Synthetic and mechanistic investigations of catalytic hydrogenation, dehydrogenation and hydrophosphination

Abstract

To truly understand a reaction, detailed mechanistic investigations need to be performed. From these studies, new routes and pre-catalysts can be developed to produce chemicals relevant to the pharmaceutical, materials and agricultural industries. These routes will either make chemicals directly used in these industries or synthesise new molecules that can be used as ligands for catalysts within these industries. Herein this thesis work is presented on the mechanistic investigations of several catalytic procedures.β-diketiminate complexes have previously been utilised within the group for the dehydrocoupling of phosphines alongside hydroboration and hydrophosphination. Chapter 2 details the substrate scope for the dehydrocoupling of both amine and phosphine boranes. This work also investigated the mechanism, with intermediate complexes isolated alongside kinetic studies. Also included are kinetic isotope studies to try and determine the bond making/breaking steps of the reaction.Following on from this Chapter 3 investigates using alternative hydrogen transfer agents for the hydrogenation of unsaturated C-C bonds. Initial work focused on the mechanism of amine/borane transfer hydrogenation. Deuterium labelling to determine the regioselectivity of the proton/hydride incorporation was investigated. High pressure hydrogenation was also carried out to determine if hydrogen release was part of the reaction. Complexes were isolated and their stability is discussed in conjunction with computational findings to suggest an alternative mechanism to the originally proposed process. This procedure was then developed further by using silanes as the hydride source, with the initial mechanistic studies and substrate scope presented.The final chapters (Chapters 4 & 5) detail work on the synthesis of a number of different phosphines using a cheap and efficient procedure that uses a commercially available base as the catalyst. The full optimisation process as well as the substrate scope for divinylphosphines, 1,2-diphosphines and 1,1-diphosphines is presented. Structural comparisons of 1,1-diphosphines has been carried out and this is also discussed. The novel 1,1-diphosphines have also been trialled as ligands for titanium and rhodium, with a view to synthesising heterobimetallic complexes.

Date of Award	4 Sept 2019
Original language	English
Awarding Institution	University of Bath
Supervisor	Ruth Webster (Supervisor) & Mary Mahon (Supervisor)