8 research outputs found
Iron and iridium molecular complex for water oxidation catalysis
Harness light from the sun is one of the 21st centuryâs major goals towards the substitution of fossil fuels for a renewable source of energy. Sustainable production of highly energetic molecules using sunlight as energy source can provide a recyclable fuel round the clock. In this regard, hydrogen from water is envisioned as an ideal cofactor as this energetic store. Viable production of solar fuels will require the use of earth-abundant based catalysts with high activity and efficiency. Long ago, Nature figured out how to take advantage of the sunlight by converting solar energy into chemical bonds, through water and carbon dioxide. This process has been perfected during millions of years and the development of an artificial system to replicate the natural photosynthesis is extremely challenging. Towards the design of these energy conversion schemes based on sunlight, CO2 and H2O, a key step is the water oxidation. The water oxidation provides the electrons needed for the production of fuel. An efficient catalyst is required to overcome the uphill energy multi-electron transformation. The main objective of this thesis is the design of artificial compounds that efficiently oxidizes water into O2, protons and electrons, as the first step towards the exploitation of the sunlight. The study of these complexes could contribute with valuable information about the oxidation mechanisms taking place during the photosynthesis. The results obtained in this thesis firstly show that readily available iron and iridium complexes can carry out the water oxidation in an efficient manner. Homogeneous high valent metal species (IrV/VI, FeV) are the responsible of this redox process. Furthermore, the characterization of a novel oxo-bridged iron-cerium complex constitutes the first direct observation of a heterodimetallic core in a synthetic water oxidation catalyst. These species can be construed as the closest structural and functional model for the essential heterodimetallic MnVâOâCaII center involved in the water oxidation in PSII.Lâaprofitament de la llum solar com a font dâenergia Ă©s un dels objectius mĂ©s prometedors alhora de substituir els combustibles fĂČssils per una font dâenergia renovable. La producciĂł sostenible de molĂšcules energĂštiques mitjançant la llum del sol pot proporcionar un combustible reciclable durant les 24 hores del dia. En aquest aspecte, lâhidrogen obtingut de lâaigua sâentreveu com un cofactor ideal per aquest emmagatzematge energĂštic. LâĂșs de catalitzadors basats en materials abundants i amb una activitat i eficiĂšncia elevades seran elements indispensables per a la producciĂł viable de combustibles solars. La natura va ser capaç de trobar un mecanisme per aprofitar lâenergia solar convertint-la en enllaços quĂmics mitjançant aigua i diĂČxid de carboni. Aquest procĂ©s ha sigut perfeccionat al llarg de milions dâanys i conseqĂŒentment, el desenvolupament de sistemes artificials capaços dâimitar la fotosĂntesi natural Ă©s extremadament complex. De camĂ cap al disseny de sistemes per a la conversiĂł dâenergia basats en la llum solar, el CO2 i lâH2O, un pas clau Ă©s lâetapa dâoxidaciĂł de lâaigua. Aquesta etapa proporciona els electrons necessaris per la producciĂł de combustible. La presĂšncia dâun catalitzador Ă©s necessĂ ria per superar aquesta transformaciĂł multielectrĂČnica, ja que requereix una elevada energia. Lâobjectiu principal dâaquesta tesi Ă©s el disseny de compostos artificials que oxidin lâaigua i alliberin oxigen, protons i electrons de manera eficient, com a primer pas cap a lâexplotaciĂł de la llum. Lâestudi dâaquests complexos pot contribuir amb informaciĂł valuosa sobre el mecanisme dâoxidaciĂł que tenen lloc durant la fotosĂntesi. Els resultats obtinguts en aquesta tesi mostren que complexos de ferro i iridi fĂ cilment a lâabat sĂłn capaços de catalitzar lâoxidaciĂł de lâaigua de manera eficient. EspĂšcies homogĂšnies en alts estat dâoxidaciĂł (IrV/VI, FeV) sĂłn les responsables de dur a terme aquest procĂ©s redox. La caracteritzaciĂł dâun nou dĂmer de ferro-ceri unit per un pont oxo constitueix la primera observaciĂł directa dâun centre heterodimetĂ lâąlic en un catalitzador artificial dâoxidaciĂł de lâaigua. Aquesta espĂšcie constitueix el model estructural i funcional mĂ©s semblant al centre de MnV-O-CaII present en el PSII
Spectroscopic, electrochemical and computational characterization of Ru species involved in catalytic water oxidation. Evidence for a [RuV(O)(Py2Metacn)] intermediate.
A new family of ruthenium complexes based on the Nâpentadentate ligand Py2Metacn (NâmethylâNâČ,NâČâČâbis(2âpicolyl)â1,4,7âtriazacyclononane) has been synthesised and its catalytic activity has been studied in the waterâoxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO4) to generate the WO intermediates [RuII(OH2)(Py2Metacn)]2+, [RuIII(OH2)(Py2Metacn)]3+, [RuIII(OH)(Py2Metacn)]2+ and [RuIV(O)(Py2Metacn)]2+, which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [RuIV(O)(Py2Metacn)]2+ has a long halfâlife (>48â
h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, 18Oâlabelling and theoretical studies, and the conclusion is that the rateâdetermining step is a singleâsite water nucleophilic attack on a metalâoxo species. Moreover, [RuIV(O)(Py2Metacn)]2+ is proposed to be the resting state under catalytic conditions. By monitoring CeIV consumption, we found that the O2 evolution rate is redoxâcontrolled and independent of the initial concentration of CeIV. Based on these facts, we propose herein that [RuIV(O)(Py2Metacn)]2+ is oxidised to [RuV(O)(Py2Metacn)]2+ prior to attack by a water molecule to give [RuIII(OOH)(Py2Metacn)]2+. Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH2)(Py2Metacn)]2+ (M=Ru, Fe) complexes is due to the difference in the redox stability of the key MV(O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions
Catalizadores para la conversiĂłn de la energĂa solar en enlaces quĂmicos
El desarrollo de mĂ©todos sintĂ©ticos limpios y sostenibles que utilicen la luz solar como fuente de energĂa sin
comprometer el medio ambiente ni los recursos naturales
del planeta es un gran reto cientĂfico y tecnolĂłgico. Actualmente nuestra sociedad se nutre principalmente de
energĂa y compuestos quĂmicos derivados del carbĂłn, gas
natural y petróleo. Estas materias primas no son renovables, pues provienen de procesos fotosintéticos llevados
a cabo desde el cĂĄmbrico y su posterior transformaciĂłn
geolĂłgica. AdemĂĄs, su uso intensivo como vector energĂ©tico durante los Ășltimos 200 años (Figura 1) ha elevado la
concentraciĂłn de CO2
en la atmosfera de 280 a 400 ppm,
posiblemente una de las causas del cambio climĂĄtico.[1]
La transformaciĂłn de la energĂa solar (renovable,
abundante y econĂłmica) en energĂa quĂmica es una de
las alternativas mĂĄs atractivas; pues la tierra recibe anualmente 20.000 veces mĂĄs energĂa de la que consume la sociedad. Este tipo de energĂa ofrece la ventaja de poder ser
fĂĄcilmente almacenada y transportada, pudiendo ser utilizada segĂșn la demanda. Un ejemplo de su potencial lo
demuestran las plantas y algas verdes, que producen compuestos quĂmicos de alto valor energĂ©tico a partir de luz
solar, H2
O y CO2
en condiciones de temperatura y presiĂłn
ambiente.[2] Este proceso de captura y conversiĂłn de luz
solar en potencial quĂmico se da durante la fotosĂntesis y
mantiene la vida en la tierra
Spectroscopic Analyses on Reaction Intermediates Formed during Chlorination of Alkanes with NaOCl Catalyzed by a Nickel Complex
The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II)(CH3CN)2](OTf)2 (1) ((Me,H)PyTACN = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = CF3SO3) is described together with its reactivity with NaOCl. 1 catalyzes the chlorination of alkanes with NaOCl, producing only a trace amount of oxygenated byproducts. The reaction was monitored spectroscopically and by high resolution electrospray-mass spectrometry (ESI-MS) with the aim to elucidate mechanistic aspects. NaOCl reacts with 1 in acetonitrile to form the transient species [(L)Ni(II)-OCl(S)](+) (A) (L = (Me,H)PyTACN, S = solvent), which was identified by ESI-MS. UV/vis absorption, electron paramagnetic resonance, and resonance Raman spectroscopy indicate that intermediate A decays to the complex [(L)Ni(III)-OH(S)](2+) (B) presumably through homolytic cleavage of the O-Cl bond, which liberates a Cl(âą) atom. Hydrolysis of acetonitrile to acetic acid under the applied conditions results in the formation of [(L)Ni(III)-OOCCH3(S)](2+) (C), which undergoes subsequent reduction to [(L)Ni(II)-OOCCH3(S)](2+) (D), presumably via reaction with OCl(-) or ClO2(-). Subsequent addition of NaOCl to [(L)Ni(II)-OOCCH3(S)](+) (D) regenerates [(L)Ni(III)-OH(S)](2+) (B) to a much greater extent and at a faster rate. Addition of acids such as acetic and triflic acid enhances the rate and extent of formation of [(L)Ni(III)-OH(S)](2+) (B) from 1, suggesting that O-Cl homolytic cleavage is accelerated by protonation. Overall, these reactions generate Cl(âą) atoms and ClO2 in a catalytic cycle where the nickel center alternates between Ni(II) and Ni(III). Chlorine atoms in turn react with the C-H bonds of alkanes, forming alkyl radicals that are trapped by Cl(âą) to form alkyl chlorides
CCDC 1438008: Experimental Crystal Structure Determination
Related Article: Apparao Draksharapu, Zoel CodolĂ , Laura GĂłmez, Julio Lloret-Fillol, Wesley R. Browne, and Miquel Costas|2015|Inorg.Chem.|54|10656|doi:10.1021/acs.inorgchem.5b01463,An entry from the Cambridge Structural Database, the worldâs repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Design of Iron Coordination Complexes as Highly Active Homogenous Water Oxidation Catalysts by Deuteration of Oxidation-Sensitive Sites.
International audienceThe nature of the oxidizing species in water oxidation reactions with chemical oxidants catalyzed by α-[Fe(OTf)2(mcp)] (1α; mcp = N, N'-dimethyl- N, N'-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, OTf = trifluoromethanesulfonate anion) and ÎČ-[Fe(OTf)2(mcp)] (1ÎČ) has been investigated. Mössbauer spectroscopy provides definitive evidence that 1α and 1ÎČ generate oxoiron(IV) species as the resting state. Decomposition paths of the catalysts have been investigated by identifying and quantifying ligand fragments that form upon degradation. This analysis correlates the water oxidation activity of 1α and 1ÎČ with stability against oxidative damage of the ligand via aliphatic C-H oxidation. The site of degradation and the relative stability against oxidative degradation are shown to be dependent on the topology of the catalyst. Furthermore, the mechanisms of catalyst degradation have been rationalized by computational analyses, which also explain why the topology of the catalyst enforces different oxidation-sensitive sites. This information has served in creating catalysts where sensitive C-H bonds have been replaced by C-D bonds. The deuterated analogues D4-α-[Fe(OTf)2(mcp)] (D4-1α), D4-ÎČ-[Fe(OTf)2(mcp)] (D4-1ÎČ), and D6-ÎČ-[Fe(OTf)2(mcp)] (D6-1ÎČ) were prepared, and their catalytic activity has been studied. D4-1α proves to be an extraordinarily active and efficient catalyst (up to 91% of O2 yield); it exhibits initial reaction rates identical with those of its protio analogue, but it is substantially more robust toward oxidative degradation and yields more than 3400 TON ( n(O2)/ n(Fe)). Altogether this evidences that the water oxidation catalytic activity is performed by a well-defined coordination complex and not by iron oxides formed after oxidative degradation of the ligands