Proton-coupled electron transfer in high-valent oxomanganese dimers: Role of the ancillary ligands

Rajesh Manchanda, H. Holden Thorp, Gary W. Brudvig, Robert H. Crabtree

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Abstract

The aqueous electrochemistry of selected binuclear mixed-valence oxo-bridged manganese clusters has been investigated. For [MnIIIMnIV(O)2(bpy)4]3+ (1, bpy = 2,2′-bipyridyl), it was observed that there is a substantial isotope effect (kH/kD = 4.3) for its electrochemical reduction, consistent with the proton-coupled electron transfer observed previously. Studies on [MnIIIMnIV-(O)2(edda)2]- (2, edda = ethylenediamine-N,N′-diacetate) show that the E1/2 values are also pH-dependent in a manner consistent with a one-proton/one-electron (slope of 0.07 ± 0.016 V/pH, R = 0.99) mechanism, as with 1. For [MnIIIMnIV(O)2(bispicen)2] 3+ (3, bispicen = N,N′-bis(2-methylpyridyl)ethane-1,2-diamine), similar measurements indicate an EC mechanism where the electron transfer and protonation are kinetically decoupled. The current response as a function of pH was measured to determine a pKa ∼ 8.35 for [MnIII 2(O)(OH)(bispicen)2]3+. Comparison of the electrochemical properties of 1-3 suggests that the proton-coupled mechanism is facilitated by low steric demand of the ancillary ligands and high basicity of the oxo bridges.

Original languageEnglish
Pages (from-to)494-497
Number of pages4
JournalInorganic Chemistry
Volume30
Issue number3
Publication statusPublished - 1991

ASJC Scopus subject areas

  • Inorganic Chemistry

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