Tuning the catalytic activity of cyclodextrin-modified palladium nanoparticles through host-guest binding interactions

Water-soluble Pd nanoparticles (diameter 3.5 +/- 1.0 mn) modified with cova lently-attached cyclodextrin (CD) receptors were prepared by the reduction of PdCl42- in dimethylformamide solution containing perthiolated beta -CD. These Pd nanoparticles behave as active catalysts for the hydrogenation of alkenes in aqueous media. For instance, the turnover frequency for the hydr ogenation of 1-butenyltrimethylammonium bromide (1) was found to be 320 (mo les of 1) (moles of Pd)(-1) h(-1) at 25 degreesC and 1.0 atm of H-2(g). The addition of cationic ferrocene derivatives, such as ferrocenylmethyltrimet hylammonium bromide (3), to the reaction medium decreases the catalytic act ivity of the Pd nanoparticles. Other CD substrates, such as anionic ferroce ne derivatives or neutral adamantanol, are much less effective as inhibitor s of the catalytic hydrogenation process.