Synthesis, Characterization and Reactivity Control of Ni-Oxygen Adducts with Organic Substrates

Abstract

The reactivity of mononuclear metal-O2 adducts, such as metal-superoxo and -peroxo species, has long fascinated researchers in many areas due to the significance of diverse biological and catalytic processes. To understand how the nature of the ligand influences reactivity patterns of the metal-O2 complexes, recently, a systematic study of the relationship between reactivity and ring size of ligand was undertaken for a series of metal-O2 complexes bearing N-tetramethylated macrocyclic chelates in biomimetic chemistry. In this study, the two ligands, CHDAP and Me3-TPADP, were designed and reactivity of Ni-O2 species bearing each ligand was investigated in part I and part II, respectively. For comparison of reactivity according to a steric effect, a set of nickel(III)-peroxo complexes bearing tetraazamacrocyclic ligands, [NiIII(CHDAP)(O2)]+ and [NiIII(TBDAP)(O2)]+, were prepared and fully characterized by various physicochemical methods. The different steric properties of the supporting ligands were confirmed by X-ray crystallography where the CHDPA ligand gives enough space around the Ni-O2 core compared to the TBDAP ligand. In the aldehyde deformylation reaction, the nucleophilic reactivity of the nicke(III)-peroxo complexes was highly dependent on the steric properties of the macrocyclic ligands, with the reactivity order of [NiIII(TBDAP)(O2)]+ < [NiIII(CHDAP)(O2)]+. This result provides fundamental insight into the mechanism of the structure (steric) – reactivity relationship of metal-peroxo intermediates. In part II, the Me3-TPADP ligand was synthesized, and the starting complex, [NiII(Me3-TPADP)(CH3CN)2]2+ (3), and Ni-O2 intermediate, [NiIII(Me3-TPADP)(O2)]+ (4), were prepared and successfully characterized by various methods. Also, the kinetic result of 4 was obtained with external organic substrates. ⓒ 2015 DGIST