Abstract
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.
Highlights
Several research groups on reactions catalyzed by transition metal compounds have been dedicated to the study of new compounds due to various academic and industrial applications
We report on the synthesis, full characterization and theoretical calculations of a new ruthenium(II) complex with 4-picoline ligand
We have described the synthesis of a mononuclear ruthenium(II) complex, which presents an octahedral geometry around the metal center, containing two bidentate ligands and two monodentate ligands suggested by Fourier transform infrared (FTIR) and 31P{1H}, 1H and 13C{1H} nuclear magnetic resonance (NMR) spectroscopy, where the ligand 4-picoline is trans to the phosphorous atom of the phosphine ligand
Summary
Several research groups on reactions catalyzed by transition metal compounds have been dedicated to the study of new compounds due to various academic and industrial applications. Reactions of transfer hydrogenation by alcohols as the hydrogen source catalyzed by metal complex have been widely reported as an effective protocol, and in this area, ruthenium catalysts stand out.[1,2,3,4] Geoffrey Wilkinson and co-workers[5] studied these compounds that show enhanced stability, good selectivity. Simplify the purification of the product; the reaction does not need pressurized hydrogen gas, nor does it produce hazardous waste. This hydrogenation transfer reaction can be performed in basic medium. This shows that the reaction mechanism involves the formation of a hydride species and ketone followed by the reduction of ketone substrates, answering the main question of catalysis, the chemical reactions involved in the catalytic process
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