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

Article abstract of DOI:10.1016/j.inoche.2012.05.017

A series of ethylene bridged di-NHC dipalladium complexes (1-5) with different substituents on N of imidazolydene were prepared. The influence of the different substituents on the structure and catalytic reactivity of the complexes were studied. The molecular structures of 3 and 4 were determined by X-ray diffraction studies. The structures of complexes consist of two perpendicular pseudo-square-planar subunits in a cis configuration. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki-Heck reaction. The complexes with aryl substituent have better activity than that with alkyl substituent, meanwhile, the different substituents on phenyl group have a little effect on both regioselectivity and the yield of the product as well.

Full text of DOI:10.1016/j.inoche.2012.05.017

Inorganic Chemistry Communications 22 (2012) 33–36
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 substituents
Long Yang , Jianfeng Zhao , Yunfei Li , Kaiqi Ge , Yongzhong Zhuang , Changsheng Cao ⁎, Yanhui Shi a,b,⁎
a
a
a
a
a
a,
a
College of Chemistry and Chemical Engineering and Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou, Jiangsu, PR China, 221116
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, PR China, 210093
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of ethylene bridged di-NHC dipalladium complexes (1–5) with different substituents on N of
imidazolydene were prepared. The influence of the different substituents on the structure and catalytic reactivity
of the complexes were studied. The molecular structures of 3 and 4 were determined by X-ray diffraction studies.
The structures of complexes consist of two perpendicular pseudo-square-planar subunits in a cis configuration.
The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki–Heck re-
action. The complexes with aryl substituent have better activity than that with alkyl substituent, meanwhile, the
different substituents on phenyl group have a little effect on both regioselectivity and the yield of the product as
well.
Received 29 March 2012
Accepted 4 May 2012
Available online 14 May 2012
Keywords:
Dipalladium
N-heterocyclic carbene
Ethylene bridge
Different substituent
Mizoroki–Heck reaction
© 2012 Elsevier B.V. All rights reserved.
Owing to their wide application in C\C and C-heteroatom bond
formation in organic synthesis, the chemistry of palladium-NHC com-
plexes has become an area of great interest and has been extensively
studied [1–3]. In particular, those bearing dicarbene ligands have re-
ceived much attention mainly due to the higher stability to heat and
air, and their improved catalytic performances. Over the last years,
several chelating palladium complexes with alkane-bridged bidentate
carbenes have been reported [4–10]. However, bimetallic palladium
complexes in which the bidentate ligand bridges the two metal cen-
ters are not very much [11–13]. The design and synthesis of binuclear
complexes with di-NHC are of considerable interest because the adja-
cent metals could function in a synergic manner in their interactions
with substrate molecules [14]. In addition, the electronic and steric
properties can be modified by substituents attached to the nitrogen
atoms of the NHC ring, which is important for their utilization as li-
gands in catalytic reactions [15,16]. Therefore, in this paper we report
the synthesis and structure of a series of ethylene bridged di-NHC
2 3
presence of K CO in pyridine, as shown in Scheme 1. The novel
dicarbene ligands L5 and all palladium complexes were fully charac-
terized by NMR spectroscopy and gave satisfactory elemental analy-
ses [19–21]. The complexes are air and moisture stable and can be
stored at air atmosphere in solid‐state for more than 6 months with-
out any noticeable decomposition.
It is interesting that proton signal of NCHN (H on pre-carbene car-
bon) of imidazolium chlorides shifted downfield from L1 to L5. It
shifted from 9.40 ppm of L1 with less steric methyl substituent, to
9.73 ppm of L2 with t-butyl substituent, to 9.79 ppm of L3 with 1,6-
dimethylphenyl substituent, to 10.09 ppm of L4 with a little steric
1,6-diethylphenyl substituent, and further to 10.17 ppm of L5 with
more steric 1,6-diisopropylphenyl substituent. Therefore, the acidity
of proton on the pre-carbene carbene of N-arylimidazolium chlorides
is stronger than that of N-alkylimidazolium chlorides; and the acidity
of proton on the pre-carbene carbon in N-arylimidazolium chlorides
was increased with the steric hindrance of substituent on ortho-
position of phenyl group. Carbene generation in palladium complexes
was confirmed by absence of the proton signal of NCHN of
dipalladium complexes with different substituents on
N of
imidazolylidene (Scheme 1). The catalytic activity of the Pd com-
plexes was also examined in the C\C coupling reaction of
Mizoroki–Heck reaction. The influence of the different substituent
on the structure and reactivity of the complexes were studied.
imidazolium chlorides (from 9.40 ppm to 10.17 ppm) in the 1
H
NMR of palladium complexes. In addition, the formation of the
metal complexes was evident from the distinctive metal-bound
carbene peak, which appeared at ca. 151.3–152.5 ppm for these com-
plexes. The resonance of carbene carbon in these C4–C5 unsaturated
palladium complexes is significantly upfield compared to that in
those C4–C5 saturated complexes (184.2–186.3 ppm) [22], which
means that the carbene in unsaturated complexes is more electron
rich than that in their saturated analogues. The 1H NMR of complex
1
-Arylimidazoles and corresponding bisimidazolium dichlorides
were prepared according to the literatures [17,18,26]. The synthesis
of di-NHC dipalladium complexes 1–5 was achieved by refluxing of
the corresponding imidazolium salts, with palladium chloride in
2
showed that only one signals for six of CH
3
of t-butyl group and
⁎
Corresponding authors. Fax: +86 516 83500349.
E-mail address: yhshi_2000@126.com (Y. Shi).
1
the H NMR patterns of four CH groups of 1,6-substituents on phenyl
3
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.05.017

34
L. Yang et al. / Inorganic Chemistry Communications 22 (2012) 33–36
Table 1
Selected crystallographic data for complexes 3 and 4.
Compound
Formula
3
4
C
34
H36 Cl
4
N
6
Pd
2
C
38
H44Cl
4
N
6
Pd
2
·0.75C
5
H
5
N
Formula weight
883.29
998.72
Temperature of measurement (K) 293(2)
293(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P2(1)/n
14.287(2)
20.337(4)
15.170(2)
90.00
114.518(9)
90.00
4010.2(11)
4
Triclinic
P-1
Scheme 1. Synthesis of the di-palladium bis-NHC complexes 1–5.
14.239(2)
19.147(3)
19.553(4)
64.466(9)
74.683(8)
89.727(8)
α (°)
β (°)
γ (°)
Volume (Å )
3
4602.6(13)
4
Z
Crystal size (mm)
F(000)
0.40×0.3×0.2
1768
0.33×0.27×0.22
2022
Theta range for data collection (°) 1.78–28.33
1.19–25.02
0.964
R =0.0449
2
Goodness-of-fit on F
1.032
1
1
Final R indices [I>2σ (I)]
R =0.0872
wR
2
=0.1310
R =0.2956
wR =0.3581
wR
2
=0.0796
R =0.1167
wR =0.1559
1
1
R indices (all data)
2
2
angle of −88.28 for 3 and −91.19 for 4 (Table 2) in a cis configura-
tion. Two complexes show slightly distorted square-planar geome-
tries around two palladium centers, which are surrounded by
imidazolylidene, two chloro ligands in a trans configuration, and a
pyridine. The bond lengths of Pd-C are equivalent within the margin
of error. The same applies to the bonds of palladium nitrogen and pal-
ladium chloride. The Pd-Ccarbene distance is 1.988(10) Å and
1.976(10) Å for 3; 1.970(6) Å and 1.963(6) Å for 4 (Table 2), similar
to that shown by other palladium-related species [22,24]. The Pd-
Fig. 1. ORTEP structure of complex 3 with the probability ellipsoids drawn at the 30%
level. Hydrogen atoms have been omitted for clarity.
(
(
methyl or ethyl) in complexes 3 and 4 showed only one signal
2.30 ppm for 3 and 1.14 ppm for 4) as well. It means the environ-
mental equivalence of these methyl groups, which is probably be-
cause these molecules have a binary symmetry and methyl groups
could rotate rapidly within NMR time scale in the solution at room
temperature. Thus, there is almost no steric hindrance around Pd cen-
ter in complexes 2–4.
Single crystals for the solid-state structure determinations of 3
could be obtained by slow evaporation of a saturated DCM solution
and 4 from a saturate toluene/DCM solution. The molecular structures
of 3 and 4 were determined by means of X-ray diffraction studies
Npyridine distance in complex 3 [2.093(9) Å and 2.090(8) Å], 4
[2.125(5) Å and 2.100(6) Å] is comparable to that of its related satu-
rated mono-palladium carbene analogues [22]. All other distances
and angles lie in the expected range (Table 2).
Owing to the rotational freedom in the ethylene linking groups
between the dicarbene of these bidentate ligands, its IMes analogue
adopts a trans arrangement, in which the metals are quite widely spa-
ced in order to minimize steric repulsions between the metal coordi-
nation spheres [17]. However, it is not the case for palladium
complexes 3 and 4, which is probably due to face-to-face π–π stac-
king of two intramolecular imidazole rings in the structure. In com-
plex 3, two imidazole rings have a 45.56° of torsion angle and two
pyridines have a 65.64° of torsion angle. The torsion angle involving
the backbone atoms N1-C1-C4-N2 is −88.28° (Table 2). The shortest
atom-to-atom distance of two imidazole rings in 3 is 2.970 Å (e.g.
[23]. The molecular diagrams of 3 and 4 are shown in Figs. 1 and 2
and selected crystallographic data are shown in Table 1.
The structure of complex 3 and 4 consist of two pseudo-square-
planar subunits bridged with ethylene, while two pseudo-square-
planar subunits are almost perpendicular to each other with torsion
Table 2
Selected bond lengths and angles for complexes 3 and 4.
Distance (Å)
3
4
Angle (°)
3
4
C1-Pd1
N1-Pd1
Pd1-Cl1
Pd1-Cl2
C4-Pd2
1.988(10)
2.093(9)
2.290(3)
2.304(3)
1.976(10)
1.970(6)
2.125(5)
2.3094(18) C1-Pd1-Cl2
C1-Pd1-N1
C1-Pd1-Cl1
178.8(4)
179.3(2)
90.0(3)
91.1(3)
89.4(3)
45.56
88.86(17)
88.91(17)
90.44(16)
50.97
2.2993(19) N1-Pd1-Cl1
a
1.963(6)
2.100(6)
Imidazole
dihedral angle
b
N2-Pd2
2.090(8)
Pyridine
65.64
89.69
dihedral angle
c
Pd2-Cl3
Pd2-Cl4
2.306(3)
2.309(3)
2.2905(17)
2.3027(17)
Torsion angle −88.28
−91.19
a
Imidazole dihedral angle=angle between LS planes: one through the C1 imidazole
ring; one through C4 imidazole ring
b
Fig. 2. ORTEP structure of complex 4 with the probability ellipsoids drawn at the 30%
level. Hydrogen atoms have been omitted for clarity.
Pyridine dihedral angle=angle between LS plans of pyridine.
Torsion angle=torsion angle involving the backbone atoms N1-C1-C4-N2.
c

L. Yang et al. / Inorganic Chemistry Communications 22 (2012) 33–36
35
Table 3
Reaction of the Mizoroki–Heck reaction.
Entry
Catalyst
R
GC yield (%)
A:B ratio
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
H
H
H
H
54
82
93
87
91
62
82
90
88
91
17
13
63
61
52
84
93
99
90
97
20.6:1
10.5:1
11.0:1
12.8:1
15.4:1
18.5:1
9.5:1
10.9:1
9.8:1
10.9:1
>99:1
>99:1
9.8:1
10.5:1
14.6:1
29.8:1
14.6:1
13.0:1
12.3:1
13.5:1
H
p-OMe
p-OMe
p-OMe
p-OMe
p-OMe
o-OMe
o-OMe
o-OMe
o-OMe
o-OMe
p-F
0
1
2
3
4
5
6
7
8
9
0
p-F
p-F
p-F
p-F
distance of N4-N6), and the distance of centroids of the rings is
.137 Å. In complex 4, two imidazole rings have a 50.97° of torsion
angle and two pyridines have a 89.69° of torsion angle. The torsion
activity than that with alkyl substituents. The different substituents on
phenyl group in complexes 3–5 have a little effect on both of
regioselectivity and yield of the product of Heck reaction.
4
angle involving the backbone atoms N1-C1-C4-N2 is −91.19°
(
Table 2). The torsion angles in complex 4 are larger than those in
Acknowledgments
complex 3, which is probably due to more steric hindrance of Et
than Me. The shortest atom-to-atom distance of two intramolecular
imidazole rings is 2.899 Å for 4, and the distance of centroids of
them is 4.043 Å.
The palladium-catalyzed arylation of olefins has found wide appli-
cation in organic synthesis. The activity of complexes 1–5 in the cata-
lytic arylation of styrene with aryl bromide was tested in order to
elucidate the influence of the ligands. The reactions were conducted
in a vial in the presence of catalytic amounts of palladium catalysts
We gratefully acknowledge Qing Lan Project of Jiangsu Education
Committee (08QLT001 and 08QLD006), Scientific Research Founda-
tion (SRF) for the Returned Overseas Chinese Scholars (ROCS), State
Education Ministry (SEM), the Priority Academic Program Develop-
ment of Jiangsu Higher Education Institutions (PAPD), 333 project
for the cultivation of high-level talents (33GC10002) and the National
Natural Science Foundation of China (NSFC) (21071121 and
2
1172188) for financial support of this work.
2 3
1–5 and K CO in a mixture of alkyl bromide and styrene [25]. From
the results shown in Table 3, we can see the complexes of 2–5 have
been shown good catalysis for the arylation of styrene with bro-
mobenzene, para-methoxybromobenzene (aryl bromides with elec-
tron donating group) and para-bromoflourobenzene (aryl bromides
with electron withdrawing group) with over 80% yield, whereas
they have been shown poor to moderate catalysis with steric hin-
drance ortho-methoxybromobenzene. Generally, the complexes
with aryl substituent attached to the nitrogen atoms of the NHC
ring (3–5) have better activity than that with alkyl substituent (1–
Appendix A. Supplementary material
CCDC-880372 and CCDC-880373 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of charge
form the Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary materials related to this article
can be found online at http://dx.doi.org/10.1016/j.inoche.2012.05.017.
References
2). The different substituents on phenyl in complexes 3–5 have a little
effect on both of regioselectivity and yield of the product as well. Gen-
erally, complex 3 showed good catalytic activity and complex 1 gave
good regioselectivity of the product.
[1] N. Marion, S.P. Nolan, Well-defined N-heterocyclic carbenes palladium(II) pre-
catalysts for cross-coupling reactions, Acc. Chem. Res. 41 (2008) 1440–1449.
[
2] S. Würtz, F. Glorius, Surveying sterically demanding N-heterocyclic carbene
ligands with restricted flexibility for palladium-catalyzed cross-coupling reac-
tions, Acc. Chem. Res. 41 (2008) 1523–1533.
In conclusion, we have synthesized a series of dicarbene dipalladium
complexes with different N-substituted imidazolylidenes. The structures
of complex 3 and 4 consist of two pseudo-square-planar subunits
bridged with ethylene, while two subunits are almost perpendicular to
each other in a cis configuration, due to π–π stacking. The new dinuclear
palladium complexes were successfully tested in the catalytic Heck reac-
tion of styrene with bromobenzene. The complexes with aryl substitu-
ents attached to the nitrogen atoms of the NHC ring have better
[3] W.A. Herrmann, M. Elison, J. Fischer, C. Koecher, G.R.J. Artus, Coordination chem-
istry and mechanisms of metal-catalyzed CC coupling reactions. 9. Metal com-
plexes of N-heterocyclic carbenes - a new structural principle for catalysts in
homogeneous catalysis, Angew. Chem. Int. Ed. 34 (1995) 2371–2374.
[4] W.A. Herrmann, J. Schwarz, M.G. Gardiner, M. Spiegler, N-heterocyclic carbenes.
20. Homoleptic chelating N-heterocyclic carbene complexes of palladium and
nickel, J. Organomet. Chem. 575 (1999) 80–86.
[
5] T. Strassner, M. Muehlhofer, A. Zeller, E. Herdtweck, W.A. Herrmann, The counter-
ion influence on the CH-activation of methane by palladium(II) biscarbene

36
L. Yang et al. / Inorganic Chemistry Communications 22 (2012) 33–36
complexes-structures, reactivity and DFT calculations, J. Organomet. Chem. 689
2004) 1418–1424.
6] M. Muehlhofer, T. Strassner, W.A. Herrmann, C-H Activation by N-heterocyclic
carbenes, part 1. New catalyst systems for the catalytic conversion of methane
into methanol, Angew. Chem. Int. Ed. 41 (2002) 1745–1747.
29.4,
bisimidazolium dichloride (L5) H NMR (400 MHz, DMSO-d
NCHN), 8.34 (s, 2H, NCH), 8.20 (s, 2H, NCH), 7.63 (m, 2H, Ar-H), 7.45 (m, 4H,
Ar-H), 5.26 (s, 4H, NCH ), 2.21 (m, 4H, CH), 1.16 (d, J=5.2 Hz, 12H, CH ), 1.09
(d, J=4.8 Hz, 12H, CH ) or in CDCl : 10.30 (s, 2H, NCHN), 9.24 (s, 2H, NCH),
7.52 (t, J=7.6 Hz, 2H, Ar-H), 7.30-7.13 (m, 4H, Ar-H, 2H, NCH), 5.56 (s, 4H,
NCH ), 2.21 (m, 4H, CH), 1.21 (d, J=6.4 Hz, 12H, CH ), 1.13 (d, J=6.4 Hz, 12H,
CH ). C NMR (CDCl , 100 MHz): δ 144.9, 137.6, 131.7, 129.6, 124.8, 124.4,
123.7, 48.0, 28.5, 24.0, 23.9. Anal. Calc. for C32 44Cl (555.63 g/mol): C,
69.17; H, 7.98; N, 10.08. Found: C, 68.86; H, 7.84; N, 9.98%.
[21] General procedures for the synthesis of palladium complexes Pd
To a mixture of bisimidazolium dichloride (3 mmol), PdCl (1.069 g, 6.0 mmol),
and K CO (8.293 g, 60 mmol) in a 50 mL round bottom flask was added
23.2,
14.5.1,1′-Di(2,6-diisopropropylphenyl)-3,3′-(1,2-ethanediyl)
1
(
6
): 10.17 (s, 2H,
[
2
3
3
3
[
7] C.M. Jin, B. Twamley, J.M. Shreeve, Low-melting dialkyl- and
bis(polyfluoroalkyl)-substituted
1,1′-methylenebis(imidazolium)
and
2
3
1
3
1,1′-methylenebis(1,2,4-triazolium) bis(trifluoromethanesulfonyl)amides: ionic
3
3
liquids leading to bis(N-heterocyclic carbene) complexes of palladium, Organo-
metallics 24 (2005) 3020–3023.
8] J.C. Slootweg, P. Chen, Cationic palladium bis-carbene carboxylate complexes, Or-
ganometallics 25 (2006) 5863–5869.
9] S. Ahrens, A. Zeller, M. Taige, T. Strassner, Extension of the alkane bridge in
bisNHC−palladium−chloride complexes. Synthesis, structure, and catalytic ac-
tivity, Organometallics 25 (2006) 5409–5415.
10] A. Biffis, C. Tubaro, G. Buscemi, M. Basato, Highly efficient alkyne hydroarylation
with chelating dicarbene palladium(II) and platinum(II) complexes, Adv. Synth.
Catal. 350 (2008) 189–196.
11] M. Poyatos, E. Mas-Marza, J.A. Mata, M. Sanau, E. Peris, Synthesis, reactivity, crys-
tal structures and catalytic activity of new chelating bisimidazolium-carbene
complexes of Rh, Eur. J. Inorg. Chem. (6) (2003) 1215.
12] E. Alcalde, R.M. Ceder, C. Lopez, N. Mesquida, G. Muller, S. Rodriguez, Coordina-
tion features of bis(N-heterocyclic carbenes) and bis(oxazolines) with
H
2 4
N
[
2 2 4 5 5
L Cl (C H N)2-
2
[
2
3
35.5 mL of pyridine. The reaction mixture was heated at 80-85 °C for 16-18 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
ether (5 mL). The pure compound was obtained as yellow solid by recrystalliza-
[
[
[
2 1 4 5 5 2
L Cl (C H N)
(1): Yield: 42% (0.886 g). 1H NMR
tion with DCM / ether. Pd
(CDCl , 400 MHz): 9.04 (d, J=4.8 Hz, 4H, Py-H), 7.79 (t, J=7.6 Hz, 2H, Py-H),
7.38 (t, J=6.8 Hz, 4H, Py-H), 7.10 (d, 2H, J=1.6 Hz, NCH), 6.72 (d, J=1.6 Hz,
3
1
3
2H, NCH), 5.41 (s, 4H, NCH
152.5, 147.8, 138.0, 124.6, 122.3, 50.4, 35.8. Anal. Calc. for C20
(703.10 g/mol): C, 34.17; H, 3.44; N, 11.95. Found: C, 33.84; H, 3.09; N,
2
), 4.11(s, 6H, CH
3
). C NMR (CDCl
3
, 100 MHz):
H
24Cl Pd
4
N
6
2
1
1,3-alkylidene-2,4,6-trimethylbenzene spacers. Synthesis of the ligands and sil-
2 2 4 5 5 2 3
12.46%.Pd L Cl (C H N) (2): Yield: 65% (0.51 g). H NMR (CDCl , 400 MHz):
ver and palladium complexes, Dalton Trans. (25) (2007) 2696–2706.
13] U.J. Scheele, M. John, S. Dechert, F. Meyer, Pyrazole-bridged NHC ligands and their
dimetallic (allyl)palladium complexes, Eur. J. Inorg. Chem. (3) (2008) 373–377.
14] N.D. Jones, B.R. James, Homo- and heterobimetallic precursor catalysts for the
Heck reaction, and a proposal for a general catalytic cooperativity index, Adv.
Synth. Catal. 344 (2002) 1126–1134.
9.00 (d, J=4.8 Hz, 4H, Py-H), 7.79 (t, J = 7.6 Hz, 2H, Py-H), 7.38 (t, J=7.2 Hz,
4H, Py-H ), 7.10 (d, J=2.0 Hz, 2H, NCH), 6.88 (d, J=2.0 Hz, 2H, NCH), 5.77 (s, 4
[
[
1
3
H, CH
124.6, 123.8, 119.3, 59.1, 51.0, 32.1. Anal. Calc. for
(787.26 g/mol): C, 39.67; H, 4.61; N, 10.68. Found: C, 39.88; H, 4.53; N,
2
), 2.09 (s, 18H, CH
3
). C NMR (100 MHz, CDCl
3
): 151.4, 145.5, 138.0,
C
26
H
36Cl Pd
4
N
6
2
1
2 3 4 5 5 2 3
10.91%.Pd L Cl (C H N) (3): Yield: 69% (1.828 g). H NMR (CDCl , 400 MHz):
[
[
[
15] S. Díez-González, N. Marion, S.P. Nolan, N-Heterocyclic carbenes in late transition
8.80 (m, 4H, Py-H), 7.72 (m, 2H, Py-H), 7.61 (d, 2H, J=2.0 Hz, NCH), 7.36-7.28
(m, 2H, Ar-H, 4H, Py-H ), 7.23-7.22 (m, 4H, Ar-H), 6.74 (d, 2H, J=2.0 Hz, NCH),
metal catalysis, Chem. Rev. 109 (2009) 3612–3676.
16] D. Enders, O. Niemeier, A. Henseler, Organocatalysis by N-heterocyclic carbenes,
Chem. Rev. 107 (2007) 5606–5655.
17] C. Cao, Y. Zhuang, J. Zhao, Y. Peng, X. Li, Z. Shi, G. Pang, Y. Shi, Binuclear palladium
complexes bridged by dicarbene with different lengths and their application in
Mizoroki–Heck reaction, Inorg. Chim. Acta 363 (2010) 3914–3918.
18] C. Cao, Y. Zhuang, J. Zhao, G. Pang, Y. Shi, Efficient synthesis of alkane-bridged
N, N′-diaryl bisimidazolium chlorides under solvent-free conditions, J.
Chem. Res. 35 (2011) 320–322.
1
3
5.82 (s, 4H, NCH
137.9, 137.2, 136.5, 129.5, 128.6, 124.9, 124.4, 123.0, 51.0, 19..0. Anal. Calc. for C-
36Cl Pd (883.34 g/mol): C, 46.23; H, 4.11; N, 9.51. Found: C, 45.79; H, 3.92;
N, 9.23%.Pd
2 3 3
), 2.30 (s, 12H, CH ). C NMR (CDCl , 100 MHz): 151.3, 150.4,
34
H
4
N
6
2
1
2 4 4 5 5 2 3
L Cl (C H N) (4): Yield: 56% (1.578 g). H NMR (CDCl , 400 MHz):
8.78 (m, 4H, Py-H), 7.73-7.68 (m, 2H, Py-H; 2H, NCH), 7.46 ( t, J=7.6 Hz, 2H,
Ar-H), 7.30-7.28 (m, 4H, Ar-H; 4H, Py-H), 6.78 (d, 2H, J=2.0 Hz, NCH), 5.80 (s,
[
[
4H, NCH
2
), 2.76 (m, 4H, CH
C NMR (CDCl , 100 MHz): 151.3, 150.7, 142.0, 137.9, 135.9, 129.9, 126.5,
124.7, 124.4, 123.8, 51.0, 24.7, 14.9. Anal. Calc. for 44Cl Pd
(939.45 g/mol): C, 48.58; H, 4.72; N, 8.95. Found: C, 48.17; H, 4.44; N, 9.17%.Pd2-
2 2 3
), 2.46 (m, 4H, CH ), 1.14 (t, J=7.6 Hz, 12H, CH ).
1
3
3
19] 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
C
38
H
4
N
6
2
1
L
5
Cl
Py-H), 7.68 (m, 2H, Py-H; 2H, NCH), 7.50 (t, J=7.6 Hz, 2H, Ar-H), 7.35-7.26 (m,
4H, Py-H; 4H, Ar-H), 6.80 (m, 2H, NCH), 5.87 (s, 4H, NCH ), 2.95 (m, 4H, CH),
1.43 (d, J=6.8 Hz, 12H, CH ), 1.01 (d, J=6.8 Hz, 12H, CH
100 MHz): 152.5, 152.0, 151.3, 146.7, 137.9, 134.4, 130.4, 129.0, 128.2, 124.9,
28.5, 26.5, 23.1. Anal. Calc. for C42 52Cl Pd (995.55 g/mol): C, 50.67; H, 5.26;
N, 8.44. Found: C, 50.89; H, 5.42; N, 8.03%.
[22] C. Dash, M.M. Shaikh, P. Ghosh, Fluoride-free Hiyama and copper- and amine-free
Sonogashira coupling in air in mixed aqueous medium by series of
4 5 5 2 3
(C H N) (5): Yield: 82% (2.449 g). H NMR (CDCl , 400 MHz): 8.80 (m, 4H,
1
obtained from common suppliers and used without further purification. H and
2
1
3
13
C spectra were recorded on a Bruker AV 400 MHz spectrometer at room tem-
3
3 3
). C NMR (CDCl ,
perature and referenced to the residual signals of the solvent. GC-MS was per-
formed on an Agilent 6890-5973N system with electron ionization (EI) mass
H
4
N
6
2
spectrometry. Elemental analyses were performed on
EA-300 elemental analyzer.
a EuroVektor Euro
[
20] General procedures for the synthesis of ligands L: N-t-butyl or N-aryl imidazoles
4 mmol) and 2 mmol of alkyl halides were heated to 80–135 °C for 4–6 h in a
0 mL of pressure tube. The completely changing of the colorless solution to
a
a
(
1
PEPPSI-themed precatalysts, Eur. J. Inorg. Chem. (12) (2009) 1608–1618.
[23] Preliminary examination and data collection were carried out on a Rigaku Mercu-
white solid is the sign of the completion of the reaction. After completion, the re-
action mixture was cooled to room temperature. All of the crudes were dissolved
in DCM and white crystalline products were precipitated out by adding diethyl
ry CCD device at the window of
a
sealed X-ray tube with
graphite-monochromated Mo Kα radiation. Absorption correction was per-
formed by SADABS program. All the structures were solved by direct methods
using the SHELXS-97 program and refined by full-matrix least squares techniques
ether into DCM solution.1,1′-Dimethyl-3,3′-(1,2-ethanediyl)bisimidazolium
1
2
dichloride (L1). HNMR (400 MHz, DMSO-d
6
): 9.40 (s, 2H, NCHN), 7.78 (s, 2H,
), 3.86 (s, 6H, CH ).1,1′--
Di-t-butyl-3,3′-(1,2-ethanediyl)bisimidazolium dichloride (L2). H NMR
400 MHz, DMSO-d ): 9.73 (s, 2H, NCHN), 8.04 (s, 2H, NCH), 7.72 (s, 2H, NCH),
.80 (s, 4H, CH ), 1.56 (s, 18H, CH ), or in D O: 8.91 (s, 2H, NCHN), 7.74 (s, 2H,
NCH), 7.40 (s, 2H, NCH), 4.70 (s, 4H, CH ), 1.57 (s, 18H, CH ).1,1′--
Di(2,6-dimethylphenyl)-3,3′-(1,2-ethanediyl)bisimidazolium dichloride (L3)
on F .
NCH), 7.75 (s, 2H, NCH), 4.78 (s, 4H, CH
2
3
[24] L. Ray, S. Barman, M.M. Shaikh, P. Ghosh, Highly convenient amine-free
Sonogashira coupling in air in a polar mixed aqueous medium by trans- and
cis-[(NHC) PdX ] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic
2 2
carbenes, Chem. Eur. J. 14 (2008) 6646–6655.
[25] Heck reaction: An oven-dried 4 mL vial containing a stirrer bar was charged with
1
(
6
4
2
3
2
2
3
bromobenzene (0.5 mmol), catalyst (0.5 mol%) and
K
2
CO
3
(103.7 mg,
1
H NMR (400 MHz, DMSO-d
6
): 9.78 (s, 2H, NCHN), 8.17 (m, 2H, NCH), 8.05 (m,
H, NCH), 7.46 (m, 2H, Ar-H), 7.35 (m, 4H, Ar-H), 5.06 (s, 4H, CH ), 2.03 (s,
O, DMSO): 134.6, 132.8, 131.2, 129.0, 128.4,
23.2, 113.2, 49.3, 16.6.1,1′-Di(2,6-diethylphenyl)-3,3′-(1,2-ethanediyl)
0.75 mmol) in the glove box and sealed with a cap containing a PTFE septum.
DMF (1 mL) and styrene (70 μL, 0.60 mmol) were injected sequentially. The mix-
ture was stirred at 110 °C for 23 h. The crude was purified by column chromatog-
raphy on silica gel with petroleum ether.
2
1
1
2
1
3
3 2
2H, CH ). C NMR (100 MHz, D
1
bisimidazolium dichloride (L4). H NMR (400 MHz, DMSO-d
NCHN), 8.40 (m, 2H, NCH), 8.14 (m, 2H, NCH), 7.57 (m, 2H, Ar-H), 7.39 (m, 4H,
Ar-H), 5.23 (s, 4H, NCH ), 2.25 (m, 8H, CH CH ), 1.04 (t, J=7.6 Hz, 12H, CH ).
, 100 MHz): 140.2, 138.4, 132.0, 131.1, 126.9, 124.6, 123.4, 48.2,
6
): 10.09 (s, 2H,
[26] R.J. Baker, M.L. Cole, C. Jones, M.F. Mahon, Bidentate N-heterocyclic carbene com-
plexes of group 13 trihydrides and trihalides, Dalton Trans. (9) (2002) 1992–1996.
2
2
3
3
1
3
C NMR (CDCl
3