Triphosphines-containing ruthenium-acetato complexes: Synthesis, characterization, DFT, mer/fac isomerization and formic acid dehydrogenation

Abstract

The triphosphines-containing ruthenium-acetato complexes [RuCl(κ2-OAc)(triphos)] (2) and the new analogue synthesized in our research group [RuCl(κ2-OAc)(etp)] (1) (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane or etp = bis[2-(diphenylphosphino)ethyl]phenylphosphine) were evaluated as pre-catalyst for the dehydrogenation of formic acid (FA). Complex [RuCl(κ2-OAc)(etp)] (1) was fully characterized by 1H, 13C and 31P{1H} NMR, vibrational spectroscopy, elemental analysis and X-ray diffraction. The electrochemical behavior of 1 and 2 was checked by cyclic voltammetry. DFT calculations for 1, 2 and for the two isomers of 1 (1′ and 1”) were performed and discussed. Due to the linear nature of etp ligand, three isomeric forms for [RuCl(κ2-OAc)(etp)] (1′ and 1”) are possible and were observed. Both complexes were active for the decomposition of FA, in three solvents (MeOH, THF and iPrOH), at 80 °C, leading solely to formation of CO2 and H2. In THF both complexes achieved quantitative conversions (in times up to 125 min) and final TOF’s up to 833 h−1, for complex 1.