Heterogenized gold(I)-carbene as a single-site catalyst in continuous flow

Article abstract of DOI:10.1002/cctc.201300997

Catalytically active gold(I)-carbene complexes on a polystyrene backbone were synthesized by treating metal-coordinated isocyanides with the nitrogen nucleophile of a piperazine group bonded to the polystyrene. The local environment of the metal was readi

Full text of DOI:10.1002/cctc.201300997

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DOI: 10.1002/cctc.201300997
Heterogenized Gold(I)–Carbene as a Single-Site Catalyst in
Continuous Flow
Christian Lothschꢀtz,[a, b] Jakub Szlachetko,[c, d] and Jeroen A. van Bokhoven*[a, b]
Catalytically active gold(I)–carbene complexes on a polystyrene
backbone were synthesized by treating metal-coordinated iso-
cyanides with the nitrogen nucleophile of a piperazine group
bonded to the polystyrene. The local environment of the
metal was readily tuned by variation of the functional group.
This versatile synthesis procedure is not restricted to gold and
can easily be extended to other metals such as Pd and Pt. The
gold carbene complexes were extensively characterized, and
resonant inelastic X-ray scattering identified the +1 oxidation
state of the supported gold. This single-site catalyst catalyzed
the synthesis of oxazoles, and the system could be used in
continuous flow.
mode. Here, we show the synthesis, characterization, and cata-
lytic reactivity of a heterogenized acyclic AuI–carbene complex
that can be applied in a continuous process. We characterized
the immobilized complexes by using IR spectroscopy, electron
microscopy, and X-ray absorption spectroscopy (XAS).[11] Het-
erogenized phosphine AuI and salen-type AuIII complexes have
been synthesized before.[12–18] Reports dealing with AuI are rela-
tively scarce, probably because of the delicate synthesis of
these metal complexes.[19–21] Instead of frequently used ordered
mesoporous silica, such as SBA-15 and MCM-41,[22,23] we used
modified polystyrene beads as a support. Polystyrene is an
often-used material in Merrifield solid-phase synthesis and in
heterogeneous catalysis.[24–26] Modified polystyrene polymers,
that is, JendaJel and TentaGel, are used as scavengers in organ-
ic chemistry and continuous flow processes. They can be
tailor-made for different applications and can be produced in
large quantities at low cost. We chose a polystyrene modified
with piperazine. Attack of the nitrogen nucleophile to a metal-
coordinated isocyanide yields an acyclic carbene (Schemes 1
Gold catalysis has emerged as a hot topic in organic chemistry.
The unique reactivity and the mild reaction conditions that can
be used make this metal attractive for a number of different
applications, such as cycloisomerization and CꢀC bond-forma-
tion reactions.[1–10] Most of the reactions are performed in the
homogeneous phase, which makes separation of products and
catalyst difficult. We introduce a versatile and simple proce-
dure to heterogenize metal carbene complexes and illustrate
that AuI–carbene-catalyzed oxazole synthesis can be per-
formed in continuous flow. Metal-coordinated isocyanides
react with the nitrogen nucleophile of a piperazine group at-
tached to a polystyrene backbone. The local environment of
the metal can be readily tuned by variation of the functional
groups, and the method is not restricted to gold.
Scheme 1. Formation of acyclic carbenes starting from metal-coordinated
The uniqueness of gold catalysts is mostly explored in the
homogeneous phase.[1–10] Because of their straightforward sep-
aration, heterogeneous processes are attractive. However, in
general heterogeneous catalysts lack the versatility that charac-
terizes homogeneous ones. Moreover, performing a reaction in
continuous mode has clear advantages above doing it in batch
isocyanides.
and 2).[27–33] In a subsequent reaction, the carbene gold com-
plex can react with an alkyne group to form a gold–acetylide
complex. By treating these compounds with an acid such as
HNTf2 (Tf=trifluoromethanesulfonyl), the acetylide is released,
which enables silver-free activation.[34] A silver salt is generally
needed to remove halogens, which is not possible in the het-
erogeneous system.[35–37] The chemical surrounding of the
metal can be modified by changing loading and type of the
modifier.
[a] Dr. C. Lothschꢀtz, Prof. Dr. J. A. van Bokhoven
Institute for Chemical and Bioengineering
ETH Zurich
8093, Zurich (Switzerland)
E-mail: j.a.vanbokhoven@chem.ethz.ch
[b] Dr. C. Lothschꢀtz, Prof. Dr. J. A. van Bokhoven
Laboratory for Catalysis and Sustainable Chemistry
Paul Scherrer Institute
Combining only 3 polymers and 4 isocyanides leads to 12
distinct materials. (Figure S1, Supporting Information), which
uniquely enables libraries of materials to be built up in a rela-
tively simple manner. We prepared half of the possible materi-
als by using goldI. Moreover, we successfully tested some of
the materials in the well-known synthesis of oxazoles. In this
reaction, a propargyl amide rearranges into the corresponding
oxazole derivative by AuI or AuIII complexes under homogene-
ous conditions.
Villigen (Switzerland)
[c] Dr. J. Szlachetko
Paul Scherrer Institute
Villigen (Switzerland)
[d] Dr. J. Szlachetko
Institute of Physics
Jan Kochanowski University
Kielce (Poland)
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Scheme 2. Synthesis of the acyclic AuI–carbene complexes onto piperazine-modified polystyrene to yield Au@PS6_Y (Y is the second ligand attached to gold).
We characterized the synthesized materials by a variety of
methods, including resonant inelastic X-ray scattering (RIXS),
which combines X-ray absorption and X-ray emission spectros-
copy (XAS and XES).[38] RIXS yields the exact local geometry
and electronic structure in an element-specific manner. Be-
cause hard X-rays are used, measurements can readily be per-
formed under catalytically relevant conditions.[11,39]
dene derivative A,[40,41] which isomerizes into the aromatic
compound either in the presence of acid or AuCl3. All hetero-
geneous catalysts yielded B directly in a cascade reaction,
most likely because any residual amine site that acts as a base
for the formation of the acetylide complex becomes protonat-
ed and acts as the acid site. We observed this site by using IR
spectroscopy (see below). A higher amount of acid (HNTF2)
during catalyst activation, while keeping all other conditions
constant, yielded higher catalytic activity. Thus, increasing the
amount of acid increases the number of activated centers,
Figure 1 shows the yield as a function of time in the rear-
rangement of a propargyl amide into the oxazole derivative
over Au@PS6_AC. Homogeneous AuI catalysts yield oxazoli-
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pletely consumed. The reaction was repeated after flushing
the catalyst with CH2Cl2, and the reaction was restarted by
pumping fresh substrate solution. The reaction was performed
five times, which yielded essentially identical results. The con-
stant catalytic performance and the absence of color change,
which would indicate gold particle formation, prove that the
catalyst is highly stable in flow mode.
There are very few related reports dealing with heterogen-
ized gold complexes,[15,21] and the support and method of syn-
thesis largely differ. Echavarren used a phosphine-containing
polymer that was treated with an already active gold(I) precur-
sor to form a heterogenized gold(I) phosphine complex. Yu
and Cao used a heterogenized triazole as a counterion for
a preformed gold(I) phosphine complex. In both reports, a sub-
strate scope different from ours was addressed, and they both
delivered results with regard to yield and catalyst loading that
were comparable to our system.
Highly dispersed gold species were observed by STEM
images (Figure S2). Exposure of the catalyst to NaHB(OAc)3 in-
dicated particle formation and complete removal of the highly
dispersed gold species. This treatment caused an instantane-
ous color change attributed to particle formation. SEM with
energy-dispersive X-ray spectroscopic elemental analysis (Fig-
ures S3–S5 and Tables S1 and S2) showed that the gold was
evenly distributed over the individual polystyrene beads,
which were between 40 and 80 mm in size. Thus, the immobi-
lized gold complexes in the polystyrene are accessible to
chemicals, they remain stable during reaction, and they de-
compose into particles under a strongly reducing environment.
Figure 2a shows the La1-RIXS plane of Au@PS6_AC. La1-RIXS
planes of Au@PS6_Cl and Au@PS6_NTf2 were also measured
(not shown). The high selectivity to the 5d orbitals of gold is
achieved as a result of the strong 2p3/2!5d resonant excita-
tion, marked by the solid line. The total fluorescence yield
(TFY) and high-energy resolution (HR) XAS curves were extract-
ed from the RIXS plane and are plotted in Figure 2a (right
panel). The HRXAS spectrum exhibits more pronounced fea-
tures than the TFY–XAS curve,[42,43] which indicates the en-
hanced sensitivity of RIXS as a selective probe for the unoccu-
pied d density of states of gold. The HRXAS spectrum shows
a distinct white line, which is the first intense feature in the
spectrum. This feature is much less pronounced in the TFY–
XAS spectrum. A quantitative analysis of the 5d unoccupied
states was performed on the basis of the energy-transfer RIXS
plane[44] plotted in Figure 2b. The correlation of the gold oxi-
dation state versus the detected intensities at the 5d reso-
nance was obtained from the integrated counts along constant
incident beam energies and constant energy transfer curves,
as marked in Figure 2b. The use of gold foil, AuCl, and Au2O3
as reference materials for Au0, AuI, and AuIII respectively, ena-
bled the oxidation state of gold in the three gold complexes
to be determined (Figure 2c). On the basis of the experimental
reference points, a linear dependence of the intensity and oxi-
dation state was assumed. A calibration curve was then em-
ployed to determine the gold oxidation state in Au@PS6_AC,
Au@PS6_Cl, and Au@PS6_NTf2. Oxidation states of 1.1, 0.9, and
0.9, respectively, were obtained; this indicates that gold is pres-
Figure 1. Reaction profile of the oxazole synthesis by using different
amounts of HNTF2 during activation of Au@PS6_AC. The yield was deter-
mined by GC by using dodecane as an internal standard. Conditions: start-
ing material (1.00 mmol), catalyst (5.00 mol%), CH2Cl2 (2.00 mL), RT.
Table 1. Direct yield of oxazole from propargyl amide over the supported
AuI catalyst.
Material
Yield [%]
Batch mode
180 min
420 min
Au@PS6_AC/HNTF2 (2 equiv.)
Au@PS6_AC/HNTF2 (3 equiv.)
Au@PS6_AC/HNTF2 (4 equiv.)
homogeneous complex[40]
pure PS_c
20
31
37
79
0
43
61
76
–
0
0
[a]
PS_c_HNTF2
0
Au@PS6_Cl
Continuous flow
Au@PS6_NTf2
0
0
>95[b]
–
[a] PS_c treated with acid (1 equiv.). [b] No change over five consecutive
runs.
which boosts the activity. In all cases, the reaction went to
complete conversion within 24 h.
Table 1 summarizes the catalytic measurements. In the ab-
sence of acid activation and in the absence of gold (with acid
activation), no catalytic activity was observed. The yield of the
homogeneous complex was similar to that of the heterogene-
ous complex that was activated with the highest amount of
acid. Because the polystyrene beads swell to a multiple of their
original volume upon immersion in liquid, large pores are pres-
ent in the polymer beads through which reactants and prod-
ucts can readily diffuse. By using the immobilized catalyst in
the continuous flow apparatus and by pumping the oxazole
substrate (0.1m in CH2Cl2) through the reactor by a syringe
pump with a flow rate of 1.5 mLhꢀ1, near complete conversion
of the propargyl amide into the corresponding oxazole deriva-
tive was observed. The amount of catalyst was 10 mol% rela-
tive to the whole amount of substrate in each single run. The
flow was maintained until the substrate solution was com-
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Figure 2. a) RIXS plane of Au@PS6_AC, b) RIXS plane of Au@PS6_AC transferred to the energy-transfer scale, and c) dependence of constant incidence energy
(CIE) and constant energy transfer (CET) along the 5d resonance on gold oxidation state [the points of Au@PS6_Cl and Au@PS6_NTf2 overlap]; d) HRXAS spec-
tra extracted from the RIXS planes.
ent as AuI in the complexes. The chemical sensitivity of RIXS to
the local environment can be further observed in the HRXAS
curves (Figure 2d). The intensity of the white line is similar in
all three spectra, and this is indicative of the AuI oxidation
state. The distinct differences in the edge position and local
features at energies higher than that of the white line reveal
that the electronic structure and geometric environment are
probed. A shift in the edge position is caused by a different
Fermi level energy. The bands at energies higher than that of
the white line originate from the d component in the anti-
bonding states between gold and the ligand. Their differences
are reminiscent of the different geometry and electronic struc-
ture in the first few coordination spheres; however, these fea-
tures were not further analyzed.
reports. Interestingly, the material containing the carbene com-
plexes derived from the perfluorinated isocyanide showed an
even stronger hypsochromic shift, which revealed the strong
electronic influence of the perfluorinated moiety on the ligand.
The same trend was observed on going from Au@PS6_Cl to
Au@PS6_NTf2. Because the chloro ligand is a stronger donor
than the trifluorimidato group, the carbene moiety experiences
a less-electron-rich metal surrounding, and this results in
a shortening of the CꢀN bond. Treatment of the polymer with
HNTf2 leads to protonation of the alkyne; this is indicated by
the disappearance of the absorption at 2110 cmꢀ1 and to the
formation of the Brønsted acid site by protonation of the basic
centers in the polymer, which results in an intense absorption
at approximately 3312 cmꢀ1 (Figure S6). As mentioned above,
the use of AuI as a catalyst requires the presence of an acid to
form the oxazole.
FTIR spectroscopy identified the characteristic vibrational
spectra of the supported complexes. The spectral features of
the heterogenized complexes were similar to those of the ho-
mogeneous analogues, which is indicative of a very similar
local structure. The frequency of the carbene group changed
significantly with variation of the ligand structure (Figure S6
and Table S3). In contrast to materials prepared from aromatic
isocyanides, Au@PS3_AC showed a hypsochromic shift in the
absorption of the carbene, which is in agreement with earlier
In conclusion, we reported a new method to prepare stable
acyclic AuI–carbene complexes that are highly dispersed on
a polystyrene support. Within a single step, heterogenization
and ligand formation was achieved, and simple variation of the
starting compounds, the isocyanide, and the polymer modifier
allowed electronic tuning of the metal complex. This on-sup-
port synthesis of metal–carbene complexes is not restricted to
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microscopes. SEM was performed with a field-emission Zeiss Ultra
55 microscope. The RIXS experiments were performed at the Su-
perXAS beamline of the Swiss Light Source. The La1 X-ray fluores-
cence from the sample was recorded by means of a von Hamos-
type spectrometer operated with a cylindrically bent Ge(660) crys-
tal[45,46] by using a position sensitive detector, the MythenII.[47] The
incident beam energy was tuned around the Au L3 absorption
edge by a double crystal monochromater equipped with a Si(111)
crystal. The use of the von Hamos geometry enabled the XES in an
energy-dispersive manner to be detected, which allowed recording
of the XES on a shot-by-shot basis. The AuI–carbene on polystyr-
ene samples were freshly dispersed in CH2Cl2 and sealed in a vial,
which was positioned in the beam.
gold; it is versatile and can be extended to other metals. The
catalytic experiments revealed activity in oxazole synthesis
from propargyl amide that is comparable to the corresponding
complexes in homogeneous catalysis. The presence of the
Brønsted acid sites catalyzed the direct formation of the oxa-
zoles. The use of polystyrene beads enabled reuse of the cata-
lyst and the stable operation of the catalyst in continuous
flow. HRXAS, RIXS, and IR spectroscopy of the immobilized
complex unequivocally identified the gold structure to be AuI.
Electron microcopy showed that gold is well distributed over
the individual polystyrene beads and that no structural
changes occurred during the reaction.
Batch reactions were performed in sealed tube vials with magnetic
stirring. Under ambient conditions, N-(prop-2-yn-1-yl)benzamide
(159 mg, 1.00 mmol) was dissolved in CH2Cl2 (4.00 mL). Au@PS6_
NTf2 (5.00 mol%, 100 mg) and dodecane (226 mL, 1.00 mmol) were
added. Samples were taken from the reaction mixture at fixed time
intervals.
Experimental Section
Synthesis of the materials
See the Supporting Information.
Continuous flow experiments were performed in a glass tube reac-
tor with inner diameter of 6 mm and a length of 250 mm. The re-
actor was closed by septa penetrated by capillaries at both ends.
The reactor was filled with the defined amount of Au@PS6_NTf2,
and CH2Cl2 was used as eluent. The amount of catalyst was
10 mol% relative to the whole amount of substrate used in
a single run. The oxazole substrate (0.1m in CH2Cl2) was pumped
through the reactor by a syringe pump with a flow rate of
1.5 mLhꢀ1. Samples were taken regularly for GC analysis, and the
syringe was refilled four times after flushing with CH2Cl2 (20 mL).
Synthesis of the catalysts
Au@PS6_Cl (Figure 1): The polymer PS_c (1.00–1.50 mmolamine gꢀ1
)
was suspended in CH2Cl2 (10.0 mL), and the suspension was mag-
netically stirred at 150 rpm. (tht)AuCl (tht=tetrahydrothiophene;
200 mg, 624 mmol) and IC_d (200 mL) were added. The suspension
was stirred for 24 h at RT and then filtered through a glass frit. The
solid was washed with CH2Cl2 (3ꢂ60.0 mL) and dried under
vacuum. The wash solution was analyzed by FTIR to detect un-
reacted metal isocyanide complex.
In both batch and continuous flow modes, the yield was deter-
mined by integration of the GC signals. GC analyses were per-
formed with an Agilent 7693/6890 GC equipped with an HP-5
column (50 mꢂ0.32 mmꢂ1.05 mm, 5% phenyl methylsiloxane),
flame ionization detector, and helium as the carrier gas.
Au@PS6_AC: The polymer PS_c (1.00–1.50 mmolamine g
ꢀ1) was sus-
pended in CH2Cl2 (10.0 mL), and the suspension was magnetically
stirred at 150 rpm. (tht)AuCl (200 mg, 624 mmol), IC_d (200 mL),
phenylacetylene (500 mL), and NEt3 (1.00 mL) were added. The sus-
pension was stirred for 72 h at RT and then filtered through a glass
frit. The solid was washed with CH2Cl2 (3ꢂ80.0 mL) and dried
under vacuum. The wash solution was analyzed by FTIR to detect
unreacted metal isocyanide complex.
Acknowledgements
Au@PS6_NTf2: The polymer Au@PS6_AC (100 mg) was suspended
in CH2Cl2 (2.00 mL), and the suspension was magnetically stirred at
150 rpm. HNTf2 (36.0 mg, 128 mmol) dissolved in CH2Cl2 (2.00 mL)
was added. The mixture was stirred for 25 min at RT. Finally, the
solid was filtered through a glass frit. The solid was washed with
CH2Cl2 (3ꢂ20.0 mL) and dried under vacuum.
C.L. is grateful for funding by the Deutsche Akademische Aus-
tauschdienst (DAAD). We thank the Paul Scherrer Institute and
the Swiss Light Source for beam time.
Keywords: carbenes · continuous flow · gold · oxazoles ·
single-site catalyst
General methods
[1] A. S. K. Hashmi, G. J. Hutchings, Angew. Chem. 2006, 118, 8064–8105;
Angew. Chem. Int. Ed. 2006, 45, 7896–7936.
[2] E. Jimꢄnez-NfflÇez, A. M. Echavarren, Chem. Commun. 2007, 333–346.
[3] R. Skouta, C. J. Li, Tetrahedron 2008, 64, 4917–4938.
[4] Z. G. Li, C. Brouwer, C. He, Chem. Rev. 2008, 108, 3239–3265.
[5] A. Arcadi, Chem. Rev. 2008, 108, 3266–3325.
[6] D. J. Gorin, B. D. Sherry, F. D. Toste, Chem. Rev. 2008, 108, 3351–3378.
[7] A. S. K. Hashmi, M. Rudolph, Chem. Soc. Rev. 2008, 37, 1766–1775.
[8] S. Sengupta, X. D. Shi, ChemCatChem 2010, 2, 609–619.
[9] C. Nevado, Chimia 2010, 64, 247–251.
[10] A. Corma, A. Leyva-Perez, M. J. Sabater, Chem. Rev. 2011, 111, 1657–
1712.
All reactions were performed under a nitrogen atmosphere by
using standard Schlenk techniques. Unless otherwise declared, all
chemicals were purchased from SigmaAldrich, Acros Organics, or
AlfaAesar and were used without further purification. Piperazine-
modified polystyrene supports were ordered from SigmaAldrich
and AlfaAesar. All solvents were dried on a column by using acti-
vated alumina and stored in the presence of activated molecular
sieves (4 ꢃ). Synthesis procedures for all compounds are provided
in the Supporting Information. NMR spectra of liquid solutions
were recorded with
a
Bruker Avance 500 spectrometer
1
(500.13 MHz for 1H) at 308C. H NMR spectra are referenced to the
residual solvent signals. Transmission electron microscopy (TEM)
was performed with FEI Tecnai F30 ST (FEG, 300 kV) and Hitachi
HD2700CS (aberration-corrected dedicated STEM, cold FEG, 200 kV)
[11] S. Bordiga, E. Groppo, G. Agostini, J. A. van Bokhoven, C. Lamberti,
Chem. Rev. 2013, 113, 1736–1850.
[12] C. Gonzµlez-Arellano, A. Corma, M. Iglesias, F. Sanchez, Eur. J. Inorg.
Chem. 2008, 1107–1115.
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 443 – 448 447

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
[13] Transition Metal Single Site Catalysts—From Homogeneous to Immobi-
lized Systems, Mod. Surf. Organomet. Chem. (Eds.: J. Basset, R. Psaro, D.
Roberto, R. Ugo), Wiley-VCH, Weinheim, Germany, 2009, p. 167.
[14] S. Chessa, N. J. Clayden, M. Bochmann, J. A. Wright, Chem. Commun.
2009, 797–799.
[33] M. C. Blanco Jaimes, C. R. N. Bçhling, J. M. Serrano-Becerra, A. S. K.
Hashmi, Angew. Chem. 2013, 125, 8121–8124; Angew. Chem. Int. Ed.
2013, 52, 7963–7966.
[34] S. Sanz, L. A. Jones, F. Mohr, M. Laguna, Organometallics 2007, 26, 952–
957.
[15] W. J. Cao, B. Yu, Adv. Synth. Catal. 2011, 353, 1903–1907.
[16] M. Egi, K. Azechi, S. Akai, Adv. Synth. Catal. 2011, 353, 287–290.
[17] G. Villaverde, A. Corma, M. Iglesias, F. Sanchez, ACS Catal. 2012, 2, 399–
406.
[18] M. P. de Almeida, S. A. C. Carabineiro, ChemCatChem 2012, 4, 18–29.
[19] A. Corma, E. Gutierrez-Puebla, M. Iglesias, A. Monge, S. Perez-Ferreras, F.
Sanchez, Adv. Synth. Catal. 2006, 348, 1899–1907.
[20] M. Flytzani-Stephanopoulos, B. C. Gates, Annu. Rev. Chem. Biomol. Eng.
2012, 3, 545–574.
[21] M. Raducan, C. Rodriguez-Escrich, X. C. Cambeiro, E. C. Escudero-Adan,
M. A. Pericas, A. M. Echavarren, Chem. Commun. 2011, 47, 4893–4895.
[22] A. Corma, Chem. Rev. 1997, 97, 2373–2419.
[35] H. Schmidbaur, A. Schier, Z. Naturforsch. B 2011, 66, 0329–0350.
[36] D. Weber, M. R. Gagne, Org. Lett. 2009, 11, 4962–4965.
[37] D. W. Wang, R. Cai, S. Sharma, J. Jirak, S. K. Thummanapelli, N. G. Akh-
medov, H. Zhang, X. B. Liu, J. L. Petersen, X. D. Shi, J. Am. Chem. Soc.
2012, 134, 9012–9019.
[38] P. Glatzel, U. Bergmann, Coord. Chem. Rev. 2005, 249, 65–95.
[39] J. Singh, C. Lamberti, J. A. van Bokhoven, Chem. Soc. Rev. 2010, 39,
4754–4766.
[40] J. P. Weyrauch, A. S. K. Hashmi, A. Schuster, T. Hengst, S. Schetter, A. Litt-
mann, M. Rudolph, M. Hamzic, J. Visus, F. Rominger, W. Frey, J. W. Bats,
Chem. Eur. J. 2010, 16, 956–963.
[41] C. Aydin, J. Lu, N. D. Browning, B. C. Gates, Angew. Chem. 2012, 124,
6031–6036; Angew. Chem. Int. Ed. 2012, 51, 5929–5934.
[42] K. Hämäläinen, D. P. Siddons, J. B. Hastings, L. E. Berman, Phys. Rev. Lett.
1991, 67, 2850–2853.
[23] D. E. De Vos, M. Dams, B. F. Sels, P. A. Jacobs, Chem. Rev. 2002, 102,
3615–3640.
[24] N. E. Leadbeater, M. Marco, Chem. Rev. 2002, 102, 3217–3273.
[25] P. Blaney, R. Grigg, V. Sridharan, Chem. Rev. 2002, 102, 2607–2624.
[26] J. Lu, P. H. Toy, Chem. Rev. 2009, 109, 815–838.
[27] C. Bartolomꢄ, D. Garcia-Cuadrado, Z. Ramiro, P. Espinet, Organometallics
2010, 29, 3589–3592.
[43] O. V. Safonova, M. Tromp, J. A. van Bokhoven, F. M. F. de Groot, J. Evans,
P. Glatzel, J. Phys. Chem. B 2006, 110, 16162–16164.
[44] J. Vµclavík, M. Servalli, C. Lothschꢀtz, J. Szlachetko, M. Ranocchiari, J. A.
van Bokhoven, ChemCatChem 2013, 5, 692–696.
[28] A. S. K. Hashmi, T. Hengst, C. Lothschutz, F. Rominger, Adv. Synth. Catal.
2010, 352, 1315–1337.
[29] C. Bartolomꢄ, Z. Ramiro, D. Garcia-Cuadrado, P. Perez-Galan, M. Radu-
can, C. Bour, A. M. Echavarren, P. Espinet, Organometallics 2010, 29,
951–956.
[45] L. von Hµmos, Naturwissenschaften 1932, 20, 705–706.
[46] J. Szlachetko, M. Nachtegaal, O. V. Safonova, J. Sa, G. Smolentsev, J. A.
van Bokhoven, J. Hoszowka, J.-Cl. Dousse, Y. Kayser, P. Jgodzinski, A. Ber-
gamaschi, B. Schmid, C. David, E. de Boni, A. Lꢀcke, Rev. Sci. Instrum.
2012, 83, 103105.
[30] A. S. K. Hashmi, M. Buhrle, M. Wolfle, M. Rudolph, M. Wieteck, F. Ro-
minger, W. Frey, Chem. Eur. J. 2010, 16, 9846–9854.
[31] A. S. K. Hashmi, T. Haffner, M. Rudolph, F. Rominger, Chem. Eur. J. 2011,
17, 8195–8201.
[47] B. Schmitt, C. Bronnimann, E. F. Eikenberry, F. Gozzo, C. Hormann, R. Ho-
risberger, B. Patterson, Nucl. Instrum. Methods Phys. Res. Sect. A 2003,
501, 267–272.
[32] W. A. Herrmann, T. Weskamp, V. P. W. Bohm, Adv. Organomet. Chem.
2001, 48, 1–69.
Received: November 21, 2013
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