Synthesis and conformational and complexation studies of 2,17-dioxa-5,14-dithia[6.6]orthocyclophane. A ligand with monodentate and bidentate properties

Abstract

2,7-Dioxa-5,14-dithia[6.6]orthocyclophane (9) was synthesized from the coupling reaction between o-xylylene-bis(1-chloro-3-oxaproprane) and o-xylene-α,α′-dithiol under high-dilution conditions. Variable-temperature 1H NMR studies suggest a high conformational mobility for 9. Complexation of 9 with mercury(II) and palladium(II) ions led to the isolation of the respective complexes 12 and 14. 1H NMR studies of 12 indicated that the mercury(II) ion readily dissociates from the ligand in solution. The structure of 12 resolved from X-ray crystallography shows that the mercury(II) ion is essentially coordinated to only one of the sulfur atoms of the ligand in an asymmetrical monodentate configuration with a Hg-S bond length of 2.508 Å. The macrocycle 9 in the palladium(II) complex 14 is shown to exhibit a symmetrical bidentate configuration, with the palladium(II) ion coordinating to the two sulfur atoms held in a cis stereochemistry without any indication of an appreciable palladium-oxygen interaction. The two benzene rings in complex 14 are found to adopt a syn conformation. Protons in the complicated 1H NMR spectrum of 14 could be assigned on the basis of several NMR experiments. © CNRS-Gauthier-Villars.