Chapter 1: Introduction: Vanadium, Its Compounds and Applications

Vanadium is an early first-row transition metal (atomic number 23) that was discovered in 1801 by Andrés Manuel del Rio in Mexico City from a specimen of vanadinite, Pb₅(VO₄)₃Cl. However, it was wrongly identified as a chromium mineral by other chemists until in 1831 when the Swedish chemist Nil Gabriel Selfström in Stockholm “discovered” vanadium and separated it from a sample of cast iron. It was confirmed as a new chemical element in the 19th century after decades of uncertainty that followed its initial discovery. The current designation of this metal was coined from the name of a Scandinavian goddess of beauty and fertility, Vanadis, due to the beautiful colours of vanadium compounds in solution. The metal in pure form was first isolated in 1867 by the English chemist Henry Enfield Roscoe by hydrogen reduction of vanadium dichloride, VCl₂, and he showed that previously isolated samples were vanadium nitride (VN). In 1925 the American chemists John Wesley Marden and Malcolm N. Rich obtained 99.7% pure vanadium by reduction of vanadium pentoxide, V₂O₅, with calcium metal through a variety of smelting, leaching and roasting processes.

Vanadium is the 20th most abundant chemical element in the Earth's crust,¹  is found in ca. 65 different minerals and can be a significant constituent of some fossil fuels. The commercial sources of vanadium are the minerals carnotite, vanadinite, roscoelite and vanadium-bearing magnetite. Vanadium exhibits a wide range of oxidation states from −3 to +5 in inorganic compounds. In its higher oxidation states, it exhibits a good Lewis acidity. Oxophilicity is also an important property. The existence of multiple oxidation states, which often can be easily interconverted, its oxophilicity and Lewis acid character, ready hydrolysis and polymerization confer to this metal a richer chemistry than that of many other elements. These properties help in the formation of, e.g., aggregated oxyanions and sulphur complexes, a diversity of types of oxido complexes, and in the broad application of its compounds in catalysis, as will be widely illustrated in the chapters of this book.

Vanadium is a suitable metal for several technological applications. It is an important component of specific steel alloys since it promotes lightness and provides additional tensile strength of these materials, as well as providing extra protection against rust and corrosion. The vanadium oxides have important applications, e.g., in manufacturing of ceramics, production of coatings for electrochemical tools of energy storage equipment, microelectronic devices and specific glasses used for the production of smart windows.^2,3  Vanadium has been applied as a component of batteries. A vanadium redox flow battery, used commercially for energy storage, is an electrochemical cell containing acid aqueous solutions of this metal with ions from +5 to +2 formal oxidation states (i.e., the electrolyte in the positive half-cell is at oxidation state five and four, and in the negative side at oxidation state three and two).⁴  Additionally, vanadium compounds have been proposed as constituents of lithium-ion batteries⁵  and for bioinspired, nonaqueous redox flow batteries.⁶ 

Vanadium has a versatile chemistry with several oxidation states that are interchangeable under adequate conditions and is an essential metal for some living organisms. Curiously, the majority of biological roles of vanadium are associated with redox reactions, including alternative nitrogenase that has been identified in some diazotrophs,⁷  specific haloperoxidases known from some seaweeds, fungi, lichen and bacteria,⁸  as well as amavadin, a metallobiomolecule that is a complex found in a few Amanita fungi.⁹  These cases have inspired models applied for catalytic purposes involving redox reactions.

Medicinal application of vanadium compounds is also a well-explored area of research. This biologically relevant element has many useful applications in vanadium-based therapeutic drugs for the treatment of several types of diseases, e.g., diabetes, cancer and diseases caused by parasites.^10–12  The antidiabetic properties of vanadium compounds have been known for more than a century¹³  and, thereafter, several vanadium compounds have been studied and explored in the search for attractive antidiabetic drugs.¹⁴  Vanadium compounds as anti-cancer agents are of high interest in recent times on account of a combination of beneficial properties for chemotherapy, i.e., strong cytotoxicity, anti-metastatic activity and relatively low systemic toxicity.¹⁵ 

Various vanadium compounds have been identified in many modes of interactions including inhibition of protein phosphatases,^16–18  interactions with circulating proteins (e.g., serum albumin and transferrin),¹⁹  effects on reactive oxygen species (ROS) levels,^20,21  etc. The effects of vanadium compounds on the plasma membrane are also known.²² 

Vanadium, as a component of catalysts, participates in diverse chemical processes, e.g., for the industrial production of sulphuric acid by the contact process, fabrication of maleic anhydride, oxidation of propane and propylene to acrylonitrile, toluene to benzonitrile, alkane oxydehydrogenation, olefin epoxidation, and in the reduction of sulphur and nitrogen oxide emissions resulting from human activities.²³ 

Vanadium compounds have a broad range of applications in catalysis, and many research papers and a considerable number of reviews on specific topics of vanadium catalysts have been recently published.^9,24–33  For instance, various catalytic oxidation reactions, e.g., oxidation of alkanes and alcohols, epoxidation, sulphoxidation, oxidative bromination, etc., are efficiently catalysed by vanadium compounds using appropriate oxidants.^9,24–33  They are active catalysts under homogeneous or heterogeneous conditions. Several VO_x based organic–inorganic nanocomposites have potential photocatalytic properties.^34,35  Vanadium compounds are also widely used in olefin metathesis, olefin oligomerization, polymerization and copolymerization reactions.^36–41  They are involved in enantioselective C–C bond-forming and oxidative–reductive coupling reactions.^28,42 

Dioxygen activation by biomimetic vanadium complexes and vanadate-dependent haloperoxidases,^43–46  as well as vanadium nitrogenase^7,47–49  and Amavadin,^9,29  shows the potential of biologically relevant catalytic functions of vanadium compounds.

This book addresses relevant topics on current vanadium catalysis, comprising 25 chapters with contributions from internationally recognised authors from various parts of the world. It is organised in three self-explanatory parts that reflect the broad scientific areas in which vanadium has found applications in catalysis: Inorganic Catalysis (fifteen chapters), Organometallic Catalysis (five chapters), and Biochemical and Biomimetic Catalysis (also five chapters). Summaries of these chapters (often based on those provided by the corresponding authors) are as follows:

Ch. 1 – Introduction: vanadium, its compounds and applications (by M. Sutradhar, J. A. L. da Silva and A. J. L. Pombeiro)

An overall view about vanadium and its compounds, as well as on the structure of the book, is outlined.

Part I – Inorganic Catalysis

Ch. 2 – Amavadin and related complexes as oxidation catalysts (by J. A. L. da Silva, M. F. C. Guedes da Silva, M. Sutradhar and A. J. L. Pombeiro)

Amavadin, a metallobiomolecule with a rare coordination chemistry and particular N-oxyiminodicarboxylate ligand whose biological role is yet unknown, mediates water oxidation and exhibits nitrite reductase-, catalase- and peroxidase-type activity, this one towards thiols (e.g., biological ones). It also mediates peroxidative oxidation, peroxidative halogenation and carboxylation of alkanes and other hydrocarbons, as well as oxidation of alcohols. Its models, non-oxido- and oxido-V complexes, namely with non-innocent ligands, are compared for the above catalytic oxidations.

Ch. 3 – Activating hydroperoxides by vanadium(V) compounds (by J. Hartung)

Vanadium(V) compounds, namely orthovanadates, promote oxygen atom transfer from hydroperoxides to various substrates, and examples for (i) bromide oxidation by H₂O₂ and (ii) alkenol oxidation by tert-butyl hydroperoxide (TBHP, a more nucleophilic oxidant) are discussed, illustrating two border mechanisms. In (i) catalysed by protonated orthovanadates in protic solvents (as in marine bromoperoxidases), H₂O₂ should be converted to an electrophile and the influence of its σ*(O,O)-orbital energy is discussed. In (ii), shown by trialkyl orthovanadate-catalysed oxidations by TBHP in aprotic solvents, no effect on orbital energies of the peroxide is observed.

Ch. 4 – The vanadate–pyrazinecarboxylic acid–hydrogen peroxide reagent and similar systems for efficient oxidations with peroxides (by G. B. Shul'pin and L. S. Shul'pina)

The oxidation of alkanes (RH) and arenes (ArH) with aqueous H₂O₂ in acetonitrile solutions under mild conditions, at low temperature, leads to the formation of the corresponding alkyl hydroperoxides (ROOH) and phenols (ArOH), in the presence of adequate homogeneous V-catalysts and promoters (e.g., pyrazine carboxylic acid or, in some cases, a strong inorganic or organic acid). This topic is addressed in this chapter, concerning different alkanes, including methane.

Ch. 5 – Peroxo-vanadium complexes as sustainable catalysts in oxidations, halogenations and other organic transformations (by F. Sabuzi, G. Pomarico, V. Conte and P. Galloni)

The application of V-peroxido complexes as catalysts in oxidation (of hydrocarbons, alcohols, phenols and sulphides) and bromination reactions is discussed, particularly in terms of sustainability (e.g., use of H₂O₂ and solvents other than toxic VOCs, and avoidance of halides). Both homogeneous and two-phase systems are addressed. Examples of lignin valorisation, fuel desulphurization and clean synthetic methodologies are summarised.

Ch. 6 – Vanadium-scorpionate catalysed oxidations (by L. M. D. R. S. Martins and A. J. L. Pombeiro)

The selective catalytic oxidation of alkanes and other hydrocarbons can potentially provide important routes for preparing large-scale commodities in the chemical industry. In this chapter, recent advances on the use of V complexes with tris(pyrazolyl)methane (C-scorpionate) ligands as homogeneous or supported oxidation catalysts towards the development of industrially significant sustainable processes are reviewed. They include oxidations of alkanes and p-xylenes, and carboxylations of alkanes.

Ch. 7 – Vanadium-aroylhydrazone catalysed oxidations (by M. Sutradhar, V. B. Arion, T. Roy Barman and A. J. L. Pombeiro)

The catalytic activity of V complexes derived from hydrazone Schiff bases towards various oxidation reactions (of alkanes and alcohols, olefin epoxidation and bromination) is illustrated in this chapter. The importance of the ligand and the relevance of its eventual non-innocent redox behaviour is discussed in metal–ligand cooperation processes. The influence on their catalytic performance of oxidants, co-catalysts, temperature and other parameters is analysed.

Ch. 8 – Vanadium-oxide molecular catalysts in non-aqueous solution (by Y. Hayashi, M. Katayama and K. Ozutsumi)

This chapter compiles the diversity of V-oxide clusters that are spontaneously formed and transformed in solution, with significance for catalytic reactions, using a vanadate source. Transformations into versatile structures, including tubes, spheres, blocks, disks and bowls are discussed.

Ch. 9 – Catalysis by oxometalates and their microheterogeneous media (by J. Lodh and S. Roy)

In addition to archiving the chemistry of polyoxometalates in catalysing oxidative, reductive and photo-redox reactions along with acid- and base-catalysed reactions, this chapter also highlights examples of reactions that can harvest energy. It further addresses micro-heterogeneous media, or the state of soft-oxometalates, in site-specific catalysis and polymerization reactions.

Ch. 10 – Use of vanadium catalysts in epoxidation and sulphoxidation reactions with Green Chemistry criteria (by A. Galindo, A. Pastor, F. Montilla and M. del Mar Conejo)

Catalytic applications of V complexes in the oxidation of olefin and sulphide substrates, following green chemistry criteria, are reviewed in this chapter, with emphasis on the use of green oxidants and non-conventional solvents, and the immobilization of V species into several supports (inorganic materials, organic polymers, ionic liquids, etc.).

Ch. 11 – Supported vanadium catalysts: heterogeneous molecular complexes, electrocatalysis and biomass transformation (by C. Freire, C. Pereira, B. Jarrais, D. Fernandes, A. Peixoto, N. Cordeiro and Filipe Teixeira)

This chapter provides an overview of supported V complexes as eco-sustainable recyclable catalysts of several chemical reactions for the production of added-value products. Different strategies for V compounds’ immobilization onto solid supports are reviewed, highlighting those that lead to enhanced catalytic performance. The application of V-based materials as electrocatalysts for reduction–oxidation reactions relevant to renewable energy storage and conversion technologies is also addressed, as well as V-mediated catalytic reactions for biomass valorisation.

Ch. 12 – Carbon-supported vanadium catalysis (by S. A. C. Carabineiro, L. M. D. R. S. Martins and M. Sutradhar)

Compared to the use of heterogenous V catalysts, much less work has been dedicated to the heterogenization (anchorage) of homogenous (soluble) V complexes on solid supports and their use as heterogenized catalysts with the advantages inherent to heterogenous catalysts. In this chapter, this interface area of research is reviewed by considering both V complexes (that can also act as soluble homogeneous catalysts) and V oxides supported on different types of C materials.

Ch. 13 – Molecularly dispersed vanadium oxide: structure-reactivity relationships for reducibility and hydrocarbon oxidation (by M. O. Guerrero-Pérez, M.V. Martínez-Huerta and M. A. Bañares)

Molecularly dispersed V oxide on oxide supports is a highly active material, and its redox and acidic properties can be tuned by its interaction with the support. The structure of the dispersed V oxide is characterised by VO, V–O–H, V–O–V and V–O–support bonds, their reactivity depending on the coverage on the support, the cation of the support, the surface density of VO_x species and the degree of hydration. The studies on such themes, including the application of real-time catalytic spectroscopic methods (namely operando Raman spectroscopy), are discussed in this chapter.

Ch. 14 – Vanadium oxides in photocatalysis, including bare oxides and VO_x-based organic–inorganic nanocomposites (by E. Benavente, J. Aliaga and G. González)

This chapter provides a critical review on the use and potential of V oxides as photocatalysts under generally mild and environment-friendly conditions, as well as their advantages and limitations. Their preparation, chemical features and photocatalytic activity, as well as theoretical approaches to understand their role in the catalyst performance, are addressed. Pure, supported, doping, composites and inorganic–organic nanocomposites are analysed.

Ch. 15 – Theoretical mechanistic analysis on vanadium oxidation catalysis (by M. L. Kuznetsov)

Advances over the past 10 years in the field of V oxidation catalysis are discussed under theoretical perspectives. This chapter is focused on the mechanistic aspects of the V-catalysed oxidation reactions and on the analysis of the main factors and driving forces which govern these processes, on the basis of theoretical methods.

Part II – Organometallic Catalysis

Ch. 16 – Vanadium-catalysed olefin oligomerization, polymerization and copolymerization (by S. Zhang and W. Zhang)

Olefin oligomerization, polymerization and copolymerization catalysed by V-based catalysts (including N-heterocyclic carbene V homogeneous catalysts) are presented in this chapter. It focuses on ethylene polymerisation and copolymerisation with α-olefins, showing the advantages of vanadium complex catalysts in controlling the molecular weight, molecular weight distribution, sequence and topological structure of the resulting ethylene–propylene copolymer.

Ch. 17 – Vanadium-catalysed olefin metathesis and related chemistry (by K. Nomura)

V-alkylidene catalysts are known to exhibit unique features that are different from those of conventional Ru and Mo complex catalysts for olefin metathesis, a widely employed method in the synthesis of fine chemicals and advanced polymeric materials. In this chapter, the basics in olefin metathesis, design of olefin metathesis catalysts with early transition metals, and recent progresses in V olefin ring-opening metathesis polymerization (ROMP) catalysis are discussed.

Ch. 18 – Vanadium-catalysed enantioselective C–C bond-forming reactions (by M. Sako, S. Takizawa and H. Sasai)

Recent advances in the enantioselective V mediated C–C bond-forming reactions via acid and redox catalysis are discussed in this chapter by addressing oxidative couplings of phenol derivatives catalysed by chiral V complexes. Catalysts with multidentate ligands prepared from salicylaldehyde derivatives and chiral amino acids are discussed, as well as applications in the synthesis of important chiral compounds, such as polycyclic biphenols, oxa[9]helicenes, bi(hydroxycarbazole)s and biresorcinols. The possible use of mild-reaction conditions under an air or oxygen atmosphere is emphasised.

Ch. 19 – Vanadium-induced oxidative and reductive coupling (by T. Amaya and T. Hirao)

V-induced oxidative and reductive couplings developed in the authors’ group are surveyed. One-electron redox propensity and Lewis acidity of oxido-V^V compounds allow achieving oxidative C–C bond formation. The combination of B enolate and silyl enol ether towards selective cross-oxidative coupling is discussed. Ligand coupling reactions of organic substituents on main-group organometallic compounds are also induced by oxidation with such V catalysts and are described in this chapter. Moreover, reductive coupling reactions, namely of pinacol, and the use of V/Ti heterobimetallic catalysts for selective cross-coupling between aryl and aliphatic aldehydes are also addressed.

Ch. 20 – Vanadium-catalysed transformations of selected functional groups (by T. Moriuchi and T. Hirao)

Oxidative halogenation, oxidative aromatization, amination and oxidative deoxygenative coupling are discussed in this chapter. It focuses on V-catalysed oxidative aromatization of 2-cyclohexenones (to the corresponding phenol derivatives), and direct amination of allyl alcohols (with both aromatic and aliphatic amines) using oxido-V^V catalysts. Direct hydrazination of allyl alcohol and deoxygenative homocoupling reaction of alcohols depending on hydrazine derivatives, catalysed by oxido-V^V, are also addressed. The role in catalysis of the Lewis acidity, oxophilicity and redox properties of the oxido-V^V catalysts is discussed.

Part III – Biochemical and Biomimetic Catalysis

Ch. 21 – Vanadium compounds as indirect activators of a G protein-coupled receptor (by D. Althumairy, H. A. Murakami, R. Colclough, B. G. Barisas, D. A. Roess and D. C. Crans)

This chapter deals with a new mechanism for activation of luteinizing hormone receptors (LHR), a G-protein-coupled receptor which demonstrates that V compounds can initiate receptor-mediated intracellular signalling via indirect effects on membrane lipids. Bis(maltolato)oxovanadium(iv) (BMOV) and VOSO₄ decrease lipid packing, increase aggregation of LHR, and initiation of LHR signalling. Membrane lipid order effects and implications for BMOV or VOSO₄ internalization are also discussed.

Ch. 22 – Reductive dioxygen activation by biomimetic vanadium complexes (by C. Drouza and A. Keramidas)

Advances on O₂ activation by simple functional biomimetic V complexes are reviewed. The O₂ activation can involve coordination to V and direct reduction or, in rare cases, attack of O₂ on an activated non-innocent organic ligand (namely catecholate and hydroquinonate). V^III, V^IV compounds are shown to be efficient catalysts for 2e⁻ and 4e⁻ reductions of O₂, and mechanistic pathways are highlighted. The importance of peroxido-complexes and of biomolecules to compensate the thermodynamic and kinetic barriers is also discussed.

Ch. 23 – Vanadium in catalytically proceeding natural processes (by D. Rehder)

The naturally occurring enzymes vanadate-dependent haloperoxidases and V-dependent nitrogenases are addressed in this chapter. The vanadate–phosphate antagonism in the context of physiologically active phosphate-based enzymes is also discussed, as well as Amavadin with catalase and peroxidase activity.

Ch. 24 – Vanadium chloroperoxidases as versatile biocatalysts (by R. Wever, R. Renirie and F. Hollmann)

In this chapter, the catalytic and structural properties of the V chloroperoxidases (VCPO) are discussed with emphasis on their activity and stability under operational conditions which make them attractive catalysts for organic synthesis. The use of VCPO in the formation of singlet oxygen, halogenation of phenols, alkenes, halocyclization of unsaturated alcohols and in the aza-Achmatowicz reaction is highlighted.

Ch. 25 – Vanadium catalysis relevant to nitrogenase (by H.-R. Pan and H.-F. Hsu)

This chapter is focused on V nitrogenase and V complexes showing nitrogenase-like reactivity. Structural and catalytic features of the enzyme are discussed. In addition, V complexes that show a reactivity relevant to nitrogen fixation, which includes N₂ reduction to ammonia, silylation of N₂ and reduction–disproportionation of hydrazine to NH₃, are also highlighted.

The catalytic applications of vanadium compounds have been well documented in a rapidly growing number of research articles and reviews. Moreover, books on vanadium chemistry, bioinorganic chemistry, biochemistry and biology, with applications in pharmacology and in industry are available,^50–54  but a book devoted to catalysis has been missing. The current book intends to fill this gap, covering chemical, biological, photochemical and theoretical standpoints in vanadium catalysis, and providing a global and integrated view on catalysis based on research topics of current interest. This publication is expected to be a reference and inspiring tool for academic staff, researchers, students of different university levels, and will also be of significance to industry.

This work has been supported by the Fundação para a Ciência e Tecnologia (FCT) 2020–2023 multiannual funding to Centro de Química Estrutural (project UIDB/00100/2020). The authors are also grateful to the FCT for financial support to project PTDC/QEQ-QIN/3967/2014. M. S. acknowledges the FCT and IST for a working contract “DL/57/2017” (Contract no. IST-ID/102/2018).