Merocyanine‐Like Chromophores as Ligands for Catalytic Active Metals of Group VIII
作者:Jörg Blumhoff、Rainer Beckert、Dirk Walther、Sven Rau、Manfred Rudolph、Helmar Görls、Winfried Plass
DOI:10.1002/ejic.200600787
日期:2007.1
4H-imidazoles as ligands have been synthesized in good yields. The complexes were characterized by elemental analyses, mass spectrometry, 1H NMR, 13C NMR spectroscopy and in the solid state by single crystal diffraction analyses. The new palladium complexes of type 4 can be regarded as new functional dyes as well as deeply coloured and redox active metallacycles that display catalytic activity. In contrast
sacrificial electrondonors that facilitate proton-coupled electron transfer. Repeated photochemical reduction and chemical oxida-tion reveals that the complex retained a charging capacity of 72% after four cycles. We demonstrate a chemical system that can decouple photochemical processes from the day-night cycle, which has been a barrier to realizing utilization of solar energy in photochemical processes
The cycloaddition of benzamidines with bis-imidoylchlorides 1 derived from oxalic acid was investigated. For example, treatment of benzamidine with 1 gives the new 4H-imidazoles (3a-1) in yields up to 92%. Because of rapid H-transfer processes in solution, the NMR-spectra of 3a-1 show only a single signal set. Apart from prototropism, 3c shows interesting properties as an amphoteric heterocycle. The protonation of 3c is accompanied by a change of color to orange to blue. Probably, protonation takes place on the exocyclic imino nitrogen to give a cyanine type chromophor. The resulting cation can also be regarded as an antiaromatic 1,3-diazacyclopentadienylium system. In order to investigate the influence of exocyclic substituents at nitrogen on the UV/VIS absorption, compounds 3d-h were synthesized. Whereas electron withdrawing groups cause hypsochromic shifts of the first UV/VIS absorption band, the dimethylamino group shifts this band bathochromically as exemplified by 3e. This novel cycloamidine shows strong acidochromism with bathochromic shifts of more than Delta-lambda-(max)=150 nm.
A New Route to Ring-Fused Pyrazines: Imidazo[4,5-b]Quinoxalines by a Simple Oxidation-Annulation Sequence
Novel tricyclic 4H-imidazo[4,5-b]quinoxalines were synthesized by a new ortho-annulation process starting from 4H-imidazoles and cerammonium nitrate (CAN) as oxidation reagent in the presence of potassium carbonate as base. This reaction is interpreted as a multi-step reaction involving oxidative radical formation, a radical aromatic substitution and a subsequent redox process. The analysis is supported
在碳酸钾为碱的存在下,以4 H-咪唑和硝酸铈铵(CAN)为氧化剂,通过新的邻位环化工艺合成了新型三环4 H-咪唑并[4,5- b ]喹喔啉。该反应被解释为涉及氧化自由基形成,自由基芳族取代和随后的氧化还原过程的多步骤反应。高级DFT计算支持该分析。这种新颖的转化为吡嗪的环稠合衍生物的构建开辟了道路。新的三环产品在溶液中显示出强荧光,此外还显示出可逆的氧化还原活性。 胺-杂环-氧化-自由基反应-闭环
Mesoionic bora-tetraazapentalenes – fully reversible two step redox systems
Bora-tetraazapentalenes have been synthesised and characterized; the radical anion shows an unusual thermodynamic stability (semiquinone formation constants KSEM of ca. 1014).