C-H activation and nucleophilic substitution in a photochemically generated high valent iron complex.

The photochemical oxidation of a (TAML)Fe complex using visible light generated Ru(bpy) produces valence tautomers (TAML)Fe ( ) and (TAML˙)Fe ( ), 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˙)Fe 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 = 1 [(TAML)Fe(CN)] 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˙)Fe 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.