The hafnium catalyst refers to the hafnium compound which has a catalytic function. Hafnium is a shiny silver-gray transition metal. The chemical properties of hafnium are relatively stable and have good corrosion resistance. It is not easily eroded by common aqueous acid and alkali solutions. At high temperatures, hafnium can also be directly combined with gases such as oxygen and nitrogen to form oxides and nitrides. The hafnium has a small content in the earth's crust and often coexists with zirconium. The valence of the hafnium is usually +4 in the hafnium compound. The common compounds containing hafnium are hafnium oxide(HfO2), hafnium tetrachloride(HfCl4) and hafnium hydroxide (H4HfO4). These hafnium compounds are also commonly used as hafnium catalysts. Hafnium and some ligands can form hafnium complexes with catalytic functions, and these complexes can also be used as ruthenium catalysts.
Figure 1. Hafnium catalyst catalyzed condensation reaction
Compared with other transition metal catalysts, hafnium catalysts are abundant in variety. At the same time, hafnium catalysts have a good and unique catalytic effect in some reactions. Therefore, hafnium catalysts are widely used in organic synthesis.
Figure 2. Hafnium catalyst catalyzed Friedel-Crafts acylation