Ruthenium‐Catalyzed E‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source

Abstract

E‐alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium‐catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer‐hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer‐hydrogenation of alkynes. Optimization reactions showed the best results for the commercially available binuclear [Ru(p‐cymene)Cl2]2 complex as pre‐catalyst in combination with 2,2‐bis(diphenylphosphino)‐1,1‐binaphthyl (BINAP) as ligand (1 : 1 ratio per Ru monomer to ligand). Mechanistic investigations showed that the origin of E‐selectivity in this reaction is the fast Z to E isomerization of the formed alkenes. Mild reaction conditions plus the use of cheap, easily available and safe materials as well as simple setup and inexpensive catalyst turn this protocol into a feasible and promising stereo complementary procedure to the well‐known Z‐selective Lindlar reduction in late‐stage syntheses. This procedure can also be used for the production of deuterated alkenes simply using d2‐paraformaldehyde and D2O mixtures.

One-Pot Rapid Access to Benzyl Silanes, Germanes, and Stannanes from Toluenes Mediated by a LiN(SiMe3)2/CsCl System

“…One resonance was not observed due to overlapping resonances. The spectroscopic data for this product match the literature …”

“…The spectroscopic data for this product match the literature. 45 1,1,1-Triethyl-N,N-bis(trimethylsilyl)silanamine (E). To an ovendried round bottom flask (100 mL) equipped with a fusiform stir bar (30 × 10 mm) under an argon atmosphere inside a glovebox were added LiN(SiMe 3 ) 2 (2.51 g, 15.0 mmol), CsCl (1.68 g, 10.0 mmol), THF (25 mL), and TESCl (0.84 mL, 5 mmol).…”

E-Selective Manganese-Catalyzed Semihydrogenation of Alkynes with H2 Directly Employed or In Situ-Generated

“…Thus far, traditional systems for the selective formation of Z -, E -, or terminal alkenes consist of Pd/C, Lindlar catalyst, Birch reduction, Raney nickel, or Wilkinson catalyst . Because of limitations regarding selectivity, activity, amount of produced waste, or catalyst price, the study and improvement of these protocols has attracted numerous research groups in academia and industry. ,, Thus, high activity and excellent selectivity-tailoring is being achieved by combining fine-tuned ligands with noble metals such as Ru, Rh, Pd, and Ir . During the last decade, the concerns with regard to green chemistry principles have been grown rapidly, and the development of catalysts based on earth-abundant metals for organic transformations has become very important .…”

Manganese-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes with iPrOH as hydrogen source

“…The stereoselective semihydrogenation of alkynes to both Z - and E -olefins is relevant since these are valuable building blocks, with defined configurations, for the synthesis of organic compounds with academic and industrial applications. 3 Hence, many stoichiometric and catalytic systems have been reported for this type of transformations, with most of them usually based on late transition metals such as Ir, 4 Rh, 5 Ru, 6 and Pd. 7 Despite the high activity of noble metals in hydrogenations, due to matters of economy, sustainability and toxicity, efforts have been made in the last decade to develop catalytic processes based on first-row transition metals ( e.g.…”