The conversion of atmospheric dinitrogen to ammonia is the starting point for the formation of all nitrogen-containing compounds on earth, and is consequently a hugely important chemical transformation. The anthropogenic production of ammonia currently requires enormous amounts of energy, and reducing this energy cost is acknowledged to be a major challenge to research chemistry. Efforts over the last 60 years to realise this goal have taken inspiration from the existing anthropogenic and biological systems capable of performing the fixation of dinitrogen to ammonia, both of which require transition metal catalysts. Synthetic transition metal complexes are capable of catalysing homogeneous dinitrogen fixation increasingly effectively, and iron complexes have moved to the forefront of research in this area. This dissertation explores a broad range of factors relevant to dinitrogen fixation at simple iron phosphine complexes, which have recently been shown to mediate this important transformation extremely efficiently. Chapter 1 introduces the broader context in which these investigations were performed, and outlines current areas of investigation in the field. Chapter 2 then details the preparation of a novel iron bisphosphine framework, and its application to homogeneous dinitrogen fixation. In Chapter 3, alternative iron phosphine complexes with tripodal ligand architectures are discussed, and the results of investigations into the functionalisation of coordinated dinitrogen with protons and other electrophiles are reported. Chapter 4 then describes the possible use of dihydrogen as a source of protons and electrons in homogeneous dinitrogen fixation, and the preparation of unusual tripodal hydride and dihydrogen complexes in this context. Chapter 5 provides the experimental details for all of the investigations performed. Additional materials, including crystallographic data, are given in the Appendix.