Activation of Dinitrogen Promoted by Adsorption of C6H6 on Fe2VC- Cluster Anions.

The introduction of organic ligands is one of the effective strategies to improve the stability and reactivity of metal clusters. Herein, the enhanced reactivity of benzene-ligated cluster anions Fe2VC(C6H6)- with respect to naked Fe2VC- is identified. Structural characterization suggests that C6H6 is molecularly bound to the dual metal site in Fe2VC(C6H6)-. Mechanistic details reveal that the cleavage of N≡N is feasible in Fe2VC(C6H6)-/N2 but hindered by an overall positive barrier in the Fe2VC-/N2 system. Further analysis discloses that the ligated C6H6 regulates the compositions and energy levels of the active orbitals of the metal clusters. More importantly, C6H6 serves as an electron reservoir for the reduction of N2 to lower the crucial energy barrier of N≡N splitting. This work demonstrates that the flexibility of C6H6 in terms of withdrawing and donating electrons is crucial to regulating the electronic structures of the metal cluster and enhancing the reactivity.