Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts

The assembly of MoVIO2 2+ and methoxy-substituted salicylaldehyde nicotinoyl hydrazone ligands afforded two classes of hybrid polyoxometalates (POMs). In the Class I architectures, [MoO2(HL1-3)(D)]2[Mo6O19]·xCH3COCH3 (D = CH3COCH3 or H2O, x = 0 or 2, and L1-3 = ligands bearing the OMe group at position 3, 4 and 5, respectively), the main driving force for self-assembly is the electrostatic interaction between the components. Class II architectures are composed of a POM anion covalently linked to two Mo-complex units through the terminal Ot or bridging μ2-OPOM oxygen atoms, as found in Lindqvist-based hybrids [{MoO2(HL1-3)}2Mo6O19]·xCH3CN (x = 0 or 2) and the asymmetrical β-octamolybdate-based hybrid [{Mo2O4(HL2)(H2L)}{MoO2(HL2)}2Mo8O26]·CH3CN·H2O. Quantum chemical calculations were applied to evaluate the impact of the POM hybrid constituents on the hybrid-type stability, showing that it strongly depends on the ligand substituent position and ancillary ligand nature. Hybrids were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP in water or decane) and with or without the addition of acetonitrile (CH3CN) as an organic solvent. The catalytic results provided by the use of TBHP in decane are the best ones and classify all the prepared catalysts as very active, with the conversion of cyclooctene >90%, and high selectivity towards epoxide, >80%. We also examined the influence of the ligand structure, POM's hybrid type, and coordination mode on the Mo-hybrid activity and selectivity.

Molybdenum Complexes Derived from 2-Hydroxy-5-nitrobenzaldehyde and Benzhydrazide as Potential Oxidation Catalysts and Semiconductors

This study aimed to synthesize molybdenum complexes coordinated with an aroyl hydrazone-type ligand (H2L), which was generated through the condensation of 2-hydroxy-5-nitrobenzaldehyde with benzhydrazide. The synthesis yielded two types of mononuclear complexes, specifically [MoO2(L)(MeOH)] and [MoO2(L)(H2O)], as well as a bipyridine-bridged dinuclear complex, [(MoO2(L))2(4,4'-bpy)]. Those entities were thoroughly characterized using a suite of analytical techniques, including attenuated total reflectance infrared spectroscopy (IR-ATR), elemental analysis (EA), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction (SCXRD). Additionally, solid-state impedance spectroscopy (SS-IS) was employed to investigate the electrical properties of these complexes. The mononuclear complexes were tested as catalysts in the epoxidation of cyclooctene and the oxidation of linalool. Among these, the water-coordinated mononuclear complex, [MoO2(L)(H2O)], demonstrated superior electrical and catalytic properties. A novel contribution of this research lies in establishing a correlation between the electrical properties, structural features, and the catalytic efficiency of the complexes, marking this work as one of the pioneering studies in this area for molybdenum coordination complexes, to the best of our knowledge.

Molybdenum, Vanadium, and Tungsten-Based Catalysts for Sustainable (ep)Oxidation

This article gives an overview of the research activity of the LAC2 team at LCC developed at Castres in the field of sustainable chemistry with an emphasis on the collaboration with a research team from the University of Zagreb, Faculty of Science, Croatia. The work is situated within the context of sustainable chemistry for the development of catalytic processes. Those processes imply molecular complexes containing oxido-molybdenum, -vanadium, -tungsten or simple polyoxometalates (POMs) as catalysts for organic solvent-free epoxidation. The studies considered first the influence of the nature of complexes (and related ligands) on the reactivity (assessing mechanisms through DFT calculations) with model substrates. From those model processes, the work has been enlarged to the valorization of biomass resources. A part concerns the activity on vanadium chemistry and the final part concerns the use of POMs as catalysts, from molecular to grafted catalysts, (ep)oxidizing substrates from fossil and biomass resources.

Discrete and polymeric ensembles based on dinuclear molybdenum(vi) building blocks with adaptive carbohydrazide ligands: from the design to catalytic epoxidation

Discrete and polymeric ensembles based on dimolybdenum(vi) units with adaptive carbohydrazide ligands are described. The polymeric complexes are efficient catalysts for cyclooctene epoxidation under eco-friendly conditions.

Stability, Stimuli-Responsiveness, and Versatile Sorption Properties of a Dynamic Covalent Acylhydrazone Gel

Gel adsorbents are promising for pollutant removal from the wastewater. Herein, an acylhydrazone gel is developed from acylhydrazide-terminated pentaerythritol (PAT) and 2,4,6-triformylphloroglucinol (TFP) based on dynamic covalent acylhydrazone chemistry. PAT-TFP gel is stable under various conditions, while it shows reversible Cu2+ adsorption and desorption. PAT-TFP gel is studied as a versatile adsorbent for the capture of a range of (bulky) organic contaminants and heavy metal ions from aqueous solutions. Fast and good adsorption capacities are achieved for various dyes (rhodamine B and methyl orange), amines (aniline, p-chloroaniline, 4-methylaniline, and p-aminobenzoic acid), phenols (phenol, 1-naphthol, p-methylphenol, and bisphenol A), and metal ions (Cu2+, Cr3+, and Hg2+). The maximum adsorption capacity is 107.5 mg g-1 for Cu2+ and the equilibrium adsorption time is 30 min. PAT-TFP gel can be regenerated efficiently and used repeatedly.

Molybdenum(vi) complexes of hemilabile aroylhydrazone ligands as efficient catalysts for greener cyclooctene epoxidation: an experimental and theoretical approach

The focus of this work was on the synthesis, characterization and catalytic activity of Mo(vi) complexes with hemilabile 2-aminobenzhydrazone ligands.

The synthesis, structure and catalytic properties of the [Mo7O24(μ-Mo8O26)Mo7O24]16− anion formed via two intermediate heptamolybdates [Co(en)3]2[NaMo7O24]Cl·nH2O and (H3O)[Co(en)3]2[Mo7O24]Cl·9H2O

Ageing a mixture of sodium molybdate, malonic acid, and tris(ethylenediamine)cobalt(iii) chloride yielded POMs.

Towards a global greener process: from solvent-less synthesis of molybdenum(vi) ONO Schiff base complexes to catalyzed olefin epoxidation under organic-solvent-free conditions

Schiff base ligands and corresponding molybdenum(vi) complexes, prepared using classical and/or mechanochemical methods, were active as epoxidation pre(catalysts).

Recent advances in the field of selective epoxidation of vegetable oils and their derivatives: a review and perspective

The present critical review reports the recent progress of the last 15 years in the selective epoxidation of vegetable oils and their derivatives, in particular unsaturated fatty acids (UFAs) and fatty acid methyl esters (FAMEs).

Copper(ii) hydrazone complexes with different nuclearities and geometries: synthetic methods and ligand substituent effects

The effect of synthetic methods on the nuclearity and geometry of copper(ii) complexes with aroylhydrazones was investigated. Thermally induced structural transformations of dinuclear complexes under solvent-free conditions are also described.

Dioxotungsten(vi) complexes with isoniazid-related hydrazones as (pre)catalysts for olefin epoxidation: solvent and ligand substituent effects

The catalytic performances (activity and selectivity) of the mononuclear dioxotungsten(vi) complexes [WO₂(L^R)(D)] towards alkene epoxidation by tert-butyl hydroperoxide (TBHP) were investigated under different conditions.