Evidence for Au(I)…Au(I) Interactions in a Sterically Congested Environment: Two-Coordinate Gold(I) Halide Phosphine Complexes

Abstract

Two-coordinate tris(2-methylphenyl)phosphine and tris(4-methylphenyl)phosphinegold(I) halide complexes, [AuP(otol)₃X], [AuP(ptol)₃X], where X = Cl, Br, and I, have been crystallized from dimethylformamide and characterized by single-crystal X-ray structure determinations. The P(otol)₃ structures comprise an isomorphous series distinct from the previously published chloride, crystallizing with two independent molecules in the asymmetric unit in the space group Pbca, with a ≈ 20.0, b ≈ 28.0, c ≈ 14.0 Å. The molecules associate to form dimers through a back-to-back sextuple phenyl embrace (6PE). The P(ptol)₃ complexes are isomorphous with the previously published chloride, crystallizing with two independent molecules in the unit cell in the space group P2₁/c, with a ≈ 10.0, b ≈ 22.0, c ≈ 19.5 Å, β ≈ 99°. The molecules associate through edge-to-face interactions along the direction of the a-axis. Preparation of the chloride by anodic dissolution of gold in an acetonitrile solution of the ligand and aqueous HCl yields a new polymorph, crystallizing in the space group Aba2, with a 19.738(2), b 11.813(3), c 17.645(1) Å. Despite the bulkiness of the phosphine ligand, this form of [AuP(ptol)₃Cl] exhibits a short intermolecular Au^…Au contact distance of 3.375(1) Å, indicative of a significant aurophilic interaction. The ranges for the Au—P, Au—Cl, Au—Br, Au—I bond lengths and P—Au—X bond angles in the series are: 2.201(3)–2.265(4), 2.255(3)–2.290(4), 2.388(2)–2.411(2), 2.542(1)–2.556(2) Å, and 173.2(2)–179.6(1)° respectively.