Phase and Redox Shifted Four Iron/Four Sulfur Clusters: Fluorous Analogs of Metalloenzyme Cofactors

Reactions of (1) Q[Fe4S4(SC(CH3)(3))(4)] and the fluorous thiols HS(CH2)(n)R-f8 (n = 2, 3; R-f8 = (CF2)(7)CF3)), or (2) Na[Fe4S4(S(CH2)(n)R-f8)(4)] (n = 2, 3) and [PhCH2P((CH2)(3)R-f6)(3)][Br] or [PPN][Cl] (PPN = Ph3P - N - PPh3), give the title compounds [Q] 2[Fe4S4(S(CH2) nRf8) 4], comprised of a fluorous dianion and in some cases fluorous cations, with (1) Q/n = Ph4P/2 (4, 67%), Ph4P/3 (5, 67%), Me4N/3 (69%), and Ph3P(CH2)(2)R-f6/2 (73%) or (2) PhCH2P((CH2)(3)R-f6)(3)/2 (14, 39%), PhCH2P((CH2)(3)R-f6)(3)/3 (15, 63%), and PPN/2 (36%). The educt Ph3P(CH2)(2)Rf(6)[Fe4S4(SC(CH3)(3))(4)] is in turn prepared from FeCl3, HSC(CH3)(3)/CH3ONa, and [Ph3P( CH2)(2)R-f6][I], and the educts Na[Fe4S4(S(CH2) nR(f8))(4)] from Na[Fe4S4(SC(CH3)(3))(4)] and HS(CH2) nRf8. The SCH2 H-1 and C-13 NMR signals of these paramagnetic salts appear 8.7-10.3 and 32.3-34.9 ppm downfield from those of the corresponding thiols, but the chemical shifts of other signals are nearly normal. The UV-visible spectra show bands similar to those of non-fluorous analogs (290-298 nm and 406-415 nm; e = 25 700 and 19 200 M-1 cm-1 for 5). The singly fluorous salts are soluble in organic solvents of moderate polarity, but not in fluorous solvents. The doubly fluorous salts 14, 15 are soluble in all fluorous solvents assayed, with partition coefficients of > 99.65 : < 0.35 (CF3C6F11/toluene) and 93.2-93.1 : 6.9-6.8 (FC-72/THF). Cyclic voltammograms carried out using a platinum working microelectrode show that 4 is 0.08 V thermodynamically easier to reduce than 5.