Dinuclear Reactivity of One Metal Exalted by the Second One

This chapter is devoted to the coordination sphere of the two metals of a dinuclear framework for which the reactivity of one metal center is exalted by the second one. Kinetic studies and theoretical calculations are efficient tools nowadays to ascertain that along the catalytic cycle, bimetallic species are operating in the various steps converting the substrate. Bimetallic coordination complexes are described, in which the nature of the bridging ligand plays an essential role, as their mutual steric and electronic influences are determined by the distance and orientation of the two metal centers. By many ways, one metal can influence the reactivity of a neighboring metal both in stoichiometric and catalytic reactions. The three elementary steps of oxidative addition, migratory insertion, and reductive elimination are analyzed in the light of the cooperative effect induced by the second metal center exalting the reactivity. The electronic effects played by the ligands of the coordination sphere appear essential, but in some examples, steric effects add a supplementary influence, which may result in an increased selectivity. The tug-in effect of one metal on the other one, especially in heterodinuclear species, can allow tuning the reactivity through an appropriate adjustment of the distance between the two metal centers and a Lewis acid functionality. These concepts can be extended to dinuclear species bonded to a surface. Of course, much progress is still necessary to anticipate the right way to design the multidentate ligands, which scaffold a dinuclear entity for a given stoichiometric or catalytic reaction.