Rigid Ruthenium PCcarbeneP Complexes for Small Molecule Activation, Hydrogenation, and Dehydrogenation
Date
2024-09-19
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Abstract
Small molecule activation is of fundamental importance to the development of catalysts for producing alternative fuels and other value-added products from abundant feedstocks. The capture and subsequent conversion of pollutant molecules like carbon dioxide and nitrous oxide can reduce their atmospheric concentrations and produce fine chemicals. Hydrogen storage and release cycles using nitrogen-ammonia or carbon dioxide-formic acid are being studied for the practical application of hydrogen fuel cells. The Piers group has developed a series of pincer ligands that form metal-carbene complexes. These metal-carbenes have shown to be competent in a wide array of small molecule activations. Previous optimizations show that the planar anthracene-based ligands are especially stable. Additionally, ruthenium catalysts have had a huge role in hydrogenation reactions and are prominently studied as catalysts for hydrogen storage using small molecules like carbon dioxide. This thesis presents the synthesis and application of ruthenium-based PCcarbeneP complexes. The synthesis of dichlorido ruthenium PCcarbeneP complexes from the previously developed proligands was found to be straightforward. These chlorido complexes could activate and split hydrogen which enabled the synthesis of hydrido-chloride PCcarbeneP complexes and later polyhydride PCalkylP complexes. The polyhydride complexes were found to have dynamic behaviour, which was studied in detail, revealing that they effectively act as monohydride complexes with stabilizing hydrogen ligands. The synthesized ruthenium hydride complexes were applied in the carbon dioxide-formic acid hydrogen storage cycle. In this study it was found that the hydrido-chloride complexes were unable to hydrogenate carbon dioxide, where the polyhydride complexes could stoichiometrically hydrogenate carbon dioxide. Catalytic carbon dioxide hydrogenation, however, was limited by off-cycle carbonate forming reactions. The release of hydrogen from formic acid was also explored and the ruthenium PCcarbeneP complexes were found to be highly active and selective on one of the rigid ligands employed, and nearly inactive on the other. On the active ligand the resting state during formic acid decomposition was identified as a ruthenium hydrido-formate PCcarbeneP complex. The inactive ligand was found to promote the desired dehydrogenation reaction along with deleterious reactions, preventing catalytic applications.
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Keywords
Organometallic, Catalysis, Small Molecule Activation
Citation
Donnelly, L. J. (2024). Rigid ruthenium PCcarbeneP complexes for small molecule activation, hydrogenation, and dehydrogenation (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.