Synthesis, variable temperature NMR investigations and solid state characterization of novel octafluorofluorene compounds

Article abstract of DOI:10.1016/j.jfluchem.2008.12.011

The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-octafluorofluorene, C₁₃H₂F₈, 1

Full text of DOI:10.1016/j.jfluchem.2008.12.011

Journal of Fluorine Chemistry 130 (2009) 341–347
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis, variable temperature NMR investigations and solid state
characterization of novel octafluorofluorene compounds
Fabio Marchetti a,1, Fabio Marchetti a,2, Francesco Masi b, Guido Pampaloni a,
*
,
Vincenzo Passarelli a,3, Anna Sommazzi c, Silvia Spera c
a
`
Universita di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa, Italy
b Polimeri Europa, Piazza Boldrini 1, I-20097 San Donato Milanese, Italy
c Eni S.p.A., Centro Ricerche per le Energie non Convenzionali–Istituto Eni Donegani, via G. Fauser 4, I-28100 Novara, Italy
A R T I C L E I N F O
A B S T R A C T
Article history:
The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR
studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-
octafluorofluorene, C13H2F8, 1; 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenylfluorene, C19HF13, 8;
1,10,2,20,3,30,4,40,5,50,6,60,7,70,8,80-hexadecafluoro-9,90-bifluorenyl, C26H2F16, 11] are reported. Variable
temperature 19F NMR investigations have been performed on the 9-aryl substituted compounds
1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenyl-9-hydroxyfluorene, C19HF13O, 4, 1,2,3,4,5,6,7,8-
octafluoro-9-(nonafluoro-40-biphenylyl)-9-hydroxyfluorene, C25HF17O, 5, and 8, and the energetic
barriers to rotation of the aryl have been determined. A lower rotational barrier is observed for
compound 4 with respect to compound 8, while 5 does not show fluxional behaviour below 338 K. The
results of the variable temperature experiments performed on 8 have been rationalized by 2D NMR
studies, and compared to the solid state data resulting from the X-ray structural analysis.
ß 2009 Published by Elsevier B.V.
Received 12 November 2008
Received in revised form 15 December 2008
Accepted 18 December 2008
Available online 5 January 2009
In memory of Roberto Santi (1948–2003).
Keywords:
Fluorine
Fluoro derivatives
Octafluorofluorene
Crystal structures
NMR spectra
1. Introduction
interest for their biological properties [7] or for their possible use
as standards in environmental analyses [8].
The fluorination of aryl groups determines important effects
in reactivity [1]. More specifically, fluoro- and polyfluoro aryl
substituents can induce stabilizing effects on carbanions, when
compared with the analogous all-hydrogen systems [2]. This
stabilization has been observed in tetraarylborate ions: for
instance, the tetraphenylborate [B(C6H5)4]ꢀ is thermally unstable
and decomposes under acidic and oxidant conditions [3], while
the 3,5-fluoroalkyl-substituted anions {B[C6H3(Rf)2]4}ꢀ [Rf = CF3,
(CF2)3CF3, CF(CF3)2] are thermally stable and resist highly acidic
conditions [4]. Relevantly, when used in olefin polymerization,
the salts of these fluorine-rich anions are better co-catalysts than
the non-fluorinated ones [5].
Within the series of fluoro-substituted fluorenes, a limited
number of octafluorofluorene species have been reported [1c,2,9].
Some of us have recently described the catalytic properties of
octafluorofluorenyl anions [10], which made us keen on the
preparation of new octafluorofluorene compounds. The synthetic
procedures are reported herein, together with the spectroscopic
characterization (1H and 19F NMR), and some X-ray molecular
determinations; furthermore, variable temperature 19F NMR
experiments will be discussed.
2. Results and discussion
Fluoro-substituted fluorene derivatives have been known for
a long time [6], and some of these compounds have attracted
2.1. Synthesis
Some of the octafluorofluorene derivatives discussed in this
paper [1,2,3,4,5,6,7,8-octafluorofluorene, C13H2F8, 1; 1,2,3,4,5,6,7,8-
octafluoro-9-(pentafluoro)phenylfluorene, C19HF13, 8; 1,2,3,4,5,6,
7,8-octafluoro-9-hydroxyfluorene, C13H2F8O, 9] have been prepared
according to the literature [2,9] while new high-yield synthetic
procedures have been developed for the derivatives 2–7, 10–11.
Compounds 2–5 (9-aryl substituted octafluoro-9-hydroxyfluor-
enes) have been obtained by reaction of octafluorofluorenone with
* Corresponding author. Tel.: +39 050 2219 219; fax: +39 050 2219 246.
E-mail address: pampa@dcci.unipi.it (G. Pampaloni).
1
Born in Bologna (Italy) in 1974.
2
Born in Castelfiorentino (FI, Italy) in 1950.
3
Present Address: CSIC-ICMA Facultad de Ciencias, C/ Pedro Cerbuna 12, E-50009
Zaragoza, Spain.
0022-1139/$ – see front matter ß 2009 Published by Elsevier B.V.
doi:10.1016/j.jfluchem.2008.12.011

342
F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
Table 1
19F NMR resonances of 8 in various solvents.
.
Scheme 1.
a
CCl4
C6D6
THF
CDCl3
1, 8
3, 6
4, 5
20(200)
200
30(300)
300
40
ꢀ143.3
ꢀ153.9
ꢀ134.7
ꢀ142.1
ꢁ
ꢀ144.3
ꢀ153.7
ꢀ134.4
ꢀ142.6
ꢀ143.6
ꢀ160.7
ꢁ
ꢀ131.3
ꢀ150.8
ꢀ140.0
ꢀ139.0
ꢀ138.5
ꢀ158.3
ꢀ157.9
ꢀ150.5
ꢀ152.1
ꢀ152.4
ꢀ143.1
ꢀ142.6
ꢀ141.6
ꢀ160.7
ꢀ160.1
ꢀ152.4
ꢀ161.5
ꢁ
ꢀ153.9
ꢀ152.0
a
d
-Values referred to CFCl3, recalculated from ref [9a].
In the 19F NMR spectra, the fluorine atoms belonging to the
fluorenyl unit resonate respectively at ca.ꢀ130 ppm (F1, F8),
ꢀ140 ppm (F4, F5) and ꢀ150 ppm (F2, F7, F3, F6).
Scheme 2.
one equivalent of LiAr [Ar = 2,4-bis(trifluoromethyl)phenyl, 3,5-
bis(trifluoromethyl)phenyl, (pentafluoro)phenyl, (nonafluoro)-4-
biphenylyl], in diethyl ether at temperatures in the range between
ꢀ70 and ꢀ20 8C, see Scheme 1.
We noticed that the 19F NMR spectrum of 8 in THF-d8 appeared
markedly different from that reported by Vlasov (recorded in CCl4)
[9a], then we decided to deepen this point. The solution structure
of 8 has been elucidated by means of 1D and 2D 19F NMR
experiments: at 298 K, the monodimensional spectrum in THF-d8
shows four resonances for the fluorenyl moiety, indicating the
equivalence of the two C6-rings. On the other hand, the presence of
five signals for the C6F5 group suggests that both the ortho- and the
meta-positions on the (pentafluoro)phenyl ring are non-equiva-
lent. The 19F,19F-COSY and NOESY spectra have led to the
assignments reported in Table 1.
The octafluorofluorenes, 6–8, have been obtained from the
hydroxo derivatives, 2–4, by bromination with PBr3 followed by
reduction with zinc in acetic acid at room temperature (Scheme 2).
Dimer 11 was obtained from 1,2,3,4,5,6,7,8-octafluorofluorenone
by the sequence of reactions illustrated in Scheme 3. Compounds
2–11 are colourless crystalline materials, and have been char-
acterized by 1H and 19F NMR spectroscopy. Moreover, the solid
state molecular structures of 1, 8 and 11 have been ascertained by
X-ray diffraction analyses.
Interestingly the 19F,19F-NOESY spectrum of 8 only shows
correlation between the fluorines F1/F8 and F20, while no cross-
peak is observed between F1/F8 and F200. According to this, the
orientation of the pentafluorophenyl with respect to the fluorenyl
moiety should be non-symmetric, making both the ortho- and meta-
positions at the aryl ring non-equivalent. However, exchange cross-
peaks have been observed both between F20 (ꢀ139.0 ppm)
and F200 (ꢀ138.5 ppm), and between F30 (ꢀ158.3 ppm) and F300
(ꢀ157.9 ppm): these features suggest that, although the aryl
rotation is slow at room temperature, it is not completely inhibited.
Hence, a variable temperature 19F NMR study was carried out
on compound 8 in THF-d8 (see Fig. 1) and, for comparison, in CDCl3,
too. As a general remark, the hindered rotation of the aryl ring is
observable both in THF-d8 and in CDCl3. Nevertheless, the
coalescences of the resonances due to the non-equivalent F20
and F200, and F30 and F300, respectively, have been seen at different
temperatures on varying the solvent (see Table 2).
2.2. NMR studies
The 1H NMR spectra of compounds 6–11 (in CDCl3) show the
presence of a relatively low-field resonance, due to the C(sp3)-H
proton, in the range 5.40 (11)–6.16 (9) ppm, as consequence of the
electron withdrawing action of the octafluorofluorenyl frame.
Otherwise, the 1H NMR spectra (CDCl3) of 2–5, 9 exhibit the peak
assigned to the OH proton in the range 2.62 (9)–3.75 (4) ppm.
The rate constants, kc, and the activation free energy, D
G#, for the
C6F5 ring rotation, have been calculated according to the equations:
ꢀ
ꢁ
pffiffiffi
kc ¼ p Dd
=
2
(Ddis the difference between the chemical shifts of
the two resonances related to either the o-fluorines or the m-
fluorines respectively) and
Tc is the coalescence temperature (K), see Table 2 [11].
D
G ¼ 4:57Tcð10:32 þ lnðTc=kcÞÞ, where
The 19F NMR spectrum of 4, which differs from 8 for the
presence of the hydroxy-substituent (see Schemes 1 and 2),
exhibits only one narrow doublet for the fluorine nuclei F20 and F200
(the multiplicity is consequence of the coupling with F30/F300) and
one multiplet for the fluorines F30 and F300 (due to the couplings
with F20/F200 and F40), in THF-d8 at room temperature. These
Scheme 3.

F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
343
overcome the rotational barrier increases significantly on passing
from 4, 8 to 5, with consequent rise of the coalescence temperature.
The higher rotational barrier of the –C6F5 unit observed in 8
with respect to 4 (see Table 2) is coherent with previous results
found for 9-substituted-9-arylfluorenes [9]. In agreement with
these reports, the activation free energy for the rotation of the aryl
would depend on the encumbrance of the R substituent (R H, OH):
the larger R is, the higher is the energetic level of the ground state,
and the smaller is the energy difference between the ground state
and the transition one.
In addition, the observed little barriers (10–15 kcal/mol)
and the negligible influence of the solvent (THF-d8 vs. CDCl3)
suggest that the aryl rotation takes place via a non-dissociative
mechanism, ruling out the dissociative mechanistic proposal
formulated by Chandross and Sheley for related substituted
fluorenes [13].
Fig. 1. Variable temperature 19F NMR study on compound 8 (solvent: THF-d8).
2.3. X-ray structural studies of 1, 8, and 11
features indicate that the rotation of the pentafluorophenyl
substituent in 4 occurs rapidly on the NMR timescale already at
room temperature. As the temperature is lowered, the doublet
observed at room temperature for F20/F200 gradually broadens and
splits into a pair of doublets below 222 K (TcF2). Analogously,
the F30/F300 resonance, which appears as a multiplet at room
temperature, splits into two false-triplets below 245 K. A similar
behaviour has been observed in CDCl3 (see Table 2 for Tc). The
activation parameters calculated from these observations for
compound 4 are reported in Table 2; the chemical shift separation
in the absence of exchange has been estimated on the lowest
temperature (208 K) spectra (THF-d8: 0.28 ppm for F20/F200 and
2.01 ppm for F30/F300; CDCl3: 0.30 ppm for F20/F200 and 2.01 ppm for
F30/F300). It is noteworthy that the o-fluorines within the aryl
substituent (F20, F200) resonate at significantly different chemical
shifts in compound 4 (ꢀ135.9 ppm) with respect to 8 (ꢀ138.5 and
ꢀ139.0 ppm), at 298 K in THF-d8. This discrepancy might be the
effect of a hydrogen-bond involving the adjacent hydroxyl group in
4. However, an interaction Fꢂ ꢂ ꢂH–O, if present [12], is evidently not
strong enough to prevent the fast rotation of the aryl ring at room
temperature.
A search on the Cambridge Crystallographic Data Centre
[14] revealed the absence of crystallographically characterized
octafluoro-substituted fluorenes. This fact prompted us to
investigate the X-ray molecular structure of some of the com-
pounds reported in the previous section, with particular regard
to 8 (we were eager to see whether the features evidenced in
solution by 19F NMR spectroscopy found correspondence in the
solid state or not).
Crystals suitable for X-ray analyses were collected by slow
evaporation of the solvents from toluene (compounds 8 and 11) or
C6D6 (compound 1) solutions. The species 1 and 8 crystallize in the
monoclinic space group C2/c. Figs. 2 and 3 show the molecular
The 19F NMR spectrum of compound 5 (see Scheme 1) in THF-d8,
exhibits three pairs of distinct resonances for the fluorines F20 and
F200, F30 and F300, F40 and F400, respectively. Such resonances are
observed at ꢀ131.9 and ꢀ132.7 ppm, ꢀ148.9 and ꢀ150.7 ppm,
ꢀ134.2 and ꢀ134.4 ppm, in the order given. On increasing the
temperature up to 338 K (the highest temperature we could reach in
THF-d8), the spectrum remains substantially unchanged, suggesting
that the rotational barrier around the C(sp3)-Ar bond is much higher
forcompound 5 than for 4 and 8. This result appears to be an effect of
the higher moment of inertia of the nonafluorobiphenylyl sub-
stituent, compared with that of the pentafluorophenyl substituent,
see Schemes 1 and 2. According to that, the energy needed to
Table 2
Spectral, kinetic and activation parameters related to the rotation of the
pentafluorophenyl ring in compounds 4 and 8.
Dd (Hz)
kc (sꢀ1
)
Tc (K)
D
G#
(kcal molꢀ1
)
F20/F200
F30/F300
F20/F200
F30/F300
F20/F200 F30/F300
THF-d8
4
8
78 ꢃ 3 567 ꢃ 4
134 ꢃ 3 71 ꢃ 6
175 ꢃ 7
1259 ꢃ 9
222
245
316
10.2 ꢃ 0.5
15.8 ꢃ 0.1
310 ꢃ 22
158 ꢃ 13 333
CDCl3
Fig. 2. View of the molecular structure (A) and of the crystal packing along the axis b
(B) of 1,2,3,4,5,6,7,8-octafluorofluorene, 1. Thermal ellipsoids are drawn at 30%
probability level.
4
8
1881 ꢃ 3 242 ꢃ 4 4176 ꢃ 7
310 ꢃ 3 132 ꢃ 3 688 ꢃ 7
537 ꢃ 9
293 ꢃ 7
265
343
245
329
9.9 ꢃ 0.7
15.4 ꢃ 0.3

344
F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
Fig. 4. View of the molecular structure (A) and of the crystal packing along the axis b
(B) of 1,10,2,20,3,30,4,40,5,50,6,60,7,70,8,80-hexadecafluoro-9,90-bifluorenyl, 11. Thermal
ellipsoids are drawn at 30% probability level.
Fig. 3. View of the molecular structure (A) and of the crystal packing along the axis b
(B) of 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluorophenyl)fluorene, 8. Thermal ellipsoids
are drawn at 30% probability level.
C(1)C(13)C(14)C(26) are displayed in the three cases: the value of
this angle is 61.98 in 9,90-bifluorenyl [16], 67.68 and 74.48 in the
two independent molecules of 1,10,2,20,3,30,4,40,5,50,6,60,7,70,8,80-
hexadecachloro-9,90-bifluorenyl [17] and 72.58 in 11.
As a general consideration, the X-ray structures of 1, 8, and 11
display similar average C–C bond distances, within the aryl rings,
which resemble the corresponding values observed in the ions
[B(C6F5)4]ꢀ [18] and [BH(C6F5)3]ꢀ [19]. The C(sp3)–C distances,
Table 3, do not vary significantly on going from phenyl [20] (or p-
tolyl- [21]) substituted fluorenes to 8. The increase of the C(sp3)–
structures and the crystal packing of the two compounds. Bond
distances and angles for 1 and 8 are given as Supporting Information.
Compound 1 (Fig. 2A) possesses a twofold symmetry and is
˚
essentially planar, the maximum deviation (0.03 A) occurring at
F(4). As shown in Fig. 2B, the molecules align along the (1 0 1)
plane.
For what concerns 8, Fig. 3A, the molecules are arranged in
infinite columns parallel to axis b, the octafluorofluorenyl
C
distances on going from the 9-aryl- to the 9-fluorenyl
¯
moieties being approximately aligned with the plane ð3 0 7Þ,
substituted species is due to fact that both these carbon atoms
are sp3-hybridized in the latter. Moreover, the C(sp2)–F lengths
appear comparable to those found in perfluorinated organic
molecules [22].
Fig. 3B. By a different point of view, the same molecules are
distributed along two planes: one of them is defined by the
˚
octafluorofluorenyl frames, the maximum deviation being 0.08 A
at F(7), while the second plane is defined by the pentafluorophenyl
˚
rings [max deviation 0.02 A at F(17)]. Noteworthy, the two planes
Table 3
form a dihedral angle of 83.58, resembling the non-equivalence of
the ortho- and meta-positions within the aryl ring, which is
observed also in solution even at room temperature (see above). A
molecular layout analogous to that found for 8 is regularly
exhibited by species containing the 9-aryl-fluorene unit [15], the
dihedral angle between the aryl and the fluorine units ranging
between 72.98 and 89.18.
3
˚
C(sp )–C(R) distances (A) in selected 9-substituted fluorenes.
.
The molecular structure of 11 is shown in Fig. 4A, whereas bond
distances and angles are provided as Supporting Information. The
structure of the two equivalent fluorenyl moieties is similar to
that observed in non-fluorinated 9,90-bifluorenyl [16] and
in 1,10,2,20,3,30,4,40,5,50,6,60,7,70,8,80-hexadecachloro-9,90-bifluor-
3
˚
R
C(sp )–C(R) distance (A)
Reference
C6H5
1.523(6)
[20]
p-CH3C6H4
C6F5
1.515(7)
[21]
1.521(4)
This work
[16a,d]
This work
C
C
13H9
1.542(5); 1.539(6)
1.577(3)
enyl [17]. Likewise these compounds, 11 shows
a gauche
13HF8
conformation, and only slight differences in the torsion angle

F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
345
3. Conclusions
1,2,3,4,5,6,7,8-Octafluoro-9-hydroxy-9-(3,5-trifluoromethylphe-
nyl)fluorene, 3: Colourless microcrystalline solid, 95% yield from
3,5-bis(trifluoromethyl)phenyllithium, freshly prepared from 1-
bromo-3,5-bis(trifluoromethyl)benzene, and 1,2,3,4,5,6,7,8-octa-
fluorofluorenone, after purification on a silica gel column [eluent:
Some novel octafluorofluorene derivatives have been described
here for the first time as prepared in high yields by standard routes.
Variable temperature 19F NMR solution studies performed
on octafluoro-9-arylfluorenes have allowed to estimate kinetic
parameters related to the aryl ring rotational motion. According to
these studies, the substitution of one hydrogen with one hydroxyl
group at the quaternary carbon makes the rotation of the aryl
moiety around the C(sp3)–aryl bond more rapid, in agreement with
previous reports regarding analogous non-fluorinated systems.
Moreover, variable temperature NMR experiments carried out
in solvents of different polarities have ruled out the possibility
that a dissociative mechanism is involved in the aryl rotational
process.
The X-ray solid state structures determined for 1,2,3,4,5,6,7,8-
octafluorofluorene, 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluorophe-
nyl)fluorene, and 1,10,2,20,3,30,4,40,5,50,6,60,-7,70,8,80-hexadeca-
fluoro-9,90-bifluorenyl represent the first crystallographic
reports concerning octafluorofluorene compounds. Comparisons
of the structural features with those available for all-hydrogen
analogous molecules have pointed out that the substitution with
fluorine atoms does not determine dramatic changes in the
geometry and in the crystal packing.
petroleum ether/acetone = 90/10 (
C, 46.86; H, 0.75. Found C 46.69; H, 0.78%. 1H NMR (CDCl3):
(s, 1 H, H40); 7.84 (s, 2 H, H20 + H200); 3.20 (s, 1 H, OH) ppm. 19F NMR
(CDCl3, see Scheme 1 for the fluorine atoms numbering):
v
/v
)]. Anal. Calcd. for C21H4F14O:
d
7.87
d
ꢀ62.9 (s,
3
6 F, CF3), ꢀ132.6 (d, JFF = 20.0 Hz, 2 F, F1 + F8), ꢀ142.1 (d,
3JFF = 19.8 Hz, 2 F, F4 + F5), ꢀ149.3 (m, 2 F, F2 + F7), ꢀ150.5 (m, 2 F,
F3 + F6) ppm.
1,2,3,4,5,6,7,8-Octafluoro-9-hydroxy-9-pentafluorophenylfluor-
ene, 4: Colourless microcrystalline solid, 93% yield from
pentafluorophenyl lithium, freshly prepared from 1-bromo-
pentafluorobenzene, and 1,2,3,4,5,6,7,8-octafluorofluorenone.
Anal. Calcd. for C19HF13O: C, 46.36; H, 0.20. Found: C, 46.31; H,
0.22%. 1H NMR (CDCl3):
d
3.75 (s, 1 H, OH) ppm. 19F NMR (CDCl3,
see Scheme 1 for the fluorine atoms numbering):
d
ꢀ133.0 (d,
3JFF = 19.5 Hz, 2 F, F1 + F8), ꢀ141.0 (d, 3JFF = 19.3 Hz, 2 F, F20 + F200),
3
ꢀ143.8 (d, JFF = 19.5 Hz, 2 F, F4 + F5), ꢀ149.7 (m, 2 F, F2 + F7);
ꢀ151.4 (m, 2 F, F3 + F6), ꢀ151.7 (t, 3JFF = 21.1 Hz, 1 F, F40), ꢀ159.8
(m, 2 F, F30 + F300) ppm. 19F NMR (THF-d8, see Scheme 1 for the
fluorine atoms numbering):
d
ꢀ131.3 (d, 3JFF = 19.8 Hz, 2 F, F1 + F8),
3
ꢀ135.9 (d, JFF = 19.3 Hz,
2
F,
2
F, F20 + F200), ꢀ140.2 (d,
4. Experimental
3JFF = 19.5 Hz, 2 F, F4 + F5), ꢀ149.3 (m, 2 F, F2 + F7), ꢀ150.0 (m,
3
2 F, F3 + F6), ꢀ151.4 (t, JFF = 21.2 Hz, 1 F, F40), ꢀ159.0 (m, 2 F,
4.1. General
F30 + F300) ppm.
1,2,3,4,5,6,7, 8-Octafluoro-9-hydroxy-9-nonafluorodiphenylfluor-
ene, 5: Colourless microcrystalline solid, 96% yield from
(nonafluoro)-4-biphenylyl lithium, freshly prepared from 4-
bromo(nonafluoro)-4-biphenylyl, and 1,2,3,4,5,6,7,8-octafluoro-
fluorenone, after purification on a silica gel column [eluent:
Unless otherwise stated, all the operations were carried out
under atmosphere of prepurified argon. Solvents were dried by
conventional methods prior to use. 1H and 19F NMR spectra at
298 K were recorded on Varian Gemini 200BB instrument
(200 MHz for 1H and 188 MHz for 19F), while variable temperature
19F NMR spectra were recorded on Varian VXR 300 (282 MHz for
19F). TMS and CFCl3 were used as standard for 1H NMR and 19F NMR
spectra, respectively. The compounds 1,2,3,4,5,6,7,8-octafluoro-
fluorene, 1 [1c], 1,2,3,4,5,6,7,8-octafluorofluorenone [23], and 4-
Br-nonafluoro-1,10-biphenyl [24] were prepared according to
literature procedures.
petroleum ether/acetone 90/10 (
v
/
v
)]. Anal. Calcd. for C25HF17O: C,
3.35 (s,
46.90; H, 0.16. Found: C, 46.81; H, 0.13%. 1H NMR (CDCl3):
d
1 H, OH) ppm. 19F NMR (CDCl3, see Scheme 1 for the fluorine atoms
numbering):
d
ꢀ133.0 (m, 2 F, F1 + F8), ꢀ133.6 (d, 3JFF = 21.5 Hz, 1
F, F20), ꢀ136.3 (d, 3JFF = 21.5 Hz, 1 F, F200), ꢀ137.9 (d, 3JFF = 19.8 Hz, 1
F, F40), ꢀ138.3 (d, 3JFF = 19.5 Hz, 1 F, F400), ꢀ141.7 (m, 2 F, F4 + F5),
ꢀ149.9 (m, 2 F, F2 + F7), ꢀ151.4 (m, 3 F, F3, F6 + F6’), ꢀ152.6 (d,
3JFF = 20.0 Hz, 1 F, F30), ꢀ153.9 (d, JFF = 19.7 Hz, 1 F, F300), ꢀ163.3
3
4.2. Preparation of 1,2,3,4,5,6,7,8-octafluoro-9-hydroxy-9-
(m, 2 F, F50 + F500) ppm. 19F NMR (THF-d8, see Scheme 1 for the
arylfluorene derivatives, 2–5
fluorine atom numbering):
d
ꢀ131.0 (m, 2 F, F1 + F8), ꢀ131.9
(d, 3JFF = 21.1 Hz, 1 F, F2), ꢀ132.7 (d, 3JFF = 21.0 Hz, 1 F, F200), ꢀ134.2
(d, 3JFF = 21.0 Hz, 1 F, F40), ꢀ134.4 (d, 3JFF = 21.1 Hz, 1 F, F400), ꢀ138.5
(m, 2 F, F4 + F5), ꢀ148.6 (m, 2 F, F2 + F7), ꢀ149.6 (m, 2 F, F3 + F6),
ꢀ151.9 (t, 3JFF = 21.0 Hz, 1 F, F60), ꢀ148.9 (d, 3JFF = 21.0 Hz, 1 F, F30),
ꢀ150.7 (d, 3JFF = 19.6 Hz, 1 F, F300), ꢀ161.2 (m, 2 F, F50 + F500) ppm.
Only the preparation of 1,2,3,4,5,6,7,8-octafluoro-9-hydroxy-9-
[2,4-bis(trifluoromethyl) phenyl]fluorene, 2, is described in detail,
those of compounds 3–5 being performed in a similar way. A
solution of 1-bromo-2,4-bis(trifluoromethyl)benzene (5.00 g,
17.1 mmol), in diethyl ether (100 ml), was added to a 2.5 M
solution of butyl-lithium in diethyl ether (7.00 mL; 17.5 mmol of
butyl-lithium), at ca. ꢀ75 8C. After 1 h stirring at this temperature,
1,2,3,4,5,6,7,8-octafluorofluorenone (6.00 g, 17.84 mmol) was
added. The mixture was additionally stirred for 1 h and then
hydrolyzed with water. The resulting two phases were separated,
then the aqueous liquor was washed with diethyl ether
(2 ꢄ 50 mL). The ether solutions were unified and dried over
Na2SO4. The solvent was evaporated to dryness and the residue
was treated with cold petroleum ether. The solution obtained was
filtered and then dried in vacuo, so obtaining 2.55 g (56% yield) of 2
as colourless crystalline solid. Anal. Calcd. for C21H4F14O: C, 46.86,
4.3. Preparation of 1,2,3,4,5,6,7,8-octafluoro-9-arylfluorene
derivatives, 6–8
Only the preparation of 1,2,3,4,5,6,7,8-octafluoro-9-[2,4-bis(tri-
fluoromethyl)phenyl]fluorene, 6, is described in detail, those of
compounds 7–8 being performed in a similar way. A mixture of 2
(0.950 g, 1.85 mmol) and PBr3 (10.0 mL, 0.106 mol) was heated at
110–120 8C for 40 min (30 min in the case of 8). Hence, the reaction
mixture was hydrolysed on ice, and washed with diethylether
(3 ꢄ 40 mL). The combined ethereal extracts were washed with a
10% aqueous solution of NaHCO3, and then were dried over Na2SO4,
filtered and finally dried in vacuo. The residue so obtained was
dissolved in 20 mL of acetic acid, and treated with zinc (1.05 g,
16.1 mmol). The resulting mixture was stirred for 1 h at 25 8C,
hydrolyzed in water, and then washed with diethyl ether
(2 ꢄ 30 mL). The ethereal extracts were unified, and washed with
a 10% aqueous solution of NaHCO3. Afterwards, the ethereal solution
H, 0.75. Found C, 46.91, H, 0.71%. 1H NMR (CDCl3):
d 8.80 (d,
3JHH = 8.1 Hz, 2 H, H300); 8.00 (d, 3JHH = 8.1 Hz, 2 H, H200); 7.90 (s, 1 H,
H30); 3.00 (s, 1 H, OH) ppm. 19F NMR (CDCl3, see Scheme 1 for the
fluorine atoms numbering):
d
ꢀ63.2, ꢀ58.2 (br, 6 F, CF3), ꢀ133.3 (d,
3JFF = 19.5 Hz, 2 F, F1 + F8), ꢀ143.3 (d, JFF = 19 Hz, 2 F, F4 + F5),
ꢀ150.2 (m, 2 F, F2 + F7), ꢀ152.0 (m, 2 F, F3 + F6).
3

346
F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
was dried over Na2SO4, filtered and dried in vacuo. The raw material
was purified by chromatography on a silica gel column using
petroleum ether as eluent. Compound 6 was obtained as a colourless
crystalline material upon removal of the solvent (0.61 g, 72% yield).
Anal Calcd. for C21H4F14: C, 48.30, H, 0.77. Found C, 48.36, H, 0.80%.
The organic phase was isolated and dried over Na2SO4, hence the
solvent was removed in vacuo. The resulting residue was dissolved
in toluene at ca. 60 8C, then the solution was filtered through
Celite/activated carbon, and finally cooled to room temperature.
Well-shaped crystals formed, and these were isolated by filtration
and dried in vacuo. Yield: 1.93 g, 64%. Anal. Calcd. for C26H2F16: C,
1H NMR (CDCl3):
6.70 (d, 3JHH = 8.2 Hz, 2 H, H300); 5.86 (s-br, 1 H, CH) ppm. 19F NMR
(CDCl3, see Scheme 2 for the fluorine atoms numbering):
d
8.05 (s, 1 H, H30); 7.60 (d, 3JHH = 8.2 Hz, 1 H, H200);
50.51, H, 0.33. Found C, 50.41, H, 0.37%. 1H NMR (CDCl3):
d 5.40 (s, 2
d
ꢀ58.3,
H, CH) ppm. 19F NMR (CDCl3, see Scheme 3 for the fluorine atoms
ꢀ63.2 (s, 6 F, CF3); ꢀ133.9 (d, 3JFF = 20 Hz, 2 F, F1 + F8), ꢀ140.9 (d,
3JFF = 19.5 Hz, 2 F, F4 + F5), ꢀ152.3 (m, 4 F, F2 + F7 + F3 + F6) ppm.
1,2,3,4,5,6,7,8-Octafluoro-9-(3,5-trifluoromethylphenyl)fluorene,
7: Colourless microcrystalline solid, 77% yield from 3. Anal. Calcd.
for C21H4F14: C, 48.30, H, 0.77. Found C, 48.40, H, 0.81%. 1H NMR
numbering):
d
ꢀ133.2 (m, 4 F, F1 + F8 + F10 + F80); ꢀ138 to ꢀ142 (d,
3JFF = 19 Hz, F4 + F5 + F40 + F50); ꢀ151.6 (m, 4 F, F2 + F7 + F20 + F70);
ꢀ152.7 (m, 4 F, F3 + F6 + F30 + F60) ppm.
4.7. Crystal structure solution and refinement of compounds 1, 8,
and 11
(CDCl3): d
7.84 (s, 1 H, H40); 7.53 (s, 2 H, H20 + H200); 5.57 (s-br, 1 H,
CH) ppm. 19F NMR (CDCl3, see Scheme 2 for the fluorine atoms
3
numbering):
d
ꢀ63.0 (s, 6 F, CF3); ꢀ133.5 (d, JFF = 19 Hz, 2 F,
Data were collected at 293 K on a Bruker P4 diffractometer,
3
F1 + F8); ꢀ141.2 (d, JFF = 19.8 Hz, 2 F, F4 + F5); ꢀ151.9 (m, 2 F,
F2 + F7); ꢀ152.2 (m, 2 F, F3 + F6) ppm.
operating with a graphite-monochromated Mo-K radiation.
a
Colourless prisms of 1 or 11 or colourless platelets of 8 were
glued on the tip of a glass fiber for lattice parameters and intensity
data collection. The results are summarized in Table 4. The
1,2,3,4,5,6,7,8-Octafluoro-9-(pentafluorophenyl)fluorene, 8: Col-
ourless microcrystalline solid, 84% yield from 4, after chromato-
graphy on silica gel [eluent: petroleum ether/CH2Cl2 98/2 (
Anal. Calcd. for C19HF13: C, 47.92; H, 0.21. Found: C, 47.81; H, 0.19%.
1H NMR (CDCl3): 5.78 (s-br, 1 H, CH) ppm. 19F NMR: see Table 1
v
/
v
)].
intensity data collection was carried out with the v/2u scan mode;
three standard reflections being measured every 97 measurements
to check sample decay. The intensities were corrected for Lorentz
d
for the assignment of the fluorine resonances and Scheme 2 for the
fluorine atoms numbering.
and polarization effects. An absorption correction by the c-scan
method [25] was applied only to the intensities of compound 8.
The structure solutions was obtained by direct methods [26] and
refined with full-matrix least-squares on F2 [26]. Some other
utilities contained in the WINGX suite [27] were also used.
The structure solution was obtained in the centrosymmetric C2/
c space group for compounds 1 and 8 and in the P21/c space group
for compound 11. The asymmetric unit of 1 contains half molecule
riding a twofold axis. Either in 1 or in 8 or in 11 the hydrogen atoms
were localized in the difference Fourier map and refined without
constraints. The reliability factors resulting from the final
refinement cycle are listed in Table 4.
4.4. Preparation of 9-hydroxy-9H-octafluorofluorene, 9
A suspension of 1,2,3,4,5,6,7,8-octafluorofluorenone (2.03 g,
6.26 mmol), in acetic acid (20 mL), was treated with finely divided
zinc (0.998 g, 15.3 mmol). The mixture was stirred at room
temperature for 1 h, then a TLC analysis [eluent: petroleum ether/
acetone 8/2 (v/v)] revealed that complete consumption of starting
fluorenone had occurred. Subsequently, water (150 mL) was added
to the mixture, then the resulting mixture was treated with diethyl
ether (3 ꢄ 50 mL). The solvent was removed from the extracted
ethereal materials, thus colourless crystalline compound 9 (1.88 g,
92% yield) was obtained. Anal. Calcd. for C13H2F8O: C, 47.87, H, 0.62.
Supplementary material
FoundC, 47.73, H,0.63%. 1HNMR (CDCl3):
d6.16(s, 1H,CH), 2.62(s, 1
H, OH) ppm. 19F NMR (CDCl3, see Scheme 3 for the fluorine atoms
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre: CCDC
numbering):
d
ꢀ134.3 (m, 2 F, F1 + F8); ꢀ142.5 (d, 3JFF = 19.3 Hz, 2 F,
F4 + F5); ꢀ151.3 (m, 2 F, F2 + F7); ꢀ152.8 (m, 2 F, F3 + F6) ppm.
Table 4
Crystal data for compounds 1, 8 and 11.
4.5. Preparation of 9-Br-9H-octafluorofluorene, 10
Compound
1
C
8
11
Compound 9 (2.05 g, 6.29 mmol) and PBr3 (10 mL, 0.11 mol)
were mixed together and heated at 80 8C for 1 h. The reaction
mixture was hydrolysed on ice, and then washed with diethyl ether
(3 ꢄ 30 mL). The ethereal extracts were washed with water
(4 ꢄ 20 mL), until the water phase reached an almost neutral pH.
Hence, the ethereal solution was dried over Na2SO4, filtered and
finally dried in vacuo. Compound 10 (2.06 g, 81% yield) was obtained
as a microcrystalline colourless material. Anal. Calcd. for C13HBrF8:
Empirical formula
F W
19HF13
C13H2F8
310.15
C26H2F16
618.28
476.20
T/K
293(2)
293(2)
293(2)
˚
l
/A
0.71073
Monoclinic
C2/c (No. 15)
23.630(1)
9.950(1)
15.955(2)
117.86(1)
3316.5(6)
8
0.71073
Monoclinic
C2/c (No. 15)
16.703(3)
7.650(1)
8.864(1)
111.03(1)
1057.2(3)
4
0.71073
Monoclinic
P21/c (No. 14)
6.992(1)
15.802(1)
19.256(2)
98.48(1)
2104.3(4)
4
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
b
/8
C, 40.13, H, 0.26. Found C, 40.22, H, 0.21%. 1H NMR (CDCl3):
d 6.14 (s,
3
˚
U/A
1 H, CH) ppm. 19F NMR (CDCl3, see Scheme 3 for the fluorine atoms
Z
numbering):
d
ꢀ133.8 (m, 2 F, F1 + F8); ꢀ137.2 (d, 3JFF = 19 Hz, 2 F,
Dcalc/Mg mꢀ3
/mmꢀ1
1.907
1.949
1.952
m
0.214
0.213
0.214
F4 + F5); ꢀ150.5 (m, 2 F, F2 + F7); ꢀ152.5 (m, 2 F, F3 + F6) ppm.
No. collected
3549
1185
4080
No. unique [Rint
No. parameters
]
2920 [0.0212]
294
923 [0.0373]
101
2930 [0.0180]
387
4.6. Preparation of 1,10,2,20,3,30,4,40,5,50,6,60,7,70,8,80-hexadecafluoro-
9,90-bifluorenyl, 11
R1, wR2 [I > 2s(I)]
0.0407, 0.0820
0.0777, 0.0978
1.012
0.0346, 0.0875
0.0570, 0.0986
1.048
0.0346, 0.0760
0.0537, 0.0843
1.015
R1, wR2 [all data]
Goodness of fit on F2
A solution of 10 (1.98 g, 4.89 mmol), in diethylether (50 mL),
was treated at room temperature with a 1.0 M solution of sec-
butylmagnesium chloride in diethylether (9.80 mL, 9.80 mmol).
After stirring for 2 h at room temperature, the reaction mixture
was hydrolysed with ice and then treated with CH2Cl2 (ca. 500 mL).
1=2
2
2
R1
=
S
jjFoj ꢀ jFcjj/
S
jFoj; wR2 ¼ ½
S
½wðFo2 ꢀ Fc2Þ ꢅ=
S
½wðFo2Þ ꢅꢅ
;
w ¼ 1=½s2ðFo2Þ þ
2
2
ðAQÞ þ BQꢅ where Q ¼ ½MAXðFo2; 0Þ þ 2Fc2ꢅ=3; goodness-of-fit ¼ ½
S
½wðFo2 ꢀ Fc2Þ ꢅ=
1=2
ðN ꢀ PÞꢅ
, where N, P are the numbers of observations and parameters,
respectively.

F. Marchetti et al. / Journal of Fluorine Chemistry 130 (2009) 341–347
347
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Acknowledgments
The authors wish to thank the Ministero dell’Istruzione,
`
dell’Universita e della Ricerca (MIUR, Roma), Programma di
A. Sommazzi, F. Masi, G. Borsotti, A. Proto, R. Santi, European Patent No.
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Ricerca Scientifica di Notevole Interesse Nazionale 2004-5.
A. Sommazzi, G. Borsotti, F. Masi, R. Santi, V. Bricco, Int. Patent WO02/50087, June
27, 2002 (to Enichem SpA).;
Appendix A. Supplementary data
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