Cross-coupling of arene-gold(III) complexes

Article abstract of DOI:10.1016/j.tet.2013.04.029

The reactivity of electron-deficient arene-gold(III) complexes toward nucleophilic aromatic and heteroaromatic counterparts has been studied. 1-Methylindole proved to be the best reaction partner while trimethoxybenzenes did not react. The ancillary ligand on gold also influenced the reactivity in the order PPh₃>P^tBu₃>IPr. An oxidative cross-coupling starting from the corresponding gold(I) complexes in presence of hypervalent iodide oxidants was also studied.

Full text of DOI:10.1016/j.tet.2013.04.029

Tetrahedron 69 (2013) 5751e5757
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Cross-coupling of areneegold(III) complexes
*
Manuel Hofer, Cristina Nevado
€
€
Organic Chemistry Institute, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactivity of electron-deficient areneegold(III) complexes toward nucleophilic aromatic and heter-
oaromatic counterparts has been studied. 1-Methylindole proved to be the best reaction partner while
trimethoxybenzenes did not react. The ancillary ligand on gold also influenced the reactivity in the order
PPh3>PtBu3>IPr. An oxidative cross-coupling starting from the corresponding gold(I) complexes in
presence of hypervalent iodide oxidants was also studied.
Received 29 January 2013
Received in revised form 5 April 2013
Accepted 8 April 2013
Available online 13 April 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Gold
Cross-coupling
Oxidation
Arenes
1. Introduction
identified a general gold-catalyzed oxidative homocoupling of
arenes using tetrachloroauric acid as catalyst and PhI(OAc)2 as
Gold-catalyzed cross-coupling reactions of arenes have scarce
precedent in the literature. The first breakthroughs in this area date
back two decades, when dimerization processes using stoichio-
metric amounts of gold complexes were reported.1 The di-
merization of nucleobases, reported by Lippert in 1999,2 and the
homocoupling of 2,6-bis(2-thienyl)pyridines (H2pthpy) reported by
Constable in 1992,3 both mediated by stoichiometric amounts of
NaAuCl4, are representative examples of these transformations. The
reactions were explained by the formation of arylgold(III) com-
plexes via Csp2eH activation, followed by a second CeH activation
to give the homocoupling product via reductive elimination on
a diaryl-gold(III) intermediate. Almost ten years later, Beller and Tse
stoichiometric oxidant (Scheme 1, Eq. 1).4 The reaction was carried
out in acetic acid as solvent and gold(III) was proposed as the cat-
alytically active redox state. Typical electrophilic aromatic sub-
stitution patterns were observed in the biaryl products, thus ruling
out free cationic radical mechanisms. More elaborated homocou-
pling products can be obtained by combining gold-catalyzed cy-
clizations or rearrangements with Au(I)/Au(III) catalytic cycles.
Stoichiometric5 as well as catalytic manifolds have been already
reported.6 A representative example is the gold-catalyzed oxidative
dimerization of propargylic acetates reported by Zhang pioneering
the use Selectfluor as sacrificing stoichiometric oxidant (Scheme 1,
Eq. 2).7
Scheme 1. Gold-catalyzed homocoupling reactions.
In contrast, the cross-coupling of two different arenes by gold has
been much less developed. In a pioneering example, pyrazine and
pyrolidine substrates were coupled with arylbromides in the pres-
ence of catalytic amounts of gold as reported by Li and Hua.8
* Corresponding author. Tel.: þ41 446353945; fax: þ41 446356812; e-mail
addresses: nevado@oci.uzh.ch, crisnevado@hotmail.com (C. Nevado).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.029

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M. Hofer, C. Nevado / Tetrahedron 69 (2013) 5751e5757
As opposed to gold, multiple examples of palladium-catalyzed single
or double CeH activation processes to form biaryl compounds have
already been reported.9 Several copper catalyzed methods have also
recently aroused.10 The synthetic utility of these transformations is
usually hampered by the harsh reaction conditions required to en-
gage both reaction partners, thus limiting the substrate scope and
the reaction’s selectivity. To overcome these problems, species able
to selectively activate one of the reaction partners result highly at-
tractive. During the preparation of this manuscript, Larrosa and co-
workers reported the use of electron-deficient areneegold(I) spe-
cies as suitable reagents for the heterocoupling with electron rich
aromatic rings in the presence of a strong oxidant.11 The redox
chemistry of gold has recently boosted the interest of synthetic or-
ganic chemists due to the demonstrated ability of Au(I)/Au(III) redox
catalytic cycles12 to trigger synthetically useful transformations.13
Herein, we would like to report our results on the cross-coupling
of areneegold(III) species with electron rich aromatic and hetero-
aromatic substrates and the influence that the ancillary ligand on
gold can exert in these transformations (Scheme 2).
hypervalent iodine reagents (PhI(OAc)2 and PhICl2) were used.15 In
addition to triphenylphosphine, two different ancillary ligands on
gold were also studied: a more sterically demanding tri-tert-
butylphosphine and a stronger sigma-donor in the form of an IPr
(1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic
carbene ligand. The results are summarized in Table 1. As we pre-
viously reported,16 the reaction of [AuI(C6F5)(PPh3)] (1) with
PhI(OAc)2 in 1,2-dichloroethane at 93 ꢀC, provided cis-chloro-(bis-
pentafluorophenyl)-triphenylphosphinegold(III) (2) in moderate
yield (Table 1, entry 1). In contrast, the reaction of 1 in the presence
of PhICl2 at room temperature using CCl4 as solvent, afforded
exclusively the cis-dichloro-(pentafluorophenyl)-triphenylphos-
phine-gold(III) (3) in 93% yield (Table 1, entry 2). The oxidation of
[AuI(C6F5)(PtBu3)] (4) with PhI(OAc)2 as oxidant gave no conversion
to the desired product even at 150 ꢀC (Table 1, entry 3) and only
traces of [Au(C6F5)4]ꢁ anion could be detected in the reaction mix-
ture. In contrast, the reaction with PhICl2 gave cis-dichloro(penta-
fluorophenyl)(tri-tert-butylphosphine)gold(III) (5) in 78% yield at
room temperature (Table 1, entry 4). The structure of [AuIII(C6F5)
Cl2(PtBu3)] (5) was confirmed by X-ray diffraction analysis showing
the exclusive formation of the cis-product (CCDC-920666). This was
a surprising result, as the trans-isomer was expected because of the
steric demand of the ancillary ligand. In fact, the crystal structure of
5 showed a distortion of the ideal square-planar geometry with the
following angle values: C(1)eAu(1)eCl(1): 81.5ꢀ, Cl(2)eAu(1)e
Cl(1): 85.4ꢀ, C(1)eAu(1)eP(1): 98.8ꢀ, and Cl(2)eAu(1)eP(1): 94.6ꢀ.
The oxidation of [AuI(C6F5)(IPr)] (6) in the presence of PhI(OAc)2
afforded trans-dichloro[N,N-bis(2,6-diisopropylphenyl)imidazol-2-
yl](pentafluorophenyl)gold(III) (7) in 48% (Table 1, entry 5). This
result confirmed the coordination and activation of dichloroethane
during the reaction course, which was already observed for the
oxidation of 1 with PhI(OAc)2 to give 2.16 Interestingly, 7 was ob-
tained as the trans-isomer and the structure could also be confirmed
by X-ray diffraction analysis (CCDC-921424). The reaction of 6 with
PhICl2 in CCl4 as solvent afforded 7 in 76% yield (Table 1, entry 6).17
Scheme 2. Csp2eCsp2 cross-coupling using areneegold(I) and areneegold(III)
complexes.
2. Results and discussion
2.1. Synthesis of electron-deficient-gold(III) species
The higher acidity of Csp2eH bonds in electron-deficient aro-
matics as compared to electron-rich ones has enabled their activa-
tion by gold(I) complexes in the presence of strong bases and silver
salts.14 We decided to start our study by oxidizing such electron-
deficient aurated species in the presence of strong oxidants to
the corresponding gold(III) complexes, which would be then sub-
sequently submitted to a cross-coupling reaction in the presence of
different aromatic nucleophiles. For this purpose, two different
2.2. Reactivity of electron-deficient-gold(III) species toward
arene and heteroarene nucleophiles
Our next goal was to test the cross-coupling of gold(III) com-
plexes 2, 3, 5, and 7 with different aromatic nucleophiles. For this
purpose, 1,3,5-trimethoxybenzene (8), 1,2,4-trimethoxybenzene
(9), and 1-methylindole (10) were selected as benchmark sub-
strates. The results of this study have been summarized in Table 2.
Table 1
Oxidation of [AuI(C6F5)(L)] using PhI(OAc)2 and PhICl2 as oxidants
Entry
Conditions
Starting material
Oxidant
Product
Yield (%)
1
2
3
4
5
6
93 ꢀC, 4 h, 1,2-DCE
25 ꢀC, 1 h, CCl4
1 L¼Ph3P
PhI(OAc)2
PhICl2
PhI(OAc)2
PhICl2
PhI(OAc)2
PhI(Cl)2
cis-[AuIII(C6F5)2Cl(PPh3)], 2
cis-[AuIII(C6F5)Cl2(PPh3)], 3
[Au(C6F5)4]ꢁ
39
93
1
93 ꢀC, 5 h, 1,2-DCE
25 ꢀC, 1 h, CCl4
4 L¼tBu3P
d
4
cis-[AuIII(C6F5)Cl2(PtBu3)], 5
trans-[AuIII(C6F5)Cl2(IPr)], 7
7
78a
48b
76b
150 ꢀC, 15 h, 1,2-DCE
93 ꢀC, 3 h, CCl4
6 L¼IPr
6
[AuICl(PtBu3)] was also observed (11% conversion of 4).
a
b
No reductive elimination product [AuICl(IPr)] was observed.

M. Hofer, C. Nevado / Tetrahedron 69 (2013) 5751e5757
5753
Table 2
Synthesis of biaryls by reaction of pentafluorophenylgold(III) complexes and electron rich arenes
Entry
Conditionsa
Starting material
Nu
Conversion (Yield) %
11
12
13
14
1
2
3
4
5
6
7
8
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
150 ꢀC, 22 h
[AuIII(C6F5)Cl2(PPh3)] 3
8
9
10
8
9
10
8
9
10
8
9
10
0b
d
d
0c
d
d
0b
d
d
0
d
0b
d
d
0c
d
d
0b
d
d
0
d
3
4
6
43
42
32
0
0
0
100
100
95
d
92 (85)
d
[AuIII(C6F5)Cl2(PtBu3)] 5
[AuIII(C6F5)Cl2(IPr)] 7
[AuIII(C6F5)2Cl(PPh3)] 2
d
8c
d
d
9
0b
d
10
11
12
d
d
d
d
0
a
The reactions were performed using: gold(III) (1 equiv), nucleophile (1.5 equiv) in 1,2-dichloroethane (0.05 M) at 150 ꢀC.
No conversion of the starting materials.
C6F5H and C6F5Cl could also be detected in the reaction mixture.
b
c
The reaction of [AuIII(C6F5)Cl2(PPh3)] (3) in presence of 1.5 equiv
Table 3
Synthesis of biaryls in presence of [AuI(C6F5)(PPh3)] (1), electron rich arenes and
PhI(OAc)2 and PhICl2
of both trimethoxybenzenes 8 and 9 gave no conversion to the
corresponding heterocoupling products even at 150 ꢀC (Table 2,
entries 1 and 2). Interestingly, the reaction with 1-methylindole
(10) afforded 1-methyl-3-(pentafluorophenyl)-indole (13) in 85%
yield (Table 2, entry 3). Analogously, [AuIII(C6F5)Cl2(PtBu3)] (5) in
presence of the trimethoxybenzenes 8 and 9 gave no conversion to
the heterocoupling products (Table 2, entries 4 and 5). However the
reaction with 1-methylindole (10) afforded traces of the hetero-
coupling product 13 according to the 1H and 19F NMR spectra of the
reaction crude (Table 3, entry 6). In all three reactions of complex 5,
decafluorobiphenyl (14) could be detected in the crude 19F NMR of
the mixture.
Entry
Oxidant
Nucleophile
Conversion (yield) %
11
12
13
14
1
2
3
4
5
6
7
PhI(OAc)2
PhI(OAc)2
PhI(OAc)2
None
PhICl2
PhICl2
8
9
10
10
8
85 (67)b
d
76 (24)b
d
d
d
0e
d
d
8
0
0
0
1
d
d
d
0d
d
d
d
93 (80)
0c
d
The reactions of [AuIII(C6F5)Cl2(IPr)] (7) showed no conversion of
the starting materials in all studied cases (Table 2, entries 7e9).
Finally, the reactions of [AuIII(C6F5)2Cl(PPh3)] (2) with the three
electro-rich arenes gave almost complete conversion to the
homocoupling product 14 (Table 2, entries 10e12), which was
explained as a result of a reductive elimination process in the
starting material at such high temperatures.
The formation of 1-methyl-3-(pentafluorophenyl)-indole (13) in
entry 3 can be explained by an electrophilic aromatic substitution
process (Scheme 3, path A)18 or, alternatively, by a concerted
metalationedeprotonation pathway (Scheme 3, path B),19 followed
by reductive elimination. Path A would involve the nucleophilic
attack of the indole onto the gold(III) species I to form the meta-
lated intermediate II, which undergoes deprotonation to form III.
On the other hand, concerted metalation would involve the
9
10
d
45e
6
10
PhICl2
aThe reactions were performed using: gold(III) (1 equiv), nucleophile (1 equiv) in
1,2-DCE at 150 ꢀC for 22 h.
b
Conversion to [AuIII(C6F5)2Cl(PPh3)] (3).
c
Reaction without oxidant.
d
Complete conversion to [AuIII(C6F5)Cl2(PPh3)] (3).
e
Partial conversion to [AuIII(C6F5)Cl2(PPh3)] (2) and C6F5H.
formation of a cyclic transition state IV and the direct formation of
the metalated species III.
Although 1-methylindole is less sterically hindered than tri-
methoxybenzenes, the small difference in nucleophilicity20

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M. Hofer, C. Nevado / Tetrahedron 69 (2013) 5751e5757
Scheme 3. Electrophilic substitution (path A) and concerted metalationedeprotonation (path B) processes followed by reductive elimination to heterocoupling products.
between these species would have predicted a comparable re-
activity in an electrophilic aromatic substitution path, which is not
in line with the experimental results. In contrast, if the formation of
the heterocoupling product takes place via concerted metal-
ationedeprotonation pathway, the cleavage of the Csp2eH bond in
IV should be the rate determining step, at least according to well-
established Pd-catalyzed processes.21 The lower pKa of indoles
would enable faster deprotonation and increased reactivity com-
pared to trimethoxybenzenes although further kinetic isotope ef-
fect would be needed to definitively distinguish between these two
mechanistic scenarios. The formation of the heterocoupling prod-
uct for indoles showed higher conversion for gold(III) complexes
supported by less strong sigma-donor and less bulky ligands in the
order PPh3>PtBu3>IPr (Table 2, entries 3, 6, 9).
entry 2). Compound 12 could only be isolated in 24% yield due to the
difficult purification of the product from the reaction mixture. The
reaction in presence of methylindole (10) gave heterocoupling
product 13 in 80% yield (Table 3, entry 3). Without oxidant, the re-
action gave no conversion of the starting materials (Table 3, entry 4).
Interestingly, when the same reactions were carried out using PhICl2
as oxidant (Table 3, entries 5e7), the results were in line to those
obtained for the corresponding gold(III) intermediates 3, 5, and 7
summarized in Table 2, so that only 1-methylindole 10 proved to be
a productive counterpart. In fact, areneegold(III) species 2 and 3
were detected in the reaction mixtures.
We hypothesized that the difference in reactivity for the gold(I)
complex (1) in the presence of PhI(OAc)2 versus PhICl2 was due to the
relative difference in basicityof the two counterions, which behave as
bases during the product formation on a metalated intermediate IV.
In other words, being AcOꢁ a stronger base than Clꢁ, it might be able
to deprotonate both the indole and the trimethoxybenzene in-
termediates. The fact that the biaryl-product formation depends on
the nature of the base present in the reaction mixture seems to re-
inforce our hypothesis of a concerted metalationedeprotonation
process responsible for product formation in these transformations
(Scheme 5, path B). In addition, the reactivity of the in situ generated
gold(III) complexes will also depend also on their stability. The higher
2.3. Synthesis of biaryl compounds by oxidative coupling of
pentafluorophenylgold(I) complexes and electron rich arenes
Next, we decided to attempt the oxidative cross-coupling of
pentafluorophenylgold(I) species with electron rich arenes in the
presence of PhI(OAc)2 and PhI(Cl)2 as oxidants to explore the pos-
sibility of a one pot-three-step process to obtain the heterocoupling
products (Scheme 4).11
Scheme 4. Au(I) to Au(III) oxidation coupled to arene-auration and cross-coupling.
2.3.1. Synthesis of biaryls in presence of [AuI(C6F5)(PPh3)] (1), elec-
tron rich arenes and PhIX2. We started our investigation with
[AuI(C6F5)(PPh3)] (1) in the presence of 1,3,5-trimethoxybenzene (8),
1,2,4-trimethoxybenzene (9) or 1-methylindole (10), and PhI(OAc)2
as oxidant. To our surprise, the reaction of 1 in presence of 8 gave the
heterocoupling product 2,3,4,5,6-pentafluo-20,40,60-trimethox-
ybiphenyl (11) in 67% yield at 150 ꢀC (Table 3, entry 1). This result is in
sharp contrast to the reaction of the presumed oxidized in-
termediate 3, which could not be transformed into 11 as previously
seen inTable 2, entry 1. Analogously, the reaction of 1 in the presence
9 gave the heterocoupling product 2,3,4,5,6-pentafluo-20,40,50-tri-
methoxybiphenyl (12) with more than 75% conversion (Table 3,
reactivity observed in the reactions carried out with PhI(OAc)2 as
oxidant, indicated a less stable gold(III) intermediate compared to the
more stable dichloro-pentafluorophenylgold(III) complexes initially
described.
3. Conclusions
We have been able to prepare, isolate, and characterize electron-
deficient pentafluorophenylgold(III) complexes and have in-
vestigated their reactivity toward other nucleophilic aromatic and
heteroaromatic counterparts. The Csp2eCsp2 heterocoupling prod-
ucts were only observed in the reactions with 1-methylindole while

M. Hofer, C. Nevado / Tetrahedron 69 (2013) 5751e5757
5755
Scheme 5. Au(I) to Au(III) oxidation, subsequent CeC bond formation and reductive elimination to biaryls by electrophilic aromatic substitution or concerted
metalationedeprotonation.
trimethoxybenzenes did not react. The ancillary ligand on gold also
influenced the reactivity in the order PPh3>PtBu3>IPr. When a one-
pot three-step procedure was applied starting from the corre-
sponding pentafluorophenyl-gold(I) complexes in presence of
hypervalent iodide oxidants, higher reactivity for electron rich are-
nes was found in presence of PhI(OAc)2 compared to the reactivity in
presence of PhI(Cl)2. These results can be explained based on the
higher reactivity of the gold(III) intermediate and/or as the result of
the increased basicity of AcOꢁ compared to Clꢁ. Although the exact
mechanism yielding the observed products is difficult to establish,
we favor the idea of a concerted metalationedeprotonation pathway
over a classical electrophilic aromatic substitution for the formation
of the bisaryl-gold(III) intermediate preceding the reductive elimi-
nation to give the cross-coupling products.
procedures. Solvents were purchased in HPLC quality, degassed
by purging thoroughly with nitrogen and dried over activated mo-
lecular sieves of appropriate size. Alternatively, they were purged
with argon and passed through alumina columns in a solvent pu-
rification system (Innovative Technology). All reactions were per-
formed under anhydrous conditions using nitrogen as protecting
gas, dry solvents and sealed Schlenk flasks. Conversion was moni-
tored by thin layer chromatography (TLC) using Merck TLC silica gel
60 F254 (Merck) with a silica layer thickness of 0.2 mm and a particle
size of 10e12 mm supported by aluminum foil. Column chroma-
tography was performed using silica gel 60 M 230e400 mesh
(MachereyeNagel) and distilled solvents.
4.2. Preparation and characterization of starting materials 4
and 6
4. Experimental section
4.1. General information
4.2.1. Pentafluorophenyl(tri-tert-butylphosphine)gold(I) (4). To
a
mixture of pentafluorobenzene (0.30 mL, 2.7 mmol), silver(I)-oxide
(104 mg, 0.45 mmol), potassium carbonate (145 mg, 1.05 mmol),
pivalic acid (153 mg, 1.5 mmol) and (tri-tert-butylphosphine)gold(I)
chloride (261 mg, 0.6 mmol), DMF (3 mL) was added. The reaction
was heated at 50 ꢀC for 5 h and the mixture was filtered through
Celite. The solvent was evaporated under reduced pressure and the
crude was purified by column chromatography (hexane/CH2Cl2 4:1)
to give 7 as a white solid. Yield: 76% (257 mg, 0.45 mmol). 1H NMR
NMR spectra were recorded on AV2 400 or AV2 500 MHz Bruker
spectrometers. Chemical shifts are given in parts per million.
Multiplicities are abbreviated as follows: singlet (s), doubled (d),
triplet (t), quartet (q), doublet-doublet (dd), quintet (quint), sextet
(sext), septet (sept), multiplet (m), and broad (br). High-resolution
electrospray ionization mass-spectrometry was performed on
a Finnigan MAT 900 (Thermo Finnigan, San Jose, CA; USA) dou-
blefocusing magnetic sector mass spectrometer. Ten spectra were
acquired. A mass accuracy ꢂ2 ppm was obtained in the peak
(400 MHz, CD2Cl2):
CD2Cl2):
d
¼1.52 (d, J¼13.4 Hz, 27H); 13C NMR (125 MHz,
d
¼148.5 (ddsext, J¼226.0, 26.0, 4.0 Hz),139.4 (ddtd, J¼153.0,
62.0, 4.0, 2.5 Hz),138.5 (dm, J¼245.0 Hz),137.2 (dm, J¼250.0 Hz), 39.3
matching acquisition mode by using a solution containing 2
ml
(d, J¼17.1 Hz), 32.2 (d, J¼4.0 Hz); 31P NMR (162 MHz, CD2Cl2):
PEG200, 2 l PP450, and 1.5 mg NaOAc (all obtained from Sigma-
m
d
d
¼93.33 (quin, J¼7.0 Hz); 19F NMR (376 MHz, CD2Cl2):
¼ꢁ(116.91e117.34) (m), ꢁ(160.33e160.69) (m), ꢁ(163.25e163.54)
eAldrich, CH-Buchs) dissolved in 100 mL MeOH (HPLC Supra grade,
Scharlau, E-Barcelona) as internal standard.
(m). EI-HRMS Calcd for C18H27AuF5P: 566.1436, found: 566.1431.
4.1.1. Materials and methods. Unless otherwise stated, starting
materials were purchased from Aldrich and/or Fluka. All reagents
were used as received except for iodobenzene diacetate, which was
recrystallized from aqueous solution of acetic acid (5 M) and dried
over night under vacuum.22 Iodobenzene dichloride,23 triphenyl-
phosphinegold(I) chloride, and tri-tert-butylphosphinegold(I) chlo-
ride, respectively,24 [N,N-bis(2,6-diisopropyl-phenyl)imidazol-2-yl]
gold(I) chloride,25 pentafluorophenyl-(triphenylphosphine)gold(I)
(1),14a cis-chloro-(bispentafluorophenyl)-(triphenylphosphine)gold(III)
(2), and cis-dichloro-(pentafluorobenzene)-(triphenylphosphine)
gold(III) (3)16 were synthesized according to previously reported
4.2.2. Pentafluorophenyl[N,N-bis(2,6-di-iso-propylphenyl)imidazol-
2-yl]gold(I) (6). To a mixture of pentafluorobenzene (0.50 mL.
4.5 mmol), silver(I)-oxide (174 mg, 0.75 mmol), potassium car-
bonate (242 mg, 1.75 mmol), pivalic acid (255 mg, 2.5 mmol), and
[N,N-bis(2,6-diisopropyl-phenyl)imidazol-2-yl]gold(I)
chloride
(622 mg, 1.0 mmol), DMF (5 mL) was added. The reaction was
heated at 50 ꢀC for 7 h and the mixture was filtered through Celite.
The solvent was evaporated under reduced pressure and the crude
was purified by column chromatography (hexane/CH2Cl2 1:1) to
give 9 as a white solid. Yield: 91% (686 mg, 0.91 mmol). 1H NMR
(400 MHz, CD2Cl2):
d
¼7.48 (t, J¼7.8 Hz, 2H), 7.29 (d, J¼7.7 Hz, 4H),

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M. Hofer, C. Nevado / Tetrahedron 69 (2013) 5751e5757
7.21 (s, 2H), 2.59 (spt, J¼6.8 Hz, 4H), 1.32 (d, J¼6.8 Hz, 12H), 1.20 (d,
150 ꢀC for 22 h. The analysis of the reaction products were per-
formed by 1H, 31P and 19F NMR. The product ratios were determined
by integration of the 1H and 19F NMR signals of the crude NMR
spectrum. For isolation, the solvent was evaporated under reduced
pressure and the crude was purified by column chromatography
(hexane/CH2Cl2 1:1) to give compounds 11, 12, 13, and 14.
J¼7.0 Hz, 12H); 13C NMR (125 MHz, CD2Cl2):
¼191.1 (s), 148.9
d
(ddquint, J¼226.0, 25.5, 3.5 Hz), 146.0 (s), 138.0 (dm, J¼245.0 Hz),
136.7 (dm, J¼250.0 Hz), 134.2 (s), 132.8 (t, J¼59.9 Hz), 130.4 (s),
124.0 (s), 123.3 (s), 28.8 (s), 24.1 (s), 23.7 (s); 19F NMR (376 MHz,
CD2Cl2):
d
¼ꢁ(116.12e116.44) (m), ꢁ161.80 (t, J¼19.8 Hz),
ꢁ(164.31e164.73) (m); MS (EI): m/z¼752 ([M]þ, 15); EI-HRMS
Calcd for C33H36AuF5N2: 752.2464, found: 752.2471.
4.6. Characterization of cross-coupling products 11e14
4.6.1. 2,3,4,5,6-Pentafluo-20,40,60-trimethoxybiphenyl (11). The com-
4.3. Preparation of areneegold(III) complexes 5, 7
pound was isolated as a white solid. 1H NMR (400 MHz, CD2Cl2):
¼6.20 (s, 2H), 3.82 (s, 3H), 3.71 (s, 6H). 13C NMR (125 MHz, CD2Cl2):
¼163.1 (s), 159.0 (s), 144.9 (dm, J¼245.0 Hz), 140.2 (dm,
4.3.1. cis-Dichloro(pentafluorobenzene)(tri-tert-butylphosphine)
gold(III) (5). To a mixture of pentafluorophenyl(tri-tert-butylphos-
phine)gold(I) (16.9 mg, 0.03 mmol) and iodobenzeneedichloride
(9.0 mg, 0.033 mmol), tetrachloromethane (1.9 mL) was added. The
reaction mixture was stirred at room temperature for 1 h. The sol-
vent was evaporated under reduced pressure to w0.2 mL and after
addition of hexane the product precipitated. The product was sep-
arated on a filter paper to give 8 as a white solid. Yield: 78% (14.8 mg,
d
d
J¼250.0 Hz), 137.4 (dm, J¼249.0 Hz), 109.3 (t, J¼19.8 Hz), 95.8 (s),
90.6 (s), 55.9 (s), 55.5 (s). 19F NMR (376 MHz, CD2Cl2):
d
¼ꢁ139.61
(dd, J¼23.5, 7.3 Hz), ꢁ158.18 (t, J¼20.5 Hz), ꢁ(164.26e166.03) (m).
MS (EI): m/z¼334 ([M]þ, 100).
4.6.2. 2,3,4,5,6-Pentafluo-20,30,50-trimethoxybiphenyl (12). The com-
0.023 mmol). 1H NMR (400 MHz, CD2Cl2):
27H); 13C NMR (125 MHz, CD2Cl2):
¼144.8 (dm, J¼235.0 Hz), 140.3
d¼1.62 (d, J¼15.0 Hz,
pound was isolated as a white solid. 1H NMR (500 MHz, CD2Cl2):
¼6.78 (s, 1H), 6.70 (s, 1H), 3.95 (s, 3H), 3.83 (s, 3H), 3.82 (s, 3H); 13
C
d
d
(dm, J¼250.0 Hz), 138.0 (dm, J¼255.0 Hz), 105.8 (t, J¼37.0 Hz),
NMR (125 MHz, CD2Cl2):
d
¼151.9 (s), 151.4 (s), 144.6 (dm,
45.8 (d, J¼10.0 Hz), 33.2 (s); 31P NMR (162 MHz, CD2Cl2):
¼106.88
d
J¼247.0 Hz), 143.2 (s), 140.3 (dm, J¼253.0 Hz), 137.6 (dm,
(s); 19F NMR (376 MHz, CD2Cl2):
d
¼ꢁ(119.29e119.74) (m), ꢁ156.10
J¼251.0 Hz), 115.1 (s), 112.7 (td, J¼19.2, 3.8 Hz), 105.5 (s), 97.6 (s),
56.6 (s), 56.4 (s), 56.0 (s); 19F NMR (376 MHz, CD2Cl2):
d¼ꢁ140.98
(t, J¼19.8 Hz), ꢁ(161.01e161.40) (m). ESI-HRMS Calcd for
C18H27AuCl2F5PNa: 659.0711, found: 659.0705.
(dd, J¼23.0, 7.5 Hz), ꢁ157.59 (t, J¼20.3 Hz), ꢁ(164.04e164.54) (m);
MS (EI): m/z¼334 ([M]þ, 100).
4.3.2. trans-Dichloro[N,N-bis(2,6-di-iso-propylphenyl)imidazol-
4.6.3. 1-Methyl-3-(pentafluorophenyl)-indole (13).19 The compound
2-yl](pentafluorophenyl)-gold(III) (7). To
a mixture of [N,N-bis
was isolated as a white solid. 1H NMR (400 MHz, CD2Cl2):
d¼3.84 (s,
(2,6-diisopropylphenyl)imidazol-2-yl](pentafluorophenyl)gold(I)
(301 mg, 0.40 mmol) and iodobenzeneedichloride (157 mg,
0.57 mmol), tetrachloromethane (20 mL) was added. The reaction
mixture was heated at 93 ꢀC for 3 h. The solvent was evaporated
under reduced pressure and the crude was purified by column
chromatography (hexane/CH2Cl2 4:1) to give 10 as a white solid.
3 H) 7.12e7.19 (m, 1H) 7.27 (td, J¼7.67, 1.04 Hz, 1H) 7.30 (s, 1H) 7.39
(d, J¼8.28 Hz, 1H) 7.42e7.49 (m, 1H). 19F NMR (376 MHz, CD2Cl2):
d
¼ꢁ141.28 (dd, J¼23.2, 7.5 Hz), ꢁ159.22 (t, J¼20.7 Hz),
ꢁ(163.81e164.07) (m); MS (EI): m/z¼397 ([M]þ, 100).
Yield: 76% (250 mg, 0.30 mmol). 1H NMR (400 MHz, CD2Cl2):
d¼7.55
4.6.4. Decafluorobiphenyl (14).26 The compound was isolated as
a white solid. 19F NMR (376 MHz, CD2Cl2):
d
¼ꢁ(137.87e138.18) (m),
(t, J¼7.8 Hz, 2H), 7.37 (d, J¼7.7 Hz, 4H), 7.33 (s, 2H), 2.86 (spt,
J¼6.8 Hz, 4H), 1.36 (d, J¼6.8 Hz, 12H), 1.11 (d, J¼7.0 Hz, 12H); 13C
ꢁ(150.63e151.12) (m), ꢁ(161.04e161.58) (m). MS (EI): m/z¼334
([M]þ, 100).
NMR (125 MHz, CD2Cl2):
d
¼167.1 (quint, J¼5.5 Hz), 146.1 (s), 145.0
(dm, J¼240.0 Hz), 139.2 (dm, J¼253.0 Hz), 137.2 (dm, J¼253.0 Hz),
132.9 (s), 131.1 (s), 125.6 (s), 124.3 (s), 113.6 (tm, J¼41.0 Hz), 29.0 (s),
Acknowledgements
26.3 (s), 22.2 (s); 19F NMR (376 MHz, CD2Cl2):
d
¼ꢁ(125.69e125.98)
(m), ꢁ159.28 (t, J¼19.8 Hz), ꢁ(162.74e163.18) (m); ESI-HRMS Calcd
We are thankful to the Swiss National Science Foundation, the
European Research Council (ERC Starting grant agreement no. 307948)
for C33H36AuCl2F5N2Na: 845.1739, found: 845.1733.
€
and the Organic Chemistry Institute of the University of Zurich for fi-
4.4. Cross-coupling of areneegold(III) complexes 2, 3, 5, and 7
with 1,3,5-trimethoxybenzene (8), 1,4,5-trimethoxybenzene
(9), and 1-methylimidazole (10)
nancial support. We would like to thank Prof. Anthony Linden for
performing the X-ray crystal structure determination of 5 and 7.27
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