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A paper-based colorimetric sensor system (PBCSS) was developed to detect the amount of bis(pinacolato)diboron (B2Pin2) and applied as a high-throughput screening protocol in Ir-catalyzed C−H borylation. First, 96 ligands were screened for the borylation of benzene, and then 12 of them were selected and tested for five substrates. These reaction mixtures were spotted in the PBCSS, showing a blue-violet color. The value of the gray scale of each reaction was obtained from these colored spots and converted to the extent of conversion of B2Pin2. The extents of conversion of B2Pin2 obtained from the PBCSS showed good correlation with those obtained from gas chromatography analysis. In addition, the modified conversion using blank data showed good correlation with the yield of products. [ABSTRACT FROM AUTHOR]

In this paper, Pd‐catalyzed [4+2] decarboxylative cycloaddition of 4‐vinylbenzodioxinones with barbiturate‐derived alkenes has been developed, leading to various spirobarbiturate−chromane derivatives in high yields with excellent diastereo‐ and enantioselectivities. The scale‐up reaction and further derivation of the product were demonstrated. A plausible reaction mechanism was also proposed. [ABSTRACT FROM AUTHOR]

Biohybrid catalysts that operate in aqueous media are intriguing for systems chemistry. In this paper, we investigate whether control over the self‐assembly of biohybrid catalysts can tune their properties. As a model, we use the catalytic activity of functional hybrid molecules consisting of a catalytic H‐dPro‐Pro‐Glu tripeptide, derivatized with fatty acid and nucleobase moieties. This combination of simple biological components merged the catalytic properties of the peptide with the self‐assembly of the lipid, and the structural ordering of the nucleobases. The biomolecule hybrids self‐assemble in aqueous media into fibrillar assemblies and catalyze the reaction between butanal and nitrostyrene. The interactions between the nucleobases enhanced the order of the supramolecular structures and affected their catalytic activity and stereoselectivity. The results point to the significant control and ordering that nucleobases can provide in the self‐assembly of biologically inspired supramolecular catalysts. [ABSTRACT FROM AUTHOR]

Transition metal radical‐type carbene transfer catalysis is a sustainable and atom‐efficient method to generate C−C bonds, especially to produce fine chemicals and pharmaceuticals. A significant amount of research has therefore been devoted to applying this methodology, which resulted in innovative routes toward otherwise synthetically challenging products and a detailed mechanistic understanding of the catalytic systems. Furthermore, combined experimental and theoretical efforts elucidated the reactivity of carbene radical complexes and their off‐cycle pathways. The latter can imply the formation of N‐enolate and bridging carbenes, and undesired hydrogen atom transfer by the carbene radical species from the reaction medium which can lead to catalyst deactivation. In this concept paper, we demonstrate that understanding off‐cycle and deactivation pathways not only affords solutions to circumvent them, but can also uncover novel reactivity for new applications. In particular, considering off‐cycle species involved in metalloradical catalysis can stimulate further development of radical‐type carbene transfer reactions. [ABSTRACT FROM AUTHOR]

Abstract: Ionic porous organic polymers have attracted much attention due to their broad applications in catalysis, energy storage/conversion, proton conduction, etc. In this paper, an ionic porous organic polymer, CMP‐PM‐Me, was synthesized through post‐synthetic modification of a pyrimidine‐based conjugated microporous polymer, CMP‐PM, which was constructed by the palladium catalyzed Sonogashira reaction of 1,3,5‐triethynylbenzen and 2,5‐dibromopyrimidine. These two polymers are porous with Brunauer–Emmett–Teller surface areas of 416 and 241 m2 g−1 for CMP‐PM and CMP‐PM‐Me, respectively. Due to the cationic framework, CMP‐PM‐Me exhibits a much faster and more efficient adsorption performance to anionic dyes such as Congo red (CR) and methyl orange (MO) than that of CMP‐PM with a neutral framework. The uptakes for CR are 400.0 mg g−1 for CMP‐PM‐Me and 344.8 mg g−1 for CMP‐PM, respectively. Furthermore, CMP‐PM‐Me could quickly and drastically separate anionic dyes from the binary mixed solution of anionic and nonanionic dyes within a short time. This work not only enriches the family of ionic organic porous polymers and widens their synthetic utility, but also demonstrates their applications in the adsorption and separation of anionic dyes in water. [ABSTRACT FROM AUTHOR]

In the last decade, numerous studies of graphene doping by various metal and nonmetal elements have been done in order to obtain tailored properties, such as non-zero band gap, electrocatalytic activity, or controlled optical properties. From nonmetal elements, boron and nitrogen were the most studied dopants. Recently, it has been shown that in some cases the enhanced electrocatalytic activity of graphene and its derivatives can be attributed to metal impurities rather than to nonmetal elements. In this paper, we investigated the electrocatalytical properties of B/N codoped graphene with respect to the content of metallic impurities introduced by the synthesis procedures. For this purpose, a permanganate (Hummers) and a chlorate (Hofmann) route were used for the preparation of the starting graphene oxides (GO). The GO used for the synthesis of B/N codoped graphene had significantly difference compositions of oxygen functionalities as well as metallic impurities introduced by the different synthetic procedures. We performed a detailed structural and chemical analysis of the doped graphene samples to correlate their electrocatalytic activity with the concentration of incorporated boron and nitrogen as well as metallic impurities. [ABSTRACT FROM AUTHOR]

Controlling the shape of the conducting polymer-noble metal composites is a key factor in determining their properties and applications. In this paper, we demonstrate a novel strategy to fabricate Au-polypyrrole (PPy) composites with unusual morphology using poly(4-vinylpyridine) (P4VP) brush grafted on graphene oxide (GO) as a reaction chamber. When the GO/P4VP brush bearing AuCl4− ions is exposed to pyrrole vapor or directly immersed into pyrrole solution, novel Au−PPy nanotubules and flower-like Au mesoparticles-PPy composites are formed on the surface of GO/P4VP brush, respectively. The application of the as-prepared GO/P4VP/Au−PPy composites in catalysis and surface-enhanced Raman scattering (SERS) are investigated. The relevant results exhibit that the GO/P4VP/Au−PPy nanotubules can act as an efficient catalyst for reduction of 4-nitrophenol, and the GO/P4VP/flower-like Au mesoparticles-PPy composites can be used as a sensor platform for the detection of organic molecules by SERS. [ABSTRACT FROM AUTHOR]

In view of their intensive use as ligands in many reactions catalyzed by transition-metal complexes, modulation of the bonding properties of N-heterocyclic carbenes (NHCs) on a rational basis is highly desirable, which should enable optimization of current applications or even promote new functions. In this paper, we provide a quantitative analysis of the chemical bond between a metal fragment AuCl and a series of 29 different NHCs in [(NHC)AuCl] complexes. NHCs electronic properties are modified through: i) variation of the groups attached to the NHC nitrogen atoms or backbone; ii) change of unsaturation/size of the NHC ring; iii) inclusion of paracyclophane moieties; or iv) heteroatom substitution on the NHC ring. For evaluating the donation and back-donation components of the Dewar-Chatt-Duncanson (DCD) model in the NHC−AuCl bond, we apply the charge-displacement (CD) analysis within the NOCV (natural orbitals for chemical valence) framework, a methodology that avoids the constraint of using symmetrized structures. We show that modulation of the NHC bonding properties requires substantial modification of their structure, such as, for instance, insertion of two ketone groups into the NHC backbone (which enhances the π back-donation bond component and introduces an effective electronic communication within the NHC ring) or replacement of a nitrogen atom in the ring with an sp3 or sp2 carbon atom (which increases and decreases the π back-donation bond component, respectively). We extend our investigation by quantitatively comparing the NHC electronic structures for a subset of 13 NHCs in [(NHC)PPh] adducts, the 31P NMR chemical shift values of which are experimentally available. The latter have been considered as a suitable tool for measuring the NHCs π acceptor properties [Bertrand et al., Angew. Chem. Int. Ed. 2013, 52, 2939-2943]. We show that information obtained using the metal fragment can be transferred to the PPh moiety and vice versa. However, the 31P NMR chemical shift values only qualitatively correlate with the π acceptor properties of the NHCs, with the stronger π acidic carbenes as the most outliners. [ABSTRACT FROM AUTHOR]

The phosphanoxy‐substituted phosphaalkene bearing the P=C−O−P skeleton can be prepared from diphosphene Mes*P=PMes* (Mes*=2,4,6‐tBu3C6H2), and their use for catalysis is of interest. In this paper, complexation of the phosphanoxy‐substituted phosphaalkenes with gold are investigated, and the catalytic activity of the mono‐ and bis(chlorogold) complexes are subsequently evaluated. Reaction of the P=C−O−P compound with (tht)AuCl (tht=tetrahydrothiophene) showed dominant coordination on the sp3 phosphorus, and complete coordination on the sp2 phosphorus required removal of tetrahydrothiophene. Atoms In Molecules (AIM) analysis based on the X‐ray structure of the mono(chlorogold) complex indicated a pseudo coordinating interaction between the gold center and the P=C unit. The bis(chlorogold) complexes displayed conformational isomerism, and catalyzed the cycloisomerization/alkoxycyclization of 1,6‐enyne and for hydration of terminal alkyne without activation treatment. Even the mono(chlorogold) complexes catalyzed the alkoxycyclization reactions without a silver co‐catalyst, indicating that the alcohols were effective in activating the AuCl unit. [ABSTRACT FROM AUTHOR]

All studies on oxygen‐evolution reaction by Mn oxides in the presence of cerium(IV) ammonium nitrate (CAN) have been so far carried out by synthesizing Mn oxides in the first step. And then, followed by the investigation of the Mn oxides in the presence of oxidants for oxygen‐evolution reaction (OER). This paper presents a case study of a new and promising strategy for in situ catalyst synthesis by the adding MnII to either CAN or KMnO4/CAN solution, resulting in the formation of Mn‐based catalysts for OER. The catalysts were characterized by scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, X‐ray absorption spectroscopy, and X‐ray photoelectron spectroscopy. Both compounds contained nano‐sized particles that catalyzed OER in the presence of CAN. The turnover frequencies for both catalysts were 0.02 (mmolO2 /molMn⋅s). [ABSTRACT FROM AUTHOR]

Colloidal quantum dot (QD) photocatalysts have the electrochemical and optical properties to be highly effective for a range of redox reactions. QDs are proven photo‐redox catalysts for a variety of reactions in organic solvents but are less prominent for aqueous reactions. Aqueous QD photocatalysts require hydrophilic ligand shells that provide long‐term colloidal stability but are not so tight‐binding as to prevent catalytic substrates from accessing the QD surface. Common thiolate ligands, which also poison many co‐catalysts and undergo photo‐oxidative desorption, are therefore often not an option. This paper describes a framework for the design of water‐solubilizing ligands that are in dynamic exchange on and off the QD surface, but still provide long‐term colloidal stability to CdS QDs. The binding affinity and inter‐ligand electrostatic interactions of a bifunctional ligand, aminoethyl phosphonic acid (AEP), are tuned with the pH of the dispersion. The key to colloidal stability is electrostatic stabilization of the monolayer. This work demonstrates a means of mimicking the stabilizing power of a thiolate‐bound ligand with a zwitterionic tail group, but without the thiolate binding group. [ABSTRACT FROM AUTHOR]

Electrocatalytic hydrogen gas production is considered a potential pathway towards carbon‐neutral energy sources. However, the development of this technology is hindered by the lack of efficient, cost‐effective, and environmentally benign catalysts. In this study, a main‐group‐element‐based electrocatalyst, SbSalen, is reported to catalyze the hydrogen evolution reaction (HER) in an aqueous medium. The heterogenized molecular system achieved a Faradaic efficiency of 100 % at −1.4 V vs. NHE with a maximum current density of −30.7 mA/cm2. X‐ray photoelectron spectroscopy of the catalyst‐bound working electrode before and after electrolysis confirmed the molecular stability during catalysis. The turnover frequency was calculated as 43.4 s−1 using redox‐peak integration. The kinetic and mechanistic aspects of the electrocatalytic reaction were further examined by computational methods. This study provides mechanistic insights into main‐group‐element electrocatalysts for heterogeneous small‐molecule conversion. [ABSTRACT FROM AUTHOR]

Lignosulfonate (LS) is an organic waste generated as a byproduct of the cooking process in sulfite pulping in the manufacture of paper. In this paper, LS was used as an anionic supporting material for immobilizing cationic species, which can then be used as heterogeneous catalysts in some organic transformations. With this strategy, three lignin-supported catalysts were prepared including 1) lignin-SO3Sc(OTf)2, 2) lignin-SO3Cu(OTf), and 3) lignin-IL@NH2 (IL=ionic liquid). These solid materials were then examined in many organic transformations. It was finally found that, compared with its homogeneous counterpart as well as some other solid catalysts that are prepared by using different supports with the same metal or catalytically active species, the lignin-supported catalysts showed better performance in these reactions not only in terms of activity but also with regard to recyclability. [ABSTRACT FROM AUTHOR]

Gallium hydrides stabilised by primary and secondary amines are scarce due to their propensity to eliminate dihydrogen. Consequently, their reactivity has received limited attention. The synthesis of two novel gallium hydride complexes HGa(THF)[ON(H)O] and H2Ga[μ2‐ON(H)O]Ga[ON(H)O] ([ON(H)O]2−=N,N‐bis(3,5‐di‐tert‐butyl‐2‐phenoxy)amine) is described and their reactivity towards aldehydes and ketones is explored. These reactions afford alkoxide‐bridged dimers through 1,2‐hydrogallation reactions. The gallium hydrides can be regenerated through Ga−O/B−H metathesis from the reaction of such dimers with pinacol borane (HBpin) or 9‐borabicyclo[3.3.1]nonane (9‐BBN). These observations allowed us to target the catalytic reduction of carbonyl substrates (aldehydes, ketones and carbon dioxide) with low catalyst loadings at room temperature. [ABSTRACT FROM AUTHOR]

Heterogenized photoredox catalysts provide a path for sustainable chemical synthesis using highly tunable, reusable constructs. Here, heterogenized iridium complexes as photoredox catalysts were assembled via covalent attachment to metal oxide surfaces (ITO, ZrO2, Al2O3) in thin film or nanopowder constructs. The goal was to understand which materials provided the most promising constructs for catalysis. To do this, reductive dehalogenation of bromoacetophenone to acetophenone was studied as a test reaction for system optimization. All catalyst constructs produced acetophenone with high conversions and yields with the fastest reactions complete in fifteen minutes using Al2O3 supports. The nanopowder catalysts resulted in faster and more efficient catalysis, while the thin film catalysts were more robust and easily reused. Importantly, the thin film constructs show promise for future photoelectrochemical and electrochemical photoredox setups. Finally, all catalysts were reusable 2–3 times, performing at least 1000 turnovers (Al2O3), demonstrating that heterogenized catalysts are a sustainable catalyst alternative. [ABSTRACT FROM AUTHOR]

In an effort to combine the favorable catalytic properties of Co3O4 and CeO2, nanocomposites with different phase distribution and Co3O4 loading were prepared and employed for CO oxidation. Synthesizing Co3O4‐modified CeO2 via three different sol‐gel based routes, each with 10.4 wt % Co3O4 loading, yielded three different nanocomposite morphologies: CeO2‐supported Co3O4 layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO‐TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co3O4 surface layer, reducing the light‐off temperature of CeO2 by about 200 °C. In contrast, intermixed oxides and Co‐doped CeO2 suffered from lower dispersion and organic residues, respectively. The performance of Co3O4‐CeO2 nanocomposites was optimized by varying the Co3O4 loading, characterized by X‐ray diffraction (XRD) and N2 sorption (BET). The 16–65 wt % Co3O4−CeO2 catalysts approached the conversion of 1 wt % Pt/CeO2, rendering them interesting candidates for low‐temperature CO oxidation. [ABSTRACT FROM AUTHOR]

The interaction of molecules, especially hydrocarbons, at the gas/ionic liquid (IL) surface plays a crucial role in supported IL catalysis. The dynamics of this process is investigated by measuring the trapping probabilities of n‐butane, iso‐butane and 1‐butene on a set of frozen 1‐alkyl‐3‐methylimidazolium‐based ILs [CnC1Im]X, where n=4, 8 and X−=Cl−, Br−, [PF6]− and [Tf2N]−. The decrease of the initial trapping probability with increasing surface temperature is used to determine the desorption energy of the hydrocarbons at the IL surfaces. It increases with increasing alkyl chain length n and decreasing anion size for the ILs studied. We attribute these effects to different degrees of alkyl chain surface enrichment, while interactions between the adsorbate and the anion do not play a significant role. The adsorption energy also depends on the adsorbing molecule: It decreases in the order n‐butane>1‐butene>iso‐butane, which can be explained by different dispersion interactions. [ABSTRACT FROM AUTHOR]

Fuel cells, water electrolyzers, and metal-air batteries are important energy systems that have started to play some roles in our renewable energy landscapes. However, despite much research works carried out on them, they have not yet found large-scale applications, mainly due to the unavailability of sustainable catalysts that can catalyze the reactions employed in them. Currently, noble metal-based materials are the ones that are commonly used as catalysts in most commercial fuel cells, electrolyzers, and metal-air batteries. Hence, there has been considerable research efforts worldwide to find alternative noble metal-free and metal-free catalysts composed of inexpensive, earth-abundant elements for use in the catalytic reactions employed in these energy systems. In this concept paper, a brief introduction on catalysis in renewable energy systems, followed by the recent efforts to develop sustainable, heteroatom-doped carbon and non-noble metal-based electrocatalysts, the challenges to unravel their structure-catalytic activity relationships, and the authors' perspectives on these topics and materials, are discussed. [ABSTRACT FROM AUTHOR]

Metal nitrenoids and metal carbenoids exhibit similar reactivity for insertion into a C−H bond and a C=C double bond. These reactions have attracted the attention of organic chemists due to their unusual bond-forming ability, but the reactivity difference between these chemical species has not been studied. In this paper, we examined the reactivity difference using the corresponding Rh nitrenoid and Rh carbenoid precursors. The Rh nitrenoid inserted into an intramolecular C( sp 3)−H bond adjacent to an amide nitrogen, affording functionalized spiroaminals that are ubiquitous in natural products, while the Rh carbenoid inserted into an amide C−N bond. The totally different reactivity was rationalized by the relatively low energy barrier for the C−H insertion reaction of the Rh nitrenoid. Computational analysis suggests that the origin of the discrepancy is the electrophilicity of the coordinating atoms to the Rh complex. [ABSTRACT FROM AUTHOR]

A phosphine‐catalyzed approach to pyrrolines has been developed that involves two mechanistically unlinked catalytic processes. The first involves the redox isomerization of amino crotonates to provide access to aliphatic tosyl imines, which then engage in a (3+2) annulation with various allenoates. The reaction shows generality, with 24 examples established, along with a low yielding and moderately enantioselective variant. Mechanistic studies indicate that the viability of the process is linked to the selection of catalysts with similar propensity to add to the two coupling partners. [ABSTRACT FROM AUTHOR]

Ruthenium‐ and copper‐catalyzed propargylic substitution reactions of propargylic alcohol derivatives with N‐monosubstituted hydrazones as ambident nucleophiles are achieved in which N‐monosubstituted hydrazones exhibit impressive different reactivities depending on different catalytic systems, behaving as carbon‐centered nucleophiles to give the corresponding propargylic alkylated products in ruthenium catalysis, or as nitrogen‐centered nucleophiles to afford the corresponding propargylic aminated products in copper catalysis. DFT calculations were carried out to investigate the detailed reaction pathways of these two systems. Further transformation of propargylic substituted products affords the corresponding multisubstituted pyrazoles as cyclization products in good to high yields. [ABSTRACT FROM AUTHOR]

The modular synthesis of Au(I)/Ru(II) decorated mono‐ and heterobimetallic complexes with π‐conjugated [2.2]paracyclophane is described. [2.2]Paracyclophane serves as a rigid spacer which holds the metal centers in precise spatial orientations and allows metal‐to‐metal distance modulation. A broad set of architectural arrangements of pseudo ‐geminal, ‐ortho, ‐meta, and ‐para substitution patterns were employed. Metal‐to‐metal distance modulation of Au(I)/Ru(II) heterobimetallic complexes and the innate transannular π‐communication of the cyclophanyl scaffold provides a promising platform for the investigations of structure‐activity relationship and cooperative effects. The Au(I)/Ru(II) heterobimetallic cyclophanyl complexes are stable, easily accessible, and exhibit promising catalytic activity in the visible‐light promoted arylative Meyer‐Schuster rearrangement. [ABSTRACT FROM AUTHOR]

The noncovalent interactions of heavy pnictogens with π‐arenes play a fundamental role in fields like crystal engineering or catalysis. The strength of such bonds is based on an interplay between dispersion and donor/acceptor interactions, and is generally attributed to the presence of π‐arenes. Computational studies of the interaction between the heavy pnictogens As, Sb and Bi and cyclohexane, in comparison with previous studies on the interaction between heavy pnictogens and benzene, show that this concept probably has to be revised. A thorough analysis of all the different energetic components that play a role in these systems, carried out with state‐of‐the‐art computational methods, sheds light on how they influence one another and the effect that their interplay has on the overall system. Furthermore, the analysis of such interactions leads us to the unexpected finding that the presence of the pnictogen compounds strongly affects the conformational equilibrium of cyclohexane, reversing the relative stability of the chair and boat‐twist conformers, and thus suggesting a possible application of tuneable dispersion energy donors to stabilise the desired conformation. [ABSTRACT FROM AUTHOR]

Two major hurdles in NP‐based catalysis are the aggregation of the NPs and their recycling. Immobilization of NPs onto a 2D support is the most promising strategy to overcome these difficulties. Herein, amphiphilicity‐driven self‐assembly of galactose‐hexaphenylbenzene‐based amphiphiles into galactose‐decorated 2D nanosheet is reported. The extremely dense decoration of reducing sugar on the surface of the sheets is used for the in situ synthesis and immobilization of ultrafine catalytically active AgNPs by using Tollens' reaction. The potential of the system as a catalyst for the reduction of various nitroaromatics is demonstrated. Enhanced catalytic activity is observed for the immobilized AgNPs when compared to the corresponding discrete AgNPs. Recovery of the catalytic system from the reaction mixture by ultrafiltration and its subsequent recycling for several cycles without dropping its activity is shown. This is the first report demonstrating the in situ synthesis and immobilization of ultrafine AgNPs onto a 2D nanosheet that exhibits excellent catalytic performance for the reduction of nitroaromatics. [ABSTRACT FROM AUTHOR]

Novel seven‐membered cyclic imine‐based 1,3‐P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These "cycloiminophosphanes" possess flexible non‐isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P‐κ1‐ and P,N‐κ2‐tungsten(0) carbonyl complexes, by determining the IR frequency of the trans‐CO ligands. Complexes with [RhCp*Cl2]2 demonstrated the hemilability of the ligands, giving a dynamic equilibrium of κ1 and κ2 species; treatment with AgOTf gives full conversion to the κ2 complex. The potential for catalysis was shown in the RuII‐catalyzed, solvent‐free hydration of benzonitrile and the RuII‐ and IrI‐catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l‐menthone, as well as their P,N‐κ2‐RhIII and a P‐κ1‐RuII complexes. [ABSTRACT FROM AUTHOR]

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications is reported. Calculations of Hydride Ion Affinity (HIA) values indicate high carbon‐based Lewis acidity at the ortho and para positions. This arises in part from extensive LUMO delocalization across the aromatic backbones. Species [C10H6R2N2CH2CH2]2+ (R=H [1 a]2+, Me [1 f]2+, tBu [1 g]2+), and [C12H4R4N2CH2CH2]2+ (R=H [2 a]2+, Me [2 b]2+) were prepared and evaluated for use in the initiation of hydrodefluorination (HDF) catalysis. Compound [2 a]2+ proved highly effective towards generating catalytically active silylium cations via Lewis acid‐mediated hydride abstraction from silane. This enabled the HDF of a range of aryl‐ and alkyl‐ substituted sp3(C−F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis‐2,4,6‐(CF3)3C6H9. The dications are shown to act as hydride acceptors with the isolation of neutral species C16H14N2 (3 a) and C16H10Me4N2 (3 b) and monocationic species [C14H13N2]+ ([4 a]+) and [C18H21N2]+ ([4 b]+). Experimental and computational data provide further support that the dications are initiators in the generation of silylium cations. [ABSTRACT FROM AUTHOR]

The nonheme iron dioxygenase 2‐(trimethylammonio)‐ethylphosphonate dioxygenase (TmpA) is an enzyme involved in the regio‐ and chemoselective hydroxylation at the C1‐position of the substrate as part of the biosynthesis of glycine betaine in bacteria and carnitine in humans. To understand how the enzyme avoids breaking the weak C2−H bond in favor of C1‐hydroxylation, we set up a cluster model of 242 atoms representing the first and second coordination sphere of the metal center and substrate binding pocket, and investigated possible reaction mechanisms of substrate activation by an iron(IV)‐oxo species by density functional theory methods. In agreement with experimental product distributions, the calculations predict a favorable C1‐hydroxylation pathway. The calculations show that the selectivity is guided through electrostatic perturbations inside the protein from charged residues, external electric fields and electric dipole moments. In particular, charged residues influence and perturb the homolytic bond strength of the C1−H and C2−H bonds of the substrate, and strongly strengthens the C2−H bond in the substrate‐bound orientation. [ABSTRACT FROM AUTHOR]

While the generation of aryl radicals by photoredox catalysis under reductive conditions is well documented, it has remained challenging under an oxidative pathway. Because of the easy photo‐oxidation of alkyl bis‐catecholato silicates, a general study of phenyl silicates bearing substituted catecholate ligands has been achieved. The newly synthesized phenyl silicates have been fully characterized, and their reactivity has been explored. It was found that, thanks to the substitution of the catecholate moiety, notably with the 4‐cyanocatecholato ligand, the phenyl radical could be generated and trapped. Computational studies provided a rationale for these findings. [ABSTRACT FROM AUTHOR]

Fluorinated heterocycles have attracted much attention in the pharmaceutical and agrochemical industries. Many strategies have already been developed to achieve the synthesis of fluorinated heterocycles. Formidable challenges remain, however, in the synthesis of fluorinated isocoumarin derivatives that are among the most alluring structural motifs. Herein, the indium‐catalyzed C−F bond transformation of 2‐(2,2‐difluorovinyl) benzoates is reported, which are readily accessible compounds, to give a diverse array of fluorinated isocoumarins. The present reaction proceeds smoothly using inexpensive reagents: a catalytic amount of indium salt in the presence of zinc salt. A theoretical calculation of potential energy profiles showed that the reaction consists of oxymetalation with the elimination of alkyl halide and the β‐fluorine elimination. [ABSTRACT FROM AUTHOR]

The article abstracts of various research papers that were recently been published in sister journals of the "Chemistry: A European Journal," including papers on synthesis of lactones, biosynthesis of lactic acid and homogeneous catalysis.

In this paper, a facile strategy is reported for the preparation of well-dispersed Pt nanoparticles in ordered mesoporous silica (Pt@OMS) by using a hybrid mesoporous phenolic resin-silica nanocomposite as the parent material. The phenolic resin polymer is proposed herein to be the key in preventing the aggregation of Pt nanoparticles during their formation process and making contributions both to enhance the surface area and enlarge the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas-phase oxidation of CO and liquid-phase hydrogenation of 4-nitrophenol. This work might open new avenues for the preparation of noble metal nanoparticles in mesoporous silica with unique structures for catalytic applications. [ABSTRACT FROM AUTHOR]

The synthesis of molecules bearing (trifluoromethylselenyl)methylchalcogenyl groups is described via an efficient two‐step strategy based on a metal‐free photoredox catalyzed decarboxylative trifluoromethylselenolation with good yields up to 88 %, which raised to 98 % in flow chemistry conditions. The flow methods allowed also to scale up the reaction. The mechanism of this key reaction was studied. The physicochemical characterization of these emerging groups was performed by determining their Hansch–Leo lipophilicity parameters with high values up to 2.24. This reaction was also extended to perfluoroalkylselenolation with yields up to 95 %. Finally, this method was successfully applied to the functionalization of relevant bioactive molecules such as tocopherol or estrone derivatives. [ABSTRACT FROM AUTHOR]

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3‐E)GaCl4 [(3‐E).+ = [{(IPr)C(Ph)E}2Fe(CO)3].+, E = P or As; IPr = C{(NDipp)CH}2, Dipp = 2,6‐iPr2C6H3] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E}2 (1‐E) with Fe2(CO)9 affords [{(IPr)C(Ph)E}2Fe(CO)3] (2‐E), in which 1‐E binds to the Fe atom in an allylic (η3‐EECvinyl) fashion and functions as a 4e donor ligand. Complexes 2‐E undergo 1e oxidation with GaCl3 to yield (3‐E)GaCl4. Spin density analysis revealed that the unpaired electron in (3‐E).+ is mainly located on the Fe (52–64 %) and vinylic C (30–36 %) atoms. Further 1e oxidation of (3‐E)GaCl4 leads to unprecedented η3‐EECvinyl to η3‐ECvinylCPh coordination shuttling to form the dications (4‐E)(GaCl4)2. [ABSTRACT FROM AUTHOR]

Catalytic carbene‐transfer reactions constitute a class of highly useful transformations in organic synthesis. Although catalysts based on a range of transition‐metals have been reported, the readily accessible nickel(II)‐based complexes have been rarely used. Herein, an air‐stable nickel(II)‐carborane complex is reported as a well‐defined, versatile and recyclable catalyst for selective carbene transfer reactions with low catalyst loading under mild conditions. This catalyst is effective for several types of reactions including diastereoselective cyclopropanation, epoxidation, selective X−H insertions (X = C, N, O, S, Si), particularly for the unprotected substrates. This represents a rare example of carborane ligands in base metal catalysis. [ABSTRACT FROM AUTHOR]

Direct arylation of most five‐membered ring heterocycles are generally easily accessible and strongly favored at the α‐position using classical palladium‐catalysis. Conversely, regioselective functionalization of such heterocycles at the concurrent β‐position remains currently very challenging. Herein, we report general conditions for regioselective direct arylation at the β‐position of pyrazoles, while C−H α‐position is free. By using aryl bromides as the aryl source and a judicious choice of solvent, the arylation reaction of variously N‐substituted pyrazoles simply proceeds via β‐C−H bond functionalization. The β‐regioselectivity is promoted by a ligand‐free palladium catalyst and a simple base without oxidant or further additive, and tolerates a variety of substituents on the bromoarene. DFT calculations revealed that a protic solvent such as 2‐ethoxyethan‐1‐ol significantly enhances the acidity of the proton at β‐position of the pyrazoles and thus favors this direct β‐C−H bond arylation. This selective pyrazoles β‐C−H bond arylation was successfully applied for the straightforward building of π‐extended poly(hetero)aromatic structures via further Pd‐catalyzed combined α‐C−H intermolecular and intramolecular C−H bond arylation in an overall highly atom‐economical process. [ABSTRACT FROM AUTHOR]

The combination of synthesis, rotating ring‐disk electrode (RRDE) and cyclic voltammetry (CV) measurements, and computational investigations with the aid of DFT methods shows how a thiourea, a squaramide, and a bissulfonamide as additives affect the EqCr equilibrium of Cp2TiCl2. We have, for the first time, provided quantitative data for the EqCr equilibrium and have determined the stoichiometry of adduct formation of [Cp2Ti(III)Cl2]−, [Cp2Ti(III)Cl] and [Cp2Ti(IV)Cl2] and the additives. By studying the structures of the complexes formed by DFT methods, we have established the Gibbs energies and enthalpies of complex formation as well as the adduct structures. The results not only demonstrate the correctness of our use of the EqCr equilibrium as predictor for sustainable catalysis. They are also a design platform for the development of novel additives in particular for enantioselective catalysis. [ABSTRACT FROM AUTHOR]

In this work, we present a new synthetic strategy for fourfold‐substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X‐ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)‐graft‐poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3S13]2− clusters in aqueous solution for stable visible light driven hydrogen evolution over three days. [ABSTRACT FROM AUTHOR]

C−H hydroxylation of aryl acetamides and alkyl phenylacetyl esters was accomplished via challenging distal weak O‐coordination by versatile ruthenium(II/IV) catalysis. The ruthenium(II)‐catalyzed C−H oxygenation of aryl acetamides proceeded through C−H activation, ruthenium(II/IV) oxidation and reductive elimination, thus providing step‐economical access to valuable phenols. The p‐cymene‐ruthenium(II/IV) manifold was established by detailed experimental and DFT‐computational studies. [ABSTRACT FROM AUTHOR]

Asymmetrically substituted tertiary phosphines and quaternary phosphonium salts are used extensively in applications throughout industry and academia. Despite their significance, classical methods to synthesize such compounds often demand either harsh reaction conditions, prefunctionalization of starting materials, highly sensitive organometallic reagents, or expensive transition‐metal catalysts. Mild, practical methods thus remain elusive, despite being of great current interest. Herein, we describe a visible‐light‐driven method to form these products from secondary and primary phosphines. Using an inexpensive organic photocatalyst and blue‐light irradiation, arylphosphines can be both alkylated and arylated using commercially available organohalides. In addition, the same organocatalyst can be used to transform white phosphorus (P4) directly into symmetrical aryl phosphines and phosphonium salts in a single reaction step, which has previously only been possible using precious metal catalysis. [ABSTRACT FROM AUTHOR]

The application of computational methods to predict mutations that can enhance the catalytic power of enzymes can be of great importance, since it allows a more rational and directed way to mutate the enzymes, which can save time and resources compared to producing mutations at random. We present computational methods to predict mutations that enhance the catalytic rate of DszD, an enzyme that intervenes in the 4S pathway together with DszA, DszB and DszC. This has potential as a cheaper and greener alternative for biodesulfurization of crude oil. More information can be found in the Full Paper by Ramos et al. on page 17231 ff. [ABSTRACT FROM AUTHOR]

Guanosine‐rich DNA sequences can fold into quadruplex structures which are not only biologically relevant, but also promising for applications in aqueous homogenous catalysis. Here, an asymmetric Michael addition is catalyzed by covalently modified G‐quadruplexes in combination with copper ions. Using systematic chemical variation and various spectrometric techniques, the key parameters that govern rate acceleration and stereoselectivity were identified. More information can be found in the Full Paper by A. Jäschke et al. on page 12162 ff. [ABSTRACT FROM AUTHOR]

The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW12O40]3− (PW12) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg0.73Al0.22(OH)2 [PW12O40]0.04⋅0.98 H2O (Mg3Al-PW12) has been successfully obtained by applying a spontaneous flocculation method. The Mg3Al-PW12 has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT-IR, NMR, BET). XRD patterns of Mg3Al-PW12 exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg3Al-PW12 as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z-CH2-Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents ( V2-propanol: Vwater=2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg3Al-PW12 composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg3Al-PW12-catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction. [ABSTRACT FROM AUTHOR]

This paper reports on the development of an efficient synthesis of enantiopure phospha[6]helicenes through a [2+2+2] alkyne cyclotrimerization reaction. The corresponding gold complexes proved to be highly efficient both in terms of catalytic activity and enantioselectivity in [2+2] and [4+2] cycloaddition reactions. Furthermore, in the presence of an external nucleophile, such as water or alcohols, the tandem cyclization/addition reactions take place in high yields and excellent diastereo- and enantioselectivities. [ABSTRACT FROM AUTHOR]

The cover picture highlights eight of the papers published in this themed issue, specially put together for the 17th International Symposium on Silicon Chemistry. In the top row from left to right: R. West et al. (p. 9184 ff.), P. Jutzi (p. 9192 ff.), and S. E. Denmark et al. (p. 9268 ff.). In the middle row: left C. Limberg and D. Pinkert (p. 9166 ff.) and right H. ‐ J. Freund et al. (p. 9176 ff.). In the bottom row from left to right: Y. Kaneko et al. (p. 9394 ff.), A. Filippou et al. (p. 9280 ff.), and G. H. Robinson et al. (p. 9208 ff.). The range of papers reflects how silicon chemistry can provide a platform for synergistic solutions through novel method developments of synthetic and analytical tools and the interconnection of different disciplines in molecular and materials chemistry. [ABSTRACT FROM AUTHOR]

Iridium stands at the center of a vortex of electrons that are transferred to and from the surrounding reaction components in this radical aminocarbonylation method. The combination of visible ‐ light irradiation and low ‐ pressure ex situ carbon monoxide generation makes this an attractive and operationally simple approach for preparing β ‐ hydride ‐ containing alkyl amides. Additional cover art acknowledgements: Bobo Skillinghaug and Johan Sjöstedt. More information can be found in the Full Paper by L. R. Odell et al. on page 9155 ff. [ABSTRACT FROM AUTHOR]

This paper describes the development of a palladium-catalyzed decarboxylative inter- and intramolecular condensation reaction of isoxazol-5(4 H)-ones with carbonyl compounds in the presence of PPh3, giving various 2-azabuta-1,3-dienes or pyrroles in moderate to high yields. [ABSTRACT FROM AUTHOR]

Highly reduced, anionic cobalt complexes supported by bis(iminoacenaphthene) diimine (BIAN) ligands catalyze the dehydrogenation of amine boranes. Using the same catalysts, transfer hydrogenations of olefins, imines, and N‐heteroarenes with ammonia borane as a dihydrogen surrogate have been developed. Challenging trisubstituted olefins can be reduced under an external H2 pressure with ammonia borane as an activator. The cover image shows a transfer hydrogenation reaction of quinoline, an ammonia borane molecule, and the molecular structure of a precatalyst complex, where 1,5‐cyclooctadiene serves as a placeholder for vacant coordination sites. The silhouette of the beautiful city of Regensburg, Germany, where most of this work was performed, is displayed in the background. More information can be found in the Full Paper by R. Wolf, A. Jacobi von Wagelin et al. on page 238. [ABSTRACT FROM AUTHOR]

Is S2N2 aromatic? According to off‐nucleus shielding calculations reported here, S2N2 is the first example of an inorganic ring showing substantial changes in aromaticity upon transition from the aromatic ground state to either the strongly antiaromatic and unstable first singlet excited, or the antiaromatic lowest triplet electronic states. More information can be found in the Full Paper by P. B. Karadakov et al. on page 16803. [ABSTRACT FROM AUTHOR]

The importance and functional relevance of S⋅⋅⋅Sn tetrel‐bonding interactions in the activation of peroxisome proliferator‐activated receptors (PPARs) by organotin molecules was evidenced using a combined theoretical and Protein Data Bank analysis. In the figure, three hummingbirds carrying sulfur atoms establish tetrel‐bonding interactions with the organotin molecules that hang from the tree trunk. These molecules are anchored to the protein through the establishment of covalent S−Sn bonds. More information can be found in the Full Paper by A. Bauzá et al. on page 16576. [ABSTRACT FROM AUTHOR]

Biocatalysis γ‐Butyrobetaine hydroxylase (BBOX) contains an aromatic cage for the recognition of the positively charged trimethylammonium group of its γ‐butyrobetaine (γBB) substrate. Enyzme binding and kinetic analyses on substrate analogues with P and As substituting for N in the trimethylammonium group show that the analogues are good BBOX substrates, which follow the efficiency trend N+>P+>As+, but an uncharged carbon analogue of γBB is not a good BBOX substrate, thus highlighting the importance of energetically favorable cation–π interactions in productive substrate recognition. For more information, see the Full Paper from J. Mecinović et al. on page 1270 ff. [ABSTRACT FROM AUTHOR]