COMPARISON BETWEEN THE FIRST AND SECOND GENERATIONS OF Grubbs CATALYSTS
In the early 1990s, Professor Robert Grubbs, an American chemist, synthesized a new type of ruthenium carbene complex and successfully applied it to the open-loop translocation polymerization of norbornene, which overcomes the disadvantage of small allowable range of other catalysts for functional groups. The catalyst is not only stable to air, but also can maintain its catalytic activity in the presence of water, alcohol or acid. On this basis, Grubbs improved the original catalyst in 1996. The new catalyst not only has higher activity and similar stability than the original catalyst, but also is easier to synthesize. It has become the most widely used catalyst for olefin decomposition reaction. Professor Grubbs won the Nobel Prize in Chemistry in 2005 for his outstanding achievements in the study of olefin metathesis.
The PCy3 ligand on the first generation Grubbs catalyst CAS:172222-30-9 has a higher steric hindrance because of the rotation of the PCy3 ligand during the polymerization process. As a contrast, the N-heterocyclic carbene ligand on the second generation Grubbs catalyst does not need this step, so the reaction energy barrier is relatively low and the catalytic activity is greatly improved. Its catalytic activity is several times higher than that of the first generation Grubbs catalysts. The amount of Grubbs catalysts used in open-loop double-decomposition polymerization can be reduced to one millionth of that, and the amount used in some closed-loop double-decomposition reactions is only five millionths of that. It is especially suitable for the synthesis of cyclic olefins with low tension and polysubstituted olefins with high steric resistance.
The second generation Grubbs catalyst CAS: 246047-72-3 has higher activity, selectivity and similar stability than the first generation Grubbs catalyst, but it is more sensitive to air and water than the first generation, so it needs to be used in nitrogen or argon inert atmosphere. The first generation Grubbs catalyst is a purple solid which is stable to air, water, acid or alcohol.
Therefore, when choosing and purchasing catalysts, we should not only consider which is the best, but also have a certain relationship with the substrates, so we should take a comprehensive view. According to experience, sometimes the second generation Grubbs catalysts can not catalyze the reaction. Using the first generation Grubbs catalysts, not only anhydrous and anaerobic control is not so strict, but also has good catalytic effect. But this is only one example. In most cases, the second generation Grubbs catalyst has very good effect and is used