Spatial control of palladium nanoparticles in flexible click-based porous organic polymers for hydrogenation of olefins and nitrobenzene

Two flexible click-based porous organic polymers (CPP-F1 and CPP-F2) have been readily synthesized. SEM images show CPP-F1 is a 3D network, while CPP-F2 exhibits a granular morphology. Pd(OAc)2 can be easily incorporated into CPP-F1 and CPP-F2 to form Pd@CPP-F1 and Pd@CPP-F2, respectively. The interactions between the polymers and palladium are confirmed by solid-state 13C NMR, IR and XPS. Palladium nanoparticles (NPs) are formed after hydrogenation of olefins and nitrobenzene. Palladium NPs in CPP-F1 are well dispersed on the external surface of the polymer, while palladium NPs in CPP-F2 are located in the interior pores and on the external surface. In comparison with NPs in CPP-F1, the dual distribution of palladium NPs in CPP-F2 results in higher selectivity in the hydrogenation of 1,3-cyclohexadiene to cyclohexane. The catalytic systems can be recycled several times without obvious loss of catalytic activity or agglomeration of palladium NPs. Hot filtration, mercury drop tests and ICP analyses suggest that the catalytic systems proceed via a heterogeneous pathway.