Is the Mechanistic Scheme of the Heck‐Type Coupling with Unsaturated Substrates needed to be revised?

• Published in: ChemCatChem Vol. 12; no. 21; pp. 5523 - 5533
• Main Authors: Schmidt, Alexander F., Kurokhtina, Anna A., Larina, Elizaveta V., Vidyaeva, Elena V., Schmidt, Elena Yu, Lagoda, Nadezhda A.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 05.11.2020
• Subjects: Aromatic compounds; Chemical reactions; Coupling; C−H activation; Halides; Heck reaction; Indoles; palladium; reaction mechanism; Regioselectivity; Selectivity; Substrates
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.202000925

Patterns of differential selectivity of two competing unsaturated substrates along with differential regioselectivity of α‐ and β‐regioisomers of arylated products formed in Heck reactions with aryl halides or with aromatic carboxylic anhydrides as well as differential regioselectivity of C2‐ and C3‐arylated indoles in direct C−H arylation with aryl halides unambiguously evidence that the commonly accepted mechanistic scheme of unsaturated substrate activation the Heck‐type coupling reactions needs to be revised. Comprehensive kinetic study points to the activation of aryl halide and unsaturated substrate by two distinct Pd species, as well as existence of an additional intermediate of their catalytic cycles being not taken into consideration earlier in the mechanistic schemes of the reactions. Comprehensive kinetic study of Heck and related reactions points to the activation of aryl halide and unsaturated substrate by two distinct Pd species, as well as existence of an additional intermediate of their catalytic cycles being not taken into consideration earlier in the mechanistic schemes of the reactions