78 research outputs found
An Iron Bis(carbene) Catalyst for Low Overpotential CO2 Electroreduction to CO: Mechanistic Insights from Kinetic Zone Diagrams, Spectroscopy, and Theory
A common challenge in molecular electrocatalysis is the relationship between maximum activity and the overpotential required to reach that rate, with faster catalysts incurring higher overpotentials. This work follows a strategy based on independent tuning of ligands in the primary coordination sphere to discover a previously unreported iron catalyst for CO2 reduction with higher activity than similar complexes while maintaining the same overpotential. Iron complexes bearing a bis-N-heterocyclic carbene ligand (methylenebis(N-methylimidazol-2-ylidene), bis-mim) and a redox active 2,2âČ:6âČ,2âł-terpyridine (tpy) ligand were synthesized and found to catalyze the selective reduction of CO2 to CO at low overpotential with water as the proton source. Mechanistic studies based on kinetic zone diagrams, spectroscopy, and computation enable comparisons with a previously studied pyridylâcarbene analogue. Changing the bidentate ligand donor ability accelerates catalysis at the same overpotential and changes the nature of the turnover-limiting step of the reaction.The synthesis, voltammetry, and spectroelectrochemistry were supported as part of the Alliance for Molecular PhotoElectrode Design for Solar Fuels (AMPED), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001011 (E.A.A and A.J.M.M). Jordi Benet assisted with crystallographic data collection. Brandie M. Ehrmann assisted with mass spectrometry. The mass spectrometry work was supported by the National Science Foundation under grant no. (CHE-1726291). Computational studies, flow electrolyses, and X-ray diffraction studies were supported by the European Commission for the ERC-CoG-2015-648304 project and the Spanish Ministry of Science for the project PID2019-110050RB-I00 (J.Ll.-F). S.G. thanks the EU for Horizon 2020 Marie SkĆodowska-Curie Fellowship (grant no. 794119, Fe-RedOx-Cat)
Oxidant-Free Au(I)-Catalyzed Halide Exchange and Csp2âO Bond Forming Reactions
Au has been demonstrated to mediate a number of organic transformations through the utilization of its Ï Lewis acid character, Au(I)/Au(III) redox properties or a combination of both. As a result of the high oxidation potential of the Au(I)/Au(III) couple, redox catalysis involving Au typically requires the use of a strong external oxidant. This study demonstrates unusual external oxidant-free Au(I)-catalyzed halide exchange (including fluorination) and Csp2âO bond formation reactions utilizing a model aryl halide macrocyclic substrate. Additionally, the halide exchange and Csp2âO coupling reactivity could also be extrapolated to substrates bearing a single chelating group, providing further insight into the reaction mechanism. This work provides the first examples of external oxidant-free Au(I)-catalyzed carbonâheteroatom cross-coupling reactions
Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(II) complexes with bulky ortho-metalated aryl phosphines
Enantiomerically pure dirhodium(II) complexes with ortho-metalated p-substituted aryl phosphines have been shown to be enantio- and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate.Estevan Estevan, Francisco, [email protected] ; Lahuerta Peña, Pascual, [email protected] ; Lloret Fillol, Julio, [email protected] ; Sanau Torrecilla, Mercedes, [email protected] ; Ubeda Picot, M Angeles, [email protected] ; Vila Gomez, Jaume Llorenc, [email protected]
The synergy between the CsPbBr 3 nanoparticle surface and the organic ligand becomes manifest in a demanding carbonâcarbon coupling reaction
We demonstrate here the suitability of CsPbBr3nanoparticles as photosensitizers for a demanding photoredox catalytic homo- and cross-coupling of alkyl bromides at room temperature by merely using visible light and an electron donor, thanks to the cooperative action between the nanoparticle surface and organic capping.Fil: Rosa-Pardo, Ignacio. Instituto de Ciencia Molecular; España. Universidad de Valencia; EspañaFil: Casadevall, Carla. Barcelona Institute Of Science And Technology. Institut CatalĂ D'investigaciĂł QuĂmica.; EspañaFil: Schmidt, Luciana Carina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; ArgentinaFil: Castro Claros, JosĂ© Miguel. Barcelona Institute Of Science And Technology. Institut CatalĂ D'investigaciĂł QuĂmica.; EspañaFil: Galian Baca, Raquel Eugenia. Instituto de Ciencia Molecular; España. Universidad de Valencia; EspañaFil: Lloret-Fillol, Julio. Barcelona Institute Of Science And Technology. Institut CatalĂ D'investigaciĂł QuĂmica.; EspañaFil: PĂ©rez-Prieto, Julia. Instituto de Ciencia Molecular; España. Universidad de Valencia; Españ
Generation, Spectroscopic, and Chemical Characterization of an Octahedral Iron(V)-Nitrido Species with a Neutral Ligand Platform
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ObservaciĂł directa de cicles redox de Ag(I)/Ag(III) de dos electrons en catĂ lisi de funcionalitzaciĂł d'halurs d'aril
La plata Ă©s avui dia Ă mpliament utilitzada en catĂ lisi homogĂšnia per a la sĂntesi de compostos orgĂ nics a causa del seu carĂ cter d'Ă cid de Lewis i el seu poder oxidant. La Ag(I) Ă©s un potent oxidant monoelectrĂČnic que troba utilitat en un gran nombre de processos catalĂtics. Tanmateix, els cicles catalĂtics de dos electrons, molt comuns en la quĂmica organometĂ l·lica dels metalls nobles, no han estat mai considerats possibles per a la plata. En aquest estudi descrivim un cicle catalĂtic Ag(I)/Ag(III) que Ă©s operatiu en una reacciĂł model d'acoblament creuat per a la formaciĂł d'enllaços CÂO. EspĂšcies arilÂAg(III) han estat inequĂvocament identificades com a intermedis d'aquest cicle catalĂtic. L'estudi de la sĂntesi i la reactivitat de l'esmentat complex ha permĂšs per primera vegada la caracteritzaciĂł de les etapes d'addiciĂł oxidant i eliminaciĂł reductiva de formaciĂł d'enllaços carboniÂnucleĂČ-
fil en centres monometĂ l·lics de plata. El present treball demostra que els processos d'eliminaciĂł reductiva en espĂšcies arilÂAg(III) sĂłn efectius en reaccions d'acoblament creuat per a la formaciĂł d'enllaços CÂO, CÂN, CÂS, CÂC i CÂhalur, incloses les reaccions de fluoraciĂł d'arils. Aquest estudi suposa un punt de partida per a l'expansiĂł de la quĂmica redox Ag(I)/Ag(III) a noves metodologies per a la sĂntesi orgĂ nica, en analogia a la quĂmica d'acoblament creuat del coure o el pal·ladi. A mĂ©s, els resultats descrits proporcionen una comprensiĂł mecanĂstica fonamental Ășnica en les reaccions d'acoblament creuat catalitzades per plata i refuten la concepciĂł generalment acceptada que la quĂmica redox de la plata nomĂ©s pot provenir de processos d'un sol electrĂł.Silver is extensively used in homogeneous catalysis for organic synthesis owing to its Lewis acidity and unique high oxidation power. The high oxidation potential of Ag(I) makes it a powerful one-electron oxidant that finds utility in a large number catalytic processes. However, two-electron redox catalytic cycles, most common in noble metal organometallic reactivity, have never been considered. Herein we show that an Ag(I)/Ag(III) catalytic cycle is operative in a model CÂO cross-coupling reaction. ArylÂAg(III) species have been unequivocally identified as an intermediate in the catalytic cycle. The study of the synthesis and reactivity of this complex has enabled for the first time the direct characterization of aryl halide oxidative addition and carbonÂnucleophile bond-forming reductive elimination steps at monometallic silver centers. This report demonstrates that reductive elimination processes at arylÂAg(III) species are effective for CÂO, CÂN, CÂS, CÂC and CÂhalide coupling reactions, including aryl fluorination. We anticipate our study as the starting point for expanding Ag(I)/Ag(III) redox chemistry into new methodologies for organic synthesis, resembling well-known copper or palladium cross-coupling catalysis. Furthermore, findings described herein provide a unique fundamental mechanistic understanding of Ag-catalyzed cross-coupling reactions and dismiss the generally accepted conception that silver redox chemistry can only arise from one-electron processes
H2 oxidation versus organic substrate oxidation in non-heme iron mediated reactions with H2O2
Herein we show that species generated upon reaction of α-[Fe(CF3SO3)2(BPMCN)] (BPMCN = N,NâČ-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane) with H2O2 (putatively [FeV(O)(OH)(BPMCN)]) is able to efficiently oxidize H2 to H2O even in the presence of organic substrates, while species formed in the presence of acetic acid (putatively [FeV(O)(OAc)(BPMCN)]) prefer organic substrate oxidation over H2 activation. Mechanistic implications have been analysed with the aid of computational methodsThis work was supported by Spanish Ministerio de Economia y Competitividad (CTQ2012-37420-C02-02 and 01) European Research Council (StG 239910), and Generalitat de Catalunya (2014 SGR 862 and ICREA Academia award to MC). J.Ll.-F. thanks the CELLEX foundation for the starting career program for financial suppor
Enhance and Control of the Selectivity in Light-driven Ketone versus Water Reduction Using Aminopyridine Cobalt Complexes
Cobalt(II) complexes with the general structure [CoII(OTf)(Y,XPy2Tstacn)](OTf) (1R, where Y,XPy2Tstacn is 1,4-di(p-Y,m-X-picolyl)-7-R-1,4,7-triazacyclononane; 1H, 1CO2Et, 1DMM) and [CoII(OTf)2(Y,XPyMetacn)] (2R, where Y,XPyMetacn is 1-(p-Y,m-X-picolyl)-7,4-di-methyl-1,4,7-triazacyclononane; 2CO2Et, 2Cl, 2H, 2DMM, 2NMe2) were active in both light-driven acetophenone (3a) and water reduction. Competition studies show that aromatic ketone/water reduction selectivity ranks from 0.2 to 8.0. Nevertheless, considering the concentrations of water and ketone in catalysis (ratio H2O/3a ⌠2000) the highest selectivity obtained is greater than 15â000. The selectivity correlates well with the CoI/II redox potential within the same cobalt catalyst series (span 240 mV (1R) and 290 mV (2R)), with electron donating ligands favoring ketone reduction over H2 evolution. Based on this finding, the operative mechanism for the reduction of aromatic ketones is consistent with a single electron transfer (SET) followed by a hydrogen atom transfer (HAT) mechanism. This new insight will be a guide to develop selective catalytic systems to produce fine solar chemicals in water
An Iron Pyridyl-Carbene Electrocatalyst for Low Overpotential CO2 Reduction to CO
Electrocatalysts for CO2 reduction based on first-row transition metal ions have attracted attention as abundant and affordable candidates for energy conversion applications. Yet very few molecular iron electrocatalysts exhibit high selectivity for CO. Iron complexes supported by a redox-active 2,2âČ:6âČ,2âł-terpyridine (tpy) ligand and a strong trans effect pyridyl-N-heterocyclic carbene ligand (1-methyl-benzimidazol-2-ylidene-3-(2-pyridine)) were synthesized and found to catalyze the selective electroreduction of CO2 to CO at very low overpotentials. Mechanistic studies using electrochemical and computational methods provided insights into the nature of catalytic intermediates that guided the development of continuous CO2 flow conditions that improved the performance, producing CO with >95% Faradaic efficiency at an overpotential of only 150 mV. The studies reveal general design principles for nonheme iron electrocatalysts, including the importance of lability and geometric isomerization, that can serve to guide future developments in the design of affordable and efficient catalysts for CO2 electroreduction
Visible-Light Reductive Cyclization of Nonactivated Alkyl Chlorides
Nonactivated alkyl chlorides are readily available and bench-stable feedstocks; however, they exhibit an inherent chemical inertness, in part, due to their large negative reduction potentials, which have precluded their widespread use as radical precursors in visible-light photocatalysis. Herein, we highlight some recent strategies for activating challenging organic halides under light irradiation, with special emphasis in C(sp3)âhalide bonds. In this line, a brief summary of the reactivity of Vitamin B12, F430 cofactor and derivatives is required to comprehend the chemistry behind our developed Cu/M (M = Co, Ni) dual catalytic system. Catalyst design has been key for developing a mild and general photoredox methodology for the intramolecular reductive cyclization of nonactivated alkyl chlorides with tethered alkenes. The cleavage of strong C(sp3)âCl bonds is mediated by a highly nucleophilic low-valent cobalt or nickel intermediate generated by visible-light photoredox reduction employing a copper photosensitizer
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