Cp* Iridium Precatalysts for Selective C鈥揌 Oxidation with Sodium Periodate As the Terminal Oxidant

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• 作者：Meng Zhou ; Ulrich Hintermair ; Brian G. Hashiguchi ; Alexander R. Parent ; Sara M. Hashmi ; Menachem Elimelech ; Roy A. Periana ; Gary W. Brudvig ; Robert H. Crabtree
• 刊名：Organometallics
• 出版年：2013
• 出版时间：February 25, 2013
• 年：2013
• 卷：32
• 期：4
• 页码：957-965
• 全文大小：461K
• 年卷期：v.32,no.4(February 25, 2013)
• ISSN：1520-6041

文摘

Sodium periodate (NaIO₄) is shown to be a milder and more efficient terminal oxidant for C鈥揌 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 (鈭?-ambroxide and sclareolide proceeded selectively, and retention of configuration was seen in cis-decalin hydroxylation. At 60 掳C, even primary C鈥揌 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 卤 0.1 was found in cyclohexane oxidation at 23 掳C, suggesting C鈥揌 bond cleavage as the rate-limiting step. Competition experiments between C鈥揌 and water oxidation show that C鈥揌 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.