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A comparison of C-F and C-H bond activation by zerovalent Ni and Pt: a density functional study

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JournalJournal of the American Chemical Society
DatePublished - 28 Apr 2004
Issue number16
Volume126
Number of pages8
Pages (from-to)5268-5276
Original languageEnglish

Abstract

Density functional theory indicates that oxidative addition of the C-F and C-H bonds in C6F6 and C6H6 at zerovalent nickel and platinum fragments, M(H2PCH2CH2PH2), proceeds via initial exothermic formation of an eta(2)-coordinated arene complex. Two distinct transition states have been located on the potential energy surface between the eta2-coordinated arene and the oxidative addition product. The first, at relatively low energy, features an eta(3)-coordinated arene and connects two identical eta(2)-arene minima, while the second leads to cleavage of the C-X bond. The absence of intermediate C-F or C-H U complexes observed in other systems is traced to the ability of the 14-electron metal fragment to accommodate the eta(3)-coordination mode in the first transition state. Oxidative addition of the C-F bond is exothermic at both nickel and platinum, but the barrier is significantly higher for the heavier element as a result of strong 5dpi-ppi repulsions in the transition state. Similar repulsive interactions lead to a relatively long Pt-F bond with a lower stretching frequency in the oxidative addition product. Activation of the C-H bond is, in contrast, exothermic only for the platinum complex. We conclude that the nickel system is better suited to selective C-F bond activation than its platinum analogue for two reasons: the strong thermodynamic preference for C-F over C-H bond activation and the relatively low kinetic barrier.

    Research areas

  • OXIDATIVE-ADDITION-REACTIONS, TRANSITION-METAL-COMPLEXES, CARBON-FLUORINE BONDS, MOLECULAR-STRUCTURE, REDUCTIVE ELIMINATION, HYDRIDE BIFLUORIDE, CRYSTAL-STRUCTURES, ROOM-TEMPERATURE, HYDROGEN-BONDS, X BOND

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