Ligand design and synthesis. III. Cyclic multidentate ligands with 12- and 18-membered rings

A number of cyclic ligands has been prepared by the high-dilution technique. All these ligands have their donor-atoms linked by ethano bridges. Examples of a non-planar quadridentate and three potential sexadentates were prepared. The cyclic quadridentete, 1-oxa-4,10- dithia-7-azacyclododecane (1), formed neutral complexes of the type [MLX2], where M = Co, X = Cl, Br and M = Ni, X = Cl, which are octahedral and presumably have the halide ligands cis to each other. Two of the cyclic ligands, 1,4,10,13-tetrathia-7,16- diazacyclooctadecane (3) and 1,4,7,10,13,16-hexathiacyolooctadecane (4), are the first reported cyclic sexadentates which form octahedral complexes, and the first examples of cyclic sexadentate ligands prepared without the aid of the metal template effect. Complexes of the type [ML](picrate)2, where M = Co, Ni, were prepared from ligands (3) and (4). A third potential sexadentate, 1,10-dioxa-4,7,13,16- tetrathiaoyolooctadecane (5), did not form complexes when treated with MX2, where M = Co, Ni, Fe, Cu and x = Cl, ClO4.