36 results on '"Megan E, Fieser"'
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2. Rare Earth Metal‐Containing Ionic Liquid Catalysts for Synthesis of Epoxide/Cyclic Anhydride Copolymers
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Yvonne Manjarrez, Allison M. Clark, and Megan E. Fieser
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Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry ,Catalysis - Published
- 2023
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Catalog
3. Controlled, one-pot synthesis of recyclable poly(1,3-diene)-polyester block copolymers, catalyzed by yttrium β-diketiminate complexes
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Sophia C. Kosloski-Oh, Yvonne Manjarrez, Taleen J. Boghossian, and Megan E. Fieser
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General Chemistry - Abstract
The one-pot synthesis of well-defined block copolymers of olefins/1,3-dienes and polar monomers, such as cyclic esters and acrylates has long been the focus of intense research. Cationic alkyl rare earth metal catalysts, activated by organoborates, have shown to be promising for the polymerization of isoprene or styrene and ε-caprolactone. In this study, we synthesize a series of yttrium bis(alkyl) complexes supported by simple β-diketiminate ancillary ligands. Subtle changes have been made to the β-diketiminate ligand framework to elucidate the effect of ligand structure on the rate and selectivity of olefin/1,3-diene and cyclic ester polymerization, with small ligand changes having a large impact on the resulting polymerizations. Generation of the active cationic species was easily streamlined by identification of appropriate catalyst : organoborate ratios, allowing for high catalyst efficiencies. Notably, we demonstrate the first cationic rare earth metal alkyl-initiated polymerization of δ-valerolactone and ε-decalactone as well as introduced five new block copolymer morphologies. In addition, selective degradation of the ester block in poly(isoprene more...
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- 2022
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4. Controlling selectivity for dechlorination of poly(vinyl chloride) with (xantphos)RhCl
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Nancy G. Bush, Mikiyas K. Assefa, Selin Bac, Shaama Mallikarjun Sharada, and Megan E. Fieser
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Mechanics of Materials ,Process Chemistry and Technology ,General Materials Science ,Electrical and Electronic Engineering - Abstract
Reactions of poly(vinyl chloride) (PVC) with a rhodium catalyst and H-donors reveal how reaction conditions can impact the selectivity for chloride removal, with sodium formate showing the highest selectivity for hydrodechlorination. more...
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- 2023
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5. Understanding the important variables to optimize glycolysis of polyethylene terephthalate with lanthanide-containing ionic liquids
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Nancy G. Bush, Caitlin H. Dinh, Casandrah L. Catterton, and Megan E. Fieser
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Lanthanide metal ionic liquids (MILs) are tunable catalysts for the glycolysis of poly(ethylene terephthalate). Enhanced cooperativity with high ionic liquid : metal salt ratios lowers the required metal content to increase catalyst sustainability. more...
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- 2023
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6. Catalytic methods for chemical recycling or upcycling of commercial polymers
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Zachary A. Wood, Sophia C. Kosloski-Oh, Juan Pablo de los Rios, Megan E. Fieser, and Yvonne Manjarrez
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chemistry.chemical_classification ,Waste management ,Polymers ,Process Chemistry and Technology ,Polymer ,Catalysis ,Waste Disposal Facilities ,Upcycling ,chemistry ,Mechanics of Materials ,Environmental science ,Recycling ,General Materials Science ,Electrical and Electronic Engineering ,Plastics - Abstract
Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers. more...
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- 2021
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7. Perfectly Alternating Copolymerization of Cyclic Anhydrides and Epoxides with Yttrium β-Diketiminate Complexes
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Yvonne Manjarrez, Mary Dana Czarinah L. Cheng-Tan, and Megan E. Fieser
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Inorganic Chemistry ,Physical and Theoretical Chemistry - Abstract
Monometallic yttrium β-diketiminate complexes are active and controlled catalysts for perfectly alternating ring-opening copolymerization of 1-butene oxide and phthalic anhydride under mild conditions. β-Diketiminate ligands with pendant neutral donors were targeted to identify both the impact of donor strength and number of donors on rates of polymerization and the presence of undesirable side reactions. Initiating groups were also varied between alkyls, chlorides, and alkoxides. In the presence of a cocatalyst, the catalysts studied were active for polymerization with minimal side reactions, whereas lack of cocatalysts led to competing homopolymerization of epoxides. While a greater donor strength and a larger number of donors both increase the rate of polymerization, donor strength generally had a bigger impact when a cocatalyst was used. Additionally, alkoxide and chloride initiators proved to be the fastest, with alkyls being more sluggish. These subtle ligand changes significantly impacting polymerization activity lend promise to the facile tunability of rare earth metal complexes to be highly active for the target copolymerization, which renders further research in this area attractive and timely. more...
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- 2022
8. Metal versus Ligand Reduction in Ln3+ Complexes of a Mesitylene-Anchored Tris(Aryloxide) Ligand
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Megan E. Fieser, Wolfgang Hieringer, Vamsee K. Voora, William J. Evans, Karsten Meyer, Dominik P. Halter, Guo P. Chen, Alan K. Chan, Chad T. Palumbo, Filipp Furche, and Joseph W. Ziller
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Tris ,010405 organic chemistry ,Ligand ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,Crystallography ,chemistry ,law ,visual_art ,visual_art.visual_art_medium ,Density functional theory ,Electron configuration ,Protonolysis ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Mesitylene - Abstract
The synthesis of 4f n Ln3+ complexes of the tris(aryloxide) mesitylene ligand, ((Ad,MeArO)3mes)3-, with Ln = La, Ce, Pr, Sm, and Yb, and their reduction with potassium have revealed that this ligand system can be redox active with some metals. Protonolysis of [Ln(N(SiMe3)2)3] (Ln = La, Ce, Pr, Sm, Yb) with the tris(phenol) (Ad,MeArOH)3mes yielded the Ln3+ complexes [((Ad,MeArO)3mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 1-Ln. Single electron reduction of each 4f n complex, 1-Ln, using potassium yielded the reduced products, [K(2.2.2-cryptand)][((Ad,MeArO)3mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 2-Ln. The Sm and Yb complexes have properties consistent with the presence of Ln2+ ions with traditional 4f n+1 electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln3+ ions and ((Ad,MeArO)3mes)4- ligands. Structural comparisons of the [((Ad,MeArO)3mes)Ln] and [((Ad,MeOAr)3mes)Ln]1- complexes along with UV-vis absorption and EPR spectroscopy as well as density functional theory calculations support these ground state assignments. more...
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- 2018
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9. Reactivity of Complexes of 4fn5d1 and 4fn+1 Ln2+ Ions with Cyclooctatetraene
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Joseph W. Ziller, Chad T. Palumbo, Megan E. Fieser, and William J. Evans
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Lanthanide ,010405 organic chemistry ,Organic Chemistry ,Inorganic chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Ion ,Inorganic Chemistry ,Cyclooctatetraene ,chemistry.chemical_compound ,Crystallography ,chemistry ,Cyclopentadienyl complex ,Reactivity (chemistry) ,Physical and Theoretical Chemistry - Abstract
The Ln2+ complexes [K(2.2.2-cryptand)][Cp′3Ln] (Ln = La, Ce, Pr, Nd, Sm, Eu, Dy, Tm, Yb; Cp′ = C5H4SiMe3) were reacted with 1,3,5,7-cyclooctatetraene, C8H8, to determine if the reactivity of the complexes of 4fn+1 ions differed from that of 4fn5d1 ions. Crystallographically characterizable (C8H8)2– complexes were obtained only for the larger metals in the lanthanide series, and two types of products were obtained: [K(2.2.2-cryptand)][Cp′2Ln(C8H8)] (Ln = La, Ce) and [K(2.2.2-cryptand)][Ln(C8H8)2] (Ln = Ce, Pr, Nd, Sm). The expected co-products of the two-electron reduction of C8H8 by 2 equiv of [K(2.2.2-cryptand)][Cp′3Ln], namely, the tetrakis(cyclopentadienyl) complexes, [K(2.2.2-cryptand)][Cp′4Ln], were crystallographically characterized for six metals (Ln = Ce, Pr, Nd, Sm, Dy, Tm). more...
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- 2017
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10. Evaluating the electronic structure of formal LnIIions in LnII(C5H4SiMe3)31−using XANES spectroscopy and DFT calculations
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Juan S. Lezama Pacheco, Gregory L. Wagner, Enrique R. Batista, David H. Woen, Jing Su, Austin J. Ryan, Maryline G. Ferrier, Stosh A. Kozimor, Samantha K. Cary, Jonathan W. Engle, Tonya Vitova, Benjamin W. Stein, Ping Yang, Angela C. Olson, William J. Evans, and Megan E. Fieser more...
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Lanthanide ,010405 organic chemistry ,Chemistry ,Transition dipole moment ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,XANES ,0104 chemical sciences ,Ion ,Computational chemistry ,Physical chemistry ,Density functional theory ,Electron configuration ,Spectroscopy - Abstract
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f n 5d1 configurations (not 4f n+1 5d0). In these 4f n 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration. more...
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- 2017
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11. Expanding Thorium Hydride Chemistry Through Th2+, Including the Synthesis of a Mixed-Valent Th4+/Th3+ Hydride Complex
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Filipp Furche, Joseph W. Ziller, Ryan R. Langeslay, Megan E. Fieser, and William J. Evans
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Hydrogen ,010405 organic chemistry ,Hydride ,Thorium ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,law.invention ,Crystallography ,Colloid and Surface Chemistry ,chemistry ,law ,Reagent ,Organic chemistry ,Density functional theory ,Reactivity (chemistry) ,Electron paramagnetic resonance ,Bimetallic strip - Abstract
The reactivity of the recently discovered Th2+ complex [K(18-crown-6)(THF)2][Cp″3Th], 1 [Cp′′ = C5H3(SiMe3)2-1,3], with hydrogen reagents has been investigated and found to provide syntheses of new classes of thorium hydride compounds. Complex 1 reacts with [Et3NH][BPh4] to form the terminal Th4+ hydride complex Cp″3ThH, 2, a reaction that formally involves a net two-electron reduction. Complex 1 also reacts in the solid state and in solution with H2 to form a mixed-valent bimetallic product, [K(18-crown-6)(Et2O)][Cp″2ThH2]2, 3, which was analyzed by X-ray crystallography, electron paramagnetic resonance and optical spectroscopy, and density functional theory. The existence of 3, which formally contains Th3+ and Th4+, suggested that KC8 could reduce [(C5Me5)2ThH2]2. In the presence of 18-crown-6, this reaction forms an analogous mixed-valent product formulated as [K(18-crown-6)(THF)][(C5Me5)2ThH2]2, 4. A similar complex with (C5Me4H)1– ligands was not obtained, but reaction of (C5Me4H)3Th with H2 in the p... more...
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- 2016
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12. Dual-catalytic decarbonylation of fatty acid methyl esters to form olefins
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Anne M. LaPointe, Emily G. Wilborn, Sydonie D. Schimler, Brooke Benson, Lauren A. Mitchell, Levi T. Hogan, William B. Tolman, Megan E. Fieser, and Alex John
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chemistry.chemical_classification ,010405 organic chemistry ,Group strategy ,Decarbonylation ,Metals and Alloys ,Fatty acid ,General Chemistry ,Transesterification ,010402 general chemistry ,Cleavage (embryo) ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Homogeneous ,Materials Chemistry ,Ceramics and Composites ,Organic chemistry ,Alkyl - Abstract
The homogeneous dehydrative decarbonylation of fatty acid methyl esters (FAMEs) to form olefins is reported. In order to facilitate cleavage of the unactivated acyl C–O bond of the alkyl ester, a one pot dual-catalytic directing group strategy was developed through optimization of the individual transesterification and decarbonylation reaction steps. more...
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- 2018
13. Dinitrogen Reduction, Sulfur Reduction, and Isoprene Polymerization via Photochemical Activation of Trivalent Bis(cyclopentadienyl) Rare-Earth-Metal Allyl Complexes
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William J. Evans, Jefferson E. Bates, Filipp Furche, Megan E. Fieser, Joseph W. Ziller, and Casey W. Johnson
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Ligand ,Organic Chemistry ,Photodissociation ,chemistry.chemical_element ,Photochemistry ,Sulfur ,law.invention ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,chemistry ,Cyclopentadienyl complex ,Polymerization ,law ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Crystallization ,Isoprene - Abstract
Dinitrogen can be reduced by photochemical activation of the trivalent rare-earth-metal bis(pentamethylcyclopentadienyl) allyl complexes (C5Me5)2Ln(η3-C3H4R) (Ln = Y, Lu; R = H, Me) to form the (N═N)2– complexes [(C5Me5)2Ln]2(μ-η2:η2-N2). This demonstrates that productive organolanthanide photochemistry is not limited to complexes of the unusual (η3-C5Me4H)− ligand in the heteroleptic complexes (C5Me5)2(C5Me4H)Ln and (C5Me5)(C5Me4H)2Ln. Photolytic activation of (C5Me5)2Ln(η3-C3H5) (Ln = Y, Lu) in the presence of isoprene provides a rare photopolymerization route to polyisoprene. Sulfur can also be reduced by photolysis of (C5Me5)2Ln(η3-C3H5) (Ln = Y, Lu) to generate the (S)2– complexes, [(C5Me5)2Ln]2(μ-S), which have variable Ln–S–Ln angles depending on crystallization conditions. more...
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- 2015
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14. Ligand Effects in the Synthesis of Ln2+ Complexes by Reduction of Tris(cyclopentadienyl) Precursors Including C–H Bond Activation of an Indenyl Anion
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Jordan F. Corbey, Joseph W. Ziller, Megan E. Fieser, Filipp Furche, William J. Evans, David H. Woen, and Chad T. Palumbo
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Tris ,Ligand ,Gadolinium ,Organic Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Yttrium ,law.invention ,Ion ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,Crystallography ,Cyclopentadienyl complex ,chemistry ,law ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance - Abstract
The tris(cyclopentadienyl) yttrium complexes Cp3Y(THF), CpMe3Y(THF), Cp″3Y, Cp″2YCp, and Cp″2YCpMe [Cp = C5H5, CpMe = C5H4Me, Cp″ = C5H3(SiMe3)2] have been treated with potassium graphite in the presence of 2.2.2-cryptand to search for more stable examples of complexes featuring the recently discovered Y2+ ion first isolated in [K(18-crown-6)][Cp′3Y] and [K(2.2.2-cryptand)][Cp′3Y], 1-Y (Cp′ = C5H4SiMe3). Reduction of the tris(cyclopentadienyl) complexes generates dark solutions like that of 1-Y, and the EPR spectra contain doublets with g values between 1.990 and 1.991 and hyperfine coupling constants of 34–47 gauss that are consistent with the presence of Y2+. [K(2.2.2-cryptand)][Cp″2YCp], 2-Y, was characterizable by X-ray crystallography. Reduction of the Cp″3Gd, Cp″2GdCp, and Cp″2GdCpMe complexes containing the larger metal gadolinium were also examined. In each case, dark solutions and EPR spectra like that of [K(2.2.2-cryptand)][Cp′3Gd], 1-Gd, were obtained, and [K(2.2.2-cryptand)][Cp″2GdCp], 2-Gd, w... more...
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- 2015
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15. Metal versus Ligand Reduction in Ln
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Chad T, Palumbo, Dominik P, Halter, Vamsee K, Voora, Guo P, Chen, Alan K, Chan, Megan E, Fieser, Joseph W, Ziller, Wolfgang, Hieringer, Filipp, Furche, Karsten, Meyer, and William J, Evans
- Abstract
The synthesis of 4f
- Published
- 2018
16. Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C5H3(SiMe3)2]3Th}1− anion containing thorium in the formal +2 oxidation state
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Ryan R. Langeslay, William J. Evans, Joseph W. Ziller, Filipp Furche, and Megan E. Fieser
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Trigonal planar molecular geometry ,010405 organic chemistry ,Chemistry ,Inorganic chemistry ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Crystallography ,Cyclooctatetraene ,chemistry.chemical_compound ,Transition metal ,Oxidation state ,Reactivity (chemistry) ,Density functional theory ,Electron configuration ,Ground state - Abstract
© The Royal Society of Chemistry 2015. Reduction of the Th3+complex Cp′′3Th, 1 [Cp′′ = C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp′′3Th], 2, a complex containing thorium in the formal +2 oxidation state. Reaction of 1 with KC8in the presence of 18-crown-6 generates the analogous Th2+compound, [K(18-crown-6)(THF)2][Cp′′3Th], 3. Complexes 2 and 3 form dark green solutions in THF with ε = 23 000 M-1cm-1, but crystallize as dichroic dark blue/red crystals. X-ray crystallography revealed that the anions in 2 and 3 have trigonal planar coordination geometries, with 2.521 and 2.525 Å Th-(Cp′′ ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp′′3Th)1-is consistent with a 6d2ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp′′2Th(C8H8), 4, and [K(18-crown-6)]Cp′′. This journal is more...
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- 2015
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17. Mechanistic Insights into the Alternating Copolymerization of Epoxides and Cyclic Anhydrides Using a (Salph)AlCl and Iminium Salt Catalytic System
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Christine R. Dunbar, Mukunda Mandal, Megan E. Fieser, Nathan J. Van Zee, William B. Tolman, Maria J. Sanford, Christopher J. Cramer, Devon M. Urness, Geoffrey W. Coates, and Lauren A. Mitchell
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010405 organic chemistry ,Oxide ,Epoxide ,Iminium ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Polymerization ,Alkoxide ,Polymer chemistry ,Copolymer ,Organic chemistry ,Carboxylate - Abstract
Mechanistic studies involving synergistic experiment and theory were performed on the perfectly alternating copolymerization of 1-butene oxide and carbic anhydride using a (salph)AlCl/[PPN]Cl catalytic pair. These studies showed a first-order dependence of the polymerization rate on the epoxide, a zero-order dependence on the cyclic anhydride, and a first-order dependence on the catalyst only if the two members of the catalytic pair are treated as a single unit. Studies of model complexes showed that a mixed alkoxide/carboxylate aluminum intermediate preferentially opens cyclic anhydride over epoxide. In addition, ring-opening of epoxide by an intermediate comprising multiple carboxylates was found to be rate-determining. On the basis of the experimental results and analysis by DFT calculations, a mechanism involving two catalytic cycles is proposed wherein the alternating copolymerization proceeds via intermediates that have carboxylate ligation in common, and a secondary cycle involving a bis-alkoxide species is avoided, thus explaining the lack of side reactions until the polymerization is complete. more...
- Published
- 2017
18. Structural, Spectroscopic, and Theoretical Comparison of Traditional vs Recently Discovered Ln2+ Ions in the [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln] Complexes: The Variable Nature of Dy2+ and Nd2+
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Brandon T. Krull, Jefferson E. Bates, Filipp Furche, William J. Evans, Matthew R. MacDonald, Joseph W. Ziller, and Megan E. Fieser
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Lanthanide ,Chemistry ,Stereochemistry ,General Chemistry ,Ring (chemistry) ,Biochemistry ,Catalysis ,Ion ,chemistry.chemical_compound ,Crystallography ,Colloid and Surface Chemistry ,Cyclopentadienyl complex ,2.2.2-Cryptand ,Coordination geometry - Abstract
The Ln3+ and Ln2+ complexes, Cp′3Ln, 1, (Cp′ = C5H4SiMe3) and [K(2.2.2-cryptand)][Cp′3Ln], 2, respectively, have been synthesized for the six lanthanides traditionally known in +2 oxidation states, i.e., Ln = Eu, Yb, Sm, Tm, Dy, and Nd, to allow direct structural and spectroscopic comparison with the recently discovered Ln2+ ions of Ln = Pr, Gd, Tb, Ho, Y, Er, and Lu in 2. 2-La and 2-Ce were also prepared to allow the first comparison of all the lanthanides in the same coordination environment in both +2 and +3 oxidation states. 2-La and 2-Ce show the same unusual structural feature of the recently discovered +2 complexes, that the Ln–(Cp′ ring centroid) distances are only about 0.03 A longer than in the +3 analogs, 1. The Eu, Yb, Sm, Tm, Dy, and Nd complexes were expected to show much larger differences, but this was observed for only four of these traditional six lanthanides. 2-Dy and 2-Nd are like the new nine ions in this tris(cyclopentadienyl) coordination geometry. A DFT-based model explains the res... more...
- Published
- 2014
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19. Differentiating Chemically Similar Lewis Acid Sites in Heterobimetallic Complexes: The Rare-Earth Bridged Hydride (C5Me5)2Ln(μ-H)2Ln′(C5Me5)2 and Tuckover Hydride (C5Me5)2Ln(μ-H)(μ-η1:η5-CH2C5Me4)Ln′(C5Me5) Systems
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Jefferson E. Bates, William J. Evans, Filipp Furche, Thomas J. Mueller, Megan E. Fieser, and Joseph W. Ziller
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Inorganic Chemistry ,1h nmr spectroscopy ,Hydrogenolysis ,Chemistry ,Hydride ,Organic Chemistry ,Rare earth ,Inorganic chemistry ,Lewis acids and bases ,Physical and Theoretical Chemistry ,Medicinal chemistry ,Bimetallic strip - Abstract
The challenge of differentiating the chemistry of two closely related Lewis acidic metals in heterobimetallic complexes was addressed by studying hydrogenolysis and C–H bond activation reactions of bimetallic rare-earth hydride complexes. Hydrogenolysis of equimolar amounts of Cp*2Lu(η3-C3H5) (1-Lu) and Cp*2Y(η3-C3H5) (1-Y) (Cp* = C5Me5) forms a mixture of hydride complexes, the heterobimetallic compound Cp*2Lu(H)2YCp*2 (2-Lu/Y) and the homobimetallic compounds (Cp*2LuH)2 (2-Lu/Lu) and (Cp*2YH)2 (2-Y/Y). This mixture can be analyzed and differentiated by 1H NMR spectroscopy due to the I = 1/2 89Y nucleus to reveal these three products in a ratio of approximately 86:10:4, respectively. Heating this mixture leads to C–H bond activation and formation of tuckover hydride complexes, the heterobimetallic compounds Cp*2Y(μ-H)(μ-η1:η5-CH2C5Me4)LuCp* (3-Y/Lu) and Cp*2Lu(μ-H)(μ-η1:η5-CH2C5Me4)YCp* (3-Lu/Y) and the homobimetallic compounds Cp*2Lu(μ-H)(μ-η1:η5-CH2C5Me4)LuCp* (3-Lu/Lu) and Cp*2Y(μ-H)(μ-η1:η5-CH2C5Me4)... more...
- Published
- 2014
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20. Identification of the +2 Oxidation State for Uranium in a Crystalline Molecular Complex, [K(2.2.2-Cryptand)][(C5H4SiMe3)3U]
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Joseph W. Ziller, Jefferson E. Bates, Filipp Furche, Matthew R. MacDonald, William J. Evans, and Megan E. Fieser
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Hydride ,Potassium ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Biochemistry ,Catalysis ,Ion ,Crystallography ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Oxidation state ,Density functional theory ,Graphite ,Ground state ,2.2.2-Cryptand - Abstract
Flash reduction of Cp'3U (Cp' = C5H4SiMe3) in a column of potassium graphite in the presence of 2.2.2-cryptand generates crystalline [K(2.2.2-cryptand)][Cp'3U], the first isolable molecular U(2+) complex. To ensure that this was not the U(3+) hydride, [K(2.2.2-cryptand)][Cp'3UH], which could be crystallographically similar, the hydride complex was synthesized by addition of KH to Cp'3U and by reduction of H2 by the U(2+) complex and was confirmed to be a different compound. Density functional theory calculations indicate a 5f(3)6d(1) quintet ground state for the [Cp'3U](-) anion and match the observed strong transitions in its optical spectrum. more...
- Published
- 2013
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21. Insertion of CO2 and COS into Bi–C Bonds: Reactivity of a Bismuth NCN Pincer Complex of an Oxyaryl Dianionic Ligand, [2,6-(Me2NCH2)2C6H3]Bi(C6H2tBu2O)
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Joseph W. Ziller, Ian J. Casely, Douglas R. Kindra, Megan E. Fieser, William J. Evans, and Filipp Furche
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Silylation ,Chemistry ,Ligand ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Biochemistry ,Small molecule ,Catalysis ,Pincer movement ,Bismuth ,Crystallography ,Colloid and Surface Chemistry ,Electrophile ,Molecule ,Reactivity (chemistry) - Abstract
The reactivity of the unusual oxyaryl dianionic ligand, (C6H2tBu2-3,5-O-4)2–, in the Bi3+ NCN pincer complex Ar′Bi(C6H2tBu2-3,5-O-4), 1, [Ar′ = 2,6-(Me2NCH2)2C6H3] has been explored with small molecule substrates and electrophiles. The first insertion reactions of CO2 and COS into Bi–C bonds are observed with this oxyaryl dianionic ligand complex. These reactions generate new dianions that have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands were identified by X-ray crystallography in Ar′Bi[O2C(C6H2tBu2-3-5-O-4)-κ2O,O′], 2, and Ar′Bi[OSC(C6H2tBu2-3-5-O-4)-κ2O,S], 3, respectively. Silyl halides and pseudohalides, R3SiX (X = Cl, CN, N3; R = Me, Ph), react with 1 by attaching X to bismuth and R3Si to the oxyaryl oxygen to form Ar′Bi(X)(C6H2tBu2-3,5-OSiR3-4) complexes, a formal addition across five bonds. These react with additional R3SiX to generate Ar′BiX2 complexes and R3SiOC6H3tBu2-2,6. The reaction of 1 with I2 forms Ar′BiI2 an... more...
- Published
- 2013
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22. Evaluating the electronic structure of formal Ln
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Megan E, Fieser, Maryline G, Ferrier, Jing, Su, Enrique, Batista, Samantha K, Cary, Jonathan W, Engle, William J, Evans, Juan S, Lezama Pacheco, Stosh A, Kozimor, Angela C, Olson, Austin J, Ryan, Benjamin W, Stein, Gregory L, Wagner, David H, Woen, Tonya, Vitova, and Ping, Yang more...
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Chemistry - Abstract
LnII(C5H4SiMe3)1– have been characterized by XANES and DFT., The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)3 1– (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)3 1– (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)3 1– (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4fn 5d1 configurations (not 4fn+1 5d0). In these 4fn 5d1 complexes, the C 3h-symmetric ligand environment provides a highly shielded 5d-orbital of a′ symmetry that made the 4fn 5d1 electronic configurations lower in energy than the more typical 4fn+1 5d0 configuration. more...
- Published
- 2017
23. Correction to Understanding the Mechanism of Polymerization of ε-Caprolactone Catalyzed by Aluminum Salen Complexes
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William B. Tolman, Christopher J. Cramer, Mukunda Mandal, Joahanna A. Macaranas, Megan E. Fieser, and Anna M. Luke
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Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Polymerization ,Metal salen complexes ,Aluminium ,Polymer chemistry ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Caprolactone ,Catalysis - Published
- 2016
24. Expanding Thorium Hydride Chemistry Through Th²⁺, Including the Synthesis of a Mixed-Valent Th⁴⁺/Th³⁺ Hydride Complex
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Ryan R, Langeslay, Megan E, Fieser, Joseph W, Ziller, Filipp, Furche, and William J, Evans
- Abstract
The reactivity of the recently discovered Th(2+) complex [K(18-crown-6)(THF)2][Cp″3Th], 1 [Cp'' = C5H3(SiMe3)2-1,3], with hydrogen reagents has been investigated and found to provide syntheses of new classes of thorium hydride compounds. Complex 1 reacts with [Et3NH][BPh4] to form the terminal Th(4+) hydride complex Cp″3ThH, 2, a reaction that formally involves a net two-electron reduction. Complex 1 also reacts in the solid state and in solution with H2 to form a mixed-valent bimetallic product, [K(18-crown-6)(Et2O)][Cp″2ThH2]2, 3, which was analyzed by X-ray crystallography, electron paramagnetic resonance and optical spectroscopy, and density functional theory. The existence of 3, which formally contains Th(3+) and Th(4+), suggested that KC8 could reduce [(C5Me5)2ThH2]2. In the presence of 18-crown-6, this reaction forms an analogous mixed-valent product formulated as [K(18-crown-6)(THF)][(C5Me5)2ThH2]2, 4. A similar complex with (C5Me4H)(1-) ligands was not obtained, but reaction of (C5Me4H)3Th with H2 in the presence of KC8 and 2.2.2-cryptand at -45 °C produced two monometallic hydride products, namely, (C5Me4H)3ThH, 5, and [K(2.2.2-cryptand)]{(C5Me4H)2[η(1):η(5)-C5Me3H(CH2)]ThH]}, 6. Complex 6 contains a metalated tetramethylcyclopentadienyl dianion, [C5Me3H(CH2)](2-), that binds in a tuck-in mode. more...
- Published
- 2016
25. Raman spectroscopy of the N-N bond in rare earth dinitrogen complexes
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Megan E. Fieser, Jordan F. Corbey, Joseph W. Ziller, William J. Evans, Thomas J. Mueller, and David H. Woen
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010405 organic chemistry ,Chemistry ,Stereochemistry ,Ligand ,Rare earth ,010402 general chemistry ,01 natural sciences ,Relative stability ,0104 chemical sciences ,Inorganic Chemistry ,Metal ,symbols.namesake ,Crystallography ,visual_art ,symbols ,visual_art.visual_art_medium ,Atomic number ,Raman spectroscopy - Abstract
Raman spectra have been collected on single crystals of over 20 different rare earth complexes containing reduced dinitrogen ligands to determine if these data will correlate with periodic properties or relative stability. Four types of complexes were examined: [(C5Me5)2Ln]2(μ-η(2):η(2)-N2), 1-Ln, [(C5Me4H)2(THF)Ln]2(μ-η(2):η(2)-N2), 2-Ln, [(C5H4Me)2Ln]2(μ-η(2):η(2)-N2), 3-Ln, and {[(Me3Si)2N]2(THF)Ln}2(μ-η(2):η(2)-N2), 4-Ln. Although each of the complexes contains a side-on bound dinitrogen ligand that is formally (N2)(2-), the N-N bond distances determined by X-ray crystallography range from 1.088(12) to 1.305(6) Å. In the 4-Ln series (Ln = Gd, Tb, Dy, Ho, Er and Tm), the 1.26-1.31 Å N-N distances do not follow any periodic trends, but the Raman stretching frequencies for Gd-Tm were found to decrease regularly with decreasing atomic number and increasing Lewis acidity of the metal. Similar correlations can be seen with the late metals in complexes of the other series, 1-Ln, 2-Ln and 3-Ln, but exceptions exist, particularly for the larger metals. Comparisons between the several types of complexes as a function of ligand were more complicated and variations in stretching frequency as a function of L in the {[(Me3Si)2N]2Y(L)}2(μ-η(2):η(2)-N2) substituted versions of 4-Y did not give trends consistent with bond distances or Gutmann donor numbers. more...
- Published
- 2016
26. Reactivity of the Y3+ Tuck-Over Hydride Complex, (C5Me5)2Y(μ-H)(μ-CH2C5Me4)Y(C5Me5)
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Benjamin M. Schmiege, Joseph W. Ziller, Megan E. Fieser, and William J. Evans
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chemistry.chemical_classification ,Hydride ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,Yttrium ,Hydride ligands ,Photochemistry ,Medicinal chemistry ,Ion ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Physical and Theoretical Chemistry ,Alkyl ,Carbodiimide - Abstract
The trivalent yttrium tuck-over hydride complex, (C5Me5)2Y(μ-H)(μ-η1:η5-CH2C5Me4)Y(C5Me5), 1, acts as a reductant in reactions in which the (μ-H)− hydride ligand and the bridging Y–C alkyl anion linkage in the (μ-η1:η5-CH2C5Me4)2– ligand combine to form a C–H bond in (C5Me5)− and deliver two electrons to a substrate. Complex 1 reacts with PhSSPh, AgOTf (OTf = OSO2CF3), and Et3NHBPh4 to form [(C5Me5)2Y(μ-SPh)]2, [(C5Me5)2Y(μ-OTf)]2, and (C5Me5)2Y(μ-Ph)2BPh2, respectively. The reactivity of the Y–H and Y–CH2C5Me4 linkages in 1 was probed via carbodiimide insertion reactions. iPrN═C═NiPr inserts into both Y–H and Y–C bonds to yield (C5Me5)[iPrNC(H)NiPr]Y{μ-η5-C5Me4CH2[iPrNCNiPr]}Y(C5Me5)2. Carbodiimide insertion with [(C5Me5)2YH]2, 2, was also examined for comparison, and (C5Me5)2Y[iPrNC(H)NiPr-κ2N,N′] was isolated and structurally characterized. To examine the possibility of selective reactivity of the bridging ligands, μ-H versus μ-CH2C5Me4, trimethylsilylchloride was reacted with 1, and the tuck-over chlo... more...
- Published
- 2012
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27. Expanding Rare-Earth Oxidation State Chemistry to Molecular Complexes of Holmium(II) and Erbium(II)
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Megan E. Fieser, Joseph W. Ziller, Filipp Furche, Matthew R. MacDonald, Jefferson E. Bates, and William J. Evans
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Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Ring (chemistry) ,Biochemistry ,Catalysis ,law.invention ,Metal ,chemistry.chemical_compound ,Crystallography ,Colloid and Surface Chemistry ,chemistry ,Oxidation state ,law ,visual_art ,visual_art.visual_art_medium ,Density functional theory ,Electron configuration ,Crystallization ,Holmium ,2.2.2-Cryptand - Abstract
The first molecular complexes of holmium and erbium in the +2 oxidation state have been generated by reducing Cp'(3)Ln [Cp' = C(5)H(4)SiMe(3); Ln = Ho (1), Er (2)] with KC(8) in the presence of 18-crown-6 in Et(2)O at -35 °C under argon. Purification and crystallization below -35 °C gave isomorphous [(18-crown-6)K][Cp'(3)Ln] [Ln = Ho (3), Er (4)]. The three Cp' ring centroids define a trigonal-planar geometry around each metal ion that is not perturbed by the location of the potassium crown cation near one ring with K-C(Cp') distances of 3.053(8)-3.078(2) Å. The metrical parameters of the three rings are indistinguishable within the error limits. In contrast to Ln(2+) complexes of Eu, Yb, Sm, Tm, Dy, and Nd, 3 and 4 have average Ln-(Cp' ring centroid) distances only 0.029 and 0.021 Å longer than those of the Ln(3+) analogues 1 and 2, a result similar to that previously reported for the 4d(1) Y(2+) complex [(18-crown-6)K][Cp'(3)Y] (5) and the 5d(1) La(2+) complex [K(18-crown-6)(Et(2)O)][Cp″(3)La] [Cp″ = 1,3-(Me(3)Si)(2)C(5)H(3)]. Surprisingly, the UV-vis spectra of 3 and 4 are also very similar to that of 5 with two broad absorptions in the visible region, suggesting that 3-5 have similar electron configurations. Density functional theory calculations on the Ho(2+) and Er(2+) species yielded HOMOs that are largely 5d(z(2)) in character and supportive of 4f(10)5d(1) and 4f(11)5d(1) ground-state configurations, respectively. more...
- Published
- 2012
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28. Isolation of +2 rare earth metal ions with three anionic carbocyclic rings: bimetallic bis(cyclopentadienyl) reduced arene complexes of La2+ and Ce2+ are four electron reductants
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Jeffrey R. Long, Christopher M. Kotyk, Filipp Furche, Megan E. Fieser, Lucy E. Darago, Chad T. Palumbo, Joseph W. Ziller, and William J. Evans
- Subjects
Metal ions in aqueous solution ,Potassium ,chemistry.chemical_element ,General Chemistry ,Photochemistry ,Medicinal chemistry ,Ion ,chemistry.chemical_compound ,Cyclopentadienyl complex ,chemistry ,Oxidation state ,Benzene ,Bimetallic strip ,Naphthalene - Abstract
© The Royal Society of Chemistry. A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp″3Ln)1- and (Cp′3Ln)1- (Cp″ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2- ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1-. The intensely colored (ε = ∼8000 M-1 cm-1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)]. more...
- Published
- 2015
- Full Text
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29. Record High Single-Ion Magnetic Moments Through 4f(n)5d(1) Electron Configurations in the Divalent Lanthanide Complexes [(C5H4SiMe3)3Ln]⁻
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William J. Evans, Katie R. Meihaus, Jordan F. Corbey, Jeffrey R. Long, and Megan E. Fieser
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Lanthanide ,Magnetic moment ,Chemistry ,Inorganic chemistry ,General Chemistry ,Electronic structure ,Biochemistry ,Magnetic susceptibility ,Catalysis ,Crystallography ,Magnetization ,Colloid and Surface Chemistry ,Magnet ,Molecule ,Electron configuration - Abstract
The recently reported series of divalent lanthanide complex salts, namely [K(2.2.2-cryptand)][Cp'3Ln] (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm; Cp' = C5H4SiMe3) and the analogous trivalent complexes, Cp'3Ln, have been characterized via dc and ac magnetic susceptibility measurements. The salts of the complexes [Cp'3Dy](-) and [Cp'3Ho](-) exhibit magnetic moments of 11.3 and 11.4 μB, respectively, which are the highest moments reported to date for any monometallic molecular species. The magnetic moments measured at room temperature support the assignments of a 4f(n+1) configuration for Ln = Sm, Eu, Tm and a 4f(n)5d(1) configuration for Ln = Y, La, Gd, Tb, Dy, Ho, Er. In the cases of Ln = Ce, Pr, Nd, simple models do not accurately predict the experimental room temperature magnetic moments. Although an LS coupling scheme is a useful starting point, it is not sufficient to describe the complex magnetic behavior and electronic structure of these intriguing molecules. While no slow magnetic relaxation was observed for any member of the series under zero applied dc field, the large moments accessible with such mixed configurations present important case studies in the pursuit of magnetic materials with inherently larger magnetic moments. This is essential for the design of new bulk magnetic materials and for diminishing processes such as quantum tunneling of the magnetization in single-molecule magnets. more...
- Published
- 2015
30. Isolation of +2 rare earth metal ions with three anionic carbocyclic rings: bimetallic bis(cyclopentadienyl) reduced arene complexes of La
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Christopher M, Kotyk, Megan E, Fieser, Chad T, Palumbo, Joseph W, Ziller, Lucy E, Darago, Jeffrey R, Long, Filipp, Furche, and William J, Evans
- Subjects
Chemistry - Abstract
A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of (C5H4SiMe3)3Ln (Ln = La, Ce) with potassium graphite and 2.2.2-cryptand in benzene., A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp′′3Ln)1– and (Cp′3Ln)1– (Cp′′ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2– ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1–. The intensely colored (ε = ∼8000 M–1 cm–1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)]. more...
- Published
- 2015
31. Structural, spectroscopic, and theoretical comparison of traditional vs recently discovered Ln(2+) ions in the [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln] complexes: the variable nature of Dy(2+) and Nd(2+)
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Megan E, Fieser, Matthew R, MacDonald, Brandon T, Krull, Jefferson E, Bates, Joseph W, Ziller, Filipp, Furche, and William J, Evans
- Abstract
The Ln(3+) and Ln(2+) complexes, Cp'3Ln, 1, (Cp' = C5H4SiMe3) and [K(2.2.2-cryptand)][Cp'3Ln], 2, respectively, have been synthesized for the six lanthanides traditionally known in +2 oxidation states, i.e., Ln = Eu, Yb, Sm, Tm, Dy, and Nd, to allow direct structural and spectroscopic comparison with the recently discovered Ln(2+) ions of Ln = Pr, Gd, Tb, Ho, Y, Er, and Lu in 2. 2-La and 2-Ce were also prepared to allow the first comparison of all the lanthanides in the same coordination environment in both +2 and +3 oxidation states. 2-La and 2-Ce show the same unusual structural feature of the recently discovered +2 complexes, that the Ln-(Cp' ring centroid) distances are only about 0.03 Å longer than in the +3 analogs, 1. The Eu, Yb, Sm, Tm, Dy, and Nd complexes were expected to show much larger differences, but this was observed for only four of these traditional six lanthanides. 2-Dy and 2-Nd are like the new nine ions in this tris(cyclopentadienyl) coordination geometry. A DFT-based model explains the results and shows that a 4f (n)5d(1) electron configuration is appropriate not only for the nine recently discovered Ln(2+) ions in 2 but also for Dy(2+) and Nd(2+), which traditionally have 4f (n+1) electron configurations like Eu(2+), Yb(2+), Sm(2+), and Tm(2+). These results indicate that the ground state of a lanthanide ion in a molecule can be changed by the ligand set, a previously unknown option with these metals due to the limited radial extension of the 4f orbitals. more...
- Published
- 2014
32. Synthesis, structure, and reactivity of crystalline molecular complexes of the {[C
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Ryan R, Langeslay, Megan E, Fieser, Joseph W, Ziller, Filipp, Furche, and William J, Evans
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Chemistry - Abstract
Structural, spectroscopic, and DFT analysis of the first molecular complexes of Th2+ indicate they have a 6d2 electron configuration of the type expected for the transactinide ions Rf2+ and Db3+., Reduction of the Th3+ complex Cp′′3Th, 1 [Cp′′ = C5H3(SiMe3)2], with potassium graphite in THF in the presence of 2.2.2-cryptand generates [K(2.2.2-cryptand)][Cp′′3Th], 2, a complex containing thorium in the formal +2 oxidation state. Reaction of 1 with KC8 in the presence of 18-crown-6 generates the analogous Th2+ compound, [K(18-crown-6)(THF)2][Cp′′3Th], 3. Complexes 2 and 3 form dark green solutions in THF with ε = 23 000 M–1 cm–1, but crystallize as dichroic dark blue/red crystals. X-ray crystallography revealed that the anions in 2 and 3 have trigonal planar coordination geometries, with 2.521 and 2.525 Å Th–(Cp′′ ring centroid) distances, respectively, equivalent to the 2.520 Å distance measured in 1. Density functional theory analysis of (Cp′′3Th)1– is consistent with a 6d2 ground state, the first example of this transition metal electron configuration. Complex 3 reacts as a two-electron reductant with cyclooctatetraene to make Cp′′2Th(C8H8), 4, and [K(18-crown-6)]Cp′′. more...
- Published
- 2014
33. Insertion of CO2 and COS into Bi-C bonds: reactivity of a bismuth NCN pincer complex of an oxyaryl dianionic ligand, [2,6-(Me2NCH2)2C6H3]Bi(C6H2(t)Bu2O)
- Author
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Douglas R, Kindra, Ian J, Casely, Megan E, Fieser, Joseph W, Ziller, Filipp, Furche, and William J, Evans
- Subjects
Anions ,Models, Molecular ,Oxygen ,Molecular Structure ,Organometallic Compounds ,Quantum Theory ,Carbon Dioxide ,Ligands ,Bismuth ,Carbon ,Sulfur - Abstract
The reactivity of the unusual oxyaryl dianionic ligand, (C6H2(t)Bu2-3,5-O-4)(2-), in the Bi(3+) NCN pincer complex Ar'Bi(C6H2(t)Bu2-3,5-O-4), 1, [Ar' = 2,6-(Me2NCH2)2C6H3] has been explored with small molecule substrates and electrophiles. The first insertion reactions of CO2 and COS into Bi-C bonds are observed with this oxyaryl dianionic ligand complex. These reactions generate new dianions that have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands were identified by X-ray crystallography in Ar'Bi[O2C(C6H2(t)Bu2-3-5-O-4)-κ(2)O,O'], 2, and Ar'Bi[OSC(C6H2(t)Bu2-3-5-O-4)-κ(2)O,S], 3, respectively. Silyl halides and pseudohalides, R3SiX (X = Cl, CN, N3; R = Me, Ph), react with 1 by attaching X to bismuth and R3Si to the oxyaryl oxygen to form Ar'Bi(X)(C6H2(t)Bu2-3,5-OSiR3-4) complexes, a formal addition across five bonds. These react with additional R3SiX to generate Ar'BiX2 complexes and R3SiOC6H3(t)Bu2-2,6. The reaction of 1 with I2 forms Ar'BiI2 and the coupled quinone, 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone, by oxidative coupling. more...
- Published
- 2013
34. Dinitrogen reduction via photochemical activation of heteroleptic tris(cyclopentadienyl) rare-earth complexes
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William J. Evans, Jefferson E. Bates, Megan E. Fieser, Filipp Furche, and Joseph W. Ziller
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Tris ,Models, Molecular ,Chemistry ,Nitrogen ,Rare earth ,Molecular Conformation ,General Chemistry ,Cyclopentanes ,Photochemistry ,Photochemical Processes ,Biochemistry ,Catalysis ,Reduction (complexity) ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Cyclopentadienyl complex ,Organometallic Compounds ,Quantum Theory ,Density functional theory ,Metals, Rare Earth ,Oxidation-Reduction - Abstract
Dinitrogen can be reduced by photochemical activation of the Ln(3+) mixed-ligand tris(cyclopentadienyl) rare-earth complexes (η(5)-C5Me5)(3-x)(C5Me4H)(x)Ln (Ln = Y, Lu, Dy; x = 1, 2). [(C5Me4R)2Ln]2(μ-η(2):η(2)-N2) products (R = H, Me) are formed in reactions in which N2 is reduced to (N═N)(2-) and (C5Me4H)(-) is oxidized to (C5Me4H)2. Density functional theory indicates that this unusual example of rare-earth photochemistry can be rationalized by absorptions involving the (η(3)-C5Me4H)(-) ligands. more...
- Published
- 2013
35. (C5Me4H)1−-based reduction of dinitrogen by the mixed ligand tris(polyalkylcyclopentadienyl) lutetium and yttrium complexes, (C5Me5)3−x(C5Me4H)xLn
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Joseph W. Ziller, Thomas J. Mueller, William J. Evans, and Megan E. Fieser
- Subjects
Tris ,Steric effects ,Stereochemistry ,Ligand ,chemistry.chemical_element ,General Chemistry ,Yttrium ,Mixed ligand ,Redox ,Medicinal chemistry ,Lutetium ,chemistry.chemical_compound ,chemistry ,Reactivity (chemistry) - Abstract
Synthesis of the mixed ligand complexes (C5Me5)(C5Me4H)2Ln (Ln = Lu, Y) for comparison with (C5Me5)2(C5Me4H)Ln to evaluate details of steric effects on reductive reactivity has revealed that (C5Me5)3−x(C5Me4H)xLn complexes can reduce dinitrogen to (NN)2−. (C5Me5)(C5Me4H)2Lu reacts with N2 to form [(C5Me5)(C5Me4H)Lu]2(μ-η2:η2-N2), (C5Me5)2(C5Me4H)Y reduces N2 to [(C5Me5)2Y]2(μ-η2:η2-N2), and (C5Me4H)3Sc converts N2 to [(C5Me4H)2Sc]2(μ-η2:η2-N2). Exclusive (C5Me4H)1− loss occurs in each case with formation of (C5Me4H)2 as the byproduct. (C5Me5)2, the signature byproduct of sterically induced reduction reactions, is not observed. Since these complexes do not exhibit unusual steric parameters and since the more crowded (C5Me5)2(C5Me4H)Lu and (C5Me5)3Y do not display analogous reactivity, these reactions do not appear to be sterically induced reductions and suggest a new type of ligand-based reduction pathway involving (C5Me4H)1−. more...
- Published
- 2011
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36. Ligand Effects in the Synthesis of Ln2+Complexes by Reduction of Tris(cyclopentadienyl) Precursors IncludingC–H Bond Activation of an Indenyl Anion.
- Author
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JordanF. Corbey, David H. Woen, Chad T. Palumbo, Megan E. Fieser, JosephW. Ziller, Filipp Furche, and William J. Evans
- Published
- 2015
- Full Text
- View/download PDF
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