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Insights into the Base-Assisted Acrylate Formation from CO/CH Coupling by Pd- and Ni-catalyst: A DFT Mechanistic Study

ChemCatChem, ISSN: 1867-3899, Vol: 10, Issue: 24, Page: 5669-5678
2018
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Metrics Details

  • Citations
    11
    • Citation Indexes
      11
  • Captures
    10

Article Description

In this work, seven base-assisted reaction paths were designed focusing on the rate-determining metallalactone deprotonation process to further promote our understanding on nickel- and palladium-catalyzed acrylate formation by CO/CH coupling in the presence of bases. The deprotonation efficiency of the bases was in accordance to the corresponding basicity, with stronger bases showing higher activity. Besides, a novel two-step β-H elimination mechanism through directly deprotonating the β-H agostic intermediate formed from the metallalactone cleavage proved to be most promising in both the nickel and palladium systems. Whereas the literature-suggested direct β-H elimination of the distorted five-membered ring was relatively inferior. Meanwhile, the high H-rotation energy barriers hindered the emerging of the cation-stabilized four-membered lactone. The effects of the ligand properties appeared to be different in the nickel and palladium systems, since the dcpe (1,2-bis(dicyclohexylphosphino)ethane) ligand facilitated the Pd-catalyzed β-H elimination yet showed minute influence in the Ni-system. In addition, the palladium center was more active than the nickel center under bulky environment during the base-assisted β-H elimination, while the nickel center behaved better in less hindered surroundings, owning to the high sensitivity of the nickel center towards the steric factor.

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