Reaction of SNSSbF
6 and DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone (
1)) in SO
2 solution in a 2:1 ratio afforded the dicycloaddition product
1(SNS)
2(SbF
6)
2 · SO
2 in 85 % isolated yield. The dicycloaddition product
1(SNS)
2(SbF
6)
2 · SO
2 was fully characterized by IR, Raman, NMR, elemental analysis, and single crystal X-ray crystallography. The product of the site selective dicycloaddition of SNS
+ at the nitrile functionalities of
1 represents the first structurally characterized
ortho-bis-1,3,2,4-dithiadiazolylium salt which adopts a conformation that utilizes the intramolecular S
δ+–O
δ− electrostatic interactions. The reaction of
1 and SNS[Al(OC(CF
3)
4] in a 1:1 ratio yielded only the monocycloaddition product
1(SNS)[Al(OC(CF
3)
3)
4] indentified by multinuclear
13C,
14N,
19F,
27Al NMR in SO
2 solution. The assignment of the
13C NMR of
1(SNS)
+ in SO
2 solution, were supported by comparison of the calculated (MPW1PW91/6-31G
*)
13C NMR and experimental chemical shifts, and by comparison of the observed chemical shifts of the related
2(SNS)
+ produced on reacting the mono-nitrile CDMQ (2-cyano-5,6-dichloro-3-methoxy-1,4-benzoquinone (
2)) with SNS
+ (as the
salt). The reaction of SNSSbF
6 with TCNE (1,1,2,2-tetracyanoethylene (
3)) gave the tri-cycloaddition product
3(SNS)
3(SbF
6)
3 · SO
2 (IR, Raman microscopy and X-ray crystallography) in 40 % yield.
The energetics of the cycloaddition reactions of SNS+ with 1–3 and other multifunctional unsaturated centers (e.g. HCC–CN, NC–CN, , o,m,p-(CN)2C6H4, 1,3,5-(NC)3C6H3, 4–10, previously reported, see Chart 1), were estimated in the gas phase (MPW1PW91/6-31G*), solution (PBE0/6-311G*) and in the solid state by the ‘volume based thermodynamics’ (VBT) approach. The general thermodynamic trends associated with the stepwise cycloaddition of SNS+ with multifunctional nitriles were established. The 1:1 cycloaddition products were calculated to be stable in the gas phase and solution, while in the solid state the larger lattice enthalpy of the 1:2 salt, relative to twice that of the 1:1 salt, favored the 1:2 cycloaddition product.