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AAA?DDD Triple Hydrogen Bond Complexes

Blight, Barry A., Camara-Campos, Amaya, Djurdjevic, Smilja, Kaller, Martin, Leigh, David A., McMillan, Fiona M., McNab, Hamish, Slawin, Alexandra M. Z. (2009) AAA?DDD Triple Hydrogen Bond Complexes. Journal of the American Chemical Society, 131 (39). pp. 14116-14122. ISSN 0002-7863. (doi:10.1021/ja906061v) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided) (KAR id:44353)

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Experiment and theory both suggest that the AAA?DDD pattern of hydrogen bond acceptors (A) and donors (D) is the arrangement of three contiguous hydrogen bonding centers that results in the strongest association between two species. Murray and Zimmerman prepared the first example of such a system (complex 3•2) and determined the lower limit of its association constant (Ka) in CDCl3 to be 105 M?1 by 1H NMR spectroscopy (Murray, T. J. and Zimmerman, S. C. J. Am. Chem. Soc. 1992, 114, 4010?4011). The first cationic AAA?DDD pair (3•4+) was described by Bell and Anslyn (Bell, D. A. and Anslyn, E. A. Tetrahedron 1995, 51, 7161?7172), with a Ka > 5 × 105 M?1 in CH2Cl2 as determined by UV?vis spectroscopy. We were recently able to quantify the strength of a neutral AAA?DDD arrangement using a more chemically stable AAA?DDD system, 6•2, which has an association constant of 2 × 107 M?1 in CH2Cl2 (Djurdjevic, S., Leigh, D. A., McNab, H., Parsons, S., Teobaldi, G., and Zerbetto, F. J. Am. Chem. Soc. 2007, 129, 476?477). Here we report on further AA(A) and DDD partners, together with the first precise measurement of the association constant of a cationic AAA?DDD species. Complex 6•10+[B(3,5-(CF3)2C6H3)4?] has a Ka = 3 × 1010 M?1 at RT in CH2Cl2, by far the most strongly bound triple hydrogen bonded system measured to date. The X-ray crystal structure of 6•10+ with a BPh4? counteranion shows a planar array of three short (NH···N distances 1.95?2.15 Å), parallel (but staggered rather than strictly linear; N?H···N angles 165.4?168.8°), primary hydrogen bonds. These are apparently reinforced, as theory predicts, by close electrostatic interactions (NH?·?N distances 2.78?3.29 Å) between each proton and the acceptor atoms of the adjacent primary hydrogen bonds.

Item Type: Article
DOI/Identification number: 10.1021/ja906061v
Subjects: Q Science > QD Chemistry
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: Barry Blight
Date Deposited: 12 Nov 2014 23:23 UTC
Last Modified: 16 Nov 2021 10:17 UTC
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