The difference one ligand atom makes – An altered oxygen transfer reaction mechanism caused by an exchange of selenium for sulfur

The influence of sulfur versus selenium coordination to molybdenum on the oxo transfer reaction mechanisms of functional models for oxidoreductases has been studied. The solution structure of the dimeric molybdenum compound with tridentate bis-anionic ligands containing a thioether function (−O(CH2)3S(CH2)3O−) has been determined using EXAFS spectroscopy to be able to compare a feature of its solution structure to that of its selenoether analogue. A significant difference is found for the solution structures of the two compounds. The thioether group remains coordinated in solution, whereas the selenoether does not. The influence of this difference on the catalytic oxo transfer has been investigated in detail by following the catalytic transition of PPh3 to OPPh3 with DMSO as oxygen donor with variation of both substrate concentrations.

A thioether versus a selenoether function coordinated to molybdenum is shown to be responsible for the complexes to follow different oxo transfer reaction mechanisms in catalysis, even though the interactions between metal and ligand are only weak and other complex properties are almost identical. A change in size and softness can have a considerable catalytic effect which may be relevant for amino acid coordination to active site metals as well.Figure optionsDownload as PowerPoint slide