Five Different Fluxional Processes in Polyfluorophenyl Palladium(II) Complexes with 2,4,6-Tris(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine. The Driving Effect of the Solvent

The polydentate N-donor ligand 2,4,6-tris(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine (Me2-TpzT) has been used to synthesize the new palladium derivatives Pd(R)2(Me2-TpzT), R = C6F5, 1; R = m-C6ClF4, 2. In the case of complex 2, four different atropisomers have been detected at low temperature. The new complexes exhibit a rich dynamic behavior, including three metallotropic processes (metal-hurdling, 1,4-metallotropic shifts, and an intermolecular process) and two processes involving restricted rotation of aromatic rings (the polyfluorophenyl groups and the uncoordinated pyrazole group adjacent to the metal fragment). The fluxional behavior has been studied by 1H and 19F NMR spectroscopy using variable temperature NMR studies and 1H,1H and 19F,19F EXSY experiments. The study of solutions of 2 in 1,1‘,2,2‘-tetrachloroethane-d 2 gave the following order for the free energy of activation: pyrazole rotation < 1,4-metallotropic shift < intermolecular exchange < polyfluorophenyl rotation. The process of metal hurdling was not found in this solvent. However, in acetone-d 6 such a process was detected and was found to be of lower energy than the 1,4-metallotropic shift. In dilute acetone-d 6 or 1,1‘,2,2‘-tetrachloroethane-d 2 solutions, the intermolecular process was not observed. Conclusions concerning the different mechanisms have been deduced from the data obtained.