Long-Lived Photoexcited State of a Mn(IV)-Oxo Complex Binding Scandium Ions That is Capable of Hydroxylating Benzene

In plain language

Photoexcitation of a manganese(IV)-oxo complex bound to scandium ions generates a long-lived photoexcited state capable of converting benzene into phenol. This reaction occurs in a mixture of trifluoroethanol and acetonitrile. The mechanism driving the photohydroxylation process involves electron transfer from benzene directly to the excited state of the metal complex. This electron transfer generates a benzene radical cation, which subsequently reacts with water to produce phenol. Laser-induced transient absorption measurements confirmed the formation of the radical intermediate and tracked its subsequent reaction with water. The findings demonstrate how combining transition metal-oxo complexes with Lewis acidic metal ions can facilitate light-driven chemical transformations of stable aromatic hydrocarbons.

Key takeaways

Light excitation of a scandium-bound manganese(IV)-oxo complex creates a long-lived excited state.
The photoexcited complex directly converts benzene to phenol in a trifluoroethanol and acetonitrile solvent system.
The reaction proceeds via electron transfer from benzene to the excited complex to generate a benzene radical cation.
Laser-induced transient absorption measurements confirmed that the resulting benzene radical cation reacts with water.

Why it matters

Benzene is an exceptionally stable chemical compound, and converting it directly into phenol typically demands harsh, energy-intensive conditions. Demonstrating that a light-activated metal complex can achieve this transformation through electron transfer offers valuable insight into the design of light-driven oxidation reactions. These findings help researchers understand fundamental mechanisms that could inform milder, light-assisted methods for functionalising inert chemical bonds.

Commercialisation angle

This work represents early-stage fundamental research into light-activated oxidation chemistry. While the direct conversion of benzene to phenol is of strong interest to industrial chemical manufacturers and fine-chemical synthesists, the abstract reports only laboratory-scale mechanistic and spectroscopic observations in specialised solvents. The research is far from practical application, and substantial development would be required before any commercial pathway could be established.

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Abstract

Photoexcitation of a MnIV-oxo complex binding scandium ions ([(Bn-TPEN)MnIV(O)]2+-(Sc(OTf)3)2) in a solvent mixture of trifluoroethanol and acetonitrile (v/v = 1:1) resulted in formation of the long-lived photoexcited state, which can hydroxylate benzene to phenol. The photohydroxylation of benzene by [(Bn-TPEN)MnIV(O)]2+-(Sc(OTf)3)2 was made possible by electron transfer from benzene to the long-lived 2 E excited state of [(Bn-TPEN)MnIV(O)]2+-(Sc(OTf)3)2 to produce a benzene radical cation, which reacted with water as revealed by laser-induced transient absorption measurements.

Research topics

Lanthanide and Transition Metal Complexes
Metal-Catalyzed Oxygenation Mechanisms
Magnetism in coordination complexes

Sustainable Development Goals

6Clean Water and Sanitation

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