Boronate self-assemblies with embedded Au nanoparticles: preparation, characterization and their catalytic activities for the reduction of nitroaromatic compounds

Abstract

Sequential boronate esterification of benzene-1,4-diboronic acid with pentaerythritol induced hierarchical molecular self-assembly to produce mono-dispersed flower-like microparticles. ATR-FT-IR, PXRD, ¹³C-CP-MAS and ¹¹B-DD-MAS NMR spectra indicate that the particles consist of zigzag-shaped packing structures of polymeric 2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane. Au nanoparticles (Au NPs) with a mean diameter of 2.7 nm were successfully deposited on the microparticles by the deposition reduction (DR) method. It is noteworthy that the resulting novel hybrids exhibited an efficient catalytic activity for the reduction of nitroaromatic compounds; in particular, high chemoselectivity in the hydrogenation of 4-nitrostyrene to the corresponding aniline was attained without reduction of the vinyl bond. Careful investigation of the catalyst suggested a synergistic effect between Au NPs and the boronate support in the selective hydrogenation. These findings strongly suggest that boronate self-assemblies are advantageous as support materials for preparation of heterogeneous catalysts based on polymer–Au hybrids.