Crystal structures of a series of 6-aryl-1,3-diphenylfulvenes

The synthesis and structures of a series of 6-aryl-1,3-diphenylfuvlenes with (fulvene is 5-methylidenecyclopenta-1,3-diene) varying methylation patterns on the 6-phenyl substituent are reported. A network of C—H⋯π ring interactions consolidates the packing in each structure.


Structural commentary
Compounds I and IV crystallize in the monoclinic space group C2/c (Fig. 1), compound II in the monoclinic space group P2 1 / c, and compound III the orthorhombic space group Pca2 1 . With the exception of III, in which the asymmetric unit contains two complete fulvene molecules, each compound crystallizes with one molecule per asymmetric unit. In each compound, the expected alternating long-short intra-ring bond lengths are observed. The phenyl substituents are ISSN 2056-9890 rotated from 19.50 (6) to 64.15 (7) from the cyclopentadiene core of the fulvene ( Table 1). The rotation is larger for each substituent in IV, likely because of the additional steric interactions provided by the pentamethyl substituent.

Supramolecular features
The packing for each compound I-IV is consolidated through a series of C-HÁ Á Á ring interactions. In I, each molecule participates in C-HÁ Á Á ring interactions with six other fulvene molecules. Each molecule acts as a C-H donor through the hydrogen atoms in the para position of each phenyl substituent, H10 and H16, as well as a meta hydrogen atom, H23, from the 6-(3-methylphenyl) substituent. Additionally, the ring of the 3-phenyl and 6-(3-methylphenyl) substituents accept C-H interactions, with the latter accepting donations from both sides of the ring (Table 2  The molecular structure of IV. Displacement ellipsoids are shown at the 50% probability level. Table 1 Fulvene-phenyl torsion angles ( ).

Figure 1
The molecular structure of I. Displacement ellipsoids are shown at the 50% probability level.

Figure 2
The molecular structure of II. Displacement ellipsoids are shown at the 50% probability level.

Figure 3
The molecular structure of III. Displacement ellipsoids are shown at the 50% probability level. and H17 as well as methyl hydrogen atom H25A act as donors.
The 3-phenyl and 6-(4-methylphenyl) substituents act as C-H acceptors, with the former accepting donations from both sides of the ring (Table 3 and Fig. 6). The interactions differ between the two molecules within the asymmetric unit of III.
One of the molecules contributes four C-H donor sites, H37, H39, H53A, and H54C, with the ring of each phenyl substituent as well as the fulvene core acting as acceptors. In the other molecule, H10 and H25C act as C-H donors with the system of the 1-phenyl and 3-phenyl substituents accepting, the latter accepting C-H interactions from both sides of the ring (Table 4 and Fig. 7). Fulvene IV interacts with four other molecules via C-HÁ Á Á ring interactions. The para hydrogen atom of the 1-phenyl substituent and one of the hydrogen atoms of the para methyl group of the 6-(2,3,4,5,6pentametyhlphenyl) substituent, H27C, serve as C-H donors The crystal packing of II. Displacement ellipsoids are shown at the 50% probability level. C-HÁ Á Á ring interactions (Table 3) are shown as dashed lines. Table 4 Hydrogen-bond geometry (Å , ) for (III).

Figure 8
The crystal packing of IV, viewed along the b axis. Displacement ellipsoids are shown at the 50% probability level. C-HÁ Á Á ring interactions (Table 5) are shown as dashed lines. Table 2 Hydrogen-bond geometry (Å , ) for (I).

Figure 5
The crystal packing of I. Displacement ellipsoids are shown at the 50% probability level. C-HÁ Á Á ring interactions (Table 2) are shown as dashed lines. Table 5 Hydrogen-bond geometry (Å , ) for (IV).

Database survey
A survey of the November 2019 release of the Cambridge Structure Database (Groom et al., 2016), with updates through February 2019, was made using the program Mogul (Bruno et al., 2004). A search for 1,3-diphenyl fulvenes and 6-aryl-1,3diphenyl fulvenes yielded 78 and 35 results, respectively. In both cases, the phenyl-fulvene torsion angles produce a bimodal distribution with broad peaks at 50 and 130 . The torsion angles in I-IV are therefore not unusual.

Figure 7
The crystal packing of III. Displacement ellipsoids are shown at the 50% probability level. C-HÁ Á Á ring interactions (Table 4) are shown as dashed lines.
temperature for 22 h. The precipitate from the reaction mixture was vacuum filtered, washed with cold absolute EtOH (3 Â 30 ml), and vacuum dried to give I as a dark-red solid (0.211 g, 63%). Red prisms suitable for single-crystal X-ray diffraction were obtained from diethyl ether solution by slow evaporation. 1,3-diphenyl-6-(4-methylphenyl)fulvene (II). To a vigorously stirred solution of 1,3-diphenylcyclopentadiene (0.336 g, 1.42 mmol) in absolute EtOH (8 ml), 4-methylbenzaldehyde (0.25 ml, 2.13 mmol) and pyrrolidine (0.14 ml, 1.70 mmol) were added. The reaction mixture was allowed to stir at room temperature for 24 h. The precipitate from the reaction mixture was vacuum filtered, washed with cold absolute EtOH (3 Â 30 ml), and vacuum dried to give II as a dark-red solid (0.251 g, 75%). Red prisms suitable for single-crystal X-ray diffraction were obtained from diethyl ether solution by slow evaporation.
3-diphenyl-6-mesitylfulvene (III). To a vigorously stirred solution of 1,3-diphenylcyclopentadiene (1.434 g, 6.57 mmol) in absolute EtOH (50 ml), mesitylaldehyde (1.173 g, 7.91 mmol) and pyrrolidine (0.789 g, 11.09 mmol) were added. The reaction mixture was allowed to stir at reflux for 24 h. The reaction mixture was cooled to 278 K and the resulting precipitate was vacuum filtered, washed with cold absolute EtOH (3 Â 30 ml), and vacuum dried to give III as a redorange solid (1.85 g, 81%). Irregular red crystals suitable for single-crystal X-ray diffraction were obtained from pentane solution by slow evaporation.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. H atoms were positioned geometrically and refined as riding with C-H = 0.93-0.96 Å and U iso (H) = 1.2-1.5U eq (C). The absolute structure of III was indeterminate in the present refinement. Compound III was refined as an inversion twin.

Data collection
Bruker APEXII CCD diffractometer φ and ω scans Absorption correction: multi-scan SADABS T min = 0.832, T max = 0.901 31841 measured reflections 3817 independent reflections 3013 reflections with I > 2σ(I) 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.

{3-[(4-Methylphenyl)methylidene]-4-phenylcyclopenta-1,4-dien-1-yl}benzene (II)
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.

{3-[(2,4,6-Trimethylphenyl)methylidene]-4-phenylcyclopenta-1,4-dien-1-yl}benzene (III)
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. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.22 e Å −3 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.