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Carbon dioxide utilization; Hydrocarboxylation; Density functional calculations; Rhodium; Energetic span model; Computational chemistry
Abstract:
One of the major challenges for the utilization of carbon dioxide as a chemical feedstock is to devise thermodynamically feasible transformations to valuable chemicals through efficient catalytic processes. In this paper, we examine the feasibility of the experimentally not yet realized direct hydrocarboxylation of alkenes, using computational methods. A conceivable catalytic cycle was devised for the addition of H2 and CO2 to ethene, which affords propionic acid. The corresponding energy profiles were calculated with state-of-the-art DFT methods for three rhodium pincer complexes as potential catalyst. Several junctions within the productive catalytic cycle were identified, leading to competing hydrogenation reactions of ethene or CO2. A profound analysis of the reaction network by means of the energetic span model allowed us to identify parameters that facilitate the carboxylation and that favor it over the hydrogenation reaction. A comparison of the relevant activation energies revealed that two of the three investigated complexes slightly favour the hydrogenation of ethene, but one complex preferentially stays within the carboxylation cycle.
