Substituent-Directed Structural and Physicochemical Controls of Diruthenium Catecholate Complexes with Ligand-Unsupported Ru−Ru Bonds

A family of diruthenium complexes with ligand-unsupported Ru−Ru bonds has been systematically synthesized, and their crystal structures and physical properties have been examined. A simple, useful reaction between Ru2(OAc)4Cl (OAc- = acetate) and catechol derivatives in the presence of bases afforded a variety of diruthenium complexes, generally formulated as [Nan{Ru2(R4Cat)4}] (n = 2 or 3; R4 = −F4, −Cl4, −Br4, −H4, −3,5-di-t-Bu, and −3,6-di-t-Bu; Cat2- = catecholate). The most characteristic feature of the complexes is the formation of short ligand-unsupported Ru−Ru bonds (2.140−2.273 Å). These comprehensive studies were carried out to evaluate the effects of the oxidation states and the substituents governing the molecular structures and physicochemical properties. The Ru−Ru bond distances, rotational conformations, and bending structures of the complexes were successfully varied. The results presented in this manuscript clearly demonstrate that the complexes with ligand-unsupported Ru−Ru bonds can sensitively respond to redox reactions and ligand substituents on the basis of the greater degree of freedom in their molecular structures.