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Walsgrove, Henry

University of British Columbia

The investigation of macromolecules containing phosphorus(III) atoms is an active area of research due to the functionality imparted by the heteroatom. Additionally, molecular Pᶦᶦᶦ-compounds are pervasive in synthetic chemistry due to their use as ligands for metal centers. This thesis outlines the investigation of the reactivity of a unique class of low-coordinate Pᶦᶦᶦ-compounds, 1-phosphabutadienes (P=C−C=C), which are phosphorus-containing analogues of organic butadienes. Chapter 1 acquaints the reader with the background and functionality of unique low-coordinate phosphorus compounds. An in-depth examination of the prior art in the polymerization, cyclization and coordination chemistries of these compounds is provided. Chapter 2 focuses on the anionic polymerization of 1-phosphaisoprene [Mes*P=C(Me)−CH=CH₂; Mes* = 2,4,6-tri-t-butylphenyl] to furnish poly(1-phosphaisoprene). Molecular model studies including isolation of the propagating anion and models displaying both 4,3- and trans-4,1-enchainment are presented. The structural data gained from these molecular models are placed into the context of the microstructure of poly(1-phosphaisoprene). Chapter 3 reports the reaction of poly(1-phosphaisoprene) with [Pd(cod)Cl₂] and [Pd(η³-C₃H₅)(μ-Cl)]₂. It is shown that a concentrated solution of the former can undergo reversible gelation. The gelation does not occur upon treatment of poly(1-phosphaisoprene) with [Pd(η³-C₃H₅)(µ-Cl)]₂, indicating that cross-linking within the polymer network is responsible for gel formation. The study is complemented with molecular models. Chapter 4 focuses on cyclization reactions of 1-phosphabutadienes. Specifically, a [4+2] adduct of 1-phosphaisoprene with unique regiochemistry is disclosed and the observed reactivity is complemented by DFT calculations. Furthermore, the synthesis and [2+2] cyclization of a novel 1-phosphabutadiene, Mes*P=C(Me)−C(Me)=CH₂, is reported. Chapter 5 focuses on the synthesis and characterization of Mes*P=C(Si(CH₃)₃)−CH=CH₂. It is shown that this compound undergoes an E/Z-isomerization in the presence of n-BuLi. The compound was also found to isomerize upon exposure to light. Chapter 6 discloses muon spin spectroscopy studies of three 1-phosphabutadienes. The major radical products in each case are identified as delocalized 1-phosphaallyl radicals. This study represents the first model of radical addition to a 1-phosphabutadiene. Chapter 7 contains concluding remarks and a summary of the work presented in this thesis. Taken together, these discoveries mark a significant advancement in the chemistry of these unique P=C−C=C species.

Text

2025-05-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84549

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/