CC Triple Bond Research Articles

Influence of external electric field on properties of Cyclotriparaphenyl[6]carbon

Cyclotriparaphenyl[6]carbon is a hypothetical derivative compound of cyclo[12]carbon, in which three CC triple bonds are replaced by three benzene rings. Comprehensive investigations of influence of external electric field (EEF) on cyclotriparaphenyl[6]carbon have been performed from theoretical aspect in this work. The maximum appropriate applied electric field strength is 0.0265 a.u., electron detachment will occur when EEF exceeds this value. When the EEF is in the range of 0–0.0265 a.u., with the increase of EEF, the shape of cyclotriparaphenyl[6]carbon turns from a circle to oval, the HOMO-LUMO gap gradually decreases from 6.046 eV at 0 a.u. to 2.322 eV at 0.0265 a.u., and its absorption band extends to VL (visible light) region and near-infrared region little by little. When the EEF are 0.025 a.u. and 0.0265 a.u., its maximum absorption wavelengths are 1220.6 nm and 1383.5 nm, respectively. HOMA (Harmonic oscillator measure of aromaticity), AV1245 and electron localization function (ELF) calculation results indicate that cyclotriparaphenyl[6]carbon has no aromaticity in the EEF range of 0–0.0265 a.u.. The compound exhibitspromising potential forapplication inthefield of colordevelopingcompound materials.

Direct Spectroscopic Identification of BN-Arynes and Subtle Steric Effects on Nitrogen Fixation.

1,2-Azaborinines are the BN analogues of arynes through exchange of the formal CC triple bond by an isoelectronic BN bond. The BN-arynes are an underexplored class of reactive intermediates. Dibenzo[c,e][1,2]azaborinine (10,9-BN-phenanthryne) 1 was inferred as reactive intermediate by trapping reactions. Here it is shown that 1 can be generated in the gas phase by thermolysis from the pyridine adduct of 9-azido-9-borafluorene by cleavage of the dative bond with pyridine and dinitrogen extrusion. The ionization potential of 1 is 8.2 eV with ionization resulting from the π HOMO. Under cryogenic matrix isolation conditions, 9-azido-9-borafluorene photolysis results in isomerization to the dinitrogen adduct of 1 without involvement of a triplet borylnitrene intermediate. Photochemical nitrogen extrusion from 1 ⋅ N2 is not possible and nitrogen fixation is irreversible under cryogenic conditions. In contrast, 2,4,7,9-tetra-tert-butyldibenzo[c,e][1,2]azaborinine can be photogenerated from the corresponding azidoborole precursor under cryogenic matrix isolation conditions, and nitrogen fixation is precluded due to steric hindrance. The BN stretching vibration at about 1750 cm-1 is much weaker than in typical linear diaryl iminoboranes.

A computational characterization of the reaction mechanisms for the reactions N(2D) + CH3CN and HC3N and implications for the nitrogen-rich organic chemistry of Titan

The reactions of atomic nitrogen in its first electronically excited state, N(2D), with acetonitrile (CH3CN) and cyanoacetylene (HC3N) have been investigated by performing electronic structure calculations of the doublet potential energy surfaces and RRKM estimates of the product branching fractions. According to our results, the insertion of N(2D) into one of the sigma CH bonds of acetonitrile leading to the formation of cyanomethanimine (also known as iminoacetonitrile) and the N(2D) addition to the CC triple bond of cyanoacetylene leading to the formation of dicyanocarbene are the main reaction pathways under the conditions typical of the upper atmosphere of Titan, the massive moon of Saturn. Other molecular products originating from other reaction pathways only give a minor contribution.Implications for the atmospheric chemistry of Titan, as well as implications in prebiotic chemistry and in the chemistry of the interstellar medium, are also noted.

Synthesis and structures of bimetallic (Mg/K) acetylide complexes from terminal alkynes and an Mg–Mg-bonded compound

The reactions of α-diimine-ligated dimagnesium(I) compound [K(THF)3]2[LMg−MgL] (1, L = [(2,6-iPr2C6H3)NC(Me)]22−) and terminal alkynes afford bimetallic (Mg/K) acetylide complexes (2–10). The reactions proceed via reductive dehydrogenation of the alkynes with release of H2, while the original Mg(I) center is oxidized to Mg(II). In the complexes, Mg atom is σ-coordinated either by one (2 and 3), two (4–9) or four (10) RCC− moieties. The (solvated) K atoms, on the other hand, are π-coordinated by the CC triple bonds and form extensive interactions with the NCCN backbone and aryl rings of the ligand and alkyl substituents of the alkyne. Interestingly, the versatile bonding modes of potassium ions result in three distinct aggregates of the complexes in the solid state, the monomer (2–7), dimer (8, 9), and polymer (10), where the latter two cases benefit from the “intermolecular” interactions of K+ ions with the ligands or acetylides.

Reactions of 1,2-Azaborinine, a BN-Benzyne, with Organic π Systems.

Ortho-benzyne and 1,2-azaborinine are related by the formal exchange of the CC triple bond by the isoelectronic BN unit. The (2 + 2) and (2 + 4) cycloaddition reactions of 1,2-azaborinine with the different organic π systems (ethene, ethyne, 1,3-butadiene, 1,3-cyclopentadiene, furan, benzene) were examined computationally using density functional, second-order perturbation, and coupled-cluster methods. All reactions of 1,2-azaborinine with the studied substrates are highly exothermic and involve the formation of Lewis acid-base complexes of 1,2-azaborinine and respective π systems. The interaction between the π bond of the substrates and the empty p orbital of the boron atom in these complexes is remarkably strong, resulting in two-step mechanisms for the (2 + 2) and (2 + 4) cycloaddition reactions. Cycloaddition reactions have lower barriers than CH insertion reactions, and (2 + 4) reactions are favored over (2 + 2) cycloadditions.

Synthesis, Characterization and Chemistry of Tetrakis(Propargylisocyanide) Copper(I) Complex

The kinetically unstable propargylisocyanide was reacted with the tetrakis(acetonitrile) copper(I) hexafluorophosphate and the formed complex was then involved in a copper-catalyzed alkyne-azide cycloaddition reaction (CuAAC). After the decomplexation of the adduct, the isocyanide was engaged in a Ugi reaction. By such a complexation, reactions can be carried out on the CC triple bond without the constraint of the instability of the free compound or the competitive reactivity of the isocyanide group.

The effect of metal silver(I) salt on CO2 conversion to α-alkylidene cyclic carbonates: A DFT study

The cycloaddition of CO2 with propargylic alcohol (PA) catalyzed by ILs has evoked great interest in the past few decades. Recent research found that metal-assisted catalytic system can achieve higher CO2 conversion and product yield than pure IL. However, the microscopic mechanisms of different catalytic systems have not been investigated in detail. In this study, considering activation sequences of the reactants, various reaction routes of PA-activated mechanism and CO2-activated mechanism in the catalytic system with or without metal participation were simulated respectively. The PA-activated mechanism was found to be the optimal path for the carboxylative cyclization of PA with CO2, and intramolecular cyclization was the rate-determining step. Due to the synergistic catalytic effect of [Ch][Triz] and AgNO3 in the reaction, the activation Gibbs free energy of 14.2 kcal/mol in metal-assisted system is lower than that in pure IL (24.9 kcal/mol). [Ch][Triz] promotes deprotonation of the hydroxyl and elimination of metal electrophile by providing hydrogen protons, while Ag salts facilitate the intramolecular cyclization step by activating CC triple bond of the substrate. Simultaneously, the influence of cations in ionic liquids is analyzed, and it is found that the weak interaction between CO2 and cations can indirectly affect the active center through electronic effects.

Titanomagnetite functionalized by amino acid-based ionic liquid and cobalt (Fe3-xTixO4-SiO2@TrpBu3+I−-Co(II)): A reusable bio-nanocomposite for the synthesis of aryl thioamides

An efficient and straightforward three-component reaction of alkynes (terminal and internal), elemental sulfur, and amides using novel bio-nanocomposite is described. The bio-nanostructure obtained from step-by-step coating the titanomagnetite core by silica, N,N,N-tributyltryptophanium iodide ionic liquid, and cobalt respectively. The Fe3-xTixO4-SiO2@TrpBu3+I−-Co(II) characterized though FT-IR, FESEM, EDAX, XRF, TGA/DTG, VSM, and XPS techniques. Its catalytic efficacy examined successfully in the solvent-free three-component reaction of alkynes (terminal and internal), S8, and amides to prepare the corresponding aryl thioamides via the CC triple bond cleavage. The reusability examination of the Fe3-xTixO4-SiO2@TrpBu3+I−-Co(II) bio-nanocomposite proceeded successfully within two runs. The recovered nanostructure characterized through EDAX and FESEM techniques that demonstrated no significant changes in the morphology and constitutive elements.

Reaction pathway change on plasmonic Au nanoparticles studied by surface-enhanced Raman spectroscopy

Gold nanoparticles (Au NPs) are nanoscale sources of light and electrons, which are highly relevant for their extensive applications in the field of photocatalysis. Although a number of research works have been carried out on chemical reactions accelerated by the energetic hot electrons/holes, the possibility of reaction pathway change on the plasmonic Au surfaces has not been reported so far. In this proof-of-concept study, we find that Au NPs change the reaction pathway in photooxidation of alkyne under visible light irradiation. This reaction produces benzil (COCO) without the presence of Au NPs. In contrast, as indicated by surface-enhanced Raman spectroscopic (SERS) results, the CC triple bonds (CC) adsorbed on Au NPs are converted into carboxyl (COOH) and acyl chloride (COCl) groups. The plasmonic Au NPs not only provide energetic charge carriers but also activate the reactant molecules as conventional heterogeneous catalysts. This study discloses the second role of plasmonic NPs in photocatalysis and bridges the gap between plasmon-driven and conventional heterogeneous catalysis.

Reactions of diborenes with terminal alkynes: mechanisms of ligand-controlled anti-selective hydroalkynylation, cycloaddition and C[triple bond, length as m-dash]C triple bond scission.

The reactions of terminal acetylenes with doubly Lewis base-stabilised diborenes resulted in different outcomes depending on the nature of the ligands at boron and the conformation of the diborene (cyclic versus acyclic). N-heterocyclic carbene (NHC)-stabilised diborenes tended to undergo anti-selective hydroalkynylation at room temperature, whereas [2 + 2] cycloaddition was observed at higher temperatures, invariably followed by a C–N bond activation at one NHC ligand, leading to the ring-expansion of the initially formed BCBC ring and formation of novel boron-containing heterocycles. For phosphine-stabilised diborenes only [2 + 2] cycloaddition was observed, followed by a rearrangement of the resulting 1,2-dihydro-1,2-diborete to the corresponding 1,3-isomer, which amounts to complete scission of both the B Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> B double and CC triple bonds of the reactants. The elusive 1,2-isomer was finally trapped by using a cyclic phosphine-stabilised diborene, which prevented rearrangement to the 1,3-isomer. Extensive density functional theory (DFT) calculations provide a rationale for the selectivity observed.

Tri-insertion with dearomatization of terminal arylalkynes using a carborane based frustrated Lewis pair template.

Intramolecular vicinal Frustrated Lewis Pairs (FLPs) have played a significant role in the activation of small molecules, and their stabilities and reactivities are found to strongly depend on the nature of the bridging units. This work reports a new carborane based FLP, 1-PPh2-2-BPh2-1,2-C2B10H10 (2), which reacts with an equimolar amount of p-R2NC6H4C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH (R = Me, Et, Ph) at room temperature to give CC triple bond addition products 1,2-[PPh2C(R2NC6H4) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHBPh2]-1,2-C2B10H10 (3) in high yields. Compounds 3 react further with two equiv. of p-R2NC6H4CCH (R = Me, Et) at 60–70 °C to give unprecedented stereoselective tri-insertion products, 3,3a,6,6a-tetrahydronaphtho[1,8a-b]borole tricycles (4), in which one of the aryl rings from arylacetylene moieties has been dearomatized with the formation of four stereocenters including one quaternary carbon center. It is noted that the phosphine unit functions as a catalyst during the reactions. After trapping and structural characterization of a key intermediate, a reaction mechanism is proposed, involving sequential alkyne insertion and 1,2-boryl migration.

On differences in substituent effects in substituted ethene and acetylene derivatives and their boranyl analogs

This article is the first attempt to present different influence of substituent effects on double and triple bonds and, conversely, to present the impact of these bonds on the electronic structure of substituents. For this purpose, quantum-mechanical calculations were made for X-substituted derivatives of ethene and acetylene with 27 diverse substituents representing a wide spectrum of electronic properties, from strongly electron-accepting to strongly electron-donating ones. In addition to these systems, their boranyl derivatives are also investigated. It turns out that the Hammett substituent constants do not correctly describe changes in the CC bond length in any of the considered family of systems. However, the relationships with the CB bond length are significantly better. It is shown that the triple bond in acetylene derivatives is much more resistant to external perturbations than the double bond in the analogs containing an ethene unit. As a consequence, in acetylene derivatives, the substituent effects on CC bond length are about half of the substituent effects in ethene derivatives. We suggest that the observed lack of a clear linear correlation between the length of the CC triple bond in acetylene derivatives and the value of electron density on this bond is due to the disturbing additional interaction between the structure of the X substituent in the xy plane and the π bond being in the same plane in the acetylene unit—on the contrary, this interaction is not possible in ethene analogs.

Theoretical prediction on the reactivity of the Co-mediated intramolecular Pauson-Khand reaction for constructing bicyclo-skeletons in natural products

The Co2(CO)8-mediated intramolecular Pauson-Khand reaction is an efficient approach for constructing polycyclic skeletons. Recently, some of us reported a series of this type reactions involving sterically-hindered enynes for synthesizing natural products with reasonable reaction rates and yields. However, the reason for the high reactivity of the reaction remains unclear. We employed density functional theory calculations to clarify the mechanism and reactivity for this reaction. In contrast with chain olefin reactants, CO insertion is considered to be the rate-determining step for the overall Pauson-Khand reaction of cyclooctene derivatives. The reduced activation free energy for the alkene insertion step is attributed to: i) the electron-withdrawing group in close proximity to the CC triple bond enhancing the reactivity of the alkyne moiety; ii) lower steric hindrance during alkene insertion when using the cyclooctene derivative. The effect of the substituent on the Co2(CO)8-mediated intramolecular Pauson-Khand reaction was then investigated. Internal alkenes exhibit lower reactivity than terminal alkenes because of the steric hindrance introduced by the substituted group. The cis internal alkene exhibits higher reactivity than the trans internal alkene. An ester group in close proximity to the CC triple bond significantly enhances the reactivity.

First-principle prediction of the existence of C64-graphyne and (BN)64

By using of the first-principles calculations based on density functional theory, a novel monolayer planar structure named C64-graphyne is predicted. Tetratomic and hexatomic rings, as well as CC triple bonds exist in this new stable structure with the lattice parameter of 9.291 Å. The carbon hexatomic ring in C64-graphyne contains two quite distinct CC bonds, which is known as cyclohexatriene. Its electronic band structures show a semiconductor nature with a narrow direct band gap of 0.35 eV. Interestingly, by substituting a carbon atom with one nitrogen atom either in the hexatomic ring or in the chain of C64-graphyne, two stable planar structures are obtained. Such doping with nitrogen atom induced metallic properties in this monolayer structure. Further investigation shows that the alternating substitution of boron and nitrogen atoms for all carbon atoms in C64-graphyne also induced a new stable structure, the (BN)64 structure. The electronic studies proved its insulator property with the band gap of 4.08 eV.

Perfect mechanical and robust electronic properties of new carbon nanothreads: A first principles study

We have investigated the mechanical and electronic properties of three types of one-dimensional carbon materials: diamond naonthreads (DNTs) and its mutational structure with CC triple bonds insertion (DNTs-C1 and DNTs-C2), using first-principles calculation. Our calculation results indicate that mechanical properties of DNTs can be obvious promoted by CC triple bonds inserted. Based on density function and deformation potential theory, electronic transport properties of DNTs are investigated. We find that DNTs, DNTs-C1 and DNTs-C2 are wide gap semiconductors. And the strain effect on band gap in DNTs, DNTs-C1 and DNTs-C2 weakens successively. Furthermore, the strain effect on carrier phonon-limited mobility in DNTs and DNTs-C1 is very limited. But the electron mobility in DNTs-C2 is very sensitive to compression stress due to the position of conduction band minimum shifted. Due to huge different between electron and hole mobility, DNTs behaves like n-type semiconductor, and DNTs-C1 behaves like p-type semiconductor. Our results suggest that DNTs, DNTs-C1 and DNTs-C2 have a wonderful application in lightweight and high-strength materials. Moreover, considering the wide gap and high mobility, they have potential applications on high-temperature devices, transparent conductors and so on.

Alkyne Activation with Gold(III) Complexes: A Quantitative Assessment of the Ligand Effect by Charge-Displacement Analysis.

A quantitative assessment of the Dewar-Chatt-Duncanson components of the Au(III)-alkyne bond in a series of cationic and dicationic bis- and monocyclometalated gold(III) complexes with 2-butyne via charge-displacement (CD) analysis is reported. Bonding between Au(III) and 2-butyne invariably shows a dominant σ donation component, a smaller, but significant, π back-donation, and a remarkable polarization of the alkyne CC triple bond toward the metal fragment. A very large net electron charge transfer from CC triple bond to the metal fragment results, which turns out to be unexpectedly insensitive to the charge of the complex and more strictly related to the nature of the ancillary ligand. The combination of σ donation, π back-donation, and polarization effects is in fact modulated by the different ligand frameworks, with ligands bearing atoms different from carbon in trans position with respect to the alkyne emerging as especially interesting for both imparting Au(III)-alkyne bond stability and inducing a more effective alkyne activation. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-alkyne is made by performing a comparative study in a model nucleophilic attack of water to the alkyne triple bond. Smaller π back-donation facilitates alkyne slippage in the transition states, which is energetically less demanding for Au(III) than for Au(I), and suggests a greater propensity of Au(III) to facilitate the nucleophilic attack.

Hidden Dicarbene Nature of Acetylenes and Captodative Bonding on Carbon.

DFT derived molecular electrostatic potential (MESP), ¹³C NMR chemical shift (δ), bond order and coordination reactions show that alkynes (RCCR) attain 1,2-dicarbene nature during CCR angle bending. Alkyne carbon atoms of bent structures exhibit MESP features unique to lone-pair bearing atoms, δ around 200 ppm typical for carbene centers and large reduction in CC triple bond character. Lone pair bearing atoms of R substituents enhance the carbene character. The bent alkynes can be trapped with Lewis acids (BH₃, BF₃, AlF₃ and AlCl₃) as the lone pairs developed on carbon centers provide strong donor type dative bonding. The dative bond gives a formal valence electron count six on carbon and suggests the for-mation of acceptor type dative bonding to carbon from Lewis base (NH₃). Reaction of alkynes with (Lewis acid-Lewis base) systems yield (Lewis acid)₂-Alkyne-Lewis base)₂ complexes which are exothermic and exergonic for many cases. These complexes are examples of captodative carbon(II) compounds.

On the electron flow sequence driving the hydrometallation of acetylene by lithium hydride.

The sequence of the electronic flow driving the hydrometallation of acetylene by lithium hydride (and that of the opposite β-hydride elimination reaction from the alkenyl metal intermediate), was examined within the perspective provided by the bonding evolution theory (BET). The analysis was based on the application of catastrophe theory to the changes of the electron localization function topology along the intrinsic reaction coordinate. The description of the electronic processes occurring on the process was represented in terms of topological structural stability domains (SSDs) and the associated elementary bifurcation catastrophes. Within such a framework of representation, the "evolution" of the system through the different SSDs reveals the key chemical events driving the transformation, including the large polarization effect as a consequence of Pauli repulsion between ions of the positive cationic metal on the hydride domain, the activation of the CC triple bond to attack the cationic center, and the agostic stabilizing interactions involving the hardest cationic metal, followed by the attack of the hydride center. These results contribute to emphasizing the intrinsic value and usefulness of using topological-based approaches and associated tools to increase our knowledge and understanding of the subtleties underlying the electronic flow as nuclei evolve along the reaction coordinate, providing detailed and complementary insights in comparison to other interpretative tool such those based on orbital-based representations, concerning the intimate nature of the electronic rearrangement of key mechanistic processes in chemistry. Graphical abstract The sequence of the electron flow (indicated by letters a and b) along the intrinsic reaction path for the hydrometallation of acetylene by lithium hydride to yield ethenyl lithium via a four-membered transition structure (TS), as determined within the bonding evolution theory to provide the key chemical events driven the changes in the key bonding patterns. Blue arrow Main event on the side HC ≡ CH + LiH → TS, red arrow the TS → HLiC=CH2 pathway, green arrows relative motion of nuclei along the imaginary frequency at the position of TS on the intrinsic reaction coordinate.

Visible-light-mediated cascade difunctionalization/cyclization of alkynoates with acyl chlorides for synthesis of 3-acylcoumarins

A new visible-light-mediated radical cyclization of alkynoates with acyl chlorides is described for the one-pot construction of diverse 3-acylcoumarins with high efficiency and selectivity. This method is successful by sequential difunctionalization of an alkynes CC triple bond with the CCl bonds of acyl chloride and aromatic C(sp2)H bonds. The cyclization is proposed to simultaneously form two new carbon–carbon bonds, and involves radical acylation, 5-exo-trig cyclization, and ester migration.

Angular Dependence of Strong Field Ionization of Haloacetylenes HCCX (X = F, Cl, Br, I), Using Time-Dependent Configuration Interaction with an Absorbing Potential

Strong field ionization of haloacetylenes was simulated by time-dependent configuration interaction using all single excitations and a complex absorbing potential. The angular dependence of ionization for HCCX was mapped with static electric fields in the range 0.01–0.06 atomic units and compared with the results for CH3X. HCCF ionizes primarily from the CC π orbital. HCCX (X = Cl, Br, I) compounds show increasing amounts of ionization from the halogen π-type lone pair orbitals and have a node perpendicular to the molecular axis. These shapes can be understood in terms of the energies and interactions of the halogen π-type lone pairs with the π orbitals of the CC triple bond.