Nonselective stabilization of nickel(III) by saturated pentaaza macrocycles of varying size

The Ni(II) complexes of the 3 pentaaza macrocycles I (n = m = 2, 3; n = 2, m = 3) were oxidized electrochem. and by oxidizing agents such as NOBF4 in MeCN or K2S2O8 in MeOH to give the corresponding Ni(III) complexes. The half-wave potentials for the Ni2+-Ni3+ couples in the complexes of I are 0.737-0.817 V vs. 0.01M Ag/AgNO3 and 0.1M Et4NBF4 in MeCN 25°, showing the relatively high stability of the Ni3+ complexes