Pd-II anionic, square planar complexes of the type [IL](2)[PdX4], where IL = imidazolium cations, X = Cl, Br, have been applied for the first time as catalyst precursors for the Suzuki-Miyaura (S-M) reaction carried Out in alcohols at 40 C. Depending on the structure of the catalyst precursor used, different yields of 2-methylbiphenyl (2-MePh-Ph) were obtained in a test reaction of 2-bromotoluene (2-MePhBr) with phenyl boronic acid (PhB(OH)(2)). The highest yield, ca. 95%, was obtained for [dmiop](2)[PdCl4] (dmiop-1,2-dimethyl-3-propoxymethylene imidazolium cation) in methanol in the presence of KOH as a base. It was found that during the reaction Pd-0 nanoparticles of 4-7 nm have been formed in situ from the palladium(II) precursor. In the first stage of this process, [(IL)(3)Pd(OH)(2)](+)-type species have been formed from [IL](2)[PdX4] precursors. Small Pd-0 clusters, [(IL)(5)Pd-3(H2O)](+) and [(IL)(3)Pd-3(H2O)(7)](+), were also identified by ESI-MS. These species reacted with ArB(OH)(2) forming palladium aryl complexes of the type [(IL)(2)PdAr](+), key intermediates in the catalytic process. The first experimental evidence of the IL stabilized No species in S-M reaction is presented. (C) 2009 Elsevier B.V. All rights reserved.