Towards the Synthesis of Redox-active Ferrocene-based Macrocycles via Successive Ring Expansion (SuRE)

Due to their exceptional properties, macrocycles have been investigated for a broad range of applications including use in therapeutics,[1] catalysis,[2] chemical sensors,[3–5] peptide mimics,[6–8] and molecular electronics.[9] Functionalisation allows these properties to be altered, allowing fine-tuning of macrocycles for these applications. Ferrocene is of interest for inclusion into macrocycles due to its unique characteristics such as its mild oxidation to ferrocenium, along with its optical and mechanical properties. Incorporation of ferrocene into a macrocycle is therefore likely to have a significant impact on the redox, optical and mechanical properties of the whole macrocycle. The synthesis of ferrocene-containing macrocycles is therefore an exciting avenue to widen the scope of macrocyclic chemistry. However, there are many drawbacks associated with current methods for the synthesis of both organic and ferrocene containing macrocycles. These include poor selectivity, difficulty synthesising larger rings and the formation of by-products resulting in lower yields. Therefore, it would be advantageous to develop alternative methods towards the synthesis of ferrocene-containing macrocycles, and this is the focus of this Master’s thesis. SuRE (Successive Ring Expansion) is an attractive alternative to currently used methods for macrocycle synthesis as it allows high control and selectivity over linear side-products and is able to be done successively.10,11 This project aimed to investigate the use of SuRE in the formation of ferrocene-containing macrocycles and analyse the optical and redox properties of ferrocene-containing precursors . Two ferrocene-containing starting materials for use in SuRE were successfully synthesised and SuRE was attempted using a variety of conditions. Unfortunately, the conditions tested led to decomposition and favoured the formation of the acid anhydride side-product. This is likely due to the proximity of the acid chloride functional group with ferrocene’s Cp ring. Nonetheless, the properties of ferrocene-containing precursors were analysed by DFT calculations, cyclic voltammetry and UV-Visible spectroscopy.