Dibenzocyclooctatetraene based poly-Lewis-acids: flapping hosts for multidentate guests†

Abstract

A synthetic route to flapping poly-Lewis acids (PLAs) based on dibenzocyclooctatetraene was developed. The reactivity of tetradentate boron and aluminium containing PLAs towards various Lewis bases (LB) including drugs was investigated in detail. By using different monodentate LBs, the different effective Lewis acidities (eLA) of the respective pairings were determined and compared with each other. The reaction with multidentate LBs yielded a range of adducts, which were analysed in solution by NMR methods, including DOSY NMR spectroscopy, and in the solid state by X-ray diffraction. The adducts include specific oligomers, and coordination polymers constructed via B–P, Al–P and Al–N interactions. The solid-state structures of these coordination polymers have been determined. The results of complexation of bidentate LB by the tetradentate PLA show that LB is preferentially chelated in the binding pockets, which does not impede the flapping movement during chelating complexation. This phenomenon can be attributed to a reduction in entropy when this flapping motion is lost. The aluminium containing PLAs were observed to form a complex with two caffeine molecules, exhibiting remarkable preference for oxygen functions. In contrast, the reaction with theobromine resulted in the degradation of the PLAs due to the presence of acidic protons in theobromine, leading to the formation of a dimeric aluminium containing theobromine derivative. These findings demonstrate the interaction of PLAs with drugs. They provide a foundation for the advancement of PLAs with a tuneable orientation of Lewis acidic functions.