Synthesis, crystal structure and DFT studies of a new dioxomolybdenum(VI) Schiff base complex as an olefin epoxidation catalyst

Schiff Base-Based Molybdenum Complexes as Green Catalyst in the Epoxidation Reaction: A Minireview

Epoxides are class of cyclic ether and have been extensively used in petrochemicals and pharmaceuticals industries as raw materials. Due to this reasons, development of the synthetic strategy of epoxides are getting enormous interest among the research chemists. In terms of "development of the synthetic strategy", the use of a catalyst, especially, Schiff base-based complex is of potential interest due to alternative easy routes and significant advances in metal-mediated pathways giving rise to diverse degree of substrate-reagent interactions. In addition, the synthetic strategy that follows the 12 principles of green chemistry, particularly (i) reduce the use of organic solvent, especially toxic solvents, and (ii) increasing the use of catalysts to obtain selective and quick processes in terms of atom economy, are of great attention now a days. The present review encompasses the Schiff base-based molybdenum complexes as green catalyst in the epoxidation reaction. Molybdenum complexes have grown interest owing to lower cost, environmental protection and commercialization as well as its abundance in different metalloenzymes. On the other hand, molybdenum complexes speed up the O-O bond break of tert-butylhydroperoxide (TBHP); as a result, it accelerates the oxygen transfer process from TBHP to the olefin. This review mainly focused on the catalytic activity of molybdenum-based Schiff base complexes for the epoxidation reaction in water/solvent free condition.

A 5-(2-Pyridyl)tetrazolate Complex of Molybdenum(VI), Its Structure, and Transformation to a Molybdenum Oxide-Based Hybrid Heterogeneous Catalyst for the Epoxidation of Olefins

There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2(pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO3(Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 °C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products.

Synthesis, characterization and anticandidal activity of dioxomolybdenum(VI) complexes of the type [MoO2{ON=C(CH3)Ar}2] and [MoO2{OC(R)CHC(R’)=NC6H5}2]

Interaction of [MoO₂(acac)₂] with internally functionalized oximes like HON=C(CH₃)Ar (Ar = C₄H₃S, C₄H₃O or C₅H₄N) and Schiff's Bases derived from β – diketones like HOC(R)CHC(R′)=NC₆H₅ (R = R’ = CH₃ or C₆H₅; R = CH₃ and R’ = C₆H₅) led to the formation of yellow dioxomolybdenum(VI) complexes of the type [MoO₂{ON=C(CH₃)Ar}₂] and [MoO₂{OC(R)CHC(R′)=NC₆H₅}₂]. Oximes were synthesized by green methodology. The newly synthesized complexes were characterized on basis of elemental analysis and various spectral findings.

Anticandidal activity of [MoO₂{ON=C(CH₃)C₆H₄N}₂] clearly reveals that the complex is biologically active against fungal diseases.

Surface-Renewable AgNPs/CNT/rGO Nanocomposites as Bifunctional Impedimetric Sensors

ABSTRACT

In this study, glassy carbon electrode modified by silver nanoparticles/carbon nanotube/reduced graphene oxide (AgNPs/CNT/rGO) composite has been utilized as a platform to immobilize cis-dioxomolybdenum (VI)-salicylaldehyde-histidine (MoO₂/Sal-His). The modified electrode shows two reversible redox couples for MoO₂/Sal-His. Electrocatalytic oxidation of cysteine (CySH) and electrocatalytic reduction of iodate on the surface of the modified electrode were investigated with cyclic voltammetry and electrochemical impedance spectroscopy methods. The presence of MoO₂/Sal-His on AgNPs/CNT/rGO shifted the catalytic current of iodate reduction to a more positive potential and the catalytic current of cysteine oxidation to a more negative potential. The change of interfacial charge transfer resistance (R _ct) recorded by the modified electrode was monitored for sensitive quantitative detection of CySH and iodate. Moreover, the sensor has a good stability, and it can be renewed easily and repeatedly through a mechanical or electrochemical process.

Syntheses and catalytic activities of new metallodendritic catalysts

Metallodendritic catalysts showed high selectivity in the epoxidation of olefins even after being used for at least five cycles.