Crystal structures of bis[2-(diphenylphosphinothioyl)phenyl] ether and bis{2-[diphenyl(selanylidene)phosphanyl]phenyl} ether

The title compounds exhibit remarkably similar structures although they are not isomorphous. In the crystal of the sulfur analogue, molecules are linked via C—H⋯S hydrogen bonds, forming chains along [001], while in the crystal of the selenium analogue, there are no C—H⋯Se hydrogen bonds present.


Chemical context
The ligand bis [2-(diphenylphosphanyl)phenyl] ether (POP) and its congeners, including the more rigid Xantphos [(9,9dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)], comprise a series of chelating diphosphines with a range of flexibility to accommodate variable bonding geometries at transition metals. Experimental and theoretical studies of metal complexes with diphosphines have shown a strong correlation between diphosphine bite angle and selectivity in catalytic transformations (Dierkes & van Leeuwen, 1999;Gathy et al., 2011). Simple functionalization of these diphosphines to form diphosphine dioxides, disulfides, and diselenides has permitted further tuning of the bonding of these ligands to metals by changing the bite-angle range as well as the electronic properties of these ligands. The -accepting phosphorous donor atoms of the parent diphosphines are profoundly altered with the addition of -donor chalcogen donor atoms (Dairiki et al., 2009). Chalcogen-modified diphosphine ligands have been utilized in strategies to tune the catalytic behavior of systems including the Pd II -catalysed hydroamination of dienes (Jahromi et al., 2012) and Ru II transfer hydrogenation of aldehydes and ketones . Hemilability, implicated in the selectivity and reactivity of some catalytic reactions (Braunstein et al., 2001), can also result from the chalcogen functionalization of phosphines as well .
Our interest in the application of chalcogen-substituted diphosphines to alter the electronic features of photoluminescent Cu I sensor materials (Smith et al., 2010) led us to study the solid-state structural features of the dichalcogen diphosphines, including the disulfide and diselenide of the ligand POP. We wanted to investigate the inter-and intramolecular features that dominate the solid-state structural behavior of these ligands. The molecular geometry and ISSN 1600-5368 packing of these chalcogen diphosphines may strongly influence the geometric features of their d 10 metal complexes, as d 10 metals typically have poor stereochemical preferences. In this study, the structures obtained for bis [2-(diphenylphosphinothioyl)phenyl] ether, (1), and bis{2-[diphenyl-(selanylidene)phosphanyl]phenyl} ether, (2), are compared.
The largest differences in the intramolecular features of (1) and (2) can be found in the closest approach of a pair of terminal phenyl rings, each bonded to different phosphorous atoms (Fig. 4). In the structure of (2), the angle between mean planes formed by atoms C1-C6 and the twofold axis-related atoms C1-C6 of the same molecule is 0.98 (12) , with a centroid-centroid distance of 3.8027 (14) Å . The analogous relationship in the structure of (1), involving phenyl rings C1-C6 and C31-C36, is a dihedral angle of 6.52 (13) and a The molecular structure of (1), showing the atom labelling and displacement ellipsoids drawn at the 50% probability level.
centroid-centroid distance of 3.6214 (16) Å . The result of these differences is that in (2) there is only one CÁ Á ÁC intramolecular contact between these phenyl rings shorter than 3.6 Å , while in (1) there are six unique contacts that meet this criteria. Although these intramolecular CÁ Á ÁC contacts are slightly longer than the van der Waals radii sum of 3.4 Å , the additional CÁ Á ÁC close-contacts in (1) may contribute to stronger intramolecularinteractions between these phenyl rings compared to (2). The dihedral angles between the mean planes formed by the ether-linked phenyl groups [(C13-C18 and C19-C24) 76.83 (11) for (1); (C13-C18 and the symmetry-related C13-C18 ring) 84.53 (11) for (2)] also show a significant difference in the twist around the ether linkage.  Table 1 Hydrogen-bond geometry (Å , ) for (1).

Supramolecular features
The intermolecular features of (1) and (2) reveal additional differences between these seemingly similar structures. In the crystal of (1), most notably there are three unique intermolecular C-HÁ Á ÁS interactions (Table 1) shorter than the sum of the van der Waals radii. Each molecule participates as a C-H donor with two different S2 acceptors as well as one S1 acceptor (Table 1 and Fig. 5). As such, each molecule is involved in C-HÁ Á ÁS intermolecular interactions with three other unique molecules. In the crystal of (2), no analogous C-HÁ Á ÁSe intermolecular interactions are present. Both structures show that several intermolecular C-HÁ Á Á contacts less than ca 3.0 Å are present but these are likely to play a weak role in packing interactions [see Table 1 for (1) and Table 2 for (2)]. Molecules of (1) stack in columns parallel to [010] (Fig. 6). The intramolecularstacking interactions of (1) are all aligned perpendicular to the column stacking axis. Molecules of (2) stack in columns parallel to [101] (Fig. 7) with intramolecularstacking perpendicular to the column stacking vector. distances to be much shorter compared with (1). The structure of POP monosulfide is also very different from (1), as intramolecular phenyl ring interactions are present but these involve a terminal phenyl ring and a bridging phenyl ring rather than two terminal phenyl rings as in (1). POP dioxide adopts a conformation unlike (1) or (2), as the P-O bond vectors are closer to antiparallel [intramolecular OPÁ Á ÁP-O angles of 37.0 (6) ]. Considering metal complexes of related ligands, the structures of only two ruthenium(II) complexes , three palladium(II) complexes (Milheiro & Faller, 2011;Saikia et al., 2012), and one rhodium(I) complex (Faller et al., 2008) have been reported with Xantphos sulfide or POP sulfide. The structure of only one palladium(II) complex of Xantphos disulfide (Jahromi et al., 2012) is reported. POP or Xantphos selenide structures are even rarer, as only one copper(I) complex of POP selenide is reported (Venkateswaran et al., 2007b). No structures to date have been reported with diselenides of POP or Xantphos.

Synthesis and crystallization
Compounds (1) and (2) were prepared using a reported procedure (Venkateswaran et al., 2007a). Crystals of each sample were obtained by diffusion of diethyl ether into a concentrated dichloromethane solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were placed in calculated positions and refined in the riding-model approximation: C-H = 0.95 Å with U iso (H) = 1.2U eq (C). A small number of low-angle reflections [nine for (1) and five for (2)] were missing from these high-quality data sets due to the arrangement of the instrument with a conservatively sized beam stop and a fixed-position detector. The large number of reflections in the data sets (and the Fourier-transform relationship of intensities to atoms) ensures that no particular bias was thereby introduced into this routine structure determination.