Fluoro‐ and Perfluoralkylsulfonylpentafluoroanilides: Synthesis and Characterization of NH Acids for Weakly Coordinating Anions and Their Gas‐Phase and Solution Acidities |
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| Authors: | Julius F. Kögel Thomas Linder Fabian G. Schröder Jörg Sundermeyer Sascha K. Goll Daniel Himmel Ingo Krossing Karl Kütt Jaan Saame Ivo Leito |
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| Affiliation: | 1. Fachbereich Chemie der Philipps‐Universit?t, Wissenschaftliches Zentrum für Materialwissenschaften (WZMW) Marburg, Hans‐Meerwein‐Str., 35043 Marburg (Germany);2. Institut für Anorganische und Analytische Chemie, Freiburger Materialforschungszentrum (FMF) and Freiburg Institute for Advanced Studies (FRIAS), Section Soft Matter Science, Universit?t Freiburg, Albertstr. 21, 79104 Freiburg (Germany);3. University of Tartu, Institute of Chemistry, Ravila 14a, 50411 Tartu (Estonia) |
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| Abstract: | Fluoro‐ and perfluoralkylsulfonyl pentafluoroanilides [HN(C6F5)(SO2X); X=F, CF3, C4F9, C8F17] are a class of imides with two different strongly electron‐withdrawing substituents attached to a nitrogen atom. They are NH acids, the unsymmetrical hybrids of the well‐known symmetrical bissulfonylimides and bispentafluorophenylamine. The syntheses, the structures of these perfluoroanilides, their solvates, and some selected lithium salts give rise to a structural variety beyond the symmetrical parent compounds. The acidities of representative subsets of these novel NH acids have been investigated experimentally and quantum‐chemically and their gas‐phase acidities (GAs) are reported, as well as the pKa values of these compounds in acetonitrile (MeCN) and DMSO solution. In quantum chemical investigations with the vertical and relaxed COSMO cluster‐continuum models (vCCC/rCCC), the unusual situation is encountered that the DMSO‐solvated acid Me2SO–H‐N(SO2CF3)2, optimized in the gas phase (vCCC model), dissociates to Me2SO‐H+–N(SO2CF3)2? during structural relaxation and full optimization with the solvation model turned on (rCCC model). This proton transfer underlines the extremely high acidity of HN(SO2CF3)2. The importance of this effect is studied computationally in DMSO and MeCN solution. Usually this effect is less pronounced in MeCN and is of higher importance in the more basic solvent DMSO. Nevertheless, the neglect of the structural relaxation upon solvation causes typical changes in the computational pKa values of 1 to 4 orders of magnitude (4–20 kJ mol?1). The results provide evidence that the published experimental DMSO pKa value of HN(SO2CF3)2 should rather be interpreted as the pKa of a Me2SO‐H+–N(SO2CF3)2? contact ion pair. |
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| Keywords: | acidity analytical methods anions density functional calculations sulfonamides |
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