Hydrogen Bonding Effect on the Oxygen Binding and Activa-tion in Cobalt(III)-peroxo Complexes

Cobalt(III)peroxo complexes serve as model metal complexes mediating oxygen activation. We report a systematic study of the effect of the hydrogen bonding on the oxygen binding and on the O-O bond activation within the cobalt(III)-peroxo complexes. To this end, we prepared a series of tris(pyridin-2-ylmethyl)amine based cobalt(III)peroxo complexes having either none, one, two or three amino groups in the secondary coordination sphere. The hydrogen bonding between the amino group(s) and the peroxo ligand was investigated within the isolated complexes in the gas phase using helium tag-ging IR photodissociation spectroscopy, energy-resolved collision induced dissociation experiments and density func-tional theory. The results show that the hydrogen bonding stabilizes the cobalt(III)-peroxo core, but the effect is on the order of units of kcal mol-1. Introduction of the first amino group to the secondary coordination sphere has the largest stabilization effect; more amino groups do not change the results significantly. The amino group can transfer a hydrogen atom to the peroxo ligands which results in the O-O bond cleavage. This process is thermodynamically favored over the O2 elimination, but entropically disfavored.