Chemical Transformations in Heterobimetallic Complexes Facilitated by the Second Coordination Sphere

This chapter is dedicated to heterobimetallic complexes in which the two metal centers are not directly bound. Complexes are described in which the second metal resides in the second coordination sphere of the first metal and enables bond activation processes via synergistic activity with the first metal that are not available to the corresponding monometallic complexes. Both stoichiometric and catalytic bond activations are analyzed in the light of the type of reactions (e.g., H₂ activation, polymerization, etc.). Both steric and electronic effects appear to play significant roles in many cases, and as such, they are examined when applicable. Indeed, spatial proximity between the two metal centers as well as electronic environment can allow for modification and tuning of reactivity. This realization has led to the development of switchable catalytic systems which are highlighted and discussed in terms of how they are manipulated (e.g., redox-switchable systems and cation-responsive systems). While significant progress has been made toward furthering our collective understanding of the behavior of these types of heterobimetallic complexes, this area is still ripe for future development. Additional systematic work is necessary to continue to push this area of chemistry forward.