No description available.

No description available.

No description available.

No description available.

This thesis is comprised of two parts. The first part describes the synthesis of cyclopentadienyltungsten complexes containing a pendant alkyne group (I), and the subsequent photo-induced intramolecular coordination of the alkyne, forming complexes such as II. Compounds containing intramolecularly coordinated alkynes are rare, and this is the first example using cyclopentadiene as the core ligand. The second part describes the synthesis and structural characterisation of a number of novel metal complexes containing N-heterocyclic carbene ligands, some containing particular functionality for taylored applications. New methods were used to form complexes of rhodium, iridium, silver and gold (eg. III, IV). Structural and spectroscopic properties of the complexes were correlated with electronic characteristics of the ancillary ligands. A number of rhodium and iridium complexes (eg. IV) derived from imidazolium-linked cyclophanes were synthesised and structurally characterised. Complexes of N-heterocyclic carbenes with pendant ionic groups were synthesised, and a preliminary examination of their catalytic activity in water was performed. N-Heterocyclic carbenes complexes containing an electron withdrawing nitro group were synthesised and the effect of the nitro group on metal-ligand bonding was examined.

Stabilization of highly strained organic species and altering normal reactivity norms of organic fragments by transition metals have been a triumphing feat of organometallic chemistry. A variety of saturated and unsaturated metallacycles result from the reactions of the transition metals with the organic entities. Understanding the structure and bonding of the metallacylces has been indispensable over the years in view of its involvement as intermediates or compounds for numerous synthetic and catalytic applications. In this context, Group 4 metallocenes have unlocked a fascinating chemistry by stabilizing strained unsaturated C4 organic fragments in the form of five-membered metallacyclomulenes, metallacyclopentynes and metallacycloallnes. These molecules do not conform to the existing bonding principles of chemistry. We have carried out a comprehensive theoretical study to understand the unsual stability and reactivity of these metallacycles. Our theoretical study reveals that the unique interaction of the internal carbon atoms along with the terminal carbon atoms with the bent metallocene moiety is the reason for unsual stability of the metallacycles. We have also investigated the mechanism of interesting C-C coupling and cleavage reactions involving metallacyocumulenes. It demonstrates unexpected reaction pathway for these metallacycles. Moreover, based on this understanding, we have predicted and unraveled the stabilization factors of a challenging four membered metallcycloallene complex. Indeed, our prediction about a four-membered heterometallacycle has been realized experimentally. This kind of bonding is intriguing from fundamental perspective and has great relevance in synthesizing unsual structures with interesting properties. Finally, the electronic structure and bonding of a metallocene-alkyne complex is analyzed to determine the nature of bonding. Our aim is to build a conceptual framework to understand these metallacycles and to exploit their chemistry.