Shaowu Wang, Zeming Huang, Xiaolong Mu, Yun Wei, Shuangliu Zhou, Xiancui Zhu, Guangchao Zhang
The reaction of 2-(2,6-DippNHCH2)C8H5NH (Dipp = 2,6-iPrC6H3, C8H5NH = indolyl) with 1 equiv of (Me3SiCH2)3Yb(THF)2 at room temperature generated mononuclear ytterbium complex 1 having the indolyl ligands in η1:η1 mode with reduction of Yb3+ to Yb2+ and oxidation of the amino to imino group. In the case of Er and Y, the reactions produced dinuclear complexes 2 and 3 having the indolyl ligands in μ-η2:η2:η1 modes with the central metals. When the rare-earth metal is dysprosium, the reaction afforded mixed ligated dinuclear complex 4a having indolyl ligands in μ-η5:η1:η1 and μ-η6:η1:η1 modes with Dy, and its isomer 4b having the indolyl ligands only in μ-η5:η1:η1 modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η5:η1:η1)-2-(2,6-DippNCH2)Ind(μ-η6:η1:η1)-2-(2,6-DippNCH2)Ind][Gd(CH2SiMe3)(thf)]2 (5), having indolyl ligands in μ-η5:η1:η1 and μ-η6:η1:η1 modes with Gd. In addition, treatment of 2-(2,6-DippNHCH2)C8H5NH with 1.25 equiv of (Me3SiCH2)3Gd(THF)2 produced the alkoxido-bridged trinuclear gadolinium complex [(μ-η3:η2:η1:η1)-2-(2,6-DippNCH2)Ind(μ-η2:η1:η1)-2-(2,6-DippNCH2)Ind-(η1:η1)-2-(2,6-DippNCH2)Ind]-Gd3[(μ3-O(CH2)5SiMe3)(μ2-O(CH2)5SiMe3)(thf)3] (6) having indolyl ligands in η1:η1, μ-η2:η1:η1, and μ-η3:η2:η1:η 1 modes with metals, respectively. In complex 6, sp2 C–H activation is observed at the 7-indolyl position producing unique 2-amido substituted indolyl-1,7-dianions having a μ-η3:η2:η1:η1 bonding modes with three metals. The O(CH2)5SiMe3 arises from the ring-opening of THF by attack of CH2SiMe3. Moreover, when 2-(2,6-DippNHCH2)C8H5NH was treated with 1 equiv of (Me3SiCH2)3Sm(THF)2, a dinuclear samarium complex [μ-η3:η1:η1-2-(2,6-DippNCH2)Ind]3Sm2(thf)3 (7) having a bridged indolyl ligand in μ-η3:η1:η1 hapticities was isolated. All structures of the complexes have been determined by X-ray crystallographic analyses. Dinuclear alkyl complexes 2–5 have been tested as isoprene polymerization initiators in the presence of AliBu3 and [Ph3C][B(C6F5)4]. The regioselectivity for isoprene polymerization is tunable from 1,4-cis (up to 93.5%) to 3,4- (up to 86.2%) selectivity by these catalysts simply by adjusting the addition order of AliBu3 and [Ph3C][B(C6F5)4].