The merger of transition metal and photocatalysis

Decarboxylative Cross-Acyl Coupling of Carboxylic Acids with Aldehydes Enabled by Nickel/Photoredox Catalysis

We present a general method for accessing unsymmetrical alkyl-aryl and alkyl-alkyl ketones via nickel/photoredox-catalyzed decarboxylative cross-acyl coupling reactions between carboxylic acids and aldehydes without the need for an additional preactivation procedure. Specifically, by using the peroxide as both an oxidant and hydrogen atom transfer (HAT) reagent, we achieved the unprecedented combination of oxidative single electron transfer (SET) of carboxylates and HAT of aldehydes, in which the generated alkyl and acyl radicals were chemoselectively coupled by nickel catalysis. This method features a broad substrate scope with good functional group compatibility and offers new access to structurally diverse ketones.

Photoinduced Ni-catalyzed carbohalogenation of monofluoro, gem-difluoro, and trifluoromethyl tethered alkenes

A photoexcited nickel-catalyzed carbohalogenation reaction of fluoroalkenes has been demonstrated to afford halofluoroalkyl oxindoles featuring a quaternary center. The broad substrate scope with retention of fluorine atoms, followed by efficient synthetic transformations of iodo-gem-difluoroalkyl oxindoles, highlights the advantages of this methodology. Additionally, control experiments and DFT calculations have been conducted to elucidate the significance of the triplet-excited state of the nickel catalyst.

Photochemistry of Ni(II) Tolyl Chlorides Supported by Bidentate Ligand Frameworks

Herein, we investigate the photoactivity of four NiII tolyl chloride complexes supported by either the new bidentate [2.2]pyridinophane (HN2) ligand or the traditional 4,4'-di-tert-butyl-2,2'-dipyridyl (tBubpy) ligand. Despite a change in the ligand framework, we observe similar quantum yields for the photodegradation of all four NiII complexes, while noting changes in their affinity for radical side reactivity and ability to stabilize the photogenerated mononuclear NiI species. Furthermore, changing from an ortho-tolyl to a para-tolyl group affects the geometry of the complexes and makes the Ni center more susceptible to side reactivity. By leveraging the newly developed HN2 ligand, a bidentate ligand that hinders axial interactions with the Ni center, we limit the radical side reactivity. Time-dependent density functional theory (TDDFT) and complete active space self-consistent field (CASSCF) calculations predict that all four complexes have accessible MLCTs that excite an electron from a Ni-aryl bonding orbital into a Ni-aryl antibonding orbital, initiating photolysis. By decreasing this energy gap and stabilizing the tetrahedral triplet excited state, we increase quantum yields of photoexcitation. Importantly, we characterize the photogenerated mononuclear NiI chloride species using X-band EPR spectroscopy and show that the HN2-supported NiI complexes do not undergo the deleterious dimerization and tetramerization observed for the (bpy)NiICl species. Overall, this study provides valuable insight into how the steric environment around the Ni center affects its photoactivity and demonstrates that such photoactivity is not unique to bipyridyl-supported Ni compounds.

Bridging chemistry and biology for light-driven new-to-nature enantioselective photoenzymatic catalysis

Merging enzymes with light-driven photocatalysis has given rise to the burgeoning field of photoenzymatic catalysis. This approach combines the high reactivity from photoexcitation with the exceptional selectivity of biocatalysis, providing exciting opportunities to tackle challenges in enantioselective radical reactions and to access new-to-nature enzyme reactivities. This tutorial review aims to provide a comprehensive introduction to this interdisciplinary topic, catering to the growing interest from communities in asymmetric catalysis, photocatalysis, radical chemistry, enzyme engineering, and synthetic biology. We summarize the fundamental principles of utilizing light to power enzymatic reactions and different strategies exploring enantioselective photoenzymatic systems, including natural cofactor-based photoenzymatic catalysis, photocatalyst/enzyme synergistic catalysis, synthetic cofactor-based artificial photoenzymes, and cofactor-free photoenzymatic catalysis. We also discuss the challenges and prospects of enantioselective photoenzymatic catalysis in advancing sustainable asymmetric synthesis.

A General Direct Aldehyde C-H Alkylation via TBADT-Nickel Synergistic Catalysis

Herein, we present a nickel/tetrabutylammonium decatungstate (TBADT)-catalyzed protocol for general C-H alkylation of aldehydes, enabling the efficient synthesis of aliphatic ketones through ligand-controlled cross-coupling. This mild and cost-effective methodology demonstrates broad substrate compatibility with various commercially available aldehydes and both activated and unactivated alkyl bromides, delivering target products in high yields. Notably, the practical utility of this catalytic system has been highlighted through a concise two-step synthesis of the commercially valuable musk odorant Aurelione from readily available starting materials.

Aryl Acid-Alcohol Cross-Coupling: C(sp3)-C(sp2) Bond Formation from Nontraditional Precursors

Alcohols and aryl carboxylic acids are among the most commercially abundant, synthetically versatile, and operationally convenient building blocks in organic chemistry. Despite their widespread availability, the direct formation of C(sp3)-C(sp2) bonds from these functional groups remains a challenge. Recently, our group developed robust protocols to harness alcohols as alkyl radical precursors, but the activation of aryl acids remains relatively unexplored. Herein, we describe the merger of N-heterocyclic carbene (NHC)-mediated deoxygenation and nickel-mediated decarbonylation of aryl acids toward C(sp3)-C(sp2) bond formation. The utility of this method is demonstrated through the synthesis of a diverse range of aryl-alkyl cross-coupled products and the late-stage functionalization of complex molecules, including drugs, natural products, and biomolecules.

PCET-mediated deconstructive cross-coupling of aliphatic alcohols

A practical deconstructive arylation of aliphatic alcohols has been developed using a synergistic photoredox proton-coupled electron transfer (PCET) and nickel dual catalytic system. The method efficiently generates alkyl radicals via concerted PCET-mediated β-scission, enabling the formation of C(sp3)-C(sp2) bonds between alcohols and aryl halides. Optimization studies revealed a broad functional group tolerance and high chemoselectivity, with good yields even for challenging tertiary alcohol substrates. Mechanistic insights from transient absorption spectroscopy confirmed the dominance of a PCET pathway for radical generation. This strategy expands the utility of alcohols as alkyl radical precursors in cross-coupling reactions, offering a versatile tool for constructing complex molecular architectures.

Ir/Ni Metallaphotoredox Catalysis for the C(sp3)─H Bond α-Arylation and Alkylation of N-Alkyl N-Heterocycles

In this work, we report a regioselective C(sp3)─H bond α-arylation and alkylation of N-alkyl heterocycles (carbazoles, indoles and indazoles) using a Ir/Ni metallaphotoredox catalysis. This approach enables the direct functionalization of unactivated C(sp3)─H bonds at the α-position of nitrogen heterocycles, offering an efficient alternative to traditional Sn2 methods and providing complementary regioselectivity to transition metal catalysis, which often results in C(sp2)─H bond arylation. The reaction employs [Ir(dF(CF3)ppy)2(dtbbpy)][PF6] as the photocatalyst and NiCl2(dtbbpy) as the nickel source, facilitating single-electron transfer (SET) to promote radical generation and organometallic elementary cross-coupling steps. The methodology allows the use of diverse aryl chlorides and alkenes demonstrating broad substrate scope and high functional group tolerance. Mechanistic investigations, including radical trapping and and Stern-Volmer experiments, support a photocatalytic radical pathway. This metallaphotoredox protocol presents a robust and atom-economical route to synthesizing valuable N-alkyl-N-aryl heterocycles.

Enantioselective Photocatalysis Using a Privileged Al-Salen Complex

ConspectusEnantioselective catalysts that exhibit broad generality are disruptive innovators in contemporary synthesis and are considered to be "privileged" on account of their expansive reactivity/selectivity profiles. Operating in the ground state, these species simultaneously regulate reactivity and orchestrate the translation of chiral information with exquisite efficiency: achieving parity in higher-energy (excited-state) scenarios remains a frontier in contemporary catalysis. Advancing this field will require new structure-activation guidelines to be delineated that reflect the energetic realities of achieving chiral induction in non-ground-state environments, thereby expediting the discovery of privileged photocatalysts. Earth-abundant aluminum-salen (Al-salen) complexes, which have a venerable history in ground-state enantioselective catalysis, show great promise in reconciling this disparity on account of their well-defined photophysical properties. In this Account, the potential of these catalysts in engaging various substrates via discrete activation modes to furnish optically enriched products with high levels of reliability is discussed. The deployment of commercial Al-salen complexes in the single electron transfer (SET)-enabled deracemization of cyclopropyl ketones is an exemplar. Irradiation of a commercial Al-salen complex augments the function of the catalyst to enable efficient deracemization (up to 98:2 e.r.), thereby eliminating the need for directing units. In stark contrast to conventional deracemization approaches that are predicated on C(sp3)-H deprotonation/reprotonation sequences, the transformation is characterized by a key C(sp3)-C(sp3) bond cleavage/cyclization process. Subsequent downstream manipulations of the enantioenriched products demonstrate the synthetic utility of the methodology. To illustrate mechanistic diversity using the same Al-salen complex, an enantioselective photocyclization under the auspices of energy transfer (EnT) catalysis is described. The photocyclization of acrylanilides under operationally simple conditions facilitates access to a diverse group of heterocyclic products (up to quantitative yield and 96:4 e.r.) using an Al-salen as the sole chiral operator. Collectively, these mechanistically distinct scenarios illustrate that light activation is a powerful strategy to augment the reactivity arsenal of a ubiquitous small molecule catalyst that is considered to be privileged in the ground state. The mechanistic foundations of reaction development are surveyed (combined experimental and computational approach), together with a perspective on the impact of this enabling technology in chiral functional molecule discovery. This Account serves to emphasize the synthetic utility of leveraging photochemical activation to mitigate intrinsic constraints of processes that might be considered to be thermochemically challenging.

Construction of planar chiral [2,2]paracyclophanes via photoinduced cobalt-catalyzed desymmetric addition

Planar chiral [2,2]paracyclophanes (PCPs) are widely used in materials science and asymmetric syntheses. Therefore, synthetic and material chemists have focused on the efficient and selective construction of planar chiral PCPs for decades. Herein, we present a photoinduced cobalt-catalyzed desymmetric addition of pseudo-para-diformyl and pseudo-gem-diformyl PCP, enabling the synthesis of planar chiral PCP alcohols with both planar and central chiralities. This method delivers 48 examples with yields up to 87%, diastereomeric ratios greater than 19:1, and an enantiomeric excess exceeding 99%. This protocol provides a original and efficient approach for the synthesis of planar chiral PCPs.

Selective Native N(in)-H Bond Activation in Peptides with Metallaphotocatalysis

The development of chemical methods enabling site-selective incorporation of noncanonical amino acids into peptide backbones with precise functional tailoring remains a critical challenge. Particularly compelling is the use of underexplored endogenous amino acid hotspots, such as the N (in) of tryptophan, as versatile anchors for diversification. Herein, we report a chemoselective N(sp2)-H bond activation strategy targeting native tryptophan residues within peptide frameworks, exemplified by GLP-1 (7-37), using nickel metallaphotocatalysis under postsynthetic solid-phase conditions. This selective N (in)-arylation reaction proceeds efficiently within 3 h of light irradiation in highly functionalized heterogeneous environments, employing minimal excesses of electrophile and base, alongside catalytic quantities of nickel, ligand, and photocatalyst. The method affords homogeneous peptide products with high chemoselectivity and operational simplicity. We envision that this strategy could contribute to advancing the design of the next-generation long-acting class II G protein-coupled receptor agonist therapeutics.

Unprecedented Tetravalent Uranium Photocatalysts for Efficient C(sp3)─C(sp3) Bond Cleavage and Formation

Photocatalysis is a pivotal area in synthetic chemistry. Despite extensive application potential in nuclear industry, uranium-based photocatalysts are historically limited to uranyl(VI/V) redox cycle. Here, we report the discovery of the first tetravalent uranium [U(IV)] photocatalyst that enables efficient C(sp3)─C(sp3) bond cleavage and formation under ideal visible light. The U(IV) alkoxy species mediates C─C bond cleavage in a wide range of cycloalkanols and promotes their coupling with electron-deficient alkenes, providing access to previously unattainable molecular architectures. These U(IV) alkoxy complexes, fully characterized by X-ray diffraction and magnetic studies, exhibit exceptional photocatalytic efficiency. Quantum chemical studies reveal that the energy barrier for C─C bond cleavage and formation is reduced to below 10 kcal · mol-1 under visible light excitation. This work introduces a new mechanistic paradigm for uranium-based photocatalysis and positions U(IV) alkoxy complexes as a versatile platform for bond activation and functionalization, expanding the potential applications of depleted uranium in synthetic chemistry.

Radical functionalization of allenes

Allenes exhibit comparatively lower stability compared to alkenes and alkynes, which confers heightened reactivity to these compounds. Recently, the radical functionalization of allenes has progressed considerably, leading to a renaissance in the synthesis of functional natural products, drugs and their analogues, but summary work addressing this aspect has not been reported. This review systematically summarizes recent advancements in the field of radical functionalization of allenes reported within the past five years. It encompasses the difunctionalization and trifunctionalization of the three carbon atoms in allenes, as well as the functionalization of C-Y bonds (Y = H, Br). The representative studies are categorized based on the type of radicals generated, including C-, N-, O-, S-, and Se-centered radicals. For individual more complex reactions, the mechanisms are explored and briefly discussed.

Visible-Light Promoted Iron-Catalyzed C-C Bond Cleavage of 1,2-Diols to Carbonyls

A simple visible-light-promoted iron-catalyzed aerobic oxidative C-C bond cleavage of vicinal diols was developed. This reaction avoids the use of noble metal catalysts or specialized oxidants, yielding aldehydes and ketones without overoxidation. The new method works under air and at room temperature and features mild conditions and simple operation. Notably, the protocol is applicable for complex natural products, achieving the bioinspired conversion of the natural abundant diterpene oridonin to the natural rare enmein-type diterpene.

Chemoselective Functionalization of Tertiary C-H Bonds of Allylic Ethers: Enantioconvergent Access to sec,tert-Vicinal Diols

While enantioenriched alcohols are highly significant in medicinal chemistry, total synthesis, and materials science, the stereoselective synthesis of tertiary alcohols with two adjacent stereocenters remains a formidable challenge. In this study, we present a dual catalysis approach utilizing photoredox and nickel catalysts to enable the unprecedented chemoselective functionalization of tertiary allylic C-H bonds in allyl ethers instead of cleaving the C-O bond. The resulting allyl-Ni intermediates can undergo coupling with various aldehydes, facilitating a novel enantioconvergent approach to access extensively functionalized homoallylic sec,tert-vicinal diols frameworks. This protocol exhibits nice tolerance towards functional groups, a broad scope of substrates, excellent diastereo- and enantioselectivity (up to 20 : 1 dr, 99 % ee). Mechanistic studies suggested that allyl-NiII acts as the nucleophilic species in the coupling reaction with carbonyls.

Photochemical Au(I)-Au(I) Bond Formation: A Battle between Intersystem Crossing and Internal Conversion

The transition metal complex Au(CN)2- has provided experimental evidence of photoinduced bond formation between Au(I) atoms in solution. However, the underlying photochemical driving force for this bond formation reaction remains unclear. In this study, we investigate the ultrafast Au-Au bonding process in the [Au(CN)2]22- dimer using nonadiabatic dynamics simulations that incorporate intersystem crossing and internal conversion pathways. Reaction pathways and transitions among photochemically accessible singlet and triplet excited states are analyzed. Computational results indicate that intersystem crossing is the primary driving force in the early stages of ultrafast photochemical dynamics, while internal conversion among triplet states plays a critical role after the system stabilizes in a higher-lying triplet state. This work provides a mechanistic perspective on modulating photochemical reactions by tuning the relative strengths of spin-orbit coupling and nonadiabatic coupling.

Construction of multi-functionalized carbon chains by Ni-catalyzed carbosulfonylation of butadiene

Multi-functionalized carbon chains are prevalent motifs existing in various natural products and drugs. How to construct multi-functionalized carbon chains represents a meaningful task. Herein, we developed a photo-induced stereoselective 1,4-carbosulfonylation of butadiene to construct multi-functionalized carbon chains under nickel catalysis. A wide variety of aryl iodides and sodium sulfinates could be facilely coupled with butadiene to generate difunctionalized olefin intermediates. Taking advantage of the internal CC bond, various functional groups have been efficiently incorporated to construct multi-functionalized aliphatic compounds. A scale-up reaction, an iterative reaction and late-stage modifications have been performed to further demonstrate the synthetic utility of this protocol.

A Self-Sustaining Supramolecular (Auto)Photocatalysis via the Synthesis of N-Vinylacetamides

Efforts to enhance photocatalysts prioritize improving their accessibility and practicality in photocatalytic applications. Supramolecular (auto)photocatalysis, which exploits transient self-assembled complexes, facilitates visible light-driven reactions, with autocatalytic systems promoting sustainable and atom-economical processes. In this study, the photocatalyst Mes-Acr-MeClO4, typically active under blue light, formed a dark red charge-transfer (CT) complex with N-bromoacetamide (NBA) in the presence of K2CO3 in DCE, enabling green-light photocatalysis. This self-assembled CT complex initiated an auto-photocatalytic process via two-photon absorption, generating an N-centered radical that drove anti-Markovnikov, syn-periplanar addition to phenylacetylene, achieving exclusive Z-selective formation of (Z)-N-(2-bromo-2-phenylvinyl)acetamide. Interestingly, the product itself functioned as a potent green-LED photocatalyst (λem = 518 nm, τ = 10 ns), driving its own synthesis with added terminal alkynes. With 100% atom economy, this work highlights a system chemistry approach, showcasing a highly efficient, self-sustaining catalytic process that advances green and sustainable synthetic strategies. This protocol emphasizes sustainability with an outstanding E-factor of 11.15, reflecting minimal waste production (11.15 kg per 1 kg of product) and demonstrating a strong commitment to green chemistry principles.

Relay Photocatalyzed Reductive Cleavage of Csp2-I To Establish Radical Cyclization/Coupling between O-Tethered Iodoarenes with Cyanoarenes

The activation of Csp2-I bonds in iodobenzenes and their derivatives is a highly valuable research topic. Most known methods predominantly rely on transition metal catalysis, which often necessitates the use of oxidants, additives, ligands, and harsh reaction conditions. Photocatalysis has emerged in the last decades as an excellent alternative to drive intriguing organic transformations via various chemical bond cleavages, while photocontrolled direct Csp2-I bond cleavage in O-tethered iodoarenes is rare due to its high reduction potential. To address this challenge, we have provided a relay reductive photocatalysis strategy to amplify the reduction function of low reduction potential photocatalysts using cyanoalkenes as photoredox mediators to achieve Csp2-I bond cleavage in O-tethered iodoarenes. Moreover, it is noteworthy that cyanoarenes are simultaneously involved as coupling reagents in the radical cyclization/coupling process between O-tethered iodoarenes and cyanoarenes to form benzo-fused oxygen-containing heterocyclic compounds with different scaffolds.

Nickel catalyzed C-N coupling of haloarenes with B2N4 reagents

Carbon-heteroatom bond (especially for C-N bond) formation through nickel catalysis has seen significant development. Well-established Ni(0)/Ni(II) redox cycle and photoinduced Ni(I)/Ni(III) redox cycle have been the dominant mechanisms. We report a thermally driven Ni-catalyzed method for C-N bond formation between haloarenes and B2N4 reagents, yielding N,N-dialkylaniline derivatives in good to excellent yields with broad functional group tolerance under base-free conditions. The catalytic protocol is useful for base-sensitive structures and late-stage modifications of complex molecules. Detailed mechanistic studies and density functional theory (DFT) calculations indicate that a Ni(I)/Ni(III) redox cycle is preferred in the C-N coupling process, and B2N4 reagent serves both as a single electron transfer donor and a N,N-dialkylation source.

Photochemically Driven Palladium- Phosphinoacridine Catalysis: A Carboxylative Approach for Arylcarbamate Synthesis

In this study, we demonstrate that phosphinoacridines are efficient bidentate ligands for palladium-catalyzed carboxylative C-N coupling reactions under blue LED irradiation. This method facilitates the direct synthesis of arylcarbamates using a range of non-activated aryl halides, such as iodides and bromides, with various amines under atmospheric pressure of CO2. The optimized conditions exhibit high tolerance to sensitive functional groups, resulting in very good to excellent yields of the desired products. This approach expands the scope of palladium-catalyzed carboxylation reactions and offers an environmentally friendly route to arylcarbamates.

A Blessing and a Curse: Remote Ligand Functionalization Modulates 3MLCT Relaxation in Group 6 Tricarbonyl Complexes

We recently reported a molecular design for carbonylpyridine molybdenum(0) complexes that unlocks long-lived luminescent and photoactive charge-transfer states. Here, we translate this strategy to chromium(0), and tungsten(0) and report three fully characterized tricarbonyl metal(0) complexes featuring a tripodal ligand with a remote n-butyl substituent in the backbone. All complexes show phosphorescence in the red to near-infrared spectral region from metal-to-ligand charge-transfer excited states. Surprisingly, the alkyl chain significantly affects excited state relaxation: lifetimes are shortened in solution but extended in the solid state by one order of magnitude compared to the molybdenum(0) complex with a methyl substituent. Temperature-dependent luminescence and NMR spectroscopy in combination with quantum chemical calculations reveal the reasons for these disparate effects. The n-butyl substituent distorts the metal coordination geometry. The resulting structural flexibility flattens the potential energy surfaces in solution, which lowers the barrier for the population of distorted metal-centered states and facilitates nonradiative relaxation. In the solid state, the rigidified alkyl chain separates neighboring molecules, which reduces self-quenching. Our study sheds light on the relationship between structure and excited state relaxation to inform the development of photoactive complexes based on earth-abundant metals.

Photocatalytic Strategy for Decyanative Transformations Enabled by Amine-Ligated Boryl Radical

Decyanation after α-functionalization by exploiting the inherent properties of cyano groups enables the strategic assembly of a carbon scaffold. Herein, we demonstrate an amine-ligated boryl radical-mediated cyano group transfer (CGT) strategy of malononitriles under photocatalytic conditions. This strategy allows for the cleavage of C(sp3)-CN and the formation of C(sp3)-D and C(sp3) to realize decyanative deuteration and cyclization via radical-polar crossover. Computational studies successfully demonstrated the reactivity of CGT promoters can be accurately assessed.

Catalysis in the Excited State: Bringing Innate Transition Metal Photochemistry into Play

Transition metal catalysis is an indispensable tool for organic synthesis that has been harnessed, modulated, and perfected for many decades by careful selection of metal centers and ligands, giving rise to synthetic methods with unparalleled efficiency and chemoselectivity. Recent developments have demonstrated how light irradiation can also be recruited as a powerful tool to dramatically alter the outcome of catalytic reactions, providing access to innovative pathways with remarkable synthetic potential. In this context, the adoption of photochemical conditions as a mainstream strategy to drive organic reactions has unveiled exciting opportunities to exploit the rich excited-state framework of transition metals for catalytic applications. This Perspective examines advances in the application of transition metal complexes as standalone photocatalysts, exploiting the innate reactivity of their excited states beyond their common use as photoredox catalysts. An account of relevant examples is dissected to provide a discussion on the electronic reorganization, the orbitals involved, and the associated reactivity of different types of excited states. This analysis aims to provide practitioners with fundamental principles and guiding strategies to understand, design, and apply light-activation strategies to homogeneous transition metal catalysis for organic synthesis.

Visible-Light-Induced Tandem Nickel-Catalyzed Heck Cyclization/Self-Promoted [2+2] Intermolecular Cycloaddition

Visible-light-induced transition metal (TM) catalysis has emerged as a new paradigm to discover unprecedented transformations. The reported nickel species as TM photocatalysts are mainly involved in the homolysis of Ni(II) complex or alkyl halide activation. Herein, we describe that the photoexcited nickel species could facilitate Heck cyclization by accelerating the anti-β-hydride elimination. Meanwhile, a tandem visible-light-induced substrate self-promoted intermolecular [2+2] photocycloaddition without the assistance of additional photocatalysts was discovered.

Unlocking Reactivity of Unprotected Oximes via Green-Light-Driven Dual Copper/Organophotoredox Catalysis

Oximes are widely used precursors in synthetic chemistry due to their broad availability and versatile chemical properties, in which N─O bond fragmentation represents a key reactivity mode. However, these transformations typically require the use of oxygen-protected oximes, and a general strategy to directly utilize free oximes remains challenging due to their vulnerability to side reaction pathways, rendering low tendency towards N─OH bond cleavage. Here a unified platform is reported to achieve direct cyclization of unprotected oximes with enals, as well as other coupling partners through dual copper/organophotoredox catalysis under green light irradiation. This protocol enables concurrent activation of both N─OH and α-C(sp3)─H bonds of free oximes to form multisubstituted pyridines with exceeding structural diversity and functional group tolerance. In this process, Rose Bengal serves as a hydrogen atom transfer agent to generate radical intermediates. In the meanwhile, copper catalyst activates of free oximes via single-electron reduction-induced N─O bond fragmentation and controls the selectivity for intermediate trapping. The synthetic utility of this approach is further demonstrated by its successful applications in late-stage modification of biologically active compounds and rapid assembly of solvatochromic fluorescent materials.

Enhanced Photocatalytic Proton-Coupled Electron Transfer by Ligand Design in a Zr Coordination Cage

Developing excited state proton and electron donors is a promising area of research that merges the benefits of proton-coupled electron transfer (PCET) with the use of light as renewable energy input. Based on the demonstrated PCET reactivity of Zr coordination cages for reductive photocatalysis, here we synthetize and characterize a new cage with enhanced photocatalytic activity. The new design targets the extended biphenyl-4,4-dicarboxylate linker with an amino group in the meta position relative to the carboxylate. Our results show that these aspects are key to increase the stability and reduction power of the excited state, features that are typically tuned by inductive effects. As a result, the new Zr-cage promotes significantly faster PCET reactions than the previous related platform, resulting in higher chemical and quantum yields. We further showcase how the solvent can impact the photophysical properties and the PCET reaction rates depending on the cage structure. These results highlight the factors that influence excited state PCET reactivity and complement similar efforts made in the realm of H2 evolution.

Recent Advances in Organic Photocatalyst-Promoted Carbohydrate Synthesis and Modification under Light Irradiation

Photoredox catalysis has been developed as a sustainable and eco-friendly catalytic strategy, which might provide innovative solutions to solve the current synthetic challenges and barriers in carbohydrate chemistry. During the last few decades, the study of organic photocatalyst-promoted carbohydrate synthesis and modification has received significant attention, which provides an excellent and inexpensive metal-free alternative to photoredox catalysis as well as introduces a new fastest-growing era to access complex carbohydrates simply. In this review, we aim to provide an overview of organic photocatalyst-promoted carbohydrate synthesis and modification under light irradiation, which is expected to provide new directions for further investigation.

Direct stereoselective C(sp3)-H alkylation of saturated heterocycles using olefins

Despite cross-coupling strategies that enable the functionalization of aromatic heterocycles, the enantioselective C(sp3)-H alkylation of readily available saturated hydrocarbons to construct C(sp3)-C(sp3) bonds remains a formidable challenge. Here we describe a nickel-catalysed enantioselective C(sp3)-H alkylation of saturated heterocycles using olefins, providing an efficient strategy for the stereoselective construction of C(sp3)-C(sp3) bonds. Using readily available and stable olefins and simple saturated nitrogen and oxygen heterocycles as prochiral nucleophiles, the coupling reactions proceed under mild conditions and exhibit broad scope and high functional group tolerance. Furthermore, the enantio- and diastereoselective C(sp3)-H alkylation of saturated hydrocarbons with alkenyl boronates has been achieved, enabling the synthesis of versatile alkyl boronates containing 1,2-adjacent C(sp3) stereocentres. Application of this approach to the late-stage modification of natural products and drugs, as well as to the enantioselective synthesis of a range of chiral building blocks and natural products, is demonstrated.

Non-noble Metal Single-Molecule Photocatalysts for the Overall Photosynthesis of Hydrogen Peroxide

Despite the great progress in molecule photocatalytic solar energy conversion, it is particularly challenging to realize a photocatalytic overall reaction in a non-noble metal complex, which represents a new paradigm for photosynthesis. In this study, a class of novel non-noble metal complexes with head-to-tail geometry were designed and readily synthesized via the coordination of triphenylamine-modified 2,2': 6',2″-terpyridine ligands with Zn2+. As expected, these complexes exhibited the desired through-space charge-transfer transition, generating both long-lived excited states (on the order of microseconds) and separate redox centers under visible-light irradiation. These complexes have particularly low exciton binding energies, which make them excellent heterogeneous single molecular photocatalysts for the overall photosynthetic production of H2O2. Remarkably, a high H2O2 evolution rate (8862 μmol g-1 h-1) was achieved in pure H2O under an air atmosphere via precise molecular tailoring, revealing the unparalleled advantages of molecular photocatalysts in improving the catalytic rate of H2O2 production. This is the first time that single-molecule photocatalysts have been used to efficiently complete the photosynthesis of H2O2. This study presents a new paradigm for photocatalytic energy conversion and provides unique insights into the design of molecular photocatalysts.

Recent advances in 4CzIPN-mediated functionalizations with acyl precursors: single and dual photocatalytic systems

4CzIPN (1,2,3,5-tetrakis(carbazole-9-yl)-4,6-dicyanobenzene) has emerged as a key metal-free photocatalyst for sustainable organic synthesis. Due to its unique design enabling high photoluminescence quantum yield, thermally activated delayed fluorescence (TADF) and long excited state lifetime, 4CzIPN facilitates diverse reactions, such as C-C and C-X bond formation reactions, under mild reaction conditions. This review highlights its application in decarboxylation, acylation and cyclisation reactions involving α-keto acids, carboxylic acids and aldehydes in a single catalytic system, as well as the combination of a dual catalytic system with transition metals to enhance selectivity and scope. 4CzIPN contributes to the advancement of sustainable chemistry by enabling green, efficient and scalable reactions and this review covers studies published between 2020 and 2024.

Constructing Donor-Acceptor Covalent Organic Frameworks for Highly Efficient H2O2 Photosynthesis Coupled with Oxidative Organic Transformations

The development of photocatalytic systems that enable the simultaneous production of H2O2 and value-added organic chemicals presents a dual advantage: generating valuable products while maximizing the utilization of solar energy. Despite the potential, there are relatively few reports on photocatalysts capable of such dual functions. In this study, we synthesized a series of donor-acceptor covalent organic frameworks (COFs), designated as JUC-675 to JUC-677, to explore their photocatalytic efficiency in the co-production of H2O2 and N-benzylbenzaldimine (BBAD). Among them, JUC-675 exhibited exceptional performance, achieving a H2O2 production rate of 22.8 mmol g-1 h-1 with an apparent quantum yield of 15.7 %, and its solar-to-chemical conversion efficiency was calculated to be 1.09 %, marking it as the most effective COF-based photocatalyst reported to date. Additionally, JUC-675 demonstrated a high selectivity (99.9 %) and yield (96 %) for BBAD in the oxidative coupling of benzylamine. The underlying reaction mechanism was thoroughly investigated through validation experiments and density functional theory (DFT) calculations. This work represents a significant advancement in the design of COF-based photocatalysts and the development of efficient dual-function photocatalytic platforms, offering new insights and methodologies for enhanced solar energy utilization and the synthesis of value-added products.

Red-Light-Active N,C,N-Pincer Bismuthinidene: Excited State Dynamics and Mechanism of Oxidative Addition into Aryl Iodides

Despite the progress made in the field of synthetic organic photocatalysis over the past decade, the use of higher wavelengths, especially those in the deep-red portion of the electromagnetic spectrum, remains comparatively rare. We have previously disclosed that a well-defined N,C,N-pincer bismuthinidene (1a) can undergo formal oxidative addition into a wide range of aryl electrophiles upon absorption of low-energy red light. In this study, we map out the photophysical dynamics of 1a and glean insights into the nature of the excited state responsible for the activation of aryl electrophiles. Transient absorption and emission techniques reveal that, upon irradiation with red light, the complex undergoes a direct S0 → S1 metal-to-ligand charge transfer (MLCT) transition, followed by rapid intersystem crossing (ISC) to a highly reducing emissive triplet state (-2.61 V vs Fc+/0 in MeCN). The low dissipative losses incurred during ISC (∼6% of the incident light energy) help rationalize the ability of the bismuthinidene to convert low-energy light into useful chemical energy. Spectroelectrochemical and computational data support a charge-separated excited-state structure with radical-anion character on the ligand and radical-cation character on bismuth. Kinetic studies and competition experiments afford insights into the mechanism of oxidative addition into aryl iodides; concerted and inner-sphere processes from the triplet excited state are ruled out, with the data strongly supporting a pathway that proceeds via outer-sphere dissociative electron transfer.

Synthesis, Characterization, and Catalytic Activity of Ni(0) (DQ)dtbbpy, an Air-Stable, Bifunctional Red-Light-Sensitive Precatalyst

Despite a well-established and growing body of work on nickel(0) precatalysts, the potential of nickel(0) complexes as bifunctional precatalysts remains underexplored. In this study, we synthesized, characterized, and evaluated the catalytic activity of (Ni(0)(DQ)dtbbpy), a bifunctional, red-light-sensitive, and air-stable nickel(0) complex. Owing to its unique photophysical properties, it effectively catalyzed the etherification and amination of aryl bromides under 620-630 nm light irradiation, functioning as both a photocatalyst and an active metal catalyst. Mechanistic studies and density functional theory (DFT) calculations further confirmed the exceptional absorption properties of Ni(0)(DQ)dtbbpy in the red-light region, as well as the electron transfer process triggered by red-light irradiation.

Radical Brook rearrangement: past, present, and future

The Brook rearrangement has emerged as one of the most pivotal transformations in organic chemistry, with broad applications spanning organic synthesis, drug design, and materials science. Since its discovery in the 1950s, the anion-mediated Brook rearrangement has been extensively studied, laying the groundwork for the development of numerous innovative reactions. In contrast, the radical Brook rearrangement has garnered comparatively less attention, primarily due to the challenges associated with the controlled generation of alkoxyl radicals under mild conditions. However, recent advancements in visible-light catalysis and transition-metal catalysis have positioned the radical Brook rearrangement as a promising alternative synthetic strategy in organic synthesis. Despite these developments, significant limitations and challenges remain, warranting further investigation. This review provides an overview of the radical Brook rearrangement, tracing its development from past to present, and offers perspectives on future directions in the field to inspire the creation of novel synthetic tools based on this transformation.

Bis-Cycloruthenated Complexes in Visible Light-Induced C-H Alkylation with Epoxides

Bis-cycloruthenated complexes (BCRCs) of the type [Ru(N^C)2L2] are proposed to be key reactive intermediates in the Ru(II)-catalyzed directed C-H functionalization of arenes. While the exceptional ground state reactivity of BCRCs toward a number of electrophiles has been explored, their reactivity upon photoexcitation is still unknown. Herein, we report studies on the photoexcitation of BCRCs that establish their capability to access chemically useful excited states. Remarkably, photoexcited BCRCs demonstrate greatly increased reactivity toward the electron transfer processes required for alkyl halide activation, overcoming current limitations of their ground-state reactivity. We have demonstrated this reactivity by expanding upon the current chemical space occupied by Ru-catalyzed C-H functionalization to include ortho-alkylation with epoxides.

Making Mo(0) a Competitive Alternative to Ir(III) in Phosphors and Photocatalysts

Iridium is used in commercial light-emitting devices and in photocatalysis but is among the rarest stable chemical elements. Therefore, replacing iridium(III) in photoactive molecular complexes with abundant metals is of great interest. First-row transition metals generally tend to yield poorer luminescence behavior, and it remains difficult to obtain excited states with redox properties that exceed those of noble-metal-based photocatalysts. Here, we overcome these challenges with a nonprecious second-row transition metal. Tailored coordination spheres for molybdenum(0) lead to photoluminescence quantum yields that rival those of iridium(III) complexes and photochemical reduction reactions not normally achievable with iridium(III) become possible. These developments open new perspectives for replacing noble metals in lighting applications with Earth-abundant metals and for advancing metal-based photocatalysis beyond current limits.

Structure Matters: Tailored Graphitization of Carbon Dots Enhances Photocatalytic Performance

The chemical structure and photoredox properties of carbon dots (CDs) are not yet fully understood. However, it has been reported that, by carefully choosing the starting materials and tuning their synthesis conditions, it is possible to obtain CDs with different chemical structures and therefore different photocatalytic performance. For this work, a family of different CDs was synthesized in Milli-Q water via a microwave-assisted protocol, using citric acid and urea as precursors. The syntheses were carried out at different times and temperatures to assess the impact of the synthetic parameters on the photocatalytic properties of the final materials. After extensive and accurate purification, the photocatalytic abilities of a selected subset of CDs were tested by performing a photocatalyzed atom transfer radical addition reaction. Among the tested CDs, the best performing ones were found to be those synthesized at the highest temperature, which were the most graphitic. A number of different characterization techniques were then used to evaluate the degree of graphitization of CDs and to elucidate the origin of their different photocatalytic performance.

Nickel/Photo-Cocatalyzed Cross-Coupling of Enol Silyl Ethers with α-Trifluoromethyl Bromides to Access β-CF3-Substituted Ketones

Herein, we introduce a nickel-photocatalyzed cross-coupling reaction between enol silyl ethers and CF3-substituted alkyl bromides. This method provides a streamlined approach for synthesizing a wide array of structurally diverse β-CF3-substituted ketones, achieving favorable yields under mild conditions. The practicality of this methodology is further underscored by its successful application in the late-stage functionalization of various pharmaceuticals and natural products.

Construction of Ultrathin BiVO4-Au-Cu2O Nanosheets with Multiple Charge Transfer Paths for Effective Visible-Light-Driven Photocatalytic Degradation of Tetracycline

In this study, unique BiVO4-Au-Cu2O nanosheets (NSs) are well designed and multiple charge transfer paths are consequently constructed. The X-ray photoelectron spectroscopy measurement during a light off-on-off cycle and redox capability tests of the photo-generated charge carriers confirmed the formation of Z-scheme heterojunction, which can facilitate the charge carrier separation and transfer and maintain the original strong redox potentials of the respective component in the heterojunction. The ultrathin 2D structure of the BiVO4 NSs provided sufficient surface area for the photocatalytic reaction. The local surface plasmon resonance (LSPR) effect of the electron mediator, Au NPs, enhanced the light absorption and promoted the excitation of hot electrons. The multiple charge transfer paths effectively promoted the separation and transfer of the charge carrier. The synergism of the abovementioned properties endowed the BiVO4-Au-Cu2O NSs with satisfactory photocatalytic activity in the degradation of tetracycline (Tc) with a removal rate of ≈80% within 30 min under visible light irradiation. The degradation products during the photocatalysis are confirmed by using ultra-high performance liquid chromatography-mass spectrometry and the plausible degradation pathways of Tc are consequently proposed. This work paves a strategy for developing highly efficient visible-light-driven photocatalysts with multiple charge transfer paths for removing organic contaminants in water.

An encodable amino acid for targeted photocatalysis

Photocatalysts are excellent scaffolds for the light-mediated control of bioactive molecules. Current photocatalytic structures are not compatible with genetic encoding and therefore cannot be directly incorporated into the sequences of native proteins. Herein, we developed new amino acids incorporating Si-rosamine photocatalytic units, and introduced them via aminoacylation of tRNAs into specific positions of different proteins to enable targeted photocatalytic reactions in defined populations of immune cells.

Catalytic Reductive Homocoupling of Benzyl Chlorides Enabled by Zirconocene and Photoredox Catalysis

The bibenzyl skeleton is prevalent in numerous natural products and other biologically active compounds. Radical homocoupling provides a straightforward approach for synthesizing bibenzyls in a single step with the reductive homocoupling of benzyl halides undergoing extensive development. Unlike benzyl bromides and other tailored precursors used in visible-light-mediated homocoupling, benzyl chlorides offer greater abundance and chemical stability. Nevertheless, achieving chemoselective cleavage of the C-Cl bond poses significant challenges, with only a limited number of studies reported to date. Herein, we demonstrate a catalytic reductive homocoupling of benzyl chlorides facilitated by zirconocene and photoredox catalysis. This cooperative catalytic system promotes C-Cl bond cleavage in benzyl chlorides under mild conditions and supports the homocoupling of a wide range of benzyl chlorides, including those derived from pharmaceutical agents. Our preliminary mechanistic investigations highlight the pivotal role of hydrosilane in the catalytic cycle.

Activation and C-C Coupling of Aryl Iodides via Bismuth Photocatalysis

Within the emerging field of bismuth redox catalysis, the catalytic formation of C-C bonds using aryl halides would be highly desirable; yet such a process remains a synthetic challenge. Herein, we present a chemoselective bismuth-photocatalyzed activation and subsequent coupling of (hetero)aryl iodides with pyrrole derivatives to access C(sp2)-C(sp2) linkages through C-H functionalization. This unique reactivity is the result of the bismuth complex featuring two redox state-dependent interactions with light, which 1) activates the Bi(I) complex for oxidative addition via MLCT, and 2) promotes the homolytic cleavage of aryl Bi(III) intermediates through a LLCT process.

Visible-Light-Induced Synthesis of Esters via a Self-Propagating Radical Reaction

We herein disclose a visible-light-induced synthesis of O-aryl esters through the cross-dehydrogenative coupling of aldehydes with phenols using BrCCl3, in which phenolate functions as both a substrate and a photosensitizer. This transition-metal- and photocatalyst-free visible-light-induced esterification is suitable for a wide range of substrates and gives moderate to excellent yields (up to 95%). Mechanistic studies provided evidence of a self-propagating radical reaction involving homolytic cleavage of the aldehydic C-H bond and the formation of acyl bromides. BrCCl3 serves as an oxidant and a hydrogen atom transfer (HAT) agent.

Photocatalytic regioselective C-H bond functionalizations in arenes

The direct functionalization of C-H bonds has revolutionized the field of synthetic organic chemistry by enabling efficient and atom-economical modification of arenes by avoiding prefunctionalization. However, the inherent challenges of inertness and regioselectivity in different C-H bonds, particularly for distal positions, necessitate innovative approaches. In this aspect, photoredox catalysis by utilizing both transition metal and organic photocatalysts has emerged as a powerful tool for addressing these challenges under mild reaction conditions. This review provides a comprehensive overview of recent progress in regioselective C-H functionalization in arenes via photocatalysis. Emphasizing the strategies for achieving ortho-, meta-, and para-selectivity, we explore the mechanistic insights, catalyst designs, and the novel methodologies that have expanded the scope of C-H bond functionalization. This discussion aims to offer valuable perspectives for advancing the field and developing more efficient and sustainable synthetic methodologies.

Efficient photocatalytic in-situ Fenton degradation of 2,4-dichlorophenol via anthraquinone-modified carbon nitride for 2e- oxygen reduction

Constructing a photocatalytic in-situ Fenton system (PISFs) is a promising strategy to address the need for continuous hydrogen peroxide (H2O2) addition and the low efficiency of H2O2 activation for hydroxyl radical generation in the traditional Fenton reaction. In this study, we constructed a photocatalytic in-situ Fenton system using anthraquinone-modified carbon nitride (AQ-C3N4) for efficient pollutant degradation. The resultant AQ-C3N4 not only enhanced the production of H2O2 but also increased the generation of hydroxyl radical (·OH). Experimental results demonstrated that, the apparent rate constant for the degradation of 2,4-Dichlorophenol (2,4-DCP) by AQ-C3N4-PISFs was 0.145 min-1, which is 2.74 times higher than that of C3N4 under visible light. Density functional theory (DFT) calculations indicate that AQ modification promotes electron-hole separation while increasing the adsorption energy of O2. Independent gradient model (IGM) analysis based on Hirshfeld Partition revealed that van der Waals interactions between AQ-C3N4 and 2,4-DCP promoted the degradation process. This work provides new ideas to overcome the problems of continuous addition of H2O2 and low utilization of ·OH that exist in conventional Fenton system.

Investigating Competing Inner- and Outer-Sphere Electron-Transfer Pathways in Copper Photoredox-Catalyzed Atom-Transfer Radical Additions: Closing the Cycle

This integrated computational and experimental study comprehensively examines the viability of competing inner-sphere electron transfer (ISET) and outer-sphere electron transfer (OSET) processes in [Cu(dap)2]+-mediated atom-transfer radical additions (ATRA) of olefins and CF3SO2Cl that can deliver both R-SO2Cl and R-Cl products. Five sterically- and electronically-varied representative alkenes were selected from which to explore and reconcile a range of experimentally observed outcomes. Findings are consistent with photoexcited [Cu(dap)2]+ initiating photoelectron transfer via ISET and the subsequent regeneration of the oxidized catalyst via ISET in the ground state to close the catalytic cycle and liberate products. R-SO2Cl/R-Cl product ratios appear to be primarily governed by the relative rates of direct catalyst regeneration {i.e., [Cu(dap)2SO2Cl]⋅++R⋅} and ligand exchange {i.e., [Cu(dap)2SO2Cl]⋅++Cl- }. Through this work, a more consistent and more complete conceptual framework has been developed to better understand this chemistry and how catalyst regeneration occurs. It is this important ground state process, which closes the catalytic cycle, and ultimately controls the enantioselectivity of ATRA reactions employing chiral copper photocatalysts.

Photoinduced Autopromoted Ni-Catalyzed Three-Component Arylsulfonation Inspired by Density Functional Theory/Time-Dependent Density Functional Theory-Simulated Photoactive Nickel Species

The structure of the novel photoactive nickel species was simulated by density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations. The application of the simplified photoactive nickel catalyst was demonstrated in a photoinduced nickel-catalyzed three-component arylsulfonation of 1,6-enynes. This reaction was autopromoted and proceeded in the absence of an additional photocatalyst. This methodology exhibited mild conditions, a broad substrate scope, and high efficiency.

A modular approach to catalytic stereoselective synthesis of chiral 1,2-diols and 1,3-diols

Optically pure 1,2-diols and 1,3-diols are the most privileged structural motifs, widely present in natural products, pharmaceuticals and chiral auxiliaries or ligands. However, their synthesis relies on the use of toxic or expensive metal catalysts or suffer from low regioselectivity. Catalytic asymmetric synthesis of optically pure 1,n-diols from bulk chemicals in a highly stereoselective and atom-economical manner remains a formidable challenge. Here, we disclose a versatile and modular method for the synthesis of enantioenriched 1,2-diols and 1,3-diols from the high-production-volume chemicals ethane-1,2-diol (MEG) and 1,3-propanediol (PDO), respectively. The key to success is to temporarily mask the diol group as an acetonide, which imparts selectivity to the key step of C(sp3)-H functionalization. Additionally, 1,n-diols containing two stereogenic centers are also prepared through diastereoselective C(sp3)-H functionalization. The late-stage functionalization of biological active compounds and the expedient synthesis of chiral ligands and pharmaceutically relevant molecules further highlight the synthetic potential of this protocol.

Stereoselective Vinylic C-H Addition via Metallaphotoredox Migration

Geometrically defined allylic alcohols with SE, SZ, RE and RZ stereoisomers serve as valuable intermediates in synthetic chemistry, attributed to the stereoselective transformations enabled by the alkenyl and hydroxyl functionalities. When an ideal scenario presents itself with four distinct stereoisomers as potential products, the simultaneous control vicinal stereochemistry in a single step would offer a direct pathway to any desired stereoisomer. Here, we unveil a metallaphotoredox migration strategy to access stereodefined allylic alcohols through vinylic C-H activation with aldehydes. This method harnesses a chiral nickel catalyst in concert with a photocatalyst to enable a 1,4-Ni migration by using readily accessible 2-vinyl iodoarenes as starting materials. The efficacy of this methodology is highlighted by the precise construction of all stereoisomers of allylic alcohols bearing analogous substituents and the efficient synthesis of key intermediates en route to Myristinin family. Experimental and computational studies have shed light on pivotal aspects including the synergy of metal catalysis and photocatalysis, the driving forces behind the migration, and the determination of absolute configuration in the C-H addition process.