69799-61-7Relevant academic research and scientific papers
Kinetics and mechanism of the oxidation of ammineruthenium(II) complexes by bromine
Plotkin, Stuart,Haim, Albert
, p. 189 - 196 (2008/10/08)
The reactions of Ru(NH3)5py2+, Ru(NH3)4bpy2+, Ru2(NH3)10pz5+,RuRh(NH 3)10pz5+ and Ru(NH3)5pz2+ with bromine are first-order in ruthenium and first-order in bromine. The rates decrease with increasing bromide ion concentration and, except for Ru(NH3)5pz2+, are independent of hydrogen ion concentration. The reactions are postulated to proceed via outer-sphere, one-electron transfer from Ru(II) to Br2 with the formation of Br2- as a reactive intermediate. The bromide inhibition is ascribed to the formation of Br3- which is unreactive in outer-sphere reactions because of the barrier imposed by the need to undergo reductive cleavage. The reaction of Ru (NH3)5pz2+ is inhibited by hydrogen ions. The hydrogen ion dependence shows that Ru(NH3)5pzH3+ has a pKa of 2.49 and is at least 500 times less reactive than Ru(NH3)5pz2+. The reaction of Ru2(NH3)10pz4+ with bromine is biphasic. The second phase has a rate identical to that of the Ru2(NH3)10pz5+-Br2 reaction. A detailed analysis shows that the reaction of Ru2(NH3)10pz4+ with bromine proceeds by a sequence of one-electron steps, Br2- being produced as an intermediate. A linear free energy relationship between rate constants and equilibrium constants, obeyed for all the reactions studied, provides an estimate of ～ 1.5×102 M-1 s-1 for the self-exchange rate constant of the Br2/Br2- couple.
