Dinuclear and mononuclear manganese(IV)-radical complexes and their catalytic catecholase activity.
Seven o-aminophenol ligands based on aniline and m-phenylenediamine, which act as mono- and di-nucleating non-innocent ligands, respectively, together with their seven Mn(IV)-complexes, 1-7 are described. One of them, 1, is dinuclear and 2-7 are mononuclear, in which the ligands are coordinated in their oxidized o-iminobenzosemiquinone radical forms. The crystal structures of 1 and 3 were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable-temperature (2-290 K) susceptibility measurements. Electrochemical measurements (CV and SQW) indicate primarily ligand-centered redox processes. The Mn(IV)-radical complexes, 1-7, catalyze the oxidation of 3,5-di-tert-butylcatechol with molecular oxygen as the sole oxidant to afford 3,5-di-tert-butylquinone quantitatively under mild conditions to mimic the function of the copper-containing enzyme catechol oxidase. An "on-off" mechanism of the radicals without redox participation of the metal center is proposed for the catalytic oxidation process. Complex 1 is found to be a good catalyst for oxidative C-C coupling of hindered phenols to diphenoquinones.
Mukherjee
Soumen
S
Max-Planck-Institut für Bioanorganische Chemie, Stiftstrassse 34-36, D-45470 Mülheim an der Ruhr, Germany.
Weyhermüller
Thomas
T
Bothe
Eberhard
E
Wieghardt
Karl
K
Chaudhuri
Phalguni
P
D000627:Aminophenols / Q000737:chemistry*; D002384:Catalysis; D004156:Catechol Oxidase / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013329:Structure-Activity Relationship
D000627:Aminophenols; D002396:Catechols; D008024:Ligands; D009942:Organometallic Compounds; C027667:2-aminophenol; D008345:Manganese; D004156:Catechol Oxidase; C034221:catechol; D010100:Oxygen