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Nitrogenase is the enzyme that converts N2 to NH3 under ambient conditions. The chemical mechanism of this catalysis at the active site FeMo‐co [Fe7S9CMo(homocitrate)] is unknown. An obligatory co‐product is H2, while exogenous H2 is a competitive inhibitor. Isotopic substitution using exogenous D2 revealed the N2‐dependent reaction D2+2H++2e−→2HD (the 'HD reaction'), together with a collection of additional experimental characteristics and requirements. This paper describes a detailed mechanism for the HD reaction, developed and elaborated using density functional simulations with a 486‐atom model of the active site and surrounding protein. First D2 binds at one Fe atom (endo‐Fe6 coordination position), where it is flanked by H−Fe6 (exo position) and H−Fe2 (endo position). Then there is synchronous transfer of these two H atoms to bound D2, forming one HD bound to Fe2 and a second HD bound to Fe6. These two HD dissociate sequentially. The final phase is recovery of the two flanking H atoms. These H atoms are generated, sequentially, by translocation of a proton from the protein surface to S3B of FeMo‐co and combination with introduced electrons. The first H atom migrates from S3B to exo‐Fe6 and the second from S3B to endo‐Fe2. Reaction energies and kinetic barriers are reported for all steps. This mechanism accounts for the experimental data: (a) stoichiometry; (b) the N2‐dependence results from promotional N2 bound at exo‐Fe2; (c) different N2 binding Km for the HD reaction and the NH3 formation reaction results from involvement of two different sites; (d) inhibition by CO; (e) the non‐occurrence of 2HD→H2+D2 results from the synchronicity of the two transfers of H to D2; (f) inhibition of HD production at high pN2 is by competitive binding of N2 at endo‐Fe6; (g) the non‐leakage of D to solvent follows from the hydrophobic environment and irreversibility of proton introduction. [ABSTRACT FROM AUTHOR]

A first‐generation pair of chemiluminescent formaldehyde (FA) probes (CFAP540 and CFAP700) was reported recently. CFAP540 and CFAP700, with high selectivity and sensitivity to FA, are, respectively, suitable in cell and in vivo. Experimentalists have confirmed that both probes utilize a general 2‐aza‐Cope FA‐reactive trigger and a chemiluminogenic phenoxydioxetane scaffold. The mechanism and detailed process of CFAP chemiluminescence (CL) remain largely unknown. In the present paper, (time‐dependent) density functional theory calculations are performed on the entire reaction process of CFAP540 with FA to produce CL. The calculations elucidated the CL‐producing process: FA initiates the decomposition of CFAP540 by dehydration condensation, and a phenoxy 1,2‐dioxetane is formed through a series of reactions of aza‐Cope rearrangement, hydrolysis of imine, and β‐elimination of alkoxyl group. Afterwards, the produced phenoxy 1,2‐dioxetane decomposes to produce the m‐oxybenzoate derivative in the first singlet state (S1) via two crossings between potential energy surfaces of the ground state (S0) and S1 state. This m‐oxybenzoate derivative was assigned as the light emitter of the CFAP540 CL. The CL‐producing process and assignment of the light emitter of CFAP700 CL are similar with the corresponding ones of CFAP540. By analyzing the D‐π‐A architecture of the light emitters of CFAP540 and CFAP700, a series of CFAPs is theoretically designed and a scheme to modulate their CL from visible to near‐infrared region is proposed by adjusting the length and structure of the π‐bridge. [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 design of new biocatalysts is a goal in biotechnology to improve the rate, selectivity and environmental impact of industrial chemical processes. In this regard, the use of computational techniques has provided valuable assistance in the design of new enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM molecular dynamics simulations have allowed insights to be gained on the origin of the limited efficiency of a computationally designed enzyme for the Kemp elimination; the HG-3. Comparison of results derived from this enzyme with those of a more evolved protein containing additional point mutations, HG-3.17, rendered important information that should be taken into account in the design of new enzymes. For this Kemp eliminase reaction, higher reactivity has been demonstrated to be related to a better electrostatic preorganisation of an environment that creates a more favourable electrostatic potential for the reaction to proceed. The limitations of HG-3 can be related to a lack of flexibility, a not well-fitted active site, and a lack of protein electrostatic preorganisation, which decrease the reorganisation around the oxyanion hole. [ABSTRACT FROM AUTHOR]

Bacterial bioluminescence with continuous glow has been applied to the fields of environmental toxin monitoring, drug screening, and in vivo imaging. Nonetheless, the chemical form of the bacterial bioluminophore is still a bone of contention. Flavin mononucleotide (FMN), one of the light-emitting products, and 4a-hydroxy-5-hydro flavin mononucleotide (HFOH), an intermediate of the chemical reactions, have both been assumed candidates for the light emitter because they have similar molecular structures and fluorescence wavelengths. The latter is preferred in experiments and was assigned in our previous density functional study. HFOH displays weak fluorescence in solutions, but exhibits strong bioluminescence in the bacterial luciferase. FMN shows the opposite behavior; its fluorescence is quenched when it is bound to the luciferase. This is the first example of flavin fluorescence quenching observed in bioluminescent systems and is merely an observation, both the quenching mechanism and quencher are still unclear. Based on theoretical analysis of high-level quantum mechanics (QM), combined QM and molecular mechanics (QM/MM), and molecular dynamics (MD), this paper confirms that HFOH in its first singlet excited state is the bioluminophore of bacterial bioluminescence. More importantly, the computational results indicate that Tyr110 in the luciferase quenches the FMN fluorescence via an electron-transfer mechanism. [ABSTRACT FROM AUTHOR]

The chemical bonding of Zintl clusters is still an evolving and hot topic in modern chemistry. In this paper we synthesized a novel [K([2.2.2]crypt)]4[In8Bi13] complex in a condensed phase. The quantum chemical calculations and X‐ray data revealed that the compound consists of the 1:1 mixture of [Bi@In8Bi12]3− and [Bi@In8Bi12]5− clusters. To the date, those clusters are the largest binary clusters composed of In and Bi elements. Herein, we introduce a spherical aromatic description of chemical bonding for such clusters. We show through AdNDP, ELF, and induced magnetic field and quantitative NICS analyzes that both clusters are spherically aromatic which explains their high symmetry, stability, and peculiar magnetic properties. We believe that this work will help researchers in the further development and understanding of chemical bonding in Zintl clusters. [ABSTRACT FROM AUTHOR]

Single-atom catalysts have attracted wide attention owing to their extremely high atom efficiency and activities. In this paper, we applied density functional theory with the inclusion of the on-site Coulomb interaction (DFT+U) to investigate water adsorption and dissociation on clean CeO2(111) surfaces and single transition metal atoms (STMAs) adsorbed on the CeO2(111) surface. It is found that the most stable water configuration is molecular adsorption on the clean CeO2(111) surface and dissociative adsorption on STMA/CeO2(111) surfaces, respectively. In addition, our results indicate that the more the electrons that transfer from STMA to the ceria substrate, the stronger the binding energies between the STMA and ceria surfaces. A linear relationship is identified between the water dissociation barriers and the d band centers of STMA, known as the generalized Brønsted-Evans-Polanyi principle. By combining the oxygen spillovers, single-atom dispersion stabilities, and water dissociation barriers, Zn, Cr, and V are identified as potential candidates for the future design of ceria-supported single-atom catalysts for reactions in which the dissociation of water plays an important role, such as the water-gas shift reaction. [ABSTRACT FROM AUTHOR]

Marseille–Provence is the European Capital of Culture in 2013. In this issue two articles from the Marseille‐based team Chirosciences analyze the role of imidazole alcohol hydrogen bonding in the nucleophlicity of dyad models (see the Full Paper by J. Leclaire, D. Bourissou, F. Fotiadu et al. on page 11301 ff.) and describe a facile synthesis and assemblies of tetraalkylporphyrins in two and three dimensions (see the Full Paper by Y. Kikkawa, T. S. Balaban et al. on page 11293 ff.). [ABSTRACT FROM AUTHOR]

Abstract: Two heptanuclear discs, [Co7(L1)6(CH3O)6]2+ (Co7‐L1) and [Co7(L2)12](ClO4)2 (Co7‐L2), have been prepared by the reaction of [Co(H2O)6](ClO4)2 with Schiff base HL1 (HL1=2‐methoxy‐6‐[(methylimino)methyl]phenolate) or benzimidazole derivative HL2 (HL2=(1H‐benzo[d]imidazol‐2‐yl)methanolate), respectively, at room temperature. In contrast, the reaction of [Co(H2O)6](ClO4)2 with a mixture of the two ligands, having similar coordination ability but different shapes, resulted in the butterfly‐structured tetranuclear cobalt cluster [Co4(L1)2(L2)4](ClO4)2⋅2H2O (Co4). Electrospray ionization mass spectrometry (ESI‐MS) analysis in real time revealed the {Co1}→{Co2}→{Co4}→{Co7} stepwise assembly when a single ligand was employed, but when both ligands were used only {Co4} was obtained, an intermediate of the former reactions. Interestingly, ligand competition was evidenced in the assembly process of the reaction with two ligands; for example, [Co4(L1)4(L2)2]2+ and [Co4(L1)3(L2)3]2+ were the primary clusters observed at the beginning of the reaction, but [Co4(L1)2(L2)4]2+ was the final product. This observation suggests ligand exchange is taking place, and DFT calculations confirmed that these transformations were possible. By varying the ratio of ligands, the abundance of a certain species in the competitive reaction could be controlled. [ABSTRACT FROM AUTHOR]

NH3 temperature‐programmed desorption (NH3‐TPD) is frequently used for probing the nature of the active sites in CuSSZ‐13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3‐TPD results, which takes into account the temperature‐induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first‐principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu‐O‐Cu]2+, [Cu‐O22−‐Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low‐, medium‐ and high‐temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3‐TPD experiment. Thus, a rigorous interpretation of the NH3‐TPD profiles of CuSSZ‐13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. [ABSTRACT FROM AUTHOR]

We report IR and UV/Vis spectroscopic signatures that allow discriminating between the oxidation states of the manganese‐based water oxidation catalyst [(Mn4O4)(V4O13)(OAc)3]3−. Simulated IR spectra show that V=O stretching vibrations in the 900–1000 cm−1 region shift consistently by about 20 cm−1 per oxidation equivalent. Multiple bands in the 1450–1550 cm−1 region also change systematically upon oxidation/reduction. The computed UV/Vis spectra predict that the spectral range above 350 nm is characteristic of the managanese‐oxo cubane oxidation state, whereas transitions at higher energy are due to the vanadate ligand. The presence of absorption signals above 680 nm is indicative of the presence of MnIII atoms. Spectroelectrochemical measurements of the oxidation from [Mn2III Mn2IV ] to [Mn4IV ] showed that the change in oxidation state can indeed be tracked by both IR and UV/Vis spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: The ability of neutral transition‐metal hydrides to serve as a source of hydride ion H− or proton H+ is well appreciated. The hydride ligands possessing a partly negative charge are proton accepting sites, forming a dihydrogen bond, M−Hδ−⋅⋅⋅δ+HX (M=transition metal or metalloid). On the other hand, some metal hydrides are able to serve as a proton source and give hydrogen bond of M−Hδ+⋅⋅⋅X type (X=organic base). In this paper we analyse recent works on transition‐metal and boron hydrides showing i) how formation of an intermolecular complex between the reactants changes the Z−H (M−H and X−H) bond polarity and ii) what is the implication of such activation in the mechanisms of hydrides reactions. [ABSTRACT FROM AUTHOR]

Evidence for the surprising formation of polymeric phases under high pressure for conjugated nanohoop molecules was found. This paper represents one of the unique cases, in which the molecular-level effects of pressure in crystalline organic solids is addressed, and provides a general approach based on vibrational Raman spectroscopy combining experiments and computations. In particular, we studied the structural and supramolecular chemistry of the cyclic conjugated nanohoop molecule [5]cyclo- para-phenylene ([5]CPP) under high pressures up to 10 GPa experimentally and up to 20 GPa computationally. The theoretical modeling for periodic crystals predicts good agreements with the experimentally obtained Raman spectra in the molecular phase. In addition, we have discovered two stable polymeric phases that arise in the simulation. The critical pressures in the simulation are too high, but the formation of polymeric phases at high pressures provides a natural explanation for the observed irreversibility of the Raman spectra upon pressure release between 6 and 7 GPa. The geometric parameters show a deformation toward quinonoid structures at high pressures accompanied by other deformations of the [5]CPP nanohoops. The quinonoidization of the benzene rings is linked to the systematic change of the bond length alternation as a function of the pressure, providing a qualitative interpretation of the observed spectral shifts of the molecular phase. [ABSTRACT FROM AUTHOR]

Despite its common use in synthesis, the structure of isopropylliyhium in THF has never been determined, a dimer being generally proposed but not supported. This paper fills this data gap through a sophisticated NMR study that shows that, in THF at low-temperature, isopropyllithium is in the form of a 1:2 mixture of a trisolvated monomer and a disolvated dimer in equilibrium. The presence of the monomer, never evoked before, together with a hypo-solvation of the dimer hinted by DFT calculations, provides a rational explanation to the remarkable reactivity of this organolithium reagent in ethereal solvents. [ABSTRACT FROM AUTHOR]

Pincer ligated coordination complexes of base metals have shown remarkable catalytic activity for hydrogenation/dehydrogenation of CO2. The recently reported MeN[CH2CH2(iPr2)]2Co(I)PNP‐pincer complex was shown to exhibit substantially higher catalytic activity in comparison to the corresponding catalyst, HN[CH2CH2(iPr2)]2Co(I)PNP, bearing a secondary nitrogen center on the pincer ligand. Here, we computationally investigate the mechanisms for hydrogenation of CO2 to formate catalyzed by these two Co‐PNP complexes to explain how such a small structural difference could have a sizable impact on their catalytic activity. Plausible hydrogenation routes were examined in details and our findings provide solid support for the experimental observations. Our results reveal that such trends in catalytic activity could be explained from the lower activation barrier for the hydride transfer step upon changing the pincer nitrogen center from secondary to tertiary. [ABSTRACT FROM AUTHOR]

Halogen‐bonded complexes are often designed by consideration of electrostatic potential (ESP) predictions. ESP predictions do not capture the myriad variables associated with halogen bond (XB) donors and acceptors; thus, binding interaction cannot be quantitatively predicted. Here, a discrepancy between predictions based on ESP energy difference (ΔVs) and computed gas phase binding energy (ΔEbind) motivated the experimental determination of the relative strength of halogen bonding interactions in solution by Raman spectroscopic observation of complexes formed from interacting five iodobenzene‐derived XB donors and four pyridine XB acceptors. Evaluation of ΔEbind coupled with absolutely‐localized molecular orbital energy decomposition analysis (ALMO‐EDA) deconvolutes halogen bonding energy contributions and reveals a prominent role for charge transfer (CT) interactions. Raman spectra reveal ΔEbind accurately predicts stronger interactions within iodopentafluorobenzene (IPFB) complexes than with 1‐iodo‐3,5‐dinitrobenzene (IDNB) complexes even though IPFB has similar electrostatics to IDNB and contains a smaller σ‐hole. [ABSTRACT FROM AUTHOR]

To protect their intracellular proteins, extremophile microorganisms synthesize molecules called compatible solutes. These molecules are the result of the attachment of a small negatively charged molecule to a sugar molecule. It has been found that these molecules, not only protect the microorganism against osmotic stress but also against other extreme conditions. They can also confer protection against extreme conditions to isolated enzymes from different organisms making them an exciting prospect for potential biotechnological applications. One of the most widespread compatible solute in hyperthermophile organisms is the molecule 2‐O‐α‐D‐mannosyl‐D‐glycerate (MG). In addition to confer protection to proteins against extreme conditions, MG was found to prevent Alzheimer's β‐amyloid aggregation and reduce α‐synuclein fibril formation in Parkinson's disease. In this work we studied, using computational methods, the catalytic mechanism of the synthesis of MG by the enzyme mannosylglycerate synthase (MGS) from the thermophilic bacteria Rhodothermus marinus. [ABSTRACT FROM AUTHOR]

The synthesis and isolation of a phosphinine selenide was achieved for the first time by reacting red selenium with 2,6‐bis(trimethylsilyl)phosphinine. The rather large coupling constant of 1JP,Se=883 Hz is in line with a P−Se bond of high s‐character. The σ‐electron donating Me3Si‐substituents significantly increase the energy of the phosphorus lone pair and hence its basicity, making the heterocycle considerably more basic and nucleophilic than the unsubstituted phosphinine C5H5P, as confirmed by the calculated gas phase basicities. NBO calculations further reveal that the lone pairs of the selenium atom are stabilized through donor‐acceptor interactions with antibonding orbitals of the aromatic ring. The novel phosphinine selenide shows a distinct reactivity towards hexafluoro‐2‐butyne, Au(I)Cl as well as iPrOH. Our results pave the way for new perspectives in the chemistry of phosphorus in low coordination. [ABSTRACT FROM AUTHOR]

Terthiazoles with redox‐active substituents like an N‐methyl pyridinium group and ferrocene have been synthesized and their photo‐ and electro‐chromic behaviors were investigated. The presence of two lateral N‐methyl pyridinium substituents in the structure of terthiazole proved to be effective in inducing not only the reductive ring‐closure of the terthiazole core but also its oxidative ring‐opening reaction, leading to the first terarylene‐based switch able to fully operate both photochemically and electrochemically. Moreover, the large increase in the redox potential between its open and closed form (700 mV) means that a part of the photon energy necessary to trigger the cyclization is stored in the form of chemical potential available for other works. Introduction of a second redox‐active unit such as ferrocene onto the central thiazolyl moiety is found to inhibit the photochromism of the switch but not its redox switchability, which, instead, got improved for the ring‐opening reaction via the redox properties of the ferrocenyl unit. The optical and redox properties of the switch in its different oxidation states are analyzed with the aid of DFT calculations in order to rationalize different switching processes. [ABSTRACT FROM AUTHOR]

The first rare‐earth‐metal iodate fluoride, Ce(IO3)2F2⋅H2O, has been synthesized by a hydrothermal method. The crystal structure can be described as CeO5F4 polyhedra connected with isolated IO3 groups to form 1D infinite ∞1[Ce(IO3)2F2] chains, which interconnect with each other through weak hydrogen bonds to construct the whole structure. The cover design combines the elements of laser frequency doubling using NLO crystals, the structure of Ce(IO3)2F2⋅H2O, and geometry to create a "surrealistic world". The good optical properties with a large second harmonic generation response confirm that the compound has potential application in the field of NLO materials. More information can be found in the Full Paper by Z. Yang, S. Pan et al. on page 1221. [ABSTRACT FROM AUTHOR]

Multisite anion receptors HAT(CN)6 and [M(CN)4]2− stack under the regime of anion–π interactions to create the platform for a sponge‐like behavior and anion → receptor charge transfer. More information can be found in the Full Paper by R. Podgajny et al. on page 16302. [ABSTRACT FROM AUTHOR]

Ethynylbenziodoxol(on)e (EBX) cyclic hypervalent iodine reagents have become popular reagents for the alkynylation of radicals and nucleophiles, but only offer limited possibilities for further structure and reactivity fine‐tuning. Herein, the synthesis of new N‐heterocyclic hypervalent iodine reagents with increased structural flexibility based on amide, amidine and sulfoximine scaffolds is reported. Solid‐state structures of the reagents are reported and the analysis of the I−Calkyne bond lengths allowed assessing the trans‐effect of the different substituents. Molecular electrostatic potential (MEP) maps of the reagents, derived from DFT computations, revealed less pronounced σ‐hole regions for sulfonamide‐based compounds. Most reagents reacted well in the alkynylation of β‐ketoesters. The alkynylation of thiols afforded more variable yields, with compounds with a stronger σ‐hole reacting better. In metal‐mediated transformations, the N‐heterocyclic hypervalent iodine reagents gave inferior results when compared to the O‐based EBX reagents. [ABSTRACT FROM AUTHOR]

A transition metal free route to phosphetes featuring an exocyclic alkene unit is presented. In this approach phosphanides are added to a variety of diynes generating phosphaallylic intermediates which depending on the reaction conditions transform either to phosphetes or the corresponding phospholes. Investigation of the reaction mechanism by combined quantum chemical and experimental means identifies phosphole formation as thermodynamically controlled reaction path, whereas kinetic control furnishes the corresponding phosphetes. Structural and luminescence properties of the rare class of phosphetes are explored, as well as for selected key intermediates. [ABSTRACT FROM AUTHOR]

Heavy atom substitution in chalcogenophenes is a versatile strategy for tailoring and ultimately improving conjugated polymer properties. While thiophene monomers are commonly implemented in polymer designs, relatively little is known regarding the molecular properties of the heavier chalcogenophenes. Herein, we use density functional theory (DFT) calculations to examine how group 16 heteroatoms, including the radioactive polonium, affect polychalcogenophene properties including bond length, chain twisting, aromaticity, and optical properties. Heavier chalcogenophenes are more quinoidal in character and consequently have reduced band gaps and larger degrees of planarity. We consider both the neutral and radical cationic species. Upon p‐type doping, bond length rearrangement is indicative of a more delocalized electronic structure, which combined with optical calculations is consistent with the polaron‐model of charge storage on conjugated polymer chains. A better understanding of the properties of these materials at their molecular levels will inevitably be useful in material design as the polymer community continues to explore more main group containing polymers to tackle issues in electronic devices. [ABSTRACT FROM AUTHOR]

Cp*Rh(III)‐catalyzed chelation‐assisted direct C−H bond functionalization of 1‐(2‐pyridyl)‐2‐pyridones with internal alkynes that can be controlled to give three different products in good yields has been realized. Depending on the reaction conditions, solvents and additives, the reaction pathway can be switched between alkenylation, alkenylation/directing group migration and rollover annulation. These reaction manifolds allow divergent access to a variety of valuable C6‐alkenylated 1‐(2‐pyridyl)‐2‐pyridones, (Z)‐6‐(1,2‐diaryl‐2‐(pyridin‐2‐yl)vinyl)pyridin‐2(1H)‐ones and 10H‐pyrido[1,2‐a][1,8]naphthyridin‐10‐ones from the same starting materials. These protocols exhibit excellent regio‐ and stereoselectivity, broad substrate scope, and good tolerance of functional groups. A combination of experimental and computational approaches have been employed to uncover the key mechanistic features of these reactions. [ABSTRACT FROM AUTHOR]

Introduction of heterocycles into the helical skeleton of helicenes allows modulation of their redox, chiroptical, and photophysical properties. This paper describes the straightforward preparation and structural characterization by single-crystal X-ray diffraction of thiadiazole-[7]helicene, which was resolved into M and P enantiomers by chiral HPLC, together with its S-shaped double [4]helicene isomer, as well as the smaller congeners thiadiazole-[5]helicene and benzothiadiazole-anthracene. A copper(II) complex with two thiadiazole-[5]helicene ligands was structurally characterized, and it shows the presence of both M and P isomers coordinated to the metal center. The emission properties of the heterohelicenes are highly dependent on the helical turn, as the [7]- and [5]helicene are poorly emissive, whereas their isomers, that is, the S-shaped double [4]helicene and thiadiazole-benzanthracene, are luminescent, with quantum efficiencies of 5.4 and 6.5 %, respectively. DFT calculations suggest quenching of the luminescence of enantiopure [7]helicenes through an intersystem-crossing mechanism arising from the relaxed excited S1 state. [ABSTRACT FROM AUTHOR]

This paper is devoted to the understanding of the reaction mechanism of mycobacterium tuberculosis glutamine synthetase (mtGS) with atomic detail, using computational quantum mechanics/molecular mechanics (QM/MM) methods at the ONIOM M06-D3/6-311++G(2d,2p):ff99SB//B3LYP/6-31G(d):ff99SB level of theory. The complete reaction undergoes a three-step mechanism: the spontaneous transfer of phosphate from ATP to glutamate upon ammonium binding (ammonium quickly loses a proton to Asp54), the attack of ammonia on phosphorylated glutamate (yielding protonated glutamine), and the deprotonation of glutamine by the leaving phosphate. This exothermic reaction has an activation free energy of 21.5 kcal mol−1, which is consistent with that described for Escherichia coli glutamine synthetase (15-17 kcal mol−1). The participating active site residues have been identified and their role and energy contributions clarified. This study provides an insightful atomic description of the biosynthetic reaction that takes place in this enzyme, opening doors for more accurate studies for developing new anti-tuberculosis therapies. [ABSTRACT FROM AUTHOR]

Diol dehydratase, dependent on coenzyme B12 (B12‐dDDH), displays a peculiar feature of being inactivated by its native substrate glycerol (GOL). Surprisingly, the isofunctional enzyme, B12‐independent glycerol dehydratase (B12‐iGDH), does not undergo suicide inactivation by GOL. Herein we present a series of QM/MM and MD calculations aimed at understanding the mechanisms of substrate‐induced suicide inactivation in B12‐dDDH and that of resistance of B12‐iGDH to inactivation. We show that the first step in the enzymatic transformation of GOL, hydrogen abstraction, can occur from both ends of the substrate (either C1 or C3 of GOL). Whereas C1 abstraction in both enzymes leads to product formation, C3 abstraction in B12‐dDDH results in the formation of a low energy radical intermediate, which is effectively trapped within a deep well on the potential energy surface. The long lifetime of this radical intermediate likely enables its side reactions, leading to inactivation. In B12‐iGDH, by comparison, C3 abstraction is an endothermic step; consequently, the resultant radical intermediate is not of low energy, and the reverse process of reforming the reactant is possible. [ABSTRACT FROM AUTHOR]

Lead‐free double perovskites have emerged as stable and non‐toxic alternatives to Pb‐halide perovskites. Herein, the synthesis of Fe‐doped Cs2AgBiCl6 lead‐free double perovskites are reported that display blue emission using an antisolvent method. The crystal structure, morphology, optical properties, band structure, and stability of the Fe‐doped double perovskites were investigated systematically. Formation of the Fe‐doped Cs2AgBiCl6 double perovskite is confirmed by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) analysis. XRD and thermo‐gravimetric analysis (TGA) shows that the Cs2AgBiCl6 double perovskite has high structural and thermal stability, respectively. Field emission scanning electron microscopy (FE‐SEM) analysis revealed the formation of dipyramidal shape Cs2AgBiCl6 crystals. Furthermore, energy‐dispersive X‐ray spectroscopy (EDS) mapping shows the overlapping of Cs, Bi, Ag, Fe, and Cl elements and homogenous incorporation of Fe in Cs2AgBiCl6 double perovskite. The Fe‐doped Cs2AgBiCl6 double perovskite shows a strong absorption at 380 nm. It extends up to 700 nm, suggesting that sub‐band gap states transition may originate from the surface defect of the doped perovskite material. The radiative kinetics of the crystals was studied using the time‐correlated single‐photon counting (TCSPC) technique. Lattice parameters and band gap value of the Fe‐doped Cs2AgBiCl6 double perovskites predicted by the density functional theory (DFT) calculations are confirmed by XRD and UV/Visible spectroscopy analysis. Time‐dependent photo‐response characteristics of the Fe‐doped Cs2AgBiCl6 double perovskite show fast response and recovery time of charge carriers. We believe that the successful incorporation of Fe in lead‐free, environmentally friendly Cs2AgBiCl6 double perovskite can open a new class of doped double perovskites with significant potential optoelectronics devices fabrication and photocatalytic applications. [ABSTRACT FROM AUTHOR]

A series of new β‐ketoimines containing a ferrocene moiety and their BF2 complexes have been synthesized and structurally characterized. The solvatochromism of the β‐ketoimines was studied, putting in evidence a redshift with increasing solvent polarity. This positive solvatochromism can be attributed to a more polarized excited state compared with the ground state, due to intramolecular charge transfer (ICT) transitions. The β‐ketoimines exhibited weak emission, attributable to the excited‐state intramolecular proton transfer (ESIPT) phenomenon. This ESIPT effect is suppressed upon restriction of the keto‐enamine tautomerism, induced upon addition of BF3⋅OEt2, which afforded the related BF2 complexes, characterized by an enhancement of the fluorescence through the ICT effect. Both the β‐ketoimines and BF2 complexes exhibited significant aggregation‐induced emission behavior in mixtures of CH3CN/H2O, due to restriction of intramolecular rotation in the aggregated state. The frontier molecular orbital levels, ground‐ and excited‐state dipole moments (μg and μe), and the origin of electronic absorption spectra were studied by time‐dependent DFT calculations. The second‐order nonlinear optical (NLO) properties were determined by the electric‐field‐induced second‐harmonic generation technique. The μβ1907 values of the β‐ketoimines increased upon the formation of the related BF2 complexes, mainly due to an enhancement of the ground‐state dipole moment. The results presented here reveal that some of these novel compounds are excellent multifunctional candidates for NLO and luminescence applications. [ABSTRACT FROM AUTHOR]

Four sodium‐based ternary IR nonlinear optical (NLO) materials, Na6MQ4 (M=Zn, Cd; Q=S, Se), were prepared through a high‐temperature flux method. The crystal structure of the compounds is built up of isolated [MQ4] tetrahedra and a 3D framework formed by the NaQn (n=4, 5) units. The two selenides, Na6MSe4 (M=Zn, Cd), as promising IR NLO materials, show moderate second‐harmonic generation (SHG) responses (0.9 and 0.5×AgGaS2) with good phase‐matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS2). The two sulfides, Na6MS4 (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS2), but smaller SHG responses (0.3 and 0.2×AgGaS2). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ4 NLO‐active units with a short Na−S bond length, which provides a new insight into the design of novel IR NLO materials. [ABSTRACT FROM AUTHOR]

Porphycene, a porphyrin isomer, is an efficient fluorophore. However, four‐fold meso substitution with alkyl groups decreases the fluorescence quantum yield by orders of magnitude. For aryl substituents, this effect is small. To explain this difference, we have synthesized and studied a mixed aryl‐alkyl‐substituted compound, 9,20‐diphenyl‐10,19‐dimethylporphycene, as well as the 9,20‐diphenyl and 9,20‐dimethyl derivatives. Analysis of the structural, spectroscopic, and photophysical data of the six porphycenes, combined with quantum chemical calculations, shows a clear correlation between the strength of the intramolecular NH⋅⋅⋅N hydrogen bonds and the efficiency of the radiationless depopulation of the lowest‐excited singlet state. This result led us to propose a model in which the delocalization of the inner protons in the cavity of the macrocycle is responsible for the nonradiative deactivation channel. The applicability of the model is confirmed by the literature data for other alkyl‐ or aryl‐substituted porphycenes. The finding of a correlation between structural and emissive characteristics enables a rational design of porphycenes with desired photophysical properties. [ABSTRACT FROM AUTHOR]

A series of 9‐borafluorene derivatives, functionalised with electron‐donating groups, have been prepared. Some of these 9‐borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB‐Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9‐borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light‐emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow‐greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m−2. These are the first two examples of 9‐borafluorene derivatives being used as light‐emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability. [ABSTRACT FROM AUTHOR]

A highly strained covalent organic cage compound was synthesized from hexahydroxy tribenzotriquinacene (TBTQ) and a meta‐terphenyl‐based diboronic acid with an additional benzoic acid substituent in 2'‐position. Usually, a 120° bite angle in the unsubstituted ditopic linker favors the formation of a [4+6] cage assembly. Here, the introduction of the benzoic acid group is shown to lead to a perfectly preorganized circular hydrogen‐bonding array in the cavity of a trigonal‐bipyramidal [2+3] cage, which energetically overcompensates the additional strain energy caused by the larger mismatch in bite angles for the smaller assembly. The strained cage compound was analyzed by mass spectrometry and 1H, 13C and DOSY NMR spectroscopy. DFT calculations revealed the energetic contribution of the hydrogen‐bonding template to the cage stability. Furthermore, molecular dynamics simulations on early intermediates indicate an additional kinetic effect, as hydrogen bonding also preorganizes and rigidifies small oligomers to facilitate the exclusive formation of smaller and more strained macrocycles and cages. [ABSTRACT FROM AUTHOR]

The [2+1] cycloaddition reaction of a metal carbene with an alkene can produce important cyclopropane products for synthetic intermediates, materials, and pharmaceutical applications. However, this reaction is often accompanied by side reactions, such as coupling and self‐coupling, so that the yield of the cyclopropanation product of non‐silver transition‐metal carbenes and hindered alkenes is generally lower than 50 %. To solve this problem, the addition of a low concentration of diazo compound (decomposition of sulfonyl hydrazones) to alkenes catalyzed by either CuOAc or PdCl2 was studied, but side reactions could still not be avoided. Interestingly, however, the yield of cyclopropanation products for such hindered alkenes were as high as 99 % with AgOTf as a catalyst. To explain this unexpected phenomenon, reaction pathways have been computed for four different catalysts by using DFT. By combining the results of these calculations with those obtained experimentally, it can be concluded that the efficiency of the silver catalyst is due to the barrierless concerted cycloaddition step and the kinetic inhibition of side reactions by a high concentration of alkene. [ABSTRACT FROM AUTHOR]

The drive to develop maximal atom‐efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever‐increasing interest in single‐atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8–10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less‐electronegative row 4 elements (Fe, Co, Ni) ranged from −1.40 to −1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between −2.20 and −2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d‐shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data. [ABSTRACT FROM AUTHOR]

A judiciously oriented external electric field (OEEF) can catalyze a wide range of reactions and can even induce endo/exo stereoselectivity of cycloaddition reactions. The Diels–Alder reaction between cyclopentadiene and maleic anhydride is studied by using quantitative activation strain and Kohn–Sham molecular orbital theory to pinpoint the origin of these catalytic and stereoselective effects. Our quantitative model reveals that an OEEF along the reaction axis induces an enhanced electrostatic and orbital interaction between the reactants, which in turn lowers the reaction barrier. The stronger electrostatic interaction originates from an increased electron density difference between the reactants at the reactive center, and the enhanced orbital interaction arises from the promoted normal electron demand donor–acceptor interaction driven by the OEEF. An OEEF perpendicular to the plane of the reaction axis solely stabilizes the exo pathway of this reaction, whereas the endo pathway remains unaltered and efficiently steers the endo/exo stereoselectivity. The influence of the OEEF on the inverse electron demand Diels–Alder reaction is also investigated; unexpectedly, it inhibits the reaction, as the electric field now suppresses the critical inverse electron demand donor–acceptor interaction. [ABSTRACT FROM AUTHOR]

The hexacoordinated antimony(V) dication [(ppy)3Sb]2+ ([1]2+; ppy=2‐(2‐pyridyl)phenyl), stabilized by three intramolecular donor–acceptor interactions, has been isolated as its hexachloroantimonate salt [1][SbCl6]2, prepared by the oxidative addition of chlorine to the neutral stibine [(ppy)3Sb] (1), followed by the abstraction of chloride. Air‐stable [1][SbCl6]2 exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the 1H and 13C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for [1][SbCl6]2 by X‐ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable‐temperature 1H NMR spectroscopy. The potential to generate dications by using a single‐electron‐transfer reagent has also been investigated. The dication [1]2+ is the first [12–Sb–6]2+ chemical species to have been structurally determined. [ABSTRACT FROM AUTHOR]

The total synthesis of dehydroantofine was achieved by employing a novel, regioselective, azahetero Diels–Alder reaction of easily accessible 3,5‐dichloro‐2H‐1,4‐oxazin‐2‐one with 14 a as a key step. Furthermore, it is demonstrated that dehydroantofine is a promising candidate as a new antimalarial agent in a biological assay with chloroquine‐resistant Plasmodium falciparum. [ABSTRACT FROM AUTHOR]

Mildly thermal air or HNO3 oxidized activated carbons catalyse oxidative dehydrogenative couplings of benzo[b]fused heteroaryl 2,2'‐dimers, e.g. 2‐(benzofuran‐2‐yl)‐1H‐indole, to chiral 3,3'‐coupled cyclooctatetraenes or carbazole‐type migrative products under O2 atmosphere. DFT calculations show that the radical cation and the Scholl‐type arenium cation mechanisms lead to different products with 2‐(benzofuran‐2‐yl)‐1H‐indole, being in accord with experimental product distributions. [ABSTRACT FROM AUTHOR]

The selectivity and rate enhancement of bifunctional hydrogen bond donor‐catalyzed Diels–Alder reactions between cyclopentadiene and acrolein were quantum chemically studied using density functional theory in combination with coupled‐cluster theory. (Thio)ureas render the studied Diels–Alder cycloaddition reactions exo selective and induce a significant acceleration of this process by lowering the reaction barrier by up to 7 kcal mol−1. Our activation strain and Kohn–Sham molecular orbital analyses uncover that these organocatalysts enhance the Diels–Alder reactivity by reducing the Pauli repulsion between the closed‐shell filled π‐orbitals of the diene and dienophile, by polarizing the π‐orbitals away from the reactive center and not by making the orbital interactions between the reactants stronger. In addition, we establish that the unprecedented exo selectivity of the hydrogen bond donor‐catalyzed Diels–Alder reactions is directly related to the larger degree of asynchronicity along this reaction pathway, which is manifested in a relief of destabilizing activation strain and Pauli repulsion. [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]

The noncovalent interactions between azides and oxygen‐containing moieties are investigated through a computational study based on experimental findings. The targeted synthesis of organic compounds with close intramolecular azide–oxygen contacts yielded six new representatives, for which X‐ray structures were determined. Two of those compounds were investigated with respect to their potential conformations in the gas phase and a possible significantly shorter azide–oxygen contact. Furthermore, a set of 44 high‐quality, gas‐phase computational model systems with intermolecular azide–pnictogen (N, P, As, Sb), –chalcogen (O, S, Se, Te), and –halogen (F, Cl, Br, I) contacts are compiled and investigated through semiempirical quantum mechanical methods, density functional approximations, and wave function theory. A local energy decomposition (LED) analysis is applied to study the nature of the noncovalent interaction. The special role of electrostatic and London dispersion interactions is discussed in detail. London dispersion is identified as a dominant factor of the azide–donor interaction with mean London dispersion energy‐interaction energy ratios of 1.3. Electrostatic contributions enhance the azide–donor coordination motif. The association energies range from −1.00 to −5.5 kcal mol−1. [ABSTRACT FROM AUTHOR]

A bifunctional MOF for selective CO2 capture and efficient aqueous‐phase sensing of 2,4,6‐trinitrophenol (TNP) has been rationally designed and synthesized. Owing to the presence of basic (−NH2) functionalized pore surface, the MOF exhibits selective adsorption of CO2 with a high value of heat of adsorption (Qst = 46.5 kJ mol−1) which is about 10 kJ mol−1 higher than that of the analogues MOF without −NH2 functionality. Further, the MOF shows highly selective, aqueous‐phase sensing of TNP over other competing NACs. The observed selectivity of MOF for CO2 capture and sensing of TNP has been correlated to the stronger interaction of the guest molecules with the basic −NH2 groups in the 1D channels, unveiled from the DFT calculations. For more information see the Full Paper by C. M. Nagaraja et al. on page 16204 ff. [ABSTRACT FROM AUTHOR]

Fusing six ‐ membered phosphorus heterocycles with different (hetero)aromatic rings provides materials with an outstanding potential for multifunctional applications. Our investigations reveal the key parameters to obtain polycyclic architectures based on six ‐ membered phosphorus heterocycles with, among others, electron ‐ accepting properties, fluorescence quantum yields up to 0.8, and versatile means to control the 3D molecular arrangement through phosphorus post ‐ functionalization. More information can be found in the Full Paper by A. de Cózar, C. Romero ‐ Nieto et al. on page 13919. [ABSTRACT FROM AUTHOR]

The reduction mechanism of [PtIV(dach)Cl4] (dach=diaminocyclohexyl) in the presence of dGMP was studied. The first step is substitution of a chloro ligand by dGMP, followed by nucleophilic attack of a phosphate or sugar oxygen atom to the C8-position of guanine. Subsequent reduction forms the [PtII(dach)Cl2] complex. The whole process is completed by a hydrolysis. Two different pathways for the substitution reaction were examined: a direct associative and a Basolo-Pearson autocatalytic mechanism. All the explored structures were optimized at the B3LYP-D3/6-31G(d) level and by using the COSMO solvation model with Klamt's radii. Single-point energetics was determined at the B3LYP-GD3BJ/6-311++G(2df,2pd)/PCM/scaled-UAKS level. Activation barriers were used for an estimation of the rate constants and these were compared with experimental values. It was found that the rate-determining step is the nucleophilic attack with a slightly faster performance in the 3′-dGMP branch than in the case of 5′-dGMP with activation barriers of 21.1 and 20.4 kcal mol−1 (experimental: 23.8 and 23.2 kcal mol−1). The reduction reaction is connected with an electron flow from guanine. The product of the reduction reaction is a chelate structure, which dissociates within the last reaction step, that is, a hydrolysis reaction. The whole redox process (substitution, reduction, and hydrolysis) is exergonic by 34 and 28 kcal mol−1 for 5′-dGMP and 3′-dGMP, respectively. [ABSTRACT FROM AUTHOR]

We have calculated the 13C NMR chemical shifts of a large ensemble of halogenated organic molecules (81 molecules for a total of 250 experimental 13C NMR data at four different levels of theory), ranging from small rigid organic compounds, used to benchmark the performance of various levels of theory, to natural substances of marine origin with conformational degrees of freedom. Carbon atoms bonded to heavy halogen atoms, particularly bromine and iodine, are known to be rather challenging when it comes to the prediction of their chemical shifts by quantum methods, due to relativistic effects. In this paper, we have applied the state-of-the-art four-component relativistic density functional theory for the prediction of such NMR properties and compared the performance with two-component and nonrelativistic methods. Our results highlight the necessity to include relativistic corrections within a four-component description for the most accurate prediction of the NMR properties of halogenated organic substances. [ABSTRACT FROM AUTHOR]

This paper deals with a systematic density functional theory (DFT) study aiming to unravel the mechanism of the thyroxine (T4) conversion into 3,3′,5-triiodothyronine (rT3) by using different bio-inspired naphthyl-based models, which are able to reproduce the catalytic functions of the type-3 deiodinase ID-3. Such naphthalenes, having two selenols, two thiols, and a selenol-thiol pair in peri positions, which were previously synthesized and tested in their deiodinase activity, are able to remove iodine selectively from the inner ring of T4 to produce rT3. Calculations were performed including also an imidazole ring that, mimicking the role of the His residue, plays an essential role deprotonating the selenol/thiol moiety. For all the used complexes, the calculated potential energy surfaces show that the reaction proceeds via an intermediate, characterized by the presence of a XIC (X=Se, S) halogen bond, whose transformation into a subsequent intermediate in which the CI bond is definitively cleaved and the incipient XI bond is formed represents the rate-determining step of the whole process. The calculated trend in the barrier heights of the corresponding transition states allows us to rationalize the experimentally observed superior deiodinase activity of the naphthyl-based compound with two selenol groups. The role of the peri interactions between chalcogen atoms appears to be less prominent in determining the deiodination activity. [ABSTRACT FROM AUTHOR]

Efficient catalytic arsa‐Wittig reactions have been developed by using 1‐phenylarsolane as a catalyst. A wide array of aldehydes was converted to the corresponding olefins in high yields with moderate to excellent E stereoselectivity in the presence of a catalytic amount of 1‐phenylarsolane. Moreover, density functional theory calculations were carried out to afford insight into the E/Z selectivity. [ABSTRACT FROM AUTHOR]

The metal‐free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal‐free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron‐ligand cooperation. [ABSTRACT FROM AUTHOR]