Understanding the influence of electronic and steric factors on transition-metal complexes is essential for advancing oxidation catalysis and small-molecule activation. Here, we explore the synthesis, characterization, and reactivity of a novel manganese(IV) bis(fluoro) complex, [Mn(TBDAP)(F)2]2+, which exhibits a high reduction potential (1.61 V vs SCE) and efficiently oxidizes mesitylene to 3,5-dimethylbenzaldehyde via an electron transfer (ET)-driven proton-coupled electron transfer (PCET) mechanism. Additionally, we investigate the effect of steric bulkiness on the spin states and reactivity of peroxocobalt(III) complexes. Among the synthesized complexes, [Co(ADDAP)(O2)]+ exhibited an S = 1 spin state, enabling nitrile oxidation, whereas the less bulky [Co(MDAP)(O2)]+ remained inactive. The correlation between spin state and reactivity was further supported by electronic structure analyses, demonstrating that a weaker ligand field induced by bulkier N-substituents stabilizes the high-spin state, thereby enhancing oxidative capabilities. These findings highlight the significance of electronic and steric tuning in controlling metal-oxygen reactivity and provide valuable insights into transition-metal-mediated catalysis, particularly in the design of novel oxidation catalysts.