NHE for complexes 1 and 2, respectively. The kinetics of oxidation of ascorbic acid by complex 1 were carried out in 50% MeCN–50% H2O (v/v) at 25°C. The high formation constant value, Q =63±7M−1, reveals that the reaction proceeds through the rapid formation of a H-bonded intermediate. The low k 2 Q 2/k 1 Q 1 ratio (13.4) for 1 points out that there is extensive H-bonding between the oxygen atom of the VV nd the OH group of ascorbic acid. [Copyright &y& Elsevier]

Reactions of HO in trifluoroacetic acid catalyzed by vanadium(v) compounds were studied. The system under study exhibits unusual behavior: along with oxygen, large quantitaties (10-15 %) of ozone are found in the products of hydrogen peroxide decomposition; difficultly oxidizable compounds (alkanes, arenes, and perfluoroalkenes) are oxidized under mild conditions. The rates of the oxidation of individual substrates are commensurable. However, when two compounds are simultaneously present in the reaction mixture, cyclohexane stops the oxidation of all of the other substrates, arenes suppress the oxidation of perfluoroolefins, and perfluoro-1-octene stops the consumption of internal perfluoroolefins. The effect of the oxidizable substrates on the amount of ozone evolved was studied. Based on the kinetic data obtained, a mechanism that involves the consecutive formation of several active complexes of vanadium(v) responsible for the oxidation of substrates and for the formation of ozone is suggested. In terms of the scheme suggested, the inner-sphere oxidation of the peroxo ligand by the coordinated peroxotrifluoroacetic acid affords a complex incorporating O as a ligand. The latter acts as the precursor of the ozone. A mathematical model that adequately describes the experimental data is proposed. [ABSTRACT FROM AUTHOR]

• Biacetylmonoxime salicyloylhydrazone (H 3 L) complexes of {VO(OMe)}2+ and {VO 2 }+. • They were characterized as [VO(μ -OMe)(HL)] 2 (1) and K[VO 2 (HL)]∙MeOH (2 ∙MeOH). • The oximate group of the tridentate (HL)2− shows ambidentate behavior in 1 and 2. • 1 is centrosymmetric edge-shared bioctahedral, while V in 2 is trigonal bipyramidal. • Both complexes were able to catalyze visible light driven degradation of rhodamine B. Reaction of equimolar amounts of bis(acetylacetonato)oxidovanadium(IV) [VO(acac) 2 ] with biacetylmonoxime salicyloylhydrazone (H 3 L, where three dissociable protons represent the oxime, the amide and the phenol protons) in methanol produced the dimeric oxidomethoxidovanadium(V) complex [VO(μ -OMe)(HL)] 2 (1) in 55% yield, while the same reaction in presence of two mole equivalents of KOH afforded a pervanadyl complex K[VO 2 (HL)]∙MeOH (2 ∙MeOH) in 60% yield. Both complexes were characterized by elemental analysis, mass spectrometry, magnetic susceptibility and electrical conductivity measurements, differential scanning calorimetry, various spectroscopy (IR, UV–Vis and 1H NMR) and cyclic voltammetry. The diamagnetic complexes are brown in color. In solution, 1 is non-electrolytic, while 2 ∙MeOH behaves as 1:1 electrolyte. In solid state, they remain thermally stable up to 132 and 269 °C, respectively. X-ray crystal structures of both 1 and 2 ∙MeOH were determined. In the centrosymmetric edge-shared bioctahedral 1 , (HL)2− acts as fused 5,6-membered chelate rings forming amidate-O, imine-N and oximate-O donor. In contrast, (HL)2− acts as fused 5,5-membered chelate rings forming amidate-O, imine-N and oximate-N donor in trigonal-bipyramidal [VO 2 (HL)]−. The infrared and 1H NMR spectroscopic features of 1 and 2 ∙MeOH are consistent with their molecular structures. The electronic spectra of them in acetonitrile display several strong absorption bands within 452–207 nm. Cyclic voltammograms of the complexes and H 3 L in acetonitrile solutions show irreversible reduction responses with the E pc values in the potential range −0.9 to −1.5 V (vs. Ag/AgCl). Both complexes exhibit decent catalytic activity for photodegradation of rhodamine B (RhB) under visible light irradiation. [ABSTRACT FROM AUTHOR]