Novel sulfonated N-heterocyclic carbene gold(I) complexes: Homogeneous gold catalysis for the hydration of terminal alkynes in aqueous media

Article abstract of DOI:10.1021/om1001292

A series of novel water-soluble Au^I complexes using sulfonated N-heterocyclic imidazolylidene carbenes as ligands was prepared by transmetalation from the corresponding bis-carbene Ag^I complexes. Monocarbene Au^I complexes were employed as catalysts in the hydration of terminal alkynes in aqueous media. Hydrations proceeded selectively according to Markovnikovs rule with high rates and turnover numbers (up to TON 935). The highest activity was achieved in hydration of p-ethynylanisole (TOF = 400.2 h^-1). Effects of additives (H₂SO₄, AgOTs, AgBF₄, NaOH) were examined. Corresponding bis-carbene Au^I complexes were also isolated and characterized. However, these exhibit no catalytic activity in the explored systems.

Full text of DOI:10.1021/om1001292

2484 Organometallics 2010, 29, 2484–2490
DOI: 10.1021/om1001292
Novel Sulfonated N-Heterocyclic Carbene Gold(I)
Complexes: Homogeneous Gold Catalysis for the Hydration of
Terminal Alkynes in Aqueous Media
ꢀ
Ambroz Almassy, Csilla E. Nagy, Attila C. Benyei, and Ferenc Joo*
ꢀ
ꢀ
ꢀ
Institute of Physical Chemistry, University of Debrecen, 1, Egyetem ter, H-4032 Debrecen, Hungary, and Research
Group of Homogeneous Catalysis, Hungarian Academy of Sciences, 1, Egyetem ter, H-4032 Debrecen, Hungary
ꢀ
Received February 18, 2010
A series of novel water-soluble AuI complexes using sulfonated N-heterocyclic imidazolylidene
carbenes as ligands was prepared by transmetalation from the corresponding bis-carbene AgI
complexes. Monocarbene AuI complexes were employed as catalysts in the hydration of terminal
alkynes in aqueous media. Hydrations proceeded selectively according to Markovnikov’s rule with
high rates and turnover numbers (up to TON 935). The highest activity was achieved in hydration of
p-ethynylanisole (TOF = 400.2 h-1). Effects of additives (H2SO4, AgOTs, AgBF4, NaOH) were
examined. Corresponding bis-carbene AuI complexes were also isolated and characterized. However,
these exhibit no catalytic activity in the explored systems.
Introduction
in rearrangements of enynes,9,10 allenynes,11 and alkynyl
sulfoxides12 has become a useful tool in organic synthesis.
In most cases, AuI complexes with tertiary phosphine
ligands are used for catalytic purposes.13 However, gold
complexes with N-heterocyclic carbene (NHC) ligands14
have gained great significance in catalysis, due to the stability
provided by the stronger σ-donation and weaker π-back-
bonding ability of such ligands in comparison to the widely
used tertiary phosphines.15 Hydrations of alkynes catalyzed
with AuI-NHC complexes have already been reported;16
Following a long latent period, research into catalysis by
soluble gold complexes recently entered an era of exponen-
tial expansion.1,2 Hydration of terminal alkynes catalyzed by
Na[AuCl4] reported by Fukuda and Utimoto in 1991 has
initiated a rapid development of research on the use of gold
in homogeneous catalysis.3 Since then, compounds of gold
have been employed as catalysts in many organic transfor-
mations, especially in reactions involving activation of CC
triple bonds in unactivated alkynes, which after π-coordina-
tion to gold atoms became prone to addition of various
nucleophiles.4 Application of gold catalysts in intramolecu-
lar hydroamination,5 hydroalkoxylation,6 hydroacylation,7
hydroarylation,8 and cyclopropanation9 of olefins as well as
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~
3539–3542. (b) Nieto-Oberhuber, C.; Munoz, M. P.; Bunuel, E.; Nevado, C.;
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*To whom correspondence should be addressed. Fax: (þ)52-512-915.
E-mail: fjoo@delfin.unideb.hu.
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pubs.acs.org/Organometallics
Published on Web 05/11/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 11, 2010 2485
such reactions were performed mostly in organic solvents
(THF, MeOH, MeCN) or in partially aqueous media using
methanol or acetone as cosolvents, improving solubilities of
the catalyst and the alkyne.
N-alkylation with 1,3-propanesultone and 1,4-butanesul-
tone were also investigated.26
The hydration of alkynes is an important synthetic
reaction,27 and partially or fully aqueous solvents are natural
reaction media for such processes. For these reasons we
synthesized a series of water-soluble AuI(NHC) complexes
and applied them as catalysts in the hydration of terminal
alkynes in aqueous media.
Performing the catalytic reactions in aqueous solution or
in aqueous-organic biphasic media brings substantial eco-
nomic as well as ecological advantages.17 Water-soluble AuI,
AuII, and AuIII phosphine complexes were introduced into
homogeneous catalysis by Laguna and co-workers.18 In
these studies, solubility in aqueous media was achieved
by using sulfonated triphenylphosphine ligands or PTA
(1,3,5-triaza-7-phosphaadamantane). Although water-soluble
NHC ligands and a few of their complexes are known,19,20
the synthesis and catalytic application of water-soluble gold-
(I) NHC complexes have not been accomplished so far. Ru,
Rh, and Pd NHC complexes soluble both in water and in
organic solvents were synthesized using NHC ligands deri-
vatized by appending polyethylene glycol substituents onto
the imidazolium ring.21 Such complexes have been success-
fully employed in ring-closing metathesis and ring-opening
metathesis polymerization reactions.22 Water-soluble NHC
complexes of RuII and RhI with imidazolylidene ligands
bearing cationic ammonium groups were used in the synth-
esis of 2,3-dimethylfuran by intramolecular alkoxylation.23
The first example of using remarkably water-soluble imida-
zolium inner salts with covalently bonded sulfonate or
carboxylate anions as ligand precursors for the synthesis of
AgI and PdII complexes was described by Shaughnessy and
co-workers.20 Sulfonated N,N-diarylimidazolium and N,N-
diarylimidazolinium zwitterions were employed as NHC
precursors in PdII-catalyzed Suzuki coupling in water.19c
Various SO3H-functionalized imidazolium-based ionic
liquids were used as organocatalysts for the Fischer indole
synthesis in water24 and oxidative carboxylation of aryla-
ldehydes.25 The electrochemical properties of imidazolium
sulfonate zwitterions prepared from N-alkylimidazole by
Results and Discussion
For the synthesis of water-soluble gold NHC complexes,
sulfonated N-alkyl- and N-arylimidazolium inner salts
(Figure 1) were applied as ligands. Zwitterion 1a has been
prepared by condensation of 2-aminoethanesulfonic acid,
glyoxal, and paraformaldehyde. Compound 1a is readily
soluble in water and in DMSO and is insoluble in other
common organic solvents. The suitable precursor sodium
4-(imidazol-1-yl)benzenesulfonate 2 for synthesis of N-ary-
limidazolium sulfonates was prepared in excellent yield
according to a modified procedure of Zhang and co-
workers.28 Monosodium imidazolium bis(sulfonate) zwitter-
ions 1b,f were obtained by N-alkylation of 2 with sodium
2-bromoethanesulfonate or propanesultone, respectively.
Other monosulfonated structures, 1c,d, were prepared by
quaternization of N-methylimidazole and N-butylimidazole,
respectively.19a,24 Compound 1e was prepared by treatment
of imidazole with propanesultone according to the method
of Ohno et al.19b
Treatment of Ag2O with imidazolium sulfonates 1a-f in
water at ambient temperature provided the [Ag(NHC)2]
complexes 3a-f in good yields (Scheme 1). Complexes 3a,
c,d are readily soluble and stable in H2O. On the other hand,
the Ag complexes 3b,f with N-aryl-substituted ligands de-
composed in aqueous solution and were used for carbene
transfer immediately as prepared.
Negative ion mode electrospray ionization mass spectra
(ESI-MS) and X-ray structural analysis of bis-carbene silver
complexes excluded the presence of halide coordinated
directly to the central silver atom as well as the presence of
a [AgX2]- anion, as was observed in complexes prepared
from imidazolium halide precursors.29
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Weinheim, Germany, 1998.
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2006, 25, 644–648. (c) Mohr, F.; Sanz, S.; Tiekink, E. R. T.; Laguna, M.
Organometallics 2006, 25, 3084–3087.
X-ray-quality crystals of complex 3a were obtained by
crystallization from H2O/MeOH. The two carbene ligands
are coplanar and are linearly coordinated to Ag, and one of
the sulfonate groups serves as a counterion toward the
silver(I) cation (Figure 2). The solid-phase structure is
stabilized by ionic interactions and extensive hydrogen-bond
network. Silver atoms are in special positions at the inversion
center. The crystal lattice includes two molecules of H2O and
two types of sodium cations, mirroring the slight asymmetry
of the ethylsulfonate side chains. The first type of sodium (Na1)
is in a general position and is surrounded by four oxygen atoms
from sulfonate groups as well as two cis-coordinated oxygen
€
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(Hoechst AG) U.S. Patent 5,663,451, 1997. (b) Yoshizawa, M.; Ohno,
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lics 2004, 23, 4817–4820. (e) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka,
M. Angew. Chem., Int. Ed. 2002, 41, 4563–4565. (f) Clavier, H.; Grela, K.;
Kirshing, A.; Mauduit, M.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46,
6786–6801. (g) Guzajski, Ł.; Michrowska, A.; Naroz_nik, J.; Kaczmarska, Z.;
Rupnicki, L.; Grela, K. ChemSusChem 2008, 1, 103–109.
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Griffin, S. T.; Rogers, R. D.; Kirk, M. C.; Shaughnessy, K. H.
Organometallics 2006, 25, 5151–5158. (b) da Costa, A. P.; Mata, J. A.;
Royo, B.; Peris, E. Organometallics 2010, 29, 1832–1838.
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Chem. 1997, 547, 357–366.
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2005, 46, 2577–3580. (b) Hong, S. H.; Grubbs, R. H. J. Am. Chem. Soc.
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Almassy et al.
2486 Organometallics, Vol. 29, No. 11, 2010
Figure 1. Imidazolium sulfonate zwitterions 1a-f.
Scheme 1. Preparation of Bis-Carbene Silver(I) Zwitterionic
Complexes 3a-f
Figure 2. ORTEP diagram (50% probability ellipsoids) of the
complex Na3[Ag(1a)2] 2H2O in the crystal state. Selected bond
3
lengths (A) and angles (deg): Ag-C2, 2.066(5); N1-C2-N3,
103.7(4); N1-C2-Ag, 127.7(3); N3-C2-Ag, 128.4(3); C2-
Ag-C20, 180.0; C2-N1-C11-C12, -117.8; C2-N3-C31-
C32, 105.8; N1-C11-C12-S1, 73.1; N3-C31-C32-S2,
-177.8.
atoms of water. The second type (Na2) is in a special position
and is surrounded by two trans-coordinated oxygen atoms
from sulfonate groups and four oxygen atoms of water, form-
ing an infinite polymeric network, with abundance of Na1/
Na2 = 2/1 (Figure 3). The distance between two adjacent silver
atoms is 5.638 A, and the Ag-C(2) bond length is 2.066(5) A,
similar to the bond lengths of other [Ag(NHC)2] complexes
reported.20,30 A search of the Cambridge Structural Database31
(CSD, Version 5.31, November 2009) resulted in 28 hits for
mononuclear NHC-Ag-NHC compounds with an average
Ag-C distance of 2.088(8) A.
Figure 3. Packing diagram showing the arrangement of Na3-
[Ag(1a)2] 2H2O units connected by infinite chains of sodium
cations. All hydrogen atoms have been omitted for clarity.
3
The target AuI-NHC complexes were obtained by car-
bene transfer from complexes 3a-f following the procedure
of Wang and Lin.32 Reaction of complexes 3a-e with
[AuCl(SMe2)] or [AuCl(tht)] (tht = tetrahydrothiophene)
provided mixtures of the mono-carbene chloro complexes
[AuCl(NHC)] (4a-e) and corresponding bis-carbene com-
plexes (5a-e) (Scheme 2, Table 1). Bis-carbene complexes
are, in general, less soluble in MeOH and EtOH. Complexes
4a-e were characterized by 1H and 13C NMR and ESI-MS.
Bis-carbene complexes were characterized by 1H and
13C NMR as byproducts. 13C NMR signals of Au-C atoms
of bis-carbene complexes 5a-f are found between 184.2 and
182.9 ppm and in mono-carbene complexes 4a-e between
168.1 and 166.0 ppm. These signals are shifted around
10 ppm upfield compared to the signals for the correspond-
ing dimethylimidazolium- and diethylimidazolium-derived
AuI mono-carbene complexes.33
with 3a and has almost identical unit cell dimensions (for
details of the X-ray structure analysis see the Supporting
Information). The distance between two adjacent gold atoms
is 5.594 A; therefore, there is no evidence for the aurophilic
interaction reported for similar AuI bis-carbene com-
plexes.14,34 The Au-C(2) distance is 2.025(10) A, in good
agreement with the average of 23 hits in the CSD of 2.026(15) A.
Alkyl-substituted mono-carbene complexes in aqueous
solution convert slowly to the corresponding bis-carbene
complexes. This change is accompanied by a violet colora-
tion of the solutions, which may be due to the presence of
gold nanoparticles. However, the mono-carbene species are
perfectly stable in the presence of electrolytes such as NaPF6,
NaCl, NaOH, and H2SO4. Conversion of aryl-substituted
monocarbene complexes proceeds more quickly. Complex
4b converts completely to the bis-carbene complex within 24
h in D2O at room temperature. The monomeric complex 4f
[AuCl(1f)] was not observed at all, and only bis-carbene
complex 5f was isolated.
X-ray-quality crystals of complex 5a were obtained by
crystallization from H2O/MeOH. Complex 5a is isostructural
(30) dit Dominique, F. J.-B.; Gornitzka, H.; Hemmert, C. J. Orga-
nomet. Chem. 2008, 693, 579–583.
(31) Allen, F. H. Acta Crystallogr. 2002, B58, 380–388.
(32) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972–975.
(33) Wang, H. M. J.; Chen, C.Y. L.; Lin, I. J. B. Organometallics
1999, 18, 1216–1223.
(34) (a) Catalano, V. J.; Moore, A. L. Inorg. Chem. 2005, 44, 6558–
6566. (b) Wang, H. M. J.; Vasam, C. S.; Tsai, T. Y. R.; Chen, S.-H.; Chang, A.
H. H.; Lin, I. J. B. Organometallics 2005, 24, 486–493.

Article
Organometallics, Vol. 29, No. 11, 2010 2487
Scheme 2. Formation of Mono-Carbene Complex 4a and
Bis-Carbene AuI Complex 5a by Transmetalation from Silver
Carbene Transfer Complexes 3a and [AuCl(tht)]
Table 2. Hydration of Terminal Alkynesa
cat. (amt
entry (mol %))
conversn
(%)c
TOF
(h-1
)
R
time (h)
1
2
3
4
5
6
7
8
4a (2.0)b
4b (2.0)b
4c (2.0)b
4d (2.0)b
4e (2.0)b
4a (0.5)
4a (0.5)
4a (2.0)
4a (0.5)
4a (2.0)
4a (0.5)
4a (0.1)
Ph
Ph
Ph
Ph
Ph
3.0
3.0
3.0
3.0
3.0
0.5
0.5
0.5
1.5
0.5
0.5
0.5
88.4
78.8
92.5
61.4
93.6
50.9d
23.4d
19.3
21.5
55.1
35.1
20.0
14.7
13.1
15.4
10.2
15.6
203.7
93.6
19.3
28.6
55.1
140.3
400.2
CH3(CH2)3
CH3(CH2)5
4-CH3-Ph
Table 1. Composition of Mixtures of Mono-Carbene/
Bis-Carbene AuI Complexes
9
4-CH3-Ph
10
11
12
4-CH3O-Ph
4-CH3O-Ph
4-CH3O-Ph
[Ag(NHC)2]
[AuCl(NHC)]/[Au(NHC)2]a
overall yield (%)
3a
3b
3c
3d
3e
3f
4a/5a 89/11
4b/5b 83/17
4c/5c 82/18
4d/5d 80/20
4e/5e 91/9
78
82
80
47
59
34
a Conditions (except where noted): substrate, 1.00 mmol; H2O/
MeOH 1/5, 5 mL; reflux. b H2O/MeOH 1/1, 5 mL. c Conversion deter-
mined by GC. d Conversion determined by 1H NMR.
4f/5f 0/100
a Determined by 1H NMR.
that with tertiary phosphine ligands (substrate phenylacety-
lene, [Au(OTf)(TPPTS)] 0.1 mol %, H2SO4 10 mol %, TOF
427 h-1).18
Complexes 4a-e were found to be active catalysts of the
hydration of aromatic and aliphatic terminal alkynes in
refluxing MeOH/H2O solutions (Table 2). In order to make
a direct comparison of the catalytic properties of the new Au
NHC complexes to those of known Au tertiary phosphine
catalysts, the reaction conditions were chosen to be identical
with those used by Laguna and co-workers.18 It is remark-
able that;although sulfuric acid could be used beneficially
(vide infra);the reactions proceed with high rates and high
conversions (Table 2, entries 3 and 5 and Figure S3 in the
Supporting Information) also in the absence of an acid
cocatalyst. This is a definite advantage in the case of acid-
sensitive substrates. These reactions could be run also in neat
water with considerably lower rate due to the low solubility
of the substrates. Such biphasic systems allow the easy
separation of the catalyst from the products (and unreacted
substrates). Addition of H2O proceeded selectively following
Markovnikov’s rule. Internal alkynes did not react at all.
With ethynylbenzene as substrate and 2.0 mol % of
[AuCl(NHC)], conversions in the range of 79-94% could
be achieved with all catalysts except 4d, the most active being
4c,e (Table 2, entries 1-5). Although these activities (a time-
average TOF of 13-16 h-1) are substantially smaller than
those obtained by Tanaka and co-workers with the
[Au(CH3)(PPh3)] þ acid catalyst,13a they are in the range
of those determined under comparable conditions with
the water-soluble Au phosphine catalysts [AuCl(P)]: P =
TPPMS (2), TPPDS (10), TPPTS (25) (TPPMS, TPPDS,
TPPTS = mono-, di-, and trisulfonated triphenylphosphine,
respectively; TOFs for hydration of phenylacetylene in
parentheses).18
Catalytic activity in hydration of alkynes can be improved
by the addition of appropriate cocatalysts such as Lewis and
Brønsted acids13,16,35 or silver salts,36 generating active [Au]þ
species by exchange of chloro ligand for a noncoordinating
anion. We explored the effect of cocatalysts on the hydration
of phenylacetylene catalyzed by complex 4a (Table 3 and
Figure S3 (Supporting Information)). Addition of 10 mol %
of H2SO4 doubled the reaction rate; however, 20 mol % of
H2SO4 led to only a slight further increase in activity
(Table 3, entries 2 and 3). The catalyst is quite robust, since
with a [substrate]/[catalyst] ratio of 1000, 93.5% conversion
(TON = 935) was obtained (Table 3, entries 4-6). Sulfuric
acid itself is catalytically inactive under the same reaction
conditions (entry 9). Surprisingly, silver triflate decreased the
activity of the catalyst (entry 7). Addition of AgOTf to an
aqueous solution of complex 4a resulted in precipitation of
AgCl, together with a violet coloration of the solution and
formation of metal particles, indicating decomposition of the
catalyst. Reaction of 4a with AgBF4 in the presence of
phenylacetylene also yielded an AgCl precipitate; however,
in this case a stable strong yellow solution was formed and
the hydration reaction did not proceed at all. Different
effects of AgOTf and AgBF4 are not unprecedented, due to
the somewhat stronger coordination ability of triflate ion. It
is also noted here that hydration of phenylacetylene did not
proceed in the presence of NaOH. It is tempting to speculate
that this inhibition may be due to the formation of a stable
Na2[Au(OH)(1a)] species similar to [Au(OH)(IPr)] described
recently by Nolan and co-workers.14c
Concerning the mechanism of gold-catalyzed alkyne hy-
drations, two possible pathways have been suggested in the
literature: one involving enol ethers and ketals16d,34 and the
other procceding by direct attack of water on the coordi-
nated alkyne.13a,35 A recent detailed study by Leyva and
Complex 4a was used as a catalyst to explore the reactivity
of various substrates. The highest TOFs were obtained with
electron-rich aliphatic and aromatic alkynes (Table 2, entries
6, 7, and 10-12). This is in accord with π-coordination of the
alkyne on a Lewis acidic catalytic species in the initial step of
the catalytic cycle. In the hydration of p-ethynylanisole using
0.1 mol % of catalyst 4a, a TOF of 400.2 h-1 was achieved
(Table 2, entry 12), showing again the reactivity of the
[AuCl(NHC)] catalysts being approximately the same as
(35) Teles, J. H.; Brode, S.; Chabanas, M. Angew. Chem., Int. Ed.
1998, 37, 1415–1418.
(36) Casado, R.; Contel, M.; Laguna, M.; Romero, P.; Sanz, S. J. Am.
Chem. Soc. 2003, 125, 11925–11935.

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Almassy et al.
2488 Organometallics, Vol. 29, No. 11, 2010
Table 3. Hydration of Phenylacetylene Catalyzed by 4a: Effect
of Additivesa
(Mo KR radiation, λ = 0.710 73 A, ω motion). The structures
were solved using SIR-92 software38 and refined on F2 using
SHELX-97 program;39 publication material was prepared with
the WINGX-97 suite.40 Significant residual electron density
remained close (<1 A) to the gold or silver atom. Non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
placed into geometric positions, except water hydrogen atoms,
which could be found in the difference electron density map but
their distances from the oxygen atom had to be constrained.
However, the orientation of some of the water molecules is
ambiguous because heavy elements of Ag or Au made it impos-
sible to determine the exact positions of water protons. This fact
also suggests that strong electrostatic interactions and coordina-
tive bonds have a much greater role in the stabilization of the
lattice than do hydrogen bonds. Further details of the structure
determination can be found in the Supporting Information.
Preparation of Sodium 2,20-(Imidazolium-1,3-diyl)bisethane-
sulfonate (Na-1a). A mixture of taurine (10.00 g, 80.0 mmol)
and glyoxal (4.2 mL, 36.3 mmol, 40% aqueous solution) in H2O
(100 mL) was stirred and heated to 75 °C for 24 h. Paraformal-
dehyde (4.36 g, 145.3 mmol) and HCl (12 mL, 145.3 mmol, 37%
aqueous solution) were added, and the mixture was stirred and
heated to 75 °C for 92 h. Water was evaporated under vacuum.
The product was dissolved in boiling MeOH (60 mL), and excess
taurine was filtered off. The filtrate was evaporated under
vacuum, and the product H-1a was recrystallized from EtOH.
The corresponding sodium salt Na-1a was prepared by neutra-
lization with an equimolar amount of NaHCO3: white crystal-
line solid, yield 60%. 1H NMR (D2O, 360 MHz): δ 8.89 (s, 1H,
amt of 4a
entry (mol %)
cocat. (amt
(mol %))
time conversn TOF
(%)b
(h)
(h-1
)
1
2
3
4
5
6
7
8
9
2.0
2.0
2.0
0.1
0.1
0.1
1.0
1.0
0.5
0.5
0.5
3.0
6.0
48.0
1.0
4.0
4.0
20.1
39.7
43.5
30.7
43.2
93.5
5.0
20.1
39.7
43.5
102.2
72.0
19.5
5.0
H2SO4 (10.0)
H2SO4 (20.0)
H2SO4 (10.0)
H2SO4 (10.0)
H2SO4 (10.0)
AgOTf (1.0)
AgOTf (1.0) H2SO4 (20.0)
H2SO4 (20.0)
1.6
n/a
0.4
n/a
a Conditions: substrate, 1.00 mmol; H2O/MeOH 1/5, 5 mL; reflux.
b Conversion determined by GC.
Corma16c has revealed that with an [Au(L)NTf2] (L =
2-(dicyclohexylphosphino)-20,60-dimethoxybiphenyl, NTf2 =
bis(trifluoromethanesulfonyl)imidate) catalyst in water/
methanol mixtures hydration of phenylacetylene involved
the active role of methanol, and this favors the enol ether/
ketal route. At this point in our investigations we do not have
enough data to draw sound conclusions in this respect.
Although no intermediates or products other than methyl
ketones have been observed in the hydration of terminal
alkynes in water-methanol mixtures with our catalysts, this
does not rule out the intermediate formation of enol ethers
and ketals. However, the effect of changing solvent composi-
tion is worth considering. In general, hydrations proceeded
with high conversions in MeOH/H2O mixtures with compo-
sitions from 1/5 to 5/1, while in the hydration of phenylace-
tylene catalyzed by complex 4a in refluxing water 17%
conversion was achieved after 3 h. Even lower conversions
were obtained under the same conditions in neat (undried)
methanol (2.7%) or in a MeOH/H2O 98/2 mixture (6.4%).
Considering these results, we suppose that hydration pro-
ceeds through the direct addition of water instead of forma-
tion of methanol adducts.
3
H-C(2)), 7.53 (s, 2H, H-C(4,5)), 4.56 (t, J = 6.5 Hz, 4H,
H2C-N), 3.38 (t, 3J = 6.5 Hz, 4H, H2C-S). 13C NMR (D2O, 75
MHz): δ 136.8, 122.6, 49.7, 45.1.
Preparation of 4-(Imidazol-1-yl)benzenesulfonic Acid (H-2). A
solution of sulfanilic acid (3.00 g, 17.22 mmol) in H2O (220 mL)
was cooled in an ice bath. Glyoxal (2.50 g, 17.2 mmol, 40%
aqueous solution) was added, and the mixture was stirred at
room temperature for 28 h. Aqueous NH3 (2.35 g, 34.4 mmol,
25% aqueous solution) and paraformaldehyde (1.03 g, 34.4 mmol)
were added. The mixture was stirred and heated to 70 °C for
2 h; then it was removed from the heating bath and HCl
(30 mL, 18.5% aqueous solution) was added slowly over
5 min. The mixture was stirred and heated to 70 °C for 60 h.
The solvent was evaporated under vacuum, EtOH (40 mL) was
added, and the resulting precipitate was filtered off, washed with
EtOH (2 ꢀ 10 mL), and dried under vacuum. The product was
In summary, we have prepared for the first time several
water-soluble gold(I) N-heterocyclic carbene complexes with
N-sulfoalkyl- and N-sulfoarylimidazolylidene ligands which
showed high activity in the catalysis of alkyne hydration,
even in the absence of an acid cocatalyst. Such complexes
provide a new entry to homogeneous and biphasic gold
catalysis in aqueous systems.
1
obtained as a brownish solid, yield 94%. H NMR (D2O, 360
MHz): δ 9.25 (s, 1H, H-C(2)), 8.00 (m, 2H, H-CPh), 7.94 (s, 1H,
H-CIm), 7.78 (m, 2H, H-CPh), 7.68 (s, 1H, H-CIm). 13C NMR
(D2O, 75 MHz): δ 144.0, 136.8, 134.0, 127.6, 122.9, 121.3, 120.6.
Sodium 4-(imidazol-1-yl)benzenesulfonate (2) was prepared by
neutralization of the acid H-2 with an equimolar amount of
NaHCO3.
Experimental Section
Ag2O was prepared by the reaction of AgNO3 and NaOH.
The precursor [AuCl(tht)] was prepared from Na[AuCl4] H2O
General Procedure for the Alkylation of Sodium 4-(Imidazol-1-yl)-
benzenesulfonate. To a solution of propanesultone or sodium
2-bromoethanesulfonate (3.0 mmol) in DMF (4 mL) was added
compound 2 (0.50 g, 2.0 mmol), and the reaction mixture was
stirred at reflux for 3 h. The resulting precipitate was filtered,
washed with acetone (2 ꢀ 10 mL), and dried under vacuum.
Sodium imidazolium bis(sulfonate) zwitterion Na-1b was obtained
as a brownish solid, yield 57%. 1H NMR (D2O, 360 MHz): δ 9.39
(s, 1H, H-C(2)), 7.93 (m, 2H, H-CPh), 7.88 (d, 3J = 1.6 Hz, 1H,
H-CIm), 7.72 (d, 3J = 1.6 Hz, 1H, H-CIm), 7.69 (m, 2H, H-CPh),
3
and tetrahydrothiophene according to a literature procedure.37
All other reagents were obtained commercially and used as
received. Reactions of organometallic compounds as well as
catalytic experiments were performed in Schlenk tubes with
1
deaerated solvents under a nitrogen atmosphere. H and 13C
NMR spectra were recorded on Bruker Avance 360 MHz
spectrometer. Coupling constants are reported in Hz. ESI mass
spectra were recorded on a Bruker BioTOF II. ESI-TOF
spectrometer. Reaction mixtures in hydrations of arylacetylenes
were analyzed by gas chromatography (HP5890 Series II;
Chrompack WCOT Fused Silica 30 m ꢀ 32 mm CP WAX52CB;
FID; carrier gas argon). X-ray diffraction data of 3a and 5a were
collected at 293(1) K on Enraf-Nonius MACH3 diffractometer
3
3
4.67 (t, J = 5.8 Hz, 2H, H2C-N), 3.45 (t, J = 5.8 Hz, 2H;
H2C-S). 13C NMR (D2O, 75 MHz): δ 144.0, 136.7, 127.6, 123.4,
122.9, 121.8, 49.7, 45.7.
(39) Sheldrick, G. M. Programs for Crystal Structure Analysis
€
ꢀ
€
(37) Uson, R.; Laguna, A.; Laguna, M. Inorg. Synth. 1989, 26, 86.
(38) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.
(Release 97-2); Institut f€ur Anorganische Chemie der Universitat, Gottingen,
Germany, 1998.
J. Appl. Crystallogr. 1993, 26, 343.
(40) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

Article
Sodium imidazolium bis(sulfonate) zwitterion Na-1f was
Organometallics, Vol. 29, No. 11, 2010 2489
Complex 4b, Na2[AuCl(1b)]. ESI-MS for C11H10AuClN2-
Na2O6S2 (m/z): 584.931 (M(35Cl) - Naþ), 281.971 (M(37Cl) -
2Naþ), 280.973 (M(35Cl) - 2Naþ). 1H NMR (D2O, 360 MHz):
δ 7.86 (d, 3J = 8.5 Hz, 2H, H-CPh), 7.79 (d, 3J = 8.7 Hz, 2H,
H-CPh), 7.41 (m, 2H, H-CIm), 4.59 (t, 3J = 6.7 Hz, 2H, H2C-
N), 3.46 (t, 3J = 6.7 Hz, 2H, H2C-S). 13C NMR (D2O, 75 MHz):
δ 166.0, 139.4, 133.9, 127.0, 126.8, 125.8, 125.5, 51.1, 46.7.
Complex 5b, Na3[Au(1b)2]. 1H NMR (D2O, 360 MHz): δ 7.77
(d, 3J = 8.3 Hz, 4H, H-CPh), 7.57 (d, 3J = 8.3 Hz, 4H, H-CPh),
7.36 (m, 4H, H-CIm), 4.44 (t, 4H; 3J = 6.4 Hz, H2C-N), 3.30 (t,
3J = 6.4 Hz, 4H, H2C-S). 13C NMR (D2O, 75 MHz): δ 182.9,
142.7, 142.2, 127.0, 124.8, 122.7, 121.7, 51.3, 47.3.
obtained as a brownish solid, yield 79%. ESI-MS for
C12H13N2NaO6S2 (m/z): 345.031 (M - Naþ). 1H NMR (D2O,
360 MHz): δ 9.35 (s, 1H, H-C(2)), 7.94 (m, 2H, H-CPh), 7.89 (s,
1H, H-CIm), 7.70 (m, 2H, H-CPh), 7.69 (s, 1H, H-CIm),
3
3
4.42 (t, J = 7.2 Hz, 2H, H2C-N), 2.92 (t, J = 7.4 Hz, 2H,
H2C-S), 2.33 (tt, 3J = 7.4 Hz, 3J = 7.2 Hz, 2H, H2C). 13C NMR
(D2O, 75 MHz): δ 143.9, 136.7, 127.6, 123.2, 122.8, 121.9, 48.4,
47.2, 25.0.
General Procedure for the Preparation of Ag(NHC)2 Com-
plexes. A mixture of imidazolium sulfonate 1a-f (2.0 mmol),
Ag2O (0.46 g, 2.0 mmol), and H2O (3 mL) was stirred at room
temperature in darkness for 3.5 h. NaCl (0.12 g, 2.0 mmol) was
added, and the mixture was passed through a short Super-Cel
pad. Solvent was evaporated under vacuum. Products were
crystallized from H2O/MeOH or H2O/EtOH.
Complex 4c, Na[AuCl(1c)]. ESI-MS for C7H11AuClN2NaO3S
1
(m/z): 434.995 (M(35Cl) - Naþ). H NMR (D2O, 360 MHz):
δ 7.18 (d, 3J = 1.6 Hz, 1H, H-CIm), 7.12 (d, 3J = 1.6 Hz, 1H,
3
H-CIm), 4.21 (t, 3J = 6.9, J = 6.9 Hz, 2H, H2C). 13C NMR
Complex 3a, Na3[Ag(1a)2]. White solid, yield 60%. ESI-MS
for C14H20AgN4Na3O12S4 (m/z): 716.901 (M - Naþ). 1H NMR
(D2O, 360 MHz): δ 7.22 (s, 4H, H-CIm), 4.53 (t, 3J = 6.6 Hz,
(D2O, 75 MHz): δ 167.5, 122.7, 121.0, 49.2, 47.8, 37.7, 26.0.
Solubility: 680 mg/1 mL of H2O (20 °C).
Complex 5c, Na[Au(1c)2]. ESI-MS for C14H22AuN4NaO6S2
(m/z): 603.007 (M - Naþ). 1H NMR (D2O, 360 MHz): δ 7.18 (d,
3J = 1.4 Hz, 2H, H-CIm), 7.15 (d, 3J = 1.4 Hz, 2H, H-CIm),
4.28 (t, 3J = 6.9 Hz, 4H, H2C-N), 3.81 (s, 6H, H3C-N), 2.87
(t, 3J = 6.8 Hz, 4H, H2C-S), 2.21 (tt, 3J = 7.7 Hz, 3J = 6.8 Hz,
4H, H2C). 13C NMR (D2O, 75 MHz): δ 183.7, 123.0, 121.4, 49.1,
47.9, 37.5, 26.4.
3
8H, H2C-N), 3.38 (t, J = 6.6 Hz, 8H, H2C-S). 13C NMR
(D2O, 75 MHz): δ 180.8, 121.7, 49.8, 45.2.
Complex 3b, Na3[Ag(1b)2]. Unstable and was not isolated. 1H
3
NMR (D2O, 360 MHz): δ 7.77 (d, J = 8.3 Hz, 4H, H-CPh),
7.57 (d, 3J = 8.3 Hz, 4H, H-CPh), 7.37 (s, 2H, H-CIm), 7.36 (s,
2H, H-CIm), 4.44 (t, 3J = 6.4 Hz, 4H, H2C-N), 3.30 (t, 3J = 6.4
Hz, 4H, H2C-S). 13C NMR (D2O, 75 MHz): δ 142.7, 142.2,
127.0, 124.8, 122.7, 121.7, 51.3, 47.3. The signal of carbon
C(2)-Ag was not resolved.
Complex 4d, Na[AuCl(1d)]. ESI-MS for C10H17AuClN2-
NaO3S (m/z): 477.039 (M - Naþ). 1H NMR (D2O, 360 MHz):
δ 7.19 (s, 1H, H-CIm), 7.17 (s, 1H, H-CIm), 4.19 (t, 2H, 3J = 6.6
1
3
Complex 3c, Na[Ag(1c)2]. White solid, yield 43%. H NMR
Hz, H2C-N), 4.05 (t, 2H, J = 6.8 Hz, H2C-N), 2.82 (t, 2H,
(D2O, 360 MHz): δ 7.18 (d, 3J = 1.8 Hz, 2H, H-CIm), 7.12 (d,
3J = 1.8 Hz, 2H, H-CIm), 4.20 (t, 3J = 6.8 Hz, 4H, H2C-N),
3.75 (s, 6H, H3C-N), 2.82 (t, 3J = 7.6 Hz, 4H, H2C-S), 2.22 (tt,
3J = 7.6 Hz, 3J = 6.8 Hz, 4H, H2C). 13C NMR (D2O, 75 MHz):
δ 179.7, 122.7, 121.3, 49.6, 47.8, 38.1, 26.5.
3J = 7.0 Hz, H2C-S), 2.20 (m, 2H, H2C), 1.72 (m, 2H, H2C),
1.22 (m, 2H, H2C), 0.82 (t, 3H, 3J = 7.0 Hz, H3C). 13C NMR
(D2O, 75 MHz): δ 166.9, 121.6, 121.2, 50.8, 49.3, 47.8, 32.5, 26.1,
19.0, 13.0.
Complex 5d, Na[Au(1d)2]. ESI-MS for C20H34AuN4NaO6S2
(m/z): 687.166 (M - Naþ). 1H NMR (D2O, 360 MHz): δ 7.24 (d,
3J = 1.4 Hz, 2H, H-CIm), 7.23 (d, 3J = 1.4 Hz, 2H, H-CIm),
Complex 3d, Na[Ag(1d)2]. White solid, yield 56%. 1H NMR
(D2O, 360 MHz): δ 7.19 (s, 2H, H-CIm), 7.17 (s, 2H, H-CIm),
4.19 (t, 3J = 6.6 Hz, 4H, H2C), 4.06 (t, 3J = 6.8 Hz, 4H, H2C),
3
3
4.27 (t, J = 6.6 Hz, 4H, H2C-N), 4.15 (t, J = 6.7 Hz, 4H,
H2C-N), 2.82 (t, 4H, H2C-S), 2.67 (m, 4H, H2C), 1.80 (t, 3J =
7.0 Hz, 4H, H2C), 1.26 (m, 4H, H2C), 0.84 (t, 3J = 7.0 Hz, 6H,
H3C). 13C NMR (D2O, 75 MHz): δ 182.9, 122.3, 122.0, 50.9,
49.3, 47.9, 33.0, 26.5, 19.3, 13.1.
2.77 (t, 3J = 7.7 Hz, 4H, H2C), 2.20 (m, 4H, H2C), 1.73 (m, 4H,
3
H2C), 1.21 (m, 4H, H2C), 0.81 (t, J = 7.0 Hz, 6H, H3C). 13
C
NMR (D2O, 75 MHz): δ 178.9, 121.8, 121.3, 51.3, 49.8, 47.9,
33.0, 26.6, 19.2, 13.0.
Complexes 3e, Na3[Ag(1e)2] and 3f, Na3[Ag(1f)2] are unstable
and were not isolated.
1
Complex 4e, Na2[AuCl(1e)]. H NMR (D2O, 360 MHz): δ
3
7.18 (s, 2H, H-CIm), 4.22 (t, J = 6.9 Hz, 4H, H2C-N), 2.82
General Procedure for Preparation of [AuCl(NHC)] Com-
plexes. .A solution of Ag[(NHC)2] 3a-f (0.5 mmol) in H2O
(2 mL) was added dropwise to a mixture of [AuCl(tht)]
(0.34 g, 1.05 mmol) and H2O (2 mL). The reaction mixture
was stirred at room temperature for 3 h. NaCl (0.30 g, 0.5 mmol)
was added, and the mixture was passed through a short Super-
Cel pad, followed by vacuum evaporation of the solvent.
Mixtures of mono- and bis-carbene AuI complexes were
obtained, except that complex 3f provided exclusively bis-
carbene complex 5f. Mono-carbene complexes were isolated
by precipitation of the bis-carbene minor product from the
concentrated aqueous solution of a product mixture by addition
of a small amount of methanol. For yields and compositions of
product mixtures, see Table 1. Bis-carbene complexes can be
prepared by using an equimolar amount of [AuCl(tht)].
Complex 4a, Na2[AuCl(1a)]. ESI-MS for C7H10AuClN2-
Na2O6S2 (m/z): 536.925 (M - Naþ), 256.9654 (M - 2Naþ).
1H NMR (D2O, 360 MHz): δ 7.22 (s, 2H, H-CIm), 4.50 (t, 3J =
6.9 Hz, 4H, H2C-N), 3.41 (t, 3J = 6.9 Hz, 4H, H2C-S).
13C NMR (D2O, 75 MHz): δ 168.1, 121.7, 51.1, 46.6. Solubility:
320 mg/1 mL of H2O (20 °C).
(t, 3J = 7.8 Hz, 4H, H2C-S), 2.20 (tt, 3J = 7.8 Hz, 3J = 6.9 Hz,
4H, H2C). 13C NMR (D2O, 75 MHz): δ 167.1, 121.5, 49.4, 47.8,
26.0. Solubility: 355 mg/1 mL of H2O (20 °C).
Complex 5e, Na3[Au(1e)2]. 1H NMR (D2O, 360 MHz): δ 7.21
(s, 2H, H-CIm), 4.28(t, 3J = 6.3, 4H, H2C-N), 2.84 (t, 3J = 7.2
Hz, 4H, H2C-S), 2.27 (tt, 3J = 7.2 Hz, 3J = 6.3 Hz, 4H, H2C).
13C NMR (D2O, 75 MHz): δ 183.3, 121.5, 49.3, 47.8, 26.4.
Complex 5f, Na3[Au(1f)2]. ESI-MS for C24H26AuN4-
Na3O12S4 (m/z): 930.982 (M - Naþ). 1H NMR (D2O, 360
MHz): δ 7.86 (m, 4H, H-CPh), 7.62 (m, 4H, H-CPh), 7.45 (d,
3J = 1.9 Hz, 2H, H-CIm), 7.42 (d, 3J = 1.9 Hz, 2H, H-CIm),
3
3
4.11 (t, J = 6.7 Hz, 4H, H2C-N), 2.79 (t, J = 7.7 Hz, 4H,
H2C-S), 2.24 (tt, 3J = 7.7 Hz, 3J = 6.7 Hz, 4H, H2C). 13C NMR
(D2O, 75 MHz): δ 181.9, 143.5, 141.1, 127.0, 125.7, 125.3, 122.8,
49.6, 47.7, 26.2.
Typical Terminal Alkyne Hydration Experiment. A solution of
the catalyst (0.02 mmol) in H2O (2.5 mL) was added to a
solution of the terminal alkyne (1.0 mmol) in MeOH (2.5 mL).
The reaction mixture was stirred and heated to reflux for 3 h.
Samples (300 μL) were extracted with toluene (1 mL), dried over
MgSO4, and subjected to gas chromatography. In the hydration
of aliphatic alkynes, the samples were extracted with CDCl3
(1 mL), washed with H2O (3 ꢀ 1 mL), and dried over MgSO4.
The composition was determined by 1H NMR.
Complex 5a, Na3[Au(1a)2]. ESI-MS for C14H20AuN4-
Na3O12S4 (m/z): 806.956 (M - Naþ). 1H NMR (D2O, 360
MHz): δ 7.25 (s, 4H, H-CIm), 4.60 (t, 3J = 6.7 Hz, 8H,
H2C-N), 3.46 (t, 3J = 6.7 Hz, 8H, H2C-S). 13C NMR (D2O,
75 MHz): δ 184.2, 122.0, 51.5, 46.5. Solubility: 300 mg/1 mL
H2O (20 °C).
Acknowledgment. This research was supported by the
EU and cofinanced by the European Social Fund through

ꢀ
Almassy et al.
2490 Organometallics, Vol. 29, No. 11, 2010
the Social Renewal Operational Programme under the
ꢀ
project CHEMIKUT (TAMOP-4.2.2-08/1-2008-0012).
Network system (project AQUACHEM; MRTN-CT-
2003-503864).
Financial support by the Hungarian National Research
and Technology Office-National Research Fund (NKTH-
OTKA K 68482) and by TEVA Hungary Ltd. is grate-
fully acknowledged. A.A. is grateful for a fellow-
ship within the FP6Marie Curie Research Training
Supporting Information Available: CIF files, figures, and
tables giving details of the X-ray structure analysis of complexes
3a and 5a and the time course of hydration of phenylacetylene
catalyzed by 4a with and without additives. This material is
available free of charge via the Internet at http://pubs.acs.org.