Silver(I), palladium(II) and mercury(II) NHC complexes based on bis-benzimidazole salts with mesitylene linker: Synthesis, structural studies and catalytic activity

Article abstract of DOI:10.1016/j.jorganchem.2013.01.026

The diimidazolium salts bis[1-R-imidazoliumylmethyl]mesitylene·2X (1: R = PhCH₂, X = Br^- and 2: R = Et, X = PF ₆^-) and the dibenzimidazolium salts bis[1-R- benzimidazoliumylmethyl]mesitylene·2X (3: R = ⁿPr, X = I ^-; 4: R = PhCH₂, X = I^-), as well as their four NHC silver(I), palladium(II) and mercury(II) complexes, {[mesitylene(CH ₂imyPhCH₂)₂]₂Ag₂· Ag₂Br₄}_n (6), {mesitylene[(CH ₂imyPhCH₂)PdCl₂(CH₃CN)] ₂} (7), {mesitylene[(CH₂imyEt)₂Hg ₂(CHCN)][HgI₄]} (8) and {[mesitylene(CH ₂bimyⁿPr)₂HgI][HgI₄]_0.5} (9), as well as one anionic complex {[1,3-bis(1-benzylbenzimidazolemethyl) mesitylene][HgI₄]} (5) (imy = imidazol-2-ylidene and bimy = benzimidazol-2-ylidene), have been prepared and characterized. In the complex 6, the macrometallocycles formed by two precursor 1 and two silver(I) atoms are connected together via Ag₂Br₄ unit to form a 1D polymeric chain. Complex 7 adopted an open structure formed by one precursor 1 and two Pd(II) atoms. In complex 8, a bidentate dicarbene from precursor 2 and a doubly deprotonated acetonitrile coordinate with two Hg(II) atoms to afford a funnel-like structure. The 10-membered macrometallocycle of 9 was formed by one precursor 3 and one Hg(II) atom. In the crystal packings of these compounds, 1D supramolecular chains, 2D supramolecular layers or 3D architectures are formed via intermolecular weak interactions, including π-π interactions, hydrogen bonds, C-H···π contacts and weak Hg·· ·N and Hg···I bonds. Additionally, the catalytic activity of the NHC palladium(II) complex 7 in Suzuki-Miyaura cross-coupling reaction was studied.

Full text of DOI:10.1016/j.jorganchem.2013.01.026

Journal of Organometallic Chemistry 731 (2013) 35e48
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Silver(I), palladium(II) and mercury(II) NHC complexes based on bis-
benzimidazole salts with mesitylene linker: Synthesis, structural studies
and catalytic activity
,
b
,
a
,
,
,
,b
Qing-Xiang Liu a , Li-Xuan Zhao b, Xiao-Jun Zhao a b, Zhi-Xiang Zhao a b, Zhi-Qiang Wang a
,
*
Ai-Hui Chen a b, Xiu-Guang Wang a
,
,b
a Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Key Laboratory of InorganiceOrganic Hybrid Functional Material Chemistry,
Ministry of Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, China
b State Key Laboratory of Elemento-organic Chemistry, Nankai University, China
a r t i c l e i n f o
a b s t r a c t
The diimidazolium salts bis[1-R-imidazoliumylmethyl]mesitylene$2X (1: R ¼ PhCH2, X ¼ Brꢀ and 2:
R ¼ Et, X ¼ PFꢀ6 ) and the dibenzimidazolium salts bis[1-R-benzimidazoliumylmethyl]mesitylene$2X (3:
R ¼ nPr, X ¼ Iꢀ; 4: R ¼ PhCH2, X ¼ Iꢀ), as well as their four NHC silver(I), palladium(II) and mercury(II)
complexes, {[mesitylene(CH2imyPhCH2)2]2Ag2$Ag2Br4}n (6), {mesitylene[(CH2imyPhCH2)PdCl2(CH3CN)]2}
Article history:
Received 22 November 2012
Received in revised form
24 January 2013
Accepted 30 January 2013
(7), {mesitylene[(CH2imyEt)2Hg2(CHCN)][HgI4]} (8) and {[mesitylene(CH2bimynPr)2HgI][HgI4]0.5
} (9),
as well as one anionic complex {[1,3-bis(1-benzylbenzimidazolemethyl)mesitylene][HgI4]} (5) (imy ¼
imidazol-2-ylidene and bimy ¼ benzimidazol-2-ylidene), have been prepared and characterized. In the
complex 6, the macrometallocycles formed by two precursor 1 and two silver(I) atoms are connected
together via Ag2Br4 unit to form a 1D polymeric chain. Complex 7 adopted an open structure formed by
one precursor 1 and two Pd(II) atoms. In complex 8, a bidentate dicarbene from precursor 2 and a doubly
deprotonated acetonitrile coordinate with two Hg(II) atoms to afford a funnel-like structure. The 10-
membered macrometallocycle of 9 was formed by one precursor 3 and one Hg(II) atom. In the crystal
packings of these compounds, 1D supramolecular chains, 2D supramolecular layers or 3D architectures are
Keywords:
Carbene
Silver
Mercury
Palladium
Catalysis
formed via intermolecular weak interactions, including
pep interactions, hydrogen bonds, CeH$$$p
contacts and weak Hg$$$N and Hg$$$I bonds. Additionally, the catalytic activity of the NHC palladiu-
m(II) complex 7 in SuzukieMiyaura cross-coupling reaction was studied.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
many bidentate bis-NHC ligands have been reported, in which a
pair of NHC moieties are connected by a bridging linker, such as
The transition metal complexes of N-Heterocyclic carbenes
(NHCs) have attracted considerable interest over the past two de-
cades due to their structural variety and easy access through
deprotonation of N, N0-disubstituted imidazolium (or benzimida-
phenylene [10e16], pyridyl and lutidinyl [17e19], ether chain [20e
23] and alkyl [24e29]. These NHC ligands with different bridging
linkers can form mainly three types of metal complexes (Scheme 1),
namely, the monometal monoligand macrocycle (I), the dimetal
diligand macrocycle (II) and the open structure composed of one
bidentate dicarbene ligand and two metal atoms (III). These
different conformations of complexes are related to the flexibility
and size of bridging linkers. Additionally, the steric hindrance of N-
substitutes on imidazole rings, and the difference of benzimidazole
ring and imidazole ring have also some influence on the structures
of complexes.
zolium) salts [1e4]. The strong s-donating ability of N-heterocyclic
carbenes leads to high stability of their metal complexes toward
heat, moisture and air. More recently, much effort has also been
devoted to the synthesis of functionalized NHC ligands and their
metal complexes [5e9]. In the family of N-heterocyclic carbenes,
* Corresponding author. Tianjin Key Laboratory of Structure and Performance for
Functional Molecules, Key Laboratory of InorganiceOrganic Hybrid Functional
Material Chemistry, Ministry of Education, College of Chemistry, Tianjin Normal
University, Tianjin 300387, China.
Among NHC-metal complexes, the NHC silver(I) [30e32], mer-
cury(II) [33e35] and palladium(II) [36e39] complexes have played
important roles in the development of the N-heterocyclic carbene
chemistry. N-heterocyclic carbene silver(I) complexes can be used as
E-mail addresses: tjnulqx@163.com, qxliu@eyou.com (Q.-X. Liu).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.01.026

36
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
analogous to that of 2, only instead of ammonium hexa-
fluorophosphate with sodium iodide in the second step (method 2
of Scheme 2). Precursors 1e4 are stable toward air and moisture,
soluble in polar organic solvents such as dichloromethane, aceto-
nitrile and methanol, and almost insoluble in benzene, diethyl ether
and petroleum ether. In the 1H NMR spectra of 1e4, the imidazolium
NHC
M
NHC
M
NHC
M
NHC
M
NHC
NHC
NHC
NHC
M
III
I
II
(or benzimidazolium) proton signals (NCHN) appear at
d
¼ 8.32e
9.77 ppm, which is consistent with the chemical shifts of reported
Scheme 1. The conformations of NHC metal complexes.
imidazolium (or benzimidazolium) salts [5e9].
carbene transfer reagents to make other NHC metal complexes, such
as Ni, Pd, Pt, Cu, Au, Rh, Ir and Ru carbene complexes [40e43]. Some
N-Heterocyclic carbene mercury(II) complexes possess interesting
structures [44,45]. Particularly, N-Heterocyclic carbene palladium(II)
complexes have been demonstrated to be efficient catalysts for some
organic reactions, such as SuzukieMiyaura and Heck cross-coupling
reactions [46e50]. In order to understand further the influence of
bridging linkers, N-substitutes, imidazole ring and benzimidazole
ring on the conformations and the crystal packings of complexes, we
inhere reported the synthesis, structures and fluorescent emission
spectra of four new NHC-metal complexes, {[mesitylene(CH2i-
myPhCH2)2]2Ag2$Ag2Br4}n (6), {mesitylene[(CH2imyPhCH2)PdCl2
(CH3CN)]2} (7), {mesitylene[(CH2imyEt)2Hg2(CHCN)][HgI4]} (8)
and {[mesitylene(CH2bimynPr)2HgI][HgI4]0.5} (9), as well as one
anionic complex {[1,3-bis(1-benzylbenzimidazolemethyl)mesity-
lene][HgI4]} (5) (imy ¼ imidazol-2-ylidene and bimy ¼ benzimida-
zol-2-ylidene). Additionally, we also describe the diverse
conformations of precursors 1e4 and their complexes 5e9. More-
over, the catalytic performance of NHC palladium(II) complex 7 in
SuzukieMiyaura cross-coupling reaction was studied.
2.2. Synthesis and general characterization of complexes 5e9
Synthetic methods of complexes 5e9 are shown in Scheme 2.
The precursor 4 was treated with anhydrous mercury(II) iodide to
afford anionic complex [1,3-bis(1-benzylbenzimidazolemethyl)
mesitylene][HgI4] (5) (Scheme 3(1)). The reaction of 1 with silver(I)
oxide afforded 1D polymeric chain {[mesitylene(CH2i-
myPhCH2)2]2Ag2$Ag2Br4}n (6) bearing 20-membered macro-
metallocycles and Ag2Br4 units. The reaction of complex 6 with
[PdCl2(CH3CN)2] via the transformation of metal gave the complex
{mesitylene[(CH2imyPhCH2)PdCl2(CH3CN)]2} (7) with an open
structure (Scheme 3(2)). The precursor 2 was treated with anhy-
drous mercury(II) iodide in the presence of KOtBu in CH3CN to
afford complex {mesitylene[(CH2imyEt)2Hg2(CHCN)][HgI4]} (8)
(Scheme 3(3)). The precursor 3 was treated with anhydrous
N
N
N
N
HgI2
(1)
4
[HgI4]2-
2. Results and discussion
5
2.1. Synthesis and general characterization of diimidazolium (or
dibenzimidazolium) salts 1e4
N
N
N
N
N
Br
Br
Br
The diimidazolium salt, bis[1-benzyl-imidazoliumylmethyl]
mesitylene bromide (1) was prepared from imidazole by alkylation
with benzyl bromide followed by quarterization with 1,3-
bis(bromomethyl)mesitylene in sequence (method 1 of Scheme 2).
Bis[1-ethyl-imidazoliumylmethyl]mesitylene hexafluorophosphate
(2) was obtained via two steps of reactions. The first step is in a
manner analogous to that of 1, and the second step is the anion
exchange with ammonium hexafluorophosphate in methanol
(method 2 of Scheme 2). Bis[1-R-benzimidazoliumylmethyl]mesi-
tylene iodide (3: R ¼ nPr, 4: R ¼ PyCH2) were prepared in a manner
Ag2O
(2)
1
Ag
Br
Ag
Ag
Ag
N
N
N
n
6
7
PdCl2(CH3CN)2
N
N
N
N
Cl Pd Cl
NCCH3
Cl Pd Cl
NCCH3
method 1
Br
R
N
N
N
N
R
Br
+
N
N
R
method 2
N
N
2X-
HgI2
Et
N
(3)
Et
2
N
CH3CN
KOtBu
Hg
1: R = PhCH2, X = Br
2: R = Et, X = PF6
Hg
[HgI4]2-
C
H
C
N
method 2
R
R
N
N
N
N
8
Br
+
Br
N
N
R
2X-
3: R = nPr, X = I
4: R = PhCH2, X = I
HgI2
N
N
N
(4)
3
Hg
I
KOtBu
N
nPr
1/2[HgI4]2-
Reagents: method 1 for 1, THF, reflux.
Prn
method 2 for 2-4, (i) THF, reflux; (ii) anionic exchange with NH4PF6
in methanol for 2, and with NaI in acetone for 3 and 4.
9
Scheme 3. Preparation of complexes 5e9.
Scheme 2. Preparation of precursors 1e4.

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
37
mercury(II) iodide in the presence of KOtBu in CH2Cl2 to afford
complex {[mesitylene(CH2bimynPr)2HgI][HgI4]0.5
(9) (Scheme
imidazole rings (the data of hydrogen bonds being given in Table 2).
These data of hydrogen bonds are comparable with those reported
[51]. The heads of two imidazole rings point to opposite directions.
In anionic complex 5, a 12-membered macrocycle is formed by
one dibenzimidazole cation unit and one iodine atom from [HgI4]2ꢀ
via two CeH$$$I hydrogen bonds (Fig. 2(a)), in which hydrogen
}
3(4)). The complexes 5e9 are stable toward air and moisture, sol-
uble in DMSO and insoluble in diethyl ether and hydrocarbon sol-
vents. The NHC silver(I) complex 6 is slightly light sensitive. In the
1H NMR spectra of 6e9, the disappearance of the resonances for the
imidazolium (or benzimidazolium) protons (NCHN) shows the
formation of the expected metal carbene complexes, and the
chemical shifts of other protons are similar to those of the corre-
sponding precursors. The 1H NMR spectrum of anionic complex 5 is
similar to that of the corresponding precursor 4. For 13C NMR
spectra, the signals of the carbene carbon in complexes 6e9 appear
at 153.3e184.1 ppm, which are similar to the reported carbene
metal complexes [30e39].
atoms are from imidazole ring (Table 2). In anionic unit [HgI4]2ꢀ
,
the mercury(II) atom is coordinated to four iodine atoms to form a
slightly distorted tetrahedral geometry. The distances of HgꢀI
ꢀ
ꢀ
bonds vary from 2.641(2) A to 2.753(3) A, and the bond angles of Ie
HgeI are in the range of 96.7(6)e119.3(5)ꢁ.
1D polymeric chain of complex 6 is formed by the cage-like
cations and anionic unit Ag2Br4 via AgeAg bonds (Ag(1)eAg(2)
ꢀ
distance ¼ 2.997(6) A) as shown in Fig. 3(a). Each cage-like cation
is constituted by two bidentate dicarbene ligands and two silver(I)
atoms (Fig. 3(b)), in which four benzene rings from four different
benzyl groups as the lids of top and bottom to close the cage. In
each cage-like structure, two mesitylene planes are nearly parallel
with the dihedral angle of 3.4(1)ꢁ, and the dihedral angle between
the benzene rings of benzyl groups and the benzene rings of
mesitylene is in the range of 5.1e18.8ꢁ. Two CeAgeC units are
crossed with the torsion angles of C(8)eAg(4)eAg(1)eC(39) of
90.3(8)ꢁ and C(53)eAg(4)eAg(1)eC(22) of 83.8(8)ꢁ. Each silver(I)
atom in the cage-like cation is tricoordinated with two carbene
carbon atoms and another silver(I) atom. The bond angles of two
CeAgeC are 156.5(2)ꢁ and 167.0(2)ꢁ, respectively, and the distance
2.3. Structures of diimidazolium salt 2 and complexes 5e9
Molecular structure of the precursor 2 and complexes 5e9 were
demonstrated by X-ray analysis. The crystals of 2, 5, 6$4CH3CN,
7$H2O, 8 and 9 suitable for X-ray diffraction were obtained by slow
diffusion of diethyl ether into their DMSO/CH3CN solutions.
In precursor 2 and complex 6, two [Rimy] arms on the same
ligand lie in the opposite sides of the mesitylene plane due to steric
hindrance (Fig. 1(a) and Fig. 3(b)). In contrast, two [Rimy] (or
[Rbimy]) arms on the same ligand of complexes 5 and 7e9 are
placed in the same side of the mesitylene plane (Fig. 2(a) and
Fig. 4(a)e6(a)). In precursor 2 and complexes 5e9, two imidazole
(or benzimidazole) rings on the same ligand form the dihedral
angles of 14.3e86.7ꢁ (Table 1). The mesitylene plane and two
imidazole (or benzimidazole) rings on the same ligand form the
dihedral angles of 75.6e89.1ꢁ. The dihedral angles between imid-
azole (or benzimidazole) ring and adjacent benzene ring of benzyl
group (or pyridine ring) in 5e7 are 68.8e88.4ꢁ. In complexes 6e9,
the internal ring angles (NeCeN) at the carbene centers are in the
range of 104.5e108.4ꢁ, which are comparable to those of the known
NHCemetal complexes [30e39], but these values are slightly
smaller than those of precursor 2 (109.5ꢁ) and anionic complex 5
(110.5ꢁ).
ꢀ
of AgeC is in the range of 2.101(5)e2.119(5) A.
The anionic unit Ag2Br4 of 6 is formed by two silver(I) atoms and
four bromine atoms (two bridging bromines Br(2) and Br(3), and
two non-bridging bromines Br(1) and Br(4)). The coplanar four
atoms Ag(2), Br(2), Ag(3) and Br(3) form a quadrangle Ag2Br2
arrangement (Br(2)eAg(2)eBr(3) angle ¼ 97.4(3)ꢁ and Ag(2)e
Br(2)eAg(3) angle ¼ 82.7(3)ꢁ). The two non-bridging bromine
atoms Br(1) and Br(4) lie in both sides of the quadrangle plane
(Br(1)eAg(2)eBr(2) angle ¼ 129.1(3)ꢁ). Each silver(I) atom in Ag2Br4
unit is tetracoordinated with three bromine atoms and another
silver(I) atom. The distance of non-bridging bromine and silver(I)
ꢀ
(Ag(2)eBr(1) distance ¼ 2.548(8) A) is slightly shorter than that of
ꢀ
bridging bromine and silver(I) (Ag(2)eBr(2) distance ¼ 2.620(9) A
In precursor 2, one cationic entity and two hexafluorophosphate
anions are held together via two CeH$$$F hydrogen bonds
(Fig. 1(a)). In hydrogen bonds, the hydrogen atoms are from
ꢀ
and Ag(2)eBr(3) distance ¼ 2.802(8) A). The Ag(2)$$$Ag(3) sepa-
ꢀ
ration of 3.543(3) A in the anionic unit shows no metalemetal
Fig. 1. (a). Perspective view of 2 and anisotropic displacement pꢁarameters depicting 50% probability. All hydrogen atoms except those participating in the CeH$$$F hydrogen bonds
ꢀ
were omitted for clarity. Selected bond lengths (A) and angles ( ): N (1)eC (5) 1.311(5), N (2)eC (5) 1.325(4); N (1)eC (5)eN (2) 109.5(3). (b). The 1D supramolecular chain via Ce
H$$$F hydrogen bonds. All hydrogen atoms except those participating in the CeH$$$F hydrogen bonds were omitted for clarity in 2.

38
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
Fig. 2. (a). Perspective view of 5 and anisotropic displacementꢁparameters depicting 50% probability. All hydrogen atoms except those participating in the CeH$$$I hydrogen bonds
ꢀ
were omitted for clarity. Selected bond lengths (A) and angles ( ): N(1)eC(14) 1.320(1), N(2)eC(14) 1.337(1); N(1)eC(14)eN(2) 110.5(1). (b). The 2D supramolecular layer by CeH$$$I
hydrogen bonds. All hydrogen atoms except those participating in the CeH$$$I hydrogen bonds were omitted for clarity in 5.
ꢀ
interactions (the van der Waals radii of silver ¼ 1.7 A). In 1D poly-
shown in Fig. 5(a). In cation of complex 8, each mercury atom is
surrounded by one carbene carbon atom (Ccarbene) and one -car-
ꢀ
meric chain, the Ag(1)$$$Ag(4) separation is 7.420(9) A.
a
Similar to precursor 2, complex 7 is also an open structure, and
the difference is that two [benzylimyPdCl2(NCCH3)] units in 7 lie in
the same side of the mesitylene plane as shown in Fig. 4(a). The X-
ray crystal structural analysis of 7 shows that there exist a sym-
metric plane in the complex. Each palladium atom is tetracoordi-
nated with one carbene carbon atom, one nitrogen atom of
acetonitrile and two chlorine atoms to adopt a square trans
conformation. The N(5)ePd(1)eC(10) and Cl(1)ePd(1)eCl(2) arrays
are almost linear with the bond angles of 178.5(3)ꢁ and 176.3(4)ꢁ.
The bond distances of Pd(1)eC(10), Pd(1)eCl(1) and Pd(1)eN(5)
bon (Ca) atom of acetonitrile. The C(1)eHg(2)eC(23) and C(17)e
Hg(3)eC(23) are nearly linear with the same bond angle of
175.3(5)ꢁ. The bond distance of HgeCcarbene is 2.068(1) A, which is
ꢀ
similar to those of known carbene mercury(II) complexes [33,60e
ꢀ
63]. The distance of HgeCa is 2.080(1) A, and it is slightly longer
than that of HgeCcarbene. The benzene ring and two imidazole rings
form the dihedral angles of 79.0(6)ꢁ and 89.1(7)ꢁ, respectively. Two
imidazole rings form a dihedral angle of 55.6(8)ꢁ. It is noteworthly
that the cyanomethyl moiety (C(23)eC(22)eN(5)) is nearly linear
with bond angle of 176.4(1)ꢁ. The C(23)eC(22) bond distance
ꢀ
ꢀ
ꢀ
are 1.926(6) Å, 2.325(1) A and 2.081(6) A, respectively.
It has been known that the -hydrogen atoms of acetonitrile can
(1.414(9) A) is shorter than that of the regular CeC single bond
ꢀ
a
(1.54e1.59 A), and it has part double-bond characteristics. The
ꢀ
be deprotonated one by one in the presence of base to form singly,
doubly and triply deprotonated acetonitrile (i.e., [CH2CN]ꢀ [52e55],
[CHCN]2ꢀ [56,57] and [CCN]3ꢀ [45,58,59]). The different formulae
of deprotonated acetonitriles could are relative to the amount of
base and the type of coordinated metal ions in the system of re-
C(22)eN(5) bond distance (1.225(9) A) is similar to that of other
complexes containing cyano groups, and this value is expected for a
triple bond with a small amount of double bond characteristics
[45,52e59,64].
In complex 9, each cation contains a 10-membered macro-
metallocycle formed by one bidentate chelate carbene ligand and
one metal atom (Fig. 6(a)). The mercury(II) atom is tricoordinated
with two carbene carbon atoms and one iodine atom. The angles of
C(7)eHg(1)eC(28) and C(7)eHg(1)eI(1) are 158.9(4)ꢁ and
100.7(3)ꢁ, and the distances of Hg(1)eC(7) and Hg(1)eI(1) are
action. The
a-carbon atoms of these deprotonated acetonitrile
along with other ligands are coordinated to metal ions to form
different metal complexes.
In the formation of complex 8, two
a-hydrogen atoms of
acetonitrile are deprotonated by strong base KOtBu to afford a
doubly deprotonated acetonitrile (CHCN2e). Then the doubly
deprotonated acetonitrile and a bidentate dicarbene ligand coor-
dinate with two Hg(II) atoms to form a funnel-like complex 8 as
ꢀ
ꢀ
2.098(9) A and 2.927(1) A. These data are analogous to those of
some known NHC mercury(II) complexes [33e35]. The structure of
[HgI4]2ꢀ in 9 is similar to that of the same unit in 5.

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
39
ꢁ
ꢀ
Fig. 3. (a). The 1D polymeric chain of 6. All hydrogen atoms and methyl groups on mesitylene were omitted for clarity. Selected bond lengths (A) and angles ( ): Ag(1)eAg(2)
2.997(6), Ag(2)eBr(1) 2.548(8), Ag(2)eBr(2) 2.620(9), Ag(2)eBr(3) 2.802(8); C(22)eAg(1)eAg(2) 139.8(1), C(39)eAg(1)eAg(2) 61.9(1), Ag(2)eBr(2)eAg(3) 82.7(3), Br(1)eAg(2)e
Br(2) 129.1(3), N(5)eC(39)eN(6) 104.5(4).(b). Perspective view of the cage-like in the cation of 6. All hydrogen atoms and methyl groups on mesitylene were omitted for clarity.
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ): Ag(1)eC(22) 2.105(6), Ag(1)eC(39) 2.116(6); C(22)eAg(1)eC(39) 156.5(2), N(3)eC(22)eN(4) 104.6(5). (c). 2D supramolecular layer of 6 via
CeH$$$N and CeH$$$Br hydrogen bonds. All hydrogen atoms except those participating in the hydrogen bonds and all methyl groups on mesitylene were omitted for clarity.
2.4. The crystal packings of precursor 2 and complexes 5e9
of supramolecular architecture. In the nonclassical hydrogen bonds
CeH$$$A, the H$$$A distance is different due to the difference of A.
Generally, when H$$$A distance is less than the sum of van der
Waals radii of H and A, CeH$$$A interactions should considered
Some weak interactions, including classical hydrogen bonds
(such as YeH$$$X hydrogen bonds, Y or X ¼ F, N, O), nonclassical
hydrogen bonds (such as CeH$$$A hydrogen bonds, A ¼ O, N, F, Cl,
ꢀ
(the sum of van der Waals radii for hydrogen atom and A atom (A):
Br, I and
p, etc.) and aromatic
pe
p
interactions play important roles
H and F ¼ 2.67, H and I ¼ 3.35, H and N ¼ 2.70, H and Br ¼ 3.15). For
in crystal packings, and they can further link discrete subunits or
low-dimensional entities into high-dimensional supramolecular
networks [65,66]. The results of theoretical and experimental in-
vestigates show that these weak interactions exist widely in the
bio-systems and organic crystals [67e69]. Moreover, these weak
interactions may result in a collective contribution to the formation
example, the Steiner put forward that CeH$$$O interactions may be
ꢀ
exist when H$$$O distance is less than 2.7 A [70]. Tiekink believed
that the CeH$$$
tance is within 2.4e3.6 A [71]. Whereas, the
p
contacts should be considered when H$$$
p
dis-
ꢀ
pep interactions of
aromatic rings should be considered when face-to-face distance is
about 3.5 Å [72].

40
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
Table 2
H-Bonding geometry (A, ꢁ) for precursor 2 and complexes 5, 6, 8 and 9.
ꢀ
DeH$$$A
DeH
H$$$A
D$$$A
DeH$$$A
2
5
C(13)eH(13)$$$F(2)
C(5)eH(5)$$$F (4)
C(14)eH(14)$$$I(4)
C(4)eH(4)$$$I(1)i
C(10)eH(10)$$$I(1)
C(24)eH(24)$$$N(9)i
C(64)eH(64)$$$Br(2)ii
C(18)eH(18)$$$I(4)i
C(52)eH(52)$$$I(1)i
C(5)eH(5)$$$I(5)
0.96(1)
0.93(1)
0.93(1)
0.93(1)
0.93(1)
0.93(1)
0.96(1)
0.93(1)
0.97(1)
0.93(1)
0.97(1)
2.655(2)
2.422(2)
2.661(2)
2.900(4)
2.998(3)
2.616(3)
2.888(2)
3.118(1)
3.058(1)
3.145(1)
3.147(1)
3.575(2)
3.324(3)
3.495(3)
3.700(4)
3.787(5)
3.544(4)
3.684(3)
3.961(1)
3.823(1)
4.025(1)
3.897(1)
160.8(9)
163.6(9)
149.7(1)
144.9(8)
143.7(1)
175.8(1)
141.0(1)
151.7(1)
136.6(1)
158.6(1)
135.1(1)
6
8
9
C(42)eH(42)$$$I(4)
Symmetry code: i: 0.5ꢀx, ꢀ0.5 þ y, 1.5ꢀz for 5. i: 1ꢀx, 0.5þy, ꢀz; ii: 2ꢀx, 0.5þy, ꢀz
for 6. i: ꢀx, ꢀy, ꢀz for 8. i: ꢀx, 1ꢀy, 1ꢀz for 9.
ꢀ
groups with the intermolecular separation of 3.501(1) A. In the 1D
tubular structure, the size of cavity is ca. 5.2 ꢂ 10.2 Å2. Additionally,
1D tubular chains are further extended into 2D supramolecular
layers via another type of
mesitylenes with intermolecular separation of 3.420(2) E. These
values of interactions are fall in the normal ranges [72,76e78].
pep interactions from benzene rings of
Fig. 4. (a). Perspective view of 7 and anisotropic displacement parameters depicting
pep
ꢀ
50% probability. All hydrogen atoms were omitted for clarity. Selected bond lengths (A)
and angles (ꢁ): Pd(1)eC(10) 1.928(6), Pd(1)eN(5) 2.081(6), Pd(1)eCl(1) 2.330(1);
C(10)ePd(1)eN(5) 178.5(2), C(10)ePd(1)eCl(2) 89.2(1), C(10)ePd(1)eCl(1) 88.2(1),
Cl(2)ePd(1)eCl(1) 176.2 (7), N(1)eC(10)eN(2) 105.0(5), C(32)eN(5)ePd(1) 172.9(6).
In the crystal packing of 8 (Fig. 5(b)), 2D supramolecular layer is
formed via weak Hg$$$N bonds (the nitrogen atom being from
ꢀ
acetonitrile, the Hg$$$N distance being 2.859(1) A, and the sum of
(b). 2D supramolecular layer of 7 via two types of
pep interactions. All hydrogen
ꢀ
van der Waals radii for mercury and nitrogen being 3.2 A) and Ce
atoms were omitted for clarity.
ꢀ
H$$$
angle being 148.9(1)ꢁ). In CeH$$$
are from CH3 of ethyl and systems are from imidazole rings. These
values of CeH$$$
p
contacts (H$$$
p
distance being 3.050(4) A, and CeH$$$
p
p
contacts, the hydrogen atoms
p
1D supramolecular chain of 2 (Fig. 1(b)) is formed via CeH$$$F
hydrogen bonds (the data of hydrogen bonds being given in
Table 2). In the hydrogen bonds, hydrogen atoms are from imid-
azole rings and methyl groups of mesitylene, respectively. These
values of hydrogen bonds are comparable with analogous those
reported [51].
As shown in Fig. 2(b), 2D supramolecular layer of 5 is formed via
CeH$$$I hydrogen bonds (Table 2), and the hydrogen atoms in
these hydrogen bonds are from benzimidazole ring and benzene
ring of benzyl groups, respectively. These values of hydrogen bonds
are similar to those of literature [73].
p
contacts are within the normal ranges [71,79e
81]. Additionally, the anionic unit [HgI4]2ꢀ is packed between
successive 2D supramolecular layers and hold layers together via
ꢀ
weak Hg$$$I bonds (the Hg$$$I distance being 2.788(1) A, and the
sum of van der Waals radii for mercury and iodine being 3.8 A) and
ꢀ
CeH$$$I hydrogen bonds to form 3D supramolecular frameworks
as shown in Fig. 5(c). In CeH$$$I hydrogen bonds, the iodine atoms
are from the anionic unit [HgI4]2ꢀ, and the hydrogen atoms are
from imidazole rings. These values of hydrogen bonds are compa-
rable with those reported [73].
In the crystal packing of 9, 1D double-strand supramolecular
In crystal packing of complex 6 (Fig. 3(c)), the adjacent 1D
polymeric chains are linked together by free bridging acetonitrile
molecules via CeH$$$Br [74] and CeH$$$N [75] hydrogen bonds to
form 2D supramolecular layers. The hydrogen atoms in CeH$$$Br
hydrogen bonds are from the methyl of acetonitrile, and the
hydrogen atoms in CeH$$$N hydrogen bonds are from the imid-
azole rings (Table 2). These values of hydrogen bonds are consistent
with those published.
chain is formed by CeH$$$I hydrogen bonds [73] and CeH$$$
contacts [71,79e81] (Fig. 6(b)). In CeH$$$I hydrogen bonds, the
iodine atoms are from the cations, and the hydrogen atoms are
p
from CH2 (Table 2). In CeH$$$
p
contacts (H$$$
angle being 146.1ꢁ), the hydrogen atoms
are from CH3 of propyl and systems are from benzimidazole rings.
p distance being
ꢀ
3.044(4) A, and CeH$$$
p
p
Additionally, the anionic unit [HgI4]2ꢀ are packed between suc-
cessive 1D supramolecular chains and hold chains together via two
new CeH$$$I hydrogen bonds to form 2D supramolecular layer
(Fig. 6(c)). In new CeH$$$I hydrogen bonds, the iodine atoms are
from the anionic unit [HgI4]2ꢀ, and the hydrogen atoms are from
CH3 and benzimidazole rings, respectively. These values of CeH$$$I
Analysis of crystal packing of complex 7 (Fig. 4(b)) reveals that
1D supramolecular tubular structure is formed by two row mole-
cules through
pep interactions from the benzene rings of benzyl
hydrogen bonds and CeH$$$p contacts are fall in normal ranges.
Table 1
Dihedral angles (ꢁ) between two imidazole (or benzimidazole) rings (A) on the same
ligand, dihedral angles (ꢁ) between the mesitylene plane and two imidazole (or
benzimidazole) rings on the same ligand (B), and dihedral angles between imidazole
(or benzimidazole) ring and adjacent benzene ring of benzyl group (or pyridine ring)
(C) For precursor 2 and complexes 5e9.
2.5. The conformations of the diimidazolium (or
dibenzimidazolium) salts and their metal complexes
As shown in Scheme 4, the diimidazolium (or dibenzimidazo-
lium) salts with mesitylene linker adopt two diverse conformations
(i.e., cis-conformation I and trans-conformation II) according to the
different arrangements of two Rimi (or Rbimi) arms. The confor-
mations I and II can converse to each other in the solution, and
their ratio may be mostly relative to two factors: (1) the weak in-
teractions between anions and two Rimi (or Rbimi) arms; (2) the
Compounds
A
B
C
2
5
6
7
8
9
14.3
21.9
51.3
86.7
55.6
21.7
85.3, 86.0
75.6, 80.2
88.9, 81.6
84.2, 88.1
79.0, 89.1
76.5, 76.9
e
68.8, 88.4
83.6, 88.0
83.8, 84.1
e
e

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
41
Fig. 5. (a). Perspective view of 8 and anisotropic displacement parameters depicting 50% probability. All hydrogen atoms except that in CHCN were omitted for clarity. Selected bond
ꢁ
ꢀ
lengths (A) and angles ( ): Hg(1)eC(17) 2.070(1), Hg(2)eC(1) 2.068(1), Hg(1)eC(23) 2.080(1), Hg(2)eC(23) 2.092(1); C(1)eHg(2)eC(23) 175.3(5), C(17)eHg(3)eC(23) 175.3(4),
N(1)eC(1)eN(2) 105.8(1). (b). 2D supramolecular layer of complex 8 via both CeH$$$ contacts and Hg$$$N interactions. All hydrogen atoms except those participating in the Ce
H$$$ hydrogen bonds were omitted for clarity. (c). 3D supramolecular network of complex 8 via CeH$$$ contacts, Hg$$$N interactions and CeH$$$I hydrogen bonds. All hydrogen
atoms except those participating in the CeH$$$ contacts and CeH$$$I hydrogen bonds were omitted for clarity.
p
p
p
p

42
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
ꢀ
Fig. 6. (a). Perspective view of 9 and anisotropic displacement parameters depicting 50% probability. All hydrogen atoms were omitted for clarity. Selected bond lengths (A) and
angles (ꢁ): Hg(1)eC(7) 2.098(9), Hg(1)eC(28) 2.100(9), Hg(1)eI(1) 2.927(1); C(7)eHg(1)eC(28) 158.9(4), C(7)eHg(1)eI(1) 100.7(3), C(28)eHg(1)eI(1) 100.2(3), N(1)eC(7)eN(2)
108.4(8). (b). 1D double-strand supramolecular chain of 9 by CeH$$$I hydrogen bonds and CeH$$$
hydrogen bonds and CeH$$$ contacts were omitted for clarity. (c). 2D supramolecular layer of 9 by CeH$$$I hydrogen bonds and CeH$$$
those participating in the CeH$$$I hydrogen bonds and CeH$$$ contacts were omitted for clarity.
p
contacts. All hydrogen atoms except those participating in the CeH$$$I
p
p
contacts. All hydrogen atoms except
p
steric hindrance between two Rimi (or Rbimi) arms. The former
may have larger effect on the ratio of conformation than the latter.
When there exist strong interactions between one anion and two
Rimi (or Rbimi) arms at the same time in a compound, the two arms
lie in the same side of mesitylene plane, and the compound adopts
mainly cis-conformation (e.g., 5). When there exist strong in-
teractions between one anion and only one Rimi (or Rbimi) arm in a
compound, two arms lie in the opposite sides of mesitylene plane
due to steric hindrance, and thus trans-conformation is predomi-
nant (e.g., 2).
NHC metal complexes 6e9 possess four different conformations,
namely, the monometal monoligand macrocycle III (e.g., 9), the
dimetal monoligand macrocycle IV (e.g., 8), the dimetal diligand
macrocycle V (e.g., 6) and the open structure composed of one
bidentate dicarbene ligand and two metal atoms VI (e.g., 7). The
conformations of the complexes may be relative to the
corresponding precursors’ conformations, metal ions, counterions,
steric hindrance.
2.6. Catalytic activity of NHC palladium(II) complex 7
The SuzukieMiyaura cross-coupling reaction of aryl halides and
arylboronic acids is of general interest to organic synthesis. The
SuzukieMiyaura reaction catalyzed by PdeNHC complexes has
been one of the most important methods for the synthesis of un-
symmetrically substituted biaryl compounds [46e48]. We choose
the cross-coupling reaction of 4-bromotoluene with phenylboronic
acid as a model reaction to investigate the solvent and base effects
(Table 3). Using absolute MeOH as solvent and KOH as base gives
96% coupling yield at 60 ꢁC in 8 h (entry 2). Coupling yield drops to
78%, however, when changing solvent to pure water (entry 3). A
mixed solvent of MeOH/H2O (5:1) in the presence of base KOH gives

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
43
moderate to good yields (entries 5, 7 and 8). Other solvents like THF
and DMF give poor yields (entries 4 and 6). The common and less
expensive inorganic bases, such as K3PO4$3H2O, K2CO3, Na2CO3 and
NaHCO3 give high yields in mixed solvent MeOH/H2O (5:1) (entries
15, 16, 19 and 20), and they may be prior reagents of choice. NaOAc
and BaCO3 give 81% and 50% yields, respectively (entries 18 and 22).
Poor yields are obtained using KBr and Ba(OH)2 as base (entries 17
and 21). Based on the extensive screen, MeOH/H2O(5:1) and KOH
are found to be the most efficient solvent and base with a catalyst
loading of 0.2 mol % complex 7 at 60 ꢁC in air, thus giving the
optimal coupling result. The reactions were monitored by GC
analysis after the appropriate intervals. In order to further study the
influence of ligand on catalysis, the control experiment was per-
formed, in which PdCl2(CH3CN)2 were added in the absence of
ligand with the optimized conditions, and only 25% coupling
product was observed (entry 23). This result shows that the ligand
has the preponderant function in the catalytic reaction.
We attempted the cross-coupling reactions of various aryl ha-
lides with phenylboronic acid under the optimal reaction condition.
In general, complex 7 can catalyze the cross-coupling of various aryl
halides with phenylboronic acid to give different yields (Table 4).
The catalyst is efficient toward the coupling of 4-bromoanisole or 1-
bromonaphthaline with phenylboronic acid to give yields of 96%
and 90%, respectively (entries 1 and 5). The coupling of 4-
nitrobromobenzene or 4-bromoacetophenone with phenylboronic
acid leads to moderate yields of 78% and 82%, respectively (entries 3
and 4). The catalyst is highly efficient toward the coupling of
iodobenzene with phenylboronic acid to give a near quantitative
yield (entry 6). The catalyst is also effective toward the coupling of
aryl chlorides with phenylboronic acid. The coupling reaction of 4-
nitrochlorobenzene with phenylboronic acid gave moderate yield
of 64% (entry 9), while 2-chlorotoluene, 4-chloroaniline, 2,4-
N
N
N
N
M
R
R
III
2X-
N
N
N
N
R N
N
N
N R
M
M
R
R
I
Y
IV
M salt
R
N
R
N N
N
R
N
N
M
M
N
2X-
II
N
N
N R
R N
N
R
V
R
N
N
N N
R
M
M
VI
Scheme 4. The diverse conformations of diimidazolium (or dibenzimidazolium) salts
and their metal complexes.
yield of 99% in 8 h (entry 11). The higher activity is attributed to the
better solubility of catalyst and KOH in the aqueous MeOH mixture
and rapid reduction of Pd(II) to Pd(0) [82,83]. Solvents such as
dichloromethane, dioxane and acetonitrile afford the product with
Table 3
Effect of solvent and base on SuzukieMiyaura cross-coupling Reactiona..
0.2 mol % cat.7, base
Br
B(OH)2
H3C
+
H3C
solvent
Entry
Solvent
Base
Time (h)b
Yield(%)c
1
2
3
4
MeOH
MeOH
H2O
THF
KOH
KOH
KOH
KOH
6
8
8
24
8
94
96
78
9
5
CH2Cl2
KOH
53
10
56
84
77
95
99
93
46
18
95
96
24
81
94
92
16
50
25
6
7
8
9
DMF
dioxane
CH3CN
MeOH/H2O(2:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH
H2O
THF
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
MeOH/H2O(5:1)
KOH
KOH
KOH
KOH
KOH
KOH
K3PO4$3H2O
K3PO4$3H2O
K3PO4$3H2O
K3PO4$3H2O
K2CO3
KBr
NaOAc
Na2CO3
NaHCO3
Ba(OH)2
BaCO3
KOH
8
8
8
8
6
8
8
8
8
8
12
8
12
12
12
12
8
10
11
12
13
14
15
16
17
18
19
20
21d
22d
23e
8
a
Reaction conditions: bromobenzene 0.50 mmol, phenylboronic acid 0.60 mmol, base 1.2 mmol, complex 7 0.2 mol%, solvent 3 mL, 60 ꢁC in air.
Reactions were monitored by TLC.
Determined by GC.
Complex 7: 0.4 mol%.
b
c
d
e
Reaction conditions are the same as [a], and only PdCl2(CH3CN)2 was added in the absence of ligand.

44
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
Table 4
3
SuzukieMiyaura cross-coupling of aryl halides with phenylboronic acida..
300
250
200
150
100
50
9
0.2 mol % cat. 7, KOH
X
B(OH)2
+
6
R
MeOH/H2O, 60 °C
R
1
Entry
Aryl halide
Time (h)b
Yield (%)
1
4-bromoanisole
4-bromoaniline
4-nitrobromobenzene
4-bromoacetophenone
1-bromonaphthaline
iodobenzene
2-chlorotoluene
4-chloroaniline
4-nitrochlorobenzene
2,4-dinitrochlorobenzene
2-chloropyridine
8
24
24
24
12
6
24
36
26
24
24
96c
35e
78e
82e
90e
99c
22e
23e
64e
24e
38c
2d
3
4
5
6
7d
8d
9d
10d
11d
0
300
350
400
Wavelength (nm)
a
Reaction conditions: Aryl halides 0.50 mmol, phenylboronic acid 0.60 mmol,
base 1.2 mmol, complex 7 0.2 mol%, MeOH/H2O (5:1) mixed solvent 3 mL, 60 ꢁC in
Fig. 7. Emission spectra of 1 (-$-$), 3 ($$$), 6 (—) and 9 (d) at 298 K in CH3CN
(5.0 ꢂ 10ꢀ6 M) solution.
air.
b
Reactions were monitored by TLC.
Determined by GC.
Complex 7: 0.4 mol%.
Isolated yield.
c
d
3. Conclusions
e
In summary, a series of new NHC silver(I), palladium(II) and
mercury(II) complexes with mesitylene linker have been synthe-
sized and characterized. The diimidazolium (or dibenzimidazo-
lium) salts adopt two diverse conformations (cis- and trans-
conformations), and their NHC metal complexes possess four
different conformations. In crystal packings of precursor 2 and
complexes 5e9, 1D supramolecular chains, 2D supramolecular
layers or 3D architectures are formed via intermolecular weak in-
dinitrochlorobenzene or 2-chloropyridine gave relatively poor
yields of 22%e38% (entries 7, 8, 10 and 11). This catalytic system
shows good tolerance toward a wide range of sensitive functional
groups. Therefore, this provides an alternative and effective
phosphine-free catalytic system for facile coupling of aryl halides
under mild and aerobic conditions.
According to literature report, the catalytic activity of bi-
palladium(II) complexes could be improved by the cooperative ef-
fect of two metal meters [84e86]. By comparison, we can see that
the catalytic activity of biePd(II) complex 2 in most Suzukie
Miyaura reactions is similar to those of known NHC monoePd(II)
complexes [87e89]. This catalyst has not shown the outstanding
superiority, and the reason could be that the distance between two
palladium centers is somewhat far away not to generate effective
cooperative interaction. The distance between two metal centers
may be an important factor for influence on cooperative interac-
tion. Only a suitable distance between two metal centers can an
effective cooperative interaction be generated. Besides, the steric
hindrance of around Pd and the structure of different bridging
linkers may also have some influence on the activity of catalyst.
teractions, including
pep interactions, hydrogen bonds, CeH$$$p
contacts, and weak Hg$$$N and Hg$$$I bonds. NHC palladium(II)
complex 7 can catalyze the most SuzukieMiyaura reaction of aryl
halides (iodide, bromide and chloride) with phenylboronic acid
using MeOH/H2O as solvent and KOH as base in air. Further studies
on new organometallic compounds from precursors 1e4 and
analogous ligands are underway.
4. Experimental section
4.1. General procedures
All manipulations were performed using Schlenk techniques,
and solvents were purified by standard procedures. All the reagents
for synthesis and analyses were of analytical grade and used
without further purification. Melting points were determined with
a Boetius Block apparatus. 1H and 13C NMR spectra were recorded
on a Varian Mercury Vx 400 spectrometer at 400 MHz and
2.7. Fluorescent emission spectra of precursors 1 and 3, and
complexes 6 and 9
As shown in Fig. 7, the fluorescent emission spectra of pre-
cursors 1 and 3, and complexes 6 and 9 in acetonitrile at room
temperature are obtained upon excitation at 250 nm (the fluores-
cent emission spectrum of 2 is similar to that of 1; the fluorescent
emission spectra of 4 and 5 are similar to that of 3; the fluorescent
emission spectra of 7 and 8 are similar to that of 6). Precursors 1
and 3 exhibit broad emission bands in the region of 325e345 nm,
corresponding to intraligand transitions [90]. Complexes 6 and 9
exhibit double emission bands, and the intense emission bonds in
the region of 325e345 nm are similar to those of corresponding
precursors, which should originate from the metal perturbed
intraligand processes [91]. It is notable that new emission bonds of
6 and 9 in the region of 298e315 nm are observed, which may arise
from the electronic transitions of the benzene ring due to the in-
fluence of metal and ligand coordination interactions [91e93]. The
results show that these metal complexes might have potential
application in photoactive materials.
100 MHz, respectively. Chemical shifts, d, are reported in ppm
relative to the internal standard TMS for both 1H and 13C NMR. J
values are given in Hz. Elemental analyses were measured using a
PerkineElmer 2400C Elemental Analyzer. The luminescent spectra
were conducted on a Cary Eclipse fluorescence spectrophotometer.
GC analysis was carried out using a Focus DSQI GCeMS equipped
with an integrator (C-R8A) with a capillary column (CBP-1 or CBP-5,
0.25 mm i.d. ꢂ 40 m).
4.2. Synthesis of 1,3-bis[1-benzylimidazolemethyl]mesitylene
bromide (1)
A THF solution (40 mL) of imidazole (1.420 g, 20.8 mmol) was
added to a suspension of oil-free sodium hydride (0.500 g,
20.8 mmol) in THF (40 mL) and stirred for 1 h at 60 ꢁC. Then benzyl

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
45
bromide (3.240 g, 19.0 mmol) was added dropwise to the above
solution. The mixture was stirred for 22 h at 60 ꢁC, and a brown
solution was obtained. The solvent was removed with a rotary
evaporator and H2O (50 mL) was added to the residue. Then the
solution was extracted with CH2Cl2 (3 ꢂ 30 mL), and the extracting
solution was dried with anhydrous MgSO4. After removing CH2Cl2,
a pale yellow solid was obtained.
CH3), 5.76 (s, 4H, CH2), 5.79 (s, 4H, CH2), 7.30 (m, 9H, PhH), 7.42 (d,
J ¼ 7.0, 2H, PhH), 7.63 (t, J ¼ 7.0, 2H, PhH), 7.70 (t, J ¼ 6.8, 2H, PhH),
7.88 (d, J ¼ 7.8, 2H, PhH), 8.20 (d, J ¼ 7.8, 2H, PhH), 9.77 (s, 2H, 2-
bimiH). 13C NMR (100 MHz, DMSO-d6):
d 141.3 and 140.4 (2-
bimiC), 134.1, 131.7, 131.1, 128.8, 128.5, 127.8, 127.5, 126.9, 126.7,
114.0 and 113.9 (PhC), 49.8 and 45.6 (NCH2Ph),19.6 and 15.7 (PhCH3).
A solution of 1-benzylimidazole (2.274 g, 14.4 mmol) and 1,3-
dibromomethylmesitylene (2.000 g, 6.5 mmol) in acetone (100 mL)
was stirred for five days under refluxing, and a white precipitate was
formed. The product was filtered and washed with acetone. The
white powder of 1,3-bis[1-benzylimidazolemethyl]mesitylene bro-
mide (1) was obtained by recrystallization from methanol/ether.
Yield: 3.656 g (90%). M.p.: 278e280 ꢁC. Anal. Calcd for C31H34N4Br2:
C, 59.82; H, 5.51; N, 9.00%. Found: C, 59.53; H, 5.72; N, 9.41%.1H NMR
(400 MHz, DMSO-d6): d 2.09 (s, 6H, CH3), 2.31 (s, 3H, CH3), 5.42 (s, 4H,
CH2), 5.50 (s, 4H, CH2), 7.19 (s,1H, PhH), 7.40 (m,10H, PhH), 7.65 (s, 2H,
imiH), 7.85 (s, 2H, imiH), 9.24 (s, 2H, 2-imiH) (imi ¼ imidazole).
4.6. Synthesis of [1,3-bis(1-benzylbenzimidazolemethyl)mesitylene]
[HgI4] (5)
Mercury iodide (0.277 g, 0.6 mmol) was added to a solution of
1,3-bis[1-benzylbenzimidazolemethyl]mesitylene
iodide
(6)
(0.200 g, 0.3 mmol) in dichloromethane (30 mL) and the solution
was stirred for 24 h under refluxing. The resulting solution was
filtered and concentrated to 5 mL, and Et2O (8 mL) was added to
precipitate a pale yellow powder. Isolation by filtration yielded
anionic complex 6. Yield: 0.182 g (52%). M.p.: 284e286 ꢁC. Anal.
Calcd for C39H38HgI4N4: C, 36.86; H, 3.01; N, 4.41%. Found: C, 36.62;
H, 3.45; N, 4.21%. 1H NMR (400 MHz, DMSO-d6):
d 2.10 (s, 6H, CH3),
4.3. Synthesis of 1,3-bis[1-ethylimidazolemethyl]mesitylene
hexafluorophosphate (2)
2.36 (s, 3H, CH3), 5.81 (s, 4H, CH2), 5.88 (s, 4H, CH2), 7.36 (m, 9H,
PhH), 7.47 (d, J ¼ 7.2, 2H, PhH), 7.69 (t, J ¼ 7.2, 2H, PhH), 7.78 (t,
J ¼ 7.0, 2H, PhH), 7.93 (d, J ¼ 7.4, 2H, PhH), 8.31 (d, J ¼ 7.4, 2H, PhH),
A solution of 1-ethylimidazole (1.382 g, 14.4 mmol) and 1,3-
dibromomethylmesitylene (2.000 g, 6.5 mmol) in THF (100 mL)
was stirred for five days under refluxing, and a white precipitate
was formed. The product was filtered and washed with THF. The
white powder of 1,3-bis[1-ethylimidazolemethyl]mesitylene bro-
mide was obtained by recrystallization from methanol/ether. Yield:
3.021 g (93%). M.p.: 258e260 ꢁC.
9.85 (s, 2H, 2-bimiH). 13C NMR (100 MHz, DMSO-d6):
d 141.2 and
140.4 (2-bimiC), 134.1, 131.7, 131.1, 128.8, 128.5, 127.7, 127.5, 126.9,
126.7, 114.0 and 113.9 (PhC), 49.9 and 45.6 (NCH2Ph), 19.6 and 15.6
(PhCH3).
4.7. Synthesis of {[mesitylene(CH2imyPhCH2)2]2Ag2$Ag2Br4}n (6)
NH4PF6 (1.439 g, 8.8 mmol) was added to a methanol solution of
1,3-bis[1-ethylimidazolemethyl]mesitylene bromide (2.000 g,
4.0 mmol) whilst stirring, and a white precipitate was formed
immediately. The product was collected by filtration, washed with
small portions of cold methanol, and dried in vacuum to give a
white powder of 1,3-bis[1-ethylimidazolemethyl]mesitylene hex-
afluorophosphate (2). Yield: 2.318 g (92%). M.p.: 192e194 ꢁC. Anal.
Calcd for C21H30F12N4P2: C, 40.14; H, 4.81; N, 8.92%. Found: C, 40.53;
Silver oxide (0.081 g, 0.4 mmol) was added to a solution of 1,3-
bis[1-benzylimidazolemethyl]mesitylene bromide (1) (0.200 g,
0.3 mmol) in dichloromethane (30 mL) and the suspension solution
was stirred for 24 h under refluxing in N2 protection. The resulting
solution was filtered and concentrated to 5 mL, and Et2O (5 mL) was
added to precipitate a white powder. Isolation by filtration yielded
complex 6. Yield: 0.174 g (59%). M.p.: 174e176 ꢁC. Anal. Calcd for
C62H64Ag4Br4N8: C, 44.53; H, 3.86; N, 6.70%. Found: C, 44.32; H,
H, 4.44; N, 8.64%. 1H NMR (400 MHz, DMSO-d6):
d
1.23 (t, J ¼ 3.6,
3.64; N, 6.91%. 1H NMR (400 MHz, DMSO-d6):
d 2.08 (s, 6H, CH3),
6H, CH3), 1.96 (s, 3H, CH3), 2.13 (s, 6H, CH3), 3.95 (q, J ¼ 3.6, 4H, CH2),
5.25 (s, 4H, CH2), 7.03 (s, 1H, PhH), 7.13 (s, 2H, imiH), 7.30 (s, 2H,
imiH), 8.32 (s, 2H, 2-imiH).
2.30 (s, 3H, CH3), 5.35 (s, 4H, CH2), 5.45 (s, 4H, CH2), 7.12 (m, 5H,
PhH), 7.39 (m, 4H, PhH), 7.64 (m, 4H, PhH or imiH), 7.78 (m, 2H, PhH
or imiH). 13C NMR (100 MHz, DMSO-d6):
d 179.3 (Ccarbene), 139.0,
The following dibenzimidazolium salts 3 and 4 were prepared in
a manner analogous to that of 2, only instead of ammonium hex-
afluorophosphate with sodium iodide in the second step.
138.4, 131.9, 131.4, 129.1, 127.6, 123.4, 122.7 and 122.6 (PhC or imiC),
56.1 and 49.9 (NCH2Ph), 21.0 and 17.5 (PhCH3).
4.8. Synthesis of {mesitylene[(CH2imyPhCH2)PdCl2(CH3CN)]2} (7)
4.4. Synthesis of 1,3-bis[1-(n-propyl)benzimidazolemethyl]
mesitylene iodide (3)
The suspension solution of complex 9 (0.668 g, 0.4 mmol) and
PdCl2(CH3CN)2 (0.092 g, 0.4 mmol) in dichloromethane (30 mL)
was stirred for 24 h under refluxing in N2 protection. The resulting
solution was filtered and concentrated to 5 mL, and Et2O (5 mL) was
added to precipitate a pale yellow powder. Isolation by filtration
yielded complex 7. Yield: 0.167 g (57%). M.p.: 264e266 ꢁC. Anal.
Calcd for C35H38Cl4N6Pd2: C, 46.85; H, 4.27; N, 9.37%. Found: C,
Yield: 3.693
C31H38N4I2: C, 51.68; H, 5.32; N, 7.78%. Found: C, 51.37; H, 5.61; N,
7.92%. 1H NMR (400 MHz, DMSO-d6):
g
(90%). M.p.: 250e252 ꢁC. Anal. Calcd for
d
1.25 (t, J ¼ 6.0, 6H, CH3), 1.91
(m, 4H, CH2), 2.09 (s, 6H, CH3), 2.36 (s, 3H, CH3), 4.25 (t, J ¼ 5.4, 4H,
CH2), 5.77 (s, 4H, CH2), 7.32 (s, 1H, PhH), 7.51 (m, 4H, PhH), 7.83 (d,
J ¼ 7.4, 2H, PhH), 8.20 (d, J ¼ 7.4, 2H, PhH), 9.62 (s, 2H, 2-bimiH). 13C
46.62; H, 4.53; N, 9.21%. 1H NMR (400 MHz, DMSO-d6):
d 2.08 (s, 6H,
NMR (100 MHz, DMSO-d6):
d
140.9 and 140.3 (2-bimiC), 139.5,
CH3), 2.32 (s, 3H, CH3), 2.35 (s, 6H, CH3CN), 5.61e5.71 (m, 8H, CH2),
6.62e6.72 (m, 3H, PhH), 7.10e7.30 (m, 2H, PhH or imiH), 7.32e7.46
(m, 8H, PhH or imiH), 7.56 (d, J ¼ 6.4, 2H, PhH). 13C NMR (100 MHz,
131.6, 131.4, 127.5, 126.8, 126.6, 113.9 and 113.8 (PhC), 48.0
(NCH2Ph), 45.4 (NCH2CH2CH3), 22.3 (CH2CH2CH3), 19.6 and 15.5
(PhCH3), 10.5 (CH2CH2CH3) (bimi ¼ benzimidazole).
DMSO-d6):
d 153.3 (Ccarbene), 139.8, 136.7, 131.4, 129.2, 129.0, 128.8,
128.6, 123.3 and 121.6 (PhC or imiC), 54.9, 50.1 and 49.9 (NCH2Ph or
4.5. Synthesis of 1,3-bis[1-benzylbenzimidazolemethyl]mesitylene
CN), 21.3 and 17.6 (PhCH3 or CH3CN). IR (KBr):
n
CN, 2150 cmꢀ1
.
iodide (4)
4.9. Synthesis of {mesitylene[(CH2imyEt)2Hg2(CHCN)][HgI4]} (8)
Yield: 3.600
C39H38N4I2: C, 57.37; H, 4.69; N, 6.86%. Found: C, 57.21; H, 4.84; N,
6.52%. 1H NMR (400 MHz, DMSO-d6):
2.09 (s, 6H, CH3), 2.30 (s, 3H,
g
(63%). M.p.: 260e262 ꢁC. Anal. Calcd for
Mercury iodide (0.454 g, 1.0 mmol) was added to a solution of
1,3-bis[1-ethylimidazolemethyl]-2,4,6-trimethylbenzene bromide
d

46
Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
Table 5
(0.200 g, 0.4 mmol) in acetonitrile (30 mL) and the suspension
solution was stirred for 24 h at refluxing. The resulting solution was
filtered and concentrated to 5 mL, and Et2O (10 mL) was added to
precipitate a yellow powder. Isolation by filtration yielded complex
8. Yield: 0.260 g (48.3%). M.p.: 176e178 ꢁC. Anal. Calcd for
C23H29Hg3I4N5: C, 18.60; H, 1.97; N, 4.72%. Found: C, 18.74; H, 2.06;
Summary of crystallographic data for 2, 5 and 6.
2
5
6$4CH3CN
Chemical formula
C
21H30F12N4P2
C39H38HgI4N4
C62H64Ag4Br4N8
$4CH3CN
1836.55
Monoclinic
P21/n
10.869(1)
24.594(3)
13.847(1)
90
100.2(2)
90
3641.6(8)
2
fw
628.43
Triclinic
ꢁ
Pı
1270.92
Monoclinic
P21/n
11.519(1)
22.071(3)
16.697(2)
90
106.0(2)
90
4080.1(9)
4
Cryst syst
space group
N, 4.53%. 1H NMR (400 MHz, DMSO-d6):
d
1.42 (t, J ¼ 2.6, 6H, CH3),
2.09 (s, 9H, PhCH3), 2.37 (s, H, CNCH), 4.25e4.32 (m, 4H, CH2CH3),
5.43 (s, 4H, CH2Ph), 7.81e7.84 (m, 4H, imiH), 7.86 (s, 1H, PhH),
ꢀ
a/A
8.973(9)
10.305(1)
15.828(1)
97.7(1)
105.1(2)
96.6(2)
1381.9(2)
2
ꢀ
b/A
(imi ¼ imidazole). IR (KBr):
n .
CN, 2137 cmꢀ1 13C NMR (100 MHz,
ꢀ
c/A
a
/deg
/deg
DMSO-d6): 180.0 (Ccarbene), 141.8, 140.7, 133.2, 130.3, 129.3, 125,1,
d
b
123.5 and 122.8 (PhC, imiC or CN), 49.6 (NCH2Ph), 48.1 (NCH2CH3),
32.1 (HgCCN), 21.4 and 20.8 (PhCH3), 17.4 (CH2CH3).
g
/deg
3
ꢀ
V/A
Z
Dcalcd, Mg/m3
Abs coeff, mmꢀ1
F(000)
1.510
0.257
644
2.069
6.830
2368
1.675
3.302
1816
4.10. Synthesis of [mesitylene(CH2bimynPr)2HgI]1/2[HgI4] (9)
Cryst size, mm
0.32 ꢂ 0.30 ꢂ
0.32 ꢂ 0.30 ꢂ
0.38 ꢂ 0.32 ꢂ
A suspension of KOtBu (0.112 g, 1.0 mmol), mercury iodide
(0.319 g, 0.7 mmol) and 1,3-bis[1-(n-propyl)benzimidazolemethyl]
mesitylene iodide (3) (0.200 g, 0.3 mmol) in dichloromethane
(30 mL) was stirred for 24 h under refluxing in N2 protection. The
resulting solution was filtered and concentrated to 5 mL, and Et2O
(10 mL) was added to precipitate a pale yellow powder. Isolation
by filtration yielded complex 9. Yield: 0.214 g (59%). M.p.: 270e
272 ꢁC. Anal. Calcd for C31H36Hg1.5I3N4: C, 32.48; H, 3.17; N,
4.89%. Found: C, 32.31; H, 3.45; N, 4.67%. 1H NMR (400 MHz,
0.22
0.20
0.28
qmin
,
qmax, deg
1.35, 25.03
296(2)
7114
4851
356
1.85, 25.03
296(2)
20364
7176
436
1.023
1.49, 25.03
296(2)
18688
12415
819
T/K
No. of data collected
No. of unique data
No. of refined params
Goodness-of-fit on F2a
1.055
1.025
Final R indicesb [I > 2
s(I)]
R1
wR2
0.0731
0.2089
0.0766
0.2286
0.0380
0.0775
R indices (all data)
R1
wR2
DMSO-d6):
d
0.97 (t, J ¼ 6.2, 6H, CH3), 2.04 (m, 4H, CH2), 2.16 (s,
0.0850
0.2239
0.1091
0.2664
0.0554
0.0841
6H, CH3), 2.62 (s, 3H, CH3), 4.42 (m, 2H, CH2), 4.55 (m, 2H, CH2),
5.73 (d, J ¼ 11.4, 2H, CH2), 6.10 (d, J ¼ 11.4, 2H, CH2), 7.33 (s, 1H,
PhH), 7.72 (m, 4H, PhH), 8.06 (d, J ¼ 7.0, 2H, PhH), 8.28 (d, J ¼ 7.0,
a
Goof ¼ [S
u
(F2o ꢀ F2c)2/(n ꢀ p)]1/2, where n is the number of reflection and p is the
number of parameters refined.
2H, PhH). 13C NMR (100 MHz, DMSO-d6):
d 184.1 (Ccarbene), 141.1,
b
R1 ¼ S(jjFoj ꢀ jFcjj)/SjFoj; wR2 ¼ [S[w(F2o ꢀ Fc2)2]/Sw(Fo2)2]1/2
.
137.9, 134.9, 134.4, 133.7, 129.1, 126.5, 126.2 and 113.4 (PhC), 51.2
(NCH2Ph), 45.7 (NCH2CH2), 31.1, 23.1 and 21.0 (PhCH3), 17.2
(CCH2C), 11.4 (CH2CH3).
Table 6
Summary of crystallographic data for 7e9.
4.11. General procedure for the SuzukieMiyaura cross-coupling
7$H2O
35H38Cl4N6Pd2
8
9
reaction
chemical formula
C
C
23H29Hg3I4N5
C31H36Hg1.5I3N4
$H2O
In a typical reaction, aryl halide (0.5 mmol), phenylboronic acid
(0.6 mmol), base (1.2 mmol) and PdeNHC complex 7 (0.2 mol %) in
organic solvent (2.5 mL) and water (0.5 mL if needed) were stirred
at 60 ꢁC in air. After the desired reaction time, the reaction was
stopped, and water (20 mL) was added to the reaction mixture. The
mixture was extracted by n-hexane (10 mL ꢂ 3), and the organic
layer was washed with water (10 mL ꢂ 3) and dried over anhydrous
MgSO4. Then the solution was filtered and concentrated to 5 mL.
The solution was analyzed by GC or separated by a column to get
the products.
fw
915.33
Monoclinic
P21/n
18.896(1)
8.818(6)
26.377(1)
90
110.3(1)
90
4121.4(5)
4
1484.88
Triclinic
ꢁ
Pı
1146.23
Triclinic
ꢁ
Pı
Cryst syst
Space group
ꢀ
a/A
11.665(1)
13.163(2)
13.284(2)
81.8(3)
68.1(3)
84.4(3)
1872.0(5)
2
13.262(3)
16.872(4)
17.247(4)
70.8(4)
89.1(3)
73.3(3)
3480.2(1)
2
ꢀ
b/A
ꢀ
c/A
a
/deg
/deg
b
g
/deg
3
ꢀ
V/A
Z
Dcalcd, Mg/m3
Abs coeff, mmꢀ1
F(000)
1.475
1.166
1840
2.634
2.187
15.588
1308
9.304
2114
4.12. X-ray structure determinations
Cryst size, mm
0.38 ꢂ 0.32 ꢂ
0.22 ꢂ 0.20 ꢂ
0.22 ꢂ 0.20 ꢂ
0.30
0.18
0.18
For complexes 2, and 5e9 selected single crystals were mounted
qmin
,
qmax, deg
1.16, 25.03
296(2)
20400
7298
2.01, 25.01
296(2)
9494
1.61, 25.01
296(2)
17576
T/K
on a Bruker APEX II CCD diffractometer at 293(2) K with Mo-K
a
No. of data collected
No. of unique data
ꢀ
radiation (
l
¼ 0.71073 A) by
u scan mode. Data collection and
6481
12119
reduction were performed using the SMART and SAINT software
[94] with frames of 0.6ꢁ oscillation in the range of 1.8ꢁ <  < 25ꢁ.
An empirical absorption correction was applied using the SADABS
program [95]. The structures were solved by direct methods and all
non-hydrogen atoms were subjected to anisotropic refinement by
full-matrix least squares on F2 using the SHELXTL package [96]. All
hydrogen atoms were generated geometrically (CeH bond lengths
fixed at 0.96 A), assigned appropriated isotropic thermal parame-
ters and included in the final calculations. Crystallographic data
were summarized in Table 5 and Table 6 for 2 and 5e9.
No. of refined params
457
1.078
321
1.061
780
1.033
Goodness-of-fit on F2a
Final R indicesb [I > 2
s(I)]
R1
wR2
R indices (all data)
R1
wR2
0.0509
0.1735
0.0568
0.1494
0.0458
0.1067
0.0681
0.1928
0.0690
0.1580
0.0862
0.1241
ꢀ
a
Goof ¼ [S
u
(F2o ꢀ F2c)2/(n ꢀ p)]1/2, where n is the number of reflection and p is the
number of parameters refined.
b
R1 ¼ S(jjFoj ꢀ jFcjj)/SjFoj; wR2 ¼ [S[w(F2o ꢀ Fc2)2]/Sw(Fo2)2]1/2
.

Q.-X. Liu et al. / Journal of Organometallic Chemistry 731 (2013) 35e48
47
[35] Q.X. Liu, L.N. Yin, J.C. Feng, J. Organomet. Chem. 692 (2007) 3655e3663.
[36] L. Ray, M.M. Shaikh, P. Ghosh, Organometallics 26 (2007) 958e964.
Acknowledgments
[37] A.R. Chianese, P.T. Bremer, C. Wong, R.J. Reynes, Organometallics 28 (2009)
5244e5252.
[38] W.N.O. Wylie, A.J. Lough, R.H. Morris, Organometallics 29 (2010) 570e581.
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[41] J.J. Van Veldhuizen, J.E. Campbell, R.E. Giudici, A.H. Hoveyda, J. Am. Chem. Soc.
127 (2005) 6877e6882.
This work was financially supported by the National Natural
Science Foundation of China (No. 21172172), Tianjin Natural Science
Foundation (No. 11JCZDJC22000) and the Open Foundation of State
Key Laboratory of Elemento-organic Chemistry, Nankai University
(No. 201203).
Appendix A. Supplementary material
[42] K.S. Coleman, H.T. Chamberlayne, S. Turberville, M.L.H. Green, A.R. Cowley,
Dalton Trans. 14 (2003) 2917e2922.
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3653e3658.
[44] Y.S. Liu, X.J. Wan, F.B. Xu, Organometallics 28 (2009) 5590e5592.
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ganometallics 26 (2007) 5627e5635.
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5415.
CCDC 794741, 794739, 794740, 794734, 891372 and 794735
contain the supplementary crystallographic data for for 2 and 5e9
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge,
CB2 1EZ, UK; fax: (þ44) 1223-336-033; or e-mail: deposit@ccdc.
cam.ac.uk.
[48] S.P. Nolan, N-Heterocyclic Carbenes in Synthesis, Wiley-VCH Verlag GmbH &
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Appendix B. Supporting information
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Supporting information related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2013.01.026.
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