Recyclable Solid Ruthenium Catalysts Supported on Metal Oxides for the Addition of Carboxylic Acids to Terminal Alkynes

Abstract

Ceria-supported ruthenium catalysts (Ru/ CeO 2 ) were found to be quite effective for the addition of various carboxylic acids to terminal alkynes, which gave the corresponding enol esters in moderate to high yields. The major products of the reaction were E-isomers of anti-Markovnikov adducts. Among the ceria-supported ruthenium catalysts examined, those prepared using ruthenium precursors with chloride ligands showed high activities. The zirconia-supported ruthenium catalyst (Ru/ZrO 2 )showed activity comparable to that of the ceria-supported catalyst. These catalysts were recyclable without a significant loss of activity, and the leaching of ruthenium species into the liquid phase was negligible after cooling the reaction mixture, which indicates marked superiority of the present solid oxide catalysts to conventional homogeneous catalysts.

Active Ruthenium Catalysts Based on Phosphine-Modified Ru/CeO2for the Selective Addition of Carboxylic Acids to Terminal Alkynes

“…Such a marked effect of the support has been observed in our previous studies on C−C bond-forming reactions 42−46 as well as in the addition of carboxylic acids to alkynes by unmodified catalysts. 48 As discussed in our previous reports, 46−48 highly dispersed Ru(IV)-oxo species is selectively formed on the surface of ceria and zirconia, and this would be a good precursor for the catalytically active Ru species. In contrast, Ru species formed on the surface of the other supports had a microstructure similar to that of crystalline RuO 2 , which could not be transformed into the active catalysts.…”

“…Furthermore, unmodified Ru/CeO 2 catalysts were found to be effective for the addition of carboxylic acids to terminal alkynes to give the (E)-isomer of vinyl esters as major products. 48 On the basis of these results as well as those using immobilized Ru catalysts, 49 we expected the modification of Ru/CeO 2 by suitable phosphines to generate highly active Ru catalysts for the regio-and stereoselective synthesis of vinyl esters via the addition of carboxylic acids to alkynes.We report here a simple method for the preparation of active Ru catalysts that can be used for the selective addition of carboxylic acids to terminal alkynes by phosphine-modification of Ru/CeO 2 . The conditions of the pretreatment of Ru/CeO 2 greatly affected their catalytic behavior, and the regio-and stereoselectivities of the products can be controlled by the choice of the phosphines used for pretreatment.…”

Ruthenium‐Catalyzed Hydrocarboxylation of Internal Alkynes

“…[15][16][17] Today, the most widely applied catalysts in the addition of carboxylic acids to alkynes are ruthenium complexes. [26][27][28] Another challenge involves the control of selectivity; this is especially relevant to the addition of carboxylic acids to unsymmetrically substituted internal alkynes, as this reaction can render up to four isomers whose separation is difficult to achieve (Scheme 1). [26][27][28] Another challenge involves the control of selectivity; this is especially relevant to the addition of carboxylic acids to unsymmetrically substituted internal alkynes, as this reaction can render up to four isomers whose separation is difficult to achieve (Scheme 1).…”

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

“…The Ru/ZrO2 catalyst showed similar activity. The reactions between various carboxylic acids and terminal alkynes were smoothly catalyzed by Ru/CeO2 (Table 4) 45) . In contrast, the modification of Ru/CeO2 in the presence of suitable phosphines under H2 at 100 com- Table 6) 46)…”