Lewis Acid Promoted Titanium Alkylidene Formation: Off-Cycle Intermediates Relevant to Olefin Trimerization Catalysis

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• 作者：Aaron Sattler ; David G. VanderVelde ; Jay A. Labinger ; John E. Bercaw
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 30, 2014
• 年：2014
• 卷：136
• 期：30
• 页码：10790-10800
• 全文大小：493K
• ISSN：1520-5126

文摘

Two new precatalysts for ethylene and 伪-olefin trimerization, (FI)Ti(CH₂SiMe₃)₂Me and (FI)Ti(CH₂CMe₃)₂Me (FI = phenoxy-imine), have been synthesized and structurally characterized by X-ray diffraction. (FI)Ti(CH₂SiMe₃)₂Me can be activated with 1 equiv of B(C₆F₅)₃ at room temperature to give the solvent-separated ion pair [(FI)Ti(CH₂SiMe₃)₂][MeB(C₆F₅)₃], which catalytically trimerizes ethylene or 1-pentene to produce 1-hexene or C₁₅ olefins, respectively. The neopentyl analogue (FI)Ti(CH₂CMe₃)₂Me is unstable toward activation with B(C₆F₅)₃ at room temperature, giving no discernible diamagnetic titanium complexes, but at 鈭?0 掳C the following can be observed by NMR spectroscopy: (i) formation of the bis-neopentyl cation [(FI)Ti(CH₂CMe₃)₂]⁺, (ii) 伪-elimination of neopentane to give the neopentylidene complex [(FI)Ti(鈺怌HCMe₃)]⁺, and (iii) subsequent conversion to the imido-olefin complex [(MeOAr₂N鈺?Ti(OArHC鈺怌HCMe₃)]⁺ via an intramolecular metathesis reaction with the imine fragment of the (FI) ligand. If the reaction is carried out at low temperature in the presence of ethylene, catalytic production of 1-hexene is observed, in addition to the titanacyclobutane complex [(FI)Ti(CH(CMe₃)CH₂CH₂)]⁺, resulting from addition of ethylene to the neopentylidene [(FI)Ti(鈺怌HCMe₃)]⁺. None of the complexes observed spectroscopically subsequent to [(FI)Ti(CH₂CMe₃)₂]⁺ is an intermediate or precursor for ethylene trimerization, but notwithstanding these off-cycle pathways, [(FI)Ti(CH₂CMe₃)₂]⁺ is a precatalyst that undergoes rapid initiation to generate a catalyst for trimerizing ethylene or 1-pentene.