K. Tanaka et al. / Tetrahedron 63 (2007) 9213–9220
9219
4.1.1. 9,90-Dichloro-9,90-bisfluorenyl 4. A mixture of 9,9-
dichlorofluorene (7.05 g, 30 mmol) and copper powder
(3.81 g) in toluene (50 ml) was heated under reflux for 4 h.
After filtration of copper powder, the resultant solution
was evaporated to dryness under vacuo and the solid residue
was recrystallized from ethyl acetate to give 9,90-dichloro-
9,90-bisfluorenyl 49 as pale yellow prisms (2.96 g) in 49%
yield. Mp 244–245 ꢀC. IR (Nujol): nmax 1603, 1377, 1190,
1034, 929, 849, 737, 695, and 647 cmꢁ1 1H NMR
.
(DMSO, 70 ꢀC): d 7.15–7.88 (16H, m, Ar). Anal. Calcd
for C26H16Cl2: C, 78.20; H, 4.04. Found: C, 78.20; H, 4.20.
4.1.2. 2,20,7,70,9,90-Hexachloro-9,90-bisfluorenyl 5. A mix-
ture of 2,7,9,9-tetrachlorofluorene9 (0.304 g, 1 mmol) and
copper powder (0.127 g) in benzene (20 ml) was heated
under reflux for 24 h. After filtration of copper powder, the
resultant solution was evaporated to dryness under vacuo
and the solid residue was recrystallized from chloroform to
give 2,20,7,70,9,90-hexachloro-9,90-bisfluorenyl 5 as color-
less prisms (0.13 g) in 48% yield. Mp 314–315 ꢀC. IR
(Nujol): nmax 1580, 1377, 1167, 1075, 956, 810, 773, and
1
688 cmꢁ1. H NMR (DMSO, 100 ꢀC): d 7.06 (4H, br s,
Ar), 7.57 (4H, d, J¼5.4 Hz, Ar), 7.60 (4H, d, J¼5.4 Hz,
Ar). Anal. Calcd for C26H12Cl6: C, 58.14; H, 2.25. Found:
C, 58.04; H, 2.37.
Figure 13. Crystal packing in the 1:1 inclusion compound between host 7
and 1,2-dibromocyclohexane. Host and guest molecules are drawn in ball-
and-stick and space-filling modes, respectively. Four unit cells are shown.
4.1.3. 2,20,7,70-Tetrabromo-9,90-dichloro-9,90-bisfluor-
enyl 6. The powdered crystals of 4 (3.22 g, 8 mmol) were
treated with a large excess of bromine in the solid state
and left for 12 h at room temperature in the draft. The crude
crystals were recrystallized from CCl4 to give 2,20,7,70-tetra-
bromo-9,90-dichloro-9,90-bisfluorenyl 69 as colorless nee-
dles (5.16 g) in 81% yield. Mp 294–296 ꢀC. IR (Nujol):
nmax 1574, 1377, 1249, 1165, 1065, 958, 895, 865, 803,
that the resulting inclusion compounds display a wide range
of thermal stabilities. X-ray analysis has shown that the host
molecules 4–7 generally adopt a conformation with C2 sym-
metry, which is stabilized by intramolecular C–H/Cl or
C–H/Br hydrogen bonds. The torsion angle X–C–C–X
(X¼Cl, Br) defining the overall host conformation varies
within a very narrow range (magnitudes 57.9–61.3ꢀ) for
the five crystals examined. All compounds crystallized
with both host enantiomeric forms present. The X-ray results
support the notion that the more highly halogenated hosts 5–
7 are generally more successful in including guest molecules
due to their ability to form favorable halogen/halogen in-
teractions (host–host and host–guest, when the latter is pos-
sible). For the inclusion compounds whose structures were
determined, it was possible to rationalize the observed ther-
mal behaviors qualitatively on the basis of the type of guest
inclusion mode (‘isolated site’, ‘channel’ inclusion), as well
as the observed hydrogen bonding and halogen bonding
interactions. This approach was particularly useful in the at-
tempt to find reasons for the significant difference in thermal
behavior of the compounds 5$(p-xylene)0.5 and 6$CHCl3,
which are based on nearly isostructural host frameworks.
1
and 766 cmꢁ1. H NMR (DMSO, 75 ꢀC): d 7.65 (12H, br
s, Ar). Anal. Calcd for C26H12Br4Cl2: C, 43.68; H, 1.69.
Found: C, 43.66; H, 1.83.
4.1.4. 2,20,7,70,9,90-Hexabromo-9,90-bisfluorenyl 7. A mix-
ture of 9,9-dichlorofluorene (3.5 g, 15 mmol) and Zn
powder (2 g) in xylene (30 ml) was heated under reflux for
24 h. After filtration of Zn powder, the resultant solution
was evaporated to dryness under vacuo and the solid residue
was recrystallized from ethyl acetate to give bifluorenyli-
dene10 as red prisms (0.98 g) in 40% yield. The powdered
crystals of bifluorenylidene (1.02 g, 3.1 mmol) were treated
with a large excess of bromine in the solid state and left
for 12 h at room temperature in the draft. The crude crystals
were recrystallized from toluene to give 2,20,7,70,9,90-hexa-
bromo-9,90-bisfluorenyl 79 as colorless prisms in 46%
yield. Mp 315–316 ꢀC. IR (Nujol): nmax 1580, 1416, 1377,
1249, 1167, 1167, 1075, 955, 896, 867, 810, 773, and
1
690 cmꢁ1. H NMR (DMSO, 75 ꢀC): d 7.62 (12H, br s,
4. Experimental
4.1. General
Ar). Anal. Calcd for C26H12Br6: C, 38.85; H, 1.50. Found:
C, 38.71; H, 1.69.
4.2. X-ray structure determinations
1H NMR spectra were recorded in CDCl3 on a JEOL JNM-
EX270 FTNMR spectrometer. IR spectra were recorded
with a JASCO FTIR 4100 spectrometer. Thermogravimetric
(TG) analyses were performed on a Rigaku TG-8120 instru-
ment. The inclusion crystals were obtained by recrystalliza-
tion of the host compound from the respective guest solvent.
For the host compound 4 and the four inclusion complexes
5$(p-xylene)0.5, 6$CHCl3, 7$CHCl3, and 7$1,2-dibromo-
cyclohexane, single crystals of high quality were isolated and
their X-ray structures determined. All intensity data were
collected on a Nonius Kappa CCD four-circle diffractometer