Neutral and Cationic N-Heterocyclic Carbene Zirconium and Hafnium Benzyl Complexes: Highly Regioselective Oligomerization of 1-Hexene with a Preference for Trimer Formation

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• 作者：Samuel Dagorne ; St茅phane Bellemin-Laponnaz ; Charles Romain
• 刊名：Organometallics
• 出版年：2013
• 出版时间：May 13, 2013
• 年：2013
• 卷：32
• 期：9
• 页码：2736-2743
• 全文大小：342K
• 年卷期：v.32,no.9(May 13, 2013)
• ISSN：1520-6041

文摘

Various zirconium and hafnium amido, chloro, and benzyl complexes supported by a tridentate N-heterocyclic carbene bis-phenolate dianionic ligand ((OCO)^{2鈥?/sup>) have been synthesized and structurally characterized. The alcohol elimination reaction of the protio ligand N,N鈥?/i>-bis(2-hydroxy-3,5-di-tert-butylphenyl)-4,5-dihydroimidazolium chloride (1) and the metal alkoxide precursors M(OiPr)₄(HOiPr) (M = Zr, Hf) and a subsequent alkoxide/chloride exchange reaction (upon addition of trimethylsilyl chloride, TMSCl) afforded the corresponding Zr and Hf carbene dichloro complexes as THF adducts: (OCO)MCl₂(THF) (2a-THF, M = Zr; 2b-THF, M = Hf). As determined by single-crystal X-ray crystallographic studies, the molecular structure of the Hf derivative 2b-THF confirmed the proposed formulation and the effective formation of a (OCO)Hf chelate. In the case of Zr, an amine elimination reaction between protio ligand 1 and Zr(NMe₂)₄ yielded the corresponding Zr amido THF adduct (OCO)Zr(NMe₂)(Cl)(THF) (3a-THF) when carried in THF as a solvent, while the Zr鈥揘HMe₂ adduct (OCO)Zr(NMe₂)(NHMe₂)(THF) (3a-NHMe₂) was isolated using CH₂Cl₂ as the reaction solvent. 3a-THF may be readily and quantitatively converted to the dichloro derivative 2a-THF upon addition of TMSCl. The toluene elimination reaction of protio ligand 1 and M(CH₂Ph)₄ (M = Zr, Hf) followed by a salt metathesis with 1 equiv of PhCH₂MgCl afforded the corresponding Zr and Hf carbene dibenzyl complexes (OCO)M(CH₂Ph)₂ (4a, M = Zr; 4b, M = Hf), whose solid-state structures were confirmed by X-ray crystallography. 4a and 4b each feature a five-coordinate metal center with both benzyl moieties binding in a 畏2 fashion. The protonolysis reaction between species 4a (or 4b) and [HNMe₂Ph][B(C₆F₅)₄] afforded the clean and quantitative formation of the corresponding Zr (or Hf) anilinium benzyl cation 5a+ (or 5b+). Remarkably, the cation 5a+ catalyzes the highly regioselective oligomerization of 1-hexene with a marked preference for trimer formation.}