Cobalt-Catalyzed Formation of Symmetrical Biaryls and Its Mechanism

A method for cobalt-catalyzed formation of symmetrical biaryls and mechanism used for the formation, were reported. The study involved a new cobalt-catalyzed homo-coupling reaction in which cobalt was used with manganese dust as reducing agent. It was observed that the presence of allylchloride significantly reduced the amount of reduction compounds without modifying kinetics of the reactions and the reaction remained un-affected by the presence of air as oxidant. It was also found that no-reactions occurred in DMF, THF, and toluene in the presence of pyridine as co-solvent at room temperature, which indicated that MeCN acted as a ligand of the cobalt active species. The coupling process can be extended to less reactive aryl chlorides by changing some experimental conditions. DFT calculations revealed that the involvement of a CoI/CoIII couple was realistic in the case of 1,3-diazadienes as ligands.