Proton transfer reactions of a bridged bis-propyl bis-imidazolium salt

Massey, Richard S. and Quinn, Peter and Zhou, Shengze and Murphy, John A. and O'Donoghue, Annmarie C. (2016) Proton transfer reactions of a bridged bis-propyl bis-imidazolium salt. Journal of Physical Organic Chemistry. ISSN 0894-3230 (https://doi.org/10.1002/poc.3567)

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Abstract

Tetraazafulvalene 1 has found broad application in reduction and other related transformations and is conveniently generated from bis-propyl bis-imidazolium salt 4 with a strong base in a non-protic solvent. The proposed mechanism for the formation of 1 involves initial deprotonation at C(2) to give a mono-carbene 9 followed by intramolecular reaction at the second azolium centre. Herein, we report the second-order rate constants for deuteroxide-catalysed exchange in aqueous solution of the C(2)-hydrogens of bis-propyl bis-imidazolium di-iodide salt 4 and related monomeric dipropyl imidazolium iodide 10 of kDO=1.37×104 and 1.79×102M-1s-1, respectively, and used these data to calculate pKa values of 21.2 and 23.1. The greater C(2)-H acidity of the doubly bridged bis-propyl bis-imidazolium salt 4 relative to 10 may be attributed to the inductive or electrostatic destabilization of the conjugate acid dicationic azolium ion 4 relative to the monocationic carbene 9, which is enhanced by bis-tethering. Formation of tetraazafulvalene 1 was not observed under the aqueous conditions employed highlighting that carbene reprotonation significantly outcompetes dimerization under these conditions.

  • Item type:Article
    ID code:56174
    Dates:
    Date
    Event
    5 May 2016
    Published
    5 May 2016
    Published Online
    14 March 2016
    Accepted
    Notes:This is the peer reviewed version of the following article: Massey, R. S., Quinn, P., Murphy, J. A., & O'Donoghue, A. (2016). Proton transfer reactions of a bridged bis-propyl bis-imidazolium salt. Journal of Physical Organic Chemistry. , which has been published in final form at [Link to final article using the DOI]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
    Subjects:Science > Chemistry
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Pure Administrator
    Date deposited:15 Apr 2016 13:54
    Last modified:11 Nov 2024 11:24
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/56174
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