Insights into the Mechanism of Photocatalytic Water Reduction by DFT‐Supported In Situ EPR/Raman Spectroscopy

Hollmann, Dirk; Gärtner, Felix; Ludwig, Ralf; Barsch, Enrico; Junge, Henrik; Blug, Matthias; Hoch, Sascha; Beller, Matthias; Brückner, Angelika

doi:10.1002/anie.201103710

Cited by 65 publications

(50 citation statements)

References 49 publications

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“…For each half reaction, one example involving the use of EPR spectroscopy is discussed in this subchapter. An important example of water reduction in which EPR spectroscopy has been used in combination with Raman Spectroscopy and DFT studies has been published by Ludwig et al [103]. The catalytic system consists of the iridium complex [Ir(ppy) 2 -(bpy)]PF 6 (ppy = 2-phenylpyridine, bpy = 2,2 0 -bipyridine) used as a photosensitizer (IrPS), [Fe 3 (CO) 12 ] as the water-reduction catalyst (WRC), and triethylamine (TEA) as a sacrificial reductant.…”

Section: Photocatalytic Water Splittingmentioning

confidence: 99%

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

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In the context of homogeneous catalysis, openshell systems are often quite challenging to characterize. Nuclear magnetic resonance (NMR) spectroscopy is the most frequently applied tool to characterize organometallic compounds, but NMR spectra are usually broad, difficult to interpret and often futile for the study of paramagnetic compounds. As such, electron paramagnetic resonance (EPR) has proven itself as a useful spectroscopic technique to characterize paramagnetic complexes and reactive intermediates. EPR spectroscopy is a particularly useful tool to investigate their electronic structures, which is fundamental to understand their reactivity. This paper describes some selected examples of studies where EPR spectroscopy has been useful for the characterization of open-shell organometallic complexes. The paper concentrates in particular on systems where EPR spectroscopy has proven useful to understand catalytic reaction mechanisms involving paramagnetic organometallic catalysts. The expediency of EPR spectroscopy in the study of organometallic chemistry and homogenous catalysis is contextualized in the introductory Sect. 1. Section 2 of the review focusses on examples of C-C and C-N bond formation reactions, with an emphasis on catalytic reactions where ligand/substrate non-innocence plays an important role. Both carbon and nitrogen centered radicals have been shown to play an important role in these reactions. A few selected examples of catalytic alcohol oxidation proceeding via related N-centered ligand radicals are included in this section as well. Section 3 covers examples of the use of EPR spectroscopy to study important commercial ethylene oligomerization and polymerization processes. In Sect. 4 the use of EPR spectroscopy to understand the mechanisms of Atom Transfer Radical Polymerization is discussed. While this review focusses predominantly on the application of EPR spectroscopy in mechanistic studies of C-C and C-N bond formation reactions mediated by organometallic catalysts, a few selected examples describing the application of EPR spectroscopy in other catalytic reactions such as water splitting, photo-catalysis, photo-redox-catalysis and related reactions in which metal initiated (free) radical formation plays a role are included as well. EPR spectroscopic investigation in this area of research are dominated by EPR spectroscopic studies in isotropic solution, including spin trapping experiments. These reactions are highlighted in Sect. 5. EPR spectroscopic studies have proven useful to discern the correct oxidation states of the active catalysts and also to determine the effective concentrations of the active species. EPR is definitely a spectroscopic technique that is indispensable in understanding the reactivity of paramagnetic complexes and in conjunction with other advanced techniques such as X-ray absorption spectroscopy and pulsed laser polymerization it will continue to be a very practical tool.

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Section: Photocatalytic Water Splittingmentioning

confidence: 99%

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

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“…In the present work, we have explored ground and excited state properties of a series of Ir-based photosensitizers, which are derivatives of the parent IrPS extensively investigated before in catalytic, spectroscopic, and theoretical studies [11,[21][22][23][24][25][26][27][28][29][30][31][32][33]. To facilitate an accurate description of the excited states, the optimally-tuned range-separated density functional approach has been chosen.…”

Section: Discussionmentioning

confidence: 99%

Chemical Tuning and Absorption Properties of Iridium Photosensitizers for Photocatalytic Applications

et al. 2017

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“…These comprehensive mechanistic studies included Raman, NMR, EPR, in situ, as well as operando FTIR spectroscopy and DFT calculations [159]. In particular, the trimeric complex [HFe 3 (CO) 11 4 ] − (M11), which acts as a resting state [160,161]. Deactivation pathways during catalysis are both CO release from the WRC mediated by light irradiation and the decomposition of the Ir-PS especially at high PS/WRC ratios.…”

Section: Improving Mechanistic Understanding By An Approach Of Combinmentioning

confidence: 99%

“…The reverse reaction from M11 to M7 and reactivation of the WRC are mediated by irradiation [76,160,161,163].…”

Section: Improving Mechanistic Understanding By An Approach Of Combinmentioning

confidence: 99%

Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes

et al. 2017

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Photocatalytic hydrogen generation is considered to be attractive due to its combination of solar energy conversion and storage. Currently-used systems are either based on homogeneous or on heterogeneous materials, which possess a light harvesting and a catalytic subunit. The subject of this review is a brief summary of homogeneous proton reduction systems using sacrificial agents with special emphasis on non-noble metal systems applying convenient iron(0) sources. Iridium photosensitizers, which were proven to have high quantum yields of up to 48% (415 nm), have been employed, as well as copper photosensitizers. In both cases, the addition or presence of a phosphine led to the transformation of the iron precursor with subsequently increased activities. Reaction pathways were investigated by photoluminescence, electron paramagnetic resonance (EPR), Raman, FTIR and mass spectroscopy, as well as time-dependent DFT-calculations. In the future, this knowledge will set the basis to design photo(electro)chemical devices with tailored electron transfer cascades and without the need for sacrificial agents.

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Insights into the Mechanism of Photocatalytic Water Reduction by DFT‐Supported In Situ EPR/Raman Spectroscopy

Cited by 65 publications

References 49 publications

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

Chemical Tuning and Absorption Properties of Iridium Photosensitizers for Photocatalytic Applications

Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes

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