New trithia- and dithioxa-macrocycles with biphenyl fused into the backbone: Structures, and molecular modelling studies

Two novel thiamacrocycles have been synthesised with a biphenyl unit and SCCSCCS or SCCOCCS linkers in the ring backbone. Their crystal structures have been determined, showing the trithia ligand to have both SCCS torsions anti (a) whilst the dithioxa ligand has both its SCCO torsions in a plus gauche (g+) conformation. Molecular dynamics simulations of these two ligands at several temperatures again show differences, the trithia being more rigid; in addition, the conformations predominating in the dynamics simulations of the dithioxa ligand are different from that of the crystal structure. No conformation occurred with any frequency which could be considered to have potential as a tridentate ligand (all-endo sulfurs or oxygens). Derivatives built with additional o-Me substituents were also examined. The cavity size provided by two of the ligands (operating as tridentate ligands) was calculated, and the implications for coordination of the new ligands are considered.