NNN-Tridentate Pyrrolyl Rare-Earth Metal Complexes: Structure and Catalysis on Specific Selective Living Polymerization of Isoprene

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• 作者：Lingfang Wang ; Dongtao Liu ; Dongmei Cui
• 刊名：Organometallics
• 出版年：2012
• 出版时间：September 10, 2012
• 年：2012
• 卷：31
• 期：17
• 页码：6014-6021
• 全文大小：377K
• 年卷期：v.31,no.17(September 10, 2012)
• ISSN：1520-6041

文摘

The acid鈥揵ase reactions of NNN-tridentate pyrrolyl ligands (HL¹: 2,5-bis((pyrrolidin-1-yl)methylene)-1H-pyrrole; HL²: 2,5-bis((piperidino)methylene)-1H-pyrrole) with rare-earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, afforded the corresponding bis(alkyl) complexes L¹Ln(CH₂SiMe₃)₂(THF)_x (Ln = Sc, x = 0 (1a); Ln = Y, x = 1 (1b); Ln = Lu, x = 1 (1c)), L²Sc(CH₂SiMe₃)₂ (2a), and L²₂Ln₂(CH₂SiMe₃)₄ (Ln = Y (2b); Lu (2c)) in moderate to high yields. X-ray diffraction analysis revealed that the scandium complexes 1a and 2a are THF solvent-free monomers where the ligands coordinate to the Sc³⁺ ion in a 魏¹:魏² mode, while the yttrium and lutetium complexes 1b and 1c have the same ligand coordination geometry to that of the scandium complex but are one-THF solvates; complex 2b, however, is a dimer bridged by two anionic L² fragments that coordinate to the two yttrium ions in mixed 畏⁵:畏⁵/魏¹:魏¹ coordination modes. Upon activation with an organoborate, all these complexes initiated the controlled polymerization of isoprene. In general, complexes 2a鈥?b>c, bearing ligand L², exhibited higher activity than the analogous complexes 1a鈥?b>c, attached to the L¹ ligand. Complex 2b, in which the L² ligand adopts the mixed 畏⁵/魏¹ coordination mode, showed the highest activity and livingness mode toward the polymerization of isoprene with high cis-1,4-selectivity (94.1%), and both scandium complexes 1a and 2a exhibited high 3,4-selectivity (87%) irrespective of the ligand type; in contrast, the lutetium complexes initiated the atactic isoprene polymerization. The influences of thell ligand structural factors, the coordination solvent, and the central metal ion on the catalytic activity and selectivity are discussed.