Gold nanoparticles supported by imidazolium-based porous organic polymers for nitroarene reduction

Two imidazolium-based porous organic polymers (Im-POP-1 and Im-POP-2) were synthesized through the Yamamoto reaction of different molar ratios of 1,3-bis(4-bromophenyl)imidazolium bromide and tetrakis(4-bromophenyl)methane, subsequent anion exchange with HAuCl4 and reduction with NaBH4 produced well-dispersed gold nanoparticles (NPs), Au@Im-POP-1 and Au@Im-POP-2. These NPs possess a small size and narrow size distribution, their application in the reduction of nitroarenes was evaluated, and the reduction process was tracked by 13C NMR experiments for reaction mechanism studies. In comparison with gold NPs supported by a non-ionic analogue from the Yamamoto reaction of tetrakis(4-bromophenyl)methane (Au@POP-TPM), Au@Im-POP-2 exhibits high catalytic activity, good selectivity of aniline and superior recyclability in nitrobenzene reduction. The gold NPs in Au@Im-POP-2 increase slightly after four consecutive reaction runs, while an apparent agglomeration of NPs in Au@POP-TPM was observed after the second run. This research provides a new type of support for the stabilization of gold NPs and for the improvement of catalytic performances.