Palladium-iminophosphine-catalyzed homocoupling of alkynylstannanes and other organostannanes using allyl acetate or air as an oxidant

Article abstract of DOI:10.1016/S0022-328X(02)02153-8

A palladium-iminophosphine complex was found to catalyze the homocoupling reaction of alkynylstannanes using allyl acetate as an oxidant, whereas aryl- and alkenylstannanes were oxidatively homocoupled with air.

Full text of DOI:10.1016/S0022-328X(02)02153-8

Journal of Organometallic Chemistry 670 (2003) 132ꢀ136
/
www.elsevier.com/locate/jorganchem
Palladiumꢀ
/
iminophosphine-catalyzed homocoupling of
alkynylstannanes and other organostannanes using allyl acetate or air
as an oxidant
Eiji Shirakawa a,*, Yoshiaki Nakao b, Yasubumi Murota b, Tamejiro Hiyama b,*
a Graduate School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan
b Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
Received 14 October 2002; received in revised form 30 November 2002; accepted 30 November 2002
Abstract
A palladiumꢀiminophosphine complex was found to catalyze the homocoupling reaction of alkynylstannanes using allyl acetate
/
as an oxidant, whereas aryl- and alkenylstannanes were oxidatively homocoupled with air.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Oxidative homocoupling; Organostannane; Palladium; Iminophosphine
1. Introduction
ability, stability and chemoselectivity of organostan-
nanes, no method utilizes such a mild but unusual
oxidant as allyl acetate [5].
Ligands often play important roles in transition metal
catalysis. We disclosed that a palladium complex
coordinated by an iminophosphine ligand shows a
marked preference for alkynylstannanes to alter the
catalytic cycle of the palladium-catalyzed cross-coupling
reaction [1,2]. Thus, in contrast to the generally accepted
catalytic cycle for the palladium-catalyzed coupling of
organostannanes including alkynylstannanes with aryl
iodides, the one using an iminophosphine ligand starts
with the oxidative addition of an alkynylstannane to a
During our investigation of the palladiumꢀiminopho-
/
sphine-catalyzed carbostannylation of alkynes, we
found that the reaction of an alkynylstannane with allyl
propiolate gave the homocoupling product of the
alkynylstannane in addition to an addition product of
the alkynylstannane to the triple bond of allyl propio-
late. Therefore, we expected that allyl acetate, which
lacks a carbonꢀcarbon triple bond, should work effec-
/
tively as an oxidant in the homocoupling of alkynyl-
stannanes.
palladium(0) complex. The activation of carbonꢀ
/tin
bonds by a palladiumꢀiminophosphine catalyst has
/
been utilized for the addition of alkynylstannanes to
alkynes [3]. Here we report that the affinity of the
2. Results and discussion
palladiumꢀiminophosphine for alkynylstannanes en-
/
The reaction of tributyl(phenylethynyl)tin (1a) with
allyl acetate (one equivalent) in the presence of a
catalytic amount of [PdCl(h3-C3H5)]2 (2.5 mol%) and
ables the homocoupling of alkynylstannanes with a
mild oxidant such as allyl acetate and that the oxidative
homocoupling was applied also to aryl- and alkenyl-
stannanes by use of air as an oxidant [4]. Although there
have been many reports on the palladium-catalyzed
homocoupling of organostannanes owing to high avail-
N-(2-diphenylphosphinobenzylidene)aniline
(IP,
5
mol%) in DMF for 4 h at 40 8C gave 1,4-diphenyl-
1,3-butadiyne (2a) in 86% yield, whereas the cross-
coupling product (3a) of 1a with allyl acetate was not
detected (Scheme 1 and entry 1 of Table 1). Use of
triphenylphosphine (10 mol%) instead of IP drastically
retarded the reaction (entry 2), whereas the reaction
* Corresponding authors. Tel./fax: ꢁ
/
81-761511631.
E-mail address: shira@jaist.ac.jp (E. Shirakawa).
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(02)02153-8

E. Shirakawa et al. / Journal of Organometallic Chemistry 670 (2003) 132ꢀ
/
136
133
Scheme 1.
Table 1
Homocoupling of alkynylstannanes catalyzed by a palladiumꢀ
/
iminophosphine complex using allyl acetate as an oxidant
a
b
Entry
Ligand (mol%)
R1 in 1
Time (h)
Conv. (%)
Yield (%) of 2
1
2
3
4
5
6
7
IP(5)
Ph
Ph
Ph
4
4
4
1
1
1
1
ꢀ
/
99
14
60
99
99
99
99
86
c
PPh3(10)
None
IP(5)
13
11
d
4-CF3 ꢀ
4-MeOꢀ
2-CF3 ꢀC6H4
Bu
/
C6H4
ꢀ
/
92
93
90
84
IP(5)
IP(5)
/C6H4
ꢀ
/
/
ꢀ
/
IP(5)
ꢀ/
The reaction was carried out at 40 8C in DMF (2 ml) under an argon atmosphere using an alkynylstannane (0.32 mmol) and allyl acetate (0.32
mmol) in the presence of [PdCl(h3-C3H5)]2 (8.0 mmol) and IP (16 mmol).
a
Determined by 1H- and/or 119Sn-NMR.
Isolated yield based on alkynylstannane.
b
c
Cross-coupling product 3a was obtained in 1% yield.
Cross-coupling product 3a was obtained in 3% yield.
d
without any ligand gave only 11% yield of 2a, which was
accompanied by the formation of cross-coupling pro-
stannanes in the presence of a palladium catalyst in spite
that some reports on the cross-coupling of allylic
electrophiles with organostannanes are recorded in the
literature [6].
duct 3a (entry 3). The PdꢀIP catalyst was applied to the
/
homocoupling of various alkynylstannanes. Arylethy-
nylstannanes generally gave the corresponding 1,3-
diynes in good yields, irrespective of the kind of the
Unfortunately, the PdꢀIP/allyl acetate system is not
/
applicable to the homocoupling reaction of organostan-
nanes other than alkynylstannanes mainly due to the
competitive cross-coupling reaction. Aryl- and alkenyl-
stannanes, however, underwent the homocoupling reac-
substituent on the phenyl ring (entries 4ꢀ6). Tributyl(1-
/
hexyn-1-yl)tin also reacted smoothly to give 5,7-dode-
cadiyne in a good yield (entry 7).
In order to pursue how the allyl moiety changes, we
used 1,3-diphenylpropen-3-yl acetate in the homocou-
pling of tributyl[(p-trifluoromethylphenyl)ethynyl]tin
(1b) as shown in Scheme 2. The allylic acetate actually
acted as an oxidant and underwent reductive coupling to
give 1,3,4,6-tetraphenyl-1,5-hexadiene as a mixture of
diastereomers, though how they were produced is yet
unclear at present. Again, the corresponding cross-
coupling product was not detected. It is worthy of
note that allylic acetates do not couple with alkynyl-
tion with the PdꢀIP catalyst in combination with air as
/
oxidant (Scheme 3 and Table 2). For example, treatment
of tributyl(phenyl)tin in an open air with [PdCl(h3-
C3H5)]2 (1 mol%) and IP (2 mol%) in DMF for 4 h at
70 8C gave biphenyl in 66% yield (entry 1). Other aryl-
and heteroarylstannanes with an electron-withdrawing
or electron-donating substituent reacted smoothly in the
presence of the Pdꢀ
corresponding biaryls in moderate to good yields
(entries 2ꢀ10). A styrylstannane underwent the homo-
/IP catalyst in the open air to give the
/
Scheme 2.

134
E. Shirakawa et al. / Journal of Organometallic Chemistry 670 (2003) 132ꢀ136
/
resonance spectra were taken on a JEOL EX-270 (1H,
270 MHz; 31P, 109 MHz; 119Sn, 101 MHz) or Varian
Mercury 200 (1H, 200 MHz; 13C, 50.3 MHz; 19F, 188
MHz) spectrometer using tetramethylsilane (1H) as an
internal standard, and 20% trifluoroacetic acid (19F),
85% phosphoric acid (31P), and tetramethyltin (119Sn) as
external standards. High-resolution mass spectra were
obtained with a JEOL JMS-HX110A spectrometer. The
preparative recycling gel permeation chromatography
was performed with a JAI LC-908 equipped with
JAIGEL-1H and -2H columns (chloroform as an
eluent). All melting points were measured with a
Scheme 3.
Table 2
Homocoupling of organostannanes catalyzed by Pdꢀ
/
IP in an open air
Entry R2 in 4
Temperature Time
(8C)
Yield (%) of
a
5
(h)
1
2
3
4
5
6
7
8
9
Ph
4-CF3 ꢀ
4-O2Nꢀ
4-OHCꢀ
4-MeOꢀC6H4
2-NCꢀC6H4
4-HOCH2 ꢀC6H4
3-MeOCOOꢀ
70
40
50
50
70
50
70
4
66
87
84
76
81
80
75
60
60
79
68
31
34
b
/
C6H4
C6H4
C6H4
4
5
YanagimotoꢀSeisakusho Micro Melting Point appara-
/
/
tus without corrected. Elemental analyses were per-
formed at the Microanalytical Center, Kyoto
University. Following compounds were prepared ac-
cording to the corresponding literature procedure: (E)-
tributyl(2-phenylethenyl)tin [7], tributyl(phenylethy-
nyl)tin [8], tributyl(1-hexyn-1-yl)tin [9], tributyl[4-(tri-
fluoromethyl)phenyl]tin [10], tributyl(4-nitrophenyl)tin
[11], tributyl(4-formylphenyl)tin [12], tributyl(4-methox-
yphenyl)tin [13], tributyl[4-(hydroxymethyl)phenyl]tin
[14], 2-(tributylstannyl)thiophene [15]. Other alkynyl-
stannanes were prepared according to the literature
procedure [16].
/
36
102
44
10
/
/
/
/
C6H4 50
2.5
2-thienyl
2-pyridyl
50
70
50
50
50
53
72
4
10
11
12
13
c
(E)-PhCHÄ
PhCÅ
BuCÅ
/
CH
/
C
6
/
C
11
The reaction was carried out in DMF (2 ml) in an open air using an
organostannane (0.80 mmol) in the presence of [PdCl(h3-C3H5)]2 (8.0
mmol) and IP (16 mmol).
Isolated yield based on organostannane.
a
b
With 5 mol% of Pdꢀ
/IP.
4.2. Preparation of N-(2-
diphenylphosphinobenzylidene)aniline (IP) [17]
c
(E,E)-1,4-Diphenyl-1,3-butadiene was obtained.
A mixture of 2-diphenylphosphinobenzaldehyde [18]
(0.50 g, 1.72 mmol) and aniline (166 mg, 1.78 mmol) in
toluene (15 ml) was stirred at a reflux temperature for 19
h. The mixture was concentrated under a reduced
pressure, and the residue was treated with hexane (20
ml). Filtration of insoluble material gave IP (0.62 g, 99%
coupling, retaining their configuration (entry 11). On the
other hand, the yields of homocoupling products of
alkynylstannanes were much lower than those using allyl
acetate (entries 12 and 13).
yield) as a light yellow solid: m.p. 109ꢀ
NMR (CDCl3) d 6.86ꢀ6.98 (m, 3H), 7.10ꢀ
15H), 8.16ꢀ8.25 (m, 1H), 9.07 (d, Jꢂ5.2 Hz, 1H);
31P{1H}-NMR (CDCl3) d ꢃ
12.7; Anal. Calc. for
/
112 8C; 1H-
7.50 (m,
3. Conclusion
/
/
/
/
We have demonstrated that the palladiumꢀiminopho-
/
/
sphine complex is an effective catalyst for the oxidative
homocoupling of organostannanes, where allyl acetate
and air complementarily work as an oxidant: the former
is effective for alkynylstannanes and the latter for aryl-
and alkenylstannanes.
C25H20NP: C, 82.17; H, 5.52; N, 3.83. Found: C,
82.07; H, 5.69; N, 3.58.
4.3. Preparation of tributyl(2-cyanophenyl)tin
A 1.67 M hexane solution of BuLi (20 ml, 33 mmol)
was added dropwise to a solution of 2-bromobenzoni-
4. Experimental
trile (6.6 g, 36 mmol) in THF (30 ml) at ꢃ
the mixture was stirred at ꢃ78 8C for 1 h. To the
mixture was added tributyltin chloride (9.1 g, 28 mmol)
at ꢃ78 8C and the temperature was allowed to rise
/
78 8C, and
/
4.1. General remarks
/
All manipulations of oxygen- and moisture-sensitive
materials were conducted with the standard Schlenk
techniques under a purified argon atmosphere (deox-
ygenated by passing through BASF-Catalyst R3-11
column at 80 8C). Silica gel column chromatography
was performed using Wakogel C-200. Nuclear magnetic
gradually up to room temperature. After 12 h, the
mixture was poured into water (50 ml) and extracted
with diethyl ether (150 mlꢄ2). The combined organic
/
layer was washed successively with water (50 ml) and
brine (50 ml), and dried over anhydrous magnesium
sulfate. Evaporation of the solvent was followed by

E. Shirakawa et al. / Journal of Organometallic Chemistry 670 (2003) 132ꢀ
/
136
135
silica gel column chromatography (hexane/ethyl acet-
ateꢂ98/2) to give tributyl(2-cyanophenyl)tin (3.0 g,
27% yield) as a colorless oil: 1H-NMR (CDCl3) d
0.82ꢀ1.78 (m, 27H), 7.31ꢀ7.42 (m, 1H), 7.43ꢀ7.58 (m,
2H), 7.59ꢀ7.71 (m, 1H). Anal. Calc. for C19H31NSn: C,
(10 ml), drying the organic layer over anhydrous
magnesium sulfate, and evaporation, followed by gel
permeation chromatography, gave the corresponding
coupling product. The results are summarized in Table
1.
/
/
/
/
/
58.19; H, 7.97; N, 3.57. Found: C, 58.00; H, 8.02; N,
3.43.
All of the products listed in Table 1 have already been
reported in the literature. Their spectroscopic data are as
follows.
4.4. Preparation of tributyl(3-
methoxycarbonyloxyphenyl)tin
1,4-Diphenyl-1,3-butadiyne [20]: 1H-NMR (CDCl3) d
7.30ꢀ
1,4-Bis(4-trifluoromethylphenyl)-1,3-butadiyne [21]:
1H-NMR (CDCl3) d 7.50ꢀ
7.80 (m).
1,4-Bis(4-methoxyphenyl)-1,3-butadiyne [22]: 1H-
NMR (CDCl3) d 3.82 (m, 6H), 6.80ꢀ6.93 (m, 4H),
7.41ꢀ7.53 (m, 4H).
1,4-Bis(2-trifluoromethylphenyl)-1,3-butadiyne [23]:
1H-NMR (CDCl3) d 7.40ꢀ
7.90 (m).
5,7-Dodecadiyne [21]: H-NMR (CDCl3) d 1.17 (t,
Jꢂ7.0 Hz, 6H), 1.20ꢀ1.85 (m, 8H), 2.52 (t, Jꢂ6.3
Hz, 4H).
/
7.40 (m, 6H), 7.49ꢀ/7.58 (m, 4H).
To a 1.0 M THF solution of Bu4NF (6.5 ml, 6.5
mmol) was added tributyl[3-tert-butyl(dimethyl)silylox-
yphenyl]tin [19] (1.63 g, 3.28 mmol), and the mixture
was stirred at room temperature. After 1 h, the mixture
was poured into a saturated NH4Cl aqueous solution
/
/
/
(16 ml) and extracted with ethyl acetate (50 mlꢄ2). The
/
/
combined organic layer was washed successively with
water (30 ml) and brine (30 ml), and dried over
anhydrous magnesium sulfate. Evaporation of the
solvent was followed by silica gel column chromatogra-
1
/
/
/
phy (hexane/ethyl acetateꢂ/20/1) to give tributyl(3-
hydroxyphenyl)tin (0.78 g, 62% yield) as a colorless
1
4.6. General procedure for the Pdꢀ
homocoupling of organostannanes using air
/
IP-catalyzed
oil: H-NMR (CDCl3) d 0.82ꢀ
/
1.72 (m, 27H), 5.62 (s,
1H), 6.73ꢀ6.80 (m, 1H), 6.90ꢀ7.28 (m, 3H). Anal. Calc.
/
/
for C18H32OSn: C, 56.42; H, 8.42. Found: C, 56.19; H,
8.45.
An organostannane (0.80 mmol) was added to a
solution of IP (6.0 mg, 16 mmol) and [PdCl(h3-C3H5)]2
(3.0 mg, 8.0 mmol) in DMF (2 ml), and the resulting
mixture was stirred at the temperature for the time both
indicated in Table 2. Quenching with water (10 ml),
A solution of tributyl(3-hydroxyphenyl)tin (3.5 g, 0.92
mmol) in THF (2 ml) was added to a suspension of NaH
(60% dispersion in mineral oil, 40 mg, 1.0 mmol) in THF
(2 ml) at 0 8C, and the mixture was stirred for 0.5 h at
room temperature. To this solution was added methyl
chloroformate (95 mg. 1.0 mmol), and the resulting
mixture was stirred overnight. The mixture was poured
into a saturated NH4Cl aqueous solution (3 ml), and
extraction with ethyl acetate (30 mlꢄ2), washing the
/
combined organic layer with water (10 ml) and brine (10
ml), drying the organic layer over anhydrous magnesium
sulfate, and evaporation, followed by gel permeation
chromatography, gave the corresponding coupling pro-
duct. The yields are listed in Table 2.
extracted with ethyl acetate (10 mlꢄ2). The combined
/
organic layer was washed with water (5 ml) and brine (5
ml), and dried over anhydrous magnesium sulfate.
Evaporation of the solvent was followed by silica gel
3,3?-Bis(methoxycarbonyloxy)biphenyl: A pale yel-
1
low oil, H-NMR (CDCl3) d 3.92 (s, 6H), 7.13ꢀ
/
7.24
7.53 (m, 6H); 13C-NMR (CDCl3) d
55.4, 119.8, 120.3, 124.8, 129.9, 141.7, 151.5, 154.2;
HRMS (FABꢁ H,
) Calc. for C16H15O6: Mꢁꢁ
303.0868. Found: m/z 303.0865.
column chromatography (hexane/ethyl acetateꢂ10/1)
/
(m, 2H), 7.36ꢀ
/
to give tributyl(3-methoxycarbonyloxyphenyl)tin (0.34
1
g, 84% yield) as a colorless oil: H-NMR (CDCl3) d
/
/
0.81ꢀ
7.18ꢀ
54.45; H, 7.77. Found: C, 54.68; H, 8.05.
/
1.75 (m, 27H), 3.91 (s, 3H), 7.04ꢀ
/
7.18 (m, 1H),
/7.45 (m, 3H). Anal. Calc. for C20H34O3Sn: C,
Other products listed in Table 2 have already been
reported in the literature. Their spectroscopic data are as
follows.
4.5. General procedure for the PdꢀIP-catalyzed
/
homocoupling of alkynylstannanes using allyl acetate
Biphenyl: 1H-NMR (CDCl3) d 7.29ꢀ
7.55ꢀ7.65 (m, 4H).
4,4?-Dinitrobiphenyl: m.p. 238ꢀ
244 8C); 1H-NMR (CDCl3) d 7.72ꢀ
8.30ꢀ8.42 (m, 4H).
4,4?-Diformylbiphenyl: m.p. 144ꢀ
145 8C); 1H-NMR (CDCl3) d 7.78ꢀ
7.98ꢀ8.03 (m, 4H), 10.10 (s, 2H).
/
7.51 (m, 6H),
An alkynylstannane (0.32 mmol) was added to a
solution of allyl acetate (0.32 mmol), IP (6.0 mg, 16
mmol) and [PdCl(h3-C3H5)]2 (3.0 mg, 8.0 mmol) in DMF
(2 ml), and the resulting mixture was stirred at 40 8C for
the time depicted in Table 1. Quenching with water (10
ml), extraction with diethyl ether (30 ml), washing the
/
/
240 8C ([24], 241ꢀ
/
/
7.83 (m, 4H),
/
/
146 8C ([25],
7.84 (m, 4H),
/
combined organic layer with water (10 mlꢄ
/
3) and brine
/

136
E. Shirakawa et al. / Journal of Organometallic Chemistry 670 (2003) 132ꢀ136
/
4,4?-Dimethoxybiphenyl [26]: 1H-NMR (CDCl3) d
3.84 (s, 6H), 6.91ꢀ7.02 (m, 4H), 7.42ꢀ7.54 (m, 4H).
2,2?-Dicyanobiphenyl [27]: 1H-NMR (CDCl3) d 7.53ꢀ
7.62 (m, 4H), 7.69ꢀ7.77 (m, 2H), 7.81ꢀ7.87 (m, 2H).
4,4?-Bis(hydroxymethyl)biphenyl: m.p. 193ꢀ194 8C
189 8C); H-NMR (CDCl3) d 4.75 (brs,
7.51 (m, 4H), 7.56ꢀ7.65 (m, 4H).
2,2?-Bithiophene [29]: H-NMR (CDCl3) d 6.96ꢀ
(m, 2H), 7.14ꢀ7.28 (m, 4H).
2,2?-Bipyridine: 1H-NMR (CDCl3) d 7.27ꢀ
2H), 7.77ꢀ7.89 (m, 2H), 8.36ꢀ8.45 (m, 2H), 8.66ꢀ
8.74 (m, 2H).
(E,E)-1,4-Diphenylbutadiene: 1H-NMR (CDCl3) d
6.52ꢀ6.75 (m, 2H), 6.80ꢀ7.05 (m, 2H), 7.15ꢀ7.52 (m,
10H).
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/
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([28], 188ꢀ
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4H), 7.41ꢀ
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1
/
7.06
/
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/
7.37 (m,
/
/
/
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/
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