Synthesis, Electrochemistry, and Reactivity of Cerium(III/IV) Methylene-Bis-Phenolate Complexes

A series of cerium complexes containing a 2,2′-methylenebis­(6-<i>tert</i>-butyl-4-methylphenolate) (MBP^2–) ligand framework is described. Electrochemical studies of the compound [Li­(THF)₂Ce­(MBP)₂(THF)₂] (<b>1</b>) reveal that the metal based oxidation wave occurs at −0.93 V vs Fc/Fc⁺. This potential demonstrates significant stabilization of the cerium­(IV) ion in the MBP^2– framework with a shift of ∼2.25 V from the typically reported value for the cerium­(III/IV) couple of <i>E°</i>′ = +1.30 V vs Fc/Fc⁺ for Ce­(ClO₄)₃ in HClO₄ solutions. Compound <b>1</b> undergoes oxidation to form stable cerium­(IV) species in the presence of a variety of common oxidants. The coordination of the redox-active ligands 2,2′-bipyridine and benzophenone to <b>1</b> result in complexes in which no apparent metal-to-ligand charge transfer occurs and the cerium ion remains in the +3 oxidation state