Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir-III precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO4 as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*Ir-2(2)(mu-OH)(3)]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (similar to 580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously.