Di-o-tolylphosphine oxide is primarily used as a ligand in coordination chemistry, where it facilitates the stabilization of metal complexes. It is often employed in catalytic processes, particularly in reactions involving transition metals, due to its ability to enhance reaction efficiency and selectivity. Additionally, it finds application in the synthesis of organic compounds, where it acts as a key intermediate or reagent. Its role in polymer chemistry is also notable, as it can be used to modify polymer properties or as a flame retardant additive. In material science, it contributes to the development of advanced materials with specific electronic or structural characteristics.