Probing the supramolecular features via π–π interaction of a di-iminopyrene-di-benzo-18-crown-6-ether compound: experimental and theoretical study

A novel DPyDB-C N-18C6 compound was synthesised by linking a pyrene moiety to each phenyl group of dibenzo-18-crown-6-ether, the crown ether, through –HC N– bonds and characterized by FTIR, ¹H-NMR, ¹³C-NMR, TGA, and DSC techniques. The quantitative ¹³C-NMR analysis revealed the presence of two position isomers. The electronic structure of the DPyDB-C N-18C6 molecule was characterized by UV-vis and fluorescence spectroscopies in four solvents with different polarities to observe particular behavior of isomers, as well as to demonstrate a possible non-bonding chemical association (such as ground- and excited-state associations, namely, to probe if there were forming dimers/excimers). The interpretation of the electronic structure was realized through QM calculations. The TD-CAM-B3LYP functional, at the 6-311+G(d,p) basis set, indicated the presence of predominant π → π* and mixed π → π* + n → π* transitions, in line with the UV-vis experimental data. Even though DPyDB-C N-18C6 computational studies revealed a π-extended conjugation effect with predominantly π → π* transitions, thorough fluorescence analysis was observed a weak emission, as an effect of PET and ACQ. In particular, the WAXD analysis of powder and thin films obtained from n-hexane, 1,2-dichloroethane, and ethanol indicated an amorphous organization, whereas from toluene a smectic ordering was obtained. These results were correlated with MD simulation, and it was observed that the molecular geometry of DPyDB-C N-18C6 molecule played a defining role in the pyrene stacking arrangement.

Herein, we report the formation of a potential supramolecular arrangement mediated by inter- and intra-molecular interactions between di-iminopyrene-dibenzo-18-crown-6-ether molecules.     

FTIR product study of the Cl-initiated oxidation products of CFC replacements: (E/Z)-1,2,3,3,3-pentafluoropropene and hexafluoroisobutylene

A product study of the reactions of (E/Z)-1,2,3,3,3-pentafluoropropene ((E/Z)-CF₃CF CHF) and hexafluoroisobutylene ((CF₃)₂C CH₂) initiated by Cl atoms were developed at 298 ± 2 K and atmospheric pressure. The experiments were carried out in a 1080 L quartz-glass environmental chamber coupled via in situ FTIR spectroscopy to monitor the reactants and products. The main products observed and their yields were as follows: CF₃C(O)F (106 ± 9)% with HC(O)F (100 ± 8)% as a co-product for (E/Z)-CF₃CF CHF, and CF₃C(O)CF₃ (94 ± 5)% with HC(O)Cl (90 ± 7)% as a co-product for (CF₃)₂C CH₂. Atmospheric implications of the end-product degradation are assessed in terms of their impact on ecosystems to help environmental policymakers consider HFOs as acceptable replacements.

An experimental product distribution study and the atmospheric implications of the reactions of Cl with two fluorinated alkenes is provided.     

Computational design and molecular modeling of the interaction of nicotinic acid hydrazide nickel-based complexes with H2S gas

The application of nickel complexes of nicotinic acid hydrazide ligand as a potential gas-sensor and adsorbent material for H₂S gas was examined using appropriate density functional theory (DFT) calculations with the ωB97XD/Gen/6-311++G(d,p)/LanL2DZ method. The FT-IR spectrum of the synthesized ligand exhibited a medium band at 3178 cm⁻¹ attributed to ν(NH) stretching vibrations and strong bands at 1657 and 1600 cm⁻¹ corresponding to the presence of ν(C O) and ν(C N) vibration modes. In the spectrum of the nickel(ii) complex, the ν(C O) and ν(C N) vibration bands experience negative shifts to 1605 cm⁻¹ and 1580 cm⁻¹, respectively, compared to the ligand. This indicates the coordination of the carbonyl oxygen and the azomethine nitrogen atoms to the Ni²⁺ ion. Thus, the sensing mechanism of the complexes indicated a short recovery time and that the work function value increases for all complexes, necessitating an excellent H₂S gas sensor material. Thus, a profound assertion was given that the complex sensor surfaces exhibited very dense stability with regards to their relevant binding energies corresponding to various existing studies.

We demonstrate the efficacy of nicotinic acid hydrazide as adsorbent/sensor materials for H₂S gas.     

Ancillary ligand effects on α-olefin polymerization catalyzed by zirconium metallocene: a computational study

The polymerization of α-olefins catalyzed by zirconium metallocene catalyst was systematically studied through experiments and density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it was found that the effect of the catalyst ligand on the C C insertion reaction was significantly greater than that on the β-H elimination reaction. Therefore, the molecular weight of polymers can be increased by improving the activity of the C C insertion. In addition, in comparison with propylene, the chain length of α-olefins can directly affect the stereotacticity of polymerization products, owing to steric hindrance between the polymer chain and monomer.

The polymerization of α-olefins catalyzed by zirconium metallocene catalyst was systematically studied through experiments and density functional theory (DFT) calculations.     

Selective production of bio-based aromatics by aerobic oxidation of native soft wood lignin in tetrabutylammonium hydroxide

Aerobic oxidation of native soft wood lignin in an aqueous solution of Bu₄NOH facilitates efficient production of vanillin (4-hydroxy-3-methoxybenzaldehyde), which is one of the platform chemicals in industry. Oxidation of Japanese cedar (Cryptomeria japonica) wood flour at 120 °C for 4 h under O₂ in Bu₄NOH-based aqueous solutions produced vanillin in 23.2 wt% yield based on the Klason lignin content of the starting material. This yield was comparable to that in alkaline nitrobenzene oxidation of the same material (27.2%), which indicated that our aerobic oxidation exploited the full potential of the wood flour for vanillin production. Further mechanical investigation with lignin model compounds suggested that the vanillin formation occurred mainly through following successive reactions: alkaline-catalyzed degradation of β-ether linkages in middle units of lignin polymer to form a glycerol end group, oxidation of the glycerol end group by O₂ to a HC_α O moiety, and release of vanillin from the HC_α O end. One of the reasons for the high performance of Bu₄NOH for the vanillin production was explained by the general understanding in organic chemistry that Bu₄OH is a stronger base than simple alkali, e.g. NaOH. The other more fundamental mechanical aspect was that Bu₄N⁺ suppressed disproportionation of the vanillin precursor (the C_αHO end group) probably due to strong interaction between the cation and the HC_α O end group.

Aerobic oxidation of native soft wood lignin in an aqueous solution of Bu₄NOH facilitates efficient production of vanillin (4-hydroxy-3-methoxybenzaldehyde), which is one of the platform chemicals in industry.     

tBuOK-triggered bond formation reactions

Recently, inexpensive and readily available tBuOK has seen widespread use in transition-metal-free reactions. Herein, we report the use of tBuOK for S–S, S–Se, N N and C N bond formations, which significantly extends the scope of tBuOK in chemical synthesis. Compared with traditional methods, we have realized mild and general methods for disulfide, azobenzenes imine etc. synthesis.

Inexpensive and readily available ^tBuOK can trigger a series of bond formation reactions, including S–S, S–Se, Se–Se, and N N and C N bonds.     

Spectral evidence for generic charge → acceptor interactions in carbamates and esters

The correlations of the ¹H NMR, ¹³C NMR and FT-IR spectral data from the R–O–C O groups in the alkyl carbamates and esters of homologous alcohols reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and their donation to generic acceptors at C^α of even alkyl alcohols (R), which explains several of their apparently anomalous properties.

NMR, FT-IR spectral correlations of the R–O–C O groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.

Electronic interactions at the R–O–C O groups in carbamates and esters are less understood than that at the R–N–C O groups in amides. Carbamates in which both these groups are fused at the carbonyl C O bond, have several ester-like rather than amide-like features^1,2 including comparable C–O bond lengths in crystals,^3–6 favourable interactions between the dipoles of the C O and O–R bonds in the predominant s-trans rotamers of the R–O–C O groups and unfavourable lone pair repulsion between the two ester oxygens in their trace s-cis rotamers^7–10 (Fig. 1a). However, several anomalous properties of carbamates and esters cannot be explained by these dipole and repulsive forces alone. For example, despite the electronic resonance at the O–C O group in esters and additionally at the N–C O group in carbamates (both of which augment the electron density at their carbonyl oxygens), their carbonyls have remarkably lower basicities than the carbonyls of amides¹¹ and even those of ketones, which lack such resonance effects.¹² The barriers to the C–N bond rotation for carbamates are 3–4 kcal mol⁻¹ lower than those for analogous amides.^13,14 Carbamate and ester carbonyl oxygens also have poor hydrogen bond accepting propensities compared to amides.^15–20Open in a separate windowFig. 1(a) Dipole–dipole, electronic and steric interactions governing the rotamer stabilities at R–O–C O frameworks in carbamates and esters; (b) earlier report of n → π* O⋯C^α interaction in phenyl carbamates; (c) current finding of generic donor → acceptor interactions: (i) charge → HCR* (ii) charge → σ*; (d) list of carbamates (1–8), esters (9–16) and alcohols (17–20) investigated. HCR is hyperconjugative resonance along the C^α–C^β bond of alcohol groups in carbamates and esters.Of particular current interest is the apparent anomaly that in the crystals of phenyl carbamates, the phenyl ring plane is oriented perpendicular to the carbamate plane^21,22 (Fig. 1b). The presence of an extraordinary n → π* orbital overlap interaction (O⋯C^α_phenyl) between the lone-pair electrons on the carbonyl (C O) oxygen and the π* orbital of the phenyl ring has been proposed as the stabilizing force for this conformer based on natural bond orbital (NBO) analysis.²² This is interesting for several reasons: (i) despite a decrease in the stretching frequency of C O in the FT-IR spectrum for this conformer, which indicates a decrease in the bond order and concomitant improvement in the charge density at the carbonyl oxygen, a discussion on the origin and role of such charge on this O⋯C^α_alcohol interaction is lacking. Rather, the interaction is assumed to originate from the lone pair on oxygen. (ii) Our investigation of CCDC revealed that the O⋯C^α_alcohol distances at the C^α–O–C O groups are quite non-variant (2.62–2.81 Å) for both aliphatic and aromatic carbamates and esters,^{3–6,23–27} notwithstanding the variations in the structure resolutions. These invoked the following questions: is the O⋯C^α interaction specific to the π* acceptors at C^α_alcohol? Can any antibonding orbital at C^α_alcohol act as an acceptor of the electrons from carbonyl oxygen? What is the generic nature and role of this O⋯C^α interaction in the C^α–O–C O groups? Here, we present the first spectral evidence for the generic nature of the O⋯C^α interactions even with non-π* orbital acceptors (like σ* and hyperconjugative resonance bonds) at C^α in the C^α–O–C O groups (Fig. 1c) of a variety of model homologous aliphatic carbamates and esters (Fig. 1d). The charge at the carbonyl oxygen is interdependent on the alkoxy groups and forms charge → acceptor O⋯C^α interactions, which influence the rotational states of the O–C^α bonds in the carbamates and esters.To explore the possibility of the O⋯C^α interactions at C^α–O–C O in aliphatic carbamates and esters, we investigated the ¹H NMR, ¹³C NMR and FT-IR spectra of the secondary and tertiary carbamates (1–4 and 5–8), acetates (9–12) and benzoates (13–16) of homologous aliphatic alcohols (H–C^αH₂–OH, MeOH; CH₃–C^αH₂–OH, ethanol; (CH₃)₂–C^αH–OH, isopropanol; and (CH₃)₃–C^α–OH, tert-butanol, 17–20) (

Theoretical screening of bistriazole-derived energetic salts with high energetic properties and low sensitivity

We designed four series of energetic anions by replacing nitro group (NO₂) with trinitromethyl group (C(NO₂)₃) or by inserting N-bridging groups (–NH–, –NH–NH–, –N N–, –N N(O)–) into the bistriazole frameworks. The properties of 40 energetic salts, based on the bistriazole-derived anions and hydroxylammonium cation, were studied by density functional theory (DFT) and volume-based thermodynamics calculations (VBT). It is found that the newly designed energetic salts have good detonation properties due to their larger nitrogen content and better oxygen balance. And one of their corresponding hydroxylammonium salts exhibits better detonation performance (D = 10.06 km s⁻¹ and P = 48.58 GPa) than CL-20 (D = 9.54 km s⁻¹ and P = 43.36 GPa). Moreover, 10 energetic salts not only exhibit excellent energetic properties superior to CL-20, but also have lower sensitivity than CL-20 (h₅₀ = 13.81 cm). In addition, we rationally selected salt B6 from the 10 salts to predict its crystal structure under pressures. By converting energetic molecules with excellent detonation properties into energetic ions, some highly bistriazole-derived energetic salts with both excellent performance and low sensitivity could be developed strategically.

We designed four series of energetic anions by replacing nitro group (NO₂) with trinitromethyl group (C(NO₂)₃) or by inserting N-bridging groups (–NH–, –NH–NH–, –N N–, –N N(O)–) into the bistriazole frameworks.     

A theoretical study of the hydrolysis mechanism of A-234; the suspected novichok agent in the Skripal attack

A-234, [EtO–P( O)(F)–N C(Me)–N(Et)₂], is the suspected A-type nerve agent used in the Skripal attack on the 4th of March 2018. Studies related to the structure and reactivity of this compound are limited. We, therefore, aimed at understanding the underlying hydrolysis mechanism of A-234 within the DFT framework. The attack of the water molecule can occur at the phosphinate and acetoamidine reactive centres. Our theoretical findings indicate that the hydrolysis at the acetoamidine centre is thermodynamically favoured compared to the hydrolysis at the phosphinate centre. The hydrolysis at the acetoamidine moiety may proceed via two pathways, depending on the nitrogen atom participating in the hydrolysis. The main pathway consists of four distinct channels to reach the final product, with the concerted 1,3-proton shift favoured kinetically and thermodynamically in the gas phase and water as solvent. The results are in good agreement with the literature, although some differences in the reaction mechanism were observed.

A theoretical study of the hydrolysis mechanism of A-234 [EtO–P( O)(F)–N C(Me)–N(Et)₂]; the suspected novichok agent in the Skripal attack.     

The effects of green waste compost on soil N,P, K,and organic matter fractions in forestry soils: elemental analysis evaluation

We study the effects of green waste compost on soil fertility to provide a theoretical basis for accurately improving forestry soil quality. This study aims to investigate the effects of green waste compost on soil N, P, K, and soil organic matter (SOM) fractions using elemental and FTIR analyses. Therefore, five fertilization treatments were set up for research, including mineral fertilization (M-fert), green waste compost fertilization (G-fert), standard rate of M-fert plus G-fert (GM-fert), half the standard rate of M-fert plus G-fert (1/2 GM-fert), and a control with no fertilizer addition (N-fert). The results showed that GM-fert treatment significantly increased the content of soil NH₄–N, available phosphorus (AP), available potassium (AK), water soluble organic carbon (WSOC), humus (HE), and humic acid (HA), which were 8.53 ± 0.67, 76.1 ± 5.96, 168 ± 3.42, 0.152 ± 0.01, 5.64 ± 0.15, and 4.69 ± 0.21 mg kg⁻¹, respectively. The content of HA (36.7%, F = 7.55, P = 0.01) was positively correlated with the soil N, P, K, and the HA absorption peak. The relative intensities of the alcohol –OH, aliphatic –CH and carbohydrate C–O peaks showed the largest changes, which were 18.6 ± 0.56%, 13.1 ± 0.33%, and 16.3 ± 0.49%. –CH/C C (49.8%, F = 12.9, P < 0.01) was also significantly positively correlated with soil N, P, K. In conclusion, green waste compost significantly increased soil N, P, K, and HA in forestry soils, and the –CH/C C of HA was the main factor related to soil nutrients.

Green waste compost significantly increased soil N, P, K, and HE fractions, and the –CH/C C components of the HA structures made the biggest contribution to soil N, P, K in forestry soil.     

Inconsistent hydrogen bond-mediated vibrational coupling of amide I

Using infrared spectroscopy and density functional theory (DFT) calculations, we scrutinized an amide (dimethylformamide) as a “model” compound to interpret the interactions of amide 1 with different phenol derivatives (para-chlorophenol (PCP) and para-cresol (CP)) as “model guest molecules”. We established the involvement of amide I in vibrational coupling with symmetric and asymmetric C C modes of different phenolic derivatives and how their coupling was dependent upon different guest aromatic phenolic compounds. Interestingly, substitution of phenol perturbed the pattern of vibrational coupling with amide I. The symmetric and asymmetric C C modes of PC were coupled significantly with amide 1. For PCP, the symmetric C C mode coupled significantly, but the asymmetric mode coupled negligibly, with amide I. Here, we reveal the nature of vibrational coupling based on the structure of a guest molecule hydrogen-bonded with amide I. Our conclusions could be valuable for depiction of the unusual dynamics of coupled amide-I modes as well as the dependency of vibrational coupling on altered factors.

The involvement of amide I in vibrational coupling with symmetric and asymmetric C C modes of different phenolic derivatives.     

Reactions of triosmium and triruthenium clusters with 2-ethynylpyridine: new modes for alkyne C–C bond coupling and C–H bond activation

The reaction of the trimetallic clusters [H₂Os₃(CO)₁₀] and [Ru₃(CO)₁₀L₂] (L = CO, MeCN) with 2-ethynylpyridine has been investigated. Treatment of [H₂Os₃(CO)₁₀] with excess 2-ethynylpyridine affords [HOs₃(CO)₁₀(μ-C₅H₄NCH=CH)] (1), [HOs₃(CO)₉(μ₃-C₅H₄NC CH₂)] (2), [HOs₃(CO)₉(μ₃-C₅H₄NC CCO₂)] (3), and [HOs₃(CO)₁₀(μ-CH CHC₅H₄N)] (4) formed through either the direct addition of the Os–H bond across the C C bond or acetylenic C–H bond activation of the 2-ethynylpyridine substrate. In contrast, the dominant pathway for the reaction between [Ru₃(CO)₁₂] and 2-ethynylpyridine is C–C bond coupling of the alkyne moiety to furnish the triruthenium clusters [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NC CHC(C₅H₄N) CH}] (5) and [Ru₃(CO)₇(μ-CO){μ₃-C₅H₄NCCHC(C₅H₄N)CHCHC(C₅H₄N)}] (6). Cluster 5 contains a metalated 2-pyridyl-substituted diene while 6 exhibits a metalated 2-pyridyl-substituted triene moiety. The functionalized pyridyl ligands in 5 and 6 derive via the formal C–C bond coupling of two and three 2-ethynylpyridine molecules, respectively, and 5 and 6 provide evidence for facile alkyne insertion at ruthenium clusters. The solid-state structures of 1–3, 5, and 6 have been determined by single-crystal X-ray diffraction analyses, and the bonding in the product clusters has been investigated by DFT. In the case of 1, the computational results reveal a rare thermodynamic preference for a terminal hydride ligand as opposed to a hydride-bridged Os–Os bond (3c,2e Os–Os–H bond).

The reactivity of 2-ethynylpyridine at low-valent triosmium and triruthenium centers has been investigated.     

Correction: Mid-infrared spectroscopy and microscopy of subcellular structures in eukaryotic cells with atomic force microscopy – infrared spectroscopy

Correction for ‘Mid-infrared spectroscopy and microscopy of subcellular structures in eukaryotic cells with atomic force microscopy – infrared spectroscopy’ by Luca Quaroni et al., RSC Adv., 2018, 8, 2786–2794.

In the article the assignment of two IR absorption bands, at 3010 and at 3070 cm⁻¹ has been confused by us in the text, resulting in two incorrect statements. The misstatement does not change any of the conclusions of the work, and can be corrected by restating the following sentences.The following sentence (p. 2790, column 1, line 10):A weak but sharp band can be seen at 3010 cm⁻¹, corresponding to the stretching mode of C–H bonds on unsaturated C C bonds in acyl chains.must be corrected to:A weak but sharp band can be seen at 3010 cm⁻¹, corresponding to the stretching mode of C–H₃ bonds on choline headgroups.In addition, the following sentence (p. 2792, column 1, line 25):Observation of a sharp band at 3010 cm⁻¹ indicates that at least part of the acyl chains have unsaturated C C bonds.must be changed to:Observation of a band at 3070 cm⁻¹, corresponding to the stretching mode of C–H bonds on unsaturated C C bonds in acyl chains, indicates that at least part of the acyl chains have unsaturated C C bonds.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Synthesis of cyclic α-pinane carbonate – a potential monomer for bio-based polymers

This work reports the first known synthesis of α-pinane carbonate from an α-pinene derivative. Pinane carbonate is potentially useful as a monomer for poly(pinane carbonate), which would be a sustainable bio-based polymer. α-Pinene is a major waste product from the pulp and paper industries and the most naturally abundant monoterpene in turpentine oil. α-Pinene is routinely converted to pinene oxide and pinanediol, but no study has yet demonstrated the conversion of pinanediol into α-pinane carbonate. Here, α-pinane carbonate was synthesised via carboxylation of α-pinanediol with dimethyl carbonate under base catalysis using triazabicyclodecene guanidine (TBD). 81.1 ± 2.8% α-pinane carbonate yield was achieved at 98.7% purity. The produced α-pinane carbonate was a white crystalline solid with a melting point of 86 °C. It was characterised using FTIR, NMR, GCMS and a quadrupole time-of-flight (QTOF) mass spectrometer. The FTIR exhibited a C O peak at 1794 cm⁻¹ confirming the presence of a cyclic carbonate. GCMS showed that the α-pinane carbonate fragments with loss of CO₂, forming pinene epoxide. Base hydrolysis of the α-pinane carbonate using NaOH/ethanol/water regenerated the pinanediol with formations of Na₂CO₃.

Synthesis of α-pinane carbonate from an α-pinene derivative.     

Insights into the nucleophilic substitution of pyridine at an unsaturated carbon center

Bimolecular nucleophilic substitution (S_N2) is a fundamental reaction that has been widely studied. So far, the nucleophiles are mainly anionic species in S_N2 reactions. In this study, we use density functional theory calculations to assess the mechanisms of substitution of carbonyl, imidoyl, and vinyl compounds with a neutral nucleophile, pyridine. Charge decomposition analysis is performed to explore the main components of the transition state''s LUMO. For reactions of imidoyl or carbonyl compounds with pyridine or Cl⁻, the LUMOs of the transition states are composed of mixed orbitals originating from the nucleophile and the substrate. Considering the unique mixed nature of the orbitals, the reaction mode is termed S_Nm (m means mix). Moreover, the main components of the transition state''s LUMO are pure σ*_C–Cl MO in the reactions of H₂C CHCl with pyridine or Cl⁻. Computations were also performed for RY CHX substrates with different X and Y groups (X= Cl⁻, Br⁻, or F⁻; Y = O, N, or C).

The nucleophilic substitution of carbonyl, imidoyl, and vinyl carbon centers with pyridine or halides is investigated in this paper.     

Nitrogen–phosphorus doped graphitic nano onion-like structures: experimental and theoretical studies

Onion-like graphitic structures are of great importance in different fields. Pentagons, heptagons, and octagons are essential features of onion-like graphitic structures that could generate important properties for diverse applications such as anodes in Li metal batteries or the oxygen reduction reaction. These carbon nanomaterials are fullerenes organized in a nested fashion. In this work, we produced graphitic nano onion-like structures containing phosphorus and nitrogen (NP-GNOs), using the aerosol assisted chemical vapor deposition method. The NP-GNOs were grown at high temperature (1020 °C) using ferrocene, trioctylphosphine oxide, benzylamine, and tetrahydrofuran precursors. The morphology, structure, composition, and surface chemistry of NP-GNOs were characterized using different techniques. The NP-GNOs showed diameters of 110–780 nm with Fe-based nanoparticles inside. Thermogravimetric analysis showed that NP-GNOs are thermally stable with an oxidation temperature of 724 °C. The surface chemistry analysis by FTIR and XPS revealed phosphorus–nitrogen codoping, and several functionalities containing C–H, N–H, P–H, P–O, P O, C O, and C–O bonds. We show density functional theory calculations of phosphorus–nitrogen doping and functionalized C₂₄₀ fullerenes. We present the optimized structures, electronic density of states, HOMO, and LUMO wave functions for P-doped and OH-functionalized fullerenes. The P O and P–O bonds attributed to phosphates or hydroxyl groups attached to phosphorus atoms doping the NP-GNOs could be useful in improving supercapacitor function.

Nitrogen–phosphorus doped graphitic nano onion-like structures.     

Catalyzed M–C coupling reactions in the synthesis of σ-(pyridylethynyl)dicarbonylcyclopentadienyliron complexes

The reactions between terminal ethynylpyridines, (trimethylsilyl)ethynylpyridines and cyclopentadienyliron dicarbonyl iodide were studied under Pd/Cu-catalyzed conditions to develop a synthetic approach to the σ-alkynyl iron complexes Cp(CO)₂Fe–C C–R (R = ortho-, meta-, para-pyridyl). Depending on the catalyst and reagents used, the yields of the desired σ-pyridylethynyl complexes varied from 40 to 95%. In some cases the reactions with ortho-ethynylpyridine gave as byproduct the unexpected binuclear FePd μ-pyridylvinylidene complex [Cp(CO)Fe{μ₂-η¹(C_α):η¹(C_α)-κ¹(N)-C_α C_β(H)(o-C₅H₄N)}(μ-CO)PdI]. The conditions, catalysts, and reagents that provide the highest yields of the desired σ-pyridylethynyl iron compounds were determined. The methods developed allowed the synthesis of the corresponding σ-4-benzothiadiazolylethynyl complex Cp(CO)₂Fe–C C–(4-C₆H₃N₂S) as well. Eventually, synthetic approaches to σ-alkynyl iron complexes of the type Cp(CO)₂Fe–C C–R (R = ortho-, meta-, para-pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated.

Two approaches were developed for the synthesis of iron σ-pyridylethynyl complexes based on Pd/Cu- and Pd-catalyzed Fe–C coupling reactions.     

Revisiting salicylidene-based anion receptors

Several salicylidene-based colorimetric and fluorimetric anion sensors are known in the literature. However, our ¹H-NMR experimental results (in DMSO-d₆) showed hydrolysis of imine (–N CH–) bonds in salicylidene-based receptors (SL, CL1 and CL2) in the presence of quaternary ammonium salts (n-Bu₄N⁺) of halides (Cl⁻ and Br⁻) and oxo-anions (H₂PO₄⁻, HSO₄⁻ and CH₃COO⁻). The mono-salicylidene compound CL1 showed the most extensive –N CH– bond hydrolysis in the presence of anions. In contrast, the di-salicylidene compound CL2 and the tris-salicylidene compound SL showed comparatively slow hydrolysis of –N CH– bonds in the presence of anions. Anion-induced imine bond cleavage in salicylidene compounds could easily be detected in ¹H-NMR due to the appearance of the salicylaldehyde –CHO peak at 10.3 ppm which eventually became more intense over time, and the –N CH– peak at 8.9–9.0 ppm became considerably weaker. Furthermore, the formation of the salicylidene O–H⋯X⁻ (X⁻ = Cl⁻/Br⁻) hydrogen-bonded complex, peak broadening due to proton-exchange processes and keto–enol tautomerism have also been clearly observed in the ¹H-NMR experiments. Control ¹H-NMR experiments revealed that the presence of moisture in the organic solvents could result in gradual hydrolysis of the salicylidene compounds, and the rate of hydrolysis has further been enhanced significantly in the presence of an anion. Based on ¹H-NMR results, we have proposed a general mechanism for the anion-induced hydrolysis of imine bonds in salicylidene-based receptors.

Salicylidene Schiff bases undergo imine bond hydrolysis in the presence of halides and oxo-anions in aprotic media, raising fundamental questions on the applicability of salicylidene-based receptors as anion sensors.     

Insights into the promotion role of phosphorus doping on carbon as a metal-free catalyst for low-temperature selective catalytic reduction of NO with NH3

The catalytic reduction of NO with NH₃ (NH₃-SCR) on phosphorus-doped carbon aerogels (P-CAs) was studied in the temperature range of 100–200 °C. The P-CAs were prepared by a one-pot sol–gel method by using phosphoric acid as a phosphorus source followed by carbonization at 600–900 °C. A correlation between catalytic activity and surface P content is observed. The P-CA-800_vac sample obtained via carbonization at 800 °C and vacuum treatment at 380 °C shows the highest NO conversion of 45.6–76.8% at 100–200 °C under a gas hourly space velocity of 500 h⁻¹ for the inlet gas mixture of 500 ppm NO, 500 ppm NH₃ and 5.0 vol% O₂. The coexistence of NH₃ and O₂ is essential for the high conversion of NO on the P-CA carbon catalysts, which can decrease the spillover of NO₂ and N₂O. The main Brønsted acid sites derived from P-doping and contributed by the C–OH group at edges of carbon sheets are beneficial for NH₃ adsorption. In addition, the C₃–P O configuration seems to have the most active sites for favorable adsorption and dissociation of O₂ and facilitates the formation of NO₂. Therefore, the simultaneous presence of acidic groups for NH₃ adsorption and the C₃–P O active sites for NO₂ generation due to the activation of O₂ molecules is likely responsible for the significant increase in the NH₃-SCR activity over the P–CAs. The transformation of C₃–P O to C–O–P functional groups after the reaction is found, which could be assigned to the oxidation of C₃–P O by the dissociated O*, resulting in an apparent decrease of catalytic activity for P-CAs. The C–O–P based functional groups are also active in the NH₃-SCR reaction.

P species can effectively enhance the catalytic activity of carbon aerogels for NO reduction at low temperature.     

Flexible selection of the functional-group ratio on a polytetrafluoroethylene (PTFE) surface using a single-gas plasma treatment

During plasma treatment of polymers, etching occurs and functional groups are introduced on their surface. We assumed that controlling the etching rate would enable plasma treatment using a single gas to control the ratio of functional groups generated on a polymer''s surface, although previous studies have indicated that several different types of functional groups are formed when the gaseous species are varied. In this study, we selected the base pressure (BP) as a parameter for controlling the etching rate and subjected polytetrafluoroethylene (PTFE) to plasma treatments using only He gas at various BPs. The chemical composition of the surface of the plasma-treated PTFE samples was evaluated by X-ray photoelectron spectroscopy (XPS), and the ratios of fluorine (CF₃, CF₂, C–F), oxygen (O–C O, C O, C–O), and carbon (C–C, C C) groups were quantified from the C 1s-XPS spectra. The fluorine-group ratio decreased and the oxygen- and carbon-group ratios increased with decreasing BP. The results demonstrated that plasma treatment using a single gas enabled flexible selection of the ratio of functional groups generated on PTFE via control of the BP.

During plasma treatment of polymers, etching occurs and functional groups are introduced on their surface.