摘要:
The complexation behaviors of O-alkylated p-t-butylcalix[n]arenes (1(n)R), calix[n]arenes (2(n)R), 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 lambda(max) values for the CT complexes with 1(6)R and 1(8)R (496-498 nm) were comparable with those for the noncyclic analogs, whereas the lambda(max) values for the CT complexes with 1(4)R shifted to longer wavelengths (525-567 nm): the order (from longer to shorter wavelength) for 1(4)Pr(n) is 1,3-alternate > partial cone > 1,2-alternate > cone. The association constants (K) for 1(4)R were small in comparion to the lambda(max). It was shown on the basis of H-1 NMR measurements that "out" - 1(4)R (four alkyl groups are turned outward) is sterically-stable but cannot accept TCNE because of steric crowding on the benzene ring whereas "in" - 1(4)R (one alkyl group is turned inward) is sterically-unstable but can provide a room to accept TCNE. In 1(4)R, therefore, the complex formation occurs in conjugation with "out"-to-"in" displacement. This is the first example for the selective CT complexation with calix[4]arene conformers.