180
M. Guo et al. / Journal of Fluorine Chemistry 127 (2006) 177–181
are indications of an effective catalytic system that has
commercial and industrial potential.
of water were added and extracted by 3 ꢂ 5 ml of ether. The
organic layers were combined, dried over MgSO4, filtered and
concentrated in vacuum. Purification of crude product by flash
chromatography on silica gel.
An advantage of this method is its simple experimental
procedure, the ease of product isolation and recycle of catalyst.
A dark red solution was always observed during the processes
of the reactions. Upon completion of the reactions, extraction
with Et2O drove the catalyst to partition predominately in the
aqueous phase of the reaction mixture. The organic product
could be conveniently isolation from Et2O. The aqueous phase
showed dark red. Therefore, it was possible to recycle the dark
red species. For example, the product resulting from the
coupling of 4-bromoacetophenone and 4-fluorophenylboronic
acid in the presence of 1.0 mol% catalyst was obtained in 99%
yield after 6 h in aqueous solvents at room temperature for the
first cycle, 93% yield after 4 h for the second cycle, and 90%
yield after 4 h for the third cycle. Soon afterwards, deposition of
palladium black was observed. This indicated that the dark red
species is likely active species here. This water-soluble active
species is likely formed based on the hemilabile behaviour of
P–O coordinated palladium complexes, the opening of Pd–O
bond may be initiated under catalytic conditions, thus
generating water-soluble active species and free coordination
sites using for catalysis [18]. Further investigations of the
mechanism of this catalyst are underway in our lab.
4.1.1. 4-Fluoro-40-(4-propyl-cyclohexyl)-bipheny
Anal. Found: C, 85.21; H, 7.49%; C21H23F Calcd.: C, 85.67;
1
H, 7.87%; H NMR (CDCI3): d 0.91(t, J = 7.2 Hz, 3H), 1.02–
1.11(m, 2 H), 1.20–1.39 (m, 5 H), 1.44–1.50 (m, 2 H), 1.90 (t,
J = 6.4, 4 H), 2.47–2.53 (m, 1 H), 7.07–7.12 (m, 2 H), 7.27 (d,
J = 8 Hz, 2 H), 7.46 (d, J = 8 Hz, 2 H), 7.50–7.54 (m, 2H). 13
C
NMR: d 14.61, 20.23, 33.77, 34.54, 37.23, 39.91, 44.47, 115.59,
115.80, 127.07, 127.49, 128.63, 137.47, 137.95, 147.26,
161.23, 163.68.
4.1.2. 3,4-Difluoro-40-(4-propyl-cyclohexyl)-biphenyl
Anal. Found: C, 80.35; H, 6.65%; C21H22F2 Calcd.: C,
80.74; H, 7.10%; 1H NMR (CDCI3): d 0.91(t, J = 7.2 Hz, 3 H),
1.05–1.11 (m, 2 H), 1.20–1.52 (m, 7 H), 1.89 (t, J = 12.4 Hz,
4 H), 2.43–2.47 (m, 1 H), 7.14–7.21 (m, 1 H), 7.26–7.28 (m,
3 H), 7.33 (m, 1 H), 7.43 (d, J = 7.6 Hz, 2 H).
4.1.3. 3,4,5-Trifluoro-40-(4-propyl-cyclohexyl)-biphenyl
Anal. Found: C, 76.04; H, 6.21%; C21H21F3 Calcd.: C,
1
76.34; H, 6.41%; H NMR (CDCI3): d 1.03–1.08 (m, 3 H),
3. Conclusions
1.14–1.23 (m, 2 H), 1.36–1.63 (m, 7 H), 1.96–2.02 (m, 4 H),
2.48–2.64 (m, 1 H), 7.11–7.16 (m, 1 H), 7.21–7.24 (m, 1 H),
7.36 (d, J = 8 Hz, 2 H), 7.48 (d, J = 8 Hz, 2 H).
The synthesis of various fluorinated biphenyl derivatives
was readily achieved via well-defined hemilabile P–O
coordinated palladium complexes-catalyzed Suzuki coupling
of aryl bromides and fluorinated phenylboronic acids in
aqueous-phase at room temperature. This approach with high
activity, good selectivity, mild reaction condition and aqueous-
phase reaction, as well as potential recycling of the catalytic
species develops environmentally sustainable chemical pro-
cesses and provides a practical procedure for the synthesis of
fluorinated liquid crystals in industry applications.
4.1.4. 4-Fluoro-400-(40-pentyl-bicyclohexyl-4-yl)-biphenyl
Anal. Found: C, 86.41; H, 8.53%; C29H35F Calcd.: C, 86.52;
H, 8.76%; 1H NMR (CDCI3): d 0.89 (t, J = 6.4 Hz, 3 H), 0.97–
1.33 (m, 18 H), 1.73–1.96 (m, 9 H), 2.49 (m, 1 H), 7.08–7.12
(m, 2 H), 7.27 (d, J = 8 Hz, 2 H), 7.46 (d, J = 8 Hz, 2 H), 7.50–
7.54 (m, 2 H). 13C NMR: 14.33, 22.93, 26.88, 30.30, 30.54,
32.45, 33.84, 34.80, 37.68, 38.12, 43.11, 43.62, 44.50, 115.59,
115.81, 127.06, 127.48, 128.63, 137.48, 137.93, 147.28,
161.23, 163.68.
4. Experiment
4.1.5. 3,4-Difluoro-40-(40-pentyl-bicyclohexyl-4-yl)-
biphenyl
All reactions were carried out using the Schlenk techniques.
Elemental analyses were measured with a Perkin-Elmer 1400C
analyzer. NMR spectra were recorded on Varian INO-
VADLG400 (1H, 13C) NMR spectrometers. In all case CDCI3
was used as solvent. The 1H and 13C chemical shifts are
expressed as d-values relative to TMS. Silica gel 60 GF254 was
used for analytical TLC.
Anal. Found: C, 82.64; H, 8.09%; C29H34F2 Calcd.: C,
82.82; H, 8.15%; 1H NMR (CDCI3): d 0.89 (t, J = 6.4 Hz, 3 H),
0.97–1.33 (m, 18 H), 1.73–1.96 (m, 9 H), 2.49 (m, 1 H), 7.17–
7.22 (m, 1 H), 7.25–7.28 (m, 3 H), 7.33–7.39 (m, 1 H), 7.43 (d,
J = 6.4 Hz, 2 H).
4.1.6. 4-Acetyl-40-fluorobiphenyl
Anal. Found: C, 78.28; H, 5.17%; C14H11OF Calcd.: C,
1
78.46; H, 5.21%; H NMR (CDCI3): d 7.14–7.18 (m, 2 H),
7.58–7.65 (m, 4 H), 8.02 (d, J = 8.0 Hz, 2 H), 2.64 (s, 3 H).
4.1. General procedure for the synthesis of fluorinated
biphenyl derivatives
In a 25.0 ml two-neck flask were placed 1.0 mmol of 4-
bromoacetophenone, 1.5 mmol of fluorinated phenylboronic
acid, 3.0 mmol of K3PO4ꢀ3H2O, 0.001 mmol of 1 and 4 ml of
THF + H2O (1:1). The mixture in flask was allowed to stir at
room temperature (25–27 8C) for 6 h. Reaction progress was
monitored by TLC and when the reaction was completed, 5 ml
4.1.7. 4-Fluoro-40-methyl-biphenyl
Anal. Found: C, 83.65; H, 5.76%; C13H11F Calcd.: C, 83.81;
l
H, 5.99%; H NMR (CDCI3): d 7.54–7.50 (m, 2 H), 7.43 (d,
J = 8.0 Hz, 2 H),7.24 (d, J = 8.0 Hz, 2 H), 7.14–7.08 (m, 2 H),
2.39 (s, 3 H).