Mechanism of rhodium(III)-catalyzed formal C(sp3)H activation/spiroannulation of α-arylidene pyrazolones with alkynes: A computational study

DFT calculations were performed to investigate the rhodium-catalyzed formal C(sp³)-H activation/ spiroannulation of α-arylidene pyrazolones with alkynes. The calculations indicate that the spiroannulation through the proposed C-C reductive elimination is kinetically unfeasible. Instead, the C-C coupling from the eight-membered rhodacycle was proposed to account for the experimental results     

Exploring the activities of vanadium,niobium, and tantalum PNP pincer complexes in the hydrogenation of phenyl-substituted CN,CN, CC,CC, and CO functional groups

The structures and stability of the designed PNP pincer amido M(NO)₂(PNP) and amino ^HM(NO)₂(PN^HP) complexes [M = V, Nb, and Ta, PNP = N(CH₂CH₂P(isopropyl)₂)₂, PN^HP = HN(CH₂CH₂P(isopropyl)₂)₂] and their hydrogenation mechanisms for phenyl-substituted unsaturated functional groups have been explored at the B3PW91 level of density functional theory. Under H₂ environment, these conjugated complexes can form equilibrium and fulfill the criteria of metal–ligand cooperated bifunctional hydrogenation catalysts. For the hydrogenation of Ph-CN, Ph-CHNH, Ph-CHNH-Ph, Ph-CHNCH₂Ph, Ph-CCH, Ph-CHCH₂, Ph-CHO, and Ph-COCH₃, the reaction prefers either a two-step or one-step mechanism for the hydridic MH and protonic NH transfer. These results clearly show that the V, Nb, and Ta complexes are promising catalysts for the hydrogenation reactions, and these provide experimental challenges.     

Copper-catalyzed NH/SH functionalization: A strategy for the synthesis of benzothiadiazine derivatives

A copper-mediated NS bond-forming reaction via NH/SH activation is described. This reaction occurs under mild conditions with high efficiency, step economy, and tolerates a wide variety of functional groups, providing an efficient means of accessing biologically important 1,2,4-benzothiadiazin-3(4H)-ones.     

A theoretical study on the alkene insertion step in Rh-Yanphos catalyzed hydroformylation

This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation （AHF） catalyzed by RhH（CO）2[（R,S）-Yanphos] using four alkene substrates （CH2=CH- Ph, CH2=CH-Ph-（p）-Me, CH2=CH-C（==O）OCH3 and CH2=CH-OC（=O）-Ph, abbreviated as A1-A4）. Interestingly, the equatorial vertical coordination mode （A mode） with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode （E mode） was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.     

Oxidation and reduction of nanodiamond particles in colloidal solutions by laser irradiation or radio-frequency plasma treatment

Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and COC groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp² shell and additional oxidation of the surface to C OC groups. On HPHT NDs the RF treatment leads to reduction of COC groups that are transformed into COH and CH moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible.     

Rh（Ⅱ） carbene S-H insertion into H2S via the stepwise mechanism

The mechanism of Rh(Ⅱ)carbene S-H insertion into H_2S in gas phase has been studied by B3LYP functional.Calculation results showed that the Rh(Ⅱ)carbene S-H insertion into H_2S took only stepwise channels and no concerted channels had been located, which was different from the Rh(Ⅱ)carbene C-H and O-H insertions.     

The Raman spectra of serine and 3,3-dideutero-serine in aqueous solution

The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH₂CH(NH₃)⁺COO⁻] and 3,3-dideutero-serine [HOCD₂CH(NH₃)⁺COO⁻] in aqueous solution were studied in the range 4000–300 cm⁻¹. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.     

Thermal decomposition mechanism of levoglucosan during cellulose pyrolysis

Levoglucosan (1,6-anhydro-β-d-glucopyranose) decomposition is an important step during cellulose pyrolysis and for secondary tar reactions. The mechanism of levoglucosan thermal decomposition was studied in this paper using density functional theory methods. The decomposition included direct CO bond breaking, direct CC bond breaking, and dehydration. In total, 9 different pathways, including 16 elementary reactions, were studied, in which levoglucosan serves as a reactant. The properties of the reactants, transition states, intermediates, and products for every elementary reaction were obtained. It was found that 1-pentene-3,4-dione, acetaldehyde, 2,3-dihydroxypropanal, and propanedialdehyde can be formed from the CO bond breaking decomposition reactions. 1,2-Dihydroxyethene and hydroxyacetic acid vinyl ester can be formed from the CC bond breaking decomposition reactions. It was concluded that CO bond breaking is easier than CC bond breaking due to a lower activation energy and a higher released energy. During the 6 levoglucosan dehydration pathways, one water molecule which composed of a hydrogen atom from C3 and a hydroxyl group from C2 is the preferred pathway due to a lower activation energy and higher product stability.     

Transition-metal-catalyzed CH functionalization for late-stage modification of peptides and proteins

The present review surveyed the progress achieved in the late-stage modification of peptides and proteins utilizing transition- metal-catalyzed C-H functionalization with C-C and C-X (F, Cl, O, N, B, etc.) bonds formation.     

DFT study of the IR and Raman spectra of a fluorescent dendron built from cyclotriphosphazene core

Combined experimental and theoretical studies on molecular structure of the zero generation dendron, built from the hexafunctional cyclotriphosphazene core, with five OC₆H₄(CH₂)₂NHSO₂C₁₀H₆N(CH₃)₂ terminal groups and one oxybenzaldehyde group G₀ are reported. The Fourier transform Raman and IR spectra of G₀ have been recorded. Conformations of low energy isomers of G₀ have been studied at quantum-chemical level. The optimized geometry has been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. The theoretical geometrical parameters, harmonic vibrational frequencies, IR intensities and Raman scattering activities are predicted in a good agreement with the experimental data. It was found that dendron molecule G₀ has a concave lens structure with planar OC₆H₄CHO fragments and slightly non-planar cyclotriphosphazene core. Relying on DFT calculations the bands of the core and terminal groups were assigned. The frequencies of ν(NH) bands in the IR spectrum reveal the presence of the H-bonds in the dendron.     

In silico quest for stable phosphastannaallenes

A computational study at different levels of theory was performed for the not yet synthesized phosphastannaallenes >SnCP– in order to evaluate the strength of the SnC bond, the main postulated factor to stabilize such species, and the geometry in R₂SnCPR derivatives. The influence of the substituents with various electronic effects (H, Me, Ph, F, Cl, OMe, SiMe₃) at the Sn or P atoms of the SnCP unit on the SnC bond order was evaluated in the quest for a substituent that would stabilize the phosphastannaallenic unit. PC bond orders have also been calculated.     

Cyanate ester resin/graphene nanocomposite: Curing dynamics and network formation

The curing dynamics and network formation of cyanate ester resin/graphene oxide (GO) nanocomposites were studied by means of Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) and Raman spectroscopies. The incorporation of GO into the resin showed a strong catalytic effect on the cure of the resin, especially in the initial stages. Addition of 4 wt.% GO resulted in the decrease of curing temperature significantly about 97 °C. Activation energy of the nanocomposites also maintained at a low level till the end of the cure. The most effective catalytic behavior was observed with 1 wt.% GO. Both FT-IR and Raman spectra revealed that OH group in GO reacted with cyanate group OCN in the resin to form O(CNH)O bond in the early stages of the cure. These results could provide a low temperature curing route for cyanate ester resins with improved curing efficiency.     

Infrared Spectral Assignment of Pyrimidine and Pyrazine in the CH Stretching Region by an Effective Spectroscopic Hamiltonian

Mid-Infrared spectra of pyrimidine (PM) and pyrazine (PZ) were recorded in the gas phase using a multi-pass long path gas cell. The IR band structure of these compounds above and below 3000 cm⁻¹ is very broad and contains many humps and shoulders. These humps and shoulders are due to various higher quantum excitation of low-frequency vibrational modes, which participate in Fermi resonance with the nearby CH stretch fundamentals and appears in this region. We constructed an Effective Spectroscopic Hamiltonian (ESH) in a mixed local mode (LM) normal mode (NM) basis to assign the various overtone and combination bands in the CH stretching region of these compounds. The CH stretching vibrations of both PZ and PM were treated as symmetrized anharmonic Morse oscillators in local coordinates and the in-plane deformations down to 1000 cm⁻¹ were treated as normal coordinates. The ESHs were diagonalized and the resulting eigenvalues were subsequently fitted in a given parameter space with the experimentally observed bands. The eigenvalues of the converged Hamiltonian are the anharmonic frequencies and the transition intensities were obtained by summing the squared eigenvector components. The overtone and combination transitions near 3000 cm⁻¹ of both PM and PZ were identified and assigned from the eigenvector coefficients of the ESH matrix. The wavefunctions of a pure CH stretch, overtone of the HCC in-plane bend and due to Type 1 Fermi coupling (resonance between a fundamental with an overtones of a low frequency mode, in this case resonance between the CH strech and the overtone of HCC in-plane bending modes) has been demonstrated pictorially.     

Theoretical calculations of the substituent effect on molecular properties of the RCN⋯HF hydrogen-bonded complexes with R = NH2, CH3O,CH3, OH,SH, H,Cl, F,CF3, CN and NO2

DFT calculations with B3LYP and PBE1PBE functionals and 6–311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the RCN?HF H-bonded complexes with R = NH₂, CH₃O, CH₃, OH, SH, H, Cl, F, CF₃, CN and NO₂. As expected, it has been verified as a red-shift of the HF stretching frequency (ν_HF), in conformity with the elongation of the bond after complexation. On the other hand, the CN stretching frequency (ν_CN) is blue-shifted and corresponds to a shortening of the bond. The binding energies (ΔE_c), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free RCN molecule (μ_RCN) has been found. This result suggests that μ_RCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed HF acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in HF using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.     

A one-pot,two-step synthesis of 3-deazacanthin-4-ones via sequential Pd-catalyzed Suzuki-Miyaura and Cu-catalyzed Buchwald-Hartwig reactions

3-Deazacanthin-4-one and nine analogues, including the 8-aza analogue, were prepared rapidly and in high yields from 8-iodoquinolones and 2-chloro(het)arylboronic acids. The strategy involves construction of the central B ring via concomitant Pd-catalyzed Suzuki-Miyaura CC and Cu-catalyzed Buchwald-Hartwig CN coupling reactions.     

Frequencies and absorption intensities of the fundamental and the first overtone of NH stretching vibrations of pyrroleacetylene and pyrroleethylene complexes studied by density-functional-theory calculation

The structures of pyrroleacetylene and pyrroleethylene complexes which form an NH–π hydrogen bonding were calculated by density-functional-theory calculation. The wavenumbers and absorption intensities of the fundamental and the first overtone of NH stretching of the complexes were investigated to compare effects of the hydrogen bonding on the fundamental and the first overtone of the NH stretching mode. One-dimensional Schrödinger equation in consideration of molecular vibrational anharmonicity was used for the estimation of the wavenumbers and absorption intensities of NH stretching modes of the complexes; it was found that the NH–π hydrogen-bond formation induced lower wavenumber shift for both the fundamentals and first-overtones of NH stretching mode and it increases absorption intensities of the fundamentals and decreases those of first overtones of NH stretching mode.     

Nucleophilic substitution of 4-bromomethyltriazolium with different nucleophiles

1,2,3-Triazolium salts draw much attentions in recent years. We developed a new synthetic method to heteroatom-functionalized triazoliums via nucleophilic substitution of 4-bromomethyltriazolium. This method afforded triazoliums with different S, N, and O heteroatom-substituents. Moreover, S_N2′ reaction was observed with alcohols or hydroxides. In addition, debromination and debromomethylation reaction occurred in some cases.     

Iron-catalyzed CC bond activation/CO bond formation: Direct conversion of ketones to esters

The iron-catalyzed oxidative activation of the (O)CC bond in ketones has been developed. This method enables direct synthesis of esters by the reaction between ketones and alcohols via conversion of the (O)CC bond to the (O)CO bond. The reaction runs selectively: the (O)CC_Alkyl bond is activated, while the (O)CC_Aryl bond remains intact (i.e., iron-catalyzed intermolecular anti-Baeyer-Villiger activation of the (O)CC bond). The reaction conditions are carefully optimized and allow the production of esters with yields of up to 95%. The method is based on the inexpensive and commercially available catalyst (FeCl₃), oxidant ((NH₄)₂S₂O₈), and solvent (DCE) without using any ligands or additives.     

Ni–Mo2C supported on alumina as a substitute for Ni–Mo reduced catalysts supported on alumina material for dry reforming of methane

In this study, alumina-supported NiMo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H₂/CH₄) and a reduced NiMo catalyst. It was shown that the passivated alumina-supported NiMo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction.     

Metal- and solvent-free,iodine-catalyzed cyclocondensation and CH bond sulphenylation: A facile access to C-4 sulfenylated pyrazoles via a domino multicomponent reaction

We describe herein a green and efficient MCRs protocol to synthesize C-4 sulfenylated pyrazoles by iodine-catalyzed cyclocondensation and direct CH bond sulphenylation reactions. Through this protocol, two new CN bonds and one CS bond are constructed simultaneously in a single step. This method provides a straightforward and sustainable way to construct valuable sulfenylated pyrazoles under metal- and solvent-free conditions.