C/O/P/S cycles derived from oxidative intramolecular disulfide (–S–S–) coupling of ferrocenyl dithiophosphonates

• Facile intramolecular oxidation with mild oxidant resulting in new ferrocenyl-based disulfides.
• Formation of small macrocycles containing C, O, P, S heteroatoms in the ring.
• Novel S–S coupled products containing ferrocenyl moiety.

The symmetrical 2,4-diferrocenyl-1,3-dithiadiphosphetane disulfide dimer, [FcP(μ-S)S]2 (Fc = ferrocenyl), reacts with ethanediol (molar ratio 1:1), trans-1,2-cyclohexanediol (molar ratio 1:1) and pentaerythritol (molar ratio 2:1) at 70 °C to form the respective dithiophosphonic acids in high yield. The acids were readily deprotonated by anhydrous ammonia to yield the corresponding ammonium salts (NH4)2[S2P(Fc)OCH2CH2O(Fc)PS2] (1), (NH4)2[(S2PFc)2(trans-1,2-O,O′-C6H10)] (2) and (NH4)4[C{CH2OPS2(Fc)}4] (3). The salts undergo facile intramolecular oxidation with the mild oxidant iodine in a I2/MeOH mixture resulting in new ferrocene-based disulfides of the type [{-CH2OP(S)(Fc)S-}2] (4), [(S2P-Fc)2(trans-1,2-O,O′-C6H10)] (5) and [C{CH2OP(S)(Fc)S}4] (6). The compounds 1–6 were characterized by 1H and 31P NMR and bulk purity were confirmed by either ESI-MS or elemental analysis. Compounds 4–6 were additionally characterized by single crystal X-ray analyses and 4 and 6 subjected to electrochemical investigations. Compounds 4–6 represent the first examples of structurally characterized intramolecular S–S coupled products derived from ferrocene-based dithiophosphonates.

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