Platinum-catalyzed cross-couplings of organoboronic acids with aryl iodides

Article abstract of DOI:10.1016/S0040-4039(02)00863-8

Tetrakis(triphenylphosphine)platinum in DMF was utilized as a mild catalyst for cross coupling reactions of organoboronic acids with aryl iodides. The present reactions exhibited excellent group-selectivity where couplings of organoboronic acids 2a-e with 4-bromo-1-iodobenzene (4) give 4-arylbromobenzenes 5a-b and 4-alkenylbromobenzenes 5c-e in excellent yields.

Full text of DOI:10.1016/S0040-4039(02)00863-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 4645–4647
Platinum-catalyzed cross-couplings of organoboronic acids with
aryl iodides
Chang Ho Oh,* Young Mook Lim and Choong Ho You
Department of Chemistry, Hanyang University, Sungdong-Gu, Seoul 133-791, South Korea
Received 16 March 2002; revised 26 April 2002; accepted 7 May 2002
Abstract—Tetrakis(triphenylphosphine)platinum in DMF was utilized as a mild catalyst for cross-coupling reactions of
organoboronic acids with aryl iodides. The present reactions exhibited excellent group-selectivity where couplings of
organoboronic acids 2a–e with 4-bromo-1-iodobenzene (4) give 4-arylbromobenzenes 5a–b and 4-alkenylbromobenzenes 5c–e in
excellent yields. © 2002 Elsevier Science Ltd. All rights reserved.
Palladium-catalyzed cross-coupling of organoboronic
acids with aryl bromides, iodides, or triflates, known as
Suzuki reaction, is a versatile synthetic method for
carbonꢀcarbon bond formation.1 Since a variety of
organoboron derivatives are now available, stable in
air, and inert to various functional groups, a number of
studies on transition-metal-catalyzed cross-coupling
reactions of organoboronic acids have been reported.
But less reactive aryl chlorides do not undergo these
cross-couplings except when they are activated by elec-
tron-withdrawing groups,2 co-catalysts,3 or additives.4
Alternatively, cross-coupling of the aryl chlorides with
arylboronic acids has been accomplished by use of
nickel catalysts.5
We have initiated a research program to search a more
selective metal catalyst capable of differentiating the
iodide and the bromide of the substrates and found a
preliminary solution from platinum-catalyzed reactions
in DMF solvent. Various platinum compounds can
Table 1. Platinum-catalyzed cross-coupling reactions of phenylboronic acid 2a with 1-iodonaphthalene 1a
(1)
Entry
Pt-catalyst (2 mol%)
Base (2 equiv.)
Solvent
Temp. (°C)/time (h)
Yield (%)
1
2
3
4
5
6
7
8
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
Pt(PPh3)4
PtCl2
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
NaOH
KF
Ba(OH)2
Cs2CO3
Cs2CO3
Cs2CO3
Ethanol
Water
1,4-Dioxane
CH3CN
DMF
DMF
DMF
DMF
DMF
Reflux/12
Reflux/12
Reflux/12
Reflux/12
120/12
120/12
120/12
120/12
120/12
26
Trace
15
19
88
46
15
19
10
9
10
11
12
DMF
DMF
DMF
120/12
120/12
120/12
Trace
Trace
Trace
PtCl4
PtCl2/PPh3
* Corresponding author. Tel.: +82-2-2290-0932; fax: +82-2-2299-0762; e-mail: changho@hanyang.ac.kr
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00863-8

4646
C. H. Oh et al. / Tetrahedron Letters 43 (2002) 4645–4647
Table 2. Platinum-catalyzed cross-coupling reactions of
arylboronic acids 2a–f with aryliodides 1b–d
catalyze Boron–E (E=B, Si, Sn) additions to unsatu-
rated bonds to give the organoboron compounds.6 It is
well-known that the hydrosilylation of terminal alkynes
with dialkylchlorosilanes can be accomplished by a
platinum catalyst (H2PtCl6, Speier’s catalyst).7 If such
organoboron, organosilicon, or organotin compounds
could undergo cross-coupling reactions with organic
halides by a platinum catalyst, a very efficient tandem
CꢀC bond-forming reaction can be developed. A few
studies on platinum-catalyzed carbonꢀcarbon bond-
forming reactions have been reported. Pt(PPh3)4-cata-
lyzed carbonylative cross-coupling of alkyl iodides with
sodiumtetraphenylborate gave the corresponding
phenylalkylketones in 40–60% yields.8 Two bis(phos-
phine)platinum complexes were developed as catalysts
for the cross-coupling of arylmagnesium halides with
alkenyl bromides to give up to 95% of the products.9
Recently, vinylation of aryl iodides using Pt(COD)Cl2/
PPh3 as a catalyst system was also reported.10 Platinum
compounds compared to the corresponding Ni- or Pd
compounds might have the low reactivity toward
organic halides presumably due to diffused d-orbitals
(5d-orbital). We expected that such low reactivity of
platinum compounds could be utilized selective cross-
coupling reactions of organoboronic acids with organic
iodides in the presence of other labile functional groups
such as organic bromides.
(2)
Ar-X
Boronic acids
Products (%yield)
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
3ba (66)
3bb (95))
3bc (58)
3bd (70)
3be (72)
3bf (94)
3ca (68)
3cb (84)
3cc (68)
3cd (67)
3ce (84)
3cf (76)
3da (64)
3db (83)
3dc (79)
3dd (86)
3de (70)
3df (90)
As a starting point of our study, we investigated the
catalytic effect of three commercially available platinum
compounds for cross-couplings of 1-iodonaphthalene
(1a) with phenylboronic acid (2a) (Eq. (1)) and summa-
rized the results in Table 1. When the reaction was
screened with a catalytic amount of Pt(PPh3)4 in vari-
ous solvents such as ethanol, water, 1,4-dioxane, aceto-
nitrile, and DMF (entries 1–5), DMF was found to be
an extraordinarily good solvent. Then, we tested vari-
ous bases such as K2CO3, NaOH, KF, and Cs2CO3 in
DMF (entries 6–9). The best result gave 1-phenylnaph-
thalene (3aa) in 88% isolated yield when the reaction
was carried out with Cs2CO3 as a base at 120°C in
DMF. The reaction did not complete at low tempera-
ture (100°C) even after 24 h. For the platinum’s oxida-
tion state, only the electron-rich Pt(0) compound could
catalyze the cross-coupling reaction, suggesting that the
rate-determining step of this reaction be the oxidative
addition of platinum compound to the CꢀI bond of
1-iodonaphthalene. A general procedure is as follows.
A mixture of 1-iodonaphthalene (86.0 mg, 0.33 mmol),
Cs2CO3 (216.0 mg, 0.66 mmol), and phenylboronic acid
(50.0 mg, 0.40 mmol) in dry N,N-dimethylformamide
(2.0 mL) was treated with 2 mol% of Pt(PPh3)4 (8.5 mg,
6.6 mmol) and stirred at 120°C for 12 h under argon
atmosphere. Extractive work-up and flash silica gel
chromatography (EtOAc:hexane=1:40) gave 1-phenyl-
naphthalene (3aa, 59.3 mg) in 88% yield.
reactions of aryl iodides 1b–d with various
organoboronic acids 2a–f under the similar conditions
(Eq. (2) and Table 2).12 The three representative aryl
iodides
were
4-iodotoluene,
electron-poor
4-
iodonitrobenzene, and electron-rich 4-iodoanisole.
Cross-couplings of aryl iodides 1b–d with arylboronic
acids 2a–b and with alkenylboronic acids 2c–f occurred
smoothly in 58–90% yields. It should be noted that the
cross-coupling reaction of 4-iodonitrobenzene 1d with
hexenylboronic acid 2e gave the unusual head-to-tail-
cross-coupling product in 70% yield (Eq. (3)).13
(3)
Overall, the yields of the coupling products were com-
parable to those of the Suzuki reactions, although the
reaction temperatures were relatively high (120°C). In
contrast to aryl iodides, bromobenzene (1e) did not
undergo cross-coupling reactions with either 2b or 2c
under these conditions (Eq. (4)). Such low reactivity of
the platinum compounds to aryl halides suggested that
the present reaction could be of a good synthetic poten-
tial as a chemoselective cross-coupling method.
The dramatic solvent dependency is highly interesting
although not yet clear. Based on the literature, we
propose that the platinum compound might be acti-
vated by DMF and then oxidatively added to iodo-
naphthalene.11 From the synthetic viewpoint of these
results, we investigated a scope of these cross-coupling
(4)

C. H. Oh et al. / Tetrahedron Letters 43 (2002) 4645–4647
4647
Table 3. Platinum-catalyzed cross-coupling reactions of
organoboronic acids with 4-bromo-1-iodobenzene (4)
1981, 11, 513; (c) Watanabe, T.; Miyaura, N.; Suzuki, A.
Synlett 1992, 207; (d) Miyaura, N.; Suzuki, A. Chem.
Rev. 1995, 95, 2457; (e) Suzuki, A. J. Organomet. Chem.
1999, 576, 147; (f) Huth, A.; Beetz, I.; Schumann, I.
Tetrahedron 1989, 45, 6679; (g) Fu, J.-M.; Snieckus, V.
Tetrahedron Lett. 1990, 31, 1665; (h) Wallow, T. I.;
Novak, B. M. J. Org. Chem. 1994, 59, 5034.
(5)
Entry
Boronic
acids
Conditionsa Product
ratiob
Combined
yields (%)
2. (a) Mitchell, M. B.; Wallbank, P. J. Tetrahedron Lett.
1991, 32, 2273; (b) Shen, W. Tetrahedron Lett. 1997, 38,
5575.
3. Zim, D.; Monteiro, A. L.; Dupont, J. Tetrahedron Lett.
2000, 41, 8199.
4. (a) Wright, S. W.; Hageman, D. L.; McClure, L. D. J.
Org. Chem. 1994, 59, 6095; (b) Littke, A. F.; Dai, C.; Fu,
G. C. J. Am. Chem. Soc. 2000, 122, 4020.
1
2
3
4
5
2a
2b
2c
2d
2e
A
B
A
B
A
B
A
B
A
B
5a only
5a:6a=1:9
5b only
5a:6a=1:4
5c only
5a:6a=1:1
5d only
5a:6a=1:2
5e only
5a:6a=2:1
80
84
92
78
65
80
80
92
82
87
5. (a) Lipshutz, B. H.; Sclafani, J. A.; Blomgren, P. A.
Tetrahedron 2000, 56, 2139; (b) Saito, S.; Oh-tani, S.;
Miyaura, N. J. Org. Chem. 1997, 62, 8024; (c) Galland,
J.-C.; Savignac, M.; Geneˆt, J.-P. Tetrahedron Lett. 1999,
40, 2323; (d) Saito, S.; Sakai, M.; Miyaura, N. Tetra-
hedron Lett. 1996, 37, 2993; (e) Indolese, A. F. Tetra-
hedron Lett. 1997, 38, 3513; (f) Zim, D.; Lando, V. R.;
Dupont, J.; Monteiro, A. L. Org. Lett. 2001, 3, 3049; (g)
Griffiths, C.; Leadbeater, N. E. Tetrahedron Lett. 2000,
41, 2487.
6. (a) Ishiyama, T.; Miyaura, N. J. Organomet. Chem. 2000,
611, 392; (b) Ishiyama, T.; Matsuda, N.; Suzuki, A. J.
Am. Chem. Soc. 1993, 115, 11018; (c) Ishiyama, T.;
Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki, A.;
Miyaura, N. Organometallics 1996, 15, 713; (d) Iverson,
C. N.; Smith, M. R., III Organometallics 1997, 16, 2757;
(e) Marder, T. B.; Norman, N. C.; Rice, C. R. Tetra-
hedron Lett. 1998, 39, 155; (f) For catalytic additions of
B-Sn bonds to alkynes, see: Onozawa, S.; Hatanaka, Y.;
Sakakura, T.; Shimada, S.; Tanaka, M. Organometallics
1996, 15, 5450; (g) For catalytic additions of B–Si to
alkynes, see: Suginome, M.; Nakamura, H.; Ito, Y. J.
Chem. Soc., Chem. Commun. 1996, 2777.
a Conditions A: Cs2CO3 (2 equiv.), 5 mol% Pt(PPh3)4, DMF, 120°C,
24 h. Conditions B: aq. 2 M Cs2CO3 (5 equiv.), 5 mol% Pd(PPh3)4,
DMF, 50°C, 2 h.
b The ratios were determined by GC integrals.
Thus, cross-couplings of the organoboronic acids 2a–e
with 4-bromo-1-iodobenzene (4) were carried out under
both palladium- and platinum catalysis (Eq. (5), Table
3).
The present method required 3.0 equiv. of organo-
boronic acids (2a–e) and 5 mol% of the platinum catalyst.
Under these conditions, both aryl- (2a–b) and alkenyl-
boronic acids (2c–e) were cleanly cross-coupled with the
carbon–iodide bond of 4-bromo-1-iodobenzene (4) to
give 4-aryl-1-bromobenzene (5a–b) and 4-alkenyl-1-bro-
mobenzenes (5c–e) in excellent yields, respectively. On
the other hand, palladium-catalyzed cross-coupling of
organoboronic acids 2 (3 equiv.) gave a mixture of the
double-coupling products 6a–e along with the mono
coupling products 5a–e, respectively. Even use of only 1
equiv. of organoboronic acids also gave a mixture of 5
and the 6.
7. Ojima, I.; Li, Z.; Zhu, J. In The Chemistry of Organic
Silicon Compounds; Rappoport, Z.; Apeloig, Y., Eds.;
John Wiley & Sons: New York, 1998; Vol. 2, Chapter 29.
8. Kondo, T.; Tsuji, Y.; Watanabe, Y. J. Organomet. Chem.
1988, 345, 397.
In summary, we have accomplished platinum-catalyzed
reactions of aryl- or alkenylboronic acids with various
aryl iodides in DMF to give the cross-coupling products
in good to excellent yields. Especially, the present method
has shown excellent chemoselectivities in the cross-cou-
pling of 4-bromo-1-iodobenzene (4) with organoboronic
acids (2a–e) to give 4-aryl-1-bromobenzene (5a–b) and
4-alkenyl-1-bromobenzenes (5c–e) in excellent yields.
9. Brown, J. M.; Cooley, N. A.; Price, D. W. J. Chem. Soc.,
Chem. Commun. 1989, 458.
10. Kelkar, A. A. Tetrahedron Lett. 1996, 37, 8917.
11. For DMF activation by platinum compounds; see:
Bezbozhnaya, T. V.; Litvinenko, S. L.; Skripnik, S. Y.;
Zamashchikov, V. V. Russ. J. Gen. Chem. 1999, 69, 1198.
12. All products were characterized by 1H and 13C NMR
spectra and new compounds 3cb, 3df, and 5b were fully
1
characterized by H, 13C NMR, IR, and HRMS spectra.
Acknowledgements
HRMS calcd for 3cb (C15H16O) 212.1201, found
212.1191; 3df (C12H15NO2) 205.1103, found 205.1115; 5b
(C14H13Br) 260.0201, found 260.0211.
This work was supported by the research fund (HYU-99-
035) of Hanyang University, Korea.
13. A similar reaction using palladium catalysts was previ-
ously reported, where reaction conditions involving cata-
lysts and bases were proposed to affect types of products.
See: (a) Miyaura, N.; Yamada, K.; Suginome, H.; Suzuki,
A. J. Am. Chem. Soc. 1985, 107, 972; (b) Miyaura, N.;
Suzuki, A. J. Organomet. Chem. 1981, 213, C53.
References
1. (a) Suzuki, A. Pure Appl. Chem. 1991, 63, 419; (b)
Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun.