A stable ruthenium(V) oxo complex. X-Ray crystal structure and oxidising properties of tetra-n-propylammonium bis-2-hydroxy-2-ethylbutyrato(oxo)-ruthenate(V)

Dengel, Andrew C.; Griffith, William P.; O'Mahoney, Caroline A.; Williams, David J.

doi:10.1039/c39890001720

Cited by 45 publications

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“…35 Its EPR spectrum was recorded at 20 K and found to be identical with the spectrum of the original report. 35 The XANES of Ru IV reference compound, ruthenium(IV) oxide, was measured to compare with that of blue dimer [3,3] and [3,4].…”

Section: Methodsmentioning

confidence: 98%

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

et al. 2012

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Catalytic O(2) evolution with cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+) (bpy is 2,2-bipyridine), the so-called blue dimer, the first designed water oxidation catalyst, was monitored by UV-vis, EPR, and X-ray absorption spectroscopy (XAS) with ms time resolution. Two processes were identified, one of which occurs on a time scale of 100 ms to a few seconds and results in oxidation of the catalyst with the formation of an intermediate, here termed [3,4]'. A slower process occurring on the time scale of minutes results in the decay of this intermediate and O(2) evolution. Spectroscopic data suggest that within the fast process there is a short-lived transient intermediate, which is a precursor of [3,4]'. When excess oxidant was used, a highly oxidized form of the blue dimer [4,5] was spectroscopically resolved within the time frame of the fast process. Its structure and electronic state were confirmed by EPR and XAS. As reported earlier, the [3,4]' intermediate likely results from reaction of [4,5] with water. While it is generated under strongly oxidizing conditions, it does not display oxidation of the Ru centers past [3,4] according to EPR and XAS. EXAFS analysis demonstrates a considerably modified ligand environment in [3,4]'. Raman measurements confirmed the presence of the O-O fragment by detecting a new vibration band in [3,4]' that undergoes a 46 cm(-1) shift to lower energy upon (16)O/(18)O exchange. Under the conditions of the experiment at pH 1, the [3,4]' intermediate is the catalytic steady state form of the blue dimer catalyst, suggesting that its oxidation is the rate-limiting step.

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Section: Methodsmentioning

confidence: 98%

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

et al. 2012

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“…EXAFS scan with 10 eV steps in the pre-edge region (21,967-22,102 eV), 1-eV steps (22,117 eV) through the edge and 0.05 Å À1 steps from k = 2.0-16 Å À1 were used. As reference compounds for high Ru oxidation states, Ru IV and Ru V , Ru IV oxide and tetra-n-propylammonium bis-2-hydroxy-2-ethylbutyrato(oxo) ruthenate(V) [22] were used.…”

Section: Ru K-edge X-ray Absorption Spectroscopy Measurementsmentioning

confidence: 99%

Unexpected ligand lability in condition of water oxidation catalysis

Yan

Zong

Pushkar

2015

Journal of Catalysis

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a b s t r a c tIn the search for rational design of improved water oxidation catalysts, enhanced catalytic activities were reported for single site Ru catalysis with Ru-iodide coordination. As these complexes are not initially capable of proton coupled electron transfer (PCET) and Ru@O formation, a proposal was put forward on the generation of catalytically active 7-coordinate Ru species. We tested this hypothesis by EPR and X-ray spectroscopy and found that [Ru II (bpy)(tpy)I] + only serves as a precursor for the formation of [Ru IV (bpy)(tpy)@O] 2+ . Upon oxidation with excess of Ce IV the RuAI bond quickly dissociates with the formation of [Ru III (bpy)(tpy)H 2 O] 3+ and [Ru IV (bpy)(tpy)@O] 2+ complexes. The catalytic steady state was composed of 95% [Ru IV (bpy)(tpy)@O] 2+ species. Thus, introducing the RuAI bond into initial catalysts does not serve to improve catalyst design. This manuscript also shows how EXAFS can directly probe transition metal-halogen interaction for in situ catalysis.

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“…The reaction mixtures were fast-freeze quenched into a precooled pentane bath (−120°C) using an SFM 20 Stopped-Flow System (Bio-Logic) equipped with an umbilical connector with a built-in ejection nozzle. For isotopic exchange, BD [3,3] was dissolved in 98% O 18 water and 60% 17 O water (Icon) and incubated for 24 h. The Ru V = O reference, tetran-propylammonium bis-2-hydroxy-2ethylbutyrato(oxo) ruthenate (V), was prepared as described by Dengel et al (49). Its EPR spectrum was recorded at 20 K and found to be identical to the spectrum of the original report (49).…”

Section: Methodsmentioning

confidence: 99%

Experimental demonstration of radicaloid character in a Ru^V=O intermediate in catalytic water oxidation

Moonshiram

Alperovich

Concepcion

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Water oxidation is the key half reaction in artificial photosynthesis. An absence of detailed mechanistic insight impedes design of new catalysts that are more reactive and more robust. A proposed paradigm leading to enhanced reactivity is the existence of oxyl radical intermediates capable of rapid water activation, but there is a dearth of experimental validation. Here, we show the radicaloid nature of an intermediate reactive toward formation of the O-O bond by assessing the spin density on the oxyl group by Electron Paramagnetic Resonance (EPR). In the study, an ) in the process of natural photosynthesis with the help of an Mn 4 Ca cluster catalyst embedded in a protein environment (1). Understanding the mechanism of water oxidation is critical for development of alternative energy solutions based on the concept of artificial photosynthesis.With the aim of uncovering the mechanism of water oxidation, the oxygen evolving complex (OEC) of Photosystem II has been intensively studied by X-Ray Diffraction (XRD) (3-5) and multiple spectroscopic (6-10) and computational approaches (1,(11)(12)(13)(14)(15). Intriguingly, Density Functional Theory (DFT) analysis of the reaction barrier for water oxidation in the OEC has shown that formation of the Mn-O • radicaloid intermediate is necessary to reproduce the experimentally observed activation energy (11,(16)(17)(18)(19). Several experimental observations are suggestive of the formation of the Mn-O • radicaloid as a species capable of reacting with H 2 O with formation of an O-O bond (6, 7), but to the best of our knowledge, no direct experimental demonstration has been reported. The experimental difficulty is in the short lifetime of the S 3 state in the OEC in the Kok cycle for which formation of the Mn-O • radicaloid fragment has been proposed (7,12,20), which given its high spin state, makes EPR measurements particularly challenging.Several Ru-based complexes have been developed as defined molecular catalysts for water oxidation (21)(22)(23)(24)(25)(26)(27) 4+ [bpy is 2,2-bipyridine], shares similarities with the OEC, because they both undergo oxidative activation by proton-coupled electron transfer to reach higher oxidation states where water oxidation occurs (21-24). It is also the most studied catalyst for which experimental data on the reaction mechanism for water oxidation are available. The results over the past 30 years are summarized in Fig. 1. BD Results and DiscussionThe BD catalyst intermediates BD [4,5] and BD [5,5], which are reactive to water, were characterized in previous studies (29,(35)(36)(37) and are characterized in more detail in this work. BD [4,5] (Fig. 2A). Extended X-Ray Absorption Fine Structure (EXAFS) analysis showed a short Ru = O bond (Fig. 2B, Table 1, and Table S1). The protonation state of the Ru IV center in BD [4,5] Fig. S1, and Table S1). To further assess the protonation states of BD [4,5], resonance Raman measurements were carried out on frozen BD [4,5] samples prepared by stopped-flow freeze quench of BD [3,4] mixed with 2...

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A stable ruthenium(V) oxo complex. X-Ray crystal structure and oxidising properties of tetra-n-propylammonium bis-2-hydroxy-2-ethylbutyrato(oxo)-ruthenate(V)

Cited by 45 publications

References 0 publications

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

Unexpected ligand lability in condition of water oxidation catalysis

Experimental demonstration of radicaloid character in a Ru^V=O intermediate in catalytic water oxidation

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A stable ruthenium(V) oxo complex. X-Ray crystal structure and oxidising properties of tetra-n-propylammonium bis-2-hydroxy-2-ethylbutyrato(oxo)-ruthenate(V)

Cited by 45 publications

References 0 publications

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

Structure and Electronic Configurations of the Intermediates of Water Oxidation in Blue Ruthenium Dimer Catalysis

Unexpected ligand lability in condition of water oxidation catalysis

Experimental demonstration of radicaloid character in a RuV=O intermediate in catalytic water oxidation

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Experimental demonstration of radicaloid character in a Ru^V=O intermediate in catalytic water oxidation