Six-membered Ring Structure Research Articles

Enhanced thermal conductivity and mechanical properties of boron nitride@polymethylacrylimide/epoxy composites with self-assembled stable three-dimensional network

Constructing a three-dimensional (3D) network of fillers with high thermal conductivity is considered to be an effective strategy to obtain ideal thermal management materials (TMM). However, 3D filler network is often disrupted by the subsequent processing and forming processes , and it is difficult to incorporate high levels of fillers into lyophilized aerogels, which is a key factor limiting their widespread use. In this work, boron nitride@polymethylacrylimide/epoxy (BN@PMI/EP) composites with a stable 3D BN network were prepared by freeze-drying and hot-pressing. A water-soluble copolymer quaternary ammonium salt has been synthesized by the solution polymerization. BN@PMI aerogel was obtained by the freeze-drying of ammonium salt and BN solution, and thermal imidization. BN@PMI aerogel has a six-membered imine ring structure that can be loaded with a high content of BN, which ensures the stability of the 3D BN network structure and facilitates the subsequent impregnation of EP in vacuum, which is one of the innovations of this work.The stable and complete 3D BN network leads to the enhancement of thermal conductivity, and the out-of-plane and in-plane thermal conductivities of BN@PMI/EP reach 1.21 W·m–1·K–1 and 2.76 W·m–1·K–1 at BN loading of 40% (mass), respectively. Meanwhile, the excellent mechanical properties and results of finite element simulation and actual experiments confirm that BN@PMI/EP is a potential TMM.

Six-membered ring-reinforced flexible high-elongation block polyamide as strong and multi-reusable hot melt adhesive

This study presented the synthesis and characterization of polyester block polyamide hot melt adhesives (PPHMAs) with high adhesion strength and toughness. The PPHMAs demonstrated an adhesion strength of 11.04 MPa and toughness of 22.54 MJ·m−3, making them suitable for various substrates such as aluminum, copper, and stainless steel. The polyamide segments synthesized from dimer acid and 2-methyl-1,5-diaminopentane exhibited characteristics of softness and high elongation. Using isophorone diamine as a reinforcing agent introduced a stable six-membered ring structure, which enhanced the polymer's rigidity and strength, thus meeting the requirements for polyamide segments to function as the hard segments in block polymers. A trace amount of Tris (2-aminoethyl) amine provided the cross-linking sites which are similar to those in neuronal structures. The polyester segments, which were synthesized from poly (propylene glycol) diglycidyl ether and sebacic acid, served as the soft segments in the block polymer and were connected to the hard segment via amide bonds. The addition of the polyester segments enhanced the non-covalent molecular interactions within PPHMAs, leading to dynamic crosslinking properties. The adhesive maintained stable adhesion even after six cycles, which showcased its durability. Furthermore, the PPHMAs exhibited notable chemical resistance. It retained over 60 % adhesion strength after exposure to some chemical solvents including artificial seawater, 5 % NaOH solution, 5 % HCl solution, and DMSO for 24 h. These findings offered a novel approach to enhancing the adhesion strength and toughness of conventional thermoplastic hot melt adhesives.

Observation of the Water-HNSO2 Complex.

Sulfamic acid (NH2SO3H, SFA) is supposed to play an important role in aerosol new particle formation (NPF) in the atmosphere, and its formation mainly arises from the SO3-NH3 reaction system in which weakly bonded donor-acceptor complexes such as SO3···NH3 and isomeric HNSO2···H2O have been proposed as the key intermediates. In this study, we reveal the first spectroscopic observation of HNSO2···H2O in two forms in a solid Ar matrix at 10 K. The major form consists of two intermolecular H bonds by forming a six-membered ring structure with a calculated dissociation energy of 7.6 kcal mol-1 at the CCSD(T)-F12a/aug-cc-pVTZ level of theory. The less stable form resembles SO3···H2O in containing a pure chalcogen bond (S···O) with a dissociation energy of 7.2 kcal mol-1. The characterization of HNSO2···H2O with matrix-isolation IR spectroscopy is supported by D- and 18O-isotope labeling and quantum chemical calculations.

Density Functional Theory Study of Mechanism of Reduction of N2O by CO over Fe-ZSM-5 Zeolites

Nitrous oxide (N2O) is an industrial waste gas (e.g., from the production of adipic acid), which damages the ozone layer and causes the greenhouse effect. Density functional theory calculations were employed to investigate the mechanism of direct catalytic decomposition of N2O and selective catalytic reduction (SCR) of N2O by CO over Fe-ZSM-5 zeolites. Two stable Fe-active sites with six-membered ring structures on Fe-ZSM-5 were considered. The calculations indicate that the decomposition of N2O is affected by the coordination environment around Fe and can occur through two reaction pathways. However, there is invariably a more considerable energy hurdle for the initiation of the second stage of N2O decomposition. When CO participated in the reaction, it showed good reactivity and stability, the reaction energy barriers of the rate-limiting step were reduced by roughly 20.57 kcal/mol compared to the direct catalytic decomposition of N2O. CO exhibited a superior electron-donating ability and orbital hybridization performance during the reaction, which enhanced the cyclicity of the N2O reduction catalytic process. Our calculations confirmed the significant role of CO in N2O reduction over Fe-ZSM-5 observed in previous studies. This study provides a valuable theoretical reference for exploring CO-SCR methods for N2O reduction over Fe-based zeolite catalysts.

Nuclear quantum effects on the intramolecular hydrogen bonds in biuret and biguanide.

We focus on the unique aspects of biuret and biguanide, which form six-membered ring structures via intramolecular hydrogen bonds. The proton donor and acceptor atoms differ between biuret and biguanide, leading to varying energy barrier heights for proton transfer. We performed path integral molecular dynamics (PIMD) simulations for biuret and biguanide to investigate the correlation between proton transfer and the degree of the delocalization of π-electrons in the six-membered ring framework structure. The results indicate that the π-electrons in the framework structure are delocalized regardless of the ease of intramolecular proton transfer.

Five-membered vs. six-membered ESIPT in 3,5-dihydroxychromone

3,5-dihydroxychromone (3,5-DHC) possesses five-membered and six-membered ring hydrogen-bonding structures that would facilitate an excited-state intramolecular proton transfer upon photoexcitation to the dipole-allowed S1 (ππ∗) state. Our investigation based on surface hopping trajectory-based simulations show that proton transfer in 3,5-DHC happens efficiently via the six-membered ring structure with an average timescale of 29 fs. The proton transfer via this pathway is a barrierless process, whereas a barrier of ∼0.46 eV exists for the other pathway that proceeds via a five-membered ring structure. The proton-transferred tautomer occurring via the former pathway is more stable than the one originating from the latter. Hence, the former tautomer exhibits a relatively larger Stokes-shifted fluorescence emission than the latter one.

(Invited) Recent Progress in the Synthesis of Functional and Three-Dimensional Carbon Nano-Composites By Gas-Liquid Interface Plasma

Carbon nanomaterials, such as fullerene, carbon nanotubes (CNT), graphene sheets, and so forth, play indispensable roles in nanotechnology research and applications. Due to their unique self-organized nanostructures and properties, various types of applications using them are expected and have been developed. Furthermore, in recent years, heteroatom-doped carbon nano-composite materials that exhibit catalytic activity are attracting much attention as non-platinum catalysts. Especially, nitrogen (N)-doped nanographene materials are well-known to have high catalytic activity. Pyridinic-N is known as a key component to express catalytic activity [1].There are two ways to obtain nitrogen-doped carbon nanomaterials. One is the addition of N into carbon nanomaterials during their synthesis, and the other is the post-nitridation after the synthesis, which often used nitrogen plasma. Especially in the latter case, the synthesis method of nanographene itself can be divided into two types of methods. One is the direct synthesis of the powder, and the other is the exfoliating from graphene oxide (GO) or bulk graphite in physical or chemical ways. Hydrothermal treatment using microwaves is one of the effective methods for simultaneous exfoliation, three-dimensional nanopore structuring, and nitrogen addition. While electronic device applications generally need high-quality graphene sheets synthesized by epitaxial growth, or chemical vapor deposition (CVD) methods at high temperatures up to 1,000°C, some kinds of applications, such as sensors, batteries, additives to polymers, and so forth, need a large amount of nanographene power. For that purpose, a reduction of GO is well known, but the quality of the synthesized graphene is not high enough.Recently, we have established a high-speed synthesis method of nanographene materials with high crystallinity by a plasma discharge at gas-liquid interfaces with alcohol sources. By this method, a synthesis rate of nanographene over 1 mg/min and higher crystallinity of nanographene than the reduced GO have been realized. On the other hand, there is a trade-off relationship between the synthesis rate and crystallinity, when different types of alcohols were used as a feedstock gas. When ethanol,1-propanol, and 1-butanol were used, it was found that the higher synthesis rates were obtained by the higher-molecular weight alcohols, while its crystallinity was lower. In the comparison between hexane (C6H14) and hexanol (C6H13OH), in the case of hexane, the synthesis rate is about twice as high as that in the case of hexanol, but the crystallinity is lowered. These results indicate that this trade-off relationship is attributed to a ratio of carbon (C) and oxygen (O) atoms. O-related radicals (O, OH, etc.) in plasma could have etching effects of amorphous or low-crystallinity carbon components. Actually, according to the results of plasma diagnostic measurements and residual liquid analyses, it was found that crystallinity of nanographene materials degraded with decrease in OH intensity in plasma. Furthermore, small radicals such as C2 and CHx contribute to the synthesis of nanographene rather than by-products with a six-membered ring structure. Furthermore, we have also found functionalization and structural control of nanographene materials by additive agents to alcohol sources at in-liquid plasma processes. Using an iron phthalocyanine with ethanol, size of carbon nanosheets increased up to micrometer. And they showed excellent catalytic characteristics thorough 4-electron reduction pathway. According to the verification results of dependence on synthesis conditions such as the type of additive, such the catalytic activity is induced by pyridinic C-N bonds. In the case of this way, to increase pyridinic C-N bonds and improve catalytic performance, iron phthalocyanine is much better than Hemin, even which also included Fe and N. These knowledges obtained in this study will open the way to the next-generation green energy solutions, such as high-performance catalytic electrode for the fuel cell.[1] D. Guo, R. Shibuya, C. Akiba, S. Saji, T. Kondo, and J. Nakamura. Science 351 (2016) 361–365.[2] J. Wang, W. Wu, H. Kondo, T. Fan, H. Zhou, Nanotechnology, NANO-132006.R1 (2022), online.[3] T. Hagino, H. Kondo, K. Ishikawa, H. Kano, M. Sekine, M. Hori, Appl. Phys. Express 5 (2012) 035101.[4] T. Amano, H. Kondo, K. Ishikawa, T. Tsutsumi, K. Takeda, M. Hiramatsu, M. Sekine, M. Hori, Appl. Phys. Express 11 (2017) 015102.[5] H. Kondo, R. Hamaji, T. Amano, K. Ishikawa, M. Sekine, M. Hiramatsu, M. Hori, Plasma Process. Polym. 19, (2022) 2100203.

Simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using pyruvic acid treatment

The efficiency of organic acid treatment in the conversion of lignocellulosic biomass fractions has been widely recognized. In this study, a novel green pyruvic acid (PA) treatment is proposed. The higher separation efficiency of eucalyptus hemicellulose was obtained at 4.0% PA and 150 °C. The hemicellulose separation yield was increased from 71.71 to 88.09% compared to glycolic acid (GA) treatment. In addition, the treatment time was significantly reduced from 180 to 40 min. The proportion of cellulose in the solid increased after PA treatment. However, the accompanying separation of lignin was not effectively controlled. Fortunately, a six-membered ring structure was formed on the diol structure of the lignin β-O-4 side chain. Fewer lignin-condensed structures were observed. High-value lignin rich in phenol hydroxyl groups were obtained. It provides a green path for the simultaneous achievement of efficient hemicellulose separation and inhibition of lignin repolymerization using organic acid treatment.

The Lanthipeptide Synthetase-like Protein CA_C0082 Is an Effector of Agr Quorum Sensing in Clostridium acetobutylicum.

Lanthipeptide synthetases are present in all domains of life. They catalyze a crucial step during lanthipeptide biosynthesis by introducing thioether linkages during posttranslational peptide modification. Lanthipeptides have a wide range of functions, including antimicrobial and morphogenetic activities. Intriguingly, several Clostridium species contain lanthipeptide synthetase-like genes of the class II (lanM) family but lack other components of the lanthipeptide biosynthetic machinery. In all instances, these genes are located immediately downstream of putative agr quorum sensing operons. The physiological role and mode of action of the encoded LanM-like proteins remain uncertain as they lack conserved catalytic residues. Here we show for the industrial organism Clostridium acetobutylicum that the LanM-like protein CA_C0082 is not required for the production of active AgrD-derived signaling peptide but nevertheless acts as an effector of Agr quorum sensing. Expression of CA_C0082 was shown to be controlled by the Agr system and is a prerequisite for granulose (storage polymer) formation. The accumulation of granulose, in turn, was shown to be required for maximal spore formation but also to reduce early solvent formation. CA_C0082 and its putative homologs appear to be closely associated with Agr systems predicted to employ signaling peptides with six-membered ring structures and may represent a new subfamily of LanM-like proteins. This is the first time their contribution to bacterial Agr signaling has been described.

Cobalt diffusion during the initial stage of CVD diamond growth on cemented carbide – A molecular dynamics and experimental study

Systematical researches on cobalt diffusion during the initial stage of diamond growth on cemented carbide (WC) are conducted by combining molecular dynamics (MD) and experimental investigations. Simulation results and characterizations indicate that temperature, WC grain size, initial cobalt distribution (including cobalt content and Co-removal depth after acid treatment), diamond crystal orientation, and the grain composition of polycrystalline diamond significantly affect cobalt diffusion. It is proven that cobalt tends to diffuse along grain boundaries in both cemented carbide and diamond, and the intricate nature of grain boundaries in smaller grain sizes results in higher activation energy for cobalt diffusion. However, due to the strong interaction between cobalt and parallel double six-membered ring structures at grain boundaries, cobalt diffusion to the diamond surface is exceedingly challenging. The accumulation of cobalt at the interface between the diamond film and substrate leads to graphitization, which ultimately deteriorates the adhesion of the diamond film during prolonged deposition. In conclusion, the reduction of cobalt diffusion in chemical vapor deposition (CVD) processes can be achieved by employing cemented carbide with smaller grain sizes and lower initial cobalt content. Additionally, decreasing the growth temperature or increasing the Co-removal depth significantly inhibits cobalt diffusion to the diamond film.

Effect of cyclic load on mechanical properties and failure mechanisms of different rank coals

Underground coal is often subjected to periodic loads caused by mining stress. To determine the effect of cyclic load on mechanical properties of coal of different ranks and failure mechanisms, nanoindentation experiments and molecular dynamics (MD) simulations were used to study different rank coals. The results indicated that cyclic hardening occurred in all the coal matrices under cyclic loading. With the increase in coal rank, the change of the elastic modulus and the hardness, the energy dissipation rate, and the damage layer decreased, the cyclic hardening weakened, and the resistance of the six-membered ring structure increased. The plastic failure of the coal matrix was mainly connected with the bending and stretching of the bond, the dihedral angle twisting, and the out-of-plane bending vibration. The elastic deformation was correlated with the variation of the Coulomb force and the van der Waals force, the twisting and recuperation of the dihedral angle, and the out-of-plane bending vibration. With increasing coal rank, the effect of the elastic deformation of the Coulomb force weakened. When the coal rank exceeded a certain range, the influence of the plastic failure of the out-of-plane bending vibration was transformed into the elastic deformation, and the effect of the elastic deformation of the van der Waals force was transformed into the plastic failure.

Promotion of the structural repair of graphene oxide thin films by thermal annealing in water-ethanol vapor

In order to apply graphene oxide (GO) materials as graphene in the electronic devices, it is an essential issue to restore the six-membered ring structure composed of sp2 carbon. Thermal annealing in ethanol vapor promotes the removal of oxygen-containing groups and the structural repair of the vacancy, efficiently. Unfortunately, the metastable carbon bonds such as phase boundaries and sp3-defects still remain in the reduced GO (rGO). In this study, thermal annealing in water-assisted ethanol vapor is used for the reduction process of GO thin films. The structural analysis using Raman spectra indicates that the crystallinity of the rGO thin films strongly depend on the concentration of water. In particular, when the concentration of ethanol and water vapor is the same value, the crystallinity is significantly improved compared to the reduction process using only ethanol. This result indicates that the metastable structures such as phase boundaries and sp3-defects are preferentially etched over stable six-membered ring structure in carbon bonds. As a result, the excellent carrier mobility exceeding 100 cm2/Vs at room temperature (140 cm2/Vs at 77 K) is observed.

Mechanical properties and failure mechanisms of different rank coals at the nanoscale

It is of great significance to explore the mechanical properties and failure mechanism of different rank coals at the nanoscale for preventing mine dynamic disasters. X-ray diffraction (XRD), mercury intrusion, and nano-indentation were used to study the relationship between rank, microstructure and mechanical properties of different rank coals, and using Mori-Tanaka method to upgrade the scale. To reveal the failure mechanism of coal, the nanoindentation process was simulated through molecular dynamics (MD). The results indicated that with the increase in coal rank, the peak load, hardness, elastic modulus, resistance of the six-membered ring structure, fracture toughness, the aromatic layer interlayer spacing (d002), positively proportional to lateral sizes (La), stacking height (Lc), and the number of aromatic layers (n) increased, while the plastic deformation, permeability, porosity, mineral content, and thickness of the damaged layer decreased. Minerals could strengthen the macro-mechanical properties of coal rock, while the pores weaken it. The load destroyed the bonds, angles, dihedral angles, and out-of-plane of coal macromolecules, which led to the plastic deformation of coal. And bonds and angles had the greatest influence on the failure of coal, followed by dihedral angles, and finally out-of-plane.

Structures and bonding properties of lithium polysulfide clusters LiSn-/0 (n = 3-5) and Li2S4-/0: size-selected anion photoelectron spectroscopy and theoretical calculations.

The structures and bonding properties of several lithium polysulfide clusters LiSn-/0 (n = 3-5) and Li2S4-/0 were investigated by size-selected anion photoelectron spectroscopy coupled with quantum chemistry calculations. The vertical detachment energies of LiS3-, LiS4-, and LiS5- were estimated to be 2.17 ± 0.08, 3.30 ± 0.08 and 3.66 ± 0.08 eV, respectively, and that of Li2S4- was estimated to be 3.21 ± 0.08 eV. It is found that LiS3- and LiS3 have planar quadrilateral structures, and LiS4- and LiS4 have distorted five-membered ring structures. LiS5- has a distorted six-membered ring structure while neutral LiS5 has a book-shaped structure. The lowest-lying structure of Li2S4- can be viewed as a S2 unit connecting to the Li-Li edge of a Li2S2 tetrahedron. The lowest-lying structure of neutral Li2S4 can be viewed as a S2 unit connecting to the S atoms of a Li2S2 quadrilateral. The natural population analysis (NPA) and electron localization function (ELF) analyses show that the excess electron of LiSn- is mainly localized over the sulfur chains, especially on the S atoms interacting with Li, thus, the most stable structures of LiSn- can be regarded as a Li+ cation interacting with a Sn2- dianion. The results may be useful for understanding the formation of lithium polysulfides in lithium sulfur batteries.

Controlled alkali etching of MOFs with secondary building units for low-concentration CO2 capture.

Low-concentration CO2 capture is particularly challenging because it requires highly selective adsorbents that can effectively capture CO2 from gas mixtures containing other components such as nitrogen and water vapor. In this study, we have successfully developed a series of controlled alkali-etched MOF-808-X (where X ranges from 0.04 to 0.10), the FT-IR and XPS characterizations revealed the presence of hydroxyl groups (-OH) on the zirconium clusters. Low-concentration CO2 capture experiments demonstrated improved CO2 capture performance of the MOF-808-X series compared to the pristine MOF-808 under dry conditions (400 ppm CO2). Among them, MOF-808-0.07 with abundant Zr-OH sites showed the highest CO2 capture capacity of 0.21 mmol g-1 under dry conditions, which is 70 times higher than that of pristine MOF-808. Additionally, MOF-808-0.07 exhibited fast adsorption kinetics, stable CO2 capture under humid air conditions (with a relative humidity of 30%), and stable regeneration even after 50 cycles of adsorption and desorption. In situ DRIFTS and 13C CP-MAS ssNMR characterizations revealed that the enhanced low-concentration CO2 capture is attributed to the formation of a stable six-membered ring structure through the interaction of intramolecular hydrogen bonds between neighboring Zr-OH sites via a chemisorption mechanism.

Sensitively detecting endogenous homocysteine in human serum and cardiomyocytes with a specific fluorescent probe.

The elevated level of homocysteine (Hcy) in circulating blood is generally regarded as a risk factor for a variety of diseases including acute myocardial infarction (AMI), but there is no clear answer to whether circulating Hcy can be used for AMI diagnosis. To address it, here we have designed a tetraazacycle-based fluorescent probe for sensitive detection of endogenous Hcy in AMI patients' serum and cardiomyocytes, showing a perfect selectivity over other biothiols (e.g. Cys and GSH). It mainly relies on the formation of a stable six-membered ring structure when this probe responds to Hcy, which is accompanied by a weakening of photoinduced electron transfer (PET) that induces a sharp increase in the fluorescence emission. In this way, Hcy can be probed in biofluids with high sensitivity. We then employed this fluorescent sensor to statistically analyze the levels of Hcy in human circulating blood, indicating a big difference between AMI patients and the healthy participants. To tell whether such a difference is applicable to AMI diagnosis, we further compare the expression levels of Hcy in cardiomyocytes and other tissue cells. It reveals a lower level of endogenous Hcy in cardiomyocytes, implying no direct relationship between the elevated Hcy and cardiomyocyte damage. This observation suggests that Hcy in circulating blood cannot be utilized as a potential biomarker for AMI diagnosis, although it is proven as a risk factor for this disease.

(Invited) Synthesis, Functionalization, and Three-Dimensional Structuring of Carbon Nanomaterials By Gas-Liquid Interface Plasma

Carbon nanomaterials, such as fullerene, carbon nanotubes (CNT), graphene sheets, and so forth, play indispensable roles in nanotechnology research and applications. Due to their unique self-organized nanostructures and properties, various types of applications using them are expected and have been developed. One of recent hottest topics among them is graphene sheets and their electric device applications. High quality graphene sheets for such the device applications, epitaxial growth or chemical vapor deposition (CVD) methods at high temperature up to 1,000°C, are used as a synthesis method in general. On the other hand, some kinds of applications, such as sensors, batteries, additives to polymers, and so forth, need a large amount of nanographene power. For that purpose, a reduction of graphene oxide (GO) is well known, but the quality of the synthesized graphene is not high enough. Recently, we have established a high-speed synthesis method of nanographene materials with high crystallinity by a plasma discharge at gas-liquid interfaces with alcohol sources. By this method, a synthesis rate of nanographene over 1 mg/min and higher crystallinity of nanographene than the reduced GO have been realized. On the other hand, there is a trade-of relationship between the synthesis rate and crystallinity, when different types of alcohols were used as a feed stock gas. When ethanol,1-propanol, and 1-butanol were used, it was found that the higher synthesis rates were obtained by the higher-molecular weight alcohols, while its crystallinity was lower. In the comparison between hexane (C6H14) and hexanol (C6H13OH), in the case of hexane, the synthesis rate is about twice as high as that in the case of hexanol, but the crystallinity is lowered. These results indicate that this trade-of relationship is attributed to a ratio of carbon (C) and oxygen (O) atoms. O-related radicals (O, OH, etc.) in plasma could have etching effects of amorphous or low-crystallinity carbon components. Actually, according to the results of plasma diagnostic measurements and residual liquid analyses, it was found that crystallinity of nanographene materials degraded with decrease in OH intensity in plasma. Furthermore, small radicals such as C2 and CHx contribute to the synthesis of nanographene rather than by-products with a six-membered ring structure. Furthermore, we have also found functionalization and structural control of nanographene materials by additive agents to alcohol sources at in-liquid plasma processes. Using an iron phthalocyanine with ethanol, size of carbon nanosheets increased up to micrometer. And they showed excellent catalytic characteristics thorough 4-electron reduction pathway. According to the verification results of dependence on synthesis conditions such as the type of additive, such the catalytic activity is induced by pyridinic C-N bonds. In the case of this way, to increase pyridinic C-N bonds and improve catalytic performance, iron phthalocyanine is much better than Hemin, even which also included Fe and N. These knowledges obtained in this study will open the way to the next-generation green energy solutions, such as high-performance catalytic electrode for the fuel cell.

Organoaluminum derived from Schiff bases: Synthesis, characterization and catalytic performance in hydroboration

In the process of the development of green chemistry, non-noble metal catalysts have become one of the research hotspots. The abundant aluminum has entered the research scope of chemists. Four organoaluminum derived from halogen-substituted Schiff bases were prepared: (2-(((2,6-difluorophenyl)imino)methyl)phenoxy)dimethylaluminum (C1), (2-(((3-chloro-4-fluorophenyl)imino)methyl)phenoxy)dimethylaluminum (C2), (2-(((2-chlorophenyl)imino)methyl)phenoxy)diethylaluminum (C3), (2-(((4-chlorophenyl)imino)methyl)phenoxy)diethylaluminum (C4). All organoaluminum compounds were characterized using 1H NMR, 13C NMR, 19F NMR spectroscopy, and X-ray single crystal diffraction. XRD proved that the aluminum centers of these organoaluminum compounds are all twisted six-membered ring structures. They were used for the hydroboration of aldehydes and ketones, showing excellent results. This provided an additional catalyst for the reduction of carbonyl compounds.

Anion Photoelectron Spectroscopy and Quantum Chemical Calculations of Bimetallic Oxide Clusters YCu2On-/0 (n = 2-5).

The structural and electronic properties of bimetallic oxide clusters, YCu2On- and YCu2On (n = 2-5), are investigated using anion photoelectron spectroscopy and density functional theory calculations. The experimental vertical detachment energies of YCu2O2-, YCu2O3-, YCu2O4-, and YCu2O5- were measured to be 1.59, 1.76, 3.85, and 3.78 eV, respectively. Vibrationally resolved photoelectron spectra have been obtained for YCu2O2-, with a spacing of 726 ± 80 cm-1 assigned to the Y-O stretching vibrational mode. It is found that YCu2O2- and YCu2O2 have C2v symmetric planar five-membered ring structures. YCu2O3- and YCu2O3 have C2v symmetric planar six-membered ring structures. The most stable structure of YCu2O4- is a quasi-planar structure which can be viewed as one O atom interacting with the Y atom of the YCu2O3 six-membered ring, while the most stable structure of YCu2O4 is a planar seven-membered ring. YCu2O5- and YCu2O5 have nonplanar structures, which can be viewed as an O2 unit interacting with the Y atom of the YCu2O3 six-membered ring. In YCu2O3,4,5-/0, the Y-O and Cu-O bonds are dominant, while the Y-Cu and Cu-Cu interactions are weak.

Efficient hydroaminomethylation of olefins catalyzed by Rh-complex ligated by P,O-hybrid ligand with chelating effect

Tandem hydroaminomethylation (HAM) represents one of the most important catalytic protocols for the one-pot synthesis of amines using low-cost and widely available olefins, syngas and amines as starting materials. In this work, the applied P,O-hybrid ligand containing phosphino-fragment and carboxylic group [L1, 2-(diphenylphosphino)benzoic acid] could stoichiometrically react with Rh(acac)(CO)2 to afford a stable Rh-complex of Z [dicarbonyl-2-(diphenylphosphino)benzoato rhodium(I)], wherein the more substantial P,O-chelation derived from L1 as a bidental pincer upon deprotonation as well as the thermodynamically favored six-membered ring structure warranted its stability. It was found that Z could serve as a highly active catalyst to accelerate the reaction rate of each individual step in the HAM, advantageous with the completely inhibited side-reaction of olefin-hydrogenation. The in situ high-pressure FT-IR spectral analysis demonstrated, for the first time, that the involvement of L1 greatly facilitated the formation of two kinds of the active Rh-H intermediates (A′ and A, v 2012 and 2043 cm−1) with well-maintained longevity. And the DFT calculations further confirmed that the Rh-complex of Z exhibited exclusive ability to activate H2, resulting in the efficient formation of Rh-H intermediates of A′ and A, the later (A) was responsible for rapid olefin-hydroformylation, and the former (A′) was in charge of imine-hydrogenation.