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

Abstract

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 (1H22+), 1,1′-bis(cyclohexylmethylammoniomethyl)ferrocene (2H22+), and 1,1′-bis(cyclohexyldimethylammoniomethyl)ferrocene (32+) were investigated in aqueous solution using 1H NMR spectroscopy, voltammetry, and electrospray (ESI) mass spectrometry. The experimental data reveal that guests 1H22+ and 2H22+ 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 32+ and CB7, but its formation is slower (k = 2.5 × 10–4 s–1) and can be monitored by NMR spectroscopy. Finally, 32+ 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.