A stable hybrid catalyst (POM-PPPh3/L/Ni) for the reduction of toxic nitroarene compounds in water

Abstract

Reduction of nitroarenes to aminoarenes using novel and selective catalysts is an important and desirable approach in green chemistry. In this work, a new heterogeneous nanocatalyst, POM-PPPh₃/L/Ni, was designed and prepared via functionalizing a Keggin-type polyoxometalate (H₃PMo₁₂O₄₀) with (3-bromopropyl)triphenylphosphonium bromide (BPPPh₃Br) through strong electrostatic interactions to prepare [PMo₁₂O₄₀][PPPh₃]₃ (denoted as POM-PPPh₃). The obtained compound was modified via nucleophilic attack of the nitrogen donor of a multidentate Schiff base ligand (L) on its propyl chain to produce [PMo₁₂O₄₀][PPPh₃/L]₂ (denoted as POM-PPPh₃/L), which was finally metallated with nickel cations to achieve [PMo₁₂O₄₀][PPPh₃/L/Ni]₂ (denoted as POM-PPPh₃/L/Ni). After full characterization of the prepared material with various physicochemical methods, its catalytic behavior was investigated in the catalytic nitroarene reduction. The influence of various factors on catalytic conversion and selectivity was considered. The synthesized nanocatalyst showed excellent performance in the reduction of nitroarenes in aqueous media in the presence of NaBH₄ as a reducing agent. Mild reaction conditions and a short reaction time (10 min) are the prominent features of this new nanocatalyst. In addition, the catalyst was recovered and reused for up to four cycles of catalytic reduction without any significant loss of conversion.