Dual role of nucleophiles in palladium-catalyzed Heck, Stille, and
Sonogashira reactions
A. Jutand
École Normale Supérieure, Département
de Chimie, UMR CNRS-ENS-UPMC
8640, 24 Rue Lhomond, F-75231,Paris Cédex 5, France
Abstract: In palladium-catalyzed Heck, Stille, or Sonogashira
reactions, the nucleophiles-respectively, alkenes, vinylstannanes, or
alkynes-are involved in carbopalladation or transmetallation steps that
follow the oxidative addition of an aryl halide or triflate to a Pd0
complex. As soon as the nucleophiles possess a C=C or a C 'triple-bond'
C bond capable of coordinating the Pd0 complex active in
the oxidative addition, they play a dual role since they interfere in
the oxidative addition by a decelerating effect due to a partial coordination
of the active Pd0 complex. Indeed, its concentration decreases
due to the formation of either unreactive complexes (η²-RCH=CH2)Pd0L2
(R = Ph, CO2Et, L = PPh3 ; R = Bu3Sn,
L = AsPh3), (η²-RCH=CH2)Pd0L2(OAc)-
(R = Ph, L = PPh3), (η²-R-C 'triple-bond' CH)Pd0L2
(R = Ph, L = PPh3) or more slowly reactive complexes (η²-R-C
'triple-bond' CH)Pd0L2 (R = CO2Et,
L = PPh3), (η²-RCH=CH2)Pd0L2
(R= CO2Me, L2 = dppf). Whenever the oxidative
addition is faster than the ensuing carbopalladation or transmetallation,
the decelerating effect of the nucleophiles in the oxidative addition
is in favor of a better efficiency for the catalytic cycle by bringing
the rate of the fast oxidative addition closer to that of the slow carbopalladation
or transmetallation steps.
[full text - pdf 304KB]
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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