The fixation of atmospheric N2 to NH3 provides all of the biotic nitrogen on Earth, and is therefore a process of utmost importance. The current anthropogenic method for achieving this transformation is the Haber-Bosch process, a highly-energy intensive process estimated to account for 1-2%of the total world’s energy consumption. Since the discovery of well-defined complexes containing N2 ligated to a transition metal, the inorganic chemistry community has worked towards an understanding of the reactivity of coordinated N2 in the hope of achieving industrially-viable, catalytic N2 fixation under ambient conditions.
This thesis discusses work undertaken on evincing the mechanism of catalytic N2 fixation by homogeneous Fe bis-phosphine complexes, with the hope that such insights may lead to the design of more effective catalysts for this important reaction.
Chapter One provides an introduction to the fundamental aspects of N2 fixation, and how
it is achieved biologically and in the chemical industry. This is followed by an overview of the current state of mechanistic understanding of N2 fixation mediated by well-defined Fe complexes.
Chapter Two discusses the catalytic reductive silylation of N2 by Fe phosphine complexes.
High catalytic turnovers are achieved, and mechanistic information about the early stages of the reaction is detailed.
Chapter Three concerns an investigation into the mechanism of catalytic N2-to-N2H4
conversion by an Fe bis-phosphine complex, with a catalytic cycle for this unusual
transformation being put forward.
Chapter Four details the experimental procedures performed in this work.
Chapter Five contains supplementary information pertaining to this work, particularly tables of crystallographic data.
A visual summary of compounds discussed in this thesis - along with their corresponding
compound numbers - may be found on page 15 and a more easily removable summary on
page 167.