Versatile Synthesis of 1, 2, 3-Triazolium-based Ionic Liquids
Sadaf S. Khan, Sven Hanelt, Jürgen Liebscher*
Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor-Str. 2, D-12489 Berlin, Germany
E-mail: Liebscher@chemie.hu-berlin.de
Abstract
1, 2, 3-Triazolium-based ionic liquids are prepared in a straightforward two-step procedure. In the first step azides and alkynes are transformed into 1, 4-disubstituted 1,2,3-triazoles by Cu- mediated click-reaction. Subsequent alkylation affords 1,3,4-trisubstituted 1,2,3-triazolium salts as ionic liquids, which can be further modified by exchanging the anion by salt metathesis. The synthesis provides access to simple ionic liquids as well as to functionalized ionic liquids, bearing organocatalytic, fluorescent or linking groups thus representing task specific ionic liquids or IL-tagged organocatalysts, respectively.
Keywords: ionic liquids, alkylation, 1,2,3-triazoles, click reaction, cycloaddition, 1,2,3- triazolium salts
Introduction
Ionic liquids (IL) are organic salts, which are liquid at temperatures below 100 °C. They have a very low vapor pressure, high boiling points and their polarity can be varied in wide range depending on the nature of both anions and cations.1,2 Thus they can be used as preferable solvents in a number of cases. In addition, recycling and reusage of IL is possible as well as their application in so called “working solutions” wherein a catalyst is dissolved and this phase can easily be separated and reused.3-7 Some of the IL are termed as “Green Solvents”.8,9 IL have gained wide interest and broad application in academia and also in industries.2,8,10-13
So-called task specific ionic liquids (TSIL) exhibit a synthetically useful function (often a catalytic function) in addition to the property to act as mere solvent.14-17 In order to provide special solubilities to catalysts, IL-units are tethered to a catalyst resulting in IL-tagged catalysts.18 Task specific ionic liquids and IL-tagged catalysts are usually based on imidazolium, pyridinium and ammonium salts as IL-tags where the functions are usually linked to the N-atom by alkylation. For example, a chiral, (S)-proline-derived pyrrolidin-2-methyl group was
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