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.