Abstract:
Density functional theory has been used to analyze the detailed reaction mechanism for the reductive cleavage of CO2 by a dinitrogen bridged bis-beta-diketoiminatediiron complex, (LFe)-Fe-tBu-N-2-FeLtBu (I), recently reported by Holland and co-workers. A number of pathways have been investigated and the most likely mechanism correlates well with experimental evidence. A rationale has been provided for the binding of CO2, the release of CO, and the ready formation of CO32-. Our results show that the insertion of CO2 into the diiron complex is the rate determining step of the reductive cleavage reaction. An intramolecular reduction step from the reduced dinitrogen bridge is proposed which serves to increase the activation of CO2. This is followed by an intersystem crossing from the septet to the nonet state which acts as a driving force for the subsequent release of CO. The overall reductive cleavage reaction is exergonic by 120 kJ/mol, and further reaction of the released CO with the starting diiron complex is also predicted to be strongly exergonic.
