Density Functional Theory Study on the Mechanism of the Reductive Cleavage of CO2 by a Bis-β-Diketoiminatediiron Dinitrogen Complex

Abstract

Density functional theory has been used to analyze the detailed reaction mechanism for the reductive cleavage of CO(2) by a dinitrogen bridged bis-beta-diketoiminatediiron complex, L(tBu)Fe-N(2)-FeL(tBu) (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 CO(2), the release of CO, and the ready formation of CO(3)(2-). Our results show that the insertion of CO(2) 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 CO(2). 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.