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61.
Dr. Aleksandrs Prokofjevs 《Angewandte Chemie (International ed. in English)》2015,54(45):13401-13405
Thermally induced dehydrogenation of the H‐bridged cation L2B2H5+ (L=Lewis base) is proposed to be the key step in the intramolecular C? H borylation of tertiary amine boranes activated with catalytic amounts of strong “hydridophiles”. Loss of H2 from L2B2H5+ generates the highly reactive cation L2B2H3+, which in its sp2‐sp3 diborane(4) form then undergoes either an intramolecular C? H insertion with B? B bond cleavage, or captures BH3 to produce L2B3H6+. The effect of the counterion stability on the outcome of the reaction is illustrated by formation of LBH2C6F5 complexes through disproportionation of L2B2H5+ HB(C6F5)3?. 相似文献
62.
Gold/Palladium Alloy for Carbon–Halogen Bond Activation: An Unprecedented Halide Dependence 下载免费PDF全文
Dr. Raghu Nath Dhital Dr. Karan Bobuatong Prof. Dr. Masahiro Ehara Prof. Dr. Hidehiro Sakurai 《化学:亚洲杂志》2015,10(12):2669-2676
New catalytic activity of gold/palladium alloy nanoclusters (NCs) for carbon–halogen bond activation is demonstrated. In the case of an aryl chloride, the inclusion of gold in a bimetallic catalyst is indispensable to achieve the coupling reactions. Gold has the unique effect of stabilizing palladium, such that Pd2+ leached from clusters by means of spillover of chloride during oxidative addition. The thus‐formed spillover intermediate further reacts heterogeneously in both Ullmann and Suzuki‐type coupling reactions through a new type of mechanism. In the case of an aryl bromide, Ullmann coupling occurs through the spillover of bromide, similar to that of aryl chloride. However, a significant fraction of palladium also leached, which diminished the Ullmann coupling activity of the aryl bromide and, as a result, the order of reactivity was ArCl>ArBr. With regard to the activation of the C?Br bond towards a Suzuki‐type reaction, the inclusion of a higher gold content in gold/palladium clusters stabilized palladium to prevent the leaching of Pd2+ from the clusters by means of spillover of bromide. The spillover intermediate reacts heterogeneously with PhB(OH)2, palladium‐rich gold/palladium, or pure palladium clusters; the oxidative addition of ArBr favors the extraction of palladium from the clusters, yielding Pd2+ intermediates. The extracted intermediates react homogenously (Pd2+/Pd0 catalysis) with PhB(OH)2, which results in the higher selectivity of the cross‐coupling product. An initial step to observe such unprecedented halide dependency, together with the dynamic behavior of palladium on the surface of gold is the oxidative addition of Ar?X. A detailed insight into the first oxidative addition process was also examined by quantum chemical calculations. 相似文献
63.
《化学:亚洲杂志》2017,12(2):239-247
Five bis(quinolylmethyl)‐(1H ‐indolylmethyl)amine (BQIA) compounds, that is, {(quinol‐8‐yl‐CH2)2NCH2(3‐Br‐1H ‐indol‐2‐yl)} ( L1H ) and {[(8‐R3‐quinol‐2‐yl)CH2]2NCH(R2)[3‐R1‐1H ‐indol‐2‐yl]} ( L2–5H ) ( L2H : R1=Br, R2=H, R3=H; L3H : R1=Br, R2=H, R3=i Pr; L4H : R1=H, R2=CH3, R3=i Pr; L5H : R1=H, R2=n Bu, R3=i Pr) were synthesized and used to prepare calcium complexes. The reactions of L1–5H with silylamido calcium precursors (Ca[N(SiMe2R)2]2(THF)2, R=Me or H) at room temperature gave heteroleptic products ( L1, 2 )CaN(SiMe3)2 ( 1 , 2 ), ( L3, 4 )CaN(SiHMe2)2 ( 3 a , 4 a ) and homoleptic complexes ( L3, 5 )2Ca ( D3 , D5 ). NMR and X‐ray analyses proved that these calcium complexes were stabilized through Ca⋅⋅⋅C−Si, Ca⋅⋅⋅H−Si or Ca⋅⋅⋅H−C agostic interactions. Unexpectedly, calcium complexes (( L3–5 )CaN(SiMe3)2) bearing more sterically encumbered ligands of the same type were extremely unstable and underwent C−N bond cleavage processes as a consequence of intramolecular C−H bond activation, leading to the exclusive formation of (E )‐1,2‐bis(8‐isopropylquinol‐2‐yl)ethane. 相似文献
64.
《化学:亚洲杂志》2017,12(1):130-144
An efficient palladium(II)‐catalyzed intermolecular direct ortho ‐alkenylation and acetoxylation of phenols has been developed. The reaction proceeded via a seven‐membered cyclopalladated intermediate and showed complete regio‐ and diastereoselectivity. The approach also provided an efficient route for the synthesis of coumarins and benzofurans. 相似文献
65.
《化学:亚洲杂志》2017,12(3):289-292
A rhodium‐catalyzed regioselective C−H olefination of indazole is described. This protocol relies on the use of an efficient and removable N ,N ‐diisopropylcarbamoyl directing group, which offers facile access to C7‐olefinated indazoles with high regioselectivity, ample substrate scope and broad functional group tolerance. 相似文献
66.
《化学:亚洲杂志》2017,12(14):1773-1779
There is increasing demand for superhydrophobic materials, which can be used for separating oil and water efficiently. To avoid secondary pollution, it is desirable to prepare such materials with green technology. Here, we present an environmentally benign method for fabricating superhydrophobic materials by using organic base based solvents in which cellulose can be dissolved and activated. The dissolved cellulose could be chemically modified with a silanization reagent, and the solvent could be recycled after CO2 was removed. The obtained cellulose nanocoating exhibited excellent hydrophobic effects. By spraying it on filter paper (water contact angle (WCA)=165°) for oil and water separation, the separation efficiency of more than 95 % was achieved; ultrasonication of an ordinary sponge in its dispersion (WCA=163°), meant it could be used as an oil absorber. It can also absorb a certain amount of bisphenol A (BPA), with the concentration decreasing by 66 % from the original concentration (0.1 mm ). Besides the high separation efficiency, it is resistant to a wide range of pH solutions, which means that it could be used in harsh environments. More importantly, the process is cost‐effective, the solvent can be recycled, and the whole process is green. Thus, the activation method provides a green route for the preparation of other cellulose‐based materials. 相似文献
67.
Joohyun Lim Xiaoyan Jin Yun Kyung Jo Seul Lee Prof. Seong-Ju Hwang 《Angewandte Chemie (International ed. in English)》2017,56(25):7093-7096
An efficient chemical way to finely control the layer-by-layer stacking of inorganic nanosheets (NS) is developed by tuning the type and composition of intercalant ion, and the reaction temperature for restacking process. The finely controlled stacking of NS relies on a kinetic control of the self-assembly of NS in the presence of coordinating organic cations. A critical role of organic cations in this assembly highlights the importance of the appropriate activation energy. Of prime importance is that a fine-control of the interstratification of 2D NS is highly effective not only in tailoring its pore structure but also in enhancing its electrode activity. The present study clearly demonstrates that the kinetically controlled restacking of NS provides a facile and powerful method to tailor their stacking number and functionality. 相似文献
68.
Ms. Orsolya Tischler Mr. Balázs Tóth Dr. Zoltán Novák 《Chemical record (New York, N.Y.)》2017,17(2):184-199
This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho‐directed C?H activation of aniline derivatives from the first attempts to up‐to‐date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented. 相似文献
69.
Frustrated Lewis pair chemistry has taken a steep development in the recent years. It offers possibilities of developing new variants of known reactions and of finding new chemical transformations. This is demonstrated and described by the recently developed FLP‐formylborane chemistry, which has led to the formation of the unique (η2‐formylborane)FLP adducts and opened a way of preparing a genuine formylborane compound, which shows an interesting follow‐up chemistry. FLPs have helped finding phosphorus analogues of the enamine Stork reaction and the Claisen reaction. These reactions lead to new organophosphorus compounds and they make new phosphane/borane systems available. P/B FLPs add to a variety of small main group element oxides. They undergo 1,2‐addition reactions to CO2, SO2 and other heterocumulenes and they feature unique 1,1‐addition reactions to carbon monoxide, to isonitriles and even to nitric oxide (NO), the latter yielding examples of a new class of persistent nitroxide radicals, the FLPNO nitroxyls. Eventually, some remarkable radical reactions of FLPs and related compounds are briefly mentioned. 相似文献
70.
多核过渡金属配合物作为一类广泛应用的均相催化剂,其设计灵感往往来自天然酶的多金属活性位点所发挥的重要作用.目前,三核金属配合物作为活化小分子的多金属催化剂受到了广泛的关注.为深入理解三核过渡金属配合物在催化反应中作用特点,对近年报道的代表性三核过渡金属配合物按金属中心进行分类,并对配体环境形成特点及催化应用进行综述.从金属中心出发,讨论了三核过渡金属配合物的几何结构和电子特征;从配体环境出发,总结了关联三个独立的金属位点的配位环境特征;在催化应用方面,重点综述了三核过渡金属配合物在涉及特定化学键活化反应的催化作用机制,最后对三核过渡金属配合物的催化应用前景进行展望. 相似文献