Selective Photochemical Alcohol Oxidation Reactions catalyzed by an Iron Complex using H₂O as O-atom Source

Thomas, Jithin (2018) Selective Photochemical Alcohol Oxidation Reactions catalyzed by an Iron Complex using H₂O as O-atom Source. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The selective oxidation of alcohols to their respective carbonyl derivative is widely known to be carried out by the heme enzyme CytP450. Both native enzymes and model complexes have been employed to understand the mechanism of this reaction extensively. It mainly shows the involvement of high-valent FeIV(O)−porphyrin•+ intermediate with alcohol substrates. Similarly, it is proposed that a high-valent manganese-oxo cluster is responsible for the oxidation of water during photosynthesis, which is an energetically uphill reaction. Combining both these concepts, this work utilizes light for the transformation of organic compounds by the generation of high valent metal oxo complex. Here, we discuss the selective photocatalytic alcohol oxidation and its mechanistic insight with FeV(O) complex of biuret TAML (bTAML), which is isoelectronic with FeIV(O)−porphyrin•+ intermediate form in CytP450. The photocatalytic alcohol oxidation reactions using water as the oxygen-atom source is selectively done by an iron complex, [(bTAML) FeIII-OH₂] - (1). In presence of H₂¹⁸O, low yield of ¹⁸O labelled oxidized aldehyde product indicates that water is the primary source of oxygen which is responsible for generating high valent oxo species. We anticipate that the starting complex 1 undergo PCET upon light irradiation forming an active [{(bTAML)FeIV}2-μ-oxo]²- (2) dimer which in the presence of substrate disproportionate to form FeVO and catalyze the alcohol oxidation reactions via a “net hydride mechanism”. In short, This work exhibits selective photocatalytic alcohol oxidation by employing [Et₄N][(bTAML)FeIII(OH₂)] (1) as a catalyst, [RuII(bpy)₃]Cl₂ as a photosensitizer, [CoIII(NH₃)₅Cl]Cl₂ as a mild one electron acceptor and water as the oxygen atom source. To the best of our knowledge, this will represent the first example of photochemical oxidation of alcohols selectively using water as O-atom donor by an iron-complex.

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