Dioxygen Activation by an in situ Reduced CuII Hydrazone Complex

Radunsky C, Kösters J, Letzel MC, Yogendra S, Schwickert C, Manck S, Sarkar B, Pöttgen R, Weigand JJ, Neugebauer J, Müller J

Abstract

A CuII hydrazone complex has been synthesized that can be reduced in situ in boiling methanol to give the corresponding CuI complex. The latter complex readily activates dioxygen under ambient conditions, as was unambiguously shown by isotopic labeling studies. As a consequence of the dioxygen activation, the thienyl moiety appended to the hydrazone ligand is easily oxidized in β position (C-H→C-O), finally leading to a change in the coordination environment of the central metal ion. All relevant complexes have been structurally characterized by single-crystal X-ray diffraction analyses. The hydrazone ligand applied in this study does not mimic a biologically relevant coordination motif in copper-containing oxygenases. Nonetheless, the reactivity of the CuI complex resembles that found in many oxygenases, indicating that hydrazone ligands may be well-suited for the generation of novel bioinspired oxidation catalysts. A CuII complex of a hydrazone ligand with N,N,S-donor functionality is reported that, after in situ reduction, is able to activate dioxygen, leading to a hydroxylation of the ligand and finally resulting in the formation of a CuII complex of a hydrazone ligand acting as an N,N,O-donor.