A Reversible Electron Relay to Exclude Sacrificial Electron Donors in the Photocatalytic Oxygen Atom Transfer Reaction with O₂ in Water

Abstract

Using light energy and O2 for the direct chemical oxidation of organic substrates is a major challenge. A limitation is the use of sacrificial electron donors to activate O2 by reductive quenching of the photosensitizer, generating undesirable side products. A reversible electron acceptor, methyl viologen, can act as electron shuttle to oxidatively quench the photosensitizer, [Ru(bpy)3]2+, generating the highly oxidized chromophore and the powerful reductant methyl‐viologen radical MV+.. MV+. can then reduce an iron(III) catalyst to the iron(II) form and concomitantly O2 to O2.− in an aqueous medium to generate an active iron(III)‐(hydro)peroxo species. The oxidized photosensitizer is reset to its ground state by oxidizing an alkene substrate to an alkenyl radical cation. Closing the loop, the reaction of the iron reactive intermediate with the substrate or its radical cation leads to the formation of two oxygenated compounds, the diol and the aldehyde following two different pathways.

Sensitization-initiated electron transfer via upconversion: mechanism and photocatalytic applications

“…This seems essential for future rational progress development in this thriving research area and could have important implications for organic synthetic photochemistry and solar energy conversion. [85][86][87]…”

Amphiphilic Polymeric Nanoparticles for Photoredox Catalysis in Water

“…Hitherto, examples for photoredox catalysis in pure water are scarce and mostly rely on water‐soluble ruthenium complexes or micellar approaches . For instance, in pioneering work of Lipshutz and co‐workers, tailor‐made micelles have been applied as reaction compartments for efficient catalysis in water.…”

Intercepting a transient non-hemic pyridine N-oxide Fe(iii) species involved in OAT reactions

“…Upon addition of PhIO, the broad dissymmetric doublet , (d = 0.45 mm s -1 , DEQ = 0.78 mm s -1 ) of the starting complex gives rise to a new spectrum that can be described as the main contribution of a broad sextet extending from -8 to 9 mm s -1 (64%, d = 0.46 mm s -1 , DEQ = 0.61 mm s -1 ) attributed to the signature of a S=5/2 species and a quadrupolar doublet (39%, d = 0.51 mm s -1 , DEQ = 1.59 mm s -1 ) most probably arising from a magnetically silent µ-oxo dimeric species generated under the high concentration of the Mössbauer analysis. 17 No genuine Fe(V) or Fe(IV)=O signatures were identified therefore ruling out such formulation for the transient species previously detected by UV and EPR. Interestingly, upon ageing of the previous solution, the main magnetic Mössbauer signal disappeared to give a 1:1 mixture of the starting signal and the diamagnetic doublet (Fig.…”