N-Heterocyclic carbene silver(I), palladium(II) and mercury(II) complexes: Synthesis, structural studies and catalytic activity

Article abstract of DOI:10.1039/c2ce25365h

The bis-benzimidazolium salts, 1,2-bis[2-(N-R-benzimidazolemethyl)phenoxy] ethane chloride (L¹H₂: R = Et, L²H₂: R = ⁿBu), 1,3-bis[2-(N-R-benzimidazolemethyl)phenoxy]propane chloride (L³H₂: R = ⁿPr, L⁴H ₂: R = ⁿBu) and bis[N-R-benzimidazolemethyl]mesitylene 2X (L⁵H₂: R = ⁿBu, X = I; L⁶H ₂: R = PyCH₂, X = Br and L⁷H₂: R = PhCH₂, X = Br), as well as their eight NHC silver(i), palladium(ii) and mercury(ii) complexes, [(L¹Ag)₂Ag₂Cl ₄] (1), [L¹(PdCl₂CH₃CN)₂] (2), [(L²Ag)₂AgCl₂][AgCl₂] (3), [(L³Ag₂Cl₂)_n] (4), [(L ⁴Ag₂Cl₂)_n] (5), [L ⁵HgI][HgI₄]_0.5 (6), [L⁶Hg][HgBr ₄] (7) and [L⁷Ag][(NO₃)_0.76Br _0.24] (8) have been prepared and characterized. The complexes 1-8 adopt four different structures: (1) with bis-macrometallocycles connected via a Ag₂Cl₄ unit for 1 and via a AgCl₂ unit for 3, (2) an open structure formed via one ligand and two metal atoms for 2, (3) 1D polymeric chains formed by the monomers of a cage-like cavity via weak Ag...Cl bonds (monomer: L³Ag₂Cl₂ for 4 and L⁴Ag₂Cl₂ for 5) and (4) a macrocyclic structure formed by one ligand and one metal for 6-8. In the crystal packing of these complexes, 1D supramolecular chains, 2D supramolecular layers and 3D supramolecular architectures are formed via intermolecular weak interactions, including π-π interactions, hydrogen bonds, C-H...π contacts and weak Hg...Br bonds. Particularly, the catalytic activity of the NHC palladium(ii) complex 2 in Suzuki-Miyaura cross-coupling reactions was studied.

Full text of DOI:10.1039/c2ce25365h

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Manuscript ID CE-ART-03-2012-025365
N-Heterocyclic carbene silver(I), palladium(II) and mercury(II)
complexes: synthesis, structural studies and catalytic activity
Qing-Xiang Liu*, Hong Wang, Xiao-Jun Zhao, Zhao-Quan Yao, Zhi-Qiang Wang,
Ai-Hui Chen and Xiu-Guang Wang
Tianjin Key Laboratory of Structure and Performance for Functional Molecule,
College of Chemistry, Tianjin Normal University, Tianjin 300387, P. R. China
* Corresponding author, E-mail: qxliu@eyou.com
The bis-benzimidazolium salts, 1,2-bis[2-(N-R-benzimidazolemethyl)phenoxy]ethane
chloride
(L1H2:
R
=
Et,
L2H2:
R
=
nBu),
1,3-bis[2-(N-R-benzimidazolemethyl)phenoxy]propane chloride (L3H2: R = nPr, L4H2:
n
n
R = Bu) and bis[N-R-benzimidazolemethyl]mesitylene 2X (L5H2: R = Bu, X = I;
L6H2: R = PyCH2, X = Br and L7H2: R = PhCH2, X = Br), as well as their eight
NHC silver(I), palladium(II) and mercury(II) complexes, [(L1Ag)2Ag2Cl4] (1),
[L1(PdCl2CH3CN)2] (2), [(L2Ag)2AgCl2][AgCl2] (3), [(L3Ag2Cl2)n] (4), [(L4Ag2Cl2)n]
(5), [L5HgI][HgI4]0.5 (6), [L6Hg][HgBr4] (7) and [L7Ag][(NO3)0.76Br0.24] (8) have been
prepared and characterized. The complexes 1-8 adopt four different structures: (1) the
bis-macrometallocycles connected via Ag2Cl4 unit for 1 and via AgCl2 unit for 3, (2)
the open structure formed via one ligand and two metal atoms for 2, (3) 1D polymeric
chains formed by the monomers of cage-like cavity via weak Ag···Cl bonds
(monomer: L3Ag2Cl2 for 4 and L4Ag2Cl2 for 5) and (4) the macrocyclic structure
formed by one ligand and one metal for 6-8. In the crystal packings of these
complexes, 1D supramolecular chains, 2D supramolecular layers and 3D
supramolecular architectures are formed via intermolecular weak interactions,
including π-π interactions, hydrogen bonds, C-H···π contacts and weak Hg···Br bonds.
Particularly, the catalytic activity of the NHC palladium(II) complex 2 in
1

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Suzuki-Miyaura cross-coupling reaction was studied.
Keywords: Carbene; Silver; Palladium; Mercury; Catalysis
Introduction
The metal complexes of N-heterocyclic carbene (NHC) have been known since 1968.1
After the isolation of the first stable free N-heterocyclic carbene by Arduengo et al. in
1991,2 metal complexes based on imidazol-2-ylidene (imy) or benzimidazol-2-ylidene
(bimy) have received considerable attention in organometallic chemistry.3 The
transition metal complexes of N-heterocyclic carbenes are frequently prepared
through deprotonation of N, N’-disubstituted imidazolium (or benzimidazolium)
salts.4 And another widely employed synthetic strategy is the use of NHC silver
complexes as carbene transfer agents to the preparation of some other metal NHC
complexes such as Ni, Pd, Pt, Cu, Au, Rh, Ir and Ru carbene complexes.5 The
relatively easy preparation of the NHC metal complexes with monodentate, bidentate
and polydentate ligands allowed that they were studied systematically.6 One of main
applications of NHC transition metal complexes is used as catalyst in some organic
reactions.7 In particular, the palladium(II) complexes containing the NHC ligands
have been demonstrated to be excellent catalysts for some organic reactions, such as
Suzuki-Miyaura and Heck cross-couplings.8 The valuable properties of the NHC
metal complexes are relevant to their higher thermal stability and lower sensitivity
toward oxygen and moisture.
In the family of N-heterocyclic carbenes, NHC metal complexes from
bis-imidazolium (or bis-benzimidazolium) salts with bridging linkers (such as
phenelene,9 pyridyl and lutidinyl,10 ether chain11 and alkyl12) are an attractive field of
research, because different bridging linkers can generate different coordination
possibilities. We are interested in bis-NHC ligands and their metal complexes.
Recently, some silver(I) and mercury(II) complexes based on bidentate bis-NHC
ligands with alkyl, oligoether and phenylene linkers have been reported by us.13 In this
paper, we report the synthesis of a group of new bis-benzimidazolium salts,
2

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1,2-bis[2-(N-R-benzimidazolemethyl)phenoxy]ethane chloride (L1H2: R = Et, L2H2:
R = nBu), 1,3-bis[2-(N-R-benzimidazolemethyl)phenoxy]propane chloride (L3H2: R =
nPr, L4H2: R = nBu) and bis[N-R-benzimidazolemethyl]mesitylene 2X (L5H2: R = nBu,
X = I; L6H2: R = PyCH2, X = Br and L7H2: R = PhCH2, X = Br), as well as the
synthesis and structures of eight NHC silver(I), palladium(II) and mercury(II)
complexes, [(L1Ag)2Ag2Cl4] (1), [L1(PdCl2CH3CN)2] (2), [(L2Ag)2AgCl2][AgCl2] (3),
[(L3Ag2Cl2)n] (4), [(L4Ag2Cl2)n] (5), [L5HgI][HgI4]0.5 (6), [L6Hg][HgBr4] (7) and
[L7Ag][(NO3)0.76Br0.24] (8). Moreover, the catalytic activity of NHC palladium(II)
complex 2 in Suzuki-Miyaura cross-coupling reaction was investigated.
Result and discussions
Synthesis and general characterization of bis-benzimidazolium salts L1H2-L7H2
The salicylic aldehyde as starting material was etherificated with 1,2-dibromoethane,
then the aldehyde groups were reduced by sodium borohydride to form
1,2-bis(2-hydroxymethylphenoxy)ethane.
The
hydroxyl
groups
of
1,2-bis(2-hydroxymethylphenoxy)ethane were substituted by chlorine atoms through
using thionyl chloride to give 1,2-bis(2-(chloromethyl)phenoxy)ethane. Finally, the
reaction of 1,2-bis(2-(chloromethyl)phenoxy)ethane with N-alkyl-benzimidazole
afforded
the
bis-benzimidazolium
salts,
1,2-bis[2-(N-R-benzimidazolemethyl)phenoxy]ethane chloride (L1H2: R = Et, L2H2:
R = nBu) (Scheme 1). 1,3-bis[2-(N-R-benzimidazolemethyl)phenoxy]propane
chloride (L3H2: R = nPr, L4H2: R = nBu) were prepared in a manner analogous to that
for L1H2 (Scheme 1). Bis[N-R-benzimidazolemethyl]mesitylene bromide (L6H2: R =
PyCH2 and L7H2:
R
=
PhCH2) was prepared via the reaction of
N-alkyl-benzimidazole with 1,3-bis(bromomethyl)mesitylene (method 1 of Scheme 2).
Bis[N-butyl-benzimidazolemethyl]mesitylene iodide (L5H2) was obtained via two
steps, and first step is in a manner analogous to that of L6H2 and section step is the
anion exchange with sodium iodide in acetone (method 2 of Scheme 2). Precursors
L1H2-L7H2 are stable toward air and moisture, soluble in polar organic solvents such
3

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as dichloromethane, acetonitrile and methanol, and almost insoluble in benzene,
1
diethyl ether and petroleum ether. In the H NMR spectra of L1H2-L7H2, the
benzimidazolium proton signals (NCHN) appear at δ = 9.47-10.03 ppm, which are
consistent with the chemical shifts of reported imidazolium (or benzimidazolium)
salts.3
OHC
CHO
HOH2C
CH2OH
CHO
Br
Br
NaBH4
2
+
( )n
OH
O
O
( )n
O
O
( )n
ClH2C
O
CH2Cl
O
N
N
R
SOCl2
R
N
N
N
N R
2Cl-
acetone, reflux
( )n
O
O
( )n
L1H2: R = Et, n = 2
n
L2H2: R = Bu
,
n = 2
L3H2: R = nPr, n = 3
L4H2: R = nBu, n = 3
Scheme 1 Preparation of precursors L1H2-L4H2
method 1
method 2
R N
N
N
N R
Br
+
Br
N
N
R
2X-
L5H2: R = nBu, X = I
L6H2: R = PyCH2, X = Br
L7H2: R = PhCH2, X = Br
Reagents: method 1 for L6H2 and L7H2, THF, reflux.
method 2 for L5H2, (i) THF, reflux; (ii) anionic exchange with NaI in acetone.
Scheme 2 Preparation of precursors L5H2-L7H2
Synthesis and general characterization of complexes 1-8
Synthetic methods of complexes 1-5 are shown in Scheme 3. The reaction of
precursor L1H2 with silver(I) oxide in dichloromethane afforded tetranuclear complex
[(L1Ag)2Ag2Cl4] (1) containing two 15-membered macrometallocycles and one
bridging Ag2Cl4 unit. Then complex 1 was treated by [PdCl2(CH3CN)2] in
dichloromethane to give an open structural complex [L1(PdCl2CH3CN)2] (2) (Scheme
4

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3(1)). The precursor L2H2 was treated with anhydrous silver(I) acetate in
dichloromethane to afford complex [(L2Ag)2AgCl2][AgCl2] (3) (Scheme 3(2)). The
precursors L3H2 and L4H2 were treated with silver(I) oxide in dichloromethane to
afford complexes [(L3Ag2Cl2)n] (4) and [(L4Ag2Cl2)n] (5), respectively (Scheme 3(3)).
Synthetic methods of complexes 6-8 are shown in Scheme 4. The precursor L5H2
was treated with anhydrous mercury(II) iodide in the presence of KOtBu in CH2Cl2 to
afford complex [L5HgI][HgI4]0.5 (6) (Scheme 4(1)). Complex [L6Hg][HgBr4] (7) was
prepared by the reaction of L6H2 with anhydrous mercury (II) bromide in the presence
of KOtBu in CH2Cl2 (Scheme 4(2)). Treatment of the precursor L7H2 with silver(I)
nitrate in the presence of KOtBu in CH2Cl2 yields complex [L7Ag][(NO3)0.76Br0.24] (8)
(Scheme 4 (3)). The complexes 1-8 are stable toward air and moisture, soluble in
1
DMSO and insoluble in diethyl ether and hydrocarbon solvents. In the H NMR
spectra of 1-8, the resonances for the benzimidazolium protons (NCHN) have
disappeared, and the chemical shifts of other protons are similar to those of the
corresponding precursors. For 13C NMR spectra, the signals of the carbene carbon in
complexes 1-8 appear at 156.0-188.0 ppm, which are similar to the reported carbene
metal complexes.5, 6 The NHC silver(I) complexes 1, 3-5 and 8 are stable in the solid
state and slightly light sensitive in solution. In the IR spectra of complex 2, the
characteristic band of the cyano group appears at 2221 cm–1, and this value is
comparable to those of reported complexes containing cyano groups.14
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Et
Et
N
N
N
N
Cl
Ag Ag
Cl
Cl
O
O
O
O
Ag2O
L1H2
(1)
Ag Ag
Cl
N
N
N
N
Et
Et
1
NCCH3
Cl
P
d
Cl
N Et
Et
N
N
Pd(CH3CN)2Cl2
N
Cl
H3CCN
Cl
O
O
2
nBu nBu
Cl
N
N
N
N
N
O
O
O
AgOAc
L2H2
Ag
Ag
Cl
(2)
Ag
O
N
N
N
nBu
nBu
[AgCl2]-
3
R
R
Cl
N
N
N
Ag
Ag
Cl
N
Ag2O
(3) L3H2 or L4H2
O
O
n
4: R = nPr
5: R = nBu
Scheme 3 Preparation of complexes 1-5
HgI2
N
N
nBu
N
N
L5
(1)
Hg
I
KOtBu
nBu
1/2[HgI4]2-
6
6

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N
N
N
Hg
N
HgBr2
KOtBu
L6
(2)
N
Br
N
Hg
Br
Br
Br
7
AgNO3
KOtBu
N
N
N
N
(3) L7
Ag
-
0.76 NO3
0.24 Br-
8
Scheme 4 Preparation of complexes 6-8
Structures of complexes 1-8
13
The complexes 1-8 were characterized by 1H NMR and C NMR spectra, and X-ray
analysis. The crystals of 1-8 suitable for X-ray diffraction were obtained by slow
diffusion of diethyl ether into their DMSO/CH2Cl2 (or DMSO/CH3CN) solution. The
internal ring angles (N-C-N) at the carbene centers in complexes 1-8 are in the range
of 105.4-108.3˚, which are comparable to those of the known NHC-metal complexes.5
In complexes 1-5, two benzimidazole rings on the same ligand form the dihedral
angles of 2.2-14.1˚ (Table S1 in Supplementary material), the dihedral angles between
benzimidazole ring and adjacent benzene ring are 76.7-88.5˚, and two benzene rings
on the same ligand form the dihedral angles of 49.5-88.1˚. In complexes 6-8, two
[Rbimy] arms are placed in the same side of the mesitylene plane, and two
benzimidazole rings on the same ligand form the dihedral angles of 6.6-86.7˚ (Table
S2). The mesitylene plane and two benzimidazole rings on the same ligand form the
dihedral angles of 71.1-89.0˚. The dihedral angles between benzimidazole ring and
adjacent pyridine ring for 7 (or benzene ring of benzyl group for 8) are 67.7-78.3˚.
The complexes 1 and 3 have similar molecular structure (Fig. 1(a) and Fig. 3(a)),
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in which each molecule contains two 15-membered macrometallocycles, and each
macrometallocycle is formed by one bidentate carbene ligand and one silver(I) atom.
The difference is that two 15-membered macrometallocycles are connected together
by Ag2Cl4 unit for 1 and by AgCl2 unit for 3 via Ag-Ag bonds (Ag-Ag distance =
2.993(6) Å for 1 and 3.077(6) Å for 3). In each 15-membered macrometallocycle of 1
and 3, the silver atom is tricoordinated with two carbene carbon atoms and another
silver(I) atom. The C-Ag-C arrangement is approximately linear with the bond angles
of 171.6(1)˚ for 1 and 171.4(3)˚ for 3. The bond distances of Ag-C are 2.107(4) Å and
2.112(3) Å for 1 and 2.104(8) Å and 2.110(7) Å for 3, respectively. The X-ray crystal
structural analysis of 1 and 3 shows that there exist inversion centers in these
complexes.
Additionally, the anionic unit Ag2Cl4 in complex 1 is formed by two silver(I)
atoms and four chlorine atoms (two bridging chlorines Cl(2) and Cl(2A), and two
non-bridging chlorines Cl(1) and Cl(1A)). The coplanar four atoms Ag(2), Cl(2),
Ag(2A) and Cl(2A) form a quadrangle Ag2Cl2 arrangement (Cl(2)-Ag(2)-Cl(2A) =
94.8(5)˚ and Ag(2)-Cl(2)-Ag(2A) = 85.2(2)˚. The two non-bridging chlorine atoms
Cl(1) and Cl(1A) lie in both sides of the quadrangle plane (Cl(1)-Ag(2)-Cl(2) =
136.4(6)˚). Each silver(I) atom in Ag2Cl4 unit is tetracoordinated with three chlorine
atoms and another silver(I) atom. The distances of non-bridging chlorine and silver(I)
(Ag(2)-Cl(1) = 2.392(1) Å) are slightly shorter than those of bridging chlorine and
silver(I) (Ag(2)-Cl(2) = 2.522(1) Å). The Ag(2)···Ag(2A) separation of 3.505(2) Å
shows no metal-metal interactions (the van der Waals radii of silver = 1.7 Å). The
Ag2Cl2 plane and two benzimidazole rings on the same ligand form the dihedral
angles are 17.4˚ and 18.7˚.
In complex 3, five atoms of Ag3Cl2 unit are coplanar. The Ag(2)-Ag(1)-Ag(2A)
and Cl(1)-Ag(1)-Cl(1A) are all linear with bond angle of 180.0(1)˚, moreover, they
are perpendicular to each other. Two Ag-Cl bonds are equal in length with the value
of 2.390(1) Å.
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Fig. 1(a)
Fig. 1(b)
Fig. 1(c)
Fig. 1 (a) Perspective view of 1 and anisotropic displacement parameters depicting
50% probability. All hydrogen atoms were omitted for clarity. Symmetry code:
i: 1-x, -y, 1-z. Selected bond lengths (Å) and angles (˚): Ag(1)-C(7) 2.107(4),
Ag(1)-Ag(2) 2.993(6), Ag(2)-Cl(1) 2.392(1), Ag(2)-Cl(2) 2.522(1),
Ag(2)-Cl(2A) 2.653(1); C(7)-Ag(1)-C(26) 171.6(1), C(7)-Ag(1)-Ag(2)
114.4(1), C(26)-Ag(1)-Ag(2) 73.7(1), Cl(2)-Ag(2)-Cl(2A) 94.8(5),
Cl(1)-Ag(2)-Cl(2) 136.4(6), Cl(2)-Ag(2)-Ag(1) 117.6(4), Cl(2A)-Ag(2)-Ag(1)
75.2(4), N(1)-C(7)-N(2) 105.7(3). (b) The 2D supramolecular layer via two
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types of π-π interactions. All hydrogen atoms and ethyl groups on nitrogen
atoms were omitted for clarity in 1. (c) 3D supramolecular network of 1 via
π-π interactions and C-H···π interactions. All hydrogen atoms except those
participating in the C-H···π hydrogen bonds and ethyl groups on nitrogen
atoms were omitted for clarity.
Fig. 3(a)
Fig. 3(b)
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Fig. 3(c)
Fig. 3 (a) Perspective view of 3 and anisotropic displacement parameters depicting
50% probability. All hydrogen atoms were omitted for clarity. Symmetry
code: i: 1-x, 2-y, 1-z. Selected bond lengths (Å) and angles (˚): Ag(1)-Cl(1)
2.390(1), Ag(1)-Ag(2) 3.077(6), Ag(2)-C(7) 2.104(8); Cl(1)-Ag(1)-Cl(1A)
180.0, Ag(2)-Ag(1)-Ag(2A) 180.0(1), C(7)-Ag(2)-C(34) 171.4(3),
C(7)-Ag(2)-Ag(1) 100.0(2), Cl(1)-Ag(1)-Ag(2) 88.6(5), Cl(1A)-Ag(1)-Ag(2)
91.4(5), N(1)-C(7)-N(2) 105.4(6). (b) The 2D supramolecular layer of 3 via
two types of π-π interactions. All hydrogen atoms and n-butyl groups on
nitrogen atoms were omitted for clarity. (c) 3D supramolecular network of 3
via π-π interactions and C-H···π interactions. All hydrogen atoms and n-butyl
groups on nitrogen atoms except those participating in the C-H···π hydrogen
bonds were omitted for clarity.
As shown in Fig. 2(a), each palladium atom in complex 2 is surrounded by one
carbene carbon atom, one nitrogen atom from acetonitrile and two chlorine atoms to
adopt a square trans conformation. The C(7)-Pd(1)-N(5) and Cl(1)-Pd(1)-Cl(2) arrays
are almost linear with the bond angles of 178.2(1)˚ and 175.8(3)˚, respectively. The
bond distances of Pd(1)-C(7), Pd(1)-Cl(1) and Pd(1)-N(5) are 1.935(3) Å, 2.302(1) Å
and 2.090(4) Å, respectively. Two PdCl2(NCCH3) arms in the same molecule point to
opposite directions.
Fig. 2(a)
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Fig. 2(b)
Fig. 2 (a) Perspective view of 2 and anisotropic displacement parameters depicting
50% probability. All hydrogen atoms were omitted for clarity. Selected bond
lengths (Å) and angles (˚): Pd(1)-C(7) 1.935(3), Pd(1)-N(5) 2.090(4),
Pd(1)-Cl(1) 2.302(1), Pd(1)-Cl(2) 2.288(1), N(5)-C(35) 1.118(5), C(35)-C(36)
1.454(6);
C(7)-Pd(1)-N(5)
178.2(1),
C(7)-Pd(1)-Cl(2)
87.4(1),
C(7)-Pd(1)-Cl(1) 89.1(1), N(1)-C(7)-N(2) 107.0(3). (b) 2D supramolecular
layer of 2 via C-H···Cl hydrogen bonds. All hydrogen atoms except those
participating in the C-H···Cl hydrogen bonds and ethyl groups on nitrogen
atoms were omitted for clarity.
Complexes 4 and 5 have similar 1D polymeric chains, and only alkyl groups on
nitrogen atoms are different as shown in Fig. 4(a) and Fig. 5(a) (nPr for 4 and nBu for
5). Each 1D polymeric chain in 4 and 5 is formed by the monomers (L3Ag2Cl2 for 4
L4Ag2Cl2 for 5) via weak Ag···Cl bonds (Ag···Cl separation = 3.167(1) Å for 4 and
3.404(1) Å for 5, and the van der Waals radii of chlorine = 1.8 Å). In each monomer
of 4 and 5, the bond distances of Ag-C and Ag-Cl are 2.087(5) Å and 2.344(2) Å for 4
and 2.100(7) Å and 2.419(1) Å for 5, respectively. In parallelogram Ag2Cl2 units of 4
and 5, the bond angles of Ag-Cl-Ag and Cl-Ag-Cl are 101.7(3)˚ and 78.3(2)˚ for 4,
and 89.8(5)˚ and 90.2(5)˚ for 5, respectively. All interval Ag2Cl2 units in 4 and 5 are
parallel, however, two adjacent Ag2Cl 2 units form the dihedral angles of 49.8(1)˚ for
4 and 35.9(6)˚ for 5, respectively. An interesting feature is that each monomer in
polymers 4 and 5 contains a cage-like cavity with the sizes of 7.30 × 4.34 Å for 4 and
7.32 × 5.93 Å for 5 (Fig. 4(b) and Fig. 5(b)).
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Fig. 4(a)
Fig. 4(b)
Fig. 4(c)
Fig. 4 (a) 1D polymeric chain of of 4. All hydrogen atoms were omitted for clarity.
Symmetry code: i: 3-x, -y, 1-z. Selected bond lengths (Å) and angles (˚):
Ag(2)-C(34) 2.087(5), Ag(2)-Cl(2) 2.344(2); C(34)-Ag(2)-Cl(2) 173.7(1),
N(3)-C(34)-N(4) 105.7(4). (b) Perspective view of the cage-like cavity in the
monomer of 4. All hydrogen atoms were omitted for clarity. (c) 2D
supramolecular layer of 4 via π-π interactions. All hydrogen atoms and
n-propyl groups were omitted for clarity.
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Fig. 5(a)
Fig. 5(b)
Fig. 5(c)
Fig. 5 (a) 1D polymeric chain of of 5. All hydrogen atoms were omitted for clarity.
Symmetry code: i: 2-x, y, 0.5-z; ii: 1+x, -y, 0.5+z. Selected bond lengths (Å)
and angles (˚): Ag(1A)-C(7A) 2.100(7), Ag(1A)-Cl(1A) 2.419(1);
C(7A)-Ag(1A)-Cl(1A) 167.9(2), N(1A)-C(7A)-N(2A) 105.5(6). (b)
Perspective view of the cage-like cavity in the monomer of 5. All hydrogen
atoms were omitted for clarity. (c) 2D supramolecular layer of 5 via π-π
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interactions. All hydrogen atoms and n-butyl groups were omitted for clarity.
Each cation in 6 contains a 10-membered macrometallocycle formed by one
bidentate chelate carbene ligand and one metal atom (Fig. 6(a)). The mercury(II) atom
in the cation of 6 is tricoordinated with two carbene carbon atoms and one iodine
atom. The angles of C-Hg-C and C-Hg-I are 166.5(4)˚ and 96.3(3)˚. The distances of
Hg-C and Hg-I are 2.110(1) Å and 3.034(1) Å. These data are analogous to those of
some known NHC mercury(II) complexes.15 In the anionic unit [HgI4]2- of 6, the
mercury(II) atom is surrounded by four iodine atoms affording a slightly distorted
tetrahedral arrangement, in which the bond angles of four I-Hg-I are in the range of
103.7(3)-115.1(3)˚, and the distance of Hg-I vary from 2.779(1) Å to 2.819(1) Å.
Compared to complex 6, each cation in complexes 7 and 8 also contains a
10-membered macrometallocycle formed by one bidentate chelate carbene ligand and
one metal atom (Fig. 7(a) and Fig. 8(a)). In complex 7, the mercury(II) atom is
tetracoordinated with two carbene carbon atoms, one nitrogen atom of pyridine ring
and one bromine atom to adopt a distorted tetrahedral geometry. The
C(13)-Hg(1)-C(25) array is approximately linear with the bond angles of 173.3(3)˚.
The bond angles of N(1)-Hg(1)-C(13) and N(1)-Hg(1)-C(25) are 76.3(2)˚ and
104.1(3)˚, respectively. The bond distances of Hg(1)-C(13) (2.093(6) Å) in 7 is
similar to that of Hg-C bond (2.110(1) Å) in 6. The distance of Hg(1)-N(1) is 2.785(2)
Å. In the anionic unit [HgBr4]2- of 7, the mercury(II) atom is surrounded by four
bromine atoms to afford a slightly distorted tetrahedral arrangement, in which the
bond angles of four Br-Hg-Br are in the range of 103.4(3)-119.6(4)˚, and the distance
of Hg-Br vary from 2.561(1) Å to 2.752(8) Å. Besides, the cation and anion are
connected together via weak Hg···Br bond (Hg···Br distance = 3.011(9) Å).
In complex 8, the silver(I) atom has a linear dicoordinated structure with a
C(14)-Ag(1)-C(32) bond angles of 178.5(1)˚. The distance of C-Ag bond (2.105(3) Å)
is similar to that of C-Ag bond (2.087(5)-2.107(4) Å) in 1 and 3-5.
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Fig. 6(a)
Fig. 6(b)
Fig. 6 (a) Perspective view of 6 and anisotropic displacement parameters depicting
50% probability. All hydrogen atoms were omitted for clarity. Selected bond
lengths (Å) and angles (˚): Hg(1)-C(7) 2.110(1), Hg(1)-I(1) 3.0345(1);
C(7)-Hg(1)-C(29) 166.5(4), C(7)-Hg(1)-I(1) 96.3(3), C(29)-Hg(1)-I(1) 97.2(3),
N(1)-C(2)-N(2) 108.3(1). (b) 1D double strand supramolecular chain of 6 via
C-H···π contacts and C-H···I hydrogen bonds. All hydrogen atoms except those
participating in the C-H···π contacts and C-H···I hydrogen bonds, and
irrelevant methyl groups on mesitylene and irrelevant butyl groups were
omitted for clarity.
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Fig. 7(a)
Fig. 7(b)
Fig. 7(c)
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Fig. 7 (a) Perspective view of 7 and anisotropic displacement parameters depicting
50% probability. All hydrogen atoms were omitted for clarity. Selected bond
lengths (Å) and angles (˚): Hg(1)-C(13) 2.108(7), Hg(1)-N(1) 2.785(2),
Hg(1)-Br(1) 3.001(9), Hg(2)-Br(1) 2.752(8); C(25)-Hg(1)-C(13) 173.3(3),
C(13)-Hg(1)-N(1) 76.3(2), C(25)-Hg(1)-N(1) 104.1(3), N(2)-C(13)-N(3)
107.7(6). (b) 2D supramolecular layer of 7 by π-π interactions, weak Hg···Br
bonds and C-H···Br hydrogen bonds. All hydrogen atoms except those
participating in the C-H···Br hydrogen bonds and the methyl groups on
mesitylene were omitted for clarity. (c) 3D supramolecular architecture of 7
via π-π interactions, weak Hg···Br bonds and C-H···Br hydrogen bonds. All
hydrogen atoms except those participating in the C-H···Br hydrogen bonds and
the methyl groups on mesitylene were omitted for clarity.
Fig. 8(a)
Fig. 8(b)
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Fig. 8(c)
Fig. 8 (a) Perspective view of 8 and anisotropic displacement parameters depicting
-
50% probability. All hydrogen atoms, NO3 and Br- were omitted for clarity.
Selected bond lengths (Å) and angles (˚): Ag(1)-C(14) 2.105(3);
C(14)-Ag(1)-C(32) 178.5(1), N(1)-C(14)-N(2) 105.7(3). (b) 2D
supramolecular layer of 8 via three types of π-π interactions. All hydrogen
atoms were omitted for clarity. (c) 3D supramolecular architecture of 8 by
three types of π-π interactions and C-H···O hydrogen bonds. All hydrogen
atoms except those participating in the C-H···O hydrogen bonds were omitted
for clarity.
The crystal packings of complexes 1-8
Complexes 1 and 3 have similar crystal packings, and their 2D supramolecular layers
are formed by two types of π-π interactions (Fig. 1(b) and Fig. 3(b)).16 One is from
intermolecular benzene rings, and another is from the intermolecular benzimidazole
rings (Table S3). Additionally, their 2D supramolecular layers are further extended
into 3D architecture through C-H···π contacts (Fig. 1(c) and Fig. 3(c)).17 In the C-H···π
contacts (Table S3), the hydrogen atoms are from CH2 of ether chains for 1, and from
CH3 of butyl group for 3, and π systems are from benzene rings for 1 and 3.
An interesting feature in the crystal packing of 2 is that 2D supramolecular layer is
formed through C-H···Cl hydrogen bonds as shown in Fig. 2(b).18 The hydrogen
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atoms in the hydrogen bonds are from methyl of acetonitrile (Table S4).
Complexes 4 and 5 have also similar crystal packings, and their 2D
supramolecular layers are formed via intermolecular π-π interactions from
benzimidazole (Fig. 4(c) and Fig. 5(c)).
Double strand 1D supramolecular chain of 6 is formed by C-H···π contacts and
C-H···I hydrogen bonds (Fig. 6(b)).19 In C-H···π contacts, the hydrogen atoms are
from CH2 of propyl groups and benzimidazole rings, respectively, and π systems are
from benzene rings of mesitylenes. In C-H···I hydrogen bonds, the iodine atoms are
from the anionic unit [HgI4]2-, and the hydrogen atoms are from CH2 of propyl groups
and benzimidazole rings, respectively.
An interesting feature in the crystal packing of 7 (Fig. 7(b)) is that 2D
supramolecular layers are formed via three types of weak interactions, including π-π
interactions from the benzimidazole rings, C-H···Br hydrogen bonds20 and weak
Hg···Br bonds (Hg···Br distance = 3.011(2) Å; the sum of van der Waals Radii of
mercury and bromine = 3.65 Å). In C-H···Br hydrogen bonds, the hydrogen atoms are
from pyridine rings and bromine atoms are from [HgBr4]2- units. Additionally, 2D
layers are further extended into 3D supramolecular architectures (Fig. 7(c)) via new
C-H···Br hydrogen bonds. In new C-H···Br hydrogen bonds, the hydrogen atoms are
from CH2 and bromine atoms from [HgBr4]2- units.
Compared to the crystal packing of 7, 2D supramolecular layer in 8 is formed two
types of π-π interactions (Fig. 8(b)). One is from intermolecular benzimidazole rings,
and another is from intermolecular benzene rings of mesitylenes. Additionally, anionic
-
unit NO3 are packed between successive layers and hold the layers together via
C-H···O hydrogen bonds,21 which extends the above 2D layers into 3D
supramolecular architectures (Fig. 8(c)). In the C-H···O hydrogen bonds, the hydrogen
atoms are from benzimidazole rings and oxygen atoms are from nitryl groups.
The effects of some experimental conditions on N-heterocyclic silver complexes
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The effects of various experimental conditions, such as different silver base (Ag2O,
Ag2CO3 or Ag(OAc)), the radio between ligand and silver base, the solvents used in
crystallization, the anion and the structures of ligands, on N-heterocyclic silver
complexes have been reviewed in detail by Lin et al in 2007.22 Additionally, the
different structures of N-heterocyclic silver complexes formed via the reaction of
benzimidazolium ( or imidazolium) salts of chloride with silver bases have also been
-
reported,5a, 5d, 6c, 13b in which the by-products bearing silver(I) are mainly AgCl, AgCl2
2-
or Ag2Cl4 , and they can transform to each other under appropriate conditions. Under
a certain condition, one of them may be predominant. These anions may be
dissociative or form N-heterocyclic silver complexes along with ligands. Therefore,
the components of crude product and single crystal in N-heterocyclic silver
complexes may be same or different under different conditions. However, there are
not clear rules to be found between the structures of N-heterocyclic silver complexes
and experimental conditions. The single crystal structure of N-heterocyclic silver
complex is mainly relevant to the crystallization condition, especially the solvent used
in crystallization.23 Besides, the structure of complex itself (such as size of N-side
arms, imidazole ring and benimidazole ring etc) could also have some effects on
single crystal structure. The effect of solvent on single crystal structure displays
mainly in two aspects. Firstly, the cation and anion in complex can conduct different
association in different solvent, which may lead to different components contained in
crude product and single crystal. Secondly, the solvent molecule can fill in the gaps of
crystal packing, and thus different solvent molecules contained in crystals can lead to
the different crystal shape. By contrast, the temperature in crystallization may have
small effect on single crystal structure, and it influences mainly both the speed of
crystallization and the size of single crystal particle.
In order to explore further the relations between N-heterocyclic silver complexes
and experimental conditions, we chose the reaction of bis-benzimidazolium salt
ligands (L1H2 and L2H2) with Ag bases (Ag2O and Ag(OAc)) to test the effects of
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some experimental conditions on the products, yields and reproducibility. In the
reaction of ligand L1H2 with Ag2O (Table 1), when the radio between L1H2 and Ag2O
(equiv/equiv) is equal to 1:1 in 40˚C in 6 h, the crude product [(L1Ag)2Ag2Cl4] (I) was
1
obtained with yield of 49% (entry 1). The crude product I was characterized by H
NMR, element analysis and melting point, and its components are the same as those
of single crystal structure 1 obtained by X-ray analysis. When time was prolonged to
8 h and 10 h under same radio and temperature, the same crude product I was
obtained with yields of 63% and 62% (entries 2 and 3). When temperature was
dropped to 25˚C and time is 10 h under same radio, only the yield of 46% was
obtained (entry 4). Thus, when L1H2/Ag2O (equiv/equiv) is equal to 1:1, 8 h and 40
˚C are found to be the optimal time and temperature. Two times repeating tests in 8 h
and in 40 ˚C were carried out when L1H2/Ag2O (equiv/equiv) is equal to 1:2 and 1:3,
and the yields of 61-63% were obtained (entries 5-8). The results show that excess
Ag2O has not obvious effect on the crude products and yields. Furthermore, this type
of reaction has good reproducibility. Similarly, the reaction of ligand L1H2 with
Ag(OAc) was also carried out (Table S5). The results obtained were similar to the
case of Ag2O, and only optimal time rose up to 16 h, which shows that different Ag
bases have not obvious effect on the crude products, yields and reproducibility.
As a comparison，the reaction of L2H2 with Ag2O (or Ag(OAc)) were also
carried out (Tables S6 and S7) under the similar experimental condition. Using Ag2O
or Ag(OAc) as silver base, the same crude product [(L2Ag)2AgCl2][AgCl2] (II) was
obtained, and other results are similar to those from L1H2. The product II was
characterized by 1H NMR, element analysis and melting point, and its components are
the same as those of single crystal structure 3 obtained by X-ray analysis. Notably, the
structures of product [(L1Ag)2Ag2Cl4] (I) from L1H2 and product
[(L2Ag)2AgCl2][AgCl2] (II) from L2H2 are different, and they contain similar
NHC-Ag unit (L1Ag and L2Ag) and different anionic units ([Ag2Cl4] for L1H2 and
[AgCl2] for L2H2). This may be attributed to the difference of ligands (N-side arms
being ethyl group for L1 and n-butyl group for L2).
Summary, the different Ag base and excess Ag base have not obvious effect on
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the crude products and yields in the preparation of N-heterocyclic silver complexes.
But use of Ag(OAc) need longer reaction time than use of Ag2O, and this may be
reason why Ag2O was used in the overwhelming majority of preparation of NHC-Ag
complexes. Temperature and time in the reactions have not obvious effect on the
crude product, however, have large effect on yields. Additionally, these reactions have
all good reproducibility as shown in Table 1 and Tables S5-S7.
Table 1 The reaction of ligand L1H2 with Ag2O[a]
Ag2O
(L1Ag)2Ag2Cl4
L1H2
(I)
L1H2/Ag2O
(equiv/equiv)
1:1
Entry Time (h) Temp. (˚C)
Crude
Ag2O
product[b] yield (%)
1
2
3
4
5
6
7
8
6
8
40
40
40
25
40
40
40
40
I
I
I
I
I
I
I
I
49
63
62
46
63
61
61
62
10
10
8
1:2
1:3
8
8
8
[a] Reaction conditions: the solvent CH2Cl2 in N2.
[b] Crude product was characterized by 1H NMR, element analysis and melting point.
Catalytic activity of NHC palladium(II) complex 2
The Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids is
of general interest to organic synthesis. The Suzuki-Miyaura reaction catalyzed by
Pd-NHC complexes has provided an efficient and powerful method for the formation
of carbon-carbon and carbon-heteroatom bonds.24 We choose the cross-coupling
reaction of 4-bromotoluene with phenylboronic acid as a model reaction to test the
solvent and base effects (Table 2). Use of absolute MeOH as solvent and K3PO4·3H2O
as base gives 69% coupling yield at 50 ˚C in 24 h in air (entry 1). Use of pure water as
solvent and K3PO4·3H2O as base gives 25% coupling yield at 50 ˚C in 24 h in air
(entry 2). Use of MeOH/H2O (1:1) as mixed solvent and K3PO4·3H2O as base gives
the yield of 90% in 5 h in air (entry 3) and the yield of 98% in 22 h in air (entry 4).
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The higher activity is attributed to the better solubility of catalyst and K3PO4·3H2O in
the aqueous MeOH mixture and rapid reduction of Pd(II) to Pd(0).25 Up on using
MeOH/H2O (1:1) as mixed solvent and using other bases (such as KOH, K2CO3 and
NaHCO3), the yields of 73-95% are obtained (entries 5-7). Based on the extensive
screen, MeOH/H2O (1:1) and K3PO4·3H2O are found to be the most efficient solvent
and base with a catalyst loading of 0.1 mol % complex 2 at 50 ˚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 performed, in which PdCl2(CH3CN)2 were added in the
absence of ligand with the optimized conditions, and only 18% coupling product was
obtained (entry 8). This result shows that the ligand has the preponderant function in
the catalytic reaction.
We attempted the cross-coupling reaction of various aryl halides with
phenylboronic acid under the optimal reaction condition (Table 3). In general,
complex 2 can catalyze the cross-coupling of various aryl halides with phenylboronic
acid to give different yields. The catalyst is high efficiency toward the coupling of
aryl bromides with phenylboronic acid to give 83-95% yields (entries 1-7). The aryl
chlorides could be also coupled with phenylboronic acid, in which 4-chloroaniline,
2-chlorotoluene and 2,4-dinitrochlorobenzene are coupled with phenylboronic acid to
lead to medium yields of 56-78% (entries 8-10), and 2-nitrochlorobenzene and
2-chlorobenzaldehyde lead to poor yields of 10% and 14% (entries 11 and 12).
Notably, the cross-coupling reaction of some aryl halides with phenylboronic acid
under the optimal reaction condition is difficult, but when 0.1 mol%
tetrabutylamonium bromide (TBAB) or 0.1 mol% PPh3 is added, the coupling
reactions can be smoothly carried out (entries 5-8). This result shows that the
cross-coupling reactions could be dramatically improved in the presence of TBAB26
or PPh3.27 It has been known that the addition of TBAB as a cocatalyst can enhance
the activity of many catalystic systems. And TBAB is able to activate and stabilize the
palladium(0) species in situ generated, which is believed to be the real catalytically
active species. Above results show that this catalyst has high stability to air and water,
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and good tolerance toward various functional groups, to make it into a valuable
precatalyst for thermally sensitive substrates. Therefore, this catalytic system provides
an effective method for facile coupling of aryl halides under mild and aerobic
conditions.
Table 2 Suzuki-Miyaura Coupling Reaction of 4-bromotoluene with phenylboronic
acid catalyzed by complex 2[a]
0.1 mol % cat, base
B(OH)2
H3C
Br
+
H3C
solvent, 50 , air
Entry
Solvent
Base
K3PO4·3H2O
Time (h)[b]
Yield (%)[c]
1
2
MeOH
24
24
5
69
25
90
98
95
74
73
18
H2O
K3PO4·3H2O
K3PO4·3H2O
K3PO4·3H2O
KOH
3
MeOH/H2O(1:1)
MeOH/H2O(1:1)
MeOH/H2O(1:1)
MeOH/H2O(1:1)
MeOH/H2O(1:1)
MeOH/H2O(1:1)
4
22
24
24
24
22
5
6
K2CO3
7
8[d]
NaHCO3
K3PO4·3H2O
[a] Reaction conditions: 4-bromotoluene 0.50 mmol, phenylboronic acid 0.60 mmol, base 1.2
mmol, complex 2 0.1 mol % , solvent 3 mL, 50 ˚C in air.
[b] Reactions were monitored by TLC.
[c] Determined by GC.
[d] Reaction conditions are the same as [a], and only PdCl2(CH3CN)2 was added in the absence of
ligand.
Table 3 Suzuki-Miyaura coupling reaction of aryl halides with phenylboronic acid
catalyzed by complex 2[a]
0.1 mol % cat, base
X
B(OH)2
+
R
MeOH/H2O, 50 , air
R
Entry
Aryl halide
Time (h)[b]
Yield (%)
91 [c]
1
2
4-bromoanisole
4-bromoanisole
3-bromoanisole
7
26
6
95 [c]
3
95 [d]
4
1-bromonaphthaline
4-bromoaniline
28
40
90 [d]
5[e]
94 [d]
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6[f]
7[f]
4-bromoacetophenone
40
40
40
36
40
40
40
86[d]
83 [d]
78 [d]
56 [d]
72[d]
10 [d]
14 [d]
4-nitrobromobenzene
4-chloroaniline
8[e]
9
2-bromotoluene
10[f]
11[f]
12[f]
2,4-dinitrochlorobenzene
2-nitrochlorobenzene
2-chlorobenzaldehyde
[a] Reaction conditions: aryl halide 0.50 mmol, phenylboronic acid 0.60 mmol, K3PO4·3H2O 1.2
mmol, complex 2 0.1 mol % , MeOH/H2O (1:1) mixed solvent 3 mL, 50˚C in air.
[b] Reactions were monitored by TLC.
[c] Determined by GC.
[d] Isolated yield.
[e] TBAB 0.1 mol % was added, complex 2 0.3 mol %, 70 ˚C.
[f] PPh3 0.1 mol % was added, complex 2 0.3 mol %, 70 ˚C.
Conclusions
In summary, a series of NHC silver(I), palladium(II) and mercury(II) complexes have
been synthesized and characterized. The complexes 1-8 adopt four different structures:
(1) the bis-macrometallocycles connected via Ag2Cl4 unit for 1 and via AgCl2 unit for
3, (2) the open structure formed via one ligand and two metal atoms for 2, (3) 1D
polymeric chains formed by the monomers of cage-like cavity via weak Ag···Cl bonds
(monomer: L3Ag2Cl2 for 4 and L4Ag2Cl2 for 5) and (4) the macrocyclic structure
formed by one ligand and one metal for 6-8. In crystal packings, 1D supramolecular
chain of 6, 2D supramolecular layers of 2, 4 and 5 and 3D supramolecular
architectures of 1, 3, 7 and 8 are formed via intermolecular weak interactions,
including π-π interactions, hydrogen bonds, C-H···π contacts and weak Hg···Br bonds.
The resultant structures of these complexes will provide valuable experimental data
for crystal engineering and supramolecular chemistry. Additionally, the
macrometallocycles of 1, 3 and 6-8 and the structures of cage-like cavity of 4 and 5
suggest that they may have potential applications in the host-guest chemistry. The
study of catalytic activity of NHC Pd(II) complex 2 in Suzuki-Miyaura cross-coupling
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reaction shows that this complex can catalyze the coupling reaction of aryl halides
(iodide, bromide and chloride) with phenylboronic acid in MeOH/H2O as solvent and
K3PO4·3H2O as base in air. Therefore, this catalytic system provides an effective
phosphine-free catalyst for facile coupling of aryl halides under mild and aerobic
conditions. Further studies on new organometallic compounds from precursors
L1H2-L7H2 and analogous ligands are underway.
Experimental Section
General procedures
All manipulations were performed using Schlenk techniques, and solvents were
purified by standard procedures. All the reagents for synthesis and analyses are of
analytical grade and used without further purification. Melting points were
determined with a Boetius Block apparatus. IR spectra were measured with a Bruker
IR Equinox-55 infrared spectrophotometer. 1H and 13C NMR spectra were recorded
on a Bruker Avance III spectrometer at 400 MHz and 100 MHz, respectively.
Chemical shifts, δ, 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
Perkin-Elmer 2400C Elemental Analyzer. GC analysis was carried out using a Focus
DSQI GC-MS equipped with an integrator (C-R8A) with a capillary column (CBP-1
or CBP-5, 0.25 mm i.d. × 40 m).
Synthesis of 1,2-bis(2-(chloromethyl)phenoxy)ethane. Salicylic aldehyde (15.601 g,
127.7 mmol) and 1,2-dibromoethane (10.000 g, 53.2 mmol) were added to DMF (80
mL) containing potassium carbonate (17.656 g, 127.7 mmol), and the mixture
solution was stirred for 24 hours at 50˚C in nitrogen protection. The colorless solution
became yellow, and finally the dark brown solution was obtained. The resulting
solution was poured into a beaker of 500 mL containing water (200 mL) with stirring,
and a brown powder of 1,2-bis(2-formylphenoxy)ethane by filtration was obtained.
1
Yield: 12.196 g (85%). M.p.: 146-148 ˚C. H NMR (400 MHz, DMSO-d6): δ 4.44 (s,
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4H, CH2), 7.01-7.08 (m, 4H, PhH), 7.53 (t, J = 8.8, 2H, PhH), 7.80 (d, J = 8.0, 2H,
PhH), 10.53 (s, 2H, CHO).
The sodium borohydride (3.359 g, 88.8 mmol) was slowly added to the solution
of 1,2-bis(2-formylphenoxy)ethane (10.000 g, 37.0 mmol) in tetrahydrofuran and
ethanol (100 mL, v/v = 1:1) in ice water bath for 1 hour, and the solution was stirred
continuously for 2 hours at room temperature, and then was refluxed for 10 hours.
The solvent was removed with a rotary evaporator and H2O (100 mL) was added to
the residue, and acetic acid was added dropwise to the solution until pH = 7. The
solution was extracted with CH2Cl2 (30 mL × 3) and washed with sodium chloride
solution, and the extracting solution was dried over anhydrous MgSO4. After
removing CH2Cl2, a white solid 1,2-bis(2-hydroxymethylphenoxy)ethane was
obtained. Yield: 9.192 g (91%). M.p.: 122-124˚C. 1H NMR (400 MHz, DMSO-d6): δ
4.31 (s, 4H, CH2), 4.49 (s, 4H, CH2), 6.95-7.00 (m, 4H, PhH), 7.18 (t, J = 7.5, 2H,
PhH), 7.37 (d, J = 7.5, 2H, PhH).
Thionyl chloride (17.348 g, 145.8 mmol) was added dropwise to the chloroform
(100 mL) solution of 1,2-bis(2-hydroxymethylphenoxy)ethane (10.000 g, 36.5 mmol)
and pyridine (11.534 g, 145.8 mmol). The mixture solution was stirred for 12 hours at
70˚C. The resulting mixture was poured into a beaker of 500 mL, and water of 300
mL was added. The chloroform layer was separated and dried over anhydrous MgSO4.
After removing CHCl3, a white solid 1,2-bis(2-(chloromethyl)phenoxy)ethane was
1
obtained. Yield: 8.475 g (75%). M.p.: 96-98˚C. H NMR (400 MHz, DMSO-d6): δ
4.43 (s, 4H, CH2O), 4.70 (s, 4H, CH2Cl), 6.96 (d, J = 7.2, 2H, PhH), 7.14 (d, J = 8.4,
2H, PhH), 7.34-7.41 (m, 4H, PhH).
Synthesis of 1,3-bis(2-(chloromethyl)phenoxy)propane. This compound was
prepared in a manner analogous to that of 1,2-bis(2-(chloromethyl)phenoxy)ethane.
Yield: 8.165 g (72.4%). M.p.: 97˚C. 1H NMR (400 MHz, DMSO-d6): δ 2.26-2.29 (m,
2H, CCH2C), 4.31 (t, J = 6.0, 4H, CH2O), 4.72 (s, 4H, CH2Cl), 6.93 (t, J = 7.2, 2H,
PhH), 7.05 (d, J = 8.0, 2H, PhH), 7.35-7.38 (m, 4H, PhH).
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Page 29 of 42
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Synthesis of 1,2-bis[2-(N-ethylbenzimidazolemethyl)phenoxy]ethane chloride
(L1H2). A solution of 1-ethylbenzimidazole (2.066 g, 14.1 mmol) and
1,2-bis(2-(chloromethyl)phenoxy)ethane (3.409 g, 6.4 mmol) in acetone (100 mL)
was stirred for 5 days under refluxing, and a white precipitate was formed. The
product was filtered and washed with acetone. The white powder of
dibenzimidazolium salt L1H2 was obtained by recrystallization from methanol/ether.
Yield：3.127 g (81%). M.p.: 154-156˚C. 1H NMR (400 MHz, DMSO-d6): δ 1.35 (t, J
= 6.9, 6H, CH3), 4.13 (q, J = 6.9, 4H, CH2), 4.35 (s, 4H, CH2), 5.50 (s, 4H, CH2),
7.05-7.09 (m, 4H, PhH), 7.34-7.38 (m, 4H, PhH), 7.52-7.56 (m, 4H, PhH), 7.75 (d, J
= 8.4, 2H, PhH), 7.93 (d, J = 8.4, 2H, PhH), 9.65 (s, 2H, 2-bimiH) (bimi =
benzimidazole).
The following bis-benzimidazolium salts L2H2-L4H2 were prepared in a manner
analogous to that of L1H2.
Synthesis of 1,2-bis[2-(N-nbutyl-benzimidazolemethyl)phenoxy]ethane chloride
1
(L2H2). Yield: 3.279 g (77%). M.p.: 273-276˚C. H NMR (400 MHz, DMSO-d6): δ
0.83 (t, J = 7.2, 6H, CH3), 1.19-1.26 (m, 4H, CH2), 1.72-1.80 (m, 4H, CH2), 4.30 (s,
4H, CH2), 4.35 (t, J = 7.2, 4H, CH2), 5.58 (s, 4H, CH2), 7.05-7.10 (m, 4H, PhH),
7.12-7.41 (m, 4H, PhH), 7.53-7.60 (m, 4H, PhH), 7.78 (d, J = 8.4, 2H, PhH), 7.98 (d,
J = 8.4, 2H, PhH), 9.70 (s, 2H, 2-bimiH).
Synthesis
of
1,3-bis[2-(N-npropyl-benzimidazolemethyl)phenoxy]propane
1
chloride (L3H2). Yield：3.223 g (81%). M.p.: 232-234˚C. H NMR (400 MHz,
DMSO-d6): δ 0.86 (t, J = 7.2, 6H, CH3), 1.81-1.83 (m, 4H, CH2), 1.86-1.88 (m, 4H,
CH2), 3.97 (t, J = 6.0, 4H, CH2), 4.52 (t, J = 8.0, 4H, CH2), 5.68 (s, 4H, CH2), 7.00 (t,
J = 8.0, 4H, PhH), 7.03 (d, J = 8.0, 2H, PhH), 7.37 (t, J = 7.8, 2H, PhH), 7.57 (m, 4H,
PhH), 7.94 (d, J = 8.0, 2H, PhH), 8.10 (d, J = 8.0, 2H, PhH), 10.01 (s, 2H, 2-bimiH).
29