Ruthenium catalysis in organic synthesis

Abstract

Ruthenium, rhodium, iridium, and rhenium hydride complexes are highly useful redox Lewis acid and base catalysts. Various substrates bearing hetero atoms are activated by these catalysts and undergo reactions with either nucleophiles or electrophiles under neutral conditions. These types of catalytic reactions are described together with their application to the preparation of various biologically active compounds.Ruthenium has various valencies (0 to 8 valene) and is not so expensive transition metal; therefore, various useful catalytic reactions for organic synthesis have been explored [1]. It is noteworthy that the medical property of ruthenium is now being recognized, and ruthenium anticancer agents have recently entered the clinic, showing promising activity on resistant tumors. We have developed various ruthenium-catalyzed reactions. Among them, I would like to focus on our findings that low-valent ruthenium hydride complexes can be used as alternatives to the conventional Lewis acids and bases. Furthermore, using iridium, rhodium, and rhenium hydride complexes, various novel and unique catalytic reactions can be explored.Reactions promoted by Lewis acids and bases are fundamental in organic synthesis; however, most such reactions are merely stoichiometric. Therefore, the development of catalytic reactions that use transition-metal complex catalysts under neutral and mild reaction conditions is particularly important; society needs forward-looking technology, which is based on environmental acceptability. The criteria include atom efficiency, formation of little inorganic waste, and selective synthesis of desired products. We should use instead environmentally friendly catalytic processes that will not produce such waste. If one could design Lewis acid and base catalysts with low redox potentials, their reactions would occur catalytically under neutral conditions. We have, therefore, been searching for transitionmetal complex catalysts, which we call redox Lewis acid and base catalysts [2]. We found that divalent ruthenium hydride complexes act as redox Lewis acid catalysts and also as redox base catalysts. Generation of carbon nucleophiles from pronucleophiles by activation of the α-C-H bond adjacent to hetero atoms followed by reaction with various electrophiles affords catalytic carbon-carbon bond forming reactions under neutral and mild reaction conditions. In principle, conventional acids and bases cannot be used at the same time because of neutralization; therefore, we developed Lewis acid base ambiphilic catalysts which can be utilized as either Lewis acid or bases in one-pot reaction. Low-valent ruthenium, iridium, rhodium, and rhenium hydride catalysts can be used as catalysts to replace both Lewis acids and strong bases, and they can be used in combinatorial chemistry.

A Novel Carbene Ruthenium Complex as Reusable and Selective Two‐Electron Catalyst for Alkene Epoxidation

“…[4] In the specific field of redox catalysis, the rationalization of catalyst performance on the basis of electronic and structural parameters is particularly complicated due to the involvement of distinct redox state species and so the development of new metal complexes with novel properties is essential to understand and optimize the mechanisms followed by such catalytic species.…”

In Vitro Anticancer Activity and Biologically Relevant Metabolization of Organometallic Ruthenium Complexes with Carbohydrate‐Based Ligands

“…[16][17][18] In recent years, the first examples of mono-and dinuclear tumor-inhibiting Ru II arene complexes ( Figure 1) were introduced. [19][20][21][22][23][24][25] The two most extensively studied approaches involve the coordination of the Ru center by 1,3,5-triaza-7-phosphaadamantane (pta) and ethylenediamine (en) ligands ( Figure 1).…”

Hydrogen adsorption on Ru(001) studied by scanning tunneling microscopy

“…Ruthenium is a good catalyst for these reactions and for reactions involving organic synthesis [2,3]. Numerous studies have been devoted to determine the structures formed by hydrogen on Ru, particularly on its closed-packed hexagonal face [4][5][6][7][8][9][10][11][12][13][14][15][16].…”