Recoverable Palladium-Catalyzed Carbon-Carbon Bond Forming Reactions under Thermomorphic Mode: Stille and Suzuki-Miyaura Reactions

Abstract

The reaction of [PdCl2(CH3CN)2] and bis-4,4’-(RfCH2OCH2)-2,2’-bpy (1a–d), where Rf = n-C11F23 (a), n-C10F21 (b), n-C9F19 (c) and n-C8F17 (d), respectively, in the presence of dichloromethane (CH2Cl2) resulted in the synthesis of Pd complex, [PdCl2[4,4’-bis-(RfCH2OCH2)-2,2’-bpy] (2a–d). The Pd-catalyzed Stille arylations of vinyl tributyltin with aryl halides were selected to demonstrate the feasibility of recycling usage with 2a as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent at 120–150 °C. Additionally, recycling and electronic effect studies of 2a–c were also carried out for Suzuki-Miyaura reaction of phenylboronic acid derivatives, 4-X-C6H4-B(OH)2, (X = H or Ph) with aryl halide, 4-Y-C6H4-Z, (Y = CN, H or OCH3; Z = I or Br) in dimethylformamide (DMF) at 135–150 °C. At the end of each cycle, the product mixtures were cooled to lower temperature (e.g., −10 °C), and then catalysts were recovered by decantation with Pd leaching less than 1%. The products were quantified by gas chromatography/mass spectrometry (GC/MS) analysis or by the isolated yield. The complex 2a-catalyzed Stille reaction of aryl iodides with vinyl tributyltin have good recycling results for a total of 8 times, with a high yield within short period of time (1–3 h). Similarly, 2a–c-catalyzed Suzuki-Miyaura reactions also have good recycling results. The electronic effect studies from substituents in both Stille and Suzuki-Miyaura coupling reactions showed that electron withdrawing groups speed up the reaction rate. To our knowledge, this is the first example of recoverable fluorous long-chained Pd-catalyzed Stille reactions under the thermomorphic mode.

Palladium-catalyzed Suzuki–Miyaura cross-coupling with α-aminophosphonates based on 1,3,4-oxadiazole as ligands

“…Interestingly, several nitrogenated ligands have been also employed for the Suzuki-Miyaura cross-coupling. We can quote for example the use of Schiff bases [44][45][46][47][48][49][50], amines [51,52], azo compounds [53], pyridines [54][55][56][57][58], pyrimidines [59,60], triazoles [61] or benzimidazoles [62]. However, despite their relevance, these catalytic systems suffer from one or more drawbacks such as the use of expensive or difficultly accessible ligands, as well as high catalyst loading, hazardous solvents and harsh reaction conditions.…”