Dioxygen Activation at a Single Copper Site: Structure, Bonding, and Mechanism of Formation of 1:1 Cu/O₂ Adducts

Aboelella, N. W.; Kryatov, S.; Gherman, B. F.; Brennessel, W. W.; Young, V. G., Jr.; Sarangi, R.; Rybak-Akimova, E.; Hodgson, K. O.; Hedman, B.; Solomon, E. I.; Cramer, C. J.; Tolman, W. B.
J. Am. Chem. Soc. 2004, 126, 16896.

In order to evaluate the fundamental process of O₂ activation at a single copper site that occurs in biological and catalytic systems, a detailed study of O₂ binding to Cu(I) complexes of b-diketiminate ligands L (L¹ = backbone Me; L² = backbone tBu) by X-ray crystallography, X-ray absorption spectroscopy (XAS), cryogenic stopped-flow kinetics, and theoretical calculations was performed. Using synchrotron radiation, an X-ray diffraction data set for L²CuO₂ was acquired which led to structural parameters in close agreement to theoretical predictions. Significant Cu(III)-peroxo character for the complex was corroborated by XAS. On the basis of stopped-flow kinetics data and theoretical calculations for the oxygenation of L¹Cu(RCN) (R = alkyl, aryl) in THF and THF/RCN mixtures between 193-233 K, a dual pathway mechanism is proposed involving (a) rate-determining solvolysis of RCN by THF followed by rapid oxygenation of L¹Cu(THF) and (b) direct, bimolecular oxygenation of L¹Cu(RCN) via an associative process.

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