An amphoteric reactivity of a mixed-valent bis(mu-oxo)dimanganese(III,IV) complex acting as an electrophile and a nucleophile

Abstract

A mixed-valent bis(mu-oxo)dimanganese(III,IV) complex, [(dpaq)Mn-III(O)(2)Mn-IV(dpaq)](+) (1), was prepared by reacting a hydroxomanganese(III) complex, [(dpaq)Mn-III(OH)](+), with hydrogen peroxide in the presence of triethylamine. The mixed-valent bis(mu-oxo)dimanganese(III,IV) complex (1) was well characterised by UV-vis, EPR and CSI-MS techniques. The electrophilic reactivity of 1 was investigated in the oxidation of 2,6-di- tert-butylphenol derivatives by 1, in which the relative rate afforded a good Hammett correlation with a rho value of -1.0. The nucleophilic character of 1 was then investigated in aldehyde deformylation reactions, using 2-phenylpropionaldehyde (2-PPA) and benzaldehyde derivatives as substrates. In contrast to the case of the reaction of 1 with 2,6-di-tert-butylphenol derivatives, a positive rho value of 0.89 was obtained in the Hammett plot, demonstrating that the bis(mu-oxo)-dimanganese(III,IV) complex is an active nucleophilic oxidant. Thus, 1 exhibited an amphoteric reactivity in both electrophilic and nucleophilic oxidative reactions.