Water oxidation by a mononuclear ruthenium catalyst: Characterization of the intermediates

Dmitry Polyansky, James Muckerman, Jonathan Rochford, Ruifa Zong, Randolph P. Thummel, Etsuko Fujita

Research output: Contribution to journalArticle

132 Citations (Scopus)

Abstract

A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [RuII-OH2] 2+ (Ru = Ru complex with one 4-t-butyl-2,6-di-(1′,8′- naphthyrid-2′-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H2 18O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [RuIV=O]2+ and [Ru IV-OO]2+. At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [RuIII-OH] 2+/[RuII-OH2]2+ couple, which is equal to or higher than the potential of the [RuIV=O] 2+/[RuIII-OH]2+ couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k1 = 2 × 104 M-1 s-1. While pH-independent oxidation of [RuIV=O]2+ takes place at 1420 mV vs NHE, bulk electrolysis of [RuII-OH2]2+ at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [RuII-OOH]+ over 2 weeks. While there remains some conflicting evidence, we have assigned this species as 1[RuIV2-OO]2+ based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer group (J. Am. Chem. Soc. 2010, 132, 1545-1557).

Original languageEnglish
Pages (from-to)14649-14665
Number of pages17
JournalJournal of the American Chemical Society
Volume133
Issue number37
DOIs
Publication statusPublished - Sep 21 2011

Fingerprint

Ruthenium
Oxidation
Catalysts
Water
Electrons
Electrospray Ionization Mass Spectrometry
Electrospray ionization
Picolines
Labeling
Pulse Radiolysis
Mass spectrometry
Ligands
Electrolysis
Electrochemistry
Raman Spectrum Analysis
Radiolysis
Oxidants
Protons
Pyridine
Cyclic voltammetry

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Water oxidation by a mononuclear ruthenium catalyst : Characterization of the intermediates. / Polyansky, Dmitry; Muckerman, James; Rochford, Jonathan; Zong, Ruifa; Thummel, Randolph P.; Fujita, Etsuko.

In: Journal of the American Chemical Society, Vol. 133, No. 37, 21.09.2011, p. 14649-14665.

Research output: Contribution to journalArticle

@article{14342b20c1074b458bf17b2cd40dbb1c,
title = "Water oxidation by a mononuclear ruthenium catalyst: Characterization of the intermediates",
abstract = "A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [RuII-OH2] 2+ (Ru = Ru complex with one 4-t-butyl-2,6-di-(1′,8′- naphthyrid-2′-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H2 18O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [RuIV=O]2+ and [Ru IV-OO]2+. At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [RuIII-OH] 2+/[RuII-OH2]2+ couple, which is equal to or higher than the potential of the [RuIV=O] 2+/[RuIII-OH]2+ couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k1 = 2 × 104 M-1 s-1. While pH-independent oxidation of [RuIV=O]2+ takes place at 1420 mV vs NHE, bulk electrolysis of [RuII-OH2]2+ at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [RuII-OOH]+ over 2 weeks. While there remains some conflicting evidence, we have assigned this species as 1[RuIV-·2-OO]2+ based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer group (J. Am. Chem. Soc. 2010, 132, 1545-1557).",
author = "Dmitry Polyansky and James Muckerman and Jonathan Rochford and Ruifa Zong and Thummel, {Randolph P.} and Etsuko Fujita",
year = "2011",
month = "9",
day = "21",
doi = "10.1021/ja203249e",
language = "English",
volume = "133",
pages = "14649--14665",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "37",

}

TY - JOUR

T1 - Water oxidation by a mononuclear ruthenium catalyst

T2 - Characterization of the intermediates

AU - Polyansky, Dmitry

AU - Muckerman, James

AU - Rochford, Jonathan

AU - Zong, Ruifa

AU - Thummel, Randolph P.

AU - Fujita, Etsuko

PY - 2011/9/21

Y1 - 2011/9/21

N2 - A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [RuII-OH2] 2+ (Ru = Ru complex with one 4-t-butyl-2,6-di-(1′,8′- naphthyrid-2′-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H2 18O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [RuIV=O]2+ and [Ru IV-OO]2+. At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [RuIII-OH] 2+/[RuII-OH2]2+ couple, which is equal to or higher than the potential of the [RuIV=O] 2+/[RuIII-OH]2+ couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k1 = 2 × 104 M-1 s-1. While pH-independent oxidation of [RuIV=O]2+ takes place at 1420 mV vs NHE, bulk electrolysis of [RuII-OH2]2+ at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [RuII-OOH]+ over 2 weeks. While there remains some conflicting evidence, we have assigned this species as 1[RuIV-·2-OO]2+ based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer group (J. Am. Chem. Soc. 2010, 132, 1545-1557).

AB - A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [RuII-OH2] 2+ (Ru = Ru complex with one 4-t-butyl-2,6-di-(1′,8′- naphthyrid-2′-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H2 18O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [RuIV=O]2+ and [Ru IV-OO]2+. At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [RuIII-OH] 2+/[RuII-OH2]2+ couple, which is equal to or higher than the potential of the [RuIV=O] 2+/[RuIII-OH]2+ couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k1 = 2 × 104 M-1 s-1. While pH-independent oxidation of [RuIV=O]2+ takes place at 1420 mV vs NHE, bulk electrolysis of [RuII-OH2]2+ at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [RuII-OOH]+ over 2 weeks. While there remains some conflicting evidence, we have assigned this species as 1[RuIV-·2-OO]2+ based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer group (J. Am. Chem. Soc. 2010, 132, 1545-1557).

UR - http://www.scopus.com/inward/record.url?scp=80052786655&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=80052786655&partnerID=8YFLogxK

U2 - 10.1021/ja203249e

DO - 10.1021/ja203249e

M3 - Article

C2 - 21815653

AN - SCOPUS:80052786655

VL - 133

SP - 14649

EP - 14665

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 37

ER -