Photo-initiated oxidation of C-H bonds by diimine complexes of vanadium(V)

Two-Phase Perchlorate Activation Enabled by a Dinuclear Fe-NHC (N-Heterocyclic Carbene) Complex

Perchlorate, initially regarded as a weakly coordinating counterion rather than a reactive oxidizing reagent due to its kinetic stability, has garnered attention for its potential in microbial systems. Under anaerobic conditions, microbes utilize perchlorate as a terminal oxidant for methane oxidation, involving two distinct stages: extraction and release of oxidizing ability. This two-phase activation process necessitates the collaborative action of multiple enzymes, a phenomenon not extensively explored in artificial systems. To address this issue, a dinuclear Fe-NHC (N-heterocyclic carbene) complex 1 was designed to enable the two-phase activation of perchlorate. Initially, complex 1 extracts the oxidative potential of perchlorate, leading to the formation of Fe(III)-O-Fe(III) complex 2 as the oxidation product. Subsequently, the extracted oxidative potential can be released by photolyzing a mixture of complex 2 and 9,10-dihydroanthracene. In contrast to the commonly observed selectivity, the homocoupling product 5 was identified as the major product in this C-H activation reaction. Further, a catalytic C-H activation reaction is initiated under anaerobic conditions to selectively form the C-C coupling product, achieving the complete two-phase activation of perchlorate using a single artificial catalyst. This work provides a new paradigm for constructing biomimetic anaerobic oxidation using kinetically inert high-valent oxygenated acid anions as oxidants.

Reactivity of metal dioxo complexes

Metal dioxo chemistry and its diverse reactivity are presented with an emphasis on the mechanisms of reactivity. Work from approximately the last decade is surveyed and organized by metal. In particular, the chemistry of cis-dioxo metal complexes is discussed at length. Reactions are grouped by generic type, including addition across a metal oxo bond, oxygen atom transfer, and radical atom transfer reactions. Attention is given to advances in deoxygenation chemistry, oxidation chemistry, and reductive transformations.

Metal-Catalyzed, Photo-Assisted Selective Transformation of Tertiary Alkylbenzenes and Polystyrenes into Carbonyl Compounds

Every year, thousands of tons of polystyrene are produced and discarded, filling landfills and polluting the marine environment. Although several degradation alternatives have been proposed, the need for an effective procedure for the chemical recycling of polystyrene still remains. Here, a vanadium-catalyzed reaction, assisted by visible light, promoted the direct, selective conversion of tertiary alkylbenzenes into acetophenone and other ketone derivatives. Likewise, standard polystyrene samples as well as polystyrenes from insulation and packaging waste could be chemically recycled into acetophenone in a scalable way regardless of their molecular weight, polydispersity, or form. Preliminary mechanistic investigations revealed the participation of singlet oxygen, superoxide, and hydroxyl radical species in this homogenously catalyzed process. Acetophenone could be used as an additive to accelerate the reaction and to increase the yields in some cases.

Spin-Orbit Natural Transition Orbitals and Spin-Forbidden Transitions

Natural transition orbitals (NTOs) are in widespread use for visualizing and analyzing electronic transitions. The present work introduces the analysis of formally spin-forbidden transitions with the help of complex-valued spin-orbit (SO) NTOs. The analysis specifically focuses on the components in such transitions that cause their intensity to be nonzero because of SO coupling. Transition properties such as transition dipole moments are partitioned into SO-NTO hole-particle pairs, such that contributions to the intensity from specific occupied and unoccupied orbitals are obtained. The method has been implemented within the restricted active space (RAS) self-consistent field wave function theory framework, with SO coupling treated by RAS state interaction. SO-NTOs have a broad range of potential applications, which is illustrated by the T₂-S₁ state mixing in pyrazine, spin-forbidden versus spin-allowed 4f-5d transitions in the Tb³⁺ ion, and the phosphorescence of tris(2-phenylpyridine) iridium [Ir(ppy)₃].