C(sp3)-H bond activation by the carboxylate-adduct of osmium tetroxide (OsO4)

Tomohiro Fujimoto, Yuka Hirata, Hideki Sugimoto, Mayuko Miyanishi, Yoshihito Shiota, Kazunari Yoshizawa, Shinobu Itoh

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3 Citations (Scopus)


The reaction of osmium tetroxide (OsO4) and carboxylate anions (acetate: X- = AcO- and benzoate: X- = BzO-) gave 1 : 1 adducts, [OsO4(X)]- (1X), the structures of which were determined by X-ray crystallographic analysis. In both cases, the carboxylate anion X coordinates to the osmium centre to generate a distorted trigonal bipyramidal osmium(viii) complex. The carboxylate adducts show a negative shift of the redox potentials (E1/2) and a red shift of the νOsO stretches as compared to those of tetrahedral OsO4 itself. Despite the negative shift of E1/2, the reactivity of these adduct complexes 1X was enhanced compared to that of OsO4 in benzylic C(sp3)-H bond oxidation. The reaction obeyed the first-order kinetics on both 1X and the substrates, giving the second-order rate constant (k2), which exhibits a linear correlation with the C-H bond dissociation energy (BDEC-H) of the substrates (xanthene, 9,10-dihydroanthracene, fluorene and 1,2,3,4-tetrahydronaphthalene) and a kinetic deuterium isotope effect (KIE) of 9.7 (k2(xanthene-h2)/k2(xanthene-d2)). On the basis of these kinetic data together with the DFT calculation results, we propose a stepwise reaction mechanism involving rate-limiting benzylic hydrogen atom abstraction and subsequent rebound of the generated organic radical intermediate to a remaining oxido group on the osmium centre.

Original languageEnglish
Pages (from-to)1123-1130
Number of pages8
JournalDalton Transactions
Issue number3
Publication statusPublished - Jan 21 2022

All Science Journal Classification (ASJC) codes

  • Inorganic Chemistry


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