Modified and environmentally friendly oxidation of phosphorane ylides to vicinal tricarbonyls using unsupported moist Oxone in dichloromethane

Abstract

Modified and eco-friendly oxidation of phosphorane ylides to the corresponding vicinal tricarbonyls (VTC) using unsupported moist Oxone in dichloromethane at room temperature is described. This green oxidation protocol is simple, mild, and highly efficient to operate, and allowing a chemoselective preparation of VTC from various phosphorane ylides without tedious workup procedures of extraction/drying process in excellent yields.     

S-O bond chemically constrained NiS2/rGO nanocomposite with enhanced Na-ion storage capacity

NiS₂ has become a research hotspot of anode materials for Na-ion batteries due to its high theoretical specific capacity. However, the volume effect, the dissolution of polysulfide intermediates and the low conductivity during the charge/discharge process lead to the low specific capacity and poor cycling stability. NiS₂/rGO nanocomposite was prepared by a facile two-step process: GO was prepared by modified Hummers method, and then NiS₂/rGO nanocomposite was synthesized by l-cys assisted hydrothermal method. NiS₂/rGO nanocomposite shows excellent cycle performance and rate performance, which could be attributed to the mesoporous structure on the graphene skeleton with high conductivity. Besides, the chemical constraint of a unique SO bond on NiS₂ could inhibit the dissolution of intermediates and the loss of irreversible capacity.     

双曲冷却塔塔筒水平地震响应分析

为明确冷却塔在水平地震下的内力环向分布特征及内在原因,同时探究不同地震波时程与规范反应谱所得内力差异的原因,以某大型双曲冷却塔为例,在动力特性分析的基础上,通过反应谱方法和时程方法的水平地震响应计算及对比分析,对上述两个问题进行了研究。研究表明:由于仅侧弯振型对水平地震有贡献,而塔筒的侧弯振型和实际响应均表现为整体侧倾并伴随微弱的截面“流动”变形,这也使塔筒各内力的环向分布分别呈现正弦、余弦分布特征;其整体侧倾可类比于悬臂杆结构,塔筒子午向轴力FY、子午向弯矩MY、剪力FXY和扭矩MXY的环向分布可借助悬臂杆侧倾时截面正应力和剪应力分布来解释;而截面“流动”变形则决定了环向轴力FX和环向弯矩MX的环向分布;整体侧移显著而截面变形极小也使FY和FXY的幅值在塔筒中下部明显大于FX;由于冷却塔第1阶侧弯振型在水平地震响应中往往起绝对主导作用,因此可先对所选地震波计算得到其反应谱,对比第1阶侧弯振型周期对应的水平地震影响系数α值,即可初步推断不同时程及规范反应谱方法所得结果的大小关系。     

On-chip multiphoton Greenberger–Horne–Zeilinger state based on integrated frequency combs

One of the most important multipartite entangled states, Greenberger–Horne–Zeilinger state (GHZ), serves as a fundamental resource for quantum foundation test, quantum communication and quantum computation. To increase the number of entangled particles, significant experimental efforts should been invested due to the complexity of optical setup and the difficulty in maintaining the coherence condition for high-fidelity GHZ state. Here, we propose an ultra-integrated scalable on-chip GHZ state generation scheme based on frequency combs. By designing several microrings pumped by different lasers, multiple partially overlapped quantum frequency combs are generated to supply as the basis for on-chip polarization-encoded GHZ state with each qubit occupying a certain spectral mode. Both even and odd numbers of GHZ states can be engineered with constant small number of integrated components and easily scaled up on the same chip by only adjusting one of the pump wavelengths. In addition, we give the on-chip design of projection measurement for characterizing GHZ states and show the reconfigurability of the state. Our proposal is rather simple and feasible within the existing fabrication technologies and we believe it will boost the development of multiphoton technologies.     

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall‐structured TiO₂ on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO₂–RGO composites had a high surface area (99 0307 m² g^?1) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g^?1 at 1.2 C and 180 mAh g^?1 at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high‐performance Li‐ion batteries.     

锡苯和铅苯二聚反应的理论研究

采用密度泛函理论B3LYP方法,研究了锡苯和铅苯的[2+2],[4+2]及[4+4]二聚反应的微观机理和势能剖面,考察了Sn(Pb)原子上的2,4,6-三甲基苯基(Mes)取代基对反应势能剖面的影响.研究结果表明,所有反应均为协同过程,且大多数情况下,2个C—Sn(Pb)键同步形成.[2+2]和[4+2]反应在热力学和动力学上均比相应的[4+4]反应容易进行,而[4+2]反应在动力学上比相应的[2+2]反应有利.Sn(Pb)原子上的Mes取代基在热力学和动力学上均不利于反应的进行.铅苯的动力学稳定性与锡苯相当,但其热力学稳定性高于锡苯.     

Propylphosphonic anhydride(T3P~) catalyzed one-pot synthesis of α-aminonitriles

The Strecker reaction was performed via a one-pot three component condensation of hetero aromatic/aromatic aldehydes, secondary amines and trimetylsilyl cyanide in the presence of propylphosphonic anhydride(T3P~) to accomplish the corresponding a-aminonitriles. The main advantages of this method are very short reaction time and excellent yields.     

Supercubooctahedron (Cs6Cl)2Cs5[Ga15Ge9Se48] Exhibiting Both Cation and Anion Exchange

A novel type of supertetrahedral connectivity is exhibited by the 72‐atom discrete supercubooctahedron in (Cs₆Cl)₂Cs₅[Ga₁₅Ge₉Se₄₈] ( 1 ), which undergoes both cation and anion exchange, as revealed by unambiguous single‐crystal X‐ray diffraction data. Electronic‐structure studies helped to understand the Ge/Ga distribution.     

Mechanism of [3+2] Cycloaddition of Alkynes to the [Mo3S4(acac)3(py)3][PF6] Cluster

A study, involving kinetic measurements on the stopped‐flow and conventional UV/Vis timescales, ESI‐MS, NMR spectroscopy and DFT calculations, has been carried out to understand the mechanism of the reaction of [Mo₃S₄(acac)₃(py)₃][PF₆] ([ 1 ]PF₆; acac=acetylacetonate, py=pyridine) with two RC?CR alkynes (R=CH₂OH (btd), COOH (adc)) in CH₃CN. Both reactions show polyphasic kinetics, but experimental and computational data indicate that alkyne activation occurs in a single kinetic step through a concerted mechanism similar to that of organic [3+2] cycloaddition reactions, in this case through the interaction with one Mo(μ‐S)₂ moiety of [ 1 ]⁺. The rate of this step is three orders of magnitude faster for adc than that for btd, and the products initially formed evolve in subsequent steps into compounds that result from substitution of py ligands or from reorganization to give species with different structures. Activation strain analysis of the [3+2] cycloaddition step reveals that the deformation of the two reactants has a small contribution to the difference in the computed activation barriers, which is mainly associated with the change in the extent of their interaction at the transition‐state structures. Subsequent frontier molecular orbital analysis shows that the carboxylic acid substituents on adc stabilize its HOMO and LUMO orbitals with respect to those on btd due to better electron‐withdrawing properties. As a result, the frontier molecular orbitals of the cluster and alkyne become closer in energy; this allows a stronger interaction.     

Cycloelimination of Imidazolidin‐2‐ylidene N‐Heterocyclic Carbenes: Mechanism and Insights into the Synthesis of Stable “NHC‐CDI” Amidinates

We report the discovery that 1,3‐bis(aryl)imidazolidin‐2‐ylidenes, one of the most widely studied classes of N‐heterocyclic carbenes (NHCs), undergo quantitative conversion to zwitterionic “NHC‐CDI” amidinates upon heating to ≈100 °C in solution. The mechanism of this novel NHC decomposition process is studied in detail. These studies enabled the rational synthesis of a new class of bench stable amidinates from a panel of NHCs and carbodiimides. We expect these constructs to find utility in a variety of applications.