Tetranuclear Vanadium Research Articles

Green Oxidation of Isochromans to Isochromanones with Molecular Oxygen Catalyzed by a Tetranuclear Vanadium Cluster

Comprehensive SummaryIsochromanone is the core structure of many bioactive compounds. Direct oxidation of isochromans is one of leading methods for the construction of isochromanones, while most established processes remain suffering from the use of environmentally unfriendly metal oxidants, harsh reaction conditions, and the difficulty in catalyst recycling and product separation. Herein, we report a convenient, cost‐effective, and green method for the synthesis of high‐value added isochromanones via isochroman oxidations with O2 by a novel heterogeneous vanadium cluster catalyst (Cat.1) under mild conditions. This reaction protocol demonstrates high catalytic activity with good catalyst recyclability and reusability for a wide scope of substrates.

Four electron selective O2 reduction by a tetranuclear vanadium(IV/V)/hydroquinonate catalyst: application in the operation of Zn–air batteries

A tetranuclear vanadium(IV/V) hydroquinonate electrocatalyst for oxygen reduction through proton-coupled electron transfer. The complex enhances the current and power of Zn–air batteries.

One Functionalized Polyoxovanadates Hybrid Material Based on Arsonic Acid with Highly Effective Catalytic Property of Sulfides

In this work, a novel 4-aminophenylarsonic acid functionalized polyoxovanadates (POVs) hybrid material, namely, (Me2NH2)4 ·[(L)8(H12V16O32)] (H2L = 4-NH2C6H4AsO3H2) POVs 1 was solvothermally synthesized and fully characterized. The results revealed POVs 1 consists of four similar tetranuclear vanadium clusters bridged by eight organic 4-aminophenylarsonic acid ligands. Remarkably, functionalized hybrid POVs 1 was further investigated as a heterogeneous stable catalyst in oxidation of sulfide derivatives, and exhibited high catalytic activities (yields up to 96.7%). Additionally, the functionalized hybrid polyoxovanadates catalyst can be reused without losing activities after three runs cycle.

Synthesis of a phosphomolybdate with a tetranuclear vanadium core by installing vanadium atoms in a lacunary template using the protecting group strategy.

Vanadium-containing phosphomolybdates have outstanding catalytic and electrochemical properties. However, their traditional one-pot synthesis in aqueous media generates a mixture of randomly distributed isomers and undesirable impurities, which has hampered the in-depth study of the catalysis and reaction mechanism of these compounds. Here, the selective synthesis of a tetranuclear vanadium-containing phosphomolybdate, [PV3Mo9O40(VO)]3-, was achieved for the first time by using a pyridine-protected [A-α-PMo9O31(py)3]3- (py = pyridine) as the template.

Di-, tri- and tetranuclear molecular vanadium phosphonates: a chloride encapsulated tetranuclear bowl

The reaction of vanadium(III) trichloride with tert-butylphosphonic acid (t-BuPO3H2) in the presence of 1,10-phenanthroline/2,2'-bipyridine as an ancillary ligand in acetonitrile at room temperature afforded two dinuclear dicationic vanadium(IV) complexes [(VO)2(phen)2{t-BuPO2(OH)}2(OH2)2]·2Cl [1] and [(VO)2(bipy)2{t-BuPO2(OH)}2(OH2)2]·2Cl [2]. On the other hand, when the reaction was carried out in methanol, the dinuclear vanadium(V) complex [(VO)2(bipy)2(μ2-O)2(t-BuPO3)2]·2CH3OH·0.5CH2Cl2 [3] was isolated. While 1 and 2 contain two six-membered V2P2O4 rings, 3 contains a unique four-membered V2O2 ring. Replacement of tert-butylphosphonic acid by tritylphosphonic acid (Ph3CPO3H2) under the same reaction conditions in methanol leads to the formation of dicationic trinuclear vanadium(IV) complexes [(VO)3(phen)3(Ph3CPO3)2(OH2)3]·CHCl3·2(OH)·2MeOH·1.5H2O [4] and [(VO)3(bipy)3(Ph3CPO3)2(CH3OH)3]·2(OH)·4CH3OH·5H2O [5]. In these complexes, the triangular V(IV) platform is held together by two bicapping tripodal phosphonate ligands. Replacement of the chelating 2,2'-bipyridine ligand with 3,5-dimethyl-1H-pyrazole, under the same reaction conditions, afforded a tetranuclear vanadium(V) complex [{(VO)4(Ph3CPO3Me)4(μ-O)4}Cl]{3,5-Me2PzH2}·3C7H8·H2O·CH3OH [6]. Remarkably 6 possesses a unique bowl-shaped structure encapsulating a chloride anion.

Preparation, Structure, and Properties of Tetranuclear Vanadium(III) and (IV) Complexes Bridged by Diphenyl Phosphate or Phosphate

Three novel tetranuclear vanadium(III) or (IV) complexes bridged by diphenyl phosphate or phosphate were prepared and their structures characterized by X-ray crystallography. The novel complexes are [{V(III)(2)(μ-hpnbpda)}(2){μ-(C(6)H(5)O)(2)PO(2)}(2)(μ-O)(2)]·6CH(3)OH (1), [{V(III)(2)(μ-tphpn)(μ-η(3)-HPO(4))}(2)(μ-η(4)-PO(4))](ClO(4))(3)·4.5H(2)O (2), and [{(V(IV)O)(2)(μ-tphpn)}(2)(μ-η(4)-PO(4))](ClO(4))(3)·H(2)O (3), where hpnbpda and tphpn are alkoxo-bridging dinucleating ligands. H(3)hpnbpda represents 2-hydroxypropane-1,3-diamino-N,N'-bis(2-pyridylmethyl)-N,N'-diacetic acid, and Htphpn represents N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine. A dinuclear vanadium(IV) complex without a phosphate bridge, [(VO)(2)(μ-tphpn)(H(2)O)(2)](ClO(4))(3)·2H(2)O (4), was also prepared and structurally characterized for comparison. The vanadium(III) center in 1 adopts a hexacoordinate structure while that in 2 adopts a heptacoordinate structure. In 1, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two diphenylphosphato and two oxo groups, resulting in a dimer-of-dimers. In 2, the two vanadium(III) units bridged by tphpn are further bridged by three phosphate ions with two different coordination modes. Complex 2 is oxidized in aerobic solution to yield complex 3, in which two of the three phosphate groups in 2 are substituted by oxo groups.

Ortho-substituent induced triradical-containing tetranuclear oxo-vanadium(iv) cluster formation via ligand C–N bond breaking and C–O bond making

Substituent having weak-coordination character, and attached at the ortho-carbon atom to the aniline moiety of 2-anilino-4,6-di-tert-butylphenol, provided a triradical-containing tetranuclear vanadium(IV) complex via ligand C-N bond breaking and C-O bond making.

A novel peculiar vanadium(IV) complex with 2-pyridinaldoxime: Synthesis, structure, electrochemical behavior and DNA binding

Abstract A novel tetranuclear vanadium(IV) complex, [V IV 4 O 4 (μ 4 -O)(μ-OCH 3 ) 2 (pyCHNO) 4 ·H 2 O] ( 1 ) (pyCHNOH = 2-pyridinaldoxime), was synthesized and characterized. The binding propensity of the complex 1 to calf thymus DNA (CT-DNA) was studied by fluorescence spectroscopy, UV–vis absorption and viscosity measurement. Single crystal X-ray diffraction analysis reveals that the complex 1 possesses centrosymmetric structure and pseudo-tetrahedron conformation. Electrochemical behavior indicates the quasi-reversible nature of the electron-transfer process in the complex 1 . The results suggest the groove-binding propensity of the complex 1 .

Synthesis and crystal structure of (H3O)2{(Na2(OH)CB[5])2[HV4O12]}Cl · 14H2O

The compound (H3O)2{(Na2(OH)CB[5])2[HV4O12]}Cl · 14H2O is synthesized by heating (120°C) of a mixture of sodium vanadate, cucurbit[5]uril (CB[5]), rubidium chloride, and water in a sealed ampule. According to the X-ray diffraction data, the binding of the [Na2(OH)]+ binuclear cation with CB[5] occurs due to the bidentate coordination of the oxygen atoms of the portals of cucurbit[5]uril to the sodium atoms. The tetranuclear vanadium complex [HV4O12]3− serves as a bridge, joining infinite chains {Na2(OH)CB[5]}∞+ in pairs.

Progress in the Compilation of an Oxovanada‐Silsesquioxane Portfolio and Catalytic Activity of Organometallic Representatives in Ethylene Polymerisation

AbstractEmploying various incompletely condensed silsesquioxanes as ligand precursors in reactions with simple oxovanadates a variety of oxovanadium silsequioxanes could be synthesised, that might be regarded as models for oxovanadium units on silica surfaces. These include a tetranuclear vanadium(IV) compound as well as two complexes where O2V+ units are coordinated to two siloxide functions as part of a silsesquioxane framework. Moreover, compounds containing Cp*V(O)2+ moieties were prepared, whose activities as polymerisation procatalysts were examined: They turned out to be moderately active for the polymerisation of ethylene. All compounds were fully characterised, in case of the tetranuclear vanadium(IV) complex this also includes the investigation of the magnetic behaviour. Moreover, for two complexes also the molecular structures could be determined with sufficient quality by X‐ray diffraction.

Tetranuclear vanadium complex, (VO)4(hpic)4: a recyclable catalyst for oxidation of benzyl alcohols with molecular oxygen

Vanadium(iv) complexes bearing 3-hydroxypicolinic acid (H(2)hpic) as ligands, VO(Hhpic)(2) (1) and the cyclic tetramer (VO)(4)(hpic)(4) (2), have excellent catalytic ability for the oxidation of a variety of primary and secondary benzyl alcohols with molecular oxygen in acetonitrile or protic solvents such as ethanol and water, affording the corresponding aldehydes and ketones, respectively. Construction of multi-nuclear complexes by the selection of ligands attains higher turnover numbers and recycling of the catalyst.

New Directions in the Preparation and Redox Chemistry of Fluoride-Templated Tetranuclear Vanadium Phosphonate Cage Compounds, Mn+[(V2O3)2(RPO3)4⊂F]n

A new and simple preparation method for fluoride-templated tetranuclear vanadium phosphonate cage compounds, M(n+)[(V2O3)2(RPO3)4<F]n is outlined. The crystalline products were characterized by X-ray diffraction, elemental analysis, and thermogravimetric analysis. Using the acceptable solubility of the products, multinuclear NMR could be performed on the corresponding solutions. Some insight into the process of formation of the cage compounds in solution could be reached by monitoring the corresponding reaction mixture by multinuclear NMR. The template function of the F(-) ion could be demonstrated together with the fact that the non-transition-metal ions (M(n+)) used here (phosphonium ions) have no direct effect on the formation of the cage. In contrast, the redox behavior of these compounds in the solid state distinctly depends on the cations. This could be easily investigated by electron paramagnetic resonance because the mixed-valence species (3V(V)/V(IV)) can be produced chemically or thermally induced in solution as well as in the solid state. In the latter case, the reaction of the cage with H2 activated on the platinum powder can be regarded as a key experiment for understanding the redox process of the title compounds in the solid state. The role of specific interactions in solution at the tumbling rate and the localization of spin density in the cage could be demonstrated by the reduction performed with 1-methylimidazole and quinoline. While the substituents R = Me and Ph have only a small influence on the cage formation in solution, they have a significant influence on the redox reaction and structural relaxation in the solid state.

Structural and Spectroscopic Evidence for the Formation of Trinuclear and Tetranuclear Vanadium(III)/Carboxylate Complexes of Acetate and Related Derivatives in Aqueous Solution

The formation of vanadium(III) complexes with nuclearity greater than two is believed to occur in aqueous solution on the basis of potentiometric, electrochemical, and/or UV-vis spectroscopy titration measurements, although structural evidence for this is limited. Upon the addition of 1-2 equiv of acetate, propionate, chloroacetate, trifluoroacetate, or bromoacetate to an aqueous, acidic solution of vanadium(III), trinuclear and tetranuclear complexes are formed. The structures of [V4(mu-OH)4(mu-OOCCF3)4(OH2)8]Cl4.7.5H2O (1), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.CH3COOH.12H2O (2), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.3H2O (3), [V3(mu3-O)(mu-OOCCH2Br)6(OH2)3]CF3SO3.H2O (4), [V3(mu3-O)(mu-OOCCH2CH3)6(OH2)3]Cl.2H2O (5), [V3(mu3-O)(mu-OOCCH3)6(OH2)3]Cl.3.5H2O (6), and [V3(mu3-O)(mu-OOCCH2Cl)6(OH2)3]CF3SO3.H2O (7) have been determined by X-ray diffraction. Importantly, electrospray mass spectrometry and 1H NMR measurements suggest that these complexes are not purely solid-state phenomena but are also present in solution. For the vanadium(III)/acetate and vanadium(III)/propionate systems, two paramagnetic 1H NMR signals corresponding to two distinct complexes (species A and B) are observed in the 40-55 ppm region for 0.20 mol equiv of acetate or propionate, at pD 3.44. No corresponding signals are observed for the vanadium(III)/bromoacetate and vanadium(III)/chloroacetate systems under the same conditions or for the vanadium(III)/ trifluoroacetate system using 19F NMR spectroscopy. UV-vis spectra suggest that species B are structurally analogous for the vanadium(III)/acetate and vanadium(III)/propionate systems, whereas structurally different complexes are the major species for the other systems. Diffusion coefficients of species B for the vanadium(III)/acetate and vanadium(III)/propionate systems determined by pulsed-field-gradient spin-echo NMR spectroscopy measurements are (3.0 +/- 0.1) x 10-6 and (3.23 +/- 0.01) x 10-6 cm2 s-1, respectively, and are most consistent with species B being trimeric, rather than tetranuclear, complexes.

Preparations, Structures, and Properties of Sulfato-Bridged Dinuclear and Tetranuclear Vanadium(III) Complexes with a Dinucleating Ligand, 2-Oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate

Abstract New dinuclear and tetranuclear vanadium(III) complexes with sulfato bridge(s), [{VIII(H2O)}2(μ-hpnbpda)(μ-OH)(μ-SO4)]·5.25H2O (1) and [VIII4(μ-hpnbpda)2(μ-OH)2(μ-SO4)2]·12H2O (2), where hpnbpda is an alkoxo-bridging dinucleating ligand, 2-oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate, were prepared, and their structures were determined by X-ray crystallography. The vanadium(III) center in 1 adopts heptacoordinate structure while that in 2 has a hexacoordinate structure. In 2, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two hydroxo and two sulfato bridging groups, resulting in a dimer-of-dimers structure. Measurement of the temperature dependence of the magnetic susceptibility of 1 revealed that the two vanadium(III) ions are antiferromagnetically coupled with J = −5.9 cm−1 and g = 1.90.

Synthesis, structure and properties of a new unsymmetric tetranuclear mixed-valence vanadium(IV/V) complex containing distinct V 2O 33+ cores

The synthesis, X-ray crystal structure, spectroscopic, and electrochemical properties of a new tetranuclear vanadium(IV,V,IV,V) complex [ ( VO) 4( btppnol) 2( μ-O) 2]( ClO 4) 2·2 DMF·2 H 2 O ( 1 ) utilizing the previously described unsymmetrical dinucleating ligand N-(2-hydroxybenzyl)- N, N ′, N ′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (H 2btppnol) are reported. The complex comprises two different [V 2O 3] 3+ core structures: one [V 2O 3] 3+ core in a syn-dioxo-μ-O(alkoxo) configurarion and another [V 2O 3] 3+ core in an anti-dioxo-μ-oxo configuration, as well as being composed of non-equivalent vanadium centers as a consequence of the use of an unsymmetrical ligand. This complex represents the first example in the literature of a vanadium complex with this particular structure and its interesting electrochemical and spectroscopic properties were investigated.

Single-Molecule Magnets

Metal cluster complexes with interesting magnetic properties characteristic of nanoscale magnetic particles have become an attractive prospect in the last few years. These complexes exhibit magnetization hysteresis loops and out-of-phase ac magnetic susceptibility signals. The advantages of such clusters over fragmented bulk ferromagnets are their easy synthesis and manipulation, their high solubility, and their potential use in storing a large density of information. Here we will focus our attention on the family of several distorted Mn4 cubane molecules with a [MnIVMnIII 3O3X]6+ core, tetranuclear vanadium (III) complexes with a butterfly structure and dodecanuclear manganese complexes, [Mn12O12(O2CR)16(H2O)4] (where R can be an aliphatic or aromatic group) and their corresponding singly reduced salts [Mn12O12(O2CR)16(H2O)4] (PPh4), which have been extensively studied in our laboratories.

Single-molecule magnets: out-of-phase ac susceptibility signals from tetranuclear vanadium(III) complexes with an S = 3 ground state

The salts of the tetranuclear vanadium(III) ions [V4O2(O2- CEt)7(L–L)2]z (L–L = bpy, z = +1; L–L = pic–, z = –1) with a V4 butterfly topology and a S = 3 ground state have been found to exhibit out-of-phase ac susceptibility signals, a signature of single-molecule magnets.

The first tetranuclear vanadium(V) peroxo complex: Preparation, vibrational spectra and X-ray crystal structure of K 6[V 4O 4(O 2) 8(PO 4)]·9H 2O

The vanadium(V) peroxo phosphato complex K 7[V 4O 4(O 2) 8(PO 4)]·9H 2O has been obtained from the KVO 3KH 2PO 4KOHH 2O 2H 2OC 2H 5OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V 2O 2(O) 2) 2( μ- η 1 : η 2-O 2) 2] units are connected by the μ 4-PO 4 group.

Tetranuclear vanadium(III) carboxylate chemistry, and a new example of a metal butterfly complex exhibiting spin frustration: structure and properties of [V4O2(O2CEt)7(bpy)2](ClO4)

Treatment of [VCl3(thf)3](thf = tetrahydrofuran) with bpy (bpy = 2,2′-bipyridine) and NaO2CEt in a 1 : 1 : 3 molar ratio in Me2CO followed by addition of ClO4– allows isolation of [V4O2(O2CEt)7(bpy)2](ClO4)[4(ClO4)], which contains a butterfly-like V4 unit; variable-temperature magnetic susceptibility studies show 1 to possess both ferro- and antiferro-magnetic exchange interactions leading to spin-frustration effects and an S= 3 ground state.

Control of aggregation through anion encapsulation in clusters of the V/O/RPO3 2? system: synthesis and crystal and molecular structures of the tetranuclear clusters [NBun 4][V V 4O6F(PhPO3)4] and [NBun 4]2[V V 3V VI O6F(PhPO3)4

The reaction of [(NBun4)][V5O7(PhPO3)5(OMe)2] with HBF4·Et2O in acetonitrile yields the tetranuclear vanadium(V) cluster [NBun4][V4O6F(PhPO3)4]1 which upon reduction with organohydrazine yields the mixed-valence cluster [NBun4]2[VV3VIVO6F (PhPO3)4]2.