Ethylene Polymerization Using -Diketimine Complexes of Zirconium

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• 作者：Rainer Vollmerhaus ; Marufir Rahim ; Robert Tomaszewski ; Shixuan Xin ; Nicholas J. Taylor ; and Scott Collins
• 刊名：Organometallics
• 出版年：2000
• 出版时间：May 29, 2000
• 年：2000
• 卷：19
• 期：11
• 页码：2161 - 2169
• 全文大小：188K
• 年卷期：v.19,no.11(May 29, 2000)
• ISSN：1520-6041

文摘

Ethylene polymerizations were conducted using ages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-diketimine complexes of Zr [LZrX₃ (1)and L₂ZrX₂ (2) with L = MeC(NAr)CHC(NAr)Me and X = Cl, R (R = Me, Bn)] as well asCp(L)ZrX₂ (3) in the presence of MAO. Complexes 1 possess low polymerization activities(ca. 10⁵ g PE/(mol Zr h)) and provide PEs with a trimodal, molecular weight distribution.Both 2 and 3 behave as single-site catalysts under these conditions, with the activity of thelatter being considerably higher than the former (ca. 10⁶-10⁷ vs 10⁵ g PE/(mol Zr h)).Induction periods of 10-20 min at 70 ages/entities/deg.gif">C were observed in polymerizations involving 3 (Ar= Ph, X = Cl, Me) when activated by MAO. The use of [Ph₃C][B(C₆F₅)₄] and 3b (Ar = Ph,X = Me) in the presence of small amounts of MAO (ca. 100:1 Al:Zr) led to rapid monomeruptake and an increase in catalytic activity by about a factor of 4. Lower activities wereobserved in the presence of Me₃Al or ⁱBu₃Al. Little or no polymerization activity was observedwhen excess 3b was used as a scrubbing agent (in the presence of [Ph₃C][B(C₆F₅)₄]), andrapid loss of activity was observed when excess 3b was added to a catalyst system alreadyproducing PE. Complex 3b reacts with [Ph₃C][B(C₆F₅)₄] in chlorobenzene-d₅ solution at 25ages/entities/deg.gif">C to provide [Cp(L)ZrMe][B(C₆F₅)₄] (4). Complex 4 is transformed on heating in chlorobenzene to a dicationic (ages/entities/mgr.gif">-Cl)₂ complex [(Cp(L)ZrCl)₂][B(C₆F₅)₄]₂ (5), which was characterizedby X-ray crystallography. Complex 4 forms dinuclear complexes with 3b or Me₃Al in solutionat room temperature. These complexes, [Cp(L)Zr(ages/entities/mgr.gif">-Me)₂AlMe₂][B(C₆F₅)₄] (6) or [(Cp(L)ZrMe)₂(ages/entities/mgr.gif">-Me)][B(C₆F₅)₄] (7), are fluxional in solution; at lower temperature, the solution NMRspectra are consistent with the structures shown. Complex 3b is a potent inhibitor of ethylenepolymerization by 4, forming 7, which is resistant to dissociation. The presence of AlMe₃ (orMAO) appears to reversibly displace 3b from 7, allowing the reaction of 3b with [Ph₃C][B(C₆F₅)₄] to proceed to completion.