Polymer-Encapsulated Metallic Nanoparticles as a Bridge Between Homogeneous and Heterogeneous Catalysis

Continuous efforts in catalysis research have been devoted towards the development of heterogeneous catalysts that can activate reactions which are catalyzed by homogeneous catalysts. Replacing homogeneous catalysts with their heterogeneous counterparts will enhance the sustainability of the catalytic system, providing a highly recyclable, scalable and efficient setup. Throughout this review we demonstrate that small (< 2 nm), metallic nanoclusters can catalyze a wide range of pi-bond activation reactions that were previously activated by homogeneous catalysts. The small size of the nanoparticles enables their reversible oxidation into catalytically active metal ions. Encapsulation of the metal within a polymeric matrix severely restricts leaching of the highly oxidized metal ions into the solution phase, inducing high catalytic stability and recyclability. Activation of complex, multistep organic transformations with heterogeneous catalysts provides novel opportunities, not accessible with homogeneous catalysts, to control and tune the products selectivity. By designing the molecular properties of the polymeric matrix that encapsulates the metal cluster, high products selectivity, diastereoselectivity and enantioselectivity can be gained. These results demonstrate the capability of mesoscale catalysts, constructed of metallic nanoparticles and an encapsulating layer, to activate a wide array of catalytic reactions with high reactivity and tunable selectivity.