Synthesis and Structure of Trinuclear and Novel Tetranuclear Gold(I) Complexes Derived from 8-Aminoquinoline

Treatment of 8-aminoquinoline with 1 mol equiv of μ₃-oxotris[(triphenylphosphine)gold(I)] tetrafluoroborate affords μ_3-[8-quinolinaminato(2-)] tris [(triphenylphosphine)gold(I)] tetrafluoroborate (1). This triply N-aurated ammonium salt reacts further with 1 equiv of (triphenylphosphine)gold(I) tetrafluoroborate to give the novel μ_3- [8-quinolinaminato-(2-)] tetrakis[(triphenylphosphine)gold(I)] bis(tetrafluoroborate) (2). The structures of both compounds have been determined by single-crystal X-ray diffraction. In the trinuclear complex 1, the three gold atoms are bound exclusively to the 8-amino nitrogen atom of the quinoline, thus putting this nitrogen at the apex of an NAu₃ pyramid. The pyridine N-atom is not attached to any of the gold atoms, and the quinoline ring has free rotation about the C-N(amino) axis, as shown by NMR spectroscopy. In the tetranuclear complex 2, the triangle of gold atoms is expanded to give a rhomboidal Au₄ unit, with three Au atoms μ³-bridged by the amino nitrogen atom and the fourth ligated to the pyridine nitrogen center. In solution the compound appears to be fluxional, with the quinolyl group interacting consecutively with all four gold atoms. In both compounds, the gold atoms show close contacts of 3.0 ± 0.1 Å, indicating significant bonding, which is probably the main driving force for the clustering of seemingly closed-shell (d¹⁰) gold(I) metal atoms. Crystal data: 1.C₄H₈O triclinic, PI (No. 2), a = 11.292 (1) Å, b = 14.774 (2) Å, c = 18.652 (2) Å, α = 95.07 (1)°, β = 104.55 (1)°, γ = 90.84 (1)°, Z = 2, R (R_w) = 0.026 (0.021); 2.C₄H₈O monoclinic, P2₁/n (No. 14), a = 13.442 (2) Å, b = 21.130 (2) Å, c = 28.040 (4) Å, β = 102.80 (1)°, Z = 4, R (R_w) = 0.036 (0.031).