Ruthenium-catalyzed coupling reaction of benzylic halides

Article abstract of DOI:10.1081/SCC-120024745

Reported herein is a novel method on dechlorination coupling reaction of halides by using RuCl₂(PPh₃)₃ catalyst under a hydrogen atmosphere with benzene as the solvent, which affords alkanes in excellent yields.

Full text of DOI:10.1081/SCC-120024745

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Ruthenium-Catalyzed Coupling Reaction of Benzylic
Halides
Yanjun Li a & Taeko Izumi a
a Department of Chemistry and Chemical Engineering, Faculty of Engineering, Yamagata
University, Yonezawa, Japan
Published online: 15 Aug 2006.
To cite this article: Yanjun Li & Taeko Izumi (2003) Ruthenium-Catalyzed Coupling Reaction of Benzylic Halides, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:20, 3583-3588, DOI:
10.1081/SCC-120024745
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 20, pp. 3583–3588, 2003
Ruthenium-Catalyzed Coupling Reaction
of Benzylic Halides
*
Yanjun Li and Taeko Izumi
Department of Chemistry and Chemical Engineering,
Faculty of Engineering, Yamagata University,
Yonezawa, Japan
ABSTRACT
Reported herein is a novel method on dechlorination coupling reac-
tion of halides by using RuCl2(PPh3)3 catalyst under a hydrogen
atmosphere with benzene as the solvent, which affords alkanes in
excellent yields.
Key Words: Dechlorination; Coupling reaction; Radical reaction;
Ruthenium catalyst.
*Correspondence: Yanjun Li, Department of Chemistry and Chemical
Engineering, Faculty of Engineering, Yamagata University, 3-16 Jonan
4-Chome, Yonezawa, 992-8510, Japan; E-mail: tr230@dip.yz.yamagata-u.ac.jp.
3583
DOI: 10.1081/SCC-120024745
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3584
Li and Izumi
INTRODUCTION
Metal-catalyzed radical coupling reaction with olefins have been car-
ried out by utilizing metal complex catalysts[1] such as CuCl2,[2] Cu2Cl2,[3]
Fe2(CO)9,[4] and (naphthalene) Cr(CO)3.[5] Also the nickel or palladium
catalyzed cross-coupling reaction of organichalides or triflates with alkenes
(the Heck reaction),[6] organoborons (the Suzuki reaction),[7] organotins
(the Stille reaction)[8] are powerful and widely used on carbon–carbon
bond formation. In addition, low valent ruthenium complexes have
proven to be one of the effective catalysts for generating radical from
various organic halides due to their ability to promote fast electron trans-
fer.[9] However to our knowledge, dechlorination coupling reaction of
halides to afford alkanes by using ruthenium catalyst has never been
reported. Here we present a novel method on dechlorination coupling
of halides to produce alkanes induced by utilizing RuCl2(PPh3)3.
The dechlorination coupling reaction was investigated, 1,1,2,2-tetra-
phenylethane, 1,2-diphenyl-1,2-di-p-tolylethane, and 1,2-diphenyl-1,2-di-
p-bromophenylethane were prepared by using RuCl2(PPh3)3 catalyst
under a hydrogen atmosphere with benzene as the solvent in high yields
respectively (Sch. 1).
RESULTS AND DISCUSSION
Benzophenone can be reduced to diphenyl methanol in 64% yield by
formic acid with ruthenium complex RuCl2(PPh3)3 without solvent.[10]
However 1,1,2,2-tetraphenylethane 3a was obtained with benzophenone
as starting material using RuCl2(PPh3)3 in the presence of concentrated
hydrochloric acid (Entry 1). The effect of concentrated hydrochloric acid
was investigated. The results are summarized in Table 1. Just a little
change of yield was observed (Entry 2), when the quality of ruthenium
catalyst was increased. Without HCl aq. 3a was obtained in 25% low
R
O
Cl
2 steps
RuCl2(PPh3)3
solvent, 15 kg/cm2 H2
90-180 oC, 24 h
R
R
R
1
2
3
1a: R = H
1b: R = CH3
1c: R = Br
Scheme 1.

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Ruthenium-Catalyzed Coupling Reaction
3585
Table 1. Synthesis of 1,1,2,2-tetraarylethane by utilizing RuCl2(PPh3)3
complex.a
Conc. HCl
(mol%)
Sub./Ru Temp.
Solvent (mol/mol) (ꢀC)
Yieldc
(%)
Entry Ketone Halide
1
2
3
4
5
6
7
8
9b
1a
1a
1a
1a
1a
1b
1b
0.1
0.1
Toluene
Toluene
Xylene
Xylene
Xylene
Xylene
Xylene
Xylene
Xylene
Benzene
Benzene
Benzene
100
50
180
180
180
180
180
180
180
180
180
90
76
78
25
90
55
15
100
100
100
100
100
100
100
100
100
100
2a
2a
0.2
0.1
2a
2a
2a
2a
2b
2c
43 (3a)
89
—
95
96
85
10
11
12
90
90
aThe reaction was carried out in autoclave under 15 kg/cm2 of hydrogen
atmosphere for 24 h.
bWithout hydrogen atmosphere.
cIsolated yield.
yield (Entry 3). The reaction of benzophenone 1a and alpha chlorodiphe-
nylmethane 2a afforded 1,1,2,2-tetraphenylethane 3a in high yield (90%),
which was carried out using RuCl2(PPh3)3 in xylene at 180ꢀC under
15 kg/cm2 hydrogen atmosphere in the presence of 0.2 mol% concen-
trated hydrochloric acid (Entry 4). The ruthenium-catalyzed reaction of
benzophenone 1a and alpha chlorodiphenylmethane 2a afforded
1,1,2,2-tetraphenylethane 3a in 55% yield in the absence of concentrated
hydrochloric acid (Entry 5). Because concentrated hydrochloric acid can
promote the yield of diphenyl methanol in the procedure of ruthenium-
catalyzed hydrogenation of benzophenone, and then converts diphenyl
methanol into alpha chlorodiphenylmethane 2a. Until now the fact we
found that it is alpha chlorodiphenylmethane 2a that presented the prod-
uct 1,1,2,2-tetraphenylethane 3a in all case. Low conversion of 4-methyl-
benzophenone led to afford 1,2-diphenyl-1,2-di-p-tolylethane 3b in 15%
yield (Entry 6). It identifies further that alpha chlorodiohenylmethane 2a
can afford 3a in high yield (Entry 7).
On the basis of these results, the dechlorination coupling reaction of
halides (2a–b) was carried out and the results were illustrated in Table 1.
The dechlorination coupling reaction of halide 2a was performed by
using ruthenium complex RuCl2(PPh3)3 with xylene as solvent at 180ꢀC

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3586
Li and Izumi
under 15 kg/cm2 hydrogen atmosphere for 24 h, and alkane 3a was pro-
duced in 89% yield (Entry 8). In the absence of hydrogen atmosphere
ruthenium-catalyzed dechlorination coupling reaction could not carry
out under the same reaction condition (Entry 9). When benzene was
employed as solvent and the reaction temperature decreased to 90ꢀC,
1,1,2,2-tetraphenylethane 3a was obtained in 95% yield (Entry 10).
Another halide 2b was investigated under the same condition, 1,2-diphe-
nyl-1,2-di-p-tolylethane 3b was obtained in 96% yield (Entry 11). Because
so many compounds can be synthesized from bromides, 2c was employed
as substrate to challenge dechlorination coupling reaction, it afforded 3c
in 85% yield (Entry 12). These results show that without corrosive con-
centrated hydrochloric acid the dechlorination coupling reaction can also
afford tetraarylethane 3a–c in high yields.[12] The crystal structure of 3a,
3b, and 3c were rendered by using Chem 3D (Fig. 1).
As a redox transfer radical chain mechanism in ruthenium(II)-
catalyzed addition of aryl or methanesulfonyl chlorides to olefin,[11] we
speculate that the mechanism is as shown in Sch. 2. At the beginning
of the reaction, ruthenium(II) catalyst RuCl2(PPh3)3 reacts with alpha
chlorodiphenyl–methane 2a to form the diphenylmethyl radicals, RuIIICl
is yielded simultaneously which will be reduced to RuII by hydrogen
atmosphere. Finally the diphenylmethyl radicals undergo nearly diffu-
sion-controlled, radical–radical coupling to quantitatively form 1,1,2,2-
tetraphenylethane 3a.
Figure 1. Chem 3D rendering of the crystal structure of 3a, 3b, and 3c.
Cl
RuII
.
+
RuIIICl
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
.
H2
2
RuII
RuIIICl
+
HCl
Ph
Ph
Scheme 2.

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Ruthenium-Catalyzed Coupling Reaction
3587
In conclusion, tris-triphenylphosphine ruthenium(II) dichloride
RuCl2(PPh3)3 is an efficient catalyst on dechlorination coupling reaction
of halides to afford alkanes in excellent yields.
REFERENCES
1. Freidlina, R.K.; Chukovskaya, E.C. Synthesis 1974, 477.
2. Mori, Y.; Tsuji, J. Tetrahedron 1973, 29, 827.
3. Martin, P.; Greuter, H.; Bellus, D. J. Am. Chem. Soc. 1979,
101, 5853.
4. Elzinga, J.; Hogeveen, H.J. Org. Chem. 1980, 45, 3957.
5. Gandolfi, O.; Cais, M. J. Organomet. Chem. 1977, 125, 141.
6. Heck, R.F. In Comprehensive Organic Synthesis; Trost, B.M.,
Fleming, I., Eds.; Pergamon Press: New York, USA, 1991; Vol. 4,
833.
7. Oh-e, T.; Miyaura, N.; Suzuki, A. J. Org. Chem. 1993, 158, 2201.
8. Scott, W.J.; Stille, J.K. J. Am. Chem. Soc. 1986, 108, 3033.
9. Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98, 2599.
10. Watanabe, Y.; Ohta, T.; Tsuji, Y. Bull. Chem. Soc. Jpn. 1982,
55, 2441.
11. Kamigata, N.; Sawada, H.; Kobayashi, M. J. Org. Chem. 1983, 48,
3793; Kamigata, N.; Ozaki, J.; Kobayashi, M. J. Org. Chem. 1985,
50, 5045.
12. Tris-triphenylphosphine ruthenium(II) dichloride RuCl2(PPh3)3 was
prepared according to the literature procedure.[13] The solvents were
used without further purification. Melting point was determined on
a Micro capillary melting point apparatus and uncorrected.
1H NMR was recorded on Varian 500 MHz spectrometer. All reac-
tions were run in autoclave under hydrogen atmosphere (15 kg/cm2).
Alpha chlorodiohenylethane (2a, 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/cm2 hydrogen pressure at 90ꢀC stirring for
24 h. After removal of benzene, the cruel product was purified by
recrystallization with chloroform to give 1,1,2,2-tetraphenylethane
3a as a colorless needle crystal 0.78 g (95%). 3a. M.p.: 212ꢀC.
1H NMR (CDCl3, 500 MHz ) ꢀ: 4.77 (2H, s), 6.99–7.17 (20H, m).
13C NMR (CDCl3, 500 MHz) ꢀ: 57.05, 126.55, 128.84, 129.22,
144.17. IR (KBr) cmꢁ1: 3420, 3025, 3014, 1494, 1449, 1072, 746,
698, 608. 3b. M.p.: 178ꢀC. H NMR (CDCl3, 500 MHz ) ꢀ: 2.17
1
(6H, d, J ¼ 8.6 Hz), 4.72 (2H, s), 6.89–7.11 (18H, m). 13C NMR
(CDCl3, 500 MHz) ꢀ: 21.65, 56.58, 126.38, 128.82, 129.00, 129.15,

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3588
Li and Izumi
129.55, 135.83, 141.30, 144.62. IR (KBr) cmꢁ1: 3430, 3019, 2913,
1513, 1492, 1108, 1070, 788, 723, 694. 3c. M.p.: 221–222ꢀC. 1H NMR
(CDCl3, 500 MHz) ꢀ: 4.70 (2H, dd, J ¼ 20.3 Hz, J ¼ 6.3 Hz),
7.04–7.28 (18H, m). 13C NMR (CDCl3, 500 Hz) ꢀ: 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) cmꢁ1: 3060, 3023, 2890, 1489, 1448,
1072, 1008, 744, 696.
13. Hallam, P.S.; Stephenson, T.A.; Wilkinson, G. Inorg. Synth. 1972,
12, 238.
Received in Japan March 17, 2003