Molecular structure of Ru(II)/diphosphine/4,6-dimethyl-2-pyrimidinethiol complexes : a combined experimental and density functional theory study.

Abstract

Reactions of cis-[RuCl2(P-P)(bipy)] precursors with the SpymMe2 ligand (4,6-dimethyl-2- pyrimidinethiol) yielded complexes of the [Ru(SpymMe2)(P-P)(bipy)]PF6 type, where P-P = 1,2- bis(diphenylphosphino)ethane (dppe - for complex 1), 1,3-bis(diphenylphosphino)propane (dppp - for complex 2) and 1,1’-bis(diphenylphosphino)ferrocene (dppf - for complex 3) and bipy = 2,2’-bipyridine. The new compounds were obtained by displacing the chlorido ligands from the precursors and coordination of one monoanionic 4,6-dimethyl-2-pyrimidinethiol ligand. All complexes were characterized by spectroscopic, electrochemical and elemental analysis techniques, as well as single-crystal X-ray diffraction, where the structures of complexes 1, 2 and 3 showed that the SpymMe2 ligand coordinates to the ruthenium(II) center as bidentated, yielding complexes with the sulfur atom trans positioned to the nitrogen atom from the bipy ligand. A theoretical study of the structures of the complexes was performed using the DFT/B3LYP method. Distances and angles of optimized structures agree with X-ray experimental data. Furthermore, the calculated IR and UV-Vis spectra are compatible with experimental data. Charge decomposition analysis (CDA) and NBO (natural bond orbitals) charges showed that there was an overall charge transfer from bipy and P-P ligands to the ruthenium centers. Higher electrochemical stability and 1H and 31P{1H} NMR shifts of 1, 2 and 3 compared with precursors could be explained by the lower values of calculated molecular orbital energies, NBO charge on atoms and CDA data. Finally, the structure of the isomers of complexes 1, 2 and 3, considering the sulfur atom trans positioned to the phosphorus atom, were optimized, showing that they are slightly less stable, presenting total energy higher, 10.4, 31.5 and 60.5 kJ/mol than 1, 2 and 3, where nitrogen is trans to the phosphorus atom.