Iron catalyzed competitive olefin oxidation and ipso-hydroxylation of benzoic acids: Further evidence for an FeV=O oxidant

Parthapratim Das, Lawrence Que

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Abstract

The iron complex [FeII(TPA)(CH3CN) 2](OTf)2 (1) [TPA = tris(2-pyridylmethyl)amine] with H2O2 as an oxidant performs ipso-hydroxylation of electron-withdrawing benzoic acids at room temperature, leading to multiple turnovers of corresponding phenols. ipso-Hydroxylation competes with olefin epoxidation and cis-dihydroxylation in the presence of olefins, with the product ratios being modulated by the relative amounts of benzoic acid, olefin, and water. It is proposed that benzoic acid and water compete for the available sixth site on the [(TPA)FeIII(OOH)] intermediate, which undergoes O-O bond heterolysis to form, respectively, the FeV(O)(O2CAr) and FeV(O)(OH) oxidants that determine the product outcome. The putative FeV(O)(O2CAr) oxidant decays either by undergoing oxidative decarboxylation and subsequent ipso-hydroxylation to form the observed phenol product or by oxo-transfer to olefins to form epoxide. The observed higher yield of phenol over epoxide or cis-diol in all cases studied, where an electronwithdrawing benzoic acid is present in the reaction mixture, suggests that intramolecular decay of the putative FeV(O)-(O 2CAr) oxidant is favored over intermolecular olefin oxidation. These results support the mechanistic framework postulated for Fe(TPA) oxidative catalysis and further strengthens the notion that oxoiron(V) species are the key oxidants in these reactions.

Original languageEnglish (US)
Pages (from-to)9479-9485
Number of pages7
JournalInorganic Chemistry
Volume49
Issue number20
DOIs
StatePublished - Oct 18 2010

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