On the Way to a Trisanionic {Cu3O2} Core for Oxidase Catalysis: Evidence of an Asymmetric Trinuclear Precursor Stabilized by Perfluoropinacolate Ligands

5 years ago

On the Way to a Trisanionic {Cu3O2} Core for Oxidase Catalysis: Evidence of an Asymmetric Trinuclear Precursor Stabilized by Perfluoropinacolate Ligands

Steven F. Hannigan, Nicole Orth, Arnold L. Rheingold, James A. Golen, Alexander Hoffmann, Ivana Ivanović-Burmazović, Thomas Rösener, Patricia Liebhäuser, June S. Lum, Linda H. Doerrer, Sarah E. Neville, Sonja Herres-Pawlis, Julia Stanek, Amanda I. Arnoff

CuI complexes of the form K[(R3P)Cu(pinF)], in which (pinF)2− is the bidentate, oxygen-donating ligand perfluoropinacolate, were synthesized and characterized. Low-temperature oxygenation of the K[(R3P)Cu(pinF)(PR3)] species resulted in a trisanionic bis(μ3-oxo) trinuclear copper(II,II,III) core characterized by UV/Vis spectroscopy (λmax [nm] = 330, 535, 630), cryospray-ionization mass spectrometry, and X-band electron paramagnetic resonance spectroscopy (derivative resonance at 3300 G, Δms=2 at 1500 G). The kinetic behavior of the trimeric {Cu3O2} species was quantified by stopped-flow spectroscopy and the associated electronic structures were investigated by DFT calculations. An asymmetric {Cu3O2} species, AsTpinF, which bears a structure similar to multicopper oxidases, forms prior to full formation of the symmetric trinuclear core, SyTpinF. The trimer catalytically oxidizes para-hydroquinone to benzoquinone (a form of oxidase chemistry). Three is a magic number: A trinuclear {Cu-O2} species stabilised by dianionic ligands has been characterised by UV/Vis stopped-flow spectroscopy in solution. A bis(μ-oxo) dicopper core forms initially, followed by an asymmetric trinuclear species that converts to a symmetric one as the final oxygenation product. For the first time, this rare biorelated, asymmetric species could be stabilised using perfluoropinacolate dianionic ligands. The trinuclear core is a functional model for the active site of multi-copper oxidases. DFT calculations yielded further insights into the electronic structure and catalytic hydroquinone oxidation proves the oxidase capability of the symmetric trinuclear core.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201605926