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- W2111491384 endingPage "14988" @default.
- W2111491384 startingPage "14981" @default.
- W2111491384 abstract "Abstract The first step in the catalytic oxidation of alcohols by molecular O 2 , mediated by homogeneous vanadium(V) complexes [LV V (O)(OR)], is ligand exchange. The unusual mechanism of the subsequent intramolecular oxidation of benzyl alcoholate ligands in the 8‐hydroxyquinolinato (HQ) complexes [(HQ) 2 V V (O)(OCH 2 C 6 H 4 ‐ p ‐X)] involves intermolecular deprotonation. In the presence of triethylamine, complex 3 (X=H) reacts within an hour at room temperature to generate, quantitatively, [(HQ) 2 V IV (O)], benzaldehyde (0.5 equivalents), and benzyl alcohol (0.5 equivalents). The base plays a key role in the reaction: in its absence, less than 12 % conversion was observed after 72 hours. The reaction is first order in both 3 and NEt 3 , with activation parameters Δ H ≠ =(28±4) kJ mol −1 and Δ S ≠ =(−169±4) J K −1 mol −1 . A large kinetic isotope effect, 10.2±0.6, was observed when the benzylic hydrogen atoms were replaced by deuterium atoms. The effect of the para substituent of the benzyl alcoholate ligand on the reaction rate was investigated using a Hammett plot, which was constructed using σ p . From the slope of the Hammett plot, ρ =+(1.34±0.18), a significant buildup of negative charge on the benzylic carbon atom in the transition state is inferred. These experimental findings, in combination with computational studies, support an unusual bimolecular pathway for the intramolecular redox reaction, in which the rate‐limiting step is deprotonation at the benzylic position. This mechanism, that is, base‐assisted dehydrogenation (BAD), represents a biomimetic pathway for transition‐metal‐mediated alcohol oxidations, differing from the previously identified hydride‐transfer and radical pathways. It suggests a new way to enhance the activity and selectivity of vanadium catalysts in a wide range of redox reactions, through control of the outer coordination sphere." @default.
- W2111491384 created "2016-06-24" @default.
- W2111491384 creator A5029356303 @default.
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- W2111491384 creator A5077048042 @default.
- W2111491384 creator A5085406259 @default.
- W2111491384 date "2012-10-18" @default.
- W2111491384 modified "2023-10-18" @default.
- W2111491384 title "A Biomimetic Pathway for Vanadium-Catalyzed Aerobic Oxidation of Alcohols: Evidence for a Base-Assisted Dehydrogenation Mechanism" @default.
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