Regioselective Synthesis and Inclusion Properties of distal-Bis[(2-pyridylmethyl) oxy]tetrathiacalix[4]arenes

Abstract

Regioselective synthesis of bis[(2-pyridylmethyl)oxy]tetrathiacalix[4]arenes was accomplished by a protection–deprotection method using benzyl groups as a protecting group. The conformational studies of distal-bis[(2-pyridylmethyl)oxy]thiacalix[4]arenes in solution and solid state are described. The two-phase solvent extraction data indicated that bis[(2-pyridylmethyl)oxy]tetrathiacalix[4]arenes show strong Ag+ (E%, 97%) affinity. In contrast, no significant E% is observed for K+. A good Job plots proves 1:1 coordination of 1,3-alternate-3 with Ag+ cation. 1H-NMR Titration of 1,3-alternate-3 with AgSO3CF3 also clearly demonstrates that a 1:1 complex is formed with retention of the original symmetry. The conformational changes of pyridine moiety from the original outward orientation of the ring nitrogen to the inside orientation toward the thiacalixarene cavity were observed in the process of Ag+ complexation. The down-field shifts of the benzene protons of the benzyl group were also observed and attributed to the conformational deviation from the original face to face overlapping.