Theoretical Study on the Thermodynamics of the Elimination of Formic Acid in the Last Step of the Hydrogenation of CO₂ Catalyzed by Rhodium Complexes in the Gas Phase and Supercritical CO₂

Abstract

How coordination of a CO 2 molecule can assist in the release of HCOOH from the [P 2 Rh-(HCOOH)] complex in the last step of the hydrogenation of CO 2 catalyzed by rhodium complexes has been investigated by density functional methods. The effect of a supercritical CO 2 solution has been included using the polarizable continuum method. It has been found that the presence of a CO 2 molecule in the model of the active site favors the thermodynamics of the HCOOH dissociation from the [P 2 Rh(HCOOH)] species.

Recycling CO2? Computational Considerations of the Activation of CO2 with Homogeneous Transition Metal Catalysts

“…In the case of [CuIH(PH 3 ) 2 ], the insertion reaction has a lower barrier of 3.5 kcal mol À1 in comparison to [RhIH(PH 3 ) 3 ] with 12 kcal mol À1 , because the RhÀH bond is stronger than CuÀH. This reaction results in the complexes [RhI(HCOO)(PH 3 [44] Release of HCOOH has been identified has the rate determining step of the catalytic cycle. In 2000, Sakaki and Musashi discovered a new type of s-bond metathesis, occurring during the product elimination step.…”

Homogeneous Hydrogenation of Carbon Dioxide

“…There is no reason why this mechanism should not also be possible for CO 2 hydrogenation (Scheme 17.8 b) [6,43,68], although it has not yet been possible to demonstrate that this mechanism operates for any of the catalysts shown in Table 17.1. There is no reason why this mechanism should not also be possible for CO 2 hydrogenation (Scheme 17.8 b) [6,43,68], although it has not yet been possible to demonstrate that this mechanism operates for any of the catalysts shown in Table 17.1.…”

Rapid hydroformylation of alkyl acrylates in supercritical CO2

“…16 In addition, coordination of CO 2 to the rhodium atom of the unsaturated intermediate and other oxygen atoms is possible, which would further shift the equilibrium to the right. 17 A similar model involving H 2 O and hydrogen bonding was earlier proposed to account for the increase in rates in the hydroformylation of acrylates in the presence of water. 5,8 In summary, we have shown that the hydroformylation of alkyl acrylates, although sluggish in conventional organic solvents, can readily be effected in scCO 2 .…”