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Paul J. Chirik - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Electronic Structure of Cationic, Neutral, and Anionic Bis(imino)pyridine Iron Alkyl Complexes: Evaluation of Redox Activity in Single-Component Ethylene Polymerization Catalysts
Journal of the American Chemical Society, 2010Co-Authors: Aaron M. Tondreau, Karl Wieghardt, Carsten Milsmann, Andrew D. Patrick, Helen M. Hoyt, Emil B. Lobkovsky, Paul J. ChirikAbstract:A family of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes has been prepared, and their electronic and molecular structures have been established by a combination of X-ray diffraction, Mossbauer spectroscopy, magnetochemistry, and open-shell density functional theory. For the cationic complexes, [(iPrPDI)Fe-R][BPh4] (iPrPDI = 2,6-(2,6-iPr2-C6H3N═CMe)2C5H3N; R = CH2SiMe3, CH2CMe3, or CH3), which are known single-component ethylene polymerization catalysts, the data establish high spin Ferrous Compounds (SFe = 2) with neutral, redox-innocent bis(imino)pyridine chelates. One-electron reduction to the corresponding neutral alkyls, (iPrPDI)Fe(CH2SiMe3) or (iPrPDI)Fe(CH2CMe3), is chelate-based, resulting in a bis(imino)pyridine radical anion (SPDI = 1/2) antiferromagnetically coupled to a high spin Ferrous ion (SFe = 2). The neutral neopentyl derivative was reduced by an additional electron and furnished the corresponding anion, [Li(Et2O)3][(iPrPDI)Fe(CH2CMe3)N2], with concomitant coordi...
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bis imino pyridine iron alkyls containing β hydrogens synthesis evaluation of kinetic stability and decomposition pathways involving chelate participation
Journal of the American Chemical Society, 2008Co-Authors: Ryan J Trovitch, Emil B. Lobkovsky, Paul J. ChirikAbstract:Bis(imino)pyridine iron alkyl complexes bearing β-hydrogens, (iPrPDI)FeR ((iPrPDI = 2,6-(2,6-iPr2−C6H3N═CMe)2C5H3N; R = Et, nBu, iBu, CH2cycloC5H9; 1-R), were synthesized either by direct alkylation of (iPrPDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced (iPrPDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin Ferrous Compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found t...
Emil B. Lobkovsky - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Electronic Structure of Cationic, Neutral, and Anionic Bis(imino)pyridine Iron Alkyl Complexes: Evaluation of Redox Activity in Single-Component Ethylene Polymerization Catalysts
Journal of the American Chemical Society, 2010Co-Authors: Aaron M. Tondreau, Karl Wieghardt, Carsten Milsmann, Andrew D. Patrick, Helen M. Hoyt, Emil B. Lobkovsky, Paul J. ChirikAbstract:A family of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes has been prepared, and their electronic and molecular structures have been established by a combination of X-ray diffraction, Mossbauer spectroscopy, magnetochemistry, and open-shell density functional theory. For the cationic complexes, [(iPrPDI)Fe-R][BPh4] (iPrPDI = 2,6-(2,6-iPr2-C6H3N═CMe)2C5H3N; R = CH2SiMe3, CH2CMe3, or CH3), which are known single-component ethylene polymerization catalysts, the data establish high spin Ferrous Compounds (SFe = 2) with neutral, redox-innocent bis(imino)pyridine chelates. One-electron reduction to the corresponding neutral alkyls, (iPrPDI)Fe(CH2SiMe3) or (iPrPDI)Fe(CH2CMe3), is chelate-based, resulting in a bis(imino)pyridine radical anion (SPDI = 1/2) antiferromagnetically coupled to a high spin Ferrous ion (SFe = 2). The neutral neopentyl derivative was reduced by an additional electron and furnished the corresponding anion, [Li(Et2O)3][(iPrPDI)Fe(CH2CMe3)N2], with concomitant coordi...
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bis imino pyridine iron alkyls containing β hydrogens synthesis evaluation of kinetic stability and decomposition pathways involving chelate participation
Journal of the American Chemical Society, 2008Co-Authors: Ryan J Trovitch, Emil B. Lobkovsky, Paul J. ChirikAbstract:Bis(imino)pyridine iron alkyl complexes bearing β-hydrogens, (iPrPDI)FeR ((iPrPDI = 2,6-(2,6-iPr2−C6H3N═CMe)2C5H3N; R = Et, nBu, iBu, CH2cycloC5H9; 1-R), were synthesized either by direct alkylation of (iPrPDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced (iPrPDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin Ferrous Compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found t...
Ryan J Trovitch - One of the best experts on this subject based on the ideXlab platform.
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bis imino pyridine iron alkyls containing β hydrogens synthesis evaluation of kinetic stability and decomposition pathways involving chelate participation
Journal of the American Chemical Society, 2008Co-Authors: Ryan J Trovitch, Emil B. Lobkovsky, Paul J. ChirikAbstract:Bis(imino)pyridine iron alkyl complexes bearing β-hydrogens, (iPrPDI)FeR ((iPrPDI = 2,6-(2,6-iPr2−C6H3N═CMe)2C5H3N; R = Et, nBu, iBu, CH2cycloC5H9; 1-R), were synthesized either by direct alkylation of (iPrPDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced (iPrPDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin Ferrous Compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found t...
S D Mineev - One of the best experts on this subject based on the ideXlab platform.
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equilibrium iron isotope fractionation factors of minerals reevaluation from the data of nuclear inelastic resonant x ray scattering and mossbauer spectroscopy
Geochimica et Cosmochimica Acta, 2007Co-Authors: V B Polyakov, Robert N Clayton, Juske Horita, S D MineevAbstract:We have critically reevaluated equilibrium iron isotope fractionation factors for oxide and sulfide minerals using recently acquired data obtained by Mossbauer spectroscopy and inelastic nuclear resonant X-ray scattering (INRXS) synchrotron radiation. Good agreement was observed in the iron b-factors of metallic iron (a-Fe) and hematite calculated using both Mossbauer- and INRXS-derived data, which supports the validity and reliability of the calculations. Based on this excellent agreement, we suggest the use of the present data on the iron b-factors of hematite as a reference. The previous Mossbauer-derived iron b-factor for magnetite has been modified significantly based on the Fe-sublattice density of states obtained from the INRXS experiments. This resolves the disagreement between naturally observed iron iso- tope fractionation factors for mineral pairs involving magnetite and those obtained from the calculated b-factors. The cor- rectness of iron b-factor for pyrite has been corroborated by the good agreement with experimental data of sulfur isotope geothermometers of pyrite-galena and pyrite-sphalerite. A good correlation between the potential energy of the cation site, the oxidation state of iron and the iron b-factor value has been established. Specifically, ferric Compounds, which have a high- er potential energy of iron than Ferrous Compounds, have higher b-factors. A similar dependence of b-factors on the oxidation state and potential energy could be extended to other transition metals. Extremely low values of INRXS-derived iron b-fac- tors for troilite and Fe3S significantly widen the range of iron b-factors for covalently bonded Compounds. � 2007 Elsevier Ltd. All rights reserved.
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the use of mossbauer spectroscopy in stable isotope geochemistry
Geochimica et Cosmochimica Acta, 2000Co-Authors: V B Polyakov, S D MineevAbstract:Abstract The use of Mossbauer spectroscopic data on the second-order Doppler (SOD) shift to determine the reduced isotopic partition function ratio (β-factor) has been considered by the example of iron. Using the relation between the β-factor and the SOD shift in Mossbauer spectra, the temperature dependence of the iron β-factors for a wide range of minerals has been evaluated from experimental data on the SOD shift. It is shown that the β-factors of Fe 3+ ions are considerably higher than those of Fe 2+ . The curve describing the temperature dependence of the β-factor for native iron is the boundary separating fields that are typical for ferric and Ferrous ions. The value of the iron β-factor increases with increasing covalence of chemical bonds. In the case of covalent chemical bonds, the iron β-factor achieves high values even for Ferrous Compounds. Possible iron isotope geothermometers magnetite–siderite and pyrite–siderite have been calibrated 10 3 ln β magnetite–siderite =0.881 776 x −0.544 105×10 −2 x 2 +0.425 639 10 −4 x 3 −0.352 191×10 −5 x 4 , 10 3 ln β pyrite–siderite =0.913 717 x −0.557 721×10 −2 x 2 +0.424 146×10 −4 x 3 −0.334 281×10 −5 x 4 , where x = 10 6 / T 2 , T is absolute temperature, ln β relates to 57 Fe/ 54 Fe fractionation. At equilibrium, a small iron isotopic shift between magnetite and pyrite along with high iron isotopic shifts between magnetite and siderite and between pyrite and siderite should be observed. A significant effect (about 7‰ at 300 K) of the aluminum substitution on the iron β-factor in hematite has been evaluated from the appropriate data on the SOD shift in Mossbauer spectra. The analogous effect of the Co-substitution in magnetite is lower (≈3.0‰ at 300 K). A new method of evaluation of the β-factor for isotopes traditionally used in geochemical studies like sulfur, oxygen, etc., is suggested. The method uses experimental Mossbauer data on the SOD shift and calorimetric data on the heat capacity. The method can be applied to Compounds consisting of two chemical elements (like oxides, sulfides) if one of them has a Mossbauer-sensitive isotope. Using the new method, the β 34 S-factor of pyrite and the β 18 O-factor of hematite have been determined: 10 3 ln β pyrite =(1.5997±0.0419) x −(6.7744±0.4279)×10 −3 x 2 +(3.8254±0.5682)×10 −5 x 3 , 10 3 ln β hematite =(5.7215±0.3891) x −(0.029 41±0.004 49) x 2 .
Steven Vancoillie - One of the best experts on this subject based on the ideXlab platform.
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relative energy of the high 5t2g and low 1a1g spin states of the Ferrous complexes fe l nhs4 caspt2 versus density functional theory
Journal of Chemical Physics, 2008Co-Authors: Kristine Pierloot, Steven VancoillieAbstract:High-level ab initio calculations using multiconfigurational perturbation theory [complete active space with second-order perturbation theory (CASPT2)] were performed on the transition energy between the lowest high-spin (corresponding to (5T2g) in Oh) and low-spin (corresponding to 1A1g in Oh) states in the series of six-coordinated Fe(II) molecules [Fe(L)(NHS4)], where NHS4 is 2,2'-bis(2-mercaptophenylthio)diethylamine dianion and L=NH3, N2H4, PMe3, CO, and NO+. The results are compared to (previous and presently obtained) results from density functional theory (DFT) calculations with four functionals, which were already shown previously by Casida and co-workers [Fouqueau et al., J. Chem. Phys. 120, 9473 (2004); Ganzenmuller et al., ibid. 122, 234321 (2005); Fouqueau et al., ibid. 122, 044110 (2005); Lawson Daku et al., ChemPhysChem 6, 1393 (2005)] to perform well for the spin-pairing problem in these and other Fe(II) complexes, i.e., OLYP, PBE0, B3LYP, and B3LYP*. Very extended basis sets were used both for the DFT and CASPT2 calculations and were shown to be necessary to obtain quantitative results with both types of method. This work presents a sequel to a previous DFT/CASPT2 study of the same property in the complexes [Fe(H2O)6]2+, [Fe(NH3)6]2+, and [Fe(bpy)3]2+ [Pierloot et al., J. Chem. Phys. 125, 124303 (2006)]. The latter work was extended with new results obtained with larger basis sets and including the OLYP functional. For all considered complexes, the CASPT2 method predicts the correct ground state spin multiplicity. Since experimental data for the actual quintet-singlet (free) energy differences are not available, the performance of the different DFT functionals was judged based on the comparison between the DFT and CASPT2 results. From this, it was concluded that the generalized gradient OLYP functional performs remarkably well for the present series of Ferrous Compounds, whereas the success of the three hybrid functionals varies from case to case.