Application of (phosphine)gold(I) carboxylates, sulfonates and related compounds as highly efficient catalysts for the hydration of alkynes

Article abstract of DOI:10.1016/j.molcata.2003.11.011

The catalytic activity of a series of six Au(I) complexes LAuX (L = Ph₃P, X = CO₂C₂F₅, SO₃-p-tol, SO₃Et, SSO₂-p-tol; L = Me₃P, (p-tol)₃P, X = CO₂C₂F₅), as well as the Ag(I) complexes Ph₃PAgOC(O)C₂F₅ and Ph₃PAgOS(O)₂-p-tol·EtOH, regarding the hdyration of 3-hexyne forming 3-hexanone in the presence of BF₃·Et₂O as a co-catalyst was studied. (Phosphine)Au(I) carboxylates and sulfonates were highly active catalysts for hydration reactions of non-activated alkynes. Analogous Ag(I) complexes were not active in this respect due to the fact that Ag(I) cations were much stronger acceptors for their ligands and counterions as compared to Au(I) cations. (Triphenylphosphine)Ag(I) pentafluoropropionate catalyzed the addition of water to 3-hexyne even at room temperature. The catalyst was successfully recycled and reused five times without any notable loss of activity. For the reaction of 3-hexyne with water, the co-catalyst concentration was optimized. The co-catalyst served more than one purpose in the catalytic cycle. Using (Ph₃P)AuOC(O)C₂F₅ as a catalyst, it was possible to add acetic acid to 3-hexyne to give 3-hexene-3-acetate. With water present in glacial acetic acid, 3-hexanone was also formed.

Full text of DOI:10.1016/j.molcata.2003.11.011

Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
Application of (phosphine)gold(I) carboxylates, sulfonates and related
compounds as highly efficient catalysts for the hydration of alkynes
Patric Roembkea, Hubert Schmidbaura,∗, Stephanie Cronjeb, Helgard Raubenheimerb
a
Anorganisch-Chemisches Institut, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany
b
Department of Chemistry, University of Stellenbosch, Private Bag X1, Matieland, Stellenbosch, South Africa
Received 23 September 2003; received in revised form 6 November 2003; accepted 13 November 2003
Abstract
The catalytic activity of a series of six gold(I) complexes LAuX (L = Ph3P, X = CO2C2F5, SO3-p-tol, SO3Et, SSO2-p-tol; L = Me3P,
(p-tol)3P, X = CO2C2F5), as well as the silver(I) complexes Ph3PAgOC(O)C2F5 and Ph3PAgOS(O)2-p-tol·EtOH, regarding the hydration of
3-hexyne forming 3-hexanone in the presence of BF3·Et2O as a co-catalyst has been investigated. It could be shown that all the gold compounds
are catalytically active with (Ph3P)AuOC(O)C2F5 (1) being the most active. Using 1, hydration of 3-hexyne takes place at room temperature and
turnover frequencies (TOFs) as high as 3900 h−1 can be reached without any notable catalyst deterioration (MeOH as solvent, 70 ◦C). The silver
complexes on the other hand did not furnish 3-hexanone under reaction conditions. This observation is explained with silver being the stronger
acceptor compared to gold which can be derived from the crystal structures of representative examples. An optimization of the co-catalyst
concentration showed that with increasing concentration the reaction rate increases significantly reaching saturation at approximately 5 mol%.
This indicates that the Lewis acid BF3·Et2O plays a role in several steps of the catalytic cycle. 1 was also successfully employed as a catalyst to
react acetic acid with 3-hexyne forming 3-hexene-3-acetate but due to water being present in the glacial acetic acid 3-hexanone was also formed.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Gold; Silver; Sulfonate complexes; Carboxylate complexes; Catalysis; Hydration; Alkynes
1. Introduction
of [cis-PtCl2(tpps)2] (tpps = P(m-C6H4SO3Na)3) with an
initial turnover frequency (TOF) of 550 h−1 and an overall
TOF of not more than approximately 100 h−1 [6c].
In 1998, Teles et al. have shown that certain (phos-
phine)gold(I) complexes of the type (R3P)Au+X− are
extremely efficient catalysts for the addition of methanol
to alkynes in the presence of Brønsted or Lewis acidic
co-catalysts [9a]. In their patent application [9b], the authors
also briefly mentioned the addition of water to propargyl
alcohol, but quoted only low yields.
These new results have been an incentive for extensive
research in gold catalysis [10], a topic which had been
neglected for a long time, as gold was often thought of
as “catalytically dead” [11]. Very recently, Tanaka and
co-workers found (triphenylphosphine)gold(I) sulfate to be
a very active catalytic system for the hydration of 1-octyne.
Conversion into 2-octanone proceeds in high yields and
with turnover frequencies of approximately 3500 h−1. Since
the catalyst deteriorates under the standard reaction condi-
tions (70 ◦C; MeOH as solvent), the addition of additives
such as carbon monoxide is necessary to stabilize the sys-
tem. With this precaution higher yields and reaction rates
One of the most straightforward ways to generate com-
pounds with carbon–oxygen bonds is the hydration of
unsaturated organic compounds. An efficient hydration
process is not only environmentally benign but also eco-
nomically attractive. Especially the synthesis of carbonyl
compounds by addition of water to alkynes has been ex-
tensively studied [1]. It has long been known that water
can be added quite easily to activated electron-rich alkynes
such as alkynylethers or alkynylthioethers in the presence
of an acid catalyst [2]. However, simple alkynes are not
readily hydrated even in the presence of a co-catalyst (typ-
ically toxic mercury(II) salts) [3]. Several transition metal
catalysts containing RuII,III [4], RhI [5], PtII [6], AuIII [7]
and other metals [8] have also been employed in the past,
but only with limited success. The best results were ob-
tained for the hydration of 3-pentyn-1-ol in the presence
∗
Corresponding author. Tel.: +49-8-9289-13124;
fax: +49-8-9289-13125.
E-mail address: patric roembke@web.de (H. Schmidbaur).
1381-1169/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2003.11.011

36
P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
(10 ml) at 20 ◦C for 3 h with stirring. The AgCl precipitate
was filtered off and the product precipitated from the clear
filtrate by addition of pentane. The product was filtered,
washed with toluene and crystallized from CH2Cl2/pentane
at −30 ◦C; colorless rods containing dichloromethane,
490 mg (78% yield), mp 162 ◦C with decomposition. NMR
(TOF = 15,600 h−1) have been achieved [12]. In the light
of this encouraging progress, we initiated a search for a
catalyst which is stable under standard reaction conditions
which could serve in an environmentally and economically
benign process without gaseous additives. In the present re-
port it is demonstrated that (phosphine)gold(I) carboxylates
and (phosphine)gold(I) sulfonates are highly active and
reusable catalysts for the addition of water to non-activated
alkynes. The addition of acetic acid to those substrates was
also successful.
1
(CDCl3, 20 ◦C), H: 7.9–7.1, m, 19H, C6H5/C6H4; 2.41, s,
3H, Me; 5.3, s, 2H, CH2Cl2. 31P{1H}: 27.9, s. 13C{1H}:
134.1, d, J = 14.0 Hz; 132.2, s; 129.3, d, J = 12.3 Hz;
127.6, d, J = 64.9 Hz for o, p, m, ipso in C6H5; 141.7,
139.2, 129.0, and 126.5, all s for ipso, o, m, and p in C6H4;
53.3, s for CH2Cl2, 21.3, s for Me. IR (KBr): 1261, 1184,
1146, 1100, 954 cm−1 (ν(SO3R)). MS (FAB): m/z 721, 11%
[(Ph3P)2Au]+; 631, 3% [M+1]+; 459, 100% [(Ph3P)Au]+;
262, 6% [Ph3P]+. C26H24AuCl2O3PS (715.35) calcd. C
43.6, H 3.4, S 4.5; found C 44.1, H 3.3, S 4.4.
2. Experiments
2.1. Materials
Syntheses of the catalysts were carried out in an atmo-
sphere of dry nitrogen. Glassware was oven-dried, evacuated
and flushed with nitrogen. Solvents were dried, distilled and
stored under a nitrogen atmosphere. Standard equipment was
used throughout. The glass apparatus was protected against
light by an aluminum foil wrapper. Silver pentafluoropro-
pionate and all tertiary phosphines are commercially avail-
able. (Phosphine)gold(I) chlorides [13] and silver sulfonates
[14] were prepared according to literature procedures. The
synthesis as well as structural and spectroscopic data for the
catalysts used has recently been published elsewhere [15].
Therefore, only four representative examples are described
in detail here.
2.4. Synthesis of (triphenylphosphine)silver(I)
pentafluoropropionate (7)
A suspension of C2F5CO2Ag (250 mg, 0.93 mmol)
in 10 ml of dichloromethane was treated with a solu-
tion of Ph3P (240 mg, 0.93 mmol) in the same volume
of the same solvent at room temperature. A clear solu-
tion was obtained, the volume of which was reduced to
ca. 5 ml in a vacuum. Addition of cold pentane (−70 ◦C)
gave a colorless precipitate which was recrystallized from
dichloromethane/pentane, yield 450 mg (91%), mp 208 ◦C.
NMR (CDCl3, 20 ◦C), 1H: 7.38–7.56, m, Ph. 13C{1H}:
163.2, t, J 25.5 Hz, CO2; CF2 and CF3 were not detected;
128.9, d, J = 37.4 Hz; 129.3, d, J = 10.1 Hz; 131.5, s;
133.9, d, J = 17.0 Hz (for C ipso, meta, para, and ortho, re-
spectively). 31P{1H}: 15.4, s. IR (KBr): 1653 cm−1 (ν(CO)).
MS (FAB): m/z 631, 31.1% [L2Ag]+; 385, 3.0% [LAgO]+;
369, 100% [LAg]+; 262, 47.5% [L]+. C21H15AgO2PF5
(533.17) calcd. C 47.3, H 2.8, P 5.8; found C 47.3, H 2.7,
P 6.2.
2.2. Synthesis of (triphenylphosphine)gold(I)
pentafluoropropionate (1)
A solution of (Ph3P)AuCl (300 mg, 0.60 mmol) in
dichloromethane (10 ml) was added to a suspension of
F5C2COOAg (200 mg, 0.74 mmol) in the same volume of
the same solvent at −78 ◦C with stirring and under protec-
tion against incandescent light. The mixture was stirred for
3 h and subsequently filtered. The product was precipitated
from the filtrate by addition of pentane, collected by filtra-
tion and recrystallized from dichloromethane (320 mg, 85%
yield), mp 134 ◦C (decomposition). NMR (CD2Cl2, 20 ◦C),
1H: 6.68–7.12, m, Ph. 13C{1H}: 128.4, d, J = 67.7 Hz,
C (ipso); 129.8, d, J = 12.3 Hz, C (meta); 132.7, d,
J = 2.3 Hz, C (para); 134.6, d, J = 13.1 Hz, C (ortho).
2.5. Synthesis of (triphenylphosphine)
silver(I)-p-tolylsulfonate (ethanol) (8)
4-MeC6H4SO3Ag (290 mg, 1.04 mmol) was suspended
in a mixture of dichloromethane and ethanol (10 ml each)
at room temperature and treated with Ph3P (270 mg,
1.04 mmol) for 2 h with stirring to give an almost clear
colorless solution. Small amounts of residue were filtered
off and the volume of the filtrate was reduced to a few
ml. The product was precipitated by addition of pentane,
filtered, washed with pentane and diethylether, and dried in
a vacuum, yield 430 mg (76%), mp 124 ◦C (with decompo-
sition). Single crystals can be grown from pentane/ethanol
19F{1H}: −6.3, t, JFF = 112 Hz, CF3; −42.7, q, JFF
=
3
3
112 Hz, CF2. 31P{1H}: 27.5, s. MS (FAB): m/z 1081, 10%
[(Ph3PAu)2OCOC2F5]+; 721, 18% [(Ph3P)2Au]+; 459,
100% [Ph3PAu]+. C21H15AuO2PF5 (619.27) calcd. C 40.5,
H 2.4; found C 40.8, H 2.5.
2.3. Synthesis of (triphenylphosphine)
gold(I)-p-tolylsulfonate (4)
1
at −30 ◦C. NMR (CDCl3, 20 ◦C), H: 6.87–7.96, m, 19H,
Ph and C6H4; 3.55, q, 2H, J = 7.4 Hz, CH2; 2.14, s,
3H, 4-Me; 1.16, t, 3H, Me. 31P{1H}: 14.2, s. MS (FAB):
m/z 910, 5.4% [(Ph3P)2Ag2SO3C6H4Me]+; 631, 16.3%
[(Ph3P)2Ag]+; 369, 100% [Ph3PAg]+; 262, 26.4% [Ph3P]+.
A
suspension of silver p-tolylsulfonate (300 mg,
1.1 mmol) in dichloromethane (20 ml) was treated with
a solution of Ph3PAuCl (500 mg, 1.0 mmol) in CH2Cl2

P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
37
C27H28AgO4PS (587.40) calcd. C 55.2, H 4.8, S 5.5; found
3. Results and discussion
C 55.4, H 4.6, S 5.7.
In preliminary experiments, the complexes Ph3PAuOC(O)
C2F5 (1), (p-tol)3PAuOC(O)C2F5 (2), Me3PAuOC(O)C2F5
(3), Ph3PAuOS(O)2-p-tol (4), Ph3PAuOS(O)2Et (5), Ph3
PAuSS(O)2-p-tol (6), Ph3PAgOC(O)C2F5 (7), and Ph3
PAgOS(O)2-p-tol·EtOH (8) were chosen for a study of their
catalytic properties and applied to the reaction of water
with 3-hexyne in THF in the presence of BF3·Et2O as a
co-catalyst at 45 ◦C (Scheme 1). The structural and spectro-
scopic data for complexes 1–8 have recently been discussed
elsewhere [15].
2.6. Addition of water to 3-hexyne
In a typical procedure, a solution of 3-hexyne (1.00 g,
12.05 mmol) in 5 ml of THF (or MeOH) was mixed with
water (870 mg, 48.2 mmol, 4 eqiv.) and BF3·Et2O (90 mg,
5.25 mol%). The mixture was heated to the reaction tem-
perature and the reaction was started by adding a gold cata-
lyst, for example, Ph3PAuOC(O)C2F5 (1, 10 mg, 0.016 mol,
0.134 mol%). At regular intervals, small samples were taken
and analyzed by gas chromatography.
The results of the catalysis experiments are summarized
in Table 1. It appears that the nature of the anions is a very
important factor with respect to the catalytic activity, as al-
ready observed by Teles et al. for the addition of alcohols to
alkynes in the presence of gold(I) catalysts [9]. The activity
of the compounds is strongly related to the “hardness” of the
anions, since the LAu+ cation (L = ligand) is likely to be the
catalytically active species [9a]. This cation coordinates to
the alkyne in the first step of the catalytic cycle, thus render-
ing it more susceptible for a nucleophilic attack. Therefore,
it is not surprising that (Ph3P)AuSS(O)2-p-tol (6) containing
the softer p-tolylthiosulfonate anion furnishes only traces
of 3-hexanone after 48 h, whereas (Ph3P)AuOS(O)2-p-tol
(4) containing the harder p-tolylsulfonate anion yields more
than 80% of the ketone product after only 4 h of reac-
tion time (TOF = 155 h−1). Even better results were ob-
tained using (Ph3P)AuOS(O)2Et (5) which leads to a TOF of
160 h−1. The most active compound however turned out to
be (Ph3P)AuOC(O)C2F5 (1) containing the extremely hard
pentafluoropropionate anion, giving rise to a turnover fre-
2.7. Addition of water to phenylacetylene
One gram of phenylacetylene (9.79 mmol) was dissolved
in THF (5 ml) and treated with water (720 mg, 39.16 mmol,
4 eqiv.) in a small flask. After heating the reaction mixture
to 45 ◦C in a water bath BF3·Et2O (73 mg, 5.25 mol%)
and (triphenylphosphine)gold(I)-p-tolylsulfonate (8.3 mg,
0.132 mol%) were added to start the catalysis. The reac-
tion mixture was analyzed in regular intervals using gas
chromatography.
2.8. Addition of water to cyclopentylacetylene
Five hundred milligrams of cyclopentylacetylene (4.60
mmol) were dissolved in THF (5 ml) and treated with
water (340 mg, 18.80 mmol, 4 eqiv.) in a small flask. Af-
ter heating the reaction mixture to 45 ◦C in a water bath,
BF3·Et2O (34 mg, 5.25 mol%) and (triphenylphosphine)gold
(I)-p-tolylsulfonate (4.0 mg, 0.132 mol%) were added to
start the reaction. The mixture was analyzed in regular
intervals using gas chromatography.
quency of 213 h−1
.
As far as the phosphine ligands are concerned, the ac-
tivity increases as poor phosphinedonors are employed.
Therefore, compound 1 containing triphenylphosphine is
more active than compounds 2 (TOF = 163 h−1) and 3
(TOF = 99 h−1) containing the more strongly donating
ligands tri-p-tolylphosphine and trimethylphosphine, re-
spectively. Even better results are therefore to be expected
using very electron-poor donors such as triphenylphosphite
(PhO)3P, but their complexes with sulfonate or carboxylate
counterions are not stable under the reaction conditions and
therefore catalyst deterioration occurs very quickly. These
observations again resemble the results obtained by Teles
et al. for the addition of alcohols to alkynes using gold(I)
sulfate complexes and sulfuric acid as the catalytic system
[9a].
2.9. Addition of acetic acid to 3-hexyne
A small flask was charged with 3-hexyne (1.00 g, 12.05
mmol), THF (5 ml), glacial acetic acid (3.61 g, 5 eqiv.)
and BF3·Et2O (90 mg, 5.25 mol%). The mixture was
heated to 60 ◦C and the reaction was started by adding
(triphenylphosphine)gold(I) pentafluoropropionate (10 mg,
0.016 mmol, 0.134 mol%). After a reaction time of 1 h, an
excess of cold (−60 ◦C) pentane was added in order to
precipitate the gold catalyst and to stop the reaction. After
filtration, the mixture was analyzed using gas chromato-
graphy.
O
H2O
thf
45 °C
catalyst
HO
Scheme 1. Catalytic hydration of 3-hexyne.

38
P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
Table 1
Hydration of 3-hexyne in the presence of various catalystsa
Catalyst
mol% Catalyst referred to 3-hexyne
Time (h)
Yield (%)b
TOF (h−1
)
(Ph3P)AuOC(O)C2F5 (1)
[(p-Tol)3P]AuOC(O)C2F5 (2)
(Me3P)AuOC(O)C2F5 (3)
(Ph3P)AuOS(O)2-p-tol (4)
(Ph3P)AuOS(O)2Et (5)
(Ph3P)AuSS(O)2-p-tol (6)
(Ph3P)AgOC(O)C2F5 (7)
(Ph3P)AgOS(O)2-p-tol·EtOH (8)
0.134
0.137
0.095
0.132
0.146
0.129
0.156
0.167
1.8
2
2
51.2
43.2
18.8c
82.1
35.0
0.12
–
213
163
99c
155
160
0.02
–
4
1.5
48
48
48
–
–
a
Reaction conditions: 1.0 g of 3-hexyne (12.05 mmol); 870 mg of H2O (4 eqiv.); 5.25 mol% BF3·Et2O; 5 ml of THF; 45 ◦C.
Determined using gas chromatography (diethyleneglycol-di-n-butylether as the internal standard).
After a few minutes decomposition to elemental gold occurred.
b
c
Under the same reaction conditions as applied for analo-
The low catalytic reactivity of LAgX as compared to
LAuX complexes, e.g. in the addition of nucleophiles to
alkynes, is readily explained by the much stronger ligand
binding at the silver atoms. The proposed active [LAg]+
species are therefore much less abundant in the corre-
sponding dissociation equilibria than the [LAu]+ species
[15a,c,16]. High [LAg]+ activity is to be expected only in
cases with counterions X− devoid of any donor capacity
and in the complete absence of donor solvent molecules.
The corresponding gold systems are much less sensitive to
the nature of X− and of the solvent owing to the strongly
reduced acceptor properties of the metal atom.
As (Ph3P)AuOC(O)C2F5 (1) turned out to be the most
active catalyst among the complexes investigated, this
compound was subsequently used for an investigation of
the influence of the reaction temperature on the activity.
The reaction of 3-hexyne with water in the presence of
BF3·Et2O was again used as a model system. Since the
results of Tanaka and co-workers indicated that the reaction
rate in their catalytic system improves significantly by using
methanol instead of THF as a solvent [12], experiments with
both solvents were carried out at different temperatures.
The results of these investigations are given in Table 2.
The results indicate that (Ph3P)AuOC(O)C2F5 (1) is a
very active catalyst for hydration reactions of non-activated
gous gold compounds the silver complexes (Ph3P)AgOC(O)
C2F5 (7) and (Ph3P)AgOS(O)2-p-tol (8) showed no catalytic
activity. An explanation for this phenomena can be based
on the comparison of the crystal structures of compounds 4
and 8 (Fig. 1) which have already been published [15a,c].
The mode of dimerization found in (Ph3P)AgOS(O)2-p-tol
(8) reflects the high acceptor character of the silver atoms
in these sulfonate complexes which leads not only to
strong binding of an extra oxygen atom of a neighbor-
ing molecule but also to a fixation of an ethanol solvent
molecule [15c]. For the corresponding gold complexes,
no such acceptor properties are discernible. In crystals of
(Ph3P)AuOS(O)2-p-tol (4), the monomers are only weakly
associated via aurophilic contacts and no solvent is accepted
in the coordination sphere of the metal atoms [15a].
Ph3P
PPh3
SO2
O
Au
Au
H
OEt
OO
Ph3P
Table 2
Temperature and solvent dependence of the hydration of 3-hexyne cat-
alyzed by (Ph3P)AuOC(O)C2F5 (1)a
Ag
Ag
O2S SO2
O
PPh3
EtO
Entry
Temperature
(◦C)
Solvent
(5 ml)
Time
(h)
Yield
(%)b
TOF
(h−1
SO2
)
H
1
2
3
4
5
6
7
22
30
45
45
60
60
70
THF
THF
THF
MeOH
THF
2
2
13.9
34.7
51.2
86.8
56.6
55.5
52.1
28
70
1.8
0.8
1
0.2
0.1
213
790
424
2078
3900
MeOH
MeOH
a
Reaction conditions: 1.0 g of 3-hexyne (12.05 mmol); 870 mg of
H2O (4 eqiv.); 5.25 mol% BF3·Et2O; 10 of mg (Ph3P)AuOC(O)C2F5 (1,
0.134 mol%).
8
4
b
Fig. 1. Comparison of the structural motifs found in complexes
Determined using gas chromatography (diethyleneglycol-di-n-buty-
(Ph3P)AuOS(O)2-p-tol (4) and (Ph3P)AgOS(O)2-p-tol (8).
lether as the internal standard).

P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
39
O
H2O / MeOH
+
catalyst
O
2%
Scheme 2. Products of the hydration of 3-hexyne in aqueous methanol as solvent.
98%
alkynes. The reaction takes place even at room tempera-
Table 4
ture (Table 2, entry 1). It is not surprising that the activ-
ity increases significantly with increasing reaction temper-
atures, and for THF as a solvent the activity rises from
28 h−1 at room temperature up to 424 h−1 at 60 ◦C. As al-
ready presumed, even higher reaction rates are observed us-
ing methanol instead of THF as a solvent. Thus, the TOF
can be raised up to 3900 h−1 at 70 ◦C without any de-
tectable catalyst deterioration. The catalyst can be recycled
and reused. Even after five catalytic cycles, the activity stays
the same within the precision range of the measurements.
The turnover number after five cycles was approximately
3400, but it should be possible to increase this value even
further. However, using methanol as a solvent gives rise to
the formation of a small amount of 3-methoxy-3-hexene as
a byproduct due to the addition of methanol to the triple
bond (Scheme 2).
In another set of experiments, the addition of water
(870 mg, 4 eqiv.) to 3-hexyne (1.00 g, 12.05 mmol) in THF
(5 ml) at 45 ◦C in the presence of (triphenylphosphine)gold
(I)-p-tolylsulfonate (4, 10 mg, 0.132 mol%) as the catalyst
was optimized in respect of the co-catalyst (BF3·Et2O)
concentration. The results are summarized in Table 3. It is
interesting to note that neither without catalyst nor without
co-catalyst any reaction is observed.
Influence of the substrate on the reaction rate and the regioselectivity
Substrate
Time
(h)
Yield
(%)
TOF
(h−1
Markovnikov
addition (%)
)
3-Hexyne
Phenylacetylene
Cyclopentylacetylene
4
4
4
82.1
6.4
7.1
155
12.0
13.6
–
98.8
99.6
These results indicate that the co-catalyst is not only
needed to remove the counterions of the gold complexes,
thus forming the catalytically active cationic species, but
should also play an important role in other steps of the cat-
alytic cycle of the reaction. In the mechanism proposed by
Teles et al. [9a], it has been proposed that organogold inter-
mediates E and F are formed during the addition of methanol
to propyne (Scheme 3), and it is likely that the addition of
water to an alkyne should proceed similarly. As BF3·Et2O
forms HF upon hydrolysis under the reaction conditions, it
is likely that the hydrofluoric acid produced in this process
also accelerates the cleavage of the gold–carbon bonds of
the reaction intermediates.
The regioselectivity and the influence of the substrate on
the reaction rate were investigated using unsymmetrically
substituted alkynes. Phenylacetylene and cyclopentylacety-
lene were reacted with water (4 eqiv.) under the same condi-
tions as described above (45 ◦C, 5.25 mol% BF3·Et2O, 5 ml
of THF) using (triphenylphosphine)gold(I)-p-tolylsulfonate
(4, 0.132 mol%) as a catalyst. The results show that in both
cases Markovnikov addition is strongly favored (Table 4). It
also appears that the substrate has a great influence on the
Moreover, it appears that with increasing co-catalyst con-
centration the reaction rate increases significantly reaching
saturation at approximately 5 mol% (referring to 3-hexyne;
Table 3, entry 7). Using even higher concentrations of
BF3·Et2O does not lead to a further increase of the reaction
rate. A visualization of these results is given in Fig. 2.
Table 3
Influence of the co-catalyst concentration on the reaction ratea
Entry
Co-catalyst
mg
Time (h)
Yield (%)b
TOF (h−1
)
mol%
1 (Without catalyst)
90 (BF3·Et2O)
–
5.25
–
0.41
0.88
1.75
2.6
24
24
2
2
2
2
2
2
–
–
0.1
0.3
18.7
27
–
–
0.38
1.1
70.8
102
159
160
2
3
4
5
6
7
8
7 (BF3·Et2O)
15 (BF3·Et2O)
30 (BF3·Et2O)
45 (BF3·Et2O)
90 (BF3·Et2O)
180 (BF3·Et2O)
5.25
10.5
42
42.4
a
Reaction conditions: 1.0 g of 3-hexyne (12.05 mmol); 870 mg of H2O (4 eqiv.); 10 mg of (Ph3P)AuOS(O)2-p-tol (4, 0.132 mol%); 5 ml of THF; 45 ◦C.
Determined using gas chromatography (diethyleneglycol-di-n-butylether as internal standard).
b

40
P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
45,0
40,0
35,0
30,0
25,0
20,0
15,0
10,0
5,0
0,0
0
7
15
30
45
90
180
amount co-catalyst [mg]
Fig. 2. Influence of the co-catalyst concentration on the reaction rate.
H3C
CH3
OH
H3COH
Me3P Au
D
H
CH3
CH3
O
H
Au
CH3
Me3P Au
Me3P Au
Me3P
A
C
E
H
H
H3C
H
B
H3C
Me3P Au
OCH3
F
OCH3
H
G
H
H3C
Scheme 3. Proposed mechanism for the addition of MeOH to propyne [9a].
reaction rates. Phenylacetylene and cyclopentylacetylene re-
act more than one order of magnitude slower as compared
to 3-hexyne.
bond was not observed. If the same quantities of acetic
acid, 3-hexyne and BF3·Et2O are mixed and heated to 60 ◦C
without adding a gold catalyst no reaction occurs at all.
Using (triphenylphosphine)gold(I) pentafluoropropionate
(1, 10 mg, 0.016 mmol, 0.134 mol%) as a catalyst it was
possible to add acetic acid (3.61 g, 5 eqiv.) to 3-hexyne
(1.00 g, 12.05 mmol). The reaction of glacial acetic acid
with 3-hexyne was carried out at 60 ◦C in 5 ml of THF and
in the presence of BF3·Et2O as a co-catalyst (5.25 mol%).
After 1 h reaction time, both 3-hexanone (yield 12.3%) and
3-hexene-3-acetate (yield 6.2%) could be detected using gas
chromatography. Not surprisingly water present in small
amounts in glacial acetic acid reacts preferentially due to
its stronger nucleophilic character as compared to acetic
acid. Addition of two molecules of acetic acid to the triple
4. Conclusion
It could be shown that (phosphine)gold(I) carboxylates
and sulfonates are highly active catalysts for hydration re-
actions of non-activated alkynes. Analogous silver(I) com-
plexes are not active in this respect due to the fact that
silver(I) cations are much stronger acceptors for their lig-
ands and counterions as compared to gold(I) cations. (Triph-
enylphosphine)gold(I) pentafluoropropionate (1), the most
active of the compounds investigated catalyzes the addition

P. Roembke et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 35–42
41
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of water to 3-hexyne even at room temperature. The com-
plex 1 can also be used at 70 ◦C. Under these conditions,
turnover frequencies as high as 3900 h−1 are reached with-
out the need for protective gaseous additives such as carbon
monoxide to prevent catalyst deterioration. The catalyst was
successfully recycled and reused five times without any no-
table loss of activity.
For the reaction of 3-hexyne with water, the co-catalyst
concentration was optimized. The results indicate that the
co-catalyst serves more than one purpose in the catalytic
cycle. Again, using 1 as a catalyst, it was possible to add
acetic acid to 3-hexyne to give 3-hexene-3-acetate. With wa-
ter present in glacial acetic acid, 3-hexanone is also formed.
The results call for further investigations in order to fi-
nally reach a level which is acceptable as an environmen-
tally as well as economically benign process for industrial
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The work was supported by Volkswagenstiftung, Fonds
der Chemischen Industrie, Deutsche Forschungsgemein-
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