Cleaving carbon–carbon bonds by inserting tungsten into unstrained aromatic rings

Abstract

The cleavage of C-H and C-C bonds by transition metal centres is of fundamental interest and plays an important role in the synthesis of complex organic molecules from petroleum feedstocks. But while there are many examples for the oxidative addition of C-H bonds to a metal centre, transformations that feature oxidative addition of C-C bonds are rare. The paucity of transformations that involve the cleavage of C-C rather than C-H bonds is usually attributed to kinetic factors arising from the greater steric hindrance and the directional nature of the sp(n) hybrids that form the C-C bond, and to thermodynamic factors arising from the fact that M-C bonds are weaker than M-H bonds. Not surprisingly, therefore, most examples of C-C bond cleavage either avoid the kinetic limitations by using metal compounds in which the C-C bond is held in close proximity to the metal centre, or avoid the thermodynamic limitations by using organic substrates in which the cleavage is accompanied by either a relief of strain energy or the formation of an aromatic system. Here, we show that a tungsten centre can be used to cleave a strong C-C bond that is a component of an unstrained 6-membered aromatic ring. The cleavage is enabled by the formation of an unusual chelating di(isocyanide) ligand, which suggests that other metal centres with suitable ancillary ligands could also accomplish the cleavage of strong C-C bonds of aromatic substrates and thereby provide new ways of functionalizing such molecules.