HF is a Lewis acid

Department of biology, chemistry, pharmacy

Our group is interested in the preparation and investigation of novel fluorinated compounds. The investigation of unusual and novel oxidation states is of particular interest. Since these compounds are usually at the limit of stability, they are z. B. intercepted and characterized in low-temperature noble gas matrices. This method, also known as matrix isolation spectroscopy, led, in combination with preparative fluorine chemistry and quantum chemical calculations, to the discovery of numerous new oxidation states such as B. EdIV or IrVIII or compounds like FeF4, OHgF or HUF.

Super acids

The chemistry of the strongest acids is closely linked to fluorine chemistry. Most strong Lewis and Brønsted acids are based on fluorinated compounds. Recently we have the very strong acids H [Al (OTeF5)4] and Al (OTeF5)3 presented. We use the pentafluoro-orthotellurate group (OTeF5), which is also known as Teflat. It shows a very similar electronegativity as fluorine, but is much larger. Structurally, we were able to characterize arenium salts formed by protonation of aromatics with the superacids mentioned above. These acids have compared to the classic systems such as HF / SbF5 or HSO3CF3/ SbF5 the advantages of a significantly lower oxidizing capacity and the lack of a readily available fluoride, which could enter into unwanted secondary reactions with the protonated and thus activated substrates. Due to these properties, the selective protonation of weak bases in low oxidation states and based on fluorophilic elements can also be achieved with these acids. We recently protonated white phosphorus.

Metal fluorides

Compared to the other gold halides, gold fluorides are very sensitive substances and are only stable under inert conditions. They are extremely strong oxidizing agents in the form of the strong Lewis acids AuF3 and up5 and also as the anionic salts Cs [AuF4] and Cs [Au2F.7] still very reactive. The synthesis of the more soluble representatives [NMe4][On4] and [NEt4][On4] enables their use in organic solvents. This allows a further synthesis of novel fluoridoorganogold (III) complexes. For complexes of the type [AuF3(L)] is that trans-Fluoratom by the transEffect of the ligand bound more weakly than the other two, which we can see from the Au ‑ F bond distances in the structure of [AuF3(SIMes)]. Through a selective substitution, compounds of the type [AuF2X (SIMes)] can be obtained with X = Cl, OTeF5 Etc.

Perfluorinated peroxides

Peroxides are an important class of compounds in organic and inorganic chemistry that have various uses in the chemical industry. They are useful oxidizing agents or radical initiators for polymerizations and play an important role in atmospheric chemistry, such as in ozone depletion. Perfluorinated dialkyl peroxides RF.OORF. can be used in synthesis as a direct source for RF.O radicals are used.

A synthesis of bis (trifluoromethyl) peroxide from carbonyl difluoride and elemental fluorine was already carried out in 1957 by Cady et al. described. In our working group we have developed a continuous process to produce this compound in larger quantities. We are currently working on the photochemical activation and subsequent transfer of CFs3O group on organic substrates. Very little is known about other perfluorinated peroxides. Accordingly, our working group has developed a metal-catalyzed and photochemical synthesis to further develop the chemistry of this class of compounds. These peroxides have promising properties. In contrast to conventional organic peroxides, the perfluorinated peroxides, as far as we have investigated, are not explosive and are therefore suitable for numerous applications.

Further subject areas

In addition, our group is working on the development of greenhouse gas substitutes, novel battery materials, as well as fluorine storage sources and novel fluorinating and oxidizing agents.

Further reading:

  • The highest oxidation states of the transition metal elements
    S. Riedel, M. Kaupp, Coord. Chem. Rev. 2009, 253, 606-624.
  • High-Valent Fluorides and Fluoro-Oxidizers
    S. Riedel, in Comprehensive Inorganic Chemistry II, Vol. 2 (Eds .: J. Reedijk, K. Poeppelmeier), Elsevier, Oxford, 2013, 187–221.
  • Novel Superacids: Formation of Pentafluoro-orthotellurate Derivatives of Aluminum
    Anja Wiesner, Thomas W. Gries, Simon Steinhauer, Helmut Beckers, Sebastian Riedel Angew. Chem. Int. Ed. 2017, 56, 8263-8266.
  • Stabilization of Lewis-Acidic AuF3 as Carbene Complexes: Preparation and Characterization of [(AuF3 (SIMes)]

    Mathias A. Ellwanger, Simon Steinhauer, Paul Golz, Thomas Braun, Sebastian Riedel Angew. Chem. Int. Ed. 2018, 57.7210-7214.