1,2-Dithiin Annelated with Bicyclo[2.2.2]octene Frameworks. One-Electron and Two-Electron Oxidations and Formation of a Novel 2,3,5,6-Tetrathiabicyclo[2.2.2]oct-7-ene Radical Cation with Remarkable Stability Owing to a Strong Transannular Interaction

• Published in: Journal of the American Chemical Society Vol. 124; no. 50; pp. 15038 - 15050
• Main Authors: Wakamiya, Atsushi, Nishinaga, Tohru, Komatsu, Koichi
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 18.12.2002; Amer Chemical Soc
• Subjects: Bridged Bicyclo Compounds - chemistry; Bridged Bicyclo Compounds, Heterocyclic - chemical synthesis; Bridged Bicyclo Compounds, Heterocyclic - chemistry; Cations; Chemistry; Chemistry, Multidisciplinary; Condensed matter: structure, mechanical and thermal properties; Cyclohexanes - chemistry; Cyclohexenes; Cyclooctanes - chemical synthesis; Cyclooctanes - chemistry; Disulfides - chemical synthesis; Disulfides - chemistry; Electrochemistry; Electron Spin Resonance Spectroscopy; Exact sciences and technology; Heterocyclic compounds; Kinetics and mechanisms; Models, Molecular; Organic chemistry; Organic compounds; Physical Sciences; Physics; Reactivity and mechanisms; Science & Technology; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; DITHIOETHER DICATIONS; DIATOMIC SULFUR; THIARUBRINE; CHARGE-PERTURBED MOLECULES; SPIN-RESONANCE; CHEMISTRY; ION; SPECTRA; BOND; ELECTROCHEMICAL OXIDATION; Reaction intermediate; MO method; Frontier orbital; Molecular structure; EPR spectrometry; Theoretical study; Polycyclic compound; Hartree Fock method; NMR spectrometry; Experimental study; Cyclic voltammetry; Sulfur heterocycle; Electronic structure; Oxidative degradation; Organic radical cation; Crystalline structure
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja028297j

A stable derivative of 1,2-dithiin annelated with bicyclo[2.2.2]octene frameworks 4 was synthesized as red crystals by the reaction of a dilithiated dimer of bicyclo[2.2.2]octene with elemental sulfur in 59% yield. The cyclic voltammetry of 4 in CH2Cl2 at −78 °C showed two reversible oxidation waves at E 1/2 +0.18 V and +0.72 V versus Fc/Fc+, indicating that the radical cation and dication of 4 are stable under these conditions. Upon chemical one-electron oxidation of 4 in a rather low concentration (4.0 × 10-4 M) with a 1.5 equiv of SbCl5 in CH2Cl2, a radical cation 4 • + was formed, whose spin distribution was determined by ESR spectroscopy and by the results of theoretical calculations (UB3LYP/6-31G*). The electronic absorption spectrum of 4 • + in CH2Cl2 exhibited a maximum absorption at 428 nm (ε = 2.3 × 103), which was hypsochromically shifted from that of neutral 4 (469 nm). When the radical cation 4 • + was produced in higher concentration (0.06 M) in CH2Cl2, a disproportionation was found to take place to give a SbCl6 - salt of remarkably stable radical cation 5 • + having a novel 2,3,5,6-tetrathiabicyclo[2.2.2]oct-7-ene structure. In the X-ray structure of 5 • +SbCl6 -, the transannular distance (2.794(3) Å) between the sulfur atoms was found to be less than the sum of the van der Waals radii of a sulfur atom (3.70 Å), suggesting the existence of a bonding interaction between the two disulfide linkages. The theoretical calculations (UB3LYP/6-31G*) suggested that this transannular interaction could be described as the resonance between the limiting structures, each of them having a two-center three-electron bond between two sulfur atoms belonging to two different disulfide linkages:  thus, both the spin and positive charge are equally delocalized to the four sulfur atoms, causing a great stabilization of 5 • +. On the other hand, the 1,2-dithiin radical cation 4 • + was found to readily react with triplet oxygen with subsequent rearrangement to give the 1,2-dithiolium derivative 6 + having a carboxyl group. Finally, the reaction of 4 with an excess amount of SbF5 gave the corresponding dication 4 2+, which was found to be a 6π aromatic system on the basis of the results of NMR measurement and theoretical calculations.