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Issue 22, 2014
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Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability

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Abstract

Reaction of [VO(OnPr)3] with the Schiff bases 3,5-(tBu)2-2-OH-C6H2CH(N(x-OR-C6H4)) (R = Me; x = 2, L1H; x = 3, L2H; x = 4, L3H; R = Et (L4H), CF3 (L5H), Ph (L6H)) or 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2′-(2′′-(OR1)C6H4)C6H4) (R = adamantyl, R1 = Ph (L7H) or R = C(Me)2Ph, R1 = Ph (L8H)) afforded the bis(chelate) vanadium(IV) complexes [VO(Ln)2] (n = 1 (1·2MeCN); n = 2 (2); n = 3 (3·2MeCN); n = 4 (4); n = 5 (5); n = 6 (6); n = 6, (7·1.5MeCN); n = 7, (8); n = 8, (9)); in the case of L6H, the oxo-bridged vanadium(V) complexes [VO(μ-O)(L6)]2 (10) was also isolated. By contrast, interaction of 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2′-(2′′-(OR1)C6H4)C6H4) (R = adamantyl, R1 = Me (L9H); R = tBu, R1 = Me (L10H); R = C(Me)2Ph, R1 = Me (L11H)) with [VO(OnPr)3] led to the isolation of the dinuclear complexes [VO(μ-OH)(μ-OnPr)(Ln)]2 (n = 9, (11·4MeCN); 10, (12); 11, (13)), respectively. The molecular structures of 1 to 13 are reported. All complexes have been screened as pre-catalysts for the polymerization of ethylene in the presence of the co-catalyst diethylaluminium chloride (DEAC) with or without ethyltrichloroacetate (ETA) present at 1 or 10 bar of ethylene. Under high pressure, all pre-catalysts exhibited high activity and afforded high molecular weight (Mw ≈ 200 000 to 675 000 g mol−1), linear polyethylene with activities (in the presence of ETA) in the range 4960–16 400 g mmol−1 h−1; at one bar, the products were generally of lower molecular weight. The use of methylaluminoxane (MAO) or modified MAO (MMAO) as co-catalyst led to trace or poor (≤110 g mmol−1 h−1) activity, respectively.

Graphical abstract: Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability

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Publication details

The article was received on 04 Jan 2014, accepted on 09 Mar 2014 and first published on 12 Mar 2014


Article type: Paper
DOI: 10.1039/C4DT00021H
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2014,43, 8300-8310
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    Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability

    J. Ma, K. Zhao, M. J. Walton, J. A. Wright, J. W. A. Frese, M. R. J. Elsegood, Q. Xing, W. Sun and C. Redshaw, Dalton Trans., 2014, 43, 8300
    DOI: 10.1039/C4DT00021H

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