Formation and X-ray Structures of Eight- and Sixteen-Membered Rings (ArC)nN2n(SPh)n [n = 2, Ar = 4-XC6H4 (X = Br, CF3); n = 4, Ar = 4-BrC6H4] and the Electronic Structures of (HC)2N4(SH)2 and (HC)2N4(SH)22-

Optimum yields of heterocyclic products are obtained when the reaction of 4-XC6H4CN2(SiMe3)3 (X = Br, CF3) with PhSCl in a 1:3 molar ratio in CH2Cl2 is carried out at -100°C followed by the mixture being warmed to -70°C for 16 h. Under these conditions the eight-membered rings (4-XC6H4)2C2N4S 2Ph2 (1b, X = Br; 1c, X = CF3) are obtained in 64 and 80% yields, respectively, in addition to the purple diazenes Z,E,Z-PhSN(4-XC6H4)-CN=NC(C6H 4X-4)NSPh (2b, 8%; 2c, 19%) and, in the case of X = Br, the sixteen-membered ring (4-BrC6H4)4C4N8S 4Ph4 (3) (8%). With a reaction time of 40 h the yield of 3 is increased to 25%. By contrast, the reaction of 3-BrC6H4CN2(SiMe3)3 with 3 equiv of PhSCl at -70°C gives Z,E,Z-PhSN(3-BrC6H4)CN=NC-(3-BrC6H 4)NSPh in 75% yield. A possible pathway for the formation of cyclic products is proposed. The solid-state structures of 1b, 1c, and 3 were determined by X-ray crystallography. The eight-membered rings 1b and 1c adopt long boat conformations with the phenyl groups (attached to S) in equatorial positions. Density functional theory (DFT) calculations for the model ring system (HC)2N4(SH)2 reveal that the observed C2ν geometry is the result of a second-order Jahn-Teller distortion of the planar (D2h) structure. The chair conformer (C2h) is only ca. 10 kJ mol^-1 higher in energy than the boat conformer. The hypothetical dianion (HC)2N4(SH)2^2- is predicted to have a transannular S⋯S contact of about 2.5 Å. The sixteen-membered ring 3 has a cradle-like structure with S4 symmetry.