Explaining the Advantageous Impact of Tertiary versus Secondary Nitrogen Center on the Activity of PNP‐Pincer Co(I)‐Complexes for Catalytic Hydrogenation of CO2. Issue 66 (5th November 2021) - Bothra, Neha
Abstract: Pincer ligated coordination complexes of base metals have shown remarkable catalytic activity for hydrogenation/dehydrogenation of CO2 . The recently reported MeN[CH2 CH2 ( i Pr2 )]2 Co(I)PNP‐pincer complex was shown to exhibit substantially higher catalytic activity in comparison to the corresponding catalyst, HN[CH2 CH2 ( i Pr2 )]2 Co(I)PNP, bearing a secondary nitrogen center on the pincer ligand. Here, we computationally investigate the mechanisms for hydrogenation of CO2 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. Abstract : Secondary PNP‐pincer complexes are found to outperform tertiary analogue in various reactions as the former one exhibits metal‐ligand cooperativity (MLC). But in a recent experiment of CO2 reduction reaction in alkaline medium, the tertiary complex has shown a much higher turnover number than the secondary complex and the underline reason is assumed to deteriorate effects of MLC on the secondary complex. So, here detailed density functional theory based kinetic calculations have been carried out explaining the actual reason for this anomaly.