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
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.
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)
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.
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.
Ligand exchange processes in zirconocene dichloride-trimethylaluminum bimetallic systems and their catalytic properties in reaction with alkenes
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.
, p. 16918 - 16937 (2019/01/03)
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.
Synthesis, structures, and dynamic features of d0 zirconocene-allyl complexes
Vatamanu, Mihaela
, p. 3683 - 3694 (2014/08/18)
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.
