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Issue 45, 2015
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Phase and redox shifted four iron/four sulfur clusters: fluorous analogs of metalloenzyme cofactors

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Abstract

Reactions of (1) [Q]2[Fe4S4(SC(CH3)3)4] and the fluorous thiols HS(CH2)nRf8 (n = 2, 3; Rf8 = (CF2)7CF3)), or (2) [Na]2[Fe4S4(S(CH2)nRf8)4] (n = 2, 3) and [PhCH2P((CH2)3Rf6)3][Br] or [PPN][Cl] (PPN = Ph3P[horiz bar, triple dot above]N[horiz bar, triple dot above]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)2Rf6/2 (73%) or (2) PhCH2P((CH2)3Rf6)3/2 (14, 39%), PhCH2P((CH2)3Rf6)3/3 (15, 63%), and PPN/2 (36%). The educt [Ph3P(CH2)2Rf6]2[Fe4S4(SC(CH3)3)4] is in turn prepared from FeCl3, HSC(CH3)3/CH3ONa, and [Ph3P(CH2)2Rf6][I], and the educts [Na]2[Fe4S4(S(CH2)nRf8)4] from [Na]2[Fe4S4(SC(CH3)3)4] and HS(CH2)nRf8. The SCH21H and 13C 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; ε = 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.

Graphical abstract: Phase and redox shifted four iron/four sulfur clusters: fluorous analogs of metalloenzyme cofactors

  • This article is part of the themed collection: Fluorine
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Publication details

The article was received on 25 May 2015, accepted on 20 Jul 2015 and first published on 30 Jul 2015


Article type: Paper
DOI: 10.1039/C5DT01959A
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Dalton Trans., 2015,44, 19615-19624

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    Phase and redox shifted four iron/four sulfur clusters: fluorous analogs of metalloenzyme cofactors

    C. Zhang, Z. Xi, K. M. Mueller, B. J. Holliday, H. S. Bazzi and J. A. Gladysz, Dalton Trans., 2015, 44, 19615
    DOI: 10.1039/C5DT01959A

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