Whilst the synthesis of ferrocene-bridged molecular boxes is hampered by rotamer effects associated with the ferrocene unit, it is now shown that, with a degree of preorganisation, macrocyclisation can be an efficient and viable process for the synthesis of an asymmetric redox-active molecular box, without the expected formation of catenanes and higher order macrocycles.In recent years, there has been considerable interest in the incorporation of redox-active centres into binding sites for ionic or neutral species. 2 Complexation can alter the redox potential of the ligand allowing such receptors to act as electrochemical sensors. For example, Chen et al. have reported 3 the asymmetrical complexation of two different Group 2 metal cations (Ba 2+ and Mg 2+ ) in a ferrocenesubstituted bis-crown ether 1, and Beer et al. 4 have prepared a novel cobalticenium receptor for Cl -and Br -. In both cases there is an electrochemical response by the host to the presence of the guest. The recognition of neutral molecular species has also been an area of intense research in the last decade, and has increased the understanding of relatively weak p-p and hydrogen bonding interactions. This has led to the design, synthesis and characterisation of the benzoquinone receptor 2, 5 which is itself an important cofactor in the primary photoinduced charge-separation process in bacterial photosynthesis. Vögtle et al. 6 have recently shown that this receptor not only binds benzoquinone, but can also recognise other simple aromatic species which, when substituted with "end stoppers", afford simple rotaxanes, such as 3.The work reported in this communication concerns the synthesis of macrocycles incorporating a redox-active centre and investigates the requirement for preorganisation in such pathways, in effect producing molecular boxes by a combination of the two concepts discussed above.Our initial studies concerned the preparation of the symmetrical, bis-ferrocenophane 6. This has been successfully obtained, albeit in low yield, through the stepwise synthetic pathway outlined in Scheme 1.
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