Chromium(II) and Chromium(III) Complexes Supported by Tris(2-pyridylmethyl)amine: Synthesis, Structures, and Reactivity

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• 作者：Nicholas J. Robertson ; Michael J. Carney ; and Jason A. Halfen
• 刊名：Inorganic Chemistry
• 出版年：2003
• 出版时间：October 20, 2003
• 年：2003
• 卷：42
• 期：21
• 页码：6876 - 6885
• 全文大小：182K
• 年卷期：v.42,no.21(October 20, 2003)
• ISSN：1520-510X

文摘

This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(II) and chromium(III) complexes ligated by tris(2-pyridylmethyl)amine (TPA), including chromium(III) organometallicderivatives. For instance, the combination of TPA with CrCl₂ yields monomeric (TPA)CrCl₂ (1). A similar reactionof CrCl₂ with TPA, followed by chloride abstraction with NaBPh₄ or NaBAr^F₄ (Ar^F = 3,5-(CF₃)₂C₆H₃), provides theweakly associated cationic dimers [(TPA)CrCl]₂[BPh₄]₂ (2A) and [(TPA)CrCl]₂[BAr^F₄]₂ (2B), respectively. X-raycrystallographic analysis reveals that each chromium(II) center in 1, 2A, and 2B is a tetragonally elongated octahedron;such Jahn-Teller distortions are consistent with the observed high spin (S = 2) electronic configurations for thesechromium(II) complexes. Likewise, reaction of CrCl₃(THF)₃ with TPA, followed by anion metathesis with NaBPh₄ orNaBAr^F₄, yields the monomeric, cationic chromium(III) complexes [(TPA)CrCl₂][BPh₄] (4A) and [(TPA)CrCl₂][BAr^F₄](4B), respectively. Treatment of 4A with methyl and phenyl Grignard reagents produces the cationic chromium(III)organometallic derivatives [(TPA)Cr(CH₃)₂][BPh₄] (5) and [(TPA)CrPh₂][BPh₄] (6), respectively. Similar reactions of4A with organolithium reagents leads to intractable solids, presumably due to overreduction of the chromium(III)center. X-ray crystallographic analysis of 4A, 5, and 6 confirms that each possesses a largely undistorted octahedralchromium center, consistent with the observed S = ³/₂ electronic ground states. Compounds 1, 2A, 2B, 4A, 4B,5, and 6 are all active polymerization catalysts in the presence of methylalumoxane, producing low to moderatemolecular weight high-density polyethylene.