Redox-active cavitand host molecules containing multiple ferrocenyl redox centres: syntheses, crystal structure, molecular mechanics calculations, and electrochemical properties

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Abstract
The design, synthesis, X-ray crystal structure, molecular mechanics calculations, and electrochemical properties of novel redox-active cavitand host molecules containing multiple ferrocenyl redox centres are described. The acid-catalysed condensation of ferrocenecarbaldehyde (1) with 1,3-dihydroxybenzene (2) afforded a new phenolic macrocycle 2,8,14,20-tetraferrocenylpentacyclo[19.3.1.13,7.19,13.115,19] octacosa-1 (25),3,5,7(28),9,11,13(27),15,17,19(26),21,23-dodecaen-4,6,10,12,16,18,22,24-octol (3) which on reaction with bromochloromethane gave the first rigid redox-active cavitand host molecule (4) containing four ferrocenyl redox centres. The reaction of compound (3) and the corresponding 2,8,14,20-tetramethyl octol (5) with 1,1′-bis(chlorocarbonyl)ferrocene (6) gave the respective redox cavitands (7) and (8) with the ferrocene moieties lining the wall of the cavitand cavity. The single-crystal X-ray structure of compound (4) reveals a dichloromethane guest molecule within the cavitand host cavity. Molecular mechanics calculations performed on the complexes of cavitand (4) with dichloromethane, toluene, and carbon dioxide suggest the cavitand cavity will only allow limited inclusion of small guest species. Electrochemical studies show the multiple ferrocene centres present in (4) and (7) to undergo independent reversible one-electron oxidations in dichloromethane. The addition of dichloromethane to or bubbling of carbon dioxide through electrochemical dimethylformamide solutions of (7) produced no significant changes in the cyclic voltammogram of (7).

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