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Recent reports have described the placement of substituents onto R-diimine ligands and their effect on the σ-donating ability to Pd(II) and thus the Lewis acidity of the metal.26,27 In response, we carried out an investigation of the polymerization behavior of a series of Pd(II) R-diimine catalysts bearing substituents in the para-aryl position on the ligand aromatic rings.28 We discovered that this substitution was able to perturb the metal electronics in a regular manner, as evidenced by the remarkably linear correlation observed in the stretching frequencies of the corresponding carbonyl complexes. Furthermore, several trends were observed in the physical properties of the resulting polymers. The introduction of substituents of increasing electron-donating ability led to catalysts that afforded polymers of higher molecular weight, slightly reduced branching density, and a corresponding shift toward less dendritic polymer topologies. In the case of copolymerizations with methyl acrylate, a clear and pronounced trend of increasing acrylate incorporation ratio and overall tolerance to polar functionality was also observed over the range of substitution explored. |
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wangxh1984(金币+2, 翻译EPI+1): 2011-03-16 15:49:17
ringzhu(金币+38): ~~ 2011-03-22 12:37:02
wangxh1984(金币+2, 翻译EPI+1): 2011-03-16 15:49:17
ringzhu(金币+38): ~~ 2011-03-22 12:37:02
仅供参考  最近的报道描述了R-二亚胺配体上取代基的位置及其影响对二羟基聚醚(II)σ-贡献的能力,进而影响金属的刘易斯酸度。 作为回应，我们对一系列的在配体方环的芳基对位存在取代基的二羟基聚醚(II)R-二亚胺催化剂的聚合作用作了调查。 我们发现这种取代基能够有规律的扰动金属电子，因为在相应羰基复合体的伸展频率中观察到明显的线性相关性。另外，在所得聚合物的物理性质中也观察到几种趋势。能够增强电子贡献能力的取代基的引入，导致催化剂提供具有更高分子量的聚合物，显著减少分枝密度，以及相应的转变为较低树状聚合物的拓扑性质。在与丙烯酸甲酯的共聚合作用中，清晰显著的增强趋势在丙烯酸盐合并率以及在研究的替换范围内对极性功能的整体容度中都有所呈现。 |
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