Synthesis and Study of Mononuclear Ruthenium(II) Complexes of Sterically Hindering Diimine Chelates. Implications for the Catalytic Oxidation of Water to Molecular Oxygen

Abstract

Bis(diimine) complexes of ruthenium(II) have been prepared. The chelates used are 6,6'-dimethyl-2,2'-bipyridine (6,6'-dmbp) or 2,9-dimethyl-1,10-phenanthroline (2,9-dmp). Due to the steric hindrance created by the methyl groups αto the nitrogen atoms, the bis chelate complexes synthesized are all cis, with respect to the two remaining coordination sites, and cannot be photoisomerized to their trans isomers, in contrast with the equivalent complexes containing unsubstituted diimines. In addition, condensation of the mononuclear species to hydroxo- or oxo-bridged species of higher nuclearity is strictly prevented. The complexes have been characterized and studied by spectroscopic methods (UV-visible, IR, and 1H and 13C NMR). Their electrochemical behavior has been investigated in relation to the oxidation of water to molecular oxygen. The most significant results are the following: dinuclear species like (bpy)2(H2O)RuORu(H2O)(bpy)24+ are required for catalytic generation of O2 from water, in agreement with previously reported data.7On the other hand, the complexes presently reported display no activity toward oxidation of water. © 1986, American Chemical Society. All rights reserved.