Trinuclear copper(I) complexes with triscarbene ligands: Catalysis of C-N and C-C coupling reactions

Article abstract of DOI:10.1039/b906730b

Novel synthetic routes for the preparation of trinuclear copper(I) complexes with triscarbene ligands are presented, which yield higher purity products than the one previously described. The first crystal structure of one of these complexes is reported an

Full text of DOI:10.1039/b906730b

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www.rsc.org/dalton | Dalton Transactions
Trinuclear copper(I) complexes with triscarbene ligands: catalysis of C–N and
C–C coupling reactions†
Andrea Biffis,*a Cristina Tubaro,a Elena Scattolin,a Marino Basato,a Grazia Papini,b Carlo Santini,*b
Eleuterio Alvarezc and Salvador Conejeroc
Received 3rd April 2009, Accepted 3rd July 2009
First published as an Advance Article on the web 27th July 2009
DOI: 10.1039/b906730b
Novel synthetic routes for the preparation of trinuclear copper(I) complexes with triscarbene ligands
are presented, which yield higher purity products than the one previously described. The first crystal
structure of one of these complexes is reported and confirms the expected structure. The trinuclear
complexes proved to be efficient catalysts of Ullmann-type reactions as well as of the Sonogashira
reaction.
Indroduction
Metal-catalyzed carbon–carbon and carbon–heteroatom coupling
reactions have become one of the most important reaction
classes in chemical synthesis.1 Most of these reactions however
need a noble metal catalyst, hence the cost may easily become
a shortcoming of their technological application. Therefore, a
flourishing area of research is the quest for catalysts made out
of non-noble metals which exhibit comparable catalytic efficiency.
In this connection, copper species are well-established promoters
of C–N and C–O couplings (the so-called Ullmann, Goldberg and
related reactions).2 These applications were recently made much
more technologically appealing by the discovery of novel catalysts
and reaction protocols that allowed for high catalytic efficiency at
comparatively mild temperatures.3 Moreover, copper species have
also been occasionally proposed as an alternative to the more
commonly employed Pd-based catalysts for technologically rele-
vant C–C couplings, such as the Heck,4 Suzuki5 and Sonogashira6
reactions.
We have recently started a research program aimed at the
synthesis, characterisation and catalytic application of copper(I)
complexes with di- and tri-N-heterocyclic carbene (NHC) ligands.7
In particular, we have reported on the synthesis of complex 1
(Fig. 1) for which we have proposed a trinuclear structure in which
every copper atom is coordinated to two imidazolin-2-ylidene
rings, belonging to two different tricarbenic units.8
Fig. 1 ORTEP drawing (30% ellipsoids probability) of complex 1-PF6.
Hydrogen atoms and PF6 anion have ◦been removed for clarity.
˚
Selected bond lengths [A] and angles [ ]: Cu(1)–Cu(2) 2.7049(10),
Cu(2)–Cu(3) 2.6965(9), Cu(1)–Cu(3) 2.6169(9), Cu(1)–C(1) 1.915(5),
Cu(1)–C(13) 1.912(5), Cu(2)–C(5) 1.901(6), Cu(2)–C(17) 1.905(5),
Cu(3)–C(21) 1.908(5), Cu(3)–C(9) 1.908(5); C(1)–Cu(1)–C(13) 171.1(2),
C(5)–Cu(2)–C(17) 168.0(3), C(21)–Cu(3)–C(9) 170.2(2).
aDipartimento di Scienze Chimiche, Universita` di Padova, via Marzolo 1,
I-35131, Padova, Italy. E-mail: andrea.biffis@unipd.it; Fax: (+39) 049
8275216; Tel: (+39) 049 8275223
bDipartimento di Scienze Chimiche, Universita` di Camerino, Via S. Agostino
1, 62032, Camerino, (MC), Italy
cInstituto de Investigaciones Quimicas, Departamento de Quimica Inorgan-
ica, CSIC and Universidad de Sevilla, Avda. Americo Vespucio 49, 41092,
Sevilla, Spain
† Electronic supplementary information (ESI) available: Full listing of
atomic coordinates, bond distances and angles, and CIF file for complex
1-PF6. CCDC reference number 726192 for complex 1-PF6. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b906730b
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7223–7229 | 7223
©

Table 1 Crystal data and structure refinement for complex 1-PF6
This complex exhibits an excellent catalytic activity in the
Ullmann coupling between azoles or phenols and aryl halides;
furthermore, its reactivity in these reactions is quite different from
that of other copper-based catalytic systems, in that it exhibits an
anomalous dependence on the nature of the substituents on the
aryl halide.
In this contribution, we report alternative synthetic procedures
for the preparation of trinuclear copper(I) complexes of this kind,
the first crystal structure of one such complex which definitely
confirms the expected structure, and further studies on the
reactivity of these complexes in C–N, C–O and also C–C coupling
reactions.
Empirical formula
C24H32B2Cu3F6N12P
Formula weight
Temperature/K
Wavelength/A
Crystal system
Space group
845.83
173(2)
0.71073
Triclinic
P¯ı
˚
a = 86.910(1)◦
b = 76.367(1)◦
g = 73.979(1)◦
˚
˚
Unit cell dimensions
a = 14.1659(6) A
b = 15.2179(8) A
˚
c = 16.9149(9) A
3
˚
Volume/A
3405.8(3)
4
1.650
Z
Density (calculated)/
mg m-3
Absorption
coefficient/mm-1
F(000)
1.973
Results and discussion
1704
Complex 1 was previously obtained upon deprotonation of the
tris-imidazolium tetrafluoroborate salt precursor with n-BuLi and
subsequent reaction with [CuBr(PPh3)3], following a procedure
already employed by Fehlhammer et al. for the preparation of
chelate triscarbene complexes of other transition metals.9 This
procedure provides the product in good yield, but also in impure
form, since the product invariably contains trace amounts of
triphenylphopshine and, most notably, large amounts of inorganic
salts that cannot be removed by recrystallisation.
Crystal size/mm3
Theta range for data
collection
0.25 ¥ 0.13 ¥ 0.13
1.77 to 30.42◦
Index ranges
-20 ≤ h ≤ 14, -21 ≤ k ≤ 21,
-24 ≤ l ≤ 24
Reflections collected
Independent reflections
55191
20099 [R(int) = 0.0306]
Completeness to theta = 98.4%
30.42◦
Absorption correction
Semi-empirical from
equivalents
0.7735 and 0.7382
Nevertheless, it has been possible to obtain a crystal structure of
Max. and min.
transmission
-
-
complex 1 bearing a PF6 instead of a BF4 counterion (complex
1-PF6). The complex was obtained through a modification of the
same synthetic route, upon deprotonation of the trisimidazolium
triflate precursor with n-BuLi and subsequent reaction with
[Cu(NCMe)4](PF6). This synthetic procedure makes it easier to
purify the complex from inorganic salts. Crystals suitable for an
X-ray diffraction study were grown by slow diffusion of concen-
trated solutions of the complex in diethyl ether. Gratifyingly, the
structure (Fig. 1 and Table 1) fully confirms the one previously
proposed by some of us on the basis of spectroscopic and analytical
methods.8 The asymmetric unit consists of two independent
molecules of almost identical metrical parameters and only one of
them will be discussed here.
Refinement method
Full-matrix-block
least-squares on F2
20099/0/865
Data/restraints/
parameters
Goodness-of-fit on F2
1.060
Final R indices [I > 2s(I)] R1 = 0.0462, wR2 = 0.1281
R indices (all data)
R1 = 0.0623, wR2 = 0.1459
1.447 and -0.956
Largest diff. peak and
-3
˚
hole/e A
Complex 1-PF6 crystallizes in a P¯ı space group with a D3
˚
symmetry. Each copper atom is bicoordinated with 1.91 A
(average) Cu–Ccarbene bond distances, similar to other previ-
ously described NHC–Cu complexes.10 The Ccarbene–Cu–Ccarbene
angles of 170◦ (average) are slightly deviating from linearity,
in contrast with the results reported by Meyer on complex
[Cu3(TIMEMe)2](PF6)3 (TIMEMe = 1,1,1-tris[(3-methylimidazol-
2-yl◦idene)-methyl]ethane) which shows C–Cu–C angles close to
178 .10 This deviation from linearity might be ascribed to the
geometric constraints exerted by the less flexible tris(imidazolin-
2-ylidene)borate ligand compared to the TIMEMe ligand. Fur-
thermore, the Ccarbene–Cu–Ccarbene plane is not perpendicular to the
plane of the three copper atoms, similarly to a recently reported
structure of a polynuclear silver(I) complex with two hexacarbene
ligands.11 Consequently, the complex exhibits a twisted, chiral
structure (Fig. 2). The imidazolin-ylidene rings in the complex
are characterised by metrical parameters comparable to other
reported Cu–NHC complexes showing N–Ccarbene distances of
Fig. 2 Top view of complex [Cu3{HB(MeIm)3}2](PF6).
of the X-ray structure of the precursor employed in this case no
definite conclusions can be drawn.
1.36 A (average) and N–Ccarbene–N angles of 105◦ (average). These
˚
˚
bond distances and angles are usually different from those of the
imidazolium precursors of the carbene ligands, but due to the lack
The Cu–Cu separations of 2.71, 2.70 and 2.62 A exceed the sum
˚
of atomic radii (2.56 A). Some authors have suggested that bond
7224 | Dalton Trans., 2009, 7223–7229
This journal is The Royal Society of Chemistry 2009
©

˚
that the complex is chiral, as in the case of the related complex
1. The ESI-MS spectrum of 3 gives a unique ion at 1157 m/z;
this confirms that 3 does indeed possess an oligomeric structure,
with two triscarbene ligands and three metal centers. No fragment
ions were observed, showing that the copper(I) complex was stable
under the conditions of the electrospray ionization and detection.
However, despite the spectroscopic purity determined by NMR,
the elemental analysis of complex 3 was lower than expected; the
data however could be reasonably fitted by taking into account the
presence of residual AgBr, which was experimentally confirmed
by ICP-AAS analysis. Consequently, on the basis of these data
and of their similarity to the spectral data of complex 1, we also
attributed to complex 3 a similar structure in which every copper
atom is coordinated to two imidazolin-2-ylidene rings, belonging
to two different triscarbene units, each one therefore coordinating
distances in the range 2.4–2.7 A may indicate the existence of some
weak d10–d10 closed-shell metal–metal interactions,12 although two
of the distances fall beyond the upper limit commonly considered
for such interactions (2.68 A).
˚
We have also developed an alternative synthetic pathway for
copper(I) triscarbene complexes, based upon the synthesis of
silver(I) triscarbene complexes as intermediates with subsequent
transmetallation to copper(I) centers. The transmetallation from
a silver(I) NHC complex, synthesized by treatment of the imi-
dazolium salt with Ag2O, is a useful coordination method in the
preparation of chelating N-heterocyclic carbene complexes.13 In
most cases this procedure can be carried out under aerobic condi-
tions, and the process has been successfully applied to a variety of
metal centers.14 Moreover, an efficient synthetic procedure for the
preparation of the silver(I) triscarbene precursors has been very
recently reported by our group.15
1
in h fashion (Fig. 3).
We have attempted to extend this synthetic procedure to the
preparation of other copper(I) triscarbene complexes with bulkier
wingtip substituents at the triscarbene ligand such as mesityl or
t-butyl. Unfortunately, although we were able to detect formation
of the desired complex in the reaction mixture by ESI-MS, we have
been unable up to now to isolate the products in satisfactory yield
and purity.
Using the intermediate silver triscarbene complex 2 and
CuBr(SMe2) as the copper source, complex 3 could be prepared
(Fig. 3), which was not accessible through the previously reported
deprotonation route, presumably due to the acidity of the benzylic
protons. The complex was obtained in lower yield compared to the
original synthesis of 1 by the deprotonation route, but in higher
purity.
We have evaluated the catalytic efficiency of complex 3 in
the Ullman coupling of aryl halides with azoles and phenols.
The obtained data were compared with those obtained with the
previously reported complex 1. In parallel, we were also keen
to perform a comparative evaluation of the catalytic activity
of other copper–NHC complexes not possessing the trinuclear
structure of 1 and 3, in order to determine the effect of the
trinuclear structure on the catalytic performance of the complex.16
Therefore, we have included in our studies an evaluation of the
catalytic potential of the commercially available copper carbene
complex 4 conventionally termed IPrCuCl.17 This complex is
arguably the most efficient copper carbene complex catalyst
known to date and it has proven useful for several reactions.18
To the best of our knowledge, though, no investigation on
its catalytic efficiency in Ullmann-type couplings is available,
although a related complex bearing a ligand with a saturated
N-heterocyclic ring was recently reported to exhibit good catalytic
activity for the amination of aryl and heteroaryl bromides with
ammonia.19
The copper(I) complex 3 has been characterized by analytical
and spectral data. The infrared spectrum carried out on the solid
sample showed all the expected bands: weak absorptions in the
range 3029–3115 cm-1 are due to the azolyl ring C–H stretchings,
a medium absorption at 1554 cm-1 is related to ring “breathing”
vibrations and a medium absorption at 2431 cm-1 is due to the B–H
stretching. The 1H-NMR spectra of the copper complex supports
the proposed structure. The product appears spectroscopically
pure, and exhibits signals slightly upfield compared to the parent
tris-azolium salt as well as to the silver precursor 2; as expected, the
C2–H signal is absent. Correspondingly, the 13C-NMR spectrum
shows the characteristic coordinated C2 signal at d ca. 177 ppm,
well downfield from the corresponding signal of the tris-azolium
salt (d ca. 140.52). Furthermore, there is only a single set of
1
signals for the imidazolin-2-ylidene rings in both the H and 13C
NMR spectra, which indicates a highly symmetric structure. It
is interesting to remark that the benzylic protons in the complex
give an AB system in the 1H NMR spectrum, which is indicative of
their diastereotopicity and consequently supports the hypothesis
Fig. 3 Reaction scheme for the synthesis of complex 3.
The Royal Society of Chemistry 2009
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Dalton Trans., 2009, 7223–7229 | 7225
©

Table 2 Arylation of azoles and phenols with different copper(I) NHC
complexes
Yield (%)a
Entry
1
Aryl halide
Azole
1b,c
3c
4d
93
nd
90
The tests were run under the optimised reaction conditions
already employed with catalyst 1, that is, using 3 mol% Cu in
◦
DMSO with Cs2CO3 as the base at 100 C for 24 h.8 Only in
2
3
4
21
50
73
nd
nd
nd
54
23
60
the case of catalyst 4, which turned out to be the least efficient
catalyst in initial tests, the amount of catalyst was set to 10 mol%
Cu in order to achieve conversions comparable with the trinuclear
complexes. The results are reported in Table 2.
It can be appreciated that complexes 1 and 3 exhibit comparable
catalytic activity, in that they are able to efficiently convert acti-
vated aryl iodides, bromides or even chlorides at a comparatively
low temperature (100 ◦C). On the other hand, the observed yields
were found to decrease smoothly on going from activated, eletron-
poor aryl halides to more electron-rich ones. The abnormally low
reactivity of aryl halides bearing weakly electron-donating groups,
previously recorded using complex 18 (see e.g. Table 2, entries 1–3
and 6–8), was not observed with complex 3.
5
6
44
nd
50
86
>99
85
Complex 4 displayed a good catalytic activity, which was
however significantly lower than that of the trinuclear complexes.
In fact, 10 mol% catalyst (10 mol% Cu) was required to reach
conversions attainable with just 1 mol% (3 mol% Cu) trinuclear
complex. Therefore, the trinuclear structure of complexes 1 or 3
seems to make a positive contribution to the catalytic efficiency of
such complexes in Ullmann-type reactions.
The catalytic activity of complexes 1, 3 and 4 has also been
studied in the Sonogashira coupling of aryl halides with terminal
alkynes. The results are reported in Table 3.
7
8
9
20
50
70
93
33
54
nd
67
86
10
11
12
50
>99
>99
24
>99
>99
57
nd
85
Initially, we investigated the standard reaction between iodoace-
tophenone and phenylacetylene, and screened with the various
catalysts for different solvents (DMSO, DMF) and bases (TBAA,
Cs2CO3) in order to determine the best reaction conditions. The
reaction time was set at a constant of 24 h and was not optimized
further. Quite interestingly, the mononuclear complex 4 turned out
to be completely inactive for the reaction under all the employed
reaction conditions. On the other hand, complexes 1 and 3 turned
out to be active. Cs2CO3 was found to be the best base in all cases.
Concerning the solvent, DMSO provided slightly better results in
terms of conversion (Table 3, entries 2 and 3), particularly with
catalyst 3. We soon realised however that DMSO also promoted
an unwanted side reaction such as the homocoupling of the arene
(Table 3, entry 3). An analogous but much more pronounced
solvent effect was observed by us in the catalysis of the Sonogashira
reaction by silver–polycarbene complexes.15 In that case, switching
from DMF to DMSO as solvent led to a complete reversal of the
reaction selectivity from the cross-coupling product to the alkyne
homocoupling product.
13
14
15
70
nd
nd
9
86
15
50
nd
71
Reaction conditions: see Experimental section; a yields determined by 1H
We then investigated the scope of the synthetic procedure
with respect to both the aryl halide and the alkyne. Interest-
ingly, the reactivity of complex 3 with the more electron-rich
aryl iodides dropped considerably in both DMF and DMSO
(Table 3, entries 4–7), whereas the catalytic performance of
complex 1 was still good, leading to a quantitative conversion in
NMR spectroscopy; b literature data, see ref. 6; c 3 mol% Cu; d 10 mol%
Cu.
the case of 4-iodotoluene and to a 54% yield in the case of
4-iodoanisole.
7226 | Dalton Trans., 2009, 7223–7229
This journal is
The Royal Society of Chemistry 2009
©

Table 3 Sonogashira reactions with different copper(I) NHC complexes
reagents, as well as of the Sonogashira reaction with aryl iodides.
Two novel routes for the preparation of these complexes have been
described, which obtain the complexes in good yields and purity
even in the presence of C–H acidic substituents on the ligand.
Finally, the structure of one of these complexes has been elucidated
and found to exhibit some peculiar features (e.g. chirality) with
interesting implications for the development of a new generation
of triscarbene complexes with tailored ligand structure and for
novel applications.
Base
Yield (%)a
Entry Aryl halide
1
Alkyne
Solvent
1
3
TBAA
DMF
95
nd
42
2
3
Cs2CO3 >99
DMF
Experimental
All manipulations were carried out using standard Schlenk
techniques under an atmosphere of dry argon or dinitrogen.
The reagents were purchased by Aldrich or Merck as high-
purity products and generally used as received. All solvents
were dried by standard procedures and distilled under dinitrogen
immediately prior to use. Complexes [Cu(NCMe)4](PF6)20 and
[Ag3{HB(BnIm)3}2](Br) 215 were prepared according to literature
procedures. NMR spectra were recorded on a Bruker Avance
Cs2CO3
DMSO
90 (5) 97 (1)
4
5
6
7
8
Cs2CO3 >99
DMF
9
0
Cs2CO3 nd
DMSO
1
300 MHz (300.1 MHz for H and 75.5 MHz for 13C); chemical
shifts (d) are reported in units of ppm relative to the residual sol-
vent signals. 11B NMR has been referenced to NaBH4. IR spectra
were run on a Perkin-Elmer FT-IR Spectrum 100. Electrospray
mass spectra (ESI-MS) were obtained in positive- or negative-
ion mode on a Series 1100 MSD detector HP spectrometer. The
crystal structure was determined on a Bruker-AXSX8 kappa
diffractometer.
Cs2CO3
DMF
54
93
10
8
Cs2CO3
DMSO
4
Cs2CO3
DMF
nd
Synthesis of hydrotris(3-methyl-imidazolium-1-yl)borate
bis(triflate)
9
10
11
Cs2CO3
DMF
0
41
37
nd
nd
nd
MeOTf (2.7 cm3, 23.7 mmol) was added at room temperature
to a suspension of potassium hydrotris(imidazolyl)borate (2 g,
7.9 mmol) in 50 cm3 of CH2Cl2. The reaction mixture was stirred
for 14 h. The solvent was then decanted and the white residue
washed with THF (3 ¥ 20 cm3) and diethyl ether (3 ¥ 50 cm3) and
dried under vacuum (76% yield). dB (100 MHz; CD3CN; NaBH4)
38.3 (d, JB-H = 124 Hz); dH (300 MHz; CD3CN; Me4Si) 3.81 (s,
Cs2CO3
DMF
Cs2CO3
DMF
=
9H, CH3), 7.22 and 7.38 (s, 3H each, CH), 8.29 (s, 3H, NCH); dC
(75 MHz; CD3CN; Me4Si) 36.3 (CH3), 124.2, 125.5 CH), 140.0
=
Reaction conditions: see Experimental section; a Yields determined by 1H
NMR spectroscopy.
(NCH). ESI-MS (positive ions, CH3OH): m/z 129 ([M]2+).
Synthesis of complex [Cu3{HB(MeIm)3}2](PF6) 1-PF6
The reactivity of complex 1 towards aryl bromides and chlorides
was low, but this appears at present to be a common feature
of all copper-based catalytic systems for this reaction. Finally,
a preliminary evaluation of the reactivity of complex 1 in the
reaction with other alkynes was performed. Moderate yields were
obtained upon reaction of 4-iodoacetophenone with both an
electron-rich substrate such as 1-octyne and an electron-poor
one such as ethyl propiolate. Given the lower reactivity of these
alkynes in the Sonogashira reaction compared to phenylacetylene,
these initial results represent a good starting point for further
optimisation.
n-BuLi (1.6 M, 1 cm3, 1.62 mmol) was added to a cooled
(-78 ◦C) suspension of the hydrotris(3-methyl-imidazolium-1-
yl)borate bis(trifluromethanesulfonate) (0.3 g, 0.54 mmol) in 4 cm3
of Et2O. The mixture was allow to warm to 0 ◦C and was further
stirred at this temperature for 3 h and then for a further 3 h at
room temperature. The solvent was removed under vacuum and
the triscarbene formed was used without further purification (the
1H-NMR spectrum in CD3CN of the crude reaction mixture shows
signals identical to those published by Fehlhammer,9 indicating
quantitative formation of the triscarbene). 0.3 g (0.80 mmol)
of [Cu(NCMe)4](PF6) were mixed with the freshly prepared
◦
triscarbene, cooled at -10 C and 3 cm3 of MeCN were slowly
Conclusions
added. The reaction mixture was warmed to room temperature
and stirred for 3 h after which the solvent was removed under
vacuum. The obtained off-white solid was washed with Et2O
Trinuclear copper(I) complexes with triscarbene ligands are effi-
cient catalysts of Ullmann-type reaction with activated aryl halide
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7223–7229 | 7227
©

(2 ¥ 20 cm3) and cold THF (2 ¥ 3 cm3). Extraction with CH2Cl2
(3 ¥ 20 cm3) yielded the complex [Cu3{HB(MeIm)3}2](PF6) in
41% yield. Crystals can be obtained by slow diffusion of diethyl
ether in an acetonitrile solution of [Cu3{HB(MeIm)3}2](PF6). dB
(100 MHz; CD3CN; NaBH4) 41.2 (d, JB-H = 115 Hz); dH (300 MHz;
CD3CN; Me4Si) 3.40 (s, 18H, CH3), 7.04 and 7.13 (s, 6H each,
identified by comparison with characterisation data found in the
literature.6f
Acknowledgements
This work was partially supported by MIUR (PRIN 2006038447
and PRIN 20078EWK9B), by Consolider-Ingenio 2010
(No. CSD2007-00006) (FEDER support) and by the Junta de
Andalucia (Project No. FQM-3151).
=
CH); dC (300 MHz; CD3CN; Me4Si) 38.3 (CH3), 121.9 and
=
127.1 ( CH), 178.4 (NCH). Anal. calcd. for C24H32B2Cu3F6N12P:
C, 34.1; H, 3.8; N, 19.9%. Found: C, 33.7; H, 3.6, N, 19.5%.
Synthesis of complex [Cu3{HB(BnIm)3}2](Br) 3
Notes and references
A solution of CuBr(SMe2) (0.145 g in 15 cm3 of anhydrous
acetonitrile) was added to a solution of [Ag3{HB(BnIm)3}2](Br) 2
(0.5 g in 15 cm3 of anhydrous acetonitrile). The reaction mixture
was stirred at room temperature for 3 h, whereby a light-grey solid
formed in suspension. The suspension was filtered and the filtrate
was evaporated to dryness to yield a white solid, which was treated
with methanol (2 cm3) and ether (5 cm3), filtered and dried. Yield
30%. dH (300 MHz; (CD3)2SO; Me4Si) 7.41 (s, 1H, CH), 7.33
(s, 1H, CH), 7.12 (m, 1H, Ar), 6.98 (m, 2H, Ar), 6.85 (m, 2H,
Ar), 5.30–5.70 (AB system, 2H, CH2). dC (75 MHz; (CD3)2SO;
Me4Si) 176.7 (NCN), 137.6, 128.8, 127.6 and 127.0 (Ar), 128.0
and 120.9 (CH), 54.3 (CH2). nmax/cm-1: 3029w, 3062w, 3115w
1 A. de Meijere, in Metal-Catalysed Cross-Coupling Reactions, 2nd edn,
ed. F. Diederichs, Wiley-VCH, Weinheim, 2004.
2 (a) J. Hassan, M. Sevignon, C. Gozzi, E. Schulz and M. Lemaire,
Chem. Rev., 2002, 102, 1359; (b) J. Lindley, Tetrahedron, 1984, 40,
1433.
3 Recent reviews: (a) F. Monnier and M. Taillefer, Angew. Chem., Int. Ed.,
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=
=
(CH), 2431 m (BH), 1554 m (C C + C N). ESI-MS (positive
ions, CH3OH), m/z 1157 [Cu3{HB(BnIm)3}2]+. Anal. calcd. for
[Cu3{HB(BnIm)3}2](Br)·0.5AgBr: C, 54.1; H, 4.2; N, 12.6; Cu,
14.3; Ag, 4.0%. Found C, 53.0; H, 3.6; N, 12.3; Cu, 14.0; Ag,
5.4%.
6 (a) K. Okuro, M. Furuune, M. Enna, M. Miura and M. Nomura, J. Org.
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General procedure for C–N and C–O coupling reaction
The required amount of complex 3 (1 mol%, 3 mol% [Cu]) or 4
(10 mol%), the aryl halide (1.0 mmol), the base (2.0 mmol), the
nitrogen- or oxygen-containing substrate (1.5 mmol), and 3 cm3 of
solvent were placed in a Schlenk tube, previously evacuated and
filled with argon. The resulting mixture was heated under stirring
to 100 ◦C for 24 h and subsequently cooled to room temperature,
diluted with dichloromethane (10 cm3) and filtered. The filtrate
was washed with a 5% w/w aqueous KHCO3 solution (2 ¥ 10 cm3)
and water (2 ¥ 10 cm3), and finally dried over MgSO4. The solvent
was removed under vacuum to yield the crude product, which
was analyzed by NMR to determine the yield. The products were
identified by comparison with characterisation data found in the
literature.21
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General procedure for the Sonogashira reaction
An oven-dried Schlenk tube equipped with a magnetic stirring bar
was charged with aryl halide (0.25 mmol), the base (0.3 mmol,
1.2 equiv.) and catalyst (3 mol% copper for complexes 1 and
3, 10% mol for complex 4). The tube was closed with a rubber
septum, evacuated and filled with argon. The alkyne (0.3 mmol,
1.2 equiv.) and solvent (2 cm3) were subsequently injected, and the
tube was placed in an oil bath preheated at 110 ◦C. The reaction
mixture was stirred at 110 ◦C for 24 h, after which it was cooled
to room temperature and diluted with 5 cm3 dichloromethane.
The resulting suspension was filtered and the solvent was removed
under vacuum to yield the crude product, which was analyzed
by NMR to determine conversions and yields. The products were
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7228 | Dalton Trans., 2009, 7223–7229
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The Royal Society of Chemistry 2009
©

16 A few scattered data on the catalytic efficiency of copper mono-
and dicarbene complexes in Ullmann-type reactions have been re-
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19 R. Ntaganda, B. Dhudshia, C. L. B. Macdonald and A. N. Thadani,
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20 G. Kubas, Inorg. Synth., 1972, 19, 90.
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This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7223–7229 | 7229
©