(P-Bis(pentafluorophenyl) substituted) PCP-pincer Ru(II) complexes: A theoretical study of the molecular structure and electronic properties

The differences between the molecular struturs of the PCP-pincer complex [RuCl{C6H3(CH2P(C6H5)2)2- 2,6}(PPh3)] ([RuCl(PCP H)(PPh3), 1) and its tetrakis-pentafluorophenyl substituted analogue [RuCl{C6H3(CH2P(C6F5)2)2- 2,6}(PPh3)] (RuCl(PCP F20)(PPh3)], 2) have been rationalised by performing calculations on the cations [Ru(PCP H)(PPh3)]+ (1cat) and [Ru(PCP F20)(PPh3)]+ (2cat). The molucular interactions between the chloride ligand and the axial rings, as found in 1 and 2, respectively, have been studied computationally in the model system [(C6X5PH2)2CL-](X = H, F). The calculations on 2cat show that in 2 it is most likely the attractive electrostatic interaction between the chloride ligand and the fluorinated phenyl rings that forces the C ipso atom to occupy an axial postion rather than an equatorial one in the observed (X-ray of 2) square pyramidal arrangement. In 1, however, repulsive steric hinderance forces the PPh3 ligand to take the apical postion. The applicability of the TD-DFT method for the calculation of the electronic spectra of the PCP-pincer compounds 1 and 2 has been tested. The results indicate that the excitation energies calculated for both complexes are in a reasonable agreement with the experimental absorption maxima. However, for 1, all the calculated transition energies are underestimated.