A novel dicobalt(II) mu-peroxo complex (3) is formed by the reaction o
f a dicobalt(II) bis(mu-hydroxo) complex, [Co(HB(3,5-iPr(2)pz)(3))](2)
(OH)(2) (2), with a stoichiometric amount of H2O2. Unusual and charact
eristic spectroscopic properties [(1) existence of two O-2(2-) to meta
l charge transfer absorption bands; (2) low v(O-O) vibration in the re
sonance Raman spectrum; (3) antiferromagnetic coupling between the two
Co(II) ions] suggest that the peroxo ligand coordinates in the planar
mu-eta(2):eta(2) binding mode as found in the oxyhemocyanin and the d
icopper(II) peroxo model complexes. Warming of a pentane solution of 3
induces aliphatic C-H bond activation concomitant with O-O bond cleav
age to yield the novel mu-alkoxo-mu-hydroxo complex 4, -5-iPrpz)(3,5-i
Pr(2)-pz)(2)][HB(3,5-iPr(2)pz)(3)], and the bis(mu-hydroxo) complex 2.