This thesis investigates the reactivity of Earth-abundant group two complexes with isoelectronic carbodiimides, isocyanates and carbon dioxide heterocumulenes as well as related reactivity with ketones and imidazoles. These studies were carried out with the intention of extending any observed reactivity into a catalytic regime via subsequent σ-bond metathesis with hydride sources such as PhSiH3 or HBpin to yield valuable compounds.
Chapters 2 demonstrates that organocarbodiimides are easily converted to the sila-amidinates through insertion chemistry with a β-diketiminate-supported magnesium silyl. A series of sila-amidinate species have been identified and fully characterised through stoichiometric reactivity studies. These data suggest that overall reduction and RN=C=NR activation occurred through insertion into the Mg-Si bond to form the C-silylated species. This reaction is further explored through a DFT study which corroborates the experimental results.
Chapter 3 demonstrates that organoisocyanates, carbon dioxide and ketones are readily converted to isonitrile, siloxide, etc through deoxygenation with a β-diketiminate-supported magnesium silyl. A series of siloxide and isonitrile species have been identified and fully characterised through stoichiometric reactivity studies. These data recommend that overall reduction and C–O activation occur through deoxygenation to form the corresponding siloxide and isonitrile species. This reaction is further explored through a DFT study which complements the experimental results.
Chapter 4 describes an investigation into the synthesis and subsequent reactivity of a THF-solvated β-diketiminato calcium silyl borohydride species towards carbodiimides, isocyanates and ketones. An initial study indicated this solvated species acts primarily as a source of reactive hydride, albeit via the same σ-bond metathesis and π-insertion pathways.
Chapter 5 investigates the performance of β-diketiminate-supported magnesium butyl and hydride complexes towards N-alkyl imidazoles and describes a deprotonative metalation approach towards the direct functionalisation of heterocycles, allowing elaboration towards more complicated molecular scaffolds.
|Date of Award
|27 Apr 2022
|Michael Hill (Supervisor) & Andrew Johnson (Supervisor)