Molecular tweezers with freely rotating porphyrin moieties

Abstract

The synthesis of molecular tweezers for the complexation of guests continues to be a highly active area of research in supramolecular chemistry. In recent times, molecular tweezers have been utilised for a variety of applications from drug release to enantiodiscrimination. In particular, the use of bis-metalloporphyrins as receptors to facilitate guest binding has allowed high association constants to be observed for various diamine ligands. Our research group has previously described the use of tetrazaanthracene linkages and a rigid polynorbornyl moiety to position two metalloporphyrins in a concave geometry to efficiently complex DABCO. Herein, we report a bis-metalloporphyrin based molecular tweezer with a bridged polycyclic linker, 3, which can freely rotate at several positions. We will present the synthesis of 3, which has been achieved by a modular approach with coupling via a microwave-accelerated 1,3-dipolar cycloaddition. In addition, the NMR and UV-Visible spectroscopic characterisation of the host-guest complex between 3 and several diamine guests, including DABCO, pyrazine, and 4,4'-bipyridine, will be presented.