<p>A novel Mn(II) complex (C) with the ligand N-nicotinyl-N′,N″-bis(hexamethylenyl)phosphoric triamide (L) was synthesized and characterized by FT-IR, ³¹P NMR, UV–Vis, AAS, VSM, GC–MS, CHN analysis, and molar conductivity. The complex was immobilized on SBA-15 mesoporous silica to form the heterogeneous catalyst C@SBA-15, as confirmed by FT-IR, TEM, BET, and XRD analyses. Both the homogeneous C and heterogeneous C@SBA-15 were evaluated for the oxidation of alcohols and sulfides using H₂O₂ as an environmentally friendly oxidant. Key reaction parameters, including solvent, temperature, catalyst loading, substrate:oxidant ratio, and recyclability, were optimized based on conversion percentages. C@SBA-15 exhibited superior performance over C, achieving 75–95% conversions for alcohols and 92–100% for sulfides in shorter reaction times and with only 10 mol% catalyst loading. Notably, both Mn-based catalysts outperformed their Ag(I) analogues, with immobilization on SBA-15 enhancing the activity of the Mn(II) complex while reducing it for Ag(I), underscoring the critical role of the metal center. These findings position C@SBA-15 as a highly efficient, recyclable catalyst for oxidation reactions, with potential mechanistic insights involving Mn-peroxo intermediates.</p>