Digold(I) Thianthrenyl Complexes. Effect of Diphosphine Ligands on Molecular Structures in the Solid State and in Solution

A series of digold complexes possessing two thianthrenyl ligands, Au₂(Thi)₂(Ph₂P­(CH₂)_nPPh₂) (Thi: 1-thianthrenyl; 1: n = 1, 2: n = 2, 3: n = 3, 4: n = 4), were prepared and characterized by crystallographic and spectroscopic measurements. X-ray crystallography of complexes 1 and 3 revealed U-shaped structures with short Au–Au distances [3.2171(3) Å and 3.0735(2) Å]. Complex 2 and three of the four structure-determined molecules of complex 4 showed structures without Au–Au contacts. UV–vis spectroscopic measurements of 1–4 and TD-DFT calculations of the two conformers of 1 revealed that complexes 1 and 3 in the solution phase contained conformers with Au­(I)–Au­(I) interactions in a much higher proportion than complexes 2 and 4. As a result, complexes with diphosphine ligands containing an odd number of methylene groups preferred structures with Au–Au interactions in the solid state and in solution. Oxidation of 1 with 2 equiv of PhICl₂ yielded a mixture of monomeric and dimeric thianthrenes and its dimer via ligand elimination and C–C coupling, respectively.