Oxidation of Styrene to Benzaldehyde Catalyzed by Schiff Base Functionalized Triazolylidene Ni(II) Complexes

Four new Schiff base functionalized 1,2,3-triazolylidene nickel complexes, [Ni-(L1NHC)2](PF6)2; 3, [Ni-(L2NHC)2](PF6)2; 4, [Ni-(L3NHC)](PF6)2; 7 and [Ni-(L4NHC)](PF6)2; 8, (where L1NHC = (E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 1, L2NHC = (E)-3-methyl-4-(2-((phenethylimino)methyl)phenyl)-1-propyl-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2, L3NHC = 4,4′-(((1E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 5, and L4NHC = 4,4′-(((1E)-(butane-1,4-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 6), were synthesised and characterised by a variety of spectroscopic methods. Square planar geometry was proposed for all the nickel complexes. The catalytic potential of the complexes was explored in the oxidation of styrene to benzaldehyde, using hydrogen peroxide as a green oxidant in the presence of acetonitrile at 80 °C. All complexes showed good catalytic activity with high selectivity to benzaldehyde. Complex 3 gave a conversion of 88% and a selectivity of 70% to benzaldehyde in 6 h. However, complexes 4 and 7–8 gave lower conversions of 48–74% but with higher (up to 90%) selectivity to benzaldehyde. Results from kinetics studies determined the activation energy for the catalytic oxidation reaction as 65 ± 3 kJ/mol, first order in catalyst and fractional order in the oxidant. Results from UV-visible and CV studies of the catalytic activity of the Ni-triazolylidene complexes on styrene oxidation did not indicate any clear possibility of generation of a Ni(II) to Ni(III) catalytic cycle.

Synthesis and Crystal Structures of Mn(II) and Co(II) Complexes as Catalysts for Oxidation of Cyclohexanone

The global demand on adipic usage in the production of plasticizers and synthetic polyamide is increasing. In line with the search for an efficient and energy-conserving way to isolate adipic acid (AA) in good yields, this paper introduces the oxidization of cyclohexanone utilizing two new coordination compounds, [Mn(2,6-pydc)2](imi) (1) and [Co(H2pza)2(H2O)2(NO3)].NO3 (2), as catalysts. Compounds 1 and 2 were synthesized by room temperature and refluxing methods, and characterized by spectral analyses (IR and UV-Vis.), SEM, BET, TGA, elemental, and X-ray crystallography. The single crystal structure of compound 1 revealed that pyridinedicarboxylate (2,6-pydc) and imidazole (imi) moieties were coordinated to the Mn(II) atom through imine nitrogen and deprotonated oxygen atoms, to form an undistorted octahedral coordination geometry with the N2O4 donor set. The axial and equatorial planes containing O2, O4, O5, and O7 atoms were from two adjacent 2,6-pydc ligands which formed the unidendate donor ligand; imi, on the other hand, acted as a bidendate donor ligand. For compound 2, the Co(II) atom was being coordinated by two pyrazinamide (H2pza) moieties, which acted as an unidendate donor ligand; two water molecules occupying the axial position, and one nitrate molecule occupying the apical position, were within the coordination sphere; a nitrate molecule was disordered outside the coordination sphere. The distance, 4.658 Å, between the Co1 atom and the N8 atom of the uncoordinated nitrate molecule, was within the range reported elsewhere. Cyclohexanone peroxidation experiments revealed that compound 1 exhibited unique catalytic performance by giving a 72.8% yield in adipic acid, in comparison to the 71.3% yield obtained with compound 2. The yields in AA were maintained by way of recyclability evaluation. The reaction kinetics of compound 2 gave less activation energy, Ea 2938 J mol−1, while the thermodynamic parameters indicated that the chemical reactivity of cyclohexanone on the active surfaces of compounds 1 and 2 was via monolayer physisorption.

Hydrogen Peroxide as a Green Oxidant for the Selective Catalytic Oxidation of Benzylic and Heterocyclic Alcohols in Different Media: An Overview

Among a plethora of known and established oxidant in organic chemistry, hydrogen peroxide stands in a special position. It is commercially and inexpensively available, highly effective, selective, and more importantly it is compatible with current environmental concerns, dictated by principles of green chemistry. Several chemicals or their intermediates that are important in our daily life such as pharmaceuticals, flavors, fragrances, etc. are products of oxidation of alcohols. In this review, we introduce hydrogen peroxide as an effective, selective, green and privileged oxidant for the catalyzed oxidation of primary and secondary benzylic and heterocyclic alcohols to corresponding carbonyl compounds in different media such as aqueous media, under solvent-free conditions, various organic solvent, and dual-phase system.

Selective catalytic oxidation of benzene to phenol by a vanadium oxide nanorod (Vnr) catalyst in CH3CN using H2O2(aq) and pyrazine-2-carboxylic acid (PCA)

A vanadium oxide nanorod (V_nr) catalyst has been synthesized without using surfactants through crystallization, which is highly active for benzene to phenol oxidation.

Synthesis and crystal structures of a copper(ii) dinuclear complex and zinc(ii) coordination polymers as materials for efficient oxidative desulfurization of dibenzothiophene

Dinuclear copper(ii) complex [Cu₂(BAc)₄(QX)₂], and 2D zinc(ii) coordination polymer, [Zn(TDPA)₂(TMPy)₂]_n, presented high oxidation and adsorption thermodynamics for dibenzothiophene sulfoxide (DBTO).