Parts-Per-Million of Soluble Pd⁰ Catalyze the Semi-Hydrogenation Reaction of Alkynes to Alkenes

Abstract

The synthesis of cis-alkenes is industrially carried out by selective semi-hydrogenation of alkynes with complex Pd catalysts, which include the Lindlar catalyst (PdPb on CaCO3) and c-Pd/TiS (colloidal ligand-protected Pd nanoparticles), among others. Here, we show that Pd0 atoms are generated from primary Pd salts (PdCl2, PdSO4, Pd­(OH)2, PdO) with H2 in alcohol solutions, independently of the alkyne, to catalyze the semi-hydrogenation reaction with extraordinarily high efficiency (up to 735 s–1), yield (up to 99%), and selectivity (up to 99%). The easy-to-prepare Pd0 species hold other potential catalytic applications.

Parametrization of Catalytic Organic Reactions with Convex Hammett Plots

“…Figure shows the Hammett plot for the Pd-catalyzed semi-hydrogenation reaction of different terminal alkynes to alkenes . Three different Pd catalysts were used: the current industrial Lindlar (Pd–Pb nanoparticles supported on CaCO 3 ) catalyst, a commercially available BASF colloidal Pd nanoparticulated catalyst (c-Pd/TiS), and a house-made catalyst composed of ultrasmall Pd clusters on CaCO 3 nanoparticles [Pd–(CaCO 3 ) n ]. , The latter combines the chemical composition of the Lindlar catalyst (Pd on CaCO 3 sites) with the nanoparticulated structure of the c-Pd/TiS catalyst, free of Pb, confirmed by electron microscopy imaging (Figures S3–S5). The points in the Hammett plots were replicated three times in order to properly assess any experimental error, and the catalytic amount of Pd was adjusted for each catalyst between 0.0001 and 0.01 mol % in order to precisely measure the initial rate for all of the substrates under the same reaction conditions.…”

Solid-catalyzed synthesis of isomers–free terpinen–4–ol

“…Zeolites are also commercially available or prepared by standard methods. [36,37] SnPt-SiO 2 was prepared following a 5-step reported procedure, [19] which consists in the incorporation of Pt on high surface area silica by exchange, calcination, incorporation of Sn by impregnation of an organostannane compound in organic solvent, evaporation of the solvent and treatment of the resulting solid on H 2 atmosphere at 200 • C. Pd-charcoal and Pd-Lindlar´s catalyst are commercially available or prepared by standard methods [38,39]. Ti 3+ -enriched nTiO 2 was prepared by the ethanol method [40].…”

“…The results are shown in Fig. 3, using different inorganic oxides of general formula MOx (TiO 2 , Al 2 O 3 , ZrO 2 , Fe 2 O 3 ) [29][30][31], also with supported transition metals (M-TiO 2 , M= Fe, Ru, Pd, Pt, Cu, Au; M-Al 2 O 3 , M= Ru, Pd, Au; and M-ZrO 2 , M= Fe, W); [35][36][37][38] bimetallics (SnPt-SiO 2 and CeZrO 2 ); [19] and Pd-charcoal and Pd-Lindlar´s catalyst as commercially-available hydrogenating catalysts [38,39]. Reaction tests were performed with 1 M solutions of 2 under two different reaction conditions: at 50 • C (solvent MeOH) and at 120 • C (solvent o-xylene) for 1-5 h reaction time.…”

Indomuscone-Based Sterically Encumbered Phosphines as Ligands for Palladium-Catalyzed Reactions

“…The semi-hydrogenation reaction of 18 proceeds with the best selectivity if the Pd/C catalyst (0.01 mol %) is treated with JohnPhos 1d, 26 SPhos 1e, 10a) or phosphine 2b (0.02 mol %) due to their ability to prevent the alkene to alkane reaction while enabling the desired semi-hydrogenation of 18. Phosphines 2a and 1a are selective as well but hinder the semi-hydrogenation rates.…”