This report describes the first example of palladium-catalyzed carbonylative difunctionalization of unactivated alkenes initiated by enolate nucleophiles. The approach involves initiation by an unstabilized enolate nucleophile under an atmospheric pressure of CO and termination with a carbon electrophile. This process is compatible with a diverse range of electrophiles, including aryl, heteroaryl, and vinyl iodides to yield synthetically useful 1,5-diketone products, which were demonstrated to be precursors for multi-substituted pyridines. A PdI-dimer complex with two bridging CO units was observed although its role in catalysis is not yet understood. 相似文献
Nonlinear Dynamics - In this paper, the problem of bounded consensus tracking for second-order multi-agent systems is addressed with fixed and randomly switching directed topologies, wherein the... 相似文献
The conventional synthetic methodology for atomically precise gold nanoclusters by using reduction in solution offers only the thermodynamically most stable nanoclusters. Herein, a solubility-driven isolation strategy is reported to access a metastable gold cluster. The cluster, with the composition of [Au9(PPh3)8]+ ( 1 ), displays an unusual, nearly perfect body-centered cubic (bcc) structure. As revealed by ESI-MS and UV/Vis measurements, the cluster is metastable in solution and converts to the well-known [Au11(PPh3)8Cl2]+ ( 2 ) within just 90 min. DFT calculations revealed that although both 1 and 2 are eight-electron superatoms, there is a driving force to convert 1 to 2 as shown by the increased cohesion and larger HOMO–LUMO energy gap of 2 . The isolation and crystallization of the metastable gold cluster were achieved in a biphasic reaction system in which reduction of gold precursors and crystallization of 1 took place concurrently. This synthetic protocol represents a successful strategy for investigations of other metastable species in metal nanocluster chemistry. 相似文献
Journal of Thermal Analysis and Calorimetry - The performance of rolling bearings is often reduced due to the additional wear introduced by sliding contact. Therefore, it is very vital to study the... 相似文献
While the enzymatic reduction of unsaturated compounds usually has high specificity, highly selective reduction processes are hardly realized by heterogeneous industrial catalysts, which is critical for the green production of many fine chemicals. Here, we report an unexpected discovery of a biomimetic behavior of dicyandiamide (DICY)-modified Pt nanocatalysts for the green hydrogenation of a wide range of nitroaromatics. We demonstrate that the surface modification by DICY not only prevents the direct contact of nitroaromatic reactants with Pt surface but also induces an effective non-contact hydrogenation mechanism mediated by protons and electrons. In such a process, the DICY layer serves as a “semi-permeable membrane” to allow the permeation of H2 molecules for being activated into electrons and protons at the Pt-DICY interface. With the generation of separated protons and electrons, the nitro group with strong electrophilic properties can be hydrogenated through the electron transfer followed by the proton transfer, which is facilitated by the hydrogen bonding network formed by protonated DICY. The unique mechanism makes it highly directional toward the hydrogenation of nitro groups without side reactions. Owing to its capability to largely eliminate the waste generation, the developed Pt-DICY catalysts have been successfully applied for the green industrial production of many important aniline intermediates.
Flapping fluorophores (FLAP) with a flexible 8π ring are rapidly gaining attention as a versatile photofunctional system. Here we report a highly photostable “flapping peryleneimide” with an unprecedented fluorogenic mechanism based on a bent-to-planar conformational change in the S1 excited state. The S1 planarization induces an electronic configurational switch, almost quenching the inherent fluorescence (FL) of the peryleneimide moieties. However, the FL quantum yield is remarkably improved with a prolonged lifetime upon a slight environmental change. This fluorogenic function is realized by sensitive π-conjugation design, as a more π-expanded analogue does not show the planarization dynamics. With strong visible-light absorption, the FL lifetime response synchronized with the flexible flapping motion is useful for the latest optical techniques such as FL lifetime imaging microscopy (FLIM). 相似文献
Photocatalysis and Fenton process are two primary and promising advanced oxidation processes to degrade organic pollutants. However, the practical applications of single photocatalysis and Fenton process are still limited. Introducing one of them into another to form a combined photocatalytic Fenton-like system has shown great potential but still faces challenges in designing a well-tailored catalyst. Herein, a confined photocatalytic Fenton-like micro-reactor catalyst with a movable Fe3O4 core and a mesoporous TiO2 shell has been constructed via a successive Stöber coating strategy, followed by an ultrasound assisted etching method. The resulting micro-reactor possesses well-defined yolk-shell structures with uniform mesopores (~4 nm), a large Brunauer-Emmett-Teller (BET) surface area (~166.7 m2/g), a high pore volume (~0.56 cm3/g) and a strong magnetization (~51 emu/g), as well as tunable reactor sizes (20?90 nm). When evaluated for degrading bisphenol A under solar light in the presence of peroxymonosulfate, the micro-reactor exhibits a superior catalytic degradation performance with a high magnetic separation efficiency and an excellent recycle ability. The outstanding performance can be attributed to its unique textual structure, which leads to a great synergistic effect from the photocatalytic and Fenton-like process. This study gives an important insight into the design and synthesis of an advanced micro-reactor for a combined advanced oxidation processes (AOPs). 相似文献
In this paper, under the genericity condition, we study the condition estimation of the total least squares (TLS) problem based on small sample condition estimation (SCE), which can be incorporated into the direct solver for the TLS problem via the singular value decomposition (SVD) of the augmented matrix [A, b]. Our proposed condition estimation algorithms are efficient for the small and medium size TLS problem because they utilize the computed SVD of [A, b] during the numerical solution to the TLS problem. Numerical examples illustrate the reliability of the algorithms. Both normwise and componentwise perturbations are considered. Moreover, structured condition estimations are investigated for the structured TLS problem. 相似文献