Showing papers on "Hydrogen bond published in 2015"
TL;DR: Using the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored, and it is clear that doubly ionsicH-bonds cover the full range of weak through to very strong H- bonds.
Abstract: Ionic liquids (IL) and hydrogen bonding (H-bonding) are two diverse fields for which there is a developing recognition of significant overlap. Doubly ionic H-bonds occur when a H-bond forms between a cation and anion, and are a key feature of ILs. Doubly ionic H-bonds represent a wide area of H-bonding which has yet to be fully recognised, characterised or explored. H-bonds in ILs (both protic and aprotic) are bifurcated and chelating, and unlike many molecular liquids a significant variety of distinct H-bonds are formed between different types and numbers of donor and acceptor sites within a given IL. Traditional more neutral H-bonds can also be formed in functionalised ILs, adding a further level of complexity. Ab initio computed parameters; association energies, partial charges, density descriptors as encompassed by the QTAIM methodology (ρBCP), qualitative molecular orbital theory and NBO analysis provide established and robust mechanisms for understanding and interpreting traditional neutral and ionic H-bonds. In this review the applicability and extension of these parameters to describe and quantify the doubly ionic H-bond has been explored. Estimating the H-bonding energy is difficult because at a fundamental level the H-bond and ionic interaction are coupled. The NBO and QTAIM methodologies, unlike the total energy, are local descriptors and therefore can be used to directly compare neutral, ionic and doubly ionic H-bonds. The charged nature of the ions influences the ionic characteristics of the H-bond and vice versa, in addition the close association of the ions leads to enhanced orbital overlap and covalent contributions. The charge on the ions raises the energy of the Ylp and lowers the energy of the X–H σ* NBOs resulting in greater charge transfer, strengthening the H-bond. Using this range of parameters and comparing doubly ionic H-bonds to more traditional neutral and ionic H-bonds it is clear that doubly ionic H-bonds cover the full range of weak through to very strong H-bonds.
572 citations
TL;DR: The studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C-H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds.
Abstract: The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C–H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds.
337 citations
TL;DR: In this article, six new 1-benzoyl-3-phenyl-thiourea and 1-(2-methylphenyl)thIourea complexes of mercury(II) were obtained in the reactions of the ligands with HgX2 in methanol (X = Cl, Br, I).
330 citations
TL;DR: The formation of synergistic halogen and hydrogen bonds between these molecules is the driving force to assemble successfully a whole series of defect-free molecular fractals, specifically Sierpiński triangles, on a Ag(111) surface below 80 K.
Abstract: A series of molecular fractals, specifically Sierpinski triangles, can be assembled on a Ag(111) surface from small, bent oligophenyls with a bromo group at each end. The self-assembly is driven by the formation of synergistic halogen and hydrogen bonds between the molecular building blocks, and defect-free structures with more than 100 individual components are observed.
274 citations
TL;DR: Evidence of the favorable noncovalent interaction between a covalently bonded atom of Group 18 and a negative site, for example, a lone pair of a Lewis base or an anion is reported.
Abstract: We report evidence of the favorable noncovalent interaction between a covalently bonded atom of Group 18 (known as noble gases or aerogens) and a negative site, for example, a lone pair of a Lewis base or an anion. It involves a region of positive electrostatic potential (σ-hole), therefore it is a totally new and unexplored σ-hole-based interaction, namely aerogen bonding. We demonstrate for the first time the existence of σ-hole regions in aerogen derivatives by means of high-level ab initio calculations. In addition, several crystal structures retrieved from the Cambridge Structural Database (CSD) give reliability to the calculations. Energetically, aerogen bonds are comparable to hydrogen bonds and other σ-hole-based interactions but less directional. They are expected to be important in xenon chemistry.
273 citations
TL;DR: Iron/Lewis acid co-catalysts hydrogenate to CO2 to formate with unprecedented turnover for a first row transition metal catalyst.
Abstract: A family of iron(II) carbonyl hydride complexes supported by either a bifunctional PNP ligand containing a secondary amine, or a PNP ligand with a tertiary amine that prevents metal–ligand cooperativity, were found to promote the catalytic hydrogenation of CO2 to formate in the presence of Bronsted base. In both cases a remarkable enhancement in catalytic activity was observed upon the addition of Lewis acid (LA) co-catalysts. For the secondary amine supported system, turnover numbers of approximately 9000 for formate production were achieved, while for catalysts supported by the tertiary amine ligand, nearly 60 000 turnovers were observed; the highest activity reported for an earth abundant catalyst to date. The LA co-catalysts raise the turnover number by more than an order of magnitude in each case. In the secondary amine system, mechanistic investigations implicated the LA in disrupting an intramolecular hydrogen bond between the PNP ligand N–H moiety and the carbonyl oxygen of a formate ligand in the catalytic resting state. This destabilization of the iron-bound formate accelerates product extrusion, the rate-limiting step in catalysis. In systems supported by ligands with the tertiary amine, it was demonstrated that the LA enhancement originates from cation assisted substitution of formate for dihydrogen during the slow step in catalysis.
249 citations
TL;DR: The combined potentials improve performance in a variety of scientific benchmarks including decoy discrimination, side chain prediction, and native sequence recovery in protein design simulations and establishes a new standard energy function for Rosetta.
Abstract: Interactions between polar atoms are challenging to model because at very short ranges they form hydrogen bonds (H-bonds) that are partially covalent in character and exhibit strong orientation preferences; at longer ranges the orientation preferences are lost, but significant electrostatic interactions between charged and partially charged atoms remain. To simultaneously model these two types of behavior, we refined an orientation dependent model of hydrogen bonds [Kortemme et al. J. Mol. Biol. 2003, 326, 1239] used by the molecular modeling program Rosetta and then combined it with a distance-dependent Coulomb model of electrostatics. The functional form of the H-bond potential is physically motivated and parameters are fit so that H-bond geometries that Rosetta generates closely resemble H-bond geometries in high-resolution crystal structures. The combined potentials improve performance in a variety of scientific benchmarks including decoy discrimination, side chain prediction, and native sequence reco...
211 citations
TL;DR: Capsular self-assemblies of the latter type of methylene-bridge cavitands, which are formed through hydrogen bonds, metal-coordination bonds, and dynamic covalent bonds are described.
Abstract: Calix[4]resorcinarene-based cavitands with a bowl-shaped aromatic cavity are widely used as scaffolds for covalently bound and self-assembled capsules. There are two main categories of calix[4]resorcinarene-based cavitands that are tetrafunctionalized at the upper (wider) rim: one category includes derivatives that have functionalized bridges between pairs of hydroxy groups of the calix[4]resorcinarene, and the second category includes derivatives with functional groups at the 2-position on the resorcinol ring and the methylene bridge between pairs of hydroxy groups. This review describes capsular self-assemblies of the latter type of methylene-bridge cavitands, which are formed through hydrogen bonds, metal-coordination bonds, and dynamic covalent bonds.
202 citations
TL;DR: The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intra-chemical hydrogen bonds between -OH group and pyridine-type nitrogen atom would be strengthened in theS1 state, which can facilitate the proton transfer process effectively.
Abstract: The excited state intramolecular proton transfer (ESIPT) mechanisms of 1,8-dihydroxydibenzo[a,h]phenazine (DHBP) in toluene solvent have been investigated based on time-dependent density functional theory (TD-DFT). The results suggest that both a single and double proton transfer mechanisms are relevant, in constrast to the prediction of a single one proposed previously (Piechowska et al. J. Phys. Chem. A 2014, 118, 144–151). The calculated results show that the intramolecular hydrogen bonds were formed in the S0 state, and upon excitation, the intramolecular hydrogen bonds between −OH group and pyridine-type nitrogen atom would be strengthened in the S1 state, which can facilitate the proton transfer process effectively. The calculated vertical excitation energies in the S0 and S1 states reproduce the experimental UV–vis absorption and fluorescence spectra well. The constructed potential energy surfaces of the S0 and S1 states have been used to explain the proton transfer process. Four minima have been f...
189 citations
TL;DR: A RhIII-catalysed tandem C–H/C–F activation for the synthesis of (hetero)arylated monofluoroalkenes and the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C–F bond cleavage step.
Abstract: Fluoroalkenes represent a class of privileged structural motifs, which found widespread use in medicinal chemistry. However, the synthetic access to fluoroalkenes was much underdeveloped with previous reported methods suffering from either low step economy or harsh reaction conditions. Here we present a Rh(III)-catalysed tandem C-H/C-F activation for the synthesis of (hetero)arylated monofluoroalkenes. The use of readily available gem-difluoroalkenes as electrophiles provides a highly efficient and operationally simple method for the introduction of α-fluoroalkenyl motifs onto (hetero)arenes under oxidant-free conditions. Furthermore, the employment of alcoholic solvent and the in-situ generated hydrogen fluoride are found to be beneficial in this transformation, indicating the possibility of the involvement of hydrogen bond activation mode with regards to the C-F bond cleavage step.
185 citations
TL;DR: Empirical correlations were observed among the hydrogen-bonding strength, ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N-H···N hydrogen bond leads to a faster ESIPt, as experimentally observed, and a more exergonic reaction thermodynamics.
Abstract: A series of new amino (NH)-type hydrogen-bonding (H-bonding) compounds comprising 2-(2′-aminophenyl)benzothiazole and its extensive derivatives were designed and synthesized. Unlike in the hydroxyl (OH)-type H-bonding systems, one of the amino hydrogens can be replaced with electron-donating/withdrawing groups. This, together with a versatile capability for modifying the parent moiety, makes feasible the comprehensive spectroscopy and dynamics studies of amino-type excited-state intramolecular proton transfer (ESIPT), which was previously inaccessible in the hydroxyl-type ESIPT systems. Empirical correlations were observed among the hydrogen-bonding strength (the N–H bond distances and proton acidity), ESIPT kinetics, and thermodynamics, demonstrating a trend that the stronger N–H···N hydrogen bond leads to a faster ESIPT, as experimentally observed, and a more exergonic reaction thermodynamics. Accordingly, ESIPT reaction can be harnessed for the first time from a highly endergonic type (i.e., prohibitio...
TL;DR: The results reveal that Reline and Glyceline form mixtures that are inhomogeneous at a microscopic level despite the hydrophilicity of the salt and HBD, showing that PFG NMR is a powerful tool to elucidate both molecular dynamics and inter-molecular interactions in complex liquid mixtures, such as the aqueous DES mixtures.
Abstract: Pulsed field gradient (PFG) NMR has been used to probe self-diffusion of molecular and ionic species in aqueous mixtures of choline chloride (ChCl) based deep eutectic solvents (DESs), in order to elucidate the effect of water on motion and inter-molecular interactions between the different species in the mixtures, namely the Ch+ cation and hydrogen bond donor (HBD). The results reveal an interesting and complex behaviour of such mixtures at a molecular level. In general, it is observed that the hydroxyl protons (1H) of Ch+ and the hydrogen bond donor have diffusion coefficients significantly different from those measured for their parent molecules when water is added. This indicates a clear and significant change in inter-molecular interactions. In aqueous Ethaline, the hydroxyl species of Ch+ and HBD show a stronger interaction with water as water is added to the system. In the case of Glyceline, water has little effect on both hydroxyl proton diffusion of Ch+ and HBD. In Reline, it is likely that water allows the formation of small amounts of ammonium hydroxide. The most surprising observation is from the self-diffusion of water, which is considerably higher that expected from a homogeneous liquid. This leads to the conclusion that Reline and Glyceline form mixtures that are inhomogeneous at a microscopic level despite the hydrophilicity of the salt and HBD. This work shows that PFG NMR is a powerful tool to elucidate both molecular dynamics and inter-molecular interactions in complex liquid mixtures, such as the aqueous DES mixtures.
TL;DR: A review of the recent C F bond cleavage examples and further transformation of compounds bearing with an aliphatic fluoride, difluoromethylene group or trifluoricomethyl groups can be found in this paper.
TL;DR: The role played by diffusion NMR in the field of hydrogen bond driven self-assembled capsules and cages is focused on and the contributions to the study and characterization of metal-ligand cages and capsules are surveyed.
Abstract: In the last decade diffusion NMR and diffusion ordered spectroscopy (DOSY) have become important analytical tools for the characterization of supramolecular systems in solution. Diffusion NMR can be used to glean information on the (effective) size and shape of molecular species, as well as to probe inter-molecular interactions and can be used to estimate the association constant (Ka) of a complex. In addition, the diffusion coefficient, as obtained from diffusion NMR, is a much more intuitive parameter than the chemical shift for probing self-association, aggregation and inter-molecular interactions. The diffusion coefficient may be an even more important analytical parameter in systems in which the formed supramolecular entity has the same symmetry as its building units, when there is a large change in the molecular weight, where many molecular species are involved in the formation of the supramolecular systems, and when proton transfer may occur which, in turn, may affect the chemical shift. Some of the self-assembled molecular capsules and cages prepared in the last decade represent such supramolecular systems and in the present review, following a short introduction on diffusion NMR, we survey the contribution of diffusion NMR and DOSY in the field of molecular containers and capsules. We will first focus on the role played by diffusion NMR in the field of hydrogen bond driven self-assembled capsules. We then survey the contributions of diffusion NMR and DOSY to the study and characterization of metal–ligand cages and capsules. Finally, we describe a few recent applications of diffusion NMR in the field of hydrophobic, electrostatic and covalent containers.
TL;DR: The results indicate that through these interactions careful control over the HAT reactivity of basic substrates toward CumO(•) and other electrophilic radicals can be achieved, suggesting moreover that these effects can be exploited in an orthogonal fashion for selective C-H bond functionalization of substrates bearing different basic functionalities.
Abstract: Hydrogen atom transfer (HAT) is a fundamental reaction that takes part in a wide variety of chemical and biological processes, with relevant examples that include the action of antioxidants, damage to biomolecules and polymers, and enzymatic and biomimetic reactions. Moreover, great attention is currently devoted to the selective functionalization of unactivated aliphatic C-H bonds, where HAT based procedures have been shown to play an important role. In this Account, we describe the results of our recent studies on the role of structural and medium effects on HAT from aliphatic C-H bonds to the cumyloxyl radical (CumO(•)). Quantitative information on the reactivity and selectivity patterns observed in these reactions has been obtained by time-resolved kinetic studies, providing a deeper understanding of the factors that govern HAT from carbon and leading to the definition of useful guidelines for the activation or deactivation of aliphatic C-H bonds toward HAT. In keeping with the electrophilic character of alkoxyl radicals, polar effects can play an important role in the reactions of CumO(•). Electron-rich C-H bonds are activated whereas those that are α to electron withdrawing groups are deactivated toward HAT, with these effects being able to override the thermodynamic preference for HAT from the weakest C-H bond. Stereoelectronic effects can also influence the reactivity of the C-H bonds of ethers, amines, and amides. HAT is most rapid when these bonds can be eclipsed with a lone pair on an adjacent heteroatom or with the π-system of an amide functionality, thus allowing for optimal orbital overlap. In HAT from cyclohexane derivatives, tertiary axial C-H bond deactivation and tertiary equatorial C-H bond activation have been observed. These effects have been explained on the basis of an increase in torsional strain or a release in 1,3-diaxial strain in the HAT transition states, with kH(eq)/kH(ax) ratios that have been shown to exceed one order of magnitude. Medium effects on HAT from aliphatic C-H bonds to CumO(•) have been also investigated. With basic substrates, from large to very large decreases in kH have been measured with increasing solvent hydrogen bond donor (HBD) ability or after addition of protic acids or alkali and alkaline earth metal ions, with kinetic effects that exceed 2 orders of magnitude in the reactions of tertiary alkylamines and alkanamides. Solvent hydrogen bonding, protonation, and metal ion binding increase the electron deficiency and the strength of the C-H bonds of these substrates deactivating these bonds toward HAT, with the extent of this deactivation being modulated by varying the nature of the substrate, solvent, protic acid, and metal ion. These results indicate that through these interactions careful control over the HAT reactivity of basic substrates toward CumO(•) and other electrophilic radicals can be achieved, suggesting moreover that these effects can be exploited in an orthogonal fashion for selective C-H bond functionalization of substrates bearing different basic functionalities.
TL;DR: To design a more reactive catalyst from edge exposed MoS2, one should focus on lowering the reaction barrier between the metal hydride and a proton from the hydronium in solution, supported by the agreement between the calculated barrier and the experimental turnover frequency.
Abstract: We report density functional theory (M06L) calculations including Poisson–Boltzmann solvation to determine the reaction pathways and barriers for the hydrogen evolution reaction (HER) on MoS2, using both a periodic two-dimensional slab and a Mo10S21 cluster model. We find that the HER mechanism involves protonation of the electron rich molybdenum hydride site (Volmer–Heyrovsky mechanism), leading to a calculated free energy barrier of 17.9 kcal/mol, in good agreement with the barrier of 19.9 kcal/mol estimated from the experimental turnover frequency. Hydronium protonation of the hydride on the Mo site is 21.3 kcal/mol more favorable than protonation of the hydrogen on the S site because the electrons localized on the Mo–H bond are readily transferred to form dihydrogen with hydronium. We predict the Volmer–Tafel mechanism in which hydrogen atoms bound to molybdenum and sulfur sites recombine to form H2 has a barrier of 22.6 kcal/mol. Starting with hydrogen atoms on adjacent sulfur atoms, the Volmer–Tafel...
TL;DR: This report briefly discusses the reusable directing group assisted functionalization of unactivated remote alkyl C–H bonds and their synthetic potential in organic chemistry and their potential utility for the rapid synthesis of complex molecular entities.
TL;DR: Energetic evaluation indicates that, in addition to the molecular compound 4, some ionic derivatives, 9, 11, 12, 17, 19, and 22, also have high densities and excellent detonation pressures and velocities, which highlight the application potential of nitramino hydrogen-bonded interactions in the design of advanced energetic materials.
Abstract: Diverse functionalization was introduced into the pyrazole framework giving rise to a new family of ternary hydrogen-bond induced high energy density materials. By incorporating extended cationic interactions, nitramine-based ionic derivatives exhibit good energetic performance and enhanced molecular stability. Performance parameters including heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. It is noteworthy to find that 5-nitramino-3,4-dinitropyrazole, 4, has a remarkable measured density of 1.97 g cm–3 at 298 K, which is consistent with its crystal density (2.032 g cm–3, 150 K), and ranks highest among azole-based CHNO compounds. Energetic evaluation indicates that, in addition to the molecular compound 4, some ionic derivatives, 9, 11, 12, 17, 19, and 22, also have high densities (1.83–1.97 g cm–3), excellent detonation pressures and velocities (P, 35.6–41.6 GPa; vD, 8880–9430 m s–1), as well as acceptable impact and friction sen...
TL;DR: Recent work has demonstrated that π-coordinating functional groups can also assist in guiding metal complexes for site-selective C - H bond activation, which significantly expands the scope of C- H activation reactions in organic synthesis.
Abstract: Transition-metal-catalyzed C - H activation is considered to be an important tool in organic synthesis and has been accepted and widely used by chemists because it is straightforward, cost-effective, and environmentally friendly. A variety of functional groups have been used to direct metal complexes and achieve regioselective C - H activation. Most directing is achieved through the σ-bond coordination of functional groups to the metal catalyst, followed by ortho-selective C - H bond cleavage. However, recent work has demonstrated that π-coordinating functional groups can also assist in guiding metal complexes for site-selective C - H bond activation. This emerging approach significantly expands the scope of C - H activation reactions in organic synthesis. Herein, recent developments in this field are summarized.
TL;DR: A continuous shape measures analysis of the coordination polyhedra of a host of transition metal complexes with bi- and multidentate ligands discloses the distortion pathway associated with each particular topology of the chelate rings formed.
Abstract: A continuous shape measures analysis of the coordination polyhedra of a host of transition metal complexes with bi- and multidentate ligands discloses the distortion pathway associated with each particular topology of the chelate rings formed. The basic parameter that controls the degree of distortion is the metal-donor atom bond distance that induces nonideal bond angles due to the rigidity of the ligands. Thus, the degree of distortion within each family of complexes depends on the atomic size, on which the high- or low-spin state has a large effect. Special attention is therefore paid to several spin-crossover systems and to the enhanced distortions that go along with the transition from low- to high-spin state affected by temperature, light, or pressure. Several families of complexes show deviations from the expected distortion pathways in the high-spin state that can be associated to the onset of intermolecular interactions such as secondary coordination of counterions or solvent molecules. Also, significant displacement of counterions in an extended solid may result from the changes in metal-ligand bond distances when ligands are involved in intermolecular hydrogen bonding.
TL;DR: It is shown here how the transition metal-catalyzed direct remote C–H functionalization of alkyl groups via C(sp3)–H bond activation can be modified for high-performance liquid chromatography.
Abstract: Correction for ‘Transition metal-catalyzed direct remote C–H functionalization of alkyl groups via C(sp3)–H bond activation’ by Guanyinsheng Qiu, et al., Org. Chem. Front., 2015, 2, 169–178.
TL;DR: In this article, density functional theory with dispersion corrections (DFT-D2) was applied to the cellulose Iβ crystal lattices with the experimentally determined carbon and oxygen coordinates, which revealed that the HO stretch vibrations of cellulose are highly coupled and delocalized through intra-and interchain hydrogen bonds involving all HO groups in the crystal.
Abstract: Hydrogen bonds play critical roles in noncovalent directional interactions determining the crystal structure of cellulose. Although diffraction studies accurately determined the coordinates of carbon and oxygen atoms in crystalline cellulose, the structural information on hydrogen atoms involved in hydrogen-bonding is still elusive. This could be complemented by vibrational spectroscopy; but the assignment of the OH stretch peaks has been controversial. In this study, we performed calculations using density functional theory with dispersion corrections (DFT-D2) for the cellulose Iβ crystal lattices with the experimentally determined carbon and oxygen coordinates. DFT-D2 calculations revealed that the OH stretch vibrations of cellulose are highly coupled and delocalized through intra- and interchain hydrogen bonds involving all OH groups in the crystal. Additionally, molecular dynamics (MD) simulations of a single cellulose microfibril showed that the conformations of OH groups exposed at the microfibril surface are not well-defined. Comparison of the computation results with the experimentally determined IR dichroism of uniaxially aligned cellulose microfibrils and the peak positions of various cellulose crystals allowed unambiguous identification of OH stretch modes observed in the vibrational spectra of cellulose.
TL;DR: In this paper, the competitive coadsorption of several small molecules in M-MOF-74 with in situ infrared spectroscopy and ab initio simulations was examined, and it was shown that the binding energy at the most favorable (metal) site is not a sufficient indicator for prediction of molecular adsorption and stability.
Abstract: The importance of coadsorption for applications of porous materials in gas separation has motivated fundamental studies, which have initially focused on the comparison of the binding energies of different gas molecules in the pores (i.e., energetics) and their overall transport. By examining the competitive coadsorption of several small molecules in M-MOF-74 (M = Mg, Co, Ni) with in situ infrared spectroscopy and ab initio simulations, we find that the binding energy at the most favorable (metal) site is not a sufficient indicator for prediction of molecular adsorption and stability in MOFs. Instead, the occupation of the open metal sites is governed by kinetics, whereby the interaction of the guest molecules with the MOF organic linkers controls the reaction barrier for molecular exchange. Specifically, the displacement of CO2 adsorbed at the metal center by other molecules such as H2O, NH3, SO2, NO, NO2, N2, O2, and CH4 is mainly observed for H2O and NH3, even though SO2, NO, and NO2 have higher binding...
TL;DR: The presented data make an interesting case for organometallic chemistry that provides inherently better results when applied to substrates containing unprotected rather than protected -OH, -NHR, or -COOH groups.
Abstract: Reactions of internal alkynes with R3M-H (M = Si, Ge, Sn) follow an unconventional trans-addition mode in the presence of [Cp*Ru(MeCN)3]PF6 (1) as the catalyst; however, the regioselectivity is often poor with unsymmetrical substrates. This problem can be solved upon switching to a catalyst comprising a [Ru-Cl] bond, provided that the acetylene derivative carries a protic functional group. The R3M unit is then delivered with high selectivity to the alkyne-C atom proximal to this steering substituent. This directing effect originates from the ability of the polarized [Ru-Cl] bond to engage in hydrogen bonding with the protic substituent, which helps upload, activate, and lock the alkyne within the coordination sphere. An additional interligand contact of the chloride with the -MR3 center positions the incoming reagent in a matching orientation that translates into high regioselectivity. The proposed secondary interactions within the loaded catalyst are in line with a host of preparative and spectral data and with the structures of the novel ruthenium π-complexes 10 and 11 in the solid state. Moreover, the first X-ray structure of a [Ru(σ-stannane)] complex (12a) is presented, which indeed features peripheral Ru-Cl···MR3 contacts; this adduct also corroborates that alkyne trans-addition chemistry likely involves σ-complexes as reactive intermediates. Finally, it is discussed that interligand cooperativity might constitute a more general principle that extends to mechanistically distinct transformations. The presented data therefore make an interesting case for organometallic chemistry that provides inherently better results when applied to substrates containing unprotected rather than protected -OH, -NHR, or -COOH groups.
TL;DR: In this article, a tetrahedral block of two H2O molecules and four O:H O bonds is proposed to explain the anomalous behavior of water ice under mechanical compression, thermal excitation, and molecular undercoordination.
TL;DR: An adsorbent was prepared by decorating alumina onto the surface of multi-wall carbon nanotubes (MWCNTs) for simultaneous removal of cadmium ion (Cd(II) ion) and trichloroethylene (TCE) from groundwater as discussed by the authors.
TL;DR: A strategy for combining covalent and non-covalent cross-links to construct multifunctional rubber materials with intelligent self-healing and shape memory ability is demonstrated and might open a promising pathway to fabricate intelligent multifunctionals polymers with versatile functions.
Abstract: A strategy for combining covalent and non-covalent cross-links to construct multifunctional rubber materials with intelligent self-healing and shape memory ability is demonstrated. Rubbers were prepared by self-assembly of complementary polybutadiene oligomers bearing carboxylic acid and amine groups through reversible ionic hydrogen bonds via the acid–base reaction, and then further covalently cross-linked by tri-functional thiol via the thiol-ene reaction. The resulting polymers exhibit self-healing and shape memory functions owing to the reversible ionic hydrogen bonds. The covalent cross-linking density can be tuned to achieve tailorable mechanical and stimuli-responsive properties: a low covalent cross-linking density maintains the remarkable self-healing capability of rubber at ambient temperature without any external stimulus, while a high covalent cross-linking density improves the mechanical strength and induces shape memory behavior, but effective self-healing needs to be triggered at high temperature. This strategy might open a promising pathway to fabricate intelligent multifunctional polymers with versatile functions.
TL;DR: This species has been found to react with ammonia and water, activating the E–H bonds in both substrates by formal oxidative addition to afford the corresponding phosphorus(V) compounds.
Abstract: The synthesis of a phosphorus(III) compound bearing a N,N-bis(3,5-di-tert-butyl-2-phenoxy)amide ligand is reported. This species has been found to react with ammonia and water, activating the E-H bonds in both substrates by formal oxidative addition to afford the corresponding phosphorus(V) compounds. In the case of water, both O-H bonds can be activated, splitting the molecule into its constituent elements. To our knowledge, this is the first example of a compound based on main group elements that sequentially activates water in this manner.
TL;DR: In this paper, the degradation mechanism of perovskite solar cells has been investigated using density functional theory calculations both with and without the van der Waals correction, and the results indicate that the CH3NH3+ (MA) cations preferentially orient with the NH3 group pointing into the surface, which allows the formation of more hydrogen-halide hydrogen bonds between the MA cations and the halides.
Abstract: Although there have been tremendous breakthroughs in perovskite solar cells over the past few years, degradation of perovskite has been a huge problem. Recently, a number of experimental studies have demonstrated that organic–inorganic halide perovskite materials are sensitive to humid air, and several degradation mechanisms have been proposed. However, the decomposition process of perovskites is only partially known and controversial. In this paper, we theoretically study the structures of the tetragonal CH3NH3PbI3 and CH3NH3PbBr3 (110) surfaces and the degradation mechanism using density functional theory calculations both with and without the van der Waals correction. The computed results indicate that the CH3NH3+ (MA) cations preferentially orient with the NH3 group pointing into the surface. This allows the formation of more hydrogen···halide hydrogen bonds between the MA cations and the halides. Moreover, the interactions of water molecules, hydroxyl radicals, and hydroxide ions with the perovskite ...
TL;DR: In this paper, a detailed chronological review of the experimental studies and insights into the complex nature of water and hydrogen bonding gained from them is presented, and a subsequent letter will review the corresponding theoretical advances.