Crystal structure of chlorido[trans-1-(diphenylphosphanethioyl-κS)-2-(diphenylphosphanoyl)ethene]gold(I) dichloromethane hemisolvate1

The title compound crystallizes with a trans-O—P⋯P—S geometry of the groups either side of the C=C double bond.


Chemical context
We are interested in phosphine chalcogenide complexes of gold (Taouss & Jones, 2016, and references therein). In general, we have synthesized complexes LAuX, where L is a phosphine chalcogenide and X is chlorine or bromine, and then oxidized these first to gold(III) complexes LAuX 3 and further to (LX) + (AuX 4 ) À . The title compound was obtained as an unexpected trans product in minimal yield (a few small crystals) during attempts to recrystallize cis-(Ph 2 PC CPPh 2 S)AuCl (Taouss & Jones, 2014). The oxidation of the second P atom to P O, presumably by atmospheric oxygen, is not unusual, but we are at a loss to explain the change of configuration at the C C bond from cis to trans. One possibility, in view of the small amounts involved, is that the cis diphosphine as purchased contained a small amount of trans impurity.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. In the absence of a free phosphorus donor atom, the gold(I) atom is, as expected, coordinated by the softer sulfur donor rather than the oxygen. Bond lengths and angles are ISSN 2056-9890 essentially as expected (Table 1). The P S bond is somewhat lengthened compared to non-coordinating phosphine sulfides (see Section 4). The torsion angle O1-P1Á Á ÁP2-S1 is 174.72 (12) , which is similar to the values observed for dppederived complexes of the type E PPh 2 CH 2 CH 2 PPh 2 AuX (E = chalcogen and X = halogen); the dppm analogues E PPh 2 CH 2 PPh 2 AuX, however, tend to display corresponding torsion angles close to zero, thus promoting short intramolecular AuÁ Á ÁE contacts (Taouss & Jones, 2014). The AuÁ Á ÁO distance in the title compound [6.127 (3) Å ] is clearly far too long for any significant interaction.

Figure 1
The molecule of the title compound in the crystal. Ellipsoids correspond to 50% probability levels. The disordered solvent is not shown. Perhaps surprisingly, there seem to be no structures of simple diphosphine dichalcogenides with the chalcogen atom(s) bonded to gold. One relevant publication, however, is that of the cyano-substituted derivative Ph 3 PAu[S PPh 2 -C(CN)-PPh 2 S] (Sithole et al., 2016). This has a torsion angle of 70 across the atom sequence S PÁ Á ÁP S because the formally noncoordinating S atom makes a short contact of 2.98 Å to the Au atom.

Synthesis and crystallization
Starting from cis-(diphenylphosphanyl)ethene, we generated the monosulfide and then the gold complex cis-(Ph 2 PC CPPh 2 S)AuCl by reaction with (tetrahydrothiophene)AuCl. This compound was successfully crystallized and its structure determined (Taouss & Jones, 2014). On one occasion, however, a few small crystals were obtained that proved not to be the intended compound, but instead the title compound.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were included using a riding model starting from calculated positions, with C-H distances fixed at 0.95 Å . The dichloromethane molecule is disordered over an inversion centre; appropriate restraints were employed to improve refinement stability, but the dimensions of disordered groups should be interpreted with caution.

Chlorido[trans-1-(diphenylphosphanethioyl-κS)-1-(diphenylphosphanoyl)ethene]gold(I) dichloromethane
hemisolvate Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Non-bonded distances: 6.1266 (0.0028) Au1 -O1 3.9827 (0.0004) Au1 -Au1_$2 3.6522 (0.0012) Au1 -Cl1_$2 Operator for generating equivalent atoms: $2 -x+1, -y+1, -z+1 Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.