Multifaceted role of silver salts as ligand scavengers and different behavior of nickel and palladium complexes: beyond halide abstraction

Abstract

The reaction of [NiArBr(PPh3)2] with AgBF4 brings about the abstraction of both the halide and phosphine from the nickel center by silver. When the reaction is carried out in CH2Cl2/toluene a mixture of the cat- ionic aquo derivatives [NiAr(H2O)(PPh3)2]BF4 (2) and [NiAr(H2O)2(PPh3)]BF4 (3) is formed, along with AgBr and [Ag(PPh3)n]BF4. When the same reaction is carried out in acetone as the solvent, it leads to the com- pletely different complex [NiAr(κ2-O, O–MeC(O)CH2C(OH)Me2)(PPh3)] (5), bearing a chelating ligand formed by the aldol self-condensation of acetone. Phosphine abstraction by silver is less favorable for the analogous palladium(II) complexes and only occurs if a large excess of AgBF4 is used. Thus, silver salts can be safely used as halide scavengers for palladium derivatives. However, the generation of cationic Ni com- plexes from neutral precursors by halide extraction with a silver salt may produce naked species, different than those expected, and highly reactive in certain media