12636-72-5Relevant articles and documents
Synthesis and chemistry of Cp2Zr(Ph)(THF)+. Selectivity of protolytic and oxidative Zr-R bond-cleavage reactions
Borkowsky, Samuel L.,Jordan, Richard F.,Hinch, Garry D.
, p. 1268 - 1274 (1991)
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
INFRARED SPECTRA AND METHYL GROUP PROPERTIES IN DICYCLOPENTADIENYLDIMETHYL-TITATIUM(IV), -ZIRCONIUM(IV) AND -HAFNIUM(IV)
McQuillan, G. P.,McKean, D. C.,Torto, I.
, p. 183 - 196 (1986)
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.
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
Jantunen, Kimberly C.,Scott, Brian L.,Kiplinger, Jaqueline L.
, p. 363 - 368 (2007)
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.
First tandem asymmetric conjugate addition of alkenyl nucleophiles and silyl trapping of the intermediate enolates
Westmeier, Johannes,Pfaff, Christopher,Siewert, Juergen,Von Zezschwitz, Paultheo
, p. 2651 - 2658 (2013)
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.
Zirconium-catalyzed carboalumination of α-olefins and chain growth of aluminum alkyls: Kinetics and mechanism
Camara, James M.,Petros, Robby A.,Norton, Jack R.
, p. 5263 - 5273 (2011)
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)
A Modular Approach to Phosphorescent π-Extended Heteroacenes
Hupf, Emanuel,Tsuchiya, Yuki,Moffat, Wayne,Xu, Letian,Hirai, Masato,Zhou, Yuqiao,Ferguson, Michael J.,McDonald, Robert,Murai, Toshiaki,He, Gang,Rivard, Eric
, p. 13323 - 13336 (2019)
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.
Three-coordinate aluminum is not a prerequisite for catalytic activity in the zirconocene - Alumoxane polymerization of ethylene
Harlan, C. Jeff,Bott, Simon G.,Barron, Andrew R.
, p. 6465 - 6474 (1995)
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.
LIGAND REDISTRIBUTION REACTIONS OF DICYCLOPENTADIENYLZIRCONIUM(IV) COMPLEXES
Jordan, Richard F.
, p. 321 - 326 (1985)
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.
Zirconium-91 chemical shifts and line widths as indicators of coordination geometry distortions in zirconocene complexes
Bühl, Michael,Hopp, Gudrun,Von Philipsborn, Wolfgang,Beck, Stefan,Prosenc, Marc-Heinrich,Rief, Ursula,Brintzinger, Hans-Herbert
, p. 778 - 785 (1996)
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.
C1-insertion reactions at cyclodimeric (η2-acetaldehyde)zirconocene complexes
Schmuck, Stefanie,Erker, Gerhard,Kotila, Sirpa
, p. 75 - 86 (1995)
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
