A tetracopper(II)-tetraradical cuboidal core and its reactivity as a functional model of phenoxazinone synthase.
The coordination chemistry of the tridentate ligand N-(2-hydroxy-3,5-di-tert-butylphenyl)-2-aminobenzylalcohol H3L has been studied with the copper(II) ion. The ligand is noninnocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato [L*]2- radical form. The crystal structure of the synthesized tetracopper(II)-tetraradical complex [CuII4(L*)4] (1), has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements of complex 1 containing eight paramagnetic centers establish the spin ground state to be diamagnetic (St=0) arising from the antiferromagnetic interactions. Electrochemical measurements (cyclic voltammograms and square wave voltammograms) indicate four one-electron reductions of the ligand prior to the reduction of the metal center. Complex 1 is found to catalyze the aerial oxidation of 2-aminophenol to 2-amino-phenoxazine-3-one, thus modeling the catalytic function of the copper-containing enzyme phenoxazinone synthase. Kinetic measurements together with electron paramagnetic resonance and electronic spectral studies have been used to decipher the complex six-electron oxidative coupling of 2-aminophenol. An "on-off" mechanism of the radicals together with redox participation of the metal center is proposed for the catalytic oxidation processes.
Mukherjee
Chandan
C
Institute for Inorganic and Analytical Chemistry, University of Mainz, D-55128 Mainz, Germany.
Weyhermüller
Thomas
T
Bothe
Eberhard
E
Rentschler
Eva
E
Chaudhuri
Phalguni
P
D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008958:Models, Molecular; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared
D003300:Copper; D010088:Oxidoreductases; C023944:2-aminophenol oxidase