Oh Sang-Keun, Niu Yanhui, Crooks Richard M
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, USA.
Langmuir. 2005 Oct 25;21(22):10209-13. doi: 10.1021/la050524i.
The synthesis and size-selective catalytic activity of Pd nanoparticles encapsulated within dendrimers functionalized with different-sized end groups is described. We designed and synthesized a series of fourth-generation poly(amidoamine) dendrimers having various extents of steric crowding on their periphery. This was accomplished by reacting the terminal amine groups of these dendrimers with epoxyalkanes substituted with different-sized alkyl groups. The modified dendrimers were characterized by 1H NMR, 13C NMR, and matrix-assisted laser desorption ionization mass spectrometry. Nearly monodisperse (1.7 +/- 0.2 nm) Pd nanoparticles were encapsulated within the interior of these dendrimers, and the resulting composite catalysts were used for the hydrogenation of three alpha-allylic alcohols having different sizes. The results showed a clear correlation between the extent of steric crowding on the dendrimer surface and the turnover frequencies (TOFs) for the substrates: more steric crowding on the dendrimer surface led to lower TOFs.
描述了封装在具有不同尺寸端基功能化树枝状大分子内的钯纳米颗粒的合成及其尺寸选择性催化活性。我们设计并合成了一系列第四代聚（酰胺胺）树枝状大分子，其外围具有不同程度的空间拥挤。这是通过使这些树枝状大分子的末端胺基与被不同尺寸烷基取代的环氧烷反应来实现的。通过1H NMR、13C NMR和基质辅助激光解吸电离质谱对改性树枝状大分子进行了表征。几乎单分散（1.7±0.2 nm）的钯纳米颗粒被封装在这些树枝状大分子内部，所得复合催化剂用于三种不同尺寸的α-烯丙基醇的氢化反应。结果表明，树枝状大分子表面的空间拥挤程度与底物的转化频率（TOF）之间存在明显的相关性：树枝状大分子表面的空间拥挤程度越高，TOF越低。
