Chemistry and crystal structures of l, 3-Bis(4’-bromophenyl)propane-l, 2, 3-trione, 3, 5-Diphenyl-l, 2-dithiolylium-4-olate and 4-Hydroxy-3, 5-diphenyl-l, 2-dithiolium perchlorate

In connection with studies on possible mesoionic systems, syntheses of l, 3-bis(4’-bromophenyl)-propane-l, 2, 3-trione (5), 3, 5-diphenyl-l, 2-dithiolylium-4-olate (9) and 4-hydroxy-3, 5-diphenyl-l, 2-dithiolium perchlorate (10) have been reexamined. The crystal structures of (5), (9) and (10) have been determined by X-ray diffraction from diffractometer data at 295 K and were refined by full-matrix least squares to residuals of 0·050 (1118 ‘observed’ reflections), 0·072 (2388) and 0·087 (2000), respectively. Crystals of (5) are monoclinic, C2/c, a 18·535(4), b 7·734(2), c 12·184(3) Å, β 126·60(3)°, Z 4. Crystals of (9) are orthorhombic, Pmcn, a 26·047(6), b 7·170(2), c 6·431(2) Å, Z4. Crystals of (10) are monoclinic, P2₁/a, a 18·601(7), b 10·636(4), c 8·152(2) Å, β 102·60(3)°, Z 4. In (5) π-character is localized in the phenyl rings and carbonyl groups [<C=O> 1·22(1) Å] and the substance is best represented as a normal vicinal triketone. In (9) and (10) S-S bonds are present and (9) is correctly regarded as a heterocyclic system. The geometry of the heterocyclic ring in (10) agrees well with that previously found for the 1, 2-dithiolium cation; <C-0> is 1 • 35(1) Å. In (9) the heterocyclic C-C distances [1·442(2) Å] are longer than in (10); this índicates diminished aromaticity on deprotonation. The C-C-C angle [111·2(2)°] in (9) is also smaller than that [118·3(8)°] in (10) and <C-0> in (9) is 1·250(3) Å. The behaviour of l, 3-diphenylpropane-l, 2, 3-trione (4) and (9) with acetylenic dipolarophiles has been studied but no evidence has been obtained that either substance undergoes a 1, 3-dipolar cycloaddition reaction.