Synthesis and characterization of a cationic phthalimido-functionalized N-heterocyclic carbene complex of palladium(II) and its catalytic activity

Article abstract of DOI:10.1002/ejic.201301277

A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been synthesized from [3-methyl-1-(2′- phthalimidoethyl)imidazolium] hexafluorophosphate ([NHC^Me,PhtH] PF₆) by transmetalation and isolated in 67 % yield. The title complex has been applied as catalyst in the Suzuki-Miyaura cross-coupling reaction under benign aqueous conditions. The catalyst is active without any observable initiation period. High average turnover frequencies (TOFs) of up to 55000 h^-1 have been reached with catalyst concentrations as low as 0.01 mol-%. A cationic phthalimido-functionalized N-heterocyclic carbene (NHC) palladium(II) complex has been prepared in high yield. The complex was activated instantly, without an initiation period, in the Suzuki-Miyaura cross-coupling reaction under benign aqueous aerobic conditions. Turnover frequencies (TOFs) up to 55000 h^-1, were achieved with 0.01 mol-% of the complex. Copyright

Full text of DOI:10.1002/ejic.201301277

FULL PAPER
DOI:10.1002/ejic.201301277
Synthesis and Characterization of a Cationic Phthalimido-
Functionalized N-Heterocyclic Carbene Complex of
Palladium(II) and Its Catalytic Activity
Serena L. M. Goh,[a,b] Manuel P. Högerl,
[a,b]
[a]
Nade zˇ da B. Joki c´ ,
[c]
[c]
[d]
Alexandrina D. Tanase, Bettina Bechlars, Walter Baratta,
[
e,f,g]
[a,c]
János Mink,
and Fritz E. Kühn*
Keywords: Carbenes / N ligands / Palladium / Cross-coupling / Homogeneous catalysis
A cationic phthalimido-functionalized N-heterocyclic carb- catalyst in the Suzuki–Miyaura cross-coupling reaction un-
ene (NHC) palladium(II) complex has been synthesized from der benign aqueous conditions. The catalyst is active without
[
3-methyl-1-(2Ј-phthalimidoethyl)imidazolium] hexafluoro- any observable initiation period. High average turnover fre-
Me,Pht
–1
phosphate ([NHC
H]PF
6
) by transmetalation and iso-
quencies (TOFs) of up to 55000 h have been reached with
lated in 67% yield. The title complex has been applied as
catalyst concentrations as low as 0.01 mol-%.
Introduction
Various strategies have been suggested in the literature.
[
3]
For example, Organ et al. support the idea of electron-
rich σ-donating ligands on palladium that facilitate oxidat-
ive addition and promote complex stability, while sterically
bulky ligands aid in reductive elimination of products in C–
C coupling reactions. Organ’s group employed aryl chlor-
ides as substrates in C–C coupling reactions with the ap-
proach of a “throw-away ligand”, using the mono-NHC
Pd–PEPPSI (PEPPSI: Pyridine-Enhanced Precatalyst Prep-
aration Stabilization and Initiation) catalyst PdCl2-
In the past decades, the search for more robust ligands
to prevent the deactivation of Pd catalysts in cross-coupling
reactions, which have been shown to be sensitive to oxi-
dation or phosphorus–carbon bond cleavage,[ has led to
the use of N-heterocyclic carbenes (NHCs). NHCs are
known to be stronger σ-donors than phosphanes and usu-
ally form more stable bonds to the palladium center, which
makes the complexes less prone to deactivation during ca-
talysis. Nevertheless, it has to be taken into account that
labile ligands are frequently required for the fast activation
or rearrangement of the catalyst environment during a cata-
lytic reaction cycle.
1]
[
2]
(
2
IDip)(Py) [IDip = 1,3-bis(2,6-diisopropylphenyl)imidazol-
-ylidene, Py = pyridine]. Similarly, Chen et al. recently
[4]
achieved good results in the activation of aryl chlorides in
C–C and C–N coupling reactions with the related PdCl -
2
[
5]
(
IDip)(NEt ). Weng et al. promote the concept of hemi-
3
[
a] Molecular Catalysis, Catalysis Research Center, Technische
lability of a ligand that can structurally and geometrically
change and adapt to the requirements of the metal center
during different stages of the catalytic cycle. This facilitates
the quick activation of the catalyst and ensures protection
of the intermediates. This concept has led us to explore a
functionalized NHC ligand with an ancillary phthalimido
Universität München,
Lichtenbergstr. 4, 85747 Garching b. München, Germany
E-mail: fritz.kuehn@ch.tum.de
http://www.ch.tum.de/molcat
[
[
[
[
b] Kaust Catalysis Center, King Abdullah University of Science
and Technology,
Thuwal 6900-23955, Saudi Arabia
c] Chair of Inorganic Chemistry, Department of Chemistry,
Technische Universität München,
Lichtenbergstr. 4, 85747 Garching b. München, Germany
d] Dipartimento di Chimica, Fisica e Ambiente, Università di
Udine,
II
unit. Imidate-based Pd bis(triphenylphosphine) complexes
were found to be more active in C–C coupling reactions
[6]
than (Ph P) PdCl . It is worth noting that imidate ligands
3
2
–
2
Via Cotonificio 108, 33100 Udine, Italy
[H
4 6
C (CON CO)] display coordination flexibility and
e] Structural Chemistry Department, Institute of Chemistry,
Chemical Research Center of the Hungarian Academy of
Sciences,
multihapticity by coordination through their N and/or O
2
[7]
atoms in a κ coordination mode.
Pusztaszeri út 59–67, 1025 Budapest, Hungary
f] Department of Analytical Chemistry, University of Veszprém,
P. O. Box 158, 8201 Veszprém, Hungary
In this work, the preparation of the easily accessible cat-
ionic palladium complex cis-[PdCl(Me–NHC–phthaloyl)-
[
[
g] Analytical Chemistry Research Group of the Hungarian
Academy of Sciences, University of Veszprém,
P. O. Box 158, 8201 Veszprém, Hungary
(CH CN) ](PF ) (2), containing a bulky phthalimido-func-
3 2 6
tionalized carbene, is reported. Complex 2 was found to
display high catalytic activity in the Suzuki–Miyaura cross-
coupling reaction.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301277.
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Results and Discussion
Synthesis of the Functionalized NHC PdII Complex 2
Phthalimido-functionalized imidazolium salt [3-methyl-
1
-(2Ј-phthalimidoethyl)imidazolium] hexafluorophosphate
Me,Pht
([NHC
H]PF ) (1) was synthesized by a slightly modi-
6
fied procedure, which led to a shorter reaction time and
increased product yield.[ After quaternization of the
methylimidazole with N-(2-bromoethyl)phthalimide in tolu-
8]
ene at 120 °C for 24 h, the N-functionalized imidazolium
Me,Pht
salt ([NHC
]Br) was obtained in quantitative yield
(
Scheme 1). Salt metathesis with KPF in water at 60 °C led
6
to the formation of 1 as a white powder, after cooling to
room temperature, in 92% yield. The corresponding Pd–
NHC complex 2 was obtained by the silver transmetalation
route and was isolated in 67% yield. As a solid, 2 is stable
to air and moisture for weeks without decomposition.
Figure 1. Solid-state structure of the cationic complex 2. Hydrogen
[
9]
atoms are omitted for clarity. Thermal ellipsoids are drawn at the
50% probability level. Selected bond lengths [Å] and angles [°]:
Pd1–C5 1.965(2), Pd1–N1 2.018(2), Pd1–N2 2.096(2), Pd1–Cl1
2
8
9
.284(1); C5–Pd1–N1 90.65(7), C5–Pd1–N2 178.5(1), N1–Pd1–N2
9.2(1), C5–Pd1–Cl1 88.1(1), N1–Pd1–Cl1 178.4(1), N2–Pd1–Cl1
2.1(1).
δ = 142.77 ppm. It is worth noting that monocationic NHC
palladium complexes generally display carbene peaks in the
[
11]
range 160–190 ppm.
Conversely, dicationic phosphine-
[
12]
[11b,13]
functionalized NHC
and cationic bis(NHC)
Pd
complexes show resonances in the range 142–157 ppm.
1
The H NMR spectra of 2 in [D ]DMSO and [D ]MeCN
6
3
show four multiplets that were assigned to two sets of chem-
ically inequivalent protons, H /H Ј and H /H Ј, of the eth-
a
a
b
b
ylene bridge, which indicates a restricted rotation of the
[
14]
Scheme 1. Synthesis of complex 2.
tethered phthalimido moiety in complex 2.
In addition to the X-ray analysis of 2, no interaction of
the phthalimido moiety with the palladium center along the
fifth coordination site was observed by IR spectroscopic
measurements in solution or in the solid state. No difference
was found in the frequency of the C=O bond stretching
between free ligand 1 and complex 2 in the solid state or in
Yellow crystals suitable for X-ray crystallographic struc-
ture analysis were grown by slow diffusion of diethyl ether
into a concentrated acetonitrile solution of compound 2 at
room temperature. Crystallographic details are summarized
in Table S1. As shown in Figure 1, the monodentate phthal-
imido-functionalized NHC ligand, two acetonitrile solvent
ligands, and one chloride ligand occupy the coordination
CD CN solution (Table 1).
3
sites of a pseudo-square-planar geometry. The plane of the Table 1. Comparison of C=O bond frequencies in the infrared spec-
NHC ligand is twisted out of the plane of the palladium
center, accommodating the bulk of the ancillary phthalim-
3
tra of ligand 1 and complex 2 in the solid state and in CD CN
solution.
ido ligand. The chloride ligand Cl1 displays a bond length Solid
of 2.284 Å to Pd, which is slightly shorter than the average
CD
1
3
CN solution
Assignments
1
2
2
value of 2.33 Å for a Pd–Cl bond. The two acetonitrile li- 1770w
1769w
1709s
1778w
1720s
1778w
1720s
νs C=O
a
ν C=O
1709vs
gands have a bond length of 2.018 Å in the position trans
to the chloride ligand and 2.096 Å in the position trans to
the NHC.
With respect to a remotely possible coordination of the
Kamisue and Sakaguchi,[10] who observed amide-func- N-donor atom of the heterocyclic structure, the weakness
tionalized NHC Pd complexes in the form of [(mono- of the Pd–N stretching features in the IR and Raman spec-
+
–
NHC)(PPh ) PdCl] Cl , suggested that these rare cationic tra makes it difficult to determine the Pd–N stretching fre-
3
2
metal centers are most probably stabilized by the strong do- quency in the low-frequency region, as this overlaps with
–1
nating capability of the NHC and phosphane. In our case, the bands for the Pd–Cl stretching mode (350–300 cm ),
–1
the cationic mono-NHC Pd center is also stable in the pres- the in-plane skeletal deformational modes (250–100 cm )
ence of the weakly σ-donating acetonitrile. of a square-planar structure, and the out-of-plane skeletal
In the C NMR spectrum, the carbene carbon atom deformation of heterocycles and aromatic rings (230–
1
3
–1
II
gives rise to an uncommonly high upfield-shifted signal at 160 cm ). It is noteworthy that only a few cationic Pd
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complexes with one NHC ligand are reported in the litera- optimized choice of solvents for the catalytic investigation
[
10,15]
ture.
ligand with a P-, N-, or S-donor functionality
monodentate NHC and other ligands such as phosphane thus better solubilizing precatalyst 2. Addition of water, the
Most of these either contain a chelating NHC of 2 with various substrates (Figure S3). DMF was chosen
[11b,12,16]
or a as cosolvent due to its high boiling point and high polarity,
[
11c–11e,17]
and allyl.
benign alternative, to the solvent mixture further increased
the conversion rate considerably, which presumably results
from the better solubility of the phenylboronic acid and the
Catalytic Application of Complex 2 in the Suzuki–Miyaura
Cross-Coupling Reaction
potassium carbonate in the reaction medium, according to
[19a,20]
the literature data.
This observation prompted us to
investigate mixtures of organic solvents and water (see the
Supporting Information for details), considering that at
higher water contents product precipitation does not allow
a kinetic-type evaluation. Conversions can only be deter-
mined after workup of the entire reaction mixture.[ In
DMF/water (1:4 by volume), at a catalyst loading of
To evaluate the catalytic potential of complex 2, we inves-
tigated its performance in Suzuki–Miyaura cross-coupling
reactions of various substrates (Scheme 2). The progress of
the coupling of 4-bromoacetophenone to 4-acetylbiphenyl
at 80 °C in the presence of 2 (0.1 mol-%) was monitored
21]
(Scheme 2). The initial optimization of the parameters tem-
0.1 mol-% of 2, 97% and full conversion (more than 99%)
perature and solvent showed two interesting results: no in-
duction period could be observed (see Figure 2) and there
was a positive effect of water as cosolvent on the activity.
after 15 and 60 min, respectively, were obtained.
With a lower catalyst loading of 0.01 mol-% of 2, 4-
bromoacetophenone was converted into 4-acetylbiphenyl
(
71%, 15 min) with a turnover frequency (TOF) of approxi-
–1
mately 28400 h . By contrast, in pure water only 39% of
the substrate was converted under otherwise identical reac-
tion conditions. This difference is attributed to the low solu-
bility of the hydrophobic 4-bromoacetophenone in water. It
Scheme 2. Suzuki–Miyaura cross-coupling (see Table 2). Reaction was further found that in MeCN/water (3:2), an even higher
conditions: 2 in DMF (1 mL) at varying catalyst loading; aryl hal-
ide (1 mmol); phenylboronic acid (1.2 mmol); water (4 mL); K CO
2 mmol); 24 h. Conversions were determined by GC; no side prod-
–1
TOF of 55000 h could be obtained, 0.01 mol-% of com-
2
3
plex 2 converting 4-bromoacetopheone to 4-acetylbiphenyl
(
(Figure S2).
ucts were observed unless otherwise stated. Reaction time 15 min.
With respect to conversion, the obtained results are com-
parable to those of other NHC-ligated Pd catalysts with
[
19a,20]
different S- and N-donor side-functionalities.
How-
ever, the reaction times are considerably shorter than those
with most other known NHC Pd complexes, which usually
[
19b,22]
require 6 to 24 h for full conversion.
The highest TOF
was reported by Huang et al. for an in situ catalyst system
of PdCl and benzimidazolium salts, achieving a TOF of
2
5
–1
9.1ϫ10 h for the conversion of iodobenzene in DMF/
water with a catalyst loading of 0.1 mmol-% in 1 h. How-
ever, they obtained poor results for bromo-substituted sub-
[
23]
strates.
6
Li and Hor also achieved a high TOF of
0000 h–1 with unsymmetrical bidentate benzimidazole–
Figure 2. Conversion of 4-bromoacetophenone over time showing
no induction period at 50 °C and 80 °C in DMF. Reaction condi-
tions: 1 mL of 2 in DMF (0.1 mol-%); 1 mmol of 4-bromoaceto- acetophenone.
pyrazole N,N-chelates in the C–C coupling of 4-bromo-
[
24]
[4]
Chen et al. coupled aryl chlorides with
phenone and 1.2 mmol of phenylboronic acid in 4 mL DMF; 1 mol-% of catalyst PdCl (mono-NHC)(NEt ) in 76 to 96%
2
3
2
2 3
mmol of K CO . Conversion was determined for two separate
yield in 20 min to 3 h at 25 °C, which resulted in an approxi-
runs, average values are used. Conversions were determined by GC,
no side-products were observed.
–1
mate TOF of 380 h . In addition, only few cationic phos-
II
phane-functionalized chelating NHC Pd complexes were
It is worth noting that mono-NHC– and carbocyclic tested as catalysts in Suzuki–Miyaura cross-coupling with
II
[12,25]
CHT–Pd complexes (CHT = cycloheptatriene), assisted by reasonable results.
A review on simple and function-
triphenylphosphine (PPh ), also showed no induction alized NHC–Pd complexes for cross-coupling reactions has
3
period in Suzuki coupling reactions at 130 °C.[ High tem- been published by Marion and Nolan.
peratures are generally required to activate the catalyst pre- To evaluate the catalyst’s versatility, the Suzuki–Miyaura
cursor, especially for bis(NHC)s and dimeric com- coupling reaction was investigated for complex 2 with a
18]
[26]
[
18,19]
plexes.
period could be observed, and 47% conversion was in a mixture of DMF/water (1:4). With 1.0 mol-% of 2, ex-
achieved in 24 h (Figure 2). cellent results were achieved within 24 h for the coupling of
With 0.1 mol-% of 2 at 50 °C, no induction range of aryl halides as substrates and phenylboronic acid
The influence of different solvents was evaluated with 4- several substrates such as 4-bromoacetophenone, 4-bromo-
bromoacetophenone as substrate, and this led to a carefully benzoic acid, 2-bromoanisole, 2-bromobenzonitrile etc.,
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with phenylboronic acid at 80 °C (Table 2). In the case of Table 2. Influence of different substrates, catalyst loadings, tem-
perature, and additives in Suzuki–Miyaura cross-coupling reactions
4
-bromobenzoic acid, homo-coupling of the phenylboronic
for 2 in DMF/water (1:4).[
a]
acid resulted in the formation of biphenyl as side product.
The coupling of 4-chloroacetophenone with phenylboronic
acid only proceeded to 26% conversion in the presence of
1.0 mol-% of 2 with formation of a small amount of bi-
phenyl and dehalogenation of the substrate (less than 3%).
More sterically hindered substrates such as 2-bromo-
acetophenone, 2-bromoanisole, 2-bromobenzonitrile, 2-
bromoaniline, 2-bromobiphenyl, and 2-bromomesitylene
were examined. When compared to the 4-bromoarenes, 2-
bromoarenes are more difficult to couple with phenyl-
boronic acid, especially in the case of bromoacetophenone.
4-Bromoacetophenone was fully converted to 4-acetobi-
phenyl, while only 19% of the 2-bromoacetophenone was
converted to 2-acetobiphenyl with 1.0 mol-% of complex 2
in 24 h. The steric hindrance of the methyl ketone group in
the ortho-position of the 2-bromoacetophenone slows down
the oxidative addition and hence the C–C coupling to a
large extent. This similarly applies to 2-bromomesitylene,
2-bromoaniline, and 2-bromobiphenyl. For 2-bromoanisole
and 2-bromobenzonitrile, which display less sterically hin-
dered substituents in the ortho-position, quantitative con-
version was attained.
To evaluate the influence of catalyst loading for each
substrate (Table 2), the catalyst concentration of 2 was low-
ered from 1.0 to 0.1 mol-% while all other reaction condi-
tions were retained. The conversions of 4-bromoanisole, 2-
bromoaniline and 2-bromobenzonitrile, 4-bromobenzene
and 2-bromoacetophenone were approximately 20–30%
lower at 0.1 mol-% than those at 1.0 mol-% catalyst loading
after 24 h. 4-Bromoarenes and 2-benzonitrile, as well as 4-
bromophenol and 2-bromoanisole, were still converted
quantitatively. The conversion of 2-bromobiphenyl and 2-
bromomesitylene was slightly lower, and no conversion was
observed for 4-chloroacetophenone. Quantitative conver-
sion was achieved for 4-bromoacetophenone with 0.01 mol-
%
of 2, whereas at 0.001 mol-% loading of the catalyst the
conversion dropped to 14% (24 h).
For selected substrates, the effect of the temperature was
investigated (Table 2). Increasing the reaction temperature
from 30 °C to 50 °C and 80 °C at a catalyst loading of
[
a] Reaction conditions: 2 in DMF (1 mL) at varying catalyst
loading; aryl halide (1 mmol); phenylboronic acid (1.2 mmol);
water (4 mL); K CO (2 mmol); 24 h. Reaction times are not opti-
0.1 mol-% of 2 led to an increase of the conversion of 4-
bromoacetophenone from 40% to 72% and 97%, respec-
tively, after 15 min. At 100 °C, all substrates were more ef-
fectively converted. It is worth noting that 4-chloroaceto-
2
3
mized. [b] Conversions were determined by GC; no side products
were observed unless otherwise stated. [c] Reaction time 15 min.
phenone gave a conversion of 59% at 100 °C, while at [d] Reaction time 60 min. [e] nBu
f] Tetra-n-butylammonium bromide (TBAB, 2.0 mol-%) was
added. [g] TBAB (0.5 mol-%) was added.
3
P (0.04 mol-%) was added.
[
80 °C, a conversion of only 26% was achieved. Homo-cou-
pling of boronic acid and dehalogenation of 4-chloroaceto-
phenone (less than 5%) were also observed in this case.
The reaction of 4-chloroacetophenone with phenyl-
boronic acid was investigated in the presence of tetra-n-but- of TBAB may be attributed to the formation of anionic Pd
[
28]
ylammonium bromide (TBAB), which was described to en- complexes, as shown by Amatore and Jutand.
hance the catalytic activity of palladium in C–C coupling Finally, addition of n-tributylphosphine (nBu P,
reactions through the stabilization of active palladium 0.04 mol-%) to a reaction mixture containing 1.0 mol-% of
3
[
27]
nanoclusters.
.5 equiv. of TBAB, while increasing the amount of TBAB This is consistent with the results obtained by Fu et al.[27b]
to 2 equiv. led to only 19% conversion. The negative effect for the conversion of 4-chloroacetobiphenyl with PdCl2-
A conversion of 43% was obtained with 2 at 100 °C gave the best result with 73% yield (Table 2).
0
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(
bis[sNHC]) {sNHC = [(1,3 diethyl)dihydroimidazole]} by 1-(2Ј-Phthalamidoethyl)-3-methylimidazolium
Bromide:
N-(2-
bromoethyl)phthalimide (1.05 g, 3.93 mmol) and 1-methylimid-
azole (0.32 g, 3.93 mmol) were sealed in an ACE pressure tube in
toluene and stirred at 120 °C for 1 d. After being allowed to cool
to room temperature, the reaction mixture was filtered, and the
colorless solid was washed with diethyl ether and dried under vac-
using tBu P and TBAB as additives.
3
Conclusions
A novel monocationic NHC–PdII complex 2, containing uum to afford a white solid. Yield: 1.12 g, 84%. C14
H16BrN
3 3
O
(
354.20): calcd. C 47.47, H 4.55, N 11.86; found C 47.29, H 4.44,
an easily accessible phthalimido-functionalized NHC li-
gand, was synthesized. It shows catalytic activity in the Su-
zuki–Miyaura cross-coupling reaction of a number of sub-
strates. Good to excellent results were achieved for the cou-
pling of phenylboronic acid with aryl bromides. Fast reac-
tions were observed with 4-bromoacetophenone, which af-
1
N 11.61. H NMR (400 MHz, [D
6
]DMSO): δ = 9.22 (s, 1 H,
NCHN), 7.88–7.83 (m, 5 H, CHPhth+Im), 7.70 (t, 1 H, CHIm), 4.43–
3
3
4
6
.40 (t,
J
HH = 6.0 Hz, 2 H, CH
2
–NIm), 4.01–3.98 (t,
J
HH
=
1
3
.0 Hz, 2 H, PthN–CH
2
3
), 3.79 (s, 3 H, NCH ) ppm. C NMR
(
[
1
100 MHz, [D
C(O)–Ctert–CH–CH], 131.49 [C(O)–Ctert–CH–CH], 123.74 (s, C4),
23.37 [C(O)–Ctert–CH–CH], 122.61 (s, C5), 48.70 (s, CH –NIm),
6
]DMSO): δ = 167.79 (s, NCO), 138.25 (s, C2), 134.56
–
1
forded a TOF value of 55000 h at 80 °C with 0.01 mol-%
2
of 2. Interestingly, the air-stable catalyst 2 shows no induc- 38.52 (s, PhtN–CH ), 36.89 (s, NCH ) ppm. MS (FAB): m/z (%) =
2
3
+
2
tion period (less than 2 min) in DMF, and good activity is 256 (100) [M – Br – H O] .
obtained in aqueous DMF solution.
1
(
2
(
-(2Ј-Phthalamidoethyl)-3-methylimidazolium Hexafluorophosphate
1): 1-(2Ј-phthalamidoethyl)-3-methylimidazolium bromide (1.0 g,
.97 mmol) was dissolved in a round-bottomed flask in water
20 mL) at 60 °C, followed by the addition KPF (0.802 g,
Further studies to evaluate the influence of the phthalim-
ido-functionalized NHC ligand on catalytic activity are cur-
rently ongoing in our laboratories, as are studies to extend
6
the use of phthalimido-functionalized NHC ligands to 3.56 mmol) in water (10 mL). The reaction mixture was heated at
other catalysts and catalytic reactions.
60 °C, and a white precipitate formed immediately. The reaction
mixture was further stirred for a further 15 min at 60 °C and then
for an hour at room temperature. The white precipitate was filtered
and washed with water twice and was then dried under vacuum to
Experimental Section
obtain white flakes. Yield: 1.09 g, 92%. C14
14 6 3 2
H F N O P (401.24):
All reactions, except for the Suzuki coupling reactions, were per-
formed under a dry argon atmosphere by using standard Schlenk
techniques. Solvents were dried by use of a solvent purification
system or standard procedures and stored under an argon atmo-
sphere over molecular sieves. The 1-(2Ј-Phthalamidoethyl)-3-meth-
ylimidazolium hexafluorophosphate salt was synthesized by follow-
ing a slightly modified literature procedure,[ leading to shorter
reaction time and increase in product yield. N-(2-bromoethyl)-
phthalimide, 1-methylimidazole, and potassium hexafluorophos-
phate were purchased from Acros and used without further purifi-
cation. 1H- and C NMR spectra were recorded with a Bruker
Avance UltraShield 400 MHz spectrometer at 300 K. Mass spectro-
metric measurements of the complexes were performed with a Fin-
nigan MAT 90 spectrometer with the FAB technique. Elemental
analyses were obtained from the Microanalytical Laboratory of the
Technische Universität München. For catalysis, gas chromato-
graphic measurements were recorded with a Varian CP 3800 instru-
ment with a FID detector and coupled triple quad Varian 1200L
mass spectrometer.
calcd. C 41.91, H 3.52, N 10.47; found C 41.11, H 3.32, N 10.35.
H NMR (400 MHz, [D ]DMSO): δ = 9.15 (s, 1 H, NCHN), 7.89–
6
1
7
4
4
.85 (m, 4 H, CHPhth), 7.84 (s, 1 H, CHIm), 7.66 (s, 1 H, CHIm),
3
3
.44–4.42 (t, JHH = 4.0 Hz, 2 H, CH
.0 Hz, 2 H, PhtN–CH
2
–NIm), 4.02–4.00 (t, JHH
=
13
2
3
), 3.82 (s, 3 H, ImN–CH ) ppm. C NMR
(
6
101 MHz, [D ]DMSO): δ = 167.67 (s, NCO), 137.12 (s, C2), 134.54
8a]
[C(O)–Ctert–CH–CH], 131.54 [C(O)–Ctert–CH–CH], 123.59 (s, C4),
1
3
23.24 [C(O)–Ctert–CH–CH], 122.89 (s, C5), 47.86 (s, CH
8.02 (s, PhtN–CH ), 35.77 (s, NCH
2 3
2
–NIm),
) ppm. P NMR (162 MHz,
]DMSO): δ = –131.03 to –157.38 ppm (septet, PF ). MS (FAB):
31
[D
6
6
13
+
6
m/z (%) = 256 (100) [M – PF ] .
Acetonitrile[1-(2Ј-phthalamidoethyl)-3-methylimidazolin-2-ylidene]-
silver(I) Hexafluorophosphate: 1-(2Ј-phthalamidoethyl)-3-methyl-
imidazolium hexafluorophosphate (0.200 g, 0.5 mmol) was dis-
3 2 2
solved in a 1:1 mixture of CH CN/CH Cl (20 mL) in a Schlenk
tube. Ag O (0.058 g, 0.25 mmol) was added, and the reaction mix-
2
ture was stirred at 60 °C in the dark for 2 d. The reaction mixture
was then filtered through a plug of Celite and concentrated to
about 5 mL. Et
white solid. The white solid was filtered and washed twice with
Et O before being dried under vacuum to afford a white powder
that is sensitive to light. Yield: 0.179 g, 65%. C16 18AgF
551.17): calcd. C 34.87, H 3.29, N 10.17; found C 35.91, H 2.86,
2
O was added to precipitate the Ag complex as a
General Procedure for the Suzuki Coupling Reaction: Catalytic test
reactions were performed with use of a Radleys® catalysis carousel.
A carousel tube was charged with a mixture of aryl halides (ArX, X
2
H
6 4 2
N O P
=
Br or Cl) (1 mmol), phenylboronic acid (1.2 mmol), and K
2 3
CO
(
(2 mmol). Water (4 mL) was added to the tube, and the reaction
1
N 9.65. H NMR (400 MHz, [D
6
]DMSO): δ = 7.75–7.70 (m, 4 H,
mixture was heated to the required temperature for 15 min in air.
Precatalyst 2 was dissolved in dimethylformamide to the appropri-
ate molar concentration, and the catalyst solution (1 mL) was then
added to the reaction mixture and stirred for the desired reaction
time. After this, hydrochloric acid (1 m) was added, and the aque-
ous phase was extracted with ethyl acetate (5 mL). The organic
phase (0.1 mL) was diluted with ethyl acetate (1.9 mL) and then
CHPhth), 7.55 (s, 1 H, CHIm), 7.38 (s, 1 H, CHIm), 4.30–4.27 (t,
3
3
J
HH = 6.0 Hz, 2 H, CH
PhtN–CH ), 3.56 (s, 3 H, ImN–CH
P NMR (162 MHz, [D ]DMSO): δ = –131.02 to –157.36 ppm
septet, PF ). MS (FAB): m/z (%) = 619 (40) [M + NHC –
2
–NIm), 3.93–3.90 (t, JHH = 6.0 Hz, 2 H,
2
3
), 2.07 (s, 3 H, CH CN) ppm.
3
31
6
(
6
+
+
3 6 3 6
CH CN – PF ] , 362 (45) [M – CH CN – PF ] , 256 (100)
NHC]+.
[
4
filtered through a NaSO -filled glass pipette; the sample was ana-
lyzed by gas chromatography. For each set of experimental param-
eters, two separate catalytic runs were performed. Each run was
analyzed twice by gas chromatography and the results were
averaged. All data were found to be in good agreement.
cis-Diacetonitrile(chloro)[1-(2Ј-phthalamidoethyl)-3-methylimid-
azolin-2-ylidene]palladium(II) Hexafluorophosphate (2): Acetonitrile
[1-(2Ј-phthalamidoethyl)-3-methylimidazolin-2-ylidene]silver(I)
hexafluorophosphate (0.100 g, 0.2 mmol) and PdCl
2 3 2
(CH CN)
Eur. J. Inorg. Chem. 2014, 1225–1230
1229
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
(
0.047 g, 0.2 mmol) were each dissolved in CH
3
CN (10 mL). The
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19ClF PPd (624.22): calcd. C 34.63, H 3.07, N 11.22;
found C 34.51, H 2.98, N 10.52. H NMR (400 MHz, [D
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CH ), 3.94 (s, 3 H, ImN–CH ]-
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DMSO): δ = 167.93 (s, NCO), 142.77 (NCN), 134.18 [C(O)–Ctert
CH–CH], 132.00 [C(O)–Ctert–CH–CH], 125.30 (s, C4), 123.63 (s,
C5), 122.96 [C(O)–Ctert–CH–CH], 118.03 (s, CH CN), 48.07 (s,
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ppm. NMR (162 MHz, [D ]DMSO): –131.01 to
157.36 ppm (septet, PF ). MS (FAB): m/z (%) = 398 (10) [M –
29]
CH
C
3
18
H
6 5 2
N O
1
6
]DMSO):
2
2
–
2
2
3
6
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Acknowledgments
The Bayerische Forschungsstiftung is acknowledged for a Ph. D.
grant to S. L. M. G., Wacker Insitut für Silicium Chemie at TUM,
Wacker AG is acknowledged for a Ph. D. grant to M. P. H., Uni-
versität Bayern e. V. is acknowledged for a Ph. D. fellowship to
N. B. J., and the Bavarian Elite Network NanoCat is acknowledged
for a Ph. D. fellowship to A. D. T. The International Graduate
School of Science and Engineering (IGSSE) and the Technische
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Received: October 7, 2013
Published Online: January 29, 2014
Eur. J. Inorg. Chem. 2014, 1225–1230
1230
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim