{Phenoxy-imine}aluminum versus -indium Complexes for the Immortal ROP of Lactide: Different Stereocontrol, Different Mechanisms
{Phenoxy-imine}aluminum versus -indium Complexes for the Immortal ROP of Lactide: Different Stereocontrol, Different Mechanisms
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DOI：
10.1021/om301155m
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发表时间：
2013-03-25
期刊：
影响因子：
2.8
通讯作者：
Carpentier, Jean-Francois
中科院分区：
文献类型：
--
作者：
Normand, Mickael;Dorcet, Vincent;Carpentier, Jean-Francois
合成了一系列苯氧亚胺(ONR)(-)配体平台稳定的R-亚氨基可变R-亚氨基取代的二烷基铝-铟(M=Al，R‘=Me；M=In，R’=Me，CH2SiMe3)配合物，并在溶液和固体中表征了它们的结构.AlMe2络合物与醇，特别是与烷基(S)-H-乳酸反应，生成相应的{ONR}Al(OR)(2)化合物。另一方面，铟的络合物{ONR}InR‘(2)对醇基本上是惰性的。当它们与醇(iPrOH，BnOH)结合时，{ONR}AlMe2络合物促进了外消旋丙交酯(RAC-LA)的活性(不朽)开环聚合((I)ROP)，并根据R-亚氨基取代基对分子质量和各种微观结构进行了很好的控制。具有苄基亚氨基取代基的络合物能够获得显著的等规度(Pm高达0.80)，基本上遵循芳基部分的大小。类似的{ONR}INR‘(2)对RAC-LA在外加酒精存在下的(I)ROP具有类似的活性，但聚合反应较不受控制，除了一个(3a，P-m=0.70)外，所有配合物都没有诱导立体选择性。动力学研究揭示了不同的速率规律，铝体系1M/iPrOH对单体具有明显的零级依赖关系，而类似的铟体系3M/iPrOH对单体具有一级依赖关系。根据模型化合物的化学计量反应性，根据金属中心的性质，提出了两种不同的作用机理：铝基配合物通过配位插入进行，而In基配合物通过活化单体机理进行操作。
A series of dialkylaluminum and -indium {ONR}MR'(2) complexes (M = Al, R' = Me; M = In, R' = Me, CH2SiMe3) stabilized by a phenoxy-imine {ONR}(-) ligand platform, with variable R-imino substituents and functionalized by a bulky o-SiPh3 in the phenoxy moiety, has been prepared and structurally characterized in solution and in the solid state. {ONR}AlMe2 complexes reacted with alcohols, in particular with alkyl (S)-H-lactate, to generate the corresponding {ONR}Al(OR)(2) compounds. On the other hand, the indium complexes {ONR}InR'(2) proved largely inert toward alcohols. When they were combined with an alcohol (iPrOH, BnOH), the {ONR}AlMe2 complexes promoted the living (immortal) ring-opening polymerization ((i)ROP) of racemic lactide (rac-LA) with a good control over the molecular weights and various microstructures, dependent on the R-imino substituent. Complexes having benzyl-type imino substituents enabled the achievement of significant isotacticity (Pm up to 0.80), following grossly the bulkiness of the aryl moiety. The analogous {ONR}InR'(2) proved similarly active for the (i)ROP of rac-LA in presence of an external alcohol, but the polymerizations were less controlled and none of the complexes induced stereoselectivity, except one (3a, P-m = 0.70). Kinetic studies revealed different rate laws, with an apparent zero-order dependence on monomer for the aluminum system 1m/iPrOH and a first-order dependence on monomer for the analogous indium system 3m/iPrOH. On the basis of the stoichiometric reactivity of model compounds, two different operative ROP mechanisms are suggested, depending on the nature of the metal center: Al-based complexes proceed through coordination-insertion, while In-based complexes are proposed to operate through an activated monomer mechanism.