Mechanisms of the Water-Gas Shift Reaction Catalyzed by Ruthenium Pentacarbonyl: A Density Functional Theory Study

Abstract

The mechanism of the water-gas shift reaction catalyzed by Ru(CO)5 is analyzed using density functional methods in solution within the conductor-like screening model. Four different mechanistic pathways have been considered. It turned out that the incorporation of solvent effects is very important for a reasonable comparison among the mechanistic alternatives. The explicit inclusion of a water solvent molecule significantly changes the barriers of those steps which involve proton transfer in the transition state. The corresponding barriers are either lowered or increased, depending on the structure of the corresponding cyclic transition states. The results show that protolysis steps become competitive due to solution effects. The formation of formic acid as an intermediate in another, alternative pathway is also found to be competitive.

Harnessing the Power of the Water‐Gas Shift Reaction for Organic Synthesis

“…[35] DFT studies also support this catalytic cycle,a lthough alternative proposals have been formulated. [36] Them echanism appears to be more complex with Ru, Os,R ha nd Ir carbonyl complexes due to the formation of metal clusters. [37] Ad ifferent pathway has been suggested for Group 6( Cr, Mo,W )m etal-carbonyl complexes.A ctivation of free CO forms anionic formate (F), which coordinates to the metal (G).…”

“…[197] In an attempt to streamline the synthesis of methyl isobutyl ketone from acetone,R ossi et al discovered that WGSR conditions can be employed to this end using aC u/ Al 2 O 3 catalyst [Eq. (36)]. [198] Scheme 17.…”

Die Wassergas‐Shift‐Reaktion in der organischen Synthese

“…[35] DFT-Untersuchungen sprechen ebenfalls fürdiesen Katalysezyklus,eswurden aber auch andere Vorschläge formuliert. [36] Bei Ru-, Os-, Rh-und Ir-Carbonylkomplexen scheint der Mechanismus wegen der Bildung von Metallclustern komplizierter zu sein. [37] Für Metallcarbonylkomplexe der Gruppe 6( Cr, Mo,W )w urde ein anderer Reaktionsweg vorgeschlagen.…”

“…[197] Bei dem Versuch, die Synthese von Methylisobutylketon aus Aceton zu rationalisieren, entdeckten Rossi et al,d ass hierfürd ie WGSR-Bedingungen mit einem Cu/Al 2 O 3 -Katalysator genutzt werden konnten [Gl. (36)]. [198] Synthetisch nützlicher ist eine Methode,b ei der aktive Methylenverbindungen mit Carbonylgruppen in einer Reaktion, die formal als reduktive Knoevenagel-Kondensation zu betrachten ist, umgesetzt werden.…”

Formation of metallacarboxylic acids through Hieber base reaction. A density functional theory study

“…The driving force for formation of the metallacarboxylic acid depends notably on the co-ligands that are present, in particular on the number of CO ligands. While large negative enthalpies and free energies are computed for the OH − uptake of Ru(CO) 5 [28, 29] ΔG = 127.7 kJ/mol and 81.6 kJ/mol are predicted for [RuH 2 (CO)(PPh 3 ) 3 ] and [RuH 2 (CO) 2 (PPh 3 ) 2 ], respectively. It therefore appears that suitable ligand design, by varying the steric or electronic properties of the ligands, could make the process of OH − uptake feasible.…”