We quantified the kinetics of precursor decomposition for the reaction between metal halide and metal alkoxide in TOPO, using the disappearance of the isopropoxide resonance in 1 H NMR spectroscopy as a convenient handle (Figures and). The original procedures 15-17 were slightly modified to improve the precision and extent of data acquisition, and to have comparable conditions for all three metals (Ti, Zr, Hf). Since TOPO is not an innocent solvent, but also coordinates the precursors and binds to the nanocrystal surface, we chose octadecane (not 1-octadecene due to issues with polymerization ) as an inert solvent with a high boiling point (317 • C). A precise number of TOPO equiva-lents was added to the reaction, thus decoupling the ligand concentration from the precursor concentration. To have a well-defined start of the reaction, we injected the isopropoxide precursor into a mixture of metal chloride, ligand and solvent at the reaction temperature. First, we considered the reaction with equimolar amounts of metal chloride and metal isopropoxide at 275 • C, with 2 equivalents of TOPO (with respect to the total metal content), see Figure . Since we know from earlier work that the metal halide and metal isopropoxide form the mixed chloroisopropoxide, we write the chemical equation succinctly, with this complex as reagent (the reaction scheme also omits the coordinated isopropanol molecule to the metal isopropoxide in case of zirconium and hafnium isopropoxide since it does not take part in the reaction ). Qualitatively, the disappearance of the isopropoxide signal is fastest for titania, slower for zirconia and slowest for hafnia. For zirconia and hafnia, it is clear that the decomposition starts slowly and subsequently accelerates, suggesting an auto-catalytic mechanism. In contrast, for titania, the decomposition appears to be linear. To quantify the kinetics we fitted titania data with a linear function (Figure ) and zirconia and hafnia data (Figures and) to the Finke-Watzky (FW) two-step model: