Advances in Phosphorus and Germanium Chemistry: Dehydrochlorination, Cyclisation and Hydrophosphination.

  • Adam Barrett

Student thesis: Doctoral ThesisPhD


This thesis contains three published articles [1-3], which are discussed in Chapters 2-4, and one unpublished body of work in Chapter 5. The work contained in these chapters bridges several areas of chemistry, throughout which a general theme of pursuing advances in the synthetic approaches and reactivity of select phosphorus compounds is found.

Chapter 1 introduces two sets of phosphorus-based cyclic moieties key to the work in this thesis: cyclopolyphosphines and the valence isomers of 1,3,5-triphosphabenzenes. Following a literature review and discussion of the chemistry of these species, Chapter 2 focuses on a new synthetic methodology for the formation of cyclopolyphosphines. A mild, rapid route to the cyclic compounds is presented, which hinges upon an initial hydrogen-halogen exchange interaction between dichlorophosphines and secondary phosphines. Optimisation of the reaction conditions to yield an array of both aryl and alkylcyclopolyphosphines precedes a discussion of the key mechanistic aspects of the transformation.

Continuing on from this, Chapter 3 details investigations into the synthesis and reactivity of a thermodynamically stable Dewar 1,3,5-triphosphabenzene species. An iron-catalysed cyclotrimerisation regime capable of providing gram-scale quantities of the product from the respective phosphaalkyne species is presented. Following exploration into the isomerisation of the Dewar 1,3,5-triphosphabenzene, the coordination chemistry and onward reactivity with a diverse array of reagents are also investigated to yield unprecedented products.

Chapter 4 diverts from the synthesis of cyclic phosphine species, focusing on the investigations into the use of germanium complexes as catalysts for hydrophosphination reactions. The synthesis and screening of low-valent Ge(II) and Ge(IV) compounds for use as pre-catalysts in various transformations is explored, and a simple Ge(IV) species is reported as an efficient pre-catalyst for the hydrophosphination of styrenes and internal alkynes. Following investigations into the scope of the reaction, mechanistic investigations led by kinetic analysis and stoichiometric reactions are detailed.

In Chapter 5, focus moves away from phosphorus chemistry, towards exploration into the use of Fe(II)-β-diketiminate compounds for the construction of metallamacrocyclic species. The role of specific amide ligands bearing exposed coordinating groups to act as bridging species in metallamacrocyclic ensembles is investigated, and an array of β-diketiminate-bound iron amides, synthesised and analysed in the solid-state by single-crystal X-ray diffraction, are presented. The effect of the structure of the amide ligand, the nature of the coordinating group and the flanking aryl groups of the β-diketiminate ligand on macrocycle formation are detailed. Alongside this, theoretical predictions and preliminary experimental studies into adsorptive properties of the metallamacrocyclic species in the solid-state are discussed.

[1] A. N. Barrett, H. J. Sanderson, M. F. Mahon, R. L. Webster, Chem. Commun. 2020, 56, 13623-13626.
[2] A. N. Barrett, C. R. Woof, C. A. Goult, D. Gasperini, M. F. Mahon, R. L. Webster, Inorg. Chem. 2021, 60, 16826-16833.
[3] A. N. Barrett, M. Diefenbach, M. F. Mahon, V. Krewald, R. L. Webster, Angew. Chem. Int. Ed. 2022, 61.
Date of Award22 Feb 2023
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorRuth Webster (Supervisor) & Michael Hill (Supervisor)

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