Chen Ting-An, Shon Young-Seok
Department of Chemistry and Biochemistry, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840, USA.
Catalysts. 2018 Oct;8(10). doi: 10.3390/catal8100428. Epub 2018 Sep 29.
Colloidal Pd nanoparticles capped with octanethiolate ligands have previously shown an excellent selectivity toward the mono-hydrogenation of both isolated and conjugated dienes to internal alkenes. This paper reports an efficient stereoselective mono-hydrogenation of cumulated dienes (allenes) to either Z or E olefinic isomers, depending on the substitution pattern around C=C bonds. Kinetic studies indicate that the reaction progresses through the hydrogenation of less hindered C=C bonds to produce internal Z olefinic isomers. In the cases of di-substitued olefinic products, this initial hydrogenation step is followed by the subsequent isomerization of Z to E isomers. In contrast, the slow isomerization of Z to E isomers for tri-substituted olefinic products results in the preservation of Z stereochemistry. The high selectivity of Pd nanoparticles averting an additional hydrogenation is steered from the controlled electronic and geometric properties of the Pd surface, which are the result of thiolate-induced partial poisoning and surface crowding, respectively. The high activity of colloidal Pd nanoparticle catalysts allows the reactions to be completed at room temperature and atmospheric pressure.
先前已表明，用硫醇盐配体封端的胶体钯纳米颗粒对孤立二烯和共轭二烯单加氢生成内烯烃具有出色的选择性。本文报道了一种高效的立体选择性反应，即累积二烯（丙二烯）根据C=C键周围的取代模式加氢生成Z或E烯烃异构体。动力学研究表明，反应通过位阻较小的C=C键加氢生成内Z烯烃异构体来进行。在二取代烯烃产物的情况下，这一初始加氢步骤之后是Z异构体随后异构化为E异构体。相比之下，三取代烯烃产物中Z异构体向E异构体的缓慢异构化导致Z立体化学得以保留。钯纳米颗粒避免额外加氢的高选择性源自钯表面可控的电子和几何性质，这分别是硫醇盐诱导的部分中毒和表面拥挤的结果。胶体钯纳米颗粒催化剂的高活性使得反应能够在室温及大气压下完成。
