2,6-二亚甲基吡啶桥联双(氨基酚氧基)钠、钾配合物的合成及催化外消旋丙交酯开环聚合研究  

Syntheses of Sodium and Potassium Complexes Based on Pyridine-2,6-diyl-bis(methylene)-bridged Bis(aminophenolate)Ligands and Catalytic Ring-opening Polymerization of rac-Lactide

作　　者：王镜焱 马海燕[1] Wang Jingyan;Ma Haiyan(Laboratory of Organometallic Chemistry,School of Chemistry and Molecular Engineering,East China University of Science and Technology,Shanghai 200237)

机构地区：[1]华东理工大学化学与分子工程学院金属有机化学研究室,上海200237

出　　处：《化学学报》2024年第10期1058-1068,共11页Acta Chimica Sinica

基　　金：国家自然科学基金(No.21871082)资助。

摘　　要：本工作基于2,6-二亚甲基吡啶桥联双(氨基酚)配体合成了四个新型双核钠、钾配合物,通过~1H NMR、^(13)C NMR以及元素分析进行了表征.典型钠配合物Na2通过X-ray单晶衍射分析确定具有双核结构,其中一个钠中心与多齿配体所有杂原子成键形成五配位构型,另一个钠中心除通过两个酚氧原子与前一钠中心桥联外,还与两分子四氢呋喃配位形成四配位构型.该类钠、钾配合物对外消旋丙交酯(racemic lactide,rac-LA)开环聚合具有很高的催化活性,其中配体骨架氮上叔丁基取代的配合物Na3活性最高,在室温、甲苯为溶剂,[rac-LA]_(0)/[Cat.]_(0)/[BnOH]_(0)=500∶1∶4时,转化频率(turnover frequency,TOF)值高达46552 h^(-1).基于核磁跟踪以及基质辅助激光解吸飞行时间质谱(matrix-assisted laser desorption ionization time-of-flight mass spectrometry,MALDI-TOF MS)的研究结果,认为不加醇条件下,双核碱金属配合物易攫取丙交酯单体次甲基氢,进而通过阴离子聚合机理催化丙交酯聚合;而加入多倍量苄醇后,阴离子过程受到部分抑制,主要以配体辅助的单体活化机理进行聚合反应.In this work,four novel binuclear sodium and potassium complexes bearing pyridine-2,6-diyl-bis(methylene)-bridged bis(aminophenolate)ligands were synthesized via the reactions of corresponding bisphenol proligands L~1H_(2)~L~3H_(2)with excess NaH or KH in tetrahydrofuran at room temperature.All the newly synthesized proligands and complexes were characterized by~1H NMR,^(13)C NMR and high-resolution mass spectrometry(HRMS)/or elemental analysis.The X-ray diffraction analysis of complex Na2 being obtained as a pair of racemic isomers shows that the molecule possesses two non-symmetrically coordinated sodium centers,with one sodium center five-coordinated by all of the heteroatoms of the multidentate ligand,the other one four-coordinated by two tetrahydrofuran molecules in addition to the two phenolate oxygen atoms,and the two sodium centers are bridged via two phenolate oxygen atoms,leading to a Na…Na distance of 0.3041 nm.Without the addition of alcohol,the catalytic activity of Na1 towards the ring-opening polymerization(ROP)of rac-lactide(rac-LA)was very low(turnover frequency(TOF)=225 h^(-1)),and the molecular weight of the obtained polymer was much lower than the theoretical one.When benzyl alcohol was used as an initiator,all these sodium and potassium complexes showed high catalytic activities and low isoselectivities of P_(m)=0.51~0.57 towards the polymerization of rac-LA.The electron-donating effect of the substituents on the skeleton nitrogen atoms of the ligand is beneficial to the improvement of catalytic activity of the corresponding complex,while increasing the steric bulkiness of those substituents is unfavorable to the reaction.Among them,complex Na3 with tert-butyl groups substituted on the skeleton nitrogen atoms showed the highest catalytic activity in the presence of four equiv.of benzyl alcohol(TOF up to 46552 h^(-1)).In addition,with the decrease of the polymerization temperature,the selectivity of complexes for rac-LA polymerization gradually increased.For example,complex Na1 showed a low

关 键 词：2 6-二亚甲基吡啶桥联双(氨基酚)配体 碱金属配合物 外消旋丙交酯 开环聚合 等规选择性 

分 类 号：O631.5[理学—高分子化学] O641.4[理学—化学] O643.36