Issue 19, 2022

Heme compound II models in chemoselectivity and disproportionation reactions

Abstract

Heme compound II models bearing electron-deficient and -rich porphyrins, [FeIV(O)(TPFPP)(Cl)] (1a) and [FeIV(O)(TMP)(Cl)] (2a), respectively, are synthesized, spectroscopically characterized, and investigated in chemoselectivity and disproportionation reactions using cyclohexene as a mechanistic probe. Interestingly, cyclohexene oxidation by 1a occurs at the allylic C–H bonds with a high kinetic isotope effect (KIE) of 41, yielding 2-cyclohexen-1-ol product; this chemoselectivity is the same as that of nonheme iron(IV)-oxo intermediates. In contrast, as observed in heme compound I models, 2a yields cyclohexene oxide product with a KIE of 1, demonstrating a preference for C[double bond, length as m-dash]C epoxidation. The latter result is interpreted as 2a disproportionating to form [FeIV(O)(TMP+˙)]+ (2b) and FeIII(OH)(TMP), and 2b becoming the active oxidant to conduct the cyclohexene epoxidation. In contrast to 2a, 1a does not disproportionate under the present reaction conditions. DFT calculations confirm that compound II models prefer C–H bond hydroxylation and that disproportionation of compound II models is controlled thermodynamically by the porphyrin ligands. Other aspects, such as acid and base effects on the disproportionation of compound II models, have been discussed as well.

Graphical abstract: Heme compound II models in chemoselectivity and disproportionation reactions

Supplementary files

Article information

Article type
Edge Article
Submitted
01 mar 2022
Accepted
11 abr 2022
First published
12 abr 2022
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2022,13, 5707-5717

Heme compound II models in chemoselectivity and disproportionation reactions

R. Gupta, X. Li, Y. Lee, M. S. Seo, Y. Lee, S. Yanagisawa, M. Kubo, R. Sarangi, K. Cho, S. Fukuzumi and W. Nam, Chem. Sci., 2022, 13, 5707 DOI: 10.1039/D2SC01232D

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