Mechanistic investigation of vinylic carbon-fluorine bond activation of perfluorinated cycloalkenes using Cp*2ZrH2 and Cp*2ZrHF |
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Authors: | Bradley M. Kraft Odile Eisenstein William D. Jones |
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Affiliation: | a St. John Fisher College, 3690 East Avenue, Rochester, NY 14618, United States b Institut Charles Gerhardt, Université Montpellier 2, CNRS 5253, Case Courrier 1501, Place E. Bataillon, 34095 Montpellier, France c Department of Chemistry, University of Rochester, Rochester, NY 14627, United States |
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Abstract: | Cp*2ZrH2 (1) (Cp*: pentamethylcyclopentadienyl) reacts with cyclic perfluorinated olefins to give Cp*2ZrHF (2) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic positions of the cycloolefin to exchange fluorine for hydrogen. Several mechanisms are discussed for this H/F exchange: (a) olefin insertion/β-fluoride elimination, (b) olefin insertion/α-fluoride elimination, and (c) hydride/fluoride σ-bond metathesis. Following H/F σ-bond metathesis exchange of both vinylic C-F bonds of perfluorocyclobutene, 1 then reacts with allylic C-F bonds by insertion/β-fluoride elimination. A similar sequence is observed with perfluorocyclopentene. Cp*2ZrHF reacts selectively with vinylic C-F bonds of perfluorocyclobutene to give 3,3,4,4-tetrafluorocyclobutene and Cp*2ZrF2 without further hydrodefluorination occurring. In the presence of excess 1 and H2, perfluorocyclobutene and perfluorocyclopentene are reduced to cyclobutane and cyclopentane in 46% and 16% yield, respectively. DFT calculations exclude the pathway by way of the olefin insertion/α-fluoride elimination and suggest that the pathway by way of hydride/fluoride σ-bond metathesis is preferred. |
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Keywords: | Perfluorocyclobutene Zirconium C-F bond activation Insertion Metathesis DFT |
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