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Jacob D. Teeter Dr. Percy Zahl Mohammad Mehdi Pour Dr. Paulo S. Costa Prof. Axel Enders Prof. Alexander Sinitskii 《Chemphyschem》2019,20(18):2281-2285
We report the on-surface synthesis and spectroscopic study of laterally extended chevron graphene nanoribbons (GNRs) and compare them with the established chevron GNRs, emphasizing the consistency of bandgap reduction of semiconducting GNRs with increased width. The laterally extended chevron GNRs grown on Au(111) exhibit a bandgap of about 2.2 eV, which is considerably smaller than the values reported for chevron GNRs in similar studies. 相似文献
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N‐Heterocyclic Carbene Catalysis via Azolium Dienolates: An Efficient Strategy for Remote Enantioselective Functionalizations 下载免费PDF全文
Dr. Xiang‐Yu Chen Qiang Liu Dr. Pankaj Chauhan Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(15):3862-3873
N‐heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in organic synthesis. In recent years a number of reviews have been published on NHC‐catalyzed transformations involving Breslow intermediates, acyl azoliums, α,β‐unsaturated acyl azoliums, homoenolate equivalents, and azolium enolates. However, the azolium dienolate intermediates generated by NHCs have been employed in asymmetric synthesis only very recently, especially in cycloadditions dealing with remote functionalization. This Minireview highlights all the developments and the new advances in NHC‐catalyzed asymmetric cycloaddition reactions involving azolium dienolate intermediates. 相似文献
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Control of N‐Heterocyclic Carbene Catalyzed Reactions of Enals: Asymmetric Synthesis of Oxindole‐γ‐Amino Acid Derivatives 下载免费PDF全文
Dr. Xiang‐Yu Chen Jia‐Wen Xiong Qiang Liu Sun Li He Sheng Dr. Carolina von Essen Prof. Dr. Kari Rissanen Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(1):300-304
A strategy to control the switch between a non‐cycloaddition reaction and a cycloaddition reaction of enals, using N‐heterocyclic carbene (NHC) catalyisis, has been developed. The new scalable protocol leads to γ‐amino‐acid esters bearing a tetrasubstituted stereocenter in good yields and high stereoselectivities by homo‐Mannich reactions of enals and isatin‐derived ketimines. By simply changing the N‐ketimine substituent to an ortho‐hydroxy phenyl group, the corresponding spirocyclic oxindolo‐γ‐lactams are obtained. 相似文献
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The asymmetric intermolecular Stetter reaction is catalyzed by a novel triazolium salt derived N-heterocyclic carbene leading to 1,4-diketones in moderate to excellent yields (49-98%) and moderate to good enantioselectivities (56-78% ee), which could be enhanced by one recrystallization to excellent levels (90-99% ee). 相似文献
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Enders D Nagao T Nakayama T Aono M 《Langmuir : the ACS journal of surfaces and colloids》2007,23(11):6119-6125
The adsorption and desorption of Au nanoparticles (AuNP) in colloidal D2O suspension on the (3-aminopropyl)triethoxysilane treated SiO2/Si surface was investigated by in situ attenuated total reflection surface enhanced infrared absorption (ATR-SEIRA) spectroscopy with a liquid flow cell. With increasing surface density of AuNP, the absorption of the vibrational modes of D2O and of the citrate molecules covering the AuNP increases due to SEIRA. Repulsive electrostatic Coulomb forces between the AuNP lead to the saturation of the AuNP surface density at submonolayer coverage. We show that the adsorption kinetics can be investigated by monitoring in situ the molecular vibrational modes of D2O and the citrate molecules. Furthermore, we clarify that the adsorption process can be described very well by a diffusion-limited first-order Langmuir kinetics model. When exposing a saturated AuNP submonolayer to 2-aminoethanethiol (AET)/D2O solution, the AuNP are removed from the surface and the IR absorption of the D2O vibrational modes become weaker again. Taking into account the time dependencies of the OD and the CH peaks, we propose a microscopic model where the AET molecules quickly adsorb on the AuNP by replacing most of the precovering citrate molecules exposed to the AET solution. As this takes place, the AuNP agglomerate-as we could detect with scanning electron microscopy-and are finally removed from the surface. 相似文献
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