Density functional theory (DFT) calculations have been performed for the investigation of a plausible mechanism of the triple bond cleavage of N-2 in a diniobium complex supported by tridentate aryloxide ligands, {Nb-V(mu-N)(2)Nb-V}(2-22) With the assumption of a tetrakis(mu-hydrido)diniobium complex {Nb-IV(mu-H)(4)Nb-IV}(2-) as an initial complex, the N N cleavage on the Nb-2 core proceeds in four steps. Dinitrogen is coordinated to the {Nb-III(mu-H)(2)Nb-III} core in a side-on/end-on manner, accompanied by the reductive elimination of H-2. The N N bond of dinitrogen is activated up to a single bond (formally N-2(4-)) by the two Nb(III) atoms, once it is bound to the Nb-2 core. Two electrons are prepared for the cleavage of the N-N single bond through the mu-H migration to an N atom, leading to the formation of an Nb-Nb bond. The N-N bond is then dissociated by the two electrons that are shared between the two Nb atoms. Finally, {Nb(mu-N)(2)Nb}(2-) is generated after H-2 elimination in which the N-bonded H atom is coupled with the remaining mu-H atom. The final H-2 elimination is calculated to be the rate-determining step.