Ni(II)-Catalyzed Transfer Hydrogenation of Azoarenes with NH₃BH₃

Abstract

A nickel-catalyzed semihydrogenation of azoarenes to hydrazoarenes with NH3BH3 is developed. The catalytic system exhibits good functional group tolerance and a high turnover frequency at room temperature. Results of control and deuterium-labeling experiments indicate that the ethanol hydroxyl and BH3 groups each donated one hydrogen to this transfer hydrogenation, and the main byproducts were B(OEt)3 and H2. Moreover, density functional theory calculations indicated that the reaction proceeded via a ligand-to-ligand hydrogen transfer mechanism. This study presents a novel nickel catalytic system for the semihydrogenation of azoarenes.

Transfer Hydrogenation of Azoarenes to Hydrazoarenes by Ammonia Borane Complex Catalyzed by Au Nanoparticles

“…AB [21] . With the exception of the Bi‐catalyzed process which requires 1 mol% of the catalyst and takes place under milder conditions, all other require excess of reducing agent, higher amounts of catalyst (5–10 mol%), heating, and prolonged reaction times [22] …”

“…[21] With the exception of the Bicatalyzed process which requires 1 mol% of the catalyst and takes place under milder conditions, all other require excess of reducing agent, higher amounts of catalyst (5-10 mol%), heating, and prolonged reaction times. [22] As noted earlier, our previous reports regarding the smooth Au/TiO 2 -catalyzed chemoselective reduction of a series of functional groups with AB (Scheme 1) urged us to examine the application of this system in the reduction of azoarenes. Au/TiO 2 is a readily available catalyst that can be obtained from commercial sources, does not require any special treatment, apart from the fact that it must be grinded in a mortar to become a fine dust prior to use, tolerates any solvent and can be used under ambient conditions.…”

Nanoarchitectonics of Non-Noble-Metal-Based Heterogeneous Catalysts for Transfer Hydrogenation Reactions: Detailed Insights on Different Hydrogen Sources

“…This characteristic enables AB to engage in transfer hydrogenation reactions with reduced energy consumption. Additionally, while using AB the majority of the byproducts of AB are water-soluble thus making it easy to separate target products from the reaction medium. − In the presence of transition metals, AB quickly produce hydrogen via hydrolysis, which is utilized for the hydrogenation reaction. One-pot tandem AB dehydrogenation and hydrogenation of unsaturated compounds offers a practical approach for producing useful compounds of high significance.…”

Cobalt-Catalyzed Borylative Reduction of Azobenzenes to Hydrazobenzenes via a Diborylated-Hydrazine Intermediate

“…Catalytic transfer hydrogenation of azo compounds with hydrogen donors other than H 2 is a promising alternative method that can provide unusual selectivity and avoids the need for a high pressure. Hydrogen sources such as alcohols, ammonia borane, hydrazine, and amine are commonly used as transfer hydrogenating reagents in catalytic transfer hydrogenation of azo compounds.…”