Silver(I) and copper(I) complexes with bis-NHC ligands: Dinuclear complexes, cubanes and coordination polymers

Article abstract of DOI:10.1016/j.jorganchem.2015.01.025

Silver(I) and copper(I) complexes containing neutral bis(N-heterocyclic carbene) (NHC) ligands and coordinated or non-coordinated chloride, bromide, iodide, or tetrafluoroborate anions, were synthesised. The nature of the anions impacts deeply the structu

Full text of DOI:10.1016/j.jorganchem.2015.01.025

Journal of Organometallic Chemistry xxx (2015) 1e9
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Silver(I) and copper(I) complexes with bis-NHC ligands: Dinuclear
complexes, cubanes and coordination polymers
a
a
b
ꢀ
Valentine Charra , Pierre de Fremont , Pierre-Alain R. Breuil ,
b
a, *
ꢀ ꢁ
Helene Olivier-Bourbigou , Pierre Braunstein
a
ꢀ
Laboratoire de Chimie de Coordination, UMR 7177 CNRS, Universite de Strasbourg, Institut Le Bel 4, Rue Blaise Pascal, CS90032,
67081 Strasbourg Cedex, France
b IFP Energies nouvelles, Rond-Point de l'Echangeur de Solaize, 69360 Solaize, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Silver(I) and copper(I) complexes containing neutral bis(N-heterocyclic carbene) (NHC) ligands and co-
ordinated or non-coordinated chloride, bromide, iodide, or tetrafluoroborate anions, were synthesised.
The nature of the anions impacts deeply the structural features of the complexes in the solid-state and
neutral cubane-, neutral coordination polymer-, or dicationic bridged-type architectures have been
characterised. The structures of (1,3-bis(30-butylimidazol-20-ylidene)benzene)disilver(I) dichloride (2a),
Received 24 December 2014
Received in revised form
24 January 2015
Accepted 27 January 2015
Available online xxx
bis(m k
-1,3-bis(30-butylimidazol-20-ylidene)benzene- -C)tetra-m3-bromotetrasilver(I) (2b), bis(1,3-bis(30-
butylimidazol-20-ylidene)benzene)disilver(I) tetrafluoroborate (2d) in 2d$CH2Cl2, (1,3-bis(30-butylimi-
dazol-20-ylidene)benzene)dicopper(I) dichloride (3a) and (1,3-bis(30-butylimidazol-20-ylidene)benzene)
dicopper(I) dibromide (3b) were established by X-ray diffraction.
Keywords:
NHC ligands
Copper
© 2015 Elsevier B.V. All rights reserved.
Silver
Cubanes
Coordination polymers
Transmetalation
Introduction
cycloaddition of CO2 to terminal epoxides [16] and CeN coupling
reactions [17]. During pharmacological studies, they proved to
Since the first stable free N-heterocyclic carbene (NHC) was
isolated by Arduengo in 1991 [1], this class of ligands has found
numerous applications in organometallic chemistry in particular
for the preparation of new metal-based catalysts [2e9]. The first
NHC silver(I) complex was prepared by Arduengo et al. by reaction
between a free carbene and silver(I) triflate [10]. Today, the reaction
of imidazol(in)ium salts with a variety of silver(I) precursors such as
Ag2O [11], Ag(OAc) [12,13], Ag2CO3 [14] or AgCl [15], with K2CO3 or
Na2CO3 as external base, allows for the formation of Ag(I)eNHC
complexes in high yields. Ag(I)eNHC complexes are stable towards
air and moisture. The reaction of Ag2O with halide imidazol(in)ium
salts, first described in 1998 by Lin, is particularly efficient to syn-
thesise halide Ag(I)eNHC complexes under mild conditions,
without having to handle free NHCs [11]. The second product
formed following Lin's protocol being water, non-distilled solvents
can be employed, which renders this approach very convenient and
popular [11]. Ag(I)eNHC complexes are potent catalysts for e.g. the
release in vivo slowly and steadily free silver cations acting as
tumour cell killers or suppressants of infections [18e21]. Ag(I)e
NHCs are mostly employed as transmetalating agents to access late
transition metal NHC complexes, without the need to handle un-
wieldy free carbenes. They are indeed known to transmetalate
efficiently their NHC ligand(s) to Cu [22], Ni [23,24] Pd [23,25], Pt
[25] and Au [26,27] precursors. The coordination geometry around
the Ag(I) centre tends to be linear. When the associated anion (Xꢀ)
is a halide, the formation of polynuclear complexes or clusters with
XeAgeX bridge(s) can lead to a broad structural diversity in the
solid-state. In Ag(I)eNHC clusters complexes, d10ed10 interactions
are often encountered [28,29], while the coordination geometry
around the Ag(I) cations may deviate from linear to trigonal or even
tetrahedral. Tetranuclear Ag(I) complexes do not always form
cubanes [30,31] but can lead to planar structures [32,33].
Copper is the cheapest coinage metal, and despite the spectac-
ular recent achievements in organogold chemistry [34e37], the
development of organocopper chemistry appears most desirable
from an economic point of view. The first reported Cu(I)eNHC
complex was also prepared by Arduengo, by reaction of a free
* Corresponding author. Tel.: þ33 368851308.
E-mail address: braunstein@unistra.fr (P. Braunstein).
http://dx.doi.org/10.1016/j.jorganchem.2015.01.025
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2
V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
carbene with copper(I) triflate [10]. Owing to the strong
s
-donor
(68%), respectively. The different reaction conditions were adjusted
according to the type of haloalkanes [54] (Scheme 1). The formation
of 1a required a temperature around 130 ꢁC, in refluxing chloro-
benzene. Lowering the temperature to 100 ꢁC resulted in poor
conversion (5%), even after 3 days. By contrast, the syntheses of 1b,c
were successful in refluxing THF but long reaction times (at least
72 h for 1b, 48 h for 1c) were still required to avoid the formation of
mono-alkylated (intermediate) products. The reported synthesis of
1c (77%), in 8 h, at 150 ꢁC, in toluene, in a sealed tube [55] was not
retained in this work due to its lack of practicality. The 1H NMR
spectra of the salts 1aec in CD2Cl2 display the characteristic reso-
nance of the NCHN proton between 11.2 and 11.7 ppm [54,55].
The salt 1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium)
tetrafluoroborate (ImidBuBF4, 1d) was first obtained in low yield
(15%) by anion metathesis using 1b and tetrafluoroboric acid in
distilled water. A second attempt, with sodium tetrafluoroborate in
acetone, afforded 1d as an off-white powder in excellent yield
(98%). The successful anion metathesis reaction was confirmed by
1H NMR, where the significant shift from 11.56 to 9.69 ppm of the
imidazolium NCHN signal of 1b and 1d, is due to the nature of the
associated anion.
properties of NHCs, the resulting complexes are often robust
against air and moisture. Several methods are known to access
Cu(I)eNHC complexes, such as the use of Ag(I)eNHCs as trans-
metalating reagents, the reaction of free carbenes with Cu(I) ha-
lides, or of imidazolium salts with Cu(I) oxide [5,38]. Recently, Cu(I)
bis- or multidentate-NHC complexes have attracted much attention
and shown interesting redox behaviour [39], luminescence prop-
erties [40,41], ability to transmetalate their NHC ligand(s) to Ru
[42], Rh [43], Pd [44,45], Ag [46], and Ni [47] precursors, and cat-
alytic properties (Sonogashira reaction [48], nitrene and carbene
transfer reactions [49]). Moreover, the nature of the metal-carbene
bond in Cu(I)eNHC complexes has been the subject of theoretical
studies [50,51] while copper belongs to the very few metals able to
form clusters with bridging imidazolinylidenes [47]. The coordi-
nation geometry around the Cu(I) centre tends to be linear but in
the presence of bidentate donor ligands and halide ion(s), “T-sha-
ped” trigonal planar or tetrahedral coordination geometries readily
arise [33,52]. By contrast with the case of silver, polymeric Cu(I)e
NHC complexes are scarce.
In this paper, we report the synthesis and the characterisation of
a series of discrete and polymeric bis-NHC Ag(I) and Cu(I) com-
plexes, and discuss their various structural features in the solid-
state.
Synthesis of the silver(I) complexes
The reaction of the imidazolium salts 1a,b with 1.5 equivalents of
Ag(I) oxide was carried out and monitored by 1H and 13C{1H} NMR
spectroscopy. The disappearance of thecharacteristic azolium proton
signals of 1a,b, and the appearance of typical downfield carbon sig-
nals for Ag(I)-bound carbenes at 179.2 ppm and 182.6 ppm,
confirmed the formation of the Ag(I)eNHC complexes 2a and 2b,
which were isolated in yields of 61% and 65%, respectively. The sig-
nals of the butyl chains remain unchanged, in both 1H and 13C{1H}
NMR spectra, when going from the imidazolium salts 1a,b to the
Ag(I) complexes 2a,b. As expected, the 1H NMR signals of the CHi-
midazole and CHaryl protons of 2b are shifted compared to the imida-
zolium precursor. Elemental analyses confirmed the clean formation
of [L þ 2Ag þ 2X]n - type products. However, they did not allow to
discriminate between neutral bridge- [XeAgeNHC∩NHCeAgX],
cationic chelate- [(∩(NHCeAgeNHC)þ∩)2][AgX2ꢀ]2, or even neutral
cubane- [∩(X∩Ag-NHC∩NHC-Ag∩X)2∩] type of complexes. The ESI
mass spectra of 2a,b display respectively the following signals for m/z
(L ¼ ligand): [L þ 2Ag þ Cl]þ ¼ 572.99, [L þ Ag þ Cl þ H]þ ¼ 467.10,
Results and discussion
Synthesis of the imidazolium salts
The imidazolium salts 1,10-(1,3-phenylene)bis(3-butyl-1H-imi-
dazol-3-ium) chloride (ImidBuCl, 1a), 1,10-(1,3-phenylene)bis(3-
butyl-1H-imidazol-3-ium) bromide (ImidBuBr, 1b) and 1,10-(1,3-
phenylene)bis(3-butyl-1H-imidazol-3-ium) iodide (ImidBuI, 1c)
were prepared in two steps: i) synthesis of 1,3-bis(imidazolyl)
benzene via Cu(II)-catalysed aryl amination [53], ii) N,N-quaterni-
sations with alkyl halides (Scheme 1). For the first step, the litera-
ture work-up was modified to avoid purification by flash
chromatography on silica: a simple filtration of a dichloromethane
solution through Celite®, followed by precipitation with pentane
was sufficient.
During the second step of the synthesis, the reaction of
2 equivalents of 1-chlorobutane, 1-bromobutane or 1-iodobutane
with 1,3-bis(imidazolyl)benzene yielded 1a (65%), 1b (63%), or 1c
[L
þ
H]þ
¼
323.22, and [2L
þ
4Ag
þ
3Br]þ
¼
1314.18,
Scheme 1. Synthesis of the imidazolium salts 1aed.
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V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
3
[2L þ 3Ag þ 3Br þ H]þ ¼ 1208.88, [2L þ 3Ag þ 2Br]þ ¼ 1126.96,
[2L
þ
2Ag
þ
Br]þ
¼
939.15, [L
þ
2Ag
þ
Br]þ
¼
616.94,
[L þ Ag þ Br þ H]þ ¼ 511.06, [2L þ 2Ag]2þ ¼ 430.12. They hint at the
likely formation of neutral dinuclear [L þ 2Ag þ 2X] or neutral tet-
ranuclear [2L þ 4Ag þ 4X] complexes even though molecular frag-
mentation may have occurred during the analyses. To remove any
doubt concerning the structures of these Ag(I) NHC halide com-
plexes, a single crystal X-ray diffraction analysis of their colourless
crystals, grown by slow evaporation of solutions of a mixture of
dichloromethane and octane, was undertaken.
The complex
m
-1,3-bis((30-butylimidazol-20-ylidene)benzene)
dichlorodisilver(I) (ImidBuAg2Cl2, 2a) is an organometallic coordi-
nation polymer, which crystallizes in the monoclinic system and
the P21/c space group (Fig. 1). Dinuclear monomeric units [Imid-
BuAg2Cl2] are held together by formation of a bridge involving the
chloride ligand Cl1. There is one carbene donor per metal and
halogen, in agreement with a [L þ 2Ag þ 2X]n¼∞-type complex. The
Ag1eC1 and Ag2eC14 bond distances are equal to 2.081(6) and
2.102(6) Å, and the Ag1eCl1, Ag2eCl2 and Ag2eCl1 distances to
2.334(2), 2.380(2) and 2.888(2) Å, respectively. These values are
similar to those found in other Ag(I) NHC complexes [56,57]. The
silver cation Ag1 has a slightly distorted linear coordination ge-
ometry with a C1eAg1eCl1 angle of 169.3(2)ꢁ, whereas the other
silver cation Ag2 is in a distorted trigonal planar coordination
environment with Cl2eAg2eCl1, C14eAg2eCl1 and C14eAg2eCl2
bond angles of 97.97(5), 108.2(2) and 152.6(2)ꢁ, respectively. Each
imidazole ring from the same ligand is oriented head to tail with a
torsion angle of 173.3ꢁ.
Fig. 2. Ball and stick representation of the cubane-type structure of [ImidBu2Ag4Br4]
(2b). Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (ꢁ): Ag1eC1 2.143(4), Ag2eC14 2.140(4), Ag3eC2 12.161(4), Ag4eC34 2.148(5),
Ag1eBr1 2.8567(6), Ag1eBr2 2.7999(6), Ag1eBr3 2.7048(6), Ag2eBr1 2.8410(6),
Ag2eBr2 2.8564(6), Ag2eBr4 2.6850(5), Ag3eBr1 2.8050(6), Ag3eBr3 2.8071(6),
Ag3eBr4 2.8456(6), Ag4eBr2 2.7869(6), Ag4eBr3 2.8493(6), Ag4eBr4 2.7593(6),
Ag1/Ag2 3.1375(5), Ag3/Ag4 3.1586(5); C1eAg1eBr1 112.9(1), C1eAg1eBr2
113.2(1), C1eAg1eBr3 127.7(1), C14eAg2eBr1 116.8(1), C14eAg2eBr2 111.1(1),
C14eAg2eBr4 134.1(1), C21eAg3eBr1 136.2(1), C21eAg3eBr3 118.7(1), C21eAg3eBr4
112.9(1), C34eAg4eBr2 126.6(1), C34eAg4eBr3 106.3(1), C34eAg4eBr4 122.6(1).
The complex bis((
zene)- -C)tetra-m3-bromotetrasilver(I) (ImidBu2Ag4Br4, 2b) crys-
m
-1,3-bis(30-butylimidazol-20-ylidene)ben-
k
NHC or phosphine Ag(I) complexes [61e70]. The AgeC and AgeBr
bond lengths fall in the range 2.140(4)e2.161(4) Å and 2.6850(5)e
2.8567(6) Å, respectively. These values are in agreement with those
found in other NHC silver halide cubane complexes [71].
tallizes in the monoclinic system with the P21/c space group and
has a cubane-type structure (Fig. 2). There is one carbene func-
tionality per metal and halogen, in agreement with
a
[2L þ 4Ag þ 4X]n¼1 -type complex. Two of the AgeAg distances
(Ag1eAg2 ¼ 3.137(1) Å and Ag3eAg4 ¼ 3.159(1) Å) are shorter than
the sum of the van der Waals radii (3.44 Å) and may be diagnostic of
d10ed10 “argentophilic” interactions [28,29,58,59], whereas the
In order to explore further the role played by the halide in Ag(I)
chemistry, the reactivity of 2a was assessed toward anion
metathesis with AgBr or LiBr, in dry acetone. 1H NMR spectroscopy
evidenced the quantitative conversion of 2a into 2b within 16 h.
Complex 2b was isolated in 98% yield, and its purity confirmed by
elemental analysis. The depolymerisation of 2a to rebuild a cubane-
structure is a clear illustration of the affinity of group 11 metals for
soft halide ligands (I > Br > Cl), as well as of the propensity of soft
halides to form higher order bridges in polynuclear complexes with
late transition metals. Interestingly, in wet acetone no conversion
was monitored after 24 h.
other
two
AgeAg
separations
are
much
longer
(Ag2eAg3 ¼ 3.945(1) Å, Ag1eAg4 ¼ 3.547(1) Å). The ratio of 0.799
between the average AgeAg distances (3.44 Å) and the average
BreBr distances (3.31 Å) is intermediate between those for an ideal
cubane (1.00) and stella quadrangular (0.667) geometries [60].
Hence, the structure of ImidBu2Ag4Br4 (2b) forms a distorted
cubane, a geometry well documented in the literature for other
During the course of our work, Hollis et al. reported the Ag(I)e
NHC complex bis((
-C)tetra-m3-iodotetrasilver(I) (ImidBu2Ag4I4, 2c), obtained in 67%
m
-1,3-bis(30-butylimidazol-20-ylidene)benzene)-
k
yield as a white powder by reaction of the pro-ligand ImidBuI (1c)
with Ag(I) oxide [71]. Similar to 2b, this complex has a distorted
cubane structure with a [Ag4I4] core. We also prepared and char-
acterised 2c using Hollis's approach and a slightly modified puri-
fication step. Hollis reported the filtration of a CH2Cl2 solution of 2c
and its direct precipitation/washing with diethyl ether, whereas
prior to precipitation, we added an additional step, without
lowering the yield (75%), by extracting with water most of the
impurities present, including possible traces of unreacted 1c.
The replacement of the halogen bound to silver by the non-
coordinating anion BFꢀ4 should have an impact on the complex
structure owing to the loss of the silver-halide bonds. The reaction
of the imidazolium salt 1d with Ag(I) oxide, following the protocols
described for 2aec, failed to give complex 2d. This is probably due
to the insufficient difference of relative acid-base strengths be-
tween 1d and Ag2O (the pKa difference between ([NHCeHþ]
[BFꢀ4 ]/[NHC]) and ([Ag2OHþ]/[Ag2O]) which is the driving force to
initiate the reaction when Ag2O is used as the silver(I) source) [72].
Fig. 1. Ball and stick representation of the molecular structure of two dinuclear,
monomeric units [ImidBuAg2Cl2] forming the polymer chains of 2a in the solid-state.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(ꢁ): Ag1eC1 2.081(6), Ag1eCl1 2.334(2), Ag2eC14 2.102(6), Ag2eCl2 2.380(2),
Ag2eCl1 2.888(2); C1eAg1eCl1 169.4(2), C14eAg2eCl2 152.6(2), C14eAg2eCl1
108.2(2), Cl1eAg2eCl2 97.97(5).
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4
V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
We thus attempted the reaction of 2b or 2c with 2.0 equivalents of
AgBF4 in dichloromethane, at room temperature for 18 h. Forma-
tion of AgX was observed and complete conversion to complex 2d
was supported by the shift of the aromatic signals in the 1H NMR
spectra and of the characteristic signal of the carbenic carbons from
182.7 ppm (2b) or 184.8 ppm (2c) to 179.6 ppm. Elemental analysis
data supported the clean formation of a [2L þ 2Ag þ 2(BF4)]n-type
complex. Consistently, the ESI mass spectrum contained a major
signal for m/z (L ¼ ligand): [2L þ 2Ag]2þ ¼ 430.12. Colourless single
crystals suitable for X-ray diffraction analysis were obtained by
stratification with pentane of a dichloromethane solution of 2d. The
exact nature of 3a,b was established by X-ray diffraction (see
below). Converting 1aec to 3aec does not induce any visible
change for the butyl chain signals in the 1H and 13C{1H} NMR
spectra. The aryl signals are slightly affected, with variations
smaller than 1.0 and 4.5 ppm in the 1H NMR or 13C{1H} NMR
spectra, respectively. Elemental analyses of 3a,b confirmed the
clean formation of [L þ 2Cu þ 2X]n -type complexes. Similarly to the
Ag(I) chemistry, these data are not sufficient to provide an insight
into the structural features of the complexes (e.g. neutral bridge-,
cationic chelate-, neutral cubane-, coordination polymer-types).
For 3c, despite numerous purification steps, no satisfactory ana-
lyses were obtained. The ESI mass spectra of complexes 3aec
display respectively the following signals for m/z (L ¼ ligand):
complex bis-(m
-1,3-bis(30-butylimidazol-20-ylidene)benzene)dis-
ilver(I) ditetrafluoroborate ({[ImidBuAg]BF4}2, 2d) has a centro-
symmetric dinuclear structure with Ag(I) ions bridged by two bis-
NHC ligands binding in a C,C0 mode. The ratio NHC/Ag has thus
changed from 1:1 in 2a,b to 2:1 in 2d. The latter crystallizes with
one molecule of dichloromethane, in the triclinic system and the P-
1 space group (Fig. 3). The structure of 2d is typical for bis-NHC
dinuclear complexes of the type {[(NHC)Ag(NHC)þ]2, 2[Xꢀ]}
where Xꢀ represents a non-coordinating anion [73e77]. There are
two carbene donors and one tetrafluoroborate anion per silver, in
agreement with a [2L þ 2Ag þ 2(BF4)]n¼1 -type complex. The
Ag1eC1 and Ag1eC14 bond distances are equal to 2.083(3) and
2.085(3) Å, respectively. The Ag(I) cations adopt a quasi-linear co-
ordination geometry in 2d (C1eAgeC14 angle of 174.28(1)ꢁ). Bond
distances and angles are similar to those reported for other cationic
bis-(NHC) Ag(I) complexes [27,78]. The planes defined by the NHC
rings bound to silver form an angle of 45.6(1)ꢁ. The planes of the
NHC rings belonging to the same ligand form an angle of ꢀ138.7(3)
and 133.5(3)ꢁ with the aryl ring. The planes of the bridging-
phenylene spacers are parallel to each other and mutually distant
[L
þ
Cu
þ
Cl
þ
H]þ
¼
421.12, [L
þ
H]þ
¼
323.22;
[L þ 2Cu þ 2Br þ H]þ ¼ 610.92, [L þ 2Cu þ Br]þ ¼ 528.99,
[L
þ
Cu
þ
Br
þ
H]þ
¼
467.07, [L
þ
H]þ
¼
323.22, and
[2L þ 5Cu þ 4I]þ ¼ 1468.70, [2L þ 4Cu þ 4I þ H]þ ¼ 1406.77,
[2L þ 4Cu þ 3I]þ ¼ 1278.86, [2L þ 3Cu þ 3I þ H]þ ¼ 1216.94,
[2L þ 3Cu þ 2I]þ ¼ 1089.03, [2L þ 2Cu þ I]þ ¼ 897.19,
[L þ 2Cu þ I þ H]þ ¼ 702.89, [L þ 2Cu þ I]þ ¼ 574.98. Despite
extensive molecular fragmentations during the analyses, these data
strongly suggest the formation of neutral dinuclear [L þ 2Cu þ 2X]
complexes for 3a and 3b, and of a neutral tetranuclear complex
[2L þ 4Cu þ 4I] for 3c. To firmly establish their structures, X-ray
diffraction analyses of 3aec were desirable. Colourless crystals of
3a and 3b were obtained by slow evaporation of solutions of a
mixture of THF and octane. Unfortunately, attempts to crystallize 3c
from various couples of solvents (THF-pentane, THF-Et2O, THF-
octane, CH2Cl2-pentane and CH2Cl2-octane), at different tempera-
tures (rt, 4 ꢁC and ꢀ20 ꢁC) resulted ultimately in amorphous solids.
The complex
m
-1,3-bis((30-butylimidazol-20-ylidene)benzene)
from 4.4 Å, which rules out any
p
e
p
stacking interaction (usually
dichlorodicopper(I) (ImidBuCu2Cl2, 3a) is an organometallic coor-
dination polymer, which crystallizes in the monoclinic system and
the P21/c space group (Fig. 4). There is one carbene donor group per
copper and chloride, in agreement with a [2L þ 2Cu þ 2X]n¼∞ -type
complex. The neutral dinuclear, monomeric units [ImidBuCu2Cl2]
are held together by formation of a chloride bridge to give a coor-
dination polymer. The copper centre Cu1 exhibits a slightly dis-
torted linear coordination geometry, with a C1eCu1eCl1 angle of
169.5(2)ꢁ whereas Cu2 is in a quasi-trigonal planar environment
with C14eCu1eCl1, C14eCu2eCl2 and Cl1eCu1eCl2 angles of
142.2(2)ꢁ, 116.4(2)ꢁ and 101.05(4)ꢁ, respectively. The bridging Cl1
ligand is bound to Cu2 via a long-range interaction (2.607(1) Å) and
to Cu1 via a shorter (covalent) bond (2.115(1) Å). The imidazole
rings from the same ligand are oriented in almost opposite di-
rections, which make the ligand an excellent bridge for coordina-
tion polymers, and the angle between their planes is equal to
171.5ꢁ.
observed between 3.3 and 3.9 Å) in the solid-state [79]. There is no
interaction between the Ag(I) centres and the BFꢀ4 anions. The
complexes 2aed are stable towards moisture in ambient day light
(Scheme 2).
Synthesis of the copper(I) complexes
The reactions of the imidazolium salts 1aec with 2 equivalents
of Cu[N(SiMe3)2] [80] were carried and monitored by 1H and 13C
{1H} NMR spectroscopy. The disappearance of the characteristic
azolium proton signals of 1aec, and the appearance of typical
downfield carbon signals for Cu(I)-bound carbenes at 176.6, 177.8,
and 184.2 ppm, confirmed the formation of three complexes 3aec
which were isolated in 98%, 98% and 86% yield, respectively. The
The complex
m
-1,3-bis((30-butylimidazol-20-ylidene)benzene)
dibromodicopper(I) (ImidBuCu2Br2, 3b) has a structure very similar
to that of 3a, with bromides replacing chlorides. This organome-
tallic coordination polymer crystallizes in the monoclinic system
and the P21/c space group (Fig. 5). There is one carbene donor per
copper and bromide with the bis-carbene ligand acting as a bridge
between two Cu centres, in agreement with a [2L þ 2Cu þ 2X]n¼∞
-type complex. Two neutral dinuclear units [ImidBuCu2Br2]
constitute a monomeric entity and are held together by a bridging
bromide. The copper centre Cu2 exhibits a slightly distorted linear
coordination geometry, with a C14eCu2eBr2 angle equal to
171.3(2)ꢁ, whereas Cu1 is in a quasi-trigonal planar environment
with C1eCu1eBr1, C1eCu1eBr2 and Br2eCu1eBr1 angles of
147.3(2)ꢁ, 113.3(2)ꢁ and 98.79(5)ꢁ, respectively. The bridging bro-
mide Br2 is bound to Cu1 via a long-range interaction (2.647(1) Å)
and to Cu2 via a shorter (covalent) bond (2.245 (1) Å). Like in 3a, the
imidazole rings from the same ligand are oriented in almost
Fig. 3. Ball and stick representation of the structure of [{(ImidBu)Ag}BF4]2 (2d) in
2d$CH2Cl2. Hydrogen atoms and a molecule of dichloromethane have been omitted for
clarity. Selected bond lengths (Å) and angle (ꢁ): Ag1eC1 2.083(3), Ag1eC14 2.085(3);
C1eAg1eC14 174.3(1).
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V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
5
Scheme 2. Summary of the diverse solid-state structures encountered in the Ag(I) complexes 2aed and their transformations.
opposite directions and the angle between their planes is equal to
168.0ꢁ.
centre is connected to a carbene and a halide to form a neutral
complex, is different: these units are held together by van der
The CueC bond distances in the complexes 3a,b are comparable
to those reported for other neutral Cu(I)eNHC complexes
[49,81e84]. The bis-NHC moiety acts as a bridging bidentate ligand
which favours the formation of 1D-polymers in the presence of
suitable anionic ligands. Furthermore, long-range halogen-copper
interactions also play a key role in the formation of coordination
polymers in preference to cubanes. To the best of our knowledge,
only three Cu(I)eNHC organometallic coordination polymers have
been characterized in the solid-state [81,83,84]. Two of them
feature pyridine- or oxazoline-functionalized NHC ligands (acting
as bidentate donors) and are of the [eN∩NHCe(CuBr)e]n type, in
which each copper is ligated by two carbenes belonging to different
ligands, and a bromide [83,84]. The third example contains bis-NHC
Waals interactions to give a (eNHCe(CuBr)e(m-Br)eCueNHCe)n-
type polymer (Scheme 3).
Unfortunately, we could not obtain single crystals for 3c suit-
able for X-ray diffraction and this prevented its unambiguous
characterisation. However, in this case the formation of a neutral
[∩(I∩Cu-NHC∩NHC-Cu∩I)2∩] cubane-type structure is strongly
supported by NMR and MS-ESI data. Furthermore, a survey of the
CSD database clearly points out that the [Cu4I8] cubane core is
often encountered (159 hits) in association with various ligands
including phosphines, arsines, amines, pyridines, acetonitrile, wa-
ter, thiols … [85e89].
Finally for the sake of comparison, three other well-known
synthetic pathways to access Cu(I)eNHC complexes were
assessed. First, the imidazolium salt 1c was reacted with 1.3 eq. of
ligands and is of the (eNHCeCue(m-Br)2eCueNHCe)n type in
which each copper is connected by two bridging bromides [81]. In
3a,b, the connection between the monomers in which the copper(I)
Fig. 4. Ball and stick representation of two dinuclear, monomeric units [ImidBuCu2Cl2]
which are held together by Cl1 and form the polymer chain of 3a in the solid-state.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(ꢁ): Cu1eC1 1.882(5), Cu1eCl1 2.115(1), Cu2eC14 1.901(5), Cu2eCl2 2.183(1), Cu2eCl1
2.607(1); C1eCu1eCl1 171.3(1), C14eCu2eCl2 147.35(15), C14eCu2eCl1 113.3(1),
Cl1eCu2eCl2 98.96(5), Cu1eCl1eCu2 89.79(5).
Fig. 5. Ball and stick representation of two dinuclear, monomeric units [ImidBuCu2Br2]
which are held together by Br2 and form the polymer chain of 3b in the solid-state.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(ꢁ): Cu1eC1 1.904(6), Cu1eBr1 2.330(1), Cu1eBr2 2.647(1), Cu2eC14 1.893(7),
Cu2eBr2 2.245(1); C1eCu1eBr1 142.2(2), C1eCu1eBr2 116.4(2), Br1eCu1eBr2
101.05(4), C14eCu2eBr2 169.5(2), Cu1eBr2eCu2 87.07(4).
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6
V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
Scheme 3. Synthesis of the copper(I) complexes 3a and 3b.
Cu(I) oxide in distilled and degassed water or in toluene under
reflux [90]. After 24 h no reaction had occurred. Secondly,1c and 1.3
eq. of Cu(I) oxide were heated in THF at 110 ꢁC in a sealed tube,
under microwave irradiation. After 1 h, the starting materials were
recovered [91]. Thirdly, Ag(I)eNHC complexes being efficient at
transmetalating their carbene ligand(s) to copper(I), 2c was placed
in presence of CuI, in dichloromethane, at room temperature for
18 h [40,92]. The 1H NMR analysis of the crude mixture showed that
the transmetalation only partially occurred but increasing the
temperature to 40 ꢁC resulted in the quantitative formation of 3c.
IR and FIR spectra were recorded in the region 4000ꢀ200 cmꢀ1 on a
Nicolet 6700 FT-IR spectrometer (ATR mode, diamond crystal).
Elemental analyses were performed by the “Service de Microanal-
ꢀ
yses”, Universite de Strasbourg. Mass spectrometry analyses (ESI-
ꢀ
MS) were performed by the “Service de Spectrometrie de Masse”,
ꢀ
Universite de Strasbourg. For X-ray diffraction studies, the intensity
data were collected at 173(2) K on a Kappa CCD diffractometer 88
(graphite-monochromated Mo-Ka radiation,
l
¼ 0.71073 Å). The
structures were solved by direct methods (SHELXS-97) and refined
by full-matrix least-squares procedures (based on F2, SHELXL-97)
with anisotropic thermal parameters for all the non-hydrogen
atoms [94]. The hydrogen atoms were introduced into the
geometrically calculated positions (SHELXL-97 procedures) and
refined riding on the corresponding parent atoms.
Conclusion
A series of bis-(NHC) Ag(I) and Cu(I) complexes was obtained in
good yield. Their structures strongly depend on the nature of the
associated anions, and range from classic di-cationic (2d), to
cubane-type (2b) to coordination polymers (2a and 3a,b). The
complexes 3a,b constitute new additions to the still rare examples
of copper-NHC coordination polymers. Overall, such a structural
diversity emphasizes the need to characterise thoroughly any Ag(I)
or Cu(I) NHC-based catalytic systems prior to use, in order to
establish the true nature of the precatalysts. In this regard, studies
exploring the relative stability/activity of the aforementioned silver
and copper complexes for coupling reactions are ongoing in our
laboratories.
Synthetic procedures
Synthesis of 1,3-di(imidazol-1-yl)benzene [53]
To a solution of 1,3-dibromobenzene (25.0 mL, 210 mmol) in
DMSO (200 mL) were added 1H-imidazole (35.0 g, 510 mmol),
potassium carbonate (72.0 g, 520 mmol) and Cu(II) oxide (2.00 g,
25.2 mmol). After 48 h at 150 ꢁC, the solvent was removed by
distillation. The crude solid was dissolved in dichloromethane
(inorganic salts were insoluble) and the solution was filtered
through Celite® and concentrated. The product was precipitated
from pentane as pale yellow powder (38.3 g, 0.18 mol). Yield: 88%.
1H NMR (300 MHz, CDCl3): 7.95 (s, 2H, NCHN), 7.63 (m,1H, CHaryl),
d
Experimental
7.51 (t, J ¼ 2.0 Hz, 1H, CHaryl), 7.45 (d, J ¼ 2.1 Hz, 1H, CHaryl), 7.42 (d,
J ¼ 1.8 Hz, 1H, CHaryl), 7.39 (t, J ¼ 1.3 Hz, 2H, CHimidazole), 7.25 (s, 1H,
General information
CHimidazole). 13C{1H} NMR (75 MHz, CDCl3):
d 138.5 (NCHN), 135.4
(Caryl), 131.3 (CHimidazole), 130.8 (CHimidazole), 119.8 (CHaryl), 117.9
(CHaryl), 114.2 (CHaryl).
Only those reactions with Cu(I) reagents where carried out
under inert atmosphere using standard Schlenk techniques. The
compound Cu[N(SiMe3)2] was synthesised according to a published
procedure [93]. All reagents were used as received from commer-
cial suppliers. Solvents were purified and dried under argon by
conventional methods. Proton (1H), carbon (13C{1H}) and fluorine
Synthesis of 1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium)
chloride (1a) [95]
(
19F{1H}) nuclear magnetic resonance (NMR) spectra were recorded
1,3-di(imidazol-1-yl)benzene (4.00 g, 19.0 mmol) and n-butyl
chloride (10.2 mL, 98.1 mmol) were stirred, in refluxing chloro-
benzene, for 72 h. After evaporation under reduced pressure, the
crude solid was dissolved in dichloromethane containing few drops
of methanol. An off-white powder was obtained after precipitation
from Et2O (4.89 g, 12.3 mmol). Yield: 65%. 1H NMR (500 MHz,
on the following instruments: Brucker AVANCE I e 300 MHz
spectrometer and Brucker AVANCE I e 500 MHz spectrometer. The
chemical shifts are given in parts per million (ppm). Data are pre-
sented as following: chemical shift, multiplicity (s ¼ singlet,
d
¼
doublet,
t
¼
triplet,
q
¼
quartet, quint
¼
quintet,
sext ¼ sextuplet, sept ¼ septet, m ¼ multiplet, br ¼ broad), coupling
constants (J/Hz) and integration. Assignments were determined
either on the basis of unambiguous chemical shifts or coupling
patterns. The residual solvent proton (1H) or carbon (13C{1H})
resonance, or the BFꢀ4 anion signals (19F{1H}) were used as refer-
CD2Cl2): d
11.76 (s, 2H, NCHN), 9.27 (s, 2H, CHimidazole), 9.11 (t,
J ¼ 2.0 Hz, 1H, CHaryl), 8.27 (dd, J ¼ 8.2 Hz, 1.9 Hz, 2H, CHaryl), 7.80 (s,
2H, CHimidazole), 7.54 (t, J ¼ 8.3 Hz, 1H, CHaryl), 4.43 (t, J ¼ 7.3 Hz, 4H,
NCH2Bu), 2.04e1.92 (m, 4H, CH2Bu), 1.44e1.32 (m, 4H, CHB2u), 0.93 (t,
J ¼ 7.4 Hz, 6H, CHB3u). 13C{1H} NMR (126 MHz, CD2Cl2):
d
137.0 (Caryl),
ence values. For 1H NMR: CDCl3 ¼
d
7.26 ppm, CD2Cl2 ¼
d
5.32 ppm
77.1 ppm, CD2Cl2 ¼
ꢀ150.6 ppm.
136.4 (NCHN),132.5 (CHaryl), 123.5 (CHimidazole), 122.3 (CHaryl), 122.0
(CHimidazole), 114.7 (CHaryl), 50.6 (NCHB2u), 32.3 (CH2Bu), 19.9 (CHB2u),
13.7 (CHB3u).
and DMSO-d6 ¼
d
2.50. For 13C NMR: CDCl3 ¼
d
d
53.8 and DMSO-d6 ¼
d
39.5 ppm. For 19F NMR: BF4ꢀ
¼
d
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V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
7
Synthesis of 1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium)
bromide (1b) [95]
A procedure similar to that used for compound 1a with 1,3-
di(imidazol-1-yl)benzene (4.00 g, 19.0 mmol) and n-butyl bro-
mide (9.70 mL, 87.6 mmol), in refluxing THF, for 72 h, gave 1b, as an
off-white powder (5.78 g, 11.9 mmol). Yield: 63%. 1H NMR
J ¼ 7.3 Hz, 6H, CH3Bu). 13C{1H} NMR (126 MHz, CDCl3):
d
179.2
(Ccarbene), 141.0 (Caryl), 131.8 (CHaryl), 124.4 (CHaryl), 122.4 (CHimida-
zole), 122.3 (CHimidazole), 120.2 (CHaryl), 52.6 (NCH2Bu), 33.5 (CH2Bu),
19.9 (CHB2u), 13.8 (CH3Bu). Anal. Calc. for C20H26N4Ag2Cl2: C, 39.44; H,
4.30; N, 9.20. Found: C, 39.35; H, 4.48; N, 9.01. ESI MS (m/z)
(L ¼ Ligand): 572.99 [L þ 2Ag þ Cl]þ, 467.10 [L þ Ag þ Cl þ H]þ,
323.22 [L þ H]þ. IR: nmax(solid)/cmꢀ1: 3087w, 2984w, 2929w,
2867w, 1605m, 1560w, 1497m, 1458m, 1412m, 1369m, 1258m,
1228m, 1196, 1110m, 1002w, 948w, 871w, 732s, 692s, 511w, 434w,
409w, 294w, 259w, 236w, 218w, 162w, 154w.
(300 MHz, CD2Cl2):
d
11.56 (s, 2H, NCHN), 9.04 (t, J ¼ 2.0 Hz, 1H),
8.91 (t, J ¼ 1.8 Hz, 2H, CHimidazole), 8.24 (dd, J ¼ 8.3, 2.0 Hz, 2H), 7.72
(t, J ¼ 8.3 Hz, 1H, CHary), 7.60 (t, J ¼ 1.8 Hz, 2H, CHimidazole), 4.45 (t,
J ¼ 7.3 Hz, 4H, NCHB2u), 2.02 (quint resulting from overlapping tt,
J ¼ 7.5 Hz, 4H, CHB2u), 1.43 (sext resulting from overlapping qt),
J ¼ 7.5 Hz, 4H, CH2Bu, 1.00 (t, J ¼ 7.3 Hz, 6H, CHB3u). 13C{1H} NMR
Synthesis of bis(
tetra-m3-bromotetrasilver(I) (2b)
m k-C)
-1,3-bis(30-butylimidazol-20-ylidene)benzene-
(126 MHz, CD2Cl2):
d
137.0 (Caryl), 136.5 (NCHN), 133.0 (CHaryl),
123.4 (CHimidazole), 122.8 (CHaryl), 122.4 (CHimidazole), 115.5 (CHaryl),
51.0 (NCHB2u), 32.4 (CH2Bu), 20.1 (CH2Bu), 13.8 (CHB3u).
A procedure similar to that used for compound 2a with 1b
(1.66 g, 3.44 mmol) and Ag2O (1.19 g, 5.16 mmol) gave 2b as a white
powder (1.47 g, 1.05 mmol). Yield: 61%. Crystals suitable for X-ray
analysis were grown by slow evaporation of a solution mixture of
Synthesis of 1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium)
iodide (1c) [54,71,95]
A procedure similar to that used for compound 1a with 1,3-
di(imidazol-1-yl)benzene (4.00 g, 19.0 mmol) and n-butyl iodide
(10.0 mL, 87.9 mmol) in refluxing THF, for 48 h, gave 1c as an off-
white powder (7.48 g, 12.9 mmol). Yield: 68%. 1H NMR (300 MHz,
2b/CH2Cl2/octane. 1H NMR (300 MHz, CD2Cl2):
d 7.88 (m, 1H,
CHaryl), 7.62 (d, J ¼ 1.9 Hz, 2H, CHimidazole), 7.59 (d, J ¼ 2.0 Hz, 2H,
CHaryl), 7.45 (dd, J ¼ 8.6, 7.4 Hz, 1H, CHaryl), 7.26 (d, J ¼ 1.9 Hz, 2H,
CHimidazole), 4.22 (t, J ¼ 7.3 Hz, 4H, NCH2Bu), 1.96e1.84 (m, 4H, CHB2u),
1.42 (m, 4H, CH2Bu), 0.99 (t, J ¼ 7.3 Hz, 6H, CHB3u). 13C{1H} NMR
CD2Cl2):
d
11.25 (s, 2H, NCHN), 8.97 (t, J ¼ 2.1 Hz, 1H, CHaryl), 8.48 (t,
(126 MHz, CD2Cl2): d
182.7 (Ccarbene), 141.5 (Caryl), 131.4 (CHaryl),
J ¼ 1.9 Hz, 2H, CHimidazole), 8.14 (dd, J ¼ 8.1, 2.2 Hz, 2H, CHaryl), 7.87 (t,
J ¼ 6.3 Hz, 1H, CHaryl), 7.51 (t, J ¼ 1.9 Hz, 2H, CHimidazole), 4.46 (t,
J ¼ 7.4 Hz, 4H, NCH2Bu), 2.11e2.00 (m, 4H, CH2Bu), 1.47 (m, 4H, CH2Bu),
124.1 (CHaryl), 122.6 (Cimidazole), 122.4 (Cimidazole), 120.5 (CHaryl), 52.7
(NCHB2u), 33.9 (CH2Bu), 20.3 (CH2Bu), 14.0 (CHB3u). Anal. Calc. for
C20H26N4Ag2Br2: C, 34.42; H, 3.75; N, 8.03. Found: C, 35.02; H, 3.76;
1.02 (t, J ¼ 7.3 Hz, 6H, CHB3u). 13C{1H} NMR (75 MHz, CD2Cl2):
d
136
N, 8.41. ESI MS (m/z) (L ¼ Ligand): 1314.18 [2L þ 4Ag þ 3Br]þ,
1208.88 [2L þ 3Ag þ 3Br þ H]þ, 1126.96 [2L þ 3Ag þ 2Br]þ, 939.15
[2L þ 2Ag þ Br]þ, 616.94 [L þ 2Ag þ Br]þ, 511.06 [L þ Ag þ Br þ H]þ,
430.12 [L þ 2Ag]2þ. IR: nmax(solid)/cmꢀ1: 3088w br, 2928m br,
2867w, 1604m, 1561m, 1497m, 1460m, 1411m, 1369m, 1257m,
1227m, 1196m, 1108m, 1059m, 1001w, 948w, 872m, 729s, 692s,
507w, 435w, 303w, 280w, 247w, 150w, 118w.
0.6 (NCHN), 136.3 (Caryl), 133.3 (CHaryl), 123.5 (CHimidazole), 123.4
(CHaryl), 122.3 (CHimidazole), 116.5 (CHaryl), 51.1 (NCH2Bu), 32.4 (CH2Bu),
20.0 (CHB2u), 13.7 (CHB3u).
Synthesis of 1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium)
tetrafluoroborate (1d)
To a solution of 1,3-bis(30-butylimidazol-l-yl)benzene dibro-
mide (1b) (0.11 g, 0.23 mmol) in acetone was added an excess of
NaBF4 (0.26 g, 2.37 mmol). The mixture was stirred at room tem-
perature overnight. NaBr was removed by filtration through Celite®
and the filtrate was precipitated with pentane, yielding a clean
product (0.12 g, 0.24 mmol). Yield: 98%. 1H NMR (500 MHz, CD2Cl2):
Formation of 2b from (1,3-bis(30-butylimidazol-20-ylidene)benzene)
disilver(I) dichloride (2a)
The complex 2a (0.66 g, 1.09 mmol), LiBr (0.19 g, 2.19 mmol) and
dry acetone were combined and stirred for 18 h under inert at-
mosphere. The solvent was evaporated and the solid was dissolved
in CH2Cl2. The solution was filtered through Celite® and concen-
trated under reduced pressure. The complex 2b was isolated
(0.75 g, 0.54 mmol) upon precipitation with pentane. Yield: 98%.
d
9.69 (s, 2H, NCHN), 8.26 (t, J ¼ 2.1 Hz,1H, CHaryl), 8.09 (t, J ¼ 1.9 Hz,
2H, CHimidazole), 7.88 (dd, J ¼ 8.2, 2.0 Hz, 2H, CHaryl), 7.76 (t,
J ¼ 4.8 Hz, 1H, CHaryl), 7.57 (t, J ¼ 1.9 Hz, 2H, CHimidazole), 4.32 (t,
J ¼ 7.4 Hz, 4H, NCH2Bu), 1.98e1.91 (m, 4H, CH2Bu), 1.40 (m, 4H, CH2Bu),
0.96 (t, J ¼ 7.4 Hz, 6H, CHB3u). 13C{1H} NMR (126 MHz, CD2Cl2):
Synthesis of bis(
tetra-m3-iodotetrasilver(I) (2c) [71]
m k-C)
-1,3-bis(30-butylimidazol-20-ylidene)benzene-
d
136.4 (NCHN),135.5 (Caryl), 133.2 (CHaryl), 123.9 (CHimidazole), 123.6
(CHaryl), 122.2 (CHimidazole), 116.5 (CHaryl), 51.1 (NCH2Bu), 32.2 (CH2Bu),
A procedure similar to that used for compound 2a with 1c
(1.00 g, 1.73 mmol) and Ag2O (0.60 g, 2.59 mmol) gave 2c as a white
powder (2.05 g, 1.29 mmol). Yield: 75%. 1H NMR (300 MHz, CD2Cl2):
19.9 (CHB2u), 13.6 (CH3Bu). 19F NMR (282 MHz, CD2Cl2):
BFꢀ4 ).
d
ꢀ149.3 (s,
d
8.38 (t, J ¼ 1.8 Hz, 1H, CHaryl), 7.58e7.47 (m, 2H, CHaryl), 7.47e7.36
Synthesis of (1,3-bis(30-butylimidazol-20-ylidene)benzene)disilver(I)
dichloride (2a)
(m, 3H, CHaryl þ CHimidazole), 7.17 (d, J ¼ 1.5 Hz, 2H, CHimidazole), 4.25
(t, J ¼ 7.1 Hz, 4H, NCH2Bu), 1.83 (m, 4H, CH2Bu), 1.35 (m, 4H, CHB2u), 0.90
1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium) chloride
(1a) (0.68 g, 1.72 mmol) and Ag2O (0.60 g, 2.58 mmol), molecular
sieves (3 Å beads), and CH2Cl2 were combined, protected from light
and stirred for 18 h under argon at room temperature. The solution
was filtered through Celite®, evaporated under reduced pressure
and the solid was washed three times with distilled water. The
organic phase was dried over MgSO4 and filtered. Upon precipita-
tion with pentane, the complex was cleanly recovered (2.05 g,
1.29 mmol). Yield: 65%. Crystals suitable for X-ray analysis were
grown by slow evaporation from a solution mixture of 2a/CH2Cl2/
(t, J ¼ 7.3 Hz, 6H, CHB3u). 13C{1H} NMR (75 MHz, CD2Cl2):
d 184.8
(Ccarbene), 141.0 (Caryl), 130.4 (CHaryl), 123.2 (CHimidazole), 121.9
(CHaryl), 121.5 (CHaryl), 121.0 (CHimidazole), 52.0 (NCH2Bu), 33.5 (CH2Bu),
19.9 (CHB2u), 13.7 (CH3Bu). Anal. Calc. for C40H52N8Ag4I4: C, 30.33; H,
3.31; N, 7.07. Found: C, 30.01; H, 3.38; N, 6.88. ESI MS (m/z)
(L
¼
Ligand): 1584.68 [2L
þ
4Ag
þ
4I
þ
H]þ, 1456.76
[2L þ 4Ag þ 3I]þ, 1348.86 [2L þ 3Ag þ 3I þ H]þ, 1222.94
[2L þ 3Ag þ 2I]þ, 1115.05 [2L þ 2Ag þ 2I þ H]þ, 987.14
[2L þ 2Ag þ I]þ, 664.92 [L þ 2Ag þ I]þ, 559.03 [L þ Ag þ I þ H]þ,
430.12 [2L þ 2Ag]þ. IR: nmax(solid)/cmꢀ1: 3158w, 3104w, 3050w,
2954w, 2928w, 2869w, 1604w, 1541w, 1491m, 1463m, 1404m,
1378w, 1343w, 1266w, 1251w, 1221w, 1192w, 1097m, 1072w,
1001w, 946w, 883w, 850w, 821w, 792m, 763w, 721s, 696m, 631w,
505m, 452m, 379w, 307w, 238w, 156w.
octane. 1H NMR (300 MHz, CD2Cl2):
d
7.98 (m, 1H, CHaryl), 7.71
(apparent d, J ¼ 1.8 Hz, 3H, CHimidazole þ CHaryl), 7.66 (d, J ¼ 2.1 Hz,
2H, CHaryl), 7.23 (d, J ¼ 1.8 Hz, 2H, CHimidazole), 4.22 (t, J ¼ 7.3 Hz, 4H,
NCH2Bu), 1.94e1.83 (m, 4H, CH2Bu), 1.41 (m, 4H, CHB2u), 0.99 (t,
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8
V. Charra et al. / Journal of Organometallic Chemistry xxx (2015) 1e9
Synthesis of bis(1,3-bis(30-butylimidazol-20-ylidene)benzene)
(Ccarbene), 141.2 (Caryl), 131.6 (CHaryl), 123.5 (CHaryl), 122.2 (CHimida-
zole), 121.6 (CHimidazole), 119.6 (CHaryl), 52.4 (NCH2Bu), 33.8 (CH2Bu),
20.2 (CHB2u), 14.0 (CH3Bu). Anal. Calc. for C20H26N4Cu2Br2: C, 39.42; H,
4.30; N, 9.19. Found: C, 39.89; H, 4.33; N, 9.82. ESI MS (m/z)
(L ¼ Ligand): 610.92 [L þ 2Cu þ 2Br þ H]þ, 528.99 [L þ 2Cu þ Br]þ,
disilver(I) tetrafluoroborate (2d)
Bis(m k-C)tetra-
-1,3-bis(30-butylimidazol-20-ylidene)benzene-
m3-bromotetrasilver(I) (2b) (0.53 g, 0.45 mmol), AgBF4 (0.18 g,
0.90 mmol) and CH2Cl2 were combined and stirred for 18 h. The
solution was filtered through Celite® and concentrated under
reduced pressure. Upon precipitation with pentane, the complex
was isolated (0.46 g, 0.44 mmol). Yield: 98%. Crystals suitable for X-
ray analysis were grown by slow evaporation of a solution mixture
467.07 [L þ Cu þ Br þ H]þ, 323.22 [L þ H]þ. IR: nmax(solid)/cmꢀ1
:
3111w br, 2959w, 2931w br, 2866w br, 1601m, 1492m, 1470w,
1459m, 1412m, 1393w, 1371w, 1343w, 1319w, 1279m, 1256m,
1232m, 1195w, 1164w, 1105w, 1081w, 1029w, 1001w, 945w, 885m,
799m, 773m, 748s, 719s, 696s, 670m, 645m, 635sw, 611w, 513w,
491w, 477w, 458w, 418w, 374w, 315w, 278w, 266w, 249w, 227w,
202w, 189w, 175w, 153w, 148w, 141w, 134w, 128w, 120w, 106w.
of 2d/CH2Cl2/octane. 1H NMR (300 MHz, CD2Cl2):
d 7.64 (br s, 2H,
CHimidazole), 7.56 (dd, J ¼ 8.0, 2.0 Hz, 2H, CHaryl), 7.50 (br s, 1H,
CHaryl), 7.33 (apparent d, J ¼ 1.7 Hz, 3H, CHarylþimidazole), 4.26 (t,
J ¼ 7.2 Hz, 4H, NCHB2u), 2.01e1.89 (quint {due to overlapping tt},
J ¼ 7.5 Hz, 4H, CHB2u), 1.46 (sext resulting from overlapping qt,
J ¼ 7.5 Hz, 4H, CH2Bu), 1.02 (t, J ¼ 7.5 Hz, 6H, CHB3u). 13C{1H} NMR
Synthesis of (1,3-bis(30-butylimidazol-20-ylidene)benzene)copper(I)
iodide (3c)
(126 MHz, CD2Cl2):
d
179.6 (d, 1J(13Ce107Ag)
¼
184 Hz,
A procedure similar to that used for 3a with 1c (0.50 g,
0.86 mmol), Cu[N(SiMe3)2] (0.38 g, 1.73 mmol) gave 3c as a white
powder (0.51 g, 0.84 mmol). Yield: 86%. 1H NMR (500 MHz, CD2Cl2):
1J(13Ce109Ag) ¼ 213 Hz, Ccarbene), 141.6 (Caryl), 131.2 (CHaryl), 124.8
(CHaryl), 124.6 (CHimidazole), 123.1 (CHimidazole), 120.3 (CHaryl), 52.8
(NCHB2u), 34.0 (CH2Bu), 20.4 (CH2Bu), 13.9 (CHB3u). 19F{1H} NMR
d
8.77 (t, J ¼ 2.1 Hz, 1H, CHaryl), 7.62 (t, J ¼ 8.0 Hz, 1H, CHaryl), 7.44
ꢀ150.6 (s, BFꢀ4 ). Anal. Calc. for
(dd, J ¼ 8.0, 2.1 Hz, 2H, CHaryl), 7.39 (d, J ¼ 1.9 Hz, 2H, CHimidazole),
7.10 (d, J ¼ 1.9 Hz, 2H, CHimidazole), 4.21 (t, J ¼ 7.3 Hz, 4H, NCH2Bu),
1.96e1.88 (m, 4H, CHB2u), 1.43 (m, 4H, CHB2u), 0.99 (t, J ¼ 6.0 Hz, 7H,
(282 MHz, CD2Cl2)
d
C
40H52N8Ag2B2F8ꢂCH2Cl2: C, 41.89; H, 4.69; N, 9.31. Found: C, 41.74;
H, 4.62; N, 9.99. ESI MS (m/z) (L ¼ Ligand): 430.12 [2L þ 2Ag]2þ. IR:
nmax(solid)/cmꢀ1: 3134w, 2956w, 2162w, 1606w, 1497m, 1463w,
1415m, 1369w, 1281w, 1261w, 1229w, 1048s br, 950w, 874w, 735m
br, 693m, 519m, 419w, 397w, 375w, 352w, 303w, 290w, 279w,
247w, 227w, 202w, 195w, 170w, 151w, 121w.
CHB3u). 13C{1H} NMR (126 MHz, CD2Cl2):
d
184.2 (Ccarbene), 141.1
(Caryl), 131.0 (CHaryl), 121.8 (CHimidazole), 121.4 (CHimidazole), 119.9
(CHaryl), 118.5 (CHaryl), 52.1 (NCH2Bu), 33.6 (CH2Bu), 20.4 (CHB2u), 14.1
(CHB3u). Anal. Calc. for C20H26N4Cu2I2: C, 34.15; H, 3.73; N, 7.97.
Despite numerous attempts to purify the product by fractional
precipitations or crystallizations, no satisfactory analyses were
obtained. ESI MS (m/z) (L ¼ Ligand): 1468.70 [2L þ 5Cu þ 4I]þ,
1406.77 [2L þ 4CuI þ H]þ, 1216.94 [2L þ 3Cu þ 3I þ H]þ, 1089.03
[2L þ 3Cu þ 2I]þ, 897.19 [2L þ 2Cu þ I]þ, 702.89 [L þ 2Cu þ 2I þ H]þ,
574.98 [L þ 2Cu þ I]þ. IR: nmax(solid)/cmꢀ1: 3087w, 2984w, 2929w,
2867w, 1605m, 1560w, 1497m, 1458m, 1412m, 1369m, 1258m,
1228m, 1196, 1110m, 1002w, 948w, 871w, 732s, 691s, 511w, 434w,
409w, 294w, 259w, 236w, 218w, 162w, 154w.
Synthesis of (1,3-bis(30-butylimidazol-20-ylidene)benzene)
dicopper(I) dichloride (3a)
1,10-(1,3-phenylene)bis(3-butyl-1H-imidazol-3-ium) chloride
(1a) (0.34 g, 0.86 mmol), Cu[N(SiMe3)2] (0.38 g, 1.73 mmol), and
THF were combined and stirred for 18 h under argon. The solution
was filtered through Celite®. Upon precipitation with pentane, the
complex was cleanly isolated (1.04 g, 0.74 mmol). Yield: 98%.
Crystals suitable for X-ray analysis were grown from a solution
mixture 3c/THF/pentane. 1H NMR (500 MHz, CD2Cl2):
d 8.17 (m, 1H,
CHaryl), 7.76 (dd, J ¼ 7.2, 1.8 Hz, 2H, CHaryl), 7.70 (dd, J ¼ 8.9, 7.0 Hz,
1H, CHaryl), 7.65 (d, J ¼ 1.9 Hz, 2H, CHimidazole), 7.16 (d, J ¼ 1.9 Hz, 2H,
CHimidazole), 4.24 (t, J ¼ 7.2 Hz, 4H, NCHB2u), 1.90 (quint {due to
overlapping tt}, J ¼ 7.5 Hz, 4H, CHB2u), 1.47e1.37 (sext resulting from
overlapping qt, J ¼ 7.5 Hz, 4H, CHB2u), 0.99 (t, J ¼ 7.5 Hz, 6H, CH3Bu).
Acknowledgements
The Centre National de la Recherche Scientifique (CNRS) and the
ꢀ
ꢁ
Region Alsace (PhD fellowship to V. C.), and the Ministere de
ꢀ
l'Enseignement Superieur et de la Recherche (MESR) and IFP En-
13C{1H} NMR (126 MHz, CD2Cl2): 176.6 (Ccarbene),141.2 (Caryl),131.6
d
ergies nouvelles are gratefully acknowledged for financial support.
(CHaryl), 123.6 (CHaryl), 122.3 (CHimidazole), 121.7 (CHimidazole), 119.6
(CHaryl), 52.3 (CH2Bu), 33.8 (CH2Bu), 20.2 (CH2Bu), 13.9 (CH3Bu). Anal.
Calc. for C20H26N4Cu2Cl2: C, 46.16; H, 5.04; N,10.77. Found: C, 46.37;
H, 4.89; N, 10.12. ESI MS (m/z) (L ¼ Ligand): 421.12 [L þ 2Cu þ Cl]þ,
323.22 [L þ H]þ. IR: nmax(solid)/cmꢀ1: 2952w, 2865w, 2362w,
2160w, 1978w, 1684w, 1601m, 1559w, 1541w, 191m, 1458m, 1412m,
1371w,1342w,1318w,1278m,1256m,1231m,1194w,1163w,1104w,
1081w, 1063w, 884w, 799m, 773m, 748s, 719s, 696s, 670m, 645w,
635w, 513w, 491w, 477w, 457w, 414w, 373w, 317w, 251w, 218w,
205w, 198w, 174w, 144w.
Appendix A. Supplementary material
CCDC 989050e985054 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.01.025.
Synthesis of (1,3-bis(30-butylimidazol-20-ylidene)benzene)
dicopper(I) dibromide (3b)
A procedure similar to that used for 3a with 1b (0.41 g,
0.86 mmol), Cu[N(SiMe3)2] (0.38 g, 1.73 mmol) gave 3b as a white
powder (0.51 g, 0.84 mmol). Yield: 98%. Crystals suitable for X-ray
analysis were grown from a solution mixture of 3b/THF/pentane. 1H
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Please cite this article in press as: V. Charra, et al., Journal of Organometallic Chemistry (2015), http://dx.doi.org/10.1016/
j.jorganchem.2015.01.025