Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

Autor: Ivana Ivanović-Burmazović, Claudia Wilfer, Patricia Liebhäuser, Leander Simon Runtsch, Sonja Herres-Pawlis, Oleg Grossmann, Alexander Hoffmann, Regina Dick, Rahel Schepper, Matthias Bauer, Hannes Erdmann, Maximilian Dürr, Eva Paffenholz
Rok vydání: 2015
Předmět:
Zdroj: Chemistry - A European Journal. 21:17639-17649
ISSN: 0947-6539
Popis: Bis(pyrazolyl)methane ligands are excellent components of model complexes used to investigate the activity of the enzyme tyrosinase. Combining the N donors 3-tert-butylpyrazole and 1-methylimidazole results in a ligand that is capable of stabilising a (μ-η(2) :η(2) )-dicopper(II) core that resembles the active centre of tyrosinase. UV/Vis spectroscopy shows blueshifted UV bands in comparison to other known peroxo complexes, due to donor competition from different ligand substituents. This effect was investigated with the help of theoretical calculations, including DFT and natural transition orbital analysis. The peroxo complex acts as a catalyst capable of hydroxylating a variety of phenols by using oxygen. Catalytic conversion with the non-biological phenolic substrate 8-hydroxyquinoline resulted in remarkable turnover numbers. In stoichiometric reactions, substrate-binding kinetics was observed and the intrinsic hydroxylation constant, kox , was determined for five phenolates. It was found to be the fastest hydroxylation model system determined so far, reaching almost biological activity. Furthermore, Hammett analysis proved the electrophilic character of the reaction. This sheds light on the subtle role of donor strength and its influence on hydroxylation activity.
Databáze: OpenAIRE
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