First row metals have been found to be efficient catalysts for both hydrogenation of CO2 and catalytic or electrocatalytic oxidation of formic acid. One of the more efficient systems is the tetraphosphine ligated iron complex by Beller and co-workers. Our initial studies showed that this catalyst reacts on a single coordination site at the metal in the dehydrogenation of formic acid. Later reports showed that this catalyst was also capable of the reverse reaction, hydrogenation of CO<sub>2</sub> or bicarbonate. Small changes in the reaction conditions, including the choice of solvent, seemed to be enough for reversing the reaction. We were intrigued by these findings and wanted to understand what determines the directionality of the reaction. Here we will present results based on density functional theory with accurate description of solvation free energies of small anions, which show a dramatic effect of the solvent. And interestingly, the effect is opposite for hydrogen bond donor solvent and non-hydrogen bond donor solvents. Our results further indicate that the choice of solvent can be further optimized to achieve significantly higher rates. The influence of the ligand on the reaction path and energies seem to be very small and is mostly affecting the thermal stability of the catalyst.

Bicarbonate hydrogenation by iron: How the choice of solvent can reverse the reaction

251st National Meeting (2016)

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