Crystal structures of eight- and ten-membered cyclic bisanisylphosphonothioyl disulfanes and comparison with their P-ferrocenyl analogues

Two new crystal structures of eight- and ten-membered cyclic bisanisylphosphonothioyl disulfanes have been determined and these are compared to the structures of their ferrocenyl analogues.

The reactions between Lawesson's reagent and diols/ diphenols have been successfully involved in the preparation of bis(anisylphosphonodithioic) acid derivatives and among them the unique eight-, nine-and ten-membered cyclic bisanisylphosphonothioyl disulfanes (Przychodzeń , 2004). A high-yielding formation of these medium-sized cyclic disulfanes upon oxidation of bis(anisylphosphonodithtioic) acid salts by iodine proceeding without oligomeric by-products may be attributed to their fixed structure, containing the most preferred a zigzag motif of the SPSSPS unit. Slightly modified procedures with respect to the original method have recently been applied for the synthesis of related cyclic bis(ferrocenylphosphonothioyl)disulfanes, e.g. eight-membered 1a (Pillay et al., 2015) and ten-membered 2a (Hua et al., 2017) and their crystal structures have been determined. Here we report ISSN 2056-9890 crystal structures compounds 1 and 2, containing anisyl groups instead of the ferrocenyl moiety.

Structural commentary
Views of molecular structures and atom-labeling scheme for 1 and 2 are given in Figs. 1 and 2, respectively. Compound 1 crystallizes in the P4 3 2 1 2 space group with a half-molecule in the asymmetric unit. It follows that the molecule obeys point group symmetry described by Schoenflies symbol C 2 (or symbol 2 in international notation). The related ferrocenyl compound 1a crystallizes in space group C2/c with non-typical three and half independent molecules in the asymmetric unit (Z = 28), which complicates comparisons.
Compound 2 forms a monoclinic crystalline phase obeying P2 1 /c space-group symmetry with one molecule in the asymmetric unit and Z = 4. The related ferrocenyl structure 2a crystallizes in space group P1 with one molecule in the asymmetric unit.
The anisyl groups as well as the ferrocenyl groups on the two phosphorus atoms are positioned in a trans arrangement, i.e. above and below the macrocycle ring plane for all compounds 1-2a, which is also typical for all open-chain bisphosphorothioyl disulfanes studied previously (Gray et al., 2004).
All phosphorus atoms in 1-2a adopt a distorted tetrahedral geometry, where the C-P S angles deviated the most (116.1-118.5 ) from the ideal tetrahedral angle. This is obviously due to the steric effects of the anisyl and ferrocenyl substituents. On the other hand, it is worthy to note that the O-P-S bond angles in 1-2a (107-108 ) are not distorted, probably due to minimal conformational strain present in those medium-sized heterocycles. Moreover, both the P S and aromatic anisyl groups in 1 are almost perfectly coplanar (unlike P S and the cyclopentadienyl ring in 1a), which provides energetically favorable conjugation [torsion angle S2-P1-C10-C15 = À3.8 It is well recognised that PSSP torsion is a characteristic feature of all disulfanes as a class of organic compounds. The structure of 1 is the most symmetric with the lowest PSSP torsion [À93.68 (8) ] and shows only a moderate deviation from a right angle. The PSSP torsion angles in 1a [À101.19 (4), À100.06 (4), À101.47 (4) and 99.89 (4) ] are 6-8 wider than in 1. Notably, ten-membered disulfanes have even wider PSSP torsion angles and the difference between them is smaller, À112.89 (11) and 114.9 (4) , for 2 and 2a, respectively.
Only non-classical hydrogen-bonding interactions of the type C-HÁ Á ÁX (X = O or S) can be found in the structures of 1 and 2 (Tables 1 and 2).

Figure 2
View of the asymmetric unit of 2, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
The molecular structure of 1, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Symmetry-equivalent atoms are generated by the operation (y + 1, x À 1, Àz).
The conformation of the eight-membered macrocycles in 1 and 1a was recognised by PLATON (Spek, 2009) as being closest to the TBC form (twist-boat chair; Evans & Boeyens, 1989;Wiberg, 2003), which is consistent with C 2 point symmetry. Fig. 3 shows the overlay of the two structures based on the best fit of the PSSP fragment. The conformation of 2 was not assigned to any border type by PLATON, but Fig. 4 shows the puckering in 2 and 2a is distinctively different.
It is probably important to note that the intramolecular C4-H4BÁ Á ÁO1 hydrogen bond (Table 2) stabilizes the tenmembered ring of 2.

Supramolecular features
The strongest intermolecular hydrogen-bonding interaction in 1 is between the anisyl ortho-hydrogen and macrocyclic O1 atoms and links the molecules into a diamondoid network.
There are no ring-stacking interactions since the shortest centroid-centroid distance is 5.0965 (3) Å . The anisyl substituents may have inhibited this kind of interaction.
Intermolecular interactions in 2 are mainly based on the anisyl methoxyl CH 3 O oxygen atoms O3 and O4 and the P S sulfur atom S3 as acceptors. Hydrogen-bond donors are the anisyl ortho-hydrogen atoms or methylene hydrogen atoms. Moreover, some C-H... interactions may play some role in the system, e.g. C16-H16AÁ Á Áring(C20-C25), see Fig. 5. Again, the stacking interactions are weak since the closest intercentroid distance is equal to 4.9213 (4) Å .

Database survey
Bisphosphonothioyl disulfanes represent a rather rare class of compounds (CSD Version 5.28, updated to Nov. 2016;Groom et al., 2016). Only three structures of cyclic bisphosphonothioyl disulfanes can be found in the database, HUGXAK, HUXEO and HUGXIS (ferrocenyl derivatives; Pillay et al., 2015) and four more will be available there soon (Hua et al., 2017) Table 1 Hydrogen-bond geometry (Å , ) for 1.
Cg is the centroid of the C20-C25 ring.

Figure 3
Superimposition of eight-membered diphosphocanes 1 (blue) and 1a (grey) based on the best PSSP fragment fit.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3  C-HÁ Á Á interaction and internal C-HÁ Á ÁO hydrogen bonding in the ten-membered ring of 2. Relatively high residual electron-density peaks in 2 (Q1-Q3 ca 2e Å 3 ), which are close to sulfur atoms (0.58 Å from S4, 0.49 Å from S2, 0.49 Å from S1), may stem from conformational flexibility of the ring. Note: the structure of 1 was determined at room temperature (due to a failure of our CryoStream unit) not at 120 K as for 2 but we believe it did not influence the qualitative conclusions drawn from the results.

sup-1
Acta Cryst. used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008). Software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010) for (1); WinGX (Farrugia, 2012) for (2).  (17) 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. Refinement. Refined as a 2-component inversion twin.