The 100 most-cited articles in Chemistry - A European Journal, 2016

Halogen bonding is a noncovalent interaction similar to hydrogen bonding, which is based on electrophilic halogen substituents. Hydrogen-bonding-based organocatalysis is a well-established strategy which has found numerous applications in recent years. In light of this, halogen bonding has recently been introduced as a key interaction for the design of activators or organocatalysts that is complementary to hydrogen bonding. This Concept features a discussion on the history and electronic origin of halogen bonding, summarizes all relevant examples of its application in organocatalysis, and provides an overview on the use of cationic or polyfluorinated halogen-bond donors in halide abstraction reactions or in the activation of neutral organic substrates.

Abstract Metal–organic frameworks (MOFs) are excellent platforms for engineering luminescence properties as their building blocks, metal ions, linkers, and guest ions or molecules, are all potential sources of light emission. Temperature is one of the most important physical properties affecting the dynamics and viability of natural and engineered systems. Because the luminescence of certain lanthanide‐bearing MOFs changes considerably with temperature, in the last few years, these materials have been explored as optical thermometers, especially in temperature sensing based on the intensity ratios of two separate electronic transitions. This review discusses the main concepts and ideas assisting the design of such ratiometric thermometers, and identifies the main challenges presented to this nascent field: develop nanothermometers for bio‐applications and nanomedicine; understand the energy transfer mechanisms determining the thermal sensitivity; achieve effective primary thermometers; realize multifunctional nanothermometers; integrate Ln 3+ ‐based thermometers in commercial…

Atomic and cationic radii have been calculated for the first 96 elements, together with selected anionic radii. The metric adopted is the average distance from the nucleus where the electron density falls to 0.001 electrons per bohr(3) , following earlier work by Boyd. Our radii are derived using relativistic all-electron density functional theory calculations, close to the basis set limit. They offer a systematic quantitative measure of the sizes of non-interacting atoms, commonly invoked in the rationalization of chemical bonding, structure, and different properties. Remarkably, the atomic radii as defined in this way correlate well with van der Waals radii derived from crystal structures. A rationalization for trends and exceptions in those correlations is provided.

Lithium-sulfur batteries are among the most promising electrochemical energy storage devices of the near future. Especially the low price and abundant availability of sulfur as the cathode material and the high theoretical capacity in comparison to state-of-the art lithium-ion technologies are attractive features. Despite significant research achievements that have been made over the last years, fundamental (electro-) chemical questions still remain unanswered. This review addresses ten crucial questions associated with lithium-sulfur batteries and critically evaluates current research with respect to them. The sulfur-carbon composite cathode is a particular focus, but its complex interplay with other hardware components in the cell, such as the electrolyte and the anode, necessitates a critical discussion of other cell components. Modern in situ characterisation methods are ideally suited to illuminate the role of each component. This article does not pretend to summarise all recently published data, but instead is a critical overview over lithium-sulfur batteries based on recent…

Abstract An ab initio methodology for the first‐principle derivation of crystal‐field (CF) parameters for lanthanides is described. The methodology is applied to the analysis of CF parameters in [Tb(Pc) 2 ] − (Pc=phthalocyanine) and Dy 4 K 2 ([Dy 4 K 2 O(O t Bu) 12 ]) complexes, and compared with often used approximate and model descriptions. It is found that the application of geometry symmetrization, and the use of electrostatic point‐charge and phenomenological CF models, lead to unacceptably large deviations from predictions based on ab initio calculations for experimental geometry. It is shown how the predictions of standard CASSCF (Complete Active Space Self‐Consistent Field) calculations (with 4 f orbitals in the active space) can be systematically improved by including effects of dynamical electronic correlation (CASPT2 step) and by admixing electronic configurations of the 5 d shell. This is exemplified for the well‐studied Er‐trensal complex (H 3 trensal=2,2′,2“‐tris(salicylideneimido)trimethylamine). The electrostatic contributions to CF parameters in this complex,…

C-C bond forming reactions incarnate the core of organic synthesis because of their fundamental applications to molecular diversity and complexity. In recent years, use of carboxylic acid as one of the coupling partners in place of conventional organometallic reagents has seen an upsurge due to its potency to generate similar organometallic intermediates after decarboxylation. This Review provides an overview on the most recent progress in the field of C-C bond formation involving decarboxylation as a key step. Different important developments, which are not included in earlier Reviews in this area, have been summarized with representative examples and discussions on their reaction mechanisms.

Enzyme mimics or artificial enzymes are a class of catalysts that have been actively pursued for decades and have heralded much interest as potentially viable alternatives to natural enzymes. Aside from having catalytic activities similar to their natural counterparts, enzyme mimics have the desired advantages of tunable structures and catalytic efficiencies, excellent tolerance to experimental conditions, lower cost, and purely synthetic routes to their preparation. Although still in the midst of development, impressive advances have already been made. Enzyme mimics have shown immense potential in the catalysis of a wide range of chemical and biological reactions, the development of chemical and biological sensing and anti-biofouling systems, and the production of pharmaceuticals and clean fuels. This Review concerns the development of various types of enzyme mimics, namely polymeric and dendrimeric, supramolecular, nanoparticulate and proteinic enzyme mimics, with an emphasis on their synthesis, catalytic properties and technical applications. It provides an introduction to enzyme…

Abstract Non‐thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma‐treated aqueous solutions was investigated by using spin‐trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and 1H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ⋅OOH, ⋅OH and ⋅H are proposed to originate from the region…

The concept of using amide bond distortion to modulate amidic resonance has been known for more than 75 years. Two classic twisted amides (bridged lactams) ingeniously designed and synthesized by Kirby and Stoltz to feature fully perpendicular amide bonds, and as a consequence emanate amino-ketone-like reactivity, are now routinely recognized in all organic chemistry textbooks. However, only recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N-C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, we discuss recent progress in this area and present a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N-C bond activation.

Abstract Layered structural Co‐MOF nanosheets were synthesized and then used as an electrode material for supercapacitors for the first time. This material exhibited a high specific capacitance, a good rate capability, and an excellent cycling stability. A maximum capacitance of 2564 F g−1 can be achieved at a current density of 1 Ag−1. Moreover, the capacitance retention can be kept at 95.8 % respectively of its initial value after 3000 cycles. To the best of our knowledge, both the specific capacitance and the capacitance retention were the highest values reported for MOF materials as supercapacitor electrodes until now. Such a high supercapacitive performance might be attributed to the intrinsic characteristics of this kind of Co‐MOF material, including its layered structure, conductive network frame, and thin nanosheet.

Highly flexible, TpPa-1@PBI-BuI and TpBD@PBI-BuI hybrid membranes based on chemically stable covalent organic frameworks (COFs) could be obtained with the polymer. The loading obtained was substantially higher (50 %) than generally observed with MOFs. These hybrid membranes show an exciting enhancement in permeability (about sevenfold) with appreciable separation factors for CO2/N2 and CO2/CH4. Further, we found that with COF pore modulation, the gas permeability can be systematically enhanced.

The selective transformation of C-H bonds is one of the most desirable approaches to creating complexity from simple building blocks. Several directing groups are efficient in controlling the regioselectivity of catalytic C-H bond functionalizations. Among them, carboxylic acids are particularly advantageous, since they are widely available in great structural diversity and at low cost. The carboxylate directing groups can be tracelessly cleaved or may serve as the anchor point for further functionalization through decarboxylative couplings. This Minireview summarizes the substantial progress made in the last few years in the development of reactions in which carboxylate groups direct C-H bond functionalizations with formation of C-C, C-O, C-N, or C-halogen bonds at specific positions. It is divided into sections on C-C, C-O, C-N, and C-halogen bond formation, each of which is subdivided by reactions and product classes. Particular emphasis is placed on methods that enable multiple derivatizations by combining carboxylate-directed C-H functionalization with decarboxylative couplings.

Abstract A novel luminescent microporous lanthanide metal–organic framework (Ln‐MOF) based on a urea‐containing ligand has been successfully assembled. Structural analysis revealed that the framework features two types of 1D channels, with urea N−H bonds projecting into the pores. Luminescence studies have revealed that the Ln‐MOF exhibits high sensitivity, good selectivity, and a fast luminescence quenching response towards Fe3+, CrVI anions, and picric acid. In particular, in the detection of Cr2O72− and picric acid, the Ln‐MOF can be simply and quickly regenerated, thus exhibiting excellent recyclability. To the best of our knowledge, this is the first example of a multi‐responsive luminescent Ln‐MOF sensor for Fe3+, CrVI anions, and picric acid based on a urea derivative. This Ln‐MOF may potentially be used as a multi‐responsive regenerable luminescent sensor for the quantitative detection of toxic and harmful substances.

Nile red and Nile blue are highly fluorescent and photostable organic dyes from the benzo[a]phenoxazine family. They have been used as histological stains for imaging lysosomes and lipids in vitro. The dyes' high quantum yields and solvent-dependent optical properties make them ideal scaffolds for the development of pH probes and local polarity indicators. Reviews of the literature in this area are scarce with only one review ever published in 2006. It has been 10 years since and the field has evolved. This review aims to expand upon topics covered by the previous reviewers and to report on recent advances in the literature. As authors, we hope to convey a sense of scope and to spark renewed interest in this useful niche of dye chemistry.

Chiral molecules with multiple stereocenters are widely distributed in nature and drugs. Asymmeric catalysis has allowed the formation of a chiral molecule's enantiomers with equal ease by applying the enantiomeric pair of a chiral catalyst. However, the diastereodivergent synthesis is a great challenge because the formation of one of the diastereomers is inherently preferred in most reactions. Under the efforts of chemists, elegant strategies have been developed to full control of absolute and relative stereochemical configurations. In this Minireview, we highlight the significant advances achieved in this field, and present the diastereo-control mechanism in the appropriate place on the expectation that new diastereodivergent strategies can be inspired and more types of enantioselective diastereodivergent reactions can be realized.

Taking advantage of the structural diversity of different biomass resources, recent efforts were directed towards the synthesis of renewable monomers and polymers, either for the substitution of petroleum-based resources or for the design of novel polymers. Not only the use of biomass, but also the development of sustainable chemical approaches is a crucial aspect for the production of sustainable materials. This review discusses the recent examples of chemical modifications and polymerizations of abundant biomass resources with a clear focus on the sustainability of the described processes. Topics such as synthetic methodology, catalysis, and development of new solvent systems or greener alternative reagents are addressed. The chemistry of vegetable oil derivatives, terpenes, lignin, carbohydrates, and sugar-based platform chemicals was selected to highlight the trends in the active field of a sustainable use of renewable resources.

Abstract Carbon electrocatalysts consisting of metal complexes such as MNx or MSx are promising alternatives to high‐cost Pt catalysts for the hydrogen evolution reaction (HER). However, the exact HER active sites remain elusive. Here, molecular metal dithiolene‐diamine (MS2N2, M=Co and Ni), metal bis(dithiolene) (MS4), and metal bis(diamine) (MN4) complexes were selectively incorporated into carbon‐rich 2D metal–organic frameworks (2D MOFs) as model carbon electrocatalysts. The 2D MOF single layers, powders, and composites with graphene were thus prepared and showed definite active sites for H2 generation. The electrocatalytic HER activity of the 2D MOF‐based catalysts with different metal complexes follow the order of MS2N2>MN4>MS4. Moreover, the protonation preferentially occurred on the metal atoms, and the concomitant heterolytic elimination of H2 was favored on the M–N units in the MS2N2 active centers. The results provide an in‐depth understanding of the catalytic active sites, thus making way for the future development of metal complexes in carbon‐rich electrode materials…

Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers.

Pyrene-based π-conjugated materials are considered to be an ideal organic electro-luminescence material for application in semiconductor devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaics (OPVs), and so forth. However, the great drawback of employing pyrene as an organic luminescence material is the formation of excimer emission, which quenches the efficiency at high concentration or in the solid-state. Thus, in order to obtain highly efficient optical devices, scientists have devoted much effort to tuning the structure of pyrene derivatives in order to realize exploitable properties by employing two strategies, 1) introducing a variety of moieties at the pyrene core, and 2) exploring effective and convenient synthetic strategies to functionalize the pyrene core. Over the past decades, our group has mainly focused on synthetic methodologies for functionalization of the pyrene core; we have found that formylation/acetylation or bromination of pyrene can selectly lead to functionalization at K-region by Lewis acid…

This Minireview describes recent advances of organophosphorus compounds as opto-electronic materials in the field of organic electronics. The progress of (hetero-) phospholes, unsaturated phosphanes, and trivalent and pentavalent phosphanes since 2010 is covered. The described applications of organophosphorus materials range from single molecule sensors, field effect transistors, organic light emitting diodes, to polymeric materials for organic photovoltaic applications.

Homogeneous catalytic hydrogenation of esters to alcohols is an industrially important, environmentally benign reaction. While precious metal-based catalysts for this reaction are now well known, only very few catalysts based on first-row metal complexes were reported. Here we present the hydrogenation of esters catalyzed by a complex of earth-abundant manganese. The reaction proceeds under mild conditions and insight into the mechanism is provided based on an NMR study and the synthesis of novel Mn complexes postulated as intermediates.

Herein, we describe an efficient coupling of alcohols and amines catalyzed by well-defined isoelectronic hydride Mn(I) and Fe(II) complexes, which are stabilized by a PNP ligand based on the 2,6-diaminopyridine scaffold. This reaction is an environmentally benign process implementing inexpensive, earth-abundant non-precious metal catalysts, and is based on the acceptorless alcohol dehydrogenation concept. A range of alcohols and amines including both aromatic and aliphatic substrates were efficiently converted in good to excellent isolated yields. Although in the case of Mn selectively imines were obtained, with Fe-exclusively monoalkylated amines were formed. These reactions proceed under base-free conditions and required the addition of molecular sieves.

The replacement of C=C units by their isoelectronic and isosteric B=N units (BN/CC isosterism) in π-conjugated organic compounds, as a strategy to produce novel organic-inorganic hybrid materials, has recently been successfully transferred to π-conjugated polymers. This Concept provides an overview of the recent advances in this quickly evolving field, with a focus on synthesis, photophysical and electrochemical properties of the new polymers and related oligomers, as well as possible future applications in organic electronics and optoelectronics.

In the past decade, there have been many extraordinary advances in the development of gold-catalyzed enantioselective annulations, such as cycloadditions, cyclizations, cycloisomerizations, and tandem annulations, which are of particular interest owing to their potential for rapid construction of optically active hetero- and carbocyclic molecules. This Review summarizes the methods to construct chiral cyclic compounds by gold-catalyzed enantioselective annulations reported since 2005. The Review is organized according to the general annulation types catalyzed by chiral gold complexes or chiral gold salts, which have four main types (cycloadditions, cyclizations of C-C multiple bonds with tethered nucleophiles, cycloisomerization or cyclization of enynes, and tandem annulations), as well as some other strategies. The general reaction mechanisms of each subcategory, key intermediates for some unusual transformations, and the application of several novel ligands and chiral gold salts are also discussed.

The calculations of NMR properties of molecules using quantum chemical methods have deeply impacted several branches of organic chemistry. They are particularly important in structural or stereochemical assignments of organic compounds, with implications in total synthesis, stereoselective reactions, and natural products chemistry. In studying the evolution of the strategies developed to support (or reject) a structural proposal, it becomes clear that the most effective and accurate ones involve sophisticated procedures to correlate experimental and computational data. Owing to their relatively high mathematical complexity, such calculations (CP3, DP4, ANN-PRA) are often carried out using additional computational resources provided by the authors (such as applets or Excel files). This Minireview will cover the state-of-the-art of these toolboxes in the assignment of organic molecules, including mathematical definitions, updates, and discussion of relevant examples.

In recent years, α-imino rhodium carbene complexes derived by ring-opening of N-sulfonyl-1,2,3-triazoles have attracted much attention from organic chemists. Many transformations of these species have been reported that involve, in most cases, nucleophilic attack at the carbene center of the α-imino rhodium carbene, facilitating the synthesis of a wide range of novel and useful compounds, particularly heterocycles. This Minireview mainly focuses on advances in the transformation of N-sulfonyl-1,2,3-triazoles during the past two years.

Indanes and indenes are among the most important carbocycles. Many indane and indene derivatives have shown important pharmacological activities, and the indane and indene nuclei are structural motifs present in several natural products of biological relevance. In spite of their importance, only a few reviews on their preparation methods have appeared so far in the literature, the most recent ones being published about ten years ago. The present Review is aimed at filling this gap, presenting some of the most important and innovative approaches to indanes and indenes that have been published in the course of the last ten years (coverage: from 2005 to May, 2015).

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h(-1) at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides.

Podophyllotoxin and its related aryltetralin cyclolignans belong to a family of important products that exhibit various biological properties (e.g., cytotoxic, insecticidal, antifungal, antiviral, anti-inflammatory, neurotoxic, immunosuppressive, antirheumatic, antioxidative, antispasmogenic, and hypolipidemic activities). This Review provides a survey of podophyllotoxin and its analogues isolated from plants. In particular, recent developments in the elegant total chemical synthesis, structural modifications, biosynthesis, and biotransformation of podophyllotoxin and its analogues are summarized. Moreover, a deoxypodophyllotoxin-based chemosensor for selective detection of mercury ion is described. In addition to the most active podophyllotoxin derivatives in each series against human cancer cell lines and insect pests listed in the tables, the structure-activity relationships of podophyllotoxin derivatives as cytotoxic and insecticidal agents are also outlined. Future prospects and further developments in this area are covered at the end of the Review. We believe that this Review…

An emerging area of homogeneous catalysis is the use of catalysts featuring two closely associated metal sites. This approach complements the traditional focus on single-site catalysts and makes available new parameters with which to optimize catalytic behavior. Single-site catalysts are optimized through changing 1) the identity of the metal, and 2) the steric and electronic properties of the ligands. Bimetallic catalysts introduce new optimization parameters such as 3) catalyst nuclearity (mononuclear vs. binuclear), and 4) bimetallic pairing (relative compatibility of two metal sites). In order to harness these new optimization parameters in developing systems, it is necessary to first understand the origin of bimetallic selectivity effects that already have been documented. This Concept article highlights bimetallic effects on the chemo-, regio-, and stereoselectivity of catalytic transformations, using selected case studies from the recent literature as illustrative examples.

The ability to reason beyond established knowledge allows organic chemists to solve synthetic problems and invent novel transformations. Herein, we propose a model that mimics chemical reasoning, and formalises reaction prediction as finding missing links in a knowledge graph. We have constructed a knowledge graph containing 14.4 million molecules and 8.2 million binary reactions, which represents the bulk of all chemical reactions ever published in the scientific literature. Our model outperforms a rule-based expert system in the reaction prediction task for 180 000 randomly selected binary reactions. The data-driven model generalises even beyond known reaction types, and is thus capable of effectively (re-)discovering novel transformations (even including transition metal-catalysed reactions). Our model enables computers to infer hypotheses about reactivity and reactions by only considering the intrinsic local structure of the graph and because each single reaction prediction is typically achieved in a sub-second time frame, the model can be used as a high-throughput generator of…

This Minireview concerns recent advances in the design, synthesis, and application of low molecular-weight peptidic hydrogelators. The sequence-specific combinations of amino acid side chain functionalities combined with hydrogen bonding of amide backbones and hydrophobic (aromatic) capping groups give these peptidic molecules the intrinsic tendency to self-assemble. The most prevalent designs include N-capped amino acid residues, bolamphiphilic peptides, and amphipathic peptides. Factors such as hydrophobic effects, the Hofmeister effect, and tunable ionization influence their aggregation properties. The self-assembly of simple bio-inspired building blocks into higher organized structures allows comparisons to be drawn with proteins and their complex functionalities, providing preliminary insights into complex biological functions and also enabling their application in a wide range of fields including catalysis, biomedical applications, and mimicry of natural dissipative systems. The Minireview is concluded by a short summary and outlook, highlighting the advances and steps…

Mixed-matrix membranes (MMMs) comprising Matrimid and a microporous azine-linked covalent organic frameworks (ACOF-1) were prepared and tested in the separation of CO2 from an equimolar CO2 /CH4 mixture. The COF-based MMMs show a more than doubling of the CO2 permeability upon 16 wt % ACOF-1 loading together with a slight increase in selectivity compared to the bare polymer. These results show the potential of COFs in the preparation of MMMs.

Metal-organic frameworks are having a tremendous impact on novel strategic applications, with prospective employment in industrially relevant processes. The development of such processes is strictly dependent on the ability to generate materials with high yield efficiency and production rate. We report a versatile and highly efficient method for synthesis of metal-organic frameworks in large quantities using continuous flow processing under microwave irradiation. Benchmark materials such as UiO-66, MIL-53(Al), and HKUST-1 were obtained with remarkable mass, space-time yields, and often using stoichiometric amounts of reactants. In the case of UiO-66 and MIL-53(Al), we attained unprecedented space-time yields far greater than those reported previously. All of the syntheses were successfully extended to multi-gram high quality products in a matter of minutes, proving the effectiveness of continuous flow microwave technology for the large scale production of metal-organic frameworks.

This artwork presents the basic reaction concept of the asymmetric catalytic aza-Diels–Alder/ring-closing cascade by the operation mode of a zipper. The two molecules (red: 2,4-dienal; blue: hydrazone) in this reaction are mosaicked into the two chains of the zipper. The chiral slider, the diarylprolinol-silyl ether catalyst, zips together the two molecules by sliding the hand down the chains forming the bicyclic aza-heterocyclic products in a highly stereoselective manner. More information can be found in the Communication by K. A. Jørgensen et al. on page 38 ff.

Abstract Gold complexes with N ‐heterocyclic carbene (NHC) ligands represent a promising class of metallodrugs for the treatment of cancer or infectious diseases. In this report, the synthesis and the biological evaluation of halogen‐containing NHC‐Au I ‐Cl complexes are described. The complexes 1 and 5 a – 5 f displayed good cytotoxic activity against tumor cells, and cellular uptake studies suggested that an intact Au‐NHC fragment is essential for the accumulation of high amounts of both the metal and the NHC ligand. However, the bioavailability was negatively affected by serum components of the cell culture media and was influenced by likely transformations of the complex. One example ( 5 d ) efficiently induced apoptosis in vincristine‐ and daunorubicin‐resistant P‐glycoprotein overexpressing Nalm‐6 leukemia cells. Cellular uptake studies with this compound showed that both the wild‐type and resistant Nalm‐6 cells accumulated comparable amounts of gold, indicating that the gold drug was not excreted by P‐glycoprotein or other efflux transporters. The effective inhibition of…

Great efforts in developing clean electrochemical water splitting technology leads to the rational design and synthesis of highly efficient oxygen evolution reaction (OER) catalysts with low overpotential and fast reaction kinetics. Herein, we focus on the role that morphology and composition play in the OER performance to rationally design freestanding 3D porous NiCo2O4 nanosheets with metal valence states alteration and abundant oxygen vacancies as robust electrocatalysts towards water splitting. Besides metal valence-state alteration, surface modification regarding the evolution of oxygen vacancies is facilely realized upon the sodium borohydride treatment, which is beneficial for the enhanced OER performance. Taking advantage of the porous nanostructures and abundant surface activity sites with high reactivity, the resultant nanostructures exhibit excellent OER activity and stability in alkaline electrolytes that outperform that of pristine NiCo2O4 and commercial RuO2, thus holding great potential for the water splitting.

An iron-catalyzed coupling reaction of O-acyloximes and O-benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6-ketonitriles, pyrrolines and imidazolines via carbon-centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring-opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3-hydrogen transfer, providing insights into iron-catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen-containing products.

This Review covers design strategies, synthetic challenges, host-guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal-organic frameworks, but the main focus is on discrete coordination architectures, that is, metal-mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana-shaped bis-pyridyl ligands together with square-planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double-cages obeying the formula [M4 L8 ]. The peculiar topology of these double-cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template-controlled selectivity. In stimuli-responsive systems,…

Resonance-assisted hydrogen bonding (RAHB), a concept introduced by Gilli and co-workers in 1989, concerns a kind of intramolecular H-bonding strengthened by a conjugated π-system, usually in 6-, 8-, or 10-membered rings. This Review highlights the involvement of RAHB as a driving force in the synthesis of organic, coordination, and organometallic compounds, as a handy tool in the activation of covalent bonds, and in starting moieties for synthetic transformations. The unique roles of RAHB in molecular recognition and switches, E/Z isomeric resolution, racemization and epimerization of amino acids and chiral amino alcohols, solvatochromism, liquid-crystalline compounds, and in synthons for crystal engineering and polymer materials are also discussed. The Review can provide practical guidance for synthetic chemists that are interested in exploring and further developing RAHB-assisted synthesis and design of materials.

Highly efficient molecular-iodine-catalyzed chalcogenations (S and Se) of imidazo[1,2-a]pyridines were achieved by using diorganoyl dichalcogenides under solvent-free conditions. This approach afforded the desired products that had been chalcogenated regioselectively at the C3 position in up to 96 % yield by using DMSO as an oxidant, in the absence of a metal catalyst, and under an inert atmosphere. This mild, green approach allowed the preparation of different types of chalcogenated imidazo[1,2-a]pyridines with structural diversity. Furthermore, the current protocol was also extended to other N-heterocyclic cores.

In this Minireview, the state of the art in the use of ionic liquids (ILs) and deep eutectic solvents (DESs) as alternative reaction media for biocatalytic processes and biomass conversion is presented. Initial, proof-of-concept studies, more than a decade ago, involved first-generation ILs based on dialkylimidazolium cations and non-coordinating anions, such as tetrafluoroborate and hexafluorophosphate. More recently, emphasis has switched to more environmentally acceptable second-generation ILs comprising cations, which are designed to be compatible with enzymes and, in many cases are derived from readily available, renewable resources, such as cholinium salts. Protic ionic liquids (PILs), prepared simply by mixing inexpensive amines and acids, are particularly attractive from both an environmental and economic viewpoint. DESs, prepared by mixing inexpensive salts with, preferably renewable, hydrogen-bond donors such as glycerol and amino acids, have also proved suitable reaction media for biocatalytic conversions. A broad range of enzymes can be used in ILs, PILs and DESs, for…

Abstract Photodynamic therapy (PDT) uses photosensitizers (PS) which only become cytotoxic upon light‐irradiation. Transition‐metal complexes are highly promising PS due to long excited‐state lifetimes, and high photo‐stabilities. However, these complexes usually absorb higher‐energy UV/Vis light, whereas the optimal tissue transparency is in the lower‐energy NIR region. Two‐photon excitation (TPE) can overcome this dichotomy, with simultaneous absorption of two lower‐energy NIR‐photons populating the same PS‐active excited state as one higher‐energy photon. We introduce two low‐molecular weight, long‐lived and photo‐stable iridium complexes of the [Ir(N^C)2(N^N)]+ family with high TP‐absorption, which localise to mitochondria and lysosomal structures in live cells. The compounds are efficient PS under 1‐photon irradiation (405 nm) resulting in apoptotic cell death in diverse cancer cell lines at low light doses (3.6 J cm−2), low concentrations, and photo‐indexes greater than 555. Remarkably 1 also displays high PS activity killing cancer cells under NIR two‐photon excitation (760…

Despite significant advances, metal-catalyzed hydrophosphination has ample room for discovery, growth, and development. Many of the key successes in metal-catalyzed hydrophosphination over the last decade have indicated what is needed and what is yet to come. Reactivity that is absent from the literature also speaks to the challenges in catalytic hydrophosphination. This Concept article discusses and highlights recent developments that address the ongoing challenges, and identifies areas in metal-catalyzed hydrophosphination that are underdeveloped. Advances in product selectivity, catalyst design, and both unsaturated and phosphine substrates illustrate the ongoing development of the field. Like all catalytic transformations, the benefits are realized through catalyst, ligand, and conditions, and consideration of those features are the route to a yet more efficient and broadly applicable reaction.

The achievements on palladium-catalyzed carbonylative multicomponent reactions (CMCR) have been summarized and discussed according to the type of carbonylation reaction involved.

Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

Recent advances in dearomatization through halofunctionalization reactions are summarized in this Minireview. Two general categories of strategies are currently employed in this field. On one hand, the reaction can be initiated with electrophilic halogenation at an alkyne or alkene moiety. The resulting halonium ion intermediate is then captured by a pendant aromatic ring at the ipso position, affording the dearomatization product. On the other hand, electrophilic halogenation can directly take place at a substituted arene, and the final dearomatization product is furnished by deprotonation or intramolecular nucleophilic trap. Highly enantioselective variants have been realized in the latter case by organocatalysis or transition metal catalysis. By applying these methods, various valuable halogenated polycyclic molecular architectures have been obtained from readily available starting materials.

The fractional occupation number weighted density (FOD) analysis is explored as a general theoretical diagnostic for complicated electronic structures. Its main feature is to provide robustly and quickly the information on the localization of "hot" (strongly correlated and chemically active) electrons in a molecule. We demonstrate its usage in four different prototypical applications: 1) As a new and fast measure of the biradical character of polycyclic aromatic hydrocarbons, 2) for the selection of active orbital spaces in multiconfigurational or complete active space self consistent field (MCSCF/CASSCF) treatments, 3) as a possibility to describe molecular-energy landscapes consistently in regions with varying biradical character, as exemplified by partial double-bond torsions, and 4) as a powerful visualization method for static electron correlation effects in large biomolecules in connection with an efficient semi-empirical tight-binding molecular orbital scheme. The last application opens a full quantum-mechanical, unbiased route to the automatic detection of errors in…

A novel graphene-like MoS2 /C3N4 (GL-MoS2/C3N4) composite photocatalyst has been synthesized by a facile ethylene glycol (EG)-assisted solvothermal method. The structure and morphology of this GL-MoS2/C3N4 photocatalyst have been investigated by a wide range of characterization methods. The results showed that GL-MoS2 was uniformly distributed on the surface of GL-C3N4 forming a heterostructure. The obtained composite exhibited strong absorbing ability in the ultraviolet (UV) and visible regions. When irradiated with visible light, the composite photocatalyst showed high activity superior to those of the respective individual components GL-MoS2 and GL-C3N4 in the degradation of methyl orange. The enhanced photocatalytic activity of the composite may be attributed to the efficient separation of electron-hole pairs as a result of the matching band potentials between GL-MoS2 and GL-C3N4. Furthermore, a photocatalytic mechanism for the composite material has been proposed, and the photocatalytic reaction kinetics has been measured. Moreover, GL-MoS2/C3N4 could serve as a novel sensor…

Abstract With our new home‐built circularly polarized luminescence (CPL) instrument, we measured fluorescence and CPL spectra of the enantiomeric pairs of two quasi‐isomeric BODIPY DYEmers 1 and 2 , endowed with axial chirality. The electronic circular dichroism (ECD) and CPL spectra of these atropisomeric dimers are dominated by the exciton coupling between the main π–π* transitions (550–560 nm) of the two BODIPY rings. Compound 1 has strong ECD and CPL spectra ( g lum =4×10 −3 ) well reproduced by TD‐DFT and SCS‐CC2 (spin‐component scaled second‐order approximate coupled‐cluster) calculations using DFT‐optimized ground‐ and excited‐state structures. Compound 2 has weaker ECD and CPL spectra ( g lum =4×10 −4 ), partly due to the mutual cancellation of electric–electric and electric–magnetic exciton couplings, and partly to its conformational freedom. This compound is computationally very challenging. Starting from the optimized excited‐state geometries, we predicted the wrong sign for the CPL band of 2 using TD‐DFT with the most recommended hybrid and range‐separated functionals,…

This Concept is aimed at describing the current state of the art in metal-organic frameworks (MOFs) as heterogeneous catalysts for liquid-phase oxidations, focusing on three important substrates, namely, alkenes, alkanes and alcohols. Emphases are on the nature of active sites that have been incorporated within MOFs and on future targets to be set in this area. Thus, selective alkene epoxidation with peroxides or oxygen catalyzed by constitutional metal nodes of MOFs as active sites are still to be developed. Moreover, no noble metal-free MOF has been reported to date that can act as a general catalyst for the aerobic oxidation of primary and secondary aliphatic alcohols. In contrast, in the case of alkanes, a target should be to tune the polarity of MOF internal pores to control the outcome of the autooxidation process, resulting in the selective formation of alcohol/ketone mixtures at high conversion.

A photo-induced carboxylation reaction of allylic C-H bonds of simple alkenes with CO2 is prompted by means of a ketone and a copper complex. The unique carboxylation reaction proceeds through a sequence of an endergonic photoreaction of ketones with alkenes forming homoallyl alcohol intermediates and a thermal copper-catalyzed allyl transfer reaction from the homoallyl alcohols to CO2 through C-C bond cleavage.

Alkyl- and aryl vinyl sulfones were obtained by eosin Y (EY)-mediated visible-light photooxidation of sulfinate salts and the reaction of the resulting S-centered radicals with alkenes. Optimized reaction conditions, the sulfinate and alkene scope, and X-ray structural analyses of several reaction products are provided. A detailed spectroscopic study explains the reaction mechanism, which proceeds through the EY radical cation as key intermediate oxidizing the sulfinate salts.

Sodium-ion batteries (SIBs) are regarded as an attractive alternative to lithium-ion batteries (LIBs) for large-scale commercial applications, because of the abundant terrestrial reserves of sodium. Exporting suitable anode materials is the key to the development of SIBs and LIBs. In this contribution, we report on the fabrication of Bi@C microspheres using aerosol spray pyrolysis technique. When used as SIBs anode materials, the Bi@C microsphere delivered a high capacity of 123.5 mAh g(-1) after 100 cycles at 100 mA g(-1) . The rate performance is also impressive (specific capacities of 299, 252, 192, 141, and 90 mAh g(-1) are obtained under current densities of 0.1, 0.2, 0.5, 1, and 2 A g(-1) , respectively). Furthermore, the Bi@C microsphere also proved to be suitable LIB anode materials. The excellent electrochemical performance for both SIBs and LIBs can attributed to the Bi@C microsphere structure with Bi nanoparticles uniformly dispersed in carbon spheres.

Azlactones (also known as oxazolones) are heterocycles usually employed in the stereoselective synthesis of α,α-amino acids, heterocycles and natural products. The versatility of the azlactone scaffold arises from the numerous reactive sites, allowing its application in a diversity of transformations. This review aims to cover classical and recent applications of oxazolones, especially those involving stereoselective processes. After a short introduction on their structures and intrinsic reactivities, dynamic kinetic resolution (DKR) processes as well as reactions involving stereoselective formation of a new σ C-C bond, such as alkylation/allylation/arylation, aldol, ene, Michael and Mannich reactions will be exposed. Additionally, cycloadditions, Steglich rearrangement and sulfenylation reactions will also be discussed. Recent developments of the well-known Erlenmeyer azlactones will be described. For the most examples, the proposed mechanism, activation modes and/or key reaction intermediates will be exposed to rationalize both the final product and the observed stereochemistry.…

Abstract Nitrogen‐doped porous carbon nanosheets were prepared from eucalyptus tree leaves by simply mixing the leaf powders with KHCO3 and subsequent carbonisation. Porous carbon nanosheets with a high specific surface area of 2133 m2 g−1 were obtained and applied as electrode materials for supercapacitors and lithium ion batteries. For supercapacitor applications, the porous carbon nanosheet electrode exhibited a supercapacitance of 372 F g−1 at a current density of 500 mA g−1 in 1 m H2SO4 aqueous electrolyte and excellent cycling stability over 15 000 cycles. In organic electrolyte, the nanosheet electrode showed a specific capacitance of 71 F g−1 at a current density of 2 Ag−1 and stable cycling performance. When applied as the anode material for lithium ion batteries, the as‐prepared porous carbon nanosheets also demonstrated a high specific capacity of 819 mA h g−1 at a current density of 100 mA g−1, good rate capability, and stable cycling performance. The outstanding electrochemical performances for both supercapacitors and lithium ion batteries are derived from the large…

Molecular solar-thermal energy storage systems are based on molecular switches that reversibly convert solar energy into chemical energy. Herein, we report the synthesis, characterization, and computational evaluation of a series of low molecular weight (193-260 g mol(-1) ) norbornadiene-quadricyclane systems. The molecules feature cyano acceptor and ethynyl-substituted aromatic donor groups, leading to a good match with solar irradiation, quantitative photo-thermal conversion between the norbornadiene and quadricyclane, as well as high energy storage densities (396-629 kJ kg(-1) ). The spectroscopic properties and energy storage capability have been further evaluated through density functional theory calculations, which indicate that the ethynyl moiety plays a critical role in obtaining the high oscillator strengths seen for these molecules.

Abstract This Concept examines strategies to design advanced polymers with high CO 2 permeability and high CO 2 /N 2 selectivity, which are the key to the success of membrane technology for CO 2 capture from fossil fuel‐fired power plants. Specifically, polymers with enhanced CO 2 solubility and thus CO 2 /N 2 selectivity are designed by incorporating CO 2 ‐philic groups in polymers such as poly(ethylene oxide)‐containing polymers and poly(ionic liquids); polymers with enhanced CO 2 diffusivity and thus CO 2 permeability are designed with contorted rigid polymer chains to obtain high free volume, such as polymers with intrinsic microporosity and thermally rearranged polymers. The underlying rationales for materials design are discussed and polymers with promising CO 2 /N 2 separation properties for CO 2 capture from flue gas are highlighted.

We report a highly efficient iodine adsorbent achieved by rational design of a porous azo-bridged porphyrin-phthalocyanine network (AzoPPN), which was synthesized by a catalyst-free coupling reaction between free-base 5,10,15,20-tetrakis(4-nitrophenyl)-porphyrin and nickel tetraaminophthlocyanine. AzoPPN has a permanent porous structure and plenty of porphyrin and phthalocyanine units in the skeleton as effective sorption sites. It displays excellent adsorption of iodine vapor up to 290 wt. % and also shows remarkable capability as adsorbent for iodine in solution. This strategy of combining physisorption with chemisorption in one adsorbent will pave the way for the development of new materials for iodine capture.

A stable and selective electrocatalyst for CO2 reduction was fabricated by covalently attaching graphitic carbon nitride onto multiwall carbon nanotubes (g-C3 N4 /MWCNTs). The as-prepared composite is able to reduce CO2 exclusively to CO with a maximum Faraday efficiency of 60 %, and no decay in the catalytic activity was observed even after 50 h of reaction. The enhanced catalytic activity towards CO2 reduction is attributed to the formation of active carbon-nitrogen bonds, high specific surface area, and improved material conductivity of the g-C3 N4 /MWCNT composite.

Abstract Herein, a conceptually new and straightforward aqueous route is described for the synthesis of hydroxyl‐ and amino‐functionalized boron nitride quantum dots (BNQDs) with quantum yields (QY) as high as 18.3 % by using a facile bottom‐up approach, in which a mixture of boric acid and ammonia solution was hydrothermally treated in one pot at 200 °C for 12 h. The functionalized BNQDs, with excellent photoluminescence properties, could be easily dispersed in an aqueous medium and applied as fluorescent probes for the detection of ferrous (Fe 2+ ) and ferric (Fe 3+ ) ions with excellent selectivity and low detection limits. The mechanisms for the hydrothermal reaction and fluorescence quenching were also simulated by using density functional theory (DFT), which confirmed the feasibility and advantages of this strategy. It provides a scalable and eco‐friendly method for preparation of BNQDs with good dispersability and could also be generalized to the synthesis of other 2D quantum dots and nanoplates.

centers and distinct three-dimensionality. We have systematically explored chemical space populated with currently available bioactive spirocycles. Compounds containing spiro systems were classified and their scaffolds and spirocyclic ring combinations analyzed. Nearly 47 000 compounds were identified that contained spirocycles in different structural contexts and were active against roughly 200 targets, among which several pharmaceutically relevant members of the G protein-coupled receptor (GPCR) family were identified. Spirocycles and corresponding compounds displayed notable scaffold diversity but contained only limited numbers of combinations of differently sized rings. These observations indicate that there should be significant potential to further expand spirocyclic chemical space for drug discovery, exploiting the privileged substructure concept. Inspired by those findings, we embarked on the design and chemical synthesis of three distinct novel spirocyclic scaffolds that qualify for downstream library synthesis, thus exploring principally new chemical space with high…

Transition-metal-catalyzed electrophilic amination has been developed into a powerful tool for C-N bond construction. So far, O-benzoylhydroxylamines are the most widely used electrophilic aminating reagents. Herein, we summarize the recent advances of O-benzoylhydroxylamines involved in electrophilic amination catalyzed by transition metals. Several pioneering studies and some of the relevant mechanisms are discussed in this review.

Azobenzenes are versatile photoswitches that can be cycled between their trans- and cis-configuration with light. The wavelengths required for this isomerization are substantially shifted from the UV to the visible range through tetra-ortho-chlorination. These halogenated azobenzenes display unique photoswitching characteristics, but their syntheses remain limited and inefficient. A new general method for the synthesis of tetra-ortho-chloro azobenzenes has been developed, which relies on direct palladium(II)-catalyzed C-H activation of pre-existing standard azobenzenes. This late-stage functionalization has a broad substrate scope and can be used to create a variety of useful building blocks for the construction of more elaborate redshifted photopharmaceuticals. This method is used to prepare red-AzCA-4, a photoswitchable vanilloid that enables optical control of the cation channel TRPV1 with visible light.

An efficient and external oxidant-free, Cp*Co(III) -catalyzed C(sp(3) )-H bond amidation of 8-methylquinoline, using oxazolone as an efficient amidating agent, is reported for the first time under mild conditions. The reaction is selective and tolerates a variety of functional groups. Based on previous reports and experimental results, the deprotonation pathway proceeds through an external base-assisted concerted metalation and deprotonation process.

We report a series of short peptides possessing the sequence (FE)n or (EF)n and bearing l-proline at their N-terminus that self-assemble into high aspect ratio aggregates and hydrogels. We show that these aggregates are able to catalyze the aldol reaction, whereas non-aggregated analogues are catalytically inactive. We have undertaken an analysis of the results, considering the accessibility of catalytic sites, pKa value shifts, and the presence of hydrophobic pockets. We conclude that the presence of hydrophobic regions is indeed relevant for substrate solubilization, but that the active site accessibility is the key factor for the observed differences in reaction rates. The results presented here provide an example of the emergence of a new chemical property caused by self-assembly, and support the relevant role played by self-assembled peptides in prebiotic scenarios. In this sense, the reported systems can be seen as primitive aldolase I mimics, and have been successfully tested for the synthesis of simple carbohydrate precursors.

Self-assembled metallocages are very promising drug-delivery systems among supramolecular complexes. Thus, exo-functionalized Pd2 L4 (L=ligand) cages were synthesized and characterized, and the encapsulation of the anticancer drug cisplatin in their cavity has been documented. The antiproliferative effects of the metallocages and their combination with cisplatin were examined in vitro in cancer cell lines, while fluorescence microscopy was used to monitor their uptake. Notably, the hydroxymethyl-functionalized Pd(II) cage encapsulating cisplatin showed improved cytotoxic effect against human ovarian cancer cells compared to free cisplatin. The toxicity of Pd2 L4 cages was evaluated for the first time ex vivo in healthy rat-liver tissues using the precision cut-tissue slices technology, demonstrating in some cases scarce effects on liver viability. These results further highlight the potential of self-assembled Pd2 L4 cages for biological applications.

Abstract The potential of many 18F‐labeled (hetero)aromatics for applications in positron emission tomography remains underexplored because convenient procedures for their radiosynthesis are lacking. Consequently, simple methods to prepare radiofluorinated (hetero)arenes are highly sought after. Herein, we report the beneficial effect of primary and secondary alcohols on Cu‐mediated 18F‐labeling. This observation contradicts the assumption that such alcohols are inappropriate solvents for aromatic fluorination. Therefore, we developed a protocol for rapid radiolabeling of an extraordinarily broad scope of boronic and stannyl substrates under general reaction conditions. Notably, radiofluorinated indoles, phenols, and anilines were synthesized directly from the corresponding unprotected precursors. Furthermore, the novel method enabled the preparation of radiofluorinated tryptophans, [18F]F‐DPA, [18F]DAA1106, 6‐[18F]FDA, and 6‐[18F]FDOPA.

Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications.

"Regiodivergent catalysis" is discussed as a class of highly selective reactions of chiral substrates in racemic or enantiomerically enriched form using one or both enantiomers of a catalyst. The key point of the reactions is the highly regioselective formation of products that are constitutional isomers. The selectivity is mediated by different interactions of the enantiomerically pure catalysts with both enantiomers of the substrate. Ideally, for racemic substrates, the reactions result in highly efficient parallel resolutions and for enantiomerically pure substrates, in highly regioselective reactions for each enantiomer of the catalyst. "Regiodivergent catalysis" is highly interesting for diversity-oriented synthesis (DOS) because it provides branching points for the generation of functional and structural diversity.

Spin-crossover metal complexes represent a highly promising class of molecular switches, the diverse physicochemical properties of which can be reversibly changed by different physical and chemical stimuli. One of the most interesting and examined features of these materials is the change of magnetic properties by changing the temperature or by irradiation with light at low temperatures. However, most prospective applications of such complexes require functioning at room temperature. This Concept article provides an overview about how the switching of spin-crossover metal complexes can be achieved at constant room temperature. The principles of switching by different physical and chemical methods in solution and in the solid state are presented in an easy-to-read form for nonspecialists. These are further supported and clarified by examples from the literature. The overview might also be interesting for experts that target spin-crossover systems functioning at ambient conditions.

Control over the local chemical environment of a molecule can be achieved by encapsulation in supramolecular host systems. In supramolecular catalysis, this control is used to gain advantages over classical homogeneous catalysis in bulk solution. Two of the main advantages concern influencing reactions in terms of substrate and product selectivity. Due to size and/or shape recognition, substrate selective conversion can be realized. Additionally, noncovalent interactions with the host environment facilitate alternative reaction pathways and can yield unusual products. This Concept article discusses and highlights literature examples utilizing self-assembled molecular capsules to achieve catalytic transformations displaying a high degree of substrate and/or product selectivity. Furthermore, the advantage of supramolecular hosts in multicatalyst tandem reactions is covered.

Abstract In recent years, much interest has been paid to difluoromethylthiolated molecules as the “SCF2” moiety is a key motif in drug and agrochemical research. Consequently, the development of versatile strategies for the selective synthesis of SCF2H‐ and SCF2FG‐containing molecules (FG=functional group) has attracted a lot of attention and inspired the scientific community to design new tools. This Minireview highlights the major progress made in this field. Particularly, methodologies developed for the difluoromethylation of sulfur‐containing molecules and the direct construction of C−SCF2 bonds in various classes of compounds are showcased and discussed.

Highly efficient and diastereodivergent aza-Diels-Alder reactions have been developed to access either diastereomeric series of benzofuran-fused δ-lactams and dihydropyridines in nearly perfect stereoselectivity (d.r. >20:1, >99 % ee for all examples). The complementarity of N-heterocyclic carbene and chiral amine as the catalyst was demonstrated for the first time, together with an excellent level of catalytic efficiency (1 mol % loading).

Black phosphorus quantum dots (BPQDs) have been prepared by a high turbulent shear rate generated from a household kitchen blender. A layer-by-layer disintegration mechanism of bulk BP crystals is suggested. As-synthesized BPQDs have shown excellent humidity sensing and photothermal converting properties. Importantly, this work not only explores potential applications for the BPQDs but also provides a successful paradigm for preparing the QDs of other layered materials.

The intrinsic bond strength of C2 in its (1)Σg(+) ground state is determined from its stretching force constant utilizing MR-CISD+Q(8,8), MR-AQCC(8,8), and single-determinant coupled cluster calculations with triple and quadruple excitations. By referencing the CC stretching force constant to its local counterparts of ethane, ethylene, and acetylene, an intrinsic bond strength half way between that of a double bond and a triple bond is obtained. Diabatic MR-CISD+Q results do not change this. Confinement of C2 and suitable reference molecules in a noble gas cage leads to compression, polarization, and charge transfer effects, which are quantified by the local CC stretching force constants and differences of correlated electron densities. These results are in line with two π bonds and a partial σ bond. Bond orders and bond dissociation energies of small hydrocarbons do not support quadruple bonding in C2.

Cyclobutenones, four-membered ketones bearing an unsaturated carbon-carbon double bond, and their structural sibling benzocyclobutenones, possess unique reactivity. Owing to their inherent high ring strain, such structures readily undergo ring opening under a variety of conditions, including thermolysis, photolysis, and transition metal catalysis, to afford reactive intermediates that can be trapped with nucleophiles, dienophiles, and unsaturated bonds. Their electron-deficient enone moieties are good electrophiles for facile nucleophilic addition. Such properties render cyclobutenones versatile synthons, serving as excellent coupling partners in a vast array of synthetically valuable transformations.

Participation of alkenes and allenes in [2+2+2] cycloaddition reactions has attracted much attention recently. This version of the well-established alkyne cyclotrimerization renders interesting products, such as cyclohexadienes and other polycycles, through cascade processes. Many mechanistic variations are observed when using certain metal complexes as catalysts. The frequent generation of stereogenic centers has prompted the development of efficient asymmetric versions. This Minireview summarizes the efforts reported to date on the use of double bonds as partners in [2+2+2] cyclotrimerizations.

Abstract Four members of a new class of cycloborylated hexa‐, octa‐, and deca‐helicenes ( 1 a – d ) have been prepared in enantiopure form, along with two cycloplatinated deca‐helicenes ( 1 d′ , 1 d 1 ), further extending the family of cycloplatinated hexa‐ and octa‐helicenes reported previously. The azabora[ n ]helicenes display intense electronic circular dichroism and large optical rotations; the dependence of the optical activity on the size of the helix ( n= 6, 8, 10) and the number of boron atoms (1 or 2) has been examined in detail both experimentally and theoretically. The photophysical properties (nonpolarized and circularly polarized luminescence) of these new fluorescent organic helicenes have been measured and compared with the corresponding organometallic phosphorescent cycloplatinated derivatives ( 1 a 1 – d 1 ).

Metal-organic frameworks (MOFs) are widely used as porous materials in the fields of adsorption and separation. However, their practical application is largely hindered by limitations to their processability. Herein, new UiO-66-Urea-based flexible membranes with MOF loadings of 50 (1), 60 (2), and 70 wt % (3) were designed and prepared by post-synthetic polymerization of UiO-66-NH2 nanoparticles and a polyurethane oligomer under mild conditions. The adsorption behavior of membrane 3 towards four hydrophilic dyes, namely, eosin Y (EY), rhodamine B (RB), malachite green (MG), and methylene blue (MB), in aqueous solution was studied in detail. It exhibits strong adsorption of EY and RB but weak adsorption of MG and MB in aqueous solution. Owing to the selective adsorption of these hydrophilic dyes, membrane 3 can remove EY and RB from aqueous solution and completely separate EY/MB, RB/MG, and RB/MB mixtures in aqueous solution. In addition, the membrane is uniformly textured, easily handled, and can be reused for dye adsorption and separation.

Abstract A series of isomorphic lanthanide metal–organic frameworks (MOFs) Ln(TATAB)⋅(DMF)4(H2O)(MeOH)0.5 (LnTATAB, Ln=Eu, Tb, Sm, Dy, Gd; H3TATAB=4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐p‐aminobenzoic acid) have been solvothermally synthesized and structurally characterized. Among these MOFs, TbTATAB exhibits good water stability and a high fluorescence quantum yield. Because mercury ions (Hg2+) have a high affinity to nitrogen atoms, and the space between multiple nitrogen atoms from triazine and imino groups is suitable for interacting with Hg2+ ions, TbTATAB shows highly selective and sensitive detection of Hg2+ in aqueous solution with a detection limit of 4.4 nm. Furthermore, it was successfully applied to detect Hg2+ ions in natural water samples.

Medicinally relevant spirocyclic indolenines, carbazoles and quinolines can each be directly synthesised selectively from common indolyl ynone starting materials by catalyst variation. The high yielding, divergent reactions all proceed by an initial dearomatising spirocyclisation reaction to generate an intermediate vinyl-metal species, which then rearranges selectively by careful choice of catalyst and reaction conditions.

Metal-organic frameworks (MOFs) feature a great possibility for a broad spectrum of applications. Hollow MOF structures with tunable porosity and multifunctionality at the nanoscale with beneficial properties are desired as hosts for catalytically active species. Herein, we demonstrate the formation of well-defined hollow Zn/Co-based zeolitic imidazolate frameworks (ZIFs) by use of epitaxial growth of Zn-MOF (ZIF-8) on preformed Co-MOF (ZIF-67) nanocrystals that involve in situ self-sacrifice/excavation of the Co-MOF. Moreover, any type of metal nanoparticles can be accommodated in Zn/Co-ZIF shells to generate yolk-shell metal@ZIF structures. Transmission electron microscopy and tomography studies revealed the inclusion of these nanoparticles within hollow Zn/Co-ZIF with dominance of the Zn-MOF as shell. Our findings lead to a generalization of such hollow systems that are working effectively to other types of ZIFs.

2,6-Divinylpyridine-appended anthracene derivatives flanked by two alkyl chains at the 9,10-position of the core have been designed, synthesized, and characterized by NMR, MALDI-TOF, FTIR, and single-crystal XRD. These anthracene derivatives are able to recognize picric acid (2,4,6-trinitrophenol, PA) selectively down to parts per billion (ppb) level in aqueous as well as nonaqueous medium. Fluorescence emission of these derivatives in solution is significantly quenched by adding trace amounts of PA, even in the presence of other competing analogues, such as 2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (NP), nitrobenzene (NB), benzoic acid (BA), and phenol (PH). The high sensitivity of these derivatives toward PA is considered as a combined effect of the proton-induced intramolecular charge transfer (ICT) as well as electron transfer from the electron-rich anthracene to the electron-deficient PA. Moreover, visual detection of PA has been successfully demonstrated in the solid state by using different substrates.

This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process.

A cooperative TEMPO and photoredox catalytic strategy was applied for the first time to the direct conversion of N-H and O-H bonds into N- and O-centred radicals, enabling a general and selective oxidative radical oxyamination and dioxygenation of various β,γ-unsaturated hydrazones and oximes. In the reaction, O2 was employed not only as a terminal oxidant but also as the oxygen source. This protocol provided efficient access to the synthesis of various synthetically and biologically important pyrazoline, pyridazine and isoxazoline derivatives under metal-free and mild reaction conditions. Mechanistic studies revealed that the cooperative organophotocatalytic system functions through two single-electron-transfer (SET) processes.

Efficient and cost-effective removal of radioactive pertechnetate anions from nuclear waste is a key challenge to mitigate long-term nuclear waste storage issues. Traditional materials such as resins and layered double hydroxides (LDHs) were evaluated for their pertechnetate or perrhenate (the non-radioactive surrogate) removal capacity, but there is room for improvement in terms of capacity, selectivity and kinetics. A series of functionalized hierarchical porous frameworks were evaluated for their perrhenate removal capacity in the presence of other competing anions.

Herein, we report a new visible-light-promoted strategy to access radical trifluoromethylthiolation reactions by combining halide and photoredox catalysis. This approach allows for the synthesis of vinyl-SCF3 compounds of relevance in pharmaceutical chemistry directly from alkenes under mild conditions with irradiation from household light sources. Furthermore, alkyl-SCF3-containing cyclic ketone and oxindole derivatives can be accessed by radical-polar crossover semi-pinacol and cyclization processes. Inexpensive halide salts play a crucial role in activating the trifluoromethylthiolating reagent towards photoredox catalysis and aid the formation of the SCF3 radical.

The high-yielding synthesis of 2-substituted benzo-1,3-tellurazoles and benzo-1,3-selenazoles through a dehydrative cyclization reaction has been reported, giving access to a large variety of benzo-1,3-chalcogenazoles. Exceptionally, these aromatic heterocycles proved to be very stable and thus very handy to form controlled solid-state organizations in which wire-like polymeric structures are formed through secondary N⋅⋅⋅Y bonding interactions (SBIs) engaging the chalcogen (Y=Se or Te) and nitrogen atoms. In particular, it has been shown that the recognition properties of the chalcogen centre at the solid state could be programmed by selectively barring one of its σ-holes through a combination of electronic and steric effects exerted by the substituent at the 2-position. As predicted by the electrostatic potential surfaces calculated by quantum chemical modelling, the pyridyl groups revealed to be the stronger chalcogen bonding acceptors, and thus the best ligand candidate for programming the molecular organization at the solid state. In contrast, the thiophenyl group is an…

Cp*-free cobalt-catalyzed alkyne annulations by C-H/N-H functionalizations were accomplished with molecular O2 as the sole oxidant. The user-friendly oxidase strategy proved viable with various internal and terminal alkynes through kinetically relevant C-H cobaltation, providing among others step-economical access to the anticancer topoisomerase-I inhibitor 21,22-dimethoxyrosettacin. DFT calculations suggest that electronic effects control the regioselectivity of the alkyne insertion step.

In this Minireview recent advances in the asymmetric reactions of meso and racemic epoxides promoted by organocatalysts is reviewed. Organic promoters, such as chiral phosphoric acids, amino- and peptidyl thioureas, and sulfinamides, have been successfully used for a variety of enantioselective transformations of epoxides under catalytic conditions, involving direct nucleophilic attack at the oxirane ring, base-catalysed β-eliminations and Brønsted acid catalysed 1,2-rearrangements. Accordingly, highly valuable enantioenriched 1,2-functionalised alcohols, carbonyl compounds and nitroepoxides are attainable. Dual activation of the reagents, provided by the organocatalysts, appears to be the most recurrent strategy, potentially suitable to face other unmet challenges in asymmetric ring-opening reactions of epoxides.

A direct connection is established between three-dimensional aromatic closo boron hydride clusters and planar aromatic [n]annulenes for medium and large boron clusters. In particular, the results prove the existence of a link between the two-dimensional Hückel rule, as followed by aromatic [n]annulenes, and Wade-Mingos' rule of three-dimensional aromaticity, as applied to the aromatic [Bn Hn ](2-) closo boron hydride clusters. The closo boron hydride clusters can be categorized into different series, according to the n value of the Hückel (4 n+2) π rule. The distinct categories studied in this work correspond to n=1, 2, and 3. Each category increases in geometrical difficulty but, more importantly, it is possible to associate each category with the number of pentagonal layers in the structure perpendicular to the main axis. Category 1 has one pentagonal layer, category 2 has two, and category 3 has three.

Described herein is a new and straightforward decarboxylative di- and trifluoromethylthiolation of alkyl carboxylic acids promoted by visible light. This approach enables the synthesis of biologically relevant alkyl SCF2H and SCF3 compounds from cheap and abundant carboxylic acids. The method is operationally simple, using irradiation from household light sources, and its mild reaction conditions make it tolerant of a range of functional groups. The strategy employs electrophilic phthalimide-derived di- and trifluoromethylthiolation reagents and exploits the ability of the imidyl radical to carry a radical chain.

Chromium and aluminium salphen complexes have been found to display remarkable catalytic activity in the synthesis of cyclic carbonates from a range of epoxides and carbon dioxide. The Al(salphen) complex is more reactive towards terminal epoxides at ambient temperature and pressure, whereas the Cr(salphen) complex exhibits higher catalytic activity towards more challenging internal epoxides at elevated temperature and pressure.

A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E-H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn )] (1-6: ERn =NHDipp, CH(SiMe3 )2 , P(SiMe3 )2 , Si(SiMe3 )3 or B(NDippCH)2 ; terphenyl=C6 H3 Mes2 -2,6=Ar(Mes) or C6 H3 Dipp2 -2,6=Ar(Dipp) ; Dipp=C6 H3 iPr2 -2,6, Mes=C6 H2 Me3 -2,4,6), while the related complex [{(Me3 Si)2 N}Ge{B(NDippCH)2 }] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ-donating boryl or silyl ancillary donors. HOMO-LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)-germylene system…

Abstract Biomass‐derived porous carbon BPC‐700, incorporating micropores and small mesopores, was prepared through pyrolysis of banana peel followed by activation with KOH. A high specific BET surface area (2741 m2 g−1), large specific pore volume (1.23 cm3 g−1), and well‐controlled pore size distribution (0.6–5.0 nm) were obtained and up to 65 wt % sulfur content could be loaded into the pores of the BPC‐700 sample. When the resultant C/S composite, BPC‐700‐S65, was used as the cathode of a Li–S battery, a large initial discharge capacity (ca. 1200 mAh g−1) was obtained, indicating a good sulfur utilization rate. An excellent discharge capacity (590 mAh g−1) was also achieved for BPC‐700‐S65 at the high current rate of 4 C (12.72 mA cm−2), showing its extremely high rate capability. A reversible capacity of about 570 mAh g−1 was achieved for BPC‐700‐S65 after 500 cycles at 1 C (3.18 mA cm−2), indicating an outstanding cycling stability.

A series of magnesium(II) complexes bearing the sterically demanding phosphinoamide ligand, L(-) =Ph2 PNDip(-) , Dip=2,6-diisopropylphenyl, including heteroleptic magnesium alkyl and hydride complexes are described. The ligand geometry enforces various novel ring and cluster geometries for the heteroleptic compounds. We have studied the stoichiometric reactivity of [(LMgH)4 ] towards unsaturated substrates, and investigated catalytic hydroborations and hydrosilylations of ketones and pyridines. We found that hydroborations of two ketones with pinacolborane using various Mg precatalysts is very rapid at room temperature with very low catalyst loadings, and ketone hydrosilylation using phenylsilane is rapid at 70 °C. Our studies point to an insertion/σ-bond metathesis catalytic cycle of an in situ formed "MgH2 " active species.

A simple one-pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders for application as anode materials in sodium-ion batteries was developed. The detailed mechanism of formation of the CoSe(x)-rGO composite powders that were selected as the first target material in the spray pyrolysis process was studied. The crumple-structured CoSe(x)-rGO composite powders prepared by spray pyrolysis at 800 °C had a crystal structure consisting mainly of Co0.85 Se with a minor phase of CoSe2. The bare CoSe(x) powders prepared for comparison had a spherical shape and hollow structure. The discharge capacities of the CoSe(x)-rGO composite and bare CoSe(x) powders in the 50th cycle at a constant current density of 0.3 A g(-1) were 420 and 215 mA h g(-1), respectively, and their capacity retentions measured from the second cycle were 80 and 46%, respectively. The high structural stability of the CoSe(x)-rGO composite powders for repeated sodium-ion charge and discharge processes resulted in superior sodium-ion storage properties compared to those of the bare CoSe(x) powders.

The host-guest composites of Hofmann-type iron(II) spin-transition (ST) porous coordination polymers incorporating guest molecules show guest-dependent ST behavior in accordance with the respective guest species, which may be a gas, solvent, halogen, or organic molecule. The guest also works as a chemical stimulant to switch the spin state of the host between high and low spin at room temperature. In this review, we discuss guest properties including size, shape, flexibility, chemical properties, and pore loading content, which impact the spin states of the host framework and the ST behavior exhibited by the host-guest composites.

Abstract The members of a series of linear and trigonal copper(I) complexes bearing a cyclic alkyl(amino)carbene (CAAC) ligand show surprising photophysical properties compared to those of the corresponding N‐heterocyclic carbene (NHC) complexes. Whereas the linear NHC complexes [CuX(NHC)] are almost non‐emissive, [CuX(CAAC)] (X=Cl, Br, I) and [Cu(CAAC)2]PF6 show very bright emissions from their triplet excited states in the blue to green region, displaying quantum yields of up to 65 % in the solid state, even though the π‐acceptor comprises only the carbene C and N atoms with no other π conjugation. [Cu(CAAC)2]PF6 is the fastest CuI‐based triplet state emitter characterized to date, not displaying thermally activated delayed fluorescence (TADF), with an intrinsic lifetime of only 10.6 μs, that is, kr=9.4×104 s−1, competitive with many PtII‐ and IrIII‐based emitters. In order to test the stability of such linear copper CAAC complexes in devices, some of our compounds have been applied in proof‐of‐principle organic light‐emitting diodes (OLEDs). This case study thus demonstrates for…