1. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Quo Vadis, Superacidity of Neutral Brønsted Acids? The Challenge for the Fluorine Chemistry Peeter Burk, Ivo Leito, Ivar Koppel, Ilmar Koppel University of Tartu

2. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Definition of Gas-Phase Acidity and Basicity

3. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Connection Between Gas-Phase Acidity and Acidity in Solution

4. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Strong Neutral Acids & Weak Anionic Bases - the common knowledge  Strong and Highly Polarizable Electron-Acceptor Substituents  Extensive Resonance Stabilization of the Anion / Delocalization of Negative Charge  Coplanarity of the Anion  Aromaticity and Antiaromaticity

5. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Superacids by ‘Brute Force’

6. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Superacids by ‘Brute Force’

7. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics A Few Milestones of  G acid CH 4 408.5 NH 3 396.1 H 2 394.2 C 6 H 6 390.1 MeOH374.0 HF365.7 SiH 4 363.8 PH 3 360.7 LiH351.1 H 2 S344.8 MeCOOH341.7 PhOH342.3 PhCOOH331.7 HONO330.4 HCl328.0 (CF 3 ) 3 CH326.8 HNO 3 317.8 HBr318.8 H o 312.5 HI308.9 Tf 2 CH 2 301.5 H 2 SO 4 302.2 CF 3 SO 3 H299.5 Tf 3 CH289.0 (C 4 F 9 SO 2 ) 2 NH 284.1 zeolites290-255

8. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Lewis Acids and Bases A + D:  AD e.g.: HF: + BF 3  HBF 4 HF: + SbF 5  HSbF 6 HSO 3 F + SbF 5  “Magic acid”

9. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Koppel et al., JACS, 2000, 122, 5114-5124 DFT B3LYP/6-311+G**

10. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle

11. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle  G acid = ~260 kcal/mol

12. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Yagupolskii Principle Koppel et al., J.Chem.Soc. Perkin 2 2001, 230-234 pK a (DMSO)GP 16.3 8.0 3.2  pK a = 14.1  pK a = 25

13. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Generalization of Yagupolskii Principle Why only =NSO 2 CF 3 substitution?  =NX 1  =CX 1 X 2  =PX 1 X 2 X 3  =SX 1 X 2 X 3 X 4  =ClX 1 X 2 X 3 X 4 X 5 X = SO 2 F, SO 2 CF 3, CN, etc. Koppel et al., JACS, 2002, 124, 5594-5600

14. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Generalization of Yagupolskii Principle Acidifying Effects of Different Yagupolskii-Type Substituents on the Acidity of CH 3 C(=X)H (B3LYP/6-311+G**) Koppel et al., JACS, 2002, 124, 5594-5600 10 91

15. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics New Paradigm for Design of Superstrong Acids - Weak Anionic Bases: Carborane Anions  No  Electrons  No “Loose” Lone Electron Pairs  3-Dimensional  -Aromaticity  Extensive Delocalization of Negative Charge  Pseudo-Icosahedral Symmetry

16. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carboranes  The strongest acids  The least coordinating anions The 1-carba-closo-dodecaborate anion CB 11 H 12 – : Koppel et al., JACS, 2000, 122, 5114-5121

17. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane anion CB 11 H 12 – : The Distribution of Negative Charge

18. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane anion CB 11 F 12 – : The Distribution of Negative Charge 10 68 Times stronger than H 2 SO 4

19. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carboranes: The Site of Protonation CB 11 F 12 – : On substituents

20. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane acids: the Acidity (DFT B3LYP 6-31+G*) and Site of Protonation

21. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Carborane Anions The acid CB 11 (CF 3 ) 12 H is expected to have  G acid < 200 kcal/mol That is: 10 80 times stronger than H 2 SO 4 ! CB 11 (CF 3 ) 12 –

22. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Alkoxymetallate-, Aryloxymetallate- and Teflate-based Acids  HM[OR F ] n e.g. HAl[OCF 3 ] 4  M = B, Al, Nb, Ta, La, etc.  HM[OAr F ] n e.g. HAl[OC 6 F 5 ] 4  M = B, Al, Nb, Ta, La, etc.  HM[OTeF 5 ] 6 e.g. HTa[OTeF 5 ] 6  M = B, Al, Nb, Ta, La, etc.

23. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Example: Alkoxyaluminate-based Acid HAl[OCF 3 ] 4 :  G acid = 240.6 kcal/mol H+H+ -

24. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Acidities of Carborane Acids

25. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Spontaneous Proton Transfer in the Gas Phase K 2 O + H + = K 2 OH +  G=324.6 ClO 4 - + H + = HClO 4  G=293.3 K 2 O + HClO 4 = K 2 OH + ClO 4 -  G=119.4 K 2 OH + + ClO 4 - = K 2 OH + · ClO 4 -  G=88.0

26. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Application of Superstrong Acids and Their Salts  “Classical” Primary and Secondary Batteries (lead/acid, Ni/Cd, Fe/Ni, etc)  Fuel Cells  Lithium-Ion Batteries  Electric Double Layer Capacitors

27. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Application of Superstrong Acids and Their Salts Requirements:  High Conductivity  Thermal and Chemical Stability  Electrochemical Stability  Cheap  User- and Environment-Friendly  Non- Corrosive  Non Hygroscopic  Non- Coordinated Li +  Low viscosity and high dielectric constant of the medium  Not “too large” anions

28. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Application of Superstrong Acids and Their Salts  Petrochemical refining and cracking of fuel (zeolites)  Organic synthesis  Reusable water-stable catalysts  Oligomerization of olefins, epoxides, ethers, etc.  Enantioselective synthesis Continued...

29. University of Tartu Faculty of Physics and Chemistry Institute of Chemical Physics Application of Superstrong Acids and Their Salts  Organic synthesis  Diels-Alder reactions  Electrophilic Aromatic Substitutions  Friedel-Crafts reactions  Ionic liquids