Coordination, electron transfer and catalytic chemistry of a ruthenium-substituted heteropolytungstate anion as revealed in its electrochemical behavior

Abstract

The rates of substitution of π-acidic ligands for the aqua ligand in the ruthenium-substituted heteropolytungstate anion (H2O)RuIIPW11O5−39 were measured and compared with those of more familiar complexes of Ru(II). The weakly π-acidic character of the heteropolytungstate anionic ligand produced a decrease in the lability of the aqua ligand. The kinetics of homogeneous electron transfer reactions involving the (H2O)RuIIPW11O5−39 anion were complicated by its high charge and tendency to precipitate with cationic oxidants. However, the specific rate of its reduction of O2 to H2O2 was in good agreement with the value calculated from the Marcus relation. The RuIIIOH2 center in (H2O)RuIIIPW11O4−39 is reversibly oxidizable in two steps to RuIV = O and RuV = O. The RuV = O complex oxidizes benzyl alcohol, methanol and 2-propanol, but the reaction rates are too small to make the complex attractive as an oxidation catalyst.