New Approaches to the Synthesis of Metal Carbenes

Metal carbenes usually possess versatile reactivities that are controlled by the presence of both the metals and the ligands. Diazo compounds are commonly used for the generation of such species through elimination of nitrogen. However, they are often unstable, explosive, and toxic, which limits their applications in large‐scale syntheses. Thus, identifying sustainable and safe surrogates for the generation of metal carbenes has attracted great attention. In this Review, we summarize some of the most important breakthroughs in the generation, catalytic reactions, and selectivity control of metal carbenes from non‐diazo starting compounds.     

Mean‐Square Radius of Gyration and Degree of Branching of Highly Branched Copolymers Resulting from the Copolymerization of AB2 With AB Monomers

Summary: The evolution of the various structural units incorporated into hyperbranched polymers formed from the copolymerization of AB₂ and AB monomers has been derived by the kinetic scheme. The degree of branching was calculated with a new definition given in this work. The degree of branching monotonously increased with increasing A group conversion (x) and the maximum value could reach 2r/(1 + r)², where r is the initial fraction of AB₂ monomers in the total. Like the average degree of polymerization, the mean‐square radius of gyration of the hyperbranched polymers increased moderately with A group conversion in the range x < 0.9 and displayed an abrupt rise when the copolymerization neared completion. The characteristic ratio of the mean‐square radius of gyration remained constant for the linear polymers. However, the hyperbranched polymers did not possess this character. In comparison with the linear polymerization, the weight average and z‐average degree of polymerization increased due to the addition of the branched monomer units AB₂ and the mean‐square radius of gyration decreased quickly for the products of copolymerization.

     

Metal‐Free Enantioselective Electrophilic Activation of Allenamides: Stereoselective Dearomatization of Indoles

The effective and unprecedented chiral BINOL phosphoric acid catalyzed (1–10 mol %) dearomatization of indoles through electrophilic activation of allenamides (ee up to 94 %), is documented. Besides the synthesis of 3,3‐disubstituted indolenine cores, a dearomatization/hydrogen transfer cascade sequence is also presented as a new synthetic shortcut toward highly enantiomerically enriched indolines.     

Hydrogen production via autothermal reforming of ethanol over noble metal catalysts supported on oxides

Hydrogen was produced over noble metal (Ir, Ru, Rh, Pd) catalysts supported on various oxides, including γ-Al₂O₃, CeO₂, ZrO₂ and La₂O₃, via the autothermal reforming reaction of ethanol (ATRE) and oxidative reforming reaction of ethanol (OSRE). The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La₂O₃ prevented the formation of methane, and Rh/La₂O₃ encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La₂O₃-supported catalysts (Ir/La₂O₃) with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4 H₂ molecules can be extracted from a pair of ethanol and water molecules over Ir(5wt%)/La₂O₃. The results presented in this paper indicate that Ir/La₂O₃ can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.     

Image segmentation method for coal particle size distribution analysis

Particle size distribution is extremely important in the coal preparation industry.It is traditionally ana-lysed by a manual screening method,which is relativel...     

On the stability of periodic motions of a two-body system with flexible connection in an elliptical orbit

Nonlinear Dynamics - This paper deals with periodic motions and their stability of a flexible connected two-body system with respect to its center of mass in a central Newtonian gravitational field...     

纳秒脉冲激光烧蚀非晶合金的研究进展

非晶合金是一类原子排列处于长程无序状态的新型结构材料,具有一系列优异的力学和物理性能,从而有望应用于国防、空天等关键领域.在这些领域的应用中,非晶合金易受到强激光或空间等离子体的作用而失效.同时,非晶合金在高能激光辐照下的结构响应本身也极具科学意义.因此,近年来这方面的研究得到了越来越多的关注.论文将重点关注纳秒脉冲激光对非晶合金在大气和水环境下的烧蚀,针对熔化、流体动力学失稳、爆炸沸腾、气泡动力学等烧蚀过程中的几种典型现象,简要介绍相关的实验和理论研究进展.最后,对未来值得进一步研究的方向进行了概述.     

偶氮苯聚合物5-NO2-PADAT及其与Pd(Ⅱ)的螯合物光存储特性

本文制备了偶氮苯聚合物5-NO₂-PADAT和它与Pd(Ⅱ)形成的螯合物,用简并四波混频的方法测量了它们的三阶非线性系数及光存储特性,通过对测量结果的分析,得到了光束在信号写入与读取过程中的关系。     

Efficient separation of surfactant and organic solvent by CO2

CO(2) can be used to separate surfactant and organic solvent completely in various surfactant/solvent solutions without contaminating the surfactants and solvents. We believe that the simple, efficient, and greener method has wide applications.