Toluene-3,4-dithiol (H2tdt) complexes of group 5B halides. Observations of lone-pair stereochemical activity and redox behaviour. Crystal and molecular structures of [AsCl(tdt)] and [PPh4][Sb(tdt)3]

Abstract

Reactions of toluene-3,4-dithiol (H₂tdt) with the Group 5B chlorides MCl₃(M = As, Sb, or Bi) have been investigated under conditions of varying stoicheiometry. Complexes of the types [MCl(tdt)](M = As, Sb, or Bi), [Sb(Htdt)(tdt)], [NEt₃H][Bi(tdt)₂], and [Y][Sb(tdt)₃](Y = NEt₄ or PPh₄) have been isolated and characterised by spectroscopic (i.r. and ¹H n.m.r.) data. For the [MCl(tdt)] series, obtained following 1:1 addition, ligand (SH) protons are removed as HCl and a tetrahedral geometry with full stereochemical participation of the lone pair of electrons associated with M^III is confirmed for M = As by an X-ray crystal structure determination. The complexes [Sb(Htdt)(tdt)] and [NEt₃H][Bi(tdt)₂], resulting from 1:2 addition, are quite dissimilar with only the latter experiencing full replacement of ligand (SH) protons. For [Sb(Htdt)(tdt)] there is strong evidence to suggest that one of the ligand (SH) protons remains intact giving rise to a neutral species based on Sb^III. Attempts to remove this proton to give the anion [Sb(tdt)₂]^– have been unsuccessful. For the [Y][Sb(tdt)₃] complexes, obtained following 1:3 addition, all ligand (SH) protons are removed and an X-ray crystal structure determination for Y = PPh₄ shows the anion as a slightly distorted octahedron following aerial oxidation Sb^III→Sb^V. Crystals of [AsCl(tdt)](1) are monoclinic, space group P2₁/c, Z= 4, a= 6.127(5), b= 15.773(11), c= 9.768(8)Å, and β= 91.0(1)°. Crystals of [PPh₄][Sb(tdt)₃](2) are monoclinic, space group P2₁, Z= 2, a= 10.464(7), b= 12.825(9), c= 16.433(8)Å, and β= 102.5(1)°. 1 113, 884 Reflections above background have been collected on a diffractometer and the structures refined to R 0.052, 0.120 respectively. In (1) the arsenic atom is three-co-ordinate [As–Cl 2.236(3); As–S 2.226(3), 2.209(3)Å]. In [Sb(tdt)₃]^–, the antimony atom is six-co-ordinate in a distorted octahedral environment with Sb–S in the range 2.34(3)–2.50(2)Å.