Crystal structure of (μ₂-1,1′-bis(diphenylphosphino)butane-κ²P,P′)-bis[(Z)-N-(3-fluorophenyl)-O-methylthiocarbamato-κS]-di-gold(I), C₄₄H₄₂Au₂F₂N₂O₂P₂S₂

Source of material

NaOH (Merck; 0.020 g, 0.50 mmol) in water (5 mL) was added to a suspension of (Ph₂P(CH₂)₄PPh₂)(AuCl)₂ (0.229 g, 0.25 mmol) in acetonitrile (20 mL), followed by the addition of MeOC(=S)N(H)C₆H₄F-3 (0.093 g, 0.50 mmol) [5] in acetonitrile (20 mL) and stirred for 3 h. The resulting mixture was left for slow evaporation at room temperature, yielding crystals after 3 weeks. Yield: 0.229 g (77%). M. pt (Biobase automatic melting point apparatus MP450): 410–411 K. Elemental Analysis for C₄₄H₄₂Au₂F₂N₂O₂P₂S₂ (Leco TruSpec Micro CHN Elemental Analyser): C, 44.45; H, 3.56; N, 2.36%. Found: C, 44.71; H, 3.72; N, 2.10%. IR (Bruker Vertex 70v FTIR Spectrophotometer; cm⁻¹): 1575 (s) ν(C=N), 1122 (s) ν(C—O), 1106 (s) ν(C—S). ¹H NMR (Bruker Ascend 400 MHz NMR spectrometer with chemical shifts relative to tetramethylsilane in CDCl₃ solution at 298 K, ppm): δ 7.58–7.41 (m, br, 20H, Ph₂P), 6.95 (dt, 2H, aryl-H5, ⁴J_HF = 6.80 Hz, ³J_HH = 7.42 Hz), 6.60–6.56 (m, br, 4H, aryl-H2,6), 6.43–6.39 (m, br, 2H, aryl-H4), 3.88 (s, 6H, OCH₃), 2.30 (s, br, 4H, PCH₂), 1.67 (s, br, 4H, PCH₂CH₂). ¹³C{¹H} NMR (as for ¹H NMR): δ 165.5 (Cq), 163.1 (d, aryl-C3, ¹J_CF = 244.50 Hz), 152.9 (d, aryl-C1, ³J_CF = 9.80 Hz), 133.2 (d, m-PC₆H₅, ³J_CP = 13.43 Hz), 131.8 (p-PC₆H₅), 129.8 (d, aryl-C5, ³J_CF = 9.54 Hz), 130.1 (d, i-PC₆H₅, ¹J_CP = 52.72 Hz), 129.2 (d, o-PC₆H₅, ²J_CP = 11.09 Hz), 117.9 (d, aryl-C6, ⁴J_CF = 2.51 Hz), 109.2 (d, aryl-C2, ²J_CF = 21.95 Hz), 109.0 (d, aryl-C4, ²J_CF = 21.19 Hz), 55.5 (OCH₃), 27.8 (d, PCH₂, ¹J_CP = 34.01 Hz), 26.9 (d, PCH₂CH₂, ²J_CP = 17.70 Hz). ³¹P{¹H} NMR (as for ¹H NMR but with chemical shift referenced to 85% aqueous H₃PO₄ as the external reference): δ 32.9.

Experimental details

The C-bound H atoms were geometrically placed (C—H = 0.95–0.99 Å) and refined as riding with U_iso(H) = 1.2–1.5U_eq(C). The maximum and minimum residual electron density peaks of 1.36 and 0.85 eÅ⁻³, respectively, were located 0.78 and 0.67 Å, from the Au2 and S2 atoms, respectively. Each of the 3-fluorophenyl rings was disordered over two co-planar orientations so the C atoms were exactly coincident but, two positions were apparent for the F atoms; the latter were refined independently. At the conclusion of the refinement, the major component of the F1- and F2-rings had a site occupancy factor of 0.639(8) and 0.665(9), respectively.

Comment

Phosphane gold(I) thioamide molecules of the general formula R₃PAu[SC(OR′)=NAr] and their binuclear analogues are a well-studied class of compound [6], [7] owing, in part, to their biological activity against cancerous cells [8] and Gram-positive bacteria [9]. The compounds are relatively easy to prepare and furnish crystals readily. For example, the 3 × 3 matrix of crystals (dppb){Au[SC(OR)=NC₆H₄Y-4]}₂ for R = Me, Et or iPr and Y = H, NO₂ or Me has been studied [10]; dppb is Ph₂P(CH₂)₄PPh₂. The specific motivation for the preparation of the title binuclear dppb molecule, i.e. (dppb){Au[SC(OMe)=N(C₆H₄F-3)]}₂ (I), with a fluorinated phenyl ring in the thiolate ligand arose from investigations into biological activity [5]. Herein, the crystal and molecular structures of (I) are described.

The molecular structure of the binuclear species in (I) is shown in the figure (50% displacement ellipsoids; the minor components of the disordered fluorophenyl rings are omitted for clarity). The Au1 atom is coordinated by thiolate-S1 [2.2933(10) Å] and phosphane-P1 [2.2552(10) Å] atoms which define a linear geometry with P1—Au1—S1 = 173.96(3)°. The equivalent parameters for the Au2 atom are Au2—S2 = 2.3097(11) Å, Au2—P2 = 2.2505(10) Å and P2—Au2—S2 = 174.67(3)°, indicating a close similarity. The mode of coordination of the thiolate ligand and the gold atom coordination geometry in (I) is as found in all previous studies [5], [6], [7], [10]. The most notable feature of the molecular structure is the relative orientation of the thiolate ligands. For the Au1 atom, the aryl ring is disposed to be proximate to the gold atom with the Au⋯Cg(C2–C7) separation being 3.70 Å. A different disposition is noted for the second thiolate ligand arising from a rotation about the C—S bond which is now orientated to place the O2 atom in close proximity to the Au2 atom with the Au2⋯O2 separation being 3.172(4) Å. While both orientations have been observed previously [7], this is the first instance where both Au⋯π and Au⋯O interactions occur within the same molecule. However, there are conformational polymorphs for specific molecules, i.e. Ph₃PAu[SC(OEt)=NPh], with intramolecular Au⋯O [11] and Au⋯π [12] interactions, and for (4-tolyl)₃PAu[SC(OEt)=NC₆H₄NO₂-4] with Au⋯O [13] and Au⋯π [14] contacts; the recently determined tetrahydrofuran (1/1) solvate of this compound features an intramolecular Au⋯O contact [15]. DFT calculations suggest the Au⋯π interaction is favoured over Au⋯O by about 6 kcal/mol [16].

A detailed analysis of the molecular packing for (I) is precluded owing to the disorder in the 3-fluorophenyl rings. Weak Au⋯S contacts [Au2⋯S1ⁱ = 3.5979(10) Å for symmetry operation (i) 1 + x, −1 + y, z] connect molecules into a linear supramolecular chain along [1 −2 0]. The chains are connected into layers in the ab-plane by methylene-C—H⋯π(F-phenyl) [C12—H12b⋯Cg(C2–C7)ⁱⁱ = 2.66 Å with angle at H12b = 163° for (ii) 1 + x, y, z] and methyl-C—H⋯π(P-phenyl) [C8—H8b⋯Cg(C41–C46)ⁱⁱⁱ = 2.70 Å with angle at H8b = 142° for (iii) −1 + x, 1 + y, z] interactions. The primary interactions between layers to consolidate the three-dimensional packing involve the disordered F atoms and are of the type C—H⋯F and F⋯π.