Abstract

Hydrogenation is an important step in the synthesis of many pharmaceuticals, and transfer hydrogenation, where a renewable source for hydrogen is used, is a green and efficient method for this process. It has been shown experimentally that alcohols can be used as a source of hydrogen with iridium (III) catalyst affecting the transfer hydrogenation. The mechanism of this process is unknown. In this research study the mechanism of transfer hydrogenation is investigated computationally, using a model system that includes carbonyl (CO), amine (NH3), and cyclopentadiene (CP) ligands with methanol as the source of hydrogen. Density Functional Theory (DFT) calculations, using the M06 and APFD functionals, along with an effective core potential on the iridium atom and a correlation consistent basis set in the rest of the atoms. These functionals are used to determine initial, transition state, and intermediate geometries for proposed mechanisms of transfer hydrogenation including stepwise, concerted, and ion pair mechanisms. The concerted mechanism was found to be feasible and has an energy barrier of 16 Kcal/mol with a favorable exothermic process. However, the ion pair mechanism did not show promising results, concluding that it is not a favorable mechanism. The intermediate geometries of stepwise mechanisms were found and BSSE was eliminated from their energies. The pathways and energies of the mechanisms, stepwise and concerted were not compared since there is not a counterpoint calculation for the concerted mechanism. The counterpoint pairs energies for the stepwise mechanism were compared to each other obtaining counterpoise 2 as the lowest in energy.

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