Hydrodebromination of Aromatic Bromides Catalyzed by Unsupported Nanoporous Gold: Heterolytic Cleavage of Hydrogen Molecule

Abstract

Unsupported nanoporous gold (AuNPore) is a highly efficient, practically applicable, and recyclable catalyst for hydrodebromination of aromatic bromides. The AuNPore-catalyzed hydrodebromination of aromatic bromides proceeded smoothly at relatively low hydrogen pressure and temperature to achieve good to excellent yields of the corresponding non-bromine variants. The selective hydrodebromination reaction occurred exclusively in the coexistence of chlorine atom. For the first time, a mechanistic study revealed that the HÀ H bond splits in a heterolysis manner on the surface of AuNPore to generate AuÀ H hydride species.

Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry

“…However, all of these reactions are most likely more complex than merely involving a H 2 dissociation. The hydrodebromination, for instance, was performed in MeOH, and a substantial, quite similar turnover was detected even in the absence of H 2 . It is also notable that there was no reaction when no base was added, making it very likely that MeOH is being oxidized to formaldehyde, thus MeOH is the reductant.…”

“…It is also notable that there was no reaction when no base was added, making it very likely that MeOH is being oxidized to formaldehyde, thus MeOH is the reductant. Moreover, the reaction is not very tolerant of other functional groups: aldehydes, carbamates, and nitro groups get reduced and esters hydrolyze . In the other cases, it is not clear whether the solvent diethylamine was entirely innocent or, indeed, why triethylamine was used in the optimization reactions, whereas diethylamine was used in reactions in which the scope was explored .…”

“…Less reactive substrates like ketones, alkenes, quinolines, and aromatic nitro groups required ethanol as a solvent (Scheme B). A bit later, the same groups reported the hydrodebromination of aromatic bromides by NPG with H 2 (Scheme C) . This reaction is useful in that there are occasions in which the Br substituent is used to block a certain otherwise reactive site.…”

“…A bit later, the same groups reported the hydrodebromination of aromatic bromides by NPG with H 2 (Scheme 5C). 633 This reaction is useful in that there are occasions in which the Br substituent is used to block a certain otherwise reactive site. If it can be removed easily, it becomes a valuable protection group.…”

Unsupported Nanoporous Platinum–Iron Bimetallic Catalyst for the Chemoselective Hydrogenation of Halonitrobenzenes to Haloanilines

“…and Huang et al ., who demonstrated that Pt-based intermetallic nanoparticles have excellent catalytic selectivity, we prepared and used an unsupported nanoporous Pt–Fe bimetallic catalyst (PtFeNPore) for the chemoselective hydrogenation of HNBs. This study is based on our previous works for developing novel types of heterogeneous catalysts . The hydrogenation proceeded successfully, affording desired HANs in good to excellent yields with excellent selectivity when PtFeNPore was used as the catalyst (Scheme ).…”