Ligand driven heterolytic O-O bond cleavage in a non-haem phenolato-Fe(III)-OOH complex to yield a formal Fe(V)=O intermediate

Fe(V)=O species can be generated by the heterolytic cleavage of the O-O bond of corresponding Fe(III)-OOH species. In haem complexes the redox non-innocence of the ligand facilitates such heterolytic cleavage, however non-haem iron complexes generally show homolytic cleavage to form an Fe(IV)=O species and a hydroxyl radical. The hydroxyl radical formed is undesirable due to its non-selective reactivity. Here we show that the redox non-innocence of a phenolato ligand moiety in the complex [LFe(III)(μ-O)Fe(III)L]²⁺, where L is 2-(((di(pyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino)methyl)phenolate, facilitates heterolytic O-O bond cleavage, similar in manner to that observed with haem Fe(iii)-OOH species, to yield a formal Fe(V)=O intermediate. Although not observed directly, the intermediacy of an Fe(V)=O species is manifested in the immediate appearance of a doubly oxidised bis-phenolato bridged complex observed by time resolved UV/vis absorption and resonance Raman spectroscopy. This complex is formed by C-C coupling at the para position of the phenolato moiety of the ligand. The pathways to form the final complex via various Fe(IV)=O and Fe(V)=O intermediates are investigated by DFT methods, which indicate that the impact of the phenolato moiety is due to its redox non-innocence primarily. The ability of the phenolato moiety to transfer charge and spin density induces a switch in the mechanism of O-O bond cleavage from homolytic to heterolytic manifested in the radical character at the para-position needed for C-C bond formation and the high oxidation state of the first observed product.