Binding Interactions between Cucurbit[n]uril Hosts and Tritopic, Dicationic Guests Containing a Central Ferrocenyl and Two Terminal Aminocyclohexyl Sites

The binding interactions between two cucurbit[n]uril hosts (n = 7, 8, CB7 and CB8) and the three new guests 1,1'-bis(cyclohexylammoniomethyl)ferrocene (1H(2)(2+)), 1,1'-bis(cyclohexylmethylammoniomethyl)ferrocene (2H(2)(2+)), Fe and 1,1'-bis(cyclohexyldimethylammoniomethyl)ferrocene (3(2+)) were investigated in aqueous solution using H-1 NMR spectroscopy, voltammetry, and electrospray (ESI) mass spectrometry. The experimental data reveal that guests 1H(2)(2+) and 2H(2)(2+) behave similarly with both hosts, leading to the formation of pseudorotaxane complexes in which the host is located centrally around the ferrocenyl residue. A similar complex forms also between 3(2+) and CB7, but its formation is slower (k = 2.5 x 10(-4) s(-1)) and can be monitored by NMR spectroscopy. Finally, 3(2+) and CB8 give rise to a ternary 2:1 complex, in which CB8 receptors are bound to the terminal cyclohexyl groups, when the concentration. of the host exceeds that of the guest.