Approaches to metallocene-bridged molecular hosts

The aim of this work was to investigate synthetic approaches to metallocene-bridged molecular hosts capable of binding and interacting with guest molecules, thereby offering routes to novel molecular-electronic devices. Particular attention was to be focused on the complexation of tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), which are known to form charge transfer complexes with ferrocene derivatives. After a review of the origins of Supramolecular Chemistry tracing the development of this area towards the construction of molecular devices, a brief overview is given of the range of ionic and molecular receptors which incorporate a metallocene moiety. The synthesis and properties of some simple novel ferrocene- and ruthenocene-based aza-crown ethers are then described. Comparative metal-ion extraction studies demonstrate that amino-linked metallocene aza-crowns are far more effective ionophores than their amido-linked analogues. Evidence is then presented which suggests that cation complexes of the amino-linked derivatives are stabilised by a cation-π interaction with one face of the metallocene sub-unit. Application of Fast Atom Bombardment Mass Spectrometry to assess the binding selectivity of the simple crown derivatives, following accepted literature procedures, produces confusing results and has led to a critical re-evaluation of the use of this technique. A series of experiments reveal that the accepted experimental method is fundamentally flawed and attempts to circumvent these limitations are then described. The final section of the work details the synthetic progress made to date in the development of routes to redox-active molecular hosts. Two synthetic routes have proved viable; one based on Friedel-Crafts acylation, and the other on sequential amide-bond formation. This latter has been used in a successful synthetic route to a novel ferrocene macrocycle. In the light of these observations concluding remarks are made concerning the future direction of this project.