Highly efficient and selective reduction of nitroarenes into anilines catalyzed by gold nanoparticles incarcerated in a nanoporous polymer matrix: Role of the polymeric support and insight into the reaction mechanism

Gold nanoparticles supported onto a nanoporous semicrystalline polymorphic polymer matrix consisting of syndiotactic polystyrene-cis-1,4-polybutadiene multiblock copolymer (AuNPs-sPSB) were investigated as catalyst in the reduction of nitroarenes into anilines using sodium borohydride as reductant. The crystalline phase and the morphology of the polymeric support were varied to assess their influence on the selectivity of the reaction pathway. The β and γ crystalline forms, which are not permeable to small molecules, led to a partial reduction of nitrobenzene into both azoxybenzene and diazobenzene whereas the porous δ and ϵ crystalline forms efficiently catalyze the complete reduction into aniline through the condensation route of the reaction mechanism proposed by Haber, achieving the highest activities reported so far for this reaction.