Dimer and trimer calixarenes containing multiple metallocene redox-active centres. Single-crystal X-ray structure of a bis(ferrocene)-bis(p-t-butylcalix-arene) hydrophobia host molecule
The condensation of 1,1′-bis(chlorocarbonyl)ferrocene (1) and 1,1′-bis(chlorocarbonyl)ruthenocene (2) with p-t-butylcalixarene gave the respective new redox-active metallocene–calixarene dimers (3) and (4). An X-ray diffraction study of (3) shows the two calixarenes to be in cone conformations with a metallocene metal atom transannular Fe ⋯ Fe separation of 5.9 Å. The reaction of 1,1′-bis(chlorocarbonyl)cobaltocenium chloride (5) and p-t-butylcalixarene gave a cobaltocenium–bis(p-t-butylcalixarene) dimer (6). A ferrocene–calixarene trimer (7) was isolated from the reaction of (1) and calixarene. Solution variable-temperature 1H n.m.r. studies show (3) and (4) to be conformationally mobile with respective low-temperature spectra consistent with either partial cone conformations or cis orientation of respective metallocene carbonyl ester moieties. Cyclic voltammetric and coulometric studies in acetonitrile reveal that compound (3) undergoes a reversible two-electron oxidation at +1.24V (versus saturated calomel electrode), suggesting the two respective ferrocene moieties are oxidised in one step. Proton n.m.r. complexation studies showed (3) to be incapable of forming a solution host–guest complex with t-butylamine.
- This article is part of the themed collection: In celebration of Paul Beer’s 60th Birthday