Bimetallic reactivity. Preparations, properties and structures of complexes formed by unsymmetrical binucleating ligands bearing 4- and 6-coordinate sites supported by alkoxide bridges

Abstract

Four binucleating ligands which potentially could provide bimetallic complexes bearing 5- and 6-coordinate sites have been prepared. These ligands, which have alkoxide bridging groups, can be regarded as more elaborate versions of binucleating ligands which have tridentate chelates on each side of the alkoxy bridge. Unlike these previous, less complex ligands, the present series of binucleating ligands have a strong tendency to form oligomers. This has been demonstrated with a series of crystal structures of copper(II) complexes of these ligands. It is probable that oligomers are formed because of the high flexibility of the present ligands. The work serves to illustrate the limits of binuclear ligand design and suggests that, with alkoxide ligand bridges, rigidity is necessary in order to obtain bimetallic complexes with extended multidentate binucleating ligands. One of the ligands gives a mixed valence Mn(II)–Mn(IV) complex after O₂ oxidation of a di-Mn(II) precursor.