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Nancy S Mills - One of the best experts on this subject based on the ideXlab platform.
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dianion and dication of tetrabenzo 5 7 Fulvalene greater antiaromaticity than aromaticity in comparable systems
Journal of the American Chemical Society, 2008Co-Authors: Ashley M Piekarski, Nancy S Mills, Abraham YousefAbstract:The dianion, 52−, and dication, 52+, of tetrabenzo[5.7]Fulvalene represent an aromaticity/antiaromaticity continuum in which the fluorenyl system changes from aromatic in 52− to antiaromatic in 52+. Conversely, the antiaromatic dibenzotropylium system of 52− becomes an aromatic system in 52+, allowing an examination of aromaticity/antiaromaticity within the same carbon framework. Dianion 52− was prepared and characterized by 1H NMR spectroscopy. The fluorenyl system of 52− showed the downfield shifts expected for an aromatic system, while the dibenzotropylium system showed the paratropic shifts expected for an antiaromatic system. The conclusions from 1H NMR spectroscopy were supported by NICS(1)zz calculations for each system. Comparison of the 1H NMR spectrum and NICS(1)zz of 52− with those of 52+ supported the assignments of aromaticity/antiaromaticity for each system. Aromaticity/antiaromaticity were further examined through comparison of the degree of bond length alternation, which showed that the bo...
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dianion and dication of tetrabenzo 5 7 Fulvalene greater antiaromaticity than aromaticity in comparable systems
Journal of the American Chemical Society, 2008Co-Authors: Ashley M Piekarski, Nancy S Mills, Abraham YousefAbstract:The dianion, 5(2-), and dication, 5(2+), of tetrabenzo[5.7]Fulvalene represent an aromaticity/antiaromaticity continuum in which the fluorenyl system changes from aromatic in 5(2-) to antiaromatic in 5(2+). Conversely, the antiaromatic dibenzotropylium system of 5(2-) becomes an aromatic system in 5(2+), allowing an examination of aromaticity/antiaromaticity within the same carbon framework. Dianion 5(2-) was prepared and characterized by (1)H NMR spectroscopy. The fluorenyl system of 5(2-) showed the downfield shifts expected for an aromatic system, while the dibenzotropylium system showed the paratropic shifts expected for an antiaromatic system. The conclusions from (1)H NMR spectroscopy were supported by NICS(1) zz calculations for each system. Comparison of the (1)H NMR spectrum and NICS(1) zz of 5(2-) with those of 5(2+) supported the assignments of aromaticity/antiaromaticity for each system. Aromaticity/antiaromaticity were further examined through comparison of the degree of bond length alternation, which showed that the bond length alternation was slightly greater for the antiaromatic ring systems than for the aromatic systems. However, when structures of 5(2-) and 5(2+) with no bond length alternation were examined, there was a dramatic increase in the degree of antiaromaticity for the antiaromatic ring systems as evaluated through NICS. This result suggests that a decrease in bond length alternation results in an increase in antiaromaticity as well as an increase in aromaticity. The magnitude of the antiaromaticity of the fluorenyl system in 5(2+) was greater than the magnitude of the aromaticity in the fluorenyl system of 5(2-), with similar effects shown by the analogous tropylium systems. This is consistent with the behavior of the antiaromatic dication of tetrabenzo[5.5]Fulvalene, compared to that of its aromatic dianion, and also with the behavior of the cyclopentadienyl cation/anion and tropylium cation/anion.
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the aromaticity antiaromaticity continuum 1 comparison of the aromaticity of the dianion and the antiaromaticity of the dication of tetrabenzo 5 5 Fulvalene via magnetic measures
Journal of Organic Chemistry, 2006Co-Authors: Nancy S Mills, Michelle BenishAbstract:The aromaticity of the dianion (2) and the antiaromaticity of the dication (3) of tetrabenzo[5.5]Fulvalene have been evaluated through magnetic criteria, 1H NMR shifts, nucleus-independent chemical shifts, NICS, and magnetic susceptibility exaltation, Λ. The sum of the NICS values, using the GIAO (gauge-independent atomic orbital) method, for 2 is −35.2; that of 3 is +38.2, indicating the aromaticity of 2 and the antiaromaticity of 3. Calculation of magnetic susceptibility exaltation using the CSGT (continuous set of gauge transformations) method gives a similar result, with Λ of −81.8 ppm cgs for 2 and 95.8 ppm cgs for 3. The general validity of these values is suppoorted by excellent agreement between the NMR shifts calculated by the GIAO and CSGT methods with experimental shifts. Comparison of 1H NMR shifts with those of model compounds allows evaluation of the magnitude of the diatropic shift in 2 and paratropic shift in 3 and supports their assignment as aromatic/antiaromatic, respectively. The agree...
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dications of fluorenylidenes the effect of substituent electronegativity and position on the antiaromaticity of substituted tetrabenzo 5 5 Fulvalene dications
Journal of Organic Chemistry, 2003Co-Authors: Amalia Levy, And Amber Rakowitz, Nancy S MillsAbstract:Oxidation of 3,6-disubstituted tetrabenzo[5.5]Fulvalenes by SbF5 results in the formation of dications that behave like two antiaromatic fluorenyl cations connected by a single bond. Both fluorenyl systems exhibit the paratropic shifts and nucleus independent chemical shifts (NICS) characteristic of antiaromatic species. Comparison with analogous 2,7-disubstituted tetrabenzo[5.5]Fulvalenes reveals that the antiaromaticity of the substituted ring system can be altered substantially by changes in the placement of the substituents, possibly due to changes in the delocalization of charge in the system. Substituents in the 3,6-position decrease the antiaromaticity because of the increase in the benzylic resonance compared to 2,7-substituents.
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dications of fluorenylidenes use of magnetic properties to evaluate the antiaromaticity of the dication of tetrabenzo 5 5 Fulvalene and substituted fluorenyl cations
Journal of the American Chemical Society, 1999Co-Authors: Nancy S MillsAbstract:The NICS values of the dication of tetrabenzo[5.5]Fulvalene (1) show substantial antiaromaticity. Substituted fluorenyl cations possess antiaromatic five-membered rings but the calculated antiaromaticity (NICS) of the six-membered rings depends on the calculational level. Through calculation of magnetic susceptibility exaltation (Λ), 1 is antiaromatic while fluorenyl cations are not. The paratropic shift seen in the 1H NMR spectra of 1 and the substituted fluorenyl cations is linearly related to NICS (six-membered ring) and to Λ. NICS values suggest that electron delocalization in the fluorenyl cations occurs to maintain the aromaticity of the benzene subunits and to localize the positive charge in the five-membered ring. In contrast, electron delocalization in 1 results in delocalization of a positive charge throughout each fluorenyl system.
Kasper Moth-poulsen - One of the best experts on this subject based on the ideXlab platform.
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Designing photoswitches for molecular solar thermal energy storage
Tetrahedron Letters, 2015Co-Authors: Anders Lennartson, Anna Roffey, Kasper Moth-poulsenAbstract:Solar energy conversion and solar energy storage are key challenges for a future society with limited access to fossil fuels. Certain compounds that undergo light-induced isomerisation to a metastable isomer can be used for storage of solar energy, so-called molecular solar thermal systems. Exposing the compound to sun light will generate a high energy photoisomer that can be stored. When energy is needed, the photoisomer can be catalytically converted back to the parent compound, releasing the excess energy as heat. This Letter gives examples of selected molecular solar thermal systems found in the literature. The focus of the Letter is on examples where molecular design has been used to improve the performance of the molecules, and as such it may serve as an inspiration for future design. The selected examples cover five widely studied systems, notably: anthracenes, stilbenes, azobenzenes, tetracarbonyl-Fulvalene-diruthenium compounds and norbornadienes.
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Fluorinated Fulvalene ruthenium compound for molecular solar thermal applications
Journal of Fluorine Chemistry, 2014Co-Authors: Karl Borjesson, Anders Lennartson, Kasper Moth-poulsenAbstract:Molecular photoswitches, i.e. molecules capable of isomerizing between two states when submitted to light stimuli, has found applications in several areas such as molecular logic, molecular electronics, and, if the two isomers differ substantially in energy, molecular solar thermal (MOST) systems. In a MOST system the photoswitchable molecule absorbs a photon where after a photoinduced isomerisation to a high energy metastable photoisomer occurs. The photon energy is thus stored within the molecule. Fulvalenediruthenium compounds, has been suggested as a candidate in MOST systems thanks to the large difference in energy between the two isomers, its relative stability, and its ability to absorb sunlight. We here present a fluorinated Fulvalene ruthenium derivative and show that its processing properties is remarkably different, while having retained photoisomerization efficiency, compared to its hydrocarbon analog. © 2014 The Authors.
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Molecular solar thermal (MOST) energy storage and release system
Energy & Environmental Science, 2012Co-Authors: Kasper Moth-poulsen, Dusan Coso, Steven K. Meier, Anirban Majumdar, Karl Borjesson, Nikolai Vinokurov, K. Peter C. Vollhardt, Rachel A SegalmanAbstract:A device for solar energy storage and release based on a reversible chemical reaction is demonstrated. A highly soluble derivative of a (Fulvalene)diruthenium (FvRu2) system is synthesized, capable of storing solar energy (110 J g-1) in the form of chemical bonds and then releasing it "on demand", when excited thermally or catalytically. A microfluidic device is designed and constructed for both the photo-harvesting and the heat-utilization steps, allowing for the recycling of material.
Peter K C Vollhardt - One of the best experts on this subject based on the ideXlab platform.
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the quest for double vicinal c h bond activation on the η5 η5 Fulvalene diiridium platform syntheses and structures of η5 η5 Fulvalene ir2 ortho μ c6h4 co 2 ir ir and related complexes
Synthesis, 2019Co-Authors: Judith Baumgartner, Peter K C Vollhardt, Bernd Kayser, Robert G Bergman, Theodore P Klupinski, Yong Kwang Park, Michael J West, Bolin ZhuAbstract:The Fulvalene diiridium platform was scrutinized for its potential to effect double vicinal C–H activation of C6H6 and C6H12, respectively. For this purpose, an improved preparation of Fv[Ir(CO)2]2 was developed, and the syntheses of the new complexes FvIr(CO)2Ir(CO)(η 2-C6F6), Fv[Ir(CO)(η 2-C6F6)]2, Fv[Ir(CH2=CH2)2]2 (X-ray), Fv[Ir(PMe3)(H)2]2 (X-ray), and (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)2]2 were accomplished. When irradiated in C6H6, these molecules succeeded to varying degrees, and best for (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)2]2, in the double metalation of the aromatic ring to engender ligating Ir2(ortho-μ-C6H4)(CO)2 (Ir–Ir) moieties, in addition to their precursor mono(phenyliridium hydride) constructs. A competing photochemical pathway is evident by the formation of diastereomers of Fv (or 2,2’,3,3’-tetra-tert-butylFv) [Ir(CO)(Ph)(H)]2 and the resulting dehydrogenated ligated [Ir(CO)(Ph)]2 (Ir–Ir). The structures of FvIr2(ortho-µ-C6H4)(CO)2 (Ir–Ir) and trans-Fv[Ir(CO)(Ph)]2 (Ir–Ir) were corroborated by X-ray analyses. Efforts to realize C–H bond activations with C6H12 generally failed or fared very poorly, with the exception of the tert-butylFv system, which enabled single, but not further, insertion to give (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)(Cy)(H)][Ir(CO)2] in 34% yield. To explore the relevant chemistry of phenyl- and alkyliridium species attached to Fv, several such derivatives were made by independent routes, adding knowledge to the fundamental behavior of this category of molecules. Where appropriate and for comparative purposes, similar reactions were performed on the corresponding Cp- and 1,2-di-tert-butylCpIr(CO)2 relatives.
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photosubstitution of Fulvalene tetracarbonyldiruthenium by alkenes and alkynes first observation of alkyne coupling on Fulvalene dimetals and synthesis of a Fulvalene dimetallacyclopentadiene alkene complex
Organometallics, 2002Co-Authors: Mingchou Chen, Peter K C Vollhardt, Michael J Eichberg, Ricardo Sercheli, Ian M Wasser, Glenn D WhitenerAbstract:Irradiation (λmax = 300−375 nm) of FvRu2(CO)4 (1, Fv = η5:η5-bicyclopentadienyl) or (μ2-η1:η5-cyclopentadienyl)2Ru2(CO)4 (2) with dimethyl cis- or trans-butenedioate resulted in FvRu2(η2-trans-CHRCHR)(CO)3 (3, R = CO2CH3). Prolonged irradiation of 1−3 provided FvRu2(η2-trans-CHRCHR)2(CO)2 (4a, R = CO2CH3) and FvRu2(η2-cis-CHRCHR)(η2-trans-CHRCHR)(CO)2 (4b, R = CO2CH3). Photocatalytic isomerization of cis to trans alkene occurred in the presence of 1−4. Irradiation of 1−3 with dimethyl butynedioate produced FvRu2(μ2-η2-dimethyl butynedioate)(CO)3 (5). Prolonged irradiation of 1−5 with the alkyne afforded FvRu2(μ2-η2:η4-CRCRCRCR)2(CO) (6, R = CO2CH3). Irradiation of a THF solution of 6 generated FvRu2(μ2-η2:η4-CRCRCRCR)2(THF) (7, R = CO2CH3). Photochemical alkyne cyclotrimerization was observed in the presence of 1−7. In the presence of CO, 7 reverted to 6 thermally. Heating 7 in the presence of dimethyl cis-butenedioate, thiophene, PPh3, or dimethyl sulfoxide (DMSO) afforded FvRu2(μ2-η2:η4-CRCRCRCR)2(L) (8...
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synthesis and crystal structures of Fulvalene w2 sh 2 co 6 Fulvalene w2 mu s2 co 6 and Fulvalene w2 mu s co 6 low valent tungsten carbonyl sulfide and disulfide complexes stabilized by the bridging Fulvalene ligand
Inorganic Chemistry, 2002Co-Authors: Kenneth B Capps, Peter K C Vollhardt, Ian M Wasser, Glenn D Whitener, Andreas Bauer, Khalil A Abboud, Carl D HoffAbstract:Reaction of FvW2(H)2(CO)6 with 2/8S8 in THF results in rapid and quantitative formation of FvW2(SH)2(CO)6. The crystal structure of this complex is reported and shows that the two tungsten−hydrosul...
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synthesis structure and fluxionality of μ diphenylsilylene Fulvalene tetracarbonyldirhenium double si h activation to the first Fulvalene silylene complex
Organometallics, 2000Co-Authors: Bernd Kayser, And Michael J Eichberg, Peter K C VollhardtAbstract:(Fulvalene)hexacarbonyldirhenium (1) furnishes the first silylene Fulvalenedimetal complex 3 by double Si−H activation. The solid-state structure of the molecule was determined by X-ray analysis and its solution dynamics by 1H NMR spectroscopy.
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photochemistry of Fulvalene tetracarbonyldiruthenium and its derivatives efficient light energy storage devices
Journal of the American Chemical Society, 1997Co-Authors: Roland Boese, Peter K C Vollhardt, Kevin J Cammack, Adam J Matzger, Kai Pflug, William B Tolman, Timothy W WeidmanAbstract:Broad-band irradiation (λmax = 350 nm) of FvRu2(CO)4 (1, Fv = η5:η5-bicyclopentadienyl) resulted in rapid isomerization to colorless (μ2-η1:η5-cyclopentadienyl)2Ru2(CO)4 (2) in a novel process involving a formal dinuclear oxidative addition to a C−C bond. The product reverted to 1 upon heating in solution or in the solid state, under the latter conditions with an enthalpy change of −29.8 (1.5) kcal mol-1. Mechanistic studies with a mixture of 1 and 1-d8 revealed the absence of label scrambling, pointing to intramolecular pathways. The quantum yield (0.15) was unaffected by the presence of CCl4, and no chlorination products were observed under these conditions. Irradiation of solutions of 1 or 2 with 300 nm light provided Fv(μ2-η1:η5-cyclopentadienyl)2Ru4(CO)6 (6) or, in the presence of alkynes, the adducts FvRu2(CO)3(RCCR) (8−10, R = H, C6H5, CO2CH3). Heating 1 and PR3 (R = CH2CH3, CH3, or OCH3) yielded FvRu2(CO)3(PR3) (12−14), in which a fluxional process occurs characterized by intramolecular terminal t...
Karl Borjesson - One of the best experts on this subject based on the ideXlab platform.
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tuning the photochemical properties of the Fulvalene tetracarbonyl diruthenium system
Dalton Transactions, 2016Co-Authors: Anders Lennartson, Karl Borjesson, Angelica Lundin, Victor Gray, Kasper MothpoulsenAbstract:In a Molecular Solar-Thermal Energy Storage (MOST) system, solar energy is converted to chemical energy using a compound that undergoes reversible endothermic photoisomerization. The high-energy photoisomer can later be converted back to the parent compound and the excess energy is released as heat. One of the most studied MOST systems is based on Fulvalene-tetracarbonyl-diruthenium, and this paper demonstrates, for the first time, the possibility to tune the photochemical properties of this system by positive steric hindrance working on the Fulvalene unit.
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Fluorinated Fulvalene ruthenium compound for molecular solar thermal applications
Journal of Fluorine Chemistry, 2014Co-Authors: Karl Borjesson, Anders Lennartson, Kasper Moth-poulsenAbstract:Molecular photoswitches, i.e. molecules capable of isomerizing between two states when submitted to light stimuli, has found applications in several areas such as molecular logic, molecular electronics, and, if the two isomers differ substantially in energy, molecular solar thermal (MOST) systems. In a MOST system the photoswitchable molecule absorbs a photon where after a photoinduced isomerisation to a high energy metastable photoisomer occurs. The photon energy is thus stored within the molecule. Fulvalenediruthenium compounds, has been suggested as a candidate in MOST systems thanks to the large difference in energy between the two isomers, its relative stability, and its ability to absorb sunlight. We here present a fluorinated Fulvalene ruthenium derivative and show that its processing properties is remarkably different, while having retained photoisomerization efficiency, compared to its hydrocarbon analog. © 2014 The Authors.
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Molecular solar thermal (MOST) energy storage and release system
Energy & Environmental Science, 2012Co-Authors: Kasper Moth-poulsen, Dusan Coso, Steven K. Meier, Anirban Majumdar, Karl Borjesson, Nikolai Vinokurov, K. Peter C. Vollhardt, Rachel A SegalmanAbstract:A device for solar energy storage and release based on a reversible chemical reaction is demonstrated. A highly soluble derivative of a (Fulvalene)diruthenium (FvRu2) system is synthesized, capable of storing solar energy (110 J g-1) in the form of chemical bonds and then releasing it "on demand", when excited thermally or catalytically. A microfluidic device is designed and constructed for both the photo-harvesting and the heat-utilization steps, allowing for the recycling of material.
Anders Lennartson - One of the best experts on this subject based on the ideXlab platform.
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tuning the photochemical properties of the Fulvalene tetracarbonyl diruthenium system
Dalton Transactions, 2016Co-Authors: Anders Lennartson, Karl Borjesson, Angelica Lundin, Victor Gray, Kasper MothpoulsenAbstract:In a Molecular Solar-Thermal Energy Storage (MOST) system, solar energy is converted to chemical energy using a compound that undergoes reversible endothermic photoisomerization. The high-energy photoisomer can later be converted back to the parent compound and the excess energy is released as heat. One of the most studied MOST systems is based on Fulvalene-tetracarbonyl-diruthenium, and this paper demonstrates, for the first time, the possibility to tune the photochemical properties of this system by positive steric hindrance working on the Fulvalene unit.
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Designing photoswitches for molecular solar thermal energy storage
Tetrahedron Letters, 2015Co-Authors: Anders Lennartson, Anna Roffey, Kasper Moth-poulsenAbstract:Solar energy conversion and solar energy storage are key challenges for a future society with limited access to fossil fuels. Certain compounds that undergo light-induced isomerisation to a metastable isomer can be used for storage of solar energy, so-called molecular solar thermal systems. Exposing the compound to sun light will generate a high energy photoisomer that can be stored. When energy is needed, the photoisomer can be catalytically converted back to the parent compound, releasing the excess energy as heat. This Letter gives examples of selected molecular solar thermal systems found in the literature. The focus of the Letter is on examples where molecular design has been used to improve the performance of the molecules, and as such it may serve as an inspiration for future design. The selected examples cover five widely studied systems, notably: anthracenes, stilbenes, azobenzenes, tetracarbonyl-Fulvalene-diruthenium compounds and norbornadienes.
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Fluorinated Fulvalene ruthenium compound for molecular solar thermal applications
Journal of Fluorine Chemistry, 2014Co-Authors: Karl Borjesson, Anders Lennartson, Kasper Moth-poulsenAbstract:Molecular photoswitches, i.e. molecules capable of isomerizing between two states when submitted to light stimuli, has found applications in several areas such as molecular logic, molecular electronics, and, if the two isomers differ substantially in energy, molecular solar thermal (MOST) systems. In a MOST system the photoswitchable molecule absorbs a photon where after a photoinduced isomerisation to a high energy metastable photoisomer occurs. The photon energy is thus stored within the molecule. Fulvalenediruthenium compounds, has been suggested as a candidate in MOST systems thanks to the large difference in energy between the two isomers, its relative stability, and its ability to absorb sunlight. We here present a fluorinated Fulvalene ruthenium derivative and show that its processing properties is remarkably different, while having retained photoisomerization efficiency, compared to its hydrocarbon analog. © 2014 The Authors.
