Palladium-catalyzed reactions of bisarenediazoniutn salts: Two-fold Heck reaction, carbonylation and cross-coupling regimen

Article abstract of DOI:10.1039/a707378j

Two-fold Heck reaction, carbonylation and cross-coupling reactions of bisarenediazonium salts have been carried out in high yields under mild, aqueous alcoholic conditions to provide a new synthetic repertoire for tetraaryls and other aromatic derivatives having extended conjugation.

Full text of DOI:10.1039/a707378j

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Palladium-catalyzed reactions of bisarenediazonium salts: two-fold
Heck reaction, carbonylation and cross-coupling regimen
Saumitra Sengupta,* Subir Kumar Sadhukhan, Sanchita Bhattacharyya and
Joydeep Guha
Department of Chemistry, Jadavpur University, Calcutta 700 032, India
Two-fold Heck reaction, carbonylation and cross-coupling reactions of bisarenediazonium salts have been
carried out in high yields under mild, aqueous alcoholic conditions to provide a new synthetic repertoire
for tetraaryls and other aromatic derivatives having extended conjugation.
diamine used in this work. While compounds 1a–c,e,f and 2
Introduction
were commercially available, compound 1d was prepared from
4,4Ј-dinitrodiphenic acid dimethyl ester11 via reduction of
the nitro groups with N2H4ؒH2O/Pd–C. The diaminostilbene
derivative 1g was prepared according to a literature procedure
via controlled reduction (Zn/NH4Cl) of 4,4Ј-dinitrostilbene.12
The latter, in turn, was prepared in high yield via our recently
disclosed stilbene synthesis involving a double Heck reaction
of p-nitrobenzenediazonium salt with triethoxy(vinyl)silane.13
Once in hand, these bisanilines were converted into the respec-
tive bisarenediazonium tetrafluoroborates 3a–g by using stan-
dard diazotization procedures.14
Palladium-catalyzed vinylation (the Heck reaction)1 and cross-
coupling reactions2 of aryl halides are powerful synthetic
methodologies for new carbon–carbon-bond formation in
aromatic domains. Extensive methodological refinements over
the last decade, particularly with regard to solvents, catalysts
and additives, have greatly improved the synthetic efficacy of
these reactions, as a result of which they are now finding almost
routine use in complex organic synthesis.3 Recently, asymmetric
versions of the Heck reaction have also emerged,4 which have
opened a whole new vista in enantiomerically pure compound
(EPC) synthesis. Increasing applications of Heck and cross-
coupling reactions are also evident in macromolecular syn-
thesis, especially in the field of poly-(p-phenylenevinylene) and
poly-(p-phenylene) types of conjugated polymers.5
R
R′
Y
Y
Y
X
Y
Although aryl halides (Br, I) and triflates are traditionally
used for Heck and cross-coupling reactions, we6 and others7,8
have shown that arenediazonium salts are promising altern-
atives to these substrates and, in fact, hold several advantages
over the aryl halides: ready availability of starting materials
(anilines are cheaper than aryl halides), short reaction times (15
min to 1 h), high yields under mild conditions (room temp. to
80 ЊC) and operational simplicity including the option of using
aqueous reaction media.6,8 In a recent development, we9 and
Genet and co-workers10 have independently reported the suc-
cessful cross-coupling of arenediazonium salts with arylboronic
acids in a new synthesis of unsymmetrical biaryls. Most signifi-
cantly, in all these reactions the diazonium nucleofuge has
been found to be far more reactive than the corresponding aryl
bromide, triflate or even the iodide, as shown by intramolecular
competition experiments.
Palladium-catalyzed reactions of bisarenediazonium salts
were a rational extension of the above studies. Since two-fold
Pd-catalyzed reactions on dibromo- and diiodo-arenes have
been intensively pursued in recent times, it was imperative on
our part to study and compare the reactivity of bisarenediazo-
nium salts in such reactions. With an ultimate goal towards
using them in the synthesis of conjugated aromatic polymers
via poly-Heck and poly-cross-coupling reactions,5 we thus
undertook a study of two-fold Heck, carbonylation and cross-
coupling reactions of a number of bisarenediazonium salts, and
in this paper we describe our results towards these ends.
R′
R
1 Y = NH2; 3 Y = N2+ BF4
2 Y = NH2
–
–
4 Y = N2+ BF4
a X = (), R = R′ = H
b X = (), R = Me, R′ = H
c X = (), R = OMe, R′ = H
d X = (), R = H, R′ = CO2Me
e X = O, R = R′ = H
X = SO2, R = R′ = H
5 Y = (E)-CH=CHCO2Me
f
g X = (E)-CH=CH-, R = R′ = H
Two-fold Heck reaction was first studied with the bisdiazo-
nium salts. Thus, the bis-salts 3a–g were subjected to Pd-
catalyzed [1–2% Pd(OAc)2] vinylation with ethyl acrylate or
styrene (4 mol equiv. each) in refluxing ethanol,6 which
smoothly produced the bis-Heck products 6 and 7 in 60–80%
yield (Scheme 1, Table 1). The bisdiazonium salt 415 derived
R
R′
i
Z
3a–g
X
ii
Z
R′
R
6 Z = CO2Et
7 Z = Ph
R
R′
MeO2C
X
CO2Me
R′
R
Results and discussion
8
In this study, the bisanilines 1a–g and 2 were chosen as sub-
strate precursors to the bisarenediazonium salts. They ranged
from substituted benzidine derivatives 1a–d to those where the
two aniline rings are separated by spacer atoms (as in com-
pounds 1e,f) or by a vinyl group (as in compound 1g). m-
Phenylenediamine 2 was the only example of a homonuclear
Scheme 1 Reagents and conditions: i, 2% Pd(OAc)2, EtOH, CH2᎐᎐
CHZ, 80 ЊC, 1 h; ii, 2% Pd(OAc)2, MeOH, CO (1 atm.), 25 ЊC, 30 min
from m-phenylenediamine 2 also underwent two-fold Heck
reaction with methyl acrylate in refluxing methanol to produce
the m-phenylenediacrylate 5 in 83% yield. Several of these bis-
J. Chem. Soc., Perkin Trans. 1, 1998
407

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Table 1 Two-fold Heck reaction and carbonylation of bis-salts 3a–g
ture consisting of the desired product 11 together with side-
products arising out of homocoupling and protodediazoniation
of substrate 3b. This was utterly surprising since the (mono)-
diazonium salt derived from o-toluidine, upon cross-coupling
with PhB(OH)2, gave a 90% yield of 2-methylbiphenyl under
identical reaction conditions.9 Nevertheless, these side-reactions
could ultimately be eliminated by replacing PhB(OH)2 with
PhBF3K, according to the recently reported Genet protocol,10a
which then produced the desired product 11 in 55% isolated
yield. Interestingly, two-fold arylation of the bis-salts could also
be achieved by a Gomberg–Bachmann procedure,17 which to
the best of our knowledge has never been explored before with
bisarenediazonium salts. Towards this end, the bis-salt 3e was
first converted into the bistriazene 12 (80%).6d The latter was
then decomposed in refluxing benzene in the presence of tri-
fluoroacetic acid (TFA) (4 mol equiv.) and a catalytic amount
Bisdiazonium
salt 3
Entry
Olefina/CO Products 6–8
Yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
3a
3b
3b
3c
3c
3c
3d
3d
3e
3e
3f
A
A
B
A
B
CO
A
B
A
6a
6b
7b
6c
7c
8c
6d
7d
6e
8e
6f
70
73
60
80
75
93
70
63
80
76
60
60
60
CO
A
A
3g
3g
6g
7g
B
18
a A = ethyl acrylate, B = styrene.
of I2 to produce the di(biphenyl) ether 10 in 54% yield
(Scheme 2), quite comparable to that obtained via two-fold
boronic acid cross-coupling of bis-salt 3e (vide supra). Despite
the fact that biaryl syntheses via Gomberg–Bachmann pro-
cedures have their limitations (poor yields with ortho-substi-
tuted diazonium salts, and regiorandom for unsymmetrically
substituted arenes), the above two-fold Gomberg–Bachmann
protocol appears to hold much promise for the synthesis of
relatively simple, symmetrically substituted p-tetraaryls.
In summary, the readily available bisarenediazonium salts,
in lieu of the conventional but often difficult-to-prepare aro-
matic dihalides and ditriflates, have been established as novel
substrates for two-fold Heck reaction, carbonylation and cross-
coupling reactions. Pd-catalyzed reactions on bisarenediazo-
nium salts provide good to excellent yields under conditions
that are mild and operationally simple, thus providing an excel-
lent repertoire for the synthesis of a wide variety of substituted
tetraaryls and other extended conjugated systems. Application
of this repertoire towards the synthesis of conjugated aromatic
polymers is currently under investigation.
Heck reactions were also performed directly on the bisanilines 1
via our ‘one-pot diazotization–Heck reaction’ protocol6f which
gave very similar yields to those obtained through Heck reac-
tion of the isolated salts 3. In either case, the reactions were
typified by short reaction times (45 min to 1 h), mild conditions
and advantageous use of aqueous alcoholic media which
greatly simplified isolation procedures. However, attempted
synthesis of unsymmetrical bisvinylated products by employing
one mol equiv. each of two different olefins has so far been
unsuccessful, resulting in complex product mixtures.
Pd-catalyzed carbonylation of the bis-salts was also investi-
gated. Thus, compounds 3c and 3e were carbonylated (1 atm. of
CO) in methanol at room temp. to produce the dimethyl esters
8c and 8e in high yield, respectively (Scheme 1, Table 1). It may
be mentioned here that carbonylations of (mono)arenediazo-
nium salts have previously been reported in CH3CN with
Pd(dba)2† as catalyst which, however, required 10 kg/cm2
pressure of CO gas and a special autoclave device in order to
conduct the reactions.16 In contrast, our methanolic reaction
conditions are operationally much simpler, and our method
merely involves passing CO gas through the reaction mixture at
ambient temperature.
Experimental
All mps were measured on a Toshniwal 301 melting point appar-
atus and are uncorrected. IR spectra were taken in a Perkin-
Two-fold cross-coupling of the bis-diazonium salts was
briefly studied. Thus, reaction of the salts 3c and 3e with two
mol equiv. of PhB(OH)2 in refluxing methanol9 gave rise to the
p-tetraaryl derivatives 9 and 10 in 72 and 60% yield, respectively
(Scheme 2). Cross-coupling of the o-toluidine derived bis-salt
3b with PhB(OH)2, however, led to an inseparable product mix-
1
Elmer R-297 spectrometer. H NMR spectra were recorded in
CDCl3–SiMe4 on Varian EM-360 (60 MHz), JEOL FX-100 (100
MHz) and Varian XL-200 (200 MHz) instruments. J-Values are
given in Hz. Column chromatography was performed on silica
gel (60–120 mesh). The bisarenediazonium salts 3a–g were pre-
pared, just prior to use, via standard tetrazotization (NaNO2,
conc. HCl, 0 ЊC, then NaBF4 or NaNO2, 42% HBF4, 0 ЊC)14 of
the bisanilines 1a–g whereas bis-salt 4 was prepared from
m-phenylenediamine according to a literature procedure.15
PhBF3K was prepared from PhB(OH)2 as described in the litera-
ture.10a Standard work-up refers to concentration of the reaction
mixture under reduced pressure, dilution with an organic sol-
vent, filtration through Celite, washing of the filtrate with
water, and drying over anhydrous Na2SO4. Light petroleum
refers to the fraction with distillation range 60–80 ЊC.
R
i or ii
3b,c,e
Ph
X
Ph
R
iii for 3e
9 X = (), R = R = OMe (72%)
10 X = O, R = H (60%)
11 X = (), R = Me (55%)
N
O
R2N
N
General procedure for two-fold Heck reaction of bis-salts 3a–g
and 4
2
12 R2N = morpholino (80%)
Pd(OAc)2 (5 mg) was added to a mixture of the bisdiazonium
salt 3 or 4 (1 mmol) and the appropriate olefin (4 mmol) in
EtOH (MeOH for 4) (10 cm3) and the mixture was heated under
reflux for 1 h. It was then cooled to room temp. and standard
work-up with CH2Cl2 followed by chromatography on silica gel
(10% EtOAc in light petroleum) (for 6a–g) or precipitation with
light petroleum (for 5, 7b–d, 7g) gave the respective bisvinylated
products. They were further purified by recrystallization from
appropriate solvents.
iv
10 (54%)
Scheme 2 Reagents and conditions: i, 10% Pd(OAc)2, PhB(OH)2,
MeOH, 60 ЊC, 1 h (for 3c,e); ii, 10% Pd(OAc)2, PhBF3K, MeOH, 60 ЊC,
1 h (for 3b); iii, excess of morpholine; iv, TFA (4 mol equiv.), I2 (cat.),
benzene, reflux
Compound 6a: 70%; mp 143–144 ЊC (from CHCl3–light
petroleum); νmax(Nujol)/cmϪ1 1700, 1630 and 1460; δH(CDCl3)
† dba = 1,3-dibenzylideneacetonato(1Ϫ).
408
J. Chem. Soc., Perkin Trans. 1, 1998

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1.35 (6 H, t, J 7.2), 4.30 (4 H, q, J 7.2), 6.47 (2 H, d, J 16) and
7.20–7.83 (10 H, m).
mixture was heated under reflux for 1 h. It was then cooled to
room temp. and standard work-up with CH2Cl2 followed by
precipitation with light petroleum (for 9 and 10) or preparative
TLC (light petroleum, for 11) gave the respective tetraaryl
products, which were further purified by recrystallization from
appropriate solvents.
Compound 9: 72%; mp 160–162 ЊC (from CH2Cl2–light
petroleum) (lit.,19c 183–184 ЊC) (Found: C, 85.72; H, 6.12.
C26H22O2 requires C, 85.24; H, 6.01%); δH(CDCl3) 3.92 (6 H, s)
and 7.18–7.60 (16 H, m).
Compound 10: 60%; mp 205–206 ЊC (from MeOH–CHCl3)
(Found: C, 89.02; H, 5.68. C24H18O requires C, 89.44; H,
5.59%); νmax(Nujol)/cmϪ1 1590, 1545, 1285, 1210, 1120, 960 and
810; δH(CDCl3) 7.06–7.60 (18 H, m).
Compound 6b: 73%; mp 137–138 ЊC (from CH2Cl2–light
petroleum) (Found: C, 76.52; H, 6.70. C24H26O4 requires C,
76.19; H, 6.87%); νmax(Nujol)/cmϪ1 1705, 1625, 1450, 1310 and
1173; δH(CDCl3) 1.34 (6 H, t, J 7.5), 2.50 (6 H, s), 4.25 (4 H, q,
J 7.5), 6.35 (2 H, d, J 15), 7.37 (4 H, s), 7.58 (2 H, d, J 7.5) and
7.93 (2 H, d, J 15).
Compound 6c: 80%; mp 155–156 ЊC (from CH2Cl2–light
petroleum) (Found: C, 69.99; H, 6.40. C24H26O6 requires C,
70.24; H, 6.34%); νmax(Nujol)/cmϪ1 1685, 1595, 1440, 1380,
1270 and 1120; δH(CDCl3) 1.35 (6 H, t, J 7.5), 3.98 (6 H, s), 4.26
(4 H, q, J 7.5), 6.52 (2 H, d, J 16), 7.04 (2 H, s), 7.15 (2 H, d,
J 8), 7.54 (2 H, d, J 8) and 7.95 (2 H, d, J 16).
Compound 6d: 70%; mp 122–123 ЊC (from MeOH) (Found:
C, 66.82; H, 5.55. C26H26O8 requires C, 66.95; H, 5.58%);
νmax(Nujol)/cmϪ1 1710, 1445, 1355 and 1175; δH(CDCl3) 1.35 (6
H, t, J 8), 3.66 (6 H, s), 4.30 (4 H, q, J 8), 6.52 (2 H, d, J 16),
7.24 (2 H, d, J 8), 7.68–7.84 (4 H, m) and 8.22 (2 H, d, J 3).
Compound 6e: 80%; mp 77–78 ЊC (from MeOH) (Found:
C, 71.67; H, 6.07. C22H22O5 requires C, 72.13; H, 6.01%);
νmax(Nujol)/cmϪ1 1700, 1620, 1580, 1490, 1355, 1230 and 1160;
δH(CDCl3) 1.36 (6 H, t, J 7), 4.26 (4 H, q, J 7), 6.34 (2 H, d,
J 16), 7.02 (4 H, d, J 8), 7.52 (4 H, d, J 8) and 7.64 (2 H, d, J 16).
Compound 6f: 60%; mp 155–156 ЊC (from MeOH) (Found:
C, 63.23; H, 5.34. C22H22O6 requires C, 63.76; H, 5.31%);
νmax(Nujol)/cmϪ1 2920, 2830, 1705, 1455, 1370, 1305 and 1150;
δH(CDCl3) 1.33 (6 H, t, J 7.2), 4.27 (4 H, q, J 7.2), 6.49 (2 H, d,
J 16), 7.65 (6 H, m) and 7.95 (4 H, d, J 7).
Compound 6g: 60%; mp 180–181 ЊC (from CH2Cl2–light
petroleum); νmax(KBr)/cmϪ1 1705, 1630, 1300 and 1170;
δH(CDCl3) 1.32 (6 H, t, J 8), 4.27 (4 H, q, J 8), 6.44 (2 H, d,
J 16), 7.16 (2 H, s), 7.56 (8 H, s) and 7.73 (2 H, d, J 16).
Compound 7b: 60%; mp 165–166 ЊC (from CH2Cl2–light
petroleum) (Found: C, 93.52; H, 6.68. C30H26 requires C, 93.26;
H, 6.74%); νmax(Nujol)/cmϪ1 1590, 1545, 1285, 1205, 1030, 960
and 805; δH(CDCl3) 2.63 (6 H, s) and 7.26–7.86 (20 H, m).
Compound 7c: 75%; mp 195–196 ЊC (from CH2Cl2–light
petroleum) (Found: C, 86.12; H, 6.22. C30H26O2 requires C,
86.28; H, 6.38%); νmax(Nujol)/cmϪ1 1590, 1540, 1280, 1010, 950
and 800; δH(CDCl3) 4.00 (6 H, s) and 6.15–6.7 (20 H, m).
Compound 7d: 63%; mp 205–206 ЊC (from CH2Cl2–light
petroleum); νmax(Nujol)/cmϪ1 1710, 1450, 1290, 1240 and 1080;
δH(CDCl3)3.65(6H, s), 7.20–7.76(18H, m)and8.16(2H, d, J3).
Compound 7g: 60%; mp >300 ЊC (from CH2Cl2–light petrol-
eum) (lit.,19a >350 ЊC); δH(CDCl3) 7.08–7.38 (24 H, m).
Compound 5: 83%; mp 126–127 ЊC (from acetone–light
petroleum); νmax(Nujol)/cmϪ1 1730, 1645 and 1460; δH(CDCl3)
3.83 (6 H, s), 6.45 (2 H, d, J 16), 7.40 (1 H, d, J 8), 7.55 (2 H, d,
J 8), 7.65 (2 H, d, J 16) and 7.70 (1 H, s).
Compound 11: 55%; mp 137–139 ЊC (from CH2Cl2–light
petroleum) (lit.,19d 141 ЊC); δH(CDCl3) 2.46 (6 H, s) and 7.23–
7.70 (16 H, m).
Preparation and two-fold Gomberg–Bachmann reaction of the
bistriazene 12
4,4Ј-Diaminodiphenyl ether 1e (1.0 g, 5.0 mmol) was added to a
solution of conc. HCl (2.6 cm3) in water (30 cm3) and the mix-
ture was stirred for 5 min at 25 ЊC. It was then cooled to 0 ЊC
and treated dropwise with aq. NaNO2 (0.703 g, 10.2 mmol in
4 cm3). After 30 min at 0 ЊC the mixture was treated dropwise
with morpholine (0.940 g, 10.8 mmol) and stirring was contin-
ued for a further 15 min. It was then basified with aq. NaHCO3
and the separated solid was filtered off, washed with water, and
dried in air. Recrystallization gave the bistriazene 12 as a crys-
talline solid (1.60 g, 80%), mp 141–142 ЊC (from light petrol-
eum); νmax(Nujol)/cmϪ1 1450, 1370, 1230 and 1100; δH(CDCl3)
3.78 (16 H, m), 7.20 (4 H, d, J 8) and 7.62 (4 H, d, J 8).
TFA (0.456 g, 4.0 mmol) was added dropwise to a refluxing
solution of the bistriazene 12 (0.396 g, 1.0 mmol) and I2 (5 mg)
in benzene (20 cm3). After the addition was complete, refluxing
was continued for a further 3 h after which it was cooled,
poured into 5% aq. Na2CO3 (10 cm3) and extracted with CHCl3
(3 × 10 cm3). Removal of solvent followed by recrystallization
from CHCl3–MeOH gave compound 10 (0.174 g, 54%), identi-
cal in all respects with the product obtained from two-fold
cross-coupling of bis-salt 3e with PhB(OH)2.
Acknowledgements
CSIR (01/1371/EMR-II/95) and Jadavpur University (JRF to
S. K. S.) are thanked for financial support.
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J. Chem. Soc., Perkin Trans. 1, 1998
409

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Paper 7/07378J
Received 13th October 1997
Accepted 4th November 1997
410
J. Chem. Soc., Perkin Trans. 1, 1998