Structural Studies Provide Insight on the Fate of 1,5-Dithiacanes: Two Electron Reversible Oxidation versus Irreversible Oxidation

Synthesis and chemical/electrochemical properties of a conformationally constrained 1,5-dithiocane -3,7-dithiatricyclo[6.4.0.0^2,10.0^9,11]dodecane (<b>norDTCO)</b> is described. Density function theory (DFT) was used to calculate the structures of the neutral <b>norDTCO</b>, the radical cation <b>norDTCO</b>^<b>+●</b>, and the dication <b>norDTCO</b>^<b>2+</b> to investigate the importance of orbital orientations in the oxidation mechanism. Results of the first oxidation were consistent with a 2-center-3-electron (2c-3e) bonding interaction between the sulfur atoms in the radical cation. Results of the second oxidation were consistent with a transannular S-S σ-bond in the dication. In acetonitrile, the electrochemical oxidation was consistent with an apparent two-electron oxidation of <b>norDTCO</b> in a single wave, which was nearly reversible at slow scan rates. Similar to the oxidation of 1,5-dithia cylooctane (<b>DTCO</b>) to <b>DTCO</b>^<b>2+</b>, <b>norDTCO</b>^<b>2+</b> was consistent with the formation of a ⁺S-S⁺ σ-bond as predicted by DFT calculations. DFT calculations of various constrained and unconstrained 1,5-dithiacanes were used to identify conditions where neighboring group participation was important and where a reversible two-electron oxidation/reduction wave could occur. However, in dichloromethane, two one-electron waves were observed, which indicates that in dichloromethane a transannular ⁺S-S⁺ σ-bond was not formed.