Donor properties of the vanadyl ion: reactions of vanadyl salicylaldimine beta-ketimine and acetylacetonato complexes with groups 14 and 15 Lewis acids

Reactions of organosilicon, -germanium, -tin, -lead, -antimony, and -tin tetrahalide Lewis acids with VO(salen) [H(2)salen = N,N'-bis(salicylidene)ethane-1,2-diamine], related vanadyl salicylaldimines, VO(acacen) [H(2)acacen = N,N'-bis(acetylacetonato)ethane-1,2-diamine], and VO(acac)(2) (acac = acetylacetonato) have been investigated, revealing VO(salen) and VO(acacen) to be significantly stronger vanadyl donors than VO(acac)(2). The vanadyl donor strength of VO(salen) significantly diminishes with the introduction of electron-withdrawing substituents on the salicylaldimine ligand, and the introduction of methyl substituents on the imine carbon atoms can result in a preference for phenolic over vanadyl oxygen donation. Vanadyl donation results in an increase in the vanadyl bond length, while it leaves the distance of vanadium from the basal plane relatively unaffected. Coordination of water trans to a vanadyl oxygen that is involved in a donor bond to tin or lead has little or no effect on the vanadyl bond length but results in a marked movement of vanadium toward the basal plane and a decrease of the V=O-D (D = Sn or Pb) bond angle by as much as 13 degrees, the latter reflecting a loss of multiple bond character of the vanadyl bond. Formation of a vanadyl donor bond results in a decrease in both the vanadyl stretching frequency (infrared spectrum) and energy of the e(pi) <-- b(2) transition (electronic spectrum), the latter being intimately related to the strength of the vanadyl donor bond, while the shift of the b(1) <-- b(2) transition to higher or lower energy is relatively small for vanadyl salicylaldimine and beta-ketimine complexes. Donation through the phenolic oxygen atoms results in an increase in the vanadyl stretching frequency and energy of the e(pi) <-- b(2) transition, which can result in e(pi) <-- b(2)/b(1) <-- b(2) energy crossover.     

P改性V-MCM-41催化剂的合成及其在丙烷直接脱氢中的应用（英文）

钒基催化剂的脱氢性能与表面氧钒物种的形态密切相关。为了进一步增强传统原位合成的V-MCM-41催化剂上钒物种的分散性,本研究通过在制备过程中添加有机磷前驱物的方法对其进行改性。采用XRD、N₂吸附-脱附、TPR、TPD、XPS、拉曼光谱及O₂脉冲等方法对催化剂的结构、钒物种形态及分散度进行了系统的表征。表征结果表明,P改性后V-MCM-41催化剂的比表面积随着P含量的增加而缓慢下降,但整体仍能保持有序的六方介孔结构;P改性后表面钒物种的还原性和分散性均得到改善,聚合形态的钒物种比例明显下降。丙烷脱氢反应结果表明P改性后催化剂的丙烷脱氢性能和稳定性均有提高。在Si/P投料物质的量比为30时制备的催化剂能够获得最大表面钒氧位点和最佳丙烷脱氢性能。     

Chemistry of Vanadyl Porphyrins

The chemistry of vanadyl porphyrins has been explored using vanadyl octaethylporphyrin as the type substance, and with special reference to the occurrence of such substances in petroporphyrins. Spectroscopic properties (electronic spectra, IR spectra, mass spectra) are described, and electronic spectra are employed to detect the occupation of the vacant axial coordination site. Direct substitution of vanadyl octaethylporphyrin furnishes meso-substituted products: various nitro, chloro and benzoyloxy derivatives are characterised. Trans alkylation is observed when vanadyl octaethylporphyrin is heated in vacuo on various supports, including clay minerals: the reaction provides a model for the generation of the homologous series of vanadyl polyalkylporphyrins found in crude oils and bitumens.     

Chromatographic isolation of vanadyl porphyrins from heavy oil resins

A broad fraction of petroleum vanadyl porphyrins of high spectral purity was isolated from heavy oil resins with high vanadium content using a two-step chromatographic method. At the first step, the primary concentrate of vanadyl porphyrins was separated from the resins on the silica gel column. At the second step, it was further purified by the gradient elution through the column packed with sulfo-cationite. According to UV—VIS spectroscopy, this technique allows one to isolate up to 70% of vanadyl porphyrins with the spectral purity corresponding to the best results of other purification methods providing only narrow fractions of vanadyl porphyrins of comparable purity. Deoxophylloerythroetioporphyrin (DPEP) and etioporphyrin (Etio) series of vanadyl porphyrins with the carbon number range of C₂₈—C₄₂ and DPEP/ Etio ratio equal to 1.18 were identified by MALDI-TOF mass-spectrometry.     

Selective oxidation of n-butane over Fe-promoted vanadyl pyrophosphate prepared from modification of nano-sized interlayer of lamellar vanadyl benzylphosphate

A novel approach for the preparation of promoted vanadyl pyrophosphate in well-defined structure was examined. Lamellar vanadyl benzylphosphate (LVBP) was used as a host material and iron acetylacetonate as a guest. It was found that iron acetylacetonate was successfully inserted into the interlayer of LVBP by heating of LVBP and iron acetylacetonate in toluene solution. Calcination of this in tercalated material resulted in a well-crystallized vanadyl pyrophosphate phase with uniform dispersion of Fe in bulk and surface. The obtained Fe-promoted vanadyl pyrophosphate showed an enhancement in the activity for selective oxidation of n-butane, especially at high temperature and long contact time.     

Effect of Vanadyl Rosiglitazone,a New Insulin-Mimetic Vanadium Complexes,on Glucose Homeostasis of Diabetic Mice

Diabetes has been cited as the most challenging health problem in the twenty-first century. Accordingly, it is urgent to develop a new type of efficient and low-toxic antidiabetic medication. Since vanadium compounds have insulin-mimetic and potential hypoglycemic activities for type 1 and type 2 diabetes, a new trend has been developed using vanadium and organic ligands to form a new compound in order to increase the intestinal absorption and reduce the toxicity of vanadium compound. In the current investigation, a new organic vanadium compounds, vanadyl rosiglitazone, was synthesized and determined by infrared spectra. Vanadyl rosiglitazone and three other organic vanadium compounds were administered to the diabetic mice through oral administration for 5 weeks. The results of mouse model test indicated that vanadyl rosiglitazone could regulate the blood glucose level and relieve the symptoms of polydipsia, polyphagia, polyuria, and weight loss without side effects and was more effective than the other three organic vanadium compounds including vanadyl trehalose, vanadyl metformin, and vanadyl quercetin. The study indicated that vanadyl rosiglitazone presents insulin-mimetic activities, and it will be a good potential candidate for the development of a new type of oral drug for type 2 diabetes.     

The 17O hyperfine interaction in V17O(H217O)52+ and Mn(H217O)62+ determined by high field ENDOR aided by DFT calculations

The 17O hyperfine interaction of the water ligands and the V=O oxygen in the vanadyl aquo complex and of the water ligands in the Mn2+ aquo complex in a frozen solution were determined by W-band (95 GHz) electron-nuclear double resonance (ENDOR). Orientation selective ENDOR spectra of the vanadyl complex exhibited two distinct signals assigned to the vanadyl oxygen and the water ligands. The assignment of the signals was done based on the orientation of the principal axis system of the hyperfine interaction and through comparison with the hyperfine interaction predicted by DFT calculations. The latter showed good agreement with the experimental values thus providing clear evidence that the vanadyl oxygen is exchangeable. The interaction of the vanadyl oxygen, especially its anisotropic part, was significantly larger than that of the water oxygens due to a relatively large negative spin density on the oxygen p orbitals. The 17O hyperfine interaction of the water ligand in the Mn2+ complex was found to be similar to that of the water ligand in the vanadyl complex and was in good agreement with earlier single-crystal data. Here, due to the large thermal polarization, it was also possible to determine the absolute sign of the hyperfine coupling by selecting different EPR transitions.     

An ESR study of some organic complexes of tetravalent vanadium

ESR results are reported for solutions and glasses containing vanadyl diethyldithiophosphate, vanadyl and vanadium diethyldithiocarbamates, and vanadium butylxanthogenate. Comparison with compounds of known structure gives the structures of these complexes.     

轮古常渣及其组分中金属钒卟啉的分离与鉴定

采用改进的溶剂萃取方法对轮古常渣及其组分中的金属钒卟啉进行分离。结果表明,从轮古常渣中分离出的卟啉钒的质量分数为18.5%,从轮古常渣正庚烷可溶质和沥青质中分离出的卟啉钒的质量分数分别为68.0%和9.2%。用紫外-可见光谱对萃取出来的金属钒卟啉和甲磺酸脱金属后得到的游离卟啉进行表征。结果表明,轮古常渣及其正庚烷可溶质和沥青质中的金属钒卟啉主要是初卟啉。对轮古常渣中的游离卟啉进行基质辅助激光解吸电离飞行时间质谱分析证明,轮古常渣中的金属钒卟啉主要是初卟啉。     

EPR monitoring of sol-gel processes

Electron Paramagnetic Resonance (EPR) spectra of paramagnetic probes (free radical, 4-oxo-Tempo for non-doped glasses and vanadyl sulfate for doped silica glass) provide a non-intrusive means of monitoring of the dynamics of the sol-gel process. The free radical spectra parameters (rotation correlation time, isotropic hyperfine interaction parameter and line width) reflect changes in viscosity and polarity in the vicinity of the spin label. The EPR spectra of vanadyl can be used for monitoring the sol-gel process in that different types of mixed vanadyl complexes are formed during glass molding.     

Tuning the intermolecular dative interactions by altering the ligand planarity and counter cations in vanadyl(IV) complexes

A vanadyl(iv) complex, K2V(O)(dtoym)2, forms polymeric interactions via intermolecular dative bonds; the intermolecular dative interaction is tuned by changes of the ligand planarity and counter cations of the vanadyl complex.     

Vanadyl salen complexes covalently anchored to an imidazolium ion as catalysts for the cyanosilylation of aldehydes in ionic liquids

Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex.     

The sign of the electron exchange interaction in binuclear vanadyl tartrate

An analysis of the asymmetric line broadening in the solution electron resonance spectrum of vanadyl tartrate demonstrates that the exchange interaction is positive. The separation between the two vanadyl units is shown to increase slightly when the complex passes from a solid to a fluid solution.     

Insulin-mimetic vanadyl(IV) complexes as evaluated by both glucose-uptake and inhibition of free fatty acids (FFA)-release in isolated rat adipocytes

We have recently proposed the existence of some potent vanadyl complexes with blood glucose-lowering activity in experimental diabetic animals based on the results of an in vitro FFA (free fatty acids)-release assay in isolated rat adipocytes treated with epinephrine and evidence of an in vivo blood glucose lowering effect in experimental diabetic animals. However, the FFA assay depends indirectly on the glucose-uptake of vanadyl complexes in adipocytes. It is therefore necessary to develop a more reliable in vitro glucose-uptake assay, in place of the glucose uptake method using radioactive compounds such as (14)C-glucose, to identify insulin-mimetic vanadyl complexes. In the present study, we proposed a combined in vitro assay by using the conventional glucose oxidase method for glucose-uptake and FFA assay in isolated rat adipocytes. Insulin, vanadyl sulfate (VOSO(4)), bis(picolinato)vanadyl (VO(pa)(2)), and bis(6-methylpicolinato)vanadyl (VO(6mpa)(2)) complexes exhibited concentration-dependent uptake of (+)-D-glucose and inhibition of FFA release in the adipocytes treated with epinephrine. Vanadyl complexes were found to accelerate glucose-uptake at lower concentrations than VOSO(4). In vitro high insulin-mimetic activity of VO(pa)(2) and VO(6mpa)(2) were thus indicated by both glucose-uptake and FFA-release, with the insulin-mimetic activity of VO(6mpa)(2) being higher than that of VO(pa)(2), as suggested by the partition coefficient (0.330 for VO(pa)(2) and 0.595 for VO(6mpa)(2)). The proposed assay provides a more reliable method than each single method for the evaluation of in vitro insulin-mimetic activity of compounds.     

Selective oxidation of sulfides to sulfoxides using a silica immobilised vanadyl alkyl phosphonate catalyst

A range of sulfides can be selectively oxidised to the corresponding sulfoxides in good yields using catalytic quantities of immobilised vanadyl, cobalt or nickel alkyl phosphonates and the reoxidant sodium bromate or vanadyl alkyl phosphonate with tert-butyl hydroperoxide or aqueous hydrogen peroxide as oxidants.     

Molecular orientation of paramagnetic metal complex by melt-drawing thermotropic liquid crystalline polymers

New liquid-crystalline polyesters and paramagnetic vanadyl complex were prepared as host polymer and guest complex. Melt-drawn fibers were made from the blend of host polymer and guest complex at the mesophase temperature. ESR spectra of the melt-drawn fibers indicated that the base of pyramidal vanadyl complex is completely oriented parallel to the fiber axis.     

Spectroscopic Evidence for Symmetry-Restricted π-Interaction in Vanadyl β-Keto-enolates

Theoretical treatments of the distorted square pyramidal co-ordination observed in vanadyl β-keto-enolates predict restricted interligand conjugation and minimal π-interaction in the oxovanadium-ligand bonds. The effects of ligand substitution on the vibrational and electronic spectra of vanadyl β-keto-enolates yield evidence that strong σ-bonding and ionic contributions are chiefly responsible for the strong vanadium-ligand bonding.     

New porphyrinoids: vanadyl(IV) complexes of meso-aryl-substituted corrphycene and 10-oxocorrole ligands

Rare vanadyl corrphycene and vanadyl 10-oxocorrole complexes were obtained via an oxidative macrocyclization process by the treatment of 6,6'-di-p-tolyl-2,2'-bidipyrrin with VO(acac)2 in a hot dioxygen atmosphere. The geometric and electronic structures of the new porpyhrinoids were determined and showed the dependency of the spectral pattern from the aromaticity of the macrocyclic ligand.     

Columnar metallomesogens based on vanadyl(VI) and cobalt(II) complexes of N,N'-bis[3-(3,4-dialkoxyphenyl)3-oxopropenyl]ethylenediamines

The preparation, characterization and mesomorphic properties of vanadyl(VI) and cobalt(II) complexes derived from N , N -bis[3-(3,4-dialkoxyphenyl)-3-oxopropenyl]ethylenediamines are described. These half-disk-shaped molecules exhibited columnar mesophases over a wide range of temperature, as characterized by DSC analysis and polarizing optical microscopy. The structure of the mesophases was also confirmed as columnar hexagonal (Col_ho) by powder XRD. The vanadyl complexes were found to have substantially higher clearing temperatures and wider mesophase temperatures than the analogous cobalt complexes. The influence of the metal centres on the mesomorphic temperatures may be attributed to better intermolecular dative association in the vanadyl complexes than in the cobalt complexes.     

Asymmetric aerobic oxidation of alpha-hydroxy acid derivatives by C4-symmetric, vanadate-centered, tetrakisvanadyl(V) clusters derived from N-salicylidene-alpha-aminocarboxylates

A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, they exist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue, the architectural nature of the vanadyl(V) complex highly depends on the base used during the complex formation event. A pentanuclear C4-symmetric complex was formed when potassium salts were employed instead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiral monomeric vanadyl(V) units together, by which a potassium ion sits on top of the four flanking units through carbonyl coordinations and serves to hold the whole cluster by cooperation with the central vanadate(V) unit. In comparison with the corresponding monomeric vanadyl(V) methoxide complex, the cluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic alpha-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (krel 40 to >500).