DFT Studies on Reactions of CO2 with Niobium and Vanadium Nitride Complexes

We have investigated the reduction of CO2 to CO mediated by the anionic niobium nitride complex [NNb((NBuMe)-Bu-t)(3)](-), a model complex of [NNb((NBuAr)-Bu-t)(3)](-), using density functional theory. We mainly calculated the energetics for the interesting reaction sequence, reported recently by Cummins and his co-workers, involving reactions of the anionic niobium nitride complex [NNb((NBuAr)-Bu-t)(3)](-) with CO2 to first give a carbamate complex. The carbamate complex then reacts with MeC(O)Cl to give an isocyanate-acetate, which can be reduced by SmI2 to give the isocyanate complex (OCN)Nb((NBuAr)-Bu-t)(3). Further reduction of the isocyanate complex by Na/Hg extrudes CO and regenerates [NNb((NBuAr)-Bu-t)(3)](-). In addition, we compare the reaction pathways for the reduction reaction of the isocyanate complexes (OCN)M((NBuMe)-Bu-t)(3) (M = Nb, V), model complexes of (OCN)M((NBuAr)-Bu-t)(3), with sodium and explain why these two reduction reactions give remarkably different products.