Reactivity of a Fe(III)-Bound Methoxide Supported with a Tris(thiolato)phosphine Ligand: Activation of C-Cl Bond in CH₂Cl₂ by Nucleophilic Attack of a Fe(III)-OCH₃ Moiety

Two mononuclear nonheme Fe^III complexes, [PPh₄][Fe^III(PS3′)(OCH₃)] (1) and [PPh₄][Fe^III(PS3′)(Cl)] (2), supported by a tris(benzenethiolato)phosphine derivative PS3′ (PS3′ = P(C₆H₃-3-Me₃Si-2-S)₃^3-) have been synthesized and characterized. The structures resolved from X-ray crystallography show that Fe^III centers in both complexes adopt distorted trigonal-bipyramidal geometry with a methoxide or a chloride binding in the axial position. The magnetic data for both are consistent with intermediate-spin Fe^III centers with a C₃ symmetry (S = 3/2 ground state). The bound methoxide in 1 is labile and can be replaced by a CH₃CN molecule. The forming Fe^III-CH₃CN species can be further reduced by cobaltcene quantitatively to a stable Fe^II-CH₃CN complex, [Fe(PS3′)(CH₃CN)]^-. One-electron oxidation of 2 by ferrocenium gave a Fe^IV analogue, [Fe^IV(PS3′)(Cl)]. Importantly, the Fe^III-OCH₃ moiety in complex 1 acts as a strong nucleophile that activates the C-Cl bond in CH₂Cl₂, leading to the formation of complex 2 quantitatively. Complex 1 also reacts with other electrophiles, benzyl chloride and benzyl bromide, to generate Fe^III-X species (X = Cl or Br). The reactions were investigated and monitored by UV-vis-NIR, NMR, and ESI-MS spectroscopies.