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71.
Li C Wang C Villa-Marcos B Xiao J 《Journal of the American Chemical Society》2008,130(44):14450-14451
When combined with a chiral phosphate counteranion, a chiral diamine-ligated Ir(III) catalyst displayed excellent enantioselectivities in the asymmetric hydrogenation of a wide range of acyclic imines, affording chiral amines in up to 99% ee. 相似文献
72.
When associated with a noncoordinating bulky counteranion, a cationic Cp*Rh(III)-diamine catalyst displayed excellent enantioselectivities in asymmetric hydrogenation of cyclic imines, affording bioactive tetrahydroisoquinolines and tetrahydro-beta-carbolines frequently with 99% ee's. 相似文献
73.
Wu X Li X Zanotti-Gerosa A Pettman A Liu J Mills AJ Xiao J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(7):2209-2222
Asymmetric transfer hydrogenation (ATH) of ketones by formate in neat water is shown to be viable with Rh-TsDPEN and Ir-TsDPEN catalysts, derived in situ from [Cp*MCl2]2 (M=Rh, Ir) and TsDPEN. A variety of ketones were reduced, including nonfunctionalized aryl ketones, heteroaryl ketones, ketoesters, and unsaturated ketones. In comparison with Ir-TsDPEN and the related Ru II catalyst, the Rh III catalyst is most efficient in water, affording enantioselectivities of up to 99 % ee at substrate/catalyst (S/C) ratios of 100-1000 even without working under an inert atmosphere. The aqueous phase reduction is shown to be highly pH-dependent; the optimum pH windows for TOF greater than 50 mol mol(-1) h(-1) for Rh- and Ir-TsDPEN are 5.5-10.0 and 6.5-8.5, respectively. Outside the pH window, the reduction becomes slow or stagnant depending on the pH. However, the enantioselectivities erode only under acidic conditions. At a higher S/C ratio, the aqueous ATH by Rh-TsDPEN is shown to be product- as well as byproduct-inhibited; the product inhibition appears to stem at least partly from the reaction being reversible. The aqueous phase reduction is simple, efficient and environmentally benign, thus presenting a viable alternative for asymmetric reduction. 相似文献
74.
Asymmetric transfer hydrogenation has become a practically useful tool in reduction chemistry in the last decade or so. This was largely triggered by the seminal work of Noyori and co‐workers in the mid‐1990s and is driven by its complementing chemistry to hydrogenation employing H2. This Focus Review attempts to present a “holistic” overview on the advances in the area, focusing on the achievements recorded around the last three years. These include more‐efficient and “greener” metal catalysts, catalysts that enable hydrogenation as well as transfer hydrogenation, biomimetic and organocatalysts, and their applications in the reduction of C?O, C?N, and C?C bonds. Also highlighted are efforts in the development of environmentally benign and reusable catalytic systems. 相似文献
75.
Jianliang Wu 《Discrete Mathematics》2008,308(24):6210-6215
In the paper, we prove that if G is a graph embeddable on a surface of Euler characteristic ε<0 and , then and . This extends a result of Borodin, Kostochka and Woodall [O.V. Borodin, A.V. Kostochka, D.R. Woodall, List-edge and list-total colorings of multigraphs, J. Comb. Theory Series B 71 (1997) 184-204]. 相似文献
76.
Zhao Dong Jie Xiong Jianliang Zhai Tusheng Zhang 《Journal of Functional Analysis》2017,272(1):227-254
77.
Iridicycle‐Catalysed Imine Reduction: An Experimental and Computational Study of the Mechanism
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Dr. Hsin‐Yi Tiffany Chen Prof. Chao Wang Dr. Xiaofeng Wu Xue Jiang Prof. C. Richard A. Catlow Prof. Jianliang Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(46):16564-16577
The mechanism of imine reduction by formic acid with a single‐site iridicycle catalyst has been investigated by density functional theory (DFT), NMR spectroscopy, and kinetic measurements. The NMR and kinetic studies suggest that the transfer hydrogenation is turnover‐limited by the hydride formation step. The calculations reveal that, amongst a number of possibilities, hydride formation from the iridicycle and formate probably proceeds by an ion‐pair mechanism, whereas the hydride transfer to the imino bond occurs in an outer‐sphere manner. In the gas phase, in the most favourable pathway, the activation energies in the hydride formation and transfer steps are 26–28 and 7–8 kcal mol?1, respectively. Introducing one explicit methanol molecule into the modelling alters the energy barrier significantly, reducing the energies to around 18 and 2 kcal mol?1 for the two steps, respectively. The DFT investigation further shows that methanol participates in the transition state of the turnover‐limiting hydride formation step by hydrogen‐bonding to the formate anion and thereby stabilising the ion pair. 相似文献
78.
Liu Yang Huan-Huan Lu Chu-Hui Lai Dr. Gang Li Prof. Dr. Wei Zhang Prof. Dr. Rui Cao Prof. Dr. Fengyi Liu Dr. Chao Wang Prof. Dr. Jianliang Xiao Prof. Dr. Dong Xue 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12814-12819
A highly effective C−O coupling reaction of (hetero)aryl electrophiles with primary and secondary alcohols is reported. Catalyzed by a NiII-aryl complex under long-wave UV (390–395 nm) irradiation in the presence of a soluble amine base without any additional photosensitizer, the reaction enables the etherification of aryl bromides and aryl chlorides as well as sulfonates with a wide range of primary and secondary aliphatic alcohols, affording synthetically important ethers. Intramolecular C−O coupling is also possible. The reaction appears to proceed via a NiI–NiIII catalytic cycle. 相似文献
79.
Jianliang Zhang Jiayong Qiu Hongwei Guo Shan Ren Hui Sun Guangwei Wang Zhengkai Gao 《Particuology》2014,(5):167-177
A three-dimensional model was established by the discrete element method (DEM) to analyze the flow and segregation of particles in a charging process in detail. The simulation results of the burden falling trajectory obtained by the model were compared with the industrial charging measurements to validate the applicability of the model. The flow behavior of particles from the weighing hopper to the top layer of a blast furnace and the heaping behavior were analyzed using this model. A radial segregation index (RSI) was used to evaluate the extent of the size segregation in the charging process. In addition, the influence of the chute inclination angle on the size segregation and burden profile during the charging process was investigated. 相似文献
80.
The vertex arboricity va(G) of graph G is defined as the minimum of subsets in a partition of the vertex set of G so that each subset induces an acyclic subgraph and has been widely studied. We define the concept of circular vertex arboricity vac(G) of graph G, which is a natural generalization of vertex arboricity. We give some basic properties of circular vertex arboricity and study the circular vertex arboricity of planar graphs. 相似文献