Synthesis and characterization of Pd/NHC complexes with fluorinated aryl groups.

The key problem of the instability of fluorine-containing diazadienes was addressed to perform the efficient synthesis of imidazolium salts containing fluorine substituents in the aryl groups. The subsequent reaction of fluorine-containing imidazolium compounds (NHC) with palladium salts under simple conditions afforded new Pd/NHC complexes. Computational and structural studies were performed to assess the effect of fluorine on the Pd-NHC bond and gave insight into the electronic effects in the molecule. The introduction of fluorine substituents into the aryl rings of the NHC ligands leads to a slight decrease in their σ-donor properties. At the same time, there is a slight increase in the π-acceptor capacity of NHC. These two effects compensate for each other, so that the Pd-NHC bonding energy remains virtually unchanged. Another observed effect is associated with a slight weakening of the influence of the NHC ligands, which is expressed in the strengthening of the Pd-Solv bond in (NHC)Pd(Solv) complexes. For the first time, a series of novel Pd/NHC complexes were synthesized a straightforward approach from fluorine-containing anilines.