Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study
Hydrogenation and dehydrogenation reactions are fundamental in chemistry and essential for all living organisms. We employ density functional theory (DFT) to understand the reaction mechanism of the oxidative dehydrogenation (ODH) of the pyridyl-amine complex [Fe<sup>III</sup>L<sup>...
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2025-01-01
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| author | Ricardo D. Páez-López Miguel Á. Gómez-Soto Héctor F. Cortés-Hernández Alejandro Solano-Peralta Miguel Castro Peter M. H. Kroneck Martha E. Sosa-Torres |
| author_facet | Ricardo D. Páez-López Miguel Á. Gómez-Soto Héctor F. Cortés-Hernández Alejandro Solano-Peralta Miguel Castro Peter M. H. Kroneck Martha E. Sosa-Torres |
| author_sort | Ricardo D. Páez-López |
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| description | Hydrogenation and dehydrogenation reactions are fundamental in chemistry and essential for all living organisms. We employ density functional theory (DFT) to understand the reaction mechanism of the oxidative dehydrogenation (ODH) of the pyridyl-amine complex [Fe<sup>III</sup>L<sup>3</sup>]<sup>3+</sup> (L<sup>3</sup>, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanonane) to the mono-imine complex [Fe<sup>II</sup>L<sup>4</sup>]<sup>2+</sup> (L<sup>4</sup>, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanon-1-ene) in the presence of dioxygen. The nitrogen radical [Fe<sup>II</sup>L<sup>3</sup><sub>N8•</sub>]<sup>2+</sup>, formed by deprotonation of [Fe<sup>III</sup>L<sup>3</sup>]<sup>3+</sup>, plays a crucial role in the reaction mechanism derived from kinetic studies. O<sub>2</sub> acts as an oxidant and is converted to H<sub>2</sub>O. Experiments with the deuterated ligand L<sup>3</sup> reveal a primary C-H kinetic isotope effect, <i>k</i><sup>CH</sup>/<i>k</i><sup>CD</sup> = 2.30, suggesting C-H bond cleavage as the rate-determining step. The DFT calculations show that (i) <sup>3</sup>O<sub>2</sub> abstracts a hydrogen atom from the α-pyridine aliphatic C-H moiety, introducing a double bond regio-selectively at the C<sub>7</sub>N<sub>8</sub> position, via the hydrogen atom transfer (HAT) mechanism, (ii) O<sub>2</sub> does not coordinate to the iron center to generate a high-valent Fe oxo species observed in enzymes and biomimetic complexes, and (iii) the experimental activation parameters (ΔH<sup>≠</sup> = 20.38 kcal mol<sup>−1</sup>, ΔS<sup>≠</sup> = −0.018 kcal mol<sup>−1</sup> K<sup>−1</sup>) fall within in the range of values reported for HAT reactions and align well with the computational results for the activated complex [Fe<sup>II</sup>L<sup>3</sup><sub>N8•</sub>]<sup>2+</sup>···<sup>3</sup>O<sub>2</sub>. |
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| spelling | doaj-art-fd4954e8e0994762a1ae9733a10de6de2025-01-24T13:35:31ZengMDPI AGInorganics2304-67402025-01-011312210.3390/inorganics13010022Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational StudyRicardo D. Páez-López0Miguel Á. Gómez-Soto1Héctor F. Cortés-Hernández2Alejandro Solano-Peralta3Miguel Castro4Peter M. H. Kroneck5Martha E. Sosa-Torres6Departamento de Química Inorgánica y Nuclear, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MexicoDepartamento de Física y Química Teórica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MexicoGIFAMol, Grupo de Investigación en Fisicoquímica Aplicada y Modelamiento Molecular, Escuela de Tecnología Química, Universidad Tecnológica de Pereira, Pereira 660003, ColombiaDepartamento de Química Inorgánica y Nuclear, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MexicoDepartamento de Física y Química Teórica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MexicoDepartment of Biology, University of Konstanz, D-78457 Konstanz, GermanyDepartamento de Química Inorgánica y Nuclear, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City 04510, MexicoHydrogenation and dehydrogenation reactions are fundamental in chemistry and essential for all living organisms. We employ density functional theory (DFT) to understand the reaction mechanism of the oxidative dehydrogenation (ODH) of the pyridyl-amine complex [Fe<sup>III</sup>L<sup>3</sup>]<sup>3+</sup> (L<sup>3</sup>, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanonane) to the mono-imine complex [Fe<sup>II</sup>L<sup>4</sup>]<sup>2+</sup> (L<sup>4</sup>, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanon-1-ene) in the presence of dioxygen. The nitrogen radical [Fe<sup>II</sup>L<sup>3</sup><sub>N8•</sub>]<sup>2+</sup>, formed by deprotonation of [Fe<sup>III</sup>L<sup>3</sup>]<sup>3+</sup>, plays a crucial role in the reaction mechanism derived from kinetic studies. O<sub>2</sub> acts as an oxidant and is converted to H<sub>2</sub>O. Experiments with the deuterated ligand L<sup>3</sup> reveal a primary C-H kinetic isotope effect, <i>k</i><sup>CH</sup>/<i>k</i><sup>CD</sup> = 2.30, suggesting C-H bond cleavage as the rate-determining step. The DFT calculations show that (i) <sup>3</sup>O<sub>2</sub> abstracts a hydrogen atom from the α-pyridine aliphatic C-H moiety, introducing a double bond regio-selectively at the C<sub>7</sub>N<sub>8</sub> position, via the hydrogen atom transfer (HAT) mechanism, (ii) O<sub>2</sub> does not coordinate to the iron center to generate a high-valent Fe oxo species observed in enzymes and biomimetic complexes, and (iii) the experimental activation parameters (ΔH<sup>≠</sup> = 20.38 kcal mol<sup>−1</sup>, ΔS<sup>≠</sup> = −0.018 kcal mol<sup>−1</sup> K<sup>−1</sup>) fall within in the range of values reported for HAT reactions and align well with the computational results for the activated complex [Fe<sup>II</sup>L<sup>3</sup><sub>N8•</sub>]<sup>2+</sup>···<sup>3</sup>O<sub>2</sub>.https://www.mdpi.com/2304-6740/13/1/22oxidative dehydrogenationhydrogen atom transferdensity functional theorynitrogen radicaldioxygen activationregio-selective C-H cleavage |
| spellingShingle | Ricardo D. Páez-López Miguel Á. Gómez-Soto Héctor F. Cortés-Hernández Alejandro Solano-Peralta Miguel Castro Peter M. H. Kroneck Martha E. Sosa-Torres Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study Inorganics oxidative dehydrogenation hydrogen atom transfer density functional theory nitrogen radical dioxygen activation regio-selective C-H cleavage |
| title | Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study |
| title_full | Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study |
| title_fullStr | Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study |
| title_full_unstemmed | Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study |
| title_short | Understanding Dioxygen Activation in the Fe(III)-Promoted Oxidative Dehydrogenation of Amines: A Computational Study |
| title_sort | understanding dioxygen activation in the fe iii promoted oxidative dehydrogenation of amines a computational study |
| topic | oxidative dehydrogenation hydrogen atom transfer density functional theory nitrogen radical dioxygen activation regio-selective C-H cleavage |
| url | https://www.mdpi.com/2304-6740/13/1/22 |
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