Cation encapsulation modulates oxygen atom transfer in O₂-reducing Fe(ii) fluorinated alkoxide complexes

Herein, we report a series of four high-spin, square-planar Fe(ii) compounds, {K(L)}₂[Fe(pin^F)₂] (pin^F = perfluoropinacolate), with modulated K⁺ encapsulations (L = Et₂O (1), 2 DME (2), 18c6 (3), crypt (4); crypt = 2.2.2-cryptand). The effect of encapsulating cations with crown or crypt ethers was quantified by solution conductivity measurements, showing that the less encapsulated 1 and 2 (with K⁺⋯O(pin^F) interactions) behave like covalent compounds in solution, whereas the more encapsulated 3 and 4 (without K⁺⋯O(pin^F) interactions in the Fe coordination sphere) behave like a 1 : 1 electrolyte. These Fe(ii) complexes readily react with O₂ to form a reactive intermediate proposed to be an Fe(iii) superoxide, n-O₂ ( n = 1-4), which performs OAT to PPh₃ as a function of the degree of K⁺ encapsulation. The less-encapsulated analogs 1-O₂ and 2-O₂ form O[double bond, length as m-dash]PPh₃ at 88(9)% and 80(2)% respectively, while the more-encapsulated analogs 3-O₂ and 4-O₂ do so to a lesser degree, at 54(2)% and 5(2)%, respectively. In addition, both d-d and LMCT electronic absorption features of 1-4 vary as a function of K⁺ encapsulation. Dioxygen reduction was monitored by VT UV-vis spectroscopy and the oxidized Fe-containing product {K(18c6)}₂[Fe^III(OH)(pin^F)₂], 5, was isolated from reaction of 3 and excess O₂. These experiments demonstrate the powerful potential of cation encapsulation to modulate OAT reactivity from reduced O₂ species.