Crystal structure of [(Z)-O-isopropyl N-(4-chlorophenyl)thiocarbamato-κS]-(triphenylphosphine-κP)-gold(I), C₂₈H₂₆AuClNOPS

Source of material

NaOH (0.020 g, 0.50 mmol) in water (5 mL) was added to a suspension of Ph₃PAuCl (0.247 g, 0.50 mmol) in acetonitrile (20 mL), followed by addition of iPrOC(=S)N(H)C₆H₄Cl-4 (0.115 g, 0.50 mmol) in chloroform (20 mL). After stirring for 2 h, the solution was left for slow evaporation at room temperature, yielding colourless crystals after 2 weeks. Yield: 0.313 g (91%). M. pt (Biobase automatic melting point apparatus MP450): 436–439 K. Elemental Analysis for C₂₈H₂₆AuClNOPS (Leco TruSpec Micro CHN Elemental Analyser): C, 48.88; H, 3.81; N, 2.04%. Found: C, 49.06; H, 3.69; N, 2.06%. IR (Bruker Vertex 70v FTIR Spectrophotometer; cm⁻¹): 1436 (s) ν(C=N), 1138 (s) ν(C—O), 1094 (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 7.54–7.42 (m, br, 15H, Ph₃P), 6.97 (dt, 2H, m-aryl-H, ³J_HH = 8.60 Hz, ⁴J_HH = 2.46 Hz), 6.75 (dt, 2H, o-aryl-H, ³J_HH = 8.56 Hz, ⁴J_HH = 2.45 Hz), 5.26 (sept, 1H, OCH, J_HH = 6.20 Hz), 1.32 (d, 6H, CH₃, J_HH = 6.20 Hz). ¹³C{¹H} NMR (as for ¹H NMR): δ 163.8 (Cq), 150.0 (aryl, C_ipso), 134.2 (d, m-Ph₃P, ³J_CP = 13.81 Hz), 131.7 (d, p-Ph₃P, ⁴J_CP = 2.34 Hz), 129.4 (d, i-Ph₃P, ¹J_CP = 57.25 Hz), 129.1 (d, o-Ph₃P, ²J_CP = 11.50 Hz), 128.8 (aryl, C_meta), 127.3 (aryl, C_para), 123.4 (aryl, C_ortho), 70.6 (OCH), 22.1 (CH₃). ³¹P{¹H} NMR (as for ¹H NMR but with chemical shift referenced to 85% aqueous H₃PO₄ as the external reference): δ 38.1.

Experimental details

The C-bound H atoms were geometrically placed (C—H = 0.95–1.00 Å) and refined as riding with U_iso(H) = 1.2–1.5U_eq(C). The maximum and minimum residual electron density peaks of 2.22 and 1.04 eÅ⁻³, respectively, were located 0.93 and 0.72 Å, respectively, from the Au atom.

Comment

The most studied case of structural mimicry relates to the chloro/methyl exchange whereby structures that differ only by a chloride versus methyl substituent are evaluated for similarity or otherwise [5]. If the chloro/methyl substituents have no major influence the molecular packing, isomorphous relationships might be apparent as the molecular volumes of a chloride atom and a methyl group are close. In this connection, the title phosphanegold(I) thioamide molecule, Ph₃PAu[SC(OR)=NC₆H₄Y-4], for R = iPr and Y = Cl, (I), has been investigated. Related structures with Y = Cl and R = Me [6] and R = Et, isolated as a dichloromethane hemi-solvate [7], are known. The three structures with Y = Me and R = Me [8], R = Et [9] and R = iPr [10] are also available in the literature. Herein, in order to complete the 2 (Y = Cl and Me) × 3 (R = Me, Et and iPr) matrix of Y and R structures, the crystal and molecular structures of (I) are described.

The molecular structure of (I) is shown in the figure (70% displacement ellipsoids) which shows the gold atom to be coordinated by thiolate-S [Au—S1 = 2.3166(10) Å] and phosphane-P [Au—P1 = 2.2551(10) Å] atoms which define an almost linear geometry [P1—Au—S1 = 173.52(3)°]. The crystal structure of the pure acid, i.e. iPrOC(=S)N(H)C₆H₄Cl-4, is available for comparison [11]. The C1—S1 [1.6708(15) Å] and C1—N1 [1.3388(18) Å] bond lengths in the acid are significantly shorter and longer than the comparable bonds in (I) of 1.769(4) and 1.272(5) Å, respectively. The deviation from the ideal 180° for the P1—Au—S1 angle may be traced to the close approach of the O1 atom towards the gold centre with Au⋯O = 2.900(3) Å.

In the crystal of (I) chlorophenyl-C—H⋯π(P-phenyl) [C4—H4⋯Cg(C11–C16)ⁱ: H4⋯Cg(C11–C16)ⁱ = 2.67 Å with an angle at H4 = 139° for symmetry operation (i): −x, −1/2 + y, 1/2 − z], P-phenyl-C—H⋯π(chlorophenyl) [C14—H14⋯Cg(C2–C7)ⁱⁱ: H14⋯Cg(C2–C7)ⁱⁱ = 2.92 Å with angle at H14 = 130° and C32—H32⋯Cg(C2–C7)ⁱⁱⁱ: H32⋯Cg(C2–C7)ⁱⁱ = 2.85 Å with an angle at H32 = 150° for (ii) x, 3/2 − y, −1/2 + z and (iii) −x, 1/2 + y, 1/2 − z] and end-on C—Cl⋯π(P-phenyl) [C5—Cl1⋯Cg(C31–C36)^iv: Cl1⋯Cg(C31–C36)^iv = 3.7658(19) Å with an angle at Cl1 = 170.73(14)° for (iv) −1 + x, 3/2 − y, 1/2 + z] connect molecules into a three-dimensional structure. In this scheme, the chlorophenyl ring accepts two C—H⋯π contacts.

Additional analysis of the molecular packing was conducted whereby the Hirshfeld surfaces were calculated along with the full and delineated two-dimensional fingerprint plots. This was achieved with Crystal Explorer 17 [12] following literature procedures [13]. The analysis shows that over 97% of all surface contacts involve hydrogen with the major contribution coming from non-directional H⋯H contacts at 47.3%. Significant contributions are apparent from H⋯C/C⋯H [26.1%] contacts reflecting, in part, the specified C—H⋯π interactions. Other notable contributions to the calculated surface occur at separations at or beyond the sums of the respective van der Waals radii, e.g. H⋯S/S⋯H [7.1%] and H⋯Cl/Cl⋯H [9.7%]. It is noted C⋯Cl/Cl⋯C contacts contribute 1.8% to the surface.

The unit cell parameters for (I) and the methyl isostere, i.e. Ph₃PAu[SC(O-iPr)=NC₆H₄Me-4] [10], (II), indicate an isostructural relationship. The molecular structures closely resemble each other but, in the molecular packing of (II), the tolyl-methyl group sits in an hydrophobic pocket and does not participate in a directional intermolecular contact in contrast to the chloride atom in (I). This difference is reflected in the calculated Hirshfeld surface of (II) where the H⋯H contacts amount to 58.3% of all contacts, which is close to the sum of H⋯H + H⋯Cl/Cl⋯H contacts of (I). It is noted a isostructural relationship also exists for the two R = Me, Y = Cl [6] and Y = Me [8] compounds but, not for the pair of R = Et structures as the Y = Cl species is a hemi-dichloromethane solvate [7] while the Y = Me compound was characterised solvent-free.