Department of Chemistry, School of Science, Tokyo Institute of Technology , 2-12-1-E1-10 Ookayama, Meguro-ku, Tokyo 152-8551, Japan.
Institute for Catalysis, Hokkaido University , N10 W21, Kita-ku, Sapporo 001-0021, Japan.
J Am Chem Soc. 2017 Dec 20;139(50):18231-18239. doi: 10.1021/jacs.7b08792. Epub 2017 Dec 7.
Unprecedented surface chemistry, governed by specific atomic arrangements and the steric effect of ordered alloys, is reported. Rh-based ordered alloys supported on SiO (RhM/SiO, M = Bi, Cu, Fe, Ga, In, Pb, Sn, and Zn) were prepared and tested as catalysts for selective hydrogenation of trans-1,4-hexadiene to trans-2-hexene. RhBi/SiO exhibited excellent regioselectivity for the terminal C═C bond and chemoselective hydrogenation to the monoene, not to the overhydrogenated alkane, resulting in a high trans-2-hexene yield. Various asymmetric dienes, including terpenoids, were converted into the corresponding inner monoenes in high yields. This is the first example of a regio- and chemoselective hydrogenation of dienes using heterogeneous catalysts. Kinetic studies and density functional theory calculations revealed the origin of the high selectivity: (1) one-dimensionally aligned Rh arrays geometrically limit hydrogen diffusion and attack to alkenyl carbons from one direction and (2) adsorption of the inner C═C moiety to Rh is inhibited by steric repulsion from the large Bi atoms. The combination of these effects preferentially hydrogenates the terminal C═C bond and prevents overhydrogenation to the alkane.
报告了一种前所未有的表面化学，由特定的原子排列和有序合金的空间位阻效应控制。制备了负载在 SiO 上的 Rh 基有序合金（RhM/SiO，M = Bi、Cu、Fe、Ga、In、Pb、Sn 和 Zn），并将其用作顺-1,4-己二烯选择性加氢制备顺-2-己烯的催化剂进行了测试。RhBi/SiO 对末端 C═C 键表现出优异的区域选择性和化学选择性加氢为单烯，而不是过度加氢的烷烃，从而得到高收率的顺-2-己烯。各种不对称二烯，包括萜烯，都以高收率转化为相应的内单烯。这是使用多相催化剂实现二烯区域和化学选择性加氢的首例。动力学研究和密度泛函理论计算揭示了高选择性的起源：（1）一维排列的 Rh 阵列在几何上限制了氢从一个方向扩散并攻击烯基碳；（2）内 C═C 部分的吸附受到来自大 Bi 原子的空间位阻的抑制。这些效应的结合优先加氢末端 C═C 键并防止过度加氢为烷烃。
