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Tris(pyrazolyl)methanide Complexes of Trivalent Rare-Earth Metals

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posted on 25.03.2016, 17:51 by Tengfei Li, Guangchao Zhang, Jingjing Guo, Shaowu Wang, Xuebing Leng, Yaofeng Chen
Three types of trivalent rare-earth-metal complexes supported by a monoanionic tris­(pyrazolyl)­methanide ligand were synthesized and structurally characterized, and the catalytic activity of the dialkyl derivatives for isoprene polymerization was investigated. Reactions of the lithium salt of tris­(3,5-dimethylpyrazolyl)­methanide LLi­(THF) with 1 equiv of ScCl3(THF)3, YCl3, or LuCl3 in THF provided the ion-pair complexes [LLnCl3]­[Li­(THF)4] (Ln = Sc (1), Y (2), Lu (3)). Dialkyl complexes LLn­(CH2SiMe3)2(THF) (Ln = Y (4), Lu (5)) were prepared by salt metathesis of LLi­(THF) with 1 equiv of [Y­(CH2SiMe3)2(THF)3]­[BPh4] or [Lu­(CH2SiMe3)2(THF)3]­[BPh4] in toluene. Reaction of 5 with PhSiH3 provided the unexpected alkylidene-bridged dinuclear complex L2Lu2(μ-η11-3,5-(CH3)­C3HN2)2(μ-CHSiMe3) (6). Complexes 16 were structurally characterized by single-crystal X-ray diffraction, showing that the tris­(pyrazolyl)­methanide ligand acts as a κ3-coordinating six-electron donor in all complexes. The dialkyl complexes catalyzed 1,4-cis polymerization of isoprene with high selectivity upon activation with borate and alkylaluminum.