Chirality Transfer in Magnetic Coordination Complexes Monitored by Vibrational and Electronic Circular Dichroism

Wu, Tao; Zhang, Xiaopeng; You, Xiao‐Zeng; Li, Yi‐Zhi; Bouř, Petr

doi:10.1002/cplu.201300429

Cited by 15 publications

(12 citation statements)

References 66 publications

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“…As all complexes are closely related except for substituents on the phenolate rings (i.e., chloride, methyl and tert -butyl groups), the bond lengths within the ligands and around the iron centers have little variation. The Fe–O phen bond distances are similar to those observed for oxo-bridged iron(III) complexes containing salen, salan, and bis(phenolate) ligands adopting distorted square pyramidal geometries. − In 8 , these distances are 1.915(3), 1.890(3), 1.895(3), and 1.912(3) Å for Fe(1)–O(1), Fe(1)–O(2), Fe(2)–O(3), and Fe(2)–O(4), respectively. The Fe(1)–O(5) distance relating to the bridging oxygen exhibits a slightly shorter bond length of 1.770(3) Å, which is also consistent with reported literature values of similar systems.…”

Section: Resultssupporting

confidence: 61%

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides

et al. 2018

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A series of iron(III) chloride and iron(III) μ-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) μ-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe–O–Fe angles between 171.7 and 180°, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high-spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around the iron center reduces catalytic activity in this case. We provide evidence that an epoxide deoxygenation step occurs when employing monometallic iron(III) chlorido species as catalysts. This affords the corresponding μ-oxo compounds which can then enter their own catalytic cycle. Deoxygenation of epoxides during their catalytic reactions with carbon dioxide is frequently overlooked and should be considered as an additional mechanistic pathway when investigating catalysts.

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Section: Resultssupporting

confidence: 61%

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides

et al. 2018

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“…IR and VCD spectra (in detail reported in a separate study35) were recorded within the range $\tilde \nu $ =1800–800 cm −1 with a IFS 66/S Fourier transform infrared spectrometer equipped with a PMA 37 VCD/IRRAS module (Bruker, Germany) 18–20. The PEM was set to $\tilde \nu $ =1500 cm −1 , the spectral resolution was 4 cm −1 , and the zero filling factor was four.…”

Section: Methodsmentioning

confidence: 99%

Comparison of the Electronic and Vibrational Optical Activity of a Europium(III) Complex

Hudecová

You

et al. 2015

Chemistry A European J

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The geometry and the electronic structure of chiral lanthanide(III) complexes are traditionally probed by electronic methods, such as circularly polarised luminescence (CPL) and electronic circular dichroism (ECD) spectroscopy. The vibrational phenomena are much weaker. In the present study, however, significant enhancements of vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectral intensities were observed during the formation of a chiral bipyridine-Eu(III) complex. The ten-fold enhancement of the vibrational absorption and VCD intensities was explained by a charge-transfer process and the dominant effect of the nitrate ion on the spectra. A much larger enhancement of the ROA and Raman intensities and a hundred-fold increase of the circular intensity difference (CID) ratio were explained by the resonance of the λ = 532 nm laser light with the (7)F0 → (5)D0 transitions. This phenomenon is combined with a chirality transfer, and mixing of the Raman and luminescence effects involving low-energy (7)F states of europium. The results thus indicate that the vibrational optical activity (VOA) may be a very sensitive tool for chirality detection and probing of the electronic structure of Eu(III) and other coordination compounds.

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“…On the other hand, researchers have increasingly recognized the dynamic nature of structures in solution. Indeed, these complexes may adopt very different structures in solution compared to those in solid. − For example, switching to another solvent can modify induced-helicity preference at the metal centers.…”

Section: Introductionmentioning

confidence: 99%

Conservation of Helicity in a Chiral Pyrrol-2-yl Schiff-Base Ligand and Its Transition Metal Complexes

et al. 2015

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Tetradentate enantiopure Schiff-base ligand (R,R) and (S,S)-bis(pyrrol-2-ylmethyleneamine)-cyclohexane (H2L) and its five transition metal complexes with Ni(II), Cu(II), Zn(II), Pd(II), and Pt(II) were synthesized. Their structural properties, in particular, the ligand chirality, coordination topology, and the resulting helicity in solution, were investigated by using IR, vibrational circular dichroism (VCD), UV-vis, and electronic circular dichroism (ECD) spectroscopies, complemented with density functional theory calculations. Conformational searches and the associated spectral simulations for the ligands and the complexes were performed at the B3LYP/Gen level. Comparison of the experimental and theoretical IR and VCD spectral signatures of these complexes reveal that the Zn complex takes on a dinuclear, distorted tetrahedral coordination topology around the metal centers, whereas the other four metal complexes adopt the mononuclear, distorted square-planar coordination arrangement in solution. The helicity of all systems studied was identified to be M with the (R,R) ligand and P with the (S,S) ligand, dictated by the ligand chirality and the strong preference for the chair configuration by the cyclohexane moiety. Furthermore, the resulting helicity was found to dominate the ECD spectral features, even though the helicity-determining angles are close to zero for the nearly square-planar metal complexes. The related VCD spectral features are sensitive to both helicity of the complex and the chirality of the ligands, as well as the coordination topology. The simulated ECD spectra for the P and M helicity of the [Zn-(R,R)-L]2 complex shows almost mirror-imaged ECD spectral features, whereas very similar ECD spectra were recently reported for the P- and M-dinuclear Mn complexes with a di-μ-oxo dimetal core as a linker. We highlight the advantages of utilizing multiple chiroptical techniques and theoretical spectral simulations to correlate chiroptical spectral features with multiple chirality and helicity elements in the systems.

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Chirality Transfer in Magnetic Coordination Complexes Monitored by Vibrational and Electronic Circular Dichroism

Cited by 15 publications

References 66 publications

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides

Comparison of the Electronic and Vibrational Optical Activity of a Europium(III) Complex

Conservation of Helicity in a Chiral Pyrrol-2-yl Schiff-Base Ligand and Its Transition Metal Complexes

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Chirality Transfer in Magnetic Coordination Complexes Monitored by Vibrational and Electronic Circular Dichroism

Cited by 15 publications

References 66 publications

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO2 and Epoxides

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO2 and Epoxides

Comparison of the Electronic and Vibrational Optical Activity of a Europium(III) Complex

Conservation of Helicity in a Chiral Pyrrol-2-yl Schiff-Base Ligand and Its Transition Metal Complexes

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Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO₂ and Epoxides