Synthesis, characterization and palladium complex formation of pyridinium- and quinolinium-3-acetylides: Mesomeric betaines or betaine-stabilized carbenes?

Article abstract of DOI:10.1016/j.tet.2015.07.053

3-Ethynyl-1-methylpyridinium- and 3-ethynyl-1-methyl-quinolinium triflates were prepared by methylation of 3-ethynylpyridine and 3-ethynylquinoline with methyl triflate, respectively. Whereas deprotonation of the former mentioned salt gave no stable produ

Full text of DOI:10.1016/j.tet.2015.07.053

Tetrahedron 71 (2015) 6665e6671
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Synthesis, characterization and palladium complex formation of
pyridinium- and quinolinium-3-acetylides: mesomeric betaines or
betaine-stabilized carbenes?
a
a
a
b
a,
Alexey Smeyanov , Jan C. Namyslo , Eike H u€ bner , Martin Nieger , Andreas Schmidt
*
a
Clausthal University of Technology, Institute of Organic Chemistry, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany
University of Helsinki, Department of Chemistry, Laboratory of Inorganic Chemistry, PO Box 55, FIN-00014 Helsinki, Finland
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2015
Received in revised form 17 July 2015
Accepted 18 July 2015
Available online 26 July 2015
3-Ethynyl-1-methylpyridinium- and 3-ethynyl-1-methyl-quinolinium triflates were prepared by meth-
ylation of 3-ethynylpyridine and 3-ethynylquinoline with methyl triflate, respectively. Whereas de-
protonation of the former mentioned salt gave no stable product, sodium hydroxide in methanol formed
1-methylquinolinium-3-acetylide which could be characterized NMR spectroscopically. Considerable
upfield shifts of the resonance frequencies in combination with DFT calculations of bond lengths reveal
that the structure has to be represented by resonance forms of a quinolinium-3-acetylide, i.e., as
mesomeric betaine, as well as by allenylidene resonance forms. The Pd complex of this species was
Keywords:
N-Heterocyclic carbenes
Allenylidene Pd complex
Alkynyl Pd complex
Quinolinium-3-ylidene
Pyridinium-3-ylidene
prepared by reaction of 3-ethynylquinoline with Pd(PPh
give bis(triphenylphosphine)bis(quinolin-3-yl-ethynyl)palladium(II) which was subsequently methyl-
ated at the nitrogen atoms. Insertion reactions of 3-(bromoethynyl)pyridine with Pd(PPh gave bis(-
3 2 2
) Cl in the presence of CuI and diethylamine to
3 4
)
triphenylphosphine)palladium(II)(pyridin-3-yl-ethynyl) bromide which was finally methylated to give
bis(triphenylphosphine)[(1-methylpyridinium-3-yl)ethynyl]palladium(II)bromide triflate. Likewise,
bis(triphenylphosphine)palladium(II) (quinolin-3-yl-ethynyl) bromide and bis(triphenylphosphine)((1-
methylquinolinium-3-yl)ethynyl)palladium(II)bromide triflate were prepared. In contrast to the non-
complexed forms, the spectroscopic data are in accordance with alkynyl palladium complexes rather
than with allenylidene complexes.
Ó 2015 Elsevier Ltd. All rights reserved.
1
. Introduction
R
N
R
HN
N
N
N O
-H
N O
Heterocyclic mesomeric betaines are compounds which can
exclusively be formulated by dipolar resonance forms in which the
N
N
N
N
N
N
Ph
Ph
Ph
Ph
R
O
R
O
+H
positive and negative charges are delocalized within a common p-
1
2
3
4
electron system. After some decades of controversial debates about
1
the adequate representation of this class of compounds a classifi-
Scheme 1. N-Heterocyclic carbenes by tautomerism and deprotonation, respectively.
2
3
cation system was proposed in 1985 which was modified in 2013.
Today, conjugated (CMB), cross-conjugated (CCMB), pseudo-cross-
conjugated (PCCMB), semi-conjugated (SCMB), and pseudo-semi-
conjugated heterocyclic mesomeric betaines (PSCMB) can be dis-
1
9056,7 and has been applied for decades as reagent to detect ni-
8
,9
trates (Busch’s reagent), it was not shown before 2012 that nitron
1 is in tautomeric equilibrium with its N-heterocyclic carbene 2. It
has also been demonstrated recently that suitably substituted
3
tinguished. During the last couple of years it was also recognized
that some mesomeric betaines are masked N-heterocyclic car-
1
0
11e13
4
conjugated mesomeric betaines including ylides
and cross-
benes. First results have been summarized in a review article. As
1
4
conjugated mesomeric betaines can form N-heterocyclic car-
benes by tautomerisation. We would also like to mention here that
sydnones 3 can be regarded as anionic N-heterocyclic carbenes 4
example, nitron 1 (Scheme 1) is a type A mesoionic compound
3
belonging to class 1B of conjugated mesomeric betaines, and
5
a masked N-heterocyclic carbene. Although it was published in
15
when they are deprotonated. Additional examples of mesomeric
betaineseN-heterocyclic carbene interconversions can be found in
the aforementioned review article.
*
Corresponding author. Tel.: þ49 5323 72 3861; e-mail address: schmidt@ioc.
4
tu-clausthal.de (A. Schmidt).
http://dx.doi.org/10.1016/j.tet.2015.07.053
0
040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

6666
A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
The cross-conjugated mesomeric betaine trigonellin 5 (1-
methylpyridinium-3-carboxylate) is widely distributed in plants
16
and marine organisms (Scheme 2).
Its isomer, 1-
N
R
N
R
N
R
N
R
methylpyridinium-2-carboxylate 6, is known as marine alkaloid
homarine and belongs to the class of pseudo-cross-conjugated
mesomeric betaines. In CCMB such as 5 the charges are strictly
VII
VIII
delocalized in separate parts of the p-electron system (I), whereas
common sites for either charge exist in PCCMBs such as 6 when
electron sextet structures without internal octet stabilization are
considered (IV). In either betaine, the pyridinium ring is joined to
the anion through union bonds (‘u’) to a nodal position of the
highest occupied molecular orbital HOMO (II, V). CCMB 5 can be
regarded as heterocumulene adduct of a remote N-heterocyclic
carbene (rNHC) (III), whereas the PCCMB 6 is a heterocumulene
adduct of a normal N-heterocyclic carbene (NHC) (VI). In general,
C
C
N
N
R
C
C
R
X
IX
Scheme 3. Architecture of pyridinium- and quinolinium-3-acetylides.
17e22
23e25
NHC such as imidazole-2-ylidenes,
pyrazole-3-ylidenes,
can be generated easily from their
PCCMBs by decarboxylation, and pyridinium-2-carboxylates be-
26,27
and indazol-3-ylidenes
2
. Results and discussion
have similarly.2
8e31
By contrast, the use of cross-conjugated het-
We prepared 3-ethynyl-1-methylpyridinium triflate 8 in very
good yield from 3-ethynylpyridine 7 by methylation (Scheme 4).
The pyridinium salt 8 shows a resonance frequency of the terminal
acetylene proton at
CD OD, and at
methylpyridinium has been mentioned as building block of semi-
erocyclic mesomeric betaines as masked N-heterocyclic carbenes is
rather limited due to the vigorous conditions which are necessary
4
,22
to induce decarboxylations.
d
¼4.94 ppm in DMSO-d
6
, at
d
¼4.28 ppm in
3
d
¼4.02 ppm in CD
3
CN. 3-Ethynyl-1-
4
0
O
conducting materials and polymers in the literature and a pat-
O
HOMO
41
u
C
ent before.
O
O
N
Me
N
N
MeOTf
DCM, 0 °C
Me
Me
Me
OTf
N
N
5
I
II
III (rNHC)
Me
7
8 (91%)
u
O
C
Scheme 4. Synthesis of 3-ethynylpyridinium triflate.
O
N
N
N
HOMO
Me
O
Me
Me
Me
O
6
VI (NHC)
To the best of our knowledge, quinolinium salts possessing
unsubstituted ethynyl residues have not yet been described in the
literature. We prepared the 3-ethynyl derivative starting from 3-
bromoquinoline 9 which was subjected to a literature-known
IV
V
sites for negative charges
sites for positive charges
common sites for positive
and negative charges in the
resonance forms
4
2
Sonogashira coupling to give 10 in excellent yield. Deprotection
43
was then accomplished by a method developed by us earlier
Scheme 2. Characteristic features of the CCMB trigonellin 5 (above) and the PCCMB
homarine 6 (below).
employing solid potassium hydroxide and potassium phosphate
in toluene to give 3-ethynylquinoline 11 in almost quantitative
yield. Next we tried several methylation conditions. Treatment of
11 with trimethyloxononium tetrafluoroborate (Meerwein’s re-
agent) gave the tetrafluoroborate salt of 12 in 69% yield, whereas
dimethyl sulfate in boiling p-xylene gave only 15e20% of the cor-
responding methylsulfate. Methyl iodide in acetone or acetonitrile
gave a 65% yield of the iodide within a reaction time of 72 h. Best
results were achieved employing methyl triflate in dichloro-
methane at low temperatures, whereupon almost quantitative
In continuation of our interest in the area of overlap between
the classes of heterocyclic mesomeric betaines and N-heterocyclic
carbenes we report on structures here in which the carboxylate
moiety of trigonelline as well as of its quinoline derivative is for-
mally replaced to acetylide groups. Thus, the pyridinium- or qui-
nolinium-acetylides VII and VIII can be formulated as
allenylidenes, respectively, which are stabilized by a conjugated
heterocyclic mesomeric betaine (VII) or a non-betainic heterocycle
1
yields of the 3-ethynylquinolinium salt 12 were obtained. The H
(VIII). They can be regarded as ethenediylidene (diatomic carbon,
NMR signals of the acetylenic protons of the quinolinium salt 12
C
2
) adduct of the N-heterocyclic carbenes pyridin- and quinolin-3-
were detected at
respectively (see Scheme 5).
d
¼4.94 ppm (DMSO-d
6
) and
d
3
¼4.01 ppm (CD CN),
ylidene as well as their 2-ylidene isomers (Scheme 3). 2-
Ethynylpyridinium derivatives are known to be unstable. They
Suitable single crystals of 12 were obtained by slow evaporation
of a saturated solution in methanol. The compound crystallized in
the triclinic space group P-1 with two crystallographic independent
moieties in the asymmetric unit. The bond length of the triple bond
[117.8(3)/117.8(3) pm] is in accordance with the bond lengths of
triple bonds as found in acetylene (118 pm), and the sp -sp bond
joining the triple bond to the quinolinium ring was detected to be
141.2(3)/144.1(3) pm. A molecular drawing of one of the crystallo-
graphic independent cations is presented in Fig. 1.
readily polymerize3
2e34
and were used for the preparation of
35
conjugated polyions, carbon nanotube graft ionic polyacetylene
nanocomposites,36 ionic polyacetylenes, and block copolymers.
37
38
Therefore, we describe the syntheses, characterizations, results of
NMR examinations and calculations, as well as complex forma-
tions of their isomeric pyridinium- and quinolinium-3-acetylides
here. To the best of our knowledge, only imidazolium-2-
4
4
2
3
9
acetylides have been described so far.

A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
6667
ꢁ
ꢁ
ꢁ
Me
CD
3
CN (ꢀ80 C/ꢀ40 C/0 C), KOtBu in THF and toluene, potassium
Me
tert-amylate in THF and toluene (rt, reflux temperature) caused
decompositions of 3-ethynyl-1-methylpyridinium triflate 8. So-
OH
Br
OH
3
dium methanolate in CD OD resulted in an H/D exchange of the
acetylenic proton as well as of the positions 2, 4, and 6 of the
Pd(PPh3)2Cl2,
CuI
N
N
pyridinium ring instead of a deprotonation to 15. Correspondingly,
13
9
10 (96%)
triplets of the C-D bonds were visible in the C NMR spectra. By
contrast, 3-ethynyl-1-methylquinolinium triflate 12 was smoothly
deprotonated by a saturated solution of sodium hydroxide in
KOH / K3PO4,
toluene
CD
nBuLi in THF or CH
CH CN resulted in the formation of yet unidentified decomposition
3
OD, whereas NaOCD
3
in CD
3
OD, NaH in DMSO-d
6
and CH
3
CN,
OTf
ꢁ
ꢁ
ꢁ
3
CN (ꢀ80 C/ꢀ40 C, 0 C), and LiCH
2
CN in
3
MeOTf
1
products. On deprotonation, the H NMR resonance frequency of
the acetylenic proton disappeared, while all aromatic signals shif-
ted considerably upfield (Fig. 2). Measurements of the 2D NMR
spectra revealed that C2-H of the quinolinium ring shifts from 9.59/
DCM, 0 °C
N
N
Me
1
2 (95%)
11 (96%)
152.2 ppm in salt 12 to 5.52/89.8 ppm in betaine 16. Likewise, C4-H
Scheme 5. Synthesis of 3-ethynylquinolinium triflate.
shifted from 9.32/148.9 ppm in 12 to 7.17/135.9 ppm in 16. The
methyl groups were detectable at 4.71/46.5 ppm in the salt 12 and
at 3.18/37.1 ppm in the betaine 16. The
6 was detected as a cross signal at
¼83.3 ppm; unfortunately we
were not able to detect the -carbon atom despite of numerous
a-carbon atom of the betaine
1
d
b
variations of the measurement parameters. Characteristic peaks of
þ
1
6 were measured at m/z¼190 (MþNa ) as base peak in the elec-
trospray ionization mass spectra (ESIMS), when the sample was
sprayed from MeCN at 30 V fragmentor voltage (see Scheme 7).
Fig. 1. Structure of one of the two crystallographic independent cations of 12 (dis-
placement parameters are drawn at the 50% probability level; crystallographic
numbering).
As a model reaction for the deprotonation of the pyridinium-
and quinolinium-acetylides to the corresponding betaines we first
examined the deprotonation of ethynylbenzene 13 to its anion 14
(
3
Scheme 6). Sodium methanolate in CD OD resulted in an H/D
Fig. 2. 1H NMR spectra of 12 (above) and 16 (below). The salt 12 contains water of
exchange reaction of the acetylenic proton; all other resonance
frequencies remained essentially unchanged, indicating that no
deprotonation took place under these conditions. On treatment of
crystallization which gives a signal at
d
¼4.90 ppm; Additional assignments: 4.71 ppm
(NeCH ), 4.30 ppm (CCeH), 3.31 ppm (CD OD). Spectrum below: 5.20 ppm (water),
3
3
3.31 ppm (CD
3 3
OD), 3.18 ppm (NeCH ).
1
3 with sodium hydride in DMSO-d
6
, however, the signal at
4
.17 ppm, assigned to the acetylenic proton, disappeared while all
1
H NMR resonance frequencies of the aromatic protons shifted
13
OTf
slightly upfield. In the C NMR spectra, the terminal carbon atom of
the acetylene moiety was shifted considerably by Dd¼ꢀ78.9 ppm
base
base
downfield and was finally detected at
d¼159.6 ppm. The second
acetylenic carbon shifted by Dd¼ꢀ30.5 ppm to 113.9 ppm.
0.7 ppm
3.4ppm
N
N
Me
8
Me
15
8
OTf
113.9 ppm
8
O
S
Na D2C
CD3
159.6 ppm
N
N
DMSO-d6
Me
Me
13
14
12
16
Scheme 6. A model reaction to gain knowledge about NMR chemical shift changes on
deprotonation. Selected C NMR values.
Scheme 7. Deprotonations to the title compounds.
13
According to a DFT calculation (B3LYP/LACVD*), the triple bond
in the betaine 16 (126.3 pm) is longer than the CC triple bond in
3
Various deprotonation conditions such as NaOH in CD OD at rt,
NaH in DMSO at rt, BuLi in THF (ꢀ80 C/ꢀ40 C/0 C), nBuLi in
ꢁ
ꢁ
ꢁ

6668
A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
acetylene (118 pm),44 whereas the CspeCsp bond length (138.9 pm)
2
solvents such as dichloromethane and chloroform as well as in
polar solvents such as DMSO and methanol, so that a complete
characterization was possible (see Scheme 10).
is shortened in comparison to the corresponding bond length in
acrylonitrile or vinylacetylene (143 pm). This is in agreement
with values calculated for an allenylidene of imidazole. According
to the calculation, the negative charge (NBO) is essentially located
4
5
3
9
on the
a
-carbon atom (see Scheme 8).
Me
N
N
selected
selected
calculated
1H NMR signals [ppm] 13C NMR signals [ppm] bond lengths [pm] charge distribution
1
. CH2Cl2,
MeOTf
2
PF6
-
0.07660
141.2
Pd(PPh3)2Cl2,
CuI, Et2NH
8
3.2
140.3
126.3
2. NH4PF6
7.17
135.9
11
Ph3P Pd PPh3
Ph3P Pd PPh3
1
42.7
38.9
1
11.5
1
5.25
89.8
N
N
N 133.6
Me
N
- 0.47907
Me 3.17
Me 37.1
Me
Scheme 8. A selection of measured and calculated values of betaine 16.
N
N
Me
The highest occupied molecular orbital (HOMO) of 16 is a
pair located on the terminal carbon atom of the acetylide
substituent and also possesses coefficients on the and carbon
atoms. As expected, the lowest unoccupied molecular orbital
LUMO) is a orbital and is located in the quinolinium ring (Fig. 3).
The calculated values in addition to the results of the afore-
mentioned NMR investigations reveal that the structure of the
quinolinium-3-acetylide 16 can be represented by the canonical
formula of a mesomeric betaine A, by resonance forms of allenyli-
denes B and C, and by the structure of a betaine-stabilized carbene
D. The resonance forms BeD are singlet carbenes which are sta-
bilized by an adjacent conjugated heterocyclic mesomeric betaine
s lone
a
b
1
7 (65%)
18 (86%)
Scheme 10. Palladium complex formations.
(
p
Whereas the complex proved to be very stable in the solid state, it
decomposed slowly in solution at rt. In the complex, 2-H is consid-
erably shifted upfield by Dd¼1.67 ppm to 7.92 ppm in comparison to
the salt 12, but considerably downfield in comparison to the free
betaine 15. The signal of 4-H can be detected at
d
¼8.31 ppm. Like-
wise, the resonance frequencies of the aromatic carbon atoms are
31
shifted upfield in comparison to 12. The P NMR resonance fre-
(Scheme 9).
quency appears at
d
¼25.95 ppm as a singlet, and this value corre-
sponds well to literature-known resonance frequencies of imidazole
3
9
derived allenylidene palladium complexes. In addition, a triplet of
13
the C^CePd (
d
¼108.1 ppm) carbon atom is visible in the C NMR
spectra of 18 (JPC¼3.85 Hz) which confirms that the two phosphine
4
8,49
ligands are mutually trans.
This value is in agreement with lit-
erature known trans-[bis(3-(pentamethyleneamino)-3-methoxy-
1
,2-propadienylidene)bis (triethylphoshine)palladium(II)] alkynyl
4
6
complexes (
d
¼104.3 ppm ), and is shifted downfield in comparison
Fig. 3. Frontier orbital profile of 16: HOMO (left) and LUMO (right).
46
to their corresponding allenylidene complexes (
the IR spectra one band of the C^C-stretching vibration is detected
at 2104 cm , and the anion hexafluorophosphate can be seen by
a signal at
We next tried insertion reactions of 3-(bromoethynyl)pyridine
19 and the corresponding quinoline with tetrakis(-
triphenylphosphine)palladium(II) and obtained 20 and 22 as pale
yellow and orange solid, respectively, when the reaction mixture
was stirred over a period of 12 h. A shorter reaction time resulted in
the formation of a cis/trans mixture (see Scheme 11).
d
¼97.3 ppm ). In
ꢀ1
31
d
¼ꢀ144.5 ppm in the P NMR spectrum.
N
N
Me
Me
B
A
The triplets of the triple bond of 20 appear at
d
¼105.0 ppm (
a-C)
N
N
and at
detected at
d
¼107.1 ppm (
b
-C). The corresponding signals of 22 were
3
1
Me
Me
d
¼105.7 ppm and 107.7 ppm, respectively. In the
P
NMR-spectra of 20 and 22 singlets at
respectively. In IR spectroscopy, the absorptions of the C^C bond
are visible at 2114 cm , respectively, and these values are in well
d
¼24.2 ppm are observable,
C
D
Scheme 9. Selected resonance forms of 16.
ꢀ
1
4
6,47,50
agreement with literature values.
DFT calculations hint at the
After these spectroscopic investigations we focused our interest
on palladium complexes. Several palladium allenylidene complexes
formation of trans configurations, as cis-20 and cis-22 are by 49 kJ/
mol in vacuo less stable than their trans configuration isomers.
Methylation of 20 and 22 at low temperatures using methyl
triflate yielded 21 and 23, respectively. In the IR spectra the char-
acteristic bands of the triflate anion are detectable between 1028
4
6,47
of open-chain acetylides are known.
We started this in-
vestigation by reaction of 3-ethynylquinoline 11 with bis(-
triphenylphosphine) palladium(II) dichloride in diethylamine in
the presence of copper iodide which gave the bis(quinoline)palla-
dium complex 17 in acceptable yields as almost insoluble orange
compound. Methyl triflate in dichloromethane at low temperatures
converted complex 17 into the corresponding Pd adduct of 1-
methyl-quinolinium-3-acetylide 18 as a brownish solid in good
yield. Fortunately, this complex was soluble in halogenated
ꢀ1
ꢀ1
and 1029 cm , as well as between 1256 and 1258 cm . CH-
ꢀ
1
absorptions of the methyl group can be seen between 3050 cm
ꢀ1
and 3052 cm . The absorption bands of the triple bond are shifted
in comparison to the starting materials, as bands at 2120 cm (21)
and 2110 cm (23) were found. The H NMR resonance frequencies
ꢀ1
ꢀ1
1

A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
6669
2
.6.18e238.el5 SMP (x86_64) on five AMD Phenom II X6 1090T
MeOTf,
DCM
Ph3P
Ph3P
processor workstations (Beowulf-cluster) parallelized with Open-
MPI. MM2 optimized structures were used as starting geometries.
Br
Br
Br
53
Pd(PPh3)4
Pd
- 30 o
C
Pd
Complete geometry optimizations were carried out on the imple-
mented LACVP* (Hay-Wadt effective core potential (ECP) basis on
heavy atoms, N31G6* for all other atoms) basis set and with the
B3LYP density functional. Plots were obtained using Maestro
DCM
PPh3
PPh3
N
N
N
OTf
21 (80%)
Me
19
20 (87%)
9
.1.207, the graphical interface of Jaguar. Partial charges were ob-
5
4
tained with NBO 5.0 from the results of the DFT calculations.
Ph3P
Ph3P
Br
Br
4.3. General considerations
Pd
Pd
PPh3
PPh3
Flash-chromatography was performed using silica gel 60
N
N
Me
(0.040e0.063 mm). Nuclear magnetic resonance (NMR) spectra
were obtained using Bruker Avance 400 and Bruker Avance III
OTf
1
6
00 MHz instruments. H NMR spectra were recorded at 400 MHz
2
2 (61%)
23 (87%)
13
or 600 MHz. C NMR spectra were recorded at 100 MHz or
150 MHz, with the solvent peak or tetramethylsilane used as the
internal reference. Multiplicities are described by using the fol-
lowing abbreviations: s¼singlet, d¼doublet, t¼triplet, q¼quartet,
and m¼multiplet. FTIR spectra were recorded on a Bruker Vector 22
Scheme 11. Palladium complexes by insertion.
of the N-methyl groups were detected between
and 4.44 ppm (23) when the spectra were taken in DMSO-d . We
6
were not able to detect the C NMR resonance frequencies of the
C NMR, DEPT-, the DEPT-Q-
technique, or 2D NMR. It is literature-known that the C NMR
detection in related complexes is difficult or impossible.
d
¼4.13 ppm (21)
ꢀ
1
13
in the range of 400e4000 cm . ATR-IR spectra were recorded on
ꢀ
1
13
a Bruker Alpha in the range of 400e4000 cm . The mass spectra
were measured with a Varian 320 MS Triple Quad GC/MS/MS with
a Varian 450-GC. The electrospray ionization mass spectra (ESIMS)
were measured with an Agilent LCMSD series HP 1100 with APIES.
Melting points are uncorrected and were determined in an appa-
ratus according to Dr Tottoli (B u€ chi). Yields are not optimized.
triple bond by off-resonance
1
3
3
9,47,49
3
. Conclusion
In view of spectroscopic results and calculations, quinolinium-
-acetylide can be represented by resonance forms of a mesomeric
betaine, allenylidenes, and a betaine-stabilized carbene. In its pal-
ladium complexes, the data correspond to alkynyl rather than to
allenylidene complexes.
4
.4. 3-Ethynyl-1-methylpyridinium tri-
3
fluoromethanesulfonate 8
Under an atmosphere of nitrogen a solution of 3-ethynylpyridine
(2 mmol, 206 mg) in anhyd dichloromethane (6 mL) was treated
ꢁ
dropwise at 0 C with methyl triflate (1 equiv). The solution was
then stirred at rt for 2 h. The resulting product was filtered off and
washed with dichloromethane. The product was obtained as
4
4
. Experimental section
.1. Crystal structure studies of 12
ꢁ
1
brownish powder. Yield 485 mg (91%). Mp: 95.8 C. H NMR (DMSO-
):
d
6
d¼9.28 (s, 1H, 2-H), 8.98 (d, JH,H¼6.1 Hz, 1H, 4-H), 8.67 (d,
The single-crystal X-ray diffraction studies of 12 was carried out
on a Bruker-D8 Venture diffractometer with Photon100 detector at
J
1
H,H¼8.0 Hz,1H, 6-H), 8.13 (dd, JH,H¼6.1, JH,H¼8.0 Hz,1H, 5-H), 4.94 (s,
13
H, C^CeH), 4.33 (s, 3H, Me) ppm; C NMR (DMSO-d
6
):
d¼148.3
ꢀ
1
(
23(2) K using CuK
a
radiation (
l
¼1.54178 A). Direct Methods
(C2), 147.0 (C4), 145.4 (C6), 127.6 (C5), 121.9 (C3), 88.5 (eC^CeH),
SHELXS-97)51 were used for structure solution, and full-matrix
least-squares refinement on F (SHELXL-2014). H atoms were
localized by difference Fourier synthesis and refined using a riding
model. A semi-empirical absorption correction was applied.
ꢀ1
76.9 (eC^CeH), 48.2 (Me) ppm; IR (ATR, cm ) 3203, 3080, 2115,
2
52
1504, 1248, 1222, 1154, 1025, 808, 757, 670, 633, 572, 515; MS (ESI-
MS) [C N]: 118.0. HR-ESI-MS [C N]: 118.0651, calcd 118.0657.
H
8 8
8 8
H
1
2: yellow crystals, C12
H
10N$CF
3
O
3
S, M¼317.28, crystal size
4
.5. 3-Ethynyl-1-methylquinolinium tri-
0
.24ꢂ0.18ꢂ0.04 mm, triclinic, space group P-1 (No.2): a¼6.6942(3)
fluoromethanesulfonate (12)
ꢀ
ꢀ
ꢀ
3
ꢁ
ꢁ
A, b¼11.1461(5) A, c¼17.9330(8) A,
a
¼88.953(2) ,
b
¼88,154(2) ,
ꢁ
ꢀ
ꢀ3
g
¼85.749(2) , V¼1333.51(10) A , Z¼4,
r
(calcd)¼1.580 Mg m
,
Under an inert atmosphere a solution of 3-ethynylquinoline
ꢀ
1
ꢁ
F(000)¼648,
m
¼2.617 mm , 16,450 reflections (2
q
max¼144.2 ),
(5 mmol, 765 mg) in anhyd dichloromethane (10 mL) was cooled
5
0
0
211 unique [Rint¼0.023], 381 parameters, R1 (for 4869 I>2
s
(I))¼
ꢁ
to 0 C and then methyl triflate (5 mmol, 0.60 mL) was added
dropwise. Then, the cooling bath was removed and the mixture was
stirred over a period of 2 h. The resulting precipitate was filtered off,
washed with dichloromethane and dried in vacuo. Yield: 1.460 g
.050, wR2 (all data)¼0.139, GooF¼1.07, largest diff. peak and hole
ꢀ
ꢀ3
.
.973 and ꢀ0.455 e A
Crystallographic data (excluding structure factors) for the
structure reported in this work have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publi-
cation no. CCDC-1407972 (12). Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: int.codeþ(1223)336-033; e-mail:
deposit@ccdc.cam.ac.uk).
ꢁ
1
(4.70 mmol, 94%), grey solid. Mp: 182.3 C. H NMR (DMSO-d ):
6
d
¼9.78 (d, JH,H¼1.3 Hz, 1H, 2-H), 9.46 (s, 1H, 4-H), 8.52 (d,
J
J
J
H,H¼9.0 Hz, 1H, 8-H), 8.43 (d, JH,H¼9.0 Hz, 1H, 5-H), 8.32 (ddd,
H,H¼1.5, JH,H¼7.0, JH,H¼9.0 Hz, 1H, 7-H), 8.10 (ddd, JH,H¼0.7,
H,H¼7.0, JH,H¼9.0 Hz,1H, 6-H), 4.94 (s,1H, C^CeH), 4.62 (s, 3H, Me)
13
ppm. C NMR (DMSO-d
6
):
d¼152.3 (C2), 148.9 (C4), 137.5 (C9),
136.2 (C7), 130.6 (C6), 130.2 (C5), 128.6 (C10), 119.2 (C8), 116.0 (C3),
ꢀ1
4
.2. Calculations
87.1 (eC^CeH), 77.4 (eC^CeH), 45.4 (Me) ppm; IR (ATR, cm
256, 3052, 2121, 1521, 1253, 1224, 1143, 1027, 777, 619, 572, 516,
433; MS (ESI-MS) [C12 10N]: 168.1. HR-ESI-MS [C12 10N]: Found
168.0814, calcd 168.0813.
)
3
All density-functional theory (DFT)-calculations were carried
out by using the Jaguar 7.7.107 software running on Linux
H
H

6670
A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
4
.6. Bis(triphenylphosphine)bis(quinolin-3-yl-ethynyl)palla-
added dropwise (0.18 mmol, 0.010 mL). After stirring for 30 min the
dium(II) (17)
solution was allowed to warm to rt, and stirring was continued for
additional 30 min. Then, thesolvent was distilledoff invacuo, and the
residue was chromatographed (dichloromethane:MeOH¼10:1). The
complex was finally obtained as yellow solid. Yield: 115 mg
3 2 2
A suspension of Pd(PPh ) Cl (0.20 mmol, 140 mg) and CuI
(
2 mg) in anhyd diethylamine was treated under a nitrogen at-
ꢁ
1
mosphere with 3-ethynylquinoline (1.00 mmol, 153 mg) and then
heated to 3 h at reflux temperature. The resulting precipitate was
then filtered off, washed with ethyl acetate, ethanol and water,
respectively, and dried. Yield: 121 mg (0.13 mmol, 65%), orange
(0.12 mmol, 80%), mp 223 C. H NMR (600 MHz, DMSO-d
(d, JH,H¼6.2 Hz, 1H, 4-H), 7.76e7.65 (m, 12H, 2-H, 5-H, PPh
7.60e7.47 (m, 20H, PPh
), 7.20 (dd, JH,H¼6.2, JH,H¼11.7 Hz, 1H, 5-H),
6
):
d
¼8.58
3
),
3
1
3
4.13 (s, 3H, Me) ppm. C NMR (150 MHz, DMSO-d
6
):
d
¼145.5 (C2),
ꢁ
ꢀ1
solid. Mp: 202.6 C (dec). IR (ATR, cm ) 2103,1479,1433,1098, 902,
43, 702, 687, 612, 521, 513, 499, 445. The complex is insoluble in all
NMR solvents which we tested.
144.4 (C4), 142.1 (C6), 134.8 (t, JP,C¼6.0 Hz, o-CPh), 131.2 (p-CPh), 130.3
31
7
(CqPh), 128.8 (m-CPh), 127.2 (C5), 126.4 (C3), 48.1 (Me) ppm. P NMR
ꢀ1
(243 MHz, DMSO-d
256,1148,1093,1028, 743, 705, 690, 682, 636, 518, 507, 496. MS (ESI-
MS) [C44 Pd] 747.1.
6
):
d¼24.2 ppm. IR (ATR, cm ) 3051, 2120, 1433,
1
4
.7. Bis(triphenylphosphine)bis((1-methylquinolinium-3-yl)
H37NP
2
ethynyl)palladium(II) hexafluorophosphate (18)
4.10. Bis(triphenylphosphine)palladium(II)(quinolin-3-yl-
A sample of bis(triphenylphosphine)bis(quinolin-3-yl-ethynyl)
ethynyl) bromide (22)
palladium(II) 17 (50
dichloromethane (10 mL) and then treated dropwise at 0 C with
m
mol, 47 mg) was suspended in anhyd
ꢁ
A solution of 3-(bromoethynyl)quinoline (0.75 mmol, 174 mg) in
anhyd dichloromethane (10 mL) was treated with tetrakis(-
triphenylphosphine) palladium(0) (0.50 mmol, 578 mg) under an
inert atmosphere and then stirred for 8 h. Then the solvent was
distilled off and the resulting residue was chromatographed (silica
gel, dichloromethane:ethyl acetate¼5:1). The complex was obtained
methyl triflate (100 mmol, 0.011 mL). After 12 h, the resulting pre-
cipitate was filtered off and washed with dichloromethane and
ethyl acetate, respectively. The complex was then dissolved in
MeOH and treated with an aqueous solution of NH
resulting precipitate was filtered off and washed with EtOH and
Et O. The complex was obtained as brown solid. Yield: 54 mg
43
4 6
PF . The
ꢁ
2
as pale yellow solid. Yield: 262 mg (0.30 mmol, 61%). Mp: 166.4 C.
ꢁ
1
1
(
m
mol, 86%), mp 202.1 C (dec). H NMR (600 MHz, DMSO-d
6
):
H NMR (600 MHz, CDCl
3
):
d
¼7.87 (d, JH,H¼0.75, JH,H¼8.3 Hz, 1H, 8-
, 5-H, 7-H), 7.60 (d, JH,H¼1.9 Hz, 1H, 4-H),
7.52 (ddd, JH,H¼2.0, JH,H¼6.3, JH,H¼8.3 Hz, 1H, 6-H), 7.46e7.36 (m,
d
¼8.34 (d, JH,H¼8.6 Hz, 2H, 8-H), 8.31 (d, JH,H¼1.0 Hz, 2H, 4-H),
H), 7.82e7.66 (m, 12H, PPh
3
8
2
6
.17e8.09 (m, 4H, 5-H, 7-H), 7.96 (t, JH,H¼8.6 Hz, 2H, 6-H), 7.92 (s,
H, 2-H), 7.83e7.75 (m, 10H, PPh ), 7.59e7.51 (20H, PPh ), 4.44 (s,
H, Me) ppm. 13C NMR (150 MHz, DMSO-d
):
¼150.9 (C2), 145.0
13
3
3
20H), 6.71 (d, JH,H¼2.0 Hz, 1H, 2-H) ppm. C NMR (150 MHz, CDCl
3
):
6
d
d
¼152.7 (C2), 145.6 (C8a), 145.3 (C4), 136.1 (C7), 135.1 (t, JP,C¼6.0 Hz,
(
(
1
C4), 136.4 (C8a), 134.9 (t, JP,C¼6.3 Hz, o-CPh), 131.5 (t, JP,C¼25.3 Hz,
qPh), 131.5 (p-CPh), 134.8 (C7) 130.7 (C6), 129.8 (C5), 129.2 (C4a),
29.1 (t, JP,C¼6.3, m-CPh), 121.3 (C3), 119.5 (C8), 108.1 (eC^CePd),
o-CPh), 133.0 (C4a), 131.4 (t, JP,C¼25.3 Hz, CqPh), 130.4 (p-CPh), 128.6
(C6), 128.5 (C5), 128.1 (t, JP,C¼6.0 Hz, m-CPh), 124.0 (C3), 122.1 (C8),
107.7 (t, JP,C¼4.7 Hz, eC^CePd), 105.7 (t, JP,C¼14.3 Hz, C^CePd)
C
31
31
ꢀ1
4
5.8 (Me) ppm. eC^CePd not detected; P NMR (243 MHz,
ppm. P NMR (243 MHz, CDCl
3
):
d
¼24.2 ppm. IR (ATR, cm ) 2114,
DMSO-d ): ) ppm.
6
d
¼25.9 (s, PPh
3
), ꢀ144.5 (sept, JF,P¼711.3 Hz, PF
6
1480, 1433, 1099, 998, 753, 740, 689, 520, 497, 457, 424. MS (ESI-MS)
[C47
ꢀ1
þ
IR (ATR, cm ) 2104, 1516, 1435, 1097, 829, 769, 747, 692, 556, 522,
11, 496. MS (ESI-MS) [C60
2
H36BrNP PdeBr]: 782.2. HR-ESI-MS [C47
H
36BrNP
2
PdþH ]:
þ
5
H
48
N
2
P
2
PdeCH
3
]: 949.1.
Found: 862.0622, Calcd 862.0619.
4
.8. Bis(triphenylphosphine)palladium(II)(pyridin-3-yl-ethy-
4.11. Bis(triphenylphosphine)((1-methylquinolinium-3-yl)
nyl) bromide (20)
ethynyl)palladium(II)bromide triflate (23)
Under a nitrogen atmosphere a solution of 3-(bromoethynyl)
pyridine 19 (0.75 mmol,139 mg) in anhyd dichloromethane (15 mL)
was treated with tetrakis(triphenylphosphine)palladium(0)
A sample of bis(triphenylphosphine)palladium(II)(quinolin-3-
yl-ethynyl) bromide 22 (0.15 mmol, 130 mg) was suspended in
anhyd dichloromethane (10 mL) under a nitrogen atmosphere.
ꢁ
(
0.5 mmol, 578 mg) and stirred for 3 h. Then the solvent was dis-
tilled off in vacuo and the remaining residue was chromatographed
silica gel, dichloromethane:ethyl acetate¼1:1). The complex was
obtained as slightly orange solid. Yield: 352 mg (0.43 mmol, 87%).
After cooling to ꢀ30 C, methyl triflate (0.18 mmol, 0.010 mL) was
added dropwise and stirring was continued at this temperature for
30 min. Then, the solution was allowed to warm to rt, and stirring
was continued for 2 h. The solvent was then distilled off in vacuo
and the resulting residue was chromatographed (silica gel,
dichloromethane:MeOH¼10:1). The complex was obtained as or-
(
ꢁ
1
Mp 177.6 C. H NMR (600 MHz, CDCl
3
):
), 7.50e7.39 (m, 20H, PPh
H, 2-H), 6.83 (dd, JH,H¼4.5, JH,H¼7.0 Hz, 1H, 5-H), 6.34 (d,
d
¼8.15 (d, JH,H¼4.5 Hz, 1H,
4
-H), 7.85e7.76 (m, 10H, PPh
3
3
), 7.37 (s,
ꢁ
1
1
J
ange solid. Yield: 126 mg (0.13 mmol, 87%). Mp 215.0 C. H NMR
13
H,H¼6.0 Hz,1H, 6-H) ppm. C NMR (150 MHz, CDCl
45.6 (C4), 137.2 (C6), 135.0 (t, JP,C¼6.0 Hz, o-CPh), 131.4 (t,
P,C¼25.3 Hz, CqPh), 130.4 (p-CPh), 128.0 (t, JP,C¼6.0 Hz, m-CPh), 124.0
C3),122.1 (C5),107.9 (t, JP,C¼4.7 Hz, C^CePd),105.0 (t, JP,C¼14.3 Hz,
3
):
d¼151.6 (C2),
(600 MHz, DMSO-d
(m, 2H, 2-H, 7-H), 7.96 (ddd, JH,H¼0.6, JH,H¼7.2, JH,H¼8.0 Hz, 1H, 6-
H), 7.89 (d, JH,H¼15.0 Hz, 1H, 5-H), 7.76e7.7 (m, 10H, PPh ),
), 4.44 (s, 3H, Me) ppm. C NMR (150 MHz,
¼150.7 (C2), 145.0 (C4), 136.2 (C8a), 134.9 (C7), 134.8
), 131.3 (PPh ), 130.9 (PPh ) 130.6 (C6), 129.7 (C5), 128,9 (C4a),
128.8 (PPh ), 119.4 (C8), 45.6 (Me) ppm. P NMR (243 MHz, DMSO-
):
¼24.3 ppm. IR (ATR, cm ) 3050, 2110, 1433, 1257, 1146, 1094,
029, 744, 690, 636, 518, 508, 494. MS (ESI-MS) [C48 Pd]
6
):
d
¼8.20 (d, JH,H¼15.0 Hz, 1H, 8-H), 8.16e8.11
1
J
3
13
(
7.56e7.50 (m, 20H, PPh
DMSO-d ):
(PPh
3
31
C^CePd) ppm. P NMR (243 MHz, CDCl
3
):
d¼24.2 ppm. IR (ATR,
6
d
ꢀ
1
cm ) 2114, 1479, 1433, 1093, 998, 742, 690, 519, 507. MS (ESI-MS)
3
3
3
ꢀ
þ
31
[C
43
H
34BrNP
2
PdeBr ]: 734.2. HR-ESI-MS [C43
H34BrNP
2
PdþH ]:
3
ꢀ
1
Found: 812.0468, Calcd 812.0463.
d
6
d
1
H39NP
2
4
.9. Bis(triphenylphosphine)[(1-methylpyridinium-3-yl)ethy-
797.2.
nyl]palladium(II) bromide triflate (21)
Acknowledgements
A sample of bis(triphenylphosphine)palladium(II)(pyridin-3-yl-
ethynyl)bromide 20 (0.15 mmol, 122 mg) was suspended in anhyd
Dr. Gerald Dr a€ ger, university of Hannover (Germany), is grate-
fully acknowledged for measuring the HR-ESI-MS spectra.
ꢁ
dichloromethane (10 mL). Aftercooling to ꢀ20 C, methyl triflate was

A. Smeyanov et al. / Tetrahedron 71 (2015) 6665e6671
6671
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