ELECTRON-TRANSFER REACTIONS OF RUTHENIUM(III) PENTAAMMINES WITH CHROMIUM(II), VANADIUM(II), AND EUROPIUM(II)

Kinetic measurements have been made on the reactions of Cr(II), V(II), and Eu(II) with pentaammineruthenium(III) complexes containing halide, aquo, and carboxylate ligands. With the exception of a possible significant contribution by outersphere paths to the reduction of the iodo and aquo complexes, the reactions with Cr(II) take place predominantly by innersphere mechanisms. The reactions with V(II) are in all cases so rapid that they cannot involve substitution by a bridging group into a normal coordination position of the reducing agent. Reactivities of corresponding Ru(III) and Co(III) complexes are compared and considered in relation to the electronic structure of the oxidizing metal ions. For most of the oxygen ligands, intermediates formed as a result of the electron-transfer reaction were detected. With Cr(II) as reductant, the intermediates are binuclear Ru(II)-Cr(III) ions. A comparison of the rate of aquation of the intermediate bridged by OH- and by a carboxylate ion leads to the conclusion that Cr(II), in reducing a carboxylate Ru(III) complex, attacks the oxygen not bearing the Ru(III) ion. The intermediates formed by V(II) and Eu(II) are identical, and it is concluded, therefore, that they are the Ru(II) complexes corresponding to the Ru(III) complexes which were reduced. Data on the rates of aquation of carboxylatopentaammine Ru(II) complexes are recorded, as are estimates of the proton affinities of these complexes. © 1969, American Chemical Society. All rights reserved.