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George G. Evens - One of the best experts on this subject based on the ideXlab platform.
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Kinetic and Mechanistic Aspects of Propene Oligomerization with Ionic Organozirconium and -Hafnium Compounds: Crystal Structures of [Cp*2MMe(THT)]+[BPh4]- (M = Zr, Hf)
Organometallics, 1992Co-Authors: J.j.w. Eshuis, Yong Y. Tan, Auke Meetsma, Jan H. Teuben, Jaap Renkema, George G. EvensAbstract:In N,N-dimethylaniline the ionic complexes [Cp*2MMe(THT)]+[BPh4]- (M = Zr, Hf) oligomerize propene to low molecular weight oligomers. At room temperature for M = Zr a rather broad molecular weight distribution is obtained (C6 to C24), whereas for M = Hf only one dimer (4-methyl-1-pentene) and one trimer (4,6-dimethyl-1-heptene) are formed. With an increase in reaction temperature the product composition shifts to lower molecular weights, but the specific formation of head-to-tail oligomers is retained. The oligomers are formed by beta-Me transfer from the growing oligopropene alkyl chain to the metal center. The molecular weight distributions of the oligomers produced at temperature between 5 and 45-degrees-C are satisfactorily described by the Flory-Schulz theory. This allows the calculation of ratios of rate coefficients for propagation (k(p)) and termination (k(t)). Values for (DELTA-G double-ended dagger p - DELTA-G double-ended dagger t)298K were calculated as -1.9 (3) and -1.4 (4) kcal.mol-1 for [Cp*2ZrMe(THT)]+[BPh4]- and [Cp*2HfMe(THT)]+[BPh4]-, respectively. Both complexes crystallize in the space group Pna2(1) with a = 31.31 (1) angstrom, b = 11.844 (4) angstrom, c = 11.084 (4) angstrom, V = 4110 (2) angstrom 3, and Z = 4 for [Cp*2ZrMe(THT)]+[BPh4]- and a = 31.32 (1) angstrom, b = 11.857 (1) angstrom, c = 11.029 (1) angstrom, V = 4096 (1) angstrom 3, and Z = 4 for [Cp*2HfMe(THT)]+[BPh4]-. A molecular modeling study based on the molecular structures using the ALCHEMY software package suggests that the conformations with the beta-Me group in the plane between the Cp* rings are more stable than the conformations with the beta-Me group pointing toward one of the Cp* ligands. Inactivation of the catalysts is caused by two different mechanisms. At room temperature allylic C-H activation of monomer and isobutene (formed by a minor beta-H transfer termination) gives inactive (meth)allyl Compounds, [Cp*2M(eta(3)-C3H5)]+ and [Cp*2M(eta(3)-C4H7)]+ (M = Zr, Hf). At elevated temperatures (> 45-degrees-C) catalytically inactive zwitterionic complexes Cp*2M+-m-C6H4-BPh3- (M = Zr, Hf) are formed through aromatic C-H activation. Reactivation of the inactive (meth)allyl complexes can be achieved by addition of hydrogen to the oligomerization mixtures.
Paul J. Chirik - One of the best experts on this subject based on the ideXlab platform.
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Group 4 Transition Metal Sandwich Complexes: Still Fresh after Almost 60 Years†
Organometallics, 2010Co-Authors: Paul J. ChirikAbstract:Metal sandwich Compounds, more commonly known as metallocenes, are some of the most enduring molecules in organometallic chemistry. Beginning with Wilkinson’s quest for titanocene, [(η5-C5H5)2Ti], the synthesis and exploration of the electronic structure and reactivity of group 4 metal sandwich complexes have been an ongoing story for almost six decades. This review recounts the historical origins of group 4 metallocenes and highlights synthetic efforts to observe and stabilize formally d2 metal sandwich Compounds. Specific attention is devoted to recent developments in the field, including dinitrogen coordination by various substituted titanocene derivatives as well as our group’s interest in bis(indenyl)zirconium and -Hafnium Compounds.
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Bis(indenyl)Hafnium Chemistry: Ligand-Induced Haptotropic Rearrangement and Fundamental Reactivity Studies at a Reduced Hafnium Center
Organometallics, 2009Co-Authors: Doris Pun, Scott M. Leopold, Christopher A. Bradley, Emil B. Lobkovsky, Paul J. ChirikAbstract:The chemistry of reduced bis(indenyl)Hafnium Compounds has been explored. Sodium amalgam reduction of (η5-C9H5-1,3-(SiMe3)2)2HfCl2 was studied in several different solvents. While reduction in tolu...
Carlos Yélamos - One of the best experts on this subject based on the ideXlab platform.
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Group 4 Half-Sandwich Tris(trimethylsilylmethyl) Complexes: Thermal Decomposition and Reactivity with N,N-Dimethylamine-Borane.
Inorganic chemistry, 2017Co-Authors: Maider Greño, Estefanía Del Horno, Miguel Mena, Adrián Pérez-redondo, Víctor Varela-izquierdo, Carlos YélamosAbstract:The thermal decomposition of group 4 trimethylsilylmethyl derivatives [M(η5-C5Me5)(CH2SiMe3)3] (M = Ti (1), Zr (2), Hf (3)) in solution and their reactivity with N,N-dimethylamine–borane were investigated. Heating of hydrocarbon solutions of Compounds 2 and 3 at 130–200 °C results in the elimination of SiMe4 and the clean formation of the singular alkylidene–alkylidyne zirconium and Hafnium Compounds [{M(η5-C5Me5)}3{(μ-CH)3SiMe}(μ3-CSiMe3)] (M = Zr (4), Hf (5)). The reaction of 2 and 3 with NHMe2BH3 (≥1 equiv) at room temperature affords the dialkyl(dimethylamidoborane) complexes [M(η5-C5Me5)(CH2SiMe3)2(NMe2BH3)] (M = Zr (6), Hf (7)). Compounds 6 and 7 are unstable in solution and decompose with formation of the alkyl(dimethylamino)borane [B(CH2SiMe3)H(NMe2)] (8), SiMe4, and other minor byproducts, including the tetranuclear zirconium(III) octahydride complex [{Zr(η5-C5Me5)}4(μ-H)8] (9) in the decomposition of 6. Addition of NHMe2BH3 to the titanium tris(trimethylsilylmethyl) derivative 1 gives the trinuc...
F. El Kamel - One of the best experts on this subject based on the ideXlab platform.
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Electrode oxygen-affinity influence on voltage nonlinearities in high-k metal-insulator-metal capacitors
Applied Physics Letters, 2010Co-Authors: C. Vallee, Corentin Jorel, Patrice Gonon, F. El KamelAbstract:This work highlights the influence of the oxygen affinity of the metal electrodes used in high-k metal-insulator-metal capacitors. Several metallic electrodes are tested in order to investigate the role of the metal work function, and the role of the electrode oxygen-affinity in nonlinear behavior of HfO2 and BaTiO3 capacitors. It is shown that the magnitude of the quadratic coefficient of nonlinearity is better explained by the electrode oxygen-affinity rather than by its work function. It is thought that electrode oxidation increases the number of oxygen vacancies at the electrode/dielectric interface, and so increases the magnitude of nonlinearity. © 2010 American Institute of Physics RELATED DATABASES Scopus View This Record in Scopus Web of Science View this record in Web of Science View Web of Science related articles KEYWORDS and PACS Keywords barium Compounds, capacitors, Hafnium Compounds, MIM devices PACS 85.30.Tv Field effect devices 84.32.Tt Capacitors ARTICLE DATA Permalink http://link.aip.org/link/doi/10.1063/1.3447795 PUBLICATION DATA ISSN: 0003-6951 (print) 1077-3118 (online) Publisher: $abstract.society.value is a Member of CrossRef American Institute of Physics
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Electrode oxygen-affinity influence on voltage nonlinearities in high-k metal-insulator-metal capacitors
Applied Physics Letters, 2010Co-Authors: C. Vallee, Corentin Jorel, Patrice Gonon, F. El KamelAbstract:This work highlights the influence of the oxygen affinity of the metal electrodes used in high-k metal-insulator-metal capacitors. Several metallic electrodes are tested in order to investigate the role of the metal work function, and the role of the electrode oxygen-affinity in nonlinear behavior of HfO2 and BaTiO3 capacitors. It is shown that the magnitude of the quadratic coefficient of nonlinearity is better explained by the electrode oxygen-affinity rather than by its work function. It is thought that electrode oxidation increases the number of oxygen vacancies at the electrode/dielectric interface, and so increases the magnitude of nonlinearity. © 2010 American Institute of Physics RELATED DATABASES Scopus View This Record in Scopus Web of Science View this record in Web of Science View Web of Science related articles KEYWORDS and PACS Keywords barium Compounds, capacitors, Hafnium Compounds, MIM devices PACS 85.30.Tv Field effect devices 84.32.Tt Capacitors ARTICLE DATA Permalink http://link.aip.org/link/doi/10.1063/1.3447795 PUBLICATION DATA ISSN: 0003-6951 (print) 1077-3118 (online) Publisher: $abstract.society.value is a Member of CrossRef American Institute of Physics
Diansheng Liu - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and structure of the lithium, zirconium and Hafnium N -silyl- N ′-benzyl-benzamidinates
Inorganica Chimica Acta, 2009Co-Authors: Yong Zhang, Xuehong Wei, Shu‐ping Huang, Jian-ping Guo, Jian-ren Xie, Diansheng LiuAbstract:The interaction of LiN(SiMe 3 )CH 2 Ph with one equivalent of benzenitrile gave the N -silyl- N ′-benzyl-benzamidinato-lithium compound [{Me 3 SiNC(Ph)N(CH 2 Ph)}Li(Et 2 O)] 2 ( 1 ). The derivative zirconium and Hafnium Compounds were produced by the treatment of 1 with ZrCl 4 or HfCl 4 in tetrahydrofuran or diethyl ether at ambient temperature, respectively, with the general formula [Me 3 SiNC(Ph)N(CH 2 Ph)] 3 MCl (M = Zr ( 2 ), Hf ( 3 )). Compounds 1 , 2 and 3 were also characterized by X-ray single crystal diffraction and NMR analysis.
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Synthesis and structures of the chelating diamido zirconium and Hafnium Compounds
Applied Organometallic Chemistry, 2005Co-Authors: Hao Junsheng, Xuehong Wei, Shu‐ping Huang, Jian-ping Guo, Diansheng LiuAbstract:The chelating diamide lithium complex [Me2Si{NLiCH(Me)Ph}2]2 (1) was synthesized. The X-ray structure of complex 1 reveals that in the solid state it is a dimer; every lithium atom is three coordinated. The [{Me2Si{NCH(CH3)Ph}2}ZrCl2LiCl(OEt2)2]2 (2) and [{Me2Si{NCH(CH3)Ph}2}HfCl2LiCl(OEt2)2]2 (3) complexes were formed by treatment of complex 1 with ZrCl4 and HfCl4 respectively in diethyl ether at ambient temperature. Complexes (2) and (3) were also characterized by X-ray single-crystal diffraction. Copyright © 2005 John Wiley & Sons, Ltd.
