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

The reaction of aromatic azines with Fe-2(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 in-Line 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. (C) 2003 Elsevier B.V. All rights reserved.