Damien Reardon - Life and Death of an Active Ethylene Polymerization Catalyst. Ligand Involvement in Catalyst Activation and Deactivation. Isolation and Characterization of Two Unprecedented Neutral and Anionic Vanadium(I) Alkyls

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  Reardon, Damien, Conan, Françoise, Gambarotta, Sandro, Yap,   Glenn, Wang, Qinyan Journal of the American Chemical   Society 1999 121 (40) 9318-9325

  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)(?-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, ? = 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, ?   = 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, ? = 96.587(4)°, Z = 4.

  Address (URL): http://dx.doi.org/10.1021/ja990263x