Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with different alkane bridge

Article abstract of DOI:10.1016/j.inoche.2012.03.041

A series of di-NHC dipalladium complexes Pd₂LPy ₂Cl₄ (L = L^C3, L^C5, L^C6 and L^C10) with alkyl bridges of different chain lengths were prepared. The molecular structures of Pd₂L^C3Py ₂Cl₄ (1) and Pd₂L^C6Py ₂Cl₄ (3) were determined by X-ray diffraction studies. The influence of the different bridges on the structure and reactivity of the complexes was studied. The structure of complex 3 consists of two pseudo-square-planar subunits in a trans configuration, however complex 1 shows an X configuration due to π-π stacking of both imidazole rings and pyridine rings. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki-Heck reaction of styrene with aryl bromides. The length of the bridged ligands had some effect on the yield and regioselectivity of the products.

Full text of DOI:10.1016/j.inoche.2012.03.041

Inorganic Chemistry Communications 20 (2012) 326–329
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with
different alkane bridge
a,b,
Jianfeng Zhao a, Long Yang a, Kaiqi Ge a, Qian Chen a, Yongzhong Zhuang a, Changsheng Cao a, , Yanhui Shi
⁎
⁎
a
College of Chemistry and Chemical Engineering and Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Xuzhou Normal University, Xuzhou, Jiangsu, 221116, PR China
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, 210093, PR China
b
a r t i c l e i n f o
a b s t r a c t
A series of di-NHC dipalladium complexes Pd2LPy2Cl4 (L = LC3, LC5, LC6 and LC10) with alkyl bridges of differ-
ent chain lengths were prepared. The molecular structures of Pd2LC3Py2Cl4 (1) and Pd2LC6Py2Cl4 (3) were de-
termined by X-ray diffraction studies. The influence of the different bridges on the structure and reactivity of
the complexes was studied. The structure of complex 3 consists of two pseudo-square-planar subunits in a
trans configuration, however complex 1 shows an X configuration due to π–π stacking of both imidazole
rings and pyridine rings. The catalytic activity of the new binuclear palladium complexes was successfully
tested in the Mizoroki–Heck reaction of styrene with aryl bromides. The length of the bridged ligands had
some effect on the yield and regioselectivity of the products.
Article history:
Received 21 February 2012
Accepted 30 March 2012
Available online 10 April 2012
Keywords:
Dipalladium
N-heterocyclic carbene
Alkane bridge, X-ray structure
Heck reaction
© 2012 Elsevier B.V. All rights reserved.
The chemistry of transition-metal complexes containing N-heterocyclic
carbenes (NHCs) has been extensively studied, and a large number
of compounds have been reported [1–5]. Owing to their wide appli-
cation as potentially useful catalysts in organic synthesis, the chem-
istry of palladium-NHC complexes has become an area of great
interest and has been extensively studied [6–8]. In particular, those
bearing dicarbene ligands have received much attention mainly due
to the higher stability to heat and air, and their improved catalytic
performances. Over the last years, several chelating palladium com-
plexes with alkane-bridged bidentate carbenes have been reported
[9–15]. However, bimetallic palladium complexes in which the
bidentate ligand bridges the two metal centers are scarce [16–18].
The design and synthesis of binuclear complexes with di-NHC are
of considerable interest because the adjacent metals can function in
a synergic manner in their interactions with substrate molecules
[19]. We have been interested in the chemistry of bimetallic di-
NHC complexes concentrated on homodinuclear and heterodinuclear
complexes. We report here the synthesis and structure of a series of
di-NHC dipalladium complexes bridged by different alkyl chain, dia-
grammed in Scheme 1.
by NMR spectroscopy and gave satisfactory elemental analyses
[21–23]. The complexes are air and moisture stable and can be stored
at air atmosphere in solid state for more than 6 months without any no-
ticeable decomposition.
The proton signal of NCHN of imidazolium chlorides (from
10.15 ppm to 10.52 ppm) was absent in the 1H NMR of palladium
complexes, confirming carbene generation. In addition, 13C NMR pro-
vides direct evidence of the metalation of the ligand, as seen by the
signal at ca. 150 ppm, which is assigned to the Pd–Ccarbene reso-
nance shifted downfield relative to that of the imidazolium NCHN
peak of the starting ligand precursor (ca. 140 ppm).
Single crystals for the solid-state structure determinations of 1
and 3 could be obtained by slow evaporation of a dichloromethane
(DCM) saturated solution. The molecular structures of 1 and 3 were
determined by means of X-ray diffraction studies [24]. The molecular
diagrams of 1 and 3 are shown in Figs. 1 and 2 and selected crystallo-
graphic data are shown in Table 1. The structure of complex 1 consists
of two pseudo-square-planar subunits in a cis configuration bridged
with propylene, while the structure of complex 3 consists of two
pseudo-square-planar subunits in a trans configuration bridged with
hexylene. Two complexes show slightly distorted square-planar ge-
ometries around two palladium centers, which are surrounded by
imidazolylidene, two chloro ligands in a trans configuration, and a
pyridine. The Pd-Ccarbene distance is 1.957(12) Å and 1.971(14) Å for
1 and 1.984(7) Å for 3 (Table 2), similar to that shown by other
palladium-related species [25,26]. The Pd-Npyridine distance in com-
plex 1 [2.115(11) Å and 2.062(14) Å], 3 [2.106(6) Å] is comparable
to that of its related saturated mono-palladium carbene analogs
[26]. All other distances and angles lie in the expected range
(Table 2).
The synthesis of di-NHC dipalladium complexes 1–4 was achieved
by refluxing of the corresponding imidazolium salt, with palladium
chloride in presence of K2CO3 in pyridine in moderate yield, according
to literature procedure [20]. The novel dicarbene ligands, e.g. bisimida-
zolium dichlorides and palladium complexes were fully characterized
⁎
Corresponding authors at: College of Chemistry and Chemical Engineering and
Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Xuzhou
Normal University, Xuzhou, Jiangsu, 221116, PR China. Fax: +86 516 83500349.
E-mail address: yhshi_2000@126.com (Y. Shi).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.03.041

J. Zhao et al. / Inorganic Chemistry Communications 20 (2012) 326–329
327
Scheme 1. di-NHC dipalladium complexes (1–4) with different alkyl bridge lengths.
Owing to the rotational freedom in the alkyl linking groups be-
tween the dicarbene of these bidentate ligands, two pseudo-square-
planar subunits around palladium centers of the complexes tend to
adopt a trans arrangement, in which the subunits are quite widely
spaced in order to minimize steric repulsions between the metal coor-
dination spheres. The complex 3 indeed adopts the trans configuration
having two pyridine ligands far away. Both the dihedral angles in com-
plex 3 between two intramolecular imidazole rings and two pyridine
rings are 0°, meaning they are parallel to each other. However, com-
plex 1 adopts a surprising X configuration. Two intramolecular pyri-
dines are almost parallel with 109.88° of torsion angle involving the
backbone atoms N1–C1–C4–N2, and two intramolecular imidazole
rings have a 32.83° of torsion angle. It is the face-to-face π–π stacking
that causes the unique structure of complex 1 as well. There are two
types of π–π stacking exiting in this structure. One is face-to-face
π–π stacking between two intramolecular imidazole rings; the other
is face-to-face π–π stacking between two intermolecular pyridines.
The distance of the centers of the two intramolecular imidazolylidene
is 3.986 Å and the shortest atom distance is 3.308 Å. Two adjacent
intermolecular pyridines are parallel to each other with a distance of
3.641 Å. The bond lengths of Pd–C in all the complexes are equivalent
within the margin of error. The same applies to the bonds of palladium
nitrogen and palladium chloride.
The palladium-catalyzed arylation of olefins (Mizoroki–Heck reac-
tion) has found wide application in organic synthesis. The activity of
complexes 1–4 in the catalytic arylation of styrene was tested in order
to elucidate the influence of the ligands. The alkyl bromides with differ-
ent electronic properties e.g. phenyl bromide, p-methoxyphenyl bro-
mide, and p-flourophenyl bromide were chosen in the reactions. The
reactions were conducted in a vial in the presence of catalytic amounts
of palladium catalysts 1–4 and K2CO3 in a mixture of aryl bromide and
styrene [27], and the results were given in Table 3. From the results, it
can be seen that the complexes of 1–4 are good catalysts with almost
100% conversion yield for the arylation of olefins with different alkyl ha-
lides. For the arylation of styrene with phenyl bromide, the highest yield
of product (93%) with 25:1 and 23:1 of A to B ratio was detected with 1
and 3 as catalyst (Table 3, entries 1 and 3), however, the highest of A to
B ratio (29:1) of product in 89% yield was obtained with 2 (Table 3,
entry 2). For the reactions with phenyl bromide substituted with elec-
tron donating group (p-OMe), complex 1 gave the highest yield of
95%, and the best regioselectivity of A to B of 17:1 (Table 3, entry 5).
For the reactions with phenyl bromide substituted with electron with-
drawing group (p-F), the highest yield of 93% and A to B ratio of 20:1
was observed with complex 3 (Table 3, entry 11), whereas the lowest
yield and A to B ratio was detected with 4 (Table 3, entry 12). Therefore,
complexes 1 (with 3 carbon of linker) and 3 (with 6 carbon of linker)
generally gave the high yield and good regioselectivity, whereas com-
plex 4 (with 10 carbon of linker) gave the poor yield. However, the dif-
ference of catalytic performance for these complexes is not significant.
In order to elutriate if a synergic manner exists in these new bimetallic
palladium complex, mono-palladium complex trans-[1,3-bis(2,4,6-
trimethylphenyl)imidazole-2-ylidene]PdCl2(pyridine) [26] was pre-
pared and its catalytic performance was tested in the above reactions.
With the mono-palladium complex, 85% yield with 27:1 of A:B in
100% of conversion was detected in the reaction of phenyl bromide. In
addition, 89% yield with 20:1 of A:B in 100% of conversion was detected
in the reaction of p-methoxyphenyl bromide, and 90% yield with 21:1 of
A:B in 98% of conversion was detected in the reaction of p-flourophenyl
bromide. From the results, it can be seen that the catalytic performance
of this mono-palladium is very much like those of complex 4 (with 10
carbon of linker). The possible reason for this is that the very long link-
age between two Pd units in 4 makes them work freely and look like
two mono-palladium complexes. Therefore, there is no synergic func-
tion in complex 4, but probably there is a weak function in complexes
1 and 3.
Fig. 1. ORTEP structure of complex 1 (n=3) with the probability ellipsoids drawn at
the 30% level. Hydrogen atoms have been omitted for clarity.
Fig. 2. ORTEP structure of complex 3 (n=6) with the probability ellipsoids drawn at the 30% level. Hydrogen atoms have been omitted for clarity.

328
J. Zhao et al. / Inorganic Chemistry Communications 20 (2012) 326–329
Table 1
We have synthesized a series of dicarbene dipalladium complexes
Selected crystallographic data for complexes 1 and 3.
with different length of linker. X-ray diffraction studies showed that
the two pseudo-square-planar subunits around palladium centers of
the complex 3 with longer linking group (hexylene bridge) adopt the
trans configuration. However, complex 1 adopts an X configuration
due to the face-to-face π–π stacking. The new binuclear complexes
were successfully tested in the catalytic Mizoroki–Heck reaction of sty-
rene with alkyl bromide. The complexes of 1–4 showed good catalysts
for the arylation of olefins.
Complex
1
C
3
Formula
Formula weight
Temperature of measurement (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
37 H44 Cl4 N6 Pd2
C40 H48 Cl4 N6 Pd2
967.44
293(2)
Monoclinic
P2(1)/c
927.38
293(2)
Monoclinic
Cc
16.4050(6)
21.5136(5)
13.2164(3)
90.00
9.7607(4)
28.3574(14)
8.8148(3)
90.00
c (Å)
α (°)
Acknowledgements
β (°)
120.963(2)
90.00
3999.8(2)
4
101.689(3)
90.00
2389.23(17)
2
We gratefully acknowledge Qing Lan Project of Jiangsu Education
Committee (08QLT001 and 08QLD006), Scientific Research Foundation
(SRF) for the Returned Overseas Chinese Scholars (ROCS), State Educa-
tion Ministry (SEM), the Priority Academic Program Development of
Jiangsu Higher Education Instititions (PAPD) and National Natural Sci-
ence Foundation of China (NSFC) (21071121 and 21172188) for finan-
cial support of this work.
γ (°)
Volume (Å3)
Z
Crystal size (mm)
F(000)
Theta range for data collection (°)
Goodness-of-fit on F2
Final R indices [I>2σ (I)]
0.50×0.40×0.20
1872
1.73–28.28
1.088
R1 =0.0332
wR2 =0.0817
R1 =0.0500
wR2 =0.0953
0.30×0.22×0.20
980
1.44–28.42
1.000
R1 =0.0766
wR2 =0.2624
R1 =0.1095
wR2 =0.2981
R indices (all data)
Appendix A. Supplementary material
CCDC-870507 and CCDC-870508 contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge form The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ UK or Fax: +44 1223 336033; Email: deposit@ccdc.cam.ac.uk
or http://www.ccdc.cam.ac.uk.
Table 2
Selected Bond Lengths and angles for complexes 1 and 3.
Distance (Å)
1
3
C1–Pd1
N1–Pd1
Pd1–Cl1
Pd1–Cl2
1.957(12)
2.115(11)
2.297(5)
2.303(5)
1.984(7)
2.106(6)
2.316(2)
2.308(2)
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Results of the Mizoroki–Heck reaction.
Entry
Catalyst
R
Conversion (%)a
Yield (%)a
A:B ratioa
1
2
3
4
5
6
7
8
1
2
3
4
1
2
3
4
1
2
3
4
H
H
H
H
100
97
93
89
93
89
95
90
91
87
93
91
93
89
25:1
29:1
23:1
23:1
17:1
5:1
11:1
12:1
19.:1
20:1
20:1
15:1
100
100
100
100
100
95
100
100
100
100
p-OMe
p-OMe
p-OMe
p-OMe
p-F
p-F
p-F
p-F
9
10
11
12
a
Determined by GC using dodecane as internal standard.

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2H, NCHN), 8.47 (s, 2H, NCH), 7.11 (s, 2H, NCH), 6.96 (s, 4H, Ar–H), 4.70 (m,
4H, NCH2), 2.31 (s, 6H, CH3), 2.15 (m, 8H, CH2), 2.03 (s, 12H, CH3).13C NMR
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24.1, 20.9, 17.3. Anal. Calc. for C30H40Cl2N4 (527.57 g/mol): C, 68.30; H, 7.64; N,
10.62. Found: C, 67.98; H, 7.33; N, 10.85%.[H2LC6]Cl2: Yield: 64% (0.675 g). 1H
NMR (CDCl3, 400 MHz): δ 10.37 (s, 2H, NCHN), 8.47 (s, 2H, NCH), 7.11 (s, 2H,
NCH), 6.96 (s, 4H, Ar–H), 4.70 (m, 4H, NCH2), 2.31 (s, 6H, CH3), 2.15 (m, 8H,
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129.6, 124.2, 122.8, 49.4, 29.2, 24.1, 20.9, 17.3. Anal. Calc. for
C30H40Cl2N4
(527.57 g/mol): C, 68.30; H, 7.64; N, 10.62. Found: C, 67.98; H, 7.33; N,
10.85%.[H2LC10]Cl2: Yield: 66% (0.771 g). 1H NMR (CDCl3, 400 MHz): 10.52 (s,
2H, NCHN), 8.17 (s, 2H, NCH), 7.18 (s, 2H, NCH), 6.94 (s, 4H, Ar–H), 4.66 (m,
4H, NCH2), 2.29 (s, 6H, CH3), 2.02 (s, 12H, CH3; 4H, CH2), 1.25–1.35 (m, 12H,
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[21] General procedures: All manipulations were carried out using standard Schlenk
techniques. Solvents were purified and degassed by standard procedures. Pyri-
dine was distilled from calcium hydride under argon atmosphere. Potassium car-
bonate was ground to a fine powder prior to use. All other chemicals were
obtained from common suppliers and used without further purification. 1H and
13C spectra were recorded on a Bruker AV 400 MHz spectrometer at room tem-
perature and referenced to the residual signals of the solvent. GC-MS was per-
formed on an Agilent 6890–5973 N system with electron ionization (EI) mass
spectrometry. Elemental analyses were performed on a EuroVektor Euro EA-
300 elemental analyzer.
123.1, 50.0, 30.2, 28.5, 28.0, 25.6, 21.1, 17.6. Anal. Calc. for C34H48Cl2N4
(583.68 g/mol): C, 69.96; H, 8.29; N, 9.60. Found: C, 69.35; H, 8.04; N, 10.01%.
[23] General procedures for the synthesis of palladium complexes Pd2L2Cl4(C5H5N)
2.To
a mixture of bisimidazolium dichloride (3.0 mmol), PdCl2 (1.069 g,
6.0 mmol), and K2CO3 (8.293 g, 60 mmol) in a 50 mL round bottom flask was
added 10.5 mL of pyridine. The reaction mixture was heated at 85 °C for 18 h,
after which time the mixture was filtered through Celite and washed with
DCM. The solvent was removed under vacuum, and the crude was washed by
diethyl ether (15 mL). The pure compound was obtained as yellow solid by re-
crystallization with DCM / ether.Pd2LC32Cl4(C5H5N)2 (1): Yield: 77 % (2.142 g).
1H NMR (CDCl3, 400 MHz): δ 8.81 (m, 4H, Py–H), 7.70 (m, 2H, NCH), 7.54 (m,
2H, Py–H), 7.32–7.23 (m, 4H, Py–H), 7.02 (s, 4H, Ar–H), 6.81 (m, 2H, NCH), 4.95
(m, 4H, NCH2), 3.40 (m, 2H, CH2), 2.36 (s, 6H, CH3), 2.29 (s, 6H, CH3), 2.25 (s,
6H, CH3),. 13C NMR (CDCl3, 100 MHz): δ 152.5 (Pd–NCN), 151.9, 151.2 (Pd–
NCN), 139.1, 137.8, 137.7, 137.6, 136.3, 136.1, 136.0, 134.7, 129.2, 124.5, 124.2,
124.0, 123.0, 122.9, 49.7, 49.5, 49.3, 30.5, 30.4, 30.3, 21.08, 19.9, 19.6, 19.1, 18.9.
Anal. Calc. for C37H42Cl4N6Pd2 (925.42 g/mol): C, 48.02; H, 4.57; N, 9.08. Found:
C, 48.62; H, 4.25; N, 9.31%.Pd2LC5Cl4(C5H5N)2 (2): Yield: 78% (2.231 g). 1H NMR
(CDCl3, 400 MHz): δ=8.79 (m, 4H, Py–H), 7.66 (m, 2H, Py–H), 7.24–7.22 ( m,
2H, NCH; 4H, Py–H ), 7.00 (s, 4H, Ar–H), 6.78 (s, 2H, NCH), 4.81 (t, J=6.8Hz,
4H, NCH2), 2.42 (m, 4H, CH2), 2.35 (s, 6H, CH3), 2.23 (s, 12H, CH3), 1.68 (m, 2H,
CH2). 13C NMR (CDCl3, 100 MHz): δ=151.4, 150.0 (Pd–NCN), 139.1, 137.7,
136.3, 134.9, 129.2, 124.2, 123.8, 122.3, 51.0, 29.8, 23.3, 21.1, 19.0. Anal. Calc.
for C39H46Cl4N6Pd2 (953.47 g/mol): C, 49.13; H, 4.86; N, 8.81. Found: C, 48.86;
H, 4.51; N, 9.07%.Pd2LC6Cl4(C5H5N)2 (3): Yield: 56 % (1.625 g). 1H NMR (CDCl3,
400 MHz): δ=8.77 (m, 4H, Py–H), 7.63 (m, 2H, Py–H), 7.22 ( m, 4H, Py–H ),
7.17 (m, 2H, NCH ), 6.99 (s, 4H, Ar–H), 6.82 (m, 2H, NCH), 4.74 (t, J=7.6Hz, 4H,
NCH2), 2.34 (s, 6H, CH3), 2.27 (m, 4H, CH2), 2.23 (s, 12H, CH3), 1.68 (m, 4H,
CH2). 13C NMR (CDCl3, 100 mHz): δ=151.2, 149.9 (Pd–NCN), 139.0, 137.7,
136.3, 134.9, 129.1, 124.2, 123.9, 121.9, 51.2, 30.1, 25.9, 21.1, 18.9. Anal. Calc.
for C40H48Cl4N6Pd2 (967.50 g/mol): C, 49.66; H, 5.00; N, 8.69. Found: C, 49.12;
H, 4.71; N, 9.24%.Pd2LC10Cl4(C5H5N)2 (4): Yield: 77% (2.365 g). 1H NMR (CDCl3,
400 MHz): δ=8.77 (m, 4H, Py–H), 7.65 (m, 2H, Py–H), 7.23 ( m, 4H, Py–H ),
7.12 (m, 2H, NCH ), 7.00 (s, 4H, Ar–H), 6.85 (m, 2H, NCH), 4.72 (t, J=7.6Hz, 4H,
NCH2), 2.35 (s, 6H, CH3), 2.25 (s, 12H, CH3), 2.17 (m, 4H, CH2), 1.50–1.36 (m,
12H, CH2). 13C NMR (CDCl3, 100 MHz): δ=151.3, 150.0 (Pd–NCN), 139.0, 137.7,
136.3, 134.9, 129.1, 124.1, 123.8, 121.6, 51.4, 30.5, 29.3, 29.1, 26.6, 21.1, 18.9.
[22] General procedures for the synthesis of ligands [H2L2]Cl2.Mesitylimidazole
(4 mmol, 0.745 g) and dichloroalkane (2 mmol) were heated to 110 °C for
4–5 h in a 10 mL of pressure tube. After the completion of the reaction, the
solid was dissolved in DCM (2.5 mL) and precipitated out with diethyl ether
Anal. Calc. for C44H56Cl4N6Pd2 (1023.61 g/mol): C, 51.63; H, 5.51; N, 8.21.
Found: C, 51.96; H, 5.32; N, 8.44%.
[24] Preliminary examination and data collection were carried out on a Rigaku Mercury
CCD device at the window of a sealed X-ray tube with graphite-monochromated
Mo Kα radiation. Absorption correction was performed by SADABS program. All
the structures were solved by directed methods using the SHELXS-97 program
and refined by full-matrix least squares techniques on F2.
[25] L. Ray, S. Barman, M.M. Shaikh, P. Ghosh, Highly convenient amine-free Sonoga-
shira coupling in air in a polar mixed aqueous medium by trans- and cis-[(NHC)2-
PdX2] (X = Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes,
Chem. Eur. J. 14 (2008) 6646–6655.
(10 mL) to give product as
a
white powder.[H2LC32]Cl2: Yield:81%. 1H NMR
(CDCl3, 400 MHz): δ 10.15 (s, 2H, NCHN), 8.67 (s, 2H, NCH), 7.08 (s, 2H, NCH),
7.00 (s, 4H, Ar–H), 4.96 (t, 4H, CH2), 3.18 (m, 2H, CH2), 2.35 (s, 6H,CH3), 1.92
(s, 12H, CH3).[H2LC5]Cl2: Yield: 79% (0.811 g). 1H NMR (CDCl3, 400 MHz):
δ
10.50 (s, 2H, NCHN), 8.70 (s, 2H, NCH), 7.07 (s, 2H, NCH), 6.97 (s, 4H, Ar–H),
4.79 (t, J=7.6 Hz, 4H, NCH2), 2.31 (s, 6H, CH3), 2.04 (s, 12H, CH3), 1.90 (m, 4H,
CH2), 1.64 (m, 2H, CH2). 13C NMR (CDCl3, 100 MHz): 140.8, 137.8, 134.0, 130.8,
129.6, 124.6, 122.5, 48.8, 28.8, 21.6, 20.9, 17.4. Anal. Calc. for
C
29H38Cl2N4
[26] C. Dash, M.M. Shaikh, P. Ghosh, Fluoride-free Hiyama and copper- and amine-
Free Sonogashira coupling in air in a mixed aqueous medium by a series of
PEPPSI-themed precatalysts, Eur. J. Inorg. Chem. 12 (2009) 1608–1618.
[27] Mizoroki–Heck reaction of styrene. An oven-dried 4 mL vial containing a stirrer
bar was charged with aryl bromide (1 mmol), catalyst (0.5 mol%) and K2CO3
(207.4 mg, 1.5 mmol) in the glove box and sealed with a cap containing a POFE
septum. DMF (1 mL) and styrene (140 μL, 1.2 mmol) were injected sequentially.
The mixture was stirred at 110 °C for 23 h.
(513.54 g/mol): C, 67.82; H, 7.46; N, 10.91. Found: C, 67.55; H, 7.32; N,
11.36%.[H2LC5]Cl2: Yield: 79% (0.811 g). 1H NMR (CDCl3, 400 MHz): δ 10.50 (s,
2H, NCHN), 8.70 (s, 2H, NCH), 7.07 (s, 2H, NCH), 6.97 (s, 4H, Ar–H), 4.79 (t,
J=7.6 Hz, 4H, NCH2), 2.31 (s, 6H, CH3), 2.04 (s, 12H, CH3), 1.90 (m, 4H, CH2),
1.64 (m, 2H, CH2). 13C NMR (CDCl3, 100 MHz): 140.8, 137.8, 134.0, 130.8, 129.6,
124.6, 122.5, 48.8, 28.8, 21.6, 20.9, 17.4. Anal. Calc. for
C29H38Cl2N4
(513.54 g/mol): C, 67.82; H, 7.46; N, 10.91. Found: C, 67.55; H, 7.32; N,
11.36%.[H2LC6]Cl2: Yield: 64% (0.675 g). 1H NMR (CDCl3, 400 MHz): δ 10.37 (s,