Synthesis and electrochemistry of heterobridged gold(I) and gold(II) complexes of pyridine-2-thiolate. Crystal structures of [Au2{µ-(CH2)2PPh2}(µ-C5H4NS)] and [Au2{µ-(CH2)2PPh2}(µ-C5H4NS)Br2]

Abstract

The reaction of [Au₂{µ-(CH₂)₂PPh₂}₂] or [Au₂(µ-L–L)₂][ClO₄]₂[L–L = dppm (Ph₂PCH₂PPh₂) or dppe (Ph₂PCH₂CH₂PPh₂)] with [Au_n(µ-C₅H₄NS)_n] led to the heterobridged dinuclear complexes [Au₂{µ-(CH₂)₂PPh₂}(µ-C₅H₄NS)] or [Au₂(µ-C₅H₄NS)(µ-L–L)]ClO₄. The structure of [Au₂{µ-(CH₂)₂PPh₂}(µ-C₅H₄NS)] has been established by X-ray crystallography and exhibits a short intermolecular gold–gold distance of 2.8623(7)Å, whereas the shortest intermolecular distance is 3.984 Å. The complex crystallized in the monoclinic space group P2₁/n with a= 9.430(2), b= 8.819(2), c= 22.786(5)Å, β= 99.08(3)°, Z= 4. Cyclic voltammograms showed that this complex is irreversibly oxidised at a platinum electrode; chemical oxidation with the ferrocenium ion in the presence of halide or pseudohalide ions gave the gold(II) complexes [Au₂{µ-(CH₂)₂PPh₂}(µ-C₅H₄NS)X₂](X = Cl, Br, I or SCN). The same derivatives can be obtained by oxidative addition of halogen and/or by subsequent substitution with other halogens or pseudohalogens. The complex [Au₂{µ-(CH₂)₂PPh₂}(µ-C₅H₄NS)Br₂] crystallized in the triclinic space group P with a= 14.810(10), b= 14.908(10), c= 17.041(12)Å, α= 70.20(5), β= 69.77(5), γ= 89.19(5)°, Z= 6 (at –100 °C). The Au–Au bond lengths in the three independent molecules are 2.564(4), 2.548(4) and 2.547(4)Å.