Supramolecular Chemistry. 60. Solvent Effects on Crown-Ether Complexations

Solov’ev, V.P.; Strakhova, N.N.; Raevsky, O.A.; Rüdiger, V.; Schneider, H.J.

Авторы: Solov’ev V.P., Strakhova N.N., Raevsky O.A., Rüdiger V., Schneider H.J.
Журнал: Journal of Organic Chemistry
Том: 61
Год издания: 1996
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 5221
Последняя страница: 5226
DOI: 10.1021/jo952250h
Аннотация: A comprehensive study of complexation between potassium salts and 18-crown-6 in 14 different solvents shows stability constant K increases by >104 from water to pure methanol or to propylene carbonate (PC), with constants increasing in the order H2O < HMPT < DMSO < DMF < MeCHOHMe < MeCN < Me2CO < MeOH < PC. The mostly calorimetrically determined thermodynamic values of complexation between metal ion m and ligand l (ΔGml, ΔHml, ΔSml) are compared with a large range of available solvent properties. Linear correlations (with coefficients R ≈ >0.95) are obtained for ΔGml with standard Gibbs transfer energies ΔG°t of the metal ion from water to the given solvent. Analyses of literature data with some other cations and ligands, including the [222] cryptand, also revealed , that the complexation constant changes are essentially a linear function of the cation desolvation free energies. Less meaningful correlations (R ≈ <0.9) are obtained with values characterizing the electron donor capacity of the solvent. Parameters characterizing the solvent polarity, such as ET, are extremely poor descriptors (R = 0.3) of the medium effects. In binary dioxane−water mixtures ΔGml and even ΔHml correlates well with the vol % of water, or with corresponding solvophobicity parameters Sp (R = 0.97). The reaction enthalpies ΔH vary much more than ΔG, for instance from 12 kJ/mol (in MeCN) to 68 kJ/mol (in Me2CHOH), without meaningful correlations to known solvent properties, or between ΔG and ΔH. An exception is the correlation of ΔH with the solvent polarity index π* (with R = 0.996, if MeCN is excluded). Solvent effects on the ligands are studied by NMR in view of the possible geometry changes of crown ethers from oxygen-in (with aprotic solvents) to oxygen-out (with water) conformations of the macrocycles. Preliminary NMR results, however, point to similar oxygen-in conformations in water as well as in chloroform, in line with molecular mechanics calculations.
Добавил в систему: Соловьев Виталий Петрович

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Supramolecular Chemistry. 60. Solvent Effects on Crown-Ether Complexationsстатья