The synthesis and stabilisation of low oxidation state complexes: utilising magnesium(I) dimers as reducing agents

Abstract

This thesis pertains to the synthesis and stabilisation of low oxidation state main group element complexes through the utilisation of novel magnesium(I) dimers as reducing agents. As such, it is an exploration of the utility of these magnesium(I) complexes in organometallic synthesis and has resulted in the isolation of a number of compounds featuring unusual structural motifs, oxidation states and bonding modes. Chapter 1 provides a general introduction to low oxidation state main group chemistry and discusses a number of concepts that are unique to this field of study. Particular attention is paid to historical concepts such as the double bond rule and the new understanding of chemical bonding that has developed as a result of this renaissance in main group chemistry, as well as a general discussion of synthetic methods to access these compounds. Chapter 2 introduces the magnesium(I) dimers reported to date and details both their synthesis and reactivity in organic and organometallic synthesis. Two new β-diketiminato magnesium(I) complexes are described, along with their β-diketiminato magnesium(II) halide precursor complexes, and efforts towards improving the synthesis of these unusual compounds are outlined. A number of other novel β-diketiminato magnesium(II) hydride, alkyl and halide complexes are also presented. Finally, efforts towards the synthesis of soluble models of magnesium amido-boranes, in which this library of magnesium(I and II) complexes is exploited, are also discussed. Chapter 3 presents a case study into the utility of magnesium(I) dimers as reducing agents in organometallic synthesis. A series of amidinato group 14 element(I) dimers [LEEL] (E = Si, Ge, Sn; L = amidinate) were synthesised in high to moderate yield, and comparisons between the magnesium(I) dimers and traditional reducing agents emphasised the efficacy of the magnesium(I) dimers in this role. The tin compound is the first of its type, while one and two previous examples exist for the silicon and germanium complexes, respectively, although they were only isolated in low yield. Chapter 4 describes the development of low oxidation state aluminium hydride chemistry, an area in which magnesium(I) dimers have been instrumental. A number of novel compounds are presented including of a series of compounds which feature remarkable [Al6H6] octahedral cores. Chapter 5 details efforts to extend the use of magnesium(I) dimers to compounds stabilised by bulky terphenyl ligands. The preparation of the second example of a diplumbyne, for which a moderate yielding synthesis was determined, is described. A dialumene and a disilyne were also desirable synthetic targets, and efforts to these ends are also outlined. Finally, Chapter 6 provides a summary of the results presented in this thesis.