Supramolecular Stabilization of Metastable Tautomers in Solution and the Solid State

被引:35
作者
Juribasic, Marina [1 ]
Bregovic, Nikola [2 ]
Stilinovic, Vladimir [2 ]
Tomisic, Vladislav [2 ]
Cindric, Marina [2 ]
Sket, Primoz [3 ,4 ]
Plavec, Janez [3 ,4 ,5 ]
Rubcic, Mirta [2 ]
Uzarevic, Krunoslav [1 ,2 ]
机构
[1] Rudjer Boskovic Inst, Zagreb, Croatia
[2] Univ Zagreb, Fac Sci, Dept Chem, Zagreb 41000, Croatia
[3] Natl Inst Chem, Slovenian NMR Ctr, Ljubljana, Slovenia
[4] EN FIST Ctr Excellence, Ljubljana 1000, Slovenia
[5] Univ Ljubljana, Fac Chem & Chem Technol, Ljubljana, Slovenia
关键词
keto-enol; metastable compounds; Schiff bases; supramolecular chemistry; tautomerism; INTRAMOLECULAR HYDROGEN-BOND; KETO-ENOL-TAUTOMERISM; SCHIFF-BASES; CRYSTAL-STRUCTURES; PROTONATION EQUILIBRIA; MOLECULAR-STRUCTURE; POLYMORPHISM; NMR; DESMOTROPY; ACID;
D O I
10.1002/chem.201403543
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non-heterocyclic, tautomeric solids. Quantum-chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3-methoxysalicylaldehyde and 2-amino-3-hydroxypyridine (ap), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen-bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable mole-cules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap. The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid-state and solvent-mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.
引用
收藏
页码:17333 / 17345
页数:13
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