JOURNAL OF CHEMICAL RESEARCH 2015 401
Table 4 Reuse of the catalyst systema
4-Formylbiphenyl (3a): White solid; m.p. 57–58 oC (lit.24 58–60 oC).
1H NMR (400 MHz, CDCl3): δ 10.06 (s, 1H), 7.95 (d, J = 8.0 Hz, 2H),
7.75 (d, J = 8.4 Hz, 2H), 7.64 (d, J = 6.8 Hz, 2H), 7.50–7.42 (m, 3H);
13C NMR (100 MHz, CDCl3): δ 191.9, 147.2, 139.7, 135.2, 130.2, 129.0,
128.4, 127.7, 127.3.
Entry
Run No.
Fresh
Reuse 1
Reuse 2
Reuse 3
Time/min
Yield/%b
94
93
86
1
2
3
4
20
20
20
40
4-Acetylbiphenyl (3b): White solid; m.p. 122–123 oC (lit.23
81
o
1
122–123 C). H NMR (400 MHz, CDCl3): δ 8.04–8.02 (m, 2H),
7.70–7.67 (m, 2H), 7.64–7.62 (m, 2H), 7.49–7.45 (m, 2H), 7.42–7.38 (m,
1H), 2.64 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 197.8, 145.8, 139.9,
135.8, 128.9, 128.9, 128.2, 127.3, 127.2, 26.7.
a
Reaction conditions: 1-bromo-4-chlorobenzene (1.0 mmol), Ph4Sn (0.25 mmol), PdCl2
1.0 mol%, DMAP (3.5 mmol), PEG-400 (3mL), microwave irradiation (616 W).
b Isolated yield.
o
o
4-Chlorobiphenyl (3c): White solid; m.p. 72–74 C (lit.23 72–74 C).
1H NMR (400 MHz, CDCl3): δ 7.56–7.49 (m, 4H), 7.45–7.33 (m, 5H);
13C NMR (100 MHz, CDCl3): δ 140.0, 139.7, 133.4, 128.9, 128.4, 127.6,
127.0.
To check the reusability of the reaction medium as well as the
catalyst, the coupling of Ph4Sn with 1-bromo-4-chlorobenzene
in Table 2, entry 3 was chosen as a model reaction. After
extraction of organic material by diethyl ether and removal
of residual diethyl ether under reduced pressure, and reduced
evaporation, PEG400 and Pd nanoparticles were subjected to
the next run of the Stille reaction by charging with the same
substrates. The results for the reuse of this catalyst system are
summarised in Table 4. It is seen that the catalytic system can be
reused twice without significant deactivation (Table 4, entries
1–3). However, only 81% of yield was obtained in reuse 3 even
when the reaction time was prolonged to 40 min. The cause of
deactivation focused mainly on the aggregation of palladium
nanoparticles during the reuse of this catalytic system, which
was identical with results previous reported by our research
group.23,24
In conclusion, we have successfully developed an efficient
and ligand-free method for the Stille coupling of aryl bromides
and iodides with Ph4Sn and PhSnBu3 catalysed by in situ formed
palladium nanoparticles from PdCl2 and PEG-400 under
microwave irradiation. The reaction of tetraphenylstannane
shows high atom-efficiency as it can react with 4 equiv. of an
electrophilic coupling partner. The method exhibits wide scope
and good tolerance of substituents and may be used for scale-up
preparations and industrial applications.
3-Chlorobiphenyl (3d): Light yellow liquid.23 1H NMR (400 MHz,
CDCl3): δ 7.58–7.57 (m, 2H ), 7.56–7.55 (m, 1H), 7.48–7.43 (m, 3H),
7.39–7.32 (m, 3H); 13C NMR (100 MHz, CDCl3): δ 142.7, 134.3, 139.5,
129.7, 128.6, 127.5, 127.0, 126.9, 126.8, 125.0.
4-Cyanobiphenyl (3e): White solid; m.p. 85–86 oC (lit.23 85–86 oC).
1H NMR (400 MHz, CDCl3): δ 7.73–7.66 (m, 4H), 7.60–7.57 (m, 2H),
7.50–7.40 (m, 3H); 13C NMR (100 MHz, CDCl3): δ 145.6, 139.1, 132.5,
129.1, 128.6, 127.7, 127.2, 118.9, 110.8.
4-Phenylbenzoic acid (3f): White solid; m.p. 228–230 oC (lit.23
o
1
228–230 C). H NMR (400 MHz, DMSO–d6): δ 12.98 (s, 1H), 8.02
(d, J = 8.4 Hz, 2H), 7.79 (d, J = 8.0 Hz, 2H), 7.72 (d, J = 7.6 Hz, 2H),
7.50–7.46 (m, 2H), 7.42–7.38 (m, 1H); 13C NMR (100 MHz, DMSO-d6):
δ 167.2, 144.3, 139.0, 130.0, 129.6, 129.1, 128.3, 127.0, 126.8.
4-Methoxybiphenyl (3g): White solid; m.p. 88–89 oC (lit.23 88–89oC).
1H NMR (400 MHz, CDCl3): δ 7.56–7.51 (m, 4H), 7.43–7.39 (m, 2H),
7.32–7.28 (m, 1H), 6.99–6.96 (m, 2H), 3.85 (s, 3H); 13C NMR (100
MHz, CDCl3): δ 159.1, 140.8, 133.7, 128.7, 128.1, 126.7, 126.6, 114.2,
55.3.
23
4-Phenylphenol (3h): White solid; m.p. 169–170 oC (lit.
169–170 oC). 1H NMR (400 MHz, CDCl3): δ 7.55–7.52 (m, 2H),
7.49–7.46 (m, 2H), 7.43–7.39 (m, 2H), 7.32–7.28 (m, 1H), 6.92–6.88
(m, 2H), 4.85 (s, 1H); 13C NMR (100 MHz, CDCl3): δ 155.0, 140.7,
134.0, 128.7, 128.4, 126.7, 115.6.
2-Methoxylbiphenyl (3i): Colourless viscous liquid.23 1H NMR (400
MHz, CDCl3): δ 7.53–7.50 (m, 2H), 7.41–7.37 (m, 2H), 7.32–7.28 (m,
3H), 7.03–6.95 (m, 2H), 3.80 (s, 3H); 13C NMR (100 MHz, CDCl3): δ
156.4, 138.5, 130.8, 130.7, 129.5, 128.6, 127.9, 126.9, 120.8, 111.2, 55.5.
Experimental
All reagents were used as obtained from commercial sources without
further purification. The 1H and 13C NMR spectra were recorded on a
Bruker Mercury-Plus 400 MHz NMR spectrometer. Chemical shifts
were reported in parts per million (ppm, δ). Melting points were
determined on an XT-4 electrothermal micromelting-point apparatus.
Microwave irradiation was carried out with a Midea MM823ESJ-PA
domestic microwave oven modified by adding a refluxing condenser.
In order to avoid unreliable and unreproducible results by using this
microwave oven, all experiments were conducted at least twice under
parallel conditions to obtain coincident yields.
o
4-Aminobiphenyl (3j): Yellowish-brown solid; m.p. 52–54 C (lit.23
52–54 oC). 1H NMR (400 MHz, CDCl3): δ 7.54–7.52 (m, 2H), 7.41–7.36
(m, 4H), 7.28–7.21 (m, 1H), 6.74 (d, J = 8.4 Hz, 2H), 3.69 (s, 2H);
13C NMR (100 MHz, CDCl3): δ 145.8, 141.1, 131.5, 128.6, 127.9, 126.3,
126.2, 115.3.
4-Methylbiphenyl (3k): White solid; m.p. 43–44 oC (lit.2343–45 oC).
1H NMR (400 MHz, CDCl3): δ 7.58 (d, J = 8.0 Hz, 2H), 7.49 (d, J =
7.6 Hz, 2H), 7.43–7.39 (m, 2H), 7.32–7.28 (m, 1H), 7.24–7.20 (m, 2H),
2.38 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 141.1, 138.3, 137.0, 129.5,
128.7, 126.9, 21.1.
CAUTION: The use of a domestic microwave oven for chemical
purposes has been found to be potentially hazardous. The behaviour
of such an oven varies and reproducibility of results may be poor.
1,4-Diphenylbenzene (3l): White solid; m.p. 213–214 oC (lit.24
o
1
216–218 C). H NMR (400 MHz, CDCl3): δ 7.69–7.63 (m, 9H), 7.45
(t, J = 7.6 Hz, 4H), 7.38–7.34 (m, 2H); 13C NMR (100 MHz, CDCl3): δ
140.7, 140.1, 128.8, 127.5, 127.3, 127.0.
1-Phenylnaphthalene (3m): Oil.16 1H NMR (400 MHz, CDCl3): δ
7.90 (d, J = 8 Hz, 2H), 7.85 (d, J = 8.0 Hz, 1H), 7.54–7.40 (m, 9H);
13C NMR (100 MHz, CDCl3): δ 140.7, 140.2, 133.8, 131.6, 130.1, 128.4,
128.2, 127.6, 127.2, 126.9, 126.0, 125.7, 125.4.
Synthesis of biphenyls; general procedure
A 50 mL round-bottom flask was charged with aryl bromide,
tetraphenyltin, DMAP, PdCl2 and PEG-400 with the amount of
indicated in the above Tables. The mixture was irradiated by
microwaves at 616 W for 20 min. After cooling to room temperature,
the mixture was extracted with diethyl ether (4×5 mL). Then, the
upper layer was decanted, combined, and washed with water and brine.
The combined organic layers were dried over anhydrous MgSO4. The
solvent was removed under reduced pressure at room temperature
to afford the crude product, which was further purified by column
chromatography on silica gel (50 µm) using 60–80oC petroleum ether
and ethyl acetate(20:1, V:V) as eluents.
Biphenyl (3n): White solid; m.p. 70–71 oC (lit.23 70–71 oC). 1H NMR
(400 MHz, CDCl3): δ 7.60–7.57 (m, 4H), 7.45–7.41 (m, 4H), 7.36–7.31
(m, 2H);13C NMR (100 MHz, CDCl3): δ 141.2, 128.7, 127.2, 127.1.
Electronic Supplementary Information
1
Electron Supplementary Information including H NMR and
13C NMR spectra of all products and is available online via