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Pierre Braunstein - One of the best experts on this subject based on the ideXlab platform.
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Changes in molecular film metallicity with minor modifications of the constitutive Quinonoid Zwitterions
RSC Advances, 2017Co-Authors: Lucie Routaboul, Alessio Ghisolfi, Bernard Doudin, Iori Tanabe, Juan A. Colón Santana, Minghui Yuan, William Serrano Garcia, Peter A. Dowben, Pierre BraunsteinAbstract:Molecular films of Quinonoid Zwitterions, of the general formula C6H2(O)2(NHR)2, have been shown to display electronic properties highly dependent on the nature of the N-substituent R when deposited on gold substrates. The different spacing and organization of the molecules can lead to molecular films with semi-metal or dielectric behavior. With the long term goal to establish how packing effects in the solid state correlate with properties as thin films, we first attempted to identify by X-ray diffraction analysis candidate molecules showing suitable packing arrangements in the crystalline state. To this end, we have prepared a series of new functionalized, enantiopure or sterically-hindered Quinonoid Zwitterions and established the crystal structure of those with R = CH2–CH2–Ph (6), CH2–CH2–CH2–Ph (7), CH2–CH2–CH2–CH2–Ph (8), CH2–CH2–CH(Ph)–Ph (9), CH(CH3)–Ph (12), CH(CH2–CH3)–Ph (13), CH2–((4–CH3)–C6H4) (15), CH2–((4–NH2)–C6H4) (19) and CH2–CH2–((3,4–(OCH3)2)–C6H3) (24). An analysis of the crystal packing of three molecules, 5, 13 and 15, selected as illustrative examples for comparisons, was carried out and it was unexpectedly found that these chemically very similar molecules gave rise to different packing in the bulk, with resulting thin films showing different electronic properties. Various methods have been used for the characterization of the films, such as synchrotron radiation-based FTIR spatial spectra-microscopy, which provided an anchoring map of Zwitterion 15 on a patterned substrate (Au/SiO2) showing its selective anchoring on gold. This is one of the best examples of preferential anchoring of a Zwitterion and the sole example of spatial localization for a Quinonoid Zwitterion thin film. We have also used combined photoemission and inverse photoemission spectra and the data were compared to occupied and unoccupied DFT density state calculations.
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Reversible switching of the coordination modes of a pyridine-functionalized Quinonoid Zwitterion; its di- and tetranuclear palladium complexes.
Inorganic chemistry, 2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in los...
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Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes
2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)]+ moieties, from the NPy sites in 3, to the N,O donor sites of the Quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic Quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2–5 and 7
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The interface bonding and orientation of a Quinonoid Zwitterion
Physical chemistry chemical physics : PCCP, 2010Co-Authors: Jie Xiao, Lucie Routaboul, Pierre Braunstein, Zhengzheng Zhang, Bernard Doudin, Yaroslav Losovyj, Orhan Kizilkaya, Luis G. Rosa, Camelia N. BorcaAbstract:We have investigated the interaction and orientation of a strongly dipolar Zwitterionic p-benzoquinonemonoimine-type molecule, with a large intrinsic dipole of 10 Debye, on both conducting and on polar insulating substrates. Specifically, we deposited (6Z)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate C(6)H(2)([horiz bar, triple dot above]NHR)(2)([horiz bar, triple dot above]O)(2) where R = n-C(4)H(9), on both gold and ferroelectric lithium niobate surfaces. An influence of both transient and static electric dipoles on the Zwitterionic adsorbate has been observed. For adsorption on gold, we find that the molecule bonds to the surface through the nitrogen atoms, forming films that remain fairly uniform down to thicknesses in the 1 nm range. Adsorption of this Zwitterionic compound from solution on insulating, periodically poled ferroelectric lithium niobate substrates, showed preferential adsorption on one type of ferroelectric domain. For both gold and the lithium niobate substrates, the Zwitterion adopts a preferential orientation with the plane of its "C(6) core" along the surface normal. This simplified geometry of strong dipole alignment provides a symmetry simplification allowing better identification of the vibrational modes responsible for Frank-Condon scattering revealed in the fine spectroscopic signature in the photoemission spectrum.
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Stepwise synthesis, structures, and reactivity of mono-, Di-, and trimetallic metal complexes with a 6π + 6π Quinonoid Zwitterion
Inorganic chemistry, 2004Co-Authors: Jean-philippe Taquet, Pierre Braunstein, Olivier Siri, Richard WelterAbstract:The benzoquinonemonoimine N,N‘-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(NHCH2t-Bu)2(O)2] 6, which is a rare example of an organic Zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N−H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10−15 in which the π-system is localized. A second in situ deprotonation of the remaining N−H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)]2 (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in ...
Lucie Routaboul - One of the best experts on this subject based on the ideXlab platform.
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Changes in molecular film metallicity with minor modifications of the constitutive Quinonoid Zwitterions
RSC Advances, 2017Co-Authors: Lucie Routaboul, Alessio Ghisolfi, Bernard Doudin, Iori Tanabe, Juan A. Colón Santana, Minghui Yuan, William Serrano Garcia, Peter A. Dowben, Pierre BraunsteinAbstract:Molecular films of Quinonoid Zwitterions, of the general formula C6H2(O)2(NHR)2, have been shown to display electronic properties highly dependent on the nature of the N-substituent R when deposited on gold substrates. The different spacing and organization of the molecules can lead to molecular films with semi-metal or dielectric behavior. With the long term goal to establish how packing effects in the solid state correlate with properties as thin films, we first attempted to identify by X-ray diffraction analysis candidate molecules showing suitable packing arrangements in the crystalline state. To this end, we have prepared a series of new functionalized, enantiopure or sterically-hindered Quinonoid Zwitterions and established the crystal structure of those with R = CH2–CH2–Ph (6), CH2–CH2–CH2–Ph (7), CH2–CH2–CH2–CH2–Ph (8), CH2–CH2–CH(Ph)–Ph (9), CH(CH3)–Ph (12), CH(CH2–CH3)–Ph (13), CH2–((4–CH3)–C6H4) (15), CH2–((4–NH2)–C6H4) (19) and CH2–CH2–((3,4–(OCH3)2)–C6H3) (24). An analysis of the crystal packing of three molecules, 5, 13 and 15, selected as illustrative examples for comparisons, was carried out and it was unexpectedly found that these chemically very similar molecules gave rise to different packing in the bulk, with resulting thin films showing different electronic properties. Various methods have been used for the characterization of the films, such as synchrotron radiation-based FTIR spatial spectra-microscopy, which provided an anchoring map of Zwitterion 15 on a patterned substrate (Au/SiO2) showing its selective anchoring on gold. This is one of the best examples of preferential anchoring of a Zwitterion and the sole example of spatial localization for a Quinonoid Zwitterion thin film. We have also used combined photoemission and inverse photoemission spectra and the data were compared to occupied and unoccupied DFT density state calculations.
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Reversible switching of the coordination modes of a pyridine-functionalized Quinonoid Zwitterion; its di- and tetranuclear palladium complexes.
Inorganic chemistry, 2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in los...
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Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes
2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)]+ moieties, from the NPy sites in 3, to the N,O donor sites of the Quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic Quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2–5 and 7
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The interface bonding and orientation of a Quinonoid Zwitterion
Physical chemistry chemical physics : PCCP, 2010Co-Authors: Jie Xiao, Lucie Routaboul, Pierre Braunstein, Zhengzheng Zhang, Bernard Doudin, Yaroslav Losovyj, Orhan Kizilkaya, Luis G. Rosa, Camelia N. BorcaAbstract:We have investigated the interaction and orientation of a strongly dipolar Zwitterionic p-benzoquinonemonoimine-type molecule, with a large intrinsic dipole of 10 Debye, on both conducting and on polar insulating substrates. Specifically, we deposited (6Z)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate C(6)H(2)([horiz bar, triple dot above]NHR)(2)([horiz bar, triple dot above]O)(2) where R = n-C(4)H(9), on both gold and ferroelectric lithium niobate surfaces. An influence of both transient and static electric dipoles on the Zwitterionic adsorbate has been observed. For adsorption on gold, we find that the molecule bonds to the surface through the nitrogen atoms, forming films that remain fairly uniform down to thicknesses in the 1 nm range. Adsorption of this Zwitterionic compound from solution on insulating, periodically poled ferroelectric lithium niobate substrates, showed preferential adsorption on one type of ferroelectric domain. For both gold and the lithium niobate substrates, the Zwitterion adopts a preferential orientation with the plane of its "C(6) core" along the surface normal. This simplified geometry of strong dipole alignment provides a symmetry simplification allowing better identification of the vibrational modes responsible for Frank-Condon scattering revealed in the fine spectroscopic signature in the photoemission spectrum.
Richard Welter - One of the best experts on this subject based on the ideXlab platform.
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Stepwise synthesis, structures, and reactivity of mono-, Di-, and trimetallic metal complexes with a 6π + 6π Quinonoid Zwitterion
Inorganic chemistry, 2004Co-Authors: Jean-philippe Taquet, Pierre Braunstein, Olivier Siri, Richard WelterAbstract:The benzoquinonemonoimine N,N‘-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(NHCH2t-Bu)2(O)2] 6, which is a rare example of an organic Zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N−H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10−15 in which the π-system is localized. A second in situ deprotonation of the remaining N−H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)]2 (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in ...
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stepwise synthesis structures and reactivity of mono di and trimetallic metal complexes with a 6π 6π Quinonoid Zwitterion
Inorganic Chemistry, 2004Co-Authors: Jean-philippe Taquet, Pierre Braunstein, Olivier Siri, Richard WelterAbstract:The benzoquinonemonoimine N,N‘-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(NHCH2t-Bu)2(O)2] 6, which is a rare example of an organic Zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N−H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10−15 in which the π-system is localized. A second in situ deprotonation of the remaining N−H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)]2 (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in ...
Alessio Ghisolfi - One of the best experts on this subject based on the ideXlab platform.
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Changes in molecular film metallicity with minor modifications of the constitutive Quinonoid Zwitterions
RSC Advances, 2017Co-Authors: Lucie Routaboul, Alessio Ghisolfi, Bernard Doudin, Iori Tanabe, Juan A. Colón Santana, Minghui Yuan, William Serrano Garcia, Peter A. Dowben, Pierre BraunsteinAbstract:Molecular films of Quinonoid Zwitterions, of the general formula C6H2(O)2(NHR)2, have been shown to display electronic properties highly dependent on the nature of the N-substituent R when deposited on gold substrates. The different spacing and organization of the molecules can lead to molecular films with semi-metal or dielectric behavior. With the long term goal to establish how packing effects in the solid state correlate with properties as thin films, we first attempted to identify by X-ray diffraction analysis candidate molecules showing suitable packing arrangements in the crystalline state. To this end, we have prepared a series of new functionalized, enantiopure or sterically-hindered Quinonoid Zwitterions and established the crystal structure of those with R = CH2–CH2–Ph (6), CH2–CH2–CH2–Ph (7), CH2–CH2–CH2–CH2–Ph (8), CH2–CH2–CH(Ph)–Ph (9), CH(CH3)–Ph (12), CH(CH2–CH3)–Ph (13), CH2–((4–CH3)–C6H4) (15), CH2–((4–NH2)–C6H4) (19) and CH2–CH2–((3,4–(OCH3)2)–C6H3) (24). An analysis of the crystal packing of three molecules, 5, 13 and 15, selected as illustrative examples for comparisons, was carried out and it was unexpectedly found that these chemically very similar molecules gave rise to different packing in the bulk, with resulting thin films showing different electronic properties. Various methods have been used for the characterization of the films, such as synchrotron radiation-based FTIR spatial spectra-microscopy, which provided an anchoring map of Zwitterion 15 on a patterned substrate (Au/SiO2) showing its selective anchoring on gold. This is one of the best examples of preferential anchoring of a Zwitterion and the sole example of spatial localization for a Quinonoid Zwitterion thin film. We have also used combined photoemission and inverse photoemission spectra and the data were compared to occupied and unoccupied DFT density state calculations.
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Reversible switching of the coordination modes of a pyridine-functionalized Quinonoid Zwitterion; its di- and tetranuclear palladium complexes.
Inorganic chemistry, 2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in los...
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Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes
2014Co-Authors: Alessio Ghisolfi, Audrey Waldvogel, Lucie Routaboul, Pierre BraunsteinAbstract:The coordination chemistry of a new functional Quinonoid Zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the Quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the Zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)]+ moieties, from the NPy sites in 3, to the N,O donor sites of the Quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic Quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2–5 and 7
Jean-philippe Taquet - One of the best experts on this subject based on the ideXlab platform.
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Stepwise synthesis, structures, and reactivity of mono-, Di-, and trimetallic metal complexes with a 6π + 6π Quinonoid Zwitterion
Inorganic chemistry, 2004Co-Authors: Jean-philippe Taquet, Pierre Braunstein, Olivier Siri, Richard WelterAbstract:The benzoquinonemonoimine N,N‘-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(NHCH2t-Bu)2(O)2] 6, which is a rare example of an organic Zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N−H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10−15 in which the π-system is localized. A second in situ deprotonation of the remaining N−H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)]2 (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in ...
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stepwise synthesis structures and reactivity of mono di and trimetallic metal complexes with a 6π 6π Quinonoid Zwitterion
Inorganic Chemistry, 2004Co-Authors: Jean-philippe Taquet, Pierre Braunstein, Olivier Siri, Richard WelterAbstract:The benzoquinonemonoimine N,N‘-dineopentyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium [C6H2(NHCH2t-Bu)2(O)2] 6, which is a rare example of an organic Zwitterion being more stable than its canonical form, is best described as constituted of two chemically connected but electronically not conjugated 6π electron subunits. The two successive acidities of 6 allow the preparation of mono-, di-, and trimetallic complexes in which the control of the π-system delocalization becomes possible. Reaction of 6 with NaOt-Bu results in monodeprotonation of one N−H function, and the isolated sodium salt 9, which is stable under N2, reacts with chloride-bridged Pd(II) homodimetallic complexes, [AuCl(PPh3)] or trans-[NiCl(Ph)(PPh3)2], to afford the monometallic complexes 10−15 in which the π-system is localized. A second in situ deprotonation of the remaining N−H amino function of 10 with NaH followed by reaction with [Pd(8-mq)(μ-Cl)]2 (8-mq = orthometalated 8-methylquinoline) affords the homodimetallic complex 17 in ...
