4.8 Article

The site-selectivity and mechanism of Pd-catalyzed C(sp2)-H arylation of simple arenes

期刊

CHEMICAL SCIENCE
卷 12, 期 1, 页码 363-373

出版社

ROYAL SOC CHEMISTRY
DOI: 10.1039/d0sc05414c

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资金

  1. National Research Foundation of Korea (Center for New Directions in Organic Synthesis) [NRF-2019R1A2C2086875, NRF-2014R1A5A1011165]
  2. Korea Institute of Science and Technology Information [KSC-2018-CHA-0068, KSC-2019-CRE-0182]
  3. National Research Foundation of Korea [NRF-2018R1D1A1B07049976]

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The site-selectivity of Pd-catalyzed direct C-H arylation reaction of simple arenes is influenced by the electronic properties of the arenes, with electron-rich arenes preferring meta-arylation and electron-deficient arenes preferring ortho-arylation. Mechanistic investigations revealed that the reaction operates through a cooperative bimetallic mechanism rather than the originally proposed monometallic CMD mechanism, with the transmetalation step suggested as the selectivity-determining step.
Control over site-selectivity is a critical challenge for practical application of catalytic C-H functionalization reactions in organic synthesis. Despite the seminal breakthrough of the Pd-catalyzed C(sp(2))-H arylation of simple arenes via a concerted metalation-deprotonation (CMD) pathway in 2006, understanding the site-selectivity of the reaction still remains elusive. Here, we have comprehensively investigated the scope, site-selectivity, and mechanism of the Pd-catalyzed direct C-H arylation reaction of simple arenes. Counterintuitively, electron-rich arenes preferably undergo meta-arylation without the need for a specifically designed directing group, whereas electron-deficient arenes bearing fluoro or cyano groups exhibit high ortho-selectivity and electron-deficient arenes bearing bulky electron-withdrawing groups favor the meta-product. Comprehensive mechanistic investigations through a combination of kinetic measurements and stoichiometric experiments using arylpalladium complexes have revealed that the Pd-based catalytic system works via a cooperative bimetallic mechanism, not the originally proposed monometallic CMD mechanism, regardless of the presence of a strongly coordinating L-type ligand. Notably, the transmetalation step, which is influenced by a potassium cation, is suggested as the selectivity-determining step.

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