Methylated cyclodextrins: an efficient protective agent in water for zerovalent ruthenium nanoparticles and a supramolecular shuttle in alkene and arene hydrogenation reactions

Zerovalent ruthenium(0) nanoparticles in the size range of 2.5 nm were easily prepared by chemical reduction of ruthenium salt with an excess amount of sodium borohydride and were efficiently stabilized by methylated cyclodextrins. The optimization of the catalytic system has been carried out in terms of stability and catalytic activity, considering the hydrogenation of olefinic compounds under biphasic liquid-liquid conditions. Efficient and controlled chemoselectivities were obtained in the hydrogenation of arene derivatives by the relevant choice of cavity and methylation degree of the cyclodextrins. Finally, the hydrogenation of alpha- and beta-pinenes leads to the major formation of cis-pinanes, interesting synthons for fine chemistry, with high diastereoisomeric excesses.