Chemoselective C=O Hydrogenation of α,β-unsaturated Carbonyl Compounds over Quasihomogeneous and Heterogeneous Nano-Au0 Catalysts Promoted by Lewis Acidity

Abstract

Lewis-acid promoted Au 0 clusters were used as quasihomogeneous or as heterogeneous metal catalysts for the chemoselective hydrogenation of a,b-unsaturated carbonyl compounds. Addition of Lewis-acid cations like Zn 2+ to amidic dispersions of size-optimized Au 0 nanocolloids led to an enhanced hydrogenation rate and allylic alcohol chemoselectivity in the hydrogenation of e.g., crotonaldehyde (83% selectivity at 92% conversion). Heterogeneous Au 0 catalysts were generated by the quantitative immobilization of the Au 0 nanocolloids on a nanosized ZnO support, followed by partial removal of the polyvinylpyrrolidone stabilizer. This deposition preserved the nanodispersed state of Au 0 , and resulted in a heterogeneous metal catalyst with stable activity and high C=O chemoselectivity in e.g., the hydrogenation of mesityl oxide (66% selectivity at 91% conversion).

Recent Progress in Heterogeneous Catalysis by Atomically and Structurally Precise Metal Nanoclusters

“…Lewis acids are already known to stimulate Au nanoparticles catalyzed organic transformations [63] . However, the mechanistic understanding is still lacking.…”

Catalytic self-cleaning coatings for thermal oxidation of organic deposits on glass

“…Different methods were used for the synthesis of noble metal coatings and vanadia coatings. Nanocolloidal suspensions of Pt, Pd and Ag were prepared according to the procedure described by Mertens et al 4,5 0.1 g of polyvinylpyrrolidone (M W = 10 000) was dissolved in 4 ml ethanol. 0.1 mmol H 2 PtCl 6 Á6H 2 O, Pd(CH 3 COO) 2 or AgNO 3 were added to this solution, which was stirred for 2 h at room temperature until complete dissolution of the metal salt.…”

Tunable Pt nanocatalysts for the aerobic selox of cinnamyl alcohol

“…3 Heterogeneous catalysts capable of such chemoselective aerobic oxidation have thus attracted great interest, 4 wherein the co-existence of reactive H 2 C-OH and C]C moieties is a challenge to high allylic aldehyde selectivity. 5,6 Consequently, a fundamental understanding of the active site and reaction network is pivotal for improving catalyst design.…”