Theoretical revisit of a Fe(CO)(5)-catalyzed water-gas shift reaction.

We have revisited the water-gas shift reaction catalyzed by iron pentacarbonyl at the DFT-B3LYP level. The reaction mechanism proposed by Rozanska and Vuilleumier (Inorg. Chem. 2008, 47, 8635-8640) has been followed and revised. The results show that transition states TS4/5 and TS5/2_a actually connect other intermediates rather than those suggested by Rozanska and Vuilleumier. Furthermore, the entire reaction has been proven to proceed with processes 1 --> 2 --> 3 --> 4 --> 6 --> 7 --> 2. It is the first time that species 6 and 7 are reported as intermediates for this reaction mechanism.