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

The binding interactions between two cucurbit­[<i>n</i>]­uril hosts (<i>n</i> = 7, 8, CB7 and CB8) and the three new guests 1,1′-bis­(cyclohexylammoniomethyl)­ferrocene (<b>1</b>H₂²⁺), 1,1′-bis­(cyclohexylmethylammoniomethyl)­ferrocene (<b>2</b>H₂2⁺), and 1,1′-bis­(cyclohexyldimethylammoniomethyl)­ferrocene (<b>3</b>²⁺) were investigated in aqueous solution using ¹H NMR spectroscopy, voltammetry, and electrospray (ESI) mass spectrometry. The experimental data reveal that guests <b>1</b>H₂²⁺ and <b>2</b>H₂²⁺ 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 <b>3</b>²⁺ and CB7, but its formation is slower (<i>k</i> = 2.5 × 10^–4 s^–1) and can be monitored by NMR spectroscopy. Finally, <b>3</b>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.