Proton-coupled electron-transfer reactions. Mechanisms of two-electron reduction of trans-dioxoruthenium(VI) to trans-aquooxoruthenium(VI) and disproportionate of trans-dioxoruthenium(V)

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)5176-5181
Journal / PublicationJournal of the American Chemical Society
Volume112
Issue number13
Publication statusPublished - 20 Jun 1990

Abstract

The kinetics and mechanism of the reduction of trans-[RuvI(TMC)(O)2]2+ to trans-[RuIv(TMC)O(H2O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) in aqueous solution by outer-sphere one-electron reductants (R), trans-[RuVI(TMC)(O)2]2+ + 2R + 2H+ → trans-[RuIv(TMC)O(H2O)]2+ + 2R+, have been studied. The first step of the reduction is a simple outer-sphere electron-transfer process, trans-[RuVI(TMC)(O)2]2+ + R → trans-[Ruv(TMC)(O)2]+ + R+ with rate = k2[Ru(VI)] [R]. The rate constants (k2) with cis-[RuII(NH3)4bpy]2+ (bpy = 2,2′-bipyridine), [RuII(NH3)5isn]2+ (isn = isonicotinamide), and [RuII(NH3)5py]2+ (py = pyridine) have been measured and can be correlated with the Marcus cross relation. The estimated self-exchange rate constant of the trans-[RuVI(TMC)(O)2]2+/ trans-[Ruv(TMC)(O)2]+ couple is 1.5 × 105 mol-1 dm3 s-1 (I = 0.1 M) at 298 K. When trans-[RuVI(TMC)(O)2]2+ is in excess, the trans-[RuV(TMC)(O)2]+ species formed will undergo rapid disproportionation, 2trans-[Ruv(TMC)(O)2]+ + 2H+ → trans-[RuVI(TMC)(O)2]2+ + trans-[RuIV(TMC)O(H2O)]2+. The disproportionation follows the rate law: rate = Kdis[Ru(V)]2 with Kdis = 2keKp[H+]/(1 + Kp[H+])2. The Kp and ke are referred to the equilibrium constant and rate constant for the respective reactions, trans-[Ruv(TMC)(O)2]2+ + H+⇄ trans-[Ruv(TMC)O(OH)]2+ and trans-(Ruv(TMC)O(OH)]2+ + trans-[Ruv(TMC)(O)2]+ → trans-[RuVI(TMC)(O)2]2+ + trans-[RuIV(TMC)O(OH)]+. At 299 K and I = 0.1 M, Kp and kc have been determined to be 615 ± 50 mol-1 dm3 and (2.72 ± 0.34) × 106 mol-1 dm3 s-1, respectively. The self-exchange rate constant of the trans-[Ruv(TMC)O(OH)]2+/trans-[Ru IV(TMC)O(OH)]+ has been estimated to be 5 × 103 mol-1 dm3 s-1 at 298 K and I = 0.1 M.

Citation Format(s)

Proton-coupled electron-transfer reactions. Mechanisms of two-electron reduction of trans-dioxoruthenium(VI) to trans-aquooxoruthenium(VI) and disproportionate of trans-dioxoruthenium(V). / Che, Chi-Ming; Lau, Keung; Lau, Tai-Chu; Poon, Chung-Kwong.

In: Journal of the American Chemical Society, Vol. 112, No. 13, 20.06.1990, p. 5176-5181.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review