Rhodium-catalyzed reaction of 1-alkynylphosphines with water yielding (E')-l-alkenylphosphine oxides

Article abstract of DOI:10.1246/bcsj.81.502

Treatment of 1-alkynylphosphines with a rhodium catalyst in l,4-dioxane/H₂0 at reflux provides (E)-1 -alkenyl-phosphine oxides in good yields with perfect stereoselectivity. The reaction proceeds as follows. Oxidative addition of 1 -alkynylphosphine to rhodium followed by hydrolysis yields the corresponding terminal alkyne and diphenylphos-phine oxide. Rhodium-catalyzed hydrophosphinylation of the terminal alkyne then proceeds to afford (E)-1 -alkenylphosphine oxide.

Full text of DOI:10.1246/bcsj.81.502

502 Bull. Chem. Soc. Jpn. Vol. 81, No. 4, 502–505 (2008)
Ó 2008 The Chemical Society of Japan
Rhodium-Catalyzed Reaction of 1-Alkynylphosphines with
Water Yielding (E)-1-Alkenylphosphine Oxides
ꢀ
ꢀ
Azusa Kondoh, Hideki Yorimitsu, and Koichiro Oshima
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510
Received November 19, 2007; E-mail: yori@orgrxn.mbox.media.kyoto-u.ac.jp
Treatment of 1-alkynylphosphines with a rhodium catalyst in 1,4-dioxane/H2O at reflux provides (E)-1-alkenyl-
phosphine oxides in good yields with perfect stereoselectivity. The reaction proceeds as follows. Oxidative addition
of 1-alkynylphosphine to rhodium followed by hydrolysis yields the corresponding terminal alkyne and diphenylphos-
phine oxide. Rhodium-catalyzed hydrophosphinylation of the terminal alkyne then proceeds to afford (E)-1-alkenylphos-
phine oxide.
We have been interested in the use of 1-alkynylphosphines
as precursors of new phosphines.1 Here, we report a new trans-
formation of 1-alkynylphosphines. 1-Alkynylphosphines react
with water in the presence of a rhodium catalyst to provide the
corresponding (E)-1-alkenylphosphine oxides2 with perfect
stereoselectivity. This is an interesting formal hydration reac-
tion of 1-alkynylphosphines from mechanistic and synthetic
points of view.
(cod)]2 catalysis in 1,4-dioxane/H2O (10/1) at reflux provided
(E)-1-octenyldiphenylphosphine oxide (2a) in 84% NMR yield
and 73% isolated yield (Table 1, Entry 1). Other rhodium
complexes such as [Rh(OH)(cod)]2 also showed catalytic ac-
tivity (Entry 2). Addition of PPh3 (2 mol. amt. to Rh) as a li-
gand had no effect on the reaction (Entry 3). In contrast, when
BINAP (1 mol. amt. to Rh) or P(OEt)3 (2 mol. amt. to Rh) was
used instead of PPh3, the reaction was completely inhibited
(Entries 4 and 5). Rh(acac)3 and an iridium catalyst, [IrCl-
(cod)]2, were inactive (Entries 6 and 7).
Results and Discussion
Treatment of 1-octynyldiphenylphosphine (1a) under [RhCl-
1,4-Dioxane/H2O was the choice of solvent. Although the
Table 1. Optimization of Reaction Conditions
0.015 mol. amt. catalyst
additive
n-C6H13
H
n-C6H13 C C PPh2
solvent / H2O =10 / 1
H
PPh2
1a
reflux, 3 h
O
2a
Entry
Catalyst
Additive
Solventf)
Yielda)/%
1
2
3
4
5
6
7
8
9
10
11
12d)
13e)
[RhCl(cod)]2
[Rh(OH)(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
Rh(acac)3
None
None
PPh3
BINAPc)
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Tolueneg)
THF
CH3CN
ClCH2CH2Clg)
1,4-Dioxane
1,4-Dioxane
84 (73)
75
85
0
0
0
0
0–84
0
0
0
0
0–84
b)
b)
P(OEt)3
None
None
None
None
None
None
None
None
[IrCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
[RhCl(cod)]2
a) Based on 31P NMR with a sufficient first decay period. Isolated yields
are in parentheses. b) 2 mol. amt. to Rh. c) 1 mol. amt. to Rh. d) The reac-
tion was performed without H2O. e) The reaction was performed with H2O
(3 mol. amt. to 1a). f) The reaction is homogeneous unless otherwise noted.
g) The reaction proceeded in a two-phase medium.
Published on the web April 10, 2008; doi:10.1246/bcsj.81.502

A. Kondoh et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
503
Table 2. Synthesis of (E)-1-Alkenylphosphine Oxidea)
MeO
R
H
0.015 mol. amt. [RhCl(cod)]2
R C C PPh2
C
1,4-Dioxane / H2O =10 / 1
reflux
H
PPh2
C
1f
PPh2
1
O
2
0.25 mmol
[RhCl(cod)]2
(0.0075 mmol)
R
Yieldb)/%
Time/h
1,4-Dioxane / H2O
=10 / 1
n-C6H13
C
Ph (1b)
i-Pr (1c)
t-Bu (1d)
72
69
0
6
8
8
C
reflux, 14 h
P
o-MeOC6H4 (1e)
p-MeOC6H4 (1f)
p-AcC6H4 (1g)
2-Pyridyl (1h)
PhCH(OH) (1i)
72
75
62
0
21
7
5
12
12
1j
0.25 mmol
MeO
ð2Þ
0
n-C6H13
H
P
a) Reaction conditions: 1 (0.50 mmol), [RhCl(cod)]2 (0.0075
mmol), 1,4-dioxane (3 mL), H2O (0.30 mL). b) Isolated yields.
H
H
O
H
PPh2
O
2f
0.11 mmol
2j
reaction proceeded in a toluene/H2O mixed solvent, the
reaction suffered from poor reproducibility (Entry 8). When
toluene was used, the reaction proceeded in a two-phase medi-
um. The erratic amount of water in the nonpolar organic phase
would be responsible for the poor reproducibility. When THF
or acetonitrile was used instead of 1,4-dioxane, the reaction
did not proceed, albeit the reaction is homogeneous (Entries
9 and 10). The reaction in a 1,2-dichloroethane/H2O biphasic
medium failed, probably because of the highly hydrophobic
nature of 1,2-dichloroethane (Entry 11). The use of 1,4-di-
oxane without H2O resulted in complete recovery of 1a
(Entry 12). When the amount of H2O was reduced to three
molar amounts to the alkynylphosphine, poor reproducibility
was observed (Entry 13). The amount of water in the organic
phase is the key for reproducibility.
The scope of 1-alkynylphosphines was investigated (Table 2).
Although a bulky t-butyl group of 1d completely suppressed
the reaction,3 phenyl- and isopropyl-substituted alkynylphos-
phines 1b and 1c underwent the reaction. The reactions of
methoxyphenyl-substituted 1e and 1f and p-acetylphenyl-sub-
stituted 1g proceeded smoothly. However, neither pyridine-
containing 1h, hydroxy group-containing 1i, nor 1-octynyldi-
cyclohexylphosphine reacted.
To reveal the mechanism of this reaction, we carried out
the following two experiments. First, D2O was used instead
of H2O. As a result, a product deuterated at the two alkenyl po-
sitions was obtained as the sole product (eq 1). From a mech-
anistic point of view, it is worth noting that the reaction in 1,4-
dioxane/D2O was slow (vide infra). Next, a mixture of 1f
and 1j was exposed to the reaction conditions. In this case,
four 1-alkenylphosphine oxides were obtained in almost equal
amounts (eq 2). This result suggests that cleavage of the
Csp–P bonds of 1-alkynylphosphines would occur.
0.11 mmol
MeO
n-C6H13
H
H
H
PPh2
O
H
P
2a
2k
O
0.11 mmol
0.10 mmol
Based on these results, we assume that the reaction mech-
anism is as follows (Scheme 1). This reaction seems to consist
of two steps. In the first step, C–P bond cleavage proceeds.
Oxidative addition of 1-alkynylphosphine to a RhI complex
occurs to yield 4. The oxidative addition would be reversible
because no reaction took place in the absence of water (vide
supra). Protonation with H2O followed by reductive elimina-
tion provides 1-alkyne 5 and diphenylphosphine oxide. In
the second step, rhodium-catalyzed hydrophosphinylation of
1-alkyne with diphenylphosphine oxide proceeds to yield 1-
alkenylphosphine oxide. Oxidative addition of diphenylphos-
phine oxide occurs to afford 7. Hydrorhodation of alkyne 5
followed by reductive elimination provides the product 2. Such
a rhodium-catalyzed hydrophosphinylation reaction has been
reported.4 Actually, treatment of 1-octyne with diphenylphos-
phine oxide under the reaction conditions provided (E)-1-oc-
tenyldiphenylphosphine oxide in high yield (eq 3). This result
supports the proposed mechanism. During the reaction, accu-
mulation of neither diphenylphosphine oxide, 1-alkyne, nor
rhodium hydride 7 was observed. Therefore, oxidative addition
of diphenylphosphine oxide to a RhI complex is not rate-deter-
mining. The protonolysis of 4 would be the rate-determining
step, since the use of D2O retarded the reaction (eq 1).
n-C6H13 C C H
n-C6H13
H
0.015 mol. amt. [RhCl(cod)]2
n-C6H13
D
0.015 mol. amt. [RhCl(cod)]2
+
n-C6H13
C
C PPh2
1a
1,4-Dioxane / H2O =10 / 1
reflux, 8 h
H
PPh2
1,4-Dioxane / D2O =10 / 1
reflux, 36 h
HPPh2
D
PPh2
O
O
O
53 %
2a 96 %
2a-D
(1.2 mol. amt.)
ð1Þ
ð3Þ

504 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
Reaction of 1-Alkynylphosphines with Water
First Step
R
C C PPh2
1
H2O
C C [Rh] PPh2
[Rh]
[Rh]
R
HO [Rh] PPh2
4
6
HPPh2
R
C C H
5
HO PPh2
O
Second Step
HPPh2
O
R
C C H
R
H
O
5
[Rh]
[Rh]
H
[Rh] PPh2
PPh2
H
[Rh]
O
7
R
H
8
H
PPh2
O
2
Scheme 1. Plausible reaction mechanism.
duced pressure. Chromatographic purification on silica gel yielded
2a (0.11 g, 0.37 mmol, 73%) as a white solid.
Conclusion
Characterization Data. Phosphines 1a,7 1b,7 1c,1a 1d,8 1e,1c
1f,9 1g,1a 1h,10 and 1i,1a and phosphine oxides 2a,11 2b,11 2c,12 and
2f13 showed the same spectroscopic data as those described in the
literature.
We have found a reaction for the synthesis of (E)-1-alkenyl-
phosphine oxides from 1-alkynylphosphines. The reaction is
an interesting formal hydration reaction that involves carbon–
phosphorus bond cleavage with a rhodium complex. Transition
metal-mediated carbon–phosphorus bond cleavage has been
an attractive topic in organometallic chemistry.5,6 The present
reaction gives new information on the reactivity of 1-alkynyl-
phosphine under rhodium catalysis.
Bis(4-methylphenyl)-1-octynylphosphine (1j):
IR (neat)
3015, 2928, 2853, 2178, 1905, 1598, 1496, 1456, 1395, 1184,
1
1094, 1019, 803, 624 cmꢂ1; H NMR (CDCl3) ꢀ 0.91 (t, J ¼ 7:0
Hz, 3H), 1.27–1.37 (m, 4H), 1.46 (dd, J ¼ 7:5, 7.5 Hz, 2H), 1.61
(dd, J ¼ 7:5, 7.5 Hz, 2H), 2.33 (s, 6H), 2.43 (dt, J ¼ 1:5, 7.5 Hz,
2H), 7.13–7.17 (m, 4H), 7.47–7.53 (m, 4H); 13C NMR (CDCl3) ꢀ
14.30, 20.64, 21.53, 22.81, 28.53, 28.55, 31.29, 76.23 (d, J ¼
1:6 Hz), 109.94 (d, J ¼ 3:9 Hz), 129.24 (d, J ¼ 7:6 Hz), 132.36 (d,
J ¼ 21:0 Hz), 133.84 (d, J ¼ 4:9 Hz), 138.68; 31P NMR (CDCl3)
ꢀ ꢂ36:38. Found: C, 82.18; H, 8.62%. Calcd for C22H27P: C,
81.95; H, 8.44%.
Experimental
General. 1H NMR (500 MHz) and 13C NMR (125.7 MHz)
spectra were taken on a Varian UNITY INOVA 500 spectrometer
and were obtained in CDCl3 or C6D6 with tetramethylsilane as
an internal standard. 31P NMR (121.5 MHz) spectra were taken
on a Varian GEMINI 300 spectrometer and were obtained in
CDCl3 or C6D6 with 85% H3PO4 solution as an external standard.
NMR yields were determined by fine 31P NMR spectra with
(MeO)3P=O as an internal standard. The first delay of 31P NMR
measurements was set for 15 s to make integrals for signals accu-
rate. IR spectra were taken on a SHIMADZU FTIR-8200PC spec-
trometer. Mass spectra were determined on a JEOL Mstation 700
spectrometer. TLC analyses were performed on commercial glass
plates bearing 0.25-mm layer of Merck Silica gel 60F254. Silica
gel (Wakogel 200 mesh) was used for column chromatography.
Elemental analyses were carried out at the Elemental Analysis
Center of Kyoto University.
(E)-1-Diphenylphosphinyl-2-(2-methoxyphenyl)ethene (2e):
IR (nujol) 2923, 2853, 1598, 1484, 1461, 1247, 1181, 1004, 821,
744, 665 cmꢂ1; 1H NMR (CDCl3) ꢀ 3.82 (s, 3H), 6.90 (d, J ¼ 8:5
Hz, 1H), 6.94 (dd, J ¼ 18:0, 24.0 Hz, 1H), 6.95 (dd, J ¼ 8:5, 8.5
Hz, 1H), 7.33 (dd, J ¼ 8:5, 8.5 Hz, 1H), 7.44–7.55 (m, 7H), 7.73–
7.83 (m, 5H); 13C NMR (CDCl3) ꢀ 55.41, 111.16, 119.69 (d, J ¼
104:1 Hz), 120.57, 124.12 (d, J ¼ 17:1 Hz), 128.49 (d, J ¼ 11:9
Hz), 128.76 (d, J ¼ 1:0 Hz), 131.20, 131.43 (d, J ¼ 10:0 Hz),
131.65 (d, J ¼ 2:4 Hz), 133.35 (d, J ¼ 104:5 Hz), 143.00 (d, J ¼
4:9 Hz), 158.08; 31P NMR (CDCl3) ꢀ 23.09. Found: C, 75.11; H,
5.62%. Calcd for C21H19O2P: C, 75.44; H, 5.73%. Mp: 150.5–
152.0 ꢃC.
Materials obtained from commercial suppliers were used
without further purification. 1-Alkynylphosphines were prepared
according to the literature.1a
4-[(E)-2-(Diphenylphosphinyl)ethenyl]acetophenone (2g):
IR (nujol) 2924, 2853, 1678, 1603, 1438, 1359, 1270, 1182, 1107,
1
1000, 806, 746, 728, 665 cmꢂ1; H NMR (CDCl3) ꢀ 2.59 (s, 3H),
Typical Procedure for Rhodium-Catalyzed Reaction to
Yield (E)-1-Alkenylphosphine Oxides. Synthesis of 2a is rep-
resentative. [RhCl(cod)]2 (3.7 mg, 0.0075 mmol) was placed in a
20-mL reaction flask under argon. 1,4-Dioxane (3.0 mL), H2O
(0.30 mL), and 1-octynyldiphenylphosphine (1a, 0.15 g, 0.50
mmol) were sequentially added. The resulting solution was stirred
for 4 h at reflux. After the mixture was cooled to room tempera-
ture, water (10 mL) was added, and the product was extracted with
dichloromethane (10 mL ꢁ 3). The combined organic layer was
dried over anhydrous sodium sulfate and concentrated under re-
6.97 (dd, J ¼ 17:5, 22.0 Hz, 1H), 7.44–7.57 (m, 7H), 7.60 (d,
J ¼ 8:0 Hz, 2H), 7.70–7.79 (m, 4H), 7.95 (d, J ¼ 8:0 Hz, 2H);
13C NMR (CDCl3) ꢀ 26.63, 122.45 (d, J ¼ 101:8 Hz), 127.83,
128.66 (d, J ¼ 11:9 Hz), 128.79, 131.29 (d, J ¼ 10:0 Hz), 132.01
(d, J ¼ 2:5 Hz), 132.47 (d, J ¼ 105:9 Hz), 137.80, 139.24 (d,
J ¼ 17:6 Hz), 145.93 (d, J ¼ 3:4 Hz), 197.26; 31P NMR (CDCl3)
ꢀ 22.00. Found: C, 76.23; H, 5.54%. Calcd for C22H19O2P: C,
76.29; H, 5.53%. Mp: 176.0–177.5 ꢃC.
(E)-1-Bis(4-methylphenyl)phosphinyl-1-octene (2j): IR (neat)
2927, 2856, 1629, 1603, 1453, 1400, 1182, 1118, 1101, 807,

A. Kondoh et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
505
656 cmꢂ1; 1H NMR (CDCl3) ꢀ 0.85 (t, J ¼ 7:0 Hz, 3H), 1.21–1.34
(m, 6H), 1.45 (tt, J ¼ 7:0, 7.5 Hz, 2H), 2.26 (dt, J ¼ 6:5, 7.5 Hz,
2H), 2.36 (s, 6H), 6.17 (dd, J ¼ 17:0, 24.0 Hz, 1H), 6.66 (ddt,
J ¼ 17:0, 19.5, 6.5 Hz, 1H), 7.21–7.26 (m, 4H), 7.51–7.59 (m,
4H); 13C NMR (CDCl3) ꢀ 13.95, 21.48 (d, J ¼ 1:0 Hz), 22.46,
27.80 (d, J ¼ 1:0 Hz), 28.73, 31.47, 34.40 (d, J ¼ 16:8 Hz), 122.00
(d, J ¼ 102:6 Hz), 129.11 (d, J ¼ 12:5 Hz), 130.05 (d, J ¼ 106:4
Hz), 131.24 (d, J ¼ 10:5 Hz), 141.92 (d, J ¼ 2:9 Hz), 152.24 (d,
J ¼ 1:4 Hz); 31P NMR (CDCl3) ꢀ 22.02. HRMS (EIþ) (m=z) Ob-
served: 340.1954 (ꢀ ¼ ꢂ0:7 ppm). Calcd for C22H29OP [Mþ]:
340.1956.
2007, 129, 4099. b) A. Kondoh, H. Yorimitsu, K. Oshima, Org.
Lett. 2007, 9, 1383. c) S. Kanemura, A. Kondoh, H. Yorimitsu,
K. Oshima, Org. Lett. 2007, 9, 2031. d) A. Kondoh, H. Yorimitsu,
K. Oshima, J. Am. Chem. Soc. 2007, 129, 6996.
2 1-Alkenylphosphine oxides are useful in organic chemis-
try: M. Niu, H. Fu, Y. Jiang, Y. Zhao, Chem. Commun. 2007,
272, and references cited therein.
3
The t-butyl group would retard the oxidative addition
(Scheme 1). Treatment of t-butylacetylene with diphenylphos-
phine oxide under conditions similar to those in eq 3 led to
smooth hydrophosphinylation.
(E)-1,2-Dideuterio-1-diphenylphosphinyl-1-octene (2a-D):
IR (nujol) 2923, 2854, 1593, 1546, 1438, 1180, 1120, 722, 665
cmꢂ1; 1H NMR (CDCl3) ꢀ 0.86 (t, J ¼ 7:0 Hz, 3H), 1.20–1.36 (m,
6H), 1.46 (tt, J ¼ 7:5, 7.5 Hz, 2H), 2.27 (dt, J ¼ 2:0, 7.5 Hz, 2H),
7.40–7.53 (m, 6H), 7.64–7.71 (m, 4H); 13C NMR (CDCl3) ꢀ
13.96, 22.48, 27.76, 28.74, 31.48, 34.27 (d, J ¼ 16:3 Hz), 121.09
(dt, J ¼ 101:3, 24.8 Hz), 128.42 (d, J ¼ 12:0 Hz), 131.23 (d,
J ¼ 10:0 Hz), 131.58 (d, J ¼ 2:9 Hz), 133.22 (d, J ¼ 104:5 Hz),
152.46 (t, J ¼ 23:4 Hz); 31P NMR (CDCl3) ꢀ 21.78. 2H NMR
(CDCl3) ꢀ 6.20, 6.73. HRMS (EIþ) (m=z) Observed: 314.1767
(ꢀ ¼ ꢂ0:4 ppm). Calcd for C20H23D2OP [Mþ]: 314.1769. Mp:
58.0–60.0 ꢃC.
4
66, 5929.
L.-B. Han, C.-Q. Zhao, M. Tanaka, J. Org. Chem. 2001,
5
a) P. E. Garrou, Chem. Rev. 1985, 85, 171. b) J. V. Ortiz,
Z. Havlas, R. Hoffmann, Helv. Chim. Acta 1984, 67, 1. c) S. A.
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6
a) A. Inoue, H. Shinokubo, K. Oshima, J. Am. Chem. Soc.
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(E)-2-Bis(4-methylphenyl)phosphinyl-1-(4-methoxyphenyl)-
ethene (2k): IR (nujol) 2924, 2855, 1602, 1511, 1464, 1438,
1378, 1307, 1257, 1176, 1100, 1020, 1002, 823, 756 cmꢂ1
;
1H NMR (CDCl3) ꢀ 2.39 (s, 6H), 2.82 (s, 3H), 6.64 (dd, J ¼
17:5, 22.0 Hz, 1H), 6.88 (d, J ¼ 8:5 Hz, 2H), 7.23–7.31 (m, 4H),
7.39 (dd, J ¼ 17:5, 19.5 Hz, 1H), 7.46 (d, J ¼ 8:5 Hz, 2H), 7.59–
7.67 (m, 4H); 13C NMR (CDCl3) ꢀ 21.53 (d, J ¼ 1:0 Hz), 55.31,
114.13, 116.78 (d, J ¼ 105:9 Hz), 128.06 (d, J ¼ 18:1 Hz), 129.21
(d, J ¼ 12:4 Hz), 129.14, 130.10 (d, J ¼ 107:4 Hz), 131.36 (d,
J ¼ 10:5 Hz), 142.06 (d, J ¼ 2:4 Hz), 146.51 (d, J ¼ 3:8 Hz),
161.01; 31P NMR (CDCl3) ꢀ 23.19. HRMS (EIþ) (m=z) Observed:
362.1433 (ꢀ ¼ ꢂ0:8 ppm). Calcd for C23H23O2P [Mþ]: 362.1436.
Mp: 148.0–149.5 ꢃC.
7
5511.
8
P. Bharathi, M. Periasamy, Organometallics 2000, 19,
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´
´
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This work was supported by Grants-in-Aid for Scientific
Research and COE Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. A.K. ac-
knowledges JSPS for financial support.
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Drzazga, G. Wojciuk, O. M. Demchuk, K. Grela, K. M.
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¨
References
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a) A. Kondoh, H. Yorimitsu, K. Oshima, J. Am. Chem. Soc.