Synthesis, Structure Determination and Catalytic Activity of a Novel Ruthenium(II) [RuCl(dppb)(44bipy)(4-pic)]PF6 Complex

This work reports the synthesis, structure and catalytic activity of a novel ruthenium(II) complex, [RuCl(dppb)(44bipy)(4-pic)]PF6 (where dppb = 1,4-bis(diphenylphosphine)butane; 44bipy = 4,4’-dimethyl-2,2’-dipyridyl; 4-pic = 4-picoline). The molecular structure and catalytic activity were studied by Fourier transform infrared (FTIR), UV-Vis and nuclear magnetic resonance (NMR) spectroscopies, cyclic voltammetry, and X-ray crystallography, while the electronic structure was investigated by density-functional theory (DFT) and time dependent DFT (TD-DFT) methods. Electrochemical studies showed the substitution of the chlorido ligand from the precursor by the 4-pic ligand, exhibiting the RuII/RuIII process at 1.21 V. The structure of the compound was optimized using DFT simulations and showed data similar to the X-ray structure. The UV-Vis absorption spectrum showed a good agreement with TD-DFT simulations. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies were determined at the Becke, 3-parameter, Lee-Yang-Parr (B3LYP) level. The study of the catalytic activity in the transfer hydrogenation of ketones by the 1H NMR showed efficient transfer hydrogenation reaction at 60 oC, employing acetophenone as substrate and resulting in a high conversion. The formation of two ruthenium-hydride species was observed.