Mechanistic Study of Chemoselectivity for Carbon Radical Hydroxylation versus Chlorination with FeIII(OH)(Cl) Complexes

• Published in: Chemistry, an Asian journal an Asian journal, 2023-03, Vol.18 (6), p.e202201311-n/a
• Main Authors: Yang, Miao, Chen, Xiahe, Su, Xingxing, She, Yuan‐Bin, Yang, Yun‐Fang
• Format: Article
• Language: English
• Subjects: Chemistry; chemoselectivity; Chlorination; Density functional theory; Energy of dissociation; Free energy; Heat of formation; Hydrogen bonding; Hydroxyl groups; Hydroxylation; Isomerization; non-heme iron complex; reaction mechanisms
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202201311

The FeIII(OH)(Cl) complex resembles the key intermediate proposed for the non‐heme iron halogenases. Goldberg and co‐workers reported that the FeIII(OH)(Cl) RC reacts with triphenylmethyl radical 1 to give an exclusive hydroxylation product. To understand the chemoselectivity of the reaction of RC with 1, density functional theory (DFT) calculations have been conducted. From RC, the competing pathways were identified as the OH‐transfer, Cl‐transfer, and isomerization pathways. The direct Cl‐transfer is more favorable than direct OH‐transfer by 2.8 kcal/mol. The hydrogen bonding interactions between the hydroxyl group and the pendent amine ligand impede the direct OH‐transfer from RC. Compared with the direct Cl‐transfer pathway, the isomerization pathways require lower barriers. In isomer RCiso2, the equatorial hydroxyl group, which has smaller diabatic bond dissociation energy, prefers to transfer to form the hydroxylation product. In FeIII(Cl)2 RC2 and RC2iso, the equatorial chloride group also prefers to transfer to give the chlorination product. DFT calculations reveal that the equatorial hydroxyl group in the isomers of the FeIII(OH)(Cl) complex prefers to transfer to rebind with the radical to form the hydroxylation product.