Anionic Pd(0) and Pd(II) intermediates in palladium-catalyzed Heck and cross-coupling reactions

The anions of PdCl2L2 and Pd(OAc)(2), precursors of palladium(0) used in cr oss-coupling and Heck reactions, play a crucial role in these reactions. Tr icoordinated anionic complexes (PdL2Cl-)-L-0 and (PdL2)-L-0(OAc)(-) are the effective catalysts instead of the usually postulated (PdL2)-L-0 complex. The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as well as the structure and reactivity of the arylpalladi um(II) complexes produced in this reaction. Thus, pentacoordinated anionic complexes are formed, ArPdI(CI)L-2(-) or ArPdI(OAC)L-2(-), the precursor of neutral trans-ArPd(OAc)L-2, instead of the usually postulated trans-ArPdIL 2 complex (L = PPh3).