Gold Nanoparticles Supported by Nanoporous Crystalline Polymer as Highly Active and Selective Catalyst for Redox Organic Syntheses

Gold nanoparticles (AuNPs) stabilized by inorganic and organic supports are active promoters in a large variety of useful synthetic transformations. The search for novel supports specifically designed for a chemical process of interest plays a crucial role for the enhancement of both the activity and selectivity of the gold catalyst. In this contribution we report on our recent efforts in designing a nanoporous crystalline polymer support based on multiblock copolymers of syndiotactic polystyrene and cis- 1,4-polybutadiene (sPSB). These copolymers exhibit a complex polymorphism comprising five crystalline phases and several co-crystalline and intercalates forms. Two of them, namely the δ and ε forms, show isolated nanovoids and nanochannels which allow conveying the reactants toward the catalytic sites. Benzyl-like and allyl alcohols were effectively and selectively oxidized aerobically to the corresponding carbonyl compounds under mild conditions1 whereas alkyl alcohols resulted unaffected. These results prompted us to explore the direct aerobic oxidative coupling of aromatic and aliphatic alcohols to yield alkyl carboxylates with unprecedented selectivity compared to conventional synthetic routes.2 Thus, the selective oxidation of 5-hydroxymethylfurfural (HMF), a platform biosourced molecule useful for the synthesis of fine chemicals and polymers (Scheme 1), was also investigated. Moreover the AuNPs-sPSB catalyst is highly effective and selective in reductive process: the study of the selective reduction of nitroarenes to aniline with sodium borohydride highlighted the crucial role of the polymeric support in determining high selectivity in the complex multistep reaction pathway (Scheme 2).3