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ic acid (6.12 g, 34.0 mmol), K2CO3 (5.63 g, 40.8 mmol), 200 mL 1,4-
dioxane, and 20 mL H2O were added in a pressure vessel equipped
with a magnetic stir bar. The resulting mixture was sparged for 1 h
with N2 gas. Pd(PPh3)4 (2.01 g, 3.41 mmol) was added into the
sparged mixture, vessel was sealed, and the mixture was heated to
reflux for 48 h. After cooling the reaction mixture to room temper-
ature the solvent was removed under reduced pressure. The resi-
due was dissolved in CH2Cl2 (200 mL) and washed with H2O (3
200 mL) followed by brine (300 mL). The organic layer was dried
over anhydrous MgSO4, filtered, and the solvent was removed
under reduced pressure. The crude product was subjected to gra-
dient column chromatography (hexanes/ethyl acetate) to yield
pure white solid (6.51 g, yield 54.8%). 1H NMR (500 MHz, CDCl3):
d=8.22 (t, 1H, J=1.6 Hz), 8.19 (t, 1H, J=1.7 Hz), 8.16–8.11 (m, 2H),
7.94 (t, 1H, J=1.84 Hz), 7.69–7.64 (m, 2H), 3.96 (s, 3H), 3.95 (s, 3H);
13C NMR (125 MHz, CDCl3): d=166.83, 165.70, 143.13, 142.38,
134.57, 134.68, 132.09, 130.47, 130.11, 127.28, 127.22, 123.20, 52.75,
52.42.
Experimental Section
Materials: Compounds 1,[15] 3,[8] and 4[11] were synthesized accord-
ing to literature methods. Heptanoic acid (98%) was purchased
from Acros Organics. The syntheses for 2 and 5 are described
below.
3,4’’,5-Trimethyl-para-terphenyl:
4-Bromo-4’-methylbiphenyl
(1.56 g, 10.4 mmol), 3,5-dimethylphenylboronic acid (2.00 g,
9.43 mmol), toluene (40 mL), EtOH (30 mL), and 2m aqueous
Na2CO3 (30 mL) were added into a pressure vessel equipped with
a magnetic stir bar. The resulting mixture was sparged with N2 gas
for 15 min. Pd(PPh3)4 was added into the mixture, vessel was
sealed, and the mixture was heated at 858C for 18 h. After cooling
the reaction mixture to room temperature diethyl ether (200 mL)
was added to the mixture. The organic and aqueous layers were
separated, and the aqueous layer was extracted with diethyl ether
(3100 mL). The organic layers were combined and dried over an-
hydrous Na2SO4. The organic layer was filtered and the solvent was
removed under reduced pressure. The residue was recrystallized
from a mixture of CH2Cl2/hexane at 08C to produce a white solid
(1.73 g, yield 67.4%). 1H NMR (500 MHz, CDCl3): d=7.64 (s, 4H),
7.56 (d, 2H, J=7.9 Hz), 7.28–7.26 (m, 4H), 7.01 (s, 1H), 2.41 (s, 3H),
2.39 (s, 6H); 13C NMR (125 MHz, CDCl3): d=140.93, 140.22, 140.00,
138.44, 138.04, 137.21, 129.67, 129.07, 127.63, 127.32, 127.02,
125.12, 21.58, 21.28.
[1,1’:3’,1’’:4’’,1’’’-Quaterphenyl]-4,4’’’,5’-tricarboxylic
Methyl 4’-pinacolatoboronbiphenyl-4-carboxylate
acid
(5):
(1.50 g,
4.44 mmol), dimethyl 5-bromo-biphenyl-3,4’-dicarboxylate (1.40 g,
4.04 mmol), K2CO3 (1.95 g, 14.1 mmol), THF (70 mL), and H2O
(10 mL) were added in a pressure vessel equipped with a magnetic
stir bar. The resulting mixture was sparged for 1 h with N2 gas.
Pd(PPh3)4 (0.465 g, 0.403 mmol) was added to the mixture, vessel
was sealed, and the mixture was heated to reflux for 48 h. After
cooling the reaction mixture to room temperature the solvent was
removed under reduced pressure. The residue was dissolved in
CH2Cl2 (150 mL) and washed with H2O (3100 mL) followed by
brine (200 mL). The organic layer was dried over anhydrous MgSO4,
filtered, and the solvent was removed under reduced pressure. The
crude product was subjected to gradient column chromatography
(hexanes/ethyl acetate) to yield pure white solid. This white solid
(1.31 g, 2.73 mmol), 1,4-dioxane (40 mL), H2O (40 mL), and KOH
(1.53 g, 27.3 mmol) were added into a pressure vessel equipped
with a magnetic stir bar. The resultant suspension was heated to
reflux for 12 h. After cooling to room temperature the reaction
mixture was filtered and the solvent was removed under reduced
pressure. The residue was dissolved in H2O (200 mL) and the solu-
tion was acidified with concentrated HCl until the pH of the solu-
tion was 2. The target compound was collected by filtration,
washed thoroughly with H2O, and dried under vacuum to afford 5
para-Terphenyl-3,4’’,5-tricarboxylic acid (2): 3,4’’,5-Trimethyl-para-
terphenyl (0.5 g, 1.8 mmol), KMnO4 (0.87 g, 5.5 mmol), H2O (20 mL),
and pyridine (20 mL) were added in
a round bottom flask
equipped with a magnetic stir bar and the mixture was heated to
reflux for 3 d. Additional aliquots of KMnO4 (80.87 g, 5.5 mmol)
were added during this period. After cooling the reaction mixture
to room temperature the mixture was filtered over a plug of celite.
The filtrate was evaporated and the residue was dissolved in water
(100 mL). Insoluble solid was filtered off and the filtrate was acidi-
fied with concentrated HCl. The white precipitate was collected by
filtration, washed thoroughly with H2O, and dried under vacuum to
afford 2 (0.75 g, yield 64.6%). 1H NMR (500 MHz, [D6]DMSO): d=
13.39 (brs, 3H), 8.49 (s, 1H), 8.42 (s, 2H), 8.05 (d, 2H, J=8.3 Hz),
7.92–7.85 (m, 6H); 13C NMR (125 MHz, [D6]DMSO): d=167.18,
166.78, 143.39, 139.97, 138.67, 138.46, 130.75, 130.10, 130.03,
129.08, 127.75, 127.55, 127.41, 126.74; HRMS (EI): m/z: calcd for
C21H14O6: 362.0790; found: 362.0791.
1
Methyl 4’-pinacolatoboronbiphenyl-4-carboxylate: Methyl 4’-bro-
mobiphenyl-4-carboxylate (2.50 g, 8.61 mmol), [bis-pinacolato]di-
boron (2.62 g, 10.32 mmol), KOAc (2.50 g, 25.8 mmol), and 1,4-diox-
ane (150 mL) were added to a pressure vessel equipped with
a magnetic stir bar. The resulting mixture was sparged for 1 h with
N2 gas. Pd(dppf)Cl2 (0.21 g, 0.43 mmol) was added into the mixture,
vessel was sealed, and the mixture was heated to reflux for 48 h.
After cooling the reaction mixture to room temperature the sol-
vent was removed under reduced pressure. The residue was dis-
solved in CH2Cl2 (150 mL) and washed with H2O (3100 mL) fol-
lowed by brine (200 mL). The organic layer was dried over anhy-
drous MgSO4, filtered, and the solvent was removed under reduced
pressure. The crude product was subjected to gradient column
chromatography (hexanes/ethyl acetate) to yield pure white solid
(1.01 g, yield 90.9%). H NMR (700 MHz, [D6]DMSO): d=13.10 (brs,
3H), 8.26–8.20 (m, 2H), 8.10–8.04 (m, 4H), 7.96–7.88 (m, 4H), 7.86–
7.80 (m, 4H); 13C NMR (175 MHz, [D6]DMSO): d=167.20, 167.17,
167.07, 143.63, 143.32, 140.78, 140.34, 138.85, 138.64, 132.52,
130.25, 130.12, 130.08, 129.84, 129.52, 127.77, 127.64, 127.41,
127.30, 127.05, 126.86, 126.79; HRMS (EI): m/z: calcd for C27H18O6:
438.1103; found: 438.1099.
Scanning tunneling microscopy: A Nanoscope E STM (Digital In-
struments) was used for all imaging. Highly oriented pyrolytic
graphite (HOPG) (SPI-1 grade, Structure Probe Inc.) was used as
a substrate for monolayer formation. A heptanoic acid solution of
the desired molecule was made, of which 2 mL was placed on
freshly cleaved HOPG to obtain a self-assembled monolayer. Each
solution was at or near saturation in heptanoic acid. STM tips were
made from Pt/Ir (20% Ir, 0.010 inch diameter, California Fine Wire)
by mechanical cutting. Imaging was performed under ambient
conditions and typical STM settings consist of 300 pA current and
700–900 mV bias voltage (sample positive). All images are unfil-
tered. For a specific image, the cell constants may vary from the
average due to the drift of the STM tip. Cell constants and symme-
1
(2.18 g, yield 73.1%). H NMR (500 MHz, CDCl3): d=8.12 (d, 2H, J=
8.3 Hz), 7.90 (d, 2H, J=8.2 Hz), 7.68 (d, 2H, J=8.3 Hz), 7.64 (d, 2H,
J=8.2 Hz), 3.94 (s, 3H), 1.37 (s, 12H); 13C NMR (125 MHz, CDCl3):
d=167.12, 145.58, 142.73, 135.51, 130.23, 129.28, 127.30, 126.71,
84.08, 52.30, 25.03.
Dimethyl 5-bromobiphenyl-3,4’-dicarboxylate: Methyl 3,5-dibro-
mobenzoate (15.0 g, 51.0 mmol), 4-(methoxycarbonyl)phenylboron-
Chem. Eur. J. 2015, 21, 5954 – 5961
5960
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