Iminophosphine-palladium(0) complexes as highly active catalysts in the Suzuki reaction. Synthesis of undecaaryl substituted corroles

Article abstract of DOI:10.1016/j.tetlet.2004.05.144

The iminophosphine-palladium(0) complex [Pd(dmfu)(P-N)] [dmfu=dimethyl fumarate; P-N=2-(PPh₂)C₆H₄-1-CH=NC ₆H₄-4-OMe] is a very efficient catalyst for the Suzuki coupling. In the reaction of aryl bromides with phenylboronic acid, turnover numbers up to ca. 200,000 are obtained at 110°C in 2h. Good rates are obtained also with the sterically hindered and electronically deactivated 2-bromo-1,3,5-trimethylbenzene. The complex is able to catalyze the exhaustive arylation of 2,3,7,8,12,13,17,18-octabromo-5,10,15-triphenylcorroleCu(III) to yield the corresponding undecaaryl substituted derivative.

Full text of DOI:10.1016/j.tetlet.2004.05.144

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 5861–5864
Iminophosphine–palladium(0) complexes as highly active catalysts
in the Suzuki reaction. Synthesis of undecaaryl substituted corroles
Alberto Scrivanti,a,* Valentina Beghetto,a Ugo Matteoli,a Simonetta Antonaroli,b
Alessia Marini,b Federica Mandoj,b Roberto Paolesseb and Bruno Crocianib,*
aDipartimento di Chimica, Universitꢀa ‘Cꢀa Foscari’ di Venezia, Calle Larga S. Marta 2137, 30123 Venezia, Italy
bDipartimento di Scienze e Tecnologie Chimiche, Universitꢀa di Roma ‘Tor Vergata’, 00173 Roma, Italy
Received 5 May 2004; revised 27 May 2004; accepted 28 May 2004
Available online 19 June 2004
Abstract—The iminophosphine–palladium(0) complex [Pd(dmfu)(P-N)] [dmfu ¼ dimethyl fumarate; P-N ¼ 2-(PPh2)C6H4-1-
CH@NC6H4-4-OMe] is a very efficient catalyst for the Suzuki coupling. In the reaction of aryl bromides with phenylboronic acid,
turnover numbers up to ca. 200,000 are obtained at 110 ꢀC in 2 h. Good rates are obtained also with the sterically hindered and
electronically deactivated 2-bromo-1,3,5-trimethylbenzene. The complex is able to catalyze the exhaustive arylation of
2,3,7,8,12,13,17,18-octabromo-5,10,15-triphenylcorroleCu(III) to yield the corresponding undecaaryl substituted derivative.
ꢁ 2004 Elsevier Ltd. All rights reserved.
The transition metal catalyzed cross-coupling reaction
of aryl halides with organoboron compounds (Suzuki
reaction) is one of the most efficient methodologies for
the formation of new carbon–carbon bonds.1 In par-
ticular, this reaction provides an effective method for the
preparation of biaryls, which are important intermedi-
ates in fine chemistry.2 A wide variety of palladium1;3;4
or nickel5;6 derivatives has been used to catalyze the
Suzuki reaction. Among the most recent achievements,
Scheme 1.
the development of catalysts able to secure extremely
high turnover frequencies3 and the use of palladium4
and nickel6 ‘ligand free’ catalysts are to be mentioned.
In the presence of 1, the coupling of 4-bromoacetophe-
none with phenylboronic acid yields 1-biphenyl-4-yl-
ethanone, the expected coupling product, with almost
complete chemoselectivity (see Table 1 for reaction
conditions).8
Recently, we have reported that zerovalent palladium-
iminophosphine species such as complex 1 of Scheme 1
are highly active catalysts in the Stille reaction.7 Owing
to the similarity of the two reactions, this finding
prompted us to investigate the activity of 1 in the Suzuki
coupling.
At 110 ꢀC, very high reaction rates are obtained: as a
matter of fact, using a 4-bromoacetophenone/catalyst
molar ratio of 200,000:1, a substrate conversion of 82%
is attained in 2 h (entry 2). Likewise, high reaction rates
are obtained with a variety of substrates (Table 1). As it
is usually found in the Suzuki coupling, the presence of
electron withdrawing groups on the aryl bromide en-
hances the reaction rate. However, the presence of such
activating groups is not essential for the catalyst activity
and comparable high reaction rates are obtained also
with substrates bearing electron donating substituents
Keywords: Suzuki reaction; Iminophosphine complexes; Palladium;
Boronic acid; Corroles.
* Corresponding authors. Tel.: +39-041-2348903; fax: +39-041-2348-
517 (A.S.); tel.: +39-06-72594389; fax: +39-06-72594328 (B.C.);
e-mail addresses: scrivanti@unive.it; crociani@stc.uniroma2.it
0040-4039/$ - see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.05.144

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A. Scrivanti et al. / Tetrahedron Letters 45 (2004) 5861–5864
Table 1. Suzuki coupling reactions catalyzed by complex 1a
Entry
Aryl bromide
1 (mmol)
[ArBr]/[1]
Yieldb (%)
1
4-CH3COC6H4Br
4-CH3COC6H4Br
4-CF3C6H4Br
4-CF3C6H4Br
C6H5Br
5 · 10ꢀ5
2 · 10ꢀ5
5 · 10ꢀ5
2 · 10ꢀ5
5 · 10ꢀ5
2 · 10ꢀ5
5 · 10ꢀ5
2 · 10ꢀ5
5 · 10ꢀ5
2 · 10ꢀ5
5 · 10ꢀ5
80,000
200,000
80,000
200,000
80,000
200,000
80,000
200,000
80,000
200,000
80,000
99
82
2
3
100
95
4
5
100
80
6
C6H5Br
7
4-CH3C6H4Br
4-CH3C6H4Br
4-CH3OC6H4Br
4-CH3OC6H4Br
2-Br-1,3,5-(CH3)3C6H2
100
76
8
9
100
68
10
11
48
a Reaction conditions. Solvent: toluene (12 mL); ArBr: 4.0 mmol; base: K2CO3; base/ArBr ¼ 2.0 (mol/mol); phenylboronic acid: 6.0 mmol; [phenyl-
boronic acid]/[ArBr] ¼ 1.5; T: 110 ꢀC, t: 2 h.
b By GLC with n-undecane as internal standard.
such as methyl or methoxy groups. Excellent activity is
also displayed in the coupling of phenylboronic acid
with 2-bromo-1,3,5-trimethylbenzene, despite the fact
that this substrate is both electronically deactivated and
sterically hindered.5d;9
It is worth noting that the catalyst seems air stable and
that the experiments can be carried out also under aero-
bic conditions.10
Scheme 2.
Encouraged by the excellent results obtained with the
aryl bromides we have investigated the use of complex 1
As a further step of our investigation, we explored the
activity of 1 to synthesize corroles bearing phenyl
groups at the b-positions, following the reaction path-
way depicted in Scheme 3. These macrocycles have
gained an increasing interest among porphyrin analogs
in the last few years,12 mainly because of their peculiar
coordination chemistry, which can result in potential
applications in catalysis and sensor fields.13b From this
point of view, fully substituted undecaaryl corroles have
not yet been reported in the literature and their prepa-
ration can further expand the number of synthetic
routes to these macrocycles, opening the way to a facile
preparation of a wide range of substituted corroles.
in the analogous reactions with aryl chlorides. Regret-
tably, a few preliminary experiments showed that 1 is a
very poor catalyst for the coupling of 4-chloroaceto-
phenone with phenylboronic acid (entries 1 and 2 of
Table 2).
The difference in the catalytic activity towards aryl
bromides and aryl chlorides can be exploited to effi-
ciently couple an aryl bromide with a chloro-substituted
aryl boronic acid in order to obtain a chloro-substituted
biaryl (Scheme 2).
At 110 ꢀC in toluene, the reaction of 4-bromoace-
tophenone with 4-chlorophenylboronic acid yields
1-(4-chloro-biphenyl-4-yl)-ethanone6b;11 with almost
complete chemoselectivity, the only by-product being
4,40-chlorobiphenyl (ca. 1%) (Table 2). The reaction rate
is lower than that obtained with the unsubstituted
phenyl-boronic acid, however it is still rather high and a
turnover number of ca. 48,000 is obtained in 2 h. Most
importantly, a total substrate conversion can be
achieved increasing the amount of catalyst and the
reaction time.
2,3,7,8,12,13,17,18-Octabromo-5,10,15-triphenyl-corrole
Cu(III)14 was reacted with 4-chlorophenylboronic acid
in toluene at 90 ꢀC in presence of 1 as catalyst, with a
corrole/catalyst ratio of 40,000:1.15 In this case, higher
yields were obtained carrying out the reaction under N2
atmosphere. The reaction was complete in 2 h, when no
more starting material was observed by TLC. Reaction
workup and chromatographic separation over neutral
alumina afforded the copper complex of undecasubsti-
Table 2. Reactions of phenylboronic acid with 4-chloroacetophenone and of 4-chlorophenylboronic acid with 4-bromoacetophenonea
Entry
Aryl bromide
Boronic acid
1 (mmol)
[ArX]/[1]
t (h)
Yieldb (%)
1
2
3
4
4-CH3COC6H4Cl
4-CH3COC6H4Cl
4-CH3COC6H4Br
4-CH3COC6H4Br
C6H5B(OH)2
C6H5B(OH)2
8 · 10ꢀ4
2 · 10ꢀ2
5 · 10ꢀ5
1 · 10ꢀ4
5000
200
24
26
2
6
17
4-ClC6H5B(OH)2
4-ClC6H5B(OH)2
80,000
40,000
60
100
4
a Reaction conditions. Solvent: toluene (12 mL); ArX: 4.0 mmol; base: K2CO3; base/ArX ¼ 2.0 (mol/mol); boronic acid: 6.0 mmol; [boronic acid]/
[ArX] ¼ 1.5; T ¼ 110 ꢀC.
b By GLC with n-undecane as internal standard.

A. Scrivanti et al. / Tetrahedron Letters 45 (2004) 5861–5864
5863
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Scheme 3.
7. (a) Scrivanti, A.; Beghetto, V.; Matteoli, U.; Antonaroli,
S.; Crociani, B. Tetrahedron 2002, 58, 6881; (b) Crociani,
B.; Antonaroli, S.; Matteoli, U.; Scrivanti, A.; Beghetto,
V. Dalton Trans. 2003, 2194.
8. Occasionally, traces of biphenyl (never exceeding 1%) were
detected together with the reaction product.
9. (a) Yin, J.; Rainka, P.; Zhang, X.-X.; Buchwald, S. L. J.
Am. Chem. Soc. 2003, 124, 1162; (b) Bedford, R. B.;
Welch, S. L. Chem. Commun. 2001, 129.
10. Typical Experimental Procedure (entry 2 of Table 1): 4-
bromoacetophenone (0.80 g, 4.0 mmol), phenylboronic
acid (0.73 g, 6.0 mmol), K2CO3 (1.10 g, 8.0 mmol), com-
plex 1 (0.013 mg, 2.0 · 10ꢀ5 mmol) and 12 mL of toluene
(freshly distilled from sodium/benzophenone) were intro-
duced into a 50 mL round bottom flask containing a small
magnetic bar. The mixture was heated under stirring at
110 ꢀC for 2 h and then cooled to RT. After filtration on
Celite the raw reaction mixture was analyzed by GLC
using n-undecane as internal standard.
11. Huwe, C. M.; Kunzer, H. Tetrahedron Lett. 1999, 40, 683.
12. (a) Paolesse, R. In The Porphyrin Handbook; Kadish, K.
M., Smith, K. M., Guilard, R., Eds.; Academic: New
York, 2000; Vol. 2, pp 201–231; (b) Erben, C.; Will, S.;
Kadish, K. M. In The Porphyrin Handbook; Kadish, K.
M., Smith, K. M., Guilard, R., Eds.; Academic: New
York, 2000; Vol. 2, pp 233–295; (c) Gryko, D. T. Eur. J.
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tuted corrole in a reasonable yield (55%). It is worth
mentioning that 1 was able to catalyze the complete
substitution of the eight peripheral bromine atoms and
no products of partial substitution were observed
among the reaction products.
In conclusion, the iminophosphine–palladium(0) com-
plex 1 is a highly efficient catalyst in the coupling of aryl
bromides with phenylboronic acids. With an appropri-
ate choice of the reaction conditions, an almost quan-
titative yield in the coupling products can be obtained.
The low activity displayed by the catalyst towards
aryl chlorides can be exploited to selectively couple
chloro-substituted arylboronic acids with aryl bromides.
Further studies aiming to extend this route to the
preparation of both free base and other metallocorroles
are in progress, and the results will be reported in due
course.
References and notes
1. Recent reviews: (a) Kotha, S.; Lahiri, K.; Kashinath, D.
Tetrahedron 2002, 58, 9633; (b) Suzuki, A. J. Organomet.
Chem. 2002, 653, 83; (c) Suzuki, A. J. Organomet. Chem.
1999, 576, 147; (d) Suzuki, A. In Metal-Catalyzed Cross-
coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-
VCH: Weinheim, 1998; (e) Miyaura, N.; Suzuki, A. Chem.
Rev. 1995, 95, 2457.
13. (a) Gross, Z. J. Biol. Inorg. Chem. 2001, 6, 733; (b)
Paolesse, R.; Di Natale, C.; Macagnano, A.; Sagone, F.;
Boschi, T.; Scarselli, M. A.; Chiaradia, P.; Troitsky, V. I.;
Berzina, T. S.; D’Amico, A. Langmuir 1999, 15, 1268.
14. Steene, E.; Dey, A.; Gosh, A. J. Am. Chem. Soc. 2003, 125,
16300.
ꢁ
2. (a) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.;
15. 2,3,7,8,12,13,17,18-Octa(4-chlorophenyl)-5,10,15-triphen-
yl-corrolato Cu(III). 2,3,7,8,12,13,17,18-Octabromo-
5,10,15-triphenylcorrolato Cu(III) (100 mg, 0.082 mmol)
and 4-chlorophenylboronic acid (205 mg, 1.31 mmol),
K2CO3 (1.10 g, 8.0 mmol), and 50 mL of toluene (freshly
distilled from sodium/benzophenone) and complex 1
Lemaire, M. Chem. Rev. 2002, 102, 1359; (b) Stanforth, S.
Tetrahedron 1998, 54, 263.
3. (a) Dai, W.-M.; Li, Y.; Zhang, Y.; Lai, K. W.; Wu, J.
Tetrahedron Lett. 2004, 45, 1999; (b) Zapf, A.; Jackstell,
R.; Rataboul, F.; Riermeier, T.; Monsees, A.; Fuhrmann,
C.; Shaikh, N.; Dingerdissen, U.; Beller, M. Chem.
Commun. 2004, 38; (c) Navarro, O.; Kelly, R. A., III;
Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 16194; (d) Rosa,
G. R.; Ebeling, G.; Dupont, J.; Monteiro, A. L. Synthesis
2003, 18, 2894; (e) Bedford, R. B.; Cazin, C. S. J.; Coles, S.
J.; Gelbrich, T.; Horton, P. N.; Hursthouse, M. B.; Light,
(0.0013 mg, 2.0 · 10ꢀ6 mmol) were introduced into
a
100 mL Schlenk flask and the solution was degassed
by the freeze–pump–thaw method (three cycles) and
then heated at 90 ꢀC under N2 for 2 h. Solvent was
then evaporated and the crude product was purified by

5864
A. Scrivanti et al. / Tetrahedron Letters 45 (2004) 5861–5864
chromatography on neutral alumina (Grade III Brock-
558, 642. FAB-MS: 1471 (M+). 1H NMR (CD2Cl2):
d ¼ 7:50–6.50 (m). Anal. Calcd for C85H47N4Cl8Cu: C,
69.39; H, 3.22; N, 3.81. Found: C, 69.12; H, 3.06; N,
3.69.
mann) using CH2Cl2 as eluant. The product was obtained
as red crystals (66 mg, 55% yield) after crystallization
from CH2Cl2/hexane. mp >300 ꢀC. UV–vis: kmax 438 nm,