Dimeric capsules formed by Tetra-CMPO derivatives of (Thia)Calix[4]arenes

Abstract

Thiacalix[4]arene 2, calix[4]-arene 3 a and its tetraether fixed in the cone conformation 3 b form homo-and heterodimeric capsules in apolar solvents, which are held together by a seam of NH-O = P hydrogen bonds between carbamoylmethyl phospine oxide functions attached to their wide rim. Their internal volume of ̃ 370 Å3 requires the inclusion of a suitable guest. Although neutral molecules such as adamantane (derivatives) or tetrae-thylammonium cations form kinetically stable complexes (1H-and 31P-time scale), the included solvent is rapidly exchanged. The internal mobility of the included tetraethylammonium cation is distinctly higher (△G = 42.5 and 49.7kJmol-1 for 3 a and 3 b) than that for similar capsules of tetraurea calix[4]arenes 1. Mixtures of 1 with 2, 3 a, or 3b contain only the two homodimers but the heterodimerization occurs with the tetraloop tetraurea 6, which cannot form homodimers. Two dimers with cationic guests (2.(C5H5)2Co+.2 and 3a^Et3NH+vH2O3a) were confirmed by single-crystal X-ray analysis.