Acta Chimica Sinica ›› 2013, Vol. 71 ›› Issue (08): 1125-1128.DOI: 10.6023/A13040433 Previous Articles     Next Articles



高东静, 胡泓梵, 崔春明   

  1. 南开大学元素有机化学国家重点实验室 天津 300071
  • 投稿日期:2013-04-22 发布日期:2013-05-24
  • 通讯作者: 崔春明, E-mail:
  • 基金资助:

    项目受973(No. 2012CB821600)资助.

Synthesis and Catalytic Isoprene Polymerization of Rare-Earth Alkyl Complexes Supported by An Arylimine-amidinate Ligand

Gao Dongjing, Hu Hongfan, Cui Chunming   

  1. State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071
  • Received:2013-04-22 Published:2013-05-24
  • Supported by:

    Project supported by 973 program (Grant No. 2012CB821600).

Reaction of the arylimine-amidinate ligand[NNN]H (1) ([NNN]=[2-C(H)NDippC6H3NHC(Ph)NDipp], Dipp=2,6-i-Pr2C6H3) with Ln(CH2SiMe3)3(THF)2 (Ln=Y, Sm) in n-hexane at -78℃ followed by stirring the mixture for 3 h at room temperature afforded[NNN]Ln(CH2SiMe3)2 (Ln=Y, 2; Ln=Sm, 3) in 75% and 50% yields after work up. 2 and 3 have been characterized by 1H NMR, 13C NMR, IR spectroscopy, elemental analysis. The molecular structure of 2 has been confirmed by X-ray analysis. Complexes 2 and 3 catalyzed the polymerization of isoprene in the presence of[Ph3C][B(C6F5)4] (1 equiv.) and AlEt3 (10 equiv.) at 25℃. 2 converted 250 equivalents of isoprene into polyisoprene with a narrow molecular weight distribution (Mw/Mn=1.20) and a 3,4-rich microstructure (3,4-selectivity: 78%, rr=50%) in 12 h. A significant increase of 3,4-selectivity was observed in the presence of one equivalent of AlEt3 (3,4-selectivity: 87%). When i-Bu2AlH (10 equiv.) was used instead of AlEt3, the catalytic activity and selectivity did not change noticeably while the resulting polyisoprenes feature a broad molecular weight distribution (Mw/Mn=2.45). When the amounts of i-Bu2AlH decreased from 5 to 1 equivalent, a significant increase of 3,4-selectivity and number-average molecular weight have been observed while the molecular distributions became small. The catalyst is active within a wide range of temperatures from low temperature to 40℃. At 40℃, a similar selectivity (3,4-selectivity: 78%, Mw/Mn=1.43) to that found at 25℃ but the increased reaction rate has been observed. High stereo- and regioselectivity and narrow molecular weight distributions were obtained at -20℃ (3,4-selectivity: 88%, rr=52%, Mw/Mn=1.15). The samarium alkyl 3 exhibited a high activity but low selectivity (25℃, 3 h, 3,4-selectivity: 67%, Mw/Mn=1.71) compared to the yttrium alkyl 2.

Key words: rare-earth metal, alkyl complex, arylimine-amidine, isoprene polymerization, 3,4-selectivity