Formation and Reactivity of a Fleeting Ni III Bisphenoxyl Diradical Species

Cytochrome P450s and Galactose Oxidases exploit redox active ligands to form reactive high valent intermediates for oxidation reactions. This strategy works well for the late 3d metals where accessing high valent states is rather challenging. Herein, we report the oxidation of Ni (salen) (salen=N,N'-bis(3,5-di-tert-butyl-salicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with mCPBA (meta-chloroperoxybenzoic acid) to form a fleeting Ni bisphenoxyl diradical species, in CH CN and CH Cl at -40 °C. Electrochemical and spectroscopic analyses using UV/Vis, EPR, and resonance Raman spectroscopies revealed oxidation events both on the ligand and the metal centre to yield a Ni bisphenoxyl diradical species. DFT calculations found the electronic structure of the ligand and the d-configuration of the metal center to be consistent with a Ni bisphenoxyl diradical species. This three electron oxidized species can perform hydrogen atom abstraction and oxygen atom transfer reactions.