Synthesis, Characterization and Chemical Behavior of Disulfide-bearing Mononuclear Transition Metal Complexes with the Rigid Structure

A novel rigid macrocyclic ligand based on the bis(pyridylimino)isoindole framework bearing the disulfide moiety was designed and synthesized to investigate the behavior of the disulfide in mononuclear transition metal complexes. Intrinsically high reactivity of the Co(II) disulfide complex was clearly found by observation of the progress of the ring-contraction reaction to form a thioether complex in the presence of cyclooctene. On the other hand, the Fe(II) disulfide complex was found to be stable even when heated at 60 degrees C under the same conditions. This difference in reactivity of disulfide complexes might be derived from the difference in the ionic radii of Co(II) and Fe(II); when the smaller Co(II) ion was installed into the disulfide-bearing macrocyclic ligand, the structural demand for square pyramidal geometry around the Co center drove ring-contraction, eliminating a sulfur atom from the strained disulfide complex.