Synthesis and Applications of tert-Alkylphosphines

Barber, Thomas (2021) Synthesis and Applications of tert-Alkylphosphines. PhD thesis, University of Nottingham.

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Abstract

tert-Alkyl-substituted phosphines are commonly used as ligands in metal catalysis due to their sterically bulky, electron-rich nature. Methods to synthesise them by P–C bond formation are inefficient and operationally complex, requiring highly reactive organometallic reagents and chlorophosphines (Chapter 1). Despite advances in varying other groups on phosphorus to improve catalytic performance, the diversity of tert-alkyl groups remains low.

Here, this challenge is addressed by taking an umpolung ‘P−/C+’ approach to the problem. Initial efforts using a silylphosphine were complicated by the observation of protodesilylation to give toxic, pyrophoric phosphine gas PH3, but this species was itself alkylated to give air-stable di-tert-alkylphosphonium salts (Chapter 2). To avoid direct handling of PH3, a two-chamber protocol for in situ generation of the gas from zinc phosphide was developed. The resulting phosphonium salts were found to be competent surrogates for free secondary phosphines (by in situ deprotonation), and were used in typical functionalisation reactions as well as the synthesis of a library of ligands based on the known JohnPhos biaryl backbone. Stereoelectronic properties of these ligands were measured and the variation in tert-alkyl group was shown to have a significant impact.

A further use for the two-chamber reactor was found in the synthesis of CagePhos (Chapter 3), a uniquely sterically bulky, electron-poor and air-stable secondary phosphine which is currently underexplored in catalysis. The operational ease and safety of the two-chamber reactor provided significant quantities of CagePhos in a convenient solid form. An exploration of the incorporation of the CagePhos moiety into novel electron-poor aryl CagePhos ligands was conducted, and CagePhos was also tert-alkylated to give a completely new class of sterically bulky yet electron-poor tertiary phosphines (isolated as their air-stable phosphonium salts).

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Ball, Liam T.
Keywords: phosphorous, phosphorus, phosphines, metal catalysts, organophosphorus compounds
Subjects: Q Science > QD Chemistry > QD241 Organic chemistry
Q Science > QD Chemistry > QD450 Physical and theoretical chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 65919
Depositing User: Barber, Thomas
Date Deposited: 31 Dec 2021 04:40
Last Modified: 31 Dec 2021 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/65919

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