Phosphine-stabilized, oxide-supported rhodium catalysts for highly efficient silylative coupling reactions

摘要

Oxide-supported rhodium catalysts with excellent activity in silylative coupling reactions have been developed. Reductive pretreatment of the catalysts in the presence of 0.5 equiv triphenylphosphine under a hydrogen atmosphere enhanced and stabilized the catalytic activity. Of the catalysts examined, ceria-supported rhodium had the highest activity in the homo-coupling of vinylsilanes to bis(silyl)ethenes at 170 A degrees C. A zirconia-supported catalyst selectively gave E-1-aryl-2-silylethenes by cross-coupling of vinylsilanes with styrenes at 130 A degrees C, and a high turnover frequency of > 8200 h(-1) was achieved at 170 A degrees C. Spectroscopic studies revealed that well-dispersed surface rhodium(I) species predominantly formed on ceria or zirconia were transformed into rhodium hydride species, which are believed to be responsible for the high activity. These catalysts were recyclable without loss of activity, and leaching of rhodium species from the catalysts was not observed.