Evidence of the reversible formation of cationic pi-allylpalladium(II) complexes in the oxidative addition of allylic acetates to palladium(0) complexes
C. Amatore et al., Evidence of the reversible formation of cationic pi-allylpalladium(II) complexes in the oxidative addition of allylic acetates to palladium(0) complexes, CHEM-EUR J, 5(2), 1999, pp. 466-473
It has been established that the oxidative addition of allylic acetate with
the palladium(o) complex, generated from a mixture of Pd(dba)(2) + 2PPh(3)
, affords a cationic pi-allylpalladium(Ii) complex. This reaction is revers
ible and proceeds through at least two successive equilibria. The overall e
quilibrium constant has been determined in THF and DME The acetate ion does
not act as a simple leaving group, but plays the role of a nucleophile abl
e to react with cationic pi-allylpalladium(Ii) complexes to reproduce the a
llylic acetate; a process that may be responsible for the racemization of c
hiral allylic acetates. In DMF, no significant ion pairing occurs and free
ions are formed. On the other hand, in THF almost complete ion pairing occu
rs and almost no free ions are produced.