Deuterium kinetic isotope effects in homogeneous decatungstate catalyzed photooxygenation of 1,1-diphenylethane and 9-methyl-9H-fluorene: evidence for a hydrogen abstraction mechanism

A density functional study of the photocatalytic degradation of polycaprolactone by the decatungstate anion in acetonitrile solution

A recent experimental study has reported that decatungstate [W10O32]4- can degrade various polyesters in the presence of light and molecular oxygen [Li et al., Nanoscale, 2023, 15, 15038]. We apply density functional theory to the photocatalyst-polycaprolactone model complex in acetonitrile solution and elucidate the degradation mechanisms and catalytic cycle. We consider hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms. The potential energy profiles show that the former proceeds exergonically in a single step but that the latter involves a subsequent proton transfer and finally yields HAT products as well. Oxygenated polymer species can regain the transferred hydrogen and regenerate the reduced photocatalyst. We propose a photocatalytic cycle that realizes both the photocatalyst regeneration and the polymer degradation.

Anaerobic Hydroxylation of C(sp3)-H Bonds Enabled by the Synergistic Nature of Photoexcited Nitroarenes

A photoexcited-nitroarene-mediated anaerobic C-H hydroxylation of aliphatic systems is reported. The success of this reaction is due to the bifunctional nature of the photoexcited nitroarene, which serves as the C-H bond activator and the oxygen atom source. Compared to previous methods, this approach is cost- and atom-economical due to the commercial availability of the nitroarene, the sole mediator of the reaction. Because of the anaerobic conditions of the transformation, a noteworthy expansion in substrate scope can be obtained compared to prior reports. Mechanistic studies support that the photoexcited nitroarenes engage in successive hydrogen atom transfer and radical recombination events with hydrocarbons, leading to N-arylhydroxylamine ether intermediates. Spontaneous fragmentation of these intermediates leads to the key oxygen atom transfer products.

Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C-H Bonds Elaboration

Direct photocatalyzed hydrogen atom transfer (d-HAT) can be considered a method of choice for the elaboration of aliphatic C–H bonds. In this manifold, a photocatalyst (PC_HAT) exploits the energy of a photon to trigger the homolytic cleavage of such bonds in organic compounds. Selective C–H bond elaboration may be achieved by a judicious choice of the hydrogen abstractor (key parameters are the electronic character and the molecular structure), as well as reaction additives. Different are the classes of PCs_HAT available, including aromatic ketones, xanthene dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin and a tris(amino)cyclopropenium radical dication. The processes (mainly C–C bond formation) are in most cases carried out under mild conditions with the help of visible light. The aim of this review is to offer a comprehensive survey of the synthetic applications of photocatalyzed d-HAT.

Hybridizing Engineering Strategy of Decatungstate. 2. Regulated Effect of Doping Transition Metal Ions on Photocatalytic Oxidation Performance of (nBu4N)4W10O32

This paper discloses a simple and productive hybridizing engineering (HE) strategy for the 3d transition-metal-ion (Mⁿ⁺ = Fe³⁺, Fe²⁺, Co²⁺, Ni²⁺)-doped (nBu₄N)₄W₁₀O₃₂ (Mⁿ⁺-TBADT) compounds as highly efficient visible-light catalysts. Ultraviolet visible (UV-vis), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectra, and cyclic voltammetry (CV) characterizations indicate that the synthetic quality, redox capacity, and visible light harvesting efficiency of TBADT, especially the separation efficiency of its photogenerated electron-hole pairs, are regulated by the metal ion dopants and gradually improved with a change of the dopant from Fe³⁺, Fe²⁺, and Co²⁺ to Ni²⁺, along with a continuous and significant enhancement of its photocatalytic efficiency in the visible-light-triggered selective oxidation of ethylbenzene with dioxygens in acetonitrile. The best 0.5 mol % Ni²⁺-doped TBADT can achieve a ca. 55% conversion under optimal reaction conditions and also exhibits much higher photocatalytic activity for the photo-oxidation of toluene, cyclohexane, and benzyl alcohol compared to pure TBADT. This HE strategy showcases great potential in improving the photocatalysis performance of TBADT.

Development of photocatalysts for selective and efficient organic transformations

One of the main goals of organic chemists is to find easy, environmentally friendly, and cost effective methods for the synthesis of industrially important compounds. Photocatalysts have brought revolution in this regard as they make use of unlimited source of energy (the solar light) to carry out the synthesis of organic compounds having otherwise complex synthetic procedures. However, selectivity of the products has been a major issue since the beginning of photocatalysis. The present article encompasses state of the art accomplishments in harvesting light energy for selective organic transformations using photocatalysts. Several approaches for the development of photocatalysts for selective organic conversions have been critically discussed with the objective of developing efficient, selective, environmental friendly and high yield photocatalytic methodologies.

Mixed-valence polyoxometalates: spin-coupling and electron distribution in the decawolframate anion reduced by two electrons

The decawolframate anion reduced by two electrons, W10O326-, is diamagnetic, and its two "extra" electrons delocalize mainly among its eight equatorial wolfram sites. In this work, we combine a phenomenological Hamiltonian with first-principles calculations to explain the origin of these properties. Through ab initio calculations and effective Hamiltonians on fragments, we determine the values of the magnetic exchange parameters, J, the transfer integrals, t, the Coulombic repulsions, V, and the orbital energies, epsilon. Then, by introducing these parameters in a model Hamiltonian simulating the whole molecule, one obtains that the singlet-triplet gap is 780 meV and that more than a 90% of the "extra" electron density resides on the eight equatorial wolfram ions. An analysis of the interplay between these parameters indicates that electron-transfer processes play a dominant role while magnetic exchange has only a minor influence.

The Neber route to substituted indoles

Two complementary procedures have been developed for the conversion of the oximes of alpha-aryl ketones to azirines. On heating, the azirines rearrange smoothly to the corresponding indoles. The overall transformation offers a versatile route to indoles, complementary to the Fischer indole synthesis.