Reduction of the Diazo Functionality of α-Diazocarbonyl Compounds into a Methylene Group by NH3BH3 or NaBH4 Catalyzed by Au Nanoparticles

Abstract

Supported Au nanoparticles on TiO2 (1 mol%) are capable of catalyzing the reduction of the carbene-like diazo functionality of α-diazocarbonyl compounds into a methylene group [C=(N2) → CH2] by NH3BH3 or NaBH4 in methanol as solvent. The Au-catalyzed reduction that occurs within a few minutes at room temperature formally requires one hydride equivalent (B-H) and one proton that originates from the protic solvent. This pathway is in contrast to the Pt/CeO2-catalyzed reaction of α-diazocarbonyl compounds with NH3BH3 in methanol, which leads to the corresponding hydrazones instead. Under our stoichiometric Au-catalyzed reaction conditions, the ketone-type carbonyls remain intact, which is in contrast to the uncatalyzed conditions where they are selectively reduced by the boron hydride reagent. It is proposed that the transformation occurs via the formation of chemisorbed carbenes on Au nanoparticles, having proximally activated the boron hydride reagent. This protocol is the first general example of catalytic transfer hydrogenation of the carbene-like α -ketodiazo functionality.

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

“…Our group was the first to use NH 3 BH 3 as an efficient reducing agent of nitroarenes into anilines catalyzed by Au nanoparticles supported on titania (Au/TiO 2 ), [4] and later in the selective cis ‐semihydrogenation of alkynes [5] . More recently, we have reported the reduction of the diazo functionality of α‐diazocarbonyl compounds into a methylene group [6] by the same system (Scheme 1). The above‐mentioned reductive transformations occur in protic solvents, such as ethanol or methanol, which act as proton donors, while borane moiety as hydride donor.…”

Au nanoparticle-catalyzed double hydrosilylation of nitriles by diethylsilane

“…Given that hydrosilanes and ammonia borane complex (NH 3 BH 3 ) can be readily activated by supported Au(0) nanoparticles and other nano Au-based materials (Au NPs), 20 we attempted to study their ability to reduce nitriles in the presence of Au/TiO 2 , a readily available and widely used catalyst in our lab. So far, hydrosilanes have been used under Au(0)-catalysis conditions as reducing agents of aldehydes/ketones, 21 imines, 22 amides, 23 nitro compounds, 24 quinolines, 25 and diazo compounds, 26 while ammonia borane for nitro compounds, 27 α-diazocarbonyl compounds, 28 and more recently to azoarenes. 29…”