1,5,2,4,6,8-Dithiatetrazocine. Synthesis, computation, crystallography and voltammetry of the parent heterocycle

Abstract

The prototypal 1,5,2,4,6,8-dithiatetrazocine has been synthesized for the first time by two routes: reaction of 1,2,3,5-dithiadiazolium chloride with N,N,N'-tris(trimethylsilyl)formamidine in acetonitrile and reaction of 1,2,3,5-dithiadiazolyl radical with dioxygen in solution. Yields are low but single crystals could be obtained for an X-ray crystal structure determination which shows it to have the planar delocalized structure predicted by B3LYP/6-311+G(2d,p) hybrid DFT calculations. The crystal structure is strongly reminiscent of that of benzene in the same Pbca space group. Aromaticity is demonstrated by a (1)H NMR chemical shift of +9.70 ppm indicative of diamagnetic ring shielding and an intense low-energy optical absorption with λ(max) = 349 nm (MeOH). The voltammetric behaviour of the title compound is compared with that of 1,3λ(4)δ(2),5,2,4-trithiadiazepine; both resist electrochemical oxidation and reduction over a wide potential range as is typical for aromatic heterocycles.

On the role of heteroatoms in aromatic rings. Insights from 10π main group elements heterorings [(EH)2S2N4]q(E = C, P, B, Si, Al and q = 0, −2)

“…The resulting backbone bears an eight-membered ring with three different atom types C/N/S in an overall D 2h symmetry, exhibiting solely heterobonds (i.e. The calculated structure exhibits C-N distances of 1.325 Å, S-N 1.590 Å in good agreement to the available experimental results (Table 1) [22] . A relevant characteristic described by the authors is the aromatic behavior [24] as given by the more deshielded exo-hydrogens in comparison to benzene (+9.70 v/s +7.36 ppm respectively; CDCl 3 ) [22] , [24] .…”

“…[22] , reveals a 10π eight-membered ring bearing three different atoms types C/N/S. A relevant characteristic described by the authors is the aromatic behavior [24] as given by the more deshielded exo-hydrogens in comparison to benzene (+9.70 v/s +7.36 ppm respectively; CDCl 3 ) [22] , [24] . C-N, N-S).…”

“…A related heterocyclic structure is given by 1,5,2,4,6,8-Dithiatetrazocine ((CH) 2 S 2 N 4 ) ring, reported by Moock et al [22] , which involves an eight-membered backbone bearing three different atom types C/N/S in a D 2h symmetry, exhibiting solely heterobonds (i.e. In such structure, hydrogens bonded to the carbon are more deshielded in comparison to benzene according to 1 H-NMR measurements (+9.70 v/s +7.36 ppm respectively; CDCl 3 ) [22] , which is characteristic of aromatic rings, suggesting a stronger aromatic behavior of (CH) 2 S 2 N 4 [24] . In such structure, hydrogens bonded to the carbon are more deshielded in comparison to benzene according to 1 H-NMR measurements (+9.70 v/s +7.36 ppm respectively; CDCl 3 ) [22] , which is characteristic of aromatic rings, suggesting a stronger aromatic behavior of (CH) 2 S 2 N 4 [24] .…”

“…An example of a real ten π-electrons aromatic is the dianion of cyclooctatetraene ([C 8 H 8 ] 2-) which exhibits a planar eight-membered ring [35] . A related heterocyclic structure is given by 1,5,2,4,6,8-Dithiatetrazocine ((CH) 2 S 2 N 4 ) ring, reported by Moock et al [22] , which involves an eight-membered backbone bearing three different atom types C/N/S in a D 2h symmetry, exhibiting solely heterobonds (i.e. C-N, N-S).…”

“…Attempts to include a carbon atom into the structural skeleton pursue the synthesis of interesting electron-rich C/N/S based rings [19][20][21][22][23][24] , as for example, 1,5,2,4,6,8-Dithiatetrazocine, which has been recently reported [22] and described as a "hybrid" aromatic molecule.…”