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 NN 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[triple bond]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.