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首页> 外文期刊>Chemistry: A European journal >The effect of counterion/ligand interplay on the activity and stereoselectivity of palladium(Il)-diimine catalysts for CO/p-methylstyrene copolymerization
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The effect of counterion/ligand interplay on the activity and stereoselectivity of palladium(Il)-diimine catalysts for CO/p-methylstyrene copolymerization

机译：抗衡离子/配体相互作用对钯/ II-二亚胺催化剂用于CO /对甲基苯乙烯共聚反应的活性和立体选择性的影响

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摘要

The catalytic activity and stereoselectivity of complexes [Pd(eta(1),eta(2)- C8H12OMe)(Ar-N=C(R')-C(R')=N-Ar)]X in the copolymerization of CO and p-methylstyrene have been correlated with their interionic structure in solution and in the solid state, as determined by F-19,H-1-HOESY NMR spectroscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine ligands bearing electron-donating substituents and with the least coordinating counterion. Copolymers with a microstructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical positions and the coordinating ability ofthe counterion increase. The counterion is located close to the diimine in both solution and the solid state but it moves toward the palladium as the steric hindrance in the apical positions decreases. When the latter is small the counterion competes with the substrate for apical coordination, and consequently it affects the productivity. In the case of ortho-dimethyl-substituted ligands the counterion is confined in the back, above the N=C(R')-C(R')=N moiety, and does not affect the productivity. However, it contributes to increasing the stereoregularity of the copolymer by making the aryl moieties more rigid. With R'=Me and Ar=o-Me2C6H3, an ll of 81% and 72% was obtained with X-=CF3SO3- or BArF-, respectively. The isotacticity of the copolymers produced by ortho-monosubstituted catalysts depends greatly on the counterion and ranges from 30% to 59% with X-=BArF- and X-= CF3SO3-, respectively, with Ar=o-EtC6H4 and R'=Me. Based on the interionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of C-s-symmetric isomers with respect to their C-2-symmetric counterparts.
机译：配合物[Pd（eta（1），eta（2）-C8H12OMe）（Ar-N = C（R'）-C（R'）= N-Ar）] X在CO共聚中的催化活性和立体选择性分别通过F-19，H-1-HOESY NMR光谱和X射线衍射研究确定，在溶液和固体状态下，对甲基苯乙烯和对甲基苯乙烯与它们的离子结构相关。使用带有供电子取代基且配位离子最少的无阻碍二亚胺配体可获得最高的生产率。获得具有从无规到主要为等规的微观结构的共聚物。等规度随顶端位置的位阻和抗衡离子的配位能力增加而增加。抗衡离子在溶液和固态均位于靠近二亚胺的位置，但随着顶端位置的空间位阻降低，抗衡离子向钯移动。当后者较小时，抗衡离子与底物竞争进行顶端配位，因此影响生产率。在邻二甲基取代的配体的情况下，抗衡离子被限制在N = C（R'）-C（R'）= N部分之上的背面，并且不影响生产率。然而，它通过使芳基部分更硬而有助于增加共聚物的立构规整度。在R'= Me和Ar = o-Me2C6H3的情况下，X- = CF3SO3-或BArF-分别得到81％和72％的II。由邻单取代催化剂生产的共聚物的全同立构规整度在很大程度上取决于抗衡离子，并且在X- = BArF-和X- = CF3SO3-且Ar = o-EtC6H4和R'= Me的情况下分别为30％至59％ 。基于离子间结构结果，可以通过相对于其C-2-对称对应物更大程度地降低C-s-对称异构体的共聚速率来解释这种效果。

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