Faster, cleaner, cheaper, better processes for industrially relevant chemicals is at the forefront of many areas of chemical research. The development of selective catalysts is important in many fields, classically; pharmaceutical chemistry and drug development, agricultural chemistry and biological activity, cosmetic chemistry and specific fragrances. But, selective catalysis is also important in many other areas including polymerisation and the fine tuning of a polystyrene, and of growing environmental importance; biodegradable and biocompatible plastics from sustainable sources. The former areas are looking towards heterogeneous systems that are tolerant to an array of substrates for a varied range of classic reactions, including asymmetric Michael reaction, Henry reaction, hydroformylation, hydrogenation, hydrosilylation reactions to name a few, to generate important chemical building blocks. An example of the latter point is the stereocontrolled production of polylactide via the ring-opening polymerisation (ROP) of the racemic cyclic ester lactide (rac-LA), with current industrial metal initiators chosen for the ROP of LA lacking chiral discrimination. This thesis, divided into four chapters, will investigate various ligands as homogeneous analogues containing a variety of transition metals for organically important reactions and the ROP of rac-LA. Chapter 1 introduces the importance of chirality and catalysis alongside the interests of heterogeneous systems. A review of the current literature is presented for the benchmark reactions undertaken in this thesis. Also introduced in this chapter is the ring-opening polymerisation of rac-LA, the importance of biopolymers, mechanism and methods involved in the preparation and characterisation of polylactic acid, alongside a review of the current literature. Chapter 2 investigates the preparation of an array of chiral pyridine containing Schiff base homogeneous ligands, as analogues to heterogeneous systems. The sterics about the chiral centre of the ligands have been varied. These ligands were trialled against benchmark reactions, and the activity and selectivity analysed. Furthermore, a selection of heterogeneous catalysts have been trialled for the same benchmark reactions. Chapter 3 describes the development of chiral Schiff base complexes, and Salalen based complexes, for the ROP of rac-LA, where the sterics and electronics of the ligand have been varied. The metal centre of these initiators includes titanium, hafnium, zirconium and aluminium, and the initiators investigated under solution and melt polymerisation conditions. Chapter 4 provides details of the reaction procedures for the synthesis of starting materials, ligands and complexes. Benchmark reaction conditions for the asymmetric Henry reaction and asymmetric hydrogenation reaction is detailed along with that of the polymerisation reaction.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:642050 |
| Date | January 2013 |
| Creators | Ready, Christopher |
| Contributors | Jones, Matthew |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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