Ruthenium Catalysts

A substance that contains ruthenium and has a catalytic function is referred to as a ruthenium catalyst. Ruthenium is a light gray multivalent rare metal element that is a member of the platinum group metals. The nature of the ruthenium is very stable and the corrosion resistance is very strong. The content of ruthenium in the earth's crust is small, but ruthenium is indeed the cheapest of the platinum group metals. Ruthenium has many different valences. Different valences of rhodium can form complexes with many substances, so the types of rhodium catalysts are very rich. Most ruthenium catalysts have good catalytic properties and are commonly used in hydrogenation, isomerization, oxidation and C-H activation reactions.

The electronic structure of the Ru atom is 4d75s1 and has many different valences. Different valences of rhodium can form complexes with many substances, so the types of rhodium catalysts are very rich.

Applications:

Ruthenium catalysts are widely used in the field of organic synthesis because of their catalytic activity, variety, and low cost.

• Oxidation reaction: Ruthenium catalysts show excellent catalytic performance in some oxidation reactions, so they are also used for oxidation catalysis. Ruthenium catalysts typically catalyze oxidation of alkanes, alkenes, and alcohols. Ruthenium complexes as catalysts, alcohols can be oxidized to form aldehydes or ester compounds. For example, using RuH₂(PPh₃)₄ as catalyst, butyl butyrate is synthesized by oxidation of n-butanol, and hydrogen is generated at the same time. Ruthenium tetroxide is a kind of strong oxidant, which can be used for oxidation of alcohols, alkenes, aromatic compounds and aliphatic hydrocarbons.
• Hydrogenation reaction: Research and development of ruthenium hydrogenation catalysts have been one of the hot spots in the organic field. The hydrogenation reaction catalyzed by ruthenium catalyst is characterized by mild reaction conditions and high yield. The ruthenium catalysts can catalyze the hydrogenation reaction of many inorganic or organic materials. Due to its high activity double bonds, cyclohexene can be used as an intermediate for fine chemicals such as pharmaceuticals, foods, and pesticide chemicals. In industrial production, a supported ruthenium catalyst is usually prepared by a precipitation method, and then a ruthenium catalyst is used to catalyze selective hydrogenation of benzene to produce cyclohexene. Similarly, cyclohexylamine and dicyclohexylamine are important organic chemical raw materials and fine chemical intermediates, which are all obtained by the selective hydrogenation of aniline by ruthenium catalyst. In addition, the complex formed by the metal ruthenium and the TolBINAP ligand can catalyze the hydrogenation of acetophenone to form chiral 1-phenylethanol.

Figure 1. Ruthenium catalyst catalyzed hydrogenation reaction

• Allylation reaction: In organic chemistry, an allyl substitution reaction induced by a metal complex is a very important reaction for forming a C-C bond and a C-O bond. The complex of ruthenium containing a living ligand has the best catalytic function for this type of reaction and can catalyze the formation of arylallyl groups of allyl halides and phenols. In addition, the catalyst formed by the coordination of the NHC ligand and the Cp*-Ru complex exhibits very good catalytic activity in the allyl alkylation reaction and the etherification reaction of phenols.
• C-H activation reaction: The C-H activation reaction is an important method for constructing the C-X (X-C, S, N) bond. Ruthenium-catalyzed c-h bond activation reactions usually have the advantages of easy availability of raw materials, environmental protection, high efficiency and economy. In recent years, the transition metal ruthenium-catalyzed C-H bond activation reaction has received extensive attention. For example, the [RuCl₂(C₆H₆)]₂ catalyst can be used to catalyze the direct arylation of 2-pyridylbenzene with an aromatic halide. With [Ru(p-cymene)Cl₂]₂ as a catalyst, pyridine can be meta-directed to the benzenesulfonylation reaction to achieve a C-S bond formation reaction.

Figure 2. Ruthenium catalyst catalyzed C-H activation reaction

References

1. Kamdar. (2019), “An overview of significant achievements in ruthenium-based molecular water oxidation catalysis.” Molecules 24(3), 494/1-494/24.
2. Kaur, Navjeet. (2019), “Synthesis of Six-Membered N-Heterocycles Using Ruthenium Catalysts.” Catalysis Letters 149(6), 1513-1559.
3. Cruz, Thais R. (2019), “New dmso-ruthenium catalysts bearing N-heterocyclic carbene ligands for the ring-opening metathesis of norbornene.” New Journal of Chemistry 43(16), 6220-6227.