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Visible-light-induced tandem reaction of o-aminothiophenols and alcohols to benzothiazoles over Fe-based MOFs: Influence of the structure elucidated by transient absorption spectroscopy
Summary:
The authors from Research Institute of Photocatalysis, Fuzhou University and Instituto de Tecnología Química, Universitat Politècnica de València, etc. developed Fe-based metal-organic frameworks (MIL-100(Fe) and MIL-68(Fe)) with visible-light photocatalytic activity, achieving efficient synthesis of 2-substituted benzothiazoles in the field of light-induced organic transformations.
Background:
1. 2-substituted benzothiazoles are important heterocyclic compounds, but traditional synthesis methods use toxic oxidants or have low atom efficiency, and existing catalytic systems have problems such as difficulty in recycling and high energy consumption.
2. The authors proposed using Fe-based MOFs as multifunctional catalysts for visible-light-induced tandem reactions of o-aminothiophenols and alcohols, realizing green and efficient synthesis of 2-substituted benzothiazoles.
Research Content:
1. Synthesis:
The authors synthesized MIL-100(Fe) via a solvothermal method using Fe(NO₃)₃·9H₂O and 1,3,5-benzenetricarboxylic acid (H₃BTC) at 180°C for 12 h; MIL-68(Fe) was synthesized by solvothermal reaction of FeCl₃·6H₂O, 1,4-benzenedicarboxylic acid (H₂BDC), hydrofluoric acid, and hydrochloric acid in N,N-dimethylformamide at 100°C for 120 h.
2. Characterizations:
1) BET results showed MIL-100(Fe) had a specific surface area of 2021 m²/g, and MIL-68(Fe) had corresponding porous properties.
2) SEM/TEM tests were not explicitly mentioned, but XRD confirmed their crystal structures matched the calculated patterns.
3) UV-vis DRS showed both had absorption in 200-550 nm; ESR confirmed superoxide radicals (O₂⁻·) were generated; transient absorption spectroscopy (TAS) revealed MIL-100(Fe) had higher concentration of long-lived positive holes (1.48 ms) than MIL-68(Fe) (0.63 ms).
3. Application:
The materials catalyzed visible-light-induced tandem reactions of o-aminothiophenols and alcohols to produce 2-substituted benzothiazoles. MIL-100(Fe) showed better performance, with o-aminothiophenol conversion up to 91% and selectivity 98% for 2-phenylbenzothiazole, applicable to various substrates and scalable.
4. Mechanism:
Upon visible light irradiation, Fe³⁺ in Fe-O clusters is reduced to Fe²⁺, which reduces O₂ to O₂⁻·. Alcohols are oxidized to aldehydes by holes and O₂⁻·. Aldehydes condense with o-aminothiophenols (promoted by Lewis acidic Fe³⁺) to form intermediates, which are oxidized by O₂⁻· to 2-substituted benzothiazoles. MIL-100(Fe) is superior due to more long-lived positive holes.
Outlook:
This research provides a green method for synthesizing 2-substituted benzothiazoles, demonstrates the structure-activity relationship of Fe-based MOFs via TAS, and highlights their potential in light-induced organic transformations.
Visible-light-induced tandem reaction of o-aminothiophenols and alcohols to benzothiazoles over Fe-based MOFs: Influence of the structure elucidated by transient absorption spectroscopy
Authors: Dengke Wang, Josep Albero, Hermenegildo García, Zhaohui Li
DOI: 10.1016/j.jcat.2017.01.014
Link: https://www.sciencedirect.com/science/article/pii/S002195171730026X
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SEO keywords: MIL-100(Fe), MIL-68(Fe), benzothiazoles, visible-light catalysis, H₃BTC, H₂BDC
SEO description: Fe-based MOFs (MIL-100, MIL-68) catalyze visible-light synthesis of benzothiazoles from alcohols and o-aminothiophenols.
