Explaining the Advantageous Impact of Tertiary versus Secondary Nitrogen Centre on the Activity of PNP-Pincer Co(I)-Complexes for Catalytic Hydrogenation of CO2.

Abstract

Pincer ligated coordination complexes of base metals have shown remarkable catalytic activity for hydrogenation/dehydrogenation of CO 2 .\xa0The recently reported MeN[CH 2 CH 2 i Pr 2 )] 2 Co(I)PNP-pincer complex was shown to exhibit substantially higher catalytic activity in comparison to the corresponding catalyst,\xa0 HN[CH 2 CH 2 i Pr 2 )] 2 Co(I)PNP, bearing a secondary nitrogen center on the pincer ligand. Here, we computationally investigate the mechanisms for hydrogenation of CO 2 to formate catalyzed by these two Co-PNP complexes to explain how such a small structural difference could have a sizable impact on their catalytic activity. Plausible hydrogenation routes were examined in details and our findings provide solid support for the experimental observations. Our results reveal that such trends in catalytic activity could be explained from the lower activation barrier for the hydride transfer step upon changing the pincer nitrogen center from secondary to tertiary.