Metal insertion into C-C bonds in solution

Metal-promoted activation of C-C bonds in homogeneous media under mild conditions may lead to the design of new selective processes for the utilization of hydrocarbons. However, examples of C-C bond activation in solution are much more scarce than those of C-H bond activation. We looked at the available data on metal insertion into C-C bonds in solution and tried to answer some important questions regarding the C-C bond activation. What kind of ligated metal center is necessary in order to cleave the "hidden" C-C bond? What are the possible mechanisms of the C-C activation in various reaction systems, and how do different metal centers influence the reactivity? How can one tune the metal center for C-C bond cleavage by varying the steric and electronic properties of ligands? Thermodynamically, insertion into a C-C bond in solution is not a forbidden process, even if no strain relief or aromatization driving force is involved. Moreover, with an appropriate system C-C activation may prevail thermodynamically and kinetically over the competing C-H activation. The relative thermodynamics of C-C versus C-H cleavage is influenced by the electron density on the metal center. When kinetics is concerned, coordinative unsaturation appears to be crucial for C-C oxidative addition.