Recent investigations have demonstrated the appeal of using Ni(II) complexes with redox-active ligands in fields like catalysis, electrochemistry, or materials sciences. Ni(salen) complexes have particularly been shown to exhibit temperature-dependent equilibrium based on the localization of the unpaired spin. However, the usage of salen as a ligand has always restricted the characterization of a Ni(IV) species with Ni bearing both the oxidizing equivalents. Hence, the current work aims to develop the biologically relevant pseudopeptide-based Ni complex that enables the formation and trapping of a high-valent Ni(IV) species from its Ni(II) precursor. The synthesized [LNiII] (2) (L = N,N’-(4,5-dimethyl-1,2-phenylene)bis(pyrrolidine-2-carboxamide)) was shown to form a high-valent [LNiIVCl2] (4Cl) species, depending on the axial coordination, upon the addition of excess ceric ammonium nitrate, in the presence of chloride ions as an exogenous ligand, as supported by X-ray absorption spectroscopic analysis. Favorably, the formed Ni(IV) species has also demonstrated electron transfer and oxygen atom transfer (OAT) reactions toward thioanisoles. Computational analysis of the mechanism revealed that the oxidation of thioanisoles proceeds via a stepwise pathway involving a single electron transfer from thioanisole, followed by OAT to the subsequent radical cation. The rate of these reactions demonstrated a strong dependence on the electronics of the substituents.