The Chemistry and Magnetic Properties of Metal Nitronyl Nitroxide Complexes

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.

A versatile synthesis of new pyrimidinyl nitronyl nitroxides

Pyrimidinyl nitronyl nitroxides where the bis-N-oxy fragment is included in a six-membered ring were prepared from diacetonamine by a sequence of reactions including a Grignard reaction, a Ritter reaction and oxidation of the intermediate pyrimidine; the properties of the 2-phenyl-substituted representative are fully described.

Synthesis and coordination chemistry of a water-soluble verdazyl radical. structures and magnetic properties of M(H2O)2(vdCO2)(2).2H2O (M = Co, Ni; vdCO2 = 1,5-dimethyl-6-oxo-verdazyl-3-carboxylate)

The synthesis of a verdazyl radical with a carboxylate substituent renders the radical highly soluble in water, thereby permitting the aqueous synthesis of Ni(II) and Co(II) verdazyl complexes which have been structurally and magnetically characterized.