Interaction of hydroquinone and substituted derivatives with two cyclophane-like hosts: X-ray, molecular modelling and NMR studies

Abstract

An investigation of the interaction of hydroquinone and selected substituted derivatives with the 28-membered tetrabenzo-cyclophane-type receptor 1 and a tetramethoxy-substituted variant, 2, each incorporating an O4N2-heteroatom set, is reported. In a preliminary solution study, aromatic solvent introduced shift (ASIS) experiments had indicated that deuterated benzene is intercalated between the two xylyl bridges of cyclophane 1. In parallel with this result, a further NMR study was consistent with the inclusion of hydroquinone between the xylyl groups of 1 to produce a face-to-face π-stacked arrangement, with additional host–guest stability being provided by a pair of simultaneous hydrogen bonds between host and guest. Owing to limited CHCl3 or CH2Cl2 solubilities no association constant (K) for this host–guest system could be determined. However, use of the more soluble substituted guests 2,5-di-tert-butylquinone and 2,3-dimethylquinone enabled K values for 1 and 2 (ranging from 54 to 162 dm3 mol−1) to be determined. Single crystal X-ray structure determinations of (solvated) 1 and 2 are reported, their highly different conformations reflecting their change in substitution pattern.