Sodium periodate (NaIO4) is shown to be a milder and more efficient terminal oxidant for C–H oxidation with Cp*Ir (Cp* = C5Me5) precatalysts than ceric(IV) ammonium nitrate. Synthetically useful yields, regioselectivities, and functional group tolerance were found for methylene oxidation of substrates bearing a phenyl, ketone, ester, or sulfonate group. Oxidation of the natural products (−)-ambroxide and sclareolide proceeded selectively, and retention of configuration was seen in cis-decalin hydroxylation. At 60 °C, even primary C–H bonds can be activated: whereas methane was overoxidized to CO2 in 39% yield without giving partially oxidized products, ethane was transformed into acetic acid in 25% yield based on total NaIO4. 18O labeling was demonstrated in cis-decalin hydroxylation with 18OH2 and NaIO4. A kinetic isotope effect of 3.0 ± 0.1 was found in cyclohexane oxidation at 23 °C, suggesting C–H bond cleavage as the rate-limiting step. Competition experiments between C–H and water oxidation show that C–H oxidation of sodium 4-ethylbenzene sulfonate is favored by 4 orders of magnitude. In operando time-resolved dynamic light scattering and kinetic analysis exclude the involvement of metal oxide nanoparticles and support our previously suggested homogeneous pathway.
Zhou, M., Hintermair, U., Hashiguchi, B. G., Parent, A. R., Hashmi, S. M., Elimelech, M., ... Crabtree, R. H. (2013). Cp* iridium precatalysts for selective C–H oxidation with sodium periodate as the terminal oxidant. Organometallics, 32(4), 957-965. https://doi.org/10.1021/om301252w