Synthesis and characterization of gold(III) complexes bearing a picoline-functionalized N-heterocyclic carbene

Article abstract of DOI:10.1002/zaac.201100341

3-Methyl-1-(2-picolyl)-imidazolium chloride (1) has been synthesized and used as a precursor for the preparation of the (NHC)AgCl complex [NHC = 3-methyl-1-(2-picolyl)imidazol-2-ylidene] (2). Transmetalation of 2 with (tht)AuBr (tht = tetrahydrothiophene) yields the corresponding (NHC)AuBr complex 3, which is further oxidized by Br₂ to give the (NHC)AuBr ₃ compound 4. Treatment of 4 with one equivalent of solid AgBF ₄ affords the [(NHC)AuBr₂][BF₄] congener 5 as a pale green, crystalline powder. The structure of 4 and 5 were determined by single-crystal X-ray diffraction, revealing for 5 a κ-N-coordination of the Au^III atom by the picolyl nitrogen atom. Further attempts to exchange all bromides by carboxylates results in the reduction to the dimeric Au^I compound [(NHC)₂Au₂][BF₄] ₂, 6. Copyright

Full text of DOI:10.1002/zaac.201100341

ARTICLE
DOI: 10.1002/zaac.201100341
Synthesis and Characterization of Gold(III) Complexes Bearing a Picoline-
functionalized N-Heterocyclic Carbene
Christoph Topf,[a] Christa Hirtenlehner,[a] Michel Fleck,[b] Manuela List,[c] and
Uwe Monkowius*[a]
Keywords: N-Heterocyclic carbenes; Silver; Gold; Crystal Structure; Picoline
Abstract. 3-Methyl-1-(2-picolyl)-imidazolium chloride (1) has been equivalent of solid AgBF4 affords the [(NHC)AuBr2][BF4] congener
synthesized and used as a precursor for the preparation of the (NHC) 5 as a pale green, crystalline powder. The structure of 4 and 5 were
AgCl complex [NHC = 3-methyl-1-(2-picolyl)imidazol-2-ylidene] (2).
Transmetalation of 2 with (tht)AuBr (tht = tetrahydrothiophene) yields
the corresponding (NHC)AuBr complex 3, which is further oxidized
determined by single-crystal X-ray diffraction, revealing for 5 a κ-N-
coordination of the AuIII atom by the picolyl nitrogen atom. Further
attempts to exchange all bromides by carboxylates results in the re-
by Br2 to give the (NHC)AuBr3 compound 4. Treatment of 4 with one duction to the dimeric AuI compound [(NHC)2Au2][BF4]2, 6.
= C6H5, C6F5, Me; X = Cl, I) were reported but the exchange
Introduction
of the halides by other anionic (or neutral) ligands seems to be
In the last decade coinage metal complexes bearing N-het-
critical and frequently leads to the reduction to AuI or decom-
erocyclic carbenes (NHC) have been thoroughly investi-
position.[4,11]
gated.[1] Particularly since Wang and Lin proved their capa-
Just recently we reported about AgI, AuI and AuIII bearing
bility as versatile carbene transfer agents NHC–AgI complexes
dialkylamino substituted NHC ligands and their unusual coor-
are reported frequently.[2] For NHC–Au complexes numerous
dination chemistry.[12,13] In the solid state as well as in solution
applications were found ranging from homogeneous catalysts
the amino function is capable to coordinate the AuIII atom
for unique C–C, C–O, and C–N bond-forming reactions[3,4] to
forming a square-pyramidal coordination geometry, whereas
their pharmaceutical uses as anticancer, antiarthritis, and anti-
upon protonation of the amino nitrogen atom the AuIII gold
bacterial agent.[5,6] Nevertheless, the chemistry of gold is still
atom exists in the standard square-planar coordination environ-
dominated by the oxidation state +1 and its linearly coordinate
ment. Catalano et al. reported in a series of publications about
complexes of the type NHC–AuI–X or [(NHC)2Au]X. They are
the multifarious coordination chemistry of picolyl- and pyr-
conveniently synthesized by the reaction of (R2S)AuX (R2S =
idyl-functionalized NHC ligands in their AgI and AuI com-
Me2S, tetrahydrothiophene, X = halide) with a NHC–Ag com-
plexes.[14,15] Particularly fascinating are the unusual μ2-coordi-
plex or the free carbene. AuIII complexes are usually synthe-
nation of the carbene carbon atom in a trimeric AgI cluster[14]
sized by the oxidation of the AuI-congener with halogens (Cl2,
and a series of complexes comprising dimeric AgIAgI, AuIAuI,
Br2, I2). The direct synthesis starting from AuIII salts (e.g.
AuIAgI, or AuICuI species.[15] To extend our work on AuIII
KAuCl4) and a carbene precursor only works with special
complexes bearing functionalized NHC ligands, we studied the
functionality on the NHC ligand.[7] Nevertheless, studies deal-
coordination chemistry of 3-methyl-1-(2-picolyl)-imidazol-2-
ing with AuIII complexes bearing functionalized NHCs are
ylidene.
rare.[8] The most publications report about simple, non-func-
tionalized NHCs which are usually of the type (NHC)AuX3 or
[(NHC)2AuX2]X.[4,6,9,10] Complexes like (NHC)Au(Ar)X2 (Ar
Results and Discussion
* Dr. U. Monkowius
E-Mail: uwe.monkowius@jku.at
The imidazolium salt 1 is prepared by the reaction of 2-
[a] Institut für Anorganische Chemie
Johannes Kepler Universität Linz
Altenbergerstr. 69
(chloromethyl)pyridine with 1-methylimidazole in methanol
under reflux conditions as a very hygroscopic, brown powder.
The reaction with Ag2O in DCM yields the complex
[(NHC)2Ag][AgCl2] (2) in good yield and high purity as a
brownish powder. It should be mentioned that both 1 and 2
were previously reported in a patent.[16] Also known are the
analogous imidazolium iodide and the NHC–silver io-
dide.[17,18] The latter was found to crystallize as a trinuclear
aggregate of the form {[(NHC)2Ag]3(μ3-I)]I2. The stoichio-
4040 Linz, Austria
[b] Geozentrum – Universität Wien
Institut für Mineralogie und Kristallographie
Althanstr. 9
1090 Wien, Austria
[c] Institut für Chemische Technologie Organischer Stoffe
Johannes Kepler Universität Linz
Altenbergerstr. 69
4040 Linz, Austria
Z. Anorg. Allg. Chem. 2011, 637, (14-15), 2129–2134
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. Topf, C. Hirtenlehner, M. Fleck, M. List, U. Monkowius
ARTICLE
metric reaction with (tht)AuBr in DCM gives the AuI complex benzyl analogue (NHC)AuBrI2.[10] The AuIII atom adopts a
3,[19] which upon oxidation with Br2 at –40 °C affords the cor- distorted square-planar environment defined by the carbene
responding (NHC)AuBr3 complex 4. Addition of AgBF4 to 4 carbon atom and three bromide ions with an angular sum of
facilitates intramolecular substitution of one bromide ligand by exact 360° (Figure 1). All interatomic distances are lying in
the nitrogen atom of the picolyl moiety that is located in spatial the expected range: The Au–C distance is 2.04(1) Å and Au–
proximity to the AuIII atom. The hereby formed κ2CN-deriva- Br distances are lying in a narrow range of 2.40–2.43 Å. The
tive 5 is obtained as a light-green, microcrystalline powder imidazolyl ring plane is almost perpendicular to the gold coor-
(Scheme 1).
dination plane. Albeit the picolyl moiety points in the direction
of the C1–Au1–Br2 vector, no close cation–arene-interactions
between the pyridyl ring and the gold atom are present.[20,21]
The shortest Au–N3 distance is 3.25 Å, i.e. the picolyl nitrogen
atom is not involved in any coordinative bond.
Figure 1. Molecular structure of 4 (ORTEP; displacement ellipsoids at
the 50% probability level, hydrogen atoms are omitted for clearity).
Selected bond lengths /Å and angles /°: Au1–C1 2.04(1), Au1–Br1
2.418(2), Au1–Br2 2.398(2), Au1–Br3 2.426(1), Br1–Au1–Br2
91.7(1), Br1–Au1–C1 86.4(3), Br2–Au1–Br3 92.46(7), Br3–Au1–C1
89.4(3).
Scheme 1.
Due to the absence of crystal structures for 2 and 3, it is not
absolutely certain if the complexes exist in the neutral or ionic
form (NHC)MX or [(NHC)2M][MX2], respectively. The car-
bene carbon atom of 2 resonates upfield shifted at 181.1 ppm,
which is very similar to the benzyl analogue complex
Slow diffusion of ethyl ether into a solution of the AuIII
[(NHC)2Ag][AgBr2] (NHC = 1-methyl-3-benzylimidazol-2- complex 5 in acetone at ambient temperature afforded crystals
ylidene, 180.7 ppm).[10] The iodide analogue of 2 also contains of the κ2CN-derivative. The compound crystallizes in the or-
the cation [(NHC)2Ag]+ and exhibits a chemical shift of the thorhombic space group Pna21 (Z = 4) with the gold atom in
carbene carbon atom at 182.1 ppm.[18] We therefore assume a square-planar coordination environment defined by one car-
that complex 2 is most likely ionic. The coordination chemistry bene carbon atom, the picolyl nitrogen atom and two bromide
of NHC-Au complexes is more settled and in the presence of ligands (Figure 2). The bite angle of the chelating carbene li-
halide ions neutral complexes of the type (NHC)AuX are gand is close to 90° [N3–Au1–C1 86.72(2)°] and the six mem-
formed. To the best of our knowledge, no complexes of the bered chelate ring adopts a boat conformation. Interestingly,
type [(NHC)2Au][AuX2] are known. This observation is sup- both Au–Br distances are very similar to the corresponding
ported by the 13C NMR shift of 172.8 ppm for the carbene Au–Br distances in
4
[Au1–Br1 2.381(5), Au1–Br2
carbon atom of 3, which is again very similar to the benzyl 2.415(5) Å]. In general, complex 5 shows comparable struc-
analogue (NHC)AuBr complex (172.7 ppm).[10] It should be tural features as found for the homologous (NHC)PdCl2 com-
noted that the presence of a signal for the cation [(NHC)2M]+ plex.[18] To the best of our knowledge, 5 is the first structurally
in mass spectra is not sufficient to determine the actual consti- characterized square-planar NHC–AuIII complex with a nitro-
tution of the complex as neutral or ionic and might be some- gen donor atom in its coordination sphere and is one of the
times misleading: The ESI mass spectra of 2 and 3 are each rare examples with the AuIII atom not exclusively coordinated
dominated by the signal representing the cationic species by the NHC and halide ligands.
[(NHC)2M]+. Particularly NHC–AgI, but also NHC–AuI com-
plexes, are generally prone to ligand scrambling reactions and ther bromide by various anionic ligands were investigated in
In subsequent preparative experiments the exchange of fur-
care has to be taken when interpreting their mass spectra.[1e]
order to find stable, isolatable compounds with different kinds
Crystals of the AuIII complex 4 suitable for X-ray diffraction of ligands capable to bind to AuIII atoms. This survey is moti-
analysis were obtained by slow diffusion of ethyl ether into a vated to explore the still underdeveloped area of gold-oxygen
solution of 4 in acetonitrile at ambient temperature. The com- chemistry.[1,22] Therefore, a main focus was laid on ligands
¯
pound crystallizes in the triclinic space group P1 (Z = 2) and with oxygen donor atoms as they might resist the oxidative
is isostructural to the recently published crystal structure of the environment of the AuIII atom. Beside the reported analysis,
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Z. Anorg. Allg. Chem. 2011, 2129–2134

Gold(III) Complexes with a Picoline-functionalized N-Heterocyclic Carbene
behavior was reported for non-functionalized NHC–AuIII
bromide complexes.[10] Catalano et al. prepared the dimer 6
from [(NHC)2Au]BF4, (tht)AuCl and NaBF4 and determined
the crystal structure.[14] The geometrical parameters of the cat-
ion in crystals of 6 are consistent with the published results
with the exception that 6 does not contain any solvent mole-
cules and that the dinuclear cation was found to be C2-symmet-
ric with the rotation axis perpendicular to the Au–Au bond,
i.e. only one half of the formula unit is present in the asymmet-
ric unit.
Figure 2. Molecular structure of the cation in crystals of 5. Selected
bond lengths /Å and angles /°: Au1–C1 2.065(4), Au1–N3 1.926(5),
Au1–Br1 2.381(5), Au1–Br2 2.415(5), N3–Au1–C1 86.72(2), N3–
Au1–Br1 88.5(2), C1–Au1–Br2 94.7(2), Br1–Au1–Br2 89.9(1).
Conclusions
In this contribution we described the synthesis of (NHC)
AuBr3, 4, by standard reactions via transmetalation of the cor-
responding (NHC)AgCl with (tht)AuBr and successive oxi-
dation with elemental bromine. The removal of one bromide
ligand form 4 with AgBF4 yields [(NHC)AuBr2]BF4, 5, with
the picolyl-nitrogen atom coordinated to the AuIII atom. Fur-
ther ligand exchange with silver carboxylates results in a re-
duction of 5 and the formation of the dimeric complex
[(NHC)2Au2][BF4]2, 6, with a bridging NHC ligand.
no excessive attempts were undertaken to identify possibly
formed reaction products. Complex 5 was treated with two
equivalents of Ag(acetate), Ag2(oxalate), Ag(benzoate), or a
mixture of AgBF4/NaOPh or AgBF4/NaSPh. After filtration of
the formed AgBr over Celite the solvent was removed and the
residue was re-crystallized from DCM/Et2O. Immediate de-
composition to elemental gold results from the reaction with
phenolate whereas the reaction with thiophenolate leads to a
yellow, insoluble solid (presumably a polymeric thiolate-AuI
compound[23]). All other reactions yield crystals of the dimeric
Experimental Section
1
AuI complex 6 as revealed by X-ray diffraction and H NMR
General. All reactions and manipulations of air- and/or moisture sensi-
tive compounds were carried out in an atmosphere of dry nitrogen
using standard Schlenk techniques. Dichloromethane was dried and
distilled from a Na/Pb alloy whereas acetone was dried and distilled
from anhydrous P2O5. The picoline derivative (2-chloromethyl)pyr-
idine was synthesized according to a published protocol[24] and the
gold precursor (tht)AuBr was prepared analogously to the procedure
described by Uson et al.[25] All other solvents and reagents were com-
mercially available and used as received. NMR spectra were recorded
either on a Bruker Digital Avance DPX 200 (200 MHz) or on an Av-
ance DRX 500 (500 MHz) spectrometer and 1H and 13C shifts are
reported in ppm relative to Si(CH3)4 and were referred internally with
respect to the residual signal of the deuterated solvent. Single crystal
structure analysis were carried out on a Bruker Smart X2S (5 and 6)
or a STOE-IPDS diffractometer (4), both operating with Mo-Kα radia-
tion (λ = 0.71073 Å). Further crystallographic and refinement data can
be found in Table 1. The structures were solved by direct methods
(SHELXS-97)[26] and refined by full-matrix least-squares an F2
(SHELXL-97).[27] The H atoms were calculated geometrically and a
riding model was applied during the refinement process.
spectroscopy (Scheme 2 and Figure 3). Just recently a similar
Scheme 2.
CCDC-836815, -836816, -836817 contain the supplementary crystallo-
graphic data for 4–6. These data can be obtained free of charge from
The
Cambridge
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
3-Methyl-1-(2-picolyl)imidazolium chloride (1): The procedure is
similar to a published protocol:[16] A Pyrex tube was charged with 2-
(chloromethyl)pyridine (1.01 g, 7.92 mmol) and MeOH (30 mL). The
mixture was heated to 60 °C and stirred thoroughly. To the solution 1-
methylimidazole (0.65 g, 7.92 mmol) was slowly added by syringe and
the temperature was raised to 150 °C. After a further stirring for 72 h
under reflux condition the reaction mixture was cooled to room tem-
perature and ethyl ether was added afterwards. Thereupon, a brown oil
precipitated which was subsequently triturated with a pentane/DCM
Figure 3. Molecular structure of the dimeric cation in crystals of 6.
Selected bond lengths /Å and angles /°: Au1–C1 1.98(1), Au1–N3
2.08(1), Au1–Au1i 3.216(1), N3–Au1–C1 174.6(3) [symmetry opera-
tion: (i) = –x+2, y, –z+½].
Z. Anorg. Allg. Chem. 2011, 2129–2134
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2131

C. Topf, C. Hirtenlehner, M. Fleck, M. List, U. Monkowius
ARTICLE
Table 1. Crystal data, data collection and structure refinement for compounds 4–6.
4
5
6
Formula
C10H11N3AuBr3
609.90
C10H11N3AuBr2BF4
616.81
C20H22N6Au2B2F8
914.00
MW /g·mol–1
Crystal size /mm
Crystal system
Space group
0.22 ϫ 0.16 ϫ 0.08
triclinic
P1
0.80 ϫ 0.80 ϫ 0.80
orthorhombic
Pna21
0.45 ϫ 0.57 ϫ 0.65
monoclinic
C2/c
¯
a /Å
b /Å
c /Å
α /°
8.35(1)
8.35(1)
11.43(1)
98.2(1)
94.8(1)
104.9(1)
755.7(2)
2.680
13.115(3)
8.890(2)
13.266(1)
90
90
90
18.008(2)
14.333(1)
13.395(1)
90
108.627(2)
90
β /°
γ /°
V /Å3
1546.8(5)
2.649
3270.5(4)
1.856
ρcalc /g·cm–3
Z
2
4
4
9.03
μ /mm–1
17.65
14.71
T /K
297
293
200
Θ range /°
2.6–25.9
6771
2742
2201
155/0
analytical
0.079, 0.152
2.80, –0.62
0.049
2.8–25.3
9566
2686
1863
109/0
multi-scan
0.03, 0.03
1.75, –0.98
0.044
2.8–25.0
10214
2861
2301
173/0
multi-scan
0.07, 0.11
1.21, –1.19
0.031
Reflections collected
Unique reflections
Observed reflections [I Ͼ 2 σ(I)]
Parameters refined /restraint
Absorption correction
Tmin, Tmax
σfin (max/min) /e·Å–3
R1 [I Ն 2σ (I)]
wR2
0.146
0.109
0.093
CCDC number
836815
836816
836817
mixture (2:1) and finally dried in vacuo. This afforded imidazolium
cipitate of AgCl was formed immediately. After a further stirring for
salt 1 as a very hygroscopic, brown powder. Yield: 73% (1.21 g). H 30 min at ambient temperature the solids were filtered off. The solvent
NMR (200 MHz, [D6]DMSO, 30 °C): δ = 9.31 (s, 1 H, NImH-CH- and volatile materials were removed in vacuo and the colourless, oily
ImH), 8.52–8.49 (m, 1 H, PyH), 7.89–7.74 (m, 3 H, PyH/ImHH), residue was recrystallized from DCM/pentane. The AuI–carbene com-
1
N
7.51–7.47 (m, 1 H, PyH), 7.39–7.33 (m, 1 H, PyH), 5.58 (s, 2 H, NImH
-
plex was obtained as a white, microcrystalline powder. Yield: 64%
1
CH2-Py), 3.87 (s,
3
H, NImH-CH3). 13C NMR (125.8 MHz, (0.18 g) H NMR (200 MHz, [D6]DMSO, 30 °C): δ = 8.52–8.48 (m,
3
[D6]DMSO, 30 °C): δ = 154.2, 150.0, 138.1, 128.8, 124.4, 123.5,
123.2, 121.4, 53.7, 36.3. MS (ESI pos): m/z 174 [M]+. EA: due to
the extraordinary hygroscopicity of the product no reliable elemental
analysis could be obtained.
1 H, PyH), 7.83–7.75 (m, 1 H, PyH), 7.49 (d, JHH = 1.84 Hz, 1 H,
3
ImHH), 7.45 (d, JHH = 1.79 Hz, 1 H, ImHH), 7.33–7.24 (m, 2 H,
PyH), 5.40 (s, 2 H, NImH-CH2-Py), 3.75 (s, 3 H, NImH-CH3). 13C NMR
(125.8 MHz, [D6]DMSO, 30 °C): δ = 172.8, 155.6, 149.4, 137.3,
123.0, 122.9, 122.4, 121.8, 55.0, 37.6. MS (ESI pos): m/z 543 [L2Au]+.
EA: calcld for C10H11N3AuBr (450.09): C 26.69, H 2.46, N 9.34.
Found: C 26.97, H 2.46, N 9.50.
Chloro-[3-methyl-1-(2-picolyl)imidazol-2-ylidene]silver(I) (2): The
procedure is similar to a published protocol:[16] A 100 mL round-bot-
tomed flask was covered with aluminum foil and charged with 1
(0.83 g, 3.96 mmol) and DCM (20 mL). To the resulting solution was Tribromo-[3-methyl-1-(2-picolyl)imidazol-2-ylidene]gold(III) (4):
added dry Ag2O (0.46 g, 1.98 mmol) whilst stirring whereby a precipi- In a 100 mL Schlenk vessel 3 (0.15 g, 0.33 mmol) was dissolved in
tate of AgCl is formed immediately. After an overall stirring time of dry DCM (20 mL) and cooled down to –40 °C (isopropanol/liquid ni-
3 h at ambient temperature the reaction mixture was filtered through trogen). To the well stirred reaction mixture a solution of Br2 (0.06 g,
Celite. The solvent was removed in vacuo and recrystallization of the 0.38 mmol) in DCM (5 mL) was slowly added by syringe. The cooling
brownish, oily residue from DCM/pentane afforded the product as a bath was removed and stirring was continued for 6 h at ambient tem-
light brown, light sensitive microcrystalline powder. Yield: 51% perature. Volatile materials were removed in vacuo and the pasty resi-
1
(0.64 g). H NMR (200 MHz, [D6]DMSO, 30 °C): δ = 8.48–8.45 (m, due was recrystallized from ACN/Et2O. This afforded 4 as an orange,
3
1 H, PyH), 7.79–7.70 (m, 1 H, PyH), 7.51 (d, JHH = 1.61 Hz, 1 H, microcrystalline powder. Yield: 60% (0.10 g). 1H NMR (200 MHz,
3
ImHH), 7.42 (d, JHH = 1.61 Hz, 1 H, ImHH), 7.31–7.25 (m, 2 H, [D6]DMSO, 30 °C): δ = 8.51–8.49 (m, 1 H, PyH), 7.86–7.72 (m, 3 H,
PyH), 5.41 (s, 2 H, NImH-CH2-Py), 3.75 (s, 3 H, NImH-CH3). 13C NMR PyH/ImHH), 7.42–7.30 (m, 1 H, PyH), 7.42–7.30 (m, 1 H, PyH), 5.49
(125.8 MHz, [D6]DMSO, 30 °C): δ = 181.1, 156.2, 149.4, 123.2, (s, 2 H, NImH-CH2-Py), 3.78 (s, 3 H, NImH-CH3). 13C NMR
123.0, 122.9, 122.7, 122.1, 55.6, 38.1. MS (ESI pos): m/z 453 [L2Ag]+. (125.8 MHz, [D6]DMSO, 30 °C): δ = 153.3, 149.5, 137.5, 135.6,
EA: calcld for C10H11N3AgCl (316.54): C 37.94, H 3.50, N 13.27. 125.9, 125.4, 123.8, 123.3, 54.7, 37.7. MS (ESI pos): m/z
Found: C 38.13, H 3.51, N 13.43.
703 [L2AuBr2]+. EA: calcld for C10H11N3AuBr3 (609.90): C 19.69, H
1.82, N 6.89. Found: C 19.82, H 1.84, N 7.03.
Bromo-[3-methyl-1-(2-picolyl)imidazol-2-ylidene]gold(I) (3):
A
100 mL Schlenk vessel was charged with 2 (0.20 g, 0.63 mmol) and
dry DCM (10 mL). The content was stirred thoroughly and to the solu-
tion was added solid (tht)AuBr (0.23 g, 0.63 mmol) whereupon a pre-
Dibromo-[3-methyl-1-(2-picolyl)imidazol-2-ylidene-
κ2C,N]gold(III)-tetrafluoroborate (5): A 100 mL Schlenk vessel was
charged with 4 (0.20 g, 0.33 mmol) and dry acetone (10 mL). To the
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Gold(III) Complexes with a Picoline-functionalized N-Heterocyclic Carbene
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well stirred solution was added solid AgBF4 (0.07 g, 0.36 mmol) upon
which a precipitate of AgBr was formed immediately. After a stirring
time of 15 min solid materials were filtered off. The solvent was re-
moved in vacuo and the residue was recrystallized from acetone/Et2O.
This afforded the title substance as a light-green microcrystalline pow-
1
der. Yield: 44% (0.09 g). H NMR (200 MHz, [D6]DMSO, 30 °C): δ
= 9.26–9.02 (m, 1 H, PyH), 8.74–8.25 (m, 1 H, PyH), 8.09–7.87 (m,
3 H, PyH/ImHH), 7.55–7.41 (m, 1 H, PyH), 6.12 (s, 2 H, NImH-CH2-
Py), 4.01 (s, 3 H, NImH-CH3). 13C NMR (125.8 MHz, [D6]DMSO,
30 °C): δ = 172.9, 148.3, 138.8, 127.3, 125.6, 123.7, 123.0, 122.5,
54.3, 37.4. MS (ESI pos): m/z 595 [M+BF3]+. EA: calcld for
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C10H11N3AuBr2BF4 (616.80): C 19.47, H 1.80, N 6.81. Found: C
19.65, H 1.89, N 6.79.
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General procedure for the reactions of 5 with various ligands: 3
(50 mg, 82 μmol) and AgBF4 (16 mg, 82 μmol) were suspended in
absolute acetone (20 mL) and stirred for 0.5 h. To this mixture two
equivalents of Ag(acetate), Ag(benzoate) or one equivalent Ag2(oxal-
ate), or a mixture of two equivalents AgBF4/NaOPh or AgBF4/NaSPh
were added at –40 °C. After the reaction mixtures were allowed to
warm to room temperature they were stirred for additional 4 h. The
formed AgBr was removed by filtration through Celite and the solvent
was distilled off in a vacuo. The residues were dissolved in a minimum
of DCM and crystallized by slow gas phase diffusion of Et2O. In the
case of the phenolate, elemental gold formed immediately and only
1
the free imidazolium salt could be detected by H-NMR spectroscopy.
From the reaction with thiophenolate a yellow, insoluble solid was
obtained, which was not further characterized. The reaction with the
silver carboxylates afforded crystals of the dimeric AuI complex 6,
which were characterized by 1H-NMR spectroscopy and X-ray diffrac-
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1
tion. H NMR (200 MHz, [D6]DMSO, 30 °C): δ = 8.91 (d, 1 H), 8.37
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3.82 (s, 3 H).
Acknowledgments
We thank Prof. G. Knör for fruitful discussions and generous support
of the experimental work.
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Received: July 27, 2011
Published Online: September 27, 2011
2134
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© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 2129–2134