Electrochemistry of the Inclusion Complexes Formed Between the Cucurbit [7]uril Host and Several Cationic and Neutral Ferrocene Derivatives

We have investigated the formal ion of inclusion complexes between the host cucurbit[7]uril (CB7) and three cationic and four neutral ferrocene-containing guests: (ferrocenylmethyl)trimethylammonium (2(+)), butyl(ferrocenylmethyl)-dimethylammonium (3(+)), (ferrocenylmethyl)heptyldimethylammonium (4(+)), hydroxymethylferrocene (5), (((methoxy)ethoxy)ethoxy)methylferrocene (6), 1,1'-di(hydroxymethyl)ferrocene (7), and 1,1'-di((((methoxy)ethoxy)ethoxy) methyl)ferrocene (8). The formation of highly stable inclusion complexes (K > 10(7) M-1) was verified in all cases using NMR spectroscopic techniques. From cyclic voltammetric experiments, we observed that CB7 complexation of the cationic guests (2(+)-4(+)) leads to significant anodic shifts oil the ferrocene oxidation half-wave potentials, while the measured potential shifts were smaller in the case of the neutral guests (5-8). Encapsulation of all guests resulted in a substantial decrease of the standard rate constant for heterogeneous electron transfer. However, inclusion complexation of the neutral guests led to quasi-reversible voltammetric behavior, in which the anodic peak potential is more sensitive to scan rate than the corresponding cathodic peak potential, suggesting a minor degree of strutural rearrangement in the neutral inclusion complex after oxidation.