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

The reaction of [NiArBr(PPh 3 ) 2 ] with AgBF 4 brings about the abstraction of both the halide and phosphine from the nickel center by silver. When the reaction is carried out in CH 2 Cl 2 /toluene a mixture of the cationic aquo derivatives [NiAr(H 2 O)(PPh 3 ) 2 ]BF 4 (2) and [NiAr(H 2 O) 2 (PPh 3 )]BF 4 (3) is formed, along with AgBr and [Ag(PPh 3 ) n ]BF 4 . When the same reaction is carried out in acetone as the solvent, it leads to the completely different complex [NiAr(κ 2 -O, O-MeC(O)CH 2 C(OH)Me 2 )(PPh 3 )] (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 AgBF 4 is used. Thus, silver salts can be safely used as halide scavengers for palladium derivatives. However, the generation of cationic Ni complexes from neutral precursors by halide extraction with a silver salt may produce naked species, different than those expected, and highly reactive in certain media.