Gold oxidative dissolution by (thioamide)-I2 adducts.

Elemental gold powder is easily oxidised under mild reaction conditions with 1 : 1 I(2)-adducts of the thioamides 3-methyl-benzothiazole-2-thione (mbtt) and 1-methyl-1H-benzimidazole-2(3H)-thione (mbit) with separation of the ionic complexes [Au(I)(mbtt)(2)]I(3) (1) and [(mtbiH)(2)](AuI(4))I(3) (2) [mtbiH = the imido protonated form of 2-(methylthio)benzimidazole] (gold oxidation yield >78% and 45%, respectively). The X-ray crystal structure of 1 shows the Au(i) centre linearly bound by two neutral ligands via the sulphur atom, whereas the X-ray crystal structure of 2 shows the Au(III) centre surrounded by four iodides in a square-planar arrangement. The oxidising/complexing properties of the mbtt·I(2) and mbit·I(2) adducts were interpreted considering the S-donor to I(2) interaction that leads to a charge separation between the I(b) and I(t) iodine atoms in the fragment S-I(b)-I(t). The oxidation of gold in a non-aqueous solvent by thioamide-I(2) adducts could be a promising alternative process to the numerous hydrometallurgical ones for the recovery of gold from secondary sources.