The voltammetric behavior of ferrocene encapsulated inside two hemicarcerand hosts was investigated in dichloromethane and tetrachloroethane solutions. Molecular encapsulation led to substantial changes in the anodic voltammetric behavior of the ferrocene nucleus. Generally, encapsulated ferrocene exhibited a more positive halfwave oxidation potential and a lower apparent standard rate constant of heterogeneous electron transfer than uncomplexed ferrocene under identical experimental conditions. Whereas the anodic shift of the half-wave potential probably results from the hindered solvation of the positively charged, oxidized ferrocene inside the nonpolar hemicarcerand cavities, the observed decrease in electron transfer rate seems to arise primarily from the increased molecular mass of the electro-inactive species and the longer distance of maximum approach between the ferrocene center and the electrode surface which is imposed by the encapsulating host. Generally, electrochemical oxidation did not significantly alter the slow rate of ferrocene guest dissociation or release from the hemicarceplexes surveyed.

The cooperative nature of non-covalent interactions which give rise to inclusion complexes involving cyclobis(paraquatp-phenylene), 1 4+ , and related cyclophane derivatives, 2 4+ -4 4+ , with substituted 1,4-phenyl and 4,4Ј-biphenyl guests has been studied by spectroscopic techniques and ab initio and semiempirical molecular orbital methods. Inclusion complex formation and stability are primarily determined by the combination of two main interaction modes involving aromatic stacking of the guest within the cyclophane cavity and external interactions between guest side arms and the exterior of the cyclophane. A balance between cavity and external forces results in supramolecular association and is shown to change depending upon the functionality and substitution of the guest. Cavity binding was probed using 1,4-phenyl and 4,4Ј-biphenyl guests, where for the 1,4-phenyl guests the primary basis for energy stabilization with 1 4+ is found to be short-range stabilizing electrostatic forces complemented by small amounts of polarizability and charge-transfer. JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 10, 369-382 (1997) © 1997 by John Wiley & Sons, Ltd.CCC 0894-3230/97/050369-14 $17.50 many rotaxanes, catenanes and other switchable molecules, but because the intermolecular interactions involved, such as electrostatics, polarizability and charge-transfer, are ubiquitous in supramolecular chemistry. The information reported on the specific interactions involving the 1 4+ -4 4+ molecular receptors with substituted aromatic guests can also be extended by analogy to many systems of broad interest.

No abstract