The field of "Frustrated Lewis Pairs" (FLPs), originally associated with the main group, has changed the manner in which the reactivity of small molecules is considered. The aim of the research described in this thesis was to develop the role of transition metals within the field of FLPs. Chapter 1 is a general introduction to the reactivity of small molecules, comparing FLPs and transition metals, focusing on drawing parallels between repOlted transition metal chemistry and FLPs. Chapter 2 describes the limits of phosphine-zirconium FLP systems. Firstly modification of the phosphine within an tethered (intramolecular) system was carried out, comparing the previously reported alkylphosphines with arylphosphines. It was found that the reduced bulk of the arylphosphines resulted in adduct formation between zirconium and phosphorus, this reduced the reactivity when the ancillary ligands on zirconium were Cp* and totally precluded reactivity when the ligands were Cpo Secondly a series of intermolecular phosphine-zirconium systems were investigated for FLP reactivity in an attempt to realise less synthetically demanding systems. Cationic alkoxyzirconocenes were combined with tertiary phosphines and trialled for FLP reactivity; removal of the linker leads to side reactions that prevented the FLP chemistry. In Chapter 3 the concept of taking a transition metal system reported for cooperative action on dihydrogen and applying it as a general frustrated Lewis pair for reaction with a range of small molecules is described. Previously it has been reported that a platinum(II) centre combined with an amine could heterolytically cleave dihydrogen and the same system has been trialled as a general FLP; although directly analogous chemistry is not observed, reactions with carbon dioxide and phenyl acetylene have been shown to occur. Chapter 4 is a description of the coordination chemistry of complexes of the type [Pt(CO)n(diphos)] (n = 1 or 2) where diphos is a xylenyl or tolyl backboned ligand with tert-butyl phosphorus substituents. X-ray diffraction and variable temperature NMR experiments have been carried out to gain better understanding of the supporting xylenyl and tolyl diphos ligands. Under an atmosphere of CO dicarbonyl complexes were observed and found to be in equilibrium with the monocarbonyls. Reaction of the complexes with hydrogen resulted in a mixture of products including the dihydridoplatinum complex. Reaction with ethene led to displacement of the carbonyl ligands. The platinum(O) complexes are shown to be basic by reaction with a Bmnsted acid. In Chapter 5 the chemistry of [Pt(CO)(diphos)] as a base for FLP-type chemistry is reported and discussed. Specifically the platinum(O) complex is combined with B(C6F5)3 and reacted with hydrogen, ethene and carbon dioxide; the products produced show the platinum(O) centre and B(C6F5)3 have acted in a cooperative manner with the small molecule .
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:682556 |
| Date | January 2014 |
| Creators | Forrest, Sebastian John Kipling |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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