Zur Stabilität und Struktur der Cu^I‐Komplexe des Imidazols und Histamins. Chemie des einwertigen Kupfers in homogener, polarer Lösung. 1. Mitteilung

Abstract

Abstract Univalent copper is stabilized in aqueous medium by the non‐protophilic ligand CH 3 CN, allowing ligand displacement reactions to be investigated as if a stable Cu I ‐hydrate did exist. Under these conditions the formation of Cu I ‐complexes with imidazole and its derivatives has been studied in polar solution in the absence of Cu II . Imidazole (ImH) acts upon Cu I as a bidentate ligand forming polynuclear chains according to the equation equation image Histamine reacts in the same way, i. e. the coordination number of Cu I does not exceed 2; by comparison of the complexes of Cu I with histamine and its N‐methyl‐derivatives it is shown that no six‐membered chelate – which sterically would be possible – is built up. Trigonal as well as tetrahedral coordination of Cu I – i. e. chelate formation – in dilute polar solutions are confined to π‐ or d ‐acceptor ligands, e. g. bipyridine or methionine. Conclusions are drawn from this on the requirements for redox‐active copper in proteins.