In recent years, visible light-induced transition metal catalysis has emerged as a new paradigm in organic photocatalysis, which has led to the discovery of unprecedented transformations as well as the improvement of known reactions. In this subfield of photocatalysis, a transition metal complex serves a double duty by harvesting photon energy and then enabling bond forming/breaking events mostly via a single catalytic cycle, thus contrasting the established dual photocatalysis in which an exogenous photosensitizer is employed. In addition, this approach often synergistically combines catalyst-substrate interaction with photoinduced process, a feature that is uncommon in conventional photoredox chemistry. This Review describes the early development and recent advances of this emerging field.

Visible Light-Induced Transition Metal Catalysis.

The mainstream applications of visible-light photoredox catalysis predominately involve outer-sphere single-electron transfer (SET) or energy transfer (EnT) processes of precious metal RuII or IrIII complexes or of organic dyes with low photostability. Earth-abundant metal-based Mn Ln -type (M=metal, Ln =polydentate ligands) complexes are rapidly evolving as alternative photocatalysts as they offer not only economic and ecological advantages but also access to the complementary inner-sphere mechanistic modes, thereby transcending their inherent limitations of ultrashort excited-state lifetimes for use as effective photocatalysts. The generic process, termed visible-light-induced homolysis (VLIH), entails the formation of suitable light-absorbing ligated metal-substrate complexes (Mn Ln -Z; Z=substrate) that can undergo homolytic cleavage to generate Mn-1 Ln and Z. for further transformations.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202100270

Visible-Light-Induced Homolysis of Earth-Abundant Metal-Substrate Complexes: A Complementary Activation Strategy in Photoredox Catalysis.

Alkoxy radicals are highly reactive species that have long been recognized as versatile intermediates in organic synthesis. However, their development has long been impeded due to a lack of convenient methods for their generation. Thanks to advances in photoredox catalysis, enabling facile access to alkoxy radicals from bench-stable precursors and free alcohols under mild conditions, research interest in this field has been renewed. This review comprehensively summarizes the recent progress in alkoxy radical-mediated transformations under visible light irradiation. Elementary steps for alkoxy radical generation from either radical precursors or free alcohols are central to reaction development; thus, each section is categorized and discussed accordingly. Throughout this review, we have focused on the different mechanisms of alkoxy radical generation as well as their impact on synthetic utilizations. Notably, the catalytic generation of alkoxy radicals from abundant alcohols is still in the early stage, providing intriguing opportunities to exploit alkoxy radicals for diverse synthetic paradigms.

Alkoxy Radicals See the Light: New Paradigms of Photochemical Synthesis.

Decarboxylative C-H functionalization reactions are highly attractive methods for forging carbon-carbon bonds considering their inherent step- and atom-economical features and the pervasiveness of carboxylic acids and C-H bonds. An ideal approach to achieve these dehydrogenative transformations is through hydrogen evolution without using any chemical oxidants. However, effective couplings by decarboxylative carbon-carbon bond formation with proton reduction remain an unsolved challenge. Herein, we report an electrophotocatalytic approach that merges organic electrochemistry with photocatalysis to achieve the efficient direct decarboxylative C-H alkylation and carbamoylation of heteroaromatic compounds through hydrogen evolution. This electrophotocatalytic method, which combines the high efficiency and selectivity of photocatalysis in promoting decarboxylation with the superiority of electrochemistry in effecting proton reduction, enables the efficient coupling of a wide range of heteroaromatic bases with a variety of carboxylic acids and oxamic acids. Advantageously, this method is scalable to decagram amounts, and applicable to the late-stage functionalization of drug molecules.

Electrophotocatalytic Decarboxylative C−H Functionalization of Heteroarenes

Despite the rich photochemistry of 3d‐metal complexes, the utilization of excited‐state reactivity of these compounds in organic synthesis has been historically overlooked. The advent of photoredox catalysis has changed the perception of synthetic chemists towards photochemistry, and nowadays the potential of photoinduced, outer‐sphere single‐electron transfer events is widely recognized. More recently, an emerging new mode of photoactivation has taken the spotlight, based on an inner‐sphere mode of reactivity triggered by population of ligand‐to‐metal charge‐transfer (LMCT) excited states. Contrarily to photoredox, LMCT‐activation does not rely on matching redox potentials, offers unique reactivity profiles and is particularly well suited on Earth‐abundant metal complexes. Those appealing features are propelling the development of methods using this blueprint to generate highly reactive open‐shell species under mild conditions. The aim of this contribution is to provide a didactical tool for the comprehension of this emerging concept and facilitate the development of new synthetic methodologies to achieve sustainable chemical transformations.

Ligand‐to‐Metal Charge Transfer (LMCT) Photochemistry at 3d‐Metal Complexes: An Emerging Tool for Sustainable Organic Synthesis

Ligand-Accelerated Iron Photocatalysis Enabling Decarboxylative Alkylation of Heteroarenes

Catalytic degradation of organic dyes using Au-poly(styrene@N-isopropylmethacrylamide) hybrid microgels

In this paper, the preparation of potassium carbonate modified SiO2-Al2O3 composite aerogel, the carbonation characteristics of K2CO3 and the decarburization characteristics of regeneration cycle were studied. The influence of loading rate on CO2 adsorption was studied by using a fixed bed reactor, and the microstructure of the samples was analyzed by combining SEM and BET. The results show that during the alkali fusion sintering of Na2CO3, the Si-O-Si and Si-O-Al bonds break, the crystal structure is destroyed, and the covalent bond of mullite is transformed into the ionic bond of nepheline. Through orthogonal test, taking the specific surface area of aerogel as the measurement index, the optimal calcination conditions are determined as follows: 900 ℃, reaction for 60 min, Na2CO3 addition ratio of 0.5. The more K2CO3 is loaded, the less the corresponding active sites on the surface of the carrier. When the loading is 30%, the maximum CO2 adsorption capacity is 2.86 mmol·g–1. Excess K2CO3 will plug the pore structure, destroy the diffusion of CO2, and reduce the diffusion and utilization efficiency. The percentage of mesoporous pore volume decreased from 94.21% to 89.32%, indicating that the active component K2CO3 was mainly filled in the mesoporous. After 10 cycle regeneration tests, the CO2 adsorption capacity of the adsorbent decreased by 10.49%. The pore structure of the adsorbent was stable and the decarburization performance was excellent.

/pdf/preparation-and-decarburization-characteristics-of-sio2-8f0n8nvj.pdf

Preparation and decarburization characteristics of SiO2-Al2O3 composite aerogel modified by potassium carbonate

In this paper, the preparation of potassium carbonate modified SiO 2 -Al 2 O 3 composite aerogel, the carbonation characteristics of K 2 CO 3 and the decarburization characteristics of regeneration cycle were studied. The influence of loading rate on CO 2 adsorption was studied by using a fixed bed reactor, and the microstructure of the samples was analyzed by combining SEM and BET. The results show that during the alkali fusion sintering of Na 2 CO 3 , the Si-O-Si and Si-O-Al bonds break, the crystal structure is destroyed, and the covalent bond of mullite is transformed into the ionic bond of nepheline. Through orthogonal test, taking the specific surface area of aerogel as the measurement index, the optimal calcination conditions are determined as follows: 900 ℃ , reaction for 60 min, Na 2 CO 3 addition ratio of 0.5. The more K 2 CO 3 is loaded, the less the corresponding active sites on the surface of the carrier. When the loading is 30%, the maximum CO 2 adsorption capacity is 2.86 mmol·g –1 . Excess K 2 CO 3 will plug the pore structure, destroy the diffusion of CO 2 , and reduce the diffusion and utilization efficiency. The percentage of mesoporous pore volume decreased from 94.21% to 89.32%, indicating that the active component K 2 CO 3 was mainly filled in the mesoporous. After 10 cycle regeneration tests, the CO 2 adsorption capacity of the adsorbent decreased by 10.49%. The pore structure of the adsorbent was stable and the decarburization performance was excellent. 2 O 3 Composite Aerogel; CO 2 Adsorption; Carbonation Characteristics; Microscopic Characteristics

Original Research Preparation and decarburization characteristics of SiO 2 -Al 2 O 3 composite aerogel modified by potassium carbonate

Here, we describe a ruthenium-catalysed decarboxylative unsymmetric ortho-C–H azaarylation/meta-C–H alkylation via a traceless directing group relay strategy. The installation of a 2-pyridyl functionality via carboxyl directed ortho-C–H activation is critical to promote decarboxylation and enable meta-C–H bond alkylation to streamline the synthesis of 4-azaaryl-benzo-fused five-membered heterocycles. This protocol is characterized by high regio- and chemoselectivity, broad substrate scopes, and good functional group tolerance under redox-neutral conditions.

/pdf/ruthenium-catalysed-decarboxylative-unsymmetric-dual-ortho-iu5bzime.pdf

Ruthenium-catalysed decarboxylative unsymmetric dual ortho-/meta-C–H bond functionalization of arenecarboxylic acids

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