- Reactions of (η5-C5Me5)ZrF3, (η5-C5Me4Et)ZrF3, (η5-C5Me5)2ZrF2, (η5-C5Me5)HfF3
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The reaction of Cp*ZrF3 (1) (Cp* = η5-CsMes) and AlMe3 resulted in the formation of cis-{[Cp*ZrMe(μ2-F)][(μ2-F) 2AlMe2]}2 (6) and [(Cp*Zr)3Al6Me8(μ3-CH 2)2(μ4-CH)4(μ3-CH)] (7), respectively. Analogously, (η5-C5Me4Et)ZrF3 (3) reacts with AlMes in a molar ratio of 1:5 with methane elimination to give the Zr3Al6C7 cluster of composition {[(η5-C5Me4Et)Zr]3Al 6Me8-(μ3-CH2) 2(μ4-CH)4(μ3-CH)} (8), which has been characterized by elemental analysis and 1H NMR and mass spectrometry. Reaction of 2 equiv of AlMe3 with Cp*2ZrF2 (2) leads quantitatively to Cp*2ZrMe2 (12). Reaction of Cp*HfF3 (4) with AlMe3 in an equimolar ratio gives {[Cp*HfMe (μ2-F)][(μ2-F)2AlMe2]} 2 (9) stereospecifically as its cis isomer in high yield. 9 crystallizes in the space group P21/c with four molecules in the elemental cell (Z = 16). From the reaction of 1 equiv of Cp*HfF3 (4) with 3 equiv of AlMe3, Cp*HfMe3 (10) can be obtained in a yield of 85%. As a byproduct of this reaction the Hf3Al6C7 cluster [(Cp*Hf)3-Al6Me8(μ3-CH 2)2(μ4-CH)4(μ3-CH)] (11) can be isolated in a yield of 5%. The characterization of 11 by single-crystal X-ray diffraction and 1H, 13C NMR and mass spectroscopic data will be discussed. Cp*TaF4 (5) reacts with a 5-fold excess of AlMe3, leading quantitatively to Cp*TaMe4 (13) without further decomposition via C-H activation processes.
- Herzog, Axel,Roesky, Herbert W.,J?ger, Felix,Steiner, Alexander,Noltemeyer, Mathias
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- Polymerization of ethylene with (C5Me5) 2Zr(NMe2)2 cocatalyzed by common alkyl aluminums
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Polymerizations of ethylene have been carried out by using Cp 2*Zr(NMe2)2 (Cp=C 5Me5) compound combined with common alkyl aluminums (AlR3) and methylaluminoxane (MAO) as cocatalysts. The Al
- Kim, Il,Ha, Chang-Sik
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- Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6F5)3
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Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal–carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal–alkyl bond cleavage (M=Zr, Ti) were studied and structure–reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.
- Berionni, Guillaume,Kurouchi, Hiroaki,Eisenburger, Lucien,Mayr, Herbert
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supporting information
p. 11196 - 11200
(2016/08/03)
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- An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate
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The reaction of a series of dimethyl zirconocenes [Me2Si(Cp) 2ZrMe2, 1; Cpt-bu2ZrMe2, 2; Cpn-bu2ZrMe2, 3; Ind2ZrMe 2, 4; CpMe42ZrMe2, 5; Cp 2ZrMe2, 6] with [HNMe2Ph][B(C6F 5)4] was investigated by means of NMR spectroscopy. It was found that protonolysis of a Zr-Me group occurred generating a coordinative vacancy at the metal center and methane. Cations coming from 1-4 dimethyl precursors bound NMe2Ph, liberated from the protonation process, and formed zirconaaziridinium ion pairs {[Me2Si(Cp)2Zr(η 2-CH2NMePh)][B(C6F5)4], 7; [Cpt-bu2Zr(η2-CH2NMePh)] [B(C6F5)4], 8; [Cpn-bu 2Zr(η2-CH2NMePh)][B(C6F 5)4], 9; [Ind2Zr(η2-CH 2NMePh)][B(C6F5)4], 10}, reasonably as a consequence of CH activation of one Me group of coordinated NMe 2Ph and methane elimination. The intramolecular/interionic structures and dynamics of 7-10 ion pairs were investigated by 1H, 13C and 19F 1D-and 2D-NMR techniques. The reactions of 7 and 10 ion pairs with 2-methyl-1-heptene afforded stable diastereoisomeric ion pairs bearing a five-member azametallacycle.
- Rocchigiani, Luca,Bellachioma, Gianfranco,Zuccaccia, Cristiano,MacChioni, Alceo
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- Zirconium-91 chemical shifts and line widths as indicators of coordination geometry distortions in zirconocene complexes
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91Zr NMR chemical shifts and line widths (Δυ1/2) are reported for a number of ring-bridged and ring-substituted zirconocene dichloride, dibromide, and dimethyl complexes. Ab initio computations at the SCF level employing basis sets of moderate size suggest that the magnitude of the electric field gradient (EFG) at the Zr atom dominates Δυ1/2 when the substituents X at Zr are varied (X = Br, Cl, Me). Substituents at the cyclopentadiene (Cp) rings affect the computed EFGs much less; in these cases, the line widths Δυ1/2 are governed by the molecular correlation times τc, which were obtained for several zirconocene dichlorides from T1(13C) measurements. Experimental trends in δ(91Zr) of zirconocenes are well reproduced computationally with the IGLO (individual gauge for localized orbitals) or GIAO (gauge including atomic orbitals) SCF methods employing large basis sets. Model calculations suggest that δ(91Zr), as well as the EFG, are quite sensitive to the inclination and twist angles of the Cp rings and, to a lesser extent, to the CpZrCp′ angle. A substantial deshielding, δ(91Zr) ca. 700 ppm, is predicted for (C5H5)2ZrMe+, presumably the active olefin-polymerizing catalyst.
- Bühl, Michael,Hopp, Gudrun,Von Philipsborn, Wolfgang,Beck, Stefan,Prosenc, Marc-Heinrich,Rief, Ursula,Brintzinger, Hans-Herbert
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p. 778 - 785
(2008/10/08)
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- Activation of benzene carbon-hydrogen bonds via photolysis or thermolysis of (η5-C5Me5)2Zr(alkyl)H. Isolation of (η5-C5Me5)2Zr(C 6H5)H and its conversion to a complex containing a tetramethylfulvene ligand
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A new high-yield synthesis of Cp*2ZrH2 (Cp* = η5-C5Me5) is described, and olefin insertion into its Zr-H bond is used to prepare several new Cp*2Zr(alkyl)H complexes. Photolysis or thermolysis of Cp*2Zr(alkyl)H in benzene yields the respective alkane by intramolecular reductive elimination of the cis alkyl and hydride ligands, as well as the benzene C-H bond activation product Cp*2Zr(C6H5)H. Photochemically induced reductive elimination is also observed for Cp*2Zr(C6H5)H and Cp*2ZrH2. Deuterium-labeling experiments show that hydrogen exchange between the hydride and Cp* methyl groups occurs in both Cp*2Zr(H)CH2CH(CH3)2 and Cp*2Zr(C6H5)H. An additional exchange process in Cp*2Zr(C6H5)H involves the hydride ligand and an ortho phenyl hydrogen atom. Thermolysis of Cp*2Zr(C6H5)H in benzene causes quantitative evolution of dihydrogen and reversibly forms the tetramethylfulvene complex Cp*(η6-C5Me4CH2)Zr(C 6H5). Reaction of this compound with iodine produces the Cp* ring substituted phenyl iodide Cp*(η5-C5Me4CH2I)Zr(C 6H5)I. Several of the transformations involving Cp*2Zr(C6H5)H are believed to proceed via β-hydrogen elimination from the phenyl group to yield a benzyne dihydride intermediate.
- Miller, Frederick D.,Sanner, Robert D.
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p. 818 - 825
(2008/10/08)
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