- Synthesis and chemistry of Cp2Zr(Ph)(THF)+. Selectivity of protolytic and oxidative Zr-R bond-cleavage reactions
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The neutral complexes Cp2Zr(R)2 (R = CH3 (1), CH2Ph (2)) react with [Cp′2Fe][BPh4] in THF via oxidative Zr-R bond cleavage to yield [Cp2Zr(R)(THF)][BPh4] (R = CH3
- Borkowsky, Samuel L.,Jordan, Richard F.,Hinch, Garry D.
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- INFRARED SPECTRA AND METHYL GROUP PROPERTIES IN DICYCLOPENTADIENYLDIMETHYL-TITATIUM(IV), -ZIRCONIUM(IV) AND -HAFNIUM(IV)
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Infrared spectra are reported for CH3-, CD3-, and CHD2-substituted Cp2MMe2 (Cp = η5-C5H5, M = Ti, Zr, Hf) in CCl4 solution.The isolated CH stretching frequencies, ν(isCH), measured in the CHD2 species are lower than any previously observed in methylmetal compounds and the methyl CH bonds in Cp2HfMe2 are predicted to be the longest and weakest such bonds yet to have been characterised by this method.The methyl groups in Cp2ZrMe2 and Cp2HfMe2 have all three CH bonds equal, but in Cp2TiMe2 each methyl group contains two strong CH bonds and one weak one.This may be the result of steric overcrowding effects around the relatively small titanium atom.The symmetric deformation δs(CH3) rises with increasing atomic number of the metal atom, the reverse of the trend observed for methyl derivatives of Main Group elements.
- McQuillan, G. P.,McKean, D. C.,Torto, I.
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- A comparative study of the reactivity of Zr(IV), Hf(IV) and Th(IV) metallocene complexes: Thorium is not a Group IV metal after all
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Thorium(IV) is often considered to show similar chemistry to Group IV transition metals. However, studies in our laboratory have shown that this generalization is incorrect. This report presents direct comparisons where the Th(IV) metallocene complexes (C5Me5)2ThR2 (R = CH3, Ph, CH2Ph) undergo unique chemical reactivity with pyridine, 2-picoline, pyridine N-oxide, 2-picoline N-oxide, and benzonitrile, while the Group IV metal analogues (C5R5)2M(CH3)2 (R = H, CH3; M = Zr, Hf) do not. We also report revised high-yield syntheses for the zirconium and hafnium starting materials, (C5H5)2MR2 (M = Zr, Hf; R = CH3, Ph, CH2Ph), using Grignard reagents for alkylation in addition to the X-ray crystal structures of (C5H5)2Hf(Ph)2 and (C5H5)2Hf(CH2Ph)2.
- Jantunen, Kimberly C.,Scott, Brian L.,Kiplinger, Jaqueline L.
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- First tandem asymmetric conjugate addition of alkenyl nucleophiles and silyl trapping of the intermediate enolates
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The tandem asymmetric conjugate addition of alkyl or aryl groups to enones and subsequent silyl trapping has already been achieved and yields valuable silyl enol ethers. Herein, the first method for the respective addition of alkenyl groups is reported, which is based on a rhodium(I)-catalyzed addition of readily available alkenylzirconocenes. As prerequisite for silyl trapping, the initially formed enolates have to be transmetalated from zirconium to lithium by treatment with methyllithium prior to addition of the silyl chloride. Starting from 5- to 7-membered cycloalkenones, the respective silyl enol ethers were obtained in excellent yields and ≥93% ee; an acyclic substrate furnished a moderate enantioselectivity. Besides trimethylsilyl chloride, the silylation was also performed with tert-butyldimethylsilyl chloride, and the synthetic scope was evaluated by employing five different alkenyl groups. Moreover, the mechanism of this sequence was elucidated by 1H NMR studies, and the efficiency of catalyst control was exemplified by synthesis of a cis-3,5-disubstituted cyclohexanone which, due to strong substrate control, cannot be obtained by copper-catalyzed conjugate addition.
- Westmeier, Johannes,Pfaff, Christopher,Siewert, Juergen,Von Zezschwitz, Paultheo
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- Zirconium-catalyzed carboalumination of α-olefins and chain growth of aluminum alkyls: Kinetics and mechanism
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A mechanism based on Michaelis-Menten kinetics with competitive inhibition is proposed for both the Zr-catalyzed carboalumination of α-olefins and the Zr-catalyzed chain growth of aluminum alkyls from ethylene. AlMe3 binds to the active catalyst in a rapidly maintained equilibrium to form a Zr/Al heterobimetallic, which inhibits polymerization and transfers chains from Zr to Al. The kinetics of both carboalumination and chain growth have been studied when catalyzed by [(EBI)Zr(μ-Me)2AlMe2] [B(C6F5)4]. In accord with the proposed mechanism, both reactions are first-order in [olefin] and [catalyst] and inverse first-order in [AlR3]. The position of the equilibria between various Zr/Al heterobimetallics and the corresponding zirconium methyl cations has been quantified by use of a Dixon plot, yielding K = 1.1(3) × 10 -4 M, 4.7(5) × 10-4 M, and 7.6(7) × 10 -4 M at 40 °C in benzene for the catalyst species [rac-(EBI)Zr(μ-Me)2AlMe2][B(C6F 5)4], [Cp2Zr(μ-Me)2AlMe 2][B(C6F5)4], and [Me 2C(Cp)2Zr(μ-Me)2AlMe2][B(C 6F5)4] respectively. These equilibrium constants are consistent with the solution behavior observed for the [Cp 2Zr(μ-Me)2AlMe2][B(C6F 5)4] system, where all relevant species are observable by 1H NMR. Alternative mechanisms for the Zr-catalyzed carboalumination of olefins involving singly bridged Zr/Al adducts have been discounted on the basis of kinetics and/or 1H NMR EXSY experiments.(Figure Presented)
- Camara, James M.,Petros, Robby A.,Norton, Jack R.
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- A Modular Approach to Phosphorescent π-Extended Heteroacenes
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A modular route to previously inaccessible classes of ring-fused π-extended heteroacenes bearing the heavy inorganic element tellurium (Te) is presented. These new materials can be viewed as n-doped analogs of molecular graphene subunits that exhibit color tunable visible light phosphorescence in the solid state and in the presence of air. The general mechanism of phosphorescence in these systems was probed experimentally and computationally via time-dependent density functional theory (TD-DFT). The incorporation of Te into π-extended oligoacene frameworks was achieved by an efficient Zr/Te transmetalation protocol; related zirconium-element exchange reactions have been used to prepare both electron-rich and electron-deficient heterocycles containing different elements from throughout the p-block. Therefore, the current study provides a clear path to incorporate inorganic elements into heteroacenes of greater complexity and side group selectivity compared to existing synthetic routes.
- Hupf, Emanuel,Tsuchiya, Yuki,Moffat, Wayne,Xu, Letian,Hirai, Masato,Zhou, Yuqiao,Ferguson, Michael J.,McDonald, Robert,Murai, Toshiaki,He, Gang,Rivard, Eric
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- Three-coordinate aluminum is not a prerequisite for catalytic activity in the zirconocene - Alumoxane polymerization of ethylene
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The interaction of (η5-C5H5)2ZrX2 (X = Me, Cl) with Al(tBu)3 and alumoxanes [(tBu)2Al{μ-OAl(tBu)2}] 2 and [(tBu)Al(μ3-O)]n (n = 6, 7, 9) has been investigated. The Lewis acid - base complexes (η5-C5H5)2Zr(X)(μ-X)-Al( tBu)3 [X = Me (1), Cl (2)] have been isolated and characterized by variable temperature NMR spectroscopy. The molecular structure of compound 2 has been obtained by X-ray crystallography, indicating the presence of a Zr(μ-Cl)Al moiety. The Zr(μ-Cl)Al interaction in compound 2 is compared to the Al-Cl bond in [PPN][AlCl-(tBu)3] (4). [(tBu)2Al{μ-OAl(tBu)2}] 2, which contains two three-coordinate (unsaturated) aluminum centers, shows no reaction with (η5-C5H5)2ZrMe2 and no catalytic activity toward ethylene polymerization. In contrast, the closed cage compound [(tBu)Al(μ3-O)]6 reacts reversibly to give the ion pair complex [(η5-C5H5)2ZrMe][( tBu)6Al6(O)6Me] (7). The temperature dependence of the equilibrium constant Keq has been determined and, hence, the enthalpy and entropy for the formation of complex 7 [ΔH = -50(1) kJ mol-1, ΔS = -156(5) J mol-1 K-1]. Complex 7 is active as a catalyst for the polymerization of ethylene. Polymerization is also observed for mixtures of (η5-C5H5)2ZrMe2 with [(tBu)Al(μ3-O)]n (n = 7, 9) despite the lack of observable complex formation. A solution structure of 7 is proposed upon the basis of NMR spectroscopy and a comparison with [(Et2O)Li]2[(tBu)6Al 6(O)6Me2] (8), formed from the reaction of [(tBu)Al(μ3-O)]6 with MeLi in Et2O. Upon the basis of NMR spectroscopy, compound 8 exists as either the anti (8a) or syn (8b) isomer as a result of endo or exo methylation of the aluminum centers. The lithium atoms in compound 8 are formally two-coordinate; however, close tert-butyl C-H?Li contacts suggest the presence of agostic stabilization. These results are discussed with respect to the commercial (η5-C5H5)2ZrMe 2-methylalumoxane (MAO) polyolefin catalyst system, and the new concept of latent Lewis acidity (TAl-O) is proposed to account for the reactivity of the cage hexamer [(tBu)Al(μ3-O)]6. Crystal data for 2: orthorhombic, Pnma, a = 32.181(9) A?, b = 14.437(4) A?, c = 10.812(3) A?, Z = 4, R = 0.1091, Rw = 0.1165. Crystal data for 4: monoclinic, P21/n, a = 15.946(2) A?, b = 18.487(2) A?, c = 16.453(2) A?, β= 110.778(7)°, Z = 4, R = 0.0496, Rw = 0.0512. Crystal data for 8: orthorhombic, Pbca, a = 18.249(8) A?, b = 15.215(6) A?, c = 18.359(9) A?, Z = 4, R = 0.0891, Rw = 0.1190.
- Harlan, C. Jeff,Bott, Simon G.,Barron, Andrew R.
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- LIGAND REDISTRIBUTION REACTIONS OF DICYCLOPENTADIENYLZIRCONIUM(IV) COMPLEXES
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The rates of several ligand redistribution reactions of dicyclopentadienylzirconium compounds Cp2ZrR2, Cp2ZrRX and Cp2ZrX2 vary as a function of ligand in the order F, I > Cl, Br and CH3 > Ph.The variation of rate with ligand is considerably larger than for the analogous Ti compounds.
- Jordan, Richard F.
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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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- C1-insertion reactions at cyclodimeric (η2-acetaldehyde)zirconocene complexes
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Carbonylation of dimethylzirconocene, followed by treatment with zirconocene dihydride, benzyl chloride and then methyllithium, gave the (η2-acetaldehyde)zirconocene dimer (9) as a mixture of trans- and cis-isomers isolated in a 1.5:1 ratio under kinetic control and in a 1:1.7 ratio under thermodynamic control, respectively.Complexes trans-9/cis-9 were treated with carbon monoxide to give the trans-10/cis-10 monoinsertion products, and with isonitriles RNC (R=CH2SiMe3 (a), CMe3 (b)) to give the mono- and bis-insertion products trans- and cis-11(a,b) and 12(a,b), respectively.Complex 12a was characterized by X-ray diffraction.In all cases the trans/cis stereochemical information was predominantly retained in the products, which indicates that dimettalic pathways are favoured in these insertion reactions of the metallatricyclic (η2-aldehyde) metallocene dimers.Keywords: (η2-Aldehyde)zirconocenes; Carbonylation; Isonitrile insertion; Iminoacyl complexes; CO insertion
- Schmuck, Stefanie,Erker, Gerhard,Kotila, Sirpa
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- Ligand exchange processes in zirconocene dichloride-trimethylaluminum bimetallic systems and their catalytic properties in reaction with alkenes
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Ligand exchange processes in the systems L2ZrCl2-AlMe3 (L2ZrCl2: Cp2ZrCl2, (CpMe)2ZrCl2, (C5Me5)2ZrCl2, Me2SiCp2ZrCl2, Me2Si(C5Me4)2ZrCl2, rac-Me2C(2-Me-4-But-Cp)2ZrCl2, meso-Me2C(2-Me-4-But-Cp)2ZrCl2, rac-Me2C(3-But-Cp)2ZrCl2, Ind2ZrCl2, rac-H2C(Ind)2ZrCl2, rac-Me2C(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-C2H4(Ind)2ZrCl2, rac-C2H4(THInd)2ZrCl2, rac-Me2Si(THInd)2ZrCl2) and Cp2ZrMeCl2-n-AlMe3 (n = 1, 2) were studied by NMR spectroscopy with the goal to establish the structures and dynamic features of probable intermediates in the zirconocene-catalyzed reactions of alkenes with AlMe3. The effect of solvent, the organoaluminum compound concentration and the addition of (ClAlMe2)2 on the activation parameters of the alkyl exchange in the trimethylaluminum dimer was studied as well. The constants and activation parameters of the methyl group exchange in the monoalkyl-substituted ansa-complexes L2ZrMeCl (L2 = rac-Me2C(2-Me-4-But-Cp)2, rac-Me2C(3-But-Cp)2, rac-H2CInd2, rac-Me2CInd2, rac-Me2SiInd2, rac-H4C2Ind2) were established for the first time. The catalytic activity and chemoselectivity of zirconocenes in the reaction of alkenes with AlMe3 were evaluated and compared with the exchange and equilibrium constants of ligand exchange processes. A mechanism of the reaction was proposed.
- Parfenova, Lyudmila V.,Kovyazin, Pavel V.,Gabdrakhmanov, Vener Z.,Istomina, Galina P.,Ivchenko, Pavel V.,Nifant'Ev, Ilya E.,Khalilov, Leonard M.,Dzhemilev, Usein M.
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p. 16918 - 16937
(2019/01/03)
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- Observation of zirconium allyl species formed during zirconocene-catalyzed propene polymerization and mechanistic insights
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Oligomeric Cp2Zr+-allyl species were detected in reaction mixtures of either [Cp2ZrMe][MeB(C6F5)3] or [Cp2ZrMe][B(C6F5)4] with propylene by a combination of 1H NMR spectroscopy and electrospray ionization (tandem) mass spectrometry techniques. Conjointly, the data imply that formation of Cp2Zr+-allyl species occurs via (re)coordination of alkene (propylene and vinylidene end groups of unsaturated polymer chains, respectively) to Cp2Zr+R (R = CH3, H, polymeryl), followed by intramolecular proton transfer from Cγ to R and release of RH. Analysis of the olefinic region of the 1H NMR spectra of the reaction mixture obtained from [Cp2ZrMe][MeB(C6F5)3] and propylene reveals the presence of a triplet resonance at δ ~ 5.2, which was attributed to the unprecedented 3-propenyl end group. A plausible mechanism for the origin of the 3-propenyl end groups is discussed. Additionally, a mechanism for incorporation of stereodefects into stereoregular polymers is also discussed. The cationic Cp2Zr+-allyl intermediates formed during polymerization may contribute to catalyst deactivation.
- Vatamanu, Mihaela
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p. 112 - 120
(2015/09/28)
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- Synthesis, structures, and dynamic features of d0 zirconocene-allyl complexes
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The reaction of [Cp2ZrMe][MeB(C6F5) 3] (1) with 2,4-dimethyl-1-pentene and 2,4-dimethyl-1-heptene, respectively, in C6D5Cl at 25 °C results in irreversible formation of the cationic Cp2Zr+-allyl complexes [Cp2Zr(η3-CH2C(CH 2R)CH2)]+ (2a, 3a) and [Cp2Zr(η 3-CH2C(Me)CHR)]+ (2b, 3b) (2a,b, R = CH(CH 3)2; 3a,b, R = CH(CH3)CH2CH 2CH3) and release of methane. The Cp2Zr +-allyl complexes were characterized with regard to their structures and rearrangement dynamics of their allyl ligands by NMR spectroscopy. Variable-temperature 1H NMR experiments show that the allyl ligands of complexes 2a,b and 3a,b are fluxional. The fluxional behavior in these complexes is mainly due to a mechanism that involves η3 to η1 isomerization, rotation of the allyl carbon-carbon π unit about the carbon-carbon σ bond, and reversion to the η3- allyl coordination mode, when both the allyl syn/anti hydrogen exchange and apparent Cp ligand exchange occur. The rotation of the C-C unit about the allyl carbon-carbon σ bond also results in a reversal of the η3-allyl coordination face relative to the Cp2Zr + moiety. A second mechanism which may account for the apparent Cp ligand exchange in the Cp2Zr+-allyl complexes under investigation consists of rotation of the η3-coordinated allyl ligand about the metal-allyl bond. The free energy of activation for the exchange processes, as estimated from the coalescence temperature of the two Cp ligands, is between 54 and 60 kJ/mol. Aside from the intramolecular allyl exchange processes described above, this study also shows that the η1- and η3-coordinated allyl forms of a particular Zr-allyl complex coexist in solution and that the equilibrium composition of these species is temperature dependent. The Cp2Zr+-allyl complexes described in this paper serve as models for similar cationic Cp 2Zr+-allyl intermediates implicated in zirconocene-catalyzed alkene polymerization reactions.
- Vatamanu, Mihaela
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p. 3683 - 3694
(2014/08/18)
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- Ti and Zr complexes of ferrocenyl amidinates
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Preparation of a N-ferrocenyl-amidinate complex was achieved by employing (TMEDA)Li[(CpFeC5H4)NC(Ph)NSiMe3] (1) to prepare Cp*Zr[(CpFeC5H4)NC(Ph)NSiMe 3]Cl2 (2). Complex 2 exhibited poor polymerization activity and thus a series of C-ferrocenyl bis(amidinate) complexes of the type M(L)2Cl2 (M = Zr, 4; M = Ti, 5; L = (CyNC(CpFeC 5H4)NCy) were synthesized via reaction of ferrocenyl-amidine, H(L) and M(NMe2)2Cl2 (M = Ti, Zr·2THF). Half sandwich mono(amidinate) complexes, Cp′ZrLCl2 (Cp′ = Cp, 7; Cp′ = Cp*, 8), were prepared by the reaction of Cp′ZrCl3 with Li(L) and subsequently alkylated to give M(L)2Me2 (M = Zr, 9; M = Ti, 11), CpZr(L)(CH2Ph)2 (12) and Cp*Zr(L)Me 2 (10) with the appropriate alkylating agent. Abstraction of a methyl group from 7 with B(C6F5)3 and [Ph 3C][B(C6F5)4] proceeded cleanly to give [{CyNC(CpFeC5H4)NCy}2ZrMe][MeB(C 6F5)3] 13 and [{CyNC(CpFeC5H 4)NCy}2ZrMe][B(C6F5)4] 14, respectively. Similarly, the analogous CpZr and Cp*Zr derivatives LZr{CyNC(CpFeC5H4)NCy}CH2Ph] [PhCH 2B(C6F5)3] L = Cp 15, Cp* 17 and [LZr{CyNC(CpFeC5H4)NCy}CH2Ph][B(C 6F5)4] L = Cp 16, Cp* 18 were prepared. Cyclic voltammetry studies on the metal complexes containing ferrocenyl-amidinates reveal quasi reversible oxidation and reduction waves for the ferrocene/ferrocenium couple. The dichloride complexes (4-8) activated with MAO and dialkyl complexes (9,10) activated with B(C6F 5)3 and [Ph3C][B(C6F 5)4] showed low ethylene polymerization activities. The Royal Society of Chemistry 2010.
- Multani, Kanwarpal,Stanlake, Louisa J. E.,Stephan, Douglas W.
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p. 8957 - 8966
(2011/01/09)
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- Fluorinated amino polyhedral borate compounds
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This invention provides a compound comprising fluorinated aminoborate monoanion of the formula: [R1R2R3N—BaHbFc]?1??I methods for preparing the same, and uses thereof, where R1, R2, R3, a, b, and c are those defined herein.
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- Monocyclopentadienyl and mono(2-methoxyethylcyclopentadienyl) zirconium methyl complexes
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The reactions of (η5-Cp)ZrCl3(DME) and (η5:η1-Cp°)ZrCl3 (Cp°=C5H4CH2CH2OMe) with 1-2 equivalents of MeLi or MeMgI and THF yield the mono- and dimethyl zirconium complexes (η5-Cp)ZrCl3-xMex(THF) and (η5:η1-Cp°)ZrCl3-xMex (x=1, 2), respectively. Reaction with three equivalents of MeMgI affords (η5-Cp)ZrMe3(THF) and (η5:η1-Cp°)ZrMe3. The reaction with three equivalents of MeLi affords (η5-Cp)2ZrMe2 or (η5-Cp°)2ZrMe2 and ZrMe4, as a result of disproportionation. The reaction of (η5:η1-Cp°)ZrMe3 with B(C6F5)3 in THF affords the cationic zirconium complex [(η5:η1-Cp°)ZrMe2(THF)][MeB(C 6F5)3]. The chloride-bridged complex [(η5:η1-Cp°)Zr(μ-Cl)Me2] 2 was characterized by single-crystal X-ray crystallography.
- Mattheis, Chris,Van Der Zeijden, Adolphus A.H.,Fr?hlich, Roland
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- Generation of perfluoropolyphenylene oligomers via carbon-fluorine bond activation by Cp2Zr(C6F5)2: A dual mechanism involving a radical chain and release of tetrafluorobenzyne
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The thermal decomposition of Cp2Zr(C6F5)2 in THF results in the slow formation of Cp2Zr(C6F5)F and tetrafluorobenzyne. The tetrafluorobenzyne is trapped by THF to give several products. The same reaction performed in the presence of durene or furan also results in the formation of Cp2Zr(C6F5)F and the respective Diels-Alder adducts of tetrafluorobenzyne. If Cp2Zr(C6F5)2 is heated in the presence of C6F6, linear chains of perfluoroarenes are rapidly generated along with Cp2Zr(C6F5)F. The disappearance of Cp2Zr(C6F5)2 is observed to slow dramatically after 30- 80% completion, with the extent of reaction being inversely dependent on the concentration of C6F6. Dual mechanisms involving a rapid radical chain- and a slower tetrafluorobenzyne-producing reaction are proposed to account for these observations.
- Edelbach,Kraft,Jones
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p. 10327 - 10331
(2007/10/03)
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- Ancillary aryloxide ligands in ethylene polymerization catalyst precursors
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The compounds CpTiCl2(OC6H3-i-Pr2) (1), CpTiCl(OC6H3-i-Pr2)2 (2), CpTi(R)(OC6H3-i-Pr2)2 (R=t-Bu 3, s-Bu 4, n-Bu 5, Me 6) have been prepared and characterized. Compounds 1 or 2 in the presence of 500 equivalents of methylaluminoxane (MAO) act as catalyst precursors for ethylene polymerization. While the catalysts derived from the monocyclopentadienyl complexes are much less active that the metallocenes, there is a clear enhancement in the activity of about 40% as a result of the inclusion of a second aryloxide ligand. Reactions of 1 with AlMe3 revealed stepwise formation of CpTi(Me)Cl(OC6H3-i-Pr2) 7 and CpTi(Me)2(OC6H3-i-Pr2) 8, while subsequent addition of AlMe3 afforded complete conversion to 8, with formation of the aluminum species [AlMe2(OC6H3-i-Pr2)]n 9. In contrast, the catecholate complex CpTi(O2C6H4)Cl 10 reacts with AlMe3 yielding the paramagnetic species [CpTi(O2(C6H4))·AlClMe2] 2 11. Incorporation of aryloxide ligands in modified metallocenes was readily accomplished with the preparation of Cp2ZrCl(OC6H3-i-Pr2) 12, Cp2ZrCl(OC6H5) 13, Cp2ZrMe(OC6H5) 14 and Cp2TiCl(OC6H3-i-Pr2) 15. In combination with MAO, 12, 14 and 15 effect the polymerization of ethylene with an 11% increase in activity over the parent metallocenedichlorides. The implications of the increased activity are considered. Crystallographic data are reported for 2, 3, 6, 9, 11, 12 and 13.
- Firth, Andrea V.,Stewart, Jeffrey C.,Hoskin, Aaron J.,Stephan, Douglas W.
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p. 185 - 193
(2007/10/03)
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- New O- and N-bonded zirconocene complexes and their catalytic properties in ethylene polymerization. X-ray crystal structure of (C5H5)2Zr{2,6-OC6H 3(CH3)2}2, (C5H5)2Zr{2,4,6-OC6H 2(CH3)3}2
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A series of zirconocene complexes of formula Cp2ZrMe2-nLn where Cp = C5H-5, Me = methyl, L = pyrazolyl, bis(N,N′-phenylformamidinato), or substituted aryloxide and n = 1,2, were synthesized by reaction of Cp2ZrCl2 and Cp2ZrMe2 with LiL or HL, respectively. The structures of Cp2Zr(2,6-OC6H3Me2)2, Cp2Zr(2,4,6-OC6H2Me3)2 and Cp2ZrMe{CH(NC6H5)2} were determined by single crystal X-ray diffraction. The complexes demonstrate appreciable activity for ethylene polymerization when used as cocatalysts with methylaluminoxane and dimethylanilinium tetrafluorophenylborate.
- Benetollo,Cavinato,Crosara,Milani,Rossetto,Scelza,Zanella
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p. 177 - 185
(2007/10/03)
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- Zirconium-catalyzed and zirconium-promoted cyclization reactions of non-conjugated dienes with alkylmagnesium halides to give cycloalkylmethylmagnesium derivatives
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The stoichiometric reaction of certain non-conjugated dienes with n-Bu2ZrCp2 provides the corresponding zirconabicycles, such as trans-3-bis(cyclopentadienyl)zirconabicyclo[3.3.0]octane, that can be fully characterized by spectroscopic means. Their treatment with EtMgBr or n-BuMgCl in THF gives the corresponding monocyclic monomagnesium derivatives along with the corresponding alkene-ZrCp2 derivatives in high yields. In cases where the Grignard reagent is either sterically hindered or lacking β-H, little or no reaction may occur, although some, e.g., s-BuMgCl, react, albeit slowly, to give the expected products in high yields. In cases where either a Grignard reagent in diethyl ether or a dialkylmagnesium (irrespective of solvent) is used, the major product is the corresponding dimagnesio derivative. A couple of intramolecular transmetallation paths are proposed for these cases. The Cp2ZrCl2-catalyzed reaction of 1,6-heptadiene with EtMgBr fails to induce the desired bicyclization-ring opening sequence to give the corresponding monocyclic monomagnesium derivatives. On the other hand, the corresponding reaction with n-BuMgBr does proceed as desired to give the monocyclic monomagnesium product which contains a minor amount of the corresponding exo-methylene derivative. Only traces, if any, of the corresponding dimagnesium derivatives reported to be the major products in Et2O are formed. This procedure has been applied to catalytically convert several other dienes, i.e., (E)-1-phenyl-1,6-heptadiene, 2,4,4-trimethyl-1,6-heptadiene, diallyl(benzyl)amine, 1,7-octadiene and 1,2-diallylbenzene, into the corresponding monocyclized compounds in moderate to excellent combined yields.
- Negishi, Ei-Ichi,Rousset, Christophe J.,Choueiry, Danièle,Maye, John P.,Suzuki, Noriyuki,Takahashi, Tamotsu
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- Binuclear zirconocene cations with μ-CH3-bridges in homogeneous Ziegler-Natta catalyst systems
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Binuclear zirconocene cartons are observed by 1H-NMR in C6D6 solutions containing B(C6F5)3 and an excess of a zirconocene dimethyl complex. The CH3-bridged cation [((C5H5)2ZrCH3)2(μ-CH3)]+, solvent- separated from the anion H3C-B(C6F5)3/-, is present in equilibrium with (C5H5)2Zr(CH3)2 and the mononuclear ion pair [((C5H5)2ZrCH3/+···H3C-B(C6F5)3/-]; in more concentrated solutions, a binuclear ion pair [((C5H5)2ZrCH3)2(μ-CH3)+···H3C- B(C6F5)3/-] is the dominant species. Similar equilibria are observed in C6,D6 solutions containing B(C6F5)3 and (CH3)4C2(C5H4)2Zr(CH3)2, (CH3)2Si(C5H4)2Zr(CH3)2 or rac-(CH3)2Si(indenyl)2Zr(CH3)2. Complexes with sterically more demanding ligands, such as (C5(CH3)5)2Zr(CH3)2 or rac-(CH3)2Si(2-methyl benz[e]indenyl)2Zr(CH3)2 do not form any binuclear species under these conditions. In the catalyst system rac- (CH3)2Si(indenyl)2Zr(CH3)2/Bu3NH+B(C6F5)4/-, activities for the polymerization of propene increase with excess of the dimethyl zirconocene complex. This effect is due in part to a sacrifice of some dimethyl zirconocene for the removal of impurities from the catalyst system and in part to a stabilization of the catalyst in the form of the binuclear cation [((CH3)2Si(indenyl)2ZrCH3)2(μ-CH3)]+. The latter appears to act, in the presence of propene, as a source of the mononuclear cation [(CH3)2Si(indenyl)2ZrCH3(C3H6)]+, rather than as a polymerization catalyst by itself.
- Beck, Stefan,Prosenc, Marc-Heinrich,Brintzinger, Hans-Herbert,Goretzki, Ralf,Herfert, Norbert,Fink, Gerhard
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- Mono(η-cyclopentadienyl)benzamidinato Alkyl Compounds of Titanium and Zirconium
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The compounds 2Cl>, Cl>2>, Cl>2(μ-O)>, (CH2Ph)Cl> (R = H or Me), (CH2Ph)2> (R = H or Me) and M(η-C5R5)CPh(NSiM
- Gomez, Rafael,Duchateau, Robbert,Chernega, Alexander N.,Meetsma, Auke,Edelmann, Frank T.,et al.
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p. 217 - 226
(2007/10/02)
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- Chalcogenametallacyclohexadienes by thermally induced migratory ring enlargement of furyl- and thienylzirconocene complexes
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Zirconocene dichloride reacts with 2 molar equiv of (2-furyl)lithium to give bis(2-furyl)zirconocene (1a). The (σ-furyl)zirconocene complexes Cp2ZrR(2-furyl) (R = CH3, Ph, SiMe3) were similarly prepared by treatment of the respective Cp2Zr(R)Cl complexes with (2-furyl)lithium. Cp2Zr(SiMe3)(2-thienyl) was obtained from the reaction of Cp2Zr(SiMe3)Cl with (2-thienyl)lithium. The Cp2ZrR(2-furyl) complexes with R = 2-furyl, methyl, or phenyl all undergo an intramolecular high-temperature (≥180°C) σ,σ-exchange reaction to give the oxazirconacyclohexadienes Cp2ZrOCH=CHCH=C(R) (2a-c). The 1a → 2a rearrangement follows first-order kinetics in the temperature range 140-180°C and is characterized by the activation parameters ΔH? = 30.9 ± 2.0 kcal mol-1 and ΔS? = -9 ± 5 cal mol-1 K-1. The complexes Cp2Zr(SiMe3)(2-furyl) (1d) and Cp2Zr(SiMe3)(2-thienyl) (1e) undergo the analogous dyotropic rearrangements much faster. The 1d → 2d isomerization is fast at 0°C and already takes place during the formation of 1d from Cp2Zr(SiMC3)Cl and (2-furyl)lithium. The activation parameters of the 1e → 2e ring enlargement reaction of the (2-thienyl)metallocene system are ΔH? = 20.4 ± 2.0 kcal mol-1 and ΔS? = -12 ± 5 cal mol-1 K-1. The oxa- and thiazirconacyclohexadienes Cp2Zr-X-CH=CHCH=C(SiMe3) (X = O, 2d; X = S, 2e) were characterized by X-ray diffraction. Complex 2d crystallizes in space group P1 with cell parameters a = 9.783 (1) A?, b = 11.514 (1) A?, c = 15.806 (1) A?, α = 96.27 (1)°, β = 101.64 (1)°, γ = 98.89 (1)°, Z = 4, R = 0.037, and Rw = 0.053. Complex 2e crystallizes in space group Cc with cell parameters a = 13.988 (4) A?, b = 30.774 (2) A?, c = 9.788 (4) A?, β = 122.93 (1)°, Z = 8, R = 0.034, and Rw = 0.035. Both chalcogenazirconacyclohexadienes are monomeric in the solid state and exhibit nonplanar metallacyclic conformations with the metal-chalcogen vectors rotated significantly relative to the planes of the endocyclic conjugated diene moieties.
- Erker, Gerhard,Petrenz, Ralph,Krüger, Carl,Lutz, Frank,Weiss, Astrid,Werner, Stefan
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p. 1646 - 1655
(2008/10/08)
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- Transfer and coupling of zirconocene-bound alkenyl ligands. An alternative route to (s-trans-η4-conjugated diene)ZrCp2 complexes
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Dibenzylzirconocene (3a) and (s-trans-η4-trans ,trans-1,4-diphenylbutadiene)zirconocene (5) are formed rapidly upon irradiation of benzyl(β-styryl)-zirconocene (2a) in benzene at ambient temperature. Trapping and crossover experiments using benzyl chloride and (β-styryl)zirconocene chloride and the kinetic influence of added moderators trimethyl phosphite and triphenylphosphine in addition to ESR experiments point to a radical reaction mechanism for alkenyl group transfer. Transfer and coupling of alkenyl ligands can also be initiated in a dark reaction when starting from methyl(β-styryl)zirconocene (2b).
- Czisch, Peter,Erker, Gerhard,Korth, Hans-Gert,Sustmann, Reiner
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p. 945 - 947
(2008/10/08)
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- The search for dimethylzirconocene. Crystal structures of dimethylzirconocene, dimethylhafnocene, chloromethylzirconocene, and (μ-Oxo)bis(methylzirconocene)
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The crystal structures of (η5-C5H5)2Zr(CH 3)2, (η5-C5H5)2Hf(CH 3)2, (η5-C5H5)2Zr(Cl)(CH 3), and [(η5-C5H5)2Zr(CH 3)]2O have been determined from X-ray data measured by counter methods. Dimethylzirconocene crystallizes in the monoclinic space group P21/n with unit-cell parameters a = 6.953 (3) A?, b = 11.902 (5) A?, c = 13.839 (5) A?, β = 91.95 (3)°, and Z = 4 for Dcalcd = 1.45 g cm-3. Full-matrix least-squares refinement has led to a final R factor of 0.029 based on 1672 independent observed reflections. Dimethylhafnocene is isostructural with a = 6.965 (4) A?, b = 11.854 (5) A?, c = 13.786 (6) A?, β = 92.02 (3)°, and Dcalcd = 1.98 g cm-3. Refinement on 1662 reflections produced R = 0.041. Chloromethylzirconocene exhibits crystallographically disordered chloro and methyl ligands and is isostructural with the dimethyl derivatives. The cell constants are a = 6.810 (8) A?, b = 11.821 (9) A?, c = 13.818 (9) A?, β = 92.30 (4)°, and Dcalcd = 1.62 g cm-3. A final R value of 0.043 resulted from the refinement on the basis of 1709 observed reflections. (μ-Oxo)bis(methylzirconocene) crystallizes in the trigonal space group P3221 with a = 8.017 (3) A?, c = 28.376 (6) A?, and Dcalcd = 1.54 g cm-3. Refinement on 1358 reflections led to R = 0.026. The most important results concern the metal-carbon σ bond lengths in the (η5-C5H5)2M(CH3) 2 compounds. For M = Zr the two independent determinations are 2.273 (5) and 2.280 (5) A?, while for M = Hf the distances are 2.233 (12) and 2.240 (12) A?. The average for the latter, 2.24 A?, is much shorter than the 2.35 A? value previously reported for (η5-C5H5)2Hf(CH 3)2. In addition, the longer Zr-C(σ) is the reverse of that found for (η5-C9H7)2M(CH3) 2, M = Zr and Hf. The answer to these apparent discrepancies is found in a consideration of the role of the disordered chloromethylzirconocene structure.
- Hunter, William E.,Hrncir, Duane C.,Bynum, R. Vann,Penttila, Rauni A.,Atwood, Jerry L.
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p. 750 - 755
(2008/10/08)
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