Cr-catalyzed allylic C(sp^(3))–H addition to aldehydes enabled by photoinduced ligand-to-metal charge transfer

Photoinduced ligand-to-metal charge transfer(LMCT) has emerged as an effective strategy for synthesizing organic molecules in a sustainable manner. However, the majority of existing reports on selective C(sp^(3))–H bond functionalization via photoinduced LMCT focus on the use of late transition metals or rare-earth metals for radical additions or cross-couplings. In contrast, the utilization of photoinduced LMCT with 3d early transition metals poses a significant challenge. Herein, we describe an unprecedented approach to allylic C(sp^(3))–H addition to aldehydes, employing chromium(Cr) complexes as catalysts through visible-light-induced LMCT. By investigating the reaction pathway through various mechanistic studies, including radical trapping, kinetic isotope effect(KIE) analysis, and transient absorption spectroscopy, valuable insights have been gained. The proposed mechanism suggests the intermediacy of bromine radicals through homolysis of the Cr–Br bond. Notably, this protocol expands our understanding of the photochemical properties of earth-abundant Cr complexes.

Tetracycline sensitizes TiO_(2) for visible light photocatalytic degradation via ligand-to-metal charge transfer

Treatment of antibiotics contaminated water remains a global environmental challenge.In this study,tetracycline(TC)was found to effectively sensitize pure TiO_(2) for visible light photocatalytic degradation via a ligand-to-metal charge transfer mechanism.The sensitization was attributed to the formation of TC-TiO_(2) complex and the overlap of the molecular orbitals of TC and the conduction band of TiO_(2).The intermediate degradation products of TC,however,did not sensitize TiO_(2),which was the reason for the low mineralization rate.Nevertheless,our results showed that the intermediate degradation products of TC had significantly reduced bactericidal effects and less induction of antibiotic-resistance genes(ARGs).This study showcases an effective treatment of antibiotics-containing wastewater using the most common photocatalyst TiO_(2) with reduced risk in the spread of ARGs.

β-C(sp^(3))−H chlorination of amide derivatives via photoinduced copper charge transfer catalysis

An atom economicβ-C(sp^(3))−H chlorination of amide derivatives has been developed.This mild protocol employs CuCl_(2) instead of palladium catalysts with atom-economic HCl as chlorine sources and enables the late-stage functionalization of medicine derivatives.Mechanism studies suggest a plausible visible light triggered ligand-to-metal charge transfer(LMCT)/1,4-hydrogen atom transfer(HAT)cascade.

Development of a bismuth-based metal-organic framework for photocatalytic hydrogen production

A novel 3 D bismuth-organic framework(called Bi-TBAPy) single crystal was synthesized by employing 1,3,6,8-tetrakis(p-benzoic acid)pyrene(H4TBAPy) as an organic linker. The study demonstrates that the Bi-TBAPy not only possesses good chemical stability and suitable band edge positions for promising photocatalytic H2 evolution, but it also exhibits a typical ligand-to-metal charge transfer for favorable charge separation. The photocatalytic H2 evolution rates on the as-obtained Bi-TBAPy with different cocatalysts modified were examined with triethanolamine as the sacrificial reagent. Based on this, the hydrogen evolution rate of 140 μmol h-1 g-1 was obtained on the optimized sample with a loading of 2 wt% Pt as a cocatalyst. To the best of our knowledge, this is the first bismuth-based metal-organic framework(MOF) that functions as an effective photocatalyst for photocatalytic water reduction. Our study not only adds a new member to the family of photocatalyst materials, but also reveals the importance of cocatalyst modification in improving photocatalytic activity of MOFs.

Recent advances in FeCl_(3)-photocatalyzed organic reactions via hydrogen-atom transfer

In recent years,FeCl_(3)-photocatalyzed direct C–H/Si–H bond functionalization reactions have attracted huge attention.In those transformations,chlorine radical(Cl·)could be generated from FeCl_(3)via a ligandto-metal charge transfer(LMCT)/homolysis process under light irradiation.The resulting chlorine radical subsequently acts as a hydrogen atom transfer(HAT)agent to abstract the hydrogen atom of aliphatic C–H,O–H,or Si–H bonds to give the corresponding C/Si/O-centered radicals for various organic transformations.In this review,we summarized the recent advances in the application of FeCl_(3)as a HAT photocatalyst for the C/Si–H functionalization to construct C–C,C–N,C–Si,C–S,C–B,and C-P bonds.

铁配合物的环境光化学及其参与的环境化学过程

铁是地壳中含量最为丰富的金属元素之一,而自然界中存在的绝大多数溶解性铁都是以有机络合形式存在的。环境中的铁配合物在光照下会发生直接光解和次级的(光)化学反应过程,生成还原性的Fe(Ⅱ)和有机自由基以及衍生的活性氧物种。铁配合物的环境光化学反应将深刻影响着氧自由基的生成与衰减、有机物降解和其他元素的环境化学循环过程,因此,成为近年来国际环境科学领域的研究热点。本文介绍了铁配合物光还原反应的类型和原理,分析了Fe(Ⅱ)(光)化学氧化的可能机理和影响因素,并对国内外关于铁参与的环境化学过程所开展的研究进行了评述。在此基础上,通过分析目前研究中所存在的问题,对今后的研究方向和趋势作了展望。

A chronological review of photochemical reactions of ferrioxalate at the molecular level:New insights into an old story

Owing to its outstanding photoactivity,ferrioxalate is originally used as an actinometer and subsequent work has discovered that photochemistry of ferrioxalate is also fundamentally or technically important in atmospheric chemistry and water treatment.While the overall products generated from photolysis of ferrioxalate are known to include Fe(Ⅱ),a series of oxidizing(e.g.,·OH,O_(2)^(·-)/HO_(2)^(·-))or reducing(C_(2)O_(4)^(·-)/CO_(2)^(·-))radicals and H_(2)O_(2),however,at the molecular level,the primary step of the photoreaction of ferrioxalate remains as an unsolved mystery due to the difficulty in examining such ultrafast processes.Benefiting from the development of time-resolved spectroscopy,this old question has been studied with increasing vigor recently,by means of such ever-more-sophisticated techniques(e.g.,flash photolysis,time-resolved X-ray absorption spectroscopy(XAS),femtosecond infrared(IR)absorption spectroscopy,ultrafast photoelectron spectroscopy(PES)).There are two contrary views on the primary reaction mechanism:(1)Intramolecular electron transfer(ET)precedes the cleavage of the metal-ligand bond;(2)The dissociation of C-C or Fe-O bond occurs before intramolecular ET.Thus,this review presents a comprehensive summary about the overall reaction mechanism and molecular level mechanism of ferrioxalates.In chronological order,we have elaborated two predominant but controversial views from the perspectives of different experimental approaches.Some challenges and research opportunities in this active field are also briefly discussed.

Visible light responsive TiO_(2) modification with nonmetal elements

Developing visible light responsive(VLR)TiO_(2) photocatalysts is essential and attractive for the consideration of solar energy utilization.A large amount of work have shown TiO_(2) modified with several nonmetal elements having VLR performance,although according to DFT calculation,Asahi denied the VLR properties of fluorine,carbon,etc.in doping TiO_(2).Therefore,the origins of VLR activity desire further delicate discussion.In this mini-review,several strategies for VLR TiO_(2) modification have been introduced,including N doping or B/N codoping,surface modification with sensitizing matter such as carbonaceous or other organic substances,surface alkoxyls modification via a ligand-to-metal charge transfer(LMCT)process,and enhanced dye sensitization by fluorine modification.Besides doping,there are much more approaches to fabricate VLR TiO_(2) modified with nonmetal elements.However,it is still in demand to explore new methods to obtain more stable and efficient VLR TiO_(2) for practical application.