Benzimidazolin-2-ylidene complexes of palladium(II) featuring a thioether moiety: Synthesis, characterization, molecular dynamics, and catalytic activities

Article abstract of DOI:10.1021/om500083r

Six benzimidazolin-2-ylidene palladium(II) complexes with an alkyl-alkyl thioether moiety in the side chain have been synthesized. Due to the hemilabile metal-sulfur bond, the complexes exhibit a marked fluxionality, as evidenced by NMR studies. The thioe

Full text of DOI:10.1021/om500083r

Article
pubs.acs.org/Organometallics
Benzimidazolin-2-ylidene Complexes of Palladium(II) Featuring a
Thioether Moiety: Synthesis, Characterization, Molecular Dynamics,
and Catalytic Activities
Jan C. Bernhammer and Han Vinh Huynh*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
*
S Supporting Information
ABSTRACT: Six benzimidazolin-2-ylidene palladium(II)
complexes with an alkyl−alkyl thioether moiety in the side
chain have been synthesized. Due to the hemilabile metal−
sulfur bond, the complexes exhibit a marked fluxionality, as
evidenced by NMR studies. The thioether moiety is readily
displaced by pyridine as well as by another NHC ligand.
Hetero(bis)-NHC complexes formally derived from all six
chelating mono-NHC complexes have been synthesized as
well. For both series of complexes, the catalytic activity has
been explored, and they were found to be active catalysts for
the intermolecular hydroamination reaction between a steri-
cally hindered aniline and an alkyne in the presence of triflic
acid. Furthermore, the complexes catalyze the direct arylation
of 1-methylpyrrole.
INTRODUCTION
to expand our chemistry and explore the coordination
chemistry of our thioether-functionalized NHCs with
palladium(II) as well as the catalytic properties of the resulting
complexes.
■
Complexes of late transition metals bearing N-heterocyclic
carbene ligands have been tremendously successful during the
past two decades, both as catalysts and for other applications.
1
,2
The extraordinarily varied chemistry of this class of ligands can
be attributed to their robustness and strong donating abilities,
the relative ease with which they can be synthesized, and the
various possibilities of fine-tuning their electronic and steric
RESULTS AND DISCUSSION
■
Complex Synthesis. Similarly to the synthesis of their
platinum(II) analogues, the palladium(II) complexes were
prepared by silver carbene transfer.
3
properties. Additionally, the presence of side chains in close
1
1,13
The corresponding
proximity to the metal center allows for the easy introduction
of ancillary, tethered donor functionalities, which gives rise to
silver(I) complexes for the previously described ligand
precursors with ethylene (1−3) and propylene (7−9) thioether
tethers were obtained by reaction with silver(I) oxide in
dichloromethane and directly added to a freshly prepared
solution of [PdBr (MeCN) ] in acetonitrile. The instantaneous
4
chelating and pincer-type ligands with interesting properties.
5
6
Besides functionalities based on oxygen, nitrogen, or
phosphorus, there has been an increasing interest in sulfur-
7
based donor moieties as well. These include functionalities as
2
2
8
,9
diverse as thiolates, thioethers, thiophenes, and sulfoxides.
precipitation of insoluble silver(I) bromide indicated rapid
Especially thioethers have emerged as a useful functionality in
the side chain of NHC ligands due to their potentially
hemilabile behavior. The metal-sulfur bond is weak enough to
allow for the rapid opening up of free coordination sites at the
metal center during catalysis, while being sufficiently strong to
stabilize the catalyst in its resting state.
Recently, we reported the synthesis and catalytic activities of
transmetalation, and the desired palladium complexes 4−6 and
1
0−12 could be isolated from the reaction mixture in good to
excellent yields (Scheme 1).
The complexes were obtained as microcrystalline, yellow
solids. All complexes are completely insoluble in hydrocarbons
and ethereal solvents and only sparingly soluble in chlorinated
solvents and polar organic solvents such as DMSO. In the
presence of small amounts of coordinating solvents such as
pyridine, the solubility in polar organic solvents and chlorinated
solvents increases markedly, due to the formation of solvent
10
a series of platinum(II) complexes with alkyl−alkyl thioether-
11
functionalized benzimidazolin-2-ylidene ligands. Due to the
relatively harder nature of palladium(II), a pronounced
1
2
hemilabile behavior is to be expected for this metal.
Furthermore, there is a close structural relationship with
other sulfur-functionalized palladium(II) NHC complexes,
which were previously prepared in our lab. This prompted us
Received: January 24, 2014
Published: February 24, 2014
©
2014 American Chemical Society
1266
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Scheme 1. Synthesis of Thioether-Functionalized
Palladium(II) NHC Complexes
cleaner and considerably faster than the reactions between the
2
i
κ C,S complexes and [AgBr( Pr -bimy], which were accom-
2
panied by the formation of byproducts arising from ligand
scrambling.
All bis-NHC complexes were obtained in good yields as
yellow solids with a markedly higher solubility than their mono-
NHC counterparts. While being fully soluble in chlorinated
solvents as well as polar organics solvents, they are not soluble
in ethereal solvents and hydrocarbons. The complexes were
fully characterized by NMR spectroscopy, mass spectrometry,
elemental analysis, and X-ray crystallography.
Dynamic Behavior and NMR Spectroscopy. The chelate
complexes 4−6 and 10−12 are only sparingly soluble in
common deuterated solvents, making the measurement of
NMR spectra difficult. Additionally, all complexes show
dynamic behavior, resulting in considerable signal broadening
in their NMR spectra due to a coalescence temperature close to
ambient temperature. Especially the signals of the thioether side
chains are affected by this phenomenon, and in most cases
some of the protons in the side chain cannot be observed at all.
Measurements at low temperature are impossible, because of
solubility problems, but high-temperature measurements up to
adducts by displacement of the weakly coordinated thioether
moiety.
The characterization of these complexes by means of NMR
spectroscopy was challenging due to their low solubility and
their dynamic behavior (vide infra). However, the complexes
were unambiguously characterized by mass spectrometry,
elemental analysis, and in some cases X-ray crystallography.
Since the thioether moiety is only weakly bound to the metal
center, it is readily displaced by stronger donor ligands such as
nitrogen, phosphorus, or carbon donors. This was demon-
strated by the synthesis of a second series of complexes, which
incorporate two different benzimidazolin-2-ylidene ligands and
a pendant thioether side chain. For the synthesis of these
hetero(bis)-NHC complexes, two routes are possible (Scheme
3
68 K were conducted as illustrated for complex 4 in Figure 1.
At ambient temperature, the methylene protons of the
thioether side chain could barely be observed due to peak
broadening, and no signal for the methine proton in the side
chain was detected at all. These signals were clearly observed at
elevated temperatures. By lowering the temperature back to
ambient temperature, the initial spectrum could be restored.
However, 4 was the only compound for which coalescence
could be observed, while the other complexes showed no
coalescence before decomposition in solution occurred.
To circumvent the problems arising from the fluxional
behavior due to the weak coordination of the thioether moiety
and the low solubility of these complexes, the complexes were
reacted with pyridine in dichloromethane. Clean pyridine
adducts were obtained for the ethylene-linked complexes 4−6,
while the propylene-linked complexes 10−12 gave a mixture of
the desired pyridine adducts and other, unidentified species.
Attempts at separating these complex mixtures were futile, since
they rapidly re-equilibrated.
2
). They can be synthesized either by the transmetalation
reaction of complexes 4−6 and 10−12 with one equivalent of
in situ prepared [AgBr( Pr -bimy] ( Pr -bimy = 1,3-diisopro-
i
i
2
2
pylbenzimidazolin-2-ylidene) or by bridge-cleavage reaction of
i
[
PdBr ( Pr -bimy)] with silver(I) complexes of the thioether-
2 2 2
NHC ligands.
Both methods lead to the formation of the desired complexes
i
1
3−18. However, the reaction with [PdBr ( Pr -bimy)] is
2
2
2
more attractive, since all six complexes can be synthesized by a
single-step reaction from a common precursor, while the
inverted approach requires the synthesis of each individual
The pyridine adducts of 4−6 were readily soluble in
chlorinated solvents, so NMR spectra could be measured in
deuterated chloroform. Upon introduction of an additional
donor ligand to the complex, no more dynamic behavior was
observed, and the spectra show sharp multiplets attributable to
the protons in the side chain. These marked changes confirm
2
mono-NHC κ C,S complex 4−6 and 10−12 first, followed by
i
the silver carbene transfer of the Pr -bimy ligand. Additionally,
2
i
the reaction between dimeric [PdBr (Pr -bimy)] and the
2
2
2
2
respective silver(I) carbene complexes was found to proceed
an initial κ C,S coordination mode, which is not feasible if the
Scheme 2. Possible Approaches for the Preparation of Palladium(II) Bis-NHC Complexes
1
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1
Figure 1. Variable-temperature H NMR spectra of 4 in DMSO-d .
6
Figure 2. Molecular structures of 4 and 12. Thermal ellipsoids are shown at 50% probability; hydrogen atoms have been omitted for clarity.
coordination site is blocked by the pyridine ligand. NCH2
groups are observed as a multiplet between 5.13 and 4.97 ppm,
hindered rotation along the metal−carbon bonds, the isopropyl
i
groups of the Pr -bimy ligands experience a different
2
SCH as a multiplet between 3.47 and 3.33 ppm, SCH either as
a multiplet or as a septet between 3.26 and 3.06 ppm, and the
environment, which results in two distinct signal sets for
these functionalities.
2
CH groups as a doublet at ∼1.40 ppm. These values are
In their 13C NMR spectra, two carbene signals are observed
3
i
slightly downfield from those observed for the salt precursors
for each complex. The resonances attributable to the Pr -bimy
2
1
−3. In the spectra of all pyridine adducts, the identity as NHC
ligand fall within the narrow range of 178.6−179.6 ppm, while
those for the sulfur-functionalized benzimidazolin-2-ylidene
ligands range from 183.5 to 186.3 ppm. These values are in line
with previously reported chemical shifts for similar com-
plexes. The nature of the thioether side chain has a smaller
impact on these shifts than the nonfunctionalized side chain,
reflecting the negligible influence of linker length on the
electronic properties of the complex.
complexes is confirmed by the absence of the characteristic
signals of the acidic proton on C2 in the ligand precursor salts.
In their 13C NMR spectra, the Ccarbene atoms resonate at 163−
15
166 ppm, which is in good agreement with reported values for
14
similar complexes.
The spectroscopic characterization of the hetero(bis)-NHC
1
complexes 13−18 was more straightforward. In the H NMR
spectra, the disappearance of the acidic proton present in the
precursor salts indicated successful formation of a carbene
complex. In 13−15, the sharp signals observed for the thioether
side chain are almost identical to the signals found for the
pyridine adducts of 4−6. For 16−18, the signals for SCH2
groups are found more upfield at 2.87−2.80 ppm as a well-
resolved triplet, while the septets attributable to the SCH
groups are found further upfield at 3.16−3.02 ppm. The
Molecular Structures. The slow evaporation of concen-
trated solutions yielded single crystals suitable for X-ray
diffraction analysis for several complexes (13, 14, and 18
from dichloromethane/acetonitrile, 5 from pure dichloro-
methane, 6 from dichloromethane/toluene, 12 from acetoni-
trile/hexane, 16 from dichloromethane/hexane). The slow
diffusion of diethyl ether in a concentrated dichloromethane
solution of 4 yielded single crystals, and crystals of 16 were
obtained by slow diffusion of hexane into a concentrated
dichloromethane solution. Despite numerous attempts, no
single crystals could be obtained for 10, 11, and 17. A likely
additional CH group in the propylene linker gives rise to
2
multiplets at 2.71−2.60 ppm. Due to the asymmetry of the
thioether-functionalized benzimidazolin-2-ylidenes and the
1
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Figure 3. Molecular structures of 5 and 6. Thermal ellipsoids are shown at 50% probability; hydrogen atoms and solvent molecules have been
omitted for clarity.
reason is the flexibility of the long, aliphatic side chains found in
these complexes, which prevents an efficient crystal packing.
Interestingly, not all mono-NHC complexes showed the
Table 1. Bond Distances (Å) and Angles (deg) in Complexes
4 and 12
2
bond parameter
4
12
expected κ C,S coordination in the solid state. While 4 and 12
Pd1−C1
Pd1−S1
Pd1−Br1
Pd1−Br2
C1−Pd1−S1
C1−Pd1−Br2
S1−Pd1−Br1
Br1−Pd1−Br2
C1−Pd1−Br1
S1−Pd1−Br2
1.974(3)
2.2955(9)
2.4739(6)
2.4392(5)
90.9(1)
1.993(5)
2.296(1)
2.4799(7)
2.4431(7)
94.1(2)
crystallized as mononuclear complexes, 5 and 6 were found to
adopt a dimeric form, in which the thioether moiety and Ccarbene
coordinate to different metal centers, forming a 12-membered
macrocycle (Figures 2 and 3). Similar species were proposed to
occur in solution as part of dynamic equilibria for related
9
b,11
92.39(9)
85.57(2)
91.22(1)
176.33(9)
173.81(3)
88.0(2)
platinum(II) and palladium(II) complexes,
and multiple
85.21(4)
92.61(2)
178.9(2)
172.93(4)
coordination modes are not uncommon for sulfur-function-
8
c,d,h,10c,16
alized palladium(II) complexes.
The metallacycles in the chelating complexes 4 and 12 adopt
a mildly distorted boat conformation. The plane defined by the
NHC ring and the coordination plane are twisted by 44.0(3)°
with respect to each other in complex 4, while the longer
propylene linker in 12 allows for a higher degree of
conformational freedom, and thus a larger twist of 58.0(5)°
can be found. In both cases, the coordination geometry around
the palladium center is distorted square planar. The Pd−C
bond in 4 has a length of 1.974(3) Å. In 12, it is slightly longer
at 1.993(5) Å. The Pd−S distances are 2.2955(9) and 2.296(1)
Å, respectively.
The two different Pd−Br bonds show a marked difference,
reflecting the difference in trans influence between the weakly
donating thioether moiety and the NHC. The bond trans to the
carbene is 2.4739(6) Å long in complex 4 and 2.4799(7) Å in
complex 12, and the bond distance between palladium and the
bromido ligand trans to the thioether is 2.4392(5) Å in 4 and
Table 2. Bond Distances (Å) and Angles (deg) in Complexes
and 6
5
bond parameter
5
6
Pd1−C1
Pd1−S2
Pd1−Br1
Pd1−Br2
C1−Pd1−Br1
C1−Pd1−Br2
S2−Pd1−Br1
S2−Pd1−Br2
C1−Pd1−S2
Br1−Pd1−Br2
1.95(1)
1.964(2)
2.3791(6)
2.4308(3)
2.4189(3)
89.08(7)
86.31(7)
89.88(2)
94.78(2)
178.77(7)
173.13(1)
2.379(3)
2.434(2)
2.427(2)
89.6(3)
85.0(3)
86.80(9)
98.93(9)
174.1(3)
173.27(6)
2
.4431(7) Å in 12.
The bond lengths are in good agreement with values
contrast, the Pd−S bonds are elongated with a length of
2.379(3) Å in 5 and 2.3791(6) Å in 6. Again, these changes are
brought about by the difference in trans influence of the
opposing ligand. The Pd−Br bond lengths fall in between the
9
b,10c
reported for similar chelate complexes (Table 1).
2
In contrast to the κ C,S chelates 4 and 12, complexes 5 and 6
were found to crystallize preferentially in a trans-coordinated,
dimeric form. In both complexes, the coordination geometry
around the palladium centers is distorted square planar. Bond
lengths fall well within the expected range, based on
comparison with similar compounds (Table 2). When
compared to the two κ C,S complexes, the Pd−C bonds are
shorter with a length of 1.95(1) Å in 5 and 1.964(2) Å in 6. In
2
extremes realized in the κ C,S complexes, with values in the
range from 2.4189(3) to 2.434(2) Å.
While the dimeric form seems to be preferred in the solid
state for these two compounds, only compound 6 showed the
peaks corresponding to the dimeric form in ESI mass
spectrometry. For complex 5, the monomeric form was
observed instead.
8
c
2
1
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Figure 4. Molecular structures of 13 and 16. Thermal ellipsoids are shown at 50% probability; hydrogen atoms and disordered atoms in the
thioether side chain have been omitted for clarity.
The hetero(bis)-NHC complexes 13−16 and 18 adopt a
square planar coordination geometry at the metal center, with a
trans arrangement of the two different benzimidazolin-2-ylidene
ligands (Figures 4−6). With the exception of 14, all molecular
complexes were found to be efficient catalysts for this kind of
19
transformation, including several palladium(II) NHC com-
20
plexes.
In light of our recent experiences with sulfur-functionalized
NHC complexes of group 10 metals as catalysts for
9e,11
hydroaminations of alkynes,
the catalytic performance of
complexes 4−6, 10−12, and 13−18 in the reaction between
phenylacetylene (19) and 2,6-dimethylaniline (20) was ex-
plored. In the absence of any additive, only low to moderate
2
yields were achieved when using the κ C,S as catalysts, and no
clear trends were discernible. The highest yield was obtained
with complex 10 (entry 5, Table 4). Considerably higher yields
were obtained in the presence of a catalytic amount of triflic
acid, which likely speeds up the protolytic cleavage of the
metal−carbon bond formed after the nucleophilic attack of the
21
2
amine. Yields were moderate to good for the κ C,S complexes
and moderate for the corresponding hetero(bis)-NHC
complexes. The best catalytic performance was found for the
chelating complexes 4 and 5, which feature a stable six-
membered metallacycle. A likely reason could be a prolonged
catalyst lifetime due to the more efficient stabilization of the
catalytically active species by the hemilabile thioether moiety.
By contrast, the hetero(bis)-NHC complexes 13−18 were
almost in all cases less efficient than their mono-NHC
counterparts. A plausible reason is the slower formation of
the catalytically active species, since the additional NHC ligand
blocks a coordination site.
Figure 5. Molecular structure of 14. Thermal ellipsoids are shown at
50% probability; hydrogen atoms have been omitted for clarity.
structures showed disordering of the long and flexible thioether
side chain. The Pd−C bonds are between 2.011(5) and
2
2
.040(4) Å long. For the Pd−Br bonds, values ranging from
.440(2) to 2.4567(9) Å are found. Only minor differences
Direct Arylation of 1-Methylpyrrole. In contrast to
classical carbon−carbon cross-coupling reactions, which require
the use of organometallic reagents as precursors, direct
arylation reactions allow the synthesis of biaryls starting from
halidoarenes and electron-poor polyfluoroarenes or hetero-
exist between the complexes, and the bond lengths are close to
those typically found for such hetero(bis)-NHC complexes
1
5a,17
(
Table 3).
Hydroamination of Phenylacteylene. The hydroamina-
tion reaction of alkynes and alkenes is an important strategy for
22
arenes by C−H activation. The direct arylation of 1-
methylpyrrole has attracted considerable interest, and palla-
dium NHC complexes have recently been shown to catalyze
18
the formation of carbon−nitrogen bonds. The direct addition
of primary and secondary amines to carbon−carbon multiple
bonds proceeds with perfect atom economy and avoids the
formation of wasteful byproducts, thus following central tenets
of green chemistry. Several late transition metal NHC
23
this reaction in good yields. Using reaction conditions
described in the literature, all complexes were evaluated for
their ability to act as catalysts in the reaction between 1-
methylpyrrole (22) and 4-bromoacetophenone (23). All
1
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Figure 6. Molecular structures of 15 and 18. Thermal ellipsoids are shown at 50% probability; hydrogen atoms, disordered atoms in the thioether
side chain, and solvent molecules have been omitted for clarity.
Table 3. Bond Distances (Å) and Angles (deg) in Complexes 13−16 and 18
bond parameter
13
14
15
16
18
Pd1−C1
Pd1−C
Pd1−Br1
Pd1−Br2
C1−Pd1−Br1
C1−Pd1−Br2
C−Pd1−Br1
C−Pd1−Br2
C1−Pd1−C
Br1−Pd1−Br1
2.031(7)
2.027(7)
2.443(2)
2.440(2)
90.9(2)
2.013(8)
2.023(8)
2.456(2)
2.453(2)
90.2(3)
2.029(5)
2.011(5)
2.443(1)
2.447(1)
91.9(9)
2.031(4)
2.021(3)
2.4567(9)
2.4383(9)
92.0(1)
2.040(4)
2.01(2)
2.4451(5)
2.4262(6)
94.3(1)
89.9(2)
92.5(3)
91.0(1)
88.9(1)
89.4(1)
89.1(2)
89.4(3)
89.5(1)
89.3(1)
89.7(1)
90.1(2)
87.9(3)
87.6(1)
89.8(1)
86.5(1)
176.6(2)
178.94(3)
179.5(4)
177.17(5)
178.4(2)
176.63(3)
176.8(2)
177.78(2)
174.8(2)
176.19(2)
Table 4. Catalyst Performance in the Hydroamination of
Phenylacetylene
Scheme 3. Hydroamination of Phenylacetylene with 2,6-
Dimethylaniline
a
b
yield (%)
entry
catalyst
no additive
+ 2% HOTf
1
2
3
4
5
6
7
8
9
0
20
34
51
53
29
48
0
88
78
56
53
38
58
37
46
60
51
55
51
4
5
6
10
11
12
13
14
15
16
17
18
There was only a minor variation in yield between the
different complexes under scrutiny, possibly because of partial
catalyst decomposition and the involvement of colloidal
palladium in the catalysis.
2
For the κ C,S complexes, no significant difference was found
1
1
1
1
0
1
2
3
between complexes 4−6 featuring an ethylene linker and
complexes 10−12 featuring a propylene linker between the
carbene and the thioether moieties. However, catalyst perform-
ance depends on the sterical bulk of the noncoordinating side
chain. The highest yields were obtained with complexes
featuring the bulky benzhydryl side chain, which might favor
a
Reaction conditions: 1 mol % precatalyst, phenylacetylene (2.0
equiv), 2,6-dimethylaniline (1.0 mmol), toluene (3 mL), 100 °C, 15 h.
Yields determined by GC-MS with decane as internal standard;
average of two runs.
b
24
the reductive elimination step in the catalytic cycle.
A similar pattern was observed for the hetero(bis)-NHC
complexes: only minor changes due to the different linker
lengths between carbene and thioether moieties, and better
results with bulkier noncoordinating side chains. In general, the
hetero(bis)-NHC complexes performed slightly better than
complexes were found to be active catalysts, and good yields of
the desired product were obtained (Table 5).
1
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cis-Dibromido(1-benzyl-3-(2-(isopropylthio)ethyl)-
Table 5. Catalyst Performance in the Direct Arylation of 1-
Methylpyrrole
2
a
benzimidazolin-2-ylidene-κ C,S)palladium(II) (4). Salt 1 (117 mg,
0
.30 mmol, 1.00 equiv) and silver(I) oxide (35 mg, 0.15 mmol, 0.50
b
entry
catalyst
yield (%)
equiv) were suspended in dichloromethane (15 mL) and stirred at
ambient temperature for 15 h shielded from light. Palladium(II)
bromide (80 mg, 0.30 mmol, 1.00 equiv) was dissolved in acetonitrile
1
2
3
4
5
6
7
8
9
0
69
75
80
67
74
77
74
77
83
71
66
86
4
(
10 mL) by stirring for 30 min at 50 °C. After cooling to ambient
5
temperature, the silver carbene complex solution was added by
filtration over a short plug of Celite, and stirring was continued for 1 h
at ambient temperature. Then the solution was filtered over Celite and
the solvent was removed under reduced pressure. The residue was
washed with diethyl ether (10 mL). The product was obtained as a
6
10
11
12
13
14
15
16
17
18
1
yellow solid (111 mg, 0.19 mmol, 64%). H NMR (300 MHz, DMSO-
3
3
d , 358 K): δ 7.87 (d, J
= 8 Hz, 1 H, Ar−H), 7.56 (d, J
= 8
6
H−H
H−H
Hz, 1 H, Ar−H), 7.49−7.25 (m, 9 H, Ar−H, NCH Ph), 6.19−6.05
1
1
1
1
0
1
2
3
2
(
m, 2 H, NCH ), 4.98−4.72 (m, 2 H, SCH ), 2.85−2.73 (m, 1 H,
2
2
13
1
SCH), 1.09−1.02 (m, 6 H, CH ). C{ H} NMR (75 MHz, DMSO-
3
d ): δ 136.4, 134.4, 133.3, 129.1, 128.4, 127.9, 124.6, 124.4, 112.3
6
(
2
Ar−C), 51.6 (NCH Ph), 47.2 (NCH ), 44.3 (SCH), 30.8 (SCH ),
2
2
2
a
Reaction conditions: 1 mol % precatalyst, 1-methylpyrrole (4.0
equiv), 4-bromoacetophenone (1.0 mmol), KOAc (2.0 equiv), DMA
1
2.6 (CH ), C
not observed. H NMR (300 MHz, CDCl , as
3
carbene 3
pyridine adduct): δ 9.06−8.99 (m, 2 H, Ar−H), 7.81−7.77 (m, 1 H,
b
(3 mL), 150 °C, 20 h. Yields determined by GC-MS with decane as
Ar−H), 7.60−7.52 (m, 2 H, Ar−H), 7.47−7.42 (m, 1 H, Ar−H),
internal standard; average of two runs.
7
(
.38−7.30 (m, 5 H, Ar−H), 7.25−7.21 (m, 1 H, Ar−H), 7.14−7.01
m, 2 H, Ar−H), 6.16 (s, 2 H, NCH Ph), 5.11−5.01 (m, 2 H, NCH ),
2
2
2
3
their κ C,S counterparts presumably due to a higher stability
3.47−3.34 (m, 2 H, SCH ), 3.22 (sept, J
= 7 Hz, 1 H, CH), 1.41
2
H−H
3
13
1
under the harsh reaction conditions.
(d, JH−H = 7 Hz, 6 H, CH
pyridine adduct): δ 164.2 (Ccarbene), 153.2, 138.7, 135.4, 135.4, 134.9,
29.5, 128.9, 128.8, 125.3, 123.9, 123.9, 112.3, 110.9 (Ar−C), 54.3
NCH Ph), 49.6 (NCH ), 36.1 (SCH), 29.6 (SCH ), 24.5 (CH ).
3
). C{ H} NMR (75 MHz, CDCl , as
3
1
(
Scheme 4. Direct Arylation of 1-Methylpyrrole
2
2
2
3
Mp: 204 °C (dec). Anal. Calcd for C H Br N PdS: C, 39.57; H,
19
22
2
2
3
.85; N, 4.86. Found: C, 39.45; H, 3.89; N, 4.85. MS (ESI): m/z 497
+
[
M − Br] .
cis-Dibromido(1-isobutyl-3-(2-(isopropylthio)ethyl)-
2
benzimidazolin-2-ylidene-κ C,S)palladium(II) (5). The compound
was prepared in analogy to 4 from 2 (107 mg, 0.30 mmol, 1.00
equiv), silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and
palladium(II) bromide (80 mg, 0.30 mmol, 1.00 equiv). The product
1
was obtained as a yellow solid (139 mg, 0.26 mmol, 85%). H NMR
CONCLUSION
A series of six thioether-functionalized κ C,S palladium(II)
■
(300 MHz, CDCl
7.85−7.74 (m, 1 H, Ar−H), 7.49−7.34 (m, 4 H, Ar−H), 7.33−7.26
3
, as pyridine adduct): δ 9.08−8.97 (m, 2 H, Ar−H),
2
3
(
m, 2 H, Ar−H), 5.10−4.97 (m, 2 H, NCH ), 4.55 (d, J
= 8 Hz, 2
H−H
NHC complexes has been synthesized. Characterization by
NMR spectroscopy proved difficult due to the marked
hemilabile behavior of the thioether moieties. X-ray crystallog-
raphy revealed the existence of two different coordination
modes, thus providing the first direct evidence for previously
postulated species. The thioether moieties were readily replaced
by other donor ligands, and a series of hetero(bis)-NHC
2
H, NCH ), 3.42−3.30 (m, 2 H, SCH ), 3.26−3.06 (m, 2 H, SCH,
2
2
3
3
CH), 1.39 (d, J
= 7 Hz, 6 H, CH ), 1.11 (d, J
= 7 Hz, 6 H,
H−H
H−H
3
CH3). 13C{ H} NMR (75 MHz, CDCl , as pyridine adduct): δ 163.3
1
3
(
Ccarbene), 153.2, 138.7, 136.1, 134.8, 125.3, 123.8, 111.5, 110.9 (Ar−
C), 56.7 (NCH ), 49.7 (NCH ), 36.1 (SCH), 29.8 (SCH ), 29.6
2
2
2
(
CH), 24.5 (CH ), 21.5 (CH ). Mp: 233 °C (dec). Anal. Calcd for
3 3
C H Br N PdS: C, 35.41; H, 4.46; N, 5.16. Found: C, 35.36; H,
16
24
2
2
2
+
complexes, formally derived from the κ C,S complexes, has
been synthesized as well.
4.72; N, 5.08. MS (ESI): m/z 1005 [2 M − Br] .
cis-Dibromido(1-benzhydryl-3-(2-(isopropylthio)ethyl)-
2
benzimidazolin-2-ylidene-κ C,S)palladium(II) (6). The compound
Both series of complexes were found to be catalytically active
in the hydroamination of phenylacetylene, although good yields
were obtained only in the presence of triflic acid. For all
complexes, a consistently good catalytic performance was
observed in the direct arylation of 1-methylpyrrole, and future
work will focus on other similar direct arylation reactions.
was prepared in analogy to 4 from 3 (140 mg, 0.30 mmol, 1.00
equiv), silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and
palladium(II) bromide (80 mg, 0.30 mmol, 1.00 equiv). The product
1
was obtained as a yellow solid (197 mg, 0.30 mmol, >99%). H NMR
(300 MHz, CDCl , as pyridine adduct): δ 8.98 (d, J
= 5 Hz, 2 H,
3
H−H
Ar−H), 8.53 (s, 1 H, Ar−H), 7.74 (t, J
= 8 Hz, 2 H, Ar−H), 7.47−
H−H
7
.39 (m, 4 H, Ar−H), 7.36−7.27 (m, 7 H, Ar−H, NCHPh ), 7.20 (t,
2
EXPERIMENTAL SECTION
■
J
H−H = 7 Hz, 1 H, Ar−H), 6.96 (t, JH−H = 8 Hz, 1 H, Ar−H), 6.74 (d,
General Considerations. All reactions were carried out without
precautions to exclude air and moisture, unless stated otherwise. All
solvents and chemicals were used as received or dried using standard
procedures when appropriate. NMR spectra were recorded on either a
JH−H = 8 Hz, 1 H, Ar−H), 5.13−5.00 (m, 2 H, NCH ), 3.47−3.33 (m,
2 H, SCH ), 3.21 (sept, J
2
3
3
= 7 Hz, 1 H, SCH), 1.39 (d, J
= 7
H−H
2
H−H
13
1
Hz, 6 H, CH3). C{ H} NMR (75 MHz, CDCl , as pyridine adduct):
3
δ 165.6 (Ccarbene), 153.1, 138.6, 137.0, 135.5, 129.7, 129.1, 128.8, 125.6,
3
00 MHz or a 500 MHz spectrometer. The chemical shifts (δ) were
125.2, 123.6, 123.6, 114.3, 110.9 (Ar−C), 69.0 (NCHPh ), 49.7
2
internally referenced to the residual solvent signals relative to
(NCH ), 36.0 (SCH), 29.3 (SCH ), 24.5 (CH ). Mp: 173 °C (dec).
2
2
3
1
13
tetramethylsilane ( H, C). Melting points were determined in
open capillaries. Elemental analyses were performed at the Depart-
ment of Chemistry, National University of Singapore. The ligand
precursors 1−3 and 7−9 as well as [PdBr ( Pr -bimy)]
prepared following established procedures.
Anal. Calcd for C H Br N PdS: C, 46.00; H, 4.01; N, 4.29. Found:
25 26 2 2
+
C, 45.89; H, 3.93; N, 4.60. MS (ESI): m/z 572 [M − Br] .
cis-Dibromido(1-benzyl-3-(3-(isopropylthio)propyl)-
11
i
25
2
were
benzimidazolin-2-ylidene-κ C,S)palladium(II) (10). The compound
2
2
2
was prepared in analogy to 4 from 7 (122 mg, 0.30 mmol, 1.00 equiv),
1
272
dx.doi.org/10.1021/om500083r | Organometallics 2014, 33, 1266−1275

Organometallics
Article
silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and palladium(II)
bromide (80 mg, 0.30 mmol, 1.00 equiv). The product was obtained as
a yellow solid (173 mg, 0.29 mmol, 98%). NMR spectra could not be
obtained due to the low solubility of the compound in all common
deuterated solvents and the fluxionality of its structure. Mp: 170 °C
C H Br N PdS: C, 46.76; H, 5.68; N, 7.52. Found: C, 46.83; H,
29
42
2
4
+
5.59; N, 7.48. MS (ESI): m/z 665 [M − Br] .
trans-Dibromido(1-benzhydryl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene)(1,3-diisopropylbenzimidazolin-2-
ylidene)palladium(II) (15). The compound was prepared in analogy to
1
3 from 3 (207 mg, 0.44 mmol, 1.00 equiv), silver(I) oxide (51 mg,
(
dec). Anal. Calcd for C H Br N PdS: C, 40.67; H, 4.10; N, 4.74.
20 24 2 2
i
+
0.22 mmol, 0.50 equiv), and [PdBr ( Pr -bimy)] (206 mg, 0.22 mmol,
Found: C, 40.21; H, 4.28; N, 4.57. MS (ESI): m/z 511 [M − Br] .
2 2 2
0
.50 equiv). The product was obtained as a yellow solid (229 mg, 0.27
cis-Dibromido(1-isobutyl-3-(3-(isopropylthio)propyl)-
2
1
benzimidazolin-2-ylidene-κ C,S)palladium(II) (11). The compound
mmol, 61%). H NMR (500 MHz, CDCl
7.60−7.57 (m, 1 H, Ar−H), 7.55−7.52 (m, 1 H, Ar−H), 7.44−7.34
(m, 11 H, Ar−H, NCHPh ), 7.22−7.18 (m, 3 H, Ar−H), 6.95 (t,
): δ 8.61 (s, 1 H, Ar−H),
3
was prepared in analogy to 4 from 8 (111 mg, 0.30 mmol, 1.00 equiv),
silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and palladium(II)
bromide (80 mg, 0.30 mmol, 1.00 equiv). The product was obtained as
a yellow solid (167 mg, 0.30 mmol, >99%). NMR spectra could not be
obtained due to the low solubility of the compound in all common
deuterated solvents and the fluxionality of its structure. Mp: 218 °C
2
3
3
J
H−H = 8 Hz, 1 H, Ar−H), 6.67 (d, JH−H = 8 Hz, 1 H, Ar−H), 6.24
3
3
(sept, JH−H = 7 Hz, 1 H, NCH), 6.02 (sept, JH−H = 7 Hz, 1 H,
), 3.12
NCH), 5.13−5.06 (m, 2 H, NCH
), 3.52−3.46 (m, 2 H, SCH
2
2
3
3
(sept, JH−H = 7 Hz, 1 H, SCH), 1.85 (d, JH−H = 7 Hz, 3 H, CH
),
).
3
3
3
(
dec). Anal. Calcd for C H Br N PdS: C, 36.68; H, 4.71; N, 5.03.
1.67 (d, JH−H = 7 Hz, 3 H, CH
3
), 1.37 (d, JH−H = 7 Hz, 3 H, CH
3
17
26
2
2
+
13
1
Found: C, 36.27; H, 4.55; N, 5.40. MS (ESI): m/z 1032 [M − Br] .
C{ H} NMR (125 MHz, CDCl
3
): δ 186.3 (Ccarbene), 179.2 (Ccarbene),
cis-Dibromido(1-benzhydryl-3-(2-(isopropylthio)propyl)-
138.9, 135.6, 134.8, 134.3, 134.2, 129.6, 129.2, 128.7, 123.4, 122.6,
2
benzimidazolin-2-ylidene-κ C,S)palladium(II) (12). The compound
114.3, 113.4, 113.3, 110.9 (Ar−C), 68.3 (NCH Ph), 54.8 (NCH), 54.5
2
was prepared in analogy to 4 from 9 (144 mg, 0.30 mmol, 1.0 equiv),
silver(I) oxide (35 mg, 0.15 mmol, 0.50 equiv), and palladium(II)
bromide (80 mg, 0.30 mmol, 1.00 equiv). The product was obtained as
a yellow solid (200 mg, 0.30 mmol, >99%). NMR spectra could not be
obtained due to the low solubility of the compound in all common
deuterated solvents and the fluxionality of its structure. Mp: 181 °C.
Anal. Calcd for C H Br N PdS: C, 46.83; H, 4.23; N, 4.20. Found:
(NCH), 49.1 (NCH ), 36.3 (SCH), 30.4 (SCH ), 24.4 (CH ), 21.7
2
2
3
(CH ), 21.5 (CH ). Mp: 136 °C. Anal. Calcd for C H Br N PdS·
3
3
38 44
2
4
0.5CH Cl : C, 51.52; H, 5.05; N, 6.24. Found: C, 51.75; H, 5.20; N,
2
2
+
6.35. MS (ESI): m/z 775 [M − Br] .
trans-Dibromido(1-benzyl-3-(2-(isopropylthio)propyl)-
benzimidazolin-2-ylidene)(1,3-diisopropylbenzimidazolin-2-
ylidene)palladium(II) (16). The compound was prepared in analogy to
2
6
28
2
2
+
C, 46.68; H, 4.30; N, 4.15. MS (ESI): m/z 585 [M − Br] .
13 from 7 (405 mg, 1.00 mmol, 1.00 equiv), silver(I) oxide (116 mg,
i
trans-Dibromido(1-benzyl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene)(1,3-diisopropylbenzimidazolin-2-
ylidene)palladium(II) (13). Salt 1 (391 mg, 1.00 mmol, 1.00 equiv)
and silver(I) oxide (116 mg, 0.50 mmol, 0.50 equiv) were suspended
in dichloromethane (15 mL) and stirred at ambient temperature for 15
0.50 mmol, 0.50 equiv), and [PdBr
2
( Pr
2
-bimy)]
2
(469 mg, 0.50 mmol,
0.50 equiv). The product was obtained as a yellow solid (485 mg, 0.61
1
mmol, 61%). H NMR (500 MHz, CDCl ): δ 7.73−7.69 (m, 2 H, Ar−
3
H), 7.66−7.63 (m, 1 H, Ar−H), 7.60−7.56 (m, 2 H, Ar−H), 7.47−
7.43 (m, 2 H, Ar−H), 7.40−7.36 (m, 1 H, Ar−H),7.34−7.30 (m, 2 H,
i
h shielded from light. [PdBr ( Pr -bimy)] (469 mg, 0.50 mmol, 0.50
Ar−H), 7.28−7.26 (m, 1 H, Ar−H), 7.25−7.20 (m, 2 H, Ar−H), 6.29
2
2
2
3
equiv) was suspended in dichloromethane (20 mL), and the filtered
silver carbene complex solution was added to this suspension. The
resulting mixture was stirred for 1 h at ambient temperature. Then it
was filtered and concentrated under reduced pressure. The residue was
purified by column chromatography (silica, dichloromethane + 5%
(sept, J
= 7 Hz, 1 H, NCH), 6.22 (s, 2 H, NCH Ph), 6.08 (sept,
H−H 2
3
JH−H = 7 Hz, 1 H, NCH), 5.10−5.05 (m, 2 H, NCH ), 3.07 (sept,
= 7 Hz, 1 H, SCH), 2.87 (t, J
.63 (m, 2 H, CH ), 1.93 (d, J
2
3J
2
=
3
= 7 Hz, 2 H, SCH ), 2.71−
H−H
3
H−H
2
3
= 7 Hz, 6 H, CH ), 1.69 (d, J
2
H−H
3 H−H
3
13
1
7 Hz, 6 H, CH ), 1.39 (d, J
= 7 Hz, 6 H, CH3). C{ H} NMR
3
H−H
EtOH). The product was obtained as a yellow solid (644 mg, 0.83
(
125 MHz, CDCl ): δ 184.1 (Ccarbene), 178.8 (Ccarbene), 136.4, 135.5,
3
1
mmol, 83%). H NMR (300 MHz, CDCl ): δ 7.68−7.50 (m, 4 H, Ar−
3
135.2, 134.3, 134.2, 129.4, 128.5, 128.4, 123.6, 123.6, 122.7, 113.3,
11.8, 111.1 (Ar−C), 54.5 (NCH), 54.5 (NCH), 53.2 (NCH Ph),
H), 7.47−7.28 (m, 5 H, Ar−H), 7.24−7.13 (m, 4 H, Ar−H), 6.23
1
2
3
(
sept, J
= 7 Hz, 1 H, NCH), 6.12 (s, 2 H, NCH Ph), 5.99 (sept,
H−H 2
48.0 (NCH ), 36.0 (SCH), 30.5 (SCH ), 28.9 (CH ), 24.1 (CH ),
2 2 2 3
3
JH−H = 7 Hz, 1 H, NCH), 5.13−5.02 (m, 2 H, NCH ), 3.50−3.38 (m,
H, SCH ), 3.13 (sept, J
2
21.8 (CH ), 21.5 (CH ). Mp: 95 °C. Anal. Calcd for C H Br N PdS:
3 3 33 42 2 4
3
3
2
= 7 Hz, 1 H, SCH), 1.86 (d, J
= 7 Hz, 6 H, CH ) 1.37 (d, J
= 7
= 7
C, 49.98; H, 5.34; N, 7.07. Found: C, 50.04; H, 5.39; N, 7.07. MS
2
H−H
H−H
3
3
+
Hz, 6 H, CH ), 1.65 (d, J
(ESI): m/z 713 [M − Br] .
3
H−H
3
H−H
13
1
Hz, 6 H, CH3). C{ H} NMR (125 MHz, CDCl ): δ 184.5 (Ccarbene),
trans-Dibromido(1-isobutyl-3-(2-(isopropylthio)propyl)-
benzimidazolin-2-ylidene)(1,3-diisopropylbenzimidazolin-2-
ylidene)palladium(II) (17). The compound was prepared in analogy to
3
1
1
5
78.6 (Ccarbene), 136.2, 135.3, 135.2, 134.3, 134.2, 129.5, 128.6, 128.5,
23.8, 123.7, 122.7, 113.4, 113.3, 112.0, 110.9 (Ar−C), 55.4 (NCH),
4.8 (NCH), 54.4 (NCH Ph), 49.1 (NCH ), 36.2 (SCH), 30.5
13 from 8 (371 mg, 1.00 mmol, 1.00 equiv), silver(I) oxide (116 mg,
2
2
i
(
SCH ), 24.4 (CH ), 21.8 (CH ) 21.6 (CH ). Mp: 224 °C (dec).
0.50 mmol, 0.50 equiv), and [PdBr
2
( Pr
2
-bimy)]
2
(469 mg, 0.50 mmol,
2
3
3
3
Anal. Calcd for C H Br N PdS·CH Cl : C, 45.88; H, 4.90; N, 6.49.
0.50 equiv). The product was obtained as a yellow solid (541 mg, 0.71
3
2
40
2
4
2
2
+
1
Found: C, 46.30; H, 4.58; N, 6.73. MS (ESI): m/z 699 [M − Br] .
trans-Dibromido(1-isobutyl-3-(2-(isopropylthio)ethyl)-
benzimidazolin-2-ylidene)(1,3-diisopropylbenzimidazolin-2-
ylidene)palladium(II) (14). The compound was prepared in analogy to
mmol, 71%). H NMR (500 MHz, CDCl
3
): δ 7.63−7.60 (m, 2 H, Ar−
H), 7.54−7.51 (m, 1 H, Ar−H), 7.45−7.41 (m, 1 H, Ar−H), 7.31−
3
7.28 (m, 2 H, Ar−H), 7.26−7.23 (m, 2 H, Ar−H), 6.35 (sept, J
=
H−H
H−H
3
3
7 Hz, 1 H, NCH), 6.27 (sept, J
= 7 Hz, 1 H, NCH), 4.99 (t, J
H−H
3
1
0
0
3 from 2 (391 mg, 1.00 mmol, 1.00 equiv), silver(I) oxide (116 mg,
= 7 Hz, 2 H, NCH ), 4.60 (d, J
JH−H = 7 Hz, 1 H, SCH), 3.01 (sept, J
= 7 Hz, 2 H, NCH ), 3.16 (sept,
2
H−H 2
i
3
3
.50 mmol, 0.50 equiv), and [PdBr ( Pr -bimy)] (469 mg, 0.50 mmol,
= 7 Hz, 1 H, CH), 2.80 (t,
= 7 Hz, 2 H, CH ), 1.88
2
2
2
H−H
3J
(d, J
= 7 Hz, 2 H, SCH ), 2.62 (quint, J
3
.50 equiv). The product was obtained as a yellow solid (635 mg, 0.85
H−H
2
H−H
2
1
mmol, 85%). H NMR (500 MHz, CDCl ): δ 7.62−7.56 (m, 2 H, Ar−
H), 7.45−7.39 (m, 2 H, Ar−H), 7.31−7.27 (m, 2 H, Ar−H), 7.23−
3
3
3
= 7 Hz, 6 H, CH ), 1.86 (d, J
= 7 Hz, 6 H, CH ), 1.16 (d, J
C{ H} NMR (125 MHz, CDCl ): δ 183.5 (Ccarbene), 179.6 (Ccarbene),
= 7 Hz, 6 H, CH ), 1.34
H−H
3
H−H
3
3
3
(
d, J
= 7 Hz, 6 H, CH3).
H−H
3
H−H
3
7
.19 (m, 2 H, Ar−H), 6.28 (sept, J
= 7 Hz, 1 H, NCH), 6.24
13
1
H−H
3
3
(
sept, J
= 7 Hz, 1 H, NCH), 5.06−5.01 (m, 2 H, NCH ), 4.56 (d,
H−H
2
136.1, 135.1, 134.3, 134.2, 123.4, 123.4, 122.7, 113.4, 113.3, 111.4,
3
JH−H = 8 Hz, 2 H, NCH ), 3.43−3.38 (m, 2 H, SCH ), 3.18−3.06 (m,
2
2
111.1 (Ar−C), 56.2 (NCH ), 54.6 (NCH), 48.0 (NCH ), 36.1
2
2
3
3
2
H, SCH, CH), 1.85 (d, J
= 7 Hz, 6 H, CH ), 1.84 (d, J
= 7 Hz, 6 H, CH ), 1.13 (d, J
= 7
= 7
H−H
3
H−H
(SCH), 30.5 (SCH ), 30.5 (CH), 28.9 (CH ), 24.2 (CH ), 21.8
2
2
3
3
3
Hz, 6 H, CH ), 1.35 (d, J
Hz, 6 H, CH3). C{ H} NMR (125 MHz, CDCl ): δ 183.9 (Ccarbene),
3
H−H
3
H−H
(CH ), 21.6 (CH ) 21.5 (CH ). Mp: 229 °C (dec). Anal. Calcd for
3 3 3
13
1
3
C H Br N PdS: C, 47.47; H, 5.84; N, 7.38. Found: C, 47.97; H,
30 44 2 4
1
1
4
79.3 (Ccarbene), 136.1, 134.7, 134.3, 134.2, 123.5, 123.5, 122.7, 113.4,
+
6.15; N, 7.63. MS (ESI): m/z 679 [M − Br] .
13.3, 111.5, 110.8 (Ar−C), 56.2 (NCH), 54.9 (NCH), 54.6 (NCH ),
2
trans-Dibromido(1-benzhydryl-3-(2-(isopropylthio)propyl)-
benzimidazolin-2-ylidene)(1,3-diisopropyl-benzimidazolin-2-
ylidene)palladium(II) (18). The compound was prepared in analogy to
9.0 (NCH ), 36.2 (SCH), 30.5 (SCH ), 30.4 (CH), 24.4 (CH ), 21.7
2
2
3
(
CH ), 21.8 (CH ) 21.4 (CH ). Mp: 235 °C (dec). Anal. Calcd for
3 3 3
1
273
dx.doi.org/10.1021/om500083r | Organometallics 2014, 33, 1266−1275

Organometallics
Article
1
0
0
3 from 9 (482 mg, 1.00 mmol, 1.00 equiv), silver(I) oxide (116 mg,
ACKNOWLEDGMENTS
i
■
.50 mmol, 0.50 equiv), and [PdBr ( Pr -bimy)] (469 mg, 0.50 mmol,
2
2
2
We thank the National University of Singapore and the
Singapore Ministry of Education for financial support (WBS R
143-000-483-112 and SINGA scholarship) and the CMMAC
staff of the department of chemistry for technical assistance.
.50 equiv). The product was obtained as a yellow solid (649 mg, 0.76
1
mmol, 76%). H NMR (500 MHz, CDCl ): δ 8.66 (s, 1 H, Ar−H),
3
7
.58−7.55 (m, 1 H, Ar−H), 7.54−7.48 (m, 2 H, Ar−H), 7.43−7.33
(
m, 10 H, Ar−H, NCHPh ), 7.21−7.16 (m, 3 H, Ar−H), 6.93 (t, J
2
H−H
=
8 Hz, 1 H, Ar−H), 6.66 (d, J
H−H
= 8 Hz, 1 H, Ar−H), 6.23 (sept,
H−H
3
3
J
= 7 Hz, 1 H, NCH), 6.01 (sept, J
= 7 Hz, 1 H, NCH),
H−H
REFERENCES
3
■
5
.04−4.99 (m, 2 H, NCH ), 3.02 (sept, J
= 7 Hz, 1 H, SCH), 2.82
2
H−H
3
(1) (a) Herrmann, W. A.; Ko
̈
cher, C. Angew. Chem., Int. Ed. Engl.
(
t, J
= 7 Hz, 2 H, SCH ), 2.68−2.60 (m, 2 H, CH ), 1.84 (d,
H−H
3
2
2
3
1997, 36, 2162. (b) Bourissou, D.; Guerret, O.; Gabbaï, F. P.;
Bertrand, G. Chem. Rev. 2000, 100, 39. (c) Herrmann, W. A. Angew.
Chem., Int. Ed. 2002, 41, 1290. (d) Peris, E.; Crabtree, R. H. Coord.
Chem. Rev. 2004, 248, 2239. (e) N-Heterocyclic Carbenes in Synthesis;
Nolan, S. P., Ed.; Wiley-VCH: Weinheim, 2007. (f) Kantchev, E. A. B.;
O’Brien, C. J.; Organ, M. G. Angew. Chem., Int. Ed. 2007, 46, 2768.
JH−H = 7 Hz, 6 H, CH ), 1.64 (d, J
= 7 Hz, 6 H, CH ), 1.33 (d,
3
3
H−H
3J
= 7 Hz, 6 H, CH3). C{ H} NMR (125 MHz, CDCl ): δ 185.9
13
1
H−H
3
(
1
(
Ccarbene), 179.3 (Ccarbene), 138.9, 135.8, 134.9, 134.2, 134.1, 129.6
29.1, 128.6, 123.3, 122.6, 114.2, 113.3, 113.3, 111.1 (Ar−C), 68.1
NCHPh ), 54.6 (NCH), 54.5 (NCH), 48.1 (NCH ), 36.0 (SCH),
2
2
3
1
0.4 (SCH ), 28.9 (CH ), 24.2 (CH ), 21.8 (CH ), 21.5 (CH ). Mp:
31 °C. Anal. Calcd for C H Br N PdS: C, 53.90; H, 5.33; N, 6.45.
2 2 3 3 3
(
(
3
g) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122.
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2) (a) Hindi, K. M.; Panzner, M. J.; Tessier, C. A.; Cannon, C. L.;
39
46
2
4
́
+
Found: C, 53.64; H, 5.25; N, 6.23. MS (ESI): m/z 789 [M − Br] .
General Procedure for Catalytic Hydroaminations. A Schlenk
tube was charged with precatalyst (10 μmol, 1.0 mol %) under an
atmosphere of dry nitrogen. Anhydrous toluene (3 mL) and triflic acid
2
̧
(
2.0 μL, 20 μmol, 2.0 mol %) were added, and the resulting suspension
was stirred for 5 min at ambient temperature. Then phenylacetylene
219 μL, 2.00 mmol, 2.00 equiv) and 2,6-dimethylaniline (123 μL,
.00 mmol, 1.00 equiv) were added, and the Schlenk tube was
(
́
(
(
Youngs, W. J. Chem. Rev. 2009, 109, 3859. (b) Melaiye, A.; Simons, R.
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Boyer, D.; Mahiou, R.; Gautier, A. Dalton Trans. 2009, 6894.
1
immersed in an oil bath preheated to 100 °C. The mixture was allowed
to react for 15 h. After this time, the Schlenk tube was taken out of the
oil bath, the suspension was diluted with diethyl ether (10 mL), and
decane as an internal standard was added. Samples were analyzed by
GC-MS.
(
(
d) Mercs, L.; Albrecht, M. Chem. Soc. Rev. 2010, 39, 1903.
e) Chang, W.-C.; Chen, H.-S.; Li, T.-Y.; Hsu, N.-M.; Tingare, Y.
General Procedure for the Direct Arylation of 1-Methyl-
pyrrole. A Schlenk tube was charged with precatalyst (10 μmol, 1.0
mol %), 4-bromoacetophenone (199 mg, 1.00 mmol, 1.00 equiv), and
potassium acetate (196 mg, 2.00 mmol, 2.00 equiv) under an
atmosphere of dry nitrogen. Degassed dimethyl acetamide (3 mL) was
added, followed by 1-methylpyrrole (354 μL, 4.00 mmol, 4.00 equiv).
The tube was immersed in an oil bath preheated to 150 °C, and the
mixture was allowed to react for 20 h. After this time, the Schlenk tube
was taken out of the oil bath, the suspension was diluted with diethyl
ether (10 mL), and decane as an internal standard was added. Samples
were analyzed by GC-MS.
S.; Li, C.-Y.; Liu, Y.-C.; Su, C.; Li, W.-R. Angew. Chem., Int. Ed. 2010,
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4
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2
2
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012, 31, 1664. (h) Oehninger, L.; Rubbiani, R.; Ott, I. Dalton Trans.
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2
(
̀
X-ray Diffraction Studies. X-ray data were collected with a
6
́
Bruker AXS SMART APEX diffractometer, using Mo Kα radiation at
2
6
1
00(2) K, with the SMART suite of programs. Data were processed
27
́
and corrected for Lorentz and polarization effects with SAINT and
for absorption effects with SADABS. Structural solution and
refinement were carried out with the SHELXTL suite of programs.
2
8
J. Org. Chem. 2013, 78, 328. (h) Bernhammer, J. C.; Frison, G.;
2
9
Huynh, H. V. Chem.Eur. J. 2013, 19, 12892.
(4) (a) Pugh, D.; Danopoulos, A. A. Coord. Chem. Rev. 2007, 251,
The structure was solved by direct methods to locate the heavy atoms,
followed by difference maps for the light, non-hydrogen atoms. All
hydrogen atoms were put at calculated positions. All non-hydrogen
atoms were generally given anisotropic displacement parameters in the
final model. A summary of crystallographic data is given in Tables 1−3
and the Supporting Information.
610. (b) Lee, H. M.; Lee, C. C.; Cheng, P. Y. Curr. Org. Chem. 2007,
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ASSOCIATED CONTENT
■
*
S
Supporting Information
1
13
Figures of H and C NMR spectra for all complexes, CIF files
for 4−6, 12−16, and 18, and tables giving crystallographic data.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
2
f) DePasquale, J.; Kumar, M.; Zeller, M.; Papish, E. T. Organometallics
013, 32, 966.
6) (a) Bonnet, L. G.; Douthwaite, R. E.; Hodgson, R.; Houghton, J.;
(
Kariuki, B. M.; Simonovic, S. Dalton Trans. 2004, 3528. (b) Mungur,
S. A.; Blake, A. J.; Wilson, C.; McMaster, J.; Arnold, P. L.
Organometallics 2006, 25, 1861. (c) Jimen
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ez, M. V.; Perez-Torrente,
AUTHOR INFORMATION
■
*
J. J.; Bartolome, M. I.; Gierz, V.; Lahoz, F. J.; Oro, L. A.
́
Corresponding Author
E-mail: chmhhv@nus.edu.sg.
Organometallics 2008, 27, 224. (d) Warsink, S.; Hauwert, P.; Siegler,
M. A.; Spek, A. L.; Elsevier, C. J. Appl. Organomet. Chem. 2009, 23,
2
25. (e) Warsink, S.; Chang, I.-H.; Weigand, J. J.; Hauwert, P.; Chen,
Notes
J.-T.; Elsevier, C. J. Organometallics 2010, 29, 4555. (f) del Pozo, C.;
The authors declare no competing financial interest.
Iglesias, M.; San
́
chez, F. Organometallics 2011, 30, 2180. (g) Cross, W.
1
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dx.doi.org/10.1021/om500083r | Organometallics 2014, 33, 1266−1275

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