Cooperative bimetallic redox reactivity

Binucleating Ligands possessing contiguous 6-coordinate and 4-coordinate sites are described, and the redox properties of their bimetallic complexes have been investigated. The design of the two parts of these ligands is based on the redox and reactivity patterns of the corresponding monometallic complexes. If the two sites were to behave as they do in the corresponding monometallic complexes, these bimetallic complexes would be expected to bind a substrate, such as dioxygen, and to reduce it by two electrons, one from each metal, as occurs in the respiratory protein, hemerythrin. This was found not to be the case. In these bimetallic complexes, oxidation of one metal leads to the deactivation of the other metal to oxidation. The origins of this mutual deactivation appear to be connected with Ligand reorganization, through-bond electronic coupling, and electrostatic interactions between neighboring metals. Iris suggested that, in the systems described, ligand reorganization is the dominant deactivating effect. It is shown that, in a bimetallic system where these deactivating effects are minimized, substrates can be added to the 4-coordinate metal and cause oxidation of both metals. The development of these types of systems could lead to new oxidative addition reactions and to the evolution of new catalysts.