Monoanionic N,N,O-Scorpionate Ligands and their Iron(II) and Zinc(II) Complexes: Models for Mononuclear Active Sites of Non-Heme Iron Oxidases and Zinc Enzymes

摘要

The chemical behavior of two bis(3,5-dialkylpyrazol-1-yl)-acetic acids and their coordination propertis towards ZnCl_2 and FeCl_2 was studied. Reaction of bis(3,5-Dimethylpyrazol-1-yl)acetic acid (bdmpza) (1) with ZnCl_2 and FeCl_2 gave the 2:1 complexes [(bdmpza)_2Zn] (4) and [(bdmpza)_2Fe] (5). Crystal structures of both complexes were obtained. In contrast, the sterically more hindered ligand bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (bdtbpza) (3) coordinates only once to zinc(II) resulting in the complex [(bdtbpza)ZnCl] (6). This provides a structural model complex for the active sites of zinc enzymes such as thermolysin or carboxypeptidase. The good agreement with these active sites was demon-strated by a crystal structure of 6. To the best of our knowledge, this is the first report of zinc complexes with a monoanionic N,N,O-tridentate ligand using a carboxylate O-donor. Substitution f benzylthiolate for the chloride ligand 6 yielded [(bdtbpza)Zn(SCH_2Ph)] (8) indicating that the bulky tert-butyl groups don not prevent access to the zinc atom. Reaction of bdtbpza (3) with FeCl_2 led to [(bdtbpza)FeCl] (7), which might serve as a structural model complex for the active sites of mononuclear non-heme iron oxidases and oxygenases such as IPNS, DAOCS or CAS.