Synthesis of cyclic polylactide catalysed by bis(salicylaldiminato)tin(ii) complexes
作者:Parichat Piromjitpong、Passachon Ratanapanee、Wipavee Thumrongpatanaraks、Palangpon Kongsaeree、Khamphee Phomphrai
DOI:10.1039/c2dt31678a
日期:——
Eight bis(salicylaldiminato)tin(II) complexes have been synthesized from the reaction of Sn[N(SiMe3)2]2 and 2 equiv of the corresponding ligands at room temperature. The ligands, synthesized from salicylaldehyde and amines, were designed to have different electronic and steric properties using different amines to synthesize the tin(II) complexes as aniline (2a), 2,6-dimethylaniline (2b), 2,6-diisopropylaniline (2c), 4-methoxyaniline (2d), 4-trifluoromethylaniline (2e), methylamine (2g), and tert-butylamine (2h). Ligand variation at the salicyl group synthesized from 4-bromosalicylaldehyde and 2,6-diisopropylaniline was used to form complex 2f. Complex 2c was characterized crystallographically. All catalysts were active for the neat polymerization of L-lactide at 115 °C. At a lactide : Sn molar ratio of 10 : 1, cyclic polylactide (PLA) was obtained as demonstrated by 1H NMR and mass spectrometry. Addition of 1 equiv of benzyl alcohol in the polymerization produced linear PLA. At a higher lactide : Sn molar ratio of 200 : 1, high molecular weight PLAs with Mn up to 132 200 Daltons were obtained. Results from GPC coupled with light scattering detector and viscometer suggested that they are cyclic PLA. The order of reactivity based on conversion was determined to be 2c < 2b < 2a in accordance with lower steric hindrance. For electronic contribution, the order of 2e < 2a < 2d was observed in agreement with the increasing electron donation of the ligands. Complex 2g having the smallest substituents was found to be the most active catalyst.
八种双(水杨醛亚氨基)锡(II)配合物已通过室温下Sn[N(SiMe3)2]2与相应配体的2当量反应合成。这些配体由水杨醛和胺合成,设计使用了不同的胺,以赋予其不同的电子和立体性质,从而合成锡(II)配合物,如苯胺(2a)、2,6-二甲基苯胺(2b)、2,6-二异丙基苯胺(2c)、4-甲氧基苯胺(2d)、4-三氟甲基苯胺(2e)、甲胺(2g)和叔丁胺(2h)。通过4-溴水杨醛和2,6-二异丙基苯胺合成的配体在水杨醛基团的变异被用来形成配合物2f。配合物2c通过晶体学进行了表征。所有催化剂在115°C下均对L-乳酸的内聚聚合活性良好。在乳酸:锡摩尔比为10:1时,通过1H NMR和质谱法证实得到了环状聚乳酸(PLA)。在聚合反应中加入1当量的苄醇产生了线性PLA。在更高的乳酸:锡摩尔比200:1下,得到了分子量高达132,200道尔顿的高分子量PLA。GPC结合光散射检测器和粘度计的结果表明它们是环状PLA。根据转化率确定的反应活性顺序为2c < 2b < 2a,这与较低的立体阻碍相符。对于电子贡献,观察到的顺序为2e < 2a < 2d,这与配体电子捐赠增加一致。具有最小取代基的配合物2g被发现是活性最高的催化剂。