One-step synthesis of biaryls under mild conditions

Article abstract of DOI:10.1002/ejoc.201300967

A one-step synthesis of symmetrical biaryls was developed and uses a nickel(III) complex containing a Schiff base and dithiolate ligands as a catalyst for the homocoupling of in situ generated Grignard reagents. The coupling reaction was performed at room temperature with molecular oxygen as the oxidant, which renders the reaction energy-efficient and environmentally friendly. The catalytic methodology is compatible with diverse functionalities, including chlorido, nitro, nitrile, and heteroatoms, and provides biaryls in appreciable yields. A practical, room-temperature nickel(III) catalytic system has been developed for the synthesis of biaryls in one step from the homocoupling of in situ generated Grignard reagents. The use of molecular oxygen as the oxidant makes the system environmentally friendly. The reaction system is compatible with diverse functionalities and affords biaryls in appreciable yields. Copyright

Full text of DOI:10.1002/ejoc.201300967

Job/Unit: O30967
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Date: 12-09-13 17:16:44
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FULL PAPER
DOI: 10.1002/ejoc.201300967
One-Step Synthesis of Biaryls under Mild Conditions
Aparna P. I. Bhat,[a] Fawad Inam,[b] and Badekai Ramachandra Bhat*[a]
Keywords: Biaryls / C–C coupling / Grignard reagents / Oxygen / Nickel
A one-step synthesis of symmetrical biaryls was developed
and uses a nickel(III) complex containing a Schiff base and
dithiolate ligands as a catalyst for the homocoupling of in
situ generated Grignard reagents. The coupling reaction was
performed at room temperature with molecular oxygen as
the oxidant, which renders the reaction energy-efficient and
environmentally friendly. The catalytic methodology is com-
patible with diverse functionalities, including chlorido, nitro,
nitrile, and heteroatoms, and provides biaryls in appreciable
yields.
salt and bipyridine in the presence of O2.[23] However, in
these methods, the Grignard reagents were prepared first
and then converted into their coupling products in a sepa-
rate reaction. This makes the process difficult to handle ow-
ing to the moisture sensitivity of Grignard reagents.
Recently, Xu et al. and Yuan et al. reported the one-step,
iron- and manganese-catalyzed direct oxidative homocou-
plings of Grignard reagents under an inert gas.[24,25] Chen
et al. developed cobalt-catalyzed homocoupling of aryl hal-
ides from metallic magnesium in air, but did not propose
a catalytic mechanism.[26] The synthesis of functionalized
biaryls was not discussed for the above-mentioned catalytic
systems. Indeed, these catalytic systems demand 2–10 mol-
% of catalyst, which is quite high in comparison with the
proposed reaction system.
Introduction
The importance of biaryls is easily shown by their broad
applications in multidisciplinary fields.[1–4] The transition-
metal-catalyzed homocoupling of aryl Grignard reagents
represents the most straightforward route to symmetrical
biaryl compounds.[5,6] There have been many reports of
coupling reactions that use a variety of metal reagents such
as NiCl2, CuCl2, TiCl4, Ce(OTf)4, FeCl3, MnCl2, and
Pd(OAc)2 in stoichiometric or catalytic amounts in the
presence of a reoxidant.[7–13] However, the field is largely
dominated by the use of palladium and nickel catalysts,
mainly because of their wide applicability and excellent
compatibility with many functional groups. Although sev-
eral methods have already been reported for nickel-cata-
lyzed coupling reactions,[14–18] the need for stoichiometric
amounts of an organic oxidant or extra ligand limits their
use in large-scale applications. In the search for alternative
protocols, environmentally benign molecular oxygen is a
more attractive oxidant for homocoupling reactions.[19] The
development of nickel complexes for C–C bond-forming re-
actions is an attractive area of endeavor, in part owing to
the utility of its heavy metal congener palladium in cou-
pling catalysis. Significantly, the lower cost and excellent
redox properties of nickel make this objective economically
as well as synthetically alluring.[20,21]
In connection with our previous work,[27] we continued
our effort to afford symmetrical biaryls by varying the li-
gands from triphenylphosphane to a Schiff base, and their
influence on the homocoupling reactions was studied.
Herein, we report the synthesis of biaryls in one step with
the nickel(III) complex NiL (Figure 1) as the catalyst. The
tetrahedral NiL was synthesized from the Schiff base 4-
{[(E)-(2,4-dihydroxyphenyl)methylidene]amino}-1,5-di-
methyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (L1) and 2-
thioxo-1,3-dithiole-4,5-dithiolate (dmit) ligands. These are
well characterized by various techniques.
Cahiez et al. successfully developed the iron- and manga-
nese-catalyzed oxidative homocoupling of Grignard rea-
gents with molecular oxygen as the oxidant.[22] Liu and Lei
also performed similar reactions with a combination of iron
[a] Catalysis and Materials Laboratory, Department of Chemistry,
National Institute of Technology Karnataka,
Surathkal, Srinivasanagar 575025, India
E-mail: chandpoorna@yahoo.com
www.nitk.ac.in
[b] Faculty of Engineering and Environment, Northumbria
University,
Newcastle upon Tyne, NE1 8ST, United Kingdom
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300967.
Figure 1. Structure of NiL.
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A. P. I. Bhat, F. Inam, B. R. Bhat
FULL PAPER
The reaction conditions were optimized for the coupling
of phenylmagnesium bromide (1e) with respect to solvent,
Results and Discussion
In the present catalytic methodology, Grignard reagents catalyst loading, and reaction time. Among tetrahydrofuran
were synthesized in situ from metallic magnesium, which is (THF), diethyl ether, and benzene, the best coupling yield
inexpensive, readily available, and environmentally friendly. was obtained in diethyl ether; this can be attributed to the
The synthesized Grignard reagents undergo homocoupling ability of diethyl ether to coordinate with the Grignard rea-
with the aid of a metal catalyst to afford biaryl compounds gent and, thus, stabilize the intermediate complex.[30,31] Ini-
in a single step. The handling of commercially available tially, for comparison, we carried out coupling reactions
Grignard reagents is very difficult owing to their highly ba- with nickel acetate as the catalyst without the addition of
sic and hygroscopic nature, which usually needs special at- ligands. The results in Table 1 indicate that better yields
tention during the experiments. As in situ preparations could be achieved by increasing the amount of nickel acet-
avoid the workup procedures for the isolation of Grignard ate (Table 1, Entries 2–8). Next, we turned our attention to
reagents, the present method is very simple and economical. NiL. To our delight, the coupling of phenylmagnesium
The important surface activation of magnesium turnings bromide at room temperature with 0.1 mol-% of catalyst
was achieved with iodine crystals.[28] The initial addition of was completed in 5 h to afford biphenyl (2e) in 89% yield
aryl halide during the preparation of the Grignard reagent (Table 1, Entry 12). The influence of air is the key factor in
is very important. Various side products were observed the present catalytic system. A good yield was observed in
when the aryl halides were added quickly, mainly ROH (R the presence of atmospheric molecular oxygen. When the
is “aryl”). When bromobenzene was used as the aryl halide, reaction was performed under an inert gas (argon), only a
we obtained phenol as the main side product.[29] With con- 7% yield of biphenyl was obtained, and this can be attrib-
trolled addition of the aryl halides, the respective Grignard uted to the lack of formation of the peroxido–nickel(III)
reagents were yielded. The thus-formed Grignard reagent active species (Table 1, Entry 16). In the absence of catalyst,
afforded biaryls in good to high yields when treated with a only traces of coupling products were obtained, which
catalytic amount of NiL. In our study, molecular oxygen shows the effective catalytic role of NiL. The complex is so
was employed as the oxidant. No extra ligand, additives, or efficient that the present homocoupling can be readily
oxidants were needed, and this renders the current reaction scaled up to the reaction of 50.0 mmol of the aryl halide
environmentally friendly and cost-effective. Notably, the with 0.5 mol-% of the catalyst, which yields 83% of bi-
coupling reaction proceeded smoothly even at room tem- phenyl with a negligible amount of byproducts (Table 1,
perature and, therefore, the catalytic system is energy-ef- Entry 17).
ficient. To the best of our knowledge, this is the first report
After optimization of the conditions, we next investigated
of a one-step synthesis of symmetrical biaryls by homocou- the scope of the reaction to various aryl Grignard reagents
pling of an in situ prepared aryl Grignard reagents with an to synthesize simple and functionalized biaryl compounds
NiIII catalyst under air at room temperature.
in good yields (Table 2). Notably, high yields of 4,4Ј-di-
Table 1. Dependence of biphenyl yield on catalyst concentration and air.[a]
Entry
Catalyst [mol-%]
Time [h]
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16[c]
17[d]
no catalyst
Ni(OAc)2 (0.04)
Ni(OAc)2 (0.06)
Ni(OAc)2 (0.08)
Ni(OAc)2 (0.1)
Ni(OAc)2 (0.13)
Ni(OAc)2 (0.17)
Ni(OAc)2 (0.21)
NiL (0.04)
NiL (0.06)
NiL (0.08)
NiL (0.1)
NiL (0.13)
10
6
6
6
6
6
6
6
5
5
5
5
5
5
5
5
8
1
10
17
22
26
29
32
37
31
42
67
89
88
88
87
7
NiL (0.17)
NiL (0.21)
NiL (0.1)
NiL (0.5)
83
[a] Reactions were performed with 10 mmol of bromobenzene in the presence of atmospheric molecular oxygen at room temperature. [b]
Isolated yield. [c] Inert gas (argon). [d] With 50.0 mmol of bromobenzene in the presence of 0.5 mol-% of catalyst for 8 h.
2
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One-Step Synthesis of Biaryls under Mild ConditionsOne-Step Synthesis of Biaryls under Mild Conditions
methoxybiphenyl (2a) and 4,4Ј-dimethylbiphenyl (2c) were a longer reaction time of 11 h, it gave the binaphthyl (2h)
obtained upon the efficient coupling of 4-methoxy- and 4- in good yield (75%; Table 2, Entry 8).
methylphenylmagnesium bromide, respectively (Table 2, En-
Then, we tried to synthesize functionalized biaryls
tries 1 and 3). The introduction of the methoxy and methyl (Table 2, Entries 9 and 10). The homocoupling of 2-
groups at the ortho position of the aryl Grignard reagent nitrophenylmagnesium bromide (1i) yielded 71% of product
resulted in comparatively lower yields (Table 2, Entries 2 (2i), and the coupling of 2-cyanophenylmagnesium bromide
and 4).
(1j) afforded 4,4Ј-dicyanobiphenyl (2j) in 69% yield. The
reactions were performed at –5 °C to room temperature
Table 2. Nickel-catalyzed homocoupling of in situ generated aryl with constant stirring to afford the products in satisfactory
Grignard reagents.[a]
yields. Nitro and nitrile groups were well tolerated and,
hence, the reaction is chemoselective. Negligible amounts of
side products were observed in the above experiments.
Enhanced yields of coupling products were obtained
with the Grignard reagents containing electron-donating
groups (1a, 1b, 1c, and 1d) compared to the yields of those
with electron-withdrawing group (1f, 1i, and 1j). This can
be attributed to two factors: the yield of Grignard reagent
and the reductive elimination step. The yield of Grignard
reagent increases with the aryl halide attached to an elec-
tron-donating group compared to that with the aryl halide
attached to an electron-withdrawing group. A higher yield
of Grignard reagent results in a higher yield of coupling
product.[32] Another factor can be attributed to the faster
reductive elimination from the complex with the aryl halide
attached to an electron-donating group than from the com-
plex with the aryl halide attached to an electron-with-
drawing group. The electron-withdrawing group on the aryl
halide increases the strength of the M–C bond and makes
it more ionic; the increase in ionic character increases the
thermodynamic bond strength.[33] Thus, aryl halides with
electronic properties that increase the strength of the M–C
bond tend to decrease the thermodynamic driving force for
the reductive elimination.
A proposed mechanism is depicted in Figure 2 for the
NiL-catalyzed reaction. The reaction system involves an
NiI–NiIII catalytic cycle.[34] A low-valent nickel species is
generated by the Grignard reagent, which is a strong reduc-
ing agent, and is involved in the catalytic cycle.[24,35] The
oxidative addition of molecular oxygen to a low-valent
nickel complex (Figure 2a) forms a peroxido–nickel(III) in-
termediate (Figure 2b), which is the key step of the catalytic
cycle.[36] Although the NiI-catalyzed coupling reactions of
aryl halides with Grignard reagents have been reported, the
intermediate then reacts with 2 equiv. of RMgX to give
a
biarylnickel(III)
intermediate
(Figure 2c)
and
XMgOOMgX.[37,22] The thus-formed biarylnickel(III) in-
termediate undergoes rapid reductive elimination, which
eventually yields the Ar–Ar coupling product, and a
nickel(I) species is regenerated. It is very reasonable to as-
sume that the formation of the unstable nickel(III) species
(Figure 2c) is required to achieve a very quick reductive eli-
[a] Reaction conditions: Mg turnings (13 mmol), aryl halide
(10 mmol), catalyst (0.1 mol-%), Et2O (10 mL). [b] Isolated yield.
[c] In THF, 60 °C, 11 h. [d] Reactions at –5 °C to room temp.
Notably, in the present reaction system, 4-chlorophen- mination that gives the Ar–Ar coupling product, as the best
ylmagnesium bromide (1f) coupled successfully to yield way to favor the reductive elimination is to increase the oxi-
4,4Ј-dichlorobiphenyl (2f, 83%; Table 2, Entry 6). Also, the dation state of the metal atom.[22] The formation of the per-
system allows the efficient coupling of 4-pyridylmagnesium oxido–nickel(III) intermediate was confirmed by UV/Vis
bromide (1g; Table 2, Entry 7). Although the sterically de- spectral analysis (Figure 2). The absorption peak of the
manding substrate 1-naphthylmagnesium bromide (1h) re- catalytic reaction mixture at 419 nm can be attributed to
quired a higher reaction temperature of 60 °C in THF and the peroxido–nickel(III) intermediate,[36] and its absence in
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FULL PAPER
the reaction mixture under inert conditions (λmax = 411 nm) is performed at room temperature in the presence of molec-
further confirms the necessity of molecular oxygen for the ular oxygen. The in situ generation of the aryl Grignard
present catalytic system. Various copper-,[38] iron-,[39] and reagents renders the reaction very simple and economical.
palladium-catalyzed[40] reactions are well reported with The oxidant, molecular oxygen, makes the system environ-
such peroxido complexes as catalytic intermediates.
mentally friendly without the need for any external ligand
or an oxidant. The peroxido–nickel(III) active species is re-
sponsible for the efficiency of the present catalytic system.
A small amount of catalyst, milder reaction conditions,
higher yields, expanded scope, diverse functional-group tol-
erance, chemoselectivity, and an eco-friendly procedure
constitute an interesting contribution to the industrial-scale
synthesis of symmetrical biaryls.
Experimental Section
General: All chemicals used were of analytical grade. The C, H, N
and S contents of the compounds were determined with a Thermo-
flash EA1112 series elemental analyzer. The magnetic susceptibility
measurements were conducted with a Sherwood Scientific magnetic
susceptibility balance (UK). Thermal analysis was carried out (EX-
STAR-6000) from room temperature to 700 °C at a heating rate of
10 °C/min. The electronic spectrum of the complex was measured
with a GBC Cintra 101 UV/Vis double-beam spectrophotometer
by using DMF in the 200–800 nm range. The FT-IR spectra werwe
recorded with a Thermo Nicolet Avatar FT-IR spectrometer in the
frequency range 400–4000 cm–1. 1H (500 MHz) and 13C (125 MHz)
NMR spectra were recorded with a Bruker AV 400 instrument by
using TMS as internal standard. Coupling reactions were moni-
tored by gas chromatography with a Shimadzu 2014 instrument.
4-{[(E)-(2,4-Dihydroxyphenyl)methylidene]amino}-1,5-dimethyl-2-
phenyl-1,2-dihydro-3H-pyrazol-3-one (L1): The Schiff base L1 was
synthesized according to the reported procedure.[43] A solution of
4-aminoantipyrine (2.03 g, 10 mmol) in ethanol was added drop-
wise to a solution of 2,4-dihdroxybenzaldehyde (2,4-DHB, 1.38 g,
10 mmol) in ethanol. The mixture was stirred at room temperature
for 15 min and then heated to reflux for 2 h. The solid yellow prod-
uct was collected by filtration, washed, recrystallized with ethanol,
and dried in vacuo.
NiIII Complex (NiL): NiL was prepared under strictly anhydrous
conditions. To a methanol (20 mL) solution containing CS2
(0.2 mL, 3 mmol) and sodium metal were added L1 (323.34 mg,
1 mmol) and nickel acetate (249 mg, 1 mmol) with constant stir-
ring. The mixture was heated to reflux for 4 h. The dark green solid
product obtained was collected by filtration, washed with methanol
and petroleum ether (60–80 °C), and dried in vacuo. The complex
is soluble in dimethyl sulfoxide (DMSO) and N,N-dimethylform-
amide (DMF).
Figure 2. Proposed mechanism and UV/Vis spectra for the con-
firmation of peroxido–nickel(III) intermediate.
The catalytic system reported herein shows appreciable
improvement in the yields of biaryls compared to those
with our previously reported ruthenium(III) catalytic sys-
tem. This can be attributed to the efficiency of NiL, which
facilitates a faster oxidative addition reaction in the cata-
lytic cycle. Hypothetically, this may be attributed to the
sterically hindered triphenylphosphane-free, electron-rich
NiI metal center[41,42] (Figure 2a) compared to that of the
low-valent ruthenium(II) center.[27]
Characterization of L1 and NiL: The ligand and complex were char-
acterized by different analytical and spectral studies. The FTIR,[44]
UV/Vis, and 1H NMR spectroscopy,[45] mass spectrometry, and ele-
mental analysis results confirm the tetrahedral geometry of the syn-
thesized complex. Magnetic susceptibility measurements further
confirmed its geometry.[46,47] From the thermogravimetric (TG)
analysis, the weight-loss steps were observed in the approximate
temperature ranges 324–395 and 431–462 °C and correspond to
33.82% (calcd. 32.7%) mass loss for the C3S5 moiety and 56.5%
(calcd. 57.7%) mass loss for one ligand molecule, respectively; these
results further support the assumed structure.
Conclusions
A nickel(III) catalyst was developed successfully for the
homocoupling of aryl Grignard reagents to synthesize sym-
Homocoupling of Aryl Grignard Reagents 1a–1h: Magnesium turn-
metrical biaryls. This is a one-step catalytic reaction, which ings (0.320 g, 13 mmol) were placed in a two-necked round-bot-
4
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One-Step Synthesis of Biaryls under Mild ConditionsOne-Step Synthesis of Biaryls under Mild Conditions
tomed flask with a calcium chloride guard tube. A crystal of iodine
was added. Aryl halide (2 mmol of total 10 mmol) in anhydrous
diethyl ether (5 mL) was added with stirring at room temperature.
Initially, an increase in the temperature of the reaction mixture was
observed, and the appearance of turbidity after a few minutes indi-
cated the initiation of the reaction. The remaining aryl halide
(8 mmol) in diethyl ether (5 mL) was added dropwise, and the reac-
tion mixture was stirred for 40 min. To the reaction mixture,
nickel(III) catalyst (0.1 mol-%) was added. The reaction mixture
darkened immediately upon addition of the catalyst, and the stir-
ring was continued. After 5 h, the reaction mixture was cooled and
hydrolyzed with a saturated solution of 10% aqueous ammonium
chloride. After extraction with diethyl ether (3ϫ 50 mL), the com-
bined organic layers were dried with anhydrous magnesium sulfate.
All volatiles were removed under reduced pressure, and the residue
was chromatographed on silica gel to afford the respective bi-
phenyl. The product obtained compared well with authentic sam-
ples by gas chromatography.
(214.26): calcd. C 78.48, H 6.59, O 14.93; found C 78.23, H 6.44,
O 14.78.
2,2Ј-Dimethoxybiphenyl (2b): White solid; m.p. 154.5–156 °C
(ref.[22] 156 °C). 1H NMR (500 MHz, CDCl3): δ= 3.77 (s, 6 H),
6.99 (m, 4 H), 7.28 (d, J= 7.0 Hz, 2 H), 7.32 (t, J= 7.0 Hz, 2 H)
ppm. 13C NMR (125 MHz, CDCl3): δ= 55.8, 111.3, 120.5, 127.9,
128.8, 131.6, 157.2 ppm. C14H14O2 (214.26): calcd. C 78.48, H 6.59,
O 14.93; found C 78.35, H 6.28, O 14.84.
4,4Ј-Dimethylbiphenyl (2c): White solid; m.p. 124–125 °C (ref.[24]
125 °C). 1H NMR (500 MHz, CDCl3): δ= 2.38 (s, 6 H), 7.24 (d,
J= 8.0 Hz, 4 H), 7.48 (d, J= 8.0 Hz, 4 H) ppm. 13C NMR
(125 MHz, CDCl3): δ= 21.3, 127.0, 129.7, 136.8, 138.5 ppm.
C14H14 (182.26): calcd. C 92.26, H 7.74; found C 92.18, H 7.64.
2,2Ј-Dimethylbiphenyl (2d): Yellow liquid; b.p. 259 °C (ref.[48]
257 °C). 1H NMR (400 MHz, CDCl3): δ= 2.05 (s, 6 H), 7.11 (d,
J= 8.8 Hz, 2 H), 7.22–7.25 (m, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ= 18.8, 124.5, 126.1, 128.2, 128.7, 134.8, 140.6 ppm.
C14H14 (182.26): calcd. C 92.26, H 7.74; found C 92.29, H 7.37.
Homocoupling of Functionalized Aryl Grignard Reagents 1i–1j:
Magnesium turnings (13 mmol, 0.320 g atom) were placed in a two-
necked round-bottomed flask with a calcium chloride guard tube.
A crystal of iodine was added. Aryl halide (2 mmol of total
10 mmol) in anhydrous diethyl ether (5 mL) was added with con-
stant stirring, and the reaction mixture was maintained at –5 °C to
avoid the decomposition of the Grignard reagent. Initially, an in-
crease in the temperature of the reaction mixture was observed,
and the appearance of turbidity after a few minutes indicated the
initiation of the reaction. The remaining aryl halide (8 mmol) in
diethyl ether (5 mL) were added dropwise, and the reaction mixture
was stirred for 40 min. To the reaction mixture, nickel(III) catalyst
(0.1 mol-%) was added. The reaction mixture darkened immedi-
ately upon addition of the catalyst, and the stirring was continued.
After 5 h, the reaction mixture was cooled and hydrolyzed with
a saturated solution of 10% aqueous ammonium chloride. After
extraction with diethyl ether (3ϫ 50 mL), the combined organic
layers were dried with anhydrous magnesium sulfate. All volatiles
were removed under reduced pressure, and the residue was chro-
matographed on silica gel to afford the respective biphenyl. The
product obtained compared well with authentic samples by gas
chromatography.
1
Biphenyl (2e): White solid; m.p. 67–69 °C (ref.[22] 68 °C). H NMR
(500 MHz, CDCl3): δ= 7.34 (t, J= 7.3 Hz, 2 H), 7.44 (t, J= 7.5 Hz,
4 H), 7.60 (d, J= 7.5 Hz, 4 H) ppm. 13C NMR (125 MHz, CDCl3):
δ= 127.3, 127.4, 128.7, 141.4 ppm. C12H10 (154.21): calcd. C 93.46,
H 6.54; found C 93.28, H 6.48.
4,4Ј-Dichlorobiphenyl (2f): White solid; m.p. 150 °C (ref.[49] 149 °C).
1H NMR (400 MHz, CDCl3): δ= 7.39 (d, J= 7.6 Hz, 4 H), 7.46
(d, J= 8 Hz, 4 H) ppm. 13C NMR (100 MHz, CDCl3): δ= 127.2,
128.0, 132.7, 137.4 ppm. C12H8Cl2 (223.10): calcd. C 64.60, H 3.61;
found C 64.12, H 3.38.
4,4Ј-Bipyridine (2g): m.p. 112 °C (ref.[22] 110 °C). 1H NMR
(500 MHz, CDCl3): δ= 7.55 (dd, J= 4.5 Hz, 4 H), 8.75 (dd, J=
4.5 Hz, 4 H) ppm. 13C NMR (125 MHz, CDCl3): δ= 121.4, 145.4,
150.6 ppm. C10H8N2 (156.19): calcd. C 76.90, H 5.16, N 17.94;
found C 76.78, H 5.10, N 17.88.
1,1Ј-Binaphthyl (2h): White solid; m.p. 157 °C (ref.[50] 155–156 °C).
1H NMR (300 MHz, CDCl3): δ= 7.26–7.62 (m, 10 H), 7.96 (d, J=
8.1 Hz, 4 H) ppm. 13C NMR (75 MHz, CDCl3): δ= 125.5, 125.9,
126.1, 126.7, 127.9, 128.0, 128.3, 133.0, 133.6, 138.6 ppm. C20H14
(254.33): calcd. C 94.45, H 5.55; found C 94.18, H 5.44.
Characterization Data: All compounds gave satisfactory spectro-
scopic values, which are given below and are similar to the spectro-
scopic data reported in the literature. Elemental analyses are given
for each compound.
2,2Ј-Dinitrobiphenyl (2i): Pale brown solid; m.p. 120–122 °C (ref.[22]
120 °C). 1H NMR (500 MHz, CDCl3): δ= 7.31 (d, J= 7.5 Hz, 2
H), 7.59 (t, J= 7.25 Hz, 2 H), 7.68 (t, J= 7 Hz, 2 H), 8.23 (d, J=
8 Hz, 2 H) ppm. 13C NMR (125 MHz, CDCl3): δ= 124.8, 129.2,
131.0, 133.6, 134.2, 147.2 ppm. C12H8N2O4 (244.21): calcd. C
59.02, H 3.30, N 11.47, O 26.21; found C 58.96, H 3.12, N 11.34,
O 26.15.
L: Yield 2.32 g, 72%. M.p. 234 °C. C18H17N3O3 (323.35): calcd. C
66.86, H 5.30, N 13.00; found C 66.85, H 5.27, N 12.98. FTIR: ν=
˜
1605, 1576, 1314 cm–1. 1H NMR (400 MHz, DMSO): δ= 13.32 (br
s, OH), 9.56 (s, CH=N), 6.2–7.6 (m, ArH), 3.26 (s, NCH3), 2.38 (s,
=CCH3) ppm. MS (ESI): m/z= 324.3 [M + H]+. UV/Vis: λmax
=
4,4Ј-Dicyanobiphenyl (2j): White solid; m.p. 234 °C (ref.[22] 233–
234 °C). 1H NMR (500 MHz, CDCl3): δ= 7.68–7.74 (m, 4 H),
7.75–7.82 (m, 4 H) ppm. 13C NMR (125 MHz, CDCl3): δ= 112.4,
118.4, 127.9, 132.8, 143.5 ppm. C14H8N2 (204.23): calcd. C 82.33,
H 3.95, N 13.72; found C 82.15, H 4.13, N 13.45.
272, 315, 354, 395 nm.
NiL: Yield 0.390 g, 65%. M.p. 320 °C. C21H15N3NaNiO3S5
(599.37): calcd. C 42.08, H 2.52, N 7.01, S 26.75; found C 41.09,
H 2.48, N 6.99, S 26.73. FTIR (KBr): ν= 1603 ν(C=O), 1535
˜
ν(C=N), 1320 ν(C–O), 1221 ν(C=C), 1022 ν(C=S), 987.5 ν(C–S),
615 ν(SC=CS) cm–1. 1H NMR (400 MHz, DMSO): δ= 9.64 (s,
CH=N), 7.18–7.89 (m, ArH), 3.24 (s, NCH3), 2.50 (s, =CCH3)
ppm. MS (ESI): m/z= 600 [M+]. UV/Vis: λmax = 292, 338, 370, 411,
443, 479 nm. μeff = 2.6.
Supporting Information (see footnote on the first page of this arti-
cle): Spectroscopic and analytical data of the products.
Acknowledgments
4,4Ј-Dimethoxybiphenyl (2a): White solid; m.p. 178–180 °C (ref.[22]
79 °C). 1H NMR (500 MHz, CDCl3): δ= 3.84 (s, 6 H), 6.96 (d, J= A. P. B. thanks the National Institute of Technology Karnataka,
9.0 Hz, 4 H), 7.48 (d, J= 8.5 Hz, 4 H) ppm. 13C NMR (125 MHz,
CDCl3): δ= 55.5, 114.4, 127.9, 133.6, 158.9 ppm. C14H14O2 Institute of Science, Bangalore for NMR analysis.
Surathkal for a research fellowship. The authors thank the Indian
Eur. J. Org. Chem. 0000, 0–0
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Job/Unit: O30967
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Date: 12-09-13 17:16:44
Pages: 7
A. P. I. Bhat, F. Inam, B. R. Bhat
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6
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Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30967
/KAP1
Date: 12-09-13 17:16:44
Pages: 7
One-Step Synthesis of Biaryls under Mild ConditionsOne-Step Synthesis of Biaryls under Mild Conditions
Nickel Catalysis
A. P. I. Bhat, F. Inam, B. R. Bhat* ... 1–7
One-Step Synthesis of Biaryls under Mild
Conditions
A practical, room-temperature nickel(III)
catalytic system has been developed for the
synthesis of biaryls in one step from the
homocoupling of in situ generated Grig-
nard reagents. The use of molecular oxygen
as the oxidant makes the system environ-
mentally friendly. The reaction system is
compatible with diverse functionalities and
affords biaryls in appreciable yields.
Keywords: Biaryls / C–C coupling / Grig-
nard reagents / Oxygen / Nickel
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7