Heteroatom-modified polymer immobilised ionic liquid-stabilised metal nanoparticles : synthesis and applications

Abstract

The exponentially increasing demand for synthetic commodities has fuelled the development of new methodologies to improve the sustainability of existing chemical processes. The use of robust, scalable and highly efficient catalyst technologies that integrate bioderived feedstock will be crucial to achieve this. In this light, chapter 1 discusses the unique physicochemical properties of ionic liquids (ILs) that have linked them to this goal, their incorporation into functional materials and their applications in metal nanoparticle (NP) catalysed transformations. Chapter 2 details the synthesis of IL and heteroatom-functionalised polymer supports which were used to support and stabilise PdNPs. Both systems are extremely efficient catalysts for the Suzuki-Miyaura cross-coupling and the TOF of 16,300 h-1 obtained with PdNP@PPh2- PEGPIILP under mild conditions is the highest reported on comparison with the literature. Chapter 3 reports that PdNP@PPh2-PEGPIILP is the most efficient system for the aqueous phase Pd-catalysed hydrogenation of α,β-unsaturated carbonyls. Catalyst modifications revealed that the phosphine, IL and PEG act in a synergistic manner, which is crucial for selectivity. In chapter 4, tris(p-vinylphenyl)phosphine was incorporated into the polymer to limit the PdP interaction through extensive cross-linking and thereby increase the surface area for catalysis. These systems were less active than their lightly cross-linked counterparts and were unable to catalyse the hydrogenation of heteroaromatic nitroarenes. Poisoning experiments and FD-XAS analysis indicated that these substrates deactivate the catalyst. In chapter 5, PIIL-supported AuNPs were shown to be efficient catalysts for the partial reduction of nitroarenes. To this end, AuNP@PPh2-PEGPIILP catalyses the solvent-dependent selective reduction of nitrobenzene to afford commodity chemicals; N-phenylhydroxylamine, azoxybenzene or aniline as the sole product. Chapter 6 describes a series of heteroatom-functionalised PEGylated PIILP-stabilised RuNPs which are highly efficient catalysts for the selective hydrogenation of model and bioderived carbonyls. The heteroatom donor was crucial for optimum performance, likely due to interfacial electronic effects.