Crystal structure of 3-(triphenylphosphoranylidene)-2,5-dihydrofuran-2,5-dione tetrahydrofuran monosolvate

The structure of the pseudopolymorph of 3-(triphenylphosphoranylidene)-2,5-dihydrofuran-2,5-dione with a THF solvent molecule is described. The compound has a hydrogen-bonded layer structure, and displays C—H⋯O hydrogen bonds connecting molecules of the dihydrofuran-2,5-dione derivative into chains.


Chemical context
Pseudopolymorphs are solvated forms of a compound that have different crystal structures and/or differ in the nature of the included solvent (Kumar et al., 1999). The investigation of this phenomenon plays an important role for both fundamental and applied reasons. Phosphorus ylides are useful intermediates, which have been used in many reactions and are involved in the synthesis of organic compounds (Selva et al., 2014;Kolodiazhnyi, 1999;Balema et al., 2002). In this paper, the structure of the pseudopolymorph of 3-(triphenylphosphoranylidene)-2,5-dihydrofuran-2,5-dione (Geoffroy et al., 1993), crystallized with a THF solvent molecule, is described. ISSN 2056-9890

Structural commentary
In the title compound ( Fig. 1), the succinic anhydride ring is almost planar (r.m.s. deviation = 0.032 Å ), with the C4 methylenic carbon atom displaced by only 0.118 (2) Å out of the least-squares mean plane through atoms C1, C2, C3 and O1 [maximum deviation of 0.007 (2) Å for C2]. The phosphorus atom deviates from the least-squares mean plane of the succinic anhydride ring by 0.1855 (4) Å . The arrangement of the phenyl rings is propeller-wise, which is common arrangement for Ph 3 P-X fragments. The THF solvent molecule is disordered over two orientations related by a pseudotwofold axis. As recently reported by Islamov et al. (2017), molecules located in general positions rotate more easily than those located on symmetry elements, and the presence of disorder increases the number of minima on the profile of the rotational barrier, making the barrier even lower (Karlen et al., 2010). However, since the quality of the anisotropic displacement parameters of the THF atoms is low, an attempt to determine the height of the rotational barrier using TLS analysis (Dunitz et al., 1988) was unsuccessful.

Database survey
A search of the Cambridge Structural Database (Version 5.39, update February 2018;Groom et al., 2016) revealed 426 structures containing the Ph 3 P C fragment. The distribution histogram of the P C distance [with a mean value of 1.729 Å and a standard deviation of 0.030 Å ] is shown in Fig. 3. The P C distance in the title compound is 1.717 (2) Å , which in good agreement with that of the dichloromethane pseudopolymorph [1.717 (6) Å ; Geoffroy et al., 1993]. In spite of the differences in the crystal packing, the conformation of the molecule is very similar to that of the CH 2 Cl 2 solvate (r.m.s. deviation = 0.032 Å ; Fig. 4).

Figure 2
Crystal packing of the title compound viewed along the b axis.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. Only the major component of the disordered THF molecule is shown.

Figure 3
Distribution histogram of the P C distance in Ph 3 P C fragments.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The THF molecule is disordered over two sites with an occupancy ratio of 0.718 (4):0.282 (4). EADP and SAME restraints were used to model this disordered molecule. The H atoms of the 3-(triphenylphosphoranylidene) dihydrofuran-2,5-dione molecule were located in difference-Fourier maps and refined freely. The THF H atoms were placed geometrically and refined using a riding-model approximation with C-H = 0.99 Å , and with U iso (H) = 1.2U eq (C).

3-(Triphenylphosphoranylidene)-2,5-dihydrofuran-2,5-dione tetrahydrofuran monosolvate
Crystal data 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.