A Co(III)-peroxo-arylboronate complex formed by nucleophilic reaction of a Co(III)-peroxo species

In this work, we report the generation and characterization of two new Co(III)-peroxo complexes 2 and 3. 2 is best described as a mononuclear Co^III-(O₂) complex that exhibits an ¹⁸O-isotope sensitive OO bond stretching vibration at 845(-49) cm^-1, indicating a relatively weak peroxo moiety compared to those of other Co^III-(O₂) complexes reported previously. Complex 3 is a Co^III-peroxo-arylboronate species having a rare {Co^IIIOOBO} five-membered metallocycle, which is structurally characterized using X-ray crystallography. Investigations of the reaction mechanism using density functional theory calculations show that 2 likely undergoes a nucleophilic attack to an arylboronic acid, which is generated by hydrolysis of the BPh₄^- anion in wet acetonitrile solution, to first form a Co^III-peroxo-arylboronic acid adduct, followed by the loss of one benzene molecule to generate the five-membered metallocycle. The entire reaction is thermodynamically favorable. Taken together, the conversion of 2 to 3 represents the discovery of a novel nucleophilic reactivity that can be carried out by mononuclear Co(III)-peroxo complexes.