Sterically Hindered Aluminum Alkyls: Weakly Interacting Scavenging Agents of Use in Olefin Polymerization
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- 作者：Russell A. Stapleton ; Abdulaziz Al-Humydi ; Jianfang Chai ; Brandon R. Galan ; Scott Collins
- 刊名：Organometallics
- 出版年：2006
- 出版时间：October 9, 2006
- 年：2006
- 卷：25
- 期：21
- 页码：5083 - 5092
- 全文大小：520K
- 年卷期：v.25,no.21(October 9, 2006)
- ISSN：1520-6041
文摘
Sterically hindered aluminum methyl compounds derived from reaction of hindered phenols with AlMe3(i.e., MeAl(BHT)2 and MeAl(BHT*)2; BHT = 2,6-di-tert-butyl-4-methylphenoxide; BHT* = 2,4,6-tri-tert-butylphenoxide) are useful scavenging agents in olefin polymerization using metallocene catalysts.They do not, or only slowly, react with activators such as B(C6F5)3 or [Ph3C][B(C6F5)4] at 25 
C, nor dothey coordinate to or react with metallocenium ion-pairs derived from metallocene dialkyls and theseactivators. A mixture of AlMe3 and a large excess of MeAl(BHT)2 proves advantageous for catalyststhat are susceptible to reaction with BHT-H, the hydrolysis product of MeAl(BHT)2. Ethylenepolymerization experiments establish that the activity of [Cp2ZrMe][MeB(C6F5)3] is only slightly inhibitedby AlMe3 in the presence of a significant excess of MeAl(BHT)2. Spectroscopic studies have revealedthat AlMe3 is in equilibrium with MeAl(BHT)2, forming Me2Al(BHT). At low temperature using 13CNMR spectroscopy, a 1:1 mixture of AlMe3 and MeAl(BHT)2 is shown to consist of Al2Me6, MeAl(BHT)2, and primarily Me2Al(
-BHT)2AlMe2. A higher temperature, both intra- and intermolecularexchange of both Al-Me and Al-BHT groups, coupled with the temperature dependence of the variousequilibria involved, lead to 1H and 13C NMR spectra that are consistent with monomeric Me2Al(BHT).1H and 19F NMR spectroscopic studies of mixtures of the ion-pairs [Me2C(Cp)IndMMe][MeB(C6F5)3](M = Zr, Hf) or [Me2SiCp2ZrMe][MeB(C6F5)3] with various quantities of AlMe3 in the presence ofMeAl(BHT)2 were conducted. The AlMe3-mediated degradation of ion-pairs that are susceptible to B(C6F5)3dissociation is largely absent in the presence of excess MeAl(BHT)2, although reversible formation of[Me2SiCp2Zr(-Me)2AlMe2][MeB(C6F5)3] and related adducts is observed at low ratios of MeAl(BHT)2to AlMe3.
C, nor dothey coordinate to or react with metallocenium ion-pairs derived from metallocene dialkyls and theseactivators. A mixture of AlMe3 and a large excess of MeAl(BHT)2 proves advantageous for catalyststhat are susceptible to reaction with BHT-H, the hydrolysis product of MeAl(BHT)2. Ethylenepolymerization experiments establish that the activity of [Cp2ZrMe][MeB(C6F5)3] is only slightly inhibitedby AlMe3 in the presence of a significant excess of MeAl(BHT)2. Spectroscopic studies have revealedthat AlMe3 is in equilibrium with MeAl(BHT)2, forming Me2Al(BHT). At low temperature using 13CNMR spectroscopy, a 1:1 mixture of AlMe3 and MeAl(BHT)2 is shown to consist of Al2Me6, MeAl(BHT)2, and primarily Me2Al(-BHT)2AlMe2. A higher temperature, both intra- and intermolecularexchange of both Al-Me and Al-BHT groups, coupled with the temperature dependence of the variousequilibria involved, lead to 1H and 13C NMR spectra that are consistent with monomeric Me2Al(BHT).1H and 19F NMR spectroscopic studies of mixtures of the ion-pairs [Me2C(Cp)IndMMe][MeB(C6F5)3](M = Zr, Hf) or [Me2SiCp2ZrMe][MeB(C6F5)3] with various quantities of AlMe3 in the presence ofMeAl(BHT)2 were conducted. The AlMe3-mediated degradation of ion-pairs that are susceptible to B(C6F5)3dissociation is largely absent in the presence of excess MeAl(BHT)2, although reversible formation of[Me2SiCp2Zr(-Me)2AlMe2][MeB(C6F5)3] and related adducts is observed at low ratios of MeAl(BHT)2to AlMe3.