Issue in Honor of Prof. Marcial Moreno-Mañas ARKIVOC 2002 (v) 92-101
Effect of the leaving group and the allylic structure on the kinetics and thermodynamics of the reaction of allylic carboxylates with palladium(0) complexes
Nicolas Agenet, Christian Amatore,* Sophie Gamez, Hadia Gérardin, Anny Jutand,* Gilbert Meyer, and Céline Orthwein
Ecole Normale Supérieure, Département de Chimie, UMR CNRS 8640, “PASTEUR“ 24 Rue Lhomond, F-75231 Paris, Cedex 5, France E-mail:
[email protected];
[email protected]
Dedicated to Professor M. Moreno-Mañas on the occasion of his 60th birthday (received 20 Dec 01; accepted 06 Mar 02; published on the web 14 Mar 02)
Abstract
The reaction of allylic carboxylates (allyl-OZ, OZ: acetate, chloroacetate, trifluoroacetate, substituted benzoates, carbonate) with Pd0 complexes ligated by monodentate (PPh3) or bidentate (dppb, dppf) ligands is a reversible multistep reaction, which eventually gives in DMF a cationic (.3-allyl)PdII(P P)+ complex with ZO- as the counter anion (free ions). The formation of an intermediate neutral complex (.2-allyl-OZ)Pd0(P P) where the Pd0 is ligated to the C=C bond of the allylic carboxylate (complexation step) has been evidenced kinetically in the case of moderate OZ leaving groups (acetate, benzoates) for monodentate and bidentate phosphine ligands. The overall equilibrium constants and the rate constants of the complexation and oxidative addition-ionization steps (when not too fast) have been determined in DMF. With very good leaving groups (carbonate, trifluoroacetate), the oxidative addition-ionization step is faster than the complexation step whereas the oxidative addition-ionization step is the slowest step for less good leaving groups (acetate, benzoate). The forward rate constant of the equilibrium in which the active Pd0(PPh3)2 is formed from Pd0(dba)(PPh3)2 has been determined.
Keywords: Allylic carboxylate reactions, palladium(0)complexes, kinetics
Introduction
We have previously established that the reaction of the allyl acetate with Pd0(P P) complexes (first step of the Tsuji-Trost reactions)1 is reversible (P P represents either 2PPh3 or one bidentate bisphosphine ligand: dppf (1,1'-bis(diphenylphosphino)ferrocene), dppb (1,4bis( diphenyl)phosphinobutane).2-4 The reaction proceeds in two successive steps: reversible
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