Theoretical, dynamic, and structural studies of the phenyl rotation in bispentafluorophenyl palladium complexes with scorpion-type ligands

Abstract

A theoretical study at a DFT level has been carried out on the pentafluorophenyl rotation in the compounds [Pd(C6F5)2(bpzmPh)] (1) and [Pd(C6F5)2(bpz*mPh)] (2) (bpzm = bis(pyrazol-1-yl)phenylmethane and bpz*mPh = bis(3,5-dimethylpyrazol-1-yl)phenylmethane). The orientation of one C6F5 with respect to the coordination plane was forced to adopt specific values to simulate ring rotation and several parameters, such as the disposition of the other C6F5 group, the energy of the system, and the skeletal conformation of the bpz'm ligand, were analysed. The maximum energy value was found when the C6F5 ring was nearly coplanar with the coordination plane. In both complexes the minimum energy corresponds to a situation where the two rings are nearly parallel. A number of distortions that mainly affect the NPdN bite angle were predicted for the complex containing the bpz*mPh ligand (methylated pyrazoles). Four structures of complexes from this family were determined by X-ray diffraction and the same types of distortion were found. The differences in the free energies of activation for the pentafluorophenyl rotation in complexes containing methylated and non-methylated ligands were theoretically calculated. The calculated values were consistent with the data experimentally determined by NMR spectroscopy. The origin of the difference was attributed to the aforementioned distortions of the complexes containing the bpz*mPh ligand, which were more remarkable in the configuration of maximum energy.Key words: N ligands, palladium, theoretical studies, DFT calculations, dynamics.