Journal article
Visible Light-Driven Ligand-to-Metal Charge Transfer-Mediated Selective Cleavage of β-O-4 Lignin Model Compounds: A Greener Route to Lignin Valorization
Green chemistry : an international journal and green chemistry resource : GC, Vol.27(17), pp.4664-4678
03/12/2025
DOI: 10.1039/D5GC00948K
Appears in UI Libraries Support Open Access
Abstract
Lignin is the most abundant renewable source of aromatics in Nature. The β-O-4 bond is the most predominant linkage in lignin; therefore, methods for the selective cleavage of the β-O-4 bond are of great importance in order to break down lignin and produce value-added aromatic compounds. Herein, we report a visible light-driven, ligand-to-metal charge transfer (LMCT)-mediated, two-step approach for cleaving Cβ-O bonds in β-O-4 alcohol model compounds using-titania (TiO2) as the photocatalyst. In the first step, the alcohol forms a visible light-absorbing LMCT-complex on the surface of titania, which enables the oxidation to the corresponding ketone under green light. The LMCT-mediated oxidation afforded high conversion of β-O-4 alcohol model compounds (79-97%) with high selectivity for β-O-4 ketones (>95%). Our studies reveal that the superoxide radical anion likely plays a key role in the oxidation. In the second step, the LMCT assisted- reductive cleavage of β-O-4 ketone is achieved by employing triethylammonium tetraphenylborate as a visible light sensitizer and proton donor. The LMCT-facilitated reductive cleavage of β-O-4 ketone exhibits high selectivity (up to 100%) for target fragmentation products under blue light. Experiments including EPR analysis suggest that in situ formed Ti3+ is responsible for the reductive cleavage of β-O-4 ketone. Moreover, a two-step, one-pot cleavage reaction was successfully carried out with good to high selectivity for Cβ-O bond cleavage productswith a single catalyst. Our work offers a promising solution for the selective cleavage of β-O-4 bond under mild conditions to promote lignin valorization. Furthermore, it provides potentially general strategies for enabling visible light-driven LMCT-mediated photocatalysis in related organic transformations.
Details
- Title: Subtitle
- Visible Light-Driven Ligand-to-Metal Charge Transfer-Mediated Selective Cleavage of β-O-4 Lignin Model Compounds: A Greener Route to Lignin Valorization
- Creators
- Ayesha KhanLogan W. EvansDavid Martin
- Resource Type
- Journal article
- Publication Details
- Green chemistry : an international journal and green chemistry resource : GC, Vol.27(17), pp.4664-4678
- Publisher
- Royal Society of Chemistry
- DOI
- 10.1039/D5GC00948K
- ISSN
- 1463-9262
- eISSN
- 1463-9270
- Language
- English
- Date published
- 03/12/2025
- Academic Unit
- Iowa Neuroscience Institute; Chemistry
- Record Identifier
- 9984799677702771
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