Hydrophosphination and related reactions

Abstract

Hydrophosphination, the addition of a P–H to an unsaturated bond, is an important, atom economic route to phosphorus(III) compounds. This thesis reports the methods used to promote hydrophosphination reactions, through radical initiators and metal catalysts, as well as the synthesis of diphosphine ligands for use in methoxycarbonylation catalysis.
Benchmarking reactions for the hydrophosphination of 1-octene by a primary alkylphosphine were performed with a radical initiator commonly used in industry, AIBN, along with blank reactions to establish the background rate of reaction. AIBN is an effective initiator at temperatures above 60 ˚C, but has disadvantages such as the uncontrollable generation of by-products and the difficulty in removing toxic decomposition products of the initiator. Heterogeneous metal oxides such as alumina and silica initiate hydrophosphination reactions at room temperature. Addition of the radical inhibitor MEHQ prevented hydrophosphination occurring, suggesting a radical pathway is operating. Variables including temperature and stirring rate were studied, and silica has been shown to be recyclable at least five times without significant loss of activity. Other metal oxides were also trialled in hydrophosphination, all showing some activity except for molecular sieves.
Chapter 3 describes the synthesis of PPP and PCP ligands and pincer complexes for the use in hydrophosphination catalysis. While the PPP pincer complexes were too water sensitive for use in catalysis, the PCP nickel hydride complex was found to catalyse the addition of diphenylphosphine to activated alkenes. The coordination chemistry with Pt(II) and Pt(0) have also been investigated, and a nickel deuteride pincer complex synthesised to probe to mechanism of the catalysis.
In Chapter 4, tertiary-diprimary triphosphines are shown to undergo Pt(0)–catalysed hydrophosphination of activated alkenes. The synthesis of three tertiary-diprimary triphosphines is described, the hydrophosphination of alkenes such as tert-butyl acrylate by these triphosphines detailed, and the platinum coordination chemistry of the resulting tritertiary phosphine products investigated. By using ³¹P NMR spectroscopy, the sequential addition of 4 equiv. of alkene was observed, generating intermediates with iii multiple isomers. Pt(0) complexation of the tertiary-diprimary substrate was attempted to probe the mechanism of catalysis, for which a cycle has been proposed.
Chapter 5 describes a novel synthetic route to a pyridyl-functionalised diphosphine ligand for the use in catalytic methoxycarbonylation of alkenes. Addition of tert-butyl(2- pyridyl)phosphine borane to α, α-dichloro-o-xylene resulted in a diastereomeric mixture, which were separated by crystallisation. The borane adduct of pytbpx was deprotected using secondary amines, and the coordination chemistry of pytbpx with platinum and palladium investigated, as well as the P=Se derivatives.

Date of Award	25 Jan 2022
Original language	English
Awarding Institution	University of Bristol
Sponsors	Solvay
Supervisor	Paul G Pringle (Supervisor)