Controlling the coordination modes of a new and highly flexible ligand bearing two N-heterocyclic carbene moieties at a bipyridine backbone

Article abstract of DOI:10.1039/b907041a

A new and highly flexible biscarbene ligand with two imidazolin-2-ylidene moieties in 6,6′-position of a 2,2′-bipyridine was prepared and structurally characterised by X-ray analysis. Various silver complexes were prepared from the imidazolium salts. Depe

Full text of DOI:10.1039/b907041a

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N-Heterocyclic Carbenes
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Controlling the coordination modes of a new and highly flexible ligand bearing
two N-heterocyclic carbene moieties at a bipyridine backbone†
Christine Deißler, Frank Rominger and Doris Kunz*
Received 7th April 2009, Accepted 17th June 2009
First published as an Advance Article on the web 22nd July 2009
DOI: 10.1039/b907041a
A new and highly flexible biscarbene ligand with two imidazolin-2-ylidene moieties in 6,6¢-position of a
2,2¢-bipyridine was prepared and structurally characterised by X-ray analysis. Various silver complexes
were prepared from the imidazolium salts. Depending on the counterion, the coordination mode of the
ligand can be mono- or bidentate. Pd complexes are feasible directly from the imidazolium salt using
palladium(II)-acetate or via transmetallation from silver carbene complexes with [PdCl2(CH3CN)2] or
[PdCl2(COD)]. Controlled by the structure of the silver complexes the biscarbenebipyridine ligand is a
di- or tetracoordinating ligand forming mono- or dinuclear complexes. The high flexibility of this
ligand is confirmed by transmetallation from silver to copper, which results in formation of a dinuclear
copper complex with two bridging biscarbene ligands.
Introduction
Multidentate ligands containing N-heterocyclic carbene moieties
are becoming increasingly popular as the electron donor properties
of the ligand can be enhanced and certain geometric arrangements
realised.1 For tetradentate ligands containing NHC moieties very
rigid backbones or macrocyclic systems2 are used, so that the
number of possible conformations is limited to only one or a
few. If such steric restrictions are not imposed, the enhanced
flexibility can lead to a variety of possible conformations, but
still certain preferred conformers are observed.3 Factors that
control formation of different conformers are plenty including
the metal precursor, counterion4, base5 and reaction conditions.6
Bipyridines are among the most common ligands in transition
metal chemistry partly due to their excellent properties in redox
active complexes.
For multidentate NHCs the use of bipyridines is scarce, only a
pincer ligand containing one imidazole moiety7 and an anthracene
based pincer ligand8 are known to date. The use of bipyridine
as a flexible backbone bearing two NHC moieties at the ortho-
positions was not realised so far. This ligand is expected to
show a rich coordination chemistry serving for mononuclear
Fig. 1 Various possible coordination modes of a bisimidazolinyli-
as well as dinuclear complexes in a bidentate as well as in
a tetradentate fashion (Fig. 1). Our aim was to synthesise
various late transition metal complexes with this new ligand
and investigate the factors that control formation of preferred
conformers.
denebipyridine ligand.
Results and discussion
Ligand synthesis
The strategy we used to synthesise the desired biscarbene lig-
and (Scheme 1) starts with an arylamination of 6,6¢-dibromo-
2,2¢-bipyridine (1) with imidazole, followed by alkylation of
bisimidazolylbipyridine 2 with various alkyl halides to give the
imidazolium salts 3–7. The free carbenes 8–10 are then obtained
by deprotonation with base.
For arylamination we tested various palladium and copper
catalysed variations. Palladium catalysed reactions with dppf or
in situ generated NHC ligands gave no or only poor yields of the
Organisch-Chemisches Institut, Ruprecht-Karls Universita¨t Heidelberg,
Im Neuenheimer Feld 270, D-69120, Heidelberg, Germany. E-mail:
Doris.Kunz@oci.uni-heidelberg.de; Fax: +49 622154-4885; Tel: +49 6221
54-8449
† CCDC reference numbers 726854–726864. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b907041a
7152 | Dalton Trans., 2009, 7152–7167
This journal is
The Royal Society of Chemistry 2009
©

spectrum formation of the bisimidazolium salts can be followed
by the characteristic signal of the acidic imidazolium proton
H2¢ at 10.3 ppm, which is independent from the counterion.
Only the signal of the benzyl substituted bisimidazolium chlo-
ride 6 is shifted to low field at 10.7 ppm. In the 13C-NMR
spectrum the characteristic imidazolium signal C2¢ is found for
all bisimidazolium salts between 135.1 and 135.9 ppm, a typical
value for unsaturated imidazolium ions.10 Imidazolium salts with
N-alkyl substituents often have melting points below 100 ◦C
and are therefore considered as Ionic Liquids.11 However, the
bisimidazolium salts 3–7 show very high melting points between
242 ◦C (7) and 299 ◦C (5).
The molecular structures of the bisimidazolium salts 3–6 were
revealed by X-ray crystal structure analyses (see Fig. 2). As it can
be expected, the nitrogen atoms of the bipyridine moiety point
in opposite directions. This can be rationalised by the molecule
avoiding nitrogen lone pair repulsion and minimalising the dipole
moment. An Npyridine-H interaction could be possible with the
imidazolium protons H2¢ or H5¢ depending on the conformation.
Indeed, the molecular structures of compounds 3–6 show a planar
zig-zag like arrangement. While the molecular structures of 3, 5
and 6 show the imidazole H2¢ pointing to the same side as the
Npyridine lone-pair, in the molecular structure of bisimidazolium
salt 4 the imidazolium moieties are rotated by 180◦ around the
C6pyridine-N1¢imidazole axis, so that the H5¢ hydrogen points toward
the Npyridine lone pairs. The molecular structures containing iodide
(5) and tetrafluoroborate counterions (3–4) show no hydrogen
bonds between the acidic H2¢ and the counterion, while in case of
chloride counterions a hydrogen bond is found between chloride
and the imidazolium H2¢ as well as between the chloride and the
hydroxyl group of included ethanol.
Scheme 1 Synthesis of the bipyridine derived bis(NHC) ligands 8–10.
desired product 2 along with some monosubstituted bipyridine.
However, the copper catalysed Ullmann coupling9 provides the
desired product 2 in almost quantitative yield. Subsequent alky-
lation with two equivalents of the highly reactive trialkyloxonium
tetrafluoroborates (Meerwein’s salts) as alkylating reagents in
acetonitrile at temperatures from -35 ◦C to room temperature
leads to the imidazolium salts 3 and 4 with the weakly coordinating
tetrafluoroborate anion in up to 90% yield. Reaction of the bisimi-
dazole 2 with benzyl chloride or methyl iodide in dimethylsulfoxide
◦
at 100 C also proceeds well with good to excellent yields of the
bisimidazolium salts 5 and 6. Upon reaction with octyltosylate in
acetonitrile under reflux only 25% of the product 7 were obtained.
All bisimidazolium salts 3–7 are white solids and almost
insoluble in organic solvents like dichloromethane or tetrahy-
drofuran, but soluble in dimethylsulfoxide. In the 1H-NMR
Synthesis of the free carbenes worked well by deprotonation
of the bisimidazolium salts 3–6 with a 20% excess of potassium
tert-butoxide. The reaction was carried out by adding the base to
a suspension of the bisimidazolium salts in toluene at -35 ◦C and
Fig. 2 Molecular structures of the bisimidazolium salts 3–6 showing 50% probability ellipsoids; hydrogen atoms in 6 except H2¢ as well as the counterions
in 4 (BF4-) and 5 (I-) are omitted for clarity. For selected bond lengths and angles see Table 1.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7152–7167 | 7153
©

◦
˚
Table 1 Selected bond distances (A) and angles ( ) for the imidazolium salts 3–6 and the carbene 8. Atom labelling is defined in Scheme 1
3
4
5
6
8
Bond distances
1st molecule
2nd molecule
N1¢-C2¢
1.318(5)
1.337(5)
1.386(5)
1.344(6)
1.354(6)
1.340(4)
1.320(4)
1.385(4)
1.338(4)
1.377(4)
1.332(4)
1.320(4)
1.382(4)
1.337(4)
1.368(4)
1.333(4)
1.318(4)
1.392(4)
1.349(5)
1.369(4)
1.3427(19)
1.3264(19)
1.3869(19)
1.347(2)
1.3799(17)/1.3763(18)
1.3541(18)/1.3574(18)
1.3954(17)/1.3911(17)
1.3388(19)/1.341(2)
1.3898(18)/1.3907(19)
C2¢-N3¢
N1¢-C5¢
C5¢-C4¢
C4¢-N3¢
1.379(2)
Bond angles
N1¢-C2¢-N3¢
N1¢-C6-N1
N1-C2-C2#
108.5(4)
113.6(3)
116.3(4)
109.0(3)
114.0(3)
115.9(3)
108.5(3)
113.6(3)
115.7(3)
108.6(3)
113.7(3)
115.6(3)
107.87(13)
113.98(12)
115.85(15)
101.41(11)/101.46(12)
115.25(11)/115.44(11)
116.00(11)/115.95(11)
stirring the reaction mixture for 6 hours at room temperature. As
the product is soluble in toluene it can be easily separated from the
inorganic salts by filtration providing the biscarbenes as an off-
white (8) and a pale yellow (9) solid in moderate to good yields. The
free biscarbenes do not show any decomposition during weeks, if
stored under an inert atmosphere and they decompose only above
202 ◦C (8) and 265 ◦C (9). The same procedure was also used
for generating biscarbene 10 in situ as an NMR experiment in
THF-d8. Stronger bases like lithium diisopropylamide and methyl
lithium turned out to be less suitable, as an excess of base led to
rapid decomposition of the carbenes in solution. Formation of the
carbenes is indicated in the 13C NMR spectrum by a characteristic
low field shift of the carbene C2¢ signals at 216.9 (8), 217.4 (9)
structure analysis. Fig. 4 shows one of the rare examples of the
molecular structure of a biscarbene.12
Biscarbene 8 adopts a planar zig-zag conformation with the
pyridine rings rotated around the C2-C2# axis by 180◦ as it was
already observed for the imidazolium salts 3–6. Compared to the
structure of its imidazolium salt 3 the imidazolinylidene rings of 8
are rotated by 180 ◦ around the N1¢-C6 bond which is most likely
due to a lone pair repulsion between the carbene and the nitrogen
lone pair. The angle N1¢-C2¢-N3¢ measures 101.4◦ (mean), a value
that is expected on basis of the chemical shift–angle correlation
we reported earlier.13
Carbene 8 is also identified by mass spectrometry (HR-EI+)
showing the molecule peak at m/z = 344.1753 (calcd. 344.17409).
Fragmentation occurs on both ethyl groups as well as the imidazole
rings.
1
and 217.5 ppm (10). Additional proof is provided by 2D H,13C
multiple bond correlation spectroscopy (Fig. 3), showing cross
peaks between the carbene signal and the proton signals of the
CH2 (8) and CH3 (9) group as well as between the H5 signal of
the pyridine ring in 8. The chemical shift for the carbene carbon
signal is typical for imidazolinylidenes showing the carbene signal
between 210 and 220 ppm.10
Synthesis of carbene complexes with basic metal salts
Attempts to react the isolated carbene 8 with the precursors
[PdCl2(COD)] and [Pd(m-Cl)(C3H5)]2 in THF-d8 did not lead to the
desired complexes, although the free carbene gets consumed. We
therefore decided to react the imidazolium salts with basic metal
By slow diffusion of pentane into a solution of carbene 8 in
tetrahydrofuran we were able to obtain crystals suitable for X-ray
Fig. 3 1H,13C HMBC spectrum of carbene 8 in THF-d8 (#), (t-BuOH (+)).
7154 | Dalton Trans., 2009, 7152–7167 This journal is The Royal Society of Chemistry 2009
©

intermediate (★) with a characteristic peak at 10.20 ppm (probably
a monocarbenemonoimidazolium salt). Using the less basic silver
carbonate as a starting material slows down the reaction rate and
increases the reaction time to 1.5 days for full conversion. Identical
spectra were obtained by synthesising the silver carbene complex
11 on a preparative scale in acetonitrile in 84% yield. The ele-
mental analysis reveals the constitution [Ag2(8)(BF4)2]. However
more information is necessary to elucidate the structure of this
complex.
The 13C NMR spectrum confirms formation of a symmetric
silver NHC complex with a single signal at 180.9 ppm which
is a typical value for silver imidazolinylidene complexes,10,16,17
however 107/109Ag-13C coupling is not observed. The 109Ag NMR
spectrum shows only one singlet at 270.1 ppm. This value is lower
than those observed for NHC complexes in the few 109Ag-NMR
spectra available for silver NHC complexes (597–727 ppm).16
Free AgBF4 can be excluded as it shows a 109Ag NMR chemical
shift of 173.0 ppm. Therefore both silver atoms are magnetically
equivalent and bound to the carbene carbon or more likely
show a fast exchange.15a The high resolution mass spectrometry
shows a cationic fragment containing one ligand and only one
silver atom using fast atom bombardment as well as electrospray
as ionisation methods. Silver carbene complexes are known to
aggregate by formation of d10-d10 Ag-Ag interactions,16,18 therefore
the structure of complex 11 can be more complicated and still
remains unresolved. The complex is best described as the overall
formula [Ag2(8)(BF4)2]n with n = 1, 2 or even higher (Scheme 2).
Reacting the imidazolium salt 4 with silver(I)-oxide in acetoni-
trile at 90 ◦C for two days leads to formation of the silver complex
12 (Scheme 2) in which one silver cation is coordinated by one
ligand according to the mass spectrum (ESI+). The signals of the
aromatic protons in the 1H NMR spectrum are identical to those
of compound 11. In the 13C NMR spectrum the carbene signal is
found at 183.5 ppm which is also similar to that of 11; 107/109Ag-
13C coupling was not found in this case either. The 109Ag NMR
spectrum of 12 could not be obtained due to its poor solubility in
DMSO-d6. However, we were able to obtain light yellow needles
Fig. 4 Molecular structure of the biscarbene 8 showing 50% probability
ellipsoids. For selected bond lengths and angles see Table 1.
salts to obtain the metal carbene complexes of silver, palladium
and copper. It is well known that palladium(II)-acetate14 and
silver(I)-oxide15,16 are suitable metal salts for the synthesis of the
corresponding carbene complexes. The silver complexes could
then be used as carbene transfer reagents.15
We monitored the reaction of imidazolium salt 3 with 1.3 equiv
of silver(I)-oxide in dimethylsulfoxide-d6 at 100 ◦C by NMR
spectroscopy. After 2 h formation of a new signal set and of
water (3.33 ppm) is observed (Fig. 5). During the course of the
reaction, the signal intensities of the new complex 11 increase,
while the signals of the starting material diminish. After 24 h the
signals of the starting material are vanished as well as those of an
Fig. 5 Monitoring the reaction of imidazolium salt 3 with Ag2O in DMSO-d6 by 1H NMR spectroscopy.
The Royal Society of Chemistry 2009 Dalton Trans., 2009, 7152–7167 | 7155
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Scheme 2 Syntheses of silver biscarbene complexes 11–14 from the bisimidazolium salts 3–6.
suitable for X-ray structure analysis by slow evaporation of a
coordination of the biscarbene ligand (Fig. 7). More interesting
however is the unusual structure of the polysilveriodide anion
that forms a waffle iron-like ribbon consisting of tetrahedral
coordinated silver atoms within one plane and the iodide anions
oriented above and below this plane. The cation and the complex
anion show weak Ag-I interactions. Due to the limited quality
of the crystal this is only proof for the connectivity, discussing
the bond lengths is not appropriate. Formation of oligomeric
or polymeric silver(I)-iodide chains in DMSO is a well known
phenomenon.19 This explains also the even decreased solubility of
compound 13 compared to its tetrafluoroborate 12 analogue.
saturated solution of 12 in acetonitrile.
The molecular structure of 12 (Fig. 6) shows an almost planar
mononuclear complex with the silver atom linearly coordinated
by the two imidazolinylidene moieties (C2¢-Ag-C2¢# = 171.3(3)◦).
˚
The mean silver-carbene distance is 2.14 A, which is typical for
Ag(NHC) complexes. Compared with the imidazolium salt, the
N1¢-C2¢-N3¢ angle at the carbene is more acute by about 5◦ (104.0◦
(mean)), but more opened compared to free imidazolinylidene 8
(101.4◦ (mean)). The tetrafluoroborate counterion does not show
any close contacts with the cationic complex.
Fig. 7 Molecular structure of the silver biscarbene complex 13 showing
the cation (left) and a fragment of the polysilveriodide anion [(Ag2I3)-]n
(right); hydrogen atoms are omitted for clarity. Due to the limited quality
of the crystal only the connectivities can be discussed.
Fig. 6 Molecular structure of the silver biscarbene complex 12 showing
50% probability ellipsoids; hydrogen atoms are omitted for clarity. For
selected bond lengths and angles see Table 2.
Starting from imidazolium iodide 5, the similar silver complex
13 was obtained after prolonged heating with silver(I)-oxide at
100 ◦C in DMSO (Scheme 2). The product is even less soluble
in DMSO than compound 12, but this is somehow expected as
imidazolium iodides are in general less soluble in organic solvents
than imidazolium tetrafluoroborates. At room temperature the
spectrum of 13 shows only broad peaks. However heating up to
100 ◦C results in a sharpening of the signals and an enhanced
resolution. The signals in the 13C NMR spectrum are almost
identical to those of complex 12, therefore structural similarities
are expected. An X-ray structure analysis of compound 13
confirms the mononuclear cationic complex with a bidentate
Reaction of the chloride containing imidazolium salt 6 with
silver(I) oxide in DMSO is performed at 120 ◦C. The product
complex 14 can be isolated in 80% yield by recrystallisation from
DMSO.
The H NMR spectrum at 22 ◦C shows only the signals of
1
the benzyl and the imidazolinylidene moieties. The signals of
the bipyridine protons are extremely broadened (7.0 to 8.8 ppm)
and can only be recognized by integration of the baseline in that
◦
region. Heating up to 67 C leads to a sharpening of the signals
with the bipyridine signals being still broad. At this tempera-
ture the carbene carbon signal can be detected by a multiple
bond correlation experiment showing a cross peak between the
7156 | Dalton Trans., 2009, 7152–7167
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The Royal Society of Chemistry 2009
©

◦
˚
Table 2 Selected bond distances (A) and angles ( ) for the silver, palladium and copper carbene complexes 12, 14–15 and 17–18. Atom labelling is
defined in Scheme 1
12
14
15
17
18
Bond distances
1st molecule
2nd molecule
N1¢-C2¢/N1¢#-C2¢#
C2¢-N3¢/C2¢#-N3¢#
N1¢-C5¢/N1¢#-C5¢#
C5¢-C4¢/C5¢#-C4¢#
C4¢-N3¢/C4¢#-N3¢#
C2¢-M/C2¢#-M
N1-M/N1#-M(#)
M-Cltrans/M-Clcis
Pd-S
1.367(8)/1.388(8)
1.321(8)/1.348(8)
1.375(9)/1.392(8)
1.357(19) 1.388(2)/1.391(2)
1.338(18) 1.334(3)/1.332(2)
1.356(3)
1.340(3)
1.385(3)
1.342(4)
1.388(4)
1.962(3)
—
1.372(7)/1.371(7)
1.368(7)/1.373(7)
1.340 (8)/1.340(8) 1.336(8)/1.341(7)
1.390(7)/1.395(7) 1.382(8)/1.393(7)
1.318(10)/1.325(9) 1.327(11)/1.311(9)
1.391(8)/1.387(8)
1.932(6)/1.922(6)
2.246(5)/2.306(5)
1.37(2)
1.386(3)/1.385(3)
1.335(3)/1.337(3)
1.396(3)/1.392(2)
1.336(11)/1.339(10) 1.33(2)
1.397(9)/1.386(9)
2.154(6)/2.124(6)
—/—
—/—
—
1.38(2)
1.388(9)/1.391(8)
1.916(6)/1.923(5)
2.314(4)/2.325(4)
—/—
2.079(15) 2.044(2)/2.0458(18)
1.9768(16)/1.9782(16)
2.307(4) —/—
—
2.3518(8)/2.3212(7) —/—
2.2229(7)
—
—
—
—
Bond angles
N1¢-C2¢-N3¢/N1¢#-C2¢#-
104.7(5)/103.4(5)
113.3(5)/113.3(5)
105.7(13) 104.00(17)/103.41(15) 105.1(2)
116.8(13) 111.23(17)/111.16(16) 114.8(2)
116.4(17) 112.87(17)/112.38(18) 115.6(3)
103.3(5)/103.4(5)
113.7(5)/113.7(5)
103.9(5)/103.7(5)
113.9(5)/114.8(5)
N3¢#
N1¢-C6-N1/N1¢#-C6¢#-
N1#
N1-C2-C2#/N1#-C2#-C2 113.7(5)/112.7(6)
115.0(5)/115.5(5)
156.7(4)/158.2(4)
78.3(2)
77.7(2)
117.1(2)/110.4(2)
116.0(5)/114.8(5)
157.3(4)/160.6(3)
77.6(2)
76.9(2)
122.1(2)/124.3(2)
C2¢-M-C2¢#/C2¢-M#-C2¢# 171.3(3)
—
—
—
—
121.54(7)
79.56(8)
79.63(7)
79.33(7)
—
—
—
—
C2¢-M-N1
—
—
—
C2¢#-M#-N1#
N1-M-N1# or N1-M-
N12/N1#-M#-N12#
methylene protons and the carbene carbon at 5.48/184.5 ppm. In
mass spectrometry, the electrospray as well as the laser induced
field desorption ionisation method lead only to detection of a
cationic fragment bearing one silver atom and the carbene ligand
(m/z = 577.2). Single crystals suitable for X-ray structure analysis
were obtained by recrystallisation from DMSO. The molecular
structure of complex 14 exhibits a dinuclear complex with one
carbene ligand (Fig. 8). Each silver atom is coordinated by one
carbene moiety and one chloro ligand in a linear fashion. The
bipyridine moiety is rotated by 180 ◦C, so that both NHC moieties
are oriented in opposite directions. The Ag-C2¢ bond length of
˚
˚
2.079(15) A is shorter than in complex 12 (Ag-C2¢ = 2.154(6) A,
˚
Ag-C2¢# = 2.124(6) A) in which the silver atom is coordinated by
two carbene atoms.
The various silver carbene complexes 11–14 demonstrate the
flexibility of the biscarbene ligand. Imidazolium salt 4 with the
weakly-coordinating tetrafluoroborate anion leads to a mononu-
clear complex with both carbene moieties coordinated to silver.
Imidazolium salt 6 containing the well coordinating chloride
anion leads to the dinuclear silver complex 14 with chloride ions
coordinated to silver. Iodide takes in a special role: it coordinates
very well with silver forming a polysilveriodide anion that behaves
as a weakly coordinating counterion and therefore leads to a
mononuclear silver complex 13 with both NHCs coordinated to
the silver atom.
Synthesis of palladium complexes
To synthesise palladium complexes with the new biscarbenebipyri-
dine ligand 8 we first chose a direct metallation of bisimidazolium
salt 3 with basic palladium(II)-acetate (Scheme 3). Monitoring
the reaction of 3 and palladium(II)-acetate in DMSO-d6 at 80 ◦C
shows formation of a new signal set along with some acetic acid.
Fig. 8 Molecular structure of the silver biscarbene complex 14 showing
50% probability ellipsoids; hydrogen atoms are omitted for clarity. For
selected bond lengths and angles see Table 2.
Scheme 3 Synthesis of Pd complexes 15 and 16 bearing the biscarbene ligands 8 and 9.
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However, despite reaction for several days and addition of
a second equivalent of palladium(II)-acetate full conversion of
the starting material was not achieved. As Ag-NHC bonds are
quite weak20 we tried a transmetallation from silver to palladium
according to Lin et al.15 The transmetallation of silver complex
8 with [PdCl2(COD)] or [PdCl2(CH3CN)2] proceeds already at
room temperature in acetonitrile with fast formation of a gray
R
precipitate that is removed by filtration over Celiteꢀ. Addition of
tetrahydrofuran and pentane to the filtrate leads to crystallisation
of the product complex 15 as colourless crystals in a 72% isolated
yield. The 1H NMR spectrum shows formation of one signal set of
a symmetric species. The signals shifted to low field in comparison
to silver complex 8. In the 13C NMR spectrum formation of the
carbene complex 15 is indicated by a carbene signal at 161.0 ppm,
which is a typical value for imidazolinylidene palladium complexes
and is shifted more than 20 ppm highfield compared to the signal of
the silver carbene complex 8. The mass spectra confirm formation
of the mononuclear complex [Pd(Et2NHC2Bipy)](BF4)2 (15) with
peaks at 537.0892 (HR-FAB+) and 537.08113 (HR-ESI+) (Calcd.
+
[M - BF4 ] m/z = 537.08080). Single crystals suitable for X-ray
analysis were obtained by slow concentration of a saturated
solution of 15 in acetonitrile. The molecular structure of the
dicationic complex shows a distorted square planar coordinated
palladium atom (Fig. 9a). Interestingly, the dication complex has
both ethyl substituents oriented to the same side. Obviously steric
hindrance is not pronounced.
Fig. 9 (a) Molecular structure of the palladium biscarbene complex
15 showing 50% probability ellipsoids; hydrogen atoms are omitted for
clarity. For selected bond lengths and angles see Table 2. (b) Overlay of the
molecular structures of silver complex 12 (white) and palladium complex
15 (black).
˚
The palladium carbene bond length (2.045 A) is typical
for NHC-palladium(II) complexes. The mean Pd-N distance
˚
(1.978 A) is rather unusually short for bipyridine complexes (1.98–
21
˚
2.12 A). The N1-Pd-N1# as well as the N1-Pd-C2¢ angle are
about 79◦ while the C2¢-Pd-C2¢# angle measures 122◦ and thus is
clearly opened up from the ideal 90◦. Fig. 9b shows the overlay
of the molecular structures of the silver complex 12 and the Pd
complex 15: The C2¢-M-C2¢# angle is changed from 171.3(3) (12)
to 121.54(7)◦ (15). The N1¢-C6-N1 angle becomes more acute,
so that the carbene distance C2¢-C2¢# gets significantly shorter
In mass spectrometry the [M - BF4]+ peak is detected at m/z =
509.2 (ESI+).
A change of the bisimidazolium salt counterion leads to a
change in the hapticity of the biscarbene ligand in the silver
carbene complexes. This observation is also to be tested for
transmetallation reactions of various silver complexes. We there-
fore reacted a suspension of the dinuclear silver complex 14
with [PdCl2(CH3CN)2] at room temperature (Scheme 4). The
transmetallation reaction is accompanied by formation of a grey
solid. Because of the low solubility of the product 17, the NMR
analysis is carried out in DMSO-d6, however, the signals are
still broad multiplets between 5.89 and 8.41 ppm. From this
saturated solution in DMSO-d6 big yellow crystals suitable for
X-ray structure analysis are formed after four weeks.
˚
(3.569(3) (15), 4.266(3) A (12)). This demonstrates nicely the high
flexibility of our new biscarbene ligand.
Under the same conditions the Ag complex 12 bearing N-methyl
substituents was reacted with [PdCl2(CH3CN)2] and complex 16
was isolated (Scheme 3). The compound is less soluble than
complex 15 and therefore the NMR spectra were recorded in
DMSO-d6. They show the same characteristic peaks as for
complex 15, especially the carbon carbene signal at 162.5 ppm.
Scheme 4 Synthesis of the dinuclear Pd biscarbene complex 17.
7158 | Dalton Trans., 2009, 7152–7167 This journal is
The Royal Society of Chemistry 2009
©

The molecular structure of 17 is the first example of a
[Pd(NHC)(DMSO)] complex (Fig. 10). The dinuclear complex
shows the two carbene moieties coordinated to two palladium
dichloride fragments. Instead of a coordination of the bipyridine
nitrogen, the fourth coordination site is occupied by DMSO
that is coordinated via sulfur. The palladium carbene distance
Ag-complex:Cu = 1:2 ratio. In the case of a 1:1 ratio only 50% of
the silver complex are consumed.
The use of CuI instead of CuCl leads to the identical copper
complex. The 1H NMR spectrum of complex 18 is identical
to that obtained by synthesis from the imidazolium salt 3 and
copper(I)-oxide. Formation of carbene complex 18 is indicated by
the signal of the carbene carbon at 185.0 ppm in the 13C NMR
spectrum. Mass spectrometry (HR-ESI) reveals a signal (53%) at
m/z = 901.21149 that can be attributed to a dinuclear complex
˚
˚
(1.962(3) A) is smaller than in the Ag complex 14 (2.079(15) A).
+
with two carbene ligands [Cu2(8)2]BF4 (calc. m/z = 901.21215)
and a signal (100%) at m/z = 407.10640 that is consistent with
the fragment [Cu2(8)]+ (calc. m/z = 407.10400). Elucidation of
the molecular structure of complex 18 was finally obtained by
X-ray analysis. Single crystals were obtained by slow diffusion of
diethylether into a saturated solution of 18 in acetonitrile. The
molecular structure (Fig. 11) shows a dicationic copper complex
consisting of two ligands and two copper atoms, each coordinated
via one carbene and one pyridine moiety of both ligands forming
a double helical arrangement. The copper atoms are coordinated
distorted tetrahedral showing copper-carbene distances of Cu1-
Fig. 10 Molecular structure of the dinuclear Pd biscarbene complex 17
showing 50% probability ellipsoids; hydrogen atoms are omitted for clarity.
For selected bond lengths and angles see Table 2.
˚
C2¢ = 1.932(6) and Cu2-C2¢# = 1.922(6) A and copper-nitrogen
˚
distances of Cu1-N1 = 2.246(5) and Cu2-N1# = 2.306(5) A. The
torsion angle of the bipyridine unit is 51.9◦. The unit cell contains
a second independent molecule that shows similar bond lengths,
however the bipyridine torsion angle of 37.4◦ is smaller by almost
Although such complexes had been postulated and observed by
NMR spectroscopy,22 the structural evidence was still missing.
We could show that the best way to synthesise palladium carbene
complexes bearing our new biscarbene ligand is via transmet-
allation from its silver complex. With the weak coordinating
tetrafluoroborate counterion the reaction leads to mononuclear
complex 15 coordinated by the ligand in a tetradentate fashion.
With chloride as a counterion the Pd-chloride bonds of the
precursor stay intact and a dinuclear complex 17 with a bridging
ligand in a monodentate fashion is formed.
Synthesis of copper complexes15c
In analogy to the reactivity with Ag2O we reacted the imidazolium
salt 3 with copper(I)-oxide in acetonitrile-d3 at 110 ◦C in a sealed
NMR tube (Scheme 5). After 16 h the spectrum shows formation
of one new signal set along with some H2O, after 7 days at 110 ◦C
about 33% of the new complex has formed.
To avoid too long reaction times we tried the transmetallation
route. Suspension of silver complex 11 with two equivalents of
CuCl in acetonitrile at -35 ◦C led immediately to formation of a
voluminous grey precipitate and a red solution. After filtration the
orange-red filtrate was concentrated and the product precipitated
by addition of pentane. After filtration 82% of product 18
were obtained as a copper-red solid. It is important to use the
Fig. 11 View of the molecular structure of the dinuclear copper(I)
biscarbene complex 18; for clarity the two bridging ligands are drawn black
and white and hydrogen atoms are omitted. For selected bond lengths and
angles see Table 2.
Scheme 5 Synthesis of the dinuclear copper complex 18 with two bridging biscarbene ligands.
The Royal Society of Chemistry 2009 Dalton Trans., 2009, 7152–7167 | 7159
This journal is
©

15◦ which leads to a significant shortening of the Cu-Cu distance
suspension. Upon cooling to room temperature a greenish solid
precipitated. The solvent was removed under reduced pressure by
slow distillation at 80 C. Subsequent removal of all volatiles in
st
nd
˚
˚
(4.106(3) A (1 molecule), 3.706(3) A (2 molecule)).
◦
vacuo gave a greenish solid. The purification of the crude product
was achieved by repeated extraction with 500 mL of boiling
ethanol. The precipitated solid was subsequently recrystallised
from ethanol. The solid was filtered and dried in vacuo to yield
Conclusions
bipy
We showed that the new R2NHC2 ligand is highly flexible and
can be prepared easily. Upon addition of base it forms thermally
stable biscarbenes. Formation of palladium and copper complexes
with this new ligand is however best achieved via transmetallation
of the respective silver complexes. The silver complexes are
obtained by reaction of the imidazolium salts with silver(I)-
oxide. The nature of the imidazolium counterion determines
the configuration of the silver complex. Weakly coordinating
anions lead to a mononuclear biscarbene complex while the
strongly coordinating chloride anion prefers dinuclear complexes.
As iodide forms a polysilveriodide anion, it acts as a weakly
coordinating anion. This principle is kept in the transmetallation
to palladium and copper. With the tetrafluoroborate anion a
◦
3.36 g (97%) of the product as a white fluffy solid. M.p. 254 C
1
(dec.); H NMR (300 MHz, DMSO-d6): d = 7.17 (s, 2H, H-4¢),
3
7.91 (d, JHH = 8.0 Hz, 2H, H-5), 8.15 (s br, 2H, H-5¢), 8.19 (t,
3JHH = 8.0 Hz, 2H, H-4), 8.49 (d, 3JHH = 8.0 Hz, 2H, H-3), 8.76
1
(s, 2H, H-2¢); 13C{ H} NMR (75 MHz, DMSO-d6): d = 113.4
(C-5), 116.7 (C-5¢), 119.0 (C-3), 130.2 (C-4¢), 135.3 (C-2¢), 141.0
(C-4), 148.3 (C-6), 153.3 (C-2); IR (KBr): n = 3106 (w), 1590 (m),
1573 (s), 1504 (s), 1476 (s), 1449 (s), 1303 (s), 1271 (m), 1108 (w),
1053 (s), 744 (s) cm-1; MS (EI)+: m/z (%) 288.1 [M]+ (100), 256.1
[M - C3H3N2]+ (21), 144.1 [M - C8H6N3]+ (6), 68.0 [C3H3N2]+
(62); elemental analysis calcd (%) for C16H12N6: C 66.66, H 4.20,
N 29.15; found: C 66.38, H 4.21, N 29.06.
4
mononuclear Pd complex with a h coordination of the ligand is
obtained, while transmetallation from the dinuclear silver carbene
complex leads to a dinuclear Pd complex. Transmetallation of the
tetrafluoroborate silver complex 8 with copper(I)-chloride leads,
as expected, to a 1:1 ratio of ligand and metal, however a dinuclear
complex with two bridging ligands is formed.
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-ethyl-1H-imida-
zolium) bistetrafluoroborate [H2(Et2NHC2bipy)](BF4)2 (3). Under
an inert atmosphere a suspension of 6,6¢-di-1H-imidazol-1-yl-
2,2¢-bipyridine (2) (500 mg, 1.73 mmol) in 50 mL acetonitrile
was cooled to -35 ◦C and triethyloxonium tetrafluoroborate
(660 mg, 3.47 mmol) was added. The mixture was stirred at
room temperature over night. The resulting white solid was
filtered off and evaporation of the filtrate under reduced pressure
led to further precipitation of the product 3. The entire solid
was collected, washed with acetone and dried in vacuo over
night. Further purification was achieved by recrystallisation from
With the results presented above, it should now be possible to
predict the ligand:metal ratio of transition metal complex with the
bipy
R2NHC2 ligand or even the conformation.
Experimental
General methods
ethanol to yield 570 mg (64%) of the product as a white solid. M.p.
◦
1
3
266 C; H NMR (300 MHz, DMSO-d6): d = 1.55 (t, JHH
=
Unless otherwise noted all reactions were carried out under an
atmosphere of dry argon using standard Schlenk techniques or
were performed in a nitrogen filled glove box. All solvents were
dried according to standard procedures and saturated with argon
prior to use. Chemicals used were obtained from commercial
suppliers and used without further purification. 6,6¢-Dibromo-
2,2¢-bipyridine was synthesised according to literature.23 1H, 13C
NMR and 109Ag NMR spectra were recorded using a Bruker ARX
7.4 Hz, 6H, CH3), 4.36 (q, 3JHH = 7.4 Hz, 4H, CH2), 8.13–8.16 (m,
2H, H-4¢), 8.15 (d, 3JHH = 8.1 Hz, 2H, H-5), 8.45 (t, 3JHH = 8.0 Hz,
3
2H, H-4), 8.76–8.78 (m, 2H, H-5¢), 8.83 (d, JHH = 8.0 Hz, 2H,
H-3), 10.29 (s, 2H, H-2¢); 13C{ H} NMR (75 MHz, DMSO-d6):
1
d = 15.0 (CH3), 45.1 (CH2), 115.0 (C-5), 119.4 (C-5¢), 121.9 (C-3),
123.3 (C-4¢), 135.1 (C-2¢), 142.0 (C-4), 146.2 (C-6), 153.0 (C-2);
IR (KBr): n = 3123 (m), 3083 (s), 2986 (w), 1604 (m), 1566 (s),
1538 (s), 1448 (s), 1223 (s), 1084 (vs), 807 (m) cm-1; HR-MS (ESI+)
calcd for C20H22N6BF4: m/z 433.19296; found m/z (%) 433.19282
[M - BF4]+ (100); calcd for C18H17N6: m/z 317.15092; found m/z
(%) 317.15096 [M - 2BF4 - C2H5]+ (50); calcd for C16H13N6: m/z
289.11962; found m/z (%) 289.11971 [M - 2BF4 - C4H9]+ (5).
Elemental analysis calcd for C20H22N6B2F8: C 46.19, H 4.26, N
16.16; found; C 46.06, H 4.30, N 16.17. Crystals suitable for X-ray
analysis were obtained from a concentrated ethanol solution.
250, DRX 300, DRX 500 or DRX 600 spectrometer. 1H and 13
C
chemical shifts are reported in ppm and calibrated to TMS on the
basis of the solvent as an internal standard (2.49 ppm DMSO-
d6, 2.13 ppm toluene-d8, 1.73 ppm THF-d8). Assignments of 13C
NMR spectra were made with the aid of 2D correlation spectra.
Unless otherwise noted, all NMR spectra were acquired at room
temperature. Mass spectra were recorded on a Jeol JMS-700 with
NBA (nitrobenzylalcohol) as matrix or a Bruker ApexQe hybrid
9.4 T FT-ICR instrument. Infrared spectra were recorded using
a Bruker Equinox 55 FT-IR-spectrometer. Melting points were
determined with aBu¨chiMeltingPoint B 540apparatus. Elemental
analyses were performed by Mikroanalytisches Laboratorium der
Chemischen Institute der Universita¨t Heidelberg.
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-methyl-1H-
imidazolium) bistetrafluoroborate [H2(Me2NHC2bipy)](BF4)2 (4).
Under an inert atmosphere a suspension of 6,6¢-di-1H-imidazol-
1-yl-2,2¢-bipyridine (2) (2.00 g, 6.94 mmol) in 70 mL acetonitrile
was cooled to -35 ◦C and trimethyloxonium tetrafluoroborate
(2.05 g, 13.9 mmol) were added. The mixture was stirred at room
temperature for 24 hours. The resulting white solid was filtered off.
Slow evaporation of the filtrate solvent under reduced pressure
led to further precipitation of the product 4. The combined
residue was collected, washed with acetone and dried in vacuo
over night. Further purification was achieved by recrystallisation
Synthesis of 6,6¢-di-1H-imidazol-1-yl-2,2¢-bipyridine (2)1.
A
Schlenk tube was charged under nitrogen atmosphere with 6,6¢-
dibromo-2,2¢-bipyridine (1) (3.76 g, 12.0 mmol), dried imidazole
(2.03 g, 30.0 mmol), potassium carbonate (4.14 g, 30.0 mmol),
copper(II) oxide (95.3 mg, 1.20 mmol) and 15 mL abs. DMSO. The
suspension was stirred for 8 hours at 150 ◦C to give an off-white
7160 | Dalton Trans., 2009, 7152–7167
This journal is
The Royal Society of Chemistry 2009
©

from acetonitrile/ethanol (1:1) to obtain 3.28 g (95%) of the
product as a white solid. M.p. 265 ◦C (dec.); 1H NMR (300 MHz,
DMSO-d6): d = 4.02 (s, 6H, CH3), 8.01–8.04 (m, 2H, H-4¢), 8.14
135.6 (C-2¢), 142.0 (C-4), 146.2 (C-6), 152.9 (C-2); IR (KBr): n =
3027 (m), 2972 (m), 1602 (m), 1565 (m), 1530 (s), 1446 (s), 1222 (s),
1116 (m), 806 (s), 769 (m), 724 (m), 710 (m) cm-1; HR-MS (ESI+)
calcd for C23H19N6: m/z 379.16657; found m/z (%) 379.16672 [M -
Cl - BnCl]+ (100); calcd for C30H26N6Cl: m/z 505.19020; found
m/z (%) 505.19038 [M - Cl]+ (33); elemental analysis calcd for
C30H26N6Cl2*H2O: C 64.40, H 5.04, N 15.02; found: C 64.55, H
4.92, N 15.33. Crystals suitable for X-ray analysis were obtained
by recrystallisation of a DMSO solution.
3
3
(d, JHH = 7.9 Hz, 2H, H-5), 8.45 (t, JHH = 7.9 Hz, 2H, H-4),
8.70–8.73 (m, 2H, H-5¢), 8.82 (d, 3JHH = 7.8 Hz, 2H, H-3), 10.28
◦
(s, 2H, H-2¢); 13C{ H} NMR (75.47 MHz, DMSO-d6, 25 C): d =
36.4 (CH3), 114.9 (C-5), 119.1 (C-5¢), 121.9 (C-3), 124.9 (C-4¢),
135.9 (C-2¢), 142.1 (C-4), 146.2 (C-6), 152.9 (C-2); IR (KBr): n =
3128 (m), 3077 (s), 2965 (w), 1602 (m), 1565 (s), 1539 (s), 1447
(s), 1231 (s), 1084 (vs br), 806 (s) cm-1; HR-MS (ESI+) calcd for
C18H18N6BF4: m/z 405.162211; found m/z 405.16170 [M - BF4]+;
elemental analysis calcd for C18H18N6B2F8: C 43.94, H 3.69, N
17.08; found C 43.73, H 3.70, N 17.04. Crystals suitable for X-ray
analysis were obtained from a concentrated ethanol/acetonitrile
solution.
1
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-octyl-1H-imida-
zolium) ditoluenesulfonate [H2(Oct2NHC2bipy)](OTs)2 (7).
A
50 mL round-bottom flask was charged with 6,6¢-di-1H-imidazol-
1-yl-2,2¢-bipyridine (2) (207 mg, 0.720 mmol), octyl toluenesul-
fonate (614 mg, 2.16 mmol) and 25 mL of abs. acetonitrile. The
mixture was stirred under reflux for 2 d. Upon cooling down the
reaction solution, a solid precipitated, which was filtered, washed
with acetone and dried in vacuo for 6 h. After recrystallisation
from ethanol and DMSO/water a white solid was obtained which
was dried in vacuum over night to yield 155 mg (25%) of the
product. M.p. 242 ◦C; 1H-NMR (500 MHz, DMSO-d6): d = 0.85
(t, 3JHH = 6.8 Hz, 6H, CH3), 1.20–1.40 (m, 20H, CH2), 1.88–1.95
(m, 4H, CH2), 2.27 (s, 6H, CH3-OTs), 4.32 (t, 3JHH = 7.3 Hz, 4H,
NCH2), 7.09 (d, 3JHH = 7.9 Hz, 4H, o-OTs), 7.46 (d, 3JHH = 7.9 Hz,
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-methyl-1H-imi-
dazolium) diiodide [H2(Me2NHC2bipy)]I2 (5). Methyl iodide
(0.3 mL, 0.6 g, 4 mmol) was added by a syringe to a suspension of
6,6¢-di-1H-imidazol-1-yl-2,2¢-bipyridine (2) (500 mg, 1.73 mmol)
in 20 mL DMSO under an inert atmosphere. The mixture was
heated to 100 ◦C for 24 h. After the removal of the solvent under
reduced pressure by distillation a pale brown residue was obtained.
Further purification was achieved by a two-fold recrystallisation
from a water/ethanol mixture. After cooling to room temperature
the precipitated solid was collected by filtration, washed with
acetone (2 ¥ 10 mL) and dried in vacuo to yield 699 mg (70%)
3,4
3
4H, m-OTs), 8.12 (t,
J
= 1.8 Hz, 2H, H-4¢), 8.16 (d, JHH
=
=
HH
7.9 Hz, 2H, H-5), 8.44 (t, 3JHH = 7.9 Hz, 2H, H-4), 8.77 (t, 3,4JHH
1.8 Hz, 2H, H-5¢), 8.84 (d, 3JHH = 7.9 Hz, 2H, H-3), 10.33 (s br, 2H,
of the product as a white solid. M.p. 299 ◦C; 1H NMR (300 MHz,
H-2¢); 13C{ H} NMR (75 MHz, DMSO-d6): d = 13.9 (CH3), 20.7
1
3,4
DMSO-d6): d = 4.02 (s, 6H, CH3), 8.02 (t,
J
= 1.7 Hz, 2H,
(CH3-OTs), 22.0 (CH2), 25.5 (CH2), 28.4 (CH2), 28.5 (CH2), 29.2
(CH2), 31.1 (CH2), 49.2 (NCH2), 115.0 (C-5), 119.4 (C-5¢), 121.9
(C-3), 123.6 (C-4¢), 125.4 (o-OTs), 128.0 (m-OTs), 135.3 (C-2¢),
137.5 (p-OTs), 142.0 (C-4), 145.8 (i-OTs), 146.2 (C-6), 152.9 (C-2);
IR (KBr): n = 3090 (m), 2957 (m), 2925 (s), 2855 (m), 1601 (m),
1565 (m), 1538 (m), 1469 (s), 1222 (vs), 1195 (vs), 1125 (s), 1070
(m), 1035 (s), 1012 (s), 816 (m), 800 (m), 681 (m), 567 (m) cm-1; HR-
MS (ESI+) calcd for C39H53N6O3S: m/z 685.38944; found m/z (%)
685.38927 [M - OTs]+ (100); calcd for C24H29N6: m/z 401.24482;
found m/z (%) 401.24487 [M - OTs - OctOTs]+ (38); elemental
analysis calcd for C46H60N6O6S2·0.3DMSO: C 63.56, H 7.07, N
9.54; found: C 63.55, H 7.05, N 9.48.
HH
3
3
H-4¢), 8.16 (d, JHH = 7.9 Hz, 2H, H-5), 8.45 (t, JHH = 7.9 Hz,
3,4
3
2H, H-4), 8.73 (t,
J
= 1.7 Hz, 2H, H-5¢), 8.83 (d, JHH
=
HH
1
7.9 Hz, 2H, H-3), 10.31 (s br, 2H, H-2¢); 13C{ H} NMR (75 MHz,
DMSO-d6): d = 36.5 (CH3), 114.9 (C-5), 119.2 (C-5¢), 121.9 (C-3),
124.9 (C-4¢), 135.9 (C-2¢), 142.1 (C-4), 146.2 (C-6), 152.9 (C-2);
IR (KBr): n = 3081 (m), 2962 (w), 1603 (m), 1566 (s), 1537 (s),
1445 (s), 1274 (s), 1090 (w), 1068 (m), 970 (s) cm-1; HR-MS (ESI+)
calcd for C18H18N6I: m/z 473.09451; found: m/z 473.09485 [M -
I]+; elemental analysis calcd. for C18H18N6I2·H2O: C 36.63, H 3.42,
N 14.24; found C 36.33, H 3.51, N 14.04. Crystals suitable for
X-ray analysis were obtained upon recrystallisation from boiling
water.
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-ethyl-1,3-dihydro-
bipy
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-benzyl-1H-imida-
zolium) dichloride [H2(Bn2NHC2bipy)]Cl2 (6). Degassed benzyl
chloride (0.40 mL, 0.40 g, 3.5 mmol) was added to a suspension of
6,6¢-di-1H-imidazol-1-yl-2,2¢-bipyridine (2) (500 mg, 1.73 mmol)
in 10 mL DMSO under an inert atmosphere. The mixture was
heated to 100 ◦C for 15 h. After the removal of the solvent
under reduced pressure by distillation an off-white residue was
obtained which was washed three times with 50 mL of ethanol
and dried in vacuum for 3 h. Further purification was achieved
by recrystallisation from ethanol. After filtration and drying of
the white precipita◦te in vacuo 0.89 g (95%) of the product were
obtained. M.p. 287 C (dec.); 1H NMR (300 MHz, DMSO-d6): d =
5.62 (s, 4H, CH2), 7.38–7.50 (m, 6H, m/p-Ph), 7.53–7.60 (m, 4H,
o-Ph), 8.11 (s br, 2H, H-4¢), 8.21 (d, 3JHH = 8.0 Hz, 2H, H-5), 8.44
2H-imidazol-2-ylidene) (Et2NHC2
)
(8). [H2(Et2NHC2bipy)]-
(BF4)2 3 (200 mg, 0.385 mmol) was suspended in 30 mL of
toluene under an argon atmosphere and cooled to -35 ◦C. KOt-Bu
(104 mg, 0.923 mmol) was added and the mixture was stirred at
room temperature for 6 h. The yellow suspension was filtered
by a syringe filter and the solvent evaporated in vacuo. The
crude product was subsequently washed three times with 3 mL of
pentane before it was dried in vacuum over night to yield 86.1 mg
(65%) of the product as an off-white solid. M.p. 202 ◦C (dec.); 1H
3
NMR (300 MHz, thf-d8): d = 1.46 (t, JHH = 7.2 Hz, 6H, CH3),
3
3
4.15 (q, JHH = 7.2 Hz, 4H, CH2), 7.17 (d, JHH = 1.8 Hz, 2H,
H-4¢), 7.91 (t, 3JHH = 7.9 Hz, 2H, H-4), 8.22 (d, 3JHH = 1.8 Hz, 2H,
H-5¢), 8.40 (dd, 3JHH = 7.9 Hz, 3JHH = 0.9 Hz, 2H, H-3), 8.43 (dd,
1
3JHH = 7.9 Hz, 4JHH = 0.9 Hz, 2H, H-5); 13C{ H} NMR (75 MHz,
(t, 3JHH = 7.9 Hz, 2H, H-4), 8.80 (s br, 2H, H-5¢), 8.87 (d, 3JHH
=
thf-d8): d = 17.0 (CH3), 46.8 (CH2), 114.8 (C-5), 116.7 (C-5¢),
118.4 (C-3), 119.9 (C-4¢), 139.5 (C-4), 154.3 (C-2), 154.6 (C-6),
216.9 (C-2¢); IR (KBr): n = 3083 (w br), 2972 (m), 2934 (w), 2851
(w), 1679 (s), 1573 (vs), 1501 (m), 1443 (vs), 1261 (m), 1153 (w),
1
7.9 Hz, 2H, H-3), 10.70 (s, 2H, H-2¢); 13C{ H} NMR (75 MHz,
DMSO-d6): d = 52.5 (CH2), 115.1 (C-5), 120.0 (C-5¢), 122.0 (C-3),
123.6 (C-4¢), 128.4 (o-Ph), 128.9 (p-Ph), 129.0 (m-Ph), 134.5 (i-Ph),
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7152–7167 | 7161
©

1109 (m), 1077 (m), 1015 (w), 808 (m), 792 (m) cm-1; HR-MS (EI+)
calcd for C20H20N6: m/z 344.17409 (%); found: m/z 344.1753 [M]+
(100); calcd for C18H15N6: m/z 315.13518 (%); found: m/z 315.1379
[M - Et]+ (15); calcd for C16H12N6: m/z 288.11183 (%); found m/z
288.125 [M - C4H8]+ (65). Crystals suitable for X-ray analysis were
obtained by diffusion of pentane into a tetrahydrofuran solution.
solid. M.p. 185 ◦C (dec.); 1H NMR (500 MHz, CD3CN): d = 1.16
3
3
(t, JHH = 7.3 Hz, 6H, CH3), 3.95 (q, JHH = 7.3 Hz, 4H, CH2),
3
3
7.32 (d, JHH = 1.9 Hz, 2H, H-4¢), 7.53 (d, JHH = 8.1 Hz, 2H,
3
3
H-5), 7.65 (d, JHH = 1.9 Hz, 2H, H-5¢), 7.94 (t, JHH = 8.1 Hz,
2H, H-4), 8.12 (d, 3JHH = 8.1 Hz, 2H, H-3); 1H NMR (300 MHz,
DMSO-d6): d = 1.22 (t, 3JHH = 7.1 Hz, 6H, CH3), 4.02 (q, 3JHH
=
3
7.1 Hz, 4H, CH2), 7.68 (d, JHH = 1.9 Hz, 2H, H-4¢), 7.72 (d,
Synthesis of 1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-methyl-1,3-di-
3JHH = 7.9 Hz, 2H, H-5), 7.93 (t, JHH = 7.9 Hz, 2H, H-4), 8.09
3
bipy
hydro-2H-imidazol-2-ylidene) (Me2NHC2
)
(9). [H2(Me2-
3
3
(d, JHH = 1.9 Hz, 2H, H-5¢), 8.15 (d, JHH = 7.9 Hz, 2H, H-3);
NHC2bipy)](BF4)2 4 (200 mg, 0.406 mmol) was suspended in
30 mL of toluene under an argon atmosphere and cooled to
-35 ◦C. KOt-Bu (109 mg, 0.976 mmol) was added and the mixture
was stirred at room temperature for 5 h. The yellow suspension
was filtered by a syringe filter and the solvent evaporated in vacuo.
The crude product was subsequently washed three times with
3 mL of pentane before it was dried in vacuum for 19 h to yield
54.1 mg (42%) of the product as a yellow solid. M.p. 265 ◦C
13C{ H} NMR (125 MHz, CD3CN): d = 17.0 (CH3), 48.5 (CH2),
1
118.2 (C-5), 121.2 (C-5¢), 123.7 (C-3/4¢), 142.7 (C-4), 151.1 (C-6),
152.7 (C-2), 182.0 (C-2¢); 13C{ H}.
1
NMR (75.47 MHz, DMSO-d6): d = 16.5 (CH3), 47.0 (CH2),
116.2 (C-5), 120.1 (C-5¢), 121.6 (C-3), 122.9 (C-4¢), 141.2 (C-
4), 149.5 (C-6), 151.4 (C-2), 180.9 (C-2¢); 109Ag{ H} NMR
1
(23.27 MHz, DMSO-d6): d = 270.1; IR (KBr): n = 3171 (w
br), 3094 (w), 2981 (w br), 2919 (m), 1850 (w), 1658 (w), 1598
(s), 1573 (s), 1479 (s), 1463 (s), 1442 (vs), 1281 (m), 1262 (m),
1084 (vs br), 794 (s), 730 (m) cm-1; HR-MS (FAB+) calcd for
C20H20N6Ag: m/z 453.07949; found: m/z 453.0821 [M - AgB2F8]+;
HR-MS (ESI+): calcd for C20H20N6Ag: m/z 453.07949; found:
m/z 453.07973 [M - AgB2F8]+; elemental analysis calcd for
C20H20N6Ag2B2F8·0.5CH3CN: C 33.44, H 2.87, N 12.07; found:
C 33.29, H 3.18, N 12.25.
1
(dec.); H NMR (300 MHz, thf-d8): d = 3.82 (s, 6H, CH3), 7.12
3
3
(d, JHH = 1.8 Hz, 2H, H-4¢), 7.92 (t, JHH = 7.9 Hz, 2H, H-4),
8.22 (d, 3JHH = 1.8 Hz, 2H, H-5¢), 8.39 (dd, 3JHH = 7.9 Hz, 4JHH
=
0.9 Hz, 2H, H-3), 8.42 (dd, JHH = 7.9 Hz, 4JHH = 0.9 Hz, 2H,
3
H-5) 13C{ H} NMR (75 MHz, thf-d8): d = 38.5 (CH3), 115.1
1
(C-5), 117.0 (C-5¢), 118.6 (C-3), 121.7 (C-4¢), 139.8 (C-4), 154.3
(C-2), 154.7 (C-6), 217.4 (C-2¢). IR (KBr): n = 3094 (w br), 2963
(w), 2925 (w), 2852 (w), 1680 (s), 1573 (vs), 1447 (vs), 1427 (w),
1261 (m), 1153 (w), 1103 (m), 1015 (w), 808 (m), 738 (w) cm-1;
HR-MS (FAB+) calcd for C18H17N6: m/z 317.1512; found: m/z
317.1460 [M + H]+.
Synthesis
of
[1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-ethyl-1H-
imidazol-1-yl-2(3H)-ylidene-j2C,C¢)disilver(I)]bistetrafluoroborate
[Ag2(Et2NHC2bipy)](BF4)2 (11) with Ag2CO3 as NMR experiment.
R
A Youngꢀ NMR tube was charged with [H2(Et2NHC2bipy)](BF4)2
Synthesis
of
1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-benzyl-1,3-
3 (15.0 mg, 28.8 mmol), Ag2CO3 (9.6 mg, 34 mmol) and 0.5 mL of
bipy
dihydro-2H-imidazol-2-ylidene) (Bn2NHC2
) (10) as NMR
DMSO-d6 in glovebox atmosphere. The NMR tube was heated
experiment. Under nitrogen atmosphere [H2(Bn2NHC2bipy)]Cl2
6 (20.0 mg, 36.9 mmol) was suspended in 0.5 mL of thf-d8 and
cooled to -35 ◦C. KOt-Bu (9.9 mg, 89 mmol) was added in one
portion. After 6 h at room temperature no further deprotonation
◦
1
at 120 C for 43 h. The reaction progress was monitored by H
NMR spectroscopy with a product:substrate ratio of 93:7).
1H-NMR (250.13 MHz, 25 ◦C, DMSO-d6): identical to spec-
trum of 11 prepared from Ag2O (vide supra).
1
1
reaction could be monitored by H nmr spectroscopy. H NMR
(500 MHz, thf-d8): d = 5.34 (s, 4H, CH2), 7.08 (d, 3JHH = 1.7 Hz,
2H, H-4¢), 7.22–7.26 (m, 2H, p-Ph), 7.33–7.34 (m, 4H, m-Ph),
7.35–7.36 (m, 4H, o-Ph), 7.94 (br t, 3JHH = 7.8 Hz, 2H, H-4), 8.25
Synthesis of [L-2]-[1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-methyl-
1H-imidazol-1-yl-2(3H)-ylidene-j2C,C¢) silver(I)] tetrafluorobo-
rate [Ag(Me2NHC2bipy)](BF4) (12). A Schlenk tube was charged
with [H2(Me2NHC2bipy)](BF4)2 4 (200 mg, 0.407 mmol), Ag2O
(104 mg, 0.447 mmol) and 5 mL of acetonitrile under glovebox
atmosphere. The mixture was refluxed for 35 h. Reaction control
3
3
4
(d, JHH = 1.7 Hz, 2H, H-5¢), 8.42 (dd, JHH = 7.8 Hz, JHH
=
3
0.7 Hz, 2H, H-3), 8.50 (dd, JHH = 7.8 Hz, 4JHH = 0.7 Hz, 2H,
H-5), spectrum contains free t-BuOH: 1.15 (s, C(CH3)3), 3.41
1
was carried out by H NMR spectroscopy in CD3CN of a small
1
(s, OH); 13C{ H} NMR (125 MHz, thf-d8): d = 56.0 (CH2),
sample and if necessary further Ag2O was added. After complete
115.3 (C-5), 117.8 (C-5¢), 118.9 (C-3), 120.9 (C-4¢), 128.5 (p-Ph),
128.7 (o-Ph), 129.4 (m-Ph), 139.7 (i-Ph), 140.0 (C-4), 154.5 (C-2),
154.9 (C-6), 217.5 (C-2¢), spectrum contains free t-BuOH: 31.9
(C(CH3)3), 67.8 (C(CH3)3); HR-MS (FAB+) calcd for C30H25N6:
m/z 469.21300; found: m/z 469.2119 [M + H]+.
R
conversion of 3 the solid was filtered off over Celiteꢀ . The solvent
was evaporated in vacuo and dried for 12 h to yield 132 mg (63%)
of 12 as an off-white solid. 1H NMR (500 MHz, DMSO-d6): d =
3
3.37 (s br, 6H, CH3), 7.50 (d, JHH = 1.7 Hz, 2H, H-4¢), 7.77 (d,
3
3JHH = 7.9 Hz, 2H, H-5), 8.01 (t, JHH = 7.9 Hz, 2H, H-4), 8.08
3
3
Synthesis
of
[1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-ethyl-1H-
(d, JHH = 1.7 Hz, 2H, H-5¢), 8.53 (d, JHH = 7.9 Hz, 2H, H-3);
imidazol-1-yl-2(3H)-ylidene-j2C2)disilver(I)] ditetrafluoroborate
[Ag2(Et2NHC2bipy)](BF4)2 (11). A Schlenk tube was charged
13C{ H} NMR (125 MHz, DMSO-d6): d = 38.9 (CH3), 113.6 (C-
1
5), 118.9 (C-5¢), 120.6 (C-3), 123.5 (C-4¢), 140.6 (C-4), 149.0 (C-6),
153.0 (C-2), 183.5 (C-2¢); IR (KBr): n = 3124 (w), 3094 (m), 2952
(w br), 2920 (m), 1599 (s), 1573 (s), 1481 (s), 1463 (s), 1442 (s),
1400 (m), 1348 (w), 1283 (m), 1239 (m), 1084 (vs br), 796 (m), 740
(m) cm-1; HR-MS (ESI+) calcd for C18H16N6107Ag: m/z 423.04819;
found: m/z 423.04823 [M - BF4]+, calcd for C36H32N12107Ag2BF4:
m/z 933.09984; found: m/z 933.09968 [2M - BF4]+; elemental
analysis calcd for C18H16N6AgBF4·0.20Ag2O: C 38.79; H 2.89,
N 15.08; found: C 38.61, H 3.07, N 14.88. Crystals suitable for
under glovebox atmosphere with [H2(Et2NHC2bipy)](BF4)2
3
(200 mg, 0.769 mmol), Ag2O (98.0 mg, 0.846 mmol) and 10 mL
of acetonitrile. The mixture was refluxed under stirring for 40 h.
1
Reaction control was carried out by H NMR spectroscopy in
CD3CN of a small probe and if necessary further Ag2O was
added. After complete conversion of 3 the solid was filtered off by
R
a Whatmanꢀ syringe filter. The solvent was evaporated in vacuum
and dried for 12 h to yield 238 mg (84%) of 11 as a light brown
7162 | Dalton Trans., 2009, 7152–7167
This journal is
The Royal Society of Chemistry 2009
©

X-ray analysis were obtained by slow evaporation of an acetoni-
trile solution.
the solvent in vacuo yielded 15 as a pale brown solid which was
dried in vacuo for 24 h. The crude product was dissolved in 5 mL of
acetonitrile and the addition of 2 mL of thf and pentane causing a
white precipitate to form. After 24 h without stirring, the residue
was filtered, washed with pentane and dried in vacuo over night
to yield 161 mg (72%) of the product as a colourless solid. M.p.
Synthesis of [L-2]-[1,1¢-(2,2¢-bipyridin-6,6¢-diyl)bis(3-methyl-
1H-imidazol-1-yl-2(3H)-ylidene-j2C,C¢) silver(I)] (l2-iodo)bis(l2-
iodo)-diargentate [Ag(Me2NHC2bipy)][Ag2I3] (13) as NMR
R
experiment.
A
Youngꢀ NMR tube was charged with
225 ◦C (dec.); 1H NMR (300 MHz, CD3CN): d = 1.57 (t, 3JHH
=
[H2(Me2NHC2bipy)]I2 5 (20.0 mg, 35.0 mmol), Ag2O (26.2 mg,
113 mmol) and 0.5 mL DMSO-d6 under glovebox atmosphere.
The NMR tube was heated at 120 ◦C for 3 d. Reaction control was
3
7.3 Hz, 6H, CH3), 4.38 (q, JHH = 7.3 Hz, 4H, CH2), 7.49 (d,
3JHH = 2.3 Hz, 2H, H-4¢), 7.93 (d, 3JHH = 8.1 Hz, 2H, H-5), 7.99
3
3
(d, JHH = 2.3 Hz, 2H, H-5¢), 8.10 (d, JHH = 8.1 Hz, 2H, H-3),
1
1
carried out by H NMR spectroscopy. H NMR (300.13 MHz,
8.45 (t, 3JHH = 8.1 Hz, 2H, H-4); 1H NMR (300 MHz, DMSO-d6):
DMSO-d6, 100 ◦C): d = 3.91 (s br, 6H, CH3), 7.60 (s br, 2H, H-4¢),
3
3
d = 1.54 (t, JHH = 7.3 Hz, 6H, CH3), 4.38 (q, JHH = 7.3 Hz,
3
7.83 (d, J(HH) = 8.1 Hz, 2H, H-5), 8.06–8.12 (m, 2H, H-3/4),
3
3
4H, CH2), 7.94 (d, JHH = 2.2 Hz, 2H, H-5¢), 8.30 (d, JHH
=
=
8.28 (s br, 2H, H-5¢), the low solubility causes a poor resolution;
8.3 Hz, 2H, H-5), 8.45 (d, 3JHH = 8.2 Hz, 2H, H-3), 8.57 (d, 3JHH
◦
1
13C{ H} NMR (75.47 MHz, DMSO-d6, 100 C): d = 38.8 (CH3),
112.0 (C-5), 118.0 (C-5¢), 118.8 (C-3), 119.4 (C-4¢), 123.7 (C-4),
140.5 (C-6), 148.6 (C-2), 184.4 (C-2¢); HR-MS (FAB+) calcd for
C18H16N6Ag: calc. m/z 423.04819; found m/z 423.0522 [M -
Ag2I3]+. Crystals suitable for X-ray analysis were obtained by
recrystallisation from boiling DMSO.
2.2 Hz, 2H, H-4¢), 8.65 (t, 3JHH = 8.3 Hz, 2H, H-4); 13C{ H} NMR
(75 MHz, CD3CN): d = 17.0 (CH3), 48.5 (CH2), 115.5 (C-5), 120.8
(C-5¢), 122.6 (C-3), 124.2 (C-4¢), 147.4 (C-4), 152.6 (C-6), 156.1 (C-
1
2), 163.1 (C-2¢); 13C{ H} NMR (75 MHz, DMSO-d6): d = 16.1
1
(CH3), 46.3 (CH2), 114.2 (C-5), 119.9 (C-5¢), 121.3 (C-3), 123.2 (C-
4¢), 146.1 (C-4), 150.8 (C-6), 154.4 (C-2), 161.0 (C-2¢); IR (KBr):
n = 3169 (w), 3139 (w), 3116 (w), 3078 (w), 2986 (w br), 1658 (w),
1607 (m), 1580 (m), 1502 (s), 1477 (m), 1454 (m), 1346 (m), 1282
(m), 1225 (w), 1195 (w), 1084 (vs), 809 (m), 730 (m) cm-1; HR-
MS (ESI+) calcd for C20H20N6PdBF4: m/z 537.08080; found: m/z
Synthesis
of
[L-2]-dichloro[l-(2,2¢bipyridin-6,6-diyl)bis(3-
disilver(I)
benzyl-1H-imidazol-1-yl-2(3H)-ylidene-1jC:2jC¢)]
[Ag2Cl2(l-Bn2NHC2bipy)] (14). A Schlenk tube was charged
under glovebox atmosphere with [H2(Bn2NHC2bipy)]Cl2 6 (300 mg,
0.554 mmol), Ag2O (167 mg, 0.720 mmol) and 8 mL of
DMSO. The mixture was stirred at 85 ◦C for 4 d. After complete
conversion the product solution was filtered at 90 ◦C over a
537.08113 [M - BF4]+; calcd for 1 (C20H20N6Pd): m/z 225.03867;
2
found: m/z 225.03865, [M - 2BF4]2+; HR-MS (FAB+) calcd for
C20H20N6PdBF4: m/z 537.08080; found: m/z 537.0892 [M - BF4]+;
elemental analysis calcd for C20H20N6PdB2F8·0.5H2O: C 37.92, H
3.41, N 13.27; found: C 37.98, H 3.42, N 13.19; Crystals suitable for
X-ray analysis were obtained by slow evaporation of a saturated
acetonitrile solution.
R
Whatmanꢀ filter and the residue was extracted four times with
4 mL of DMSO. The solvent was removed under reduced pressure
by distillation. The resulting brown solid was washed with
acetonitrile and dried in vacuo over night. Further purification
was achieved by recrystallisation from DMSO to yield 298 mg
Synthesis of [SP-4-3]-[1,1¢-(2,2¢-bipyridin-6,6¢-diyl-j2N,N¢)-
bis(3-ethyl-1H-imidazol-1-yl-2(3H)-ylidene-j2C,C¢)palladium(II)]
ditetrafluoroborate [Pd(Et2NHC2bipy)](BF4)2 (15) with Pd(OAc)2 as
◦
(71%) of the product as a light brow◦n solid. M.p. 261 C (dec.);
1H NMR (600 MHz, DMSO-d6, 67 C): d = 5.47 (s, 4H, CH2),
R
NMR experiment. A Youngꢀ NMR tube was charged under
7.29–7.37 (m, 10H, o/m/p-Ph), 7.50–8.50 (m, 6H, H-3/4/5), 7.78
1
(s br, 2H, H-4¢), 8.28 (s br, 4H, H-5¢); 13C{ H} NMR (150 MHz,
glovebox atmosphere with [H2(Et2NHC2bipy)](BF4)2 3 (10.0 mg,
28.8 mmol), palladium(II) acetate (6.5 mg, 29 mmol) and 0.5 mL
of DMSO-d6. The NMR tube was heated at 80 ◦C for 48 h.
Reaction control was carried out by 1H NMR spectroscopy.
Yield: product:substrate 2:1 (by 1H NMR).
DMSO-d6, 67 ◦C): d = 55.5 (CH2), 120.2 (C-5¢), 123.4 (C-4¢),
127.1 (o-Ph), 127.7 (p-Ph), 128.4 (m-Ph), 137.2 (i-Ph), 183.7
(C-2¢), signals for C-2/3/4/5/6 are not observed; IR (KBr): n =
3161 (w), 3122 (w), 3093 (w), 3028 (w), 2924 (w), 1594 (m), 1565
(s), 1442 (vs), 1412 (m), 1356 (m), 1281 (m) 1244 (m), 1082 (s),
1028 (s), 800 (s), 732 (s) cm-1; MS (LIFDI): m/z (%) = 575.2
[M(107Ag)]+; 577.2 [M(109Ag)]+; MS (ESI+): m/z (%) = 577.3
[M+] (100); 485.3 [M+ - Bn] (7); 379.4 [M+ - Bn - Ag] (10),
contains unidentified products at m/z = 361.3, 179.4; elemental
analysis calcd for C30H24N6Ag2Cl2·2H2O: C 45.54, H 3.57, N
10.62; found: C 45.35, H 3.17, N 10.48; Crystals suitable for
X-ray analysis were obtained by recrystallisation from boiling
DMSO.
1H-NMR (250.13 MHz, 25 ◦C, DMSO-d6): identical to spec-
trum of 15 prepared by transmetallation (vide supra).
HR-MS (ESI+) calcd for C20H20N6PdBF4: m/z 537.08080; found
m/z 537.08113 [M - BF4]+.
Synthesis of [1,1¢-(2,2¢-bipyridin-6,6¢-diyl-j2N,N¢)bis(3-methyl-
1H-imidazol-1-yl-2(3H)-ylidene-j2C,C¢)palladium(II)]ditetrafluo-
roborate [Pd(Me2NHC2bipy)](BF4)2 (16).
A
solution of
[Ag(Me2NHC2bipy)](BF4) 12 (100 mg, 142 mmol) in 4 mL of
acetonitrile was cooled to -35 ◦C. [PdCl2(CH3CN)2] (36.8 mg,
142 mmol) was added. Immediately a large amount of grey solid
precipitated. The mixture was kept under nitrogen atmosphere at
rt for 16 h without stirring. The solution was decanted and after
evaporation of the solvent the product was obtained as a pale
brown solid which was dried in vacuo for 24 h.
[SP-4-3]-[1,1¢-(2,2¢-bipyridin-6,6¢-diyl-j2N,N¢)bis(3-ethyl-1H-
imidazol-1-yl-2(3H)-ylidene-j2C,C¢)palladium(II)]ditetrafluorobo-
rate [Pd(Et2NHC2bipy)](BF4)2 (15).
A solution of [Ag2(Et2-
NHC2bipy)](BF4)2 11 (100 mg, 136 mmol) in 5 mL of acetonitrile
was cooled to -35 ◦C. [PdCl2(COD)] (38.9 mg, 136 mmol) was
added. Immediately a large amount of grey solid precipitated. The
mixture was kept under nitrogen atmosphere at rt for 16 h without
1H NMR (300.13 MHz, DMSO-d6): d = 4.15 (s, 6H, CH3), 7.78
3
3
(d, JHH = 1.6 Hz, 2H, H-4¢), 8.28 (d, JHH = 8.1 Hz, 2H, H-5),
8.42 (d, 3JHH = 8.1 Hz, 2H, H-3), 8.48 (d, 3JHH = 1.6 Hz, 2H, H-5¢),
8.62 (t, 3JHH = 8.1 Hz, 2H, H-4), the spectrum contains impurities;
R
stirring. The solution was decanted and filtered over Celiteꢀ. The
residue was extracted with 5 mL of acetonitrile. Evaporation of
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7152–7167 | 7163
©

7164 | Dalton Trans., 2009, 7152–7167
This journal is
The Royal Society of Chemistry 2009
©

This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7152–7167 | 7165
©

1
13C{ H} NMR (75 MHz, DMSO-d6): d = 40.3 (CH3), 114.5 (C-
X-Ray crystal data and refinement details for 3–6, 8, 12–15, 17–18
(Tables 3 and 4)
5), 119.5 (C-5¢), 121.6 (C-3), 125.4 (C-4¢), 146.3 (C-4), 151.1 (C-
6), 154.7 (C-2), 162.5 (C-2¢), spectrum contains impurities; MS
(ESI+): m/z (%) = 509.2 [M - BF4]+ (100); 687.0 [M - BF4 +
PdCl2]+ (25); 1103.1 [2M - BF4]+ (18).
X-Ray structures were obtained with a Bruker Smart diffractome-
ter (4–6, 12, 13, ) or a Bruker APEX diffractometer (3, 8, 14, 15, 17,
18) at 200 K, both equipped with a Mo Ka radiation source (l =
˚
0.71073 A) and a graphite monochromator. All intensities were
corrected for Lorentz and polarisation effects, and an absorption
correction was applied in each case using SADABS24 based on the
Laue symmetry of the reciprocal space. The structures were solved
by direct methods. The structural parameters of the non hydrogen
atoms were refined anisotropically according to a full-matrix least
squares technique against F2 with exception of the light atoms of
13, which could only be described isotropically. The hydrogen atom
locations were calculated according to stereochemical aspects.
We have observed and modelled some disorder in the anions or
incorporated solvent molecules. Structure solution and refinement
were carried out with the SHELXTL (6.10) software package.25
Synthesis of [SP-4-3]-tetrachloro[l-(2,2¢-bipyridin-6,6-diyl)-
bis(3-benzyl-1H-imidazol-1-yl-2(3H)-ylidene-1jC:2jC¢)]-bis-[(sul-
finyl-jS)bis(methan)] dipalladium(II) [Pd2Cl4(l-Bn2NHC2bipy)-
R
(DMSO)2] (17) as NMR experiment. A Youngꢀ NMR tube was
charged with [Ag2Cl2(m-Bn2NHC2bipy)] 14 (15.0 mg, 19.9 mmol),
[PdCl2(CH3CN)2] (10.3 mg, 39.7 mmol) and 0.5 mL of CD3CN
under glovebox atmosphere. A lot of grey solid precipitated.
1
As the reaction progress could not be monitored by H NMR
spectroscopy in CD3CN, the solvent was evaporated in vacuo.
The residue was subsequently suspended in 0.5 mL of DMSO-d6.
After four weeks at room temperature big yellow crystals had
1
grown out of the suspension. H NMR (300 MHz, DMSO-d6,
100 ◦C): d = 5.89 (m, CH2), 7.30–7.47 (m, m/p-Ph), 7.54–7.62
(m, o-Ph), 8.07–8.17 (m), 8.26–8.41 (m), poor solubility causes
bad resolution. Crystals suitable for X-ray analysis were obtained
from the DMSO-d6 suspension at rt.
Notes and references
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Synthesis of [T-4]-[bis-(l-1,1¢-(2,2¢-bipyridin-6,6-diyl-1jN:
2jN¢)bis(3-ethyl-1H-imidazol-1-yl-2(3H)-ylidene-1jC:2jC¢) di-
copper(I)]-ditetrafluoroborate [Cu2(l-Et2NHC2bipy)2](BF4)2 (18).
A solution of [Ag2(Et2NHC2bipy)](BF4)2 11 (100 mg, 136 mmol)
in 5 mL of acetonitrile were cooled to -35 ◦C. Copper(I)-
chloride (27.0 mg, 273 mmol) was added. Immediately a large
amount of grey solid precipitated. The mixture was kept under
nitrogen atmosphere at rt for 16 h without stirring. The solution
R
R
was decanted and filtered over Celiteꢀ . The Celiteꢀ pad was
extracted with an additional 5 mL of acetonitrile. The solvent
was evaporated and the product was obtained as a copper-red
solid which was dried in vacuo for 12 h. The orange-coloured
residue was dissolved in 5 mL of acetonitrile and the addition
of 2 mL of thf and pentane causing a copper-red precipitate to
form. After 24 h without stirring, the solid was filtered, washed
with pentane and dried in vacuo over night to yiel◦d the product
6 M. Poyatos, E. Mas-Marza´, J. A. Mata, M. Sanau´ and E. Peris,
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1
7 (a) J. A. Wright, A. A. Danopoulos, W. B. Motherwell, R. J. Carroll,
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in 55 mg (82%) as a copper-red solid. M.p. 275 C; H NMR
3
(300 MHz, CD3CN): d = 1.15 (t, JHH = 7.3 Hz, 12H, CH3),
3
3
3.62 (q, JHH = 7.3 Hz, 8H, CH2), 7.10 (d, JHH = 1.9 Hz, 4H,
3
3
H-4¢), 7.40 (d, JHH = 8.1 Hz, 4H, H-5), 7.54 (d, JHH = 8.1 Hz,
3
3
4H, H-3), 7.56 (d, JHH = 1.9 Hz, 4H, H-5¢), 7.83 (t, JHH
=
8.1 Hz, 4H, H-4); 13C{ H} NMR (75 MHz, CD3CN): d = 16.0
(CH3), 47.5 (CH2), 112.6 (C-5), 116.8 (C-5¢), 122.1 (C-3), 123.2
(C-4¢), 141.0 (C-4), 150.5 (C-6), 155.1 (C-2), 185.0 (C-2¢); IR
(KBr): n = 3164 (w), 3134 (w), 3114 (w), 2983 (m), 1601 (m),
1572 (m), 1486 (m), 1469 (m), 1443 (m), 1415 (m), 1346 (m), 1262
(s), 1228 (m), 1084 (vs br), 806 (s) cm-1; HR-MS (ESI+) calcd
for C40H40N12Cu2BF4: m/z 901.21146 (%); found: m/z 901.21149
1
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13 M. Nonnenmacher, D. Kunz, F. Rominger and T. Oeser, Chem.
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[2M - BF4]+ (52); calcd for 1 (C40H40N12Cu2): m/z 407.10400
2
(%); found: m/z 407.10413, [M]2+ (100); elemental analysis calcd
for C20H20N6CuBF4·CuBF4·CH3CN: C 38.51, H 3.38, N 14.29;
found: C 38.48, H 3.60, N 14.34; Crystals suitable for X-ray
analysis were obtained by slow diffusion of diethyl ether into a
saturated acetonitrile solution at rt.
7166 | Dalton Trans., 2009, 7152–7167
This journal is
The Royal Society of Chemistry 2009
©

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This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7152–7167 | 7167
©