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

The reaction of [PdCl(2)(CH(3)CN)(2)] and bis-4,4′-(R(f)CH(2)OCH(2))-2,2′-bpy (1a–d), where R(f) = n-C(11)F(23) (a), n-C(10)F(21) (b), n-C(9)F(19) (c) and n-C(8)F(17) (d), respectively, in the presence of dichloromethane (CH(2)Cl(2)) resulted in the synthesis of Pd complex, [PdCl(2)[4,4′-bis-(R(f)CH(2)OCH(2))-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-C(6)H(4)-B(OH)(2), (X = H or Ph) with aryl halide, 4-Y-C(6)H(4)-Z, (Y = CN, H or OCH(3); 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.