Recent Advances in Polyoxometalate-Catalyzed Reactions

Recent advances in the Suzuki–Miyaura cross-coupling reaction using efficient catalysts in eco-friendly media

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.

Catalytic Applications of Vanadium: A Mechanistic Perspective.

Oxovanadium complexes in catalytic oxidations

Polyoxometalates (POMs) are molecular metal-oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self-assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM-cation interactions in solution, the resulting solid-state compounds, and behavior and properties that emerge from these POM-cation interactions. We will explore how application-inspired research has exploited cation-controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM-cation interactions.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/anie.201905600

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

In this article we discussed synthesis and catalytic applications of heterogeneous catalysts based on lacunary polyoxometalates (LPOMs) and transition metal substituted polyoxometalates (TMSPOMs), however exclusively the focus has been given to the mono LPOMs and mono-TMSPOMs. As the field of supported LPOMs/TMSPOMs is upcoming important field, some aspects about choice of support as well as methods of supporting have also been described. We also include a few of our new research results in order to understand the effect of support and active species as well as choice of organic transformation.

Keggin-type lacunary and transition metal substituted polyoxometalates as heterogeneous catalysts: A recent progress

Supported undecamolybdophosphate was synthesized and characterized by various physicochemical techniques and successfully used for solvent free oxidation of styrene and of benzyl alcohol to benzaldehyde. Influence of the reaction parameters (molar ratio of substrate to H2O2, amount of the catalyst, reaction time, and reaction temperature) were studied. The catalyst was reused three times without any significant loss in the catalytic activity. FT-IR, XRD, and DRS of regenerated catalyst indicated that the catalyst was undegraded and stable after the reaction. The novelty of the work lies in obtaining a single selective product, benzaldehyde, as well as a high TON for the same, under mild conditions.

Solvent Free Selective Oxidation of Styrene and Benzyl Alcohol to Benzaldehyde over an Eco-Friendly and Reusable Catalyst, Undecamolybdophosphate Supported onto Neutral Alumina

1-Phenyl-3-methyl-4-touloyl-5-pyrazolone (ligand) was synthesized and used to prepare an oxovanadium(IV) complex. The complex was characterized by single-crystal X-ray analysis and various spectroscopic techniques. The single-crystal X-ray analysis of the complex shows that the ligands are coordinated in a syn configuration to each other and create a distorted octahedral environment around the metal ion. A heterogeneous catalyst comprising an oxovanadium(IV) complex and hydrous zirconia was synthesized, characterized by various physicochemical techniques, and successfully used for the solvent-free oxidation of styrene. The influence of the reaction parameters (percent loading, molar ratio of the substrate to H(2)O(2), amount of catalyst, and reaction time) was studied. The catalyst was reused three times without any significant loss in the catalytic activity.

Synthesis and crystal structure of an oxovanadium(IV) complex with a pyrazolone ligand and its use as a heterogeneous catalyst for the oxidation of styrene under mild conditions.

Traditional procedures for synthesis of carbonyl compounds suffer from a lack of selectivity, use of organic solvents, toxicity of the reagents, and waste production. As a cleaner alternative, an environmentally benign solvent free oxidation of alcohols catalyzed by mono transition metal-substituted Keggin-phosphomolybdates, PMo 11 M (M = Co, Mn, Ni) using hydrogen peroxide was carried out under mild conditions. The influence of different parameters such as mole ratio of benzyl alcohol to H 2 O 2 , amount of the catalyst, reaction time and reaction temperature on oxidation of benzyl alcohol was investigated. Further, oxidation of various alcohols such as cyclopentanol, 1-hexanol and 1-octanol with PMo 11 M was carried out under optimized conditions. The catalytic activity of recycled catalysts was also evaluated and it was found that catalysts are stable under present reaction conditions. All the catalysts are very much efficient, especially in terms of % selectivity of the desire product.

Solvent free clean selective oxidation of alcohols catalyzed by mono transition metal (Co, Mn, Ni)-substituted Keggin-phosphomolybdates using hydrogen peroxide

A novel heterogeneous catalyst comprising undecamolybdophosphate and hydrous zirconia was synthesized, characterized by various physicochemical techniques and used as an efficient heterogeneous catalyst for oxidation of styrene using H2O2 as an oxidant. The novelty of the present work lies in obtaining >99% conversion of styrene with >99% selectivity for benzaldehyde under solvent free mild reaction conditions.

Soyeb Pathan

Papers

Keggin-type lacunary and transition metal substituted polyoxometalates as heterogeneous catalysts: A recent progress

Solvent Free Selective Oxidation of Styrene and Benzyl Alcohol to Benzaldehyde over an Eco-Friendly and Reusable Catalyst, Undecamolybdophosphate Supported onto Neutral Alumina

Synthesis and crystal structure of an oxovanadium(IV) complex with a pyrazolone ligand and its use as a heterogeneous catalyst for the oxidation of styrene under mild conditions.

Solvent free clean selective oxidation of alcohols catalyzed by mono transition metal (Co, Mn, Ni)-substituted Keggin-phosphomolybdates using hydrogen peroxide

Novel heterogeneous catalyst, supported undecamolybdophosphate: synthesis, physico-chemical characterization and solvent-free oxidation of styrene