Catalytic Transformations at Phosphorus

: (Alternative Format Thesis)

Abstract

This thesis encapsulates four published works and one manuscript in preparation. The project began with an investigation of phosphorus based catalysts for the polymerisation of lactide, followed by exploring the thermolysis reactivity of phosphorus heterocycles. Copper(I) catalysed reactions involving phosphorus based substrates were then investigated. This thesis fundamentally focusses on the development of new catalytic transformations themed around phosphorus.

Chapter 1 introduces polymerisation and polymer degradation reactions that are mediated by main group catalysts. Building on this theme, Chapter 2 investigates the use of N-heterocyclic phosphines as main group catalysts for the polymerisation of lactide and the breakdown of poly(lactic acid). The selectivity of the reaction is then probed and the catalyst speciation elucidated, leading to isolation of the active catalytic species.

In Chapter 3 the thermal decomposition of other phosphorus heterocycles is investigated, in an attempt to isolate monomeric dioxo-, bisimino- and oxo(imino)phosphoranes. It is shown that the use of pyridines can act as catalysts for this transformation, lowering the temperature required to facilitate the reactions. Solid-state and solution speciation studies are also undertaken in order to determine if monomeric products can be isolated.

Chapter 4 builds upon work previously reported by the Liptrot group involving the observation of the selective hydroboration of isocyanates under NHC-copper(I) catalysed hydrophosphination conditions. The work in this chapter shows that the presence of phosphorus reagents is not necessary for the transformation, which can be performed on a range of heterocumulene substrates. Computational analysis of the mechanism is used to help to explain the origin of the observed hydroboration selectivity.

Chapter 5 extends the investigation of NHC-copper(I) catalysed transformations to include reductive P-P bond formation of phosphinites through deboroxycoupling. Stoichiometric reactivity and kinetic analyses give evidence of a complex mechanism. Computational modelling helps to elucidate this, providing a possible pathway for the reaction.

Date of Award	11 Oct 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	David Liptrot (Supervisor), Matthew Jones (Supervisor) & Chris Bowen (Supervisor)