The gallium catalyst refers to a metal gallium, gallium salt or gallium complex having a catalytic function. Gallium is gray-blue or silver-white. It is an amphoteric metal located in the fourth cycle Group IIIA of the chemical periodic table. Gallium is chemically stable and does not react in dry air. Gallium oxidizes and tarnishes in humid air and ignites when heated to 500 °C. Gallium reacts slowly with water at room temperature, and reacts with boiling water to form gallium hydroxide, releasing hydrogen. Gallium has +1, +2, and +3 valences in chemical reactions. Its valence in most gallium catalysts is +3. The content of gallium in the earth's crust is very low. It is widely distributed but does not exist in a pure metal state. Instead, it exists in the form of CuGaS2.
Figure 1. Metal gallium catalyzed allylation
Gallium catalysts are widely used in organic reactions due to their rich and special aqueous phase stability, strong Lewis acidity, high selectivity, easy recycling and environmental friendliness.
Figure 2. Ga(OTf)3 catalyzed ring opening reaction