Furan- and thiophene-functionalised bis-carbene ligands: Synthesis, silver(I) complexes, and catalysis

Article abstract of DOI:10.1016/j.jorganchem.2005.08.023

New furan- and thiophene-functionalised nucleophilic heterocyclic carbene (NHC) complexes of Ag(I) were prepared via the reaction of novel furan- and thiophene-functionalised bis-imidazolium salts with Ag₂O. Samples of both the N-methyl substit

Full text of DOI:10.1016/j.jorganchem.2005.08.023

Journal of Organometallic Chemistry 690 (2005) 6133–6142
www.elsevier.com/locate/jorganchem
Furan- and thiophene-functionalised bis-carbene ligands:
Synthesis, silver(I) complexes, and catalysis
a,b
b,
c
c
*
David J. Nielsen , Kingsley J. Cavell d , Mihai S. Viciu , Steven P. Nolan ,
d
Brian W. Skelton , Allan H. White
a
School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania 7001, Australia
b
School of Chemistry, Cardiff University, P.O. Box 912, Cardiff, CF10 3TB, UK
Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA
Chemistry M313, University of Western Australia, Crawley, Western Australia 6009, Australia
c
d
Received 2 June 2005; accepted 5 August 2005
Available online 29 September 2005
Abstract
New furan- and thiophene-functionalised nucleophilic heterocyclic carbene (NHC) complexes of Ag(I) were prepared via the reaction
of novel furan- and thiophene-functionalised bis-imidazolium salts with Ag O. Samples of both the N-methyl substituted furan- and
thiophene-functionalised Ag(I) complexes suitable for single crystal X-ray studies were obtained following anion metathesis to the tet-
rafluoroborate salts. The structural characterisations revealed dinuclear [Ag MeCEC) ](BF (E = O, S) formulations with discrete
2
2
(
2
4 2
)
twenty-membered dimetallacycles present in both instances; however, the overall molecular conformation varies considerably, notably
in the orientations of the two bridging furan or thiophene heterocycles to the silver coordination plane. The functionalised bis-imidazo-
lium salts were tested as in situ additives in a Pd(0)-catalysed aryl amination coupling reaction, with the best observed activities around
t
2
0% of those seen with 1,3-bis(2,6-di-iso-propylphenyl)imidazolium chloride under identical conditions. The bulkier N- Bu and N-mesityl
substituted salts were found to be more active than the N-methyl substituted analogues.
2005 Elsevier B.V. All rights reserved.
ꢀ
Keywords: Imidazolium salts; Functionalised; NHC; Silver carbenes; X-ray structures; Amination
1
. Introduction
Pd, Rh, Ru, and Ir of interest for catalytic and fundamen-
tal studies [3]. Thus, Ag (NHC) complexes have played an
I
Nucleophilic heterocyclic carbene (NHC) ligands have
enjoyed wide applicability as ligands for transition and
main group elements since they were first isolated in 1991
important part in the rapid development of functionalised
NHC ligands and their application in homogeneous catal-
ysis; despite the first Ag (NHC) report appearing as re-
I
[
1]. NHC complexes of Ag(I) have proven popular due to
cently as 1998 the subject has already been reviewed [3,4].
The concept of two NHC groups separated by a weaker
donor ligand has been explored by several groups; most
interest has focused on the incorporation of pyridine func-
tionalities [5–7] with the structural characterisation of
a combination of their ready accessibility through a num-
ber of synthetic routes (most notably through the reaction
of an imidazolium salt with Ag O by the method of Wang
and Lin [2]), stability and functional group tolerance, and
their usefulness as facile transmetallation reagents. The lat-
ter property has notably seen their application in the syn-
thesis of NHC complexes of late transition metals such as
2
0
several Ag(I) complexes of RCNC (I) and RCNC (II)
(R = various alkyl/aryl) ligands reported, e.g., III [5]. More
recently, Ag(I) complexes of more flexible bis-NHC ligands
bearing linkages incorporating amino/amido [8], and ether
[
9] functionalities have been reported, the latter structurally
*
characterised and found to be dinuclear [10], as well as li-
gands with chiral linker groups [11].
Corresponding author. Tel./fax: +44 29 20875899.
E-mail address: cavellkj@cf.ac.uk (K.J. Cavell).
0
022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.023

6134
D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
2. Results and discussion
N
N
N
N
N
N
Me
Me
Me
N
N
N
N
N
N
N
N
Ag
Ag
2.1. Furan- and thiophene-functionalised bis-imidazolium
salts
:
:
N
N
Me
N
N
R
N
R
N
R
R
.2BF4
Methodology similar to that used for the preparation of
the pyridine-functionalised bis-imidazolium salt analogues
I
II
III
(RCNC)
(RCNC')
[
5] was employed to prepare a range of furan- and thio-
phene-functionalised bis-imidazolium salts. The precursors
,5-bis(bromomethyl)thiophene, 1, and 2,5-bis(bromom-
2
We were motivated to produce potentially tridentate
ethyl)furan, 2, were obtained as colourless, crystalline,
temperature sensitive solids in moderate yields from 2,5-
dimethylfuran and 2,5-dimethylthiophene, respectively,
using a modification of Offermannꢁs [21] radical bromina-
tion methodology, Scheme 1.
functionalised bis-NHC ligands for Pd(II) with similar
geometries to I but with the pyridine donor replaced by
weaker furan and thiophene moieties, and report here some
examples of Ag(I) complexes of these ligands.
In recent years the number of crystallographically
characterised Ag (NHC) complexes has increased consid-
erably with a rich structural diversity revealed, especially
when halide ions are present in the compound [4,12,13].
However, when non-coordinating anions are present the
complexes invariably adopt a quasi-linearly dicoordinated
Ag(I) cation [2,12,14,15]; bis-NHC ligands typically yield
dinuclear [Ag (bis-NHC) ] complexes [5,16–18], some-
times stabilised by Agꢀ ꢀ ꢀAg interactions in the solid state
16,18]. Syntheses conducted in the presence of excess
Reaction of 1 and 2 with N-methyl-, N-mesityl- and N-
tert-butylimidazole gave functionalised bis-imidazolium
salts 3–8 as colourless to pale tan coloured solids in good
yields, Scheme 2. Extended reaction times were required
to ensure complete disubstitution of halogenated precur-
sors 1 and 2.
I
1
Bis-imidazolium salts 3–8 were characterised by H and
C NMR spectroscopy and by mass spectrometry; simple
2
+
1
3
2
2
spectraconsistentwiththeproposedstructureswereobserved
[
1
inallcases.Acomparisonofthe HNMRspectraofthefuran-
+
Ag O or Ag may yield products incorporating addi-
2
and thiophene-functionalised bis-imidazolium salts shows
that variation of the functional group has a negligible effect
on the chemical shifts of the imidazolium ring imC2,4,5-H pro-
tons although replacing the N-methyl groups of 3 and 4 with
tional silver ions that participate in metal–metal interac-
tions [15,19]. Notably, Ag(I) has little affinity for
additional nucleophilic functional groups when ligated
by two NHC ligands so these have little structural influ-
ence [5,15–17,20]. This lack of interaction may, at least in
t
bulkier N-mesityl or N- Bu groups consistently shifts the sig-
nals of all imidazolium ring protons to lower field.
part, explain the compatibility of the ꢀAg O routeꢁ to
2
complexes of functionalised NHC ligands, although it
2.2. Ag(I) complexes
would seem that the tolerance of Ag O towards activated
2
hydrogens adjacent to functional groups is key to its
versatility.
Bis-imidazolium salts 3–6 were reacted with Ag O in
DCM–MeOH solutions giving the Ag (NHC) complexes
2
I
C H , reflux
6
6
O
O
Br
Br
+
N
Me
Me
E
E
Visible light,
Radical initiator
Br
E = O, S
NBS
1: E = O
2: E = S
Scheme 1. Synthesis of 1 and 2 via radical bromination.
.
2Br
R
N
R
N
N
N
Br
Br
+ 2
N
N
R
E
E
1
2
(E = O)
(E = S)
3 (E = O, R = Me)
4
5
6
7
8
(E = S, R = Me)
(E = O, R = Mes)
(E = S, R = Mes)
t
(E = O, R = Bu)
t
(E = S, R = Bu)
Scheme 2. Synthesis of thiophene- and furan-functionalised bis-imidazolium salts.

D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
6135
9
–12 as pale grey to pale tan solids in reasonable yields,
of 13 showed only signals attributable to mononuclear spe-
cies. Nonetheless, the H NMR spectrum of 13 mirrors that
of 14 with respect to the imC4,5-H signals; chemical shift
discrepancies about the functionalised cores of the ligands
are consistent with those observed in the precursor imi-
dazolium salts 3 and 4.
1
1
Scheme 3. H NMR spectra of 9–12 were consistent with
symmetrical Ag (NHC) complexes, but mass spectrometry
data for 11 and 12 suggested different metal–ligand associ-
ations. Thus, while LSIMS of 11 showed exclusively signals
due to mononuclear [Ag(MesCOC)] species, the thiophene-
I
+
substituted analogue 12 showed a small peak cluster at
m/z = 1255.2 corresponding to the association of a dinu-
When Ag(NHC) complexes 9–14 are divided into furan-
and thiophene-functionalised examples it is apparent that
the nature of the anion and the N-substituent have little
2
+
clear [Ag2(MesCSC)2] cation and a bromide ion, together
+
1
13
with a strong signal corresponding to [Ag(MesCSC)] . Lim-
impact on the H and C NMR shifts common across each
set. Thus, when those signals due to the N-substituents are
ited solubility in common organic solvents precluded
LSIMS results being obtained for 9 and 10; similar prob-
lems have been encountered before in Ag(I) complexes of
bis-NHC ligands with N–Me substituents [5,9]. Further-
more, elemental analysis of 11 and 12 gave less than opti-
mal results, perhaps stemming from compositional
1
13
excluded, the H and C NMR spectra of the N-methyl
substituted 9 and 13 closely resemble that of the N-mesityl
substituted 11, and 10 closely resembles both 12 and 14.
1
3
However, signals in the C NMR due to imC were only
2
observed in the N-methyl substituted 13 and 14, at d
ꢁ
uncertainty with regards to the putative [AgBr2] anion.
180.6 and 180.1, respectively. These observations suggest
2
+
Elemental analysis results for 11 led to the anionic compo-
that a dinuclear [Ag ( CEC) ] association such as that
2 R 2
ꢁ
nent being formulated as an equal mixture of [AgBr ] and
found in 13 and 14 (vide infra) is present in all of the
furan- and thiophene-functionalised Ag(NHC) complexes
described herein. However, NMR data cannot distinguish
between the two different MeCEC ligand orientations
described below.
2
bromide ions, while 12 yielded compositional data close to
that required by a [Ag2(MesCSC) ] Æ 2[AgBr ] formulation,
2
2
albeit with an unsatisfactorily high %H value.
Anion substitution yielding tetrafluoroborate complexes
of Ag(bis-NHC) complexes has proved useful in preparing
crystalline samples with well-defined compositions, notably
with the pyridine analogue of the title furan- and thio-
phene-functionalised bis-NHC ligands [5]. Thus, 9 and 10
were treated with AgBF4 in MeCN to obtain Ag(I)
complexes 13 and 14 containing the MeCOC and MeCSC
ligands, respectively, as colourless, crystalline tetrafluoro-
borate salts, Scheme 4.
Complex 14 was crystallised from MeCN and the pro-
posed dinuclear structure of two Ag(I) ions bridged by two
0
NHC ligands binding in a C,C mode confirmed by a single
crystal X-ray crystallographic investigation, Fig. 1. Com-
pound 14 crystallises in the triclinic system accompanied
2
+
by two molecules of MeCN per dinuclear [Ag ( CSC)2]
2 Me
cation; one half of the cation, a tetrafluoroborate anion
and a molecule of MeCN comprise the asymmetric unit.
1
2+
The H NMR spectra of 13 and 14 closely resembled
The centrosymmetric dinuclear [Ag2(MeCSC)2] motif in
those of 9 and 10, respectively, suggesting that the [Ag -
14 is similar to that seen in the pyridine-functionalised III
[5]. The preferred quasi-linear orientation of Ag(I) bridging
between two NHC moieties is observed, with C(22)–Ag–
C(22 ) (1 ꢁ x, 1 ꢁ y, ꢀz ) = 173.05(8)ꢁ; the Ag–C(22,22 )
2
2
+
(MeCEC)2]
association (vide infra) was unaffected by
the anion substitution. However, while 14 showed a peak
cluster in the MS due to a dinuclear association, the spectra
0
0
.2Br
Ag O
2
N
N
N
N
0.5 [Ag2(RCEC)2 ].2X
R
R
E
DCM-MeOH
3
4
5
6
(E = O, R = Me)
(E = S, R = Me)
(E = O, R = Mes)
(E = S, R = Mes)
9
(E = O, R = Me, X = AgBr2)
10 (E = S, R = Me, X = AgBr2)
11 (E = O, R = Mes, 2X = AgBr .Br)
12 (E = S, R = Mes, X = AgBr2)
2
Scheme 3. Syntheses of Ag(I) complexes of thiophene- and furan-functionalised bis-NHC ligands.
N
N
N
N
N
N
Me
Me
Me
Me
E
E
AgBF4
MeCN
[
Ag2(MeCEC) ].2[ AgBr ]
Ag
Ag
2
2
N
N
.
2BF4
9
1
(E = O)
0 (E = S)
13 (E = O)
14 (E = S)
Scheme 4. Synthesis of tetrafluoroborate complexes.

6136
D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
Fig. 1. Projection of the cation of 14 oblique to the plane of the NHC rings, showing the zig-zag conformation and the atom labelling scheme.
˚
˚
distances (2.079(1), 2.086(1) A) are similar to those in III [5],
Table 1. In the solid state 14 shows no significant silver–
Agꢀ ꢀ ꢀAg distances of 3.5420(6) A, slightly greater than the
˚
sum of the van der Waals radii (3.40 A) [22]. The NHC ring
0
sulphur interactions, but quasi-planar (NHC)Ag(NHC )
arrays stack, inversion-related, up a yielding successive
planes have an interplanar dihedral angle of 4.95(8)ꢁ, and an-
gles of 77.90(8)ꢁ and 82.78(8)ꢁ to the central thiophene ring.
Vapour diffusion of Et O into an MeCN–CHCl solu-
2
3
tion of 13 yielded a sample of lower crystallinity than that
of 14; nevertheless, single crystal X-ray diffraction showed
that the dinuclear [Ag2(MeCOC)2] motif is also present
Table 1
0
Bond distances and angles about the im
MeCEC) ](BF
Ag MeCNC)
C
2
–Ag–im
C
units of [Ag
2
-
2+
2
(
2
4 2
) (E = O, S) complexes 13 and 14, and previously reported
in 13, Fig. 2. The cation has mm symmetry, and the complex
crystallises together with half a molecule of chloroform and
one molecule of MeCN, one quarter of the formula unit
being crystallographically independent. Complex 13 shows
no close inter- or intra-molecular contacts to Ag or O(1),
but in a significant deviation from the structures observed
for 14 and III, the furan rings of 13 are disposed to the same
side of the plane defined by the two Ag and the four
[
2
(
2
4 2
](BF ) III
a
Complex
im
C
A)
2
–Ag distance
im 2 2
C –Ag–imC
˚
b
(
angle (ꢁ)
1
3
4
[Ag
[Ag
[Ag
2
2
2
(
(
(
MeCOC)
2
](BF
](BF
](BF
4
)
2
2.081(1)
176.3(3)
173.05(8)
176.78(9)
1
MeCSC)
MeCNC)
2
4
)
2
2.079(1), 2.086(1)
2.088(4), 2.093(4)
c
III
a
2
4 2
)
Solvent of crystallisation omitted.
Data for imC (unprimed, primed), respectively, where not crystallo-
2
b
0
graphically identical.
C(22,22 ) atoms. The pair of NHC rings within the MeCOC
c
Ref. [5].
ligand are inclined at 27.7(3)ꢁ to each other and at 78.7(4)ꢁ
0
Fig. 2. Projection of the cation of 13 along the Ag–Ag axis. Labelled non-hydrogen atoms are those included in the asymmetric unit.

D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
6137
to the furan ring plane, Table 2. Apart from this gross struc-
tural disparity the dimensions about the silver atoms in 13
are comparable to those in 14, Table 1. However, the larger
size of the sulphur atom in 14 compared to the oxygen atom
in 13 results in an increased span across the heterocycle a-
methylene groups, i.e., C(21)ꢀ ꢀ ꢀC(21 ), of almost 0.5 A in
the former complex. It is thus possible for the furan and thi-
ophene functionalities to influence the disparate conforma-
tions of 13 and 14 wholly through geometric factors;
however, the greater size and reduced electronegativity of
S compared to O should make the MeCSC ligand more suit-
able for ꢀpincerꢁ complexation of the late transition metals.
Compared to 1,3-bis(dipp)imidazolium chloride (Entry
16, 91% conversion) all of the functionalised bis-imidazo-
lium salts tested show low activity. Significant amounts of
toluene, a product of the hydrodehalogenation of 4-bromo-
toluene, was observed for the runs employing furan- and
thiophene-functionalised bis-imidazolium salts (Entries 4–
9) but not for those using the pyridine-functionalised
examples or 1,3-bis(dipp)imidazolium chloride. Under
conditions identical to that of Entry 13 the best conversions
were shown by 4 (Entry 6, 19% conversion with 11% toluene
0
˚
by-product), and (MesCNC)(HBr) (Entry 3, 18% conver-
2
sion). Both of these salts feature bulky N-Mes substituents,
and the furan-functionalised analogue 5 also performed
relatively well over a longer reaction time (Entry 9, 30%
conversion), albeit with significant formation of toluene
byproduct. Increasing the reaction temperature for the
pyridine-functionalised salts from 100 to 120 ꢁC, Entries
10–12, gave little improvement. It is of interest to note that
2
.3. Catalytic testing – aryl amination
The furan- and thiophene-functionalised bis-imidazolium
salts, together with the previously reported pyridine-
functionalised analogues [5,7,23], were applied in conjunc-
t
t
tion with Pd(dba) and KO Bu to the aryl amination of
the N- Bu substituted furan-functionalised 7 outperforms
2
morpholine with 4-bromotoluene, Scheme 5. The results of
thesecatalytictrialsaregiveninTable3, benchmarkedagainst
the highly active 1,3-bis(dipp)imidazolium chloride [24].
the N-Mes substituted 5 (Entry 9, 30% conversion with
10% toluene), the opposite result to that observed for the
pyridine- and thiophene-functionalised salts at 100 ꢁC.
Table 2
Selected bond lengths and angles in [Ag
2
(
MeCEC)
2
](BF
4
)
2
(E = O, S) complexes 13 and 14, and previously reported [Ag
2
(
MeCNC)
2
](BF
4
)
2
, III
a,b
c
Complex
[Ag
2
(
MeCOC)
2
](BF
4
)
2
(13) [Ag MeCSC) ](BF (14)
2
(
2
4
)
2
[Ag MeCNC)
2
(
2
4 2
](BF ) (III)
˚
Bond distance (A)
N(21)–C(22)
C(22)–N(23)
N(23)–C(24)
C(24)–C(25)
C(25)–N(21)
C(21)–N(21)
C(21)–C(2)
1.355(9)
1.352(10)
1.332(13)
1.352(14)
1.380(11)
1.439(9)
1.507(2)
1.353(9)
1.342(13)
1.411(14)
1.353(2), 1.351(3)
1.351(3), 1.354(3)
1.381(2), 1.383(2)
1.343(3), 1.339(4)
1.382(2), 1.390(2)
1.464(3), 1.469(3)
1.503(2), 1.497(2)
1.7269(17), 1.726(2)
1.360(3), 1.361(3)
1.419(2)
1.350(3), 1.354(3)
1.353(4), 1.354(4)
1.381(5), 1.382(5)
1.347(4), 1.344(4)
1.385(5), 1.383(5)
1.468(4), 1.475(4)
–
–
–
–
E(1)–C(2)
C(2)–C(3)
0
C(3)–C(3 )
Bond angles (ꢁ)
N(21)–C(22)–N(23)
C(22)–N(23)–C(24)
N(23)–C(24)–C(25)
C(24)–C(25)–N(21)
C(22)–N(21)–C(25)
C(21)–N(21)–C(22)
N(21)–C(21)–C(2)
E(1)–C(2)–C(21)
E(1)–C(2)–C(3)
104.0(7)
104.32(13), 104.57(13)
111.28(17), 110.95(18)
106.59(17), 106.96(17)
106.75(15), 106.64(17)
111.06(18), 110.88(18)
124.02(13), 124.16(13)
111.55(19), 112.13(15)
121.04(16), 121.45(16)
110.73(12), 111.02(12)
92.09(9)
104.3(3), 104.2(3)
111.1(2), 111.3(2)
107.0(3), 106.6(3)
106.1(3), 106.8(3)
111.5(3), 111.2(2)
124.3(3), 123.0(3)
–
–
112.0(7)
107.6(8)
105.9(8)
110.5(7)
125.4(6)
112.1(6)
117.8(7)
110.1(7)
106.8(7)
106.5(9)
128.7(5)
127.2(5)
–
–
–
0
0
C(2)–E(1)–C(2 )
C(2)–C(3)–C(3 )
113.36(18), 112.8(2)
131.68(15), 131.18(14)
123.99(13), 124.25(14)
Ag–C(22)–N(21)
Ag–C(22)–N(23)
125.5(2), 130.2(2)
129.4(2), 125.6(2)
d
Interplanar dihedral angles (ꢁ)
Funct./MeIm
MeIm/MeIm
Coord./MeIm
Coord./Funct.
a
78.7(4)
27.7(3)
76.2(3)
39.2(3)
77.90(8), 82.78(8)
4.95(8)
32.81(6), 36.21(6)
54.25(5)
74.4(1), 70.5(1)
9.2(1)
77.55(9), 75.17(10)
50.36(9)
0
Solvent of crystallisation omitted.
Data for Ag(unprimed, primed), respectively, where not crystallographically identical.
Ref. [5].
b
c
d
3 2
Funct. = furan, thiophene, or pyridyl ring; MeIm = C N ring of imidazolin-2-ylidene; Coord. = the plane described by the four C atoms coordinated
to the two Ag atoms.

6138
D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
Pd(dba) , L
2
Me
Br + H N
O
Me
N
O
t
KO Bu,
1,4-dioxane
IV
Scheme 5. Pd(0)/imidazolium salt aryl amination coupling protocol. L = functionalised bis-imidazolium salt.
Table 3
Results of the aryl amination reaction of morpholine with 4-bromotoluene catalysed by Pd(dba)
2
and functionalised bis-imidazolium salts
a
b
Entry
Imidazolium salt
Time (h)
Temperature (ꢁC)
Conversion (%)
Toluene (%)
1
2
3
4
5
6
(
(
(
(
(
(
MeCNC)(HBr)
BuCNC)(HBr)
MesCNC)(HBr)
2
24
24
24
24
24
24
100
100
100
100
100
100
14
11
18
8
10
19
–
–
–
7
5
11
t
2
2
4
8
6
MeCSC)(HBr)
BuCSC)(HBr)
2
t
2
MesCSC)(HBr)
2
7
8
9
3
7
5
(
(
(
MeCOC)(HBr)
BuCOC)(HBr)
2
48
48
48
100
100
100
24
36
30
4
7
10
t
2
MesCOC)(HBr)
MeCNC)(HBr)
BuCNC)(HBr)
MesCNC)(HBr)
2
1
1
1
1
0
1
2
3
(
(
(
2
24
24
24
24
120
120
120
100
14
14
12
91
–
–
–
–
t
2
2
c
1,3-bis(dipp)Im Æ Cl
t
Reaction conditions: 1.0 mmol 4-bromotoluene, 1.2 mmol morpholine, 1.5 mmol KO Bu, 2.0 mol% Pd(dba)
2
, 2.0 mol% imidazolium salt, 3 mL dioxane.
a
GC yields.
b
Hydrodehalogenation side product; yield relative to substrate.
Pd:L ratio = 1:2. 1,3-bis(dipp)Im Æ Cl = 1,3-bis(2,6-di-iso-propylphenyl)imidazole.
c
Nonetheless, the provision of steric bulk at the N-substitu-
ents is clearly of benefit to the overall activity of the system,
and similar behaviour should follow in preformed catalyst
systems [25].
preformed complexes of the reported bis-NHC ligands with
catalytically interesting metals such as Pd(II) will yield bet-
ter insights into the influences of the donor group, N-sub-
stituent steric bulk, and potentially chelating nature of
these ligands in a catalytic situation.
3
. Conclusions
4. Experimental
New furan- and thiophene-functionalised bis-imidazo-
lium salts have been synthesised, characterised, and reacted
4.1. General
I
with Ag O to give Ag (NHC) complexes of functionalised
2
bis-NHC ligands. Single crystal X-ray structures of dinu-
All reactions were performed under an atmosphere of dry
dinitrogen or argon using standard Schlenk techniques. Sol-
vents were purified and dried by usual methods [26], unless
otherwise indicated. N-substituted imidazoles bearing tert-
butyl [27] and mesityl [28] substituents were prepared
according to literature procedures; N-(2,6-di-iso-propylphe-
nyl)imidazole was prepared by modification of the proce-
dure for N-mesitylimidazole. All other reagents were used
2
+
clear [Ag L ] complexes bearing the MeCOC and MeCSC
2
2
ligands are presented in which the ligands adopt similar
geometries but for the positions of the functional group
rings relative to the Ag C plane. Notably, Ag atoms from
2
4
successive molecules in the complex containing MeCSC ap-
proach close to the sum of the van der Waals radii and it is
possible that a weak Ag(I)ꢀ ꢀ ꢀAg(I) bonding interaction
contributes to the stability of the observed structure. The
described Ag(NHC) complexes are expected to find use
as transmetallation reagents to catalytically interesting
metals such as Pd(II). Although the described furan- and
thiophene-functionalised bis-imidazolium salts performed
relatively poorly in catalytic testing in combination with
a Pd(0) source for a model aryl amination reaction, the
addition of bulky N-substituents showed increased product
yield. Furthermore, increased product yields when ex-
tended reaction times were used suggests that although
the catalytically active species exhibit poor performance,
they are stable over the long term. However, it is likely that
1
13
as received. H and C (proton decoupled) NMR spectra
were run on Varian Gemini 200, Unity Inova 400, Bruker
DPX 400, or JEOL Eclipse 300 instruments at ambient tem-
1
3
perature and referenced to residual solvent signals [29].
C
DEPT spectra were used to aid assignments where necessary.
Elemental analyses (Carlo Erba EA1108 or ThermoFinni-
gan Flash 1112 Series EA) and Liquid Secondary Ion Mass
Spectrometry (LSIMS, Kratos Concept ISQ) were per-
formed by the Central Science Laboratory, University of
Tasmania. Electrospray Mass Spectrometry (ESMS) was
performed at Cardiff University. All reactions involving sil-
ver compounds were performed with the exclusion of light.

D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
6139
4
.1.1. 2,5-Bis(bromomethyl)furan (1)
This compound was prepared in 46% yield in an identi-
(100 MHz, d -DMSO, d): 148.4 (furC2,5), 140.3 (MesC1),
6
137.7 ( C ), 134.2 (MesC2,6), 131.1 (MesC ), 129.3 (MesC3,5),
im
2
4
cal manner to 2 and showed similar decomposition be-
124.2 and 123.1 ( C4,5), 112.4 (furC3,4), 45.4 (CH ), 20.6
im 2
1
haviour. H NMR (400 MHz, CDCl , d): 6.36 (s, 2H,
(MesC -Me), 17.0 (MesC2,6-Me).
3
4
furC3,4-H), 4.48 (s, 4H, CH2).
4
.2.3. 2,5-Bis[(3-tert-butylimidazolium-1-yl)methyl]furan
4
.1.2. 2,5-Bis(bromomethyl)thiophene (2)
N-bromosuccinimide (15.47 g, 86.9 mmol) was sus-
dibromide (7) ” (
tBuCOC)(HBr)2
Compound 1 (1.93 g, 7.60 mmol) and N-tert-butylimi-
pended in benzene (150 mL) and 2,5-dimethylthiophene
dazole (2.08 g, 16.7 mmol) were dissolved in acetone
0
(
4.5 mL, 39.5 mmol) added, followed by 1,1 -azobis(cyclo-
(30 mL) and stirred at room temperature for 30 min, then
hexanecarbonitrile) (0.2 g) as radical initiator. The result-
ing mixture was refluxed under a 150 W incandescent
bulb for 6 h, yielding a red solution. On cooling the super-
natant was decanted off and washed with saturated NaH-
refluxed for 72 h. The solvent was removed in vacuo and
the residue washed with Et O (3 · 25 mL) and hexanes
2
(
20 mL) and dried in vacuo giving 7 (3.76 g, 99%) as a
+
cream powder. MS (ESMS): m/z 423.1 [M ꢁ Br] , 341.5
CO solution (3 · 50 mL) and water (50 mL) then dried
+ 1
M ꢁ 2Br ꢁ H] . H NMR (400 MHz, d -DMSO, d): 9.59
3
[
(
6
over MgSO . The solvent was removed in vacuo and the
4
s, 2H, C -H), 8.11 and 7.88 (t · 2, J = 1.8 Hz, each
im
2
residue extracted with hot hexanes (3 · 50 mL). Colourless
crystals of 2 (6.34 g, 59%) deposited on cooling at 0 ꢁC.
Compound 2 blackens and generates HBr during storage
at ꢁ20 ꢁC; however, pure material may be obtained by
2
1
H, imC4,5-H), 6.70 (s, 2H, furC3,4-H), 5.53 (s, 4H, CH2),
13
.59 (s, 18H, N-CMe3). C NMR (100 MHz, d -DMSO,
6
d): 148.5 (furC2,5), 134.7 ( C ), 122.6 and 120.7 ( C4,5),
im
2
im
1
12.0 (furC3,4), 59.8 (N-CMe ), 44.8 (CH ), 29.0 (N-CMe ).
3 2 3
extracting the partially decomposed mass with Et O and
2
1
removing the solvent (and HBr) in vacuo. H NMR
4
4
.3. Thiophene-functionalised bis-imidazolium salts
.3.1. 2,5-Bis[(3-methylimidazolium-1-yl)methyl]thiophene
(
400 MHz, CDCl , d): 6.94 (s, 2H, thioC3,4-H), 4.67 (s,
3
4
4
4
H, CH2).
dibromide (4) ” (MeCSC)(HBr)2
.2. Furan-functionalised bis-imidazolium salts
Compound 2 (1.00 g, 3.70 mmol) and N-methylimidaz-
ole (1.0 mL, 12.5 mmol) were dissolved in THF (20 mL)
and stirred at 40 ꢁC for 24 h, then refluxed for 4 h. The sol-
vent was removed in vacuo and the residue washed with
.2.1. 2,5-Bis[(3-methylimidazolium-1-yl)methyl]furan
dibromide (3) ” (MeCOC)(HBr)2
Compound 1 (0.70 g, 2.76 mmol) and N-methylimidaz-
ole (0.8 mL, 10.0 mmol) were dissolved in THF (20 mL)
and stirred at room temperature for 12 days, then refluxed
for 24 h. The solvent was removed in vacuo and the residue
Et O (3 · 20 mL) and petroleum (b.p. 40–60 ꢁC, 20 mL)
2
then dried in vacuo giving 4 (1.37 g, 85%) as a white pow-
+
der. MS (ESMS): m/z 353.3 and 355.3 [M ꢁ Br] , 273.3
+
1
[
(
M ꢁ 2Br ꢁ H] . H NMR (400 MHz, d -DMSO, d): 9.36
6
washed with hexanes (3 · 20 mL) and Et O (20 mL) and
2
s, 2H, C -H), 7.86 and 7.75 (s · 2, each 2H,
C -H),
im 4,5
im
2
dried in vacuo giving 3 (1.08 g, 94%) as a cream powder.
+
7.29 (s, 2H, thio
C
3,4-H), 5.70 (s, 4H, CH
Me). C NMR (75 MHz, DMSO-d , d): 138.1 (thio
36.4 ( C ), 129.4 (thioC3,4), 124.0 and 122.1 ( C4,5),
2
), 3.87 (s, 6H, N-
MS (ESMS): m/z 337.3 and 339.3 [M ꢁ Br] , 257.4
1
3
+
1
6
C2,5),
[
(
6
M ꢁ 2Br ꢁ H] . H NMR (400 MHz, d -DMSO, d): 9.34
6
1
4
im
2
im
s, 2H, C -H), 7.82 and 7.77 (m · 2, each 2H,
C -H),
im 4,5
im
2
6.2 (CH ), 36.0 (N-Me).
2
.69 (s, 2H,
C -H), 5.55 (s, 4H, CH ), 3.89 (s, 6H, N-
fur 3,4 2
1
3
Me). C NMR (100 MHz, d -DMSO, d): 148.6 (furC2,5),
6
1
36.6 ( C ), 124.0 and 122.3 ( C4,5), 112.1 (furC3,4), 44.7
4.3.2. 2,5-Bis[(3-mesitylimidazolium-1-yl)methyl]thiophene
dibromide (6) ” (MesCSC)(HBr)
im
2
im
(
CH ), 36.0 (N-Me).
2
2
Compound 2 (1.00 g, 3.70 mmol) and N-mesitylimidaz-
ole (1.59 g, 8.51 mmol) were dissolved in acetone (25 mL)
and refluxed for 48 h. The solvent was removed in vacuo
4
.2.2. 2,5-Bis[(3-mesitylimidazolium-1-yl)methyl]furan
dibromide (5) ” (MesCOC)(HBr)2
Compound 1 (0.40 g, 1.6 mmol) and N-mesitylimidazole
and the residue washed with Et O (4 · 10 mL) and dried
2
(
0.65 g, 3.5 mmol) were dissolved in THF (20 mL) and re-
in vacuo giving 6 (1.86 g, 78%) as a cream powder. MS
+
fluxed for 72 h, giving incomplete substitution. The solvent
was removed in vacuo, the residue stirred in acetone
(ESMS): m/z 561.4 and 563.4 [M ꢁ Br] , 481.0
+
1
[M ꢁ 2Br ꢁ H] . H NMR (400 MHz, d
-DMSO, d): 9.72
6
(
30 mL) for 72 h and then refluxed a further 24 h. The sol-
(s, 2H, im
2H, im 4,5-H), 7.37 (s, 2H, thio
3,5-H), 5.83 (s, 4H, CH ), 2.33 (s, 6H, Mes
2,6-Me). C NMR (100 MHz, d -DMSO,
), 138.2 (thio 2,5), 137.6 (im ), 134.2
2,6), 131.1 (Mes ), 129.6 (thio 3,4), 129.3 (Mes
124.3 and 123.0 (im 4,5), 47.1 (CH ), 20.6 (Mes
17.0 (Mes 2,6-Me).
C
2
-H), 8.14 and 7.98 (t · 2, J = 1.8 Hz, each
3,4-H), 7.15 (s, 4H,
-Me),
vent was removed in vacuo and the residue washed with
C
C
acetone (3 · 4 mL) giving 5 (0.56 g, 57%) as a tan powder.
Mes
C
2
C
4
+
1
13
MS (ESMS): m/z 547.6 [M ꢁ Br] . H NMR (400 MHz,
1.99 (s, 12H, Mes
d): 140.3 (Mes
C
C
6
d -DMSO, d): 9.66 (s, 2H, C -H), 8.11 and 8.00 (t · 2,
1
C
C
2
6
im 2
J = 1.6 Hz, each 2H, imC4,5-H), 7.14 (s, 4H, Mes
C
-H),
3,5
(
Mes
C
C
4
C
C3,5),
C -Me),
4
6
.78 (s, 2H, furC3,4-H), 5.67 (s, 4H, CH ), 2.33 (s, 6H,
C
2
2
1
3
C -Me), 1.98 (s, 12H, MesC2,6-Me).
4
C
NMR
C
Mes

6140
D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
4
.3.3. 2,5-Bis[(3-tert-butylimidazolium-1-yl)methyl]thiophene
BuCSC)(HBr)2
Compound 2 (1.50 g, 5.56 mmol) and N-tert-butylimi-
supernatant was decanted off and stripped in vacuo, the res-
dibromide (8) ” (
t
idue washed with acetone (3 · 10 mL) and dried in vacuo
giving 11 as a dark cream coloured powder (0.81 g, 69%).
Required for C H Ag Br N O : C, 48.28; H, 4.32; N,
dazole (1.52 g, 12.22 mmol) were dissolved in acetone
6
0
64
3
3
8
2
(
30 mL) and refluxed for 65 h. The solvent was removed
7.51. Found: C, 50.48; H, 3.96; N, 7.69%. MS (LSIMS):
+
in vacuo and the residue washed with Et O (2 · 20 mL)
m/z 571.0 and 573.0 [(M ꢁ AgBr ꢁ Br)/2] , dinuclear ion
2
2
1
then acetone (4 · 7 mL) until the washes were almost col-
not observed. H NMR (400 MHz, d -DMSO, d): 7.67
6
ourless. The product was washed with Et O (15 mL) and
and 7.44 (d · 2, J = 1.6 Hz, each 4H, imC4,5-H), 6.96 (s,
2
dried in vacuo giving 8 (2.08 g, 73%) as a pale tan powder.
8H, MesC3,5-H), 6.53 (s, 4H, furC3,4-H), 5.41 (s, 8H, CH ),
2
+
13
MS (ESMS): m/z 437.4 and 439.2 [M ꢁ Br] , 357.7
2.54 (s, 12H, MesC -Me), 1.68 (s, 24H, MesC2,6-Me).
C
4
+
1
[
(
M ꢁ 2Br ꢁ H] . H NMR (300 MHz, d -DMSO, d): 9.73
NMR (100 MHz, d -DMSO, d): 150.6 (furC2,5), 138.4 and
6
6
s, 2H, C -H), 8.10 and 7.93 (t · 2, J = 1.7 Hz, each
135.6 (MesC and
C ), 134.2 (MesC2,6), 128.8 (MesC3,5),
Mes 4
im
2
1
2
1
H, imC4,5-H), 7.32 (s, 2H, thioC3,4-H), 5.68 (s, 4H, CH2),
123.3 and 122.4 ( C4,5), 111.1 (furC3,4), 47.0 (CH ), 20.7
im 2
1
3
.58 (s, 18H, N-CMe3). C NMR (100 MHz, d -DMSO,
(MesC -Me), 17.1 (MesC2,6-Me), imC not observed.
6
4
2
d): 138.0 (thioC2,5), 134.6 ( C ), 129.4 (thioC3,4), 122.4 and
im
2
1
4
4
20.8 ( C ), 59.8 (N-CMe ), 46.3 (CH ), 28.9 (N-CMe ).
im 4,5 3 2 3
0
.4.4. [Ag2(MesCSC) ][AgBr ] (12) ( CSC = C,C -2,
2 2 2 Mes
-bis[(3-mesitylimidazolin-2-yliden-1-yl)methyl]thiophene)
Compound 6 (1.000 g, 1.56 mmol) was dissolved in 20:1
4
5
.4. Ag(I) complexes
DCM:MeOH (75 mL) and Ag O (0.354 g, 1.53 mmol)
0
2
.4.1. [Ag2(MeCOC) ][AgBr ] (9) ( COC = C,C -2,5-
Me
2
2 2
added. The resulting black suspension was stirred over-
bis[(3-methylimidazolin-2-yliden-1-yl)methyl]furan)
Compound 3 (0.207 g, 0. 0.495 mmol) was dissolved in
night at room temperature after which time the Ag O
2
had reacted and a little pale grey powder remained. The
supernatant was decanted from the precipitate and stripped
in vacuo, the residue washed with acetone (3 · 10 mL) and
dried in vacuo giving 12 as a pale yellow powder (0.58 g,
2
0:3 DCM:MeOH (23 mL) and Ag O (0.117 g,
2
0
.505 mmol) added. The resulting black suspension was
stirred overnight at room temperature after which time
the Ag O had been replaced by a pale grey powder. The
solvent was removed in vacuo and the residue washed with
2
4
3
4%). Required for C H N Ag Br S : C, 42.08; H,
60 64 8 4 4 2
.77; N, 6.54. Found: C, 41.94; H, 4.36; N, 7.00%. MS
1
0:1 DCM:MeOH (3 · 5 mL) giving 9 (0.172 g, 55%) as a
+
(
LSIMS): m/z 1255.2 [M ꢁ 2(AgBr ) + Br] , 587.1 and
1
2
pale grey solid. H NMR (400 MHz, d -DMSO, d): 7.49
6
+
1
5
89.1 [M/2 ꢁ AgBr ] . H NMR (400 MHz, d -DMSO,
2
6
and 7.43 (d · 2, J = 1.6 Hz, each 4H, imC4,5-H), 6.48 (s,
d): 7.76 and 7.42 (d · 2, J = 1.6 Hz, each 4H,
.97 (br s, 12H,
C -H),
im 4,5
C
3,4-H), 5.49 (s, 8H,
thio
4
H,
C -H), 5.30 (s, 8H, CH ), 3.70 (s, 12H, N-Me).
fur 3,4 2
C NMR: insufficient solubility.
6
C
Mes 3,5
-H and
1
3
CH ), 2.39 (s, 12H,
C NMR (100 MHz, d -DMSO, d): 140.5 and 138.5 and
C -Me), 1.62 (s, 24H, MesC2,6-Me).
4
2
Mes
1
3
0
6
4.4.2. [Ag2(MeCSC) ][AgBr ] (10) ( CSC = C,C -2,5-
bis[(3-methylimidazolin-2-yliden-1-yl)methyl]thiophene)
2
2 2
Me
1
1
4
35.4 (thioC2,5 and MesC1 and
28.8 (MesC3,5), 127.1 (thioC3,4), 123.4 and 122.5 ( C4,5),
C ), 134.2 (MesC2,6),
Mes 4
im
Compound 4 (0.317 g, 0.73 mmol) was dissolved in 20:1
9.1 (CH ), 20.7 ( C -Me), 17.0 (MesC2,6-Me), imC not
2
Mes
4
2
DCM:MeOH (32 mL) and Ag O (0.169 g, 0.73 mmol)
added. The resulting black suspension was stirred over-
2
observed.
night at room temperature after which time the Ag O
had been replaced by a pale tan-grey powder. The solvent
was removed in vacuo, the residue suspended in MeOH
2
0
4.4.5. [Ag2(MeCOC) ](BF ) (13) ( COC = C,C -2,5-
Me
2
4 2
bis[(3-methylimidazolin-2-yliden-1-yl)methyl]furan)
Compound 3 (0.410 g, 0.981 mmol) was dissolved in 9:1
DCM:MeOH (45 mL) and Ag O (0.232 g, 1.00 mmol)
(
30 mL) and the solids filtered off. The filtrate was stripped
1
in vacuo giving 10 (0.31 g, 66%) as a pale grey solid. H
2
NMR (400 MHz, d -DMSO, d): 7.52 and 7.41 (d · 2,
added. The resulting black suspension was stirred overnight
at room temperature giving a suspension of pale grey 9. The
solvent was stripped in vacuo, the residue suspended in
6
J = 1.6 Hz, each 4H, imC4,5-H), 7.04 (s, 4H,
C3,4-H),
thio
1
3
5
.47 (s, 8H, CH ), 3.72 (s, 12H, N-Me). C NMR
2
(
100 MHz, d -DMSO, d): 180.2 ( C ), 140.4 (thioC2,5),
MeCN (40 mL) and AgBF (0.382 g, 1.96 mmol) added.
6
im
2
4
1
27.1 (thioC3,4), 123.3 and 121.9 ( C ), 48.9 (CH ), 38.3
After stirring at ca. 40 ꢁC for 1 h the precipitated AgBr was
removed by filtration and the solvent stripped in vacuo giv-
ing a pale grey residue that was washed with MeCN
(2 · 2 mL) and recrystallised from warm MeCN by cooling
at ꢁ20 ꢁC. The product was washed with cold MeCN
(2 · 1 mL) and dried in vacuo giving 13 as a very pale grey
microcrystalline solid (0.261 g, 59%). X-ray diffraction qual-
im 4,5
2
(
N-Me).
0
.4.3. [Ag2(MesCOC) ][AgBr ]Br (11) ( COC = C,C -
2 2 Mes
4
2
,5-bis[(3-mesitylimidazolin-2-yliden-1-yl)methyl]furan)
Compound 5 (1.000 g, 1.60 mmol) was dissolved in 10:1
DCM:MeOH (55 mL) and Ag O (0.363 g, 1.57 mmol)
2
added. The resulting black suspension was stirred overnight
ity crystals were grown by diffusion of Et O into an MeCN–
2
at room temperature after which time the Ag O had reacted
CHCl solution of 13. Required for C H Ag B F N O :
2
3
28 32
2
2
8
8
2
and a little pale grey coloured precipitate remained. The
C, 37.29; H, 3.58; N, 12.42. Found: C, 36.79; H, 3.56; N,

D.J. Nielsen et al. / Journal of Organometallic Chemistry 690 (2005) 6133–6142
6141
+
1
1.27%. MS (LSIMS): m/z 363.0 and 365.0 [M/2 ꢁ BF ] ,
0.13. CCDC No. 239232. Variata: Solvent residues were
4
1
dinuclear ion not observed. H NMR (400 MHz, d -DMSO,
modeled as a mixture of CHCl and MeCN.
6
3
d): 7.51 and 7.45 (d · 2, J = 1.8 Hz, each 4H, imC4,5-H), 6.45
1
3
(
s, 4H, furC3,4-H), 5.33 (s, 8H, CH ), 3.58 (s, 12H, N-Me). C
4.6.2. 14 Æ 2MeCN ” [Ag ( CSC) ](BF ) Æ 2MeCN
2
2 Me
2
4 2
NMR (100 MHz, d -DMSO, d): 180.6 ( C ), 150.5 (furC2,5),
C H Ag B F N S , M = 1016.2. Triclinic, space group
32 38 2 2 8 10 2
6
im
2
ꢀ
1
23.2 and 122.2 ( C4,5), 110.4 (furC3,4), 47.1 (CH ), 37.8 (N-
P1, Z = 1 (dimeric f.u.), a = 10.562(2), b = 10.833(2),
im
2
˚
Me).
c = 11.160(2) A, a = 114.459(3), b = 116.135(3), c =
3
ꢁ3
˚
9
4.572(3)ꢁ, V = 988 A . D = 1.707 g cm . 2hmax = 76ꢁ,
c
0
ꢁ1
4.4.6. [Ag2(MeCSC) ](BF ) (14) ( CSC = C,C -2,5-
bis[(3-methylimidazolin-2-yliden-1-yl)methyl]thiophene)
lMo = 1.17 mm
;
specimen:
0.25 · 0.13 · 0.10 mm,
2
4 2
Me
ꢀT ꢁmin/max = 0.90. N = 20238, N = 10137 (R = 0.026),
t int
Compound 10 (0.30 g, 0.46 mmol) was suspended in
N = 7955; R = 0.032, R = 0.033. CCDC No. 239231.
o w
MeCN (30 mL) and AgBF (0.096 g, 0.49 mmol) added.
Variata: The fluorine atoms of the anion were modeled as
disordered over two sets of sites, occupancies refining to
0.872(3) and complement. All (x, y, z, Uiso)H were refined
throughout.
4
The resulting suspension was stirred at 40 ꢁC for 1 h, then
filtered to remove AgBr. The solvent was removed in vacuo
giving 14 (0.16 g, 74%) as an off-white powder. X-ray dif-
fraction quality crystals were grown by slowly cooling a
warm MeCN solution of 14. MS (LSIMS): m/z 847.1
Acknowledgements
+
+
1
[
(
M ꢁ BF ] , 379.0 and 381.0 [M/2 ꢁ BF ] . H NMR
4
4
400 MHz, d -DMSO, d): 7.55 and 7.44 (d · 2,
J = 1.6 Hz, each 4H, imC4,5-H), 7.06 (s, 4H,
.49 (s, 8H, CH ), 3.70 (s, 12H, N-Me). C NMR
2
6
We thank the Australian Research Council, National
Science Foundation and the Louisiana Board of Regents
for financial support and the University of Tasmania for
providing a Tasmania Postgraduate Scholarship for
D.J.N. We thank the staff of the Central Science Labora-
tory, University of Tasmania for valuable assistance and
the use of instruments.
C3,4-H),
thio
3
1
5
(
100 MHz, d -DMSO, d): 180.1 ( C ), 140.5 (thioC2,5),
6 im 2
1
27.1 (thioC3,4), 123.4 and 122.0 ( C ), 49.0 (CH ), 38.2
im 4,5 2
(
N-Me).
4
.5. Structure determination
Appendix A. Supplementary data
Full spheres of ꢀlow-temperatureꢁ CCD area-detector
diffractometer data were measured (Bruker AXS instru-
Data files in the .cif format for compounds 13 and
4, preparation and characterisation data for the N- Bu
ment, x-scans; monochromatic Mo Ka radiation,
t
1
˚
k = 0.7107 A; T ca. 153 K), yielding N
reflections,
3
t(otal)
substituted pyridine-functionalised bis-imidazolium salt
CNC)(HBr) , and procedure for the aryl amination
these merging to N unique (Rint cited) after ꢀempiricalꢁ/mul-
tiscan absorption correction (proprietary software), No
with F > 4r(F) being considered ꢀobservedꢁ and used in
the full matrix least squares refinements, refining aniso-
tropic displacement parameter forms for the non-hydrogen
(
tBu
2
reactions. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2005.08.023.
atoms, (x, y, z, U ) being constrained at estimates. Con-
iso H
2
2 ꢁ1
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