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Masayuki Yagi - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of photoisomerization and water Oxidation Catalysis of mononuclear ruthenium ii monoaquo complexes
Inorganic Chemistry, 2013Co-Authors: Masanari Hirahara, Hirosato Yamazaki, Manabu Komi, Mehmed Z Ertem, Christopher J Cramer, Masayuki YagiAbstract:A ligation of Ru(tpy)Cl3 (tpy = 2,2′:6′,2″-terpyridine) with 2-(2-pyridyl)-1,8-naphthyridine) (pynp) in the presence of LiCl gave distal-[Ru(tpy)(pynp)Cl]+ (d-1Cl) selectively, whereas the ligation gave proximal-[Ru(tpy)(pynp)OH2]2+ (p-1H2O) selectively in the absence of halide ions. (The proximal/distal isomers were defined by the structural configuration between the 1,8-naphthyridine moiety and the aquo or chloro ligand.) An aquation reaction of d-1Cl quantitatively afforded distal-[Ru(tpy)(pynp)OH2]2+ (d-1H2O) in water, and d-1H2O is quantitatively photoisomerized to p-1H2O. The mechanism of the photoisomerization was investigated by transient absorption spectroscopy and quantum chemical calculations. The temperature dependence of the transient absorption spectral change suggests existence of the thermally activated process from the 3MLCT state with the activation energy (ΔE = 49 kJ mol–1), which is close to that (41.7 kJ mol–1) of the overall photoisomerization reaction. However, quantum chemical calc...
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stoichiometric photoisomerization of mononuclear ruthenium ii monoaquo complexes controlling redox properties and water Oxidation Catalysis
Journal of the American Chemical Society, 2011Co-Authors: Hirosato Yamazaki, Tomoya Hakamata, Manabu Komi, Masayuki YagiAbstract:Although various reactions involved in photoexcited states of polypyridyl ruthenium(II) complexes have been extensively studied, photoisomerization of the complexes is very rare. We report the first illustration of stoichiometric photoisomerization of trans-[Ru(tpy)(pynp)OH2]2+ (1a) [tpy = 2,2′:6′,2′′-terpyridine; pynp = 2-(2-pyridyl)-1,8-naphthyridine] to cis-[Ru(tpy)(pynp)OH2]2+ (1a′) and the isolation of 1a and 1a′ for X-ray crystallographic analysis. Polypyridyl ruthenium(II) aquo complexes are attracting much attention related to proton-coupled electron transfer and water Oxidation Catalysis. We demonstrate that the photoisomerization significantly controls the redox reactions and water Oxidation catalyses involving the ruthenium(II) aquo complexes 1a and 1a′.
Daniel G Nocera - One of the best experts on this subject based on the ideXlab platform.
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Water Oxidation Catalysis by Co(II) Impurities in Co(III)4O4 Cubanes
2015Co-Authors: Andrew M. Ullman, David C. Powers, Yi Liu, Michael Huynh, Kwabena D. Bediako, Hongsen Wang, Bryce L. Anderson, John J. Breen, Héctor D. Abruña, Daniel G NoceraAbstract:The observed water Oxidation activity of the compound class Co4O4(OAc)4(Py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water Oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water Oxidation activity that has been reported for Co4O4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials and demonstrate that such electrode materials should be used with caution for the study of water Oxidation Catalysis
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water Oxidation Catalysis by co ii impurities in co iii 4o4 cubanes
Journal of the American Chemical Society, 2014Co-Authors: Andrew M Ullman, David C. Powers, Yi Liu, Michael Huynh, Kwabena D. Bediako, Hongsen Wang, Bryce L. Anderson, John J. Breen, Hector D Abruna, Daniel G NoceraAbstract:The observed water Oxidation activity of the compound class Co4O4(OAc)4(Py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water Oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water Oxidation activity that has been reported for Co4O4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials and demonstrate that such electrode materials should be used with caution for the study of water Oxidation Catalysis.
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structure and valency of a cobalt phosphate water Oxidation catalyst determined by in situ x ray spectroscopy
Journal of the American Chemical Society, 2010Co-Authors: Matthew W Kanan, Yogesh Surendranath, Mircea Dinca, Junko Yano, Vittal K Yachandra, Daniel G NoceraAbstract:A water Oxidation catalyst generated via electrodeposition from aqueous solutions containing phosphate and Co2+ (Co−Pi) has been studied by in situ X-ray absorption spectroscopy. Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water Oxidation Catalysis and at open circuit. Extended X-ray absorption fine structure (EXAFS) spectra indicate the presence of bis-oxo/hydroxo-bridged Co subunits incorporated into higher nuclearity clusters in Co−Pi. The average cluster nuclearity is greater in a relatively thick film (∼40−50 nmol Co ions/cm2) deposited at 1.25 V vs NHE than in an extremely thin film (∼3 nmol Co ions/cm2) deposited at 1.1 V. X-ray absorption near edge structure (XANES) spectra and electrochemical data support a Co valency greater than 3 for both Co−Pi samples when catalyzing water Oxidation at 1.25 V. Upon switching to open circuit, Co−Pi undergoes a continuous reduction due to residual water Oxidation Catalysis, as indicated by the negative s...
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epr evidence for co iv species produced during water Oxidation at neutral ph
Journal of the American Chemical Society, 2010Co-Authors: Gregory J Mcalpin, Yogesh Surendranath, Mircea Dinca, Troy A Stich, Sebastian A Stoian, William H Casey, Daniel G Nocera, David R BrittAbstract:Thin-film water Oxidation catalysts (Co−Pi) prepared by electrodeposition from phosphate electrolyte and Co(NO3)2 have been characterized by electron paramagnetic resonance (EPR) spectroscopy. Co−Pi catalyst films exhibit EPR signals corresponding to populations of both Co(II) and Co(IV). As the deposition voltage is increased into the region where water Oxidation prevails, the population of Co(IV) rises and the population of Co(II) decreases. The changes in the redox speciation of the film can also be induced, in part, by prolonged water Oxidation Catalysis in the absence of additional catalyst deposition. These results provide spectroscopic evidence for the formation of Co(IV) species during water Oxidation Catalysis at neutral pH.
Robert H Crabtree - One of the best experts on this subject based on the ideXlab platform.
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the stability of organometallic ligands in Oxidation Catalysis
Journal of Organometallic Chemistry, 2014Co-Authors: Robert H CrabtreeAbstract:Abstract Organometallic precatalysts are increasingly applied to Oxidation Catalysis, where the spectator character of such ligands as Cp and Cp* is often assumed without definite proof. A number of reports of ligand lability under oxidative conditions have now appeared in the literature, raising concerns in reactions where primary oxidants are present. In such a case, partial or complete degradative loss of the organometallic ligand from the metal may need to be considered. This loss can sometimes deactivate a catalyst but it may also activate it by opening up labile sites at the metal. The highest risk applies to Oxidation of the least reactive substrates, such as alkanes, since the catalyst may then also oxidize the CH bonds of its own ligands. More reactive substrates such as alkenes are likely to provide greater stabilization to the catalysts by providing a pathway for faster reaction of the substrate with the oxidized form of the catalyst. We therefore look at these and some related reactions to probe organometallic ligand loss under oxidative conditions, a topic that has received too little attention considering its important implications. Ligand loss can also affect applications to asymmetric Catalysis and heterogenized homogeneous catalysts where the organometallic ligand is functionalized with a homochiral substituent or a tether to a surface. Ligands covered include CO, alkyls, aryls, alkenes, arenes, NHCs, cyclopentadienyls and other soft ligands.
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precursor transformation during molecular Oxidation Catalysis with organometallic iridium complexes
Journal of the American Chemical Society, 2013Co-Authors: Ulrich Hintermair, Alexander R Parent, Stafford W Sheehan, Daniel H Ess, David T Richens, Patrick H Vaccaro, Gary W Brudvig, Robert H CrabtreeAbstract:We present evidence for Cp* being a sacrificial placeholder ligand in the [Cp*IrIII(chelate)X] series of homogeneous Oxidation catalysts. UV–vis and 1H NMR profiles as well as MALDI-MS data show a rapid and irreversible loss of the Cp* ligand under reaction conditions, which likely proceeds through an intramolecular inner-sphere Oxidation pathway reminiscent of the reductive in situ elimination of diolefin placeholder ligands in hydrogenation Catalysis by [(diene)MI(L,L′)]+ (M = Rh and Ir) precursors. When oxidatively stable chelate ligands are bound to the iridium in addition to the Cp*, the oxidized precursors yield homogeneous solutions with a characteristic blue color that remain active in both water- and CH-Oxidation Catalysis without further induction period. Electrophoresis suggests the presence of well-defined Ir-cations, and TEM-EDX, XPS, 17O NMR, and resonance-Raman spectroscopy data are most consistent with the molecular identity of the blue species to be a bis-μ-oxo di-iridium(IV) coordination...
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comparison of primary oxidants for water Oxidation Catalysis
Chemical Society Reviews, 2013Co-Authors: Alexander R Parent, Robert H Crabtree, Gary W BrudvigAbstract:In this tutorial review, we compare chemical oxidants for driving water-Oxidation catalysts, focusing on the advantages and disadvantages of each oxidant.
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particle formation during Oxidation Catalysis with cp iridium complexes
Journal of the American Chemical Society, 2012Co-Authors: Ulrich Hintermair, Sara M Hashmi, Menachem Elimelech, Robert H CrabtreeAbstract:Real-time monitoring of light scattering and UV–vis profiles of four different Cp*IrIII precursors under various conditions give insight into nanoparticle formation during Oxidation Catalysis with NaIO4 as primary oxidant. Complexes bearing chelate ligands such as 2,2′-bipyridine, 2-phenylpyridine, or 2-(2′-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and Oxidation Catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*2Ir2(μ-OH)3]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV–vis data with light scattering profiles revealed that the formation of a deep purple-blue color (∼580 nm) is not indicative of particle formation during Oxidation Catalysis with molecular iridium precursors as suggested previously.
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half sandwich iridium complexes for homogeneous water Oxidation Catalysis
Journal of the American Chemical Society, 2010Co-Authors: James D Blakemore, Gary W Brudvig, Nathan D Schley, David Balcells, Jonathan F Hull, Gerard Olack, Christopher D Incarvito, Odile Eisenstein, Robert H CrabtreeAbstract:Iridium half-sandwich complexes of the types Cp*Ir(N−C)X, [Cp*Ir(N−N)X]X, and [CpIr(N−N)X]X are catalyst precursors for the homogeneous Oxidation of water to dioxygen. Kinetic studies with cerium(IV) ammonium nitrate as primary oxidant show that oxygen evolution is rapid and continues over many hours. In addition, [Cp*Ir(H2O)3]SO4 and [(Cp*Ir)2(μ-OH)3]OH can show even higher turnover frequencies (up to 20 min−1 at pH 0.89). Aqueous electrochemical studies on the cationic complexes having chelate ligands show catalytic Oxidation at pH > 7; conversely, at low pH, there are no Oxidation waves up to 1.5 V vs NHE for the complexes. H218O isotope incorporation studies demonstrate that water is the source of oxygen atoms during cerium(IV)-driven Catalysis. DFT calculations and kinetic experiments, including kinetic-isotope-effect studies, suggest a mechanism for homogeneous iridium-catalyzed water Oxidation and contribute to the determination of the rate-determining step. The kinetic experiments also help distin...
Richard G Finke - One of the best experts on this subject based on the ideXlab platform.
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electrochemically driven water Oxidation Catalysis beginning with six exemplary cobalt polyoxometalates is it molecular homogeneous Catalysis or electrode bound heterogeneous coo x Catalysis
Journal of the American Chemical Society, 2018Co-Authors: Scott J Folkman, Joaquin Sorianolopez, Jose Ramon Galanmascaros, Richard G FinkeAbstract:A series of six exemplary cobalt-polyoxometalate (Co-POM) precatalysts have been examined to determine if they are molecular water-Oxidation catalysts (WOCatalysts) or if, instead, they actually form heterogeneous, electrode-bound CoOx as the true WOCatalyst under electrochemically driven water-Oxidation Catalysis (WOCatalysis) conditions. Specifically, WOCatalysis derived from the following six Co-POMs has been examined at pH 5.8, 8.0, and 9.0: [Co4(H2O)2(PW9O34)2]10– (Co4P2W18), [Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]16– (Co9P5W27), [ββ-Co4(H2O)2(P2W15O56)2]16– (Co4P4W30), [Co(H2O)PW11O39]5– (CoPW11), [α1-Co(H2O)P2W17O61]8– (α1-CoP2W17), and [α2-Co(H2O)P2W17O61]8– (α2-CoP2W17). The amount of Co(II)aq in 500 μM solutions of each Co-POM was measured after 3 h of aging as well as from t = 0 for pH = 5.8 and 8.0 by μM sensitive Co(II)aq-induced 31P NMR line broadening and at pH = 9.0 by cathodic stripping. The amount of detectable Co(II)aq after 3 h for the six Co-POMs ranges from ∼0.25 to ∼90% of the total cobalt...
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distinguishing homogeneous from heterogeneous water Oxidation Catalysis when beginning with polyoxometalates
ACS Catalysis, 2014Co-Authors: Jordan J Stracke, Richard G FinkeAbstract:Polyoxometalates (POMs) have been proposed to be excellent homogeneous water Oxidation catalysts (WOCs) due to their oxidative stability and activity. However, recent literature indicates that even these relatively robust compounds can be transformed into heterogeneous, metal-oxide WOCs under the oxidizing reaction conditions needed to drive O2 evolution. This review covers the experimental methodology for distinguishing homogeneous and heterogeneous WOCs; it then addresses the “what is the true catalyst?” problem for POMs used as precatalysts in the Oxidation of water to O2. These results are also compared to the broader WOC literature. The primary findings in this review are the following: (1) Multiple, complementary experiments are needed to determine the true catalyst, including determination of catalyst stability, speciation, and kinetics under operating conditions. (2) Controls with hypothetical heterogeneous metal-oxide catalysts are required to determine their kinetic competence in the reaction an...
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electrocatalytic water Oxidation beginning with the cobalt polyoxometalate co4 h2o 2 pw9o34 2 10 identification of heterogeneous coox as the dominant catalyst
Journal of the American Chemical Society, 2011Co-Authors: Jordan J Stracke, Richard G FinkeAbstract:The question of “what is the true catalyst?” when beginning with the cobalt polyoxometalate (POM) [Co4(H2O)2(PW9O34)2]10– in electrochemical water Oxidation Catalysis is examined in pH 8.0 sodium phosphate buffer at a glassy carbon electrode. Is [Co4(H2O)2(PW9O34)2]10– a true water Oxidation catalyst (WOC), or just a precatalyst? Electrochemical, kinetic, UV–vis, SEM, EDX, and other data provide four main lines of compelling evidence that, under the conditions used herein, the dominant WOC is actually heterogeneous CoOx and not homogeneous [Co4(H2O)2(PW9O34)2]10–.
Seth M Cohen - One of the best experts on this subject based on the ideXlab platform.
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reusable Oxidation Catalysis using metal monocatecholato species in a robust metal organic framework
ChemInform, 2014Co-Authors: Honghan Fei, Jaewook Shin, Ying Shirley Meng, Mario Adelhardt, Joerg Sutter, Karsten Meyer, Seth M CohenAbstract:UiO-66 metal-organic framework, modified with catechol-substructures and metalated with Cr provides an efficient, completely recyclable and reusable catalyst for Oxidation of alcohols to ketones.
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reusable Oxidation Catalysis using metal monocatecholato species in a robust metal organic framework
Journal of the American Chemical Society, 2014Co-Authors: Honghan Fei, Jaewook Shin, Ying Shirley Meng, Mario Adelhardt, Joerg Sutter, Karsten Meyer, Seth M CohenAbstract:An isolated metal-monocatecholato moiety has been achieved in a highly robust metal-organic framework (MOF) by two fundamentally different postsynthetic strategies: postsynthetic deprotection (PSD) and postsynthetic exchange (PSE). Compared with PSD, PSE proved to be a more facile and efficient functionalization approach to access MOFs that could not be directly synthesized under solvothermal conditions. Metalation of the catechol functionality residing in the MOFs resulted in unprecedented Fe-monocatecholato and Cr-monocatecholato species, which were characterized by X-ray absorption spectroscopy, X-band electron paramagnetic resonance spectroscopy, and (57)Fe Mossbauer spectroscopy. The resulting materials are among the first examples of Zr(IV)-based UiO MOFs (UiO = University of Oslo) with coordinatively unsaturated active metal centers. Importantly, the Cr-metalated MOFs are active and efficient catalysts for the Oxidation of alcohols to ketones using a wide range of substrates. Catalysis could be achieved with very low metal loadings (0.5-1 mol %). Unlike zeolite-supported, Cr-exchange Oxidation catalysts, the MOF-based catalysts reported here are completely recyclable and reusable, which may make them attractive catalysts for 'green' chemistry processes.
