Fluorolytic sol-gel route

This situation has resulted in new, recently developed synthesis routes toward nanometal fluorides. Most of these methods were recently reviewed by Fedorov et al. [4], In fact, there are two sol-gel-based synthesis approaches, one representing a rather indirect (trifluoroactetate (TFA) sol-gel route) and the other a direct (fluorolytic sol-gel route) sol-gel process. 

The fluorolytic sol-gel route follows rather strictiy the classical hydrolytic one by reacting metal alkoxides in anhydrous solution with hydrogen fluoride instead of the hydrogen oxide of the classical process. Consequentiy, it results eventually in metal fluorides instead of metal oxides. 

Thus, even for the Suzuki coupling reaction, noble metals supported on nano-scopic metal fluorides obtained via the fluorolytic sol-gel-route are very active and selective although there is just a small advantage over the state-of-the-art Pd /C-catalyst. 

St. Rudiger and E. Kemnitz, The fluorolytic sol-gel route to metal fluorides - a versatile process opening a variety of application fields, Dalton Trans., 1105-1252 (2008). 

Although several slightly differing synthesis routes toward nanoscaled metal fluorides have been explored very recently (reviewed by, e.g., Fedorov et al. [4]), they are not sol-gel based but bear several drawbacks. However, besides and in fact earlier than the fluorolytic, another indirect sol-gel route - the TFA route - was developed that will be briefly mentioned as well. 

This new fluorolytic route was first time published for the synthesis of nanoscopic high-surface-area aluminum fluoride (HS-AIF3) in 2003 [9], which has been proven in the meantime to be a general synthesis approach for nanoscopic metal fluorides [10-25]. For deeper insights into the mechanism of the fluorolytic sol-gel approach see Ref. [26]. 

Bearing in mind all NMR spectra recorded for sols, thin wet gels and dried gels (Figures 1.7, 1.12-1.16) in comparison with those of solid and liquid educts, the following mechanism can be derived for the fluorolytic sol-gel reaction. In the first step of the synthesis route of HS-AIF3, which is usually applied, the tetrameric structure of Al(OiPr)3... 

In conclusion, the new access towards nanoscopic metal fluorides via this recently developed fluorolytic sol-gel synthesis route opens a wide range of applications for metal fluorides due to the distinctive different properties of these nano materials. 

---