Regio- and Chemoselective Hydrogenation of Dienes to Monoenes Governed by a Well-Structured Bimetallic Surface

Unprecedented surface chemistry, governed by specific atomic arrangements and the steric effect of ordered alloys, is reported. Rh-based ordered alloys supported on SiO₂ (Rh_<i>x</i>M_<i>y</i>/SiO₂, M = Bi, Cu, Fe, Ga, In, Pb, Sn, and Zn) were prepared and tested as catalysts for selective hydrogenation of <i>trans</i>-1,4-hexadiene to <i>trans</i>-2-hexene. RhBi/SiO₂ exhibited excellent regioselectivity for the terminal CC bond and chemoselective hydrogenation to the monoene, not to the overhydrogenated alkane, resulting in a high <i>trans</i>-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

A 2D Ba₂N Electride for Transition Metal-Free N₂ Dissociation under Mild Conditions

N2 activation is a key step in the industrial synthesis of ammonia and other high-value-added N-containing chemicals, and typically is heavily reliant on transition metal (TM) sites as active centers to reduce the large activation energy barrier for N2 dissociation. In the present work, we report that a 2D electride of Ba2N with anionic electrons in the interlayer spacings works efficiently for TM-free N2 dissociation under mild conditions. The interlayer electrons significantly boost N2 dissociation with a very small activation energy of 35 kJ mol–1, as confirmed by the N2 isotopic exchange reaction. The reaction of anionic electrons with N2 molecules stabilizes (N2)2– anions, the so-called diazenide, in the large interlayer space (∼4.5 Å) sandwiched by 2 cationic slabs of Ba2N as the main intermediate