Synthesis and characterization of organopalladium complexes containing a fluoro ligand

The synthesis of organopalladium complexes containing a fluoro ligand, [(Ph3P)(2)Pd(F)R], is described. Two general synthetic strategies have been developed: (i) neutralization of hydroxo palladium dimers, [(Ph3P)(2)Pd-2(R)(2)(mu-OH)(2)] (R = Me or Ph), with TREAT HF ([(HF)(3) . NEt3]) in the presence of PPh3 and (ii) the ultrasound-promoted exchange between [(Ph3P)(2)Pd(I)R] and AgF in benzene. It is essential for the synthesis with TREAT HF that no excess of the HF source is used; otherwise, the corresponding bifluorides, [(Ph3P)(2)Pd-(FHF)R], are formed instead. Conducting the I/F exchange in the presence of 5-10% of the corresponding organic iodide, RI, is beneficial for purity of the desired fluoro complexes. All complexes 1-10 have been fully characterized by a variety of methods. The fluoro ligand in [(Ph3P)(2)Pd(F)R] is inert in anhydrous media of low polarity. However, in the presence of trace amounts of water, F ligand exchange is observed. No irreversible hydrolysis of the Pd-F bond takes place as [(Ph3P)(2)Pd(F)R] remains the only observable (NMR) species in the system. VT NMR studies of various [(Ph3P)(2)Pd(F)R] in CH2Cl2 saturated with water have been conducted, revealing a push/pull-type, "ambiphilic" mechanism of the H2O-promoted F ligand-exchange process. The Pd-F bond cleavage likely involves nucleophilic attack of water on the metal center, concomitantly occurring with the formation of a hydrogen bond between the fluoro ligand and H2O.