Nanoporous Gold Catalyst for Highly Selective Semihydrogenation of Alkynes: Remarkable Effect of Amine Additives

Abstract

We report for the first time the highly selective semihydrogenation of alkynes using the unsupported nanoporous gold (AuNPore) as a catalyst and organosilanes with water as a hydrogen source. Under the optimized reaction conditions, the present semihydrogenation of various terminal- and internal-alkynes affords the corresponding alkenes in high chemical yields and excellent Z-selectivity without any over-reduced alkanes. The use of DMF as solvent, which generates amines in situ, or pyridine as an additive is crucial to suppress the association of hydrogen atoms on AuNPore to form H(2) gas, which is unable to reduce alkynes on the unsupported gold catalysts. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity. In addition, the SEM and TEM characterization of nanoporosity show that the AuNPore catalyst has a bicontinuous 3D structure and a high density of atomic steps and kinks on ligament surfaces, which should be one of the important origins of catalytic activity.

The Intermetalloid Cluster [(Cp*AlCu)6H4], Embedding a Cu6 Core Inside an Octahedral Al6 Shell: Molecular Models of Hume–Rothery Nanophases

“…Hume-Rothery nanophases, for example, Fe 4 Al 13 , [20] PdGa, [21] and NiGa, [22] attracted attention as selective semihydrogenation catalysts of alkynes to alkenes (active site isolation concept). These findings suggest inexpensive and abundant alternatives for established but rare and precious noble metal catalysts (for example, Pt, [23] Pd, [24] Ru, [25] Rh, [26] or Au [27] ). The insertion of a nitrile into the MÀH bonds of 1 leading to 2 in a clean reaction provides a first study case (molecular model) for surface reactions on hydrogenated Hume-Rothery type intermetallic nanophases showing cooperative interaction of A and B sites.…”

Nanoporous Metals as Novel Catalysts for Chemical Transformations☆

“…In order to reduce seemingly less reactive C]N bond, it is required to hold a proton of water, which avoids rapid elimination of hydrogen gas. 46 This was experimentally verified by carrying out the following experiment. AuNPore/SiH/water system was treated with either aldehyde alone or aldehyde plus imine; interestingly, in the former case, rapid evolution of H 2 could be seen, while no H 2 evolution was observed in the latter case.…”

“…It was found that during screening of amine additives in the semihydrogenation of alkynes, 46 when quinoline was used as a base, the reduced product tetrahydroquinoline was obtained in 30% yield. Inspired with these results, the same group turned attention to the reduction of quinoline separately.…”

Three-dimensional nanoporous gold–cobalt oxide electrode for high-performance electroreduction of hydrogen peroxide in alkaline medium

“…It has been regarded as a very promising candidate material for application in various areas such as catalysis [21], energy storage [22], metal-enhanced fluorescence [23] and sensors/biosensors [24,25]. NPG films are typically prepared by chemically dealloying commercial AueAg alloy leaves in a concentrated HNO 3 solution.…”