Ullmann homocoupling catalysed by gold nanoparticles in water and ionic liquid

Article abstract of DOI:10.1002/adsc.201200422

The gold-catalysed Ullmann-type homocoupling of aryl halides is carried out with two different methodologies: (i) under micellar catalysis conditions in water and (ii) using a molten tetralkylammonium ionic liquid as the reaction medium. Glucose is used as a clean and renewable reductant. Morphology, size, and chemical composition of the gold nanoparticles were ascertained by X-ray photoelectron spectroscopy, transmission electron microscopy and dynamic light scattering analyses. A plausible reaction mechanism is proposed.

Full text of DOI:10.1002/adsc.201200422

Supporting Information
©
Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2012

S1
Ullmann Homocoupling Catalyzed by Gold nanoparticles in
Water and Ionic Liquid
a
a
a
a
Antonio Monopoli, * Pietro Cotugno, Gerardo Palazzo, Nicoletta Ditaranto, Bruno
a
a
a
a,b
Mariano, Nicola Cioffi, Francesco Ciminale, and Angelo Nacci*
a
Department of Chemistry, Università degli Studi di Bari “Aldo Moro”, Via Orabona 4, 70126-Bari, Italy
Phone: +39.080.544.2119. Fax: +39.080.544.2129. E-mail: antomono@libero.it; nacci@chimica.uniba.it
b
CNR – ICCOM, Department of Chemistry, Università degli Studi di Bari “Aldo Moro”, Via Orabona 4, 70126-Bari,
Italy.
Supporting information
General Remarks: All chemicals used for synthetic procedures such as aryl halides, reductants and
tetraalkylammonium salts, were commercially available and were used without further purification.
Reactions were monitored by GLC and GC-MS techniques by using an Agilent 5890 A
gaschromatograph and an Agilent 6850/MSD 5975C instrument, respectively. Both the instruments
were equipped with a capillary column HP-5MS (Agilent, l. 30 m, i.d. 0.25 mm, s.p.t. 0.25 µ).
NMR spectra were recorded on a Varian Inova 400 MHz spectrometer. UV-vis spectra were
recorded on a V-530 spectrophotometer from JASCO, and dynamic light scattering experiments
were executed on Zetasizer-Nano S instrument from Malvern. TEM analyses were performed by a
Tecnai 12 instrument (120 kV, Tungsten filament) by dropping proper aliquots of colloidal samples
on a carbon-Cu grid. XP spectra were acquired by a Theta Probe VG Scientific spectrometer
equipped with a monochromatised AlKα source (spot size 300 ꢀm). Survey and high-resolution
spectra were acquired in constant analyzer energy (CAE) mode with a pass energy of 150 and 100
eV, respectively. The zeta-potential on the nanoparticle surface was measured through a Zetasizer
Nano ZS90 apparatus.
Identification of known compounds was made by comparison of their spectral data with those
reported in the literature (most of them are identified with the help of the NIST library).
Catalyst preparation
In general, gold nanoparticles catalysts were prepared in situ during catalytic test by reduction of a
gold(III) source with a proper reductant. For the protocol in water, preparation procedure was
similar to the our previous one adopted for palladium [21a]. For selected experiments gold
nanoparticles were prepared ex situ according to the following literature procedure [30]: 45 mg of
glucose were dissolved in 4 mL of an aqueous solution of CTAB (125 mM) and HAuCl (50 mM).
4
The solution was thermostated at 70°C and the reaction was triggered by increasing the pH through

S2
the addition of 2 mL of NaOH (0.1 M) at 70°C. The relatively low temperature and pH (pH∼ 10)
avoided the formation of coloured by-products of glucose alkaline oxidative degradation, thus
allowing for characterization of the gold nanoparticles through optical techniques directly in
solution. Absorbance spectroscopy in the visible shows the presence of a plasmonic peak centred at
5
50 nm and dynamic light scattering reveals particle with an average hydrodynamic diameter of 21
nm. The surfactant cetyltrimethylammonium bromide (CTAB) was added to control the Au-NPs
growth acting as capping agent. The nanoparticles are stabilised against aggregation by the products
of oxidative degradation of glucose (mainly gluconate under these mild conditions) that adsorb on
their surface conferring an overall negative charge (the zeta-potential was -25 mV). The gold
nanoparticles have been subsequently extensively dialyzed against twice-distilled water thus
obtaining a suspension of Au(0) nanoparticles without unreacted gold ions.
Catalysts characterization
At the end of the coupling reaction, the mixture was analyzed by the transmission electron
microscopy (TEM) technique to ascertain both NP core morphology and size dispersion.
Colloidal Au-NPs shape was almost spherical, and nanoparticles showed an appreciable
dimensional homogeneity with a mean core diameter of ca. 1 nm (aqueous colloids, fig. 1A) or 20
±
6 nm (Au-NPs in TBAA, fig. 3B). Below, are reported further TEM images of Au nanoparticles
prepared in tetrabutylammonium acetate confirming those sizes an morphology.
Figure S1. TEM images of Au nanoparticles prepared in tetrabutylammonium acetate.

S3
Surface chemical composition information of nanocolloids was obtained by means of X-ray
photoelectron Spectroscopy (XPS). The analysis was performed on gold nanoparticles catalysts
prepared both in situ and ex situ and most of results are presented in the text in figures 2B, 3A and
6
. Below are reported the XP wide scan spectra for Au-NPs prepared ex situ (fig. S2) and for the
post-reaction catalyst (protocol in water).
Figure S2. Wide scan XP spectrum of Au-NPs prepared ex situ
Figure S3. Wide scan XP spectrum of the post-reaction catalyst (protocol in water).

S4
Catalytic tests
In a 1 ml gas-tight vial, equipped with a screw cap and a magnetic bar, aryl halide (0.5 mmol),
glucose (0.5 mmol), TBAOH (1.5 mL of 1M solution in water, 1.5 mmol) and gold triacetate
(2mol%) were placed. In the case of the reaction in ionic liquids the TBAOH solution was replaced
by 0.5 g of TBAA. For a better reproducibility of experiments, the use of a gas-tight vial having a
proper capacity (leaving a very small head space) to avoid the formation of droplets of the reaction
mixture on the walls of vial, is recommended. The flask was heated under air and under stirring at
the reaction temperature for a maximum of 6 hours (see tables 1-2). Then, the reaction mixture was
washed with HCl 5% and extracted with dichloromethane. To the organic phase a known amount of
an external standard (in almost all cases biphenyl) was added and examined by glc and GC-MS,
providing both conversions and products identification by comparison with spectral data reported in
the literature. Isolated yields in table 3 were determined by purification of the extracted
dichloromethane solutions, after evaporation of the solvent in vacuo, with a short pad of silica gel
(eluent petroleum ether).
Recycling experiments
In a typical run, at the end of the reaction, the aqueous mixture was extracted with diethyl ether
(3x5mL) and the collected organic layers were evaporated under vacuum to isolate the reaction
product. To the aqueous layer, containing gold nanoparticles, were added the fresh reagents p-
iodoanisole, glucose, and TBAOH, and the reaction mixture was stirred at 90°C for the proper time.
Results are collected in fig. S4.
Recycling experiments
100
80
60
40
20
0
1
2
3
4
run
Figure S4. Recycling experiments

S5
1
List of the H NMR signals of the reaction products:
1
1
Biphenyl. (Lit. ) H-NMR (CDCl ): δ 7.63 (m, 4H), 7.48 (m, 4H), 7.38 (m, 2H).
3
1
1
4
,4’-Dimethylbiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.49 (d, 4H, J= 8.4 Hz), 7.25 (d, 4H, J= 8.4
3
Hz), 2.34 (s, 6H).
1
1
2
,2′-dimethylbiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.27-7.20 (m, 6 H), 7.11-7.09 (m, 2 H), 2.06 (s,
3
6
H).
1
1
4
,4′-Dimethoxybiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.49 (d, J = 8.8 Hz, 4 H), 6.97 (d, J = 8.4 Hz,
3
4
H), 3.84 (s, 6 H).
2
1
4
,4′-dibromobiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.53 (d, J = 8.6 Hz, 4 H), 7.38 (d, J = 8.6 Hz, 4
3
H).
3
1
4
,4’-Difluorobiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.41 (dd like, 4H, J= 9.2 and 4.8 Hz), 7.12 (t
3
like, 4H, J=8.2 Hz).
4
1
4
,4'-Bis(trifluoromethyl)biphenyl. (Lit. ) H-NMR (CDCl ): δ 7.72 (m, 8H).
3
1
1
1
,1´-Binaphthyl. (Lit. ) H-NMR (CDCl ): δ 7.92-7.99 (4H, m), 7.59 (m, 2H), 7.55-7.40 (m, 4H),
3
7
.39 (m, 2H), 7.29 (2H, m).
5
1
2
,2'-Dimethoxybiphenyl. (Lit. ) H-NMR (CDCl ): δ 7.22-7.35 (m, 4H), 6.94-7.04 (m, 4H), 3.76
3
(s, 6H).
1
1
1
,4-Diphenyl-1,3-butadiene. (Lit. ) H-NMR (CDCl ): δ 7.44 (d, J = 7.4 Hz, 4 H), 7.33 (t, J = 7.6
3
Hz, 4 H), 7.26-7.22 (m, 2 H), 6.93 (m, 2 H), 6.69 (m, 2 H).
1
B. Kaboudin, Y. Abedi, T. Yokomatsu Eur. J. Org. Chem. 2011, 33, 6656.
B. Karimi, F. K. Esfahani, Chem. Commun. 2011, 47¸ 10452.
K. Kude, S. Hayase, M. Kawatsura, T. Itoh, Heteroatom Chem. 2010, 22, 397.
A. Monopoli, V. Calò, F. Ciminale, P. Cotugno, C. Angelici, N. Cioffi, A. Nacci, J. Org. Chem. 2010, 75, 3908.
2
3
4
5
C. Liu, Q. Ni, F. Bao, J. Qiu Green Chem. 2011, 13, 1260.

S6
1
Images of H NMR and MS spectra for the reaction products:
1
H-NMR (CDCl3)
biphenyl
MS

S7
1
H-NMR (CDCl3)
Me
Me
4
,4'-Dimethylbiphenyl
4.0 4.3
6.0
1
0
9
8
7
6
5
4
3
2
1
MS

S8
Me
1
H-NMR (CDCl3)
Me
,2'-Dimethylbiphenyl
2
MS

S9
MeO
OMe
1
H-NMR (CDCl3)
4
,4'-Dimethoxybiphenyl
MS

S10
Br
Br
1
H-NMR (CDCl3)
4,4'-Dibromobiphenyl
4
.03.9
1
0
9
8
7
6
5
4
3
2
1
MS

S11
1
H-NMR (CDCl3)
F
F
4
,4'-Difluorobiphenyl
3.9 4.0
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
MS

S12
F3C
CF3
1
H-NMR (CDCl3)
4,4'-Bis(trifluoromethyl)biphenyl
MS

S13
1
H-NMR (CDCl3)
1,1´-Binaphthyl
MS

S14
OMe
MeO
1
H-NMR (CDCl3)
2,2'-Dimethoxybiphenyl
3.9 4.0
6.4
8
.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
MS

S15
1
H-NMR (CDCl3)
1,4-diphenylbuta-1,3-diene
MS