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C-H activation and nucleophilic substitution in a photochemically generated high valent iron complex
J.H. Lim, X. Engelmann, S. Corby, , K. Ray, H.S. Soo
Published in Royal Society of Chemistry
Volume: 9
Issue: 16
Pages: 3992 - 4002
The photochemical oxidation of a (TAML)FeIII complex 1 using visible light generated Ru(bpy)33+ produces valence tautomers (TAML)FeIV (1+) and (TAML+)FeIII (1-TAML+), depending on the exogenous anions. The presence of labile Cl- or Br- results in a ligand-based oxidation and stabilisation of a radical-cationic (TAML+)FeIII complex, which subsequently leads to unprecedented C-H activation followed by nucleophilic substitution on the TAML aryl ring. In contrast, exogenous cyanide culminates in metal-based oxidation, yielding the first example of a crystallographically characterised S = 1 [(TAML)FeIV(CN)2]2- species. This is a rare report of an anion-dependent valence tautomerisation in photochemically accessed high valent (TAML)Fe systems with potential applications in the oxidation of pollutants, hydrocarbons, and water. Furthermore, the nucleophilic aromatic halogenation reaction mediated by (TAML+)FeIII represents a novel domain for high-valent metal reactivity and highlights the possible intramolecular ligand or substrate modification pathways under highly oxidising conditions. Our findings therefore shine light on high-valent metal oxidants based on TAMLs and other potential non-innocent ligands and open new avenues for oxidation catalyst design. © 2018 The Royal Society of Chemistry.
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