グリーン有機分子変換プロセスを指向したセリア担持ルテニウム触媒の開発

Abstract

Solid Ru/CeO2 catalysts, which are effective for the catalysis of various highly atom-efficient organic transformations such as dehydrogenative synthesis of indole, regio-and stereo-selective coupling of unsaturated hydrocarbons, C _ C bond-forming reactions via the activation of aromatic C _ H bonds, and selective addition of carboxylic acids to alkynes, have been developed. For these reactions, CeO2-supported and, in some cases, ZrO2-supported catalysts show excellent activities, whereas ruthenium catalysts on other oxide supports are not effective. Spectroscopic studies have revealed that various types of catalytically active, low-valent ruthenium species are generated from ruthenium(IV) oxo species that are exclusively formed on the surface of CeO2 under appropriate conditions. These solid ruthenium catalysts can be recycled without loss of activity or significant leaching of ruthenium species into the solution, and these features, as well as the wide range of applicable reactions, make the present catalytic system quite attractive from both practical and environmental perspectives.

Carboxylate-Directed Addition of Aromatic C–H Bond to Aromatic Aldehydes under Ruthenium Catalysis

“…On the other hand, considerable attention has recently focused on the use of supported metal catalysts for organic transformations from the viewpoint of green chemistry due to the ease of separation from the reaction mixture and recycling of the catalyst. − In the course of our study on the development of supported Ru catalysts that are effective for organic synthesis, − we demonstrated that phosphine-modified Ru/CeO 2 catalysts efficiently promoted various kinds of C–C bond-forming reactions involving C–H bond activation. − Fortunately, we found that Ru/CeO 2 catalysts modified with 3 equiv of PCy 3 to Ru (3PCy 3 -Ru/CeO 2 ) promoted the coupling reaction of 1a with 2a to give 3aa in a good yield (Scheme ). Notably, the supported Ru catalyst required no external base for the reaction to proceed thanks to the basic surface of CeO 2 .…”

“…Supported Ru catalysts were prepared through the method reported in our previous literature. − A 1.0 g amount of a support was added to a solution of [RuCl 2 ( p -cymene)] 2 (0.20 mmol) in 10 mL of methanol in air at 50 °C After impregnation, the resulting powder was calcined in air for 30 min to afford the Ru­(2.0 wt %)/CeO 2 catalyst. The modification of Ru/CeO 2 catalyst by 3 equiv of PCy 3 to Ru was performed as follows: 250 mg (0.050 mmol as Ru) of Ru/CeO 2 and PCy 3 (0.15 mmol) was heated at 100 °C for 20 min under hydrogen atmosphere (1 atm) without any solvent.…”

C–h結合の活性化を経る環境調和型有機分子変換のためのルテニウム触媒系の開発

“…This result indicates that Ru(IV)＝O species functioned as a precursor of the active species for the C _ C bond-forming reaction 14),15) . Ru/CeO2 and Ru/ZrO2 catalysts showed high activity for C _ C bond-forming reactions 16) via C _ H bond activation, such as aromatic C _ H arylation 17) , alkylation 18) and alkenylation 19) . The appropriate choice of support enabled to control precise structure of Ru species on their surface, thereby allowed highly dispersed Ru(IV)＝O species function as a catalyst precursor for C _ C bond-forming reactions via the activation of inactive C _ H bonds 20),21) .…”

Ruthenacyclopentanes as Intermediates in the Regio- and Stereoselective Linear Codimerization ofN-Vinylamides with Electron-Deficient Alkenes

“…Codimerization of alkenes is a promising, atom-efficient synthetic method that affords highly substituted alkenes with various functionalities from simple alkenes. − Thus far, Co, − Ni, − ,,− Ru, − Rh, ,,, Pd, − other transition-metal − complexes, and Lewis or Brønsted acids − have been used as catalysts for this r...…”