Synthesis and structure of dinuclear silver(I) and palladium(II) complexes of 2,7-Bis(methylene)naphthalene-bridged bis-N-heterocyclic carbene ligands

Article abstract of DOI:10.1021/om1008583

We synthesized a series of new Ag₂(bis-NHC)₂ complexes from the corresponding bisimidazolium salts tethered with 2,7-dimethylnaphthalene-bridged bis-NHC ligands. The reaction proceeded in a selective manner, and the Ag₂(bi

Full text of DOI:10.1021/om1008583

ARTICLE
pubs.acs.org/Organometallics
Synthesis and Structure of Dinuclear Silver(I) and Palladium(II)
Complexes of 2,7-Bis(methylene)naphthalene-Bridged Bis-N-
Heterocyclic Carbene Ligands
Shinichi Saito,*,† Mitsuya Saika,† Ryu Yamasaki,† Isao Azumaya,‡ and Hyuma Masu‡
†Department of Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
‡Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, Shido, Sanuki-city, Kagawa 769-2193, Japan
S Supporting Information
b
ABSTRACT: We synthesized a series of new Ag2(bis-NHC)2
complexes from the corresponding bisimidazolium salts teth-
ered with 2,7-dimethylnaphthalene-bridged bis-NHC ligands.
The reaction proceeded in a selective manner, and the Ag2(bis-
NHC)2 complexes were isolated in good to high yields. The Ag
complexes were converted to the Pd2(bis-NHC)2 complexes
efficiently. It is important to choose proper conditions for the
conversion of the silver complexes to the palladium complexes,
depending on the structure of the ligand: the effect of the counteranion was significant. The structures of the complexes were studied
by X-ray crystallographic analyses and compared with the corresponding monodentate NHC complexes. The catalytic activity of the
Pd complexes for the Mizoroki-Heck reaction was examined.
The chemistry of transition-metal complexes containing
N-heterocyclic carbenes (NHCs) has been extensively studied,
and a large number of compounds have been reported. Among
various metal complexes, the Ag-NHC complexes turned out to
be very unique, since they are fluxional molecules and also
efficient carbene-transferring reagents. The structures of these
complexes were also interesting, and many examples have been
reported in the literature.1 The compounds could be readily
prepared by the reaction of the imidazolium salt with Ag2O, and
it is not necessary to isolate NHC, which is a less stable species.
Interestingly, few 1:1 complexes were reported,2 while a series of
2:1 (Ag2(bis-NHC)) complexes3,4 and 2:2 (Ag2(bis-NHC)2)
complexes5-7 were characterized. Even cyclic bisimidazolium
salts reacted with Ag2O to give interesting 2:2 complexes.8 Many
of these Ag-NHC complexes were known as good carbene-
transfer agents, and various metal-NHC complexes have been
synthesized. Among the complexes, the Pd-NHC complexes9
have been extensively studied since the complexes are potentially
useful catalysts for organic synthesis. In contrast to the corre-
sponding Ag-NHC complexes, a limited number of dinuclear Pd
complexes have been reported in the literature.10
’ RESULTS AND DISCUSSION
Synthesis and Structure of the Silver Complexes. The
syntheses of dinuclear Ag complexes are summarized in
Schemes 1 and 2. Thus, the reaction of bis(2,7-bromo-
methyl)naphthalene (1)13 with substituted imidazoles (2a-c)
proceeded smoothly to give the corresponding bisimidazolium
bromides (3a-c) in good yields. It was important to carry out
the reaction in acetonitrile for the synthesis of 3a and 3c: the
solubility of the substituted imidazoles in organic solvents was
low, and the formation of monoimidazolium salt was observed.
On the other hand, the solubility of 2b was sufficiently high, and
the reaction proceeded smoothly in acetone or other common
organic solvents. The bromides (3a and 3c) were converted to
the corresponding hexafluorophosphates. The reactions of bisi-
midazolium bromides (3a and 3b) with Ag2O in the presence of
molecular sieves in CH2Cl214 gave 5a and 5b in moderate yields
(Scheme 2). Though the formation of various isomeric com-
pounds such as 1:1 complex, 2:1 (Ag2(bis-NHC)) complex, 2:2
(Ag2(bis-NHC)2) complex, and other oligomeric (polymeric)
complexes is possible, only the 2:2 complexes were isolated. The
bisimidazolium hexafluorophosphates 4a and 4c were treated
with Ag2O in the presence of a phase-transfer catalyst15 to give
similar 2:2 complexes (6a and 6c). Compound 6a was also
synthesized by the reaction of 5a in the presence of an excess (20
equiv) of KPF6 in CH2Cl2.
We have been interested in the chemistry of metal-bis-NHC
and metal-NHC-oxazoline complexes and synthesized some Pd
complexes with unique structures.11 In this paper we report the
synthesis and structure of new dinuclear silver and palladium
complexes that are connected with 2,7-dimethylnaphthalene-
bridged bis-NHC ligands.11 The catalytic activities of the Pd
complexes were also examined.
Received: September 4, 2010
Published: February 22, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Bisimidazolium Salts
Scheme 2. Synthesis of Dinuclear Silver-Carbene Complexes
Figure 1. Crystal structure of 5a (a) and 6a (b) drawn as thermal
ellipsoid models. Solvent molecules are omitted for clarity.
Table 1. Selected Bond Lengths and Angles for the Silver
Complexes
compound
Ag-C (Å) C-Ag-C (deg) dihedral anglea (deg)
5a
6a
2.09(1)
173.5(4)
174.9(3)
173.9(2)
63
49
70
2.09(1)
2.072(8)
2.102(8)
2.077(4)
2.074(4)
b
[Ag(IPr)2 ]PF6
a The angle between the planes of the two imidazolin-2-ylidene rings.
See ref 18. b Data collected from ref 17.
doublets at 1.11 and 1.09 ppm. The resonance of the methyl
group of the corresponding Ag complex (6a) shifted signifi-
cantly, and the doublets appeared at 1.06 and 0.85 ppm. The
observed high-field shift of the resonance of the methyl group
could be explained in terms of the effect of the other aromatic
ring located close to the methyl group in 6a.
Recrystallization of 5a from acetone/hexane gave a single
crystal, and the X-ray structure is shown in Figure 1a. This
complex consists of a dinuclear Ag2(bis-NHC)22þ cation and a
2-
rather uncommon Ag2Br4 anion,16 and it exists as a trans
isomer. The molecular structure of 6a was also analyzed, and the
crystal structure is shown in Figure 1b. The selected bond
distances and angles of 5a and 6a are compared with structurally
similar complexes, and the results are summarized in Table 1.
The bond angles and the bond distances between the Ag atom
and the adjacent C atoms in 5a and 6a are similar to those of a
mononuclear Ag complex, [Ag(IPr)2]PF6.17 On the other hand,
the dihedral angles18 between the plains of the two imidazolin-2-
ylidene rings (63° for 5a and 49° for 6a) are smaller compared to
the dihedral angle in [Ag(IPr)2]PF6. The observed smaller angles
could be explained in terms of the presence of a less bulky
substituent (naphthylmethyl group, instead of the diisopropyl-
phenyl group) bound to the imidazolin-2-ylidene ring.
1
The structures of the complexes were studied by H NMR
spectroscopy, and the observed spectra were in accordance with
the expected structures of the complexes. For example, the
resonance of the methyl group of 4a appeared as two pairs of
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Scheme 3. Synthesis of Dinuclear Palladium-Carbene Com-
plexes from 6
Scheme 4. Synthesis of Dinuclear Palladium-Carbene Com-
plexes from 5
Figure 2. Crystal structure of Pd complexes 7a (a), 8a (b), and 9b (c)
drawn with thermal ellipsoid models. Solvent molecules are omitted for
clarity.
(8a) by carrying out the reaction of 6a with Pd(cod)Br2-n-
Bu4NBr. On the other hand, the synthesis of the palladium
complexes from 5a turned out to be less successful (Scheme 4).
Thus, the treatment of 5a with Pd(cod)Cl2 and NaI19 resulted in
the formation of a complex mixture. We speculated that the
halogen exchange reaction might cause the decomposition and
used Pd(cod)Br2 for the reaction so that the halogen exchange
reaction is unnecessary, but the formation of a complex mixture
was observed, together with a small amount of 8a. The synthesis
of the corresponding palladium complex from 5b was successful,
and compound 9b was isolated in 71% yield. The successful
synthesis of 9b and the formation of a complex mixture in the
reaction of 5a with palladium complexes could be explained in
terms of the bulkiness of the ligands. In the presence of a bulky
substituent, the formation of the 2:2 (Pd2(bis-NHC)2) complex
would be prevented due to the steric hindrance, and the
oligomerization reaction will proceed preferentially.
The molecular structures of 7a, 8a, and 9b were analyzed by
X-ray diffraction, and the crystal structures are shown in Figure 2.
The selected bond distances and angles of the palladium com-
plexes and a structurally similar palladium complex, [Pd(IPr)2
]Cl220 (14), are summarized in Table 2.
The lengths of the Pd-C bonds were similar to those of 14,
and the effects of the structure of the complexes on the lengths of
the Pd-C bonds were not significant. The C-Pd-C angles
were 175-180°, and all of the complexes analyzed in this study
exist as trans isomers. On the other hand, the dihedral angle
between the two NHC moieties of the Pd complexes were
different from each other. For example, the dihedral angle of
The syntheses of dinuclear palladium complexes were
achieved by the metal exchange reaction of the corresponding
silver complexes. For example, the PdCl2 complex 7a was
prepared by the reaction of 6a with Pd(MeCN)2Cl2 in the
presence of tetraethylammonium chloride in 61% yield
(Scheme 3). The addition of tetraethylammonium chloride is
essential for the isolation of 7a in pure form. We assume that the
supply of the halogen anion from the ammonium salt is
important for the efficient synthesis of 7a. Compound 6c reacted
in a similar manner, and the palladium complex 7c was synthe-
sized. We also succeeded in the synthesis of the PdBr2 complex
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Table 2. Selected Bond Lengths and Angles for the Palladium Complexes
compound
Pd-C (A)
C-Pd-C (deg)
dihedral anglea (deg)
32
Pd-halogen (Å)
7a
2.027(3)
2.030(3)
1.997(8)
2.016(8)
2.031(7)
2.045(7)
2.02(1)
175.7(1)
2.316(1)
8ab
177.3(3)
176.9(3)
176.0(4)
179.0(2)
36
32
24
40
2.439(1)
2.443(1)
2.438(6)
2.6112(6)
2.6058(6)
2.6112(6)
2.299(2)
2.303(2)
9b
2.03(1)
[Pd(IPr)2 ]Cl2c (14)
2.054(4)
2.019(6)
a Ref 18. b Two molecules of 8a are included in the asymmetric unit of the crystal. c Data collected from ref 20.
Table 3. Catalytic Activity of the Pd Complexes for the
Mizoroki-Heck Reaction between 4-Iodoanisole (15) and
Butyl Acrylate (16)
Table 4. Catalytic Activity of the Pd Complexes for the
Mizoroki-Heck Reaction between Aryl Bromides (18a-d)
and 16
entry
Pd cat.
amount (mol %)
time (h)
yield of 17d (%)
entry
Pd cat.
cmpd
R
time (h)
yield of 17 (%)
1
9b
1
2
23
6
94
88
92
93
93
1
2
9b
18a
18b
18c
18d
18a
18b
18d
18a
18b
18c
NO2
17
14
24
24
19
19
24
6
88
92
5
2
3a
0.01
COCH3
H
1
1
1
3
4
7a
7c
1
4
OMe
NO2
18
79
78
trace
94
75
15
5
1
5
7a
7c
a The reagent-grade DMF was used as the solvent, and the reaction was
carried under air.
6
COCH3
OMe
NO2
7
8
7a was smaller than that of 14. The observed smaller angles of 7a
as well as 8a could be explained in terms of the presence of a
smaller substituent (naphthylmethyl group) or the dimeric
structure of the complex. The dihedral angle of 9b was even
smaller compared to that of 14. We assume that the presence of a
less bulky substituent (butyl group) instead of the bulkier IPr
group induced the reduction of the dihedral angle.
Finally, the catalytic activity of the Pd complexes in the
Mizoroki-Heck reaction was examined. We employed the
reaction conditions reported by Roland, Jutand, and co-
workers.21 Thus, the aryl halide and butyl acrylate (16) were
reacted in the presence of the Pd complex, sodium formate, and
diisopropylethylamine in DMF. The results are summarized in
Tables 3 and 4.
4-Methoxy-1-iodobenzene (15) reacted with 16 in the pre-
sence of 9b (1 mol %) at 80 °C for 2 h, and the coupling product
(17d) was isolated in 94% yield (Table 3, entry 1). The reaction
proceeded even when the amount of 9b was reduced to 0.01 mol
%, and compound 17d was isolated in 88% yield after heating the
reaction mixture for 23 h (entry 2). In this reaction, the turnover
number (TON) reached 8800, which is comparable to the TON
9
COCH3
H
5
10
24
(14 600, 73% conversion in the reaction of iodobenzene with
butyl acrylate) reported by Roland, Jutand, and co-workers.21
The product was isolated in 92% yield when the reaction was
carried under air and reagent-grade DMF was used; however, the
catalytic activity of 9b decreased and a longer reaction time was
required (entry 3). Other Pd complexes such as 7a and 7c were
efficient catalysts for this reaction (entries 4 and 5).
We also examined the Mizoroki-Heck reaction of aryl
bromides (Table 4). The reactions of electron-deficient aryl
bromides such as 1-bromo-4-nitrobenzene (18a) or 4-nitroben-
zophenone (18b) with 16 proceeded smoothly in the presence of
1 mol % of 9b at 120 °C, and the products were isolated in high
yields (entries 1 and 2). Bromobenzene (18c) and 4-bromoani-
sole (18d) turned out to be inferior substrates for this reaction,
and the yields of the product were very low even when the
reaction mixture was heated for 24 h (entries 3 and 4). The
catalytic activity of 7a was lower compared to that of 9b, and the
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yields of the coupling products slightly decreased (entries 5 and
6). The reactivity of 4-bromoanisole (18d) turned out to be very
low when the reaction was carried out in the presence of 7a, and
only a trace amount of the product was isolated (entry 7).
Meanwhile, the catalytic activity of 7c was much higher com-
pared to other complexes: the reaction of 18a completed in 6 h
and the product was isolated in 94% yield (entry 8). The reaction
of 18b also proceeded smoothly (entry 9). The reaction of 18c
was, however, sluggish, and the yield of 17d was low (entry 10).
In our study, the Pd complex with the ICy-type ligand (N-
cyclohexylimidazolidene ligand, i.e., 7c) turned out to be a better
catalyst compared to the Pd complex with the IPr ligand or the N-
butylimidazolidene ligand (9b or 7a). The result is in contrast to
the generally observed high reactivity of the Pd-IPr complex for
various reactions.9c The reason for the high catalytic activity of 7c
is not clear at present.
(quint, J = 7.2 Hz, 4H), 1.25 (sext, J = 7.2 Hz, 4H), 0.88 (t, J = 7.2 Hz,
6H); 13C NMR (150 MHz, DMSO-d6) δ 136.5, 133.3, 132.7, 129.0,
127.9, 126.7, 123.1, 122.9, 52.2, 49.0, 31.5, 19.0, 13.5 (2-imidazolium-
CH was not observed); IR (KBr) 3422, 3128, 3062, 2959, 2872, 2407,
2056, 1742, 1610, 1560, 1515, 1459, 1358, 1156, 1022, 948, 920, 855,
743, 630, 554, 475; HRMS-ESI (m/z) [M - Br]þ calcd for
C26H34BrN4, 481.1961; found, 481.1985.
[2,7-Bis(2-N-cyclohexyl)imidazolinium]methyl] Bromide, [Napht-
Cy2]-Br2 (3c). The crude product was purified by silica gel chromatog-
raphy to give a very hygroscopic yellow, amorphous solid: 1H NMR (600
MHz, DMSO-d6) δ 9.62 (s, 2H), 8.01 (s, 2H) 8.00 (d, J = 8.4 Hz, 2H),
7.97 (s, 2H), 7.92 (s, 2H), 7.63 (dd, J = 9.0, 1.2 Hz, 2H), 5.64 (s, 4H),
4.32 (tt, J = 12.0, 3.6 Hz, 2H), 2.07 (d, J = 10.8 Hz, 4H), 1.81 (d, J = 13.8
Hz, 4H), 1.71-1.63 (m, 6H), 1.37 (qt, J = 12.6, 3.6 Hz, 4H), 1.20 (qt, J =
13.2, 3.6 Hz, 2H); 13C NMR (150 MHz, DMSO-d6) δ 135.3, 133.3,
132.6, 128.9, 128.0, 126.8, 122.7, 121.4, 58.9, 52.7, 32.6, 24.6, 24.5 (2-
imidazolium-CH was not observed); IR (KBr) 3418, 3127, 3063, 2933,
2856, 2365, 2053, 1634, 1556, 1510, 1449, 1363, 1269, 1241, 1154, 1028,
989, 924, 897, 854, 750, 650, 628, 471, 441, 411; HRMS-ESI (m/z)
[M - Br]þ calcd for C30H38BrN4, 533.2274; found, 533.2269.
General Procedure for the Synthesis of the Bis-imidazo-
lium Hexafluorophosphosphates (Scheme 1, 4a and 4c).
The imidazolium salt 3 (1 mmol) was dissolved in a mixture of water (5
mL) and acetone (5 mL), and then potassium hexafluorophosphate
(0.55 g, 3 mmol) was added. The reaction mixture was stirred at rt for 3 h
and monitored by TLC. The acetone was evaporated under reduced
pressure, and the water layer was extracted with CH2Cl2 (3 ꢀ 10 mL).
The combined organic layer was washed three times with water (3 ꢀ 10
mL) and dried over Na2SO4. The solvent was removed in vacuo to give
hexafluorophosphate salt 4.
[2,7-Bis(2-N-(2,6-diisopropylphenyl)imidazolinium)methyl] Hexa-
fluorophosphate, [Napht-Ipr2]-2PF6 (4a): colorless solid; mp 289.0-
289.9 °C; 1H NMR (600 MHz, DMSO-d6) δ 9.75 (s, 2H), 8.15 (dt, J =
13.2, 1.2 Hz 4H), 8.07 (d, J = 8.4 Hz, 2H), 7.97 (s, 2H), 7.62 (t, J = 7.8
Hz, 2H), 7.58 (d, J = 8.4 Hz, 2H), 7.44 (d, J = 7.8 Hz, 4H), 5.74 (s, 4H),
2.23 (sept, J = 6.0 Hz, 4H), 1.11 (dd, J = 10.8, 6.6 Hz, 24H); 13C NMR
(75 MHz, DMSO-d6) δ 145.2, 138.3, 133.3, 132.7, 131.7, 130.7, 129.2,
127.8, 126.3, 125.7, 124.6, 124.6, 123.8, 52.9 28.3, 24.0, 23.8; IR (KBr)
3154, 3094, 3080, 2968, 2931, 2874, 2360, 2342, 1616, 1548, 1458, 1416,
1368, 1184, 1107, 1071, 840, 740, 671, 627, 558, 457. Anal. Calcd for
C42H50F12N4P2: C, 56.00; H, 5.59; N, 6.22. Found: C, 55.70; H, 5.37;
N, 6.14.
’ CONCLUSION
We synthesized a series of new Ag2(bis-NHC)2 complexes
from the corresponding bisimidazolium salts tethered with a rigid
linker that contains the naphthalene moiety. The reaction
proceeded in a selective manner, and the Ag2(bis-NHC)2 com-
plexes were isolated in good to high yields. The Ag complexes
were converted to the Pd2(bis-NHC)2 complexes efficiently. The
structures of the complexes were elucidated and compared with
the corresponding monodentate NHC complexes. The catalytic
activity of the Pd complexes for the Mizoroki-Heck reaction was
examined. The study revealed that the bisimidazolium salts
connected with the rigid 2,7-bis(methylene)naphthalene moiety
are useful precursors for the synthesis of (metal)2(bis-NHC)2
complexes.
’ EXPERIMENTAL SECTION
General Procedure for the Synthesis of the Bis-imidazo-
lium Bromide Salts (Scheme 1, 3a-c). To a stirred solution of
2,7-bis(bromomethyl)naphthalene (1) (1.0 mmol) in solvent (acetone
(4 mL, for 3b) or acetonitrile (12 mL, for 3a and 3c)) was added
1-substituted-imidazole (2a-c) (2.1 mmol). After the mixture was
refluxed for 3-16 h, the resulting precipitate was separated and washed
by Et2O. The collected solid was purified by recrystallization or silica gel
column chromatography (MeOH/CH2Cl2, 10:1).
[2,7-Bis(2-N-(2,6-diisopropylphenyl)imidazolinium)methyl] Bro-
mide, [Napht-Ipr2]-Br2 (3a). The crude product was purified by
recrystallization (CH2Cl2/Et2O) to give a colorless solid: mp 194.0-
197.0 °C; 1H NMR (300 MHz, CDCl3) δ 10.49 (s, 2H) 8.28 (s, 2H),
8.14 (s, 2H) 7.65 (d, J = 8.4 Hz, 2H), 7.50-7.43 (m, 4H), 7.26-7.23 (m,
4H), 7.11 (s, 2H), 6.23 (s, 4H), 2.20 (quint, J = 6.9 Hz, 4H), 1.18 (d, J =
6.6 Hz, 12 H), 1.08 (d, J = 6.6 Hz, 12H); 13C NMR (150 MHz, CDCl3)
δ 145.3, 137.5, 132.8, 132.6, 131.9, 131.7, 130.2, 129.6, 128.7, 126.3,
124.6, 124.2, 124.1, 52.7, 28.6, 24.5, 23.9; IR (KBr) 3465, 2958, 2742,
2471, 2374, 2074, 1717, 1640, 1560, 1540, 1513, 1458, 1415, 1387, 1367,
1336, 1309, 1278, 1256, 1242, 1188, 1147, 1116, 1070, 1042, 1022, 957,
936, 857, 807, 760, 673, 631, 576, 558, 526, 499, 470; HRMS-ESI (m/z)
[M - Br]þ calcd for C42H50BrN4, 689.3213; found, 689.3232.
[2,7-Bis(2-N-cyclohexyl)imidazolinium]methyl]
Hexafluoropho-
sphate, [Napht-Cy2]-2PF6 (4c): colorless solid; mp 206.0 °C-
1
209.2 °C; H NMR (600 MHz, DMSO-d6) δ 9.37 (s, 2H), 8.00 (d,
J = 8.4 Hz, 2H) 7.93 (d, J = 12.6 Hz 4H), 7.83 (s, 2H), 7.58 (d, J = 9.0 Hz,
2H), 5.57 (s, 4H), 4.29 (tt, J = 12.0, 3.6 Hz, 2H), 2.07 (d, J = 12.6 Hz,
4H), 1.83 (d, J = 13.2 Hz, 4H), 1.70-1.65 (m, 6H), 1.37 (qt, J = 13.2,
3.6, 4H), 1.19 (qt, J = 13.2, 3.6, 2H); 13C NMR (75 MHz, DMSO-d6) δ
135.3, 133.2, 132.7, 129.0, 127.9, 126.8, 122.8, 121.5, 59.0, 52.3, 32.6,
24.7, 24.6 (2-imidazolium-CH was not observed); IR (KBr) 3674, 3396,
3168, 3108, 2930, 2860, 2671, 1557, 1454, 1348, 1270, 1177, 1154, 1109,
1025, 992, 843, 779, 738, 704, 650, 629, 558, 479, 419. Anal. Calcd for
C30H38F12N4P2: C, 48.39; H, 5.14; N, 7.52. Found: C, 48.60; H, 5.13;
N, 7.40.
Synthesis of Dinuclear Silver-Carbene Complexes
(Scheme 2). General Procedure for Synthesis of Dinuclear Silver-
Carbene Complex Ag2Br3 Salts (5a,b). A mixture of CH2Cl2 (40 mL),
imidazolium salt (Br-) 3 (1 mmol), 4 Å molecular sieves (2 g), and
silver(I) oxide (1.5 mmol) was stirred vigorously in the dark at rt for
24 h. The reaction was monitored by 1H NMR. After filteration through
Celite, the filtrate was evaporated to give the crude product. The crude
product was purified by recrystallization (CH2Cl2/Et2O) to afford
Ag(Ag2Br42-) complexes 5.
[2,7-Bis(2-N-n-butyl)imidazolinium]methyl] Bromide, [Napht-n-
Bu2]-Br2 (3b). The crude product was dissolved in CH2Cl2 (1 mL),
and Et2O (16 mL) was added to the solution to give a brown, gummy
solid, which was washed by Et2O and dried to give a very hygroscopic
1
yellow, amorphous solid: H NMR (600 MHz, DMSO-d6) δ 9.42 (s,
2H), 8.00 (d, J = 9.0 Hz, 2H), 7.97 (s, 2H), 7.85 (d, J = 13.2 Hz, 4H),
7.58 (d, J = 8.4 Hz, 2H), 5.62 (s, 4H), 4.18 (t, J = 7.2 Hz, 4H), 1.77
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[Napht-Ipr2]2Ag2-Ag2Br4 (5a): colorless solid; yield 57% (0.440 g);
mp 241.5-242.5 °C; H NMR (300 MHz, CDCl3) δ 7.90-7.84 (m,
the mixture was filtered through Celite and the volatiles were removed
under vacuum to give the crude product. The crude product was passed
through short silica gel column and purified by recrystallization.
[Napht-Ipr2]2Pd2-Cl4 (7a). This compound was prepared following
the general procedure from complex 6a (86 mg, 0.05 mmol), Pd-
(MeCN)2Cl2 (31 mg, 0.12 mmol), and Et4NCl (25 mg, 0.15 mmol) in
CH2Cl2 (80 mL). The product was purified by recrystallization (acetone/
hexane). Pale yellow solid: yield 73% (58.3 mg); mp 280 °C (dec);
1H NMR (500 MHz, CDCl3) δ 7.68 (d, J = 8.5 Hz, 4H), 7.59 (s, 4H),
7.35 (t, J = 7.5 Hz, 4H), 7.10 (d, J = 7.5 Hz, 12H), 6.71 (d, J = 1.5 Hz,
4H), 6.67 (d, J = 1.5 Hz, 4H), 5.62 (s, 8H), 2.70 (quint, J = 6.5 Hz, 8H),
0.96 (d, J = 6.5 Hz, 24H), 0.90-0.89 (d, J = 7.0 Hz, 24H); 13C NMR
(150 MHz, CDCl3) δ 172.0, 146.3, 135.1, 134.0, 132.6, 132.1, 129,4,
128.2, 126.6, 126.0, 124.1, 123.6, 120.6, 54.0, 28.1, 26.3, 22.9; IR (KBr)
3452, 3169, 3138, 3066, 2965, 2922, 2868, 2365, 1938, 1638, 1514, 1458,
1417, 1385, 1364, 1292, 1251, 1222, 1180, 1120, 1060, 958, 936, 899, 840,
802, 757, 730, 703, 667, 632, 607, 590, 577, 547, 539, 529, 517, 500, 470, 463,
440, 410; HRMS-ESI (m/z) [M þ Na]þ calcd for for C84H96Cl4N8Pd2Na,
1591.4494; found, 1591.4458. Anal. Calcd for C84H96Cl4N8Pd2: C, 64.16; H,
6.15; N, 7.13. Found: C, 63.99; H, 6.20; N, 7.12.
1
8H), 7.48-7.39 (m, 8H), 7.25-7.20 (m, 12H), 7.01 (s, 4H), 5.58 (s,
8H), 2.39 (quant, J = 5.7 Hz, 8H), 1.24 (d, J = 6.6 Hz, 24H), 1.11 (d, J =
6.9 Hz, 24H); 13C NMR (150 MHz, CDCl3) δ 145.6, 134.6, 133.8,
130.6, 129.3, 127.7, 125.7, 124.3, 121.1, 56.0, 28.4, 24.7, 24.3 (carbene-C
and four aromatic C were not observed: at higher concentration, the
broadening of the signals was observed); IR (KBr) 3482, 3155, 3124,
3077, 2965, 2922, 2869, 2597, 2360, 1536, 1514, 1472, 1416, 1385, 1362,
1317, 1249, 1225, 1181, 1105, 1058, 1032, 959, 939, 902, 839, 806, 757,
628, 470, 433, 419. Anal. Calcd for C84H96Ag4Br4N8: C, 51.24; H, 4.91;
N, 5.69. Found: C, 51.18; H, 4.89; N, 5.54.
[Napht-n-Bu2]2Ag2-Ag2Br4 (5b): colorless solid; yield 67% (0.520
g); mp 102.2-105.0 °C; 1H NMR (300 MHz, CDCl3) δ 7.78 (d, J = 8.4
Hz, 4H), 7.72 (s, 4H), 7.31 (dd, J = 8.4, 1.8 Hz, 4H), 7.03 (d, J = 1.8 Hz,
4H), 6.98 (d, J = 1.5 Hz, 4H), 5.37 (s, 8H), 4.09 (t, J = 6.9 Hz, 8H), 1.78
(quint, J = 7.5 Hz, 8H), 1.33 (quint, J = 7.5 Hz, 8H), 0.93 (t, J = 7.2 Hz,
12H); 13C NMR (150 MHz, CDCl3) δ 181.2, 133.9, 133.0, 132.8, 129.0,
127.5, 125.9, 121.4, 121.3, 55.7, 52.0, 33.4, 19.7, 13.7; IR (KBr) 3469,
3145, 3117, 3092, 2955, 2922, 2868, 2370, 2328, 1684, 1636, 1559, 1515,
1457, 1417, 1373, 1229, 1180, 1104, 962, 845, 737, 666, 500, 470, 458.
Anal. Calcd for C52H64Ag4Br4N8: C, 40.24; H, 4.16; N, 7.22. Found: C,
40.15; H, 4.20; N, 7.09.
General Procedure for Synthesis of Dinuclear Silver-Carbene Com-
plex Hexafluorophosphate Salts (6a, 6c). Ag2O (0.75 mmol) and n-
Bu4NPF6 (5 μmol) were added to a solution of the imidazolium
hexafluorophosphate 4 (0.5 mmol) in CH2Cl2 (50 mL). The mixture
was stirred for 26-41 h under dark conditions after addition of
NaOH(aq) (1 M, 3 mL). The reaction was monitored by TLC and
1H NMR. The mixture was filtered through Celite, and the filtrate was
evaporated to give the crude product. The product was further purified
by recrystallization (CH2Cl2/Et2O).
[Napht-n-Bu2]2Ag2-2PF6 (6a): colorless solid; yield 84% (0.319 g);
mp >300 °C; 1H NMR (300 MHz, DMSO-d6) δ 7.81 (d, J = 8.7 Hz,
4H), 7.63 (s, 8H), 7.48 (t, J = 7.5 Hz, 4H), 7.23 (d, J = 7.8 Hz, 8H), 7.15
(s, 4H), 7.01 (d, J = 8.7 Hz, 4H), 4.95 (s, 8H), 2.17 (quint, J = 6.9 Hz,
8H), 1.06 (d, J = 6.9 Hz, 24H), 0.85 (d, J = 6.9 Hz, 24H); 13C NMR (75
MHz, DMSO-d6) δ 181.1 (dd, JC-107Ag = 181 Hz, JC-109Ag = 211 Hz),
145.2, 135.3, 134.6, 132.2, 131.8, 130.5, 128.6, 125.5, 125.4, 125.0, 124.9,
123.3, 53.5, 28.1, 24.7, 23.6; IR (KBr) 3170, 2964, 2931, 2871, 1640,
1559, 1508, 1473, 1417, 1386, 1364, 1316, 1252, 1183, 1105, 1059, 959,
843, 760, 689, 623, 557, 472. Anal. Calcd for C84H96Ag2F12N8P2: C,
58.54; H, 5.61; N, 6.50. Found: C, 58.25; H, 5.54; N, 6.36.
[Napht-Cy2]2Pd2-Cl4 (7c). Complex 6c (0.28 g, 0.2 mmol), Pd-
(MeCN)2Cl2 (0.12 g, 0.48 mmol), and Et4NCl (0.10 g, 0.60 mmol)
in CH2Cl2 (320 mL). were used to prepare this complex following
the general procedure. The product was purified by recrystalliza-
tion (CHCl3/hexane). Pale yellow solid: yield 79% (0.199 g); mp
1
>300 °C; H NMR (600 MHz, CDCl3) δ 7.55 (d, J = 8.4 Hz, 4H),
7.43 (s, 4H), 7.09 (d, J = 8.4 Hz, 4H), 6.84 (d, J = 1.2 Hz, 4H), 6.62 (d, J =
1.8 Hz, 4H), 5.38 (s, 8H), 5.29-5.30 (m(br), 4H), 2.47-2.48 (m, 8H),
1.95-1.97 (m, 8H), 1.80 (d, J = 7.8 Hz, 4H), 1.47-1.63 (m, 16H),
1.24-1.28 (m, 4H); 13C NMR (150 MHz, CDCl3) δ 170.0, 134.3,
132.6, 132.1, 128.1, 126.2, 125.7, 121.2, 117.0, 59.9, 53.7, 34.1, 25.9,
25.5; IR (KBr) 3471, 3122, 3089, 2933, 2854, 2676, 2365, 2328, 1636,
1559, 1516, 1452, 1425, 1379, 1224, 1182, 990, 894, 840, 819, 728, 697,
668, 629, 577, 569, 560, 530, 518, 507, 500, 488, 480, 470, 459, 440, 430,
422. Anal. Calcd for C60H72Cl4N8Pd2: C, 57.20; H, 5.76; N, 8.89.
Found: C, 56.92; H, 5.65; N, 8.67.
[Napht-Ipr2]2Pd2-Br4 (8a). This compound was prepared from
complex 6a (43 mg, 0.025 mmol), Pd(cod)Br2 (19 mg, 0.05 mmol),
and n-Bu4NBr (16 mg, 0.05 mmol) following the general procedure.
X-ray diffraction quality crystals were obtained by layering an acetone
solution with hexane. Pale yellow solid: yield 35% (15.6 mg); mp 272.0-
275.0 °C; 1H NMR (500 MHz, CDCl3) δ 7.70 (s, 4H), 7.63 (d, J = 8.0 Hz,
4H), 7.34 (t, J = 7.5 Hz, 4H), 7.12 (d, J = 8.5 Hz, 4H), 7.08 (d, J = 8.0 Hz,
8H), 6.71 (d, J = 2.0 Hz, 4H), 6.70 (d, J = 2.0 Hz, 4H), 5.65 (s, 8H), 2.81
(quint, J = 6.5 Hz, 8H), 0.96 (d, J = 7.0 Hz, 24H), 0.88 (d, J = 6.5 Hz, 24H);
13C NMR (150 MHz, CDCl3) δ 171.3, 146.6, 135.2, 133.7, 132.6, 132.2,
129.4, 128.2, 127.1, 126.3, 124.6, 123.7, 120.7, 54.7, 28.2, 26.4, 23.1; IR (KBr)
3429, 3136, 3061, 3029, 2963, 2928, 2867, 2372, 1702, 1637, 1562, 1543,
1518, 1508, 1467, 1415, 1384, 1362, 1291, 1249, 1214, 1180, 1121, 1098,
1059, 959, 932, 842, 802, 758, 727, 702, 628, 473, 419; HRMS-ESI (m/z)
[M - Br]þ calcd for C84H96Br3N3Pd2, 1667.3385; found, 1667.3328. Anal.
[Napht-Cy2]2Ag2-2PF6 (6c): colorless solid; yield 76% (0.268 g);
mp 203.5-208.2 °C; 1H NMR (300 MHz, DMSO-d6) δ 7.83 (d, J = 9.0
Hz, 4H), 7.57 (m, 8H), 7.31 (s, 8H), 5.15 (s, 8H), 4.13 (t, J = 11 Hz,
4H), 1.82-1.53 (m, 28H), 1.16-1.04 (m, 12H); 13C NMR (150 MHz,
DMSO-d6) δ 178.4, 135.8, 132.3, 131.8, 128.4, 125.7, 125.3, 122.3,
119.9, 60.8, 53.9, 34.0, 25.0, 24.5; IR (KBr) 3447, 3173, 3150, 3048,
2934, 2857, 2667, 2363, 2344, 2335, 2324, 1616, 1515, 1449, 1421, 1242,
1181, 1114, 1037, 989, 837, 740, 668, 559. Anal. Calcd for
C60H72Ag2F12N8P2: C, 51.08; H, 5.14; N, 7.94. Found: C, 50.79; H,
5.11; N, 7.83.
Calcd for C84H102Br4N8O3Pd2 (8a 3H2O): C, 55.81; H, 5.75; N, 5.96.
3
Found: C, 55.92; H, 5.70; N, 6.21.
Synthesis of Dinuclear Silver-Carbene Complex Hexa-
fluorophosphate Salt (6a) from 5a (Scheme 2). Compound
5a (0.488 g, 0.25 mmol) was suspended in CH2Cl2 (60 mL), and KPF6
(0.92 g, 5 mmol) was addded in one portion. After being stirred
overnight, the bluish mixture was filtered through Celite and evaporated.
A quantitative amount of 6a was obtained.
General Procedure for Synthesis of Dinuclear Palladium-
Carbene Complexes (Scheme 3). A dry CH2Cl2 solution of
complex 6, Pd complex [Pd(MeCN)2Cl2 or Pd(cod)Br2], and ammo-
nium salt (n-Bu4NBr or Et4NCl) was stirred at rt for 7-11 h under Ar.
The reaction was monitored by TLC. After completion of the reaction,
Synthesis of Dinuclear Palladium-Carbene Complexes
(Scheme 4). [Napht-n-Bu2]2Pd2-I4 (9b). A dry CH2Cl2 (40 mL)
solution of complex 5b (78 mg, 0.05 mmol) and Pd(cod)Cl2 (29 mg, 0.1
mmol) was stirred at rt for 24 h under Ar. The reaction was monitored by
TLC and 1H NMR. After completion of the reaction, the mixture was
filtrated through Celite and the volatiles were removed under vacuum.
The remaining solid was washed with Et2O and dried under vacuum.
The resulting solid and NaI (150 mg, 1 mmol) in CH2Cl2 (10 mL) were
stirred for 24 h at rt, then filtered through Celite and evaporated to give
the crude product. The crude product was purified by recrystallization
(CH2Cl2/hexane). X-ray diffraction quality crystals were obtained from
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Organometallics
ARTICLE
a CH2Cl2 solution after the Pd complex was dissolved in CH2Cl2 and
then kept at rt. Pale yellow solid: yield 71% (55 mg); mp 277.0-
282.0 °C; 1H NMR (300 MHz, CDCl3) δ 7.54 (s, 4H), 7.51 (d, J = 7.8
Hz, 4H), 7.08 (dd, J = 1.2, 8.1 Hz, 4H), 6.83 (d, J = 1.8 Hz, 4H), 6.65 (d, J
= 1.8 Hz, 4H), 5.24 (s, 8H), 4.38 (t, J = 7.8 Hz, 8H), 2.02 (quint, J = 7.5
Hz, 8H), 1.43 (quint, J = 7.5 Hz, 8H), 0.99 (d, J = 7.2 Hz, 12H); 13C
NMR (150 MHz, CDCl3) δ 167.9, 133.5, 132.5, 132.2, 128.3, 127.0,
126.6, 121.9, 121.0, 54.9, 51.7, 32.2, 20.1, 13.7; IR (KBr) 3447, 3161,
3126, 2958, 2928, 2869, 2369, 1637, 1560, 1543, 1517, 1459, 1417, 1375,
1309, 1224, 1177, 1129, 1031, 963, 898, 850, 796, 756, 722, 696, 473.
Anal. Calcd for C52H64I4N8Pd2: C, 41.05; H, 4.24; N, 7.36. Found: C,
41.26; H, 4.30; N, 7.07.
General Procedure for the Mizoroki-Heck Reaction
(Tables 3 and 4). To a solution of the Pd complex in dry DMF
(2.5 mL) were added aryl halide (1 mmol), sodium formate (6.8 mg, 0.1
mmol), i-Pr2NEt (0.19 mL, 1.1 mmol), and n-butyl acrylate (0.2 mL, 1.4
mmol) under an argon atmosphere. After being heated at the indicated
temperature for the specified period, the reaction mixture was cooled to
rt. The solution was diluted with CH2Cl2 and washed with water three
times. The organic layer was dried over Mg2SO4 and evaporated. The
residue was purified by silica gel chromatography (CH2Cl2/hexane).
Anderson, K. M.; Paterson, M. J.; Junk, P. C.; Barbour, L. J.; Steed,
J. W. Eur. J. Inorg. Chem. 2009, 2009, 2835–2843. (e) Pugh, D.; Boyle, A.;
Danopoulos, A. A. Dalton Trans. 2008, 1087–1094. (f) Jean-Baptiste dit
Dominique, F.; Gornitzka, H.; Hemmert, C. J. Organomet. Chem. 2008,
693, 579–583. (g) Liu, A.; Zhang, X.; Chen, W.; Qiu, H. Inorg. Chem.
Commun. 2008, 11, 1128–1131. (h) Papini, G.; Bandoli, G.; Dolmella,
A.; Lobbia, G. G.; Pellei, M.; Santini, C. Inorg. Chem. Commun. 2008,
11, 1103–1106. (i) Nielsen, D. J.; Cavell, K. J.; Skelton, B. W.; White,
A. H. Organometallics 2006, 25, 4850–4856. (j) Wang, D.-Q. Acta
Crystallogr. E 2006, 62, m1565–m1566. (k) Wang, J.-W.; Song, H.-B.;
Li, Q.-S.; Xu, F.-B.; Zhang, Z.-Z. Inorg. Chim. Acta 2005,
358, 3653–3658. (l) Qin, D.; Zeng, X.; Li, Q.; Xu, F.; Song, H.; Zhang,
Z.-Z. Chem. Commun. 2007, 147–149. (m) Wan, X. J.; Xu, F. B.; Li, Q. S.;
Song, H. B.; Zhang, Z. Z. Organometallics 2005, 24, 6066–6068. (n)
Nielsen, D. J.; Cavell, K. J.; Viciu, M. S.; Nolan, S. P.; Skelton, B. W.;
White, A. H. J. Organomet. Chem. 2005, 690, 6133–6142.
(6) For polymeric 2:2 complexes, see: (a) Chiu, P. L.; Chen, C. Y.;
Zeng, J. Y.; Lu, C. Y.; Lee, H. M. J. Organomet. Chem. 2005,
690, 1682–1687. (b) Lee, K. M.; Wang, H. M. J.; Lin, I. J. B. J. Chem.
Soc., Dalton Trans. 2002, 2852–2856.
(7) For tripodal NHC complexes, see: (a) Wang, D.; Zhang, B.; He,
C.; Wu, P.; Duan, C. Chem. Commun. 2010, 46, 4728–4730. (b) Hu, X.;
Tang, Y.; Gantzel, P.; Meyer, K. Organometallics 2003, 22, 612–614.
(8) (a) Hahn, F. E.; Radloff, C.; Pape, T.; Hepp, A. Chem.—Eur. J.
2008, 14, 10900–10904. (b) Melaiye, A.; Sun, Z.; Hindi, K.; Milsted, A.;
Ely, D.; Reneker, D. H.; Tessier, C. A.; Youngs, W. J. J. Am. Chem. Soc.
2005, 127, 2285–2291. (c) Baker, M. V.; Brown, D. H.; Haque, R. A.;
Skelton, B. W.; White, A. H. Dalton Trans. 2004, 3756–3764.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures,
b
characterization data, copies of NMR spectra, and X-ray analysis
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
(9) Reviews: Díez-Gonzꢀalez, S.; Marion, N.; Nolan, S. P. Chem. Rev.
2009, 109, 3612–3676. Organ, M. G.; Chass, G. A.; Fang, D.-C.;
Hopkinson, A. C.; Valente, C. Synthesis 2008, 2008, 2776–2797. (a)
Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2008, 2781–2800.
(b) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008,
47, 3122–3172. (c) W€urtz, S.; Glorius, F. Acc. Chem. Res. 2008,
41, 1523–1533. (d) Marion, N.; Nolan, S. P. Acc. Chem. Res. 2008,
41, 1440–1449. (e) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G.
Angew. Chem., Int. Ed. 2007, 46, 2768–2813. (f) Díez-Gonzꢀalez, S.;
Nolan, S. Top. Organomet. Chem. 2007, 21, 47–82. (g) Kantchev,
E. A. B.; O’Brien, C. J.; Organ, M. G. Aldrichim. Acta 2006,
39, 97–111. (h) Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004,
248, 2239–2246. (i) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: þ81-3-5228-8715. E-mail: ssaito@rs.kagu.tus.ac.jp.
’ REFERENCES
(1) Reviews: (a) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009,
109, 3677–3707. (b) Lin, J. C. Y.; Huang, R. T. W.; Lee, C. S.;
Bhattacharyya, A.; Hwang, W. S.; Lin, I. J. B. Chem. Rev. 2009,
109, 3561–3598. (c) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev.
2007, 251, 642–670. (d) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005,
105, 3978–4008. (e) Lin, I. J. B.; Vasam, C. S. Comments Inorg. Chem.
2004, 25, 75–129. (f) Polly, L. A. Heteroat. Chem. 2002, 13, 534–539.
(2) (a) Wang, J.-W.; Li, Q.-S.; Xu, F.-B.; Song, H.-B.; Zhang, Z.-Z.
Eur. J. Org. Chem. 2006, 2006, 1310–1316. (b) Wan, X.-J.; Xu, F.-B.; Li,
Q.-S.; Song, H.-B.; Zhang, Z.-Z. Inorg. Chem. Commun. 2005,
8, 1053–1055. (c) Perry, M. C.; Cui, X.; Burgess, K. Tetrahedron:
Asymmetry 2002, 13, 1969–1972.
(3) (a) Nielsen, D. J.; Cavell, K. J.; Skelton, B. W.; White, A. H. Inorg.
Chim. Acta 2006, 359, 1855–1869. (b) Simons, R. S.; Custer, P.; Tessier,
C. A.; Youngs, W. J. Organometallics 2003, 22, 1979–1982. (c) Bonnet,
L. G.; Douthwaite, R. E.; Hodgson, R. Organometallics 2003,
22, 4384–4386. (d) Douthwaite, R. E.; Houghton, J.; Kariuki, B. M.
Chem. Commun. 2004, 698–699. (e) Nielsen, D. J.; Cavell, K. J.; Skelton,
B. W.; White, A. H. Inorg. Chim. Acta 2002, 327, 116–125. (f) Chen, W.;
Wu, B.; Matsumoto, K. J. Organomet. Chem. 2002, 654, 233–236.
(4) For polymeric 2:1 complexes, see: (a) Edworthy, I. S.; Rodden,
M.; Mungur, S. A.; Davis, K. M.; Blake, A. J.; Wilson, C.; Schr€oder, M.;
Arnold, P. L. J. Organomet. Chem. 2005, 690, 5710–5719. (b) Melaiye,
A.; Simons, R. S.; Milsted, A.; Pingitore, F.; Wesdemiotis, C.; Tessier,
C. A.; Youngs, W. J. J. Med. Chem. 2004, 47, 973–977.
€
2004, 248, 2247–2273. (j) Herrmann, W. A.; Ofele, K.; v. Preysing, D.;
Schneider, S. K. J. Organomet. Chem. 2003, 687, 229–248. (k) Hillier,
A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H. M.; Yang, C.; Nolan, S. P. J.
Organomet. Chem. 2002, 653, 69–82. (l) Herrmann, W. A. Angew. Chem.,
Int. Ed. 2002, 41, 1290–1309.
(10) For Pd2(bis-NHC)2 complexes, see: Houghton, J.; Dyson, G.;
Douthwaite, R. E.; Whitwood, A. C.; Kariuki, B. M. Dalton Trans.
2007, 3065–3073, and ref 5d.
(11) (a) Makino, T.; Masu, H.; Katagiri, K.; Yamasaki, R.; Azumaya,
I.; Saito, S. Eur. J. Inorg. Chem. 2008, 4861–4865. (b) Saito, S.;
Yamaguchi, H.; Muto, H.; Makino, T. Tetrahedron Lett. 2007,
48, 7498–7501.
(12) For a previous study that reported the synthesis of naphthalene-
bridged bis-NHC ligands, see: Wong, W. W. H.; Phipps, D. E.; Beer,
P. D. Polyhedron 2004, 23, 2821–2829.
(13) Terfort, A.; G€orls, H.; Brunner, H. Synthesis 1997, 1997, 79–86.
(14) (a) Tulloch, A. A. D.; Danopoulos, A. A.; Winston, S.;
Kleinhenz, S.; Eastham, G. J. Chem. Soc., Dalton Trans.
2000, 4499–4506. (b) Danopoulos, A. A.; Tulloch, A. A. D.; Winston,
S.; Eastham, G.; Hursthouse, M. B. Dalton Trans. 2003, 1009–1015.
(15) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972–975.
(16) (a) Busetto, L.; Cristina Cassani, M.; Femoni, C.; Macchioni,
A.; Mazzoni, R.; Zuccaccia, D. J. Organomet. Chem. 2008,
693, 2579–2591. (b) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton,
B. W.; White, A. H. Dalton Trans. 2004, 3756–3764. (c) Chen, W.; Liu,
F. J. Organomet. Chem. 2003, 673, 5–12. (d) Helgesson, G.; Jagner, S. J.
Chem. Soc., Dalton Trans. 1990, 2413–2420.
(5) Recent examples: (a) Brown, D. H.; Nealon, G. L.; Simpson,
P. V.; Skelton, B. W.; Wang, Z. Organometallics 2009, 28, 1965–1968.
(b) Liu, A.; Zhang, X.; Chen, W. Organometallics 2009, 28, 4868–4871.
(c) Baker, M.; Brown, D.; Haque, R.; Skelton, B.; White, A. J. Incl.
Phenom. Macrocycl. Chem. 2009, 65, 97–109. (d) Willans, C. E.;
1372
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Organometallics
ARTICLE
(17) Yu, X.-Y.; Patrick, B. O.; James, B. R. Organometallics 2006,
25, 2359–2363.
(18) The dihedral angle is defined as the angle between the two
planes, which are defined through three atoms of the imidazolin-2-
ylidene ring (N, C(carbene), N).
(19) An excess of NaI was added to convert the palladium complexes
with a mixture of halogen atoms to the palladium iodide complex.
(20) Campeau, L. C.; Thansandote, P.; Fagnou, K. Org. Lett. 2005,
7, 1857–1860.
(21) Pytkowicz, J.; Roland, S.; Mangeney, P.; Meyer, G.; Jutand, A. J.
Organomet. Chem. 2003, 678, 166–179.
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