Synthesis, Characterization And Voltammetric Of Ferrocenyl Alkyl Imidazole Compounds

Electrostatic interactions of both intra- and intermolecular nature are present in the natural world,particularly in various forms of life.They are the main driving forces for signalling in macromolecules and supramolecules.Their influences exert on the host-guest combination,recognition and dissociation processes in biological systems. The establishment of intra- and intermolecular electrostatics is important for not only understanding many naturally occurring biological processes but also the designing and fabrication of molecular devices,such as a new generation of electrochemical sensors. This goal can only start from qualitative and quantitative observations and analyses but, unfortunately,possibly due to the complexity of macromolecules,it is generally considered that studies of inter- and intramolecular electrostatics may be challenging via experimental techniques and require sophisticated theoretical modelling.It is evident from literature that qualitative or semi-quantitative research has been rarely reported,and there is not any systematic investigation.This thesis reports a novel approach to the investigation and understanding of intramolecular electrostatics through supramolecular chemistry and electrochemistry.Electrochemically active or redox responsive host molecules are composed of at least three parts:a redox centre and a guest binding group linked by a suitable spacer group.These molecular systems present two type of functionalities:complexation with and provision of information of the complexed guest species.Such a bi-functionality is achieved often through intra-molecular electrostatic interactions either through space or through bond.Therefore,it is possible to design and synthesise different electrochemically active host molecules of desired structures to complex with various guest species and investigate the intra-molecular interactions.This thesis describes the synthesis of a number of redox active ferrocenyl imidazole molecules in which the spacer group,an alkyl chain,is systematically changed in length and hence provides a variable that can be used to alter the electrostatic interaction between the redox centre and the complexed anion.In addition to the interaction distance, the alkyl chain also forms part of the local dielectric medium through which the electrostatic interaction is communicated.By varying the bonding anion,it is then possible to evaluate the interaction strength variation through the potential of the ferrocene centre in response to different anions.This is experimentally achieved using cyclic voltammetry.The work is more specifically described below.1.In synthesis design and practice,one redox active group,ferrocene was investigated to combine with one or two imidazole binding moieties linked by a alkyl chain of varying length.The synthesis of the ferrocenecompounds were successful,leading to 9 new compounds,2-12～2-20 and 2-22. All these molecules were confirmed structurally by ¹H NMR and¹³C NMR.2.In electrochemical studies,the mean potential(E1/2) of the compounds were measured and compared,revealing the changes were greater of the bis-substituted compounds than that of the mono-substituted ones.Increasing the alkyl spacer length, shifted E_1/2 negatively from-(CH₂)₀-to-(CH₂)₄-.This unusual variation is attributed to the combined electron donating and withdrawing influences,and also the steric effect from the substituentes on the ferrocene moiety.3.The electrochemical responses of the ferrocenyl imidazole compounds2-12～2-20, towards halogen anions,HSO₄^- and H₂PO₄^- were found to be very different.The hosts exhibit very strong responses to HSO₄^- and H₂PO₄^-.The changes were greater of the bis-substituted compounds than that of the mono-substituted ones.Increasing the alkyl spacer length,shifted E_1/2 negatively from-(CH₂)₀-to-(CH₂)₄-.