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.