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

oleh: Eskedar Tessema, Vijayanath Elakkat, Chiao-Fan Chiu, Zong-Lin Tsai, Ka Long Chan, Chia-Rui Shen, Han-Chang Su, Norman Lu

Format: Article
Diterbitkan: MDPI AG 2021-03-01

Deskripsi

The reaction of [PdCl<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>] and bis-4,4′-(R<sub>f</sub>CH<sub>2</sub>OCH<sub>2</sub>)-2,2′-bpy (<b>1a–d</b>), where R<sub>f</sub> = <i>n</i>-C<sub>11</sub>F<sub>23</sub> (<b>a</b>), <i>n</i>-C<sub>10</sub>F<sub>21</sub> (<b>b</b>), <i>n</i>-C<sub>9</sub>F<sub>19</sub> (<b>c</b>) and <i>n</i>-C<sub>8</sub>F<sub>17</sub> (<b>d</b>), respectively, in the presence of dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>) resulted in the synthesis of Pd complex, [PdCl<sub>2</sub>[4,4′-bis-(R<sub>f</sub>CH<sub>2</sub>OCH<sub>2</sub>)-2,2′-bpy] (<b>2a–d</b>). The Pd-catalyzed Stille arylations of vinyl tributyltin with aryl halides were selected to demonstrate the feasibility of recycling usage with <b>2a</b> as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent at 120–150 °C. Additionally, recycling and electronic effect studies of <b>2a–c</b> were also carried out for Suzuki-Miyaura reaction of phenylboronic acid derivatives, 4-X-C<sub>6</sub>H<sub>4</sub>-B(OH)<sub>2</sub>, (X = H or Ph) with aryl halide, 4-Y-C<sub>6</sub>H<sub>4</sub>-Z, (Y = CN, H or OCH<sub>3</sub>; 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 <b>2a</b>-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, <b>2a–c</b>-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.