Tris(pyrazolyl)methanide Complexes of Trivalent Rare-Earth Metals
datasetposted 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-η1:η1-3,5-(CH3)C3HN2)2(μ-CHSiMe3) (6). Complexes 1–6 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.