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Life and death of an active ethylene polymerization catalyst. Ligand involvement in catalyst activation and deactivation during the polymerization catalyzed by a vanadium di-imine complex. Isolation and characterization of two unprecedented neutral and anionic vanadium (I) alkyls.

Abstract : Reaction of {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(C5H3N)}VCl3·1.3(CH2Cl2) (1) with stoichiometric amount of methyl alumoxane (PMAO) in toluene resulted in the methylation of the pyridine ring ortho position affording {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(2-MeC5H3N)}VCl2·0.5 (toluene) (2). In the process the ligand became an anionic amide, one chlorine atom was eliminated by the metal center, and the vanadium coordination number decreased by one unit. This new trivalent compound is a potent ethylene polymerization precatalyst, and polymers produced by the complex activated with PMAO showed a bimodal character in the GPC. Its bimodality is tentatively explained with the existence of two catalytically active species (mono and dialkylation of the vanadium center). Further attack of a strong alkylating agent such as MeLi occurs at the pyridine ring to either remove the methyl group, or to place an additional methyl group on the ring meta position. Both processes imply two-electron reduction of the metal center and formation of the corresponding V(I) derivatives {2,6-bis[2,6-(i-Pr)2PhNC (Me)]2(C5H3N)}V(CH3)(μ-CH3)Li(Et2O)3 (3) and the ionic [{2,6-bis[2,6-(i-Pr)2PhNC(Me)]2 (2,3-Me2C5H3N)}V(CH3)2][Li(THF)2(TMEDA)2]·0.5(Et2O) (4) which were isolated in crystalline form. Crystal data are as follows. 1:  monoclinic, space group P21/n, a = 18.267(5) Å, b = 16.643(4) Å, c = 38.195(9) Å, β = 96.061(5)°, Z = 12; 2:  monoclinic, space group P21/c, a = 15.741(2) Å, b = 16.565(2) Å, c = 15.849(2) Å, β = 100.316(3)°, Z = 4; 3:  orthorhombic space group Pnma, a = 19.724(6) Å, b = 22.001(7) Å, c = 11.035(3) Å, Z = 4; 4:  monoclinic space group P21/n, a = 11.932(3) Å, b = 25.363(6) Å, c = 18.957(4) Å, β = 96.587(4)°, Z = 4.
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https://hal.univ-brest.fr/hal-01765391
Contributor : Françoise Conan <>
Submitted on : Thursday, April 12, 2018 - 6:44:07 PM
Last modification on : Thursday, February 7, 2019 - 2:50:12 PM

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Françoise Conan, Damien Reardon, Sandro Gambarotta, Glenn Yap, Qinyang Wang. Life and death of an active ethylene polymerization catalyst. Ligand involvement in catalyst activation and deactivation during the polymerization catalyzed by a vanadium di-imine complex. Isolation and characterization of two unprecedented neutral and anionic vanadium (I) alkyls. . Journal of the American Chemical Society, American Chemical Society, 1999, ⟨10.1021/ja990263x⟩. ⟨hal-01765391⟩

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