Ruthenium-catalyzed carbon-carbon formation to synthesize tetraarylethanes and tetraarylxylylene through dechlorinative dimeric reaction

Article abstract of DOI:10.1016/j.jorganchem.2003.08.019

Dechlorinative coupling-dimerization reaction is studied to synthesize alkanes by using tris-triphenylphosphine ruthenium (II) in the presence of hydrogen atmosphere. Two types of halides (α-chlorodiarylmethanes 1a-d and bis(chlorophenylmethyl)-1, 3-phenylene 6) are employed as substrates to form radical species and then dimerized to generate alkanes in high yields. To our knowledge, it is the first time that the formation of 1,1,2,2-tetraarylethanes and 1,2,9,10-tetraphenyl-di- m -xylylene over typical ruthenium-catalyzed dehalogenative coupling-dimerization conditions is reported.

Full text of DOI:10.1016/j.jorganchem.2003.08.019

Journal of Organometallic Chemistry 687 (2003) 12ꢀ15
/
www.elsevier.com/locate/jorganchem
Ruthenium-catalyzed carbonꢀ
/
carbon formation to synthesize
tetraarylethanes and tetraarylxylylene through dechlorinative dimeric
reaction
Yanjun Li *, Tatsuro Kijima, Taeko Izumi
Department of Chemistry and Chemical Engineering, Faculty of Engineering, Yamagata University, 3-16 Jonan 4-Chome, Yonezawa 992-8510, Japan
Received 26 June 2003; received in revised form 30 July 2003; accepted 6 August 2003
Abstract
Dechlorinative couplingꢀ
the presence of hydrogen atmosphere. Two types of halides (a-chlorodiarylmethanes 1aꢀ
/
dimerization reaction is studied to synthesize alkanes by using tris-triphenylphosphine ruthenium (II) in
d and bis(chlorophenylmethyl)-1,3-
/
phenylene 6) are employed as substrates to form radical species and then dimerized to generate alkanes in high yields. To our
knowledge, it is the first time that the formation of 1,1,2,2-tetraarylethanes and 1,2,9,10-tetraphenyl-di-m-xylylene over typical
ruthenium-catalyzed dehalogenative couplingꢀ/dimerization conditions is reported.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Dechlorination; Radical reaction; Couplingꢀdimerization; Ruthenium catalyst
/
1. Introduction
been reported. Although Sawamoto et al. [5] described
the generation of radical species R+ via the reaction of
1a with ruthenium complex RuCl2(PPh3)3 in living
radical polymerizations, it is called Kharasch [6] or
atom-transfer radical addition reactions in organic
chemistry. We focus on the dehalogenation dimerization
The Ullmann reaction [1], initially reported in 1901,
illustrated dechlorinative coupling-dimerization reac-
tions of aryl halides to generate a CꢀC bond between
/
two aromatic nuclei. Considerable improvements have
been made through the last century, Sessler et al. [2]
developed an efficient procedure for the preparation of
alkyl-substituted 2,2?-bipyrroles through dechlorination
symmetrical coupling reaction. Liebeskind et al. [3]
reported a CuTC-mediated Ullmann-reductive coupling
of substituted aromatic iodides and bromides, 2-iodo-
heteroaromatics, at room temperature. As already
mentioned, Kende et al. [4] reported a simple method
to generate in situ tris(triphenylphosphine)nickel(0), the
reactive species undergoing further oxidative additions
with aryl halides. Ruthenium complex catalyzed de-
of halides (1aꢀd and 6) by using ruthenium complex
/
RuCl2(PPh3)3 in the presence of hydrogen atmosphere.
Herein we report the synthesis of 1,1,2,2-tetraary-
lethanes (2aꢀd) and 1,2,9,10-tetraphenyl-di-m-xylylene
/
(1,2,9,10-TPDX, 9) using ruthenium-catalyzed dechor-
inative dimeric reaction.
chlorination couplingꢀdimerization reaction has never
/
* Corresponding author. Tel.: ꢁ
3413.
E-mail address: tr230@dip.yz.yamagata-u.ac.jp (Y. Li).
/
81-23-826-3126; fax: ꢁ81-23-826-
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.08.019

Y. Li et al. / Journal of Organometallic Chemistry 687 (2003) 12ꢀ
/15
13
Table 1
Ruthenium-catalyzed dechlorination coupling reaction of halides (1aꢀ
/
d)a
Entry
Substrate
R1
R2
Solvent
Temperature (8C)
Yieldb (%)
1
1a
1a
1b
1c
1d
H
H
Xylene
180
90
89
95
96
85
86
2
H
H
Benzene
Benzene
Benzene
Benzene
3
Me
Br
H
90
90
4
5c
H
OMe
OMe
90
a
All reactions were carried out in the autoclave under 15 kg cmꢂ2 for 24 h, the mole ratio of substrate and catalyst was 100, except for Entry 5.
Isolated yields.
The mole ratio of substrate and catalyst was 50.
b
c
Table 2
Effect of free radical inhibitors in the Ru(II)-catalyzed reaction of a-
chlorodiphenylmethanea
Entry
Radical inhibitor
Yieldb (%)
1
2
3
4
5
None
95
90
61
24
78
p-Benzoquinone (0.3%)
p-Benzoquinone (0.5%)
p-Benzoquinone (1.0%)
Galvinoxyl (0.3%)
Scheme 1.
a
All reactions were carried out in autoclave under 15 kg cmꢂ2, at
90 8C for 24 h.
Dechlorination coupling reaction of bromide 1c was
carried out, which afforded product 2c in 85% (Entry 4).
4,4?-Dimethoxybenzhydrylchloride 1d was practiced,
when the mole ratio of substrate 1d and ruthenium
catalyst was 100, it afforded 2d in 56% yield and 40% of
starting material was recovered. When the mole ratio
was changed to 50, the product 2d was obtained in 86%
yield (Entry 5) (Table 1).
b
Isolated yields.
2. Results and discussion
2.1. Ruthenium-catalyzed dechlorination coupling of
halides
The reaction of a-chlorodiphenylmethane was carried
out in benzene, using ruthenium (II) complex
RuCl2(PPh3)3 as a catalyst, by heating the reaction
mixture at 90 8C, for 24 h in the autoclave. In the
absence of the hydrogen atmosphere, no reaction was
observed, and all the starting material was recovered. In
the absence of RuCl2(PPh3)3 the reaction could not
performed. Roberge et al. [7] gave an example about the
formation of 4,4?-dimethylbiphenyl though dehalogena-
tion under 101 kPa hydrogen, however in this case
Ru(1%)/silica was employed as a catalyst, and the yield
was too low. Therefore all the reactions were carried out
using RuCl2(PPh3)3 under 15 kg cmꢂ2 hydrogen atmo-
sphere, and the results were shown in Table 1. The
dechlorination coupling reaction of halide 1a was
performed by using ruthenium complex RuCl2(PPh3)3
with xylene as solvent at 180 8C under 15 kg cmꢂ2
hydrogen atmosphere for 24 h, and alkane 2a was
produced in 89% yield (Entry 1). When benzene was
employed as solvent and the reaction temperature
decreased to 90 8C, 1,1,2,2-tetraphenylethane 2a was
obtained in 95% yield (Entry 2). Another halide 1b was
investigated under the same condition, 1,2-diphenyl-1,2-
di-p-tolylethane 2b was obtained in 96% yield (Entry 3).
One plausible reaction mechanism for the ruthenium
(II)-catalyzed reaction involves a free-radical, redox-
transfer chain process (Scheme 1).
In Scheme 1, the ruthenium catalyst RuCl2(PPh3)3
first abstracts a chlorine atom from a-chlorodiaryl-
methane to give a diarylmethane radical 3 and the Ru
(III) species 4 (eq 1). In the second step, the Ru (III)
species 4 is hydrogenated by hydrogen atmosphere to
regenerate the ruthenium (II) catalyst (eq 2). Finally the
diarylmethane radicals undergo nearly diffusion con-
trolled, radicalꢀradical coupling to quantitatively form
/
tetraarylethane 2 (eq 3).
Inhibitors can stop every radical and radical reaction
is completely halted until they are consumed [8]. The
effect of free-radical inhibitors was also studied and the
results were shown in Table 2. When 0.3% mol of p-
benzoquinone employed as an inhibitor was added, the
yield of 1,1,2,2-tetraphenylethane (2a) was affected to
only a small extent. However, addition of 0.5% mol and
1.0% mol of p-benzoquinone led to a definite reduction
in yields of 2a. Another inhibitor, galvinoxyl (0.3% mol)
afforded 2a in 78% yield. All these results support the
free-radical mechanism of Scheme 1.

14
Y. Li et al. / Journal of Organometallic Chemistry 687 (2003) 12ꢀ15
/
2.2. Didechlorination coupling reactions
4. Experimental
In order to popularize and apply this novel method of
4.1. General considerations
carbonꢀ
/
carbon formation, the dechlorinative couplingꢀ
/
Tris-triphenylphosphine ruthenium (II) dichloride
RuCl2(PPh3)3 was prepared according to the literature
procedure [9]. The solvents were used without further
purification. Melting point was determined on a Micro
dimerization reaction of 1,2-dichloro-1,2-dipheny-
lethane 5 and 1,3-dichlorobenzylbenzene 6 have been
carried out using ruthenium catalyst RuCl2(PPh3)3 in
the presence of hydrogen atmosphere. Herein these
experimental results are reported.
1
capillary melting point apparatus and uncorrected. H-
NMR and 13C-NMR were recorded on Varian 500 MHz
spectrometer. IR spectra were recorded on a Horiba FT-
710 infrared spectrophotometer as KBr pellets. Mass
spectra were performed with a Hitachi RMU-6M mass
spectrograph. All reactions were run in autoclave under
hydrogen atmosphere (15 kg cmꢂ2).
4.2. Synthesis of 1,1,2,2-tetraarylethanes
Alpha chlorodiphenylethane (1a, 1.0 g, 5.0 mmol),
RuCl2(PPh3)3 (0.049 g, 0.05 mmol) and benzene (20 ml)
were added to autoclave (100 ml), under 15 kg cmꢂ2
hydrogen pressure at 90 8C stirring for 24 h. After
removal of benzene, the cruel product was purified by
recrystallization with chloroform to give 1,1,2,2-tetra-
phenylethane 2a as a colorless needle crystal 0.78 g
(95%).
The reaction of 1,2-dichloro-1,2-diphenylethane 5 was
carried out in benzene using ruthenium (II) complex
RuCl2(PPh3)3 as a catalyst under 15 kg cmꢂ2 hydrogen
atmosphere at 90 8C for 24 h. After purification, trans-
1,2-diphenylethylene 8 was obtained in 70% yield, but
no 1,2,3,4-tetraphenylcyclobutane 7 at all could be
detected by NMR and MS. These results show that
adjacent chlorine contained compound 5 can practice
4.2.1. 2a
M.p.: 211ꢀ
MHz) d: 4.77 (2H, s), 6.99ꢀ
(CDCl3, 500 MHz) d: 57.05, 126.55, 128.84, 129.22,
144.17. IR (KBr) cmꢂ1: 3420, 3025, 3014, 1494, 1449,
1072, 746, 698, 608.
/
212 8C (lit. 211 8C). 1H-NMR (CDCl3, 500
7.17 (20H, m). 13C-NMR
/
4.2.2. 2b
M.p.: 178ꢀ
2.17 (6H, d, Jꢃ
dechlorination reaction, but couplingꢀdimerization re-
/
1
/
179 8C. H-NMR (CDCl3, 500 MHz) d:
action is never practiced in this case. In addition, under
the same reaction condition, ruthenium-catalyzed de-
chlorination coupling reaction of bis(chlorophenyl-
/
8.6 Hz), 4.72 (2H, s), 6.89ꢀ7.11 (18H,
/
m). 13C-NMR (CDCl3, 500 MHz) d: 21.65, 56.58,
126.38, 128.82, 129.00, 129.15, 129.55, 135.83, 141.30,
144.62. (KBr) cmꢂ1: 3430, 3019, 2913, 1513, 1492, 1108,
1070, 788, 723, 694. Anal. Calc. for C28H26: C, 92.77; H,
7.23. Found: C, 92.17; H, 7.23%.
methyl)-1,3-phenylene
afforded compound 1,2,9,10-TPDX, 9 in 80% yield.
6
was performed, which
4.2.3. 2c
M.p.: 221ꢀ
1
3. Conclusion
/
222 8C. H-NMR (CDCl3, 500 MHz) d:
4.70 (2H, dd, Jꢃ
/
20.3 Hz, Jꢃ
/
6.3 Hz), 7.04ꢀ7.28 (18H,
/
m). 13C-NMR (CDCl3, 500 MHz) d: 57.04, 126.55,
126.68, 128.85, 128.98, 129.05, 129.13, 129.22, 130.92,
131.96, 142.92, 144.17. IR (KBr) cmꢂ1: 3060, 3023,
2890, 1489, 1448, 1072, 1008, 744, 696. Anal. Calc. for
C26H26Br2: C, 63.44; H, 4.10. Found: C, 63.85; H,
4.21%.
We have described that dechlorination of halides (1aꢀ
/
d), 1,2-dichloro-1,2-diphenylethane 5 and bis-(chloro-
phenylmethyl)-1,3-phenylene
6
catalyzed
by
RuCl2(PPh3)3 lead to radical coupling reaction. The
ruthenium complex RuCl2(PPh3)3 is found to be an
efficient catalyst on dechlorination couplingꢀ
tion reaction, which affords a novel significant method
of carbonꢀcarbon formation. Numerous benzylic ha-
/dimeriza-
/
4.2.4. 2d
1
lides have successfully been converted to the corre-
sponding alkanes in high yields.
M.p.: 192ꢀ
/
193 8C. H-NMR (CDCl3, 500 MHz) d:
3.69 (12H, s), 4.57 (2H, s), 6.64 (8H, d, Jꢃ7.7 Hz), 7.02
/

Y. Li et al. / Journal of Organometallic Chemistry 687 (2003) 12ꢀ
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15
(8H, d, Jꢃ
/
7.7 Hz). 13C-NMR (CDCl3, 500 MHz) d:
References
55.64, 55.77, 114.20, 129.99, 137.03, 158.07. IR (KBr)
cmꢂ1: 3534, 3029, 2929, 2834, 1608, 1509, 1249, 1172,
1035, 809, 767. Anal. Calc. for C30H30O4: C, 79.37; H,
6.65. Found: C, 79.01; H, 6.61%.
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(b) P.E. Fanta, Synthesis 1 (1974) 9;
(c) G. Bringmann, R. Walter, R. Weirich, Angew. Chem. Int. Ed.
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[2] J.L. Sessler, M.C. Hoehner, Synlett 3 (1994) 211.
[3] S. Zhang, D. Zhang, L.S. Liebeskind, J. Org. Chem. 62 (1997)
2312.
4.3. Synthesis of 1,2,9,10-tetraphenyl-di-m-xylylene (9)
[4] A.S. Kende, L.S. Liebeskind, D.M. Braitsch, Tetrahedron Lett.
(1975) 3375.
Bis(chlorophenylmethyl)-1,3-phenylene (6, 1.0 g, 3.1
mmol), RuCl2(PPh3)3 (0.06 g, 0.031 mmol) and benzene
(20 ml) were added to autoclave (100 ml), under 15 kg
cmꢂ2 hydrogen pressure at 90 8C stirring for 24 h. After
removal of benzene, the cruel product was purified by
recrystallization with chloroform to give 1,2,9,10-tetra-
phenyl-di-m-xylylene (9) as a colorless solid 0.63 g
(80%).
[5] (a) M. Kato, M. Kamigaito, M. Sawamoto, T. Higashimura,
Polym. Prepr. Jpn. 43 (1994) 1792;
(b) M. Kato, M. Kamigaito, M. Sawamoto, T. Higashimura,
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Organic Synthesis, vol. 4, Pergamon, Oxford, UK, 1991, p. 715;
(b) J. Iqbal, B. Bhatia, N.K. Nayyar, Chem. Rev. 94 (1994) 519.
4.3.1. 1,2,9,10-tetraphenyl-di-m-xylylene (9)
Column chromatography (SiO2, Chloroform); m.p.:
[7] D.M. Roberge, W.F. Holderich, Appl. Catal. A 194ꢀ
/
195 (2000)
341.
[8] (a) W.T. Anderson, Jr., H.S. Taylor, J. Am. Chem. Soc. 45 (1923)
190ꢀ192 8C. MS/FAB (70 eV), m/z (relative intensity)
/
650;
512 (6.5), 345 (13.5), 256 (37.0), 165 (100.0), 91 (60.0), 77
1
(13.0). H-NMR (CDCl3, 500 MHz) d: 4.33 (4H, s),
(b) H.S. Taylor, A.A. Vernon, J. Am. Chem. Soc. 53 (1931) 2527.
[9] P.S. Hallam, T.A. Stephenson, G. Wilkinson, Inorg. Synth. 12
(1972) 238.
6.43ꢀ
7.20 (28H, m). 13C-NMR (CDCl3, 500 MHz) d:
/
56.72, 126.25, 127.26, 128.55, 129.19, 144.15. IR (KBr)
cmꢂ1: 3083, 3023, 1598, 775, 754, 698, 678. Anal. Calc.
for C40H32: C, 93.71; H, 6.29. Found: C, 93.31; H,
6.38%.