Ruthenium (II) thiacrown complexes as hydrogen-transfer reduction catalysts

An investigation into the potential of a series of Ruthenium (II) thiacrown complexes with general formula [Ru([9]aneS3)Cl2(L)] and [Ru([n]aneS4)Cl(L)]+, where L = DMSO or Ph3P, n = 12, 14, or 16, as hydrogen transfer reduction catalysts is reported. As part of these studies two new complexes incorporating [Ru([12]aneS4)] and [Ru([16]aneS4)] metal centres have been synthesised and fully characterised. The X-ray structure of one of these complexes is also reported. The UV/Vis spectra of these complexes are dominated by π → π* transitions, with weaker d → d transitions also being apparent. Using these eight structurally related complexes, studies on the transfer hydrogenation of acetophenone using propan-2-ol as the hydride source were carried out. This work revealed that the complexes displayed catalytic activity in the presence of a base promoter. Although the activity of these complexes were considerably lower than that of structurally related mixed-donor ligand systems, there was some evidence that the flexibility of the ligand did have an effect on initial catalytic activity.