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Decelerating Effect of Alkynes in the Oxidative Addition of Phenyl Iodide to Palladium(0) Complexes in Palladium‐Catalyzed Multicomponent Reactions and Sonogashira Reactions
Author(s) -
Amatore Christian,
Bensalem Samia,
Ghalem Said,
Jutand Anny,
Medjour Youcef
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200300618
Subject(s) - chemistry , transmetalation , palladium , oxidative addition , sonogashira coupling , alkyne , medicinal chemistry , catalysis , iodide , reductive elimination , oxidative phosphorylation , reagent , catalytic cycle , organic chemistry , biochemistry
The oxidative addition of PhI to [Pd 0 (PPh 3 ) 4 ] in DMF is slower when performed in the presence of the terminal alkynes (PhC≡CH, EtO 2 C−C≡CH) that are reagents in palladiumcatalyzed Sonogashira or multicomponent reactions. The concentration of the reactive [Pd 0 (PPh 3 ) 2 ] complex decreases because of its partial coordination to the alkyne to form [(η 2 ‐RC≡CH)Pd 0 (PPh 3 ) 2 ] (R = Ph, EtCO 2 ), which is in equilibrium with [Pd 0 (PPh 3 ) 2 ]. The complex [(η 2 ‐PhC≡CH)Pd 0 (PPh 3 ) 2 ] was found to be unreactive whereas [(η 2 ‐EtO 2 C− C≡CH)Pd 0 (PPh 3 ) 2 ] was found to be the unique reactive complex at high concentrations of EtO 2 C−C≡CH. As has been reported for alkenes, terminal alkynes play an unexpected role because they interfere in the oxidative addition before their usual reactions in the carbopalladation and transmetallation steps that follow it. Decreasing the rate of the fast oxidative addition with PhI may promote the efficiency of the catalytic cycle by bringing its rate closer to that of the slower carbopalladation or transmetallation steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)