Scientists Have Found Out That Addition of Silver to Organocatalyst Increases Its Stability

Russian scientists have found out that a mixture of iodine-derived organic salts and silver reduce their total catalytic activity — that is the ability to speed up chemical reactions, — but such a hybrid catalyst turned out to be more stable than corresponding organic catalysts in the absence of the metal. Such stabilization of the organocatalyst by the metal increases its turnover number of the catalyst and, as a consequence, decreases expenses on conducting reactions with it. The research was published in the ChemPlusChem journal.

Organocatalysts are organic substances that consist of carbon, hydrogen and other nonmetal elements, that are used in chemistry for increasing a rate of chemical reactions. These substances are more safe and less toxic than traditional catalysts on the base of metals, and also, they don’t demand additional expenses on utilization, because they can be isolated from reaction mixture and used again. These catalysts also have low sensibility to air and moisture, that sufficiently reduces time loss on preparation of conditions of reaction and greatly simplifies the conduction of chemical experiment.

One of the most promising types of such organocatalysts is based on iodonium salts, which effectively accelerate a great number of chemical transformations due to unusual type of binding of reacting molecules with a region of positive charge on the atom of iodine, that is known as a sigma-hole. These complexes can be used in various reactions, for example, oxidative modifications in molecules, or polymerization, that is connection of small molecules in long chains. Iodonium salts are also used for preparation of new types of materials, such as metal-organic frameworks—structures, that consist of organic molecules, connected with atoms of metals.

Scientists from Saint-Petersburg State University have found out that addition of a metal to the organic catalyst leads to increasing of stability of such catalysts in reactions. Authors have conducted experiment on the model iodonium salts and silver center and showed that despite iodonium and silver are both positively charged species and must push off each other due to Coulumb repulsion, their interaction in solution is possible and leads to a series of reversible associations, that decrease general catalytic activity of these species. Nevertheless, it stabilizes the organic catalysts and significantly decreases expenses on their usage. Such observation also shed light onto rational preparation of new types of catalytically active substances.

“We have shown that our new-generation-organocatalysts are able to bind with metal center, which may be present in the reaction mixture as a special additive of metal or impurity in the chemical reactor. Such cooperation significantly influences the general catalytical activity of the mixture. The obtained results point out the fact that cooperation of organic catalyst with metal cation helps to prevent decomposition of organocatalysts during a reaction progress. This factor should be taken into consideration while projecting chemical reactors,” – tells the author of the project, Mikhail Il’in, assistant professor of department of organic chemistry of Saint Petersburg State University.