Novel β-diketiminates and β-diketiminate derivatives for the synthesis of main group complexes

Abstract

This thesis is primarily concerned with the synthesis of low oxidation state alkaline earth metal complexes featuring novel β-diketiminate ligands and their derivatives. The syntheses of a variety of different β-diketiminates possessing extreme steric bulk, as well as those that have been electronically modified are detailed. These ligands have been used to produce a variety of different alkali metal, alkaline earth metal and lanthanide complexes. Chapter 1 provides a general introduction to low oxidation state alkaline earth metal chemistry. Particular attention is given to metal complexes featuring β-diketiminates, given their central role in the research making up this thesis. Chapter 2 deals with the synthesis of a range of novel, sterically hindered β-diketimines. These pro-ligands were targeted in the belief that their extreme bulk would allow the synthesis of currently unknown structural motifs. Chapter 3 is primary concerned with the exploitation of the developed sterically hindered β-diketimines in the synthesis of a variety of alkali metal, alkaline earth metal and lanthanide complexes. A range of three coordinate magnesium complexes were produced using the developed ligands, most notably, the first crystallographically characterised β-diketiminato magnesium hydride. In our quest for a calcium(I) dimer, a complex type which is currently unknown, a variety of β-diketiminato calcium iodides were produced. The attempted reduction of these heteroleptic metal iodide complexes resulted not in the targeted low oxidation state complexes, but in two different calcium(II) dimers. In Chapter 4, the β-diketimine ligand was adapted, resulting in two separate classes of pro-ligands. The first, a 1,3,5-triazapentadiene, has had the central carbon replaced by nitrogen. The second, instead of having the typical methyl groups on the ligand backbone, has dialkylamino groups. In each instance, it was envisaged that the ligands would donate additional electron density, and bind more strongly to the metal centre in coordination complexes, when compared to the standard β-diketiminate ligand class. Six separate heteroleptic magnesium(II) iodide complexes have been developed from these ligands, the majority of which show promise as precursors to low oxidation state magnesium complexes. Chapter 5 details several new secondary amines which have been produced as pro-ligands for low oxidation state main group chemistry. In addition, preliminary studies have shown that these ligands have potential in coordination chemistry.