Influence of Solvent-Dependent Carbene–Carbanion Equilibrium for Tris(2-pyridylthio)methanido Ligand on the Dioxygen Reactivity of Bioinspired Iron–Benzilate Complexes

Starting from the iron(II) complex, [(L¹)Fe^II(CH₃CN)₂]⁺ (<b>1</b>), of the tris(2-pyridylthio)methanido (L¹) ligand, an iron(II)-benzilate complex, [(L²)Fe^II(PyS)(benzilate)] (<b>2</b>), (L² = bis(2-pyridylthio)carbene and PyS = pyridine-2-thiolate) was isolated and characterized. Single crystal X-ray diffraction studies of <b>2</b> reveal that the iron(II) center is coordinated by the carbene ligand (L²) in a tridentate N₂C mode, along with a bidentate PyS formed upon C–S bond cleavage of L¹.

A solvent-dependent carbene-carbanion equilibrium for L¹ is favored toward carbene in the presence of anionic benzilate in dichloromethane, leading to the formation of <b>2</b>. Complex <b>2</b>, upon reaction with dioxygen, undergoes a rearrangement of the carbene (L²) to carbanion (L¹), ultimately affording an iron(III)-benzilate complex, [(L¹)Fe^III(benzilate)] (<b>3</b>).