Synthesis of bis(polyfluoroalkylated)imidazolium salts as key intermediates for fluorous NHC ligands |
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Authors: | Martin Skalický Ond?ej Kysilka Josef Cva?ka Jaroslav Kví?ala |
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Institution: | a Department of Organic Chemistry, Institute of Chemical Technology, Prague, Technická 5, 16628 Prague 6, Czech Republic b Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Husinec-?e? 1001, 25068 ?e?, Czech Republic c Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo nám. 2, 16610 Prague 6, Czech Republic d Department of Chemistry of Solid State, Institute of Chemical Technology, Prague, Technická 5, 16628 Prague 6, Czech Republic |
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Abstract: | 1,3-Bis(polyfluoroalkyl)- and 1-mesityl-3-(polyfluoroalkyl)imidazolium salts differing in the length of a polyfluorinated chain and a non-fluorinated spacer were synthesized as key building blocks for fluorous NHC (N-heterocyclic carbene) ligands. A new approach using polyfluoroalkyl triflates instead of the corresponding iodides was employed allowing fine tailoring of fluorous properties, as well as of the electron density of the imidazolium ring. Using bis(polyfluoroalkylated)imidazolium salt, a fluorous analogue of the PEPPSI™ catalyst was synthesized and its structure confirmed by X-ray diffraction. The catalyst was employed in model Heck and Suzuki couplings with moderate yields, however, its recycle was not successful. Fluorophilicity of bis(polyfluoroalkylated)imidazolium salts was found to be surprisingly low compared with the analogous perfluoropolyether-based salts. |
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Keywords: | Imidazolium Fluorous Fluorophilic Triflate Carbene Mesityl NHC ligand |
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