Diastereomeric 1,4,7,10-tetrakis((S)-2-hydroxypropyl)- 1,4,7,10-tetraazacyclododecane and its alkali metal complex ions. A nuclear magnetic resonance, potentiometric titration, and molecular orbital study
Date
1997
Authors
Dhillon, R.
Madmak, S.
Ciccone, F.
Buntine, M.
Lincoln, S.
Wainwright, K.
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Journal of the American Chemical Society, 1997; 119(26):6126-6134
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Ramesh S. Dhillon, Samer E. Madbak, Frank G. Ciccone, Mark A. Buntine, Stephen F. Lincoln, and Kevin P. Wainwright
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Abstract
<sup>13</sup>C NMR studies are consistent with 1,4,7,10-tetrakis((S)-2- hydroxypropyl)-1,4,7,10-tetraazacyclododecane (ΔS-thpcl2) and its eight- coordinate alkali metal complex ions (Δ[M(S-thpcl2)]<sup>+</sup>) existing predominantly as single distorted cubic diastereomers in methanol in accord with structures predicted through molecular orbital calculations. Intramolecular exchange in ΔS-thpcl2 is characterized by k(298.2 K) = 34 800 ± 1600 s<sup>-1</sup>, ΔH(≠) = 53.9 ± 0.6 kJ mol<sup>-1</sup> and ΔS(≠) = 22.8 ± 2.5 J K<sup>-1</sup> mol<sup>-1</sup> in methanol. This process is slowed in [M(S-thpc12)]<sup>+</sup>, for which k(298.2 K) = 332 ± 6, 125 ± 2, and 3020 ± 30 s<sup>-1</sup> ΔH(≠) = 21.4 ± 0.2, 26.3 ± 0.5, and 46.3 ± 0.2 kJ mol<sup>-1</sup>, and ΔS(≠) = -125 ± 1, -116 ± 2, and -23.1 ± 0.9 J K<sup>-1</sup> mol<sup>-1</sup>, respectively, when M<sup>+</sup> = Li<sup>+</sup>, Na<sup>+</sup>, and K<sup>+</sup>. For intermolecular ligand exchange on Δ[M(S-thpc12)]<sup>+</sup>, decomplexation is characterized by k(d)(298.2 K) = 2200 ± 10, 64.3 ± 1.6, and 11 900 ± 300 s<sup>-1</sup>, ΔH(d)(≠) = 35.3 ± 0.5, 62.8 ± 0.5, and 41.8 ± 0.4 kJ mol<sup>-1</sup>, and ΔS(d)(≠) = -62.6 ± 2.1, 0.3 ± 2.0, and -26.8 ± 1.6 J K<sup>-1</sup> mol<sup>-1</sup>, respectively, when M<sup>+</sup> = Li<sup>+</sup>, Na<sup>+</sup>, and K<sup>+</sup>. The stability constant, K, of [M(S-thpc12)]<sup>+</sup> varies as M<sup>+</sup> changes in the sequence Li<sup>+</sup> (4.0 ± 0.1), Na<sup>+</sup> (4.8 ± 0.1), K<sup>+</sup> (3.5 ± 0.1), Rb<sup>+</sup> (3.4 ± 0.1), Cs<sup>+</sup> (3.2 ± 0.1), and Ag<sup>+</sup> (12.8 ± 0.1), where the figures in parentheses are 1og(K/dm<sup>3</sup> mol<sup>-1</sup>) determined in methanol by potentiometric titration at 298.2 K and I = 0.05 mol dm<sup>-3</sup> (NEt<inf>4</inf>ClO<inf>4</inf>). Stability constants in acetonitrile, propylene carbonate, and dimethylformamide are also reported.
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© 1997 American Chemical Society