Direct Hydrogenation of Carbon Dioxide by an Artificial Reductase Obtained by Substituting Rhodium for Zinc in the Carbonic Anhydrase Catalytic Center. A Mechanistic Study

Recently,
a new artificial carbonic anhydrase enzyme in which the
native zinc cation has been replaced with a Rh­(I) has been proposed
as a new reductase that is able to efficiently catalyze the hydrogenation
of olefins. In this paper, we propose the possible use of this modified
enzyme in the direct hydrogenation of carbon dioxide. In our theoretical
investigation, we have considered different reaction mechanisms such
as reductive elimination and σ-bond metathesis. In addition,
the release of the formic acid and the restoring of the catalytic
cycle have also been studied. Results show that the σ-bond metathesis
potential energy surface lies below the reactant species. The rate-determining
step is the release of the product with an energy barrier of 12.8
kcal mol–1. On the basis of our results, we conclude
that this artificial enzyme can efficiently catalyze the conversion
of CO2 to HCOOH by a direct hydrogenation reaction.