9 results on '"Warren E. Piers"'
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2. A Mesoionic Carbene-Pyridine Bidentate Ligand That Improves Stability in Electrocatalytic CO
- Author
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Thorsten, Scherpf, Cody R, Carr, Laurie J, Donnelly, Zachary S, Dubrawski, Benjamin S, Gelfand, and Warren E, Piers
- Abstract
Tricarbonyl Group 7 complexes have a longstanding history as efficacious CO
- Published
- 2022
Catalog
3. Oxygen Atom Transfer to Cationic PCPNi(II) Complexes Using Amine-N-Oxides
- Author
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Warren E. Piers, Etienne A. LaPierre, Laurent Maron, Marissa L. Clapson, Denis M. Spasyuk, Chris Gendy, University of Calgary, Laboratoire de physique et chimie des nano-objets (LPCNO), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut de Chimie de Toulouse (ICT), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes (IRSAMC), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Canadian Light Source Inc., University of Saskatchewan [Saskatoon] (U of S), NSERC of Canada (Discovery Grant) the Canada Research Chair secretariat (Tier I CRC), Alexander von Humboldt Foundation, Chinese Academy of Science, and CNRS through the PICS program more...
- Subjects
010405 organic chemistry ,Ligand ,Aryl ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Pincer movement ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Bromide ,Lewis acids and bases ,[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph] ,Physical and Theoretical Chemistry ,Pincer ligand ,Trifluoromethanesulfonate ,Phosphine - Abstract
International audience; Three PCsp3P pincer ligands differing in the aryl group linking the phosphine arms with the anchoring carbon donor were used to support square planar Ni(II) bromide complexes 1-3(Br) Exchange of the coordinating bromide anion for the more wealdy coordinating triflate (OTf) or hexafluoroantimonate (SbF6) anions was accomplished by treatment with AgX or TIX salts to give compounds 1-3(x); compounds 1(OTf) 1(sbF6), 2(Br), 2(OTf), 3(Br) and 3(sbF6) were all characterized by X-ray crystallography. The reactions of these Ni(II) compounds with the amine-N-oxide oxygen atom transfer agents ONMe3 and ONMePh2 were explored. For ONMe3, reactions with 2 equiv gave products in which one arm of the pincer ligand was oxidized to a P=0 unit, with the other amine-N-oxide ligated to the Ni(II) center, forming products 5-6(x); compounds 4(OTf), 5(OTf), and 6(sbF6) were characterized crystallographically. Transient amine-N-oxide adducts prior to ligand oxidation were observed in some reactions. For the more effective 0 atom donor ONMePh2, reactions were very rapid and a second oxidation of the remaining phosphine arm was observed, producing a Ni(II) species with an OCO pincer ligand (7(sbF6)). All compounds were fully characterized. Experiments aimed at trapping transient Ni(IV) oxo intermediates (with cyclohexadiene, KH, and various Lewis acids) indicated that such species were not involved in the reaction. This was supported by density functional theory (DFT) computations at the B3PW91 level, which indicated that direct 0 atom insertion into the Ni-P bonds without the intermediacy of a Ni oxo species was the low-energy pathway. more...
- Published
- 2017
- Full Text
- View/download PDF
4. Reactions of Neutral Cobalt(II) Complexes of a Dianionic Tetrapodal Pentadentate Ligand: Cobalt(III) Amides from Imido Radicals
- Author
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Laurent Maron, Lucie Nurdin, Denis M. Spasyuk, and Warren E. Piers
- Subjects
Steric effects ,010405 organic chemistry ,Chemistry ,Ligand ,Aryl ,Coordination number ,Radical ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Adduct ,Inorganic Chemistry ,chemistry.chemical_compound ,Polymer chemistry ,Reactivity (chemistry) ,Azide ,Physical and Theoretical Chemistry - Abstract
Neutral cobalt(II) complexes of the dianionic tetrapodal pentadentate ligand B2Pz4Py, in which borate linkers supply the anionic charges, are reported. Both the six-coordinate THF adduct 1-THF and the five-coordinate THF-free complex 1 are in a high-spin S = 3/2 configuration in the ground state and have been structurally characterized by X-ray crystallography. These two Co(II) starting materials react rapidly with aryl azides of moderate steric bulk. The thermodynamic products of these reactions are low-spin, diamagnetic, Co(III) amido complexes that are either monomeric, when an external hydrogen atom source such as 1,4-cyclohexadiene is present, or dimeric products formed via C-C coupling of the azide aryl group and internal transfer of H• to the nitrogen. These products are fully characterized and are rare examples of octahedral Co amido compounds; structural determinations reveal significant pyramidalization of the amido nitrogens due to π-π repulsion wherein the amido ligand is primarily a σ donor. The amido products arise from highly reactive Co(III) imido radical intermediates that are the kinetic products of the reactions of 1 or 1-THF with the azide reagents. The imido radicals can be detected by X-band EPR spectroscopy and have been probed by density functional theory computations, which indicate that this doublet species is characterized by a high degree of spin localization on the imido ligand, accounting for the reactivity with hydrogen atom sources and dimerization chemistry observed. The high coordination number and the electron-rich nature of the dianionic B2Pz4Py ligand framework render the imido ligand formed highly reactive. more...
- Published
- 2017
5. Synthesis and Characterization of Cationic Tungsten(V) Methylidynes
- Author
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Edwin F. van der Eide, Warren E. Piers, Robert McDonald, and Masood Parvez
- Subjects
Ligand ,Stereochemistry ,Trimethylphosphine ,Cationic polymerization ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Tungsten ,law.invention ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Deprotonation ,chemistry ,law ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Tetrahydrofuran - Abstract
Cationic tungsten(V) methylidynes [L4W(X)[triple bond]CH]+[B(C6F5)4]- [L = PMe3, 0.5dmpe (dmpe = Me2PCH2CH2PMe2), X = Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV) methylidynes L4W(X)[triple bond]CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of L4W(X)[triple bond]CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1/2 is approximately -0.68 to -0.91 V vs Fc). The paramagnetic d1 (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023-2.048, quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (mu = 2.0-2.1 muB). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl)[triple bond]CH was deprotonated with a strong base at the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W[triple bond]CH, a tungsten(IV) methylidyne complex that features a (dimethylphosphino)methyl ligand. more...
- Published
- 2006
- Full Text
- View/download PDF
6. Monomeric platinum(II) hydroxides supported by sterically dominant α-diimine ligands
- Author
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Tracy L. Lohr, Masood Parvez, and Warren E. Piers
- Subjects
Steric effects ,Chemistry ,Cationic polymerization ,Halide ,chemistry.chemical_element ,Photochemistry ,Medicinal chemistry ,Inorganic Chemistry ,chemistry.chemical_compound ,Monomer ,Deprotonation ,Physical and Theoretical Chemistry ,Metal aquo complex ,Platinum ,Diimine - Abstract
The use of two new highly sterically bulky α-diimine ligands for the stabilization of neutral, monomeric platinum(II) hydroxo complexes is described. Halide abstraction from LPtCl(2) complexes of these ligands in the presence of water, followed by deprotonation of the cationic aquo complex, leads to LPt(OH)Cl and LPt(OH)(2). The latter can be reprotonated with HNTf(2) to yield a highly fluxional hydroxoaquoplatinum(II) cation. more...
- Published
- 2012
7. Sterically Enforced Linearity in a Bridging Telluride Ligand. X-ray Structure of{(CH3)2Si[(tert-C4H9)C5H3]2Sc(PMe3)}2(.mu.-Te).cntdot.C6H6
- Author
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John F. Gallagher, Warren E. Piers, and George Ferguson
- Subjects
Inorganic Chemistry ,Steric effects ,chemistry.chemical_compound ,Crystallography ,Bridging (networking) ,chemistry ,Telluride ,X-ray ,Linearity ,Physical and Theoretical Chemistry - Published
- 1994
- Full Text
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8. Mechanistic aspects of bond activation with perfluoroarylboranes
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Warren E. Piers, Adam J. V. Marwitz, and Lauren G. Mercier
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Fluorocarbons ,Magnetic Resonance Spectroscopy ,Molecular Structure ,Chemistry ,Hydrosilylation ,Imine ,Boranes ,Borane ,Silanes ,Frustrated Lewis pair ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Mechanism (philosophy) ,Computational chemistry ,Electrophile ,Organic chemistry ,Physical and Theoretical Chemistry ,Hydrogen - Abstract
In the mid-1990s, it was discovered that tris(pentafluorophenyl)borane, B(C(6)F(5))(3), was an effective catalyst for hydrosilylation of a variety of carbonyl and imine functions. Mechanistic studies revealed a counterintuitive path in which the function of the borane was to activate the silane rather than the organic substrate. This was the first example of what has come to be known as "frustrated Lewis pair" chemistry utilizing this remarkable class of electrophilic boranes. Subsequent discoveries by the groups of Stephan and Erker showed that this could be extended to the activation of dihydrogen, initiating an intense period of activity in this area in the past 5 years. This article describes the early hydrosilylation chemistry and its subsequent applications to a variety of transformations of importance to organic and inorganic chemists, drawing parallels with the more recent hydrogen activation chemistry. Here, we emphasize the current understanding of the mechanism of this process rather than focusing on the many and emerging applications of hydrogen activation by fluoroarylborane-based frustrated Lewis pair systems. more...
- Published
- 2011
9. Permethyltitanocene Tellurides and Ditellurides. X-ray Structures of [(C5Me5)2Ti]2(.mu.-Te) and (C5Me5)2Ti(.eta.2-Te2)
- Author
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Leonard R. MacGillivray, Jason M. Fischer, Warren E. Piers, and Michael J. Zaworotko
- Subjects
Inorganic Chemistry ,Crystallography ,Chemistry ,X-ray ,Physical and Theoretical Chemistry - Published
- 1995
- Full Text
- View/download PDF
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