Activation of tert-Butyl Hydroperoxide by Zr(IV) Stabilized by Polyoxotungstate Scaffolds.

Zr-monosubstituted polyoxometalates (Zr-POMs) of the Keggin (BuN)[{PWOZr(μ-OH)}] (Zr-K), Lindqvist (BuN)[{WOZr(μ-OH)}] (Zr-L), and Wells-Dawson (BuN)H[{PWOZr(μ-OH)}] (Zr-WD) structures are capable of heterolytic activation of the environmentally benign oxidant tert-butyl hydroperoxide (TBHP) and catalyze epoxidation of alkenes and oxidation of alcohols to carbonyl compounds. Catalytic activity of corresponding Ti-POMs is much lower. Among Zr-POMs, Zr-K revealed higher epoxide yields.

Heterogeneous HO-based selective oxidations over zirconium tungstate α-ZrWO.

Catalytic properties of a crystalline zirconium tungstate, ZrWO, the material known mainly for its isotropic negative coefficient of thermal expansion, have been assessed for the liquid-phase selective oxidation of a range of organic substrates comprising CC, OH, S and other functional groups using aqueous hydrogen peroxide as the green oxidant. Samples of ZrWO were prepared by hydrothermal synthesis and characterised by N adsorption, PXRD, SEM, EDX, FTIR and Raman spectroscopic techniques. Studies by IR spectroscopy of adsorbed probe molecules (CO and CDCl) revealed the presence of Brønsted acidic and basic sites on the surface of ZrWO.

Catalytic Performance of Zr-Based Metal-Organic Frameworks Zr-abtc and MIP-200 in Selective Oxidations with H O.

The catalytic performance of Zr-abtc and MIP-200 metal-organic frameworks consisting of 8-connected Zr clusters and tetratopic linkers was investigated in H O -based selective oxidations and compared with that of 12-coordinated UiO-66 and UiO-67. Zr-abtc demonstrated advantages in both substrate conversion and product selectivity for epoxidation of electron-deficient C=C bonds in α,β-unsaturated ketones. The significant predominance of 1,2-epoxide in carvone epoxidation, coupled with high sulfone selectivity in thioether oxidation, points to a nucleophilic oxidation mechanism over Zr-abtc.

Heterogeneous epoxidation of menadione with hydrogen peroxide over the zeolite imidazolate framework ZIF-8.

The zeolite imidazolate framework ZIF-8 exhibits superior catalytic performance in the epoxidation of the electron-deficient C[double bond, length as m-dash]C bond in menadione using aqueous hydrogen peroxide as the oxidant. The catalysis has a truly heterogeneous nature and the framework structure remains intact. This is the first example of oxidation catalysis with ZIF-8.

Nucleophilic versus Electrophilic Activation of Hydrogen Peroxide over Zr-Based Metal-Organic Frameworks.

Zr-based metal-organic frameworks (Zr-MOF) UiO-66 and UiO-67 catalyze thioether oxidation in nonprotic solvents with unprecedentedly high selectivity toward corresponding sulfones (96-99% at ca. 50% sulfide conversion with only 1 equiv of HO). The reaction mechanism has been investigated using test substrates, kinetic, adsorption, isotopic (O) labeling, and spectroscopic tools.

Carbon Nanotubes Modified by Venturello Complex as Highly Efficient Catalysts for Alkene and Thioethers Oxidation With Hydrogen Peroxide.

In this work, we elaborated heterogeneous catalysts on the basis of the Venturello complex [PO{WO(O)}] (PW) and nitrogen-free or nitrogen-doped carbon nanotubes (CNTs or N-CNTs) for epoxidation of alkenes and sulfoxidation of thioethers with aqueous hydrogen peroxide. Catalysts PW/CNTs and PW/N-CNTs (1.8 at.

Alkene oxidation by Ti-containing polyoxometalates. Unambiguous characterization of the role of the protonation state.

Kinetic and DFT studies revealed that protonation of Ti-containing polyoxometalates (Ti-POM) lowers significantly the energy barrier for the heterolytic oxygen transfer from the Ti hydroperoxo intermediate to the alkene, increasing the activity and selectivity of alkene oxidation.

Mechanistic insights into oxidation of 2-methyl-1-naphthol with dioxygen: autoxidation or a spin-forbidden reaction?

Oxidation of 2-methyl-1-naphthol (MNL) with molecular oxygen proceeds efficiently under mild reaction conditions (3 atm O(2), 60-80 °C) in the absence of any catalyst or sensitizer and produces 2-methyl-1,4-naphthoquinone (MNQ, menadione, or vitamin K(3)) with selectivity up to 80% in nonpolar solvents. (1)H NMR and (1)H,(1)H-COSY studies revealed the formation of 2-methyl-4-hydroperoxynaphthalene-1(4H)-one (HP) during the reaction course. Several mechanistic hypotheses, including conventional radical autoxidation, electron transfer mechanisms, photooxygenation, and thermal intersystem crossing (ISC), have been evaluated using spectroscopic, mass-spectrometric, spin-trapping, (18)O(2) labeling, kinetic, and computational techniques.