The aluminum catalyst refers to an elemental aluminum or aluminum compound which has a catalytic function. Trivalent aluminum has unique electron-deficient structure and is easily combined with some ligands to form an aluminum compound. Some aluminum compounds have a good spatial localization effect on the reaction substrate, which can effectively induce the reaction and increase the enantioselectivity of the reaction, and thus has been highly valued by people. Most of the aluminum catalysts themselves have good catalytic performance and can be directly used for the catalysis of the reaction. However, when some aluminum catalysts are used alone as catalysts, the catalytic effect is not ideal. Therefore, this type of aluminum catalyst is usually attached to activated carbon, diatomaceous earth or some polymer skeleton to improve the catalytic efficiency. In addition, the adhesion type aluminum catalyst has a lower selectivity than the unsupported catalyst. And when the reaction is completed, the catalyst is easily separated and can be recycled.
Figure 1. Aluminum catalyst
Due to the wide variety of aluminum catalysts, good catalytic performance and relatively low price, it has a wide range of applications in organic synthesis. The reaction catalyzed by the aluminum catalyst includes Diels-Alder reaction, Michael addition reaction, Mannich reaction, Ene reaction, cyanide silicidation reaction, free radical allylation reaction, cycloaddition reaction, Hydrogenation reaction, Claisen rearrangement reaction, cyclopropanation reaction of allyl alcohol, cross condensation reaction, epoxy compound rearrangement reaction, and the like. Among them, the aluminum catalyst is the most widely used in the Diels-Alder reaction, the Michael addition reaction, and the cyanidation reaction. In addition, different types of aluminum catalysts have different types of catalytic reactions. Aluminum catalysts supported on polymers are commonly used to catalyze Diels-Alder reactions and Michael addition reactions. Chiral multifunctional aluminum catalysts and chiral Salen aluminum catalysts are commonly used in cyanide silicidation. Chiral bisamine aluminum catalysts are commonly used in cross condensation reactions. However, the use of different types of aluminum catalysts has an effect on the yield and corresponding selectivity of the product.
Aluminum catalysts can be classified into achiral aluminum catalysts and chiral aluminum catalysts by classification from chirality. The chiral aluminum catalyst can be further divided into a chiral aluminum catalyst supported on an organic polymer, a chiral multifunctional aluminum catalyst, a chiral Salen aluminum catalyst, a chiral bis-naphthol aluminum catalyst, and a chiral tartaric acid derivative aluminum catalyst, chiral menthol aluminum catalyst, chiral diamine (triamine) aluminum catalyst, and the like.