New structural motifs of silver and gold complexes of pyridine-functionalized benzimidazolylidene ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.03.031

Reaction of 1,3-bis(picolyl)benzimidazolium chloride ([HL1]Cl) with Ag₂O yields mononuclear complex [Ag(L1)Cl] (2), further reaction of 2 with Au(Et₂S)Cl afforded [Au(L1)Cl] (3). Treatment of 2 with AgBF₄ gave the trinuclear silver cluster [Ag₃(L1)₃](BF₄)₃ (4), whereas the digold complex [Au₂(L1)₂](BF₄)₂ (5) can be easily obtained from the carbene transfer reaction of 4 with Au(Et₂S)Cl. A one-dimensional coordination polymer {[Ag(L2)](BF₄) · CH₃CN}_n (8) was isolated from the reaction of [Ag(L2)Cl] (7, L2 = 1-benzyl-3-picolylbenzimidazolylidene) with additional Ag⁺ in good yield. The dinuclear [Ag₂(L3)₂](PF₆)₂ (12, L3 = 1,4-di(N-benzylbenzimidazolylidene)but-2-yne) is a 18-membered macrocycle. All these complexes have been structurally characterized. Complex 2 shows a dimeric structure because of intermolecular Ag?Cl interactions. Complex 4 consists of a triangular Ag₃ ring with very short Ag-Ag contacts 2.777(1) A?, the Au-Au distance in 5 is 3.206(2) A? showing very weak Au-Au interaction and the macrocyclic cations in 12 are aligned one above another to form channels filled with hexafluorophosphate anions. The complexes 2-5, 8, and 12 are intensely luminescent upon irradiation of uv light, and their emission properties are briefly described.

Full text of DOI:10.1016/j.jorganchem.2009.03.031

Journal of Organometallic Chemistry 694 (2009) 2359–2367
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New structural motifs of silver and gold complexes of pyridine-functionalized
benzimidazolylidene ligands
*
Xiaoming Zhang, Shaojin Gu, Qinqin Xia, Wanzhi Chen
Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of 1,3-bis(picolyl)benzimidazolium chloride ([HL1]Cl) with Ag2O yields mononuclear complex
[Ag(L1)Cl] (2), further reaction of 2 with Au(Et2S)Cl afforded [Au(L1)Cl] (3). Treatment of 2 with AgBF4
gave the trinuclear silver cluster [Ag3(L1)3](BF4)3 (4), whereas the digold complex [Au2(L1)2](BF4)2 (5)
can be easily obtained from the carbene transfer reaction of 4 with Au(Et2S)Cl. A one-dimensional coor-
dination polymer {[Ag(L2)](BF4) Á CH3CN}n (8) was isolated from the reaction of [Ag(L2)Cl] (7, L2 = 1-ben-
zyl-3-picolylbenzimidazolylidene) with additional Ag+ in good yield. The dinuclear [Ag2(L3)2](PF6)2 (12,
L3 = 1,4-di(N-benzylbenzimidazolylidene)but-2-yne) is a 18-membered macrocycle. All these complexes
have been structurally characterized. Complex 2 shows a dimeric structure because of intermolecular
AgÁ Á ÁCl interactions. Complex 4 consists of a triangular Ag3 ring with very short Ag–Ag contacts
2.777(1) Å, the Au–Au distance in 5 is 3.206(2) Å showing very weak Au–Au interaction and the macro-
cyclic cations in 12 are aligned one above another to form channels filled with hexafluorophosphate
anions. The complexes 2–5, 8, and 12 are intensely luminescent upon irradiation of uv light, and their
emission properties are briefly described.
Received 19 February 2009
Received in revised form 18 March 2009
Accepted 18 March 2009
Available online 26 March 2009
Keywords:
Silver
Gold
Imidazolylidene
Metal–metal interaction
Emission
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
azolium salts with silver salts under basic phase transfer condi-
tions [33–35]. Among these approaches, route (2) is more conve-
The organometallic chemistry of N-heterocyclic carbene (NHCs)
has been extensively studied in the recent decade [1–7]. The me-
tal–NHC complexes exhibit excellent catalytic activity for many
practically useful organic transformation especially for olefin
metathesis [8–13], C–C [14–19], and C–N [20–24] bond formation
reactions. Although metal NHC complexes can be prepared via var-
ious procedures, the use of silver carbene complexes as carbene
transfer reagent for the synthesis of other metal complexes is
one of most convenient way [25–30]. Such a route overcomes the
difficulties arising from the isolation of unstable free heterocyclic
carbenes and avoids the hard conditions when azolium salts react
directly with metal salts.
A large number of silver complexes of N-heterocyclic carbenes
have been synthesized and structurally characterized, and their
potential uses as catalysts, medicine, and luminescent materials
have also been studied. The achievement such as their synthetic
routes, structural features, and applications of Ag–NHC complexes
has been summarized by Youngs and coworkers [31,32] and Lin
et al. [33–35], respectively. These complexes are normally pre-
pared according to three different procedures: (1) reaction of free
NHC with silver salts [36]; (2) reaction of azolium salts with silver
bases such Ag2O, Ag2CO3, and AgOAc [35,37–39]; (3) reaction of
nient and most frequently used. So far, most of the known
silver–NHC complexes are reported to be prepared by treatment
of Ag2O with the corresponding imidazolium salts. Benzimidazo-
lin-2-ylidenes as a class of NHC ligands are easily accessible from
commercially available benzimidazole or o-phenylenediamine
[40,41]. The preparation, structures, and reactions of benzannulat-
ed NHCs have been well studied by Hahn’s group [42–52],
however, compared to their imidazolylidene analogues,
benzimidazolin-2-ylidenes complexes are less studied both in
structural diversity and homogeneous catalysis [53–57]. Free
benzimidazolin-2-ylidene usually forms dimeric complexes, thus
the preparation of metal–benzimidazolin-2-ylidene complexes
through Ag–benzimidazolin-2-ylidene transmetallation approach
is convenient and practical. The p–p interaction between the benz-
imidazolylidene rings might provide structural diversity to form
1D, 2D, and 3D structures.
Our recent research focuses on the design and preparation of
multinuclear metal complexes or coordination polymers contain-
ing direct metal–metal interactions, and a number of metal com-
plexes having short Pt–Ag, Pt–Tl, Pt–Pt, Pt–Pd, Ag–Ag, and Cu–Cu
contacts have been characterized [58–62]. Heteroarene functional-
ized N-heterocyclic carbene ligands have proven to be good donat-
ing ligands for the assemblage of new metal clusters [63–70]. As a
continuation, we report here the preparation and characterization
of new silver and gold–carbene complexes, [Ag(L1)Cl], [Au(L1)Cl],
* Corresponding author. Fax: +86 571 88273314.
E-mail address: chenwzz@zju.edu.cn (W. Chen).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.031

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X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
[Ag3(L1)3](BF4)3, [Au2(L1)2](BF4)2, [Ag(L2)Cl], {[Ag(L2)](BF4) ? CH3-
CN}n, and [Ag2(L3)2](PF6)2, (L1 = 1,3-bis(picolyl)benzimidazolylid-
ene, L2 = 1-benzyl-3-picolylbenzimidazolylidene, L3 = 1,4-di(N-
benzylbenzimidazoliumyl)but-2-yne) containing bidentate or tri-
dentate functionalized benzimidazolin-2-ylidene ligands. Seven
silver and gold complexes were analyzed by X-ray single-crystal
diffraction. The emission properties of these complexes in acetoni-
trile solution were also briefly described.
(68%). 1H NMR (400 MHz, CDCl3): d 8.57 (d, J = 4.8 Hz, pyridine,
2H), 7.70 (m, pyridine, 2H), 7.58 (m, benzimidazolylidene, 2H),
7.34 (m, benzimidazolylidene, 2H), 7.47 (d, J = 7.2 Hz, pyridine,
2H), 7.28–7.25 (m, pyridine, 2H), 5.87 (s, CH2, 4H). 13C NMR
(100 MHz, CDCl3): d 179.2 (Au–C), 154.2, 149.4, 137.5, 133.4,
124.8, 123.5, 122.4, 112.6, 54.4. Anal. Calc. for C19H16N4ClAu: C,
42.83; H, 3.03; N, 10.52. Found: C, 42.50; H, 3.27; N, 10.36%.
2.2.4. Synthesis of [Ag3(L1)3](BF4)3 ? 2CH3CN (4)
To a solution of 2 (134 mg, 0.3 mmol) in 10 mL of acetonitrile
was added AgBF4 (160 mg, 0.81 mmol). A white precipitate was
produced immediately. The mixture was protected from light and
stirred overnight. The filtrate was reduced to a minimum volume
and addition of Et2O (20 mL) afforded a white powder. Yield:
108 mg (73%). 1H NMR (400 MHz, DMSO-d6): d 8.10–8.02 (m,
18H), 7.52 (d, J = 2.8 Hz, 6H), 7.32 (t, J = 5.6 Hz, 12H), 5.81 (br,
CH2, 12H). No satisfactory elemental analysis was obtained due
to its sensitivity towards light and partial loss of the solvent
molecules.
2. Experimental
2.1. General procedures
All the chemicals were obtained from commercial suppliers and
used without further purification. N-picolylbenzimidazole [71] and
Au(Et2S)Cl [72] were prepared according to the known procedures.
The C, H, and N elemental analyses were carried out with a Carlo
Erba 1106 elemental analyzer. 1H and 13C NMR spectra were re-
corded on Bruker Avance-400 (400 MHz) spectrometer. Chemical
shifts (d) are expressed in ppm downfield to TMS at d = 0 ppm
and coupling constants (J) are expressed in Hz. The photolumines-
cence study was carried out in the solution of acetonitrile at room
temperature using a Hitachi 850 spectrometer.
2.2.5. Synthesis of [Au2(L1)2](BF4)2 (5)
The compound was prepared as described for 3 from 4 (44 mg,
0.089 mmol) and Au(Et2S)Cl (36 mg, 0.11 mmol) in 10 mL of aceto-
nitrile. The compound was isolated as a white solid. Yield 38 mg
(61%). 1H NMR (400 MHz, DMSO-d6): d 8.60 (br, 8H), 7.80 (s, 8H),
7.49 (m, 8H), 5.94 (br, CH2, 8H). Anal. Calc. for C38H32N8B2F8Au2:
C, 39.07; H, 2.76; N, 9.59. Found: C, 38.85; H, 2.96; N, 9.46%.
2.2. Synthesis of imidazolium salts and metal complexes
2.2.1. 1,3-Bis(picolyl)benzimidazolium chloride hydrate (1)
A mixture of NaHCO3 (8.4 g, 0.1 mol), picolyl chloride hydro-
chloride (8.15 g, 50 mmol) and benzimidazole (2.95 g, 25 mmol)
in 100 mL of EtOH was refluxed for 2 days and cooled to room tem-
perature. The solvent was removed and the resulted viscous brown
liquid was dissolved in CH2Cl2 (150 mL). After filtration, the filtrate
was dried with anhydrous MgSO4. The solvent was removed and
the brown solid was washed with THF and dried to give a light
brown powder. Yield: 6.1 g (69%). 1H NMR (400 MHz, CDCl3): d
11.82 (s, NCHN, 1H), 8.50 (d, J = 4.0 Hz, pyridine, 2H), 7.85 (m, pyr-
idine and benzimidazole, 4H), 7.74 (t, J = 7.2 Hz, pyridine, 2H), 7.53
(m, benzimidazole, 2H), 7.26 (m, pyridine, 2H), 6.01 (s, CH2, 4H).
13C NMR (100 MHz, CDCl3): d 152.0, 149.2, 143.6, 137.3, 131.2,
126.5, 123.5, 123.3, 113.8, 52.2. Anal. Calc. for C19H19N4ClO: C,
64.31; H, 5.40; N, 15.79. Found: C, 64.11; H, 5.71; N, 15.48%.
2.2.6. Synthesis of 1-benzyl-3-picolylbenzimidazolium chloride
hydrate (6)
N-picolylbenzimidazole (2.1 g, 10 mmol) and benzyl chloride
(5.0 g, 40 mmol) were mixed together in 100 mL of toluene. The
mixture was refluxed overnight, then the white solid was isolated
and washed with several portions of toluene (2 Â 10 mL) and Et2O
(2 Â 10 mL). Yield: 2.7 g (77%). 1H NMR (400 MHz, CDCl3): d 12.04
(s, NCHN, 1H), 8.49 (d, J = 4.8 Hz, pyridine, 1H), 7.91 (d, J = 8.0 Hz,
2H), 7.75 (m, 1H), 7.56–7.47 (m, 5H), 7.40–7.35 (m, 3H), 7.27–
7.24 (m, 1H), 6.07 (s, CH2, 2H), 5.83 (s, CH2, 2H). 13C NMR
(100 MHz, DMSO-d6): d 152.1, 149.2, 143.6, 137.3, 132.1, 131.5,
130.7, 129.0, 128.8, 127.9, 127.8, 126.6, 123.5, 123.4, 114.2,
112.9, 52.1, 51.2. Anal. Calc. for C20H18N3ClO: C, 67.89; H, 5.70;
N, 11.88. Found: C, 67.68; H, 5.96; N, 11.73%.
2.2.2. Synthesis of [Ag(L1)Cl] (2)
2.2.7. Synthesis of [Ag(L2)Cl] (7)
A suspension of Ag2O (128 mg, 0.55 mmol) in 20 mL of CH2Cl2
was treated with 1,3-bis(picolyl)benzimidazolium chloride hy-
drate (1) (355 mg, 1.0 mmol). The mixture was stirred for 5 h with
exclusion of light at room temperature. The resulted mixture was
then filtered through Celite, and the filtrate was concentrated to
about 2 mL under vacuum. A light brown solid was obtained by
adding 20 mL of Et2O. Yield: 364 mg (82%). 1H NMR (400 MHz,
CDCl3): d 8.59 (d, J = 4.8 Hz, pyridine, 2H), 7.67 (m, pyridine, 2H),
7.53 (m, benzimidazolylidene, 2H), 7.33 (m, benzimidazolylidene,
2H), 7.28 (d, J = 8.0 Hz, pyridine, 2H), 7.24 (m, pyridine, 2H), 5.75
(s, CH2, 4H). 13C NMR (100 MHz, DMSO-d6): d 190.9 (Ag–C),
155.7, 149.9, 137.7, 134.1, 124.4, 123.6, 122.5, 112.7, 53.8. Anal.
Calc. for C19H16N4ClAg: C, 51.43; H, 3.63; N, 12.63. Found: C,
51.49; H, 3.83; N, 12.75%.
The product was prepared as described for 2 employing 6
(177 mg, 0.50 mmol) and Ag2O (64 mg, 0.28 mmol) in 20 mL of
CH2Cl2. Yield: 178 mg (80%), colorless crystals. 1H NMR
(400 MHz, CDCl3): d 8.59 (d, J = 4.8 Hz, pyridine, 1H), 7.55–7.52
(m, 1H), 7.69–7.65 (m, 1H), 7.36–7.24 (m, 10H), 5.75 (s, 2H), 5.65
(s, 2H). 13C NMR (CDCl3) d 155.7, 149.9, 137.8, 136.7, 134.3,
133.7, 129.2, 128.5, 127.7, 124.6, 124.5, 123.7, 122.6, 112.9,
112.8, 53.9, 52.4. Anal. Calc. for C20H17ClN3Ag: C, 54.26; H, 3.87;
N, 9.49. Found: C, 54.35; H, 4.09; N, 9.38%.
2.2.8. Synthesis of {[Ag(L2)](BF4) Á CH3CN}n (8)
The compound was prepared as described for 4 by starting from
7 (88 mg, 0.2 mmol) and AgBF4 (103 mg, 0.52 mmol) in 15 mL of
CH3CN. Yield: 72 mg (82%), a white powder. 1H NMR (400 MHz,
DMSO-d6): d 8.66 (s, pyridine, 1H), 8.09–8.06, 7.99–7.95 (both m,
pyridine, each 1H), 7.77–7.75, 7.69–7.67 (both m, benzimidazoly-
lidene, each 1H), 7.55–7.56 (m, 1H), 7.43–7.39 (m, 4H), 7.32–7.26
(m, 3H), 6.03 (s, CH2, 2H), 5.74 (s, 2H), 2.07 (s, CH3CN, 3H). 13C
NMR (100 MHz, DMSO-d6): d 188.7 (Ag–C), 154.7, 151.9, 139.7,
136.5, 134.5, 134.0, 129.1, 128.4, 127.9, 125.4, 124.8, 124.7,
124.6, 118.5 (CH3CN), 113.0, 112.8, 54.71, 52.29, 1.52 (CH3CN).
2.2.3. Synthesis of [Au(L1)Cl] (3)
Au(Et2S)Cl (70 mg, 0.22 mmol) was added to the colorless solu-
tion of 2 (88 mg, 0.2 mmol) in 20 mL of CH2Cl2. The mixture was
protected from light and stirred at room temperature overnight.
The resulted mixture was filtered through Celite to remove AgCl,
and the filtrate was reduced to about 2 mL. After addition of
20 mL of Et2O, a white precipitate was obtained. Yield: 72 mg

X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
2361
Anal. Calc. for C22H20N4BF4Ag: C, 49.38; H, 3.77; N, 10.47. Found: C,
49.07; H, 3.92; N, 10.23%.
C32H28N4P2F12: C, 50.67; H, 3.72; N, 7.39. Found: C, 50.53; H,
3.88; N, 7.20%.
2.2.9. Synthesis of [H(L2)](PF6) (9)
2.2.12. Synthesis of [Ag2(L3)2](PF6)2 (12)
To the aqueous solution of 6 (1.06 g, 3 mmol) was added an ex-
cess of NH4PF6 (1.2 g, 7.3 mmol) led to an immediate white precip-
itate. The white solid was collected and wash with water and Et2O.
Yield: 1.25 g (94%). 1H NMR (400 MHz, DMSO-d6): d 10.09 (s,
NCHN, 1H), 8.49 (d, J = 4.0 Hz, pyridine, 1H), 8.00–7.90 (m, 3H),
7.70–7.63 (m, 3H), 7.54–7.52 (m, 2H), 7.47–7.37 (m, 4H), 5.96 (s,
CH2, 2H), 5.86 (s, CH2, 2H). 13C NMR (100 MHz, DMSO-d6): d
153.3, 150.0, 143.9, 138.0, 134.4, 131.9, 131.2, 129.5, 129.2,
129.1, 128.6, 127.3, 127.2, 124.2, 123.2, 114.3, 51.31, 50.35. Anal.
Calc. for C20H18N3PF6: C, 53.94; H, 4.07; N, 9.44. Found: C, 53.66;
H, 4.33; N, 9.17%.
The compound was prepared as described for 2 employing 11
(227 mg, 0.3 mmol) and Ag2O (76 mg, 0.33 mmol) in 10 mL of
CH3CN. Workup gave compound 12 as a white solid. Yield:
125 mg (58%). 1H NMR (400 MHz, DMSO-d6): d 7.94 (s, 2H), 7.79
(s, 4H), 7.52–7.43 (m, 14H), 7.27–7.13 (m, 16H), 5.85 (s, CH2, 4H),
5.58 (s, CH2, 8H), 5.37 (s, CH2, 4H). Anal. Calc. for C64H52N8P2F12Ag2:
C, 53.42; H, 3.64; N, 7.79. Found: C, 53.41; H, 3.73; N, 7.66%.
For all complexes, X-ray quality crystals were obtained by slow
diffusion of Et2O into their CH3CN solution at room temperature.
2.3. X-ray structural determination
2.2.10. Synthesis of [Ag(L2)](PF6) (10)
Single-crystal X-ray diffraction data were collected at 298(2) K
on a Siemens Smart/CCD area-detector diffractometer with a Mo
Ka radiation (k = 0.71073 Å) by using an x–2h scan mode. Unit-cell
The compound was prepared as described for 2 employing 9
(134 mg, 0.3 mmol) and Ag2O (38 mg, 0.165 mmol) in 10 mL of
CH3CN. Workup gave a white powder. Yield: 120 mg (93%), 1H
NMR (400 MHz, DMSO-d6): d 8.54 (d, J = 4.0 Hz, pyridine, 1H),
7.90 (m, 1H), 7.75 (m, 1H), 7.71 (m, 2H), 7.43–7.37 (m, 5H),
7.31–7.26 (m, 3H), 5.96 (s, CH2, 2H), 5.77 (s, CH2, 2H). 13C NMR
(100 MHz, DMSO-d6): d 155.5, 149.9, 137.7, 136.7, 134.3, 133.7,
129.2, 129.1, 128.4, 127.7, 124.7, 124.6, 123.7, 122.7, 112.8, 53.7,
52.3. Anal. Calc. for C40H34N6PF6Ag: C, 56.42; H, 4.02; N, 9.87.
Found: C, 56.42; H, 4.07; N, 9.69%.
dimensions were obtained with least-squares refinement. Data col-
lection and reduction were performed using the SMART and SAINT
software [73]. The structures were solved by direct methods, and
the non-hydrogen atoms were subjected to anisotropic refinement
by full-matrix least-squares on F2 using SHELXTXL package [74].
Hydrogen atom positions for all of the structures were calculated
and allowed to ride on their respective C atoms with C–H distances
of 0.93–0.97 Å and Uiso(H) = À1.2 À 1.5Ueq(C). Further details of the
structural analyses are summarized in Tables 1 and 2.
2.2.11. Synthesis of 1,4-di(N-benzylbenzimidazoliumyl)but-2-yne
hexafluorophosphate [H2(L3)](PF6)2 (11)
3. Results and discussion
Addition of 1,4-dibromobut-2-yne (2.1 g, 10 mmol) to a solu-
tion of N-benzylbenzimidazole (5.2 g, 25 mmol) in 20 mL of tolu-
ene. The mixture was refluxed overnight. After the solvent was
decanted, the resulting precipitate was dissolved into 20 mL of
water. To the aqueous solution an excess of NH4PF6 (30 mmol) in
10 mL of H2O was added affording a white precipitate, which
was collected by filtration. Yield: 4.9 g, (65%). 1H NMR (400 MHz,
DMSO-d6): 9.96 (s, NCHN, 2H), 8.00 (s, benzimidazole, 4H), 7.66
(d, J = 8.8 Hz, benzyl, 4H), 7.51 (s, benzimidazole, 4H), 7.41 (s, ben-
zyl, 6H), 5.80 (s, CH2, 4H), 5.64 (s, CH2, 4H). 13C NMR (100 MHz,
DMSO-d6): d 142.8, 134.1, 131.3, 131.1, 129.4, 129.2, 128.7,
127.5, 127.3, 114.5, 114.3, 79.9, 50.4, 37.4. Anal. Calc. for
3.1. Synthesis and spectral characterization
According to the procedure developed by Lin et al. [35,37–39],
the direct reaction of Ag2O and 1,3-bis(picolyl)benzimidazolium
chloride afforded [Ag(L1)Cl] (2) as a colorless crystalline solid
(Scheme 1). The analogous gold compound [Au(L1)Cl] (3) could
be easily obtained via carbene transfer reaction of 2 with one
equivalent of Au(SEt2)Cl. Their 1H and 13C NMR spectra are consis-
tent with the proposed formula. 13C NMR spectra exhibit singlets at
190.9 and 179.2 ppm for 2 and 3, respectively, characteristic of the
carbenic carbon resonances. In the ESI spectrum of 2 in acetonitrile,
Table 1
Summary of X-ray crystallographic data for complexes 2–5.
2
3
4
5
Formula
C19H16AgClN4
443.68
C19H16AuClN4
532.77
C61H54Ag3B3F12N14
1567.22
C38H32Au2B2F8N8
1168.27
Monoclinic
P21/n
8.1923(14)
21.338(2)
23.013(2)
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
Triclinic
Hexagonal
PÀ62c
ꢀ
ꢀ
P1
P1
8.087(2)
10.965(3)
11.025(3)
67.299(2)
89.359(3)
79.213(3)
884.0(4)
2
9.6903(14)
9.7451(15)
9.9664(15)
85.913(3)
84.206(3)
76.512(2)
909.4(2)
2
13.3009(11)
13.3009(11)
22.4938(19)
a
(°)
b (°)
92.014(2)
c
(°)
V (Å3)
3446.3(5)
2
1.475
4020.4(9)
4
1.930
Z
Dcalc (Mg/m3)
1.667
1.300
1.946
8.244
l
(mmÀ1
)
0.922
7.366
F(000)
444
508
1518
2224
Reflections collected
Reflections unique, Rint
Goodness-of-fit on F2
4433
3048, 0.0110
1.005
4782
3152, 0.0279
1.037
14558
2088, 0.0848
1.107
15370
6751, 0.0942
1.100
R [I > 2
r
I]
0.0260, 0.0606
0.0334, 0.0647
0.522, À0.361
0.0280, 0.0639
0.0345, 0.0674
0.673, À1.107
0.0503, 0.1277
0.0681, 0.1387
0.530, À0.485
0.1089, 0.2679
0.1719, 0.3049
1.543, À3.625
R (all data)
Largest difference in peak and hole (e ÅÀ3
)

2362
X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
Table 2
[Ag(L2)Cl] (7), generated from the reaction of 1-benzyl-3-picol-
ylbenzimidazolium chloride and Ag2O, reacted with AgBF4 led to
isolation of the coordination polymer 8 (Scheme 2). The compound
shows a singlet at 188.7 ppm in its 13C NMR spectrum assignable to
the carbene carbon atom, and the chemical shift is well consistent
with those of the known silver–NHC complexes in the range of
Summary of X-ray crystallographic data for complexes 8, 10, and 12.
8
10
12
Formula
C22H20AgBF4N4 C40H34AgF6N6P C64H52Ag2F12N8P2
535.10
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
851.57
1438.82
Tetragonal
P42/nbc
17.549(2)
17.549(2)
19.994(3)
Monoclinic
Pn
5.597(9)
9.4250(14)
20.540(2)
Triclinic
ꢀ
P1
213.7–163.2 ppm [59–61]. The ESI spectrum of
8 displays
8.292(3)
10.812(4)
11.763(5)
70.289(5)
87.961(4)
69.055(4)
922.9(6)
1
1.532
4764
3185, 0.0155
1.045
peaks at 852.86, 706.20, and 406.19 amu which can be assigned
to [Ag2(L2)2CH3CN)]+ (calc. 853.12 amu), [Ag(L2)2]+ (calc. 705.19
amu), and [Ag(L2)]+ (calc. 406.05 amu). As expected, the deproto-
nation of 1-benzyl-3-picolylbenzimidazolium hexafluorophos-
phate with Ag2O yielded the [Ag(NHC)2]+ compound (10), shown
in Scheme 3. Compounds 7 and 10 did not show the resonance sig-
nals of carbenic carbons in their 13C NMR spectra. The reason is not
clear, probably because of the dynamic behaviour of the complexes
arising from the dissociation and association processes in solution.
The ESI spectra of 10 shows peaks at 705.22 and 300.39 amu which
can be assigned to [Ag(L2)2]+ (calcd 705.19 amu), and [L2]+ (calc.
299.14 amu).
[H2(L3)](PF6)2 (11) is a diimidazolium salt with two N-benzyl-
benzimidazolium bridged by a rigid –CH2–C„C–CH2– linker. As
shown in Scheme 4, reaction of 11 with Ag2O afforded a macrocy-
clic complex [Ag2(L3)2](PF6)2 (12). The disappearance of downfield
carbene proton signal in its precursor 11 clearly demonstrates the
formation of Ag–carbene complex. However, the signals in 1H NMR
spectra of 12 are broad and no satisfactory 13C NMR spectra could
be obtained though the data were repeatedly collected. ESI of
complex 12 shows peaks at 1292.53 and 573.16 amu correspond-
ing to [Ag2(L3)2(PF6)]+ (calc. 1291.20 amu), and [Ag(L3)]+ (calc.
573.12 amu).
a
(°)
b (°)
97.234(2)
c
(°)
V (Å3)
1074.9(17)
2
1.653
5037
3297, 0.0189
1.045
0.0403, 0.0990 0.0326, 0.0741 0.0887, 0.1665
0.0452, 0.1028 0.0424, 0.0825 0.1269, 0.1801
0.735, À0.421
6157.8(14)
4
1.552
24846
2714, 0.0683
1.302
Z
Dcalc (Mg/m3)
Reflections collected
Reflections unique, Rint
Goodness-of-fit on F2
R [I > 2
r
I]
R (all data)
Largest difference in peak
0.297, À0.238
0.554, À0.583
and hole (e ÅÀ3
)
the most intense peaks were observed at 850.23 and 442.53 amu
corresponding to [Ag2(L1)2Cl]+ (calc. 849.05 amu) and [Ag(L1)Cl]+
(calc. 442.01 amu). The ESI spectrum of 3 shows the most intense
peaks at 1029.07 amu due to [Au2(L1)2Cl]+ (calc. 1029.18 amu),
whereas the peak at 797.36 amu can be assigned to [Au(L1)2]+
(calc. 797.24 amu). Treatment of 2 with an excess of AgBF4 gave
the trinuclear complex [Ag3(L1)3]3+ (4) after removal of the result-
ing AgCl precipitate. However, reaction of 4 with 3 equiv. of
Au(SEt2)Cl did not afford the expected [Au3(L1)3]3+, instead, a di-
gold complex 5 with a formula of [Au2(L1)2]2+ was obtained. Com-
pound 5 could also be obtained from the reaction of 3 with an
excess of AgBF4. An ESI spectrum of 4 in acetonitrile displays the
most intense peaks at 1396.54, 902.71, and 407.29 amu due to
[Ag3(L1)3- (BF4)2]+ (calc. 1395.16 amu), [Ag2(L1)2(BF4)]+ (calc.
901.09 amu), and [Ag(L1)]+ (calc. 407.04 amu). The peaks at
1080.65, 797.34, and 497.58 amu are seen for 5, arising from the
fragments [Au2(L1)2(BF4)]+ (calc. 1081.21 amu), [Au(L1)2]+ (calc.
797.24 amu), and [Au(L1)]+ (calc. 497.10 amu). Compound 4 is
not stable in solution and also light sensitive, and thus no satisfac-
tory 13C NMR spectrum and elemental analysis were obtained.
3.2. X-ray structural description
The structures of 2 and 3 are shown in Figs. 1 and 2, respec-
tively. The two compounds are isostructural and crystallize in the
same space group. Both metal atoms are bicoordinated by chloride
and 1,3-bis(picolyl)benzimidazolydene ligands. The pyridine
groups do not interact with the central metal atoms. The silver
atom is bicoordinated with a carbene carbon atom and a chloride
ion, with the Ag–C and Ag–Cl bond distances of 2.088(3) and
2.353(1) Å. These bonds distances are consistent with those of
the known silver–NHC complexes having C–Ag–Cl motif [75,76].
Interestingly, the X-ray diffraction analysis showed that complex
Au(Et2S)Cl
N
Ag2O
N
N
N
N
N
N
N
CH2Cl2
N
N
Ag
Cl
N
N
Au
Cl
Cl
3
1
2
AgBF4
CH3CN
CH3CN
AgBF4
3+
2+
N
N
3BF4
N
N
N
2BF4
N
N
Au(Et2S)Cl
N
Au
Ag
N
Ag
N
N
N
Au
N
N
N
Ag
N
N
N
N
N
5
4
Scheme 1. Synthesis of complexes 2–5.

X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
2363
N
N
Ag
AgBF4
Ag2O
N
N
N
N
N
CH3CN
CH2Cl2
N
N
Ag
Cl
Cl
Ag
N
N
7
6
N
8
Scheme 2. Synthesis of complexes 7 and 8.
N
N
N
Ag2O
N
N
Ag
PF 6
CH3CN
N
PF 6
N
N
N
10
9
Scheme 3. Synthesis of complex 10.
N
N
N
Br
Br
NH4PF6
H2O
toluene
reflux
2PF 6
N
N
Fig. 1. Molecular structure of 2. Selected bond distances (Å) and angles (°): Ag(1)–
C(1) 2.088(3), Ag(1)–Cl(1) 2.353(1), C(1)–Ag(1)–Cl(1) 164.93(8).
N
11
2+
N
N
N
N
N
N
Ph
Ph
Ph
Ag2O
CH3CN
Ag
Ag
2PF 6
Ph
N
N
12
Scheme 4. Synthesis of complex 12.
2 associates via weak AgÁ Á ÁCl interaction to give a dimeric struc-
ture. The intermolecular Ag–Cl distance is 3.071 Å, whereas the
intermolecular AgÁ Á ÁAg contact is 3.993 Å, illustrating that there
is no Ag–Ag interaction. The C–Ag–Cl is more bent than those of
other Ag(NHC)Cl complexes that is obviously resulted from the
dimerization. Unlike 2, the gold complex 3 does not associate,
which is evidenced by the quite long intermolecular AuÁ Á ÁCl dis-
tances of 4.766 Å. It should be noted that both Au–Cl and Au–C
bond distances of 3 are shorter than those of its silver analogous.
Another feature of the gold complex is that the Cl–Au–C axis
(177.89(14)°) is much more linear than C–Ag–Cl (164.93(8)°).
The two pyridine rings are located below and up the coordination
plane defined by benzimidazolydene ring and MCl, and the dihe-
dral angles are 87.04 and 82.57° for 2 and 3, respectively. Mononu-
Fig. 2. Molecular structure of 3. Selected bond distances (Å) and angles (°): Au(1)–
C(1) 1.982(5), Au(1)–Cl(1) 2.278(2), C(1)–Au(1)–Cl(1) 177.89(14).
clear gold–NHC complexes often show intermolecular gold–gold
interactions [77]. The closest intermolecular AuÁ Á ÁAu distance is
3.593 Å for 3 showing very weak aurophilic interaction.
Complex [Ag(L2)2](PF6) (10) is also mononuclear crystallizing in
ꢀ
a space group P1. The silver atom is coordinated by two 1-benzyl-
3-picolylimidazolydene ligands in perfectly linear C–Ag–C coordi-
nation geometry. The Ag–C bond distances are the same as that
of 2. As shown in Fig. 3, the phenyl and pyridyl rings of the same
1-benzyl-3-picolylbenzimidazolydene are directed towards the

2364
X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
are also quit long. The three benzimidazolylidene rings are per-
fectly perpendicular to the Ag3 plane as evidenced by the dihedral
angles of 90°.
Another structural feature of 4 is the very short Ag–Ag distances
(2.777(1) Å), remarkably shorter than those found in our previ-
ously reported linear chain Ag4, square-planar Ag4 clusters
[63,64]. Although a large number of silver–NHC complexes have
been reported, silver clusters with short Ag–Ag contacts supported
by NHC ligands are still rare [31–37]. The Ag–Ag contacts are sim-
ilar to the trimetallic Ag(I) complex stabilized by bridging NHC li-
gands [82].
The molecular structure of 5 established by an X-ray diffraction
study is depicted in Fig. 5. The digold complex crystallizes in
monoclinic space group P21/n. Its asymmetric unit consists of
two independent gold atoms which are bonded together by two
1,3-bis(picolyl)benzimidazolydene ligands. Each benzimidazolyd-
ene links two gold atoms in a bidentate mode, and only one pyri-
dine is coordinated. The two gold atoms are both bicoordinated
by a pyridine and an benzimidazolydene ligands in nearly linear
geometry with C–Au–N angles of 175.2°. The Au–C and Au–N bond
distances are normal and consistent with those of the known Au–
NHC complexes. The Au–Au distance is 3.206(2) Å showing weak
gold–gold interaction. No intermolecular Au–Au interaction is ob-
served due to steric hindrance of the ligand.
Gold–NHC complexes have proven their potential applications
in pharmaceuticals, chemical vapour depositions, liquid crystals,
and optical devices. The Au(I)–NHC chemistry has been reviewed
by Lin et al. in 2005 [34]. The reported gold–NHC complexes are
normally have linear [Au(NHC)2]+ or Au(NHC)X (X = halogen ions)
structural motifs, few Au(NHC)X (X = N, O ligands) have been pre-
pared and structurally characterized. Complex 5 represents one of
the rare examples having Au(NHC)X.
Fig. 3. Molecular structure of the cation of 10. Selected bond distances (Å) and
angles (°): Ag(1)–C(1) 2.086(3), C(1)#1–Ag(1)–C(1) 180.0. Symmetry transforma-
tions used to generate equivalent atoms: #1 Àx + 1, Ày + 2, Àz + 1.
same side of the silver coordination plane. The two benzimidazo-
lydene rings are coplanar, quite different from most of the
[Ag(NHC)2]+ complexes in which the two NHC rings are normally
bisected [78–80].
Reaction of 2 with Ag+ in acetonitrile yielded 4 as a trinuclear
silver complex which contains a triangular Ag3 ring. The asymmet-
ric unit consists of one third of the molecule with a threefold axis
passing through the center of the Ag3 ring. As shown in Fig. 4, the
silver atom is coordinated by two pyridine and two benzimidazol-
ylidene ligands in severely distorted tetrahedron geometry. Each
side of the Ag3 ring is capped by a benzimidazolylidene acting as
a bridging ligand. This unusual coordination mode of imidazolylid-
ene was only observed in a few silver(I) [81–83] and copper(I) [84]
complexes. This bonding situation of Ag2C ring can be best viewed
as 3c2e bonding. As a result of this bridging fashion, the Ag–C (av.
2.26 Å) distances become exceptionally long, remarkably longer
than those found for 2 and 10. The Ag–N (2.40 Å) distances of 4
The complex 8 is a one-dimensional chain polymer (Fig. 6). The
X-ray structural analysis revealed that the asymmetric unit con-
tains one silver atom and one 1-benzyl-3-picolylbenzimidazolilyd-
ene. Each silver atom is bonded to an benzimidazolydene and a
pyridine group forming 1D chain structure. The Ag–C (2.104(7) Å)
distance is slightly longer than those found in 2 and 10. The Ag–
N (2.182(6) Å) distance is much shorter than those of the trinuclear
complex 4 presented above. These Ag–C and Ag–N bond distances
Fig. 4. Molecular structure of the cation of 4. Selected bond distances (Å) and angles
(°): Ag(1)–Ag(1)#1 2.777(1), Ag(1)–C(1) 2.230(11), Ag(1)–C(1)#1 2.301(10), Ag(1)–
N(2)#2 2.399(7), Ag(1)–N(2) 2.399(7), C(1)–Ag(1)–C(1)#1 164.4(3), C(1)#1–Ag(1)–
N(2) 85.1(2), N(2)#2–Ag(1)–N(2) 102.7(3), Ag(1)#1–Ag(1)–Ag(1)#3 60.0. Symme-
try transformations used to generate equivalent atoms: #1 Ày + 1, x À y, z; #2 x, y,
Àz + 3/2; #3 Àx + y + 1, Àx + 1, z.
Fig. 5. Molecular structure of the cation of 5. Selected bond distances (Å) and angles
(°): Au(1)–C(1) 1.93(3), Au(1)–N(7) 2.06(2), Au(2)–C(20) 2.00(3), Au(2)–N(3)
2.057(19), Au(1)–Au(2) 3.206(2), C(1)–Au(1)–N(7) 175.2(10), C(20)–Au(2)–N(3)
175.2(9).

X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
2365
N(3)
Ag(1)
C(1)
Fig. 6. Molecular structure of the cation of 8. Selected bond distances (Å) and angles (°): Ag(1)–C(1) 2.104(7), Ag(1)–N(3) 2.182(6), C(1)–Ag(1)–N(3) 168.7(2).
are approximately consistent with those of our previously reported
multinuclear silver complexes containing NHC ligands. The
dihedral angles between the benzimidazolydene ring, phenyl and
pyridyl rings are 89.50 and 86.28°, respectively, and the two six-
membered rings are located at the same side of the coordination
plane of silver. This arrangement prohibits any possible silver–sil-
ver interaction along the chain. Furthermore, the silver atoms are
perfectly arranged into a linear chain along the crystallographic a
axis with AgÁ Á ÁAgÁ Á ÁAg angles being 180°. The 1D chain structure
supported by NHC ligands is rare. The successful isolation and
characterization of 8 illustrates that it is possible to construct coor-
dination polymers using bifunctional NHC ligands as building
blocks [85].
X-ray diffraction analysis revealed that complex 12 is a disilver
complex displaying twisted square conformation. The molecular
structure of 12 is shown in Fig. 7. The asymmetric unit of 12 con-
tains one fourth of the molecule and there is a fourfold axis passing
through the center of the molecule. Two silver ions are linked by
two 1,4-di(N-benzylbenzimidazolylidenyl)but-2-yne ligands form-
ing a molecular square. Both silver ions show linear C–Ag–C geom-
etry with C–Ag–C angles of 179.8(5)°. The Ag–C bond distance of
12 is longer than that of 10 having the same coordination environ-
Fig. 7. Molecular structure of the cation of 12. Selected bond distances (Å) and
angles (°): Ag(1)–C(1) 2.111(11), C(1)#1–Ag(1)–C(1) 179.8(5). Symmetry code: #1
Ày + 1, x À y, z.
(a)
(b)
(c)
Fig. 8. (a) Stack diagram of 12 showing one-dimensional channel in its solid state. (b) and (c) Channels filled with hexafluorophosphate anions showing weak interactions of
cations and anions.

2366
X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
ment. The two benzimidazolylidene rings coordinated to the same
silver ions are nearly perpendicular with a dihedral angle of 87.01°.
The macrocyclic cations are aligned one above another to form
one-dimensional channels filled with hexafluorophosphate anions
(Fig. 8). Weak AgÁ Á ÁF and HÁ Á ÁF interactions can be observed. Every
broad emission band at 362 nm upon excitation at 323 nm.
Although complex 3 has the same structure as 2, complex 3 show
a high-energy emission band at 388 nm and a low-energy band at
407 nm when irradiated at 342 nm. For comparison, [Au(Me2bi-
my)Cl] (Me2bimy = N,N-dimethylbenzimidazolylidene) displays
two emission bands at 420 nm and 620 nm, and the large red shifts
could be ascribed to the existence of intermolecular AuI–AuI and
four channels assemble together through
p–p interactions be-
tween the adjacent benzimidazolylidene rings to form another
channel which is also filled with hexafluorophosphate anions. Cat-
ionic channels formed in crystals of metal complexes of crown
ethers are known [86,87], however, to the best of our knowledge,
this is the first example of receptor and guest channel complex
supported by NHC ligands.
ring p–p interactions.
The digold complex has a C–Au–N structural motif show quite
different emission property from the mononuclear complex 3. At
room temperature, the emission spectrum of 5 in acetonitrile
shows two emission bands at 412, 431 nm with nearly the same
intensities, and a less intensive shoulder peak at 465 nm upon
excitation at 371 nm. The emission spectrum of the Ag3 complex
only shows one broad band at 450 nm in aectonitrile, very similar
to that of the previously reported Ag3 cluster also supported by
NHC ligand. For the polymeric complex 8, only a very broad band
at 410 nm was observed upon excitation at 310 nm. Complex 12
in acetonitrile exhibits its emission band at 305 nm. The lumines-
cence of these complexes may be originated from the mixed exci-
tation states. Either intraligand or metal-centered electronic
transfer processes can be possible. Further work is required to clar-
ify the nature of the emission properties.
3.3. Luminescence properties
The photoluminescent properties of complexes 2–5, 8, and 12
in acetonitrile at room temperature have been studied. The emis-
sion spectra are given in Figs. 9 and 10. Complex 2 displays strong
[Au(L1)Cl] (3)
600
[Au2(L1)2](BF4)2 (5)
500
400
300
200
100
4. Conclusions
In summary, we have successfully prepared and structurally
characterized a few mono-, di-, trinuclear, and polymeric silver
and gold complexes containing pyridine-functionalized imidazoly-
lidene. These ligands show diverse coordination abilities and coor-
dination mode leading unexpected structural motifs of silver–NHC
complexes. The complexes 2–5, 8, and 12 are intensely lumines-
cent in their acetonitrile solution at room temperature. It implies
that coinage complexes with novel structures and unique optical
properties may be obtained by using rationally designed N,C-
mixed NHC ligands.
0
220
270
32 0
37 0
42 0
470
520
Wavelength (nm)
Fig. 9. Emission (right) and excitation (left) spectra of [Au(L1)Cl] (3) (solid line,
c = 9.30 Â 10À5 M) and [Au2(L1)2](BF4)2 (5) (dashed line, c = 9.67 Â 10À5 M) in
acetonitrile.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (20872129 and J0830413), the Ph.D. Programs Foundation
of Ministry of Education of China (200803350011), and Zhejiang
University K.P. Chao’s High Technology Development Foundation
for financial support.
[Ag3(L1)3](BF4)3 (4)
[Ag(L1)Cl] (2)
[Ag(L2)](BF4) (8)
[Ag2(L3)2](PF6)2 (12)
800
Appendix A. Supplementary material
700
600
500
400
300
200
CCDC 663000, 663001–663005 and 726622 contain the supple-
mentary crystallographic data for 2–5, 8, 10, and 12. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.jorganchem. 2009.03.031.
References
100
0
[1] F.E. Hahn, M.C. Jahnke, Angew. Chem., Int. Ed. 47 (2008) 3122.
[2] O. Kaufhold, F.E. Hahn, Angew. Chem., Int. Ed. 47 (2008) 4057.
[3] D. Bourissou, O. Guerret, F.P. Gabbai, G. Bertrand, Chem. Rev. 100 (2000) 39.
[4] W.A. Herrmann, Angew. Chem., Int. Ed. Engl. 41 (2002) 1290.
[5] L. Jafarpour, S.P. Nolan, Adv. Organomet. Chem. 46 (2000) 181.
22 0
270
320
370
420
470
520
570
Wavelength (nm)
[6] R.H. Crabtree, Coord. Chem. Rev. 251 (2007) 595:
A volume completely
Fig. 10. Emission (right) and excitation (left) spectra of [Ag(L1)Cl] (2) (black,
c = 1.02 Â 10À4 M), [Ag3(L1)3](BF4)3 (4) (red, c = 9.47 Â 10À5 M), [Ag(L2)](BF4) (8)
(green, c = 9.55 Â 10À5 M), and [Ag2(L3)2](PF6)2 (12) (blue, c = 9.69 Â 10À5 M) in
acetonitrile. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
dedicated to recent developments in the organometallic chemistry of N-
heterocyclic carbenes.
[7] S. Díez-González, S.P. Nolan, Top. Organomet. Chem. 21 (2007) 47.
[8] T.M. Trnka, R.H. Grubbs, Acc. Chem. Res. 34 (2001) 18.
[9] A. Fürstner, Angew. Chem., Int. Ed. 39 (2000) 3012.

X. Zhang et al. / Journal of Organometallic Chemistry 694 (2009) 2359–2367
2367
[10] T. Weskamp, W.C. Schattenmann, M. Spiegler, W.A. Herrmann, Angew. Chem.,
Int. Ed. Engl. 37 (1998) 2490.
[46] F.E. Hahn, L. Wittenbecher, D.L. Van, R. Fröhlich, Angew. Chem. 39 (2000) 541.
[47] F.E. Hahn, C. Holtgrewe, T. Pape, M. Martin, E. Sola, L.A. Oro, Organometallics
24 (2005) 2203.
[48] M. Tamm, F.E. Hahn, Coord. Chem. Rev. 182 (1999) 175.
[49] F.E. Hahn, V. Langenhahn, N. Meier, T. Lügger, W.P. Fehlhammer, Chem. Eur. J.
9 (2003) 704.
[50] F.E. Hahn, C.G. Plumed, M. Münder, T. Lügger, Chem. Eur. J. 10 (2004) 6285.
[51] H.V. Huynh, C. Holtgrewe, T. Pape, L.L. Koh, F.E. Hahn, Organometallics 25
(2006) 245.
[52] F.E. Hahn, C. Radloff, T. Pape, A. Hepp, Organometallics 27 (2008) 6408.
[53] H.V. Huynh, H.H.J. Ho, T.C. Neo, L.L. Koh, J. Organomet. Chem. 690 (2005) 3854.
[54] C. Metallinos, F.B. Barret, J.L. Chaytor, M.E.A. Heska, Org. Lett. 6 (2004) 3641.
[55] F.E. Hahn, M.C. Jahnke, V. Gomez-Benitez, D. Morales-Morales, T. Pape,
Organometallics 24 (2005) 6458.
[11] R.E. Giudici, A.H. Hoveyda, J. Am. Chem. Soc. 129 (2007) 3824.
[12] T. Ritter, M.W. Day, R.H. Grubbs, J. Am. Chem. Soc. 128 (2006) 11768.
[13] L. Jafarpour, A.C. Hillier, S.P. Nolan, Organometallics 21 (2002) 442.
[14] E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Angew. Chem., Int. Ed. 46 (2007)
2768.
[15] C. Zhang, J. Huang, M.L. Trudell, S.P. Nolan, J. Org. Chem. 64 (1999) 3804.
[16] S.K. Schneider, P. Roembke, G.R. Julius, H.G. Raubenheimer, W.A. Herrmann,
Adv. Synth. Catal. 348 (2006) 1862.
[17] W.A. Herrmann, V.P.W. Böhm, C.W.K. Gstöttmayr, M. Grosche, C.-P. Reisinger,
T. Weskamp, J. Organomet. Chem. 617–618 (2001) 616.
[18] S.B. Blakey, D.W.C. MacMillan, J. Am. Chem. Soc. 125 (2003) 6046.
[19] J. Liu, M. Robins, Org. Lett. 7 (2005) 1149.
[20] V. Cesar, S. Bellemin-Laponnaz, L.H. Gade, Organometallics 21 (2002) 5204.
[21] K. Arentsen, S. Caddick, F.G.N. Cloke, Tetrahedron 61 (2005) 9710.
[22] L.R. Titcomb, S. Caddick, F.G.N. Cloke, D.J. Wilson, D. McKerrecher, Chem.
Commun. (2001) 1388.
[23] S. Caddick, F.G.N. Cloke, G.K.B. Clentsmith, P.B. Hitchcock, D. McKerrecher, L.R.
Titcomb, M.R.V. Williams, J. Organomet. Chem. 617–618 (2001) 635.
[24] R. Omar-Amrani, A. Thomas, E. Brenner, R. Schneider, Y. Fort, Org. Lett. 5
(2003) 2311.
[56] F.E. Hahn, M.C. Jahnke, T. Pape, Organometallics 25 (2006) 5927.
[57] F.E. Hahn, M.C. Jahnke, T. Pape, Organometallics 26 (2007) 150.
[58] F. Liu, W. Chen, D. Wang, Dalton Trans. (2006) 3445.
[59] F. Liu, W. Chen, D. Wang, Dalton Trans. (2006) 3015.
[60] W. Chen, F. Liu, K. Matsumoto, J. Autschbach, B. Le Guennic, T. Ziegler, M.
Maliarik, J. Glaser, Inorg. Chem. 45 (2006) 4526.
[61] W. Chen, F. Liu, D. Xu, K. Matsumoto, S. Kishi, M. Kato, Inorg. Chem. 45 (2006)
5552.
[25] R.S. Simons, P. Custer, C.A. Tessier, W.J. Youngs, Organometallics 22 (2003)
1979.
[26] A.R. Chianese, X. Li, M.C. Janzen, J.W. Faller, R.H. Crabtree, Organometallics 22
(2003) 1663.
[62] Y. Zhou, W. Chen, Dalton Trans. (2007) 5123.
[63] Y. Zhou, W. Chen, Organometallics 26 (2007) 2742.
[64] B. Liu, W. Chen, S. Jin, Organometallics 26 (2007) 3660.
[65] Y. Zhou, W. Chen, Dalton Trans. (2008) 1444.
[27] X. Wang, S. Liu, L.-H. Weng, G.-X. Jin, Organometallics 25 (2006) 3565.
[28] C.A. Quezada, J.C. Garrison, M.J. Panzner, C.A. Tessier, W.J. Youngs,
Organometallics 23 (2004) 4846–4848.
[29] Y.A. Wanniarachchi, M.A. Khan, L.M. Slaughter, Organometallics 23 (2004)
5881–5884.
[30] X.-Y. Yu, B.O. Patrick, B.R. James, Organometallics 25 (2006) 2359.
[31] J.C. Garrison, W.J. Youngs, Chem. Rev. 105 (2005) 3978.
[32] A. Kascatan-Nebioglu, M.J. Panzner, C.A. Tessier, C.L. Cannon, W. Youngs, J.
Coord. Chem. Rev. 251 (2007) 884.
[66] X. Zhang, Z. Xi, A. Liu, W. Chen, Organometallics 27 (2008) 4401.
[67] Z. Xi, X. Zhang, W. Chen, S. Fu, D. Wang, Organometallics 26 (2007) 6636.
[68] C. Chen, H. Qiu, W. Chen, D. Wang, J. Organomet. Chem. 693 (2008) 3273.
[69] Y. Zhou, X. Zhang, W. Chen, H. Qiu, J. Organomet. Chem. 693 (2008) 205.
[70] A. Liu, X. Zhang, W. Chen, H. Qiu, Inorg. Chem. Commun. 11 (2008) 1129.
[71] R.J. Sundberg, I. Yilmaz, D.C. Mente, Inorg. Chem. 16 (1977) 6.
[72] R. Uson, A. Laguna, M. Laguna, Inorg. Synth. 26 (1989) 85.
[73] SMART-CCD Software, version 4.05; Siemens Analytical X-ray Instruments,
Madison, WI, 1996.
[33] I.J.B. Lin, C.S. Vasam, Comment. Inorg. Chem. 23 (2004) 534.
[34] C.S. Vasam, I.J.B. Lin, Coord. Chem. Rev. 251 (2007) 642.
[35] H.M.J. Wang, I.J.B. Lin, Organometallics 17 (1998) 972.
[36] A.J. Arduengo, H.V.R. Dias, J.C. Calabrese, F. Davidson, Organometallics 12
(1993) 3405.
[74] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Program for X-ray Crystal Structure
Refinement, University of Göttingen, Göttingen, Germany, 1997.
[75] A.D. Tulloch, A.A. Danopoulos, S. Winston, S. Kleinhenz, G. Eastham, J. Chem.
Soc., Dalton Trans. (2000) 4499.
[76] W. Chen, B. Wu, K. Matsumoto, J. Organomet. Chem. 654 (2002) 233.
[77] C.S. Vasam, I.J.B. Lin, Can. J. Chem. 83 (2005) 812.
[78] W. Huang, R. Zhang, G. Zou, J. Tang, J. Sun, J. Organomet. Chem. 692 (2007)
3804.
[79] H.M. Lee, P.L. Chiu, C.-H. Hu, C.-L. Lai, Y.-C. Chou, J. Organomet. Chem. 690
(2005) 403.
[80] W. Chen, F. Liu, J. Organomet. Chem. 673 (2003) 5.
[81] J.C. Garrison, R.S. Simons, W.G. Kofron, C.A. Tessier, W.J. Youngs, Chem.
Commun. (2001) 1780.
[82] V.J. Catalano, M.A. Malwitz, Inorg. Chem. 42 (2003) 5483.
[83] V.J. Catalano, A.L. Moore, Inorg. Chem. 44 (2005) 6558.
[84] S. Gischig, A. Togni, Organometallics 24 (2005) 203.
[85] F.E. Hahn, C. Radloff, T. Pape, A. Hepp, Chem. Eur. J. 14 (2008) 10900.
[86] J.-P. Behr, J.-M. Lehn, A.-C. Dock, D. Moras, Nature 295 (1982) 526.
[87] C.M. Evans, S.F. Watkins, G.W. Gokel, Inorg. Chim. Acta 300–302 (2000) 333.
[37] C.K. Lee, C.S. Vasam, T.W. Huang, H.M.J. Wang, R.Y. Yang, C.S. Lee, I.J.B. Lin,
Organometallics 25 (2006) 3768.
[38] C.K. Lee, K.M. Lee, I.J.B. Lin, Organometallics 21 (2002) 10.
[39] H.M.J. Wang, C.Y.L. Chen, I.J.B. Lin, Organometallics 18 (1999) 1216.
[40] F.E. Hahn, L. Wittenbecher, R. Boese, D. Bläser, Chem. Eur. J. 5 (1999) 1931.
[41] E. Cetinkayk, P.B. Hitchcock, H. Kücükbay, M.F. Lappert, S. Al-Juaid, J.
Organomet. Chem. 481 (1994) 89.
[42] F.E. Hahn, V. Langenhahn, T. Lügger, T. Pape, D.L. Van, Angew. Chem. 44 (2005)
3759.
[43] F.E. Hahn, M. Foth, J. Organomet. Chem. 585 (1999) 241.
[44] F.E. Hahn, L. Wittenbecher, M. Kühn, T. Lügger, R. Fröhlich, J. Organomet.
Chem. 617–618 (2001) 629.
[45] C. Holtgrewe, C. Diedrich, T. Pape, S. Grimme, F.E. Hahn, Eur. J. Org. Chem.
(2006) 3116.