Bimetallic reactivity. Factors controlling one-site addition two-metal oxidation reactions in bimetallic complexes

A number of bimetallic complexes bearing five- and six-coordinate sites are described for the purpose of achieving one-site addition two-metal oxidation reactions where a substrate adds to the metal at the five-coordinate site and is reduced by both metals. One set of such bimetallic cobalt complexes is found to be either oxidatively unreactive or in some cases when one or the other of the metals is oxidized, the other becomes unreactive to oxidation. This oxidative deactivation is evident even when it is demonstrated that the monometallic constituent parts of the bimetallic complex allow for ready oxidation. It is concluded that the major impediment to bimetallic oxidation is mechanical coupling where the ligand conformation cannot adjust to the structural demands of the higher oxidation state metal. When mechanical coupling is minimized, it is shown that one-site addition two-metal oxidation reactions are observed. With such bimetallic Co2+ complexes NO2+, Br2 and O2 are shown to undergo the expected reactions.