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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.
Original language | English |
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Number of pages | 6 |
Journal | Journal of Physical Organic Chemistry |
Early online date | 5 May 2016 |
DOIs | |
Publication status | E-pub ahead of print - 5 May 2016 |
Keywords
- acidity
- bis-imidazolium
- deuterium exchange
- N-heterocyclic carbene
- tetraazafulvalene
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Dive into the research topics of 'Proton transfer reactions of a bridged bis-propyl bis-imidazolium salt'. Together they form a unique fingerprint.Projects
- 1 Finished
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Light-Activated Approaches to Highly Challenging Organic Electron Transfer Reactions
Murphy, J. (Principal Investigator) & Zhou, S.-Z. (Research Co-investigator)
EPSRC (Engineering and Physical Sciences Research Council)
1/07/13 → 30/06/15
Project: Research