Silver(I) and palladium(II) complexes of new pentamethylene-functionalized bis-imidazolium dication ligands and its application in Heck and Suzuki-Miyaura coupling reaction

Article abstract of DOI:10.1016/j.ica.2016.04.039

Two new pentamethylene-functionalized bis-imidazolium dication ligands L¹ and L² (L¹ = 1,5-bis(4-(imidazolium-1-yl-phenol)pentane dibromide; L² = 1,5-bis(1-vinylimidazolium-1-yl)pentane dibromide) bearing IP (4-(imidazol-1-yl)phenol) and VI (1-vinylimidazole)-functionality have been prepared via the reaction of 1,5-dibromopentane with a substituted imidazole derivative. The bis-imidazolium dication ligands L¹ and L² on reaction with Ag₂O in DCM:MeOH, followed by anion substitution with AgBF₄ led to the formation of silver(I) complexes [Ag₂(_PC(CH₂)₅C_P)₂][BF₄]₂ (_PC(CH₂)₅C_P = 1,5-bis(4-(imidazolium-1-yl-phenol) pentane (1) and [Ag₂(_VC(CH₂)₅C_V)₂][BF₄]₂ (_VC(CH₂)₅C_V = 1,5-bis(1-vinylimidazolium-1-yl)pentane (2). Transmetalation of the bis-NHC ligand from [Ag₂(_PC(CH₂)₅C_P)₂][BF₄]₂ and [Ag₂(_VC(CH₂)₅C_V)₂][BF₄]₂ by palladium(II) salt [PdCl₂(CH₃CN)₂] in DMSO gave [PdCl(_PC(CH₂)₅C_P)(CH₃CN)]BF₄ (3) and [PdCl(_VC(CH₂)₅C_V)(CH₃CN)]BF₄ (4), respectively. The new ligands as well as their silver(I) and palladium(II) complexes have been characterized by elemental analysis, electronic, IR, ¹H and ¹³C NMR, and FAB-MS spectroscopy. The molecular structure of the representative ligand L¹ has been determined by single crystal X-ray analysis. The palladium^II NHC complexes 3 and 4 exhibited good activity in a model Heck and Suzuki-Miyaura coupling reaction.

Full text of DOI:10.1016/j.ica.2016.04.039

Inorganica Chimica Acta 449 (2016) 1–8
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Silver(I) and palladium(II) complexes of new pentamethylene-
functionalized bis-imidazolium dication ligands and its application
in Heck and Suzuki–Miyaura coupling reaction
Manoj Trivedi a, , Bhaskaran , Gurmeet Singh , Abhinav Kumar , Nigam P. Rath
⇑
a
a,
⇑
b
c,
⇑
a
Department of Chemistry, University of Delhi, Delhi 110007, India
Department of Chemistry, University of Lucknow, Lucknow 226007, India
Department of Chemistry & Biochemistry and Centre for Nanoscience, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO 63121-4499, USA
b
c
a r t i c l e i n f o
a b s t r a c t
Two new pentamethylene-functionalized bis-imidazolium dication ligands L and L2 (L = 1,5-bis(4-(imi-
1
1
Article history:
Received 4 November 2015
Received in revised form 17 March 2016
Accepted 19 April 2016
2
dazolium-1-yl-phenol)pentane dibromide; L = 1,5-bis(1-vinylimidazolium-1-yl)pentane dibromide)
bearing IP (4-(imidazol-1-yl)phenol) and VI (1-vinylimidazole)-functionality have been prepared via
the reaction of 1,5-dibromopentane with a substituted imidazole derivative. The bis-imidazolium dica-
Available online 27 April 2016
1
2
tion ligands L and L on reaction with Ag
led to the formation of silver(I) complexes [Ag
zolium-1-yl-phenol) pentane (1) and [Ag C(CH
zolium-1-yl)pentane (2). Transmetalation of the bis-NHC ligand from [Ag
Ag C(CH ][BF by palladium(II) salt [PdCl (CH CN) in DMSO gave [PdCl(
(CH CN)]BF (3) and [PdCl( C(CH )(CH CN)]BF (4), respectively. The new ligands as well as their
silver(I) and palladium(II) complexes have been characterized by elemental analysis, electronic, IR,
2
O in DCM:MeOH, followed by anion substitution with AgBF
C(CH ][BF C(CH = 1,5-bis(4-(imida-
C(CH = 1,5-bis(1-vinylimida-
C(CH ][BF and
2 5 P
C(CH ) C )
4
2
(
P
2
)
5
C
)
P 2
4
]
2
(
P
2 5 P
) C
Keywords:
Bis-imidazolium dication ligand
Silver(I) complex
Palladium(II) complex
X-ray crystal structure
Cross-coupling reaction
2
(
V
2
5
) C
V 2
) ][BF
4
]
2
(
V
2 5 V
) C
2
(
P
2
)
5
C
)
P 2
4 2
]
[
2
(
V
)
2 5
V
C )
2
4
]
2
2
3
2
]
P
3
4
V
2 5
) C
V
3
4
1
H
1
3
1
and C NMR, and FAB-MS spectroscopy. The molecular structure of the representative ligand L has been
determined by single crystal X-ray analysis. The palladium NHC complexes 3 and 4 exhibited good
II
activity in a model Heck and Suzuki–Miyaura coupling reaction.
Ó 2016 Elsevier B.V. All rights reserved.
1
. Introduction
N-heterocyclic carbenes (NHCs) are nowadays ubiquitous
[13–20], and catalytic applications [21–28] have been entirely
devoted to this type of ligand. The concept of two NHC groups sep-
arated by various spacer such as pyridine, benzene, amido, ether,
methylene, ethylene, propylene, butylene, m-xylylene, o-xylylene
and pentamethylene functionalities have been explored by several
groups, yielding various pincer complexes containing various
alkyl/aryl groups [29–38]. These ligands are highly ‘‘tunable” and
active precatalysts for C–C coupling reactions and exhibit excellent
thermal stability and resistance to degradation reactions
[29,32,33,35,39,25]. Ag(I) (NHC) complexes have been shown to
be facile reagents for the transmetalation of a variety of function-
alized NHC ligands to Pd(II) [40–45]. They are readily accessed
ligands in organometallic chemistry as well as catalysis due to
their unique properties. After the pioneering reports by Öfele and
Wanzlick [1,2], and the early studies by Lappert [3–8] on the coor-
dination to late transition-metal complexes, NHC chemistry
remained quiescent for more than twenty years, until Arduengo
pointed out the idea that NHCs could be stable enough for crystal-
lographic characterization [9]. In 1995, Herrmann took the story a
step forward, with the use of NHCs in the preparation of the first
NHC-based homogeneous catalysts [10]. Since then, several
research groups have synthesized a large number of NHC-based
catalysts for a wide variety of reactions, and many reviews cover-
ing different aspects such as preparation [11–14], stability [15],
stereoelectronic properties [16–18], coordination strategies
2
through the reaction of an imidazolium salt with Ag O by the
method of Wang and Lin [46]. In recent years the number of crys-
II
tallographically characterized Pd (NHC) complexes has increased
considerably with a rich structural diversity revealed, especially
when halide ions are present in the compound [47–49]. Because
of our interests in the development of Ag and Pd complexes
based on NHCs [50], herein, we present the syntheses, spectral
characterization of two new pentamethylene-functionalized
⇑
Corresponding authors. Tel.: + 91 (0) 9811730475 (M. Trivedi). Tel.: +1 (314)
5
16 5333 (N.P. Rath).
E-mail addresses: manojtri@gmail.com (M. Trivedi), gurmeet123@yahoo.com
(
G. Singh), rathn@umsl.edu (N.P. Rath).
http://dx.doi.org/10.1016/j.ica.2016.04.039
020-1693/Ó 2016 Elsevier B.V. All rights reserved.
0

2
M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
1
bis-imidazolium dication ligands (L = 1,5-bis(4-(imidazolium-1-
(s, 2H), 7.24–7.38 (m, 4H, 8.5 Hz), 5.38–5.90 (dd, 4H, 3.0 Hz),
4.71 (d, 2H, 4.2 Hz), 3.44–3.95 (m, 2H, 4.2 Hz), 2.53–2.68 (quintet,
2
yl-phenol)pentane dibromide and L = 1,5-bis(1-vinylimida-
1
3
zolium-1-yl)pentane dibromide) bearing IP (4-(imidazol-1-yl)phe-
nol) and VI (1-vinylimidazole)-functionality and their silver(I) and
Pd(II) complexes. We, also report the comparative catalytic activi-
ties of Pd(II) bis-NHC complexes in the Heck and Suzuki–Miyaura
coupling reaction.
2H, 6.8 Hz), 1.33 (m, 2H, 43.9 Hz). C NMR (d ppm, 400 MHz,
CDCl , 298 K): 136.24, 130.41, 129.04, 125.77, 118.86, 101.21,
51.12, 32.59, 29.94, 27.86, 23.32, 15.76. FAB-MS (m/z): 418(418),
3
2
+
2
[M] (80ꢀ); 258 (258), [M] –Br (80ꢀ).
2.3. Syntheses of complexes
2
. Experimental
2
1
.3.1. [Ag
-yl-phenol) pentane (1)
L1 (0.550 g, 1 mmol) was dissolved in 5:1 DCM-MeOH (60 mL)
O (0.232 g, 1 mmol) added. The resulting suspension was
2 P 2 5 P 2 4 2 P 2 5 P
( C(CH ) C ) ][BF ] ( C(CH ) C = 1,5-bis(4-(imidazolium-
2.1. Materials and physical measurements
and Ag
2
All the synthetic reactions were performed under an atmo-
stirred at room temperature for 6 h, yielding a gray precipitate
and colorless solution. The supernatant was separated and stripped
in vacuo and the sticky white residue washed with MeOH
sphere of nitrogen using standard Schlenk techniques. The solvents
were dried and distilled before use following the standard
procedures [51]. 1,5-dibromopentane (Aldrich), 4-(imidazol-1-yl)-
(
5 ꢁ 5 mL). The resultant white powder was dried in vacuo but
2 3 2
phenol (IP) (Aldrich), 1-vinylimidazole (Aldrich), [PdCl (CH CN) ]
rapidly discolored, giving 1 (0.349 g, 30ꢀ) as a dark cream powder
(
Aldrich) was used as received.
that showed no further signs of decomposition at room tempera-
ture. Anal. Calc. for C46
9
KBr):m = 3420, 3090, 2924, 2230, 1605, 1546, 1511, 1458, 1251,
1
4
Elemental analysis was performed on a Carlo Erba Model EA-
108 elemental analyzer and data of C, H and N is within ±0.4ꢀ
H
48
N
8
Br
4 4 2 8 2
O B F Ag : C, 47.42; H, 4.12; N,
1
ꢀ1
.62; O, 5.49. Found: C, 47.64; H, 4.41; N, 9.81; O, 5.64. IR(cm
,
of calculated values. IR(KBr) was recorded using Perkin–Elmer
FT-IR spectrophotometer. Electronic spectra were obtained on a
Perkin Elmer Lambda-35 spectrometer. FAB mass spectra were
recorded on a JEOL SX 102/DA 6000 mass spectrometer using
Xenon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was
1
183, 1117, 1054, 1025, 833, 732, 624, 554. H NMR (d ppm,
00 MHz, CDCl , 298 K): 9.85 (s, 4H), 7.50 (m, 12H, 8.1 Hz), 7.30
3
(
m, 12H, 7.8 Hz), 4.12–4.84 (m, 4H, 6.4 Hz), 3.01–3.35 (m, 4H,
4
.8 Hz), 1.98–2.23 (m, 4H, 7.2 Hz), 1.20-1.58 (m, 4H, 3.6 Hz),
1
0 kV and the spectra were recorded at room temperature with
1
3
1
13
0.85–0.95 (m, 4H, 8.1 Hz).
3
C NMR(d ppm, 400 MHz, CDCl ,
m-nitrobenzyl alcohol as the matrix. The H and C NMR spectra
were recorded on a JEOL DELTA2 spectrometer at 400 MHz using
TMS as an internal standard. The chemical shift values are recorded
on the d scale and the coupling constants (J) are in Hz. GCMS stud-
ies were done with the Shimadzu-2010 instrument containing a
DB-5/RtX-5MS-30Mt column of 0.25 mm internal diameter.
2
1
6
1
98 K): 156.42, 132.01, 131.40, 128.50, 128.23, 127.47, 127.34,
27.17, 127.09, 126.22, 125.53, 116.66, 74.58, 72.40, 70.44, 67.99,
5.98, 31.66, 29.48, 29.12, 28.61, 27.40, 23.43, 22.63, 22.32,
ꢀ1
ꢀ1
3.88. UV–Vis {DMSO, kmax nm (e/M cm )}: 285(5275), 365
(
(
8346). FABMS (m/z): 1163 (1164), (M) (40ꢀ), 990 (990),
M ) (50ꢀ).
2
+
2
2
.2. Syntheses of ligands
2
.3.2. [Ag
2 V 2 5 V 2 4 2 V 2 5 V
( C(CH ) C ) ][BF ] ( C(CH ) C = 1,5-bis(1-
vinylimidazolium-1-yl)pentane (2)
L (0.418 g, 1 mmol) was dissolved in 5:1 DCM-MeOH (60 mL)
and Ag O (0.232 g, 1 mmol) added. The resulting suspension was
stirred at room temperature for 6 h, yielding a white precipitate
with colorless solution. The solution was evaporated and the sticky
white residue washed with MeOH (5 ꢁ 5 mL). The resultant white
powder was dried in vacuo, giving 2 (0.270 g, 30ꢀ) as a creamy
powder that showed no further signs of decomposition at room
.2.1. 1,5-bis(4-(imidazol-1-yl)phenol-imidazolium-1-yl)pentane
2
1
dibromide (L )
2
4
-(Imidazol-1-yl)phenol (5.029 g, 31.4 mmol) was added to 1,5-
dibromopentane (2.0 mL, 14.7 mmol) in THF (60 mL) and refluxed
for 24 h. The resultant yellow solid was filtered on a glass frit,
washed with Et O (20 mL), and dried in vacuo, yielding L
2
1
(
4.853 g, 60ꢀ) as a yellow powder that was handled and stored
in a vacuum dessicator. Anal. Calc. For C23 Br : C, 50.15;
H, 4.72; N, 10.17. Found: C, 50.43; H, 4.88; N, 10.34. IR(cm
KBr): = 3450, 2930, 2857, 1640, 1520, 1472, 1384, 1255, 1165,
H
26
N
4
O
2
2
temperature. Anal. Calc. for C30
N, 12.44. Found: C, 39.98; H, 4.65; N, 12.58. IR(cm , KBr):
H
40
N
8
2
B F
8
Ag
2
: C, 40.00; H, 4.44;
ꢀ
1
,
ꢀ1
m
m
1
2
5
6
= 3047, 2921, 2852, 1604, 1583, 1477, 1432, 1309, 1251, 1180,
054, 1024, 995, 744, 500, 429. H NMR (d ppm, 400 MHz, CDCl ,
3
98 K): 7.78 (s, 4H), 7.59 (s, 4H), 7.28–7.44 (m, 8H, 8.4 Hz), 5.31–
.98 (dd, 8H, 3.6 Hz), 4.72 (d, 4H, 5.2 Hz), 3.48–4.01 (m, 4H,
1
1
2
4
030, 998, 740, 720, 697, 540. H NMR (d ppm, 400 MHz, CDCl
98 K): 9.71(s, 2H), 7.55 (m, 6H, 8.4 Hz), 7.14 (m, 8H, 8.1 Hz),
.04–4.74 (m, 2H, 8.2 Hz), 3.00–3.23 (m, 2H, 7.3 Hz), 1.99–2.15
3
,
1
(
m, 2H, 6.6 Hz), 1.19–1.54 (m, 2H, 6.6 Hz), 0.81–0.91 (m, 2H,
13
.4 Hz), 2.51–2.78 (quintet, 4H, 4.8 Hz), 1.31 (m, 4H, 8.4 Hz).
C
1
3
7
1
1
2
.3 Hz).
3
C NMR (d ppm, 400 MHz, CDCl , 298 K): 154.82,
NMR(d ppm, 400 MHz, CDCl
1
UV–Vis {DMSO, kmax nm (e/M cm )}: 280(8981), 355(8097).
FABMS (m/z): 900(900), (M) (80ꢀ), 726(726), (M ) (80ꢀ).
3
, 298 K): 136.64, 130.11, 129.18,
31.71, 131.60, 128.55, 128.33, 127.97, 127.84, 127.47, 127.39,
26.72, 125.43, 116.56, 74.23, 72.39, 70.32, 67.89, 65.93, 31.67,
9.44, 29.15, 28.66, 27.44, 23.47, 22.73, 22.42, 13.87. FAB-MS (m/
25.86, 119.01, 101.56, 51.25, 32.88, 29.94, 27.66, 23.54, 15.88.
ꢀ1
ꢀ1
2+
2+
2 .
z): 550(550), [M] (100ꢀ); 390(390), [M] –Br (30ꢀ)
2
.3.3. [PdCl(
1 (0.2863 g, 0.246 mmol) was dissolved in DMSO (4 mL) at
room temperature and [PdCl (MeCN) ] (0.0650 g, 0.251 mmol)
P 2 5 P 3 4
C(CH ) C )(CH CN)]BF (3)
2
2
.2.2. 1,5-bis(1-vinyl-imidazolium-1-yl)pentane dibromide (L )
-Vinylimidazole (2.955 g, 31.4 mmol) was added to 1,5-dibro-
mopentane (2.0 mL, 14.7 mmol) in THF (60 mL) and refluxed for
4 h. The resultant white solid was filtered on a glass frit, washed
1
2
2
added. The resulting yellow solution lightened and became turbid
over a period of 10 min. After 1 h, the reaction was filtered and the
filtrate stripped in vacuo. The residue was taken up in MeCN
(3 mL), centrifuged to remove AgCl, and concentrated to one-third
volume. The crude product was precipitated by the addition of
Et
MeCN (2 mL). Diffusion of Et
40ꢀ) as pale yellow solid. Anal. Calc. for C25
2
2
with Et
a white powder that was handled and stored in a vacuum dessica-
tor. Anal. Calc. For C15 Br : C, 43.06; H, 5.26; N, 13.39. Found:
C, 43.16; H, 5.48; N, 13.57. IR(cm , KBr):
2
O (20 mL), and dried in vacuo, yielding L (3.937 g, 60ꢀ) as
H
22
N
4
2
ꢀ1
m
= 3300, 2920, 2856,
2
O (5 mL), washed with Et
2
O (2 ꢁ 5 mL), then extracted into
O into this extract gave 3 (0.263 g,
ClBF Pd: C,
1
5
640, 1540, 1471, 1380, 1250, 1160, 1040, 990, 745, 726, 696,
2
1
41. H NMR (d ppm, 400 MHz, CDCl
3
, 298 K): 7.67 (s, 2H), 7.55
H
27
N
5
O
2
4

M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
3
4
5.59; H, 4.10; N, 10.64. Found: C, 45.80; H, 4.35; N, 10.88. IR
2.6. General procedure for Suzuki coupling reaction
ꢀ
1
(
cm , KBr):
m
= 3420, 3090, 2924, 2327, 2301, 1605, 1546, 1511,
1
1
458, 1251, 1183, 1117, 1054, 1025, 833, 732, 624, 554. H NMR
K
2
CO
3
(553 mg, 4.0 mmol) was added to a 100 ml three-necked
(
6
d ppm, 400 MHz, CDCl
.8 Hz), 7.10 (m, 6H, 8.8 Hz), 4.34–4.88 (m, 2H, 5.2 Hz), 2.98–3.22
3
, 298 K): 9.78 (s, 2H), 7.40 (m, 6H,
flask with a stirring bar and the flask was dried under vacuum and
then filled with nitrogen, aryl halide or 4-halotolune (2.0 mmol)
and phenylboronic acid (244.0 mg, 2.0 mmol) in DMF (10 mL).
Then 0.1 molꢀ palladium complexes in DMF were added via a syr-
inge under nitrogen atmosphere. The mixture was stirred at 120 °C
for the indicated reaction time. The mixture was cooled and the
precipitate was removed by filtration and the product was
extracted from the filtrate with diethyl ether. The combined
(
(
m, 2H, 4.8 Hz), 2.35(s, 3H), 1.98–2.05 (m, 2H, 6.8 Hz), 1.15–1.50
m, 2H, 7.6 Hz), 0.88–1.05 (m, 2H, 6.3 Hz).
13
C NMR(d ppm,
4
1
2
00 MHz, CDCl , 298 K): 155.82, 132.01, 128.65, 128.22, 127.67,
3
26.32, 125.13, 118.11, 74.03, 72.09, 70.11, 67.32, 65.63, 31.01,
9.14, 29.01, 28.06, 27.04, 23.37, 22.43, 22.02, 13.07, 1.6. UV–VIS
ꢀ1
ꢀ1
{
DMSO, kmax nm (e/M cm )}: 280(5421), 358(8346). FABMS
+
+
(m/z): 571(571), (M ) (80ꢀ), 535(535), (M ꢀCl) (50ꢀ).
2 4
organic layer was dried over anhydrous Na SO and filtered. After
evaporation, the obtained residue was purified by silica-gel column
chromatography to give the coupling product. Product identities
2
.3.4. [PdCl( C(CH )(CH CN)]BF (4)
V
2 5
) C
V
3
4
1
13
2
(0.221 g, 0.246 mmol) was dissolved in DMSO (4 mL) at room
were confirmed by H and C NMR and GC–MS.
temperature and [PdCl (MeCN) ] (0.0650 g, 0.251 mmol) added.
2
2
The resulting yellow solution lightened and became turbid over a
period of 10 min. After 1 h, the reaction was filtered and the filtrate
stripped in vacuo. The residue was taken up in MeCN (3 mL), cen-
trifuged to remove AgCl, and concentrated to one-third volume.
3
. Results and discussion
3
3
.1. Synthesis
2
The crude product was precipitated by the addition of Et O
.1.1. Pentamethylene-functionalized bis-imidazolium dication ligands
(
(
5 mL), washed with Et
2 mL). Diffusion of Et O into this extract gave 4 (0.220 g, 42ꢀ) as
BClPd: C, 38.78; H,
2
O (2 ꢁ 5 mL), then extracted into MeCN
Methodology similar to that used for the preparation of the
2
alkyl-functionalised bis-imidazolium salt analogues [36] was
employed to prepare pentamethylene-functionalized bis-imida-
zolium dication ligands. Reaction of 1,5-dibromopentane with
23 5 4
pale yellow solid. Anal. Calc. for C17H N F
ꢀ1
4
m
1
.37; N, 13.30. Found: C, 38.88; H, 4.45; N, 13.38. IR(cm , KBr):
= 3434, 3047, 2921, 2852, 2332, 2305, 1604, 1583, 1477, 1432,
4
-(imidazolium-1-yl-phenol/1-vinylimidazole in refluxing THF
1
309, 1251, 1180, 1054, 1024, 995, 744, 500, 429. H NMR (d
1
2
gave bis-imidazolium dication ligands L and L as white powder
in good yields (Scheme 1).
3
ppm, 400 MHz, CDCl , 298 K): 7.60 (s, 2H), 7.50 (s, 2H), 7.20–7.48
(
m, 4H, 6.4 Hz), 5.39–5.88 (dd, 4H, 6.0 Hz), 4.75 (d, 2H, 5.2 Hz),
1
2
Bis-imidazolium dication ligands L and L were characterized
3
3
2
3
M
.46–3.91 (m, 2H, 7.2 Hz), 2.45–2.69 (quintet, 2H, 8.8 Hz), 2.09 (s,
1
13
by elemental analysis, IR, H & C NMR and FAB-MS spectroscopy.
Analytical data of L , and L corroborated well with their respective
formulations (See F-1 to F-6, Supporting material). A comparison
of the H and C NMR spectra of the IP and VI-functionalised
bis-imidazolium dication ligands shows that variation of the
functional group has a negligible effect on the chemical shifts of
the imidazolium ring protons.
H), 1.33 (m, 2H, 8.8 Hz). 13C NMR (d ppm, 400 MHz, CDCl
3
,
1
2
98 K): 135.94, 130.21, 129.22, 125.76, 118.86, 101.21, 51.22,
2.49, 29.88, 27.46, 23.11, 15.46, 1.2. UV–Vis {DMSO, kmax nm (
e
/
1
13
ꢀ1
ꢀ1
+
cm )}: 286(7981), 362(8099). FABMS (m/z): 440(439), (M )
+
(
100ꢀ), 403 (403), (M ꢀCl) (20ꢀ).
2.4. X-ray crystallographic study
X-ray data for L1 was collected on a Bruker APEX II CCD
3.1.2. Ag (I) and Pd(II) complexes
1
2
Bis-imidazolium dication ligands L and L were reacted with
O in 1:1 stoichiometric ratio in a mixture of methanol and
dichloromethane (1:5 v/v) under stirring for 6 h followed by
anion substitution with AgBF gave silver(I) complexes
[Ag ( C(CH ) C ) ][BF ] ( C(CH ) C = 1,5-bis(4-(imidazolium-1-
diffractometer at 100(2) K using Mo K
a radiation (k = 0.71073 Å).
Ag
2
Structure solution was followed by full-matrix least squares
refinement and was performed using the WinGX-1.70 suite of
programs [52]. ApexII, and SAINT software packages were used for
4
1
2
P
2 5 P 2
4 2
P
2 5 P
data collection and data integration for L . Structure solution and
2 2 5 VI 2 4 2 V 2 5 V
yl-phenol) pentane [1] and [Ag (VIC(CH ) C ) ][BF ] ( C(CH ) C =
refinement were carried out using the SHELXL97-Program [53]. The
non-hydrogen atoms were refined with anisotropy thermal
parameters. All the hydrogen atoms were treated using
appropriate riding models. The computer programme PLATON was
used for analyzing the interaction and stacking distances [54,55].
1
,5-bis(1-vinylimidazolium-1-yl)pentane [2] in reasonable yields
(
30ꢀ) as shown in Scheme 2.
Attempts for the syntheses of Pd(II) complexes of the bis-car-
1
2
1
2
bene ligands L and L via reaction of imidazolium salts L and L
II
2 3 2
with [PdCl (CH CN) ] gave a mixture of poorly soluble Pd (NHC)
complexes that could not be satisfactorily separated by chromatog-
raphy on silica. NHC ligand transmetalation from Ag(I) to Pd(II) has
proved useful method for the synthesis of palladium(II) complexes
2
.5. General procedure for Mizoroki–Heck reaction
K
2
CO (553 mg, 4.0 mmol) was added to a 100 ml three-necked
3
[
P 2 5 P 3 4 V 2 5 V 3
PdCl( C(CH ) C )(CH CN)]BF [3] and [PdCl( C(CH ) C )(CH CN)]
flask with a stirring bar and the flask was dried under vacuum and
then filled with nitrogen, aryl halide or 4-halotolune (2.0 mmol)
and n-butylacrylate or styrene (2.0 mmol) in DMF (10 mL). Then
BF [4], respectively in reasonable yields (40–42ꢀ) as shown in
4
Scheme 3.
0
.1 molꢀ palladium complexes in DMF were added through syringe
under nitrogen atmosphere. The mixture was stirred at 120 °C for
the indicated reaction time. After the completion of the reaction,
the mixture was cooled, the precipitate was removed by filtration
and the product was extracted from the filtrate with diethyl ether.
3.2. Characterization
All the complexes were isolated as air-stable, non-hygroscopic
solids and soluble in dichloromethane, chloroform, methanol,
dimethylformamide, and dimethylsulfoxide but insoluble in petro-
leum ether and diethyl ether. Analytical data of 1–4 corroborated
well with their respective formulations. Information about compo-
sition of the complexes was also obtained from FAB-MS spectra of
the complexes (recorded in the Section 2). The position of various
2 4
The combined organic layer was dried over anhydrous Na SO and
filtered. After evaporation, the obtained residue was purified by
silica-gel column chromatography to give the Mizoroki–Heck
product. Product identities were confirmed by 1H and C NMR
and GC–MS.
13

4
M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
.
2Br
N
N
N
THF
Reflux for 24 h
Br
Br
+
N
N
N
R
R
R
1
2
R=
OH(L ) , CH CH (L )
2
Scheme 1. Synthesis of L1 and L2.
.2BF4
R
N
N
N
N
N
R
.
2Br
N
N
Ag2O, DCM-MeOH
Ag
Ag
N
N
AgBF4, CH3CN
R
R
N
N
N
R
R
1
2
R=
OH(L ) , CH CH (L )
2
R=
OH(1) , CH CH (2)
2
Scheme 2. Synthesis of silver(I) complexes 1 and 2.
.BF4
.2BF4
R
N
N
N
N
N
N
R
[
N
N
PdCl (CH CN) ]
2 3 2
N
Ag
Ag
N
Pd
DMSO, room temp.
R
N
R
Cl
R
N
N
R
C
Me
R=
OH(1) , CH CH (2)
R=
OH(3) , CH CH2(4)
2
Scheme 3. Synthesis of palladium(II) complexes 3 and 4.
peaks and overall fragmentation pattern in the FAB-MS spectra of
the respective complexes confirmed well to their respective formu-
lations (See F-7 to F-10, Supporting material). More information
about the structure and bonding in the complexes has been
deduced from the spectral studies. Poor quality of crystals of the
complexes 1–4 has restricted us to provide any structural support
at this stage.
Table 1
Crystallographic data for L .
1
Empirical formula
FW
Crystal system
Space group
a (Å)
2 4 2
C23H26Br N O
550.30
Orthorhombic
Pccn
12.5824(7)
13.0703(8)
17.6434(10)
90.00
90.00
90.00
2901.6(3)
4
1.260
b (Å)
Infrared spectrum of 1 and 3 in KBr displayed broad band
c (Å)
ꢀ
1
around 3450 cm corresponding to
630–1640 cm in 2 and 4 corresponds to olefinic C = C stretching
that is usually found in the region of 1680–1630 cm . The charac-
m
(OH). The band observed at
a
(°)
b (°)
(°)
ꢀ1
1
c
ꢀ1
3
V (Å )
ꢀ1
teristic bands for
m
(C„N) in 3 and 4 appears at 2327–2332 cm
.
Z
D
calc (g cmꢀ3)
The vibrations corresponding to
m
(C@N) in all the complexes which
ꢀ
1
ꢀ1
l
(mm
)
2.816
appeared at ꢂ1590–1600 cm are because of the imidazole moi-
ꢀ1
T (K)
100(2)
0.1037
0.0754
0.2258
0.2020
1.038
ety. All the complexes exhibit intense bands at 1054 cm which
R
R
1
all
[I > 2r(I)]
ꢀ
is due to presence of counterion BF
4
. The purity and composition
1
1
2
of both the ligands L and L , and their complexes have been
checked by NMR spectroscopy. Both the ligands and their com-
wR2
wR
Goodness-of-fit (GOF) on F
2
[I > 2r(I)]
2
1
13
plexes display sharp H and C NMR signals which integrate well
to the corresponding hydrogens and carbons. Further, it was
observed that the signals associated with various protons and car-
bons of the complexes displayed little change on coordination in
comparison to the bis-imidazolium salts. The electronic absorption
spectra of all the complexes 1–4 display bands at 280–286 and
lengths and angles are presented in Table 2. L1 crystallise in the
orthorhombic space group Pccn, with one formula unit, devoid of
crystallographic symmetry, comprising the asymmetric unit in
each case. The X-ray structure of L is depicted in Fig. 1. The bond
lengths and angles within the C N rings of L are comparable to
those found in the complex [Ag ( C(CH ) C) ][AgBr ] (MeC
2 Me 2 5 2 2 2
2 5
(CH ) C) = C,C -1,5-bis(3-methylimidazolin-2-yliden-1-yl)pentane)
3 2
[36] and in other related complexes [29–37]. The two C N rings in
1
3
55–365 nm. The higher energy band corresponds to the intra-
⁄
1
ligand
p
–p
transition, whilst the lower energy band can be
3
2
assigned to MLCT transition.
0
One X-ray structure emerged in the current study. The refine-
1
ment details of L are summarized in Table 1, and selected bond

M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
5
Table 2
interactions having contact distances of 2.51–2.70 Å. The C–Hꢃ ꢃ ꢃBr
contact distances in the crystal packing are in the range of
2.51–2.70 Å and the associated angles having range from 139° to
161°. These are within the range for analogous distances reported
in the literature [56,57].
1
Selected bond lengths (Å), and bond angles (°) for L .
O(1)–C(1)
N(1)–C(7)
N(1)–C(9)
N(1)–C(4)
N(2)–C(7)
N(2)–C(8)
N(2)–C(10)
C(10)–C(11)
1.358(6)
1.322(6)
1.378(6)
1.437(6)
1.315(6)
1.379(6)
1.478(6)
1.505(7)
1.528(6)
1.528(6)
108.0(4)
125.6(4)
126.4(4)
108.3(4)
125.2(4)
126.5(4)
122.6(4)
117.6(4)
109.4(4)
113.2(4)
113.8(5)
112.1(6)
173.0(5)
63.8(5)
3.3. Catalysis
3.3.1. Catalytic activities for Heck coupling reaction
C(11)–C(12)
The palladium-catalyzed Heck coupling reaction has been
C(12)–C(11)#1
C(7)–N(1)–C(9)
C(7)–N(1)–C(4)
C(9)–N(1)–C(4)
C(7)–N(2)–C(8)
C(7)–N(2)–C(10)
C(8)–N(2)–C(10)
O(1)–C(1)–C(6)
O(1)–C(1)–C(2)
N(2)–C(7)–N(1)
N(2)–C(10)–C(11)
widely employed for the preparation of aryl olefins. The Heck cou-
pling reactions of activated, non-activated and deactivated aryl
halides with vinyl compounds were examined in DMF at 120 °C
by using 0.1 molꢀ of complex 3 and 4 as the catalyst precursors.
The results are summarized in Table 3. As can be seen from Table 3,
our catalysts are so active that allows the olefination reactions of
activated, non-activated and deactivated aryl halides with vinyl
compounds such as n-butyl acrylate or styrene proceed at 120 °C
by using only 0.1 molꢀ of 3 or 4. The corresponding coupled prod-
ucts could be isolated in 40–98ꢀ yields. In the case of n-butyl acry-
late, only the trans isomer was detected, whereas for the coupling
reactions of styrene cis olefins were also observed as minor prod-
ucts in not more than 20ꢀ yields. For the activated bromide and
iodide substrates, the palladium-NHC catalysts are even more
effective than most of known palladium catalysts such as phos-
pha-palladacycle [58–60] and Pd-phosphine-imidazolium salt sys-
tems [61]. A high yield for the Heck coupling product was obtained
for activated aryl iodides or bromides (Table 3, entry 4, 5, 10, 11
and 13–16) than activated aryl chlorides (Table 3, entry 6, 12
and 17) by using complex 3 in comparison to complex 4. Extending
the reaction time up to 48 h did not give better results for activated
aryl chlorides. However, for non-activated iodo or bromo or
chlorobenzene, the desired coupled product yield was obtained
in 68–96ꢀ for 3 as compared to 64–92ꢀ yield with in complex 4
(Table 3, entry 1, 2, 3, 7, 8 and 9). The low yields obtained with aryl
C(10)–C(11)–C(12)
C(11)#1–C(12)–C(11)
#
1
C(10)–C(11)–C(12)–C(11)
N(2)–C(10)–C(11)–C(12)
C
N
3 2
interplanar dihedral (h,°)
63.24
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 3/2,
y + 1/2, z.
ꢀ
L1 have similar torsions for each section, being relatively rotated
about the C(10)-N(2) bond and dispersed to either side of the alkyl
linkage. The C(sp )-O bond distances in L are 1.358(6) Å. The
ligand 4-(imidazol-1-yl)phenol has lost planarity upon coordina-
tion with pentamethylene linkage. The phenyl group of the 4-(imi-
dazol-1-yl) phenol is not coplanar with imidazole ring and is tilted
with respect to the imidazole ring plane at an angle of 31.20°.
2
1
1
Crystal packing in L is stabilized by inter- and intra-molecular
C–Hꢃ ꢃ ꢃBr weak interactions. An interesting feature of the crystal
chloride or non-activated aryl chlorides are due to the stronger
1
2
packing in L is a linear chain motif (Fig. 2) resulting from C–Hꢃ ꢃ ꢃBr
Csp–Cl bonds of aryl chlorides than those of the heavier congeners.
Fig. 1. Projection view of L1 shown with 50ꢀ ellipsoids; hydrogen atoms are omitted for clarity.
Fig. 2. Linear chain motif resulting from C–Hꢃ ꢃ ꢃBr interactions.

6
M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
Table 3
Results of the Heck cross-coupling reactions of aryl halides with vinyl compounds using complex 3 and 4.a
R2
0
.1 mol%
R1
R2
Pd Complex (3, 4)
X
+
2
1
eq. K
2
CO
3
, DMF
o
20 C
R1
Entry
R1
R2
X
Isolated yield (ꢀ)b
3
4
n
2
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
H
H
H
CH
CH
CH
H
H
H
CH
CH
CH
OCH
OCH
OCH
OCH
OCH
NC
NC
NC
NC
NO
NO
CO
CO
CO
CO
CO
CO
Bu
Bu
Bu
Bu
Bu
Bu
Br
I
Cl
Br
I
Cl
Br
I
Cl
Br
I
95
96
80
95
96
66
95/4
96/3
68/15
96/3
98/2
70/18
75/15
85
80/10
88
45
60/18
58
92
90
75
93
92
62
n
2
n
2
n
3
3
3
2
n
2
n
2
c
c
C
C
C
C
C
C
C
6
6
6
6
6
6
6
H
H
H
H
H
H
5
5
5
5
5
5
90/8
c
88/10c
c
c
64/15
c
c
1
1
1
1
1
1
1
1
1
1
2
2
2
2
3
3
3
92/6
c
93/5c
c
c
Cl
Br
Br
I
66/16
c
70/20c
80
3
3
3
3
3
H
5
n
CO
2
Bu
c
75/16c
80
C
6
H
5
n
CO
CO
2
Bu
Bu
I
n
2
Cl
Br
Br
I
Cl
Br
Br
40
c
55/15c
62
C
6
H
5
n
CO
2
Bu
c
60/15c
42
C
6
H
5
65/20
45
55/15
58
n
CO
2
Bu
c
50/14c
56
2
2
C
6
H
5
n
CO
2
Bu
a
2 3
All reactions were carried out using 2.0 mmol activated or non-activated or decativated aryl halide, 2.0 mmol vinyl compound, 4.0 mmol K CO , 0.1 molꢀ Pd complex and
1
0 ml DMF at 120 °C for 24 h.
b
Isolated yield.
c
Yield of cis-product.
With the best conditions in hand, we explored substrate scope of
the reaction. In particular, our target was to verify the ability of
our catalysts to promote the reaction with different aryl halides.
It was found that activated bromo and iodo arenes reacted
smoothly and in good yields (Table 3, entry 13–16) than chloro
arene (Table 3, entry 17). On the other hand, deactivated haloare-
nes had an adverse effect on the reactivity, resulting in moderate to
poor yields of isolated product (Table 3, entry 18–23). Further
investigation of the true activation mechanism for pen-
tamethylene-functionalized quasi-pincer carbene containing palla-
dium(II) and its practical applications are undergoing in our
laboratory.
3.3.2. Catalytic activities for Suzuki–Miyaura reaction
The catalytic activities of the palladium complexes (3 and 4)
were studied for C–C formation reactions. Suzuki coupling
Table 4
a
Results of the Suzuki–Miyaura cross-coupling reactions of aryl halides with phenylboronic acid using complex 3 and 4 .
B(OH)
2
0.1 mol%
Pd Complex (3, 4)
R1
R1
X
+
2
eq. K CO , DMF
2
3
ο
120 C
Entry
R1
X
Isolated yield (ꢀ)b
3
4
1
2
3
4
5
6
7
8
9
CH
H
H
3
I
Br
I
Br
Br
I
Br
I
98
80
85
94
90
95
60
65
58
60
91
66
72
82
86
90
55
58
54
52
CH
3
OCH
OCH
NC
NC
NO
NO
3
3
2
Br
I
1
0
2
a
All reactions were carried out using 2.0 mmol aryl halide, 2.0 mmol phenylboronic acid, 4.0 mmol K
Isolated yield.
2 3
CO , 0.1 molꢀ Pd complex and 10 ml DMF at 120 °C for 12 h.
b

M. Trivedi et al. / Inorganica Chimica Acta 449 (2016) 1–8
7
reactions have been the most versatile and important method for
the synthesis of unsymmetrically substituted biaryl compounds
62–71]. The coupling reaction of selected aryl halides with
phenylboronic acid in DMF with 0.001 equivalent catalysts loading
using K CO as base at 120° was studied. Both the catalysts are
effective towards activated, non-activated and deactivated aryl
bromides and aryl iodides. The data clearly show that complex 3
is more active than 4; that is, the reaction of aryl halides with
phenylboronic acid in the presence of 0.001 equivalent of Pd com-
plex in DMF at 120 °C for 12 h gave 52–98ꢀ yield of the Suzuki–
Miyaura coupling product. The results are presented in Table 4.
In general, the activities of these palladium complexes are similar
to other palladium(II) catalysts based on phosphine-NHC ligands
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(
mance of palladium(II) complexes in the Heck and Suzuki–Miyaura
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Acknowledgements
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We gratefully acknowledge financial support by the Depart-
ment of Science and Technology, New Delhi, India (Grant No. SR/
FT/CS-104/2011). We also thank to the Director, USIC, University
of Delhi, Delhi, for providing analytical, spectral and Single Crystal
X-ray Diffraction facilities. The authors sincerely thank the review-
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sor P.J. Sadler, University of Warwick, UK, Professor Qiang Xu,
National Institute of Advanced Industrial Science and Technology
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