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

An investigation of the interaction of hydroquinoneand selected substituted derivatives with the28-membered tetrabenzo-cyclophane-type receptor 1 and atetramethoxy-substituted variant, 2, each incorporating anO4N2-heteroatom set, is reported. In a preliminary solutionstudy, aromatic solvent introduced shift (ASIS) experimentshad indicated that deuterated benzene is intercalatedbetween the two xylyl bridges of cyclophane 1. In parallelwith this result, a further NMR study was consistent withthe inclusion of hydroquinone between the xylyl groups of1 to produce a face-to-face p-stacked arrangement, withadditional host–guest stability being provided by a pair ofsimultaneous hydrogen bonds between host and guest.Owing to limited CHCl3 or CH2Cl2 solubilities no associationconstant (K) for this host–guest system could bedetermined. However, use of the more soluble substitutedguests 2,5-di-tert-butylquinone and 2,3-dimethylquinoneenabled K values for 1 and 2 (ranging from 54 to162 dm3 mol-1) to be determined. Single crystal X-raystructure determinations of (solvated) 1 and 2 are reported,their highly different conformations reflecting their changein substitution pattern.