Dinitrogen activation and reduction with iron phosphine complexes

• Main Author: Doyle, Laurence
• Other Authors: Ashley, Andrew
• Published: Imperial College London 2015
• Subjects: 546
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.724100

The conversion of dinitrogen to ammonia is a fundamental process for sustaining life on our planet. Ammonia provides a source of fixed nitrogen for nitrification and assimilation into plants, and is the ultimate source of almost all nitrogenated compounds. Synthetic ammonia is produced on a colossal scale by the Haber Bosch process, with an annual ammonia output exceeding 130 million tonnes. However, the intensive operating conditions of this process require a staggering energy cost; hence, the development of a lower energy solution is recognised as one of the major challenges of modern chemistry. This dissertation explores the chemistry of homogeneous systems based on iron diphosphine complexes that are able to transform coordinated dinitrogen into ammonia. A greater understanding of these systems may provide insight into the iron-based catalysts utilised in both biological nitrogen fixation and the industrial Haber Bosch process. Ultimately, this could lead to a more sustainable process for meeting the global requirement for fixed nitrogen. Chapter 1 provides a general introduction into dinitrogen fixation chemistry, with a particular focus on homogeneous systems involving iron. Chapter 2 describes a convenient synthetic protocol to 1,2-bis(dialkylphosphino)ethanes. These are among the most versatile ligands used in inorganic chemistry, although issues with prior syntheses, often involving extremely hazardous phosphine precursors, has limited their accessibility. Chapter 3 is an exploration of a seminal work on dinitrogen fixation involving iron complexes, which facilitate the conversion of coordinated dinitrogen to ammonia in what is known as the Leigh cycle. Mechanistic understanding of the key ammonia producing step has provided the focus of considerable interest and speculation for over a decade. Chapter 4 provides insight into the dinitrogen and dihydrogen affinity of an iron(I) complex. Chapter 5 details the experimental procedures performed in this work.