DFT study on N₂ activation by a hydride-bridged diniobium complex. N≡N Bond cleavage accompanied by H₂ evolution

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(μ-N)₂Nb^v}^2-. ²²With the assumption of a tetrakis(μ-hydrido)diniobium complex {Nb^lv(μ-H)₄Nb^lv}^2- as an initial complex, the N≡N cleavage on the Nb₂ core proceeds in four steps. Dinitrogen is coordinated to the {Nb'''-H)Nb'''} core in a side- on/end-on manner, accompanied by the reductive elimination of H₂. The N≡N bond of dinitrogen is activated up to a single bond (formally N ₂⁴-) by the two Nb(lll) atoms, once it is bound to the Nb₂ core. Two electrons are prepared for the cleavage of the N-N single bond through the μ-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(μ-N)₂Nb} ^2- is generated after H₂ elimination in which the N-bonded H atom is coupled with the remaining μ-H atom. The final H₂ elimination is calculated to be the rate-determining step.