Mechanism of the carbopalladation of alkynes by aryl-palladium complexes

The reaction between trans-PhPdI(PPh3)2 and EtO2C–Ctriple bond; length of mdashCH has been investigated. This carbopalladation step involved in palladium-catalyzed multicomponent reactions with alkynes gives the unusual trans-adduct EtO2C–C(PdIL2)double bond; length as m-dashCHPh 1 as the major complex formed by isomerization of the primary cis-adduct EtO2C–C(PdIL2)double bond; length as m-dashCHPh 2. The carbopalladation was regiospecific. A multicarbopalladation was also observed by successive carbopalladation of EtO2C–Ctriple bond; length of mdashCH by the vinyl-palladium complexes themselves generated in carbopalladation steps, leading to cationic complexes.