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[6.4.0.02,10.09,11]dodecane (norDTCO) is described. Density function theory (DFT) was used to calculate the structures of the neutral norDTCO, the radical cation norDTCO+●, and the dication norDTCO2+ 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 norDTCO in a single wave, which was nearly reversible at slow scan rates. Similar to the oxidation of 1,5-dithia cylooctane (DTCO) to DTCO2+, norDTCO2+ 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.