Ruthenium(II)-catalyzed hydrogenation of carbon dioxide to formic acid. Theoretical study of real catalyst, ligand effects, and solvation effects.

Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
Journal of the American Chemical Society (Impact Factor: 11.44). 04/2005; 127(11):4021-32. DOI: 10.1021/ja043697n
Source: PubMed

ABSTRACT Ruthenium-catalyzed hydrogenation of carbon dioxide to formic acid was theoretically investigated with DFT and MP4(SDQ) methods, where a real catalyst, cis-Ru(H)2(PMe3)3, was employed in calculations and compared with a model catalyst, cis-Ru(H)2(PH3)3. Significant differences between the real and model systems are observed in CO2 insertion into the Ru(II)-H bond, isomerization of a ruthenium(II) eta1-formate intermediate, and metathesis of the eta1-formate intermediate with a dihydrogen molecule. All these reactions more easily occur in the real system than in the model system. The differences are interpreted in terms that PMe3 is more donating than PH3 and the trans-influence of PMe3 is stronger than that of PH3. The rate-determining step is the CO2 insertion into the Ru(II)-H bond. Its deltaG(o++) value is 16.8 (6.8) kcal/mol, where the value without parentheses is calculated with the MP4(SDQ) method and that in parentheses is calculated with the DFT method. Because this insertion is considerably endothermic, the coordination of the dihydrogen molecule with the ruthenium(II)-eta1-formate intermediate must necessarily occur to suppress the deinsertion. This means that the reaction rate increases with increase in the pressure of dihydrogen molecule, which is consistent with the experimental results. Solvent effects were investigated with the DPCM method. The activation barrier and reaction energy of the CO2 insertion reaction moderately decrease in the order gas phase > n-heptane > THF, while the activation barrier of the metathesis considerably increases in the order gas phase < n-heptane < THF. Thus, a polar solvent should be used because the insertion reaction is the rate-determining step.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Recent significant progress in the homogeneous catalytic hydrogenation of CO2 to formate (the conjugate base of formic acid) and dehydrogenation of formic acid in various solvents including water is summarized. While formic acid is not the perfect H-2 storage solution, many researchers consider it better than other methods at this time because the interconversion of CO2 and formic acid can take place cleanly to form H-2 without detectable CO under mild conditions. In this chapter, we explain how inspirations from biological systems guide us to design homogeneous transition-metal catalysts for carrying out the interconversion of CO2 and formate under ambient conditions in environmentally benign and economically desirable water solvent.
    01/2014: pages 189-222;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In recent years, the utilization of carbon dioxide as alternative C-1 building block has gained more and more scientific interest and has been intensely investigated. Especially the homogeneously catalyzed hydrogenation of carbon dioxide to formic acid and its derivates has been well studied. Recently, an increase in product formation was achieved by further development of the homogeneous catalysts. Currently, iridium-based catalysts offer the highest catalytic activity known in the hydrogenation of carbon dioxide. The present chapter gives a wide overview of various catalyst systems, which have been investigated so far. In addition, current research on the continuously operated hydrogenation of carbon dioxide in miniplant scale with a promising concept for catalyst recycling is presented.
    01/2014: pages 223-258;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the mechanisms of chemical reactions, especially catalysis, has been an important and active area of computational organic chemistry and close collaborations between experimentalists and theorists represent an increasing trend. This perspective provides examples of such productive collaborations. The understanding of various reaction mechanisms and the insight gained from these studies are emphasized. The applications of various experimental techniques in elucidation of reaction details as well as the development of various computational techniques to meet the demand of emerging synthetic methods, e.g. C-H activation, organocatalysis, and single electron transfer, are presented as are some conventional developments of mechanistic aspects. Examples of applications are selected to demonstrate the advantages and limitations of these techniques. Some challenges in the mechanistic studies and predictions of reactions are also analyzed.
    Journal of the American Chemical Society 01/2015; 137(5). DOI:10.1021/ja5112749 · 11.44 Impact Factor