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 (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.