Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Paul J. Ragogna

Abstract

Traditionally low coordinate and low oxidation state main group compounds are isolated utilizing hard anionic donors based on carbon and nitrogen based ligands. Conversely, employing anionic phosphines for this role has been essentially unexplored. In this context, this dissertation describes the synthesis of a number of main group complexes, ranging from group 13 to group 15, utilizing the bis(phosphino)borate ligand class in a supporting role. The remote anionic borate backbone renders the complexes zwitterionic and provides access to unique compounds that possess structures, and exhibit onwards reactivity, that is very different to the analogous compounds stabilized with neutral phosphines. For example, chapter two describes the stabilization of formally positively charged triel ({Ga2I4}2+) and tetrel ({GeCl}+ and {SnCl}+) fragments via common low oxidation state precursors. These structures have no precedent with neutral phosphines and represent a stable and isolable main group element source that is ready for onwards chemistry. For the group 14 compounds, upon removal of the chloride substituent the reactive tetrel centre quantitatively inserts into the ligand backbone. Zwitterionic group 15 compounds were prepared in good yields exploiting known redox chemistry and possess a pnictogen atom (Pn = P, As) in the unusual +1 oxidation state (Chapter 3). The anionic backbone is shown to be critical in accessing the coordination chemistry of these compounds as there are very few examples of the traditional cationic variants being used in subsequent transformations. Both pnictogen proligands form isolable coordination compounds with chromium, molybdenum, tungsten, and iron carbonyl reagents (Chapter 4) while rhodium, palladium, and mercury complexes are also isolated with the phosphorus derivative (Chapter 5). This diverse range of products represents the first such series of transition metal complexes for these types of Pn(I) compounds. The highlight of the thesis is the discovery that the phosphorus proligand acts as a 4-electron μ-type ligand to two gold, cobalt, or platinum centres simultaneously. Such coordination chemistry is unprecedented and provides the first experimental evidence for the P(I) compound to be described as a phosphanide-type bonding arrangement. These novel structures further underscore the importance of the borate backbone in synthesizing compounds that have otherwise not been observed. Throughout the thesis all of the compounds were fully characterized using a range of solution and solid-state techniques, including single crystal X-ray crystallography, allowing for a detailed data comparison.


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