Synthesis, properties, and bishomoaromaticity of the first tetrahalogenated derivative of a 1, 5-diphosphadithiatetrazocine: a combined experimental and computational investigation.

The first example of a tetrahalogenated derivative of a diphosphadithiatetrazocine, 1,5-Cl(2)P(NSN)(2)PCl(2) (3), was synthesized by cyclocondensation of a 2:1 mixture of SCl(2) and SO(2)Cl(2) with Cl(2)P(NSiMe(3))N(SiMe(3))(2) in CH(2)Cl(2). The heterocycle 3 was isolated as an orange, moisture-sensitive, thermally labile solid and characterized by mass spectrometry, (31)P NMR, and UV-visible spectroscopy. The low-field (31)P NMR chemical shift (93.7 ppm) is indicative of a cross-ring S-S interaction in the eight-membered P(2)N(4)S(2) ring, and this conclusion is supported by density-functional computations. Compound 3 exhibits unusual physical properties compared with those of the known tetraalkyl or aryl derivatives; mild heating (90 degrees C) produces an orange rubbery material. The bishomoaromatic character of the diphosphadithiatetrazocine 1,5-R(2)P(NSN)(2)PR(2) (R = Me, Cl, F) is evinced by the negative nucleus-independent chemical shift (NICS) values, and the through-space bishomoconjugation in the eight-membered ring decreases with increasing electronegativity of the substituents attached to the P atoms.