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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. [ABSTRACT FROM AUTHOR]

Differential selectivity in the competitive Heck reaction with aromatic carboxylic anhydrides has been found to depend on the nature of both the cation and anion of a salt used as an additive for the catalytic system. This fact indicates that the anions present in the system are involved in active anionic species. [ABSTRACT FROM AUTHOR]