Organoosmium complexes of imidazole-containing chelate acceptor ligands

The complexes [(L)Os(eta(6)-Cym)Cl](PF6), Cym = p-cymene and L = bis(1-methylimidazol-2-yl) ketone (bik) or bis(1-methylimidazol-2-yl) glyoxal (big), were obtained and characterized with respect to spectroscopy, crystal structure (big complex) and (spectro)electrochemical behaviour at variable temperatures. DFT calculations confirm the structure of [(big)Os(eta(6)-Cym)Cl](+) with imidazolyl-N-bonded Os-II in a boat-shaped seven-membered chelate ring with small N-Os-N angles (<84 degrees). Reduction of this compound proceeds reversibly to a neutral complex of the alpha-semidione radical anion ligand big; EPR and IR spectroelectrochemistry indicate very little participation from the heavy metal in the spin distribution. The analogous [(bik)Os(eta(6)-Cym)Cl](+) could not be reduced reversibly to the ketyl radical complex but displayed a more reversible oxidation at high potential. (C) 2010 Elsevier B.V. All rights reserved.