Bis-phenol A Cyclophanes: Synthesis, Crystal Structures and Binding Studies

The synthesis and structural characterisation of three new macrocyclicbis-phenol A cyclophane ethers are described. The solid state structuresof two of the cyclophanes were determined by single crystal X-raydiffraction. Cyclophane 3 crystallises in the orthorhombic spacegroup Pbca with unit cell dimensions of a = 11.533(7), b = 29.383(8),c = 14.927(8) Å and cyclophane 4 in the monoclinic spacegroup P2₁/n with cell dimensions of a = 11.585(4), b = 11.839(2), c = 18.866(2) Å, = 94.48(2)°.The X-ray crystalstructures reveal distorted conformations, thus supporting the weak bindingof quats in solution observed by the NMR studies. In the crystalline state bothmacrocycles were found to form self-complementary dimers held together byweak intermolecular - and CH- interactions. The bindingbehaviour towards a series of tetralkylammonium cations was determinedby ¹H NMR titration in CDCl₃ solution. The interactions between the hosts and the quats were clearly detectable but too weak to be translated into meaningful equilibrium constants.