3 years ago

Synthesis and Characterization of Rare-Earth Metal Complexes Supported by 2-Imino or Amino Appended Indolyl Ligands with Diverse Hapticities: Tunable Selective Catalysis for Isoprene Polymerization

Synthesis and Characterization of Rare-Earth Metal Complexes Supported by 2-Imino or Amino Appended Indolyl Ligands with Diverse Hapticities: Tunable Selective Catalysis for Isoprene Polymerization
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 η11 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-η221 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-η511 and μ-η611 modes with Dy, and its isomer 4b having the indolyl ligands only in μ-η511 modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η511)-2-(2,6-DippNCH2)Ind(μ-η611)-2-(2,6-DippNCH2)Ind][Gd(CH2SiMe3)(thf)]2 (5), having indolyl ligands in μ-η511 and μ-η611 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-η3211)-2-(2,6-DippNCH2)Ind(μ-η211)-2-(2,6-DippNCH2)Ind-11)-2-(2,6-DippNCH2)Ind]-Gd3[(μ3-O(CH2)5SiMe3)(μ2-O(CH2)5SiMe3)(thf)3] (6) having indolyl ligands in η11, μ-η211, and μ-η3211 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-η3211 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-η311-2-(2,6-DippNCH2)Ind]3Sm2(thf)3 (7) having a bridged indolyl ligand in μ-η311 hapticities was isolated. All structures of the complexes have been determined by X-ray crystallographic analyses. Dinuclear alkyl complexes 25 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].

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00575

DOI: 10.1021/acs.organomet.7b00575

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