Control of the redox activity of anthraquinone through an appended nickel(II)-cyclam side chain. A two-site three-electron redox system

The conjugate system 1-anthraquinonyl-1,4,8,11-tetraazocyclotetradecane (cyaqO2), was prepd. through reaction of 2-chloromethylanthraquinone with a 5-fold excess of cyclam in CHCl3 at room temp. Reaction of cyaqO2 with NiX2.6H2O (X = Cl, ClO4) gave Ni(cyaqO2), in which the metal center was incorporated by the tetraaza-macrocyclic subunit. The redox behavior of the Ni(II) complexes was investigated in a CH2Cl2 soln. of 0.1 M Bu4NX, by voltammetric techniques. Two-phase redn. of the quinone subunit of Ni(cyaqO2) in CH2Cl2 by aq. CrII takes place at a rate higher than that obsd. for anthraquinone mol., but the reduced conjugate system partitions between CH2Cl2 and H2O.