Characterization of the O2-Evolving Reaction Catalyzed by [(terpy)(H2O)MnIII(O)2MnIV(OH2)(terpy)](NO3)3 (terpy = 2,2‘:6,2‘ ‘-Terpyridine)
- 28 December 2000
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 123 (3), 423-430
- https://doi.org/10.1021/ja001090a
Abstract
The complex [(terpy)(H(2)O)Mn(III)(O)(2)Mn(IV)(OH(2))(terpy)](NO(3))(3) (terpy = 2,2':6,2' '-terpyridine) (1)catalyzes O(2) evolution from either KHSO(5) (potassium oxone) or NaOCl. The reactions follow Michaelis-Menten kinetics where V(max) = 2420 +/- 490 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 53 +/- 5 mM for oxone ([1] = 7.5 microM), and V(max) = 6.5 +/- 0.3 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 39 +/- 4 mM for hypochlorite ([1] = 70 microM), with first-order kinetics observed in 1 for both oxidants. A mechanism is proposed having a preequilibrium between 1 and HSO(5-) or OCl(-), supported by the isolation and structural characterization of [(terpy)(SO(4))Mn(IV)(O)(2)Mn(IV)(O(4)S)(terpy)] (2). Isotope-labeling studies using H(2)(18)O and KHS(16)O(5) show that O(2) evolution proceeds via an intermediate that can exchange with water, where Raman spectroscopy has been used to confirm that the active oxygen of HSO(5-) is nonexchanging (t(1/2) >> 1 h). The amount of label incorporated into O(2) is dependent on the relative concentrations of oxone and 1. (32)O(2):(34)O(2):(36)O(2) is 91.9 +/- 0.3:7.6 +/- 0.3:0.51 +/- 0.48, when [HSO(5-)] = 50 mM (0.5 mM 1), and 49 +/- 21:39 +/- 15:12 +/- 6 when [HSO(5-)] = 15 mM (0.75 mM 1). The rate-limiting step of O(2) evolution is proposed to be formation of a formally Mn(V)=O moiety which could then competitively react with either oxone or water/hydroxide to produce O(2). These results show that 1 serves as a functional model for photosynthetic water oxidation.Keywords
This publication has 30 references indexed in Scilit:
- Mechanism of Water Oxidation by the μ-Oxo Dimer [(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+Journal of the American Chemical Society, 2000
- Hydrogen Bonding in Metal Oxo Complexes: Synthesis and Structure of a Monomeric Manganese(III)−Oxo Complex and Its Hydroxo AnalogueJournal of the American Chemical Society, 2000
- Reversible Cleavage and Formation of the Dioxygen O-O Bond Within a Dicopper ComplexScience, 1996
- Designing Ligands for Oxidizing ComplexesAccounts of Chemical Research, 1994
- Air Oxidation of a Five-Coordinate Mn(III) Dimer to a High-Valent Oxomanganese(V) ComplexJournal of the American Chemical Society, 1994
- Pathways for water oxidation catalyzed by the (.mu.-oxo)bis[aquabis(bipyridine)ruthenium](4+) ionInorganic Chemistry, 1992
- Kinetic and equilibrium studies of the complexation of aqueous iron(III) by daunomycin, quinizarin, and quinizarin-2-sulfonateInorganic Chemistry, 1991
- Determination of sulphate isotopomers by vibrational spectroscopySpectrochimica Acta Part A: Molecular Spectroscopy, 1990
- Water oxidation by .mu.-oxobis[bis(bipyridine)oxoruthenium(V)](4+). An oxygen-labeling studyInorganic Chemistry, 1990
- The Measurement of Very Slow Reaction Rates; Decarboxylation of Alanine1aJournal of the American Chemical Society, 1958