Computationally synthesised inorganic and organometallic complexes : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Chemistry at Massey University, Albany, New Zealand
Catalytic aromatic ring C–H bond functionalisations by transition metal cyclometallation reactions are important for organic transformation reactions. The cyclometallated product, which contains a new metal–carbon bond is formed as a consequence of different types of carbon–hydrogen····metal (C–H····M) interactions. These C–H···M interactions have been known as anagostic, preagostic and agostic interactions. By nature, the anagostic interaction has mainly electrostatic components, the preagostic interaction has electrostatic components with some back-bonding from metal to C–H antibonding orbital involved and the agostic interaction has mainly covalent components when the C–H bond donates electron density to the partially occupied metal centre. Prior to the current thesis work, an in-depth study that addresses the influence of steric and electronic factors on the anagostic, preagostic and agostic carbon–hydrogen····metal interaction was missing. In this thesis, the influence of both the steric and electronic factors on the anagostic, preagostic and agostic C–H···M interactions has been studied. It is seen that the electronic and steric influences play differently for different ligand systems as with the flexible tetralone ligand, a maximum of steric and electronic influence results into another type of anagostic interaction named as the 'C-anagostic' interaction. It is also seen that a stronger steric and electronic effect can trigger agostic covalency at the anagostic stage of the reaction. The inflexible ligand ensures the short anagostic approach, which has some back-bonding character and the nature of the interaction lies into the preagostic category. Finally, the aromatic ring agostic interactions have more complexity as new donations named as 'syndetic' from C–C pi bond to metal antibonding orbitals were recognised which shares the same antibonding acceptor orbitals as the agostic donation does. The recognition of new bonding situations in C–H····M interactions can have significant implications for C–H bond functionalisation reactions.