LAUSR

Cleavage of carbon-carbon bonds has been found in some important industrial processes, e.g. petroleum cracking, and has inspired development of numerous synthetic methods. However, non-polar unstrained C(aryl)-C(aryl) bonds remain one of the toughest bonds to be activated. As a detailed study of a fundamental reaction mode, here a full story is described about our development of a Ru-catalyzed reductive cleavage of unstrained C(aryl)-C(aryl) bonds. A wide range of biaryl compounds that contain directing groups (DGs) at 2,2' positions can serve as effective substrates. Various heterocycles, such as pyridine, quinoline, pyrimidine and pyrazole, can be employed as DGs. Besides hydrogen gas, other reagents, such as Hantzsch ester, silanes and alcohols, can be employed as terminal reductants. The reaction is pH neutral and free of oxidants, thus a number of functional groups are tolerated. Notably, a one-pot C-C activation/C-C coupling has been realized. Computational and experimental mechanistic studies indicate that the reaction involves a ruthenium(II) monohydride-mediated C(aryl)-C(aryl) activation and the resting state of the catalyst is a η4-coordinated ruthenium(II) dichloride complex, which could inspire development other transformations based on this reaction mode.