Hydrogen Peroxide Coordination to Cobalt(II) Facilitated by Second-Sphere Hydrogen Bonding

M(H2O2) adducts have been postulated as intermediates in biological and industrial processes; however, only one observable M(H2O2) adduct has been reported, where M is redox‐inactive zinc. Herein, direct solution‐phase detection of an M(H2O2) adduct with a redox‐active metal, cobalt(II), is described. This CoII(H2O2) compound is made observable by incorporating second‐sphere hydrogen‐bonding interactions between bound H2O2 and the supporting ligand, a trianionic trisulfonamido ligand. Thermodynamics of H2O2 binding and decay kinetics of the CoII(H2O2) species are described, as well as the reaction of this CoII(H2O2) species with Group 2 cations. Finally confirmed: The first M(H2O2) adduct with a redox‐active metal, cobalt(II), could be directly detected in solution. This CoII(H2O2) compound is made observable by incorporating second‐sphere hydrogen‐bonding interactions between bound H2O2 and the supporting ligand, a trianionic trisulfonamido ligand. The decay kinetics and binding constant of this compound are discussed.