Amine-Decorated Polymer Immobilised Ionic Liquid Stabilised Metal Nanoparticles: Synthesis and Applications in Catalysis

Abstract

Polymer-immobilised ionic liquid (PIIL) phase catalysis has gained attention due to the increased demand for efficient synthetic protocols and sustainable transformation processes. New methods are needed to improve the sustainability of current chemical processes. The Doherty-Knight group has been focused on developing modified polymer-immobilised ionic liquids to stabilise and modify the reactivity of nanoparticle catalysts. The first chapter explores the unique physical and chemical properties of ionic liquids (ILs) that make them suitable for various applications, including the stabilisation of metal nanoparticles (NPs), as well as the synthesis and application of polymer-immobilized ionic liquids (PIILs). Chapter 2 describes the synthesis of monomers and heteroatom-functionalised polymer immobilised ionic liquids as supports for the stabilisation of RuNPs. The amino-modified catalyst was found to catalyse the aqueous hydrolysis of NaBH4 efficiently to produce hydrogen under mild conditions. RuNP@NH2-PIILS exhibited higher activity than RuNP@NH2 PEGPIILS. Notably, RuNP@NH2-PIIL achieves one of the highest turnover frequencies (TOF) reported for RuNP-based catalysts (171 molH2.molcat-1 .min-1). In addition, it was recycled up to five times. Chapter 3 highlights the efficiency of the RuNP@NH2-PEGPIILS catalyst for the reduction of quinolines to 1,2,3,4-tetrahydroquinoline (THQ) via 1,2-dihydroquinoline (DHQ). The initial TOF of 610 mol quinoline converted mol Ru-1 h-1 for the reduction of quinoline is among the highest to be reported for a metal nanoparticle-based catalyst with a conversion of 96% obtained after 4 h at 65°C. A wide range of substituted quinolines were successfully reduced to either the corresponding 1,2-dihydroquinoline or 1,2,3,4-tetrahydroquinoline in short reaction times. Hot filtration experiments showed that the active species was heterogeneous. Chapter 4 describes a comparison of RuNP@NH2-PEGPIILS and PtNP@NH2-PEGPIILS as catalysts for the dehydrogenation of DMAB and AB. It demonstrated that RuNP@NH2 PEGPIILS is a more efficient catalyst than PtNP@NH2-PEGPIILS for the dehydrogenation of DMAB and AB, as RuNP@NH2-PEGPIILS gave initial TOFs of 8,300 molesH2.molcat−1.h−1 and 21,200 molesH2.molcat−1.h−1, respectively, compared with 3,050 molesH2.molcat−1.h−1 and 8,500 molesH2.molcat−1.h−1, respectively, for PtNP@NH2-PEGPIILS. In addition, RuNP@NH2 PEGPIILS showed high stability and reusability for the hydrolysis of DMAB over multiple cycles. Chapter 5 describes the synthesis of a range of RuNPs and PtNPs stabilised by an amine modified ordered mesoporous silica immobilised ionic liquid (OMSIIL). The examined nanoparticles were shown to be highly efficient catalysts for hydrogen evolution from NaBH4. This work aims to achieve a deeper understanding of this system and identify more effective catalysts for scale-up purposes.