Vanadium Catalysis Research Articles

Preparation of SiC from carbonaceous vanadium-bearing stone coal via carbothermal reduction method

In the present study, silicon carbide (SiC) was prepared via carbothermal reduction method using carbonaceous vanadium-bearing stone coal at 1400 °C. Compared to other reported raw materials, SiC was prepared at a relatively low the reaction temperature. The effects of temperature, duration and vanadium catalysis on the process of SiC preparation were investigated, and the kinetics of SiC nucleation and growth were analyzed. The results indicate that the SiC conversion of samples with 0 wt% and 2 wt% V2O3 additions reached to 68.9 wt% and 80.7 wt% at 1450 °C for 5 h. It was observed that the reduction of vanadium oxides resulted in the formation of vanadium carbide (VC), which played an important role in catalyzing the nucleation of SiC and accelerating its growth. The mechanism of SiC nucleation and growth is consistent with the Johnson-Mehl-Avrami-Erofeev-Kolmogorov (JMAEK) model, and the apparent activation energy values of the carbothermal reduction reaction are 213.17 kJ/mol and 109.66 kJ/mol for samples with 0 wt% and 2 wt% V2O3 additions. Therefore, this method not only expanded the source of raw material but also reduced energy consumption and economic costs.

Direct Amination of α-Triaryl Alcohols via Vanadium Catalysis

α-Triaryl amines have been used as pharmaceuticals and pharmaceutical intermediates for antifungal and anticancer applications. Current methods to synthesize such compounds require at least two steps, and no direct amination of tertiary alcohols has been reported. Herein, we disclose efficient catalytic conditions for the direct amination of α-triaryl alcohols to access α-triaryl amines. VO(OiPr)3, a commercially available reagent, has been identified as an effective catalyst for the direct amination of several α-triaryl alcohols. This process is scalable, as demonstrated by a gram-scale synthesis, and the reaction still works at as low as a 0.01 mol % catalyst loading with the turnover number reaching 3900. Moreover, commercial pharmaceuticals including clotrimazole and flutrimazole have been successfully prepared rapidly and efficiently using this newly developed method.

Ethylene Polymerization with Thermally Robust Vanadium(III) Tris(2-pyridyl)borate Complexes

Despite the useful selectivity offered by vanadium catalysts for olefin polymerization, their implementation under practical conditions remains limited by poor productivity and thermal stability. This report describes phenyl tris(2-pyridyl)borate (Tpy–) complexes of vanadium(III) that are amenable to ethylene polymerization at temperatures approaching industrial conditions (>100 °C). We developed metal tris(2-pyridyl)borate precursors TpyLi, TpyK, and TpyAg, which undergo smooth metathesis with VCl3(THF)3 to provide solvated complexes TpyVCl2(DMF) and TpyVCl2(THF). In contrast, soft deprotonation of TpyH with triethylamine and VCl3(THF)3 gave the anionic complex [TpyVCl3][Et3NH], our optimal precatalyst. Thus, [TpyVCl3][Et3NH] polymerizes ethylene with low dispersity (∼2) and a moderate molecular weight (∼350000) at temperatures up to 135 °C. This work advances the use of tris(2-pyridyl)borates, an emerging ligand class, in catalysis and provides a platform for vanadium catalysis in demanding applications.

Atroposelective Synthesis of C-C Axially Chiral Compounds via Mono- and Dinuclear Vanadium Catalysis.

Axially chiral compounds with rotationally constrained σ-bonds that exhibit atropisomerism are lucrative synthetic targets because of their ubiquity in functional materials and natural products. The metal complex-catalyzed enantioselective fabrication of axially chiral scaffolds has been widely investigated, and thus far, considerable progress has been made. Over the past two decades, we have developed a highly efficient strategy for constructing axially chiral biarenol derivatives using chiral mono- and dinuclear vanadium complexes. These complexes are readily prepared from vanadium(IV) salts and Schiff base ligands (generated from the condensation of (S)-tert-leucine and di- or monoformyl-(R)-1,1'-bi-2-naphthol (BINOL) derivatives) under O2 and act as highly active catalysts for highly stereoselective C-C bond formation. In particular, the vanadium complex-catalyzed enantioselective oxidative coupling of 2-naphthols 1 under oxygen or in air, which is a green oxidant, affords the desired axially chiral molecules in high yields and high stereoselectivity (up to quantitative yield and 97% ee), along with water as the sole coproduct. This coupling reaction tolerated various functional groups (such as halogens, alkoxys, and boryls) and avoided overoxidation of coupling products.The key feature of dinuclear vanadium(V) catalysts such as (Ra,S,S)-5a is an outstanding mode of the homocoupling reaction, in which a single molecule of the catalyst activates two molecules of the starting material (e.g., 2-naphthols) simultaneously. With this "dual activation" mechanism, the oxidative coupling promoted by the dinuclear catalyst proceeds in an intramolecular manner. The homocoupling rate using 5 mol % of the dinuclear vanadium(V) complex (Ra,S,S)-5a was measured to be 111 times faster than that of the mononuclear vanadium(IV) complex (S)-4a bearing a half motif of the dinuclear vanadium complex.In the case of the heterocoupling reaction utilizing two different kinds of arenol derivatives, only a starting arenol having lower oxidation potential seems to be activated by the mononuclear vanadium complex. The reaction rate of the heterocoupling using either mono- or dinuclear vanadium complexes showed no difference to give the coupling product in high yields but with a different enantioselective manner; chiral mononuclear vanadium(V) complexes showed better enantioselectivites than that of the dinuclear vanadium(V) complexes. A competing heterocoupling study and a linear correlation between the ee of the mononucaler vanadium catalyst and ee of the heterocoupling suggested that the heterocoupling involves an intermolecular radical-anion coupling pathway.In this Account, we summarize the recent advances in vanadium-catalyzed coupling reactions that produced important chiral molecules, such as biresorcinols, polycyclic biphenols, oxa[9]helicenes, bihydroxycarbazoles, and C1-symmetrical biarenols, and their coupling reaction mechanisms. By pursuing vanadium catalysis, we believe numerous additional transformations as well as a renewed interest in catalytic and chemo-, regio-, and enantioselective aryl-aryl bond constructions will be manifested.

Synthesis of Carboxylic Acids from Styrene Derivatives and Fatty Acids through Oxidative C=C Bond Cleavage

Key words carboxylation - styrenes - fatty acids - C=C bond cleavage - oxidation - vanadium catalysis

Oxidative C=C Cleavage of Styrenes with Supported Cobalt Vanadium Oxide

Key words cobalt catalysis - vanadium catalysis - graphene oxide - styrenes - oxidation - aldehydes

Catalytic Applications of Vanadium: A Mechanistic Perspective.

The chemistry of vanadium has seen remarkable activity in the past 50 years. In the present review, reactions catalyzed by homogeneous and supported vanadium complexes from 2008 to 2018 are summarized and discussed. Particular attention is given to mechanistic and kinetics studies of vanadium-catalyzed reactions including oxidations of alkanes, alkenes, arenes, alcohols, aldehydes, ketones, and sulfur species, as well as oxidative C-C and C-O bond cleavage, carbon-carbon bond formation, deoxydehydration, haloperoxidase, cyanation, hydrogenation, dehydrogenation, ring-opening metathesis polymerization, and oxo/imido heterometathesis. Additionally, insights into heterogeneous vanadium catalysis are provided when parallels can be drawn from the homogeneous literature.

Vanadium-Catalyzed Oxidative C(CO)–C(CO) Bond Cleavage for C–N Bond Formation: One-Pot Domino Transformation of 1,2-Diketones and Amidines into Imides and Amides

A novel vanadium-catalyzed one-pot domino reaction of 1,2-diketones with amidines has been identified that enables their transformation into imides and amides. The reaction proceeds by dual acylation of amidines via oxidative C(CO)-C(CO) bond cleavage of 1,2-diketones to afford N,N'-diaroyl-N-arylbenzamidine intermediates. In the reaction, these intermediates are easily hydrolyzed into imides and amides through vanadium catalysis. This method provides a practical, simple, and mild synthetic approach to access a variety of imides as well as amides in high yields. Moreover, one-step construction of imide and amide bonds with a long-chain alkyl group is an attractive feature of this protocol.

Vanadium in asymmetric synthesis: emerging concepts in catalyst design and applications.

In recent years vanadium catalysis has been extended to a range of different and even complementary directions in asymmetric synthesis. Inspired by nature's way to activate both substrate and reagent in many cases, the design of efficient bifunctional and dinuclear vanadium catalysts has been achieved. Furthermore, vanadium catalysis has been an early field in which "hybrid catalysts" have been studied in detail by incorporation of oxovanadium complexes into proteins, thus giving artificial enzymes. In addition, a high compatibility of vanadium with proteins enabled the use of vanadium chemocatalysts for combinations with enzyme catalysis in one-pot, thus leading to dynamic kinetic resolutions. In this contribution, these three concepts of vanadium catalysis opening up new perspectives for asymmetric synthesis are reviewed.

Asymmetric vanadium- and iron-catalyzed oxidations: new mild (R)-modafinil synthesis and formation of epoxides using aqueous H2O2 as a terminal oxidant

The enantioselective oxidation of thioanisole to methyl phenyl sulfoxide and the epoxidation of several alkenes, including terminal ones, have been realized by using new iron(III) complexes, generated in situ from primary amine-derived non-symmetrical Schiff base ligands and aqueous H2O2 as environmentally benign oxidant. Further investigations on vanadium catalysis and the application of both catalytic systems in the synthesis of enantiomerically-enriched chiral drug (R)-modafinil were undertaken. It was found that the vanadium-based catalytic system (VO(acac)2/ligand 6), is able to provide (R)-modafinil in quantitative yield and acceptable enantiomeric excess within a very short reaction time (15min).

Synthesis of LY2784544

Key words LY2784544 - Janus kinase inhibitors - vanadium catalysis - aminomethylation - N-arylation

Preface

Abstract The following 10 papers are selections from the 4th International Symposium on Chemistry and Biological Chemistry of Vanadium held 3-5 September 2004 in Szeged, Hungary. This conference attracted over 110 participants from 25 countries and 4 continents. Plenary and invited lectures as well as posters discussed the inorganic chemistry of vanadium, vanadium chemistry in catalysis and organic synthesis, and biological aspects of vanadium chemistry. A new feature was introduced: the presentation of the Vanadis Award. The purpose of the Vanadis Award is to recognize an outstanding contributor to the advancement of vanadium science. The award will be presented at each International Vanadium Symposium prior to a lecture to be given by the recipient. It is awarded on the basis of contributions to a discipline or combination of disciplines of vanadium science, and is presented to an investigator who has produced innovative research with impact on the direction of the field. The nominee is selected on the basis of the following criteria: (1) Innovative research: A history of development or expansion of techniques and procedures and discovery of new chemical, biochemical, biological, technological, or pharmaceutical systems; (2) Development of new applications in one or more of the following areas: chemistry, biochemistry, biology, pharmaceutical science, materials science, and nanotechnology; (3) Wide-ranging influence of the nominee's work on the research of others in one or more disciplines; (4) History of highquality and -impact publications; and (5) Service of the nominee to progress, application, and exploration of vanadium in science. The recipient of the first Vanadis Award is Prof. Debbie C. Crans of Colorado State University, whose award address is the first contribution to be presented herein. The additional contributions begin with papers covering various aspects of the inorganic chemistry of vanadium. These papers are followed by descriptions of recent results in the use of vanadium compounds to further organic synthesis, and on the catalytic behavior of interesting vanadium complexes. The final selection includes papers dealing with the role of vanadium in haloperoxidases, or as insulin-mimetic compounds, which may be orally administered replacements of insulin injections. A tremendous increase in studies of aqueous vanadium chemistry over the past decade has been driven by the need to comprehend the diverse biological effects of vanadium. Examples of the rich array of data and concepts needed to explain the biological role of vanadium are given by models of the vanadium-containing haloperoxidase enzyme activity. However, this selection of papers from the 4th International Vanadium Symposium indicates that basic inorganic studies and a wide range of applications of vanadium chemistry to fundamental chemical problems of synthesis, reactivity, and catalysis are not lacking. Indeed, we look forward to the 5th International Vanadium Symposium to be held in San Francisco, CA USA in the fall of 2006, where additional fundamental studies linked to the need to better understand vanadium nutritional essentiality, vanadium toxicity, vanadium therapy, and vanadium catalysis, including "green chemical" industrial applications will be presented. Kenneth Kustin and Tamas Kiss Conference Editors

Vanadium Catalysis in Bromoperoxidation Reaction

Peroxidative bromination of phenol red to its tetrabromo derivative, bromophenol blue, required vanadate in addition to H2O2when carried out in the pH range of 5–7. Excess H2O2, with ratio of H2O2:vanadate of 2:1 and above, prevented the reaction. Diperoxovanadate, known to be formed in such reaction mixtures, was ineffective by itself and needed uncomplexed vanadate (Vv) or vanadyl (Viv) to support bromination. Bromide-assisted reduction of the excess vanadate to vanadyl appeared to be an essential secondary reaction. In the absence of phenol red oxygen was released, and concomitantly bromide was oxidized to a form competent to brominate phenol red added after termination of oxygen release. These findings indicated participation of reactions leading to an intermediate derived from vanadyl and diperoxovanadate, previously described from this laboratory (Arch. Biochem. Biophys.316, 319–326, 1995). Continuous bromination of phenol red occurred when glucose oxidase–glucose system was used as a source of continuous flow of H2O2. A scheme of reactions involving peroxovanadates (mono-, di-, μ-, and bromo-) is proposed for the formation and utilization of an active brominating species and for the recycling of the product, mono-peroxovanadate, by H2O2, which explains the catalytic role of vanadium in the bromoperoxidation reaction.

Kinetics of the bromate–iodide–ascorbic acid clock reaction: different mechanism of the molybdenum and vanadium catalysis

The kinetics of the molybdenum(VI)- and vanadium(V)-catalysed bromate–iodide–ascorbic acid clock reaction has been studied by means of spectrophotometry and pH-metric measurements. Two different types of catalysis were detected in this clock reaction. It was shown that MoVI catalyses the component process bromate + iodide of the clock system, while VV catalyses the direct reaction between bromate and ascorbic acid. The rate equation r=k2[BrO3–][I–][H+]2+k′2[BrO3–][I–][H+]2[MoVI] describes the kinetics of the Mo-catalysed system, where k2= 44 ± 2 dm9 mol–3 s–1 and k′2=(4.3 ± 1)× 106 dm12 mol–4 s–1. In the vanadium-catalysed clock reaction the equation r=k′1[BrO3–][VV]+k2[BrO3–][I–][H+]2 was found, where k′1= 9.6 ± 1 dm3 mol–1 s–1 and k2= 42.6 ± 2 dm9 mol–3 s–1. At lower acidities (pH > 3) more complex kinetics appeared and further study was abandoned.

Vanadium Catalysis in the Nonenzymatic Transamination of δ-Aminolevulinic Acid

Abstract By nonenzymatic model reactions, the influence of vanadium (VO2+, VO3 −) and other metal ions (Al3+, Fe2+, Fe3+, Zn2+, Ni2+, Cr3+) on the transamination of 4,5-dioxovaleric acid (DOVA) with ʟ-alanine (Ala) to δ -aminolevulinic acid (δ-ALA) and pyruvic acid (PA) with pyridoxal phosphate (PLP) is investigated. The examinations of the partial reactions show that VO2+, VO3 − and Fe2+ effectively enhance both conversions, while Ni2+ only promotes the conversion of DOVA to δ -ALA with pyridoxamine phosphate (PMP). Besides Cr3+ , which inhibits the transaminations, all other metals tried slightly enhance both reactions. The coupled transamination DOVA/Ala to δ-ALA/PA with PLP as a catalyst is performed at 40 °C , the extent of the reaction being judged by the amount of δ-ALA formed. Among all metal ions tested, VO2+ and VO3 − were found to be the most effective ones. Fe2+, Al3+ and Fe3+ also slightly enhance the reaction, but all other metals do not influence or inhibit the transamination. In presence of VO2+ or VO3 − ions, the optimum pH of the reaction shifts from pH 4 to pH 7.4. The positive influence of vanadium on δ-ALA transamination is discussed in connection with known structures of analogous Schiff base complexes with metal ions.

Metal ion catalysis of oxygen transfer reactions. I. Vanadium catalysis of the epoxidation of cyclohexene

Metal ion catalysis of oxygen transfer reactions. I. Vanadium catalysis of the epoxidation of cyclohexene

Vanadium catalysis of the oxidation of catechol amines, dihydroxyphenylalanine and 5-hydroxyindoles.

IN the course of an investigation of the mechanism of enzymatic oxidation of serotonin (5-hydroxytryptamine) by human serum1, we found that apparently identical chromatographic reaction products2 resulted when this oxidation was catalysed non-enzymatically by cupric ion. We became curious as to what extent transitional metals other than copper catalysed this reaction, and expanded our investigation to include a study of the relative catalytic effectiveness of 18 transitional elements in the oxidations of related compounds of biological interest.