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Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination.
Inorg Chem. 2020 Feb 03; 59(3):1622-1632.IC

Abstract

The formation mechanism and electronic structures of iron porphyrin nitrene intermediates, as well as the nitrene-mediated intermolecular C-H amination, have been studied by performing DFT and ab initio complete active space self-consistent field (CASSCF) calculations. Compared with that of cobalt porphyrin nitrene and iron porphyrin carbene, the formation of iron porphyrin nitrene shows similar but different characteristics. The common feature is that all their formation is required to undergo the "far" or "close" complexes, but these complexes correspond to different energies relative to their respective reactants (isolated metalloporphyrins and azides), which is considered as one main reason to determine the reaction barriers. The overall free energy barrier for the formation of iron porphyrin nitrene was calculated to be 10.6 kcal/mol on a triplet-state surface, which is lower than those of cobalt porphyrin nitrene and iron porphyrin carbene. The departure of N2 from the close complexes formed by iron porphyrin and tosyl azide is nearly barrierless. For iron porphyrin nitrene, both CASSCF and unrestricted DFT calculations revealed that the triplet and open-shell singlet complexes correspond to very similar energies. The triplet nitrene complex can be described as [(por)(-OCH3)FeII═NTs]- ↔ [(por)(-OCH3)FeIII═N•-Ts]- ↔ [(por)(-OCH3)FeIV═N2-Ts]-, while the oss nitrene complex can be described as [(por)(-OCH3)FeIII-N•-Ts]-. Since the N atom bears a similar spin density as in cobalt porphyrin nitrene, the iron porphyrin nitrene exhibits similar activity in hydrogen abstraction. In addition, the intermolecular C-H amination catalyzed by iron porphyrin nitrene follows the hydrogen atom abstraction/radical recombination mechanism with a free energy barrier of 7.1 kcal/mol on the triplet-state surface. In general, the medium reactivity and easily prepared characteristic of iron porphyrin nitrene makes it a potential catalyst for C-H amination.

Authors+Show Affiliations

School of Chemistry and Chemical Engineering , Shandong University , Jinan , Shandong 250100 , China.School of Chemistry and Chemical Engineering , Qilu Normal University , Jinan , Shandong 250013 , China.School of Chemistry and Chemical Engineering , Shandong University , Jinan , Shandong 250100 , China.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31927910

Citation

Li, Xinyi, et al. "Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination." Inorganic Chemistry, vol. 59, no. 3, 2020, pp. 1622-1632.
Li X, Dong L, Liu Y. Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination. Inorg Chem. 2020;59(3):1622-1632.
Li, X., Dong, L., & Liu, Y. (2020). Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination. Inorganic Chemistry, 59(3), 1622-1632. https://doi.org/10.1021/acs.inorgchem.9b02216
Li X, Dong L, Liu Y. Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination. Inorg Chem. 2020 Feb 3;59(3):1622-1632. PubMed PMID: 31927910.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Theoretical Study of Iron Porphyrin Nitrene: Formation Mechanism, Electronic Nature, and Intermolecular C-H Amination. AU - Li,Xinyi, AU - Dong,Lihua, AU - Liu,Yongjun, Y1 - 2020/01/13/ PY - 2020/1/14/pubmed PY - 2020/1/14/medline PY - 2020/1/14/entrez SP - 1622 EP - 1632 JF - Inorganic chemistry JO - Inorg Chem VL - 59 IS - 3 N2 - The formation mechanism and electronic structures of iron porphyrin nitrene intermediates, as well as the nitrene-mediated intermolecular C-H amination, have been studied by performing DFT and ab initio complete active space self-consistent field (CASSCF) calculations. Compared with that of cobalt porphyrin nitrene and iron porphyrin carbene, the formation of iron porphyrin nitrene shows similar but different characteristics. The common feature is that all their formation is required to undergo the "far" or "close" complexes, but these complexes correspond to different energies relative to their respective reactants (isolated metalloporphyrins and azides), which is considered as one main reason to determine the reaction barriers. The overall free energy barrier for the formation of iron porphyrin nitrene was calculated to be 10.6 kcal/mol on a triplet-state surface, which is lower than those of cobalt porphyrin nitrene and iron porphyrin carbene. The departure of N2 from the close complexes formed by iron porphyrin and tosyl azide is nearly barrierless. For iron porphyrin nitrene, both CASSCF and unrestricted DFT calculations revealed that the triplet and open-shell singlet complexes correspond to very similar energies. The triplet nitrene complex can be described as [(por)(-OCH3)FeII═NTs]- ↔ [(por)(-OCH3)FeIII═N•-Ts]- ↔ [(por)(-OCH3)FeIV═N2-Ts]-, while the oss nitrene complex can be described as [(por)(-OCH3)FeIII-N•-Ts]-. Since the N atom bears a similar spin density as in cobalt porphyrin nitrene, the iron porphyrin nitrene exhibits similar activity in hydrogen abstraction. In addition, the intermolecular C-H amination catalyzed by iron porphyrin nitrene follows the hydrogen atom abstraction/radical recombination mechanism with a free energy barrier of 7.1 kcal/mol on the triplet-state surface. In general, the medium reactivity and easily prepared characteristic of iron porphyrin nitrene makes it a potential catalyst for C-H amination. SN - 1520-510X UR - https://www.unboundmedicine.com/medline/citation/31927910/Theoretical_Study_of_Iron_Porphyrin_Nitrene:_Formation_Mechanism_Electronic_Nature_and_Intermolecular_C_H_Amination_ L2 - https://doi.org/10.1021/acs.inorgchem.9b02216 DB - PRIME DP - Unbound Medicine ER -
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