Complexes of Zirconium and Hafnium in Oxidation State iv

Chen, E.Y.-X.; Rodríguez‐Delgado, Antonio

doi:10.1016/b0-08-045047-4/00064-9

Cited by 14 publications

(16 citation statements)

References 960 publications

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“…In the molecular structure of 9 , the Zr atom is η 2 -bound to one OCCCO unit, σ-bound to one cage carbon atom and two oxygen atoms, and coordinated to two THF molecules in a capped -octahedral geometry (Figure ), which is not common in group 4 metal complexes . As expected, the Zr−C cage distance of 2.391(3) Å is significantly larger than the average values observed in 1 − 8 .…”

Section: Resultsmentioning

confidence: 68%

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

et al. 2009

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A series of Zr-carboryne (carboryne = 1,2-dehydro-1,2-carborane) complexes were prepared and fully characterized. Both the electronic and steric factors of the ligands have significant effects on the formation of the resultant metal complexes. The reaction of organozirconium dichloride with 1 equiv of Li 2 C 2 B 10 H 10 gave a new class of zirconium-carboryne complexes, including (η 2 -C 2 B 10 H 10 )ZrCl 2 -(THF) 3 ( 6). Treatment of 6 with 2 equiv of amidinatolithium, guanidinatolithium, or t BuOK afforded the complex 9) was isolated from the reaction of 6 with ( t BuCOCHCO t Bu)Na. All complexes were fully characterized by 1 H, 13 C, and 11 B NMR techniques as well as elemental analyses. Their structures were further confirmed by singlecrystal X-ray analyses.

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Section: Resultsmentioning

confidence: 68%

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

et al. 2009

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“…Remarkably, structurally characterized Cr benzyl (C 6 H 5 CH 2 – , Bz) complexes are relatively rare (26 hits in the CSD, including 4 for Cr II , 20 for Cr III , and 2 for Cr VI ), despite the important role of this ligand in the development of stable transition metal organometallics and, consequently, its widespread use in group 4 metal model compounds (e.g., [MBz 4 ], M = Ti, Zr, Hf) and in catalytic precursors. , …”

Section: Resultsmentioning

confidence: 99%

Angular Distortions at Benzylic Carbons Due to Intramolecular Polarization-Induced Metal–Arene Interactions: A Case Study with Open-Shell Chromium(II) NHC Complexes

et al. 2013

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The synthesis and full characterization of the unprecedented open-shell Cr(II) benzyl organometallic complexes [Cr(NHC)2(benzyl)2] (2) and [Cr(NHC*)(benzyl)2] (3) (NHC = N,N′-diisopropylimidazol-2-ylidene; NHC* = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) from [Cr(benzyl)3(THF)3] and [CrCl2(THF)2]/[Mg(benzyl)2], respectively, uncovered unusually acute angles (93° in 2 and 76° in 3) at the sp3 benzylic C of the coordinated benzyl ligands. Detailed theoretical analyses (DFT and CASPT2) of the four- and three-coordinate Cr(II) species were performed to elucidate the physical origin of the benzyl bending and led to the recognition of a noncovalent, intramolecular polarization-induced metal–arene (PIMA) interaction as being responsible for it. The energetic contribution from a single PIMA interaction is estimated to be ca. 50 kJ/mol. A comparison with the origin of the angular distortions in the d0 [Zr(benzyl)4] complex will also be presented. Sharing the common origin of an induced-dipole charge density scheme with intermolecular anion−π interactions, the intramolecular PIMA interaction concept involving a transition metal unpaired d electron and arene−π orbitals can be viewed as an extension of intermolecular anion−π interactions and leads to remarkable quantitative prediction of the observed structural distortions. PIMA interactions may manifest themselves in diverse structural and dynamic phenomena and have broad implications in chemical sciences.

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“…In contrast, homogeneous chromium systems have been ignored for a long time. , During the past decade, however, the development of homogeneous chromium-based catalysts for olefin polymerization has attracted particular attention, – since significant advances have been made in this area by the use of cyclopentadienyl chromium(III) precatalysts bearing an additional neutral donor, either bridged or unbridged to the Cp unit. – Theoretical studies have shown that a high donor concentration in the vicinity of the metal atom is essential for high activities and, thus, that a bridge linking the donor group and the cyclopentadienyl moiety is favorable. , Furthermore, a large number of non-Cp chromium-based catalysts have been developed in recent years, which are able to match the polymerization activities and properties described for systems containing Cp ligands. ,,– A selection of chromium complexes with nitrogen-donor-functionalized cyclopentadienyl ligands is shown in Figure . Apart from complexes with neutral N-donor groups such as aminoethyl ( I ), anilinyl ( II ), quinolinyl ( III ), and pyridylethyl ( IV ), the silicon-bridged ansa -cyclopentadienyl-amido complex V (R = tetramethyl) is one of the most important systems that have been studied as homogeneous model systems for industrially applied heterogeneous catalysts. , Monoalkylation of V leads to neutral single-site catalysts of the type [(η 5 -C 5 Me 4 -SiMe 2 -N t Bu)CrR] (R = alkyl), which are isostructural with the cationic active sites generated from prototypical “contrained-geometry” half-sandwich group 4 catalysts, , e.g., from [η 5 -C 5 Me 4 -SiMe 2 -NR)MCl 2 ] (M = Ti, Zr, Hf), by addition of an appropriate cocatalyst.…”

Section: Introductionmentioning

confidence: 99%

Chromium Complexes with Me₂Si-Bridged Cyclopentadienyl-imidazolin-2-imine Ligands: Synthesis, Structure, and Use in Ethylene Polymerization Catalysis

2008

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Imidazolin-2-imino-functionalized tetramethylcyclopentadienes 3-H have been prepared in high yields by the reaction of 2 equiv of 1,3,4,5-tetramethylimidazolin-2-imine (1a), 1,3-diisopropyl-4,5-dimethylimidazolin-2-imine (1b), and 1,3-di-tert-butylimidazolin-2-imine (1c) with 5-(chlorodimethylsilyl)-1,2,3,4-tetramethyl-1,3-cyclopentadiene (2), whereas the corresponding indene 6-H has been obtained from the reaction of 1b with 1-(chlordimethylsilyl)indene ( 5). Deprotonation of 3-H and 6-H with the Schlosser base (KOtBu/nBuLi) affords the highly reactive potassium salts (3)K and (6)K, which are useful precursors for the coordination of these ligands to transition metals. The chromium complexes 4a, 4b, 4c, and 7 have been prepared by salt metathesis reactions of (3)K and (6)K with [CrCl 3 (THF) 3 ], and the molecular structures of all four paramagnetic complexes have been established by X-ray diffraction analyses. In the case of 4a, 4b, and 7, the formation of constrained-geometry complexes with chelating Me 2 Si-bridged cyclopentadienyl-imidazolin-2-imine ligands is observed. The presence of short Cr-N bonds is indicative of the strong electron-donating capacity of the imidazoline-2-imino-nitrogen atom, which is based on the ability of the imidazolium ring to effectively stabilize a positive charge. In contrast, the steric bulk of the tert-butyl groups in 4c prevents coordination of the imine moiety. Activation of the chromium complexes 4 and 7 with methylaluminoxane (MAO) affords catalysts for the polymerization of ethylene at ambient temperature and under normal pressure.

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Complexes of Zirconium and Hafnium in Oxidation State iv

Cited by 14 publications

References 960 publications

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

Angular Distortions at Benzylic Carbons Due to Intramolecular Polarization-Induced Metal–Arene Interactions: A Case Study with Open-Shell Chromium(II) NHC Complexes

Chromium Complexes with Me₂Si-Bridged Cyclopentadienyl-imidazolin-2-imine Ligands: Synthesis, Structure, and Use in Ethylene Polymerization Catalysis

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Complexes of Zirconium and Hafnium in Oxidation State iv

Cited by 14 publications

References 960 publications

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

Synthesis and Structural Characterization of Zirconium−Carboryne Complexes

Angular Distortions at Benzylic Carbons Due to Intramolecular Polarization-Induced Metal–Arene Interactions: A Case Study with Open-Shell Chromium(II) NHC Complexes

Chromium Complexes with Me2Si-Bridged Cyclopentadienyl-imidazolin-2-imine Ligands: Synthesis, Structure, and Use in Ethylene Polymerization Catalysis

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Chromium Complexes with Me₂Si-Bridged Cyclopentadienyl-imidazolin-2-imine Ligands: Synthesis, Structure, and Use in Ethylene Polymerization Catalysis