| 1. |
- Agarwala, Hemlata, et al.
(författare)
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Alternating Metal-Ligand Coordination Improves Electrocatalytic CO2 Reduction by a Mononuclear Ru Catalyst**
- 2023
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 62:17
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Tidskriftsartikel (refereegranskat)abstract
- Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, due to the large barrier for C−O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO2 to form [Ru-CO2]0, while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [Ru-CO2CO2]0,c, by addition of a second CO2 molecule and intramolecular cyclization. The calculated activation barrier for C−O bond cleavage via the metallacycle is decreased by 34.9 kcal mol−1 as compared to the non-cyclic adduct in the two electron reduced state of complex 1. Such metallacyclic intermediates in electrocatalytic CO2 reduction offer a new design feature that can be implemented consciously in future catalyst designs.
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| 2. |
- Agarwala, Hemlata, et al.
(författare)
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An Elusive Intermediate Uncovered in the Pathway for Electrochemical Carbon Dioxide Reduction by Ruthenium Polypyridyl Catalyst - Combined Spectroscopic and Computational Investigation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A scrutinous study of the catalytic cycle for electrochemical CO2 reduction by the ruthenium 2,2:6,2-terpyridine (tpy) 2,2-bipyridine (bpy) class of catalysts is presented. An unprecedented 2-(C,O)-carboxycarboxylatoruthenium(II) metalacyclic intermediate, critical for C-O bond dissociation at low overpotentials, so far precluded from mechanistic considerations of polypyridyl transition metal complex catalysts, is unearthed by infra-red spectroscopy coupled to controlled potential electrolysis in corroboration with density functional theory (DFT) investigations. Thermodynamic and kinetic analyses of the intermediate reveal the important role of the structural flexibility of polypyridyl ligands and fine electronic tunability of the metal center, along with kinetic trans effect, in propelling catalysis at lower overpotentials. The choice of metal center, Ru in the present case, points to the fact that the requirement of an additional Lewis acid to enhance C-O bond dissociation, hence increase the catalytic rate or turnover, can be circumvented.
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| 3. |
- Amaro-Gahete, Juan, et al.
(författare)
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Catalytic systems mimicking the [FeFe]-hydrogenase active site for visible-light-driven hydrogen production
- 2021
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Ingår i: Coordination chemistry reviews. - : Elsevier. - 0010-8545 .- 1873-3840. ; 448
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Forskningsöversikt (refereegranskat)abstract
- A global hydrogen economy could ensure environmentally sustainable, safe and cost-efficient renewable energy for the 21st century. Solar hydrogen production through artificial photosynthesis is a key strategy, and the activity of natural hydrogenase metalloenzymes an inspiration for the design of synthetic catalyst systems. [FeFe]-hydrogenase enzymes, present in anaerobic bacteria and green algae, are the most efficient class of biological catalysts for hydrogen evolution. The enzymes operate in an aqueous environment, utilizing electrons that ultimately stem from photosynthesis as the only energy source. Functional synthetic models of the [FeFe]-hydrogenase enzyme active site have garnered intense interest as potential catalysts for the reduction of protons to molecular hydrogen. Herein, we take an extensive journey through the field of biomimetic hydrogenase chemistry for lightdriven hydrogen production. We open with a brief presentation of the structure and redox mechanism of the natural enzyme. Synthetic methodologies, structural characteristics, and hydrogen generation metrics relevant to the synthetic diiron catalysts ([2Fe2S]) are discussed. We first examine multicomponent photocatalysis systems with the [2Fe2S] cluster, followed by photosensitizer-[2Fe2S] dyads and molecular triads. Finally, strategies for the incorporation of [2Fe2S] complexes into supramolecular assemblies, semiconductor supports, and hybrid heterogeneous platforms are laid out. We analyze the individual properties, scope, and limitations of the components present in the photocatalytic reactions. This review illuminates the most useful aspects to rationally design a wide variety of biomimetic catalysts inspired by the diiron subsite of [FeFe]-hydrogenases, and establishes design features shared by the most stable and efficient hydrogen producing photosystems. (C) 2021 The Author(s). Published by Elsevier B.V.
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| 4. |
- Amaro-Gahete, Juan, et al.
(författare)
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Hydroxyl-Decorated Diiron Complex as a [FeFe]-Hydrogenase Active Site Model Complex : Light-Driven Photocatalytic Activity and Heterogenization on Ethylene-Bridged Periodic Mesoporous Organosilica
- 2022
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Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.
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| 5. |
- Andersson, Claes-Henrik, et al.
(författare)
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Synthesis and IR Spectroelectrochemical Studies of a [60]Fulleropyrrolidine-(tricarbonyl)chromium Complex : Probing C-60 Redox States by IR Spectroscopy
- 2011
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Ingår i: European Journal of Inorganic Chemistry. - : John Wiley & Sons. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :11, s. 1744-1749
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a new fulleropyrrolidine-(tricarbonyl)chromium complex: 1-methyl-2-(4-methoxyphenyl)-3,4-[60]fulleropyrrolidine-(tricarbonyl)chromium is described together with its characterization by IR, NMR and cyclic voltammetry. IR spectro-electrochemistry has been used to probe the redox level of the fullerene derivative via the relative position of the vibrational bands of the CO ligands, which are sensitive to the electronic state of the complex. Other strategies to incorporate a tricarbonylchromium moiety to fullerene C60 are also briefly discussed and evaluated.
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| 6. |
- Antila, Liisa J., et al.
(författare)
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Dynamics and Photochemical H-2 Evolution of Dye-NiO Photocathodes with a Biomimetic FeFe-Catalyst
- 2016
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Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 1:6, s. 1106-1111
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous NiO films were cosensitized with a coumarin 343 dye and a proton reduction catalyst of the [Fe-2(CO)(6)(bdt)] (bdt = benzene-1,2-dithiolate) family. Femtosecond ultraviolet visible transient absorption experiments directly demonstrated subpicosecond hole injection into NiO from excited dyes followed by rapid (t(50%) similar to 6 ps) reduction of the catalyst on the surface with similar to 70% yield. The reduced catalyst was long-lived (2 mu s to 20 ms), which may allow protonation and a second reduction step of the catalyst to occur. A photo electrochemical device based on this photocathode produced H-2 with a Faradaic efficiency of similar to 50%. Fourier transform infrared spectroscopy and gas chromatography experiments demonstrated that the observed device deterioration with time was mainly due to catalyst degradation and desorption from the NiO surface. The insights gained from these mechanistic studies, regarding development of dye-catalyst cosensitized photocathodes, are discussed.
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| 7. |
- Arkhypchuk, Anna I., et al.
(författare)
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[2+2] Cycloaddition of phosphaalkenes as a key step for the reductive coupling of diaryl ketones to tetraaryl olefins
- 2022
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 13:41, s. 12239-12244
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Tidskriftsartikel (refereegranskat)abstract
- Procedures for the reductive coupling of carbonyl compounds to alkenes in the literature rely either on a radical coupling strategy, as in the McMurry coupling, or ionic pathways, sometimes catalysed by transition metals, as in more contemporary contributions. Herein, we present the first example of a third strategy that is based on the [2 + 2] cycloaddition of ketone-derived phosphaalkenes. Removal of P-trimethylsilyl groups at the intermediary 1,2-diphosphetane dimer results in its collapse and concomitant release of the tetraaryl-substituted alkene. In fact, the presented strategy is the only alternative to the McMurry coupling in the literature that allows tetraaryl alkene formation from diaryl ketones, with yields as high as 85%. The power of the methodology is illustrated in the reaction of tethered bis-benzophenones which engage in intramolecular reductive carbonyl couplings to form unusual macrocycles without the need for high dilution conditions or templating.
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| 8. |
- Arkhypchuk, Anna I., et al.
(författare)
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Cascade Reactions Forming Highly Substituted, Conjugated Phospholes and 1,2-Oxaphospholes
- 2012
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 51:31, s. 7776-7780
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of a phospha-Wittig–Horner reagent with diacetylenic ketones (see scheme) results in a cascade of reactions that can lead to both an oxaphosphole-terminated cumulene system and an alkene-bridged bis-phosphole. The reaction outcome is determined by the nature of the acetylene termini, with phenyl groups stabilizing a carbene intermediate that dimerizes to give the bis-phosphole product.
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| 9. |
- Arkhypchuk, Anna I., et al.
(författare)
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Mechanistic Insights and Synthetic Explorations of the Photoredox-Catalyzed Activation of Halophosphines
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:45, s. 18391-18398
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Tidskriftsartikel (refereegranskat)abstract
- The light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent–child reaction to form diphosphines R2P–PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEA•+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations.
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| 10. |
- Arkhypchuk, Anna I., et al.
(författare)
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One-Pot Intermolecular Reductive Cross-Coupling of Deactivated Aldehydes to Unsymmetrically 1,2-Disubstituted Alkenes
- 2018
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 20:17, s. 5086-5089
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Tidskriftsartikel (refereegranskat)abstract
- The phospha-Peterson reaction between a lithiated secondary phosphane, MesP(Li)TMS, and an aldehyde affords Mes-phosphaalkenes which, upon methanol addition and P-oxidation, react with a second carbonyl compound site specifically to produce unsymmetric alkenes. The E/Z selectivity of the one-pot cross coupling is largely determined by the electronic nature of the aryl substituent of the first aldehyde, with electron-donating groups giving rise to increased amounts of Z-alkenes.
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| 11. |
- Arkhypchuk, Anna I., et al.
(författare)
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Oxaphospholes and Bisphospholes from Phosphinophosphonates and alpha,beta-Unsaturated Ketones
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:41, s. 13692-13704
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of a {W(CO)(5)}-stabilized phosphinophosphonate 1, (CO)(5)WPH(Ph)P(O)(OEt)(2), with ethynyl- (2a-f) and diethynylketones (7-11, 18, and 19) in the presence of lithium diisopropylamide (LDA) is examined. Lithiated 1 undergoes nucleophilic attack in the Michael position of the acetylenic ketones, as long as this position is not sterically encumbered by bulky (iPr)(3)Si substituents. Reaction of all other monoacetylenic ketones with lithiated 1 results in the formation of 2,5-dihydro-1,2-oxaphospholes 3 and 4. When diacetylenic ketones are employed in the reaction, two very different product types can be isolated. If at least one (Me)(3)Si or (Et)(3)Si acetylene terminus is present, as in 7, 8, and 19, an anionic oxaphosphole intermediate can react further with a second equivalent of ketone to give cumulene-decorated oxaphospholes 14, 15, 24, and 25. Diacetylenic ketones 10 and 11, with two aromatic acetylene substituents, react with lithitated 1 to form exclusively ethenyl-bridged bisphospholes 16 and 17. Mechanisms that rationalize the formation of all heterocycles are presented and are supported by DFT calculations. Computational studies suggest that thermodynamic, as well as kinetic, considerations dictate the observed reactivity. The calculated reaction pathways reveal a number of almost isoenergetic intermediates that follow after ring opening of the initially formed oxadiphosphetane. Bisphosphole formation through a carbene intermediate G is greatly favored in the presence of phenyl substituents, whereas the formation of cumulene-decorated oxaphospholes is more exothermic for the trimethylsilyl-containing substrates. The pathway to the latter compounds contains a 1,3-shift of the group that stems from the acetylene terminus of the ketone substrates. For silyl substituents, the 1,3-shift proceeds along a smooth potential energy surface through a transition state that is characterized by a pentacoordinated silicon center. In contrast, a high-lying transition state TS(E-F)(R=Ph) of 37kcalmol(-1) is found when the substituent is a phenyl group, thus explaining the experimental observation that aryl-terminated diethynylketones 10 and 11 exclusively form bisphospholes 16 and 17.
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| 12. |
- Arkhypchuk, Anna I., et al.
(författare)
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Redox Switching in Ethenyl- Bridged Bisphospholes
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 20:49, s. 16083-16087
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Tidskriftsartikel (refereegranskat)abstract
- A 2e(-)/2H(+) redox platform has been implemented in the ethenyl-bridged bisphosphol-3-ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol-3-one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest-energy absorption maximum by 100nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2. This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200nm compared to those of 2.
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| 13. |
- Arkhypchuk, Anna I., et al.
(författare)
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Reductive Diphosphene Formation From W(CO)5-Coordinated Dichlorophosphanes
- 2011
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Ingår i: Phosphorus Sulfur and Silicon and the Related Elements. - : Informa UK Limited. - 1042-6507 .- 1563-5325. ; 186:4, s. 664-665
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Tidskriftsartikel (refereegranskat)abstract
- A bis-[W(CO)(5)]-coordinated (Bu-t)(2)diphosphene was prepared from the corresponding [W(CO)(5)]-(BuPCl2)-Bu-t by treatment with LiAlH4.
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| 14. |
- Arkhypchuk, Anna I., et al.
(författare)
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Revisiting the Phospha-Wittig - Horner Reaction
- 2012
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Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 31:3, s. 1118-1126
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Tidskriftsartikel (refereegranskat)abstract
- P,P-Dichlorophosphines 2a-c (RPCl2, R = Ph (a), t-Bu (b), 2,4,6-Me3Ph (c)) and P,P-dibromophosphines 4d,e (RPBr2, R = (i-Pr)(3)SiC C (d) and H2C=CH (e)) react with triethylphosphite under Michaelis-Arbuzov conditions to give phosphinodiphosphonates 3a-e in quantitative yields. After complexation to W(CO)(5) and treatment with CH3ONa, phospha-Wittig-Horner reagents 9a,b are obtained on a multigram scale in good overall yield. Phospha-Wittig-Horner reagents with unsaturated, substituents at P-III (10d,e) can be prepared in analogous procedures; however, their prevail in an unusual ylide form that allows conjugation between the lone pair and the acetylene and vinyl pi-systems, respectively. Phosphinophosphonate 9a has been characterized by X-ray crystallography and is shown to react smoothly with acetone within minutes. The resulting W(CO)(5)-coordinated phosphaalkene is shown to dimerize to a 1,2-diphosphitane or to undergo a 1,3-proton shift depending on the reaction conditions. In addition, a one-pot synthetic sequence starting from W(CO)(5)-coordinated phosphinodiphosphonates 5d,e has been developed to engage compounds with vinyl and acetylene substituents in phospha-Wittig-Horner reactions.
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| 15. |
- Arkhypchuk, Anna I., et al.
(författare)
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Triarylalkenes from the site-selective reductive cross-coupling of benzophenones and aldehydes
- 2019
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 55:43, s. 6030-6033
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Tidskriftsartikel (refereegranskat)abstract
- PhP(Li)TMS converts benzophenones to phosphaalkenes which upon activation under oxidizing, basic conditions react with aromatic aldehydes under the formation of triarylalkenes. The one-pot reaction omits transition metals, proceeds at room temperature and precludes the formation of any homo-coupling products. Systematic substrate variations reveal reactivity patterns that are useful for the identification of ketone/aldehyde combinations that can be coupled in yields up to 80%.
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| 16. |
- Arkhypchuk, Anna I., et al.
(författare)
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Tuning the Optical Properties of 1,1'-Biphospholes by Chemical Alterations of the P-P Bridge
- 2014
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2014:10, s. 1760-1766
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Tidskriftsartikel (refereegranskat)abstract
- 2,5-Di(1-naphthyl)-1-phenylphosphole (2) was prepared from phenylphosphine and dinaphthylbutadiyne in 70% yield, and oxidized to its oxide 3. Treatment of 2 with a solution of potassium naphthalide results in selective formation of phospholide anion 4, which can be oxidized with iodine to afford biphosphole 5. The crystal structure of 5 exhibits an unusual s-trans conformation across the P-P bridge that is most stabilized by - stacking of the naphthyl substituents. Biphosphole 5 can be oxidized to its mono-oxidized 6 and dioxide 7. Generally, all phosphole oxidations lead to decreased pyramidalization of the P centres and, consequently, to significantly redshifted lowest-energy absorption maxima. Mono-oxidized biphosphole 6, which consists of an ordinary phosphole and an electron-deficient oxidized phosphole, features a unique low-energy optical transition (shoulder at 430 nm), which is tentatively assigned to a charge-transfer transition. The UV/Vis spectrum of dioxide 7 lacks this transition. At the same time, the emission maximum of 7 is bathochromically shifted by 80 nm relative to that of 5.
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| 17. |
- Arkhypchuk, Anna I., et al.
(författare)
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Versatile Approach to 3-Phosphahexatrienes Bearing Low Coordinated Phosphorus
- 2015
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Ingår i: Phosphorus Sulfur and Silicon and the Related Elements. - : Informa UK Limited. - 1042-6507 .- 1563-5325. ; 190:5-6, s. 638-646
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Tidskriftsartikel (refereegranskat)abstract
- lambda(3)-phosphahexatrienes were prepared from ethoxyvinyl phosphinophosphonates using the phospha-Wittig-Horner reaction. The title compounds can be easily prepared in three steps starting from dichlorophosphines with good overall yields. Although these were found to be thermally unstable, these can be trapped, for instance, with methanol. The resulting methoxyphosphines are isolated in high yields in case of aldehyde starting materials with more bulky substituents.
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| 18. |
- Arkhypchuk, Anna, et al.
(författare)
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Mechanism of the Phospha-Wittig-Horner Reaction
- 2013
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 52:25, s. 6484-6487
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Tidskriftsartikel (refereegranskat)
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| 19. |
- Arkhypchuk, Anna, 1984-
(författare)
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Novel Approaches to Phosphorus-containing Heterocycles and Cumulenes
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fast development in all areas of life and science over the last 50 years demands versatile, energy efficient and cheap materials with specific but easily tuneable properties which can be used for example in organic light emitting diodes (OLEDs), thin-film transistors, photovoltaic cells, etc. This thesis is devoted to the development of novel synthetic approaches to molecules with potential applications in the field of molecular electronics. The acquisition of a detailed mechanistic understanding of the newly developed reactions is central to the work presented in this thesis.The first chapter is dedicated to the development of a new procedure for the preparation of phospha-Wittig-Horner (pWH) reagents, i.e. a reagents that has been known to convert carbonyl compounds into compounds with P=C double bonds. Each step of the synthetic sequence, i.e. preparation of the starting P,P-dichlorophosphines, their phosphorylation using the Michaelis-Arbuzov protocol, coordination to the metal centre and final hydrolysis, are presented in detail. A possible route to uncoordinated pWH reagents is also discussed.The second chapter focuses on the reactivity of the pWH reagents with acetone under different reaction conditions. The results show how changes in the ratio of starting material vs. base as well as reaction time or structure of the pWH reagent can influence the reaction outcome and the stability of the obtained products. The possibility to prepare unusual phosphaalkenes with unsaturated P-substituents is presented.The third chapter of the thesis is dedicated to the reactivity of pWH reagents towards symmetric and asymmetric ketones which contain one or two acetylene units. The proposed mechanisms of the reactions are studied by means of in situ FTIR spectroscopy as well as theoretical calculations. Physical-chemical properties of oxaphospholes, cumulenes and bisphospholes are presented.The last chapter is dedicated to reactivity studies of pWH reagents towards ketenes, and the exploration of a reliable route to 1-phosphaallenes. Detailed mechanistic studies of the pWH reaction that are based on the isolation and crystallographic characterization of unique reaction intermediates are presented. The reactivity of phosphaallenes towards nucleophiles such as water and methanol are examined.In summary, this thesis presents synthetic routes to novel phosphorus-containing molecules, together with detailed studies of the reaction mechanisms of the observed transformations.
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| 20. |
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| 21. |
- Bagnall, Andrew J.
(författare)
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Novel electrode and photoelectrode materials for hydrogen production based on molecular catalysts
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The PhD project focussed on the application of a cobalt tetraazamacrocyclic complex, in the literature commonly referred to as [Co(CR)Cl2]+ as a molecular catalyst for the hydrogen evolution reaction (HER). This was within the broader scope of the EU MSCA H2020 ITN ‘eSCALED’ project, which primarily aimed to create artificial leaf devices for the storage of solar energy in chemical fuels and, as part of this, sought the development of novel bio-inspired and scalable materials. This included researching molecular catalysts without platinum group metals (PGMs) currently relied upon in commercial technology.Three main projects were pursued: firstly, studies of the mechanism of the catalyst itself under organic electrocatalytic conditions. Catalytic intermediates were generated and identified using spectroscopy (UV-vis, NMR, EPR) and the catalytic behaviour was followed with electrochemical techniques. An ECEC mechanism with a rate-determining second protonation step associated with the release of H2 was identified, noting in particular an initial protonation step on the macrocycle at the Co(II) state that was hypothesised to involve the macrocycle amine group acting as a proton relay under the investigated conditions.Secondly, a new synthetic strategy towards novel derivatives of [Co(CR)Cl2]+ was developed to prepare a derivative for anchoring onto sp2-carbon surfaces by pi-stacking interactions. The immobilised catalyst was studied by electrochemical methods and compared with another derivative from collaborators at ICIQ, showing that both derivatives work as heterogenised electrocatalysts for the HER with high faradaic efficiencies and good stability over one hour at pH 2 and especially pH 7, but one derivative displays higher current densities and stability, invoking some consideration of rational design principles for modifying molecular catalysts.Thirdly, studies of a photocatalytic system made up of copper indium sulfide quantum dots (CuInS2 QDs) as a photosensitiser with either [Co(CR)Cl2]+ or its benzoic acid-functionalised derivative were carried out in ascorbate buffer, focussing on the photocatalytic performance and electron transfer (ET) processes between the CuInS2 QDs and the catalyst to explain the remarkable activity and robustness reported for closely related systems. CuInS2 QDs modified to have a ‘hybrid-passivation’ ligand system for compatibility with NiO films were used. Rapid QD-catalyst ET processes were noted for both catalysts. A static binding model with a strong binding equilibrium was adapted for the system, applying a Poisson distribution. This prompts a reconsideration of the importance of anchoring groups for QD-catalyst ET efficiency in solution.
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| 22. |
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| 23. |
- Bedin, Michele, 1984-
(författare)
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A dinuclear manganese complex with an asymmetric ligand as a functional mimic of manganese catalase
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Tidskriftsartikel (refereegranskat)abstract
- Reactive Oxygen Species (ROS) in the form of H2O2, OH radicals, and superoxide, are oxygen species generated in the respiratory chain. In high concentrations, these species can cause pathological conditions like ischemia-reperfusion related injuries and neurodegenerative diseases. A series of enzymes exists in nature to protect from this danger: superoxide dismutases (SOD), glutathione peroxidases (GSH), and catalases (CAT). The catalases catalyse the decomposition of H2O2 into water and molecular oxygen. In this work, we focus on mimicking the MnCAT, a subclass of CAT that contains two Mn ions in the cofactor. An asymmetric and dinucleating ligand H2DPCPMP (2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino acetic acid) that contains three pyridine groups, one carboxylate group, and one phenol was used. The ligand can create two pockets where two Mn ions can be accommodated. The dimanganese complex of H2DPCPMP was synthesized and characterized with mass spectrometry, electrochemistry, IR, UV-vis and EPR. The complex can act as a catalyst for the disproportionation of H2O2 but unlike many previously reported mimics of MnCAT, the rate of oxygen evolution is not saturated at high concentrations of H2O2.
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| 24. |
- Bedin, Michele, 1984-, et al.
(författare)
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Dinuclear iron and manganese complex with an asymmetric ligand
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Three complexes using the same asymmetric and dinucleating ligand DPCPMP (2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino acetic acid) have been synthesised. The ligand contains one pocket with three nitrogen donors and another pocket with two nitrogen donors and one oxygen donor. The complexes were containing two iron ions ([Fe2(DPCPMP)(CH3COO)2]), two manganese ions ([Mn2(DPCPMP)(CH3COO)2]) or one iron and one manganese ion ([FeMn(DPCPMP)(CH3COO)2]) mimicing the metal content in the three different subclasses of class I ribonucleotide reductases. The asymmetric ligand was chosen in order to investigate if a small alteration of the coordiantion environment (pyridine versus carboxylate donor) could steer the metal ions in the heterobimetallic complex into a specific pocket of the ligand or not. The complexes have been characterized and investigated with mass spectrometry, electrochemistry, IR, UV-vis, EPR and Mössbauer spectroscopy. From CV and Mössbauer spectroscopy of the heterobimetallic complex it is proposed that the asymmetry is not able to steer the metals into different pockets and instead a mixture of two different isomers is created in the synthesis.
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| 25. |
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| 26. |
- Bedin, Michele, PhD, 1984-
(författare)
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Iron, Manganese and Iridium Complexes From Models of RNR and Catalase to Water Oxidation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis has been synthesise and study metal complexes that mimic the structure and function of the active site in two particular metalloenzymes, ribonucleotide reductase (RNR) and manganese catalase (MnCAT). These two metalloenzymes both have two transition metals ions in the cofactor: two manganese ions in MnCAT and either two iron, iron-manganese or two manganese ions in RNR.Three different ligands were synthetized to make model complexes for these cofactors. The first ligand, BPMP, can bind two metal ions and provides two symmetric pockets with two pyridine groups and one amine each, plus a phenolate group that can bridge the two metals. The second ligand DPCPMP had one carboxylate group instead of a pyridine group in one pocket, creating an asymmetric ligand, and the third ligand BPCPMP, had two carboxylate groups, one in each pocket. From the first and the second ligands it was possible to obtain six complexes: low-valent homometallic Mn/Mn and Fe/Fe complexes and a heterometallic complex for each ligand. For the third ligand, only the Fe/Fe complex was synthetized.All seven complexes were characterized by a number of spectroscopic methods. The presence of carboxylate groups in the ligand shifted the redox potential for the metal complexes towards more negative values, particularly in the case of the homometallic Fe/Fe complexes. Surprisingly, for the asymmetric ligand the placement of the metal ions in the two pockets was not dictated by the asymmetry. Additionally, the relative stability of the homometallic complexes versus the heterometallic complexes and the possibility to transform a homometallic complex into a heterometallic complex were investigated. By titrating one metal into a solution containing the other homometallic dimer it was possible to observe that Fe2+ added to a solution of a Mn/Mn complex led to the replacement of one Mn ion in the complex with a Fe ion.The manganese complex of DPCPMP was investigated as a functional model for MnCAT, catalysing the disproportionation of H2O2 to oxygen and water. In the presence of H2O2 this complex also forms a high-valent species with a di-µ-oxo bridge similar to the MnCAT and RNR.Finally, the methodology used for the study of these complexes was also applied to a set of Ir complexes that act as water oxidation catalysts, and we could show that the presence of a pendant group stabilizes the metal at higher oxidation states leading to higher activity for the catalyst.
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| 27. |
- Bedin, Michele, et al.
(författare)
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Synthesis and properties of a heterobimetallic iron-manganese complex and its comparison with homobimetallic analogues
- 2019
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Ingår i: Inorganica Chimica Acta. - : ELSEVIER SCIENCE SA. - 0020-1693 .- 1873-3255. ; 490, s. 254-260
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Tidskriftsartikel (refereegranskat)abstract
- Heterobimetallic cofactors containing one manganese and one iron ion have recently been found within the di-metal carboxylate protein family. Herein we report the synthesis and characterization of three binuclear metal complexes with Fe-Fe, Mn-Mn, and Fe-Mn metal composition. All three complexes use the same ligand framework, the BPMP ligand (HBPMP=2,6-bis[(bis (-2-pyridylmethyl)amine) methyl]-4-methylphenol)) with two additional acetate ligands bridging the two metals. In terms of stability towards metal exchange, the Fe-Mn is more stable than the Mn-Mn complex but less stable than the Fe-Fe complex. Cyclic voltammetry shows that the Fe-Mn complex behaves markedly different than the homobimetallic complexes. The Fe-Mn complex also shows higher reactivity with O-2 than both the Fe-Fe and the Mn-Mn counterparts.
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| 28. |
- Beiler, Anna M., et al.
(författare)
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Enhancing photovoltages at p-type semiconductors through a redox-active metal-organic framework surface coating
- 2020
-
Ingår i: Nature Communications. - : NATURE RESEARCH. - 2041-1723. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Surface modification of semiconductors can improve photoelectrochemical performance by promoting efficient interfacial charge transfer. We show that metal-organic frameworks (MOFs) are viable surface coatings for enhancing cathodic photovoltages. Under 1-sun illumination, no photovoltage is observed for p-type Si(111) functionalized with a naphthalene diimide derivative until the monolayer is expanded in three dimensions in a MOF. The surface-grown MOF thin film at Si promotes reduction of the molecular linkers at formal potentials >300mV positive of their thermodynamic potentials. The photocurrent is governed by charge diffusion through the film, and the MOF film is sufficiently conductive to power reductive transformations. When grown on GaP(100), the reductions of the MOF linkers are shifted anodically by >700mV compared to those of the same MOF on conductive substrates. This photovoltage, among the highest reported for GaP in photoelectrochemical applications, illustrates the power of MOF films to enhance photocathodic operation. Photoelectrochemical performance is often hindered by sluggish charge transfer at the semiconductor interface. Here, the authors illustrate that a thin film coating made of a conductive metal-organic framework can improve the photovoltage of the underpinning semiconductors.
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| 29. |
- Beyler, Maryline, et al.
(författare)
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Pentacoordinate iron complexes as functional models of the distal iron in [FeFe] hydrogenases
- 2011
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 47:42, s. 11662-11664
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Tidskriftsartikel (refereegranskat)abstract
- Mononuclear pentacoordinate iron complexes with a free coordination site were prepared as mimics of the distal Fe (Fe(d)) in the active site of [FeFe] hydrogenases. The complexes catalyze the electrochemical reduction of protons at mild overpotential.
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| 30. |
- Bhunia, Asamanjoy, et al.
(författare)
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Formal water oxidation turnover frequencies from MIL-101(Cr) anchored Ru(bda) depend on oxidant concentration
- 2018
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 54, s. 7770-7773
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Tidskriftsartikel (refereegranskat)abstract
- The molecular water oxidation catalyst [Ru(bda)(L)(2)] has been incorporated into pyridine-decorated MIL-101(Cr) metal-organic frameworks. The resulting MIL-101@Ru materials exhibit turnover frequencies (TOFs) up to ten times higher compared to the homogenous reference. An unusual dependence of the formal TOFs on oxidant concentration is observed that ultimately arises from differing amounts of catalysts in the MOF crystals being active.
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| 31. |
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| 32. |
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| 33. |
- Bourrez, Marc, et al.
(författare)
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Concerted proton-coupled electron transfer from a metal-hydride complex
- 2015
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Ingår i: Nature Chemistry. - 1755-4330 .- 1755-4349. ; 7:2, s. 140-145
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Tidskriftsartikel (refereegranskat)abstract
- Metal hydrides are key intermediates in the catalytic reduction of protons and CO2 as well as in the oxidation of H-2. In these reactions, electrons and protons are transferred to or from separate acceptors or donors in bidirectional proton-coupled electron transfer (PCET) steps. The mechanistic interpretation of PCET reactions of metal hydrides has focused on the stepwise transfer of electrons and protons. A concerted transfer may, however, occur with a lower reaction barrier and therefore proceed at higher catalytic rates. Here we investigate the feasibility of such a reaction by studying the oxidation-deprotonation reactions of a tungsten hydride complex. The rate dependence on the driving force for both electron transfer and proton transfer-employing different combinations of oxidants and bases-was used to establish experimentally the concerted, bidirectional PCET of a metal-hydride species. Consideration of the findings presented here in future catalyst designs may lead to more-efficient catalysts.
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| 34. |
- Bozal-Ginesta, Carlota, et al.
(författare)
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Self-Recovery of Photochemical H2 Evolution with a Molecular Diiron Catalyst Incorporated in a UiO-66 Metal-Organic Framework
- 2020
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Ingår i: ChemPhotoChem. - : Wiley. - 2367-0932. ; 4:4, s. 287-290
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Tidskriftsartikel (refereegranskat)abstract
- Photochemical hydrogen evolution from a UiO‐66‐incorporated Fe2(dcbdt)(CO)6 catalyst in conjunction with a ruthenium photosensitizer and an ascorbate donor ceases after a period of irradiation, but is restored after a 60 min. resting period in the dark. Control experiments show that neither product inhibition nor pore clogging is responsible for this surprising behaviour, and intra‐crystal linker scrambling is proposed as a potential explanation.
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| 35. |
- Brown, Allison, et al.
(författare)
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Ultrafast Electron Transfer between Dye and Catalyst on a Mesoporous NiO Surface
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 26, s. 8060-8063
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)(6) (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (tau approximate to 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t(1/2) approximate to 10 ps) and efficient surface electron transfer from C343 to the coadsorbed [FeFe] (mcbdt)(CO)(6). The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on. DSSFDs.
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| 36. |
- Canton, S. E., et al.
(författare)
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Watching the dynamics of electrons and atoms at work in solar energy conversion
- 2015
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Ingår i: Faraday discussions. - : Royal Society of Chemistry. - 1359-6640 .- 1364-5498. ; 185, s. 51-68
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Tidskriftsartikel (refereegranskat)abstract
- The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray
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| 37. |
- Castner, Ashleigh T.
(författare)
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From Peak to Peak: Exploring Electron Hopping and Mass Transport in Metal-Organic Frameworks
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Incorporating molecular electrocatalysts into solid support structures combines the best of two worlds: their molecular nature allows precise structural tunability for selective and efficient conversion of small molecule substrates, while their structural integrity is greatly improved by the heterogeneous support matrix to allow for long-term stability and potentially industrial-scale applications. Metal-organic frameworks (MOFs) represent a potential class of materials to act as viable support scaffolds for hosting molecular catalysts for sustainable energy conversion, exhibiting well-ordered porous structures that can support high loading densities of catalyst species. The utilization of such heterogeneous electrocatalyst materials then relies on the transport of both mass and charge throughout the MOF to sustain electrocatalytic reactions. The concomitant transport of charge to activate the embedded catalyst species and mass transport of substrate and product molecules, as well as charge-balancing ions, to these activated catalysts must all maintain a balance within the framework to optimize the catalytic efficiency of the MOF-based material. The aim of this thesis is to explore mass and charge transport behaviors in electroactive and electrocatalytic MOF materials to gain insight into the mechanisms for these interwoven transport-related processes.The first part of this thesis introduces two novel electrocatalytic MOF materials and discusses the charge transport behaviors exhibited in each. Potential limitations in mass and charge transport processes which could influence the catalytic efficiency of the material are identified in each system. The second part of this thesis is centered on discussions of two electroactive MOF materials without embedded catalysts to gain a mechanistic understanding of mass and charge transport processes. The first of these studies focuses on the influences of imposed mass transport properties on the observed charge transport in a MOF, revealing the potential for multiple mechanisms of charge transport to be exhibited in one framework. The second study presents the mediated charge transport through an electroactive framework to a dissolved acceptor species to drive a chemical process, and kinetic analysis of the model pseudo-catalytic reaction is discussed.The work in this thesis highlights the importance of understanding the influences of mass and charge transport in electroactive and electrocatalytic MOFs for understanding the underlying mechanisms of these processes. Such knowledge would allow for the optimization of transport phenomena and result in more efficient MOF-based electrocatalysts.
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| 38. |
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| 39. |
- Castner, Ashleigh T., et al.
(författare)
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Microscopic Insights into Cation-Coupled Electron HoppingTransport in a Metal-Organic Framework br
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:13, s. 5910-5920
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Tidskriftsartikel (refereegranskat)abstract
- Electron transport through metal-organic frameworks by ahopping mechanism between discrete redox active sites is coupled to diffusion-migration of charge-balancing counter cations. Experimentally determinedapparent diffusion coefficients,Deapp, that characterize this form of chargetransport thus contain contributions from both processes. While this is wellestablished for MOFs, microscopic descriptions of this process are largelylacking. Herein, we systematically lay out different scenarios for cation-coupledelectron transfer processes that are at the heart of charge diffusion throughMOFs. Through systematic variations of solvents and electrolyte cations, it isshown that theDeappfor charge migration through a PIZOF-type MOF,Zr(dcphOH-NDI) that is composed of redox-active naphthalenediimide(NDI) linkers, spans over 2 orders of magnitude. More importantly, however,the microscopic mechanisms for cation-coupled electron propagation arecontingent on differing factors depending on the size of the cation and its propensity to engage in ion pairs with reduced linkers,either non-specifically or in defined structural arrangements. Based on computations and in agreement with experimental results, weshow that ion pairing generally has an adverse effect on cation transport, thereby slowing down charge transport. In Zr(dcphOH-NDI), however, specific cation-linker interactions can open pathways for concerted cation-coupled electron transfer processes thatcan outcompete limitations from reduced cationflux.
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| 40. |
- Castner, Ashleigh T., et al.
(författare)
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Mimicking the Electron Transport Chain and Active Site of [FeFe] Hydrogenases in One Metal-Organic Framework : Factors That Influence Charge Transport
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:21, s. 7991-7999
-
Tidskriftsartikel (refereegranskat)abstract
- [FeFe] hydrogenase (H2ase) enzymes are effective proton reduction catalysts capable of forming molecular dihydrogen with a high turnover frequency at low overpotential. The active sites of these enzymes are buried within the protein structures, and substrates required for hydrogen evolution (both protons and electrons) are shuttled to the active sites through channels from the protein surface. Metal–organic frameworks (MOFs) provide a unique platform for mimicking such enzymes due to their inherent porosity which permits substrate diffusion and their structural tunability which allows for the incorporation of multiple functional linkers. Herein, we describe the preparation and characterization of a redox-active PCN-700-based MOF (PCN = porous coordination network) that features both a biomimetic model of the [FeFe] H2ase active site as well as a redox-active linker that acts as an electron mediator, thereby mimicking the function of [4Fe4S] clusters in the enzyme. Rigorous studies on the dual-functionalized MOF by cyclic voltammetry (CV) reveal similarities to the natural system but also important limitations in the MOF-enzyme analogy. Most importantly, and in contrast to the enzyme, restrictions apply to the total concentration of reduced linkers and charge-balancing counter cations that can be accommodated within the MOF. Successive charging of the MOF results in nonideal interactions between linkers and restricted mobility of charge-compensating redox-inactive counterions. Consequently, apparent diffusion coefficients are no longer constant, and expected redox features in the CVs of the materials are absent. Such nonlinear effects may play an important role in MOFs for (electro)catalytic applications.
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| 41. |
- Chen, Xiaoyu, et al.
(författare)
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Understanding the Mechanism of CO2 to CO Conversion by Ruthenium Polypyridyl Catalysts
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A detailed mechanistic study of ruthenium 2,2:6,2-terpyridine (tpy) 2,2-bipyridine (bpy) class of catalysts is presented, with all three key stages (i.e. solvent dissociation, C-O bond cleavage and CO dissociation) discussed. DFT calculations together with kinetic studies revealed that the introduction of a methyl substituent on the bipyridine ligand eases solvent dissociation and hence allow catalysis to take place at the first reduction potential as the five coordinated Ru complex is easier to reduce. This highlights the importance of steric effect in catalyst-design. For C-O bond cleavage, DFT calculations suggest that proton acts as a much better oxide accepter compared to CO2, explaining the improved activity when water is added to the system. To further understand how the electronic nature of the ring substitutes affects the reactivity, we designed a hypothetical catalyst with fluorine substitutes and found out electron withdrawing groups lower the reductive potentials at a cost of harder solvent dissociation. For the final CO dissociation, due to the special nature of carbonyl ligands, neither steric nor electronic alternations can ease the step and here is where kinetic trans effect comes into play. In line with a recent experimental work, our DFT calculations showed that when a carbene group is trans to CO, the dissociation rate is increased dramatically.
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| 42. |
- Das, Biswanath, et al.
(författare)
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Iron Pentapyridyl Complexes as Molecular WaterOxidation Catalysts : Strong Influence of a Chloride Ligandand pH in Altering the Mechanism
- 2016
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:10, s. 1178-1186
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Tidskriftsartikel (refereegranskat)abstract
- The development of molecular water oxidation catalysts basedon earth-abundant, non-noble metals is essential for artificial photosynthesis research. Iron, which is the most abundant transition metal in the earth's crust, is a prospective candidate for this purpose. Herein, we report two iron complexes based on the polypyridyl ligand Py5OH (Py5OH=pyridine-2,6-diylbis[di(pyridin-2-yl)methanol]) that can catalyse water oxidation to produce O2 in RuIII-induced (at pH 8, highest turnover number (TON)=26.5; turnover frequency (TOF)=2.2 s-1), CeIV-induced(at pH 1.5 highest TON=16; TOF=0.75 s-1) and photo-induced(at pH 8, highest TON=43.5; TOF=0.6 s-1) reactions. A chloride ligand in one of the iron complexes is shown to affect the activity strongly, improve stability and, thereby, the performance at pH 8 but it inhibits oxygen evolution at pH 1.5. The observations are consistent with a change in mechanism for catalytic water oxidation with the Fe(Py5OH) complexes between acidic (CeIV) and near-neutral pH (RuIII).
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| 43. |
- Das, Biswanath, et al.
(författare)
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Structural features of molecular electrocatalysts in multi-electron redox processes for renewable energy : recent advances
- 2019
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 3:9, s. 2159-2175
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Forskningsöversikt (refereegranskat)abstract
- Understanding the structural features of molecular electrocatalysts for carbon dioxide reduction and water oxidation is essential for manufacturing next generation catalysts for renewable energy. We will discuss the crucial structural motifs of those catalysts that have shown novel characteristics in recent years in terms of electrocatalytic efficacy (high TON, TOF and low overpotential), product selectivity and mechanisms. Both inorganic and organic homogeneous catalysts are scrutinized in this review. We will also highlight electrocatalysts with dual activity (i.e. they are able to catalyze both water oxidation and CO2 reduction) as an interesting prospect from the point of view of a single catalyst electrolyzer: a possible design for future easy-to-manufacture effective electrolyzers. This discussion will enrich the overall knowledge on the electrocatalyst design, an important step towards the development of efficient catalysts with cutting edge designs for a renewable energy future and practical applications.
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| 44. |
- Das, Biswanath, et al.
(författare)
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Water oxidation catalysed by a mononuclear CoII polypyridine complex; possible reaction intermediates and the role of the chloride ligand
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 51:66, s. 13074-13077
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Tidskriftsartikel (refereegranskat)abstract
- A mononuclear cobalt(II) complex as a homogeneous molecular catalyst for photochemically, electrochemically and chemically induced oxygen evolution reactions is presented. Experimental evidence points towards the presence of a chloride ligand at the cobalt centre throughout the catalytic cycle, and the temporary detachment of a pyridine ligand to open a coordination site for substrate binding.
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| 45. |
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| 46. |
- D'Imperio, Nicolas Daniele, 1991-
(författare)
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Olefins from carbonyls : Development of new phosphorus-based cross-coupling reactions
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Olefins, compounds containing C=C double bonds, are omnipresent in nature and serve as useful starting materials for various chemical modifications. Olefins are of crucial importance in Medicinal Chemistry and are also present in essential objects like dyes, polymers and plastics. Thus, developing methodologies for synthesizing olefins is at the heart of Organic Chemistry.In this regard, many reactions have been developed over the years for the production of olefins from different starting materials. To date only one reaction, namely the McMurry coupling, is available for constructing olefins from two carbonyls. This reaction is frequently applied in an academic context, but suffers many drawbacks that limit its wider use. This thesis offers innovative phosphorus-based methodologies for coupling two carbonyls into olefins. All the methods presented herein are based on a one-pot sequence in which a first carbonyl is transformed into a phosphaalkene (P=C double bond containing molecule) which, upon activation, reacts with a second carbonyl with formation of desired alkenes.The first two chapters of this thesis give a general overview on literature protocols for the formation of olefins, along with a comparison between P=C and C=C double bonds containing molecules.The third chapter is dedicated to the presentation of a new potential phosphorus-based coupling reagent. The studies presented in this chapter set the basis for the development of a new cross-coupling reaction of aldehydes to olefins.In the fourth chapter a new method for the one-pot synthesis of disubstituted alkenes from aldehydes is presented. The reactivity of phosphaalkene intermediates proved to be crucial in determining the reaction scope of the process. In the fifth chapter, a closer look into the E-Z stereoselectivity of the protocol is described.The following two chapters deal with more reactive phosphaalkenes. Studies on their chemical properties showed to be fundamental for developing an unprecedent cross-coupling of ketones and aldehydes to trisubstituted alkenes.In summary, this thesis represents the development of new phosphorus-based cross-couplings of carbonyls to olefins. Protocols for the stereoselective synthesis of disubstituted alkenes from two aldehydes, and trisubstituted olefins from ketones and aldehydes are presented. These innovative methodologies offer precious alternatives to the McMurry coupling.
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| 47. |
- D'Imperio, Nicolas, et al.
(författare)
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E,Z-Selectivity in the reductive cross-coupling of two benzaldehydes to stilbenes under substrate control
- 2020
-
Ingår i: Organic & Biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 18, s. 6171-6179
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Tidskriftsartikel (refereegranskat)abstract
- Unsymmetrical E- and Z-stilbenes can be synthesized from two differently substituted benzaldehydes in a MesP(TMS)Li-promoted reductive coupling sequence. Depending on the order of addition of the two coupling partners, the same olefin can be produced in either E- or Z-enriched form under identical reaction conditions. A systematic study of the correlation between the stereochemical outcome of the reaction and the substitution pattern at the two aldehydes is presented. The results can be used as guidelines to predict the product stereochemistry.
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| 48. |
- D'Imperio, Nicolas, et al.
(författare)
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Highly Conjugated Bis(benzo[b]phosphole)-P-oxides : Synthesis and Electrochemical, Optical, and Computational Studies
- 2023
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Ingår i: European Journal of Organic Chemistry. - : John Wiley & Sons. - 1434-193X .- 1099-0690. ; 26:4
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Tidskriftsartikel (refereegranskat)abstract
- The first examples of a pi-conjugated benzo[b]phosphole P-oxide in which two phosphole P-oxide units are connected by a carbon-carbon double bond are described. The molecules are synthesized as E isomers with respect to the carbon-carbon double bond and exist as stable cis and trans isomers (chiral and meso one respectively) relatively to the two stereogenic P atoms. The optical and electrochemical properties of both isomers have been investigated by experiment and computations.
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| 49. |
- D'Imperio, Nicolas, et al.
(författare)
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Triphenylphosphaalkenes in Chemical Equilibria
- 2019
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :11-12, s. 1562-1566
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Tidskriftsartikel (refereegranskat)abstract
- Triphenylphosphaalkenes 1a-c were prepared in good to excellent yields in a modified phospha-Peterson reaction between PhP(Li)TMS and benzophenones with different para-substituents at the C-phenyl groups (a: R = H, b: R = O-octyl, c: R = F). Owing to the low kinetic stabilization that is provided by the P-phenyl group, compounds 1a-c engage in reversible dimerization and oligomerization reactions, some of which are not detectable by 31P NMR monitoring. The dimers and oligomers are in chemical equilibria with monomeric 1a-c, and can be converted quantitatively to phosphinites 4a-c by the irreversible addition of methanol across the P=C double bond.
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| 50. |
- Eilers, Gerriet, et al.
(författare)
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Ligand versus metal protonation of an iron hydrogenase active site mimic
- 2007
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 13:25, s. 7075-7084
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Tidskriftsartikel (refereegranskat)abstract
- The protonation behavior of the iron hydrogenase active-site mimic [Fe2(u-adt)(CO)4(PMe3)2] (1; adt=N-benzyl-azadithiolate) has been investigated by spectroscopic, electrochemical, and computational methods. The combination of an adt bridge and electron-donating phosphine ligands allows protonation of either the adt nitrogen to give [Fe2(μ-Hadt)(CO)4(PMe3)2]+ ([1H]+), the Fe-Fe bond to give [Fe2-(μ-adt)(μ-H)(CO)4(PMe3)2]+ ([1Hy]+), or both sites simultaneously to give [Fe2(μ-Hadt)(μ-H)(CO)4(PMe3)2]2+ ([1HHy]2+). Complex 1 and its protonation products have been characterized in acetonitrile solution by IR, 1H, and 31PNMR spectroscopy. The solution structures of all protonation states feature a basal/basal orientation of the phosphine ligands, which contrasts with the basal/apical structure of 1 in the solid state. Density functional calculations have been performed on all protonation states and a comparison between calculated and experimental spectra confirms the structural assignments. The ligand protonated complex [1H]+ (pKa =12) is the initial, metastable protonation product while the hydride [1Hy]+ (pKa=15) is the thermodynamically stable singly protonated form. Tautomerization of cation [1H]+ to [1Hy]+ does not occur spontaneously. However, it can be catalyzed by HCl (k=2.2M-1s-1), which results in the selective formation of cation [1Hy]+. The protonations of the two basic sites have strong mutual effects on their basicities such that the hydride (pKa=8) and the ammonium proton (pKa=5) of the doubly protonated cationic complex [1HHy]2+ are considerably more acidic than in the singly protonated analogues. The formation of dication [1HHy]2+ from cation [1H]+ is exceptionally slow with perchloric or trifluoromethanesulfonic acid (k= 0.15 M-1s-1), while the dication is formed substantially faster (k > 102 M-1 s-1) with hydrobromic acid. Electrochemically, 1 undergoes irreversible reduction at -2.2V versus ferrocene, and this potential shifts to -1.6, - 1.1, and -1.0 V for the cationic complexes [1H]+, [1Hy]+, and [1HHy]2+, respectively, upon protonation. The doubly protonated form [1HHy]2+ is reduced at less negative potential than all previously reported hydrogenase models, although catalytic proton reduction at this potential is characterized by slow turnover.
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