Cyclopentadienyl Titanium Imido Compounds and Their Ethylene Polymerization Capability: Control of Molecular Weight Distributions by Imido N-Substituents
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- 作者：Christopher T. Owen ; Paul D. Bolton ; Andrew R. Cowley ; Philip Mountford
- 刊名：Organometallics
- 出版年：2007
- 出版时间：January 1, 2007
- 年：2007
- 卷：26
- 期：1
- 页码：83 - 92
- 全文大小：236K
- 年卷期：v.26,no.1(January 1, 2007)
- ISSN：1520-6041
文摘
Reaction of the previously reported Cp*Ti(NtBu)Cl(py) (1) with bulky ortho-substituted anilines ArNH2afforded the corresponding aryl imido derivatives Cp*Ti(NAr)Cl(py) (Ar = 2,6-C6H3iPr2 (2), 2,6-C6H3Br2 (3), 2-C6H4tBu (4), and 2-C6H4iPr (5)). Reaction of 2 with B(C6F5)3 in C6D6 or heating in vacuo at200 
C afforded the imido-bridged dimer Cp*2Ti2(
-N-2,6-C6H3iPr2)2Cl2 (8). Activation of 1-5 withMAO gave moderately active catalyst systems for the polymerization of ethylene in contrast to thepreviously reported, highly active titanium imido systems Ti(Me3[9]aneN3)(NR)Cl2/MAO and Ti{HC(Me2pz)3}(NR)Cl2/MAO, which are isolobal and isoelectronic with 1-5. The Cp*-supported precatalystproductivities were sensitive to both the imido N-substituents and initial precatalyst/cocatalyst concentrations. Depending upon the imido N-substituents and initial precatalyst/cocatalyst concentrations,polyethylene with unimodal (either rather low or very high molecular weight) or bimodal molecularweight distributions can be obtained. Excess AlMe3 suppresses catalyst productivity but does not affectthe overall molecular weight distribution in the system evaluated (1/MAO). Both chain transfer to aluminumand 
-hydrogen transfer appear to be active pathways for formation of the low molecular weight fractionsof the polymers formed with 1-5/MAO. Under otherwise identical polymerization conditions the catalystsystems 2/MAO and 8/MAO had comparable productivities and gave polyethylene with very similarmolecular weight and molecular weight distributions, suggesting a potential role for binuclear species inthe catalyst systems 1-5/MAO.
C afforded the imido-bridged dimer Cp*2Ti2(-N-2,6-C6H3iPr2)2Cl2 (8). Activation of 1-5 withMAO gave moderately active catalyst systems for the polymerization of ethylene in contrast to thepreviously reported, highly active titanium imido systems Ti(Me3[9]aneN3)(NR)Cl2/MAO and Ti{HC(Me2pz)3}(NR)Cl2/MAO, which are isolobal and isoelectronic with 1-5. The Cp*-supported precatalystproductivities were sensitive to both the imido N-substituents and initial precatalyst/cocatalyst concentrations. Depending upon the imido N-substituents and initial precatalyst/cocatalyst concentrations,polyethylene with unimodal (either rather low or very high molecular weight) or bimodal molecularweight distributions can be obtained. Excess AlMe3 suppresses catalyst productivity but does not affectthe overall molecular weight distribution in the system evaluated (1/MAO). Both chain transfer to aluminumand -hydrogen transfer appear to be active pathways for formation of the low molecular weight fractionsof the polymers formed with 1-5/MAO. Under otherwise identical polymerization conditions the catalystsystems 2/MAO and 8/MAO had comparable productivities and gave polyethylene with very similarmolecular weight and molecular weight distributions, suggesting a potential role for binuclear species inthe catalyst systems 1-5/MAO.