RUTHENIUM COMPLEXES WITH DIAZADIENES. VIII. DIAZADIENEDICARBONYL-RUTHENIUM(II) AND -RUTHENIUM(0) COMPLEXES: SYNTHESIS, PHOTOCHEMISTRY AND ELECTROCHEMISTRY

Article abstract of DOI:10.1016/S0022-328X(00)99781-X

The easily accessible diazadieneruthenium carbonyl complexes <(DAD)Ru-(CO)2I2> (I, DAD = RN=CR'CR'=NR) are photolytically labile and undergo CO substitution.The reactions can be monitored by UV/VIS spectroscopy and by cyclic voltammetry (CV), in which there are points of constant current and potential analogous to isosbestic points.A CV study of the irreversible two-electron reduction of I has also been carried out, and found to give free iodide ion and the anionic intermediate <(DAD)Ru(CO)2I>^-.This latter complex undergoes replacement of the iodide ligand by the solvent, carbon monoxide, or triphenylphosphine.The differences in reoxidation potentials and reversibility criteria provide information about the nature of the various electrochemically-formed ruthenium(0) complexes <(DAD)Ru(CO)2L> and their kinetic behaviour.The outcome of chemical reduction of I in solutions of higher concentration depends on the steric effect of the DAD ligand; with smaller ligands the final products are the DAD-bridged dimers <(DAD)Ru(CO)2> (V).In the presence of phosphine or carbon monoxide the corresponding five-coordinate complexes IV and VI, <(DAD)Ru(CO)2L>, are formed, and can be isolated and characterized spectroscopically.Addition of methyl iodide or an ammonium salt as a proton donor leads to oxidative addition products <(DAD)Ru(CO)2(CH3)I> (VII) and <(DAD)Ru(CO)2(H)I> (VIII).Photochemical substitution and reductive activation enable the introduction and elimination of ligands in a predictable manner.