Novel S–N ring contractions using the 4-phenyl-1,2,3,5-dithiadiazole dimer, the synthesis and X-ray crystal structures of [(PhCN2S2)2Cl][S3N3], [PhCN2S2][S3N3], and [PhCN2S2][S3N2]Cl, and an ab initio molecular-orbital study of the bonding in [PhCN2S2][S3N3]

Abstract

When the 4-phenyl-1,2,3,5-dithiadiazole dimer (1) dehalogenates [S₅N₅]Cl a novel ring contraction occurs producing [(PhCN₂S₂)₂Cl][S₃N₃], (2), in acetonitrile, and a mixture of (2) and [PhCN₂S₂][S₃N₃], (3), in pentane. The salt [S₄N₃]Cl is also dehalogenated by (1) in acetonitrile giving [PhCN₂S₂][S₃N₂]Cl, (4). The X-ray crystal structures of (2)–(4) provide an insight into the electronic state of the CN₂S₂ rings in these three compounds by comparison of the S–S bond length with the known lengths in compound (1), [PhCN₂S₂][AsF₆], and [PhCN₂S₂]Cl. Extended-Hückel and ab initio molecular-orbital calculations were carried out on compound (3) and high-yield preparations of (2)–(4) are also described. The reactions of [S₅N₅]Cl or [S₅N₃]Cl with (1), in acetonitrile, produced in both cases the new e.s.r.-active compound [PhCN₂S₂]₂Cl, whose solid-state preparation is described. The reaction between the vapours of (SN)_x and (1) produced (3) providing further evidence for S₃N₃˙ being the major vapour-phase species above (SN)_xin vacuo at ca. 160 °C.