From Salts to Ionic Liquids by Systematic Structural Modifications: A Rational Approach Towards the Efficient Modular Synthesis of Enantiopure Imidazolium Salts |
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Authors: | Nicolás Ríos‐Lombardía Eduardo Busto Dr. Vicente Gotor‐Fernández Dr. Vicente Gotor Prof. Raúl Porcar Eduardo García‐Verdugo Dr. Santiago V. Luis Prof. Ignacio Alfonso Dr. Santiago García‐Granda Prof. Amador Menéndez‐Velázquez Dr. |
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Affiliation: | 1. Departamento de Química Orgánica e Inorgánica, Instituto Universitario de Biotecnología de Asturias, Universidad de Oviedo, 33071 Oviedo (Spain), Fax: (+34)?985103448;2. Departamento de Química Inorgánica y Orgánica, Universitat Jaume I, 12071 Castellón de la Plana (Spain), Fax: (+34)?964‐728‐214;3. Instituto de Catálisis y Petroleoquímica, CSIC, Campus de la UAM, C/ Marie Curie, 2;4. Cantoblanco;5. Madrid;6. 28049 (Spain);7. Departamento de Química Biológica y Modelización Molecular, Instituto de Química Avanzada de Catalu?a (IQAC), Consejo Superior de Investigaciones Científicas (CSIC), Jordi Girona 18‐26, 08034 Barcelona (Spain).;8. Departamento de Química Física y Analítica, Universidad de Oviedo, 33071 (Spain);9. Centro de Investigación en Nanomateriales y Nanotecnología (CINN), Instituto Tecnológico de Materiales de Asturias (ITMA), Parque Tecnológico de Asturias, 33428 Llanera (Spain) |
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Abstract: | This paper reports a simple and robust modular synthetic strategy that leads to a large variety of configurationally and structurally diverse imidazole‐based chiral ionic liquids (CILs) by lipase‐catalyzed resolution. The intimate microscopic interactions of the supramolecular ionic network of these imidazolium chiral salts at the molecular level are investigated both spectroscopically (NMR, FT‐IR‐ATR) and theoretically, and a topological analysis of the experimental electron densities obtained by X‐ray dif fr action of single crystals is performed. Our results support the key role played by the relative configuration of the ‐OR group on the hydrogen‐bonding pattern and its strong influence on the final physical properties of the imidazolium salt. We also obtained a reasonable correlation between the observed melting point and the non‐covalent interactions. The spectroscopic data and the topological analysis reflect the key role played by hydrogen bonds between the OH and imidazolium C2H groups in both cation–anion and cation–cation interactions, with the presence of an OH group leading to an additional inter‐cation interaction. This interaction significantly affects the properties of stereoisomeric salts. Even more interestingly, we also studied the effect of the chirality by comparing enantiopure CILs with their racemic mixtures and found that, with the exception of trans‐Cy6‐OH‐Im‐Bn‐Br, the melting points of the racemic mixtures are higher than those of the corresponding enantiomerically pure forms. For stereoisomeric examples, we have successfully explained the differences in melting temperatures in light of the corresponding structural data. Chirality should therefore be taken into account as a highly attractive design vector in the preparation of ILs with specifically desired properties. |
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Keywords: | chirality green chemistry imidazolium salts ionic liquids lipases |
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