Steric Effect on the Nucleophilic Reactivity of Nickel(III) Peroxo Complexes KimJalee ShinBongki KimHyunjeong LeeJunhyung KangJoongoo YanagisawaSachiko OguraTakashi MasudaHideki OzawaTomohiro ChoJaeheung 2015 A set of nickel­(III) peroxo complexes bearing tetraazamacrocyclic ligands, [Ni<sup>III</sup>(TBDAP)­(O<sub>2</sub>)]<sup>+</sup> (TBDAP = <i>N</i>,<i>N</i>′-di-<i>tert</i>-butyl-2,11-diaza­[3.3]­(2,6)­pyridinophane) and [Ni<sup>III</sup>(CHDAP)­(O<sub>2</sub>)]<sup>+</sup> (CHDAP = <i>N</i>,<i>N</i>′-dicyclohexyl-2,11-diaza­[3.3]­(2,6)­pyridinophane), were prepared by reacting [Ni<sup>II</sup>(TBDAP)­(NO<sub>3</sub>)­(H<sub>2</sub>O)]<sup>+</sup> and [Ni<sup>II</sup>(CHDAP)­(NO<sub>3</sub>)]<sup>+</sup>, respectively, with H<sub>2</sub>O<sub>2</sub> in the presence of triethylamine. The mononuclear nickel­(III) peroxo complexes were fully characterized by various physicochemical methods, such as UV–vis, electrospray ionization mass spectrometry, resonance Raman, electron paramagnetic resonance, and X-ray analysis. The spectroscopic and structural characterization clearly shows that the NiO<sub>2</sub> cores are almost identical where the peroxo ligand is bound in a side-on fashion. However, the different steric properties of the supporting ligands were confirmed by X-ray crystallography, where the CHDAP ligand gives enough space around the Ni core compared to the TBDAP ligand. The nickel­(III) peroxo complexes showed reactivity in the oxidation of aldehydes. In the aldehyde deformylation reaction, the nucleophilic reactivity of the nickel­(III) peroxo complexes was highly dependent on the steric properties of the macrocyclic ligands, with a reactivity order of [Ni<sup>III</sup>(TBDAP)­(O<sub>2</sub>)]<sup>+</sup> < [Ni<sup>III</sup>(CHDAP)­(O<sub>2</sub>)]<sup>+</sup>. This result provides fundamental insight into the mechanism of the structure (steric)–reactivity relationship of metal peroxo intermediates.