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(pinF)2] (pinF = 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(pinF) interactions) behave like covalent compounds in solution, whereas the more encapsulated 3 and 4 (without K+⋯O(pinF) 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[FeIII(OH)(pinF)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.