Unexpected Competition between Vanadium and Zinc in the Synthesis of Sterically Bulky Metallocenes

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• 作者：Jason S. Overby ; Kumudini C. Jayaratne ; Nathan J. Schoell ; and Timothy P. Hanusa
• 刊名：Organometallics
• 出版年：1999
• 出版时间：April 26, 1999
• 年：1999
• 卷：18
• 期：9
• 页码：1663 - 1668
• 全文大小：83K
• 年卷期：v.18,no.9(April 26, 1999)
• ISSN：1520-6041

文摘

Attempts to form (Cp³ⁱ)₂V and (Cp⁴ⁱ)₂V (Cpⁿⁱ = C₅(iPr)_nH_5-n) from the reaction of zinc-reduced VCl₃ and K[Cpⁿⁱ] in THF at room temperature produces the corresponding zincocenes(Cp³ⁱ)₂Zn and (Cp⁴ⁱ)₂Zn instead. In refluxing THF, the same reactions generate the expected(Cpⁿⁱ)₂V vanadocenes. The latter are also formed from the reaction of aluminum-reducedVCl₃ with K[Cpⁿⁱ] at room temperature. Reaction of 3 equiv of K[Cp³ⁱ] or K[C₅Ph₄H] withVCl₃ in THF produces (Cp³ⁱ)₂V and (C₅Ph₄H)₂V, respectively, whereas the equivalent reactionwith K[Cp⁴ⁱ] generates (Cp⁴ⁱ)₂VCl. These experiments suggest that zincocenes are intermediates whenever vanadocenes are synthesized from zinc-reduced VCl₃ but that zinc complexeswill be isolated only when certain cyclopentadienyl rings and temperature conditions areused. A single-crystal X-ray diffraction study of (Cp³ⁱ)₂V found the metal to reside on acrystallographically imposed inversion center, with an average V-C(ring) distance of 2.274(9) Å; the isopropyl groups orient themselves to minimize unfavorable steric interactionsbetween the rings.