Superacids are essential in the plastics and petrochemical industries where they are used to prepare and stabilize reactive carbocations. The utility of superacids is derived from pronounced acidity, which exceeds that of conventional strong Lewis and Brønsted acids such as antimony pentafluoride and sulfuric acid, and from a weakly coordinating counteranion with stabilizing properties.
Sebastian Riedel and colleagues, Freie Universität Berlin, Germany, have developed two aluminum pentafluoroorthotellurate containing superacids, which are at the top of the acidity scale. The Lewis superacid Al(OTeF5)3 and the Brønsted superacid H[Al(OTeF5)4] are prepared by a one-pot procedure starting from triethylaluminum and pentafluoroorthotelluric acid.
Starting from the formed Brønsted acid, five different salts were prepared. Single crystals of highly reactive benzenium, mesitylenium, and tritylium carbocations, stabilized by [Al(OTeF5)4]–, were isolated and characterized by X-ray crystallography. The weakly coordinating [Al(OTeF5)4]– anion may be suitable for industrial applications because it can be prepared in large quantities by a straightforward synthesis.
- Superacids Based on Pentafluoroorthotellurate Derivatives of Aluminum,
Anja Wiesner, Thomas W. Gries, Simon Steinhauer, Helmut Beckers, Sebastian Riedel,
Angew. Chem. Int. Ed. 2017, 56, 8263–8266.