Ligand properties of aromatic azines: C–H activation, metal induced disproportionation and catalytic C–C coupling reactions

The reaction of aromatic azines with Fe2(CO)9 yields dinuclear iron carbonyl cluster compounds as the main products. The formation of these compounds may be rationalized by a C–H activation reaction at the aromatic substituent in ortho position with respect to the exocyclic C–N double bond followed by an intramolecular shift of the corresponding hydrogen atom toward the former imine carbon atom. The second imine function of the ligand does not react. Additional products arise from the metal induced disproportionation of the azine into a primary imine and a nitrile. So also one of the imine C–H bonds may be activated during the reaction. Depending on the aromatic substituent of the azine ligands iron carbonyl complexes of the disproportionation products are isolated and characterized by X-ray crystallography. C–C coupling reactions catalyzed by Ru3(CO)12 result in the formation of ortho-substituted azines. In addition, ortho-substituted nitriles are identified as side-products showing that the metal induced disproportionation reaction also takes place under catalytic conditions.