This study is focused on examining the mechanism and selectivity of C-H activation by the iridium(III)-1,10-phenanthroline dichloride catalyst on 1-butanol and 1-methoxybutane. Ethers are compounds with inherent low reactivity and alcohols are one of the most widely used precursors in synthesis. Therefore, the selective activation of these molecules will be greatly beneficial in many synthetic applications. The experiments were carried out on a modified mass spectrometer where the iridium complex is introduced via the ESI and trapped. Our modified mass spectrometer allows introduction of a second reagent into the ion trap via the helium flow. Thus the ion trap behaves as a reaction cell. As shown in Figure 1, the initial study showed that C-H activation is accompanied by a loss of HCl. By using selectively deuterated compounds, the loss of DCl instead of HCl would indicate the site of activation. The substrates used in this study were selectively deuterated butanol and methoxybutane. The selectively deuterated methoxybutane ethers were synthesized from the corresponding alcohols. The experimental results were further supported using DFT calculations. Studies carried out with the substrates showed that the iridum(III) complex selectively activates the C-H bonds in the gamma position of methoxybutane while activation in butanol occurs on both the gamma and delta carbons. Kinetic isotope effect studies showed that there is a higher preference of activation on the delta compared to the gamma carbon in butanol. This indicates that the iridium(III) complex can selectively activate C-H bonds in methoxybutane but in moving towards butanol, the selectivity is compromised. DFT calculations show that the driving force of these reactions are the formation of either a 6-membered (delta) or 5-membered (gamma) ring transition state. In methoxybutane the presence of the methyl group tilts the preference towards the 5-membered ring transition state thus allowing selective C-H activation on the gamma position. This study proves that the iridium(III)-1,10-phenanthroline dichloride complex can be used as a potential catalyst for selective C-H activation.

C-H activation of alcohols and ethers by a cationic iridium(III)-1,10-phenanthroline dichloride complex: Gas-phase study

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.