Synthesis and catalytic application of palladium complexes with picoline-functionalized benzimidazolin-2-ylidene ligands

Article abstract of DOI:10.1002/ejic.200801214

The picoline-functionalized benzimidazolium salts N-alkyl- N'-picolylbenzimidazolium bromide [alkyl = methyl (1), ethyl (2), n-propyl (3), n-butyl (4)] and the dipicoline-function-alized benzimidazolium bromide 5 have been synthesized. Reaction of the sal

Full text of DOI:10.1002/ejic.200801214

FULL PAPER
DOI: 10.1002/ejic.200801214
Synthesis and Catalytic Application of Palladium Complexes with Picoline-
Functionalized Benzimidazolin-2-ylidene Ligands
Mareike C. Jahnke,[a] Tania Pape,[a] and F. Ekkehardt Hahn*[a]
Keywords: Carbenes / Palladium / C–C coupling
The picoline-functionalized benzimidazolium salts N-alkyl-
NЈ-picolylbenzimidazolium bromide [alkyl = methyl (1), ethyl
(2), n-propyl (3), n-butyl (4)] and the dipicoline-function-
alized benzimidazolium bromide 5 have been synthesized.
Reaction of the salts 1–4 with palladium acetate leads to the
formation of the palladium complexes of the type [Pd(L)2]Br2
(6–9; L = N-alkyl-NЈ-picolylbenzimidazolin-2-ylidene). Sub-
sequent reaction of these complexes with AgBF4 gave the
salt 5 with n-butyllithium and subsequent coordination of the
unstable carbene intermediate to [PdBr2cod]. The molecular
structures of the benzimidazolium salts 3 and 5 and the palla-
dium complexes 7–9 and 11 have been determined by X-ray
diffraction. The bis(carbene) palladium complexes 6–9 as
well as the monocarbene pincer-type complex 14 have been
used as precatalysts in Heck-type coupling reactions of sev-
eral aryl halides with styrene and n-butyl acrylate as olefinic
palladium complexes 10–13. The pincer-type palladium com- substrates.
plex [PdBrL]Br (14, L = N,NЈ-dipicolylbenzimidazolin-2-ylid-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ene) was prepared by deprotonation of the benzimidazolium
Germany, 2009)
still a subject of debate.[16] The good σ-donor properties
lead to highly stable NHC complexes. In contrast to the
more-labile coordinated phosphane ligands, the carbene do-
nor groups tend to remain coordinated to the metal center
during catalytic transformation. Another positive aspect of
the strong σ-donation is the efficient compensation of a
charge deficiency at the metal atom during catalytic pro-
cesses.[17]
A number of complexes with bridged bis(carbene) li-
gands[18] have been described in addition to complexes
bearing bidentate heteroatom-functionalized carbene li-
gands with an additional heteroatom donor such as P
(A),[19] N,[20] O (B)[21] or S.[22] Moreover, pincer-type com-
plexes with one carbene (C)[23] and two additional group 15
donors or two carbene donor moieties and a pyridine- or
phenylene-based bridging unit (D)[24] have been prepared.
Introduction
The isolation of the first stable N-heterocyclic carbene
(NHC) in 1991 by Arduengo et al.[1] caused a renewed and
intense interest in this type of compounds.[2] A large
number of different NHCs derived from imidazole,[3] imid-
azolidine,[4] benzimidazole,[5] and triazole[6] have been syn-
thesized in addition to NHCs with extended ring sizes de-
rived from six-[7] and seven-membered[8] heterocycles.
Moreover, stable heterocyclic carbenes containing only one
nitrogen atom within the heterocycle (CAAC)[9] or with two
phosphorus atoms for the stabilization of the carbene center
(PHC)[10] have been prepared by Bertrand et al.
Apart from the free carbenes, the number of complexes
with NHC ligands has increased enormously because of the
application of such complexes as catalysts in a variety of
chemical transformations.[11] NHC ligands have become a
cheap and easy accessible alternative to phosphanes in the
design of new organometallic catalysts. In addition to the
rhodium-catalyzed hydroformylation[12] and the ruthenium-
catalyzed olefin metathesis reactions,[13] the most common
applications for complexes bearing NHC ligands are the
palladium- and nickel-catalyzed Heck- and Suzuki-type C–
C coupling reactions.[11,14]
Relative to phosphane ligands, NHCs are widely consid-
ered stronger σ-donors without any significant MǞL π-
backbonding,[15] although the absence of backbonding is
Complexes bearing donor-functionalized NHC ligands
sometimes show an increased catalytic activity.[11,14] The
combination of NHCs with additional donor functions also
allows for fine tuning of the catalyst’s electronic properties.
Normally, the σ-donor properties of the NHC ligand and
that of the additional heteroatom are different, and this sit-
uation can lead to the generation of a vacant coordination
[a] Institut für Anorganische und Analytische Chemie Westfälische
Wilhelms-Universität Münster,
Corrensstraße 30, 48149 Münster, Germany
Fax: +49-251-8333108
E-mail: fehahn@uni-muenster.de
1960
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Pd Complexes of Picoline-Functionalized Benzimidazolin-2-ylidene Ligands
site for substrate binding during the catalytic process by
Preparation of the free carbene ligands or their dibenzo-
temporary dissociation of the heteroatom donor from the tetraazafulvalene dimers by deprotonation of the acidic
metal.[25]
NCHN group failed. This is most likely due to the acidity
Most heterodonor-functionalized NHC ligands contain of the methylene protons of the bridge. Attempted depro-
imidazolin-2-ylidenes as the carbene source, while benz- tonation of the C2 carbon atom of the heterocycle with
imidazolin-2-ylidenes are much less encountered as the car- strong bases leads to undesired side reactions.[29]
bene moiety, although several complexes with donor-func-
Crystals suitable for an X-ray diffraction study of the
tionalized benzimidazolin-2-ylidene ligands are known.[26] benzimidazolium salts 3 and 5 were obtained by slow evap-
The preparation of N-methyl-NЈ-picolylbenzimidazolium oration of the solvent from methanol solutions of the salts.
chloride has recently been described.[27] We have modified The molecular structures of the benzimidazolium cations in
this synthesis and prepared a series of picoline-function- 3 and 5·H2O are depicted in Figure 1. The N1–C1 and N2–
alized benzimidazolium salts. These compounds have been C1 bond lengths and the N1–C1–N2 bond angles are typi-
used for the synthesis of palladium complexes containing cal for benzimidazolium salts.[26a,26c,28] No interaction be-
bi- and tridentate picoline-functionalized benzimidazolin-2- tween the nitrogen donor function of the picoline group
ylidene ligands. Here we report the molecular structures of and the acidic hydrogen atom of the benzimidazolium het-
selected palladium complexes with these ligands, together erocycle exists since the N···H separations are too great to
with their catalytic activity in Heck-type C–C coupling re- indicate such an interaction (in 3 3.063 Å; in 5 2.845 Å and
actions.
3.409 Å).
Results and Discussion
Picoline-Functionalized Benzimidazolium Salts
Reaction of a suitably N-substituted benzimidazole deriv-
ative[26e,28] with 2-picolyl bromide hydrobromide in aceto-
nitrile gave the picoline-functionalized benzimidazolium
salts 1–4 with yields in the range 71–85% (Scheme 1). The
dipicoline-functionalized benzimidazolium salt 5 was pre-
pared by reaction of 2 equiv. 2-picolyl bromide hydrobro-
mide with 1 equiv. benzimidazole and sodium carbonate as
a base in acetonitrile with a yield of 76%.
Figure 1. Molecular structures of the picoline-functionalized benz-
imidazolium cations in 3 and 5·H2O. Hydrogen atoms, the bromide
counteranion, and solvent molecules have been omitted for clarity.
Selected bond lengths [Å] and angles [°] in 3: N1–C1 1.328(3), N1–
C8 1.464(4), N2–C1 1.328(3), N2–C14 1.472(3), N3–C9 1.341(4),
N3–C13 1.335(4); N1–C1–N2 110.4(2), N1–C8–C9 110.3(2), C9–
N3–C13 116.7(3). Selected bond lengths [Å] and angles [°] in
5·H2O: N1–C1 1.318(6), N1–C14 1.468(6), N2–C1 1.325(7), N2–
C8 1.462(6), N3–C9 1.341(7), N3–C13 1.346(7), N4–C15 1.342(6),
N4–C19 1.344(7); N1–C1–C2 111.6(5), N2–C8–C9 111.2(4), N1–
C14–C15 110.8(4), C9–N3–C13 116.7(5), C15–N4–C19 116.3(5).
Palladium Complexes with Picoline-Functionalized
Benzimidazolin-2-ylidene Ligands
Whereas a monocarbene palladium complex bearing an
N-methyl-NЈ-picolyl-benzimidazolin-2-ylidene ligand has
been prepared,[27] bis(carbene) palladium complexes with
N-picoline-functionalized benzannulated carbene ligands
have not yet been reported. Bis(carbene) palladium com-
plexes bearing two N-picoline-functionalized benzimidaz-
olin-2-ylidene ligands were synthesized by in situ deproton-
ation of the benzimidazolium salts 1–4 with palladium ace-
tate and subsequent coordination of the carbene species to
the palladium center (Scheme 2). After purification, the
bright yellow palladium complexes 6–9 were obtained with
yields in the range 75–86%. Complexes 6–9 are soluble in
Scheme 1. Synthesis of the picoline-functionalized benzimidazol-
ium salts 1–5.
1
The H NMR spectra of the benzimidazolium salts 1–5 dichloromethane or a mixture of dichloromethane and
exhibit the signal for the NCHN proton as a singlet be- methanol.
tween δ = 9.90 and 11.50 ppm.[26–28] The resonances of the
The formation of complexes 6–9 was verified by NMR
NCHN groups in the 13C NMR spectra of 1–5 (δ = 143.8– spectroscopy. The characteristic 1H NMR resonance for the
143.1 ppm) are also found in the expected range.[26,28]
acidic proton of the NCHN group in 1–4 (δ ≈ 10 ppm) is
Eur. J. Inorg. Chem. 2009, 1960–1969
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1961

M. C. Jahnke, T. Pape, F. E. Hahn
FULL PAPER
Scheme 2. Synthesis of palladium complexes with picoline-func-
tionalized benzimidazolin-2-ylidene ligands.
missing in the spectra of complexes 6–9. In contrast to the
rather simple spectra of the salts 1–4, the spectra of com-
plexes 6–9 show multiple resonances for the aromatic pro-
tons. The 13C NMR spectra of 6–9 exhibit a double set of
resonances that can be assigned to the picoline carbon
atoms. The resonances of the carbene carbon atoms that
are cis to each other are broad signals found in the narrow
range 166.1–167.9 ppm.
Figure 2. Molecular structures of the dicationic palladium com-
plexes in 7 (top), 8·2MeOH (middle), and 9·2H2O (bottom). Hy-
drogen atoms, bromide counterions, and solvent molecules have
been omitted for clarity.
The NMR spectra indicate that the palladium complexes
6–9 do not possess C2 symmetry in solution. This might be
due to a dynamic process involving the picoline donors,
The Pd–Ccarbene bond lengths in 7 [1.962(3) Å], 8
which could be coordinated to the metal center or act as a [1.975(5) Å], and 9 [1.965(5) Å] fall in the expected range
dangling ligand arm. The decoordination of a picoline do- for complexes with a cis arrangement of the two benzimid-
nor was also indicated by mass spectrometry, which, instead azolin-2-ylidene donors [1.972(3)–1.991(7) Å].[30] They are
of the dicationic complexes depicted in Scheme 2, shows shorter than the Pd–Ccarbene separations in both neutral and
one bromido ligand coordinated to the metal center instead cationic palladium complexes with a trans orientation of the
of a picoline donor.
two benzimidazolin-2-ylidene ligands [Pd–Ccarbene 2.019(4)–
Crystals suitable for an X-ray diffraction study of com- 2.047(4) Å].[26a–26c,31] The Pd–Npicoline bond lengths in 7–9
pounds 7, 8·2MeOH, and 9·2H2O were grown by slow evap- fall in the range 2.082(3)–2.104(4) Å. They are similar to
oration of the solvents from dichloromethane/methanol the Pd–N distances observed in palladium complexes with
solutions of the complexes. The molecular structures of 7, lutidine-bridged bis(benzimidazolin-2-ylidene) ligands re-
8, and 9 are depicted in Figure 2, and selected bond lengths ported recently [2.048(2)–2.072(3) Å].[26a,26b]
and angles for these complexes are summarized in Table 1.
The palladium atoms in 7–9 have a slightly distorted
All three complexes possess a C2 symmetry in the solid square-planar arrangement of the coordinating ligands. The
state, and the palladium atom resides on a crystallographic bond angle N3–Pd–N3* [for 7 94.65(2)°; for 8 96.3(2)°; for
twofold axis. Contrary to the dynamic behavior observed in 9 96.8(2)°] shows the greatest deviation from a perfect
solution, the picoline-functionalized NHC ligands act as a square-planar arrangement. The complexes appear to exist
bidentate chelate ligand in all cases.
without strain, and the N–C–C bond angles at the methyl-
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Eur. J. Inorg. Chem. 2009, 1960–1969

Pd Complexes of Picoline-Functionalized Benzimidazolin-2-ylidene Ligands
Table 1. Selected bond lengths [Å] and angles [°] in 7, 8·2MeOH, C2/c for 7 (Z = 4) and P21/n for 11·CH2Cl2 (Z = 4). Ad-
9·2H2O, and 11·CH2Cl2.
ditional crystal data for 11·CH2Cl2 are summarized in
Table 1, and Figure 3 shows a plot of the complex cation.
7
8·2MeOH 9·2H2O
11·CH2Cl2
Bond lengths
Pd–C1
1.962(3) 1.975(5) 1.965(5) 1.976(3)
1.974(3)
2.082(3) 2.087(4) 2.104(4) 2.086(3)
2.097(3)
1.341(4) 1.355(6) 1.341(6) 1.355(4)
1.351(4) 1.331(6) 1.349(6) 1.346(4)
Pd–C21
Pd–N3
Pd–N6
N1–C1
N2–C1
N4–C21
N5–C21
–
–
–
–
–
–
–
–
–
–
–
–
1.357(4)
1.340(4)
Bond angles
C1–Pd–C1*
C1–Pd–C21
N3–Pd–C1
N6–Pd–C21
N3*–Pd–C1
N3–Pd–C21
N6–Pd–C1
N3–Pd–N3*
N3–Pd–N6
N1–C1–N2
N4–C21–N5
C9–N3–C13
C29–N6–C33
93.92(2) 93.3(3)
93.8(3)
–
85.1(2)
–
–
Figure 3. Molecular structure of the dicationic palladium complex
in 11·CH2Cl2. Hydrogen atoms and the two tetrafluoroborate
anions have been omitted for clarity.
–
–
97.91(14)
86.82(13)
84.93(13)
–
174.42(12)
177.08(12)
–
85.74(12) 85.2(2)
–
–
178.48(12) 176.9(2) 173.3(2)
The potentially tridentate dipicoline-functionalized
benzimidazolin-2-ylidene ligand obtained from 5 should be
capable of forming a pincer-type palladium carbene com-
plex like 14. However, reaction of the benzimidazolium salt
5 with palladium acetate only afforded the undesired
bis(carbene) palladium complex.[26a,26b,30a,31] Pincer com-
plex 14 was obtained by in situ deprotonation of the benzi-
midazolium salt 5 with nBuLi at –78 °C, followed by trap-
ping of the unstable carbene with [PdBr2(cod)] (Scheme 3).
–
–
–
–
–
–
94.65(15) 96.3(2)
96.8(2)
–
–
–
90.38(3)
107.2(3) 109.0(4) 107.2(4) 106.6(3)
107.5(3)
118.8(3) 118.7(5) 119.4(4) 118.9(3)
119.3(3)
–
–
–
–
–
–
ene carbon atom that links the carbene and the picoline
donors are close to that for a tetrahedral arrangement [for
7 111.1(3)°; for 8 110.2(5)°; for 9 110.7(4)°].
The N–C–N angles at the carbene center fall in the range
107.2(3)°–109.0(4)°. They are, as expected,[2] slightly smaller
than the equivalent angles in the benzimidazolium salts 3
and 5, but larger than the N–C–N angles observed for the
free benzimidazolin-2-ylidenes.[5a,5c] The C–N–C bond
angles within the picoline donor functions [for 7 118.8(3)°;
for 8 118.7(5)°; for 9 119.4(4)°] increase slightly upon coor-
dination relative to the angles observed for the benzimid-
azolium salts 3 and 5.
Scheme 3. Preparation of the pincer-type palladium complex 14.
Formation of the palladium complex 14 was detected by
NMR spectroscopy. The characteristic downfield signal for
the NCHN proton of salt 5 at δ = 11.5 ppm is absent in
Reaction of the palladium complexes 6–9 with 2 equiv.
silver tetrafluoroborate gave the complexes 10–13
(Scheme 2). This anion exchange removes the potentially
competing ligand Br–, which is capable of coordinating to
the palladium atom. Consequently, both donor functions of
the picoline-functionalized carbene ligands remain coordi-
nated in solution. This behavior is revealed by the NMR
spectra of compounds 10–13, which exhibit only one set of
resonances for the picoline functions. In addition, the pro-
tons of the methylene bridge become diastereotopic and
1
the H NMR spectrum of the palladium complex 14. The
resonance of the proton in the ε position of the pyridine
ring (δ = 8.45 ppm in 5) is shifted downfield upon coordina-
tion of the pyridine nitrogen to the palladium atom (δ =
9.42 ppm in 14). The 13C NMR spectrum exhibits the reso-
nance of the coordinated carbene carbon atom at δ =
160.4 ppm.
1
2
lead to two doublets in the H NMR spectra. The J coup-
ling constants exhibit values of about 14 Hz, which is typi-
cal for geminal coupling of diastereotopic protons.[26c]
Catalysis
The palladium complexes 6–9 and 14 were tested as pre-
Crystals of 11·CH2Cl2 suitable for an X-ray diffraction catalysts in Heck-type coupling reactions of differently
study were obtained by slow evaporation of the solvents para-functionalized aryl bromides with styrene and n-butyl
from a dichloromethane/methanol solution of 11. As the acrylate. Because of the thermal stability of these complexes
complex cations in 7 and 11 are identical, they exhibit al- and their inertness towards air and moisture both in the
most identical structural parameters. The major differences solid state and in solution, the catalytic experiments were
between 7 and 11·CH2Cl2 is found in the space groups – carried out under aerobic conditions.
Eur. J. Inorg. Chem. 2009, 1960–1969
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1963

M. C. Jahnke, T. Pape, F. E. Hahn
FULL PAPER
Initially we studied the catalytic Heck-type coupling re- Table 3. Palladium-catalyzed Heck-type coupling reactions.[a]
action of 4-bromobenzaldehyde and styrene with the cat-
ionic palladium complexes 6–9 and 14 as precatalysts
(Table 2). After a reaction time of 24 h, almost complete
conversion was observed with the four palladium complexes
6–9 bearing two picoline-functionalized benzimidazolin-2-
ylidene ligands (Entries 1–4). Shortening of the reaction
time to 2 h led to a drastic decrease in the conversion to
between 27 and 32% (Entries 5–8). Only the pincer-type
palladium complex 14 exhibited an acceptable conversion
of 82% after a reaction time of only 2 h (Entry 9). We can-
not rule out the formation of palladium colloids from the
palladium complexes 6–9, which then catalyzed the reaction
heterogeneously.
Entry Catalyst
R
RЈ
Time
[h]
Conversion
[%]
1
2
3
4
5
6
7
8
6
COMe
COMe
COMe
COMe
COMe
OMe
OMe
OMe
OMe
CHO
CHO
CHO
CHO
CHO
COMe
COMe
COMe
COMe
COMe
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2
2
2
2
18
26
31
34
57
5
5
12
4
21
20
19
22
65
16
15
17
22
34
7
8
9
14
6
2
24
24
24
24
2
2
2
2
2
2
2
7
8
9
9
Ph
Table 2. Palladium-catalyzed Heck-type coupling reaction of 4-bro-
mobenzaldehyde and styrene.[a]
10
11
12
13
14
15
16
17
18
19
6
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
nBuOC(O)
7
8
9
14
6
7
8
2
2
2
9
14
Entry
Catalyst
Time [h]
Conversion [%]
[a] Reaction conditions: 1 mmol 4-aryl halides, 1.4 mmol styrene,
2 mmol NaOAc, 1 mol-% palladium catalyst, and 3 mL dmac.
Yields were determined by gas chromatography.
1
2
3
4
5
6
7
8
9
6
24
24
24
24
2
2
2
98
99
100
100
30
28
32
27
82
7
8
9
The application of the palladium complexes 6–9 and 14
as precatalysts for the C–C coupling reaction of 4-bromo-
benzaledehyde or 4-bromoacetophenone with n-butyl acryl-
ate was also studied. In both coupling reactions the pincer-
type palladium complex 14 is superior to the bis(carbene)
palladium complexes 6–9. After a reaction time of 2 h, a
conversion of 65% (Entry 14) and 34% (Entry 19), respec-
tively, was found for catalyst 14, while the conversion for
both investigated coupling reactions are much lower for the
palladium complexes 6–9.
6
7
8
9
2
2
14
[a] Reaction conditions: 1 mmol 4-bromobenzaldehyde, 1.4 mmol
styrene, 2 mmol NaOAc, 1 mol-% palladium catalyst, and 3 mL di-
methylacetamide (dmac). Yields were determined by gas
chromatography.
Attempts to use the less-reactive 4-chlorobenzaldehyde
as substrate also showed no satisfying results. In a manner
similar to the less-reactive 4-bromoanisole, the conversion
for the C–C coupling reaction of 4-chlorobenzaldehyde
with styrene catalyzed by the bis(carbene) palladium com-
plexes 6–9 was low (2–4%) after a reaction time of 24 h.
Therefore, we conclude that the application of palladium
complexes with picoline-functionalized benzimidazolin-2-
ylidene ligands seems to be limited to activated aryl bro-
mides. Moreover, the bis(carbene) palladium complexes 6–
9 with two bidentate ligands are less active than the pincer-
type palladium complex 14. We suppose that the difference
in catalytic activity is based on steric effects, which makes
substrate coordination to the catalytically active metal cen-
ter more difficult in complexes 6–9.
The palladium complexes 6–9 and 14 were also tested
as precatalysts in several other coupling reactions of para-
functionalized aryl bromides with styrene and n-butyl acryl-
ate as olefinic substrates (Table 3). The first five entries in
Table 3 show the conversions for the reaction of 4-bromo-
acetophenone with styrene catalyzed by the palladium com-
plexes 6–9 and 14 for 2 h. Again, over this short reaction
time, the pincer-type complex 14 exhibited the highest con-
version, although the total conversion is not satisfying when
compared to related complexes bearing benzimidazolin-2-
ylidenes as the carbene source.[26d]
As previously observed, the conversion rate in catalytic
Heck-type coupling reactions is also influenced by the elec-
tronic nature of the aryl bromides. In the reaction of 4-
bromoanisole with styrene even after 24 h only low conver-
sions to the desired coupling product were observed with
the palladium complexes 6–9 (Entries 6–9). The conversion
for aryl bromides with electron-withdrawing groups such as
4-bromoacetophenone and 4-bromobenzaldehyde (Table 2)
is relatively high when compared to this data.
Conclusions
New picoline-functionalized benzimidazolium salts have
been obtained by the reaction of benzimidazole derivatives
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Pd Complexes of Picoline-Functionalized Benzimidazolin-2-ylidene Ligands
(s, 2 H, NCH2-pyridine), 4.60 (q, 3J = 7.2 Hz, 2 H, NCH2CH3),
with picolyl bromide hydrobromide. Reaction of these salts
with palladium acetate gives the square-planar bis(carbene)
palladium complexes 6–9 in which the picoline-function-
alized benzimidazolin-2-ylidene ligands and the carbene do-
nors are in cis positions. A hemilabile coordination of the
picoline arms was observed in solution for these complexes.
Nevertheless, X-ray diffraction studies with single crystals
of compounds 7–9 reveal picolyl coordination in the solid
state. Anion exchange of the bromide anions with silver tet-
rafluoroborate gives the palladium complexes 10–13 in
which the picolyl donors are coordinated in the solid state
and in solution. Complexes 6–9 and 14 exhibit catalytic ac-
tivity in Heck-type coupling reactions of activated aryl bro-
mides with styrene or n-butyl acrylate. The highest catalytic
activity is observed for the pincer-type complex 14. All
3
1.57 (t, J = 7.2 Hz, 3 H, NCH2CH3) ppm. 13C NMR (50.3 MHz,
[D6]dmso): δ = 153.4 (pyridine-Cα), 149.9 (pyridine-Cε), 143.1
(NCHN), 137.9 (pyridine-Cγ), 131.7, 131.3, 127.1, 126.9 (Ar-C),
124.0 (pyridine-Cδ), 123.2 (pyridine-Cβ), 114.3, 114.2 (Ar-C), 51.2
(NCH2-pyridine), 42.6 (NCH2CH3), 14.7 (NCH2CH3) ppm. MS
(MALDI): m/z = 238 [M – Br]+. C15H16BrN3 (318.22): calcd. C
56.62, H 5.07, N 13.20; found C 56.40, H 5.21, N 12.82.
N-Propyl-NЈ-picolylbenzimidazolium Bromide (3): Yield: 0.268 g
(81%). 1H NMR (400.1 MHz, [D6]dmso): δ = 10.14 (s, 1 H,
NCHN), 8.47 (d, 3J = 4.5 Hz, 1 H, pyridine-Hε), 8.13 (d, 3J =
3
3
7.8 Hz, 1 H, Ar-H), 7.97 (d, J = 7.8 Hz, 1 H, Ar-H), 7.89 (t, J =
7.8 Hz, 1 H, Ar-H), 7.71 (d, 3J = 7.8 Hz, 1 H, Ar-H), 7.69–7.60
(m, 2 H, pyridine-Hβ, pyridine-Hγ), 7.36 (d, J = 4.5 Hz, 1 H, pyr-
3
3
idine-Hδ), 5.98 (s, 2 H, NCH2-pyridine), 4.57 (t, J = 7.3 Hz, 2 H,
NCH2CH2CH3), 1.95 (sext, 3J = 7.3 Hz, 2 H, NCH2CH2CH3), 0.94
complexes show a low catalytic activity in coupling reac- (t, 3J = 7.3 Hz, 3 H, NCH2CH2CH3) ppm. 13C NMR (100.1 MHz,
[D6]dmso): δ = 153.4 (pyridine-Cα), 149.9 (pyridine-Cε), 143.5
(NCHN), 137.9 (pyridine-Cγ), 131.7, 131.4, 127.1, 126.9 (Ar-C),
124.1 (pyridine-Cβ), 123.1 (pyridine-Cδ), 114.3 (Ar-C), 51.2
(NCH2-pyridine), 48.6 (NCH2CH2CH3), 22.4 (NCH2CH2CH3),
11.0 (NCH2CH2CH3) ppm. MS (MALDI): m/z = 252 [M – Br]+.
C16H18BrN3 (332.25): calcd. C 57.84, H 5.46, N 12.65; found C
57.72, H 5.67, N 12.38.
tions of aryl chlorides or deactivated aryl bromides.
Experimental Section
General Procedures: All operations except for the preparation of
complex 14 were carried out in air by using commercially available
solvents. 2-Picolyl bromide hydrobromide and palladium acetate
were purchased from Sigma–Aldrich or Fluka. The N-alkylated
benzimidazole derivatives were prepared by using published pro-
cedures.[26e,28] Mass spectra were measured on a Varian MAT 212
instrument. Elemental analyses (C, H, N) were obtained for all
compounds with a Vario EL III elemental analyzer at the Westfälis-
che Wilhelms-Universität, Münster.
N-Butyl-NЈ-picolylbenzimidazolium Bromide (4): Yield: 0.293 g
(85%). 1H NMR (300.1 MHz, [D6]dmso): δ = 10.14 (s, 1 H,
NCHN), 8.46 (d, 3J = 4.5 Hz, 1 H, pyridine-Hε), 8.13 (d, 3J =
3
3
7.7 Hz, 1 H, Ar-H), 7.96 (d, J = 7.7 Hz, 1 H, Ar-H), 7.89 (d, J
= 7.7 Hz, 1 H, Ar-H), 7.11 (d, 3J = 7.7 Hz, 1 H, Ar-H), 7.68–
7.62 (m, 2 H, pyridine-Hβ, pyridine-Hγ), 7.36 (d, J = 4.5 Hz, 1 H,
pyridine-Hδ), 5.97 (s, 2 H, NCH2-pyridine), 4.59 (t, J = 7.3 Hz, 2
3
3
H, NCH2CH2CH2CH3), 1.91 (m, 2 H, NCH2CH2CH2CH3), 1.35
2 = 7.3 Hz, 3 H,
H, NCH2CH2CH2CH3), 0.93 (t, 3J
General Procedure for the Synthesis of N-Alkyl-NЈ-picolylbenzimid-
azolium Bromides 1–4: The N-alkylated benzimidazole derivative
(1.2 mmol), 2-picolyl bromide hydrobromide (1.0 mmol, 0.252 g),
and excess potassium carbonate (2.0 mmol, 0.276 g) as base were
suspended in acetonitrile (50 mL). This mixture was heated under
reflux for 48 h. The solvent was then removed in vacuo, and the
residue was suspended in dichloromethane (30 mL). Filtration and
removal of the solvent from the filtrate yielded a viscous residue,
which was again dissolved in a small amount of dichloromethane.
This solution was added dropwise to ice-cold diethyl ether
(200 mL). A brown precipitate formed, which was separated by fil-
tration. The solid was washed three times diethyl ether (25 mL
each) and dried in vacuo.
(m,
NCH2CH2CH2CH3) ppm. 13C NMR (75.5 MHz, [D6]dmso): δ =
153.4 (pyridine-Cα), 149.9 (pyridine-Cε), 143.5 (NCHN), 137.9
(pyridine-Cγ), 131.7, 131.1, 127.1, 126.9 (Ar-C), 124.0 (pyridine-
Cβ), 123.1 (pyridine-Cδ), 114.3, 114.2 (Ar-C), 51.2 (NCH2-pyr-
idine), 46.9 (NCH2CH2CH2CH3), 30.9 (NCH2CH2CH2CH3), 19.4
(NCH2CH2CH2CH3), 13.7 (NCH2CH2CH2CH3) ppm. MS
(MALDI): m/z = 266 [M – Br]+. C17H20BrN3 (346.27): calcd. C
57.97, H 5.82, N 12.14; found C 57.77, H 5.61, N 11.91.
N,NЈ-Dipicolylbenzimidazolium Bromide (5): Benzimidazole
(0.45 mmol, 0.054 g), 2-picolyl bromide hydrobromide (1.0 mmol,
0.250 g), and an excess of sodium carbonate as base (0.212 g,
2.0 mmol) were suspended in acetonitrile (80 mL). The reaction
mixture was heated under reflux for 48 h. Subsequently, the solvent
was removed in vacuo, and the oily residue was dissolved in a small
amount of dichloromethane. This solution was added dropwise to
ice-cold diethyl ether (200 mL) whilst stirring. A reddish precipitate
formed, which was isolated by filtration. The solid was washed
three times with diethyl ether (25 mL each) and dried in vacuo.
N-Methyl-NЈ-picolylbenzimidazolium Bromide (1): Yield: 0.215 g
(71%). 1H NMR (200.1 MHz, [D6]dmso): δ = 9.90 (s, 1 H, NCHN),
3
8.49 (d, J = 4.8 Hz, 1 H, pyridine-Hε), 8.05–7.95 (m, 2 H, Ar-H),
7.94–7.89 (m, 2 H, pyridine-Hβ and pyridine-Hγ), 7.73–7.65 (m, 2
H, Ar-H), 7.37 (d, 3J = 4.8 Hz, 1 H, pyridine-Hδ), 5.93 (s, 2 H,
NCH2-pyridine), 4.15 (s, 3 H, NCH3) ppm. 13C NMR (50.3 MHz,
[D6]dmso): δ = 153.4 (pyridine-Cα), 150.0 (pyridine-Cε), 143.8
(NCHN), 137.9 (pyridine-Cγ), 132.2, 131.5, 127.1 (Ar-C), 124.1
(pyridine-Cδ), 123.1 (pyridine-Cβ), 114.1, 114.0 (Ar-C), 51.2
(NCH2-pyridine), 33.9 (CH3) ppm. MS (MALDI): m/z = 224 [M –
Br]+. C14H14BrN3 (304.19): calcd. C 55.28, H 4.64, N 13.81; found
C 55.23, H 4.96, N 13.39.
1
Yield: 0.131 g (76%). H NMR (300.1 MHz, CDCl3): δ = 11.50 (s,
1 H, NCHN), 8.45 (d, 3J = 4.7 Hz, 2 H, pyridine-Hε), 7.84–7.77
3
(m, 4 H, Ar-H), 7.33–7.65 (m, 4 H, Ar-H), 7.48 (d, J = 5.0 Hz, 2
H, pyridine-Hγ), 7.22, 7.19 (both d, 3J = 5.0 Hz, 2 H, pyridine-
Hβ, pyridine-Hδ), 5.97 (s, 4 H, NCH2-pyridine) ppm. 13C NMR
(75.5 MHz, CDCl3): δ = 152.7 (pyridine-Cα), 150.1 (pyridine-Cε),
143.8 (NCHN), 138.1 (pyridine-Cγ), 132.0, 127.5 (Ar-C), 124.3
(pyridine-Cβ), 124.1 (pyridine-Cδ), 114.6 (Ar-C), 53.0 (NCH2-pyr-
idine) ppm. MS (MALDI): m/z = 301 [M – Br]+. C19H17BrN4
(381.3): calcd. C 59.85, H 4.49, N 14.69; found C 59.31, H 4.12, N
14.23.
N-Ethyl-NЈ-picolylbenzimidazolium Bromide (2): Yield: 0.262 g
(82%). 1H NMR (200.1 MHz, [D6]dmso): δ = 10.11 (s, 1 H,
3
NCHN), 8.49 (d, J = 4.8 Hz, 1 H, pyridine-Hε), 8.15–8.06 (m, 2
H, Ar-H), 7.98–7.84 (m, 2 H, pyridine-Hβ and pyridine-Hγ), 7.74–
3
7.61 (m, 2 H, Ar-H), 7.37 (d, J = 4.8 Hz, 1 H, pyridine-Hδ), 5.95
Eur. J. Inorg. Chem. 2009, 1960–1969
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1965

M. C. Jahnke, T. Pape, F. E. Hahn
FULL PAPER
General Synthesis of {Bis[N-alkyl-NЈ-(α-picolyl)benzimidazolin-2-
ylidene]palladium(II)} Dibromides 6–9: Palladium acetate
(0.22 mmol, 0.050 g) and one of the benzimidazolium salts 1–4
(0.44 mmol) were dissolved in argon-saturated dmso (10 mL). The
orange solution was stirred at room temperature for 2 h. The tem-
perature was then raised to 50 °C for another 12 h. Finally, the
solution was stirred at 120 °C for 3 h. The solvent was removed in
vacuo, and the solid residue was dissolved in a mixture of dichloro-
methane and methanol (1:1, v/v). This solution was added dropwise
to ice-cold diethyl ether (200 mL). A bright yellow precipitate
formed, which was isolated by filtration. The isolated solid was
washed twice with diethyl ether (5 mL each) and dried in vacuo.
NCH2CH2CH2CH3), 1.41–1.22 (m, 4 H, NCH2CH2CH2CH3), 0.56
(t, 3J = 7.3 Hz, 6 H, NCH2CH2CH2CH3) ppm. 13C NMR
(50.3 MHz, [D6]dmso): δ = 167.85 (NCN), 153.7, 152.4 (pyridine-
Cα), 149.9 (pyridine-Cε), 140.9, 140.4 (pyridine-Cγ), 133.2, 132.7,
125.1, 124.9 (Ar-C), 124.1, 123.9 (pyridine-Cβ, pyridine-Cδ), 112.0,
111.5 (Ar-C), 52.3, 52.2 (NCH2 -pyridine), 48.3, 47.4
(NCH2CH2CH2CH3), 31.1, 30.8 (NCH2CH2CH2CH3), 19.1
(NCH2CH2CH2CH3), 13.2 (NCH2CH2CH2CH3) ppm. MS
(MALDI): m/z = 717 [M – Br]+. C34H38Br2N6Pd (796.9): calcd. C
51.24, H 4.81, N 10.55; found C 50.87, H 4.43, N 10.21.
General Procedure for the Synthesis of {Bis[N-alkyl-NЈ-(α-picolyl)-
benzimidazolin-2-ylidene]palladium(II)} Tetrafluoroborate 10–13:
One of the palladium complexes 6–9 (1.0 mmol) and silver tetra-
fluoroborate (2.1 mmol, 0.220 g) were dissolved in dichlorometh-
{Bis[N-methyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium(II)}
Dibromide (6): Yield: 0.118 g (75%). 1H NMR (200 MHz, [D6]-
dmso): δ = 9.06–9.04 (m, 1 H, pyridine-H), 8.12–7.10 (m, 15 H, ane (60 mL). The solution was stirred under exclusion of light for
Ar-H, pyridine-H), 6.01 (s br., 4 H, NCH2-pyridine), 4.15 (s, 6 H,
NCH3) ppm. 13C NMR (100.1 MHz, [D6]dmso): δ = 167.9 (NCN),
154.2, 153.0 (pyridine-Cα), 150.7, 149.4 (pyridine-Cε), 140.6 (pyr-
idine-Cγ), 134.2, 133.9, 124.2, 123.9 (Ar-C), 122.7 (pyridine-Cβ,
pyridine-Cδ), 111.7, 111.2 (Ar-C), 51.7 (NCH2-pyridine), 34.5
12 h. It was then filtered, and the filtrate was dried in vacuo. A
bright yellow residue was obtained, which was dissolved in dichlo-
romethane (2 mL) and added dropwise to diethyl ether while stir-
ring. A yellow precipitate formed, which was collected by filtration.
The solid was washed twice with diethyl ether (5 mL each) and
(NCH3) ppm. MS (MALDI): m/z = 633 [M – Br]+. C28H26Br2N6Pd dried in vacuo.
(712.8): calcd. C 47.18, H 3.68, N 11.79; found C 45.97, H 3.45, N
11.53.
{Bis[N-methyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium-
(II)} Tetrafluoroborate (10): Yield: 0.487 g (67 %). 1H NMR
(200.1 MHz, [D6]dmso): δ = 8.79 (d, 3J = 5.4 Hz, 2 H, pyridine-
{Bis[N-ethyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium(II)}
Dibromide (7): Yield: 0.134 g (82%). 1H NMR (200.1 MHz, [D6]- Hε), 8.46–8.04 (m, 5 H, Ar-H and pyridine-H), 7.87–7.65 (m, 4 H,
3
dmso): δ = 9.01 (d, J = 5.5 Hz, 1 H, pyridine-H), 8.10–8.06 (m, 1
Ar-H and pyridine-H), 7.62–7.56 (m, 5 H, Ar-H and pyridine-H),
6.50, (d, 2J = 14.0 Hz, 2 H, NCH2-pyridine), 6.36 (d, 2J = 14.0 Hz,
2 H, NCH2-pyridine), 4.23 (s, 6 H, NCH3) ppm. 13C NMR
(50.3 MHz, [D6]dmso): δ = 167.2 (NCN), 153.9 (pyridine-Cα),
152.2 (pyridine-Cε), 141.8 (pyridine-Cγ), 134.0, 132.6 (Ar-C), 125.5,
3
H, pyridine-H), 7.99 (d, J = 7.9 Hz, 4 H, Ar-H), 7.82–7.79 (m, 2
H, pyridine-H), 7.77–7.74 (m, 2 H, pyridine-H), 7.56 (t, 3J =
7.9 Hz, 4 H, Ar-H), 7.45–7.41 (m, 2 H, pyridine-H), 6.09–5.99 (m,
2 H, NCH2-pyridine), 5.97–5.91 (m, 2 H, NCH2-pyridine), 4.88–
4.68 (m, 4 H, NCH2CH3), 1.47 (t, 3J = 7.2 Hz, 6 H, NCH2CH3) 125.1 (Ar-C), 124.5, 124.2 (pyridine-Cβ, pyridine-Cδ), 112.0, 111.5
ppm. 13C NMR (50.3 MHz, [D6]dmso): δ = 167.8 (NCN), 154.4,
153.7 (pyridine-Cα), 152.6, 148.0 (pyridine-Cε), 140.8, 140.4 (pyr-
idine-Cγ), 132.8, 132.3, 124.7, 124.4 (Ar-C), 124.0, 123.9 (pyridine-
Cβ, pyridine-Cδ), 112.2, 111.8 (Ar-C), 51.6 (NCH2-pyridine), 42.2
(NCH2CH3), 13.6 (NCH2CH3) ppm. MS (MALDI): m/z = 661
[M – Br]+. C30H30Br2N6Pd (740.8): calcd. C 48.64, H 4.08, N 11.34;
found C 48.33, H 3.87, N 10.98.
(Ar-C), 50.5 (NCH2-pyridine), 34.8 (NCH3) ppm. MS (MALDI):
m/z = 551 [M + H – 2BF4]+.
{Bis[N-ethyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium-
(II)} Tetrafluoroborate (11): Yield: 0.556 g (74 %). 1H NMR
(200.1 MHz, [D6]dmso): δ = 8.39 (d, 3J = 5.5 Hz, 2 H, pyridine-
3
Hε), 8.28–8.16 (m, 6 H, Ar-H, pyridine-H), 7.86 (d, J = 8.1 Hz, 2
H, Ar-H), 7.69–7.59 (m, 4 H, Ar-H, pyridine-Hβ, pyridine-Hδ), 7.56
(d, 3J = 5.5 Hz, 2 H, pyridine-H), 6.44 (d, 2J = 14.1 Hz, 2 H,
NCH2-pyridine), 6.39 (d, 2J = 14.1 Hz, 2 H, NCH2-pyridine), 4.43–
4.23 (m, 2 H, NCH2CH3), 3.88–3.65 (m, 2 H, NCH2CH3), 1.17 (t,
{Bis[N-propyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium-
(II)} Dibromide (8): Yield: 0.146 g (86%). 1H NMR (200.1 MHz,
[D6]dmso): δ = 9.01 (d, 3J = 5.4 Hz, 1 H, pyridine-H), 8.10–8.06
(m, 1 H, pyridine-H), 8.03–7.97 (m, 4 H, Ar-H), 7.85–7.81 (m, 2 H, 3J = 7.2 Hz, 6 H, NCH2CH3) ppm. 13C NMR (50.3 MHz, [D6]-
pyridine-H), 7.79–7.76 (m, 2 H, pyridine-H), 7.56 (t, 3J = 8.0 Hz, 4
H, Ar-H), 7.48–7.41 (m, 2 H, pyridine-H), 6.28–6.20 (m, 2 H, 141.8 (pyridine-Cγ), 133.4, 132.8, 125.4, 125.1 (Ar-C), 124.6, 124.2
NCH2-pyridine), 5.96–5.88 (m, 2 H, NCH2-pyridine), 4.66–4.46 (pyridine-Cβ, pyridine-Cδ), 112.0, 111.6 (Ar-C), 51.3 (NCH2-pyr-
dmso): δ = 167.1 (NCN), 153.9 (pyridine-Cα), 152.7 (pyridine-Cε),
(m, 4 H, NCH2CH2CH3), 2.03–1.82 (m, 4 H, NCH2CH2CH3), 0.88 idine), 43.6 (NCH2CH3), 14.7 (NCH2CH3) ppm. MS (MALDI):
3
(t, J = 7.3 Hz, 6 H, NCH2CH2CH3) ppm. 13C NMR (50.3 MHz,
[D6]dmso): δ = 166.1 (NCN), 154.9, 154.4 (pyridine-Cα), 153.1,
149.6 (pyridine-Cε), 141.4, 141.0 (pyridine-Cγ), 133.8, 133.3, 125.8,
125.6 (Ar-C), 125.2, 124.7 (pyridine-Cβ, pyridine-Cδ), 112.7, 112.1
(Ar-C), 52.8, 52.3 (NCH2-pyridine), 50.3 (NCH2CH2CH3), 23.3
(NCH2CH2CH3), 11.6 (NCH2CH2CH3) ppm. MS (MALDI): m/z
= 689 [M – Br]+. C32H34Br2N6Pd (768.9): calcd. C 49.99, H 4.46,
N 10.93; found C 49.53, H 4.21, N 10.52.
m/z = 579 [M + H – 2BF4]+.
{Bis[N-propyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium-
(II)} Tetrafluoroborate (12): Yield: 0.604 g (77 %). 1H NMR
(200.1 MHz, [D6]dmso): δ = 8.43 (d, 3J = 5.6 Hz, 2 H, pyridine-
3
Hε), 8.32–8.14 (m, 6 H, Ar-H, pyridine-H), 7.88 (d, J = 8.2 Hz, 2
H, Ar-H), 7.69–7.47 (m, 6 H, Ar-H, pyridine-H), 6.46 (d, 3J =
3
14.1 Hz, 2 H, NCH2-pyridine), 6.40 (d, J = 14.1 Hz, 2 H, NCH2-
pyridine), 4.39–4.19 (m, 2 H, NCH2CH2CH3), 3.61–3.41 (m, 2 H,
3
{Bis[N-butyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium-
(II)} Dibromide (9): Yield: 0.148 g (85%). 1H NMR (200.1 MHz,
[D6]dmso): δ = 9.01 (d, 3J = 5.5 Hz, 1 H, pyridine-H), 8.11–8.05
NCH2CH2CH3), 1.61–1.40 (m, 4 H, NCH2CH2CH3), 0.54 (t, J =
7.2 Hz, 6 H, NCH2CH2CH3) ppm. 13C NMR (50.1 MHz, [D6]-
dmso): δ = 167.1 (NCN), 153.9 (pyridine-Cα), 152.6 (pyridine-Cε),
(m, 1 H, pyridine-H), 8.02–7.95 (m, 4 H, Ar-H), 7.87–7.83 (m, 2 H, 141.8 (pyridine-Cγ), 133.3, 133.1, 125.1, 124.9 (Ar-C), 124.2, 124.1
pyridine-H), 7.81–7.77 (m, 2 H, pyridine-H), 7.56 (t, 3J = 8.0 Hz, 4
(pyridine-Cβ, pyridine-Cδ), 111.8, 111.4 (Ar-C), 51.5 (NCH2-pyr-
H, Ar-H), 7.53–7.41 (m, 2 H, pyridine-H), 6.33–6.14 (m, 2 H, idine), 49.7 (NCH2 CH2 ) , 2 2. 5 ( NC H2 CH2 CH3 ), 11.4
NCH2-pyridine), 6.01–5.82 (m, 2 H, NCH2-pyridine), 4.66–4.46 (NCH2CH2CH3) ppm. MS (MALDI): m/z = 607 [M + H –
( m , 4 H , N C H 2 C H 2 C H 2 C H 3 ) , 1 . 9 6 – 1 . 6 9 ( m , 4 H , 2BF4]+.
1966
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1960–1969

Pd Complexes of Picoline-Functionalized Benzimidazolin-2-ylidene Ligands
{Bis[N-butyl-NЈ-(α-picolyl)benzimidazolin-2-ylidene]palladium(II)}
Tetrafluoroborate (13): Yield: 0.586 g (72%). 1H NMR
(200.1 MHz, [D6]dmso): δ = 8.43 (d, 3J = 5.5 Hz, 2 H, pyridine-
(Ar-C), 127.0 (pyridine-Cβ), 125.7 (pyridine-Cδ), 124.9, 112.7 (Ar-
C), 51.0 (NCH2-pyridine) ppm. MS (MALDI): m/z = 486 [M –
Br]+. C19H16Br2N4Pd (566.6): calcd. C 40.28, H 2.85, N 9.89; found
C 40.01, H 2.53, N 9.73.
3
Hε), 8.30–8.15 (m, 6 H, Ar-H, pyridine-H), 7.87 (d, J = 8.2 Hz, 2
H, Ar-H), 7.69–7.61 (m, 4 H, Ar-C, pyridine-H), 7.57 (d, 3J =
General Method for the Heck Reactions: One of the palladium com-
plexes 6–9 or 14 (1.0 mol-%), an aryl halide (1.0 mmol), styrene or
n-butyl acrylate (1.4 mmol), and sodium acetate as base (2.0 mmol)
were dissolved in dimethylacetamide (dmac, 3 mL). The reaction
mixture was heated to 110 °C with stirring. After the selected reac-
tion time had lapsed, the mixture was cooled down to ambient
temperature, and the organic phase was cleaned by elution over a
short silica gel column. The solution was then analyzed by quanti-
tative GC chromatography (GC-FID) with a Shimadzu GC-2100
equipped with an Aglient Technologies HP 5 capillary column
(30.0 m).
5.5 Hz, 2 H, pyridine-H), 6.47 (d, 3J = 14.6 Hz, 2 H, NCH2-pyr-
3
idine), 6.40 (d, J = 14.6 Hz, 2 H, NCH2-pyridine), 4.39–4.20 (m,
2 H, NCH2CH2CH2CH3), 3.74–3.54 (m, 2 H, NCH2CH2CH2CH3),
1.96–1.69 (m, 2 H, NCH2CH2CH2CH3), 1.40–1.20 (m, 2 H,
NCH2CH2CH2CH3), 1.03–0.87 (m, 4 H, NCH2CH2CH2CH3), 0.51
(t, 3J = 7.3 Hz, 6 H, NCH2CH2CH2CH3) ppm. 13C NMR
(50.1 MHz, [D6]dmso): δ = 167.3 (NCN), 153.9 (pyridine-Cα),
152.6 (pyridine-Cε), 141.9 (pyridine-Cγ), 133.3, 133.1, 125.9, 125.5
(Ar-C), 124.9, 124.7 (pyridine-Cβ, pyridine-Cδ), 112.6, 112.0
(Ar-C), 51.5 (NCH2-pyridine), 49.7 (NCH2CH2CH2CH3),
29.9 (NCH2CH2CH2CH3), 22.5 (NCH2CH2CH2CH3), 11.0
(NCH2CH2CH2CH3) ppm. MS (MALDI): m/z = 635 [M + H –
2BF4]+.
X-ray Diffraction Studies: Diffraction data for 3, 5·H2O, 7, and
11·CH2Cl2 were collected with a Bruker AXS APEX CCD dif-
fractometer equipped with a rotation anode by using graphite-mo-
nochromated Mo-Kα radiation (λ = 0.71073 Å). For compounds
8·2MeOH and 9·2H2O, diffraction data were obtained on a Bruker
SMART CCD diffractometer with a rotating anode by using Cu-
Kα radiation (λ = 1.54184 Å). Data were collected over the full
sphere and were corrected for absorption. Data reduction was per-
formed with the Bruker SMART[32] program package. For further
crystal and data collection details see Table 4. All crystal structures
were solved with SHELXS-97[33] by employing the heavy-atom
method and were refined with SHELXL-97[34] by using first iso-
tropic and later anisotropic thermal parameters for all non-hydro-
gen atoms. Hydrogen atoms were added to the structure models at
calculated positions, and their thermal parameters were fixed to
1.3 Ueqv. of the parent atom. Ortep-3 for Windows[35] was used for
all molecular plots. CCDC-713489 (3), -713490 (5·H2O), -713491
(7), -713492 (8·2MeOH), -713493 (9·2H2O), and -713494
(11·CH2Cl2) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk./data/request/cif.
{Bromo[N,NЈ-Dipicolylbenzimidazolin-2-ylidene]palladium(II)} Bro-
mide (14): Compound 5 (1.0 mmol, 0.380 g) was suspended in thf
(70 mL), and the suspension was cooled down to –78 °C. nBuLi
(1.1 mmol, 0.44 mL of a 2.5  hexane solution) was then added
dropwise to the suspension. After stirring at –78 °C for 30 min,
[PdBr2(cod)] (1.0 mmol, 0.374 g) was added. The reaction mixture
was warmed to ambient temperature, and it was then heated under
reflux for an additional 12 h. The solvent was removed in vacuo,
and the solid residue was extracted twice with dichloromethane
(20 mL each). The resulting solution was filtered, and the solvent
was removed in vacuo. A red solid was obtained, which was dis-
solved in a small amount of dichloromethane. This solution was
added dropwise to stirred diethyl ether (200 mL). A precipitate
formed, which was collected by filtration, washed with diethyl ether
(5 mL), and dried in vacuo. Yield: 0.358 g (63%). 1H NMR
(300.1 MHz, [D6]dmso): δ = 9.42 (d, 3J = 6.4 Hz, 2 H, pyridine-
3
Hε), 8.27–8.18 (m, 6 H, Ar-H, pyridine-Hγ), 7.71 (t, J = 6.4 Hz, 2
H, pyridine-Hβ), 7.50 (m, 2 H, pyridine-Hδ), 6.19 (s, 4 H, NCH2-
pyridine) ppm. 13C NMR (75.1 MHz, [D6]dmso): δ = 160.4 (NCN),
156.1 (pyridine-Cα), 153.2 (pyridine-Cε), 141.0 (pyridine-Cγ), 132.6
Table 4. Summary of crystallographic data for 3, 5·H2O, 7, 8·2MeOH, 9·2H2O, and 11·CH2Cl2.
3
5·H2O
7
8·2MeOH
9·2H2O
11·CH2Cl2
Formula
Mr
C16H18N3Br
332.24
C19H19N4BrO
399.29
C30H30N6Br2Pd
740.82
C34H42N6Br2O2Pd
832.96
C34H42N6Br2O2Pd
832.96
C31H32N6B2Cl2F8Pd
839.55
Crystal size [mm] 0.25ϫ0.25ϫ0.21
0.17ϫ0.06ϫ0.03
16.847(2)
10.456(13)
20.068(3)
90
0.09ϫ0.05ϫ0.03
8.972(3)
21.584(6)
15.981(5)
90
0.31ϫ0.25ϫ0.24
9.6057(3)
21.9015(5)
16.6005(5)
90
0.22ϫ0.13ϫ0.06
19.4769(5)
11.0235(3)
18.4314(5)
90
0.10ϫ0.06ϫ0.04
9.464(2)
15.022(4)
24.112(6)
90
a [Å]
10.328(2)
14.559(3)
11.502(2)
90
b [Å]
c [Å]
α [°]
β [°]
114.854(3)
90
1569.2(5)
4
90
90
3521.4(8)
8
90.331(7)
90
3095(2)
4
97.118(2)
90
3465.5(2)
4
121.776(2)
90
3364.1(2)
4
98.732(5)
90
3388.3(15)
4
γ [°]
V [Å3]
Z
Space group
ρcalcd. [gcm–3]
µ [mm–1]
2θ range [°]
Data collected
P21/c
1.406
2.614 (Mo-Kα)
4.3–55.0
15094
Pbca
1.506
2.349 (Mo-Kα)
4.0–50.0
26727
C2/c
1.590
3.211 (Mo-Kα)
3.8–60.2
17675
C2/c
1.596
7.333 (Cu-Kα)
8.1–139.8
9819
C2/c
1.645
7.554 (Cu-Kα)
9.6–139.9
9386
P21/n
1.646
0.783 (Mo-Kα)
3.2–50.0
26798
Unique data, Rint 3595, 0.0336
3099, 0.0856
2508
4531, 0.0787
3235
3214, (0.0726)
2250
2880
1805
5951
4849
Obsd. data
2935
[IՆ2σ(I)]
R (all data)
0.0599
0.0820
0.0789
0.0755
0.0668
0.0543
wR (all data)
No. of variables
Peak/hole [eÅ3]
0.1095
191
1.323/–1.099
0.1730
238
0.681/–0.757
0.0880
178
1.124/–0.711
0.1348
216
1.138/–2.966
0.0837
205
0.805/–0.557
0.0948
453
0.675/–0.388
Eur. J. Inorg. Chem. 2009, 1960–1969
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1967

M. C. Jahnke, T. Pape, F. E. Hahn
FULL PAPER
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Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft (SFB
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Published Online: February 19, 2009
699.
Eur. J. Inorg. Chem. 2009, 1960–1969
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1969