Cooperative bimetallic redox reactivity

Binucleating Ligands possessing contiguous 6-coordinate and 4-coordinate si tes are described, and the redox properties of their bimetallic complexes h ave been investigated. The design of the two parts of these ligands is base d on the redox and reactivity patterns of the corresponding monometallic co mplexes. If the two sites were to behave as they do in the corresponding mo nometallic 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 fou nd not to be the case. In these bimetallic complexes, oxidation of one meta l 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 r eorganization is the dominant deactivating effect. It is shown that, in a b imetallic 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 addi tion reactions and to the evolution of new catalysts.