IDENTIFICATION OF THE EFFECTIVE PALLADIUM(0) CATALYTIC SPECIES GENERATED IN-SITU FROM MIXTURES OF PD(DBA)(2) AND BIDENTATE PHOSPHINE-LIGANDS - DETERMINATION OF THEIR RATES AND MECHANISM IN OXIDATIVE ADDITION

Mixtures of Pd(dba)(2) + 2L-L (where L-L is a bidentate ligand such as dppm, dppe, dppp, dppb, dppf, and DIOP) lead to the formation of Pd(L -L)(2) complexes which do not undergo an oxidative addition with pheny l iodide. Mixtures of Pd(dba)(2) + 2 BINAP do not afford Pd(BINAP)(2) but Pd(dba)(BINAP). Mixtures of Pd(dba)(2) + 1L-L (L-L = dppm, dppe, d ppp, dppb, dppf, DIOP, and BINAP) lead to Pd(dba)(L-L) complexes via t he formation, at short time, of the complex Pd(L-L)(2), except for dpp f and BINAP where the complex Pd(dba)(L-L) is directly formed. Pd(dba) (L-L) is the main complex in solution but is involved in an endergonic equilibrium with the less ligated complex Pd(L-L) and dba. Pd(L-L) is the more reactive species in the oxidative addition with phenyl iodid e. However, Pd(dba)(L-L) also reacts in parallel with phenyl iodide. F rom the kinetic data concerning the reactivity of these different cata lytic systems in the oxidative addition with phenyl iodide, one observ es the following order of reactivity: Pd(dba)(2) + 1DIOP > Pd(dba)(2) + 1dppf >> Pd(dba)(2) + 1BINAP. All these systems associated to one bi dentate ligand are less reactive than Pd(dba)(2) + 2PPh(3).