Tuning the Catalytic Activity of Cyclodextrin-Modified\nPalladium Nanoparticles through Host−Guest Binding\nInteractions

Abstract

Water-soluble Pd nanoparticles (diameter 3.5 ± 1.0 nm) modified with covalently-attached cyclodextrin\n(CD) receptors were prepared by the reduction of PdCl₄^2- in dimethylformamide solution containing\nperthiolated β-CD. These Pd nanoparticles behave as active catalysts for the hydrogenation of alkenes in\naqueous media. For instance, the turnover frequency for the hydrogenation of 1-butenyltrimethylammonium\nbromide (<b>1</b>) was found to be 320 (moles of <b>1</b>) (moles of Pd)^-1 h^-1 at 25 °C and 1.0 atm of H₂(g). The addition\nof cationic ferrocene derivatives, such as ferrocenylmethyltrimethylammonium bromide (<b>3</b>), to the reaction\nmedium decreases the catalytic activity of the Pd nanoparticles. Other CD substrates, such as anionic\nferrocene derivatives or neutral adamantanol, are much less effective as inhibitors of the catalytic\nhydrogenation process.