Synthesis and structural studies of metallacarboranes

Abstract

The properties of some new metallacarboranes are described in this thesis, along with the results of a study to determine structural patterns in compounds published by others. Chapter 1 introduces heteroborane cluster compounds and a description of the bonding in these compounds. The synthesis and structure of supraicosahedral heteroboranes are discussed in detail with reference to literature examples throughout. A brief description of the trans influence is also given. Chapter 2 describes the synthesis and structures of a series of thirteen vertex indenyl cobaltacarboranes and a single fourteen vertex bimetallic indenyl cobaltacarborane. The crystallographically-determined orientation of the exo-polyhedral indenyl ligand in each compound is used to probe the relative strengths of the metal-carborane bonds. Rotation of a related exo-polyhedral ligand about 360o is explored computationally and the results used to help rationalise the orientations of the indenyl ligands. Chapter 3 describes the synthesis and structures of a single twelve vertex and a series of thirteen vertex naphthalene ruthenacarboranes. As for the isoelectronic indenyl cobaltacarboranes, the orientations of the naphthalene ligands are explored crystallographically and computationally. The details of some unexpected side products are also discussed. Chapter 4 is an analysis of the results of a crystallographic database search which showed clear structural patterns in previously published metallacarboranes. Cage atoms which are relatively weakly bonded to the metal tend to lie trans to exo-polyhedral ligands which are relatively strongly bonded to the metal. Chapter 5 describes the structures of thirteen and fourteen vertex bimetallic pentamethylcyclopentadienyl ruthenacarboranes with unconventional electron counts, which were synthesised by metallation followed by direct electrophilic insertion. The structures of an exo-polyhedral metal-bound species and three solvent-bound zwitterionic metallacarboranes prepared from attempted direct electrophilic insertion reactions are also presented. Chapter 6 gives the experimental procedures used to synthesise and purify each new compound and provides details of how they were characterised. Appendix 1 lists the crystallographic data relevant to each compound. Appendix 2 gives details of the literature structures found during the structural database search described in chapter four. Appendix 3 (electronic appendix - see CD-ROM) contains rtf and CIF files (crystallographic data) for all compounds (where available). Appendix 4 (electronic appendix - see CD-ROM) contains CIF and mol2 files for all literature compounds discussed in chapter four.