3,9′-Bi(9H-fluorene)

The title compound [systematic name: 9-(9H-fluoren-3-yl)-9H-fluorene], C26H18, was obtained unintentionally as the product of the synthesis of a compound based on fluorene–thiophene units. The two fluorene rings are connected through C atoms in the 3- and 9′-positions, and the dihedral angle between the mean planes of the two fluorene units is 78.57 (6)°.

The title compound [systematic name: 9-(9H-fluoren-3-yl)-9H-fluorene], C 26 H 18 , was obtained unintentionally as the product of the synthesis of a compound based on fluorenethiophene units. The two fluorene rings are connected through C atoms in the 3-and 9 0 -positions, and the dihedral angle between the mean planes of the two fluorene units is 78.57 (6) .

Jie Liu and Wentao Yu Comment
The molecule of the title complound (I) (Fig. 1) as the isomer of 9,9′-bi-9H-fluorene (9,9′-BF) is noncentrosymmetric, and the space group is P2 1 2 1 2 1 . The two fluorene groups of the compound are like the letter ′T′ in shape with a dihedral angle of 78.57 (6)°. Also, it is found that benzene rings of the fluorene units are not in the same plane, and the dihedral angles are 10.54 (6) and 5.84 (6)°, respectively. The crystal packing is stabilized by intermolecular C--H···π interactions ( Fig. 3).

Experimental
The title compound, 3,9′-BF, was obtained unintentionally as the product of an attempted synthesis of 2,5-bis(9Hfluoren-9-yl)thiophene through Still reaction method. n-Butyllithium (20 ml, 2.5 M in hexane, 50 mmol) was added dropwise at -78 °C into a consistently stirred mixture of thiophene (22 mmol, 1.8 ml) and dry THF (80 ml), and the mixture would be with further stirring for 2 h at room temperature under an atmosphere of dry argon. After cooling the reaction mixture to -78 °C tri-n-butyltin chloride (15 ml) was added drop-wise to the mixture system. Then, the mixture was stirred continuously over one night before being poured into saturated NH 4 Cl water solution (100 ml). After extraction with diethyl ether, the organic layer was dried over anhydrous MgSO 4 and the yellow fluid bis[tri-n-butyltin] thiophene (TBSB) was obtained. Furthermore, DMF (10 ml) was added to the mixture of TBSB (2.5 mmol, 1.654 g), 9bromo-fluorene (6.25 mmol, 1.53 g) and potassium fluoride (2.5 mmol, 0.145 g) with stirring about 15 min. Appropriate amount of tetrakis (triphenylphosphine) palladium (0) was added to the stirring system and refluxed at 100 °C for 16 h under an atmosphere of dry argon. After extraction with dichloromethane (30 ml), the mixture was purified by silica-gel column chromatography to give 3,9′-BF, 9,9′-BF and 2,5-bis(9H-fluoren-9-yl)thiophene. Finally, single crystals of 3,9′-BF were obtained by recrystallizing from dichloromethane.

Refinement
All the H atoms were positioned geometrically [C-H = 0.93, 0.96 and 0.98 Å] and refined using a riding model with Uiso In the absence of significant anomalous scattering, Friedel pairs were merged; the absolute configuration was not determined.

3,9′-Bi(9H-fluorene)
Crystal data 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 > σ(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.