New pyridazine-bridged NHC/pyrazole ligands and their sequential silver(I) coordination

Article abstract of DOI:10.1002/ejic.201100264

A family of new pyridazine-bridged NHC/pyrazole ligand precursors HL ^1-5 were prepared and fully characterized including analysis by XRD {HL¹ = 3-[3-(2,6-diisopropylphenyl)-3H-imidazolium-1-yl]-6-(3- pyridin-2-yl-pyrazol-1-yl)-pyrida

Full text of DOI:10.1002/ejic.201100264

FULL PAPER
DOI: 10.1002/ejic.201100264
New Pyridazine-Bridged NHC/Pyrazole Ligands and Their Sequential Silver(I)
Coordination
Jan Wimberg,[a] Ulrich J. Scheele,[a] Sebastian Dechert,[a] and Franc Meyer*[a]
Keywords: Carbene ligands / Nitrogen heterocycles / Ligand design / Silver / Oligometallic complexes
A family of new pyridazine-bridged NHC/pyrazole ligand
precursors HL1–5 were prepared and fully characterized in-
cluding analysis by XRD {HL1 = 3-[3-(2,6-diisopropylphenyl)-
3H-imidazolium-1-yl]-6-(3-pyridin-2-yl-pyrazol-1-yl)-pyrid-
azine, HL2 = 3-[3-(2,4,6-trimethylphenyl)-3H-imidazolium-1-
yl]-6-(3-pyridin-2-yl-pyrazol-1-yl)-pyridazine, HL3 = 3-[3-
(2,4,6-trimethylphenyl)-3H-imidazolium-1-yl]-6-(3,5-dimeth-
ylpyrazol-1-yl)-pyridazine, HL4 = 3-(3-tert-butyl-3H-imid-
[(L4)2Ag](PF6) (4Ј) the single silver(I) ion is coordinated in a
linear fashion by the NHC moieties of the two ligand strands.
An NMR titration with AgBF4 reveals that 4 can bind two
more silver(I) ions. The complex [(L5)2Ag2](PF6)2 (5Ј) features
an additional silver(I) centre bound to the two pyrazole rings,
whereas in [(L3)2Ag2](BF4)2 (6) ligand reshuffling has oc-
curred to give antiparallel ligand strands with {CNHCNpyrazole
coordination of each metal ion. Secondary interactions with
}
azolium-1-yl)-6-(3,5-dimethylpyrazol-1-yl)-pyridazine, HL5 = the pyridazine N-atom are observed in some cases. An ad-
3-[3-(2,4,6-trimethylphenyl)-3H-imidazolium-1-yl]-6-(3-
ditional third silver(I) ion can be accommodated between the
central pyridazine bridges, as shown in [(L3)2Ag3](PF6)2(BF4)
(7). The sequence of binding events and the identity of the
species in solution have been investigated by NMR spec-
troscopy and ESI mass spectrometry.
–
methyl-5-phenylpyrazol-1-yl)-pyridazine, X = PF6 or BF4–}.
Reaction of the ligand precursors with Ag2O yielded various
silver(I) complexes whose structures have been elucidated
crystallographically. In complexes [(L3)2Ag](PF6) (4) and
ativity.[10] Starting from cheap 3,6-dichloropyridazine, che-
late arms may be readily attached to the 3- and 6-positions
of the pyridazine bridge in order to increase preorganiza-
tion of the dimetallic array.[11] The simple pyridazine/NHC
hybrid ligands A (Scheme 1) have previously been employed
in palladium chemistry,[12] and the dinucleating type B scaf-
folds have been used for the synthesis of oligonuclear mer-
cury(II) and silver(I) complexes.[13]
Introduction
N-Heterocyclic carbenes (NHCs) are currently among
the most popular ligands in transition-metal chemistry and
are finding widespread use in catalysis.[1,2] As part of their
further elaboration, NHC units in recent years have been
increasingly incorporated in multidentate ligand scaffolds,[3]
including compartmental ligands for di- and oligometallic
complexes.[4,5] Such complexes in which two (or more)
metal ions are held in close proximity offer interesting per-
spectives for catalytic applications, as new reaction path-
ways may become available if the adjacent metal centres act
in concert.[6] Although the number of symmetric dinucleat-
ing ligands with two identical binding pockets is growing
rapidly,[7] asymmetric dinucleating ligands that feature two
different compartments are still relatively scarce.[8] Interest
in such asymmetric systems stems from the expectation that
they may enable the targeted synthesis of preorganized het-
erodimetallic complexes in which the metal centres play dis-
tinct roles during cooperative action.[6a,9]
Scheme 1.
Pyridazine is well established as a versatile bridging unit
that is capable of spanning two metal ions through its two
N-atoms, with metal–metal distances suitable for cooper-
Silver(I) complexes of NHC-based ligands are attracting
much attention because of their large structural diversity,[14]
their potentially interesting photophysical properties[15] and
their convenient use in transmetallation reactions for the
preparation of various other NHC complexes.[16] They are
readily synthesized from imidazolium ligand precursors by
the addition of basic silver salts such as silver acetate, silver
[a] Institut für Anorganische Chemie, Georg-August-Universität
Göttingen,
Tammannstrasse 4, 37077 Göttingen, Germany
E-mail: franc.meyer@chemie.uni-goettingen.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100264.
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Pyridazine-Bridged NHC/Pyrazole Ligands and Their Silver(I) Coordination
carbonate or the most commonly used Ag2O.[17–19] Often
they are the first complexes that are prepared for newly de-
veloped NHC ligands in order to probe their general coor-
dination patterns.
In this work we present a synthetic entry to new, asym-
metric, pyridazine-bridged NHC/pyrazole ligand precursors
(type C, Scheme 1). These are closely related to type B sys-
tems,[13] as they formally represent a switching of the posi-
tions of two adjacent C and N atoms in one of the five-
membered heterocycles attached to the central pyridazine
unit. However, ligands derived from B provide two identical
organometallic {CNHCNpyridazine} compartments, whereas
ligands derived from C are quite different and will offer one
organometallic {CNHCNpyridazine} site and a classical (Wer-
ner-type) {NpyrazoleNpyridazine} site. We also report the step-
wise coordination of silver(I) by the new type C ligand pre-
cursors, which gave rise to an interesting sequence of bind-
ing events and various structural motifs for the resulting
complexes. Silver(I) complexes of the related symmetric
pyridazine/pyrazole ligand D have been reported re-
cently.[20]
Results and Discussion
Scheme 2. Syntheses of ligand precursors HL1–5
.
A series of differently substituted pyridazine-based type
C NHC/pyrazole ligand precursors were prepared by two (CHim2) appear at high frequency in the range of δ = 9.3–
general synthetic routes, starting from 3,6-dichloropyrid- 9.7 ppm; these signals disappear due to H/D exchange when
azine (Scheme 2).[21] Addition of potassium hydride plus the the spectra are recorded in CD3OD. Also noticeable are the
appropriate pyrazole in stoichiometric amounts initially pyridazine protons (CHpdz) in positions C4 and C5, which
yields monosubstituted pyrazole/pyridazine compounds 1 can be observed as two separate doublets with a 3J coupling
and 2,[22] which can then be treated with different N-substi- of 9.5 Hz because of the asymmetric substitution of the
tuted imidazoles to yield the type C ligand precursors. In pyridazine.
the second step, a neat mixture of 1 or 2 and 5 equiv. of the
In Figure 1 the ORTEP plots of HL3(PF6) and HL2(PF6)
respective imidazole is melted in an evacuated Schlenk are shown as representative examples for the molecular
flask; both the temperature and reaction time are crucial structures of the new ligand precursors. The X-ray struc-
for obtaining good yields. The excess imidazole can be reco- tures of several other ligand precursors with either hexaflu-
vered by sublimation. Subsequent treatment with an aque- orophosphate or tetrafluoroborate anions are given in the
ous solution of NH4PF6 or NH4BF4 allows exchange of Supporting Information. In most cases the nitrogen atoms
the chloride for hexafluorophosphate or tetrafluoroborate of the pyridazine point away from the imidazolium C2 pro-
anions, which impart better solubility and improved tons and from the nitrogen atoms of the pyrazoles, as is
crystallization behaviour on the ligand precursors. Four li- seen in HL3(PF6). The only exception is the molecular
gands HL1–4 were prepared by this route, all carrying bulky structure of HL2(PF6), where the imidazolium C2 hydrogen
substituents (tert-butyl or substituted aryl) at the imid- atom and the pyridazine N atoms point in the same direc-
azolium ring and a 2-pyridyl group (HL1, HL2) or two tion, with the pyrazole N6 atom oriented towards the back.
methyl groups (HL3, HL4) at the pyrazole side. For ligand The planes of the pyrazole and imidazolium rings are more
precursor HL5, the pyrazole ring in the intermediate or less twisted (9–45°) in all of these structures, suggesting
compound 3 is preferably formed by a known two-step con- free rotation of the heterocycles. This should enable the che-
densation reaction[23] by sequentially adding hydrazine lating binding mode to form the desired complexes. In al-
and 1-phenylbutane-1,3-dione to 3,6-dichloropyridazine most all structures the anion is located near the imid-
(Scheme 2). In a subsequent step the (2,4,6-trimethylphen- azolium C2 proton with C···F distances of between 3.08 and
yl)imidazolium ring is attached by heating a neat mixture of 3.21 Å and C–H···F angles ranging from 139 to 176°. These
3 and (2,4,6-trimethylphenyl)imidazole, followed by anion values are within the usually accepted limits for such hydro-
exchange.
gen bonds.[24] Only in the case of HL2(PF6) do two ligand
All of the ligand precursors HL1–5 were fully charac- precursors form a face-to-face dimer stabilized by interac-
terized by elemental analysis, mass spectrometry (ESI-MS tions between the pyridine N-atoms and the imidazolium
and HRMS) and NMR spectroscopy. Characteristic 1H C2 protons of the opposing ligand (Figure 1). The anions
NMR signals for the acidic imidazolium C2 protons are located on either side of the ligand dimer plane.
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J. Wimberg, U. J. Scheele, S. Dechert, F. Meyer
FULL PAPER
with literature reports for other complexes with a linear
CNHC–AgI–CNHC motif.[14b] Solid-state structures for com-
plexes 4 and 4Ј are shown in Figures 2 and 3, respectively.
In both cases a single silver ion is coordinated in a linear
fashion by the NHC subunits of both ligand strands. In 4,
the bond length between the NHC and the silver ion is
about 2.09 Å and the C–Ag–C bond angle is close to linear-
ity (179°). Just as in the free ligands, the pyridazine N-
atoms point backwards, away from the silver ion.
Figure 1. ORTEP plots (30% probability thermal ellipsoids) of the
molecular structures of HL3(PF6) (top) and HL2(PF6) (bottom)
emphasizing the hydrogen bonding (dashed lines). For the sake of
clarity most hydrogen atoms have been omitted. Selected bond
lengths [Å] and angles [°] for HL3(PF6): C1···F1 3.101(2); C1–
H1···F1 170(2), N2–C1–N3 108.6(1); for HL2(PF6): C1···N7Ј
3.188(2); C1–H1···N7Ј 161(2), N2–C1–N3 108.3(2). Symmetry
transformation used to generate equivalent atoms (Ј): 1 – x, 1 – y,
1 – z.
Figure 2. ORTEP plot (30% probability thermal ellipsoids) of the
molecular structure of the cation of 4. Hydrogen atoms have been
omitted for clarity. Selected bond lengths [Å] and angles [°]: Ag1–
C1 2.0852(15), Ag1–C1Ј 2.0852(15); C1–Ag1–C1Ј 179.24(8), N2–
C1–N3 104.29(13). Symmetry operation used to generate equiva-
lent atoms (Ј): 1 – x, y, –z + 1/2.
According to the method established by Lin et al.,[19] ad-
dition of Ag2O to an MeCN or acetone solution of the
respective ligand precursor allows the straightforward prep-
aration of silver–NHC complexes (Scheme 3). In this reac-
tion Ag2O is used as a base that deprotonates the relatively
acidic imidazolium C2 atom. The reaction is not air- or
moisture-sensitive, no additional base is needed, and the
surplus Ag2O can easily be removed by filtration. Yields
are generally about 80% after 48 h of stirring at ambient
temperature.
Figure 3. ORTEP plot (30% probability thermal ellipsoids) of the
molecular structure of the cation of 4Ј. Hydrogen atoms have been
omitted for clarity. Selected bond lengths [Å] and angles [°]: Ag1–
C1 2.106(3), Ag1–C21 2.104(3), Ag1–N1 2.824(3), Ag1–N14
2.819(3); C1–Ag1–C21 174.3(1), N1–Ag1–N14 126.3(1), N2–C1–
N3 104.3(2), N12–C21–N13 104.3(2).
In contrast, the molecular structure of complex 4Ј sug-
gests a weak secondary interaction of the pyridazine N1 and
N14 atoms with the silver ion (Figure 3), as the pyridazine
N atoms are orientated towards the metal atom, and the
corresponding Ag···N distances are relatively short at ap-
Scheme 3. Preparation of the various silver(I) complexes 4–5Ј.
Silver(I) complexes of the type [L2Ag](PF6) were isolated proximately 2.82 Å. This may be the reason why the bond
with ligands HL3 (4) and HL4 (4Ј) and have been fully char- between the NHC and the silver ion in 4Ј is slightly longer
acterized. They are stable as solids but slowly decompose (2.15 Å) than in 4, and the C–Ag–C angle is slightly more
in solution and should be stored under exclusion of light. bent (174°).
1
In the H NMR spectra recorded in aprotic solvents the
The availability of noncoordinating pyrazole N- and
signals for the imidazolium C2 protons are missing, which pyridazine N-atoms in 4 and 4Ј suggests that binding of
reflects coordination of the generated carbenes. Signals for additional silver ions should be possible under appropriate
the NHC C2 atoms in the 13C NMR spectra are shifted by conditions. Complex 4 was thus titrated with AgBF4 and
1
about 50 ppm downfield compared to those of the free the reaction mixture analyzed by H NMR spectroscopy.
ligands, from about δ = 136 to 184 ppm, in agreement The chemical shift of the pyrazole C4 proton (CHpz4) usu-
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Pyridazine-Bridged NHC/Pyrazole Ligands and Their Silver(I) Coordination
ally is a good indicator for the involvement of the pyrazole
N-atom in metal ion binding. Figure 4 shows the changes
of the chemical shift for the pyrazole C4H signal upon ad-
dition of up to 3 equiv. of AgBF4 to a solution of 4 in
MeCN.[25] The slope of the curve changes after the addition
of 1 equiv., and the chemical shift finally remains constant
after addition of 2 equiv. This suggests the sequential for-
mation of species [(L3)2Ag2]2+ (6) and [(L3)2Ag3]3+ (7) in
solution. Both complexes were subsequently isolated as
crystalline materials, and their molecular structures were
determined by XRD (Figures 5 and 6, respectively).
Figure 6. ORTEP plot (30% probability thermal ellipsoids) of the
molecular structure of the cation of 7. Hydrogen atoms and disor-
dered parts have been omitted for clarity. Selected bond lengths
[Å] and angles [°]: Ag1–N1 2.290(4), Ag1–N11 2.272(4), Ag1–O1A
2.322(8), Ag1–O2 2.456(5), Ag2–C1 2.103(5), Ag2–N16 2.284(5),
Ag2–N14 2.422(4), Ag3–C31 2.090(5), Ag3–N6 2.266(4), Ag3–N4
2.407(5), Ag1···Ag2 3.410(1), Ag1···Ag3 3.332(1); N11–Ag1–N1
114.80(14), N11–Ag1–O1A 140.4(2), N1–Ag1–O1A 93.3(2), N11–
Ag1–O2 91.05(17), N1–Ag1–O2 140.93(17), O1A–Ag1–O2 82.3(2),
C1–Ag2–N16 156.97(18), C1–Ag2–N14 131.58(17), N16–Ag2–N14
69.04(15), C31–Ag3–N6 155.36(17), C31–Ag3–N4 133.92(17), N6–
Ag3–N4 69.61(15), N2–C1–N3 103.2(4), N12–C31–N13 103.1(4).
environment of the metal ions is thus best described as
{2 + 1}; the Ag···Ag distance is about 5.58 Å.
Addition of one more equivalent of AgBF4 produces the
trinuclear complex 7, which was isolated and crystallized as
the salt [(L3)2Ag3](PF6)2(BF4) from an acetone/Et2O solu-
tion. Its molecular structure (Figure 6) is closely related to
that of 6 with two antiparallel ligand strands, but a third
silver(I) ion (Ag1) is now accommodated in a central posi-
tion, bound to the pyridazine N1 and N11 atoms that were
still available for metal ion binding in the precursor 6. Two
acetone molecules are loosely bound to Ag1 (Ag1–O1A
2.32, Ag1–O2 2.46 Å), resulting in a distorted tetrahedral
coordination and an acute N1–Ag1–N11 angle of 114°.
Distances between the central Ag1 and the peripheral Ag2
and Ag3 atoms are 3.41 and 3.33 Å, respectively. These dis-
tances are well above 2.9 Å, albeit shorter than the sum of
the van der Waals radii (3.44 Å); we assume that d10–d10
interactions are weak, if present at all.[26,27]
1
Figure 4. Changes of the H NMR chemical shift of the pyrazole
C4 proton upon addition of AgBF4 to a solution of 4 in MeCN.
Figure 5. ORTEP plot (30% probability thermal ellipsoids) of the
molecular structure of the cation of 6. Hydrogen atoms have been
omitted for clarity. Selected bond lengths [Å] and angles [°]: Ag1–
C1 2.090(3), Ag1–N16 2.190(2), Ag1–N14 2.580(2), Ag2–C31
2.087(2), Ag2–N6 2.175(2), Ag2–N4 2.613(2), Ag1···Ag2 5.5828(4);
C1–Ag1–N16 154.19(10), C1–Ag1–N14 133.50(9), N16–Ag1–N14
69.27(7), C31–Ag2–N6 153.40(10), C31–Ag2–N4 133.83(9), N6–
Ag2–N4 68.52(8), N2–C1–N3 104.1(2), N12–C31–N13 104.2(2).
It is interesting to note that binding a second silver(I) ion
to 4 and formation of dinuclear 6 requires the breaking of
an Ag–CNHC bond and reorganization of the ligands, as
both metal ions in 6 feature a CNHC–Ag–N motif. One may
suggest that this process occurs by an intermediate complex
5 with parallel ligand strands, which subsequently re-
arranges to the thermodynamically more stable
6
Complex 6, which was obtained after addition of 1 equiv. (Scheme 4). Support for this assumption comes from the
of AgBF4, features two antiparallel ligand strands that are molecular structure of the dinuclear complex [(L5)2Ag2]-
held together by two silver(I) ions, each coordinated by an (PF6)2 (5Ј, Figure 7), which was isolated from the reaction
NHC C2- and a pyrazole N-atom. Additional interactions of HL5 and Ag2O in acetone.
between the metal ions and adjacent pyridazine N-atoms
In 5Ј one of the silver ions (Ag1) still retains the
are significantly more pronounced than in 4Ј, as judged C–Ag–C coordination motif from the precursor complex
from the shorter Ag···N distances (2.58 and 2.61 Å) as well [(L5)2Ag]+ {assuming that the structure for [(L5)2Ag]+ is
as the strong deviation of the C1–Ag1–N15 and C31–Ag2– similar to that of 4 or 4Ј}, and the second silver ion is
N6 axes from linearity (153 and 154°). The coordination hosted in the open {N4} site with two shorter Ag–Npyrazole
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J. Wimberg, U. J. Scheele, S. Dechert, F. Meyer
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However, the proposed intermediate 5 was not detected
during the reaction of 4 to 6, and the conversion of 5Ј to a
rearranged product was not observed by NMR spec-
troscopy (see below). It is likely that the putative rearrange-
ment 5 Ǟ 6 does not proceed by simple dissociation, rota-
tion and rebinding of one of the ligands, but by a more
complex reaction sequence that may even be an intermo-
lecular process. Some indication for this can be seen in the
molecular structure of the trinuclear complex [(L3)3Ag3]3+
(8), which has the same ligand/metal ratio as in 5 and 6
(1:1). Only a few crystals of this compound were obtained
by crystallization from an acetone/Et2O solution in one ex-
periment, and the moderate quality of its crystallographic
structure determination does not permit any detailed dis-
cussion of metric parameters. However, the overall structure
is revealed (Figure 8) and features three silver atoms in dis-
tinct coordination environments, namely CNHC–Ag–CNHC
,
CNHC–Ag–Npyrazole, and Npyrazole–Ag–Npyrazole (all with ad-
ditional weak Npyridazine–Ag interactions). Complex 8 may
thus be viewed as a potential intermediate of the multistep
ligand reshuffling process from 5 to 6. These interconver-
sions likely involve various oligonuclear species and are ra-
pid on the NMR time scale.
Scheme 4. Proposed sequence for the formation of 4–7.
Figure 8. Plot of the molecular structure of the cation of 8. Hydro-
gen atoms have been omitted for clarity.
Characterization of the multinuclear silver complexes by
NMR spectroscopy and ESI mass spectrometry is ham-
pered by rapid dynamic processes and the presence of mul-
tiple species in solution. In all cases the ion [L2Ag]+ repre-
sents the major signal in the ESI mass spectra (acetone
solution), although the ion [LAg]+ is also detected.
Figure 7. ORTEP plot (30% probability thermal ellipsoids) of the
molecular structure of the cation of 5Ј. Hydrogen atoms have been
omitted for clarity. Selected bond lengths [Å] and angles [°]: Ag1–
C1 2.080(2), Ag1–C31 2.077(2), Ag2–N6 2.2105(18), Ag2–N16
2.2424(19), Ag2–N14 2.5065(19), Ag2–N4 2.5971(19), Ag1···Ag2
5.4269(3); C1–Ag1–C31 170.90(8), N6–Ag2–N16 138.03(7), N6–
Ag2–N14 150.10(6), N16–Ag2–N14 69.18(6), N6–Ag2–N4
67.35(6), N16–Ag2–N4 152.73(6), N14–Ag2–N4 89.65(6), N2–C1–
N3 104.2(2), N12–C31–N13 103.8(2).
1
Room-temperature H NMR spectra of 4 feature sharp
signals in [D3]MeCN, which are broadened in [D6]acetone.
Upon cooling of a solution in [D6]acetone to 233 K the
resonances split into two major and several minor sets,
which may tentatively be assigned to different rotational
isomers with one or both pyridazine groups pointing their
N atoms towards or away from the metal ion (as reflected
by the structures of 4 and 4Ј in the solid state). 13C NMR
spectroscopy reveals just two doublets for C2 at low tem-
1
bonds (2.21/2.24 Å) and two longer Ag–Npyridazine bonds perature {233 K, [D6]acetone: δ = 182.6 ppm, J(13C107Ag)
(2.51/2.60 Å). The distance between the metal ions is about = 182.5 Hz, 1J(13C109Ag) = 203.8 Hz} and a broadened res-
5.43 Å without any direct interaction between them.
onance at room temperature. The ESI mass spectrum of 4
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Pyridazine-Bridged NHC/Pyrazole Ligands and Their Silver(I) Coordination
only shows the dominant signals for [(L3)2Ag]+ and [(L3) contributes to fluxional processes. Transmetallation of the
Ag]+, besides some free ligand [L3]+.
silver complexes may give rise to interesting pyridazine-
When a solution of 4 in [D6]acetone is treated with bridged homo- and heterodimetallic complexes, and is cur-
1 equiv. of AgBF4 at 233 K, a single set of resonances is rently under investigation.
discernible in the 1H NMR spectrum that is identical to the
spectrum obtained by dissolving crystals of 6 in the same
solvent. This suggests that reshuffling of the ligands is rapid
even at low temperature and that the intermediate 5 cannot
be detected for this particular ligand scaffold, L3. In the
ESI mass spectrum of 6 (acetone solution) the ions
[(L3)2Ag]+ and [(L3)Ag]+ again give rise to the most intense
signals, but [(L3)2Ag2]+ (3% intensity) and [(L3)2Ag2-
Experimental Section
2
General: Compounds 1,[22] [22] and 3[23] were synthesized according
to the published procedures with slight modifications. All other
reagents were purchased from commercial sources and employed
without further treatment. Melting points were determined with an
OptiMelt system (Stanford Research Systems, Inc.) by using open
1
(PF6)]+ (6%) are also observed. H NMR spectra of the
capillaries, and values are uncorrected. H and 13C NMR spectra
1
were recorded with Bruker Avance 300 and Bruker Avance 500
spectrometers. 13C resonances were obtained with broad-band pro-
ton decoupling, and spectra were recorded at 298 or 233 K. 1H
and 13C NMR chemical shifts were referenced internally to solvent
signals. ESI mass spectra were recorded by using an Applied Biosy-
stems API 2000. HRMS measurements were recorded with a
Bruker FTICR-MS APEX IV. IR spectra from KBr pellets were
recorded with a Digilab Excalibur Series FTS 3000 spectrometer.
Elemental analyses were performed at the analytical laboratory of
the Institute for Inorganic Chemistry at the Georg August Univer-
sity by using an Elementar Vario EL III instrument. Details of the
X-ray crystallographic determinations can be found in the Support-
ing Information. CCDC-806607 [for HL1(PF6)], -806608 [for
HL2(PF6)], -806609 [for HL3(PF6)], -806610 [for HL4(BF4)],
-806611, [for HL5(PF6)], -806612 (for 4), -806613 (for 4Ј), -806614
(for 5Ј), -806615 (for 6) and -806616 (for 7) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
related 5Ј show relatively strong solvent dependence, yet
only a single set of signals is seen in both CD3CN and
[D6]acetone. Basically the same spectrum is observed upon
dissolving crystals of 5Ј in [D6]acetone at low temperature
(233 K) although the chemical shifts undergo some revers-
ible changes upon warming to 318 K. A 1:1 mixture of 5Ј
1
and 6 in [D6]acetone shows several signal sets in the H
NMR spectrum (including those for the parent com-
pounds) as well as ESI-MS peaks for, among others,
[(L3)2Ag]+, [(L3)(L5)Ag]+ and [(L5)2Ag]+. This confirms
that rapid ligand scrambling occurs in solution. In line with
this conclusion, compounds 6 and 8 show very similar ESI
mass spectra, and [(L3)3Ag2(PF6)]+ is detected as a minor
1
signal (Ͻ1%). H diffusion ordered spectroscopy (DOSY)
experiments reveal that 6 and 7 have similar diffusion coeffi-
cients, in accordance with the similar radii of the complexes
[(L3)2Ag2]2+ and [(L3)2Ag3]3+. We assume that the central
third Ag+ ion is only weakly bound by the two pyridazine
N atoms in 7.
3-[3-(2,6-Diisopropylphenyl)-3H-imidazolium-1-yl]-6-(3-pyridin-2-yl-
pyrazol-1-yl)pyridazine Tetrafluoroborate [HL1(BF4)]: A neat mix-
ture of 3 (1.50 g, 5.82 mmol) and 1-(2,6-diisopropylphenyl)-1H-
imidazole (6.65 g, 29.1 mmol) was heated in an evacuated flask at
150 °C for 48 h. The residue was dissolved in MeOH (30 mL) and
poured into Et2O (800 mL). The excess imidazole was recycled
from the organic phase. A brownish residue was collected by fil-
Conclusions
Members of the new family of ligand precursors HL1–5
with different diazole rings attached to both the 3- and 6- tration, dissolved in H2O (30 mL) and MeCN (30 mL) and stirred
with NH4BF4 (1.23 g, 11.7 mmol) for 2 h. The solvent was removed
under reduced pressure and the residue was again dissolved in
MeCN (50 mL). HL1 (2.15 g, 3.85 mmol, 66%) was obtained as
a pale brown powder after filtration and removal of the solvent.
Crystallization by slow diffusion of diethyl ether into an MeCN
solution of the crude product at room temperature afforded colour-
less crystals. M.p. 252 °C. C27H28BF4N7 (537.23): calcd. C 60.35,
positions of a central pyridazine core, namely a pyrazole
and an imidazolium group, offer two topologically similar
yet electronically distinct potential binding compartments,
complemented by the hemilabile pyridazine N-atom of the
bridge. Upon treatment with Ag2O sequential coordination
of up to three silver(I) ions is observed. It starts at the orga-
nometallic NHC site, yielding species [L2Ag]+ with two li-
gand strands attached by their carbene C2 atoms. Coordi-
nation of a second Ag+ ion to the classical pyrazole N-
H 5.25, N 18.25; found C 59.94, H 5.31, N 18.03. IR (KBr): ν =
˜
3431 (w, br.), 3153 (w), 2968 (w), 2932 (w), 2873 (vw), 1591 (w),
1538 (m), 1483 (m), 1456 (s), 1429 (w), 1367 (m), 1325 (vw), 1284
site may induce ligand reshuffling to give antiparallel ligand (w), 1059 (vw), 1027 (w), 943 (w), 843 (s), 772 (w), 558 (m) cm–1.
1H NMR (300 MHz, CD3CN): δ = 1.20 (d, 3J = 6.8 Hz, 6 H,
strands and a mixed {C/N} coordination of both metal
CH3ipr), 1.22 (d, 3J = 6.8 Hz, 6 H, CH3ipr), 2.52 (sept, 3J = 6.8 Hz,
ions, although this seems to depend on the peripherial li-
2 H, CHipr), 7.24 (d, 3J = 2.8 Hz, 1 H, CHpz4), 7.39 (ddd, 3J =
gand substituents. A third Ag+ ion can be accommodated
4
3
7.5 Hz, 3J = 4.9 Hz, J = 1.2 Hz 1 H, CHpy5), 7.48 (d, J = 7.8 Hz,
by two of the central pyridazine N atoms, but is just loosely
bound. The systems appear to be labile in solution, with
multiple species and several rotational isomers detected by
ESI mass spectrometry and low-temperature NMR spec-
troscopy. We assume that the hemilabile character of the
pyridazine N-atom and its temporary involvement in metal
2 H, CHar3,5), 7.64 (t, 3J = 7.8 Hz, 1 H, CHar4), 7.85 (t, 3J = 1.9 Hz,
1 H, CHim4), 7.88 (dt, J = 7.8 Hz, J = 1.8 Hz, 1 H, CHpy4), 8.17
(d, 3J = 7.8 Hz, 1 H, CHpy3), 8.31 (d, 3J = 9.5 Hz, 1 H, CHpdz),
8.50 (t, 3J = 1.9 Hz, 1 H, CHim5), 8.64 (ddd, 3J = 4.9 Hz, 3J =
3
4
1.8 Hz, J = 1 Hz, 1 H, CHpy6), 8.66 (d, J = 9.5 Hz, 1 H, CHpdz),
4
3
8.84 (d, 3J = 2.8 Hz, 1 H, CHpz5), 9.66 (t, 3J = 1.9 Hz, 1 H, CHim2
)
ion binding, as reflected by some of the crystal structures, ppm. 13C NMR (75 MHz, CD3CN): δ = 24.3 (CH3ipr), 24.5
Eur. J. Inorg. Chem. 2011, 3340–3348
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3345

J. Wimberg, U. J. Scheele, S. Dechert, F. Meyer
(CH3ipr), 29.5 (Cipr), 109.5 (Cpz4), 121.6 (Cpy3), 121.7 (Cim5), 122.2 1 H, CHpz4), 7.17 (s, 2 H, CHar3,5), 7.74 (t, 3J = 1.7 Hz, 1 H,
FULL PAPER
3
3
(Cpdz), 124.0 (Cpdz), 125.0 (Cpy5), 125.8 (Car3,5), 127.3 (Cim4), 130.5 CHim4), 8.15 (d, J = 9.5 Hz, 1 H, CHpdz), 8.44 (t, J = 1.7 Hz, 1
(Cpz5), 131.1 (Car1), 133.2 (Car4), 136.2 (Cim2), 138.5 (Cpy4), 146.5 H, CHim5), 8.48 (d, J = 9.5 Hz, 1 H, CHpdz), 9.51 (t, J = 1.7 Hz,
3
3
(Car2,6), 150.5 (Cpy6), 150.8 (CPdz), 151.5 (Cpy2), 156.6 (Cpz3), 156.6 1 H, CHim2) ppm. 13C NMR (75 MHz, CD3CN): δ = 13.9 (CH3pz3),
(Cpdz) ppm. MS (ESI+): m/z (%) = 450.2 (100) [M – BF4]+. MS
(ESI–): m/z (%) = 87.0 (100) [BF4]–. HRMS (ESI+): calcd. for
C27H28N7 450.2401; found 450.2399.
15.4 (CH3pz5), 17.7 (CH3ar2,6), 21.3 (CH3ar4), 112.1 (Cpz4), 121.6
(Cim5), 123.3 (Cpdz), 124.6 (Cpdz), 126.5 (Cim4), 130.7 (Car3,5), 131.9
(Car1), 135.8 (Car2,6), 136.1 (Cim2), 142.8 (Car4), 144.0 (Cpz5), 149.7
(Cpdz), 153.4 (Cpz3), 158.9 (Cpdz) ppm. MS (ESI+): m/z (%) = 359.3
(100) [M – PF6]+. MS (ESI–): m/z (%) = 144.9 (100) [PF6]–. HRMS
(ESI+): calcd. for C21H23N6 359.1979; found 359.1980.
3-(3-Pyridin-2-ylpyrazol-1-yl)-6-[3-(2,4,6-trimethylphenyl)-3H-
imidazolium-1-yl]pyridazine Hexafluorophosphate [HL2(PF6)]: A
neat mixture of 3 (1.50 g, 5.82 mmol) and 2,4,6-trimethylphenyl-
1H-imidazole (5.42 g, 29.1 mmol) was heated in an evacuated flask
at 150 °C for 48 h. The residue was dissolved in MeOH (30 mL)
and poured into Et2O (800 mL). The excess imidazole was recycled
from the organic phase. The brownish residue was collected by fil-
tration and dissolved in H2O (30 mL) and MeCN (30 mL) and
stirred with NH4PF6 (1.89 g, 11.6 mmol) for 2 h. The solvent was
removed under reduced pressure, and the residue was again dis-
solved in MeCN (60 mL). HL2 (2.08 g, 4.20 mmol, 72%) was ob-
tained as a pale brown powder after removal of the solvent.
Crystallization by slow diffusion of diethyl ether into an MeOH
solution of the crude product at room temperature afforded colour-
3-(3-tert-Butyl-3H-imidazolium-1-yl)-6-(3,5-dimethylpyrazol-1-yl)-
pyridazine Tetrafluoroborate [HL4(BF4)]: A solution of 1 (1.00 g,
2.60 mmol) and 1-tert-butyl-1H-imidazole (1.62 g, 13.0 mmol) was
heated in an evacuated flask at 140 °C for 48 h. The residue was
dissolved in MeOH (20 mL) and poured into Et2O (600 mL). The
excess imidazole was recycled from the organic phase. The white-
yellow residue was collected by filtration and dissolved in H2O
(25 mL) and MeCN (25 mL) and stirred with NH4BF4 (0.55 g,
5.20 mmol) for 2 h. The solvent was removed under reduced pres-
sure, and the residue was dissolved in MeCN (20 mL). HL4 (0.68 g,
1.77 mmol, 68%) was obtained as a white powder after removal of
less crystals. M.p. 267 °C. C24H22F6N7P (553.16): calcd. C 52.08, the solvent. Crystallization by slow diffusion of diethyl ether into
H 4.01, N 17.72; found C 52.37, H 3.65, N 17.99. IR (KBr): ν = an MeOH solution of the crude product at room temperature af-
˜
3426 (w, br), 3165 (w), 3143 (w), 3091 (w), 3017 (w), 2924 (vw), forded colourless crystals. M.p. 203 °C. C16H21BF4N6 (384.18):
1586 (m), 1554 (m), 1542 (m), 1485 (m), 1457 (s), 1372 (m), 1253 calcd. C 50.02, H 5.51, N, 21.88; found C 49.30, H 5.29, N 21.94.
(w), 1057 (w), 961 (vw), 944 (w), 855 (s), 831 (s), 778 (m), 558 (m) IR (KBr): ν = 3425 (m, br.), 3169 (m), 3143 (m), 3107 (m), 2987
˜
cm–1. 1H NMR (300 MHz, CD3CN): δ = 2.15 (s, 6 H, CH3ar2,6), (m), 2933 (w), 2873 (w), 1591 (m), 1573 (m), 1556 (s), 1479 (s),
3
2.39 (s, 3 H, CH3ar4), 7.17 (s, 2 H, CHar3,5), 7.24 (d, J = 2.8 Hz, 1
1450 (s), 1416 (m), 1380 (m), 1364 (m), 1335 (w), 1270 (w), 1219
H, CHpz4), 7.36 (ddd, J = 7.5 Hz, J = 4.8 Hz, J = 1.2 Hz, 1 H, (m), 1054 (vs), 972 (m), 842 (m), 807 (m), 739 (w), 657 (w), 525 (w)
3
3
4
CHpy5), 7.76 (t, J = 1.7 Hz, 1 H, CHim4), 7.89 (dt, J = 7.5 Hz, J
cm–1. 1H NMR (300 MHz, CD3OD): δ = 1.72 (s, 9 H, CH3tbu),
3
3
4
= 1.8 Hz, 1 H, CHpy4), 8.16 (dt, 3J = 8 Hz, 4J = 1.1 Hz, 1 H,
2.24 (s, 3 H, CH3pz3), 2.70 (s, 3 H, CH3pz5), 6.19 (s, 1 H, CHpz4),
3
3
3
3
CHpy3), 8.24 (d, J = 9.5 Hz, 1 H, CHpdz), 8.46 (t, J = 1.7 Hz, 1 7.84 (pseudo-t, J = 2.1 Hz, 1 H, CHim4), 8.15 (d, J = 9.5 Hz, 1
H, CHim5), 8.64 (ddd, J = 4.8 Hz J = 1.8 Hz, J = 1.1 Hz 1 H, H, CHpdz), 8.25 (pseudo-t, J = 2.1 Hz, 1 H, CHim5), 8.42 (d, J =
CHpy6), 8.66 (d, 3J = 9.5 Hz, 1 H, CHpdz), 8.84 (d, 3J = 2.8 Hz, 1 H, 9.5 Hz, 1 H, CHpdz), 9.32 (pseudo-t, 3J = 1.9 Hz, 1 H, CHim2) ppm.
CHpz5), 9.55 (t, 3J = 1.7 Hz, 1 H, CHim2) ppm. 13C NMR (75 MHz, 13C NMR (75 MHz, CD3OD): δ = 13.8 (CH3pz3), 15.2 (CH3pz5),
CD3CN): δ = 17.7 (CH3ar2,6), 21.3 (CH3ar4), 109.5 (Cpz4), 121.4 29.5 (CH3tbu), 61.4 (Ctbu), 111.8 (Cpz4), 121.0 (Cim5), 122.4 (Cim4),
3
3
4
3
3
(Cpy3), 121.5 (Cim5), 122.3 (Cpdz), 123.9 (Cpdz), 124.9 (Cpy5), 126.5
(Cim4), 130.6 (Cpz5), 130.7 (Car3,5), 131.8 (Car1), 135.8 (Car2,6), 136.2
123.2 (Cpdz), 124.6 (Cpdz), 133.8 (Cim2) 143.8 (Cpz5), 149.6 (Cpdz),
153.2 (Cpz3), 158.6 (Cpdz) ppm. MS (ESI+): m/z (%) = 297.3 (35)
(Cim2), 138.2 (Cpy4), 142.8 (Car4), 150.7 (Cpy6), 150.7 (Cpdz), 151.7 [M – BF4]+, 241.2 (100) [M – BF4 – tBu]+. MS (ESI–): m/z (%) =
(Cpy2), 156.6 (Cpz3), 156.9 (Cpdz) ppm. MS (ESI+): m/z (%) = 408.1
(100) [M – PF6]+. MS (ESI–): m/z (%) = 144.9 (100) [PF6]–. HRMS
(ESI+): calcd. for C24H22N7 408.1931; found 408.1933.
87.0 (100) [BF4]–. HRMS (ESI+): calcd. for C16H21N6 297.1822;
found 297.1828.
3-(3-Methyl-5-phenylpyrazol-1-yl)-6-[3-(2,4,6-trimethylphenyl)-3H-
imidazolium-1-yl]pyridazine Hexafluorophosphate [HL5(PF6)]: A
solution of 2 (1.58 g, 5.84 mmol) and 2,4,6-trimethylphenyl-1H-
3-(3,5-Dimethylpyrazol-1-yl)-6-[3-(2,4,6-trimethylphenyl)-3H-
imidazolium-1-yl]pyridazine Hexafluorophosphate [HL3(PF6)]: A
solution of 1 (2.00 g, 9.60 mmol) and 2,4,6-trimethylphenyl-1H- imidazole (5.42 g, 29.1 mmol) was heated in an evacuated flask at
imidazole (8.92 g, 47.9 mmol) was heated in an evacuated flask at
150 °C for 48 h. The residue was dissolved in MeOH (50 mL) and
poured into Et2O (1 L). The excess imidazole was recycled from
the organic phase. The white-yellow residue was collected by fil-
tration and dissolved in H2O (50 mL) and MeCN (30 mL) and
stirred with NH4PF6 (3.13 g, 19.2 mmol) for 2 h. The solvent was
then removed under reduced pressure, and the residue was dis-
solved in MeCN (80 mL). HL3 (3.15 g, 7.98 mmol, 83%) was ob-
tained as a white powder after removal of the solvent. Crystalli-
zation by slow diffusion of diethyl ether into an MeCN solution of
the crude product at room temperature afforded colourless crystals.
M.p. 271 °C. C21H23F6N6P (504.16): calcd. C 50.00, H 4.60, N
150 °C for 48 h. The residue was dissolved in MeOH (30 mL) and
poured into Et2O (800 mL). The excess imidazole was recycled
from the organic phase. The white-yellow residue was collected by
filtration and dissolved in H2O (30 mL) and MeCN (30 mL) and
stirred with NH4PF6 (1.90 g, 11.7 mmol) for 2 h. The solvent was
removed under reduced pressure, and the residue was again dis-
solved in MeCN (50 mL). HL5 (2.65 g, 4.67 mmol, 80%) was ob-
tained as a white powder after solvent removal. Crystallization by
slow diffusion of diethyl ether into an MeCN solution of the crude
product at room temperature afforded colourless crystals. M.p.
243 °C. C26H25F6N6P (566.18): calcd. C 55.13, H 4.45, N 14.84;
found C 55.71, H 4.29, N 15.18. IR (KBr): ν =3434 (m, br.), 3190
˜
16.66; found C 49.69, H 4.47, N, 16.48. IR (KBr): ν = 3431 (w, (w), 3155 (w), 2964 (w), 1584 (w), 1554 (m), 1499 (w), 1464 (m),
˜
br.), 3155 (w), 2976 (vw), 2929 (w), 1589 (w), 1570 (m), 1555 (m), 1390 (w), 1359 (w), 1333 (w), 1260 (s), 1194 (w), 1098 (s), 1059 (m),
1481 (m), 1450 (s), 1406 (w), 1384 (w), 1361 (w), 1334 (w), 1245 1026 (m), 969 (w), 841 (s), 828 (s), 760 (m), 698 (w), 558 (m) cm–1.
(w), 1124 (w), 1032 (w), 973 (w), 842 (s), 738 (w), 558 (m) cm–1.
1H NMR (300 MHz, CD3CN): δ = 2.14 (s, 6 H, CH3ar2,6), 2.28 (s,
3 H, CH3pz3), 2.38 (s, 3 H, CH3ar4), 2.72 (s, 3 H, CH3pz5), 6.21 (s,
1H NMR (300 MHz, CD3CN): δ = 2.10 (s, 6 H, CH3ar2,6), 2.36 (s,
3 H, CH3ar4), 2.37 (s, 3 H, CH3pz3), 6.50 (s, 1 H, CHpz4), 7.14 (s, 2
H, CHar3,5), 7.36 (m, 5 H, CHph), 7.69 (pseudo-t, 3J = 1.7 Hz, 1
3346
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 3340–3348

Pyridazine-Bridged NHC/Pyrazole Ligands and Their Silver(I) Coordination
3
3
H, CHim4), 8.17 (d, J = 9.5 Hz, 1 H, CHpdz), 8.36 (pseudo-t, J = (0.45 mmol, 85%) of 5Ј. Crystallization by slow diffusion of diethyl
1.7 Hz, 1 H, CHim5), 8.38 (d, 3J = 9.5 Hz, 1 H, CHpdz), 9.43 ether into an acetone solution of the crude product at room tem-
(pseudo-t, 3J = 1.7 Hz, 1 H, CHim2) ppm. 13C NMR (75 MHz,
CD3CN): δ = 13.8 (CH3pz3), 17.5 (CH3ar2,6), 21.2 (CH3ar4), 112.4
perature afforded colourless crystals of the composition [(L5)
2Ag2](PF6)2. M.p. 186 °C. Elemental analysis suggests, however,
(Cpz4), 121.5 (Cim5), 123.3 (Cpdz4), 126.4 (Cim4), 126.7 (Cpdz5), 129.4 that the bulk material is [(L5)2Ag](PF6): C52H48AgF6N12
P
(Cph2,6), 129.5 (Cph4), 129.6 (Cph3,5), 130.6 (Car3,5), 131.7 (Car1),
132.2 (Cph1), 135.6 (Car2,6), 136.1 (Cim2), 142.7 (Car4), 146.5 (Cpz5), N 15.47. IR (KBr): ν = 3435 (m, br.), 3145 (w), 2923 (w), 1584 (w),
(1093.24): calcd. C 57.10, H 4.42, N 15.37; found C 56. 87, H 4.32,
˜
150.2 (Cpdz), 153.7 (Cpz3), 158.0 (Cpdz) ppm. MS (ESI+): m/z (%) =
1552 (m), 1497 (w), 1446 (s), 1396 (m), 1355 (m), 1265 (m), 966
421.0 (100) [M – PF6]+. MS (ESI–): m/z (%) = 144.9 (100) [PF6]–. (m), 841 (s), 752 (m), 698 (w), 558 (m) cm–1. H NMR (500 MHz,
1
HRMS (ESI+): calcd. for C26H25N6 421.2135; found 421.2134.
CD3CN): δ = 1.78 (s, 6 H, CH3ar2,6), 2.33 (s, 3 H, CH3pz3), 2.40 (s,
3 H, CH3ar4), 6.51 (s, 1 H, CHpz4), 7.00 (s, 2 H, CHar3,5), 7.17 (m,
3 H, CHph), 7.25 (m, 2 H, CHph) 7.35 (d, 3J = 2.0 Hz, 1 H, CHim4),
7.83 (d, 3J = 9.5 Hz, 1 H, CHpdz), 8.04 (d, 3J = 2.0 Hz, 1 H, CHim5),
8.13 (d, 3J = 9.5 Hz, 1 H, CHpdz) ppm. 13C NMR (125 MHz,
CD3CN): δ = 14.1 (CH3pz3), 17.5 (CH3ar2,6), 21.3 (CH3ar4), 112.2
(Cpz4), 121.5 (Cim5), 124.6 (Cpdz), 125.7 (Cim4), 126.4 (Cpdz), 129.5
(Cph2,6), 129.6 (Cph4), 129.7 (Cph3,5), 130.3 (Car3,5), 131.5 (Cph1),
135.6 (Car2,6), 136.7 (Car1), 140.7 (Car4), 146.5 (Cpz5), 153.7 (Cpz3),
General Procedure for the Preparation of the Silver Complexes
[(Lx)2Ag](PF6) and [(Lx)2Ag2](PF6)2: A solution of the ligand pre-
cursor [HLx](PF6) (2.0 equiv.) in MeCN or acetone was treated
with Ag2O (2.2 equiv.), and the mixture was stirred at room tem-
perature in the absence of light for 48 h. After addition of activated
carbon, the reaction mixture was slowly filtered through Celite 545
to remove unreacted Ag2O, yielding a clear solution. After the re-
moval of the solvent under reduced pressure, the product was ob-
tained. Crystals suitable for XRD analysis were grown by slow dif-
fusion of diethyl ether into a solution of the crude product in either
acetone or MeCN at room temperature.
Complex [(L3)2Ag](PF6) (4): Reaction of [HL3](PF6) (1.34 g,
2.66 mmol) according to the general procedure yielded 1.27 g
(1.31 mmol, 98%) of 4. Crystallization by slow diffusion of diethyl
ether into an acetone solution of [(L3)2Ag](PF6) at room tempera-
ture afforded colourless crystals. M.p. 178 °C. C42H44AgF6N12
(969.21): calcd. C 52.02, H 4.57, N 17.33; found C 51.79, H 4.64,
1
154.2 (Cpdz), 156.6 (Cpdz), 183.7 (Cim2) ppm. H NMR (500 MHz,
[D6]acetone, 233 K): δ = 1.72 (s, 6 H, CH3ar2,6), 2.32 (s, 3 H,
CH3pz3), 2.44 (s, 3 H, CH3ar4), 6.58 (s, 1 H, CHpz4), 7.08 (s, 2 H,
3
CHar3,5), 7.12 (m, 3 H, CHph), 7.42 (m, 2 H, CHph) 7.76 (d, J =
3
3
2 Hz, 1 H, CHim4), 8.18 (d, J = 9.5 Hz, 1 H, CHpdz), 8.51 (d, J
= 2 Hz, 1 H, CHim5), 8.53 (d, J = 8.7 Hz, 1 H, CHpdz) ppm. MS
3
(ESI+): m/z (%) = 949.2 (100) [L2Ag]+. MS (ESI–): m/z (%) = 144.9
(100) [PF6]–. HRMS (ESI+): calcd. for C52H48AgN12 947.3170;
found 947.3158.
P
N 17.27. IR (KBr): ν = 3441 (m, br.), 3180 (m), 2966 (m), 2927
Complex [(L3)2Ag2](PF6)(BF4) (6): Complex 6 was prepared by ad-
dition of 1 equiv. of AgBF4 to a solution of [(L3)2Ag](PF6) (4) in
acetone. Crystallization by slow diffusion of diethyl ether into an
acetone solution at room temperature afforded colourless crystals
˜
(m), 1582 (m), 1559 (m), 1443 (s), 1397 (m), 1354 (w), 1265 (vw),
1034 (vw), 842 (s), 739 (m), 558 (m) cm–1. 1H NMR (500 MHz,
CD3CN): δ = 1.86 (s, 6 H, CH3ar2,6), 2.24 (s, 3 H, CH3pz3), 2.36 (s,
3 H, CH3ar4), 2.61 (s, 3 H, CH3pz5), 6.18 (s, 1 H, CHpz4), 6.99 (s, 2 of 6. C42H44Ag2BF10N12P (1164.07): calcd. C 43.32, H 3.81, N
H, CHar3,5), 7.37 (d, 3J = 2.0 Hz, 1 H, CHim4), 8.08 (t, 3J = 2.0 Hz,
1 H, CHim5), 8.19 (d, 3J = 9.5 Hz, 1 H, CHpdz), 8.24 (d, 3J = 9.5 Hz,
14.44; found C 43.93, H 3.54, N 14.15. H NMR (500 MHz, [D6]
1
acetone, 233 K): δ = 2.13 (s, 3 H, CH3pz3), 2.16 (s, 6 H, CH3ar2,6),
1 H, CHpdz) ppm. 13C NMR (125 MHz, CD3CN): δ = 14.0 2.33 (s, 3 H, CH3ar4), 2.70 (s, 3 H, CH3pz5), 6.53 (s, 1 H, CHpz4),
(CH3pz3), 15.1 (CH3pz5), 17.8 (CH3ar2,6), 21.3 (CH3ar4), 111.7 (Cpz4), 7.15 (s, 2 H, CHar3,5), 7.99 (s, 1 H, CHim4), 8.57 (s, 1 H, CHim5),
121.7 (Cim5), 124.2 (Cpdz), 124.7 (Cpdz), 125.6 (Cim4), 130.3 (Car3,5),
8.75 (s, 2 H, CHpdz) ppm. 13C NMR (125 MHz, [D6]acetone,
135.8 (Car2,6), 136.7 (Car1), 140.7 (Car4), 143.7 (Cpz5), 153.1 (Cpz3), 233 K): δ = 13.9 (CH3pz3), 14.2 (CH3pz5), 17.9 (CH3ar2,6), 20.8
153.8 (Cpdz), 157.7 (Cpdz), 183.3 (Cim2) ppm. MS (ESI+): m/z (%)
= 825.3 (100) [L2Ag]+. MS (ESI–): m/z (%) = 144.9 (100) [PF6]–.
HRMS (ESI+): calcd. for C42H44AgN12 823.2857; found 823.2860.
(CH3ar4), 112.8 (Cpz4), 118.9, 123.3, 125.7, 126.5, 126.9, 135.5
(Cph2,6), 136.2, 140.5, 145.5, 153.3, 154.3, 154.5, 181.3 (Cim2) ppm.
(300 MHz, [D6]acetone, 293 K): δ = 2.09 (s, 6 H, CH3ar2,6), 2.20 (s,
3 H, CH3pz3), 2.37 (s, 3 H, CH3ar4), 2.69 (s, 3 H, CH3pz5), 6.51 (s,
1 H, CHpz4), 7.12 (s, 2 H, CHar3,5), 7.86 (d, 3J = 1.9 Hz, 1 H,
Complex [(L4)2Ag](PF6) (4Ј): Reaction of [HL4](PF6) (300 mg,
0.68 mmol) according to the general procedure yielded 237 mg
(0.28 mmol, 82 %) of the crude product [(L3)2Ag](PF6). The 1H
NMR spectrum shows an impurity of ca. 10 % free ligand.
Crystallization by slow diffusion of diethyl ether into an acetone
solution of the crude product at room temperature afforded colour-
3
3
CHim4), 8.41 (d, J = 1.9 Hz, 1 H, CHim5), 8.65 (d, J = 9.5 Hz, 1
H, CHpdz), 8.70 (d, 3J = 9.5 Hz, 1 H, CHpdz) ppm. 13C NMR
(75 MHz, [D6]acetone, 293 K): δ = 14.0 (CH3pz3), 14.5 (CH3pz5),
18.0 (CH3ar2,6), 21.1 (CH3ar4), 113.1 (Cpz4), 123.1 (Cim5), 126.1
(Cpdz), 126.8 (Cim4), 129.3 (Cpdz), 130.2 (Car3,5), 135.7 (Car2,6), 136.8
(Car1), 140.8 (Car4), 145.7 (Cpz5), 154.1 (Cpdz), 154.9 (Cpdz), 155.1
(Cpz3), 189.4 (Cim2) ppm.
less crystals. IR (KBr): ν = 3669 (w), 3588 (w), 3442 (w, br.), 3192
˜
(w), 3160 (m), 2981 (m), 2935 (w), 1623 (w), 1583 (m), 1555 (m),
1468 (s), 1449 (s), 1383 (m), 1371 (m), 1332 (m), 1294 (w), 1240
(m), 1218 (w), 1058 (m), 956 (w), 847 (s, br.), 738 (m), 609 (w), 558
Complex [(L3)2Ag3](PF6)(BF4)2 (7): Complex 7 was prepared by ad-
dition of 2 equiv. of AgBF4 to a solution of complex [(L3)2Ag](PF6)
(4) in acetone. Crystallization by slow diffusion of diethyl ether into
this acetone solution at room temperature afforded a few colourless
crystals. Satisfactory elemental analysis could not be obtained be-
cause of the small amount of crystalline material. 1H NMR
(300 MHz, [D6]acetone): δ = 2.11 (s, 6 H, CH3ar2,6), 2.15 (s, 3 H,
CH3pz3), 2.36 (s, 3 H, CH3ar4), 2.70 (s, 3 H, CH3pz5), 6.49 (s, 1 H,
1
(s) cm–1. H NMR (300 MHz, CD3CN): δ = 1.79 (s, 9 H, CH3tbu),
2.29 (s, 3 H, CH3pz3), 2.46 (s, 3 H, CH3pz5), 6.23 (s, 1 H, CHpz4),
7.64 (d, 3J = 2.1 Hz, 1 H, CHim4), 7.70 (d, 3J = 2.1 Hz, 1 H, CHim5),
8.06 (d, 3J = 9.5 Hz, 1 H, CHpdz), 8.10 (d, 3J = 9.5 Hz, 1 H, CHpdz
)
ppm. 13C NMR (75 MHz, CD3CN): δ = 14.4 (CH3pz3), 14.7
(CH3pz5), 31.8 (CH3tbu), 59.9 (Ctbu), 112.0 (Cpz4), 120.2 (Cim5),
122.6 (Cim4), 124.6 (Cpdz), 125.3 (Cpdz), 144.1 (Cpz5), 153.6 (Cpz3),
154.7 (Cpdz), 156.3 (Cpdz), 180.4 (im2) ppm. MS (ESI+): m/z (%) =
699.3 (100) [L2Ag]+. MS (ESI–): m/z (%) = 144.9 (100) [PF6]–.
HRMS (ESI+): calcd. for C32H40AgN12 699.2544; found 699.2545.
3
CHpz4), 7.12 (s, 2 H, CHar3,5), 7.86 (d, J = 2.0 Hz, 1 H, CHim4),
8.42 (d, 3J = 2.0 Hz, 1 H, CHim5), 8.64 (d, 3J = 9.5 Hz, 1 H, CHpdz),
3
8.68 (d, J = 9.5 Hz, 1 H, CHpdz) ppm. 13C NMR (75 MHz, [D6]-
Complex [(L5)2Ag2](PF6) (5Ј): Reaction of [HL5](PF6) (600 mg,
1.06 mmol) according to the general procedure yielded 495 mg
acetone): δ = 14.1 (CH3pz3), 14.4 (CH3pz5), 18.1 (CH3ar2,6), 21.0
(CH3ar4), 113.2 (Cpz4), 123.6 (Cim5), 126.3 (Cpdz), 126.9 (Cim4),
Eur. J. Inorg. Chem. 2011, 3340–3348
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3347

J. Wimberg, U. J. Scheele, S. Dechert, F. Meyer
FULL PAPER
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Published Online: July 4, 2011
3348
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Eur. J. Inorg. Chem. 2011, 3340–3348