Gold(I) dimers. The synthesis and reactions of [tert-BuC≡CAu(dmpm—P)], and the crystal and molecular structures of [Au2(µ-dmpm)2]X2•2H2O, X = Cl, I

Acetylide complexes of formula [tert-BuC≡CAu(R2PCH2PR2)], R = CH3 (6a) and C6H5 (6b), have been prepared, and characterized by spectroscopic methods. These complexes undergo a fluxional process involving a three-coordinate Au(I) centre. Complex 6a dimerizes by a first-order process in chlorinated solvents, with substitution of the acetylide ligand by chloride ion, to form [Au2(µ-dmpm)2]Cl2•2H2O (7a). The crystal and molecular structures of 7a and the iodide salt 7b have been determined by single crystal X-ray diffraction methods. Both crystallize in the triclinic space group [Formula: see text] with Z = 1; unit cell dimensions are a = 7.962(1), b = 9.987(1), c = 7.895(1) Å, α = 90.11, β = 109.13(1), and γ = 112.84(1)° for 7a; a = 8.243(1), b = 9.057(1), c = 8.167(1) Å, α = 90.23, β = 110.33(1), and γ = 89.92(1)° for 7b. The analyses refined to final agreement factors on F of R = 0.035 based on 3225 unique reflections with I > 3σ (I) for 7a, and R = 0.030 based on 2971 unique reflections with I > 3σ(I) for 7b. The structures are closely related, with the cations containing an eight-membered centrosymmetric ring formed by the Au(I) centres and the bridging dmpm ligands. The Au … Au′ distances are 3.014(1) and 3.019(1) Å in 7a and 7b, respectively. In the solid state, the halide ions bridge the two Au centres, and, together with the water molecules, form a network of hydrogen bonds running at an angle of 104° to the eight-membered Au2P4C2 rings.