Reactive Bond Research Articles

Theoretical investigations of the interaction between diatomic molecules and coinage metal atoms

In this contribution, we investigate the nature of the electronic interaction between gas phase CO and NO with coinage metal atoms {Cu, Ag, Au} in different charge states. The electronic structure is first characterised by means of state-of-the-art coupled-cluster calculations for a wide range of configurations. An analytical Reactive Bond Order (REBO) force field is used to fit the data, revealing a strong corrugation of the potential energy landscape in some cases. The fundamental vibrational bands are variationally computed for the different system. It is found that the metal determines the binding interaction and the spectroscopic signature of the complexes, as well as their structure and geometry.

Effect of graphene and carbon-nitride nanofillers on the thermal transport properties of polymer nanocomposites: A combined molecular dynamics and finite element study.

Low thermal conductivity of polymers, which is one of the considerable drawbacks of commonly used composite structures, has been the focus of many researchers aiming to achieve high-performance polymer-based nanocomposites through the inclusion of highly thermally conductive fillers inside the polymer matrices. Thus, in the present study, a multiscale scheme using nonequilibrium molecular dynamics and the finite element method is developed to explore the impact of different nanosized fillers (carbon-nitride and graphene) on the effective thermal conductivity of polyethylene-based nanocomposites. We show that the thermal conductivity of amorphous polyethylene at room temperature using the reactive bond order interatomic potential is nearly 0.36±0.05W/mK. Also, the atomistic results predict that, compared to the C_{3}N and graphene nanosheets, the C_{2}N nanofilm presents a much stronger interfacial thermal conductance with polyethylene. Furthermore, the results indicate that the effective thermal conductivity values of C_{2}N-polyethylene, C_{3}N-polyethylene, and graphene-polyethylene nanocomposite, at constant volume fractions of 1%, are about 0.47, 0.56, and 0.74W/mK, respectively. In other words, the results of our models reveal that the thermal conductivity of fillers is the dominant factor that defines the effective thermal conductivity of nanocomposites.

Energy transfers in a weakly coupled gas-surface system: The scattering of CO from MgO(001)

This work reports on quasi-classical dynamics simulations of the non-reactive scattering of CO from a prototypical cubic ionic surface. We shed light on the role of the incidence energy, the initial ro-vibrational state of impinging CO, and the effect of surface atom motion on the scattering behaviour of the molecules. Our results rely on a novel high-dimensional potential energy surface, which is fitted using a modified reactive bond order force field to reproduce reference energy data obtained from periodic embedding density functional theory. The scattering process is found to be strongly influenced by the anisotropy of the potential for CO impinging either from the C-end or O-end of the molecule. The distinct scattering features are significant at low incidence energies when surface atom motion is included in the simulations. This suggests that modelling energy transfer to phonons is very important to describe the dynamics of such weakly interacting systems.

Synthesis and Characterization of a New Aluminosilicate Molecular Sieve from Aluminosilica Perhydrate Hydrogel.

A novel structure aluminosilicate molecular sieve, named BUCT-3, was prepared by dynamic hydrothermal synthesis, and the critical factor to obtain the new structure is using an active silicon and aluminum source, aluminosilica perhydrate hydrogel. Meanwhile, only high content of O-O bonds can ensure the pure phase of BUCT-3. Through the characterization of x-ray powder diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), and so on, some structure and morphology information of BUCT-3 molecular sieves as well as the special silicon and aluminum source was obtained. It’s worth noticing that the O-O bonds of reactants can be reserved in the products, and thus, help us to get a new structure with cell parameters a = 8.9645 Å, b = 15.2727 Å, c = 11.3907 Å, α = 90°, β = 93.858°, γ = 90°. The crystal system is monoclinic. Though the thermostability of BUCT-3 is not satisfactory, its potential application derived from O-O bonds cannot be neglected.

The specific features of the liquid-phase oxidation of saturated esters. Kinetics, reactivity and mechanisms of formation of destruction products

Data on kinetics, reactivity, and mechanisms of formation of destruction products of the liquid-phase oxidation of saturated esters by molecular oxygen have been systematized and discussed. The ester group has both an activating and deactivating effects on the reactivity of the CH bonds of the alkoxyl (α′-, β′-, γ′-, and δ′-) and acyl (α-, β-, and γ-) groups. The activating effect in esters is weaker than in alcohols, ketones, and ethers and extends to the α- and α′-CH bonds. The reactivity of the β-, β′-, and γ′-CH bonds is significantly lower than that of the secondary CH bonds of hydrocarbons. Oxidation of the β-CH bonds of the acyl moieties of esters leads to HOO· radical, α,β-epoxy-, α,β-dihydroxy-, and α,β-unsaturated esters, but not to hydroperoxides. Upon the oxidation of esters, the highly active α-carboxy-alkylperoxy-, α-acyloxyperoxy-, and HOO· -radicals are formed. The recombination reactions involving these radicals occur both with and without chain termination. The specificity of the decomposition of ester hydroperoxides are due to intra- and intermolecular interactions of the hydroperoxide groups with the ester groups. Labile peroxide intermediates (α-hydroxyperoxy-esters, peroxyesters, and peroxylactones) are formed through the corresponding tetrahedral intermediates and decay predominantly by the non-radical pathway. The recombination of the peroxyl radicals and the decay of labile peroxides result in the parallel accumulation of peroxide and non-peroxide products during the oxidation of esters.

Bond reactivity indices approach analysis of the [2+2] cycloaddition of jatrophane skeleton diterpenoids from Euphorbia gaditana Coss to tetracyclic gaditanone

The reaction mechanism of the intramolecular [2 + 2] cycloaddition from a jatrophane precursor to the gaditanane skeleton, an unprecedented 5/6/4/6-fused tetracyclic ring framework recently isolated from Euphorbia spp., was studied using the bond reactivity indices approach. Furthermore, six diterpenoids, including three undescribed jatrophanes isolated from E. gaditana Coss, were described. The structures of these compounds were deduced by a combination of 2D NMR spectroscopy and ECD data analysis.

Hydrosilylation of High Porosity Porous Silicon with 1-Hexene in Supercritical CO2 Fluid

The surface of as-formed porous silicon (PSi) is terminated by Si-H bonds. Hydrogen-terminated PSi is generally unstable due to the high reactivity of these Si-H bonds. Thermally activated hydrosilylation of organic groups on hydride-terminated PSi enhances PSi stability because Si-C bonds and much more stable than Si-H bonds and also because of steric hindrance provided by the long organic molecules. In our previous work, gas-phase hydrosilylation for PSi with porosity of 68% was achieved by using 1-hexene, and highly stable luminescence was obtained by organic group termination [1].The higher the porosity, the higher the luminescent efficiency of PSi. When the porosity is higher than ~75%, however, it is extremely difficult for the as-formed PSi to preserve its fine structure due to the surface tension induced during air-drying. The supercritical fluid is characterized for its zero surface tension [2]. In this work, the process of both drying and hydrosilylation in the supercritical fluid for high porosity PSi was developed. The effect of this process was investigated in terms of FTIR and photoluminescence (PL) measurement.PSi layers were formed by anodization of p-type, (100)-oriented, and 5-10 Ω・cm silicon substrates with an Al back contact. Layers with porosity of 80% and thickness of approximately 1, 2, 5, and 10 mm were obtained by etching 200, 400, 1000, and 2000 s in the solution of HF (55 wt. %): ethanol = 1:1, at a constant current density of 10 mA/cm2. Following formation, PSi was rinsed in ethanol, then, without drying, placed inside a high-pressure reactor (volume: 5.5 ml) filled with ethanol. The drying and hydrosilylation were accomplished through the following procedures. First, liquid CO2 was flowed through the reactor to expel the ethanol inside and continuously purged until the reactor pressure was up to 10 MPa. Then, the reactor was heated at 80°C to yield the supercritical fluid CO2. The supercritical condition of 10 MPa and 80°C was maintained for 30 min to dry the PSi sample. After drying, the CO2 was continuously pumped into until the reactor pressure up to 15 MPa, and the reactor was heated at 150 °C. At this supercritical condition of 15 MPa and 150°C, CO2 - 1-hexene solution was supplied for 4 hours to achieve hydrosilylation. Finally, the reactor was cooled to the room temperature, and the supercritical CO2 was released.FTIR spectra of PSi samples before and after the hydrosilylation process were investigated. The FTIR results showed substitution of hydrogen on the PSi surface by organic groups via hydrosilylation.Photoluminescence of these samples were measured by exciting with a laser diode (wavelength is 405 nm) for 4 hours. Figure 1 illustrates the PL vs. time results of two samples (porosity 80%, thickness 2mm). Compared with the PL of the sample dried in the supercritical fluid, the sample after drying and hydrosilylation process shows good stability. The result indicates the availability of supercritical process for high porosity PSi. Gelloz, T. Iriyama, N. Takura, and E. Kondoh, and L. Jin, ECS Journal of Sol. Stat. Sci. and Tech. 8 (9), R109-R113 (2019).Kondoh and H. Kato, Microeletron, Eng. 64, 495-499 (2002). Figure 1

Temporary or removable directing groups enable activation of unstrained C-C bonds.

Carbon-carbon (C-C) bonds constitute basic skeletons in most organic molecules. One can imagine that selective manipulation of C-C bonds would provide a direct approach to edit or alter molecular scaffolds but has been an ongoing challenge. Due to the kinetic inertness of C-C bonds, the common strategies of activating these bonds by transition metals rely on either the use of highly strained substrates or the assistance of a permanent directing group (DG), in which strain relief or formation of stable metallocycles becomes the driving force. To allow more common and less strained compounds utilized as substrates for C-C activation, the use of temporary and removable DGs has emerged as an attractive strategy in the past two decades. A variety of C-C bonds in unstrained or less strained organic molecules now can be converted to more reactive metal-carbon bonds, and further downstream transformations have led to diverse synthetic methods. This review highlights the development of catalytic approaches that can activate unstrained C-C bonds enabled by temporary or removable DGs. The content is mainly divided based on the nature of the DGs: temporary and removable. Applications of these methods in syntheses of natural products or bioactive molecules are also discussed.

Enantiospecific Generation and Trapping Reactions of Aryne Atropisomers

Enantioenriched aryne atropisomers having a biaryl stereogenic axis vicinal to the reactive triple bond are demonstrated to exist. These reaction intermediates are easily produced in situ and can undergo the standard aryne cycloaddition chemistry in an enantiospecific manner. Notably, the aryne atropisomers herein have allowed the practical syntheses of a small nanographene as well as some triptycene and anthracene derivatives that embed stereogenic axes of controlled absolute configurations.

Bond Dissociation and Reactivity of HF and H2O in a Nano Test Tube.

Molecular motion and bond dissociation are two of the most fundamental phenomena underpinning the properties of molecular materials. We entrapped HF and H2O molecules within the fullerene C60 cage, encapsulated within a single-walled carbon nanotube (X@C60)@SWNT, where X = HF or H2O. (X@C60)@SWNT represents a class of molecular nanomaterial composed of a guest within a molecular host within a nanoscale host, enabling investigations of the interactions of isolated single di- or triatomic molecules with the electron beam. The use of the electron beam simultaneously as a stimulus of chemical reactions in molecules and as a sub-angstrom resolution imaging probe allows investigations of the molecular dynamics and reactivity in real time and at the atomic scale, which are probed directly by chromatic and spherical aberration-corrected high-resolution transmission electron microscopy imaging, or indirectly by vibrational electron energy loss spectroscopy in situ during scanning transmission electron microscopy experiments. Experimental measurements indicate that the electron beam triggers homolytic dissociation of the H-F or H-O bonds, respectively, causing the expulsion of the hydrogen atoms from the fullerene cage, leaving fluorine or oxygen behind. Because of a difference in the mechanisms of penetration through the carbon lattice available for F or O atoms, atomic fluorine inside the fullerene cage appears to be more stable than the atomic oxygen under the same conditions. The use of (X@C60)@SWNT, where each molecule X is "packaged" separately from each other, in combination with the electron microscopy methods and density functional theory modeling in this work, enable bond dynamics and reactivity of individual atoms to be probed directly at the single-molecule level.

3-Ylidene-1-pyrrolines: Synthesis, reactions and perspectives

3-Ylidene-1-pyrrolines are a class of five-membered cyclic imines possessing reactive imine bond and exocyclic double carbon–carbon bond, as well as nucleophilic nitrogen atom. In contrast to parent 1-pyrrolines, these compounds received much less attention from researchers. Neither methods of synthesis nor reactions of 3-ylidene-1-pyrrolines have ever been reviewed. However, a unique combination of reactive sites renders them suitable precursors for various pyrrolidine derivatives and complex polyheterocyclic molecules, as was demonstrated by recent papers. Thus, this digest reviews approaches to 3-ylidene-1-pyrrolines and their reactions and is aimed to provide a reader a general insight into chemistry of these heterocycles.

N-Tosylcarboxamide in C–H Functionalization: More than a Simple Directing Group

C–H activation with transition metal catalysis has become an important tool in organic synthesis for the functionalization of low reactive bonds and the preparation of complex molecules. The choice of the directing group (DG) proves to be crucial for the selectivity in this type of reaction, and several different functional groups have been used efficiently. This review describes recent advances in C–H functionalization of aromatic rings directed by a N-tosylcarboxamide group. Results regarding alkenylation, alkoxylation, halogenation, and arylation of C–H in the ortho position to the tosylcarboxamide are presented. Moreover, the advantage of this particular directing group is that it can undergo further transformation and act as CO or CON fragment reservoir to produce, in sequential fashion or one-pot sequence, various interesting (hetero)cycles such as phenanthridinones, dihydroisoquinolinones, fluorenones, or isoindolinones.

Covalent functionalization of fluorinated graphene through activation of dormant radicals for water-based lubricants

Targeted covalent functionalization of graphene derivatives and simultaneously preserving their intrinsic structure and property are an underexplored, urgent and challenging task in two-dimensional chemistry. Herein, we develop a novel and facile method to achieve lossless covalent functionalization of fluorinated graphene (FG) through activating dormant radicals, derived from stabilization from conjugation effect of surrounding aromatic regions/fluorine atoms and particular two-dimensional skeleton. The activated radicals under definite temperature initiate acrylic acid (AA) to be grafted onto FG surface without any catalyst, completely different from traditional nucleophilic substitution (SN) reaction through sacrificing fluorocarbon bonds. Compared to destructive self-lubricating ability of FG-PEI from SN reaction, obtained FG-AA improves water dispersibility of hydrophobic FG and simultaneously maintains intrinsic self-lubricating ability with limited commensurate stacking and week interlayer interactions. Therefore, FG-AA presents excellent tribological performance as water-based lubricant additive, regarded as eco-friendly and sustainable system, whose friction coefficient and wear rate have about 66% and 82% decrease compared to that of FG-PEI, respectively. Moreover, taking advantage of such FG chemistry, the activated radicals and originally reactive fluorocarbon bonds also offer two non-interfering routes to implement stepwise double functionalization of graphene. Designing this strategy in mind expands the applications of FG in aqueous environment and enriches graphene chemistry.

DFT Investigation on the Electronic Properties and Intramolecular Hydrogen Bond of Trans-Cisand Cis-TransMethyl Substituted N-Benzoyl-N’-(2-pyridyl)thiourea

Five single molecule methyl substituted Benzoyl pyridinylthiourea compounds namely N-benzoyl-N’-(2-pyridyl)thiourea, N-benzoyl-N’-(6-methyl-2-pyridyl)thiourea, N-benzoyl-N’-(5-methyl-2-pyridyl)thiourea, N-benzoyl-N’-(4-methyl-2-pyridyl) thiourea and N-benzoyl-N’-(3-methyl-2-pyridyl)thiourea are investigate theoretically for trans-cis and cis-trans conformation at B3LYP 6-31G(d,p) level of theory. Electronic properties have been analyzed by Gaussian 09W package and AIMAll code. Methyl substituent and its position give noticeable effect to reactivity, stabilization, and hydrogen bond interaction strength. AIM prove that 6-methyl substituted on pyridyl ring has significant effect to preferent conformation.

Selective breakage of C[sbnd]H bonds in the key oxidation intermediates of gaseous formaldehyde on self-doped CaSn(OH)6 cubes for safe and efficient photocatalysis

Production of toxic intermediates is a vital issue that remains as the major hindrance to the advancement of photocatalysts for air purification applications. It is predicted theoretically that the reaction pathway of photocatalysis can be regulated effectively by the interactions between key intermediate reactant (e.g., HCOOH) and photocatalyst. Inspired by such prediction, a new strategy is proposed and validated to control the reaction pathway and the associated formation of toxic intermediates via selective breakage of chemical bonds of reactants. Herein, we introduce a Sn self-doped CaSn(OH)6 photocatalyst to realize safe and efficient photocatalytic oxidation of formaldehyde through selective breakage of C–H bonds in HCOOH formed as reaction intermediate. This photocatalyst altered the charge transfer direction to promote charge separation and to modify the surface distribution of electrons for the activation of the C–H bond. Through selective attack on the C–H bond by hydroxyl radicals, the reaction pathway was altered to avoid generation of toxic by-products (e.g., CO). The combination of in situ DRIFTS and continuous flow reaction tests indicated that enhanced photochemical destruction of formaldehyde can be achieved by effectively suppressing generation of toxic intermediates. The obtained Sn-CaSn(OH)6 reached a quantum efficiency of 1.43 × 10−8 molecules/photon and a high photocatalytic formaldehyde degradation activity of 79 %, much higher than those of Sn-CaSn(OH)6(m) (30 %) and pristine CaSn(OH)6 (no activity). This is attributed to the advantages of Sn self-doping that optimized the local electron structure. This research could provide new insight for pursuit of safe and efficient photocatalysts for air pollution control.

Assembly of Materials Building Blocks into Integrated Complex Functional Systems

Assembly of Materials Building Blocks into Integrated Complex Functional Systems

Modifying the Metal Oxide Filler with a Silicon-Organic Oligomer in a Solution of an Organic Solvent

The use of tungsten dioxide as a filler for a non-polar polymer matrix is limited due to its high hydrophilicity and abrasiveness, which degrades the properties of the filled polymers. The paper presents the results of studies on the surface modification of tungsten oxide with organosilicon polyethylsiloxane. The mechanisms for modifying the surface of tungsten dioxide, based on the fixation of the modifier under the action of intermolecular forces of attraction and interaction of the hydroxyl groups of the oxide surface with the reactive bonds of the Si-H oligomer, have been established. To create additional active centers in the form of groups (–OH) on the surface of tungsten dioxide, it was boiled, which contributes to the forced hydroxylation of the surface. The adsorption of polyethylsiloxane with powdered tungsten dioxide from n-hexane solution was investigated. The results on determination of the wetting angle of unmodified and modified tungsten dioxide powder are presented. It has been established that modification with polyethylsiloxane leads to an increase in the wetting angle of tungsten dioxide to 121o, which indicates its hydrophobic properties.

A conceptual DFT analysis of the plausible mechanism of some pericyclic reactions

Out of several pericyclic reactions, Diels-Alder (DA) reaction is one of the most widely used synthetic processes. In the present work, several models and methodologies have been used to determine and to analyze the plausible mechanism of some representative DA cycloaddition reactions. A comparison between the dual descriptor and the bond reactivity indices corresponding to the natural bond orbital of the reagents is included, which provides a complete description of the plausible reaction mechanism. In the next step, two very recent models are used to determine the local electronic density transfer and redistribution between the reactants involved. The description of the local electronic density transfer has been made in two stages; first, the variation in the net charge on the atoms is obtained, and then, the electronic density transfer between the natural bond orbitals is calculated. The values obtained using the two models are correlated with the experimental rate constants of the reactions. Finally, the natural bond orbitals are obtained at several steps along the reaction path and the variation in their partial occupation is compared with the corresponding electron density transfer among these orbitals. Furthermore, frontier molecular orbital (FMO) approach has been employed to understand the more feasible way of interaction between the DA pair. Relative electrophilicity descriptors like net electrophilicity (∆ω±), net reactivity index (NRI, Δ $$ {\omega}_R^{\pm } $$ ), and electrophilicity difference (∆ω) between DA pairs have also been employed to describe the studied reaction mechanisms especially whether they follow non-polar-concerted/polar-stepwise pathway along with their classification in terms of normal or inverse electron demand. Furthermore, adaptive natural density partitioning method (AdNDP) and energy decomposition analyses (EDA) in conjunction with natural orbital for chemical valence (NOCV) have been made use of in order to analyze the actual bonding situation in the transition state (TS).

Ultra-thin anodized aluminium dielectric films: the effect of citric acid concentration and low-voltage electronic applications

Anodically oxidized, ultra-thin (d < 10 nm) aluminium films emerge as the dielectric of choice for low-cost thin film capacitors (TFCs), thin film transistors (TFTs), and bio- and chemical sensors. In this work, the dielectric properties of ultra-thin aluminium oxide films grown by anodization in aqueous solutions of citric acid (CA) have been studied. It is observed that the electrolyte strength variation from 0.1 mM to 1000 mM has virtually no influence on the chemical composition, surface morphology and the dielectric properties of the fabricated alumina films. The anodized films are very smooth having RMS area roughness around ∼5 Å. This was further improved after deposition of n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) to ∼4 Å. Also, the XRD and elemental analysis using EDS and XPS unambiguously confirms that the obtained oxide films are amorphous, stoichiometric Al2O3 without any carbon contamination. The fabricated Al/Al2O3/Al MIM capacitors show almost ideal capacitor characteristics from 10 Hz to 100 kHz. It has been found that the OTS coating does not only improve the capacitor frequency response further but also reduces the leakage current through the dielectric layer by passivating reactive dangling bonds on the oxide surface. As a result of the favourable properties of the anodized Al2O3/OTS films, high-performance, low threshold voltage organic thin film transistors (OTFTs) operating below 1 V are successfully demonstrated.

From Pd(OAc)2 to Chiral Catalysts: The Discovery and Development of Bifunctional Mono-N-Protected Amino Acid Ligands for Diverse C-H Functionalization Reactions.

The functionalization of unactivated carbon-hydrogen bonds is a transformative strategy for the rapid construction of molecular complexity given the ubiquitous presence of C-H bonds in organic molecules. It represents a powerful tool for accelerating the synthesis of natural products and bioactive compounds while reducing the environmental and economic costs of synthesis. At the same time, the ubiquity and strength of C-H bonds also present major challenges toward the realization of transformations that are both highly selective and efficient. The development of practical C-H functionalization reactions has thus remained a compelling yet elusive goal in organic chemistry for over a century.Specifically, the capability to form useful new C-C, C-N, C-O, and C-X bonds via direct C-H functionalization would have wide-ranging impacts in organic synthesis. Palladium is especially attractive as a catalyst for such C-H functionalizations because of the diverse reactivity of intermediate palladium-carbon bonds. Early efforts using cyclopalladation with Pd(OAc)2 and related salts led to the development of many Pd-catalyzed C-H functionalization reactions. However, Pd(OAc)2 and other simple Pd salts perform only racemic transformations, which prompted a long search for effective chiral catalysts dating back to the 1970s. Pd salts also have low reactivity with synthetically useful substrates. To address these issues, effective and reliable ligands capable of accelerating and improving the selectivity of Pd-catalyzed C-H functionalizations are needed.In this Account, we highlight the discovery and development of bifunctional mono-N-protected amino acid (MPAA) ligands, which make great strides toward addressing these two challenges. MPAAs enable numerous Pd(II)-catalyzed C(sp2)-H and C(sp3)-H functionalization reactions of synthetically relevant substrates under operationally practical conditions with excellent stereoselectivity when applicable. Mechanistic studies indicate that MPAAs operate as unique bifunctional ligands for C-H activation in which both the carboxylate and amide are coordinated to Pd. The N-acyl group plays an active role in the C-H cleavage step, greatly accelerating C-H activation. The rigid MPAA chelation also results in a predictable transfer of chiral information from a single chiral center on the ligand to the substrate and permits the development of a rational stereomodel to predict the stereochemical outcome of enantioselective reactions.We also describe the application of MPAA-enabled C-H functionalization in total synthesis and provide an outlook for future development in this area. We anticipate that MPAAs and related next-generation ligands will continue to stimulate development in the field of Pd-catalyzed C-H functionalization.