The complexation behaviors of O-alkylated p-t-butylcalix[n]arenes (1nR), calix[n]arenes (2nR), and their noncyclic analogs were investigated in dichloromethane. All compounds formed a 1:1 complex with TCNE, indicating that complexation with the first TCNE suppresses further complexation with the second TCNE. The λmax values for the CT complexes with 16R and 18R (496-498 nm) were comparable with those for the noncyclic analogs, whereas the λmax values for the CT complexes with 14R shifted to longer wavelengths (525-567 nm): the order (from longer to shorter wavelength) for 14Prn is 1,3-alternate > partial cone > 1,2-alternate > cone. The association constants (K) for 14R were small in comparion to the λmax. It was shown on the basis of 1H NMR measurements that "out" - 14R (four alkyl groups are turned outward) is sterically-stable but cannot accept TCNE because of steric crowding on the benzene ring whereas "in" -14R 14R (one alkyl group is turned inward) is sterically-unstable but can provide a room to accept TCNE. In 14R, therefore, the complex formation occurs in conjugation with "out"-to-"in" displacement. This is the first example for the selective CT complexation with calixarene conformers.
All Science Journal Classification (ASJC) codes
- Drug Discovery
- Organic Chemistry