NHC Hg(II) and Pd(II) complexes based on 1,8-dihydroxy-9,10-anthraquinone: synthesis, structure and catalysis

Article abstract of DOI:10.1039/c8nj02029a

Three bis-azolium salts, 1,8-bis[3′-(N-R-azoliumyl)propoxy]-9,10-anthraquinone hexafluorophosphate L¹H₂(PF₆)₂-L²H₂(PF₆)₂ (R = ethyl or picolyl, azoliumyl = imidazoliumyl or benzimidazoliumyl) and 1,3-bis[8′-(3′′-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane hexafluorophosphate (L³H₂(PF₆)₂), as well as their three macrometallocycle N-heterocyclic carbene mercury(ii) complexes [L^1′HgBr₂] (1), [L²Hg](PF₆)₂ (3) and [L³Hg](PF₆)₂ (3) were prepared and characterized by ¹H NMR and ¹³C NMR spectroscopy and X-ray crystallography. In complexes 1-3, each macrometallocycle (18-membered macrometallocycle for 1, one 18-membered and two 6-membered macrometallocycles for 2, and 28-membered macrometallocycle for 3) was formed by one biscarbene ligand (L^1′ for 1, L² for 2, and L³ for 3) and one Hg(ii) ion. Interestingly, the carbonyl group on the 9-position in complex 1 reacted with two acetonitrile molecules in the presence of the strong base KO^tBu through losing one molecule of H₂O to form L^1′. As a result, two-CH₂CN units were introduced to anthraquinone, in which the two-CH₂CN units lie on two flanks of the anthraquinone plane. In the crystal packings of 1-3, 2D supramolecular layers and 3D supramolecular frameworks are formed via hydrogen bonds and ππ interactions. Additionally, the catalytic activity of the L¹-Pd(ii) complex in situ in the Suzuki-Miyaura reaction was studied. The results show that this catalyst is efficient in the Suzuki-Miyaura reaction.

Full text of DOI:10.1039/c8nj02029a

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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NHC Hg(II) and Pd(II) complexes based on 1,8-dihydroxy-9,10-anthraqinone:
Synthesis, structure and catalysis
Zhi-Xiang Zhao,a,b Ze-Liang Hu,a,b Shao-Cong Yua,b and Qing-Xiang Liu*a,b
aKey Laboratory of Inorganic-Organic Hybrid Functional Materials Chemistry
(Tianjin Normal University), Ministry of Education, College of Chemistry, Tianjin
Normal University, Tianjin 300387, China
bTianjin Key Laboratory of Structure and Performance for Functional Molecules,
College of Chemistry, Tianjin Normal University, Tianjin 300387, China.
*Corresponding Author.
E-mail address: tjnulqx@163.com
Three bis-azolium salts, 1,8-bis[3‘-(N-R-azoliumyl)propoxy]-9,10-anthraquinone
hexafluorophosphate L1H2(PF6)2-L2H2(PF6)2 (R = ethyl or picolyl, azoliumyl =
imidazoliumyl
or
benzimidazoliumyl)
and
1,3-bis[8‘-(3‘‘-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane
hexafluorophosphate (L3H2(PF6)2), as well as their three macrometallocycle
N-heterocyclic carbene mercury(II) complexes [L1‘HgBr2] (1), [L2Hg](PF6)2 (3) and
[L3Hg](PF6)2 (3) were prepared and characterized by 1H NMR, 13C NMR
spectroscopy and X-ray crystallography. In complexes 1-3, each macrometallocycle
(18-membered macrometallocycle for 1, one 18-membered and two 6-membered
macrometallocycles for 2, 28-membered macrometallocycle for 3) was formed by one
biscarbene ligand (L1‘ for 1, L2 for 2, and L3 for 3) and one Hg(II) ion. Interestingly,
the carbonyl group on 9-position in complex 1 reacted with two acetonitrile molecules
in the presence of strong base KOtBu through losing one molecule H2O to form L1‘.
As a result, two -CH2CN units were introduced to anthraquione, in which two
-CH2CN lie on two flanks of anthraquinone plane. In the crystal packings of 1-3, 2D
supramolecular layers and 3D supramolecular frameworks are formed via hydrogen
bonds and ŒđđđŒ interactions. Additionally, the catalytic activity of L1-Pd(II) complex
1

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in situ in Suzuki-Miyaura reaction was studied. The results show that this catalyst is
efficient to Suzuki-Miyaura reaction.
Introduction
After the isolation of the first stable free N-heterocyclic carbene (NHC) by Arduengo
et al. in 1991,1 N-heterocyclic carbene chemistry has received considerable attention
in organometallic chemistry.2 NHC ligands can be easily derived by changing the
substituents on nitrogen atoms and the backbone of carbenes, and they are easy to
tune steric and electronic properties by modifying substituents. NHCs can form metal
complexes with various structures via coordinating with metal ions, such as
macrocycles,3 molecular rectangles4, 5 and grooves.6 These NHC metal complexes
have high stability toward heat, moisture and air due to the strong 1-donating ability
of NHCs.7 In view of these advantages, NHC metal complexes have been widely
applied in several fields, such as catalytic reactions8 and materials science.9 Among
NHC metal complexes, the NHC silver(I) and mercury(II) complexes have played
important roles in the development of carbene chemistry. N-heterocyclic carbene
silver(I) complexes can be used as carbene transfer reagents to prepare other NHC
metal complexes which are relatively difficult to synthesis (such as Ni, Pd, Pt and Cu,
etc).10 In addition, a recent study reveals that NHC silver(I) complexes have shown
biological activity as antimicrobial and antimitochondrial agents.11 Among NHC
metal complexes, NHC mercury(II) complexes are the first known NHC metal
complexs and they have various coordination mode and interesting characteristics of
structures.12
In this paper, we report the preparation of bis-azolium salts,
1,8-bis[3‘-(N-R-azoliumyl)propoxy]-9,10-anthraquinone
hexafluorophosphate
L1H2(PF6)2-L2H2(PF6)2 (R = ethyl or picolyl, azoliumyl = imidazoliumyl or
benzimidazoliumyl)
and
1,3-bis[8‘-(3‘‘-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane
hexafluorophosphate (L3H2(PF6)2), as well as their three macrometallocycle
N-heterocyclic carbene silver(I) or mercury(II) complexes [L1‘HgBr2] (1),
2

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[L2Hg](PF6)2 (2) and [L3Hg](PF6)2 (3). Additionally, the catalytic activity of
NHC-Pd(II) complex in situ in Suzuki-Miyaura reaction was researched. The results
show that this catalyst is efficient to Suzuki-Miyaura reactions.
Results and discussion
Synthesis and characterization of precursors L1H2(PF6)2-L3H2(PF6)2
As shown in Scheme 1(1), 1,8-dihydroxy-9,10-anthraquinone as a starting material
was
treated
by
2
equiv.
of
1,3-dibromopropane
to
afford
1,8-bis(3‘-bromopropoxy)-9,10-anthraquinone (yield: 50%), which further reacted
with N-R-azole to generate bis-azolium salts L1H2Br2 and L2H2Br2, and subsequent
anion exchange with ammonium hexafluorophosphate in methanol was carried out to
give 1,8-bis[3‘-(N-R-azoliumyl)propoxy]-9,10-anthraquinone hexafluorophosphate
L1H2(PF6)2 (yield: 90%) and L2H2(PF6)2 (yield: 88%) (R = ethyl and azoliumyl =
imidazoliumyl for L1H2(PF6)2, and R = picolyl and azoliumyl = benzimidazoliumyl
for L2H2(PF6)2). The reaction of 1,8-dihydroxy-9,10-anthraquinone with 1.5 equiv. of
1,3-dibromopropane
afforded
1,3-bis[8‘-(3‘‘-bromopropoxy)anthraquinon-l-yloxy]propane (yield: 45%), which
reacted with N-ethyl-imidazole to form bis-imidazolium salt L3H2(Br)2, and
subsequent anion exchange with ammonium hexafluorophosphate in methanol gave
1,3-bis[8‘-(3‘‘-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane
hexafluorophosphate L3H2(PF6)2 (Scheme 1(2), yield: 72%). Precursors
L1H2(PF6)2-L3H2(PF6)2 are stable toward air, heat and moisture, and soluble in
DMSO, CH2Cl2 and CH3CN. However, the solubility is poor in diethyl ether and
hydrocarbon solvents. In the 1H NMR spectra of L1H2(PF6)2-L3H2(PF6)2, the
imidazolium (or benzimidazolium) proton signals (NCHN) appear at / = 9.14-9.88
ppm, which are consistent with the chemical shifts of reported imidazolium or
benzimidazolium salts.6, 13 In the 13C NMR spectra of L1H2(PF6)2-L3H2(PF6)2, the
resonances for C=O appear at / = 180.5-183.1 ppm.
3

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Scheme 1 Preparation of precursors L1H2(PF6)2-L3H2(PF6)2.
Synthesis and characterization of complexes 1-3
As shown in Scheme 2(1), [L1‘HgBr2] (1) was prepared via the reaction between
L1H2(PF6)2 and HgBr2 in the presence of strong base KOtBu in
CH2Cl2/CH3CN/DMSO. L2H2(PF6)2 or L3H2(PF6)2 reacted with Hg(OAc)2 in the
presence of NaOAc in CH3CN afforded complexes [L2Hg](PF6)2 (2) and [L3Hg](PF6)2
(3) (Scheme 2(2) and 2(3)). Complexes 1-3 were obtained in the yields of 55-60%. In
order to understand the reason for low yields, we isolated the resulting mixtures in
these experiments carefully. The results showed that the conversion rates of
L1H2(PF6)2-L3H2(PF6)2 were about 80%, however, some insoluble species were also
obtained besides complexes 1-3. The structures of these insoluble species were unable
to be confirmed via common methods, and this case has been reported in some
literatures.14
The single crystals of complexes 1-3 suitable for X-ray diffraction were grown by
slow diffusion of diethyl ether into their solutions. Complexes 1-3 demonstrate good
stability to heat, air and moisture. They are soluble in CH3CN and DMSO, but almost
1
insoluble in diethyl ether and hydrocarbon solvents. In H NMR spectra of 1-3, the
4

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resonances for the imidazolium (or benzimidazolium) protons (NCHN) disappear and
the chemical shifts of other hydrogen atoms are similar to those of corresponding
precursors. In 13C NMR spectra, the signals for the carbene carbons of 1-3 are
observed at / = 174.5-179.9 ppm, which are consistent with the known metal carbene
complexes.15
Scheme 2 Preparation of complexes 1-3.
Crystal structure of complexes 1-3
In each macrometallocycle of 1-3 (Fig. 1-Fig. 3), the dihedral angles between
5

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anthraquinone and two azole rings are from 2.5(2)˘ to 64.3(9)˘ (Table S1). And the
dihedral angles of two azole rings in the same NHC-M-NHC units for 1-3 are from
19.7(6)˘ to 63.9(4)˘. The O(2) atoms in 2 and 3 lie in the outside of anthraquinone
plane, and the slip angles between O(2) and anthraquinone planes are from 17.1(5)˘ to
23.2(5)˘ (Table S2). The internal ring angles (N-C-N) at the carbene centers for 1-3
are from 105.5(4)˘ to 108.3(6)˘, which are corresponding to those of known NHC
metal complexes.16, 17
In complex 1 (Fig. 1(a)), the cationic unit contains one 18-membered
macrometallocycle, which is formed by one biscarbene ligand (L1‘) and one Hg(II)
ion. Different from 1, complex 2 is formed by one tetradentate mixed ligand L2 and
one Hg(II) ion, in which one 18-membered ring and two 6-membered rings are
contained. It is worth noting that one larger 28-membered macrometallocycle in 3 is
formed by one L3 and one Hg(II) ion. The Hg(1) in 1 is tetra-coordinated with two
carbene carbon atoms and two bromide ions to adopt a tetrahedral geometry. The
bond distances of Hg(1)-C(3) and Hg(1)-Br(1) are 2.100(5) Å and 2.859(5) Å. The
bond angles of C(3)-Hg(1)-C(3A) and Br(1)-Hg(1)-Br(1A) are 156.8(3)˘ and
109.2(2)˘. The bond angles of C-Hg-Br are 94.6(1)-98.7(1)˘. Interestingly, the
carbonyl group on 9-position reacted with two acetonitrile molecules in the presence
of strong base KOtBu through losing one molecule H2O to form L1‘. As a result, two
-CH2CN units were introduced to anthraquione, in which two -CH2CN lie on two
flanks of anthraquinone plane. The C(18)-N(3) distance is 1.132(8) Å, and the bond
angles of N(3)-C(18)-C(17) and C(17)-C(16)-C(17A) are 175.9(6)˘ and 108.4(5)˘.
In complex 2, Hg(II) ion is also tetra-coordinated with two carbene carbon atoms
and two nitrogen atoms from two pyridine rings to adopt a square-planar geometry
(Fig. 2(a) and 2(b)). The bond distances of Hg-C and Hg-N are 2.073(6)-2.087(7) Å
and 2.585(7)-2.648(6) Å, and the bond angles of C(7)-Hg(1)-C(34) and
N(1)-Hg(1)-N(6) are 175.6(3)˘ and 86.1(2)˘. The bond angles of C-Hg(1)-N are in the
range of 80.7(2)-102.0(2)˘. The dihedral angles between benzimidazole rings and
adjacent pyridine rings are 56.2(4)˘ and 61.6(9)˘. Two pyridine rings formed the
dihedral angle of 48.0(7)˘, and the two pyridine rings and the anthraquinone ring
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formed the dihedral angles of 61.8(8)˘ and 70.2(8)˘.
Differed from 1 and 2, Hg(1) in complex 3 is di-coordinated with two carbon
atoms (Fig. 3(a)). The bond distance of C(3)-Hg(1) is 2.090(6) Å, and the bond angle
of C(3)-Hg(1)-C(3A) is 167.0(3)˘. The dihedral angles between two anthraquinone
planes is 64.7(2)˘. Intramolecular Œ-Œ interactions between anthraquione rings and
imidazole rings are observed (Table S4).
The crystal packings of complexes 1-3
In the crystal packing of 1 (Fig. 1(b)), 2D supramolecular layer is formed by two
types of C-H···N hydrogen bonds and two types of C-H···Br hydrogen bonds (Table
S3).18 In these hydrogen bonds, hydrogen atoms are from imidazole rings. 3D
frameworks are formed via the same C-H···Br hydrogen bonds (Fig. 1(c), Table S3).
In the crystal packing of 2 (Fig. 2(c)), 2D supramolecular layer is formed by three
types of C-H···F hydrogen bonds (Table S3). In the C-H···F hydrogen bonds,19
hydrogen atoms are from pyridine rings and methylene groups. Additionally, 2D
layers are further extended into 3D frameworks via two types of Œ···Œ interactions
(between intermolecular benzimidazole rings and between intermolecular
anthraquione and benzimidazole rings) (Fig. 2(d), Table S4).
In Fig. 3(b), 2D supramolecular layer of 3 is formed four types of C-H···F
hydrogen bonds. In the C-H···F hydrogen bonds, hydrogen atoms are from
anthraquinone rings and methylene groups. 2D layers are further extended into 3D
frameworks via two types of new C-H···F hydrogen bonds (Fig. 3(c), Table S3). In
the C-H···F hydrogen bonds, hydrogen atoms are from anthraquinone rings and
imidazole rings.
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(a)
(b)
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(c)
Fig. 1 (a) Perspective view of 1 and anisotropic displacement parameters depicting
30% probability. Selected bond lengths (Å) and angles (˘): Hg(1)-C(3) 2.100(5),
Hg(1)-Br(1) 2.859(5), C(18)-N(3) 1.128(8); C(3)-Hg(1)-C(3A) 156.8(3),
Br(1)-Hg(1)-Br(1A) 109.2(2), C(3)-Hg(1)-Br(1) 98.7(1), N(3)-C(18)-C(17) 175.8(6),
C(17)-C(16)-C(17A) 108.1(5), N(1)-C(3)-N(2) 105.3(4). Symmetry code: i = -x, y,
0.5 - z. (b) The 2D supramolecular layer of 1 via C-H···Br and C-H···N hydrogen
bonds. (c) The 3D supramolecular architecture of 1 via C-H···Br and C-H···N
hydrogen bonds. All hydrogen atoms in (b) and (c) were omitted for clarity except
those participating in hydrogen bonds.
(a)
(b)
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(c)
(d)
Fig. 2 (a) Perspective view of 2 and anisotropic displacement parameters depicting
30% probability. Selected bond lengths (Å) and angles (˘): Hg(1)-C(7) 2.087(7),
Hg(1)-C(34) 2.073(6), Hg(1)-N(1) 2.585(7), Hg(1)-N(6) 2.648(6); C(7)-Hg(1)-C(34)
175.6(3), N(1)-Hg(1)-N(6) 86.1(2), C(34)-Hg(1)-N(1) 102.0(2), C(7)-Hg(1)-N(1)
82.3(3), C(34)-Hg(1)-N(6) 80.7(2), C(7)-Hg(1)-N(6) 99.1(2), N(2)-C(7)-N(3)
108.3(6). (b) The coordination environment of Hg(II) ions and anisotropic
displacement parameters depicting 30% probability. (c) The 2D supramolecular layer
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of 2 via C-H···F hydrogen bonds. (d) The 3D supramolecular architecture of 2 via
C-H···F hydrogen bonds ŒđđđŒ interactions. All hydrogen atoms in (c) and (d) were
omitted for clarity except those participating in hydrogen bonds.
(a)
(b)
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(c)
Fig. 3 (a) Perspective view of 3 and anisotropic displacement parameters depicting
30% probability. Selected bond lengths (Å) and angles (˘): C(3)-Hg(1) 2.090(6);
C(3)-Hg(1)-C(3A) 167.0(3), N(1)-C(3)-N(2) 108.0(5). Symmetry code: i = 2 - x, y,
0.5 - z. (b) The 2D supramolecular layer of 3 via C-H···F hydrogen bonds. (c) The 3D
supramolecular architecture of 3 via C-H···F hydrogen bonds. All hydrogen atoms in
(b) and (c) were omitted for clarity except those participating in hydrogen bonds.
Study of catalytic activity of NHC metal complexes
We tried the catalytic performance of complexes 1-3 in the Suzuki-Miyaura reaction,
but these complexes are noneffecitive to this C-C coupling reaction. Afterwards, we
prepared L1-Pd(II) complex in situ, and studied the catalytic activity of this complex
in the Suzuki-Miyaura reaction, the result showed that this complex is efficient for
this coupling reaction. Unfortunately, the crystal structure of L1-Pd complex was not
obtained.
Catalytic activity of L1-Pd(II) complex in the Suzuki-Miyaura reaction
The Suzuki-Miyaura reaction, a cross-coupling process between an organoboron
reagent and an aryl halide, is of general interest to organic synthesis. The
Suzuki-Miyaura reaction catalyzed by NHC-Pd(II) complexes has become one of the
most versatile and powerful tools for the formation of biaryls.20 In order to examine
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the catalytic activity of L1-Pd(II) complex in situ in the Suzuki-Miyaura reaction, we
chose the cross-coupling reaction of 4-bromotoluene with phenylboronic acid as a
model reaction to investigate the effects of solvent, base, temperature and so on in air
(Table 1), and the reactions were monitored by GC analysis after the appropriate
intervals. Use of ethanol as solvent and K2CO3 as base gave 43% coupling yield at 50
˘C in 24 h (Entry 1). Under the same condition, use of DMF or pure water as solvents
gave 11% or 9% coupling yields (Entries 2 and 3). Then, the mixed solvents were also
tested. With the ratio of ethanol to water changing from 5:1 to 1:1, and the coupling
yields varied from 32% to 85% in 24 h (Entries 4-6). The reason may be that the
solubility of substrates, catalyst and bases was improved effectively in the mixed
solvents. But when the reaction time was prolonged to 48 h, the coupling yields had
no significant improvement (40-86%). After adding 10 mol% TBAB in EtOH/H2O
(1:1), the yield of 92% in 14 h was obtained (Entry 7). Under the same conditions, the
reactions gave the coupling yields of 97% at 60 ˘C and 96% at 70 ˘C (Entries 8 and 9)
and prolonged time had no effect on improving the yields. With the same conditions
as Entry 3, the reaction gave 11% coupling yield after adding 10 mol% TBAB (Entry
10). The result indicated that the reaction could be e¡ectively improved in the
presence of TBAB. It has been known that the addition of TBAB as a co-catalyst can
enhance the activity of many catalytic systems. Besides, TBAB is able to activate and
stabilize palladium(0) species generated in situ, which is believed to be the real
catalytically active species.21 Other bases, such as K3PO4·3H2O, KOH and Cs2CO3,
were also tested, they only gave moderate coupling yields of 61-73% in 24 h at the
same condition as Entry 7 (Entries 11-13). Based on the extensive screen, EtOH/H2O
(v:v = 1:1) and K2CO3 were proved to be the efficient solvent and base in the presence
of 10 mol% TBAB with a catalyst loading of 0.2 mol% L1-Pd(II) complex at 60 ˘C in
air, thus giving the optimal coupling result. In order to further study the influence of
the ligand on catalysis, the control experiment was performed, in which
[PdCl2(CH3CN)2] was added in the absence of ligand L1 with the optimized
conditions, and only 43% coupling product was obtained (Entry 14). This result
showed that ligand L1 had the preponderant function in the catalytic reactions.
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We attempted the cross-coupling reaction of various aryl halides with
phenylboronic acid under the optimal reaction conditions (Table 2). Activated aryl
bromides with electronic withdrawing substituents in the para-position (such as
4-nitrobromobenzene and 4-bromoacetophenone) could be transformed to biaryl
products with 99% yield (5a(1) and 5b(1)). Deactivated aryl bromides with an
electronic donating moiety (such as 4-bromoanisole, 3-bromoanisole, 2-bromotoluene
and 4-bromoaniline) also could be effciently coupled with phenylboronic acid with
moderate to high yields of 75-99% (5c, 5d, 5e(1) and 5f). The coupling of
1-bromonaphthalene and bromobenzene with phenylboronic acid gave 88% and 94%
yields (5g and 5l(2)). And the high yields of 93% and 96% were obtained in the
coupling reactions
of
aryl
dibromides
(1,4-dibromonaphthalene
and
1,4-dibromoanthracene) with phenylboronic acid (5h and 5i). Coupling of aryl
chlorides with phenylboronic acid gave relatively poor yields of 0-41% (5a(2), 5b(2),
5e(2), 5j, 5k and 5l(1)), which may be attributed to the low activity of aryl chlorides.
The catalyst was also highly efficient in the coupling of iodobenzene with
phenylboronic acid to give quantitative yield of desired coupling product (5l(3)).
Above results showed that L1-Pd(II) complex had high stability to air and good
tolerance toward various sensitive functional groups. These advantages made it into a
valuable precatalyst for thermally sensitive substrates. Therefore, this provided an
effective phosphine-free catalyst system for facile coupling of aryl halides in
EtOH/H2O (1:1) under mild and aerobic conditions. The favorable reaction condition
of this catalytic system for Suzuki-Miyaura cross-coupling reaction was important to
the protection of enviroment and the reduction of cost in the field of fine chemical and
pharmaceutical industries.
Table 1 Suzuki-Miyaura reaction of 4-bromotoluene with phenylboronic acid
catalyzed by L1-Pd(II) complex[a]
0.2 mol% cat., base
Br
Me
Me
(HO)2B
+
solvent
Ancillary
T
Time Yield
Entry
Solvent
Base
catalysts (˘C) (h)[b] (%)[c]
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1
2
3
4
5
6
7
C2H5OH
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
-
50
50
50
50
50
50
50
12
24
12
24
12
24
24
48
24
48
24
48
12
14
24
12
14
24
12
14
24
12
24
12
24
12
24
12
24
14
42
43
10
11
8
-
H2O
-
9
C2H5OH/H2O
(5:1)
-
32
43
38
40
85
86
67
92
96
86
97
97
84
96
96
11
12
60
61
71
73
62
70
43[d]
C2H5OH/H2O
(3:1)
-
-
C2H5OH/H2O
(1:1)
C2H5OH/H2O
(1:1)
TBAB
8
9
C2H5OH/H2O
(1:1)
K2CO3
K2CO3
TBAB
TBAB
60
70
C2H5OH/H2O
(1:1)
10
11
12
13
14
H2O
K2CO3
K3PO4·3H2O
KOH
TBAB
TBAB
TBAB
TBAB
TBAB
50
50
50
50
50
C2H5OH/H2O
(1:1)
C2H5OH/H2O
(1:1)
C2H5OH/H2O
(1:1)
Cs2CO3
C2H5OH/H2O
(1:1)
K2CO3
[a] Reaction conditions: 4-bromotoluene (0.5 mmol), phenylboronic acid (0.6 mmol), base (1.2
mmol), TBAB (10 mol%), L1-Pd(II) complex (0.2 mol%), solvent (6.0 mL) in air .
[b] Monitered by TLC.
[c] Determined by a GC method using n-tridecane as internal standard, and using 4-bromotoluene
as a standard.
[d] Reaction conditions are the same as [a], and only PdCl2(CH3CN)2 (0.2 mol%) was added in the
absence of ligand L1.
Table 2 Suzuki-Miyaura Reaction with different aryl halides catalyzed by L1-Pd(II)
complex[a]
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0.2 mol% cat. K2CO3, TBAB
Ar
(HO)2B
Ar
X
C2H5OH/H2O (1:1), 60 ꢀ
in air
5a-5l
X = Cl, Br, I
O2N
H3CO
H3COC
5a
5b
5c
(1) X = Br, 14 h, 99%
(2) X = Cl, 14 h, 28%
(1) X = Br, 14 h, 99%
(2) X = Cl, 14 h, 26%
X = Br, 14 h, 98%
H2N
H3CO
CH3
5d
5e
5f
X = Br, 14 h, 99%
(1) X = Br, 14 h, 96%
(2) X = Cl, 14 h, trace
X = Br, 14 h, 75%
5g
5h
5i
X = Br, 14 h, 88%
X = Br, 14 h, 93%
X = Br, 14 h, 96%
O2N
NO2
NO2
5j
5k
5l
X = Cl, 14 h, 35%
X = Cl, 14 h, trace
(1) X = Cl, 14 h, 41%
(2) X = Br, 14 h, 94%
(3) X = I, 14 h, 99%
[a] Reaction conditions: aryl halide (0.5 mmol), phenylboronic acid (0.6 mmol), K2CO3 (1.2
mmol), cat. (0.2 mol %) , C2H5OH/H2O (1:1) (3 mL), TBAB (10 mol%), 60 ˘C in air.
Experimental section
General procedures
All manipulations were performed using Schlenk techniques, and solvents were
puri›ed by standard procedures. All the reagents for synthesis and analyses were of
analytical grade and used without further puri›cation. Melting points were determined
1
with a Boetius Block apparatus. H and 13C NMR spectra were recorded on a Varian
Mercury Vx 400 spectrometer at 400 MHz and 100 MHz, respectively. Chemical
shifts, /, are reported in ppm relative to the internal standard TMS for both 1H and 13C
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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).
Preparation of 1,8-bis(3‘-bromopropoxy)anthraquinone
A suspension of 1,8-dihydroxy-9,10-anthraquinone (5.000 g, 20.8 mmol), K2CO3
(15.000 g, 109 mmol), TBAB (0.134 g, 2.1 mmol) and 1,3-dibromopropane (8.404 g,
41.6 mmol) in acetone (50 mL) was stirred under refluxing for 4 days. After removing
the solvent, H2O (50 mL) was added to the residue, and the suspension was extracted
with CH2Cl2 (3 × 30 mL) and the extracting solution was dried over anhydrous
MgSO4.
After
removing
CH2Cl2,
a
yellow
solid
of
1,8-bis(3‘-bromopropoxy)anthraquinone was obtained. Yield: 5.100 g (50 %). M.p.:
120-122 ˘C. Anal. Calcd for C20H18Br2O4: C, 49.82; H, 3.76%. Found: C, 47.73; H,
3.54%. 1H NMR (400 MHZ, DMSO-d6): / 2.04-2.10 (m, 4H, CH2), 3.64 (t, J = 6.6 Hz,
4H, CH2), 4.00 (t, J = 5.6 Hz, 4H, CH2), 7.27-7.33 (m, 2H, ArH), 7.45-7.53 (m, 4H,
ArH); 13C NMR (100 MHZ, DMSO-d6): / 31.2 (CH2), 31.8 (CH2), 66.4 (CH2), 118.40
(ArC), 118.45 (ArC), 120.1 (ArC), 123.5 (ArC), 134.0 (ArC), 134.3 (ArC), 157.8
(ArC), 183.2 (CO).
Preparation of 1,3-bis[8‘-(3‘‘-bromopropoxy)anthraquinon-l-yloxy]propane
This compound was prepared in an analogous manner to that of
1,8-bis(3‘-bromopropoxy)anthraquinone,
only
the
molar
ratio
of
1,8-dihydroxy-9,10-anthraquinone (5.000 g, 20.8 mmol) with 1,3-dibromopropane
1,3-dibromopropane (6.303 g, 31.2 mmol) was 1:1.5. Yield: 2.871 g (45%). M.p.:
170-172 ˘C. Anal. Calcd for C37H30Br2O8: C, 58.28; H, 3.96%. Found: C, 58.35; H,
3.82%. 1H NMR (400 MHZ, DMSO-d6): / 2.13 (q, J = 2.7 Hz, 2H, CH2), 2.33 (t, J =
1.8 Hz, 4H, CH2), 3.78 (t, J = 3.8 Hz, 4H, CH2), 4.43 (s, 4H, CH2), 4.53 (s, 4H, CH2),
6.56 (q, J = 2.8 Hz, 2H, ArH), 6.93 (q, J = 2.8 Hz, 2H, ArH), 7.77 (q, J = 6.3 Hz, 4H,
ArH), 8.246 (t, J = 7.6 Hz, 4H, ArH); 13C NMR (100 MHZ, DMSO-d6): / 26.0 (CH2),
30.4 (CH2), 30.6 (CH2), 64.8 (CH2), 65.1 (CH2), 66.5 (CH2), 118.9 (ArC), 120.1
(ArC), 120.7 (ArC), 122.4 (ArC), 122.9 (ArC), 124.0 (ArC), 133.3 (ArC), 134.3
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(ArC), 135.0 (ArC), 157.3 (ArC), 180.7 (CO), 183.0 (CO).
Preparation
hexafluorophosphate (L1H2(PF6)2)
solution of N-ethyl-benzimidazole (0.875 g, 9.1 mmol) and
of
1,8-bis[3‘-(N-ethyl-imidazoliumyl)propoxy]anthraquinone
A
1,8-bis(3‘-bromopropoxy)anthraquinone (2.000 g, 4.1 mmol) in acetone (100 mL)
was stirred for 5 days under refluxing, and an orange oil was formed. After the
solvent was removed, the precipitate was dissolved in methanol (60 mL), and then a
solution of NH4PF6 (1.497 g, 9.1 mmol) in methanol (60 mL) was added and stirred
continuously
for
72
h
at
room
temperature.
The
1,8-bis[3‘-(N-ethyl-imidazoliumyl)propoxy]anthraquinone
hexafluorophosphate
(L1H2(PF6)2) was obtained as orange solid through filtering. Yield: 3.026 g (90%).
M.p.: 144-146 ˘C. Anal. Calcd for C30H34N4O4P2F12: C, 44.78; H, 4.25; N, 6.96%.
1
Found: C, 44.83; H, 4.18; N, 6.78%. H NMR (400 MHZ, DMSO-d6): / 1.36 (t, J =
7.2 Hz, 6H, CH3), 2.37 (t, J = 6 Hz, 4H, CH2), 4.12-4.18 (m, 8H, CH2), 4.51 (t, J = 6.6
Hz, 4H, CH2), 7.57 (t, J = 4 Hz, 2H, ArH), 7.71 (t, J = 8.4 Hz, 8H, ArH), 9.14 (s, 2H,
2-imiH); 13C NMR (100 MHZ, DMSO-d6): / 14.9 (CH3), 28.7 (CH2), 44.2 (CH2), 45.9
(CH2), 65.1 (CH2), 118.7 (ArC), 120.2 (ArC), 122.1 (ArC), 122.5 (ArC), 123.3 (ArC),
134.0 (ArC), 134.5 (ArC), 135.7 (ArC), 157.6 (ArC), 181.8 (CO), 183.1 (CO) (imi =
imidazolium).
Preparation of 1,8-bis[3‘-(N-picolyl-benzimidazoliumyl)propoxy]anthraquinone
hexafluorophosphate (L2H2(PF6)2)
This compound was prepared in an analogous manner to that of L1H2(PF6)2, only
N-picolyl-benzimidazole (1.904 g, 9.1 mmol) was used instead of N-ethyl-imidazole.
Yield: 3.792 g (88%), M.p.: 192-194 ˘C. Anal. Calcd for C46H40N6O4P2F12: C, 53.59;
1
H, 3.91; N, 8.15%. Found: C, 53.44; H, 3.84; N, 8.36%. H NMR (400 MHZ,
DMSO-d6): / 4.23 (s, 4H, CH2), 4.84 (s, 4H, CH2), 5.84 (s, 4H, CH2), 7.31 (s, 2H,
ArH), 7.49-7.61 (m, 8H, ArH), 7.77-7.85 (m, 8H, ArH), 8.03 (s, 2H, ArH), 9.88 (s, 2H,
2-bimiH); 13C NMR (100 MHZ, DMSO-d6): / 28.0 (CH2), 43.6 (CH2), 50.7 (CH2),
65.0 (CH2), 113.1 (ArC), 113.7 (ArC), 118.7 (ArC), 120.0 (ArC), 122.6 (ArC), 123.0
(ArC), 123.1 (ArC), 123.6 (ArC), 126.4 (ArC), 126.5 (ArC), 126.6 (ArC), 130.9
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(ArC), 131.1 (ArC), 134.0 (ArC), 134.6 (ArC), 137.4 (ArC), 143.0 (ArC), 149.4
(ArC), 152.7 (ArC), 157.7 (ArC), 182.1 (CO), 183.1 (CO) (bimi = benzimidazolium).
Preparation
of
1,3-bis[8‘-(3‘‘-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane
hexafluorophosphate (L3H2(PF6)2)
This compound was prepared in an analogous manner to that of L1H2(PF6)2, only
1,3-bis[8‘-(3‘‘-bromopropoxy)anthraquinon-l-yloxy]propane (2.000 g, 2.6 mmol) was
used instead of 1,8-bis(3‘-bromopropoxy)anthraquinone. Yield: 2.080 g (72%). M.p.:
202-204 ˘C. Anal. Calcd for C47H46N4O8P2F12: C, 52.03; H, 4.27; N, 5.16%. Found: C,
52.19; H, 4.35; N, 5.27%. 1H NMR (400 MHZ, DMSO-d6): / 1.35 (t, J = 7.4 Hz, 6H,
CH3), 2.21 (q, J = 4.4 Hz, 2H, CH2), 2.46 (t, J = 5.2 Hz, 4H, CH2), 4.26-4.34 (m, 8H,
CH2), 4.66 (t, J = 3.0 Hz, 8H, CH2), 7.54 (d, J = 7.2 Hz, 2H, ArH), 7.54 (t, J = 3.4 Hz,
6H, ArH), 7.77 (t, J = 7.8 Hz, 4H, ArH), 7.83 (d, J = 1.6 Hz, 4H, ArH), 9.21 (s, 2H,
2-imiH); 13C NMR (100 MHZ, DMSO-d6): / 14.8 (CH3), 15.5 (CH3), 25.3 (CH2), 29.3
(CH2), 45.2 (CH2), 46.6 (CH2), 64.6 (CH2), 66.3 (CH2), 118.0 (ArC), 119.3 (ArC),
119.8 (ArC), 121.9 (ArC), 122.3 (ArC), 123.3 (ArC), 133.6 (ArC), 133.8 (ArC), 157.7
(ArC), 180.5 (CO), 182.9 (CO).
Preparation of [L1‘HgBr2] (1)
HgBr2 (0.197 g, 0.5 mmol) and KOtBu (0.061 g, 0.5 mmol) were added to a solution
of precursor L1H2(PF6)2 (0.200 g, 0.2 mmol) in DMSO (5 mL), CH2Cl2 (5 mL) and
CH3CN (20 mL) in N2, and the suspension solution was stirred for 24 h under reflux.
The resulting solution was filtered and concentrated to 5 mL, and Et2O (5 mL) was
added to precipitate [L1‘HgBr2] (1) as a brown powder. Yield: 0.141 g (60%). M.p.:
266-268 ˘C. Anal. Calcd for C34H36Br2HgN6O3: C, 43.57; H, 3.87; N, 8.96%. Found:
1
C, 43.65; H, 3.74; N, 8.83%. H NMR (400 MHZ, DMSO-d6): / 1.35 (t, J = 7.2 Hz,
6H, CH3), 2.07 (s, 4H, CH2), 2.40-2.47 (m, 4H, CH2), 4.31 (t, J = 4.8 Hz, 4H, CH2),
4.40 (q, J = 7.2 Hz, 4H, CH2), 4.71 (t, J = 6.8 Hz, 4H, CH2), 7.51 (s, 1H, ArH), 7.53 (s,
1H, ArH), 7.68 (t, J = 4.6 Hz, 4H, ArH), 7.76 (t, J = 8 Hz, 2H, ArH), 7.81 (d, J = 1.6
Hz, 2H, ArH); 13C NMR (100 MHZ, DMSO-d6): / 14.7 (CH3), 28.4 (CH2), 44.4 (CH2),
47.8 (CH2), 65.2 (CH2), 71.2 (CH2CN), 117.2 (CN), 118.5 (ArC), 121.1 (ArC), 121.5
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(ArC), 122.4 (ArC), 132.7 (ArC), 133.4 (ArC), 156.9 (ArC), 174.5 (2-imiC), 179.4
(2-imiC), 182.1 (CO).
Preparation of [L2Hg](PF6)2 (2)
Hg(OAc)2 (0.092 g, 0.2 mmol) and NaOAc (0.127 g, 1.5 mmol) were added to a
solution of L2H2(PF6)2 (0.200 g, 0.1 mmol) in CH3CN (30 mL), and the suspension
solution was stirred for 24 h under reflux. The resulting solution was filtered and
concentrated to 5 mL, and Et2O (5 mL) was added to precipitate [L2Hg](PF6)2 (2) as a
yellow powder. Yield: 0.132 g (55%). M.p.: 258-260 ˘C. Anal. Calcd for
C46H38F12HgN6O4P2: C, 44.94; H, 3.11; N, 6.83%. Found: C, 44.88; H, 3.26; N,
1
6.75%. H NMR (400 MHZ, DMSO-d6): / 4.43 (t, J = 4.4 Hz, 4H, CH2), 5.12 (t, J =
7.2 Hz, 4H, CH2), 6.08 (s, 4H, CH2), 7.38 (q, J = 4 Hz, 2H, ArH), 7.46 (q, J = 3 Hz,
2H, ArH), 7.59-7.66 (m, 4H, ArH), 7.72 (q, J = 7.3 Hz, 4H, ArH), 7.85 (d, J = 7.6 Hz,
2H, ArH), 7.92-7.96 (m, 2H, ArH), 8.14 (d, J = 8 Hz, 2H, ArH), 8.20 (d, J = 7.6 Hz,
2H, ArH), 8.34 (d, J = 4.4 Hz, 2H, 2-bimiH); 13C NMR (100 MHZ, DMSO-d6): / 28.0
(CH2), 46.0 (CH2), 50.1 (CH2), 65.9 (CH2), 111.7 (ArC), 112.0 (ArC), 117.5 (ArC),
118.6 (ArC), 120.6 (ArC), 122.8 (ArC), 123.3 (ArC), 124.8 (ArC), 131.5 (ArC), 131.9
(ArC), 132.7 (ArC), 133.6 (ArC), 137.6 (ArC), 148.7 (ArC), 151.9 (ArC), 157.2
(ArC), 179.9 (2-bimiC), 180.5 (CO), 181.9 (CO).
Preparation of [L3Hg](PF6)2 (3)
Hg(OAc)2 (0.040 g, 0.1 mmol) and NaOAc (0.120 g, 1.4 mmol) were added to a
solution of precursor L3H2(PF6)2 (0.200 g, 0.1 mmol) in CH3CN (30 mL), and the
suspension solution was stirred for 24 h under reflux. The resulting solution was
filtered and concentrated to 5 mL, and Et2O (5 mL) was added to precipitate
[L3Hg](PF6)2 (3) as a yellow powder. Yield: 0.140 g (58%). M.p.: 268-270 ˘C. Anal.
Calcd for C47H44F12HgN4O8P2: C, 43.98; H, 3.45; N, 4.36%. Found: C, 43.79; H, 3.34;
N, 4.26%. 1H NMR (400 MHZ, DMSO-d6): / 1.42 (t, J = 8.8 Hz, 6H, CH3), 2.06-2.08
(m, 2H, CH2), 2.32-2.33 (m, 4H, CH2), 4.45-4.47 (m, 4H, CH2), 4.61-4.63 (m, 4H,
CH2), 4.99 (d, J = 3.2 Hz, 4H, CH2), 5.07 (t, J = 2.0 Hz, 4H, CH2), 6.90 (t, J = 8.2 Hz,
2H, ArH), 7.01 (d, J = 8.0 Hz, 2H, ArH), 7.17 (d, J = 8.0 Hz, 2H, ArH), 7.50 (t, J =
7.8 Hz, 2H, ArH), 7.66 (q, J = 3.5 Hz, 4H, ArH), 8.23 (d, J = 8.4 Hz, 2H, ArH), 8.35
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(d, J = 7.6 Hz, 2H, ArH); 13C NMR (100 MHZ, DMSO-d6): / 15.1 (CH3), 15.8 (CH3),
25.6 (CH2), 29.6 (CH2), 45.5 (CH2), 48.9 (CH2), 64.8 (CH2), 66.3 (CH2), 118.3 (ArC),
119.6 (ArC), 122.2 (ArC), 122.6 (ArC), 123.6 (ArC), 133.9 (ArC), 134.5 (ArC), 158.0
(ArC), 175.8 (2-imiC), 180.6 (CO), 183.2 (CO).
Preparation of L1-Pd(II) complex
Silver oxide (0.086 g, 0.3 mmol) was added to a solution of L1H2(PF6)2 (0.200 g, 0.2
mmol) in DMSO (5 mL) and CH3CN (25 mL) under N2, and the suspension solution
was stirred for 24 h under reflux. The resulting solution was filtered, and
PdCl2(CH3CN)2 (0.05 g, 0.1 mmol) was added to the filtrate, and stirred continuously
for another 24 h under refluxing. The resulting solution was filtered and concentrated
to 5 mL, and Et2O (5 mL) was added to precipitate a deep yellow powder L1-Pd(II).
Anal. Calcd for C30H32N4O4PdCl2: C, 52.22; H, 4.67; N, 8.12%. Found: C, 52.33; H,
1
4.76; N, 8.08%. H NMR (400 MHZ, DMSO-d6): / 1.35 (t, J = 8.6 Hz, 6H, CH3),
2.31-2.34 (m, 4H, CH2), 4.48 (t, J = 3.8 Hz, 4H, CH2), 4.63 (d, J = 3.2 Hz, 4H, CH2),
5.00 (s, 4H, CH2), 7.43 (d, J = 7.2 Hz, 2H, ArH), 7.52 (d, J = 8.0 Hz, 4H, ArH), 7.68
(q, J = 7.8 Hz, 4H, ArH); 13C NMR (100 MHZ, DMSO-d6): / 14.8 (CH3), 28.5 (CH2),
44.5 (CH2), 47.8 (CH2), 65.2 (CH2), 117.1 (ArC), 118.4 (ArC), 121.1 (ArC), 121.6
(ArC), 122.5 (ArC), 132.6 (ArC), 133.3 (ArC), 156.8 (ArC), 174.6 (2-imiC), 182.1
(CO).
General procedure for the Suzuki-Miyaura cross-coupling reaction
In a typical reaction, aryl halide (0.5 mmol), phenylboronic acid (0.6 mmol), base (1.2
mmol) and NHC-Pd complex (0.2 mol %) in mixture solvent (3 mL, methanol/water
= 3/1, V/V) 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 CH2Cl2 (10 mL × 3), and the organic layer was washed with water (10
mL × 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.
X-ray data collection and structure determinations
X-ray single-crystal diffraction data for complex 1-3 were collected by using a Bruker
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Apex II CCD diffractometer at 173(2) K for 1 and 3, and 296(2) K for 2 with Mo-Ka
radiation (ꢀ = 0.71073 Å) by & scan mode. There was no evidence of crystal decay
during data collection in all cases. Semiempirical absorption corrections were applied
by using SADABS and the program SAINT was used for integration of the diffraction
profiles.22 All structures were solved by direct methods and refined with the
full-matrix least-squares technique using the the ShelXT and ShelXL programs
programs.23 Hydrogen atoms bonded to C atoms were placed geometrically and
presumably solvent H atoms were first located in difference Fourier maps and then
fixed in the calculated sites. Further details for crystallographic data and structural
analysis are listed in Table 3. Fig.s were generated by using Crystal-Maker.24 The
platon squeeze program was used to solve the structure of complex 1.25
Table 3 Crystal data and structure refinements for 1-3
1
2·0.75CH3CN
3
Chemical formula
C34H36Br2HgN6O3 C46H38F12HgN6O4P2
·0.75CH3CN
C47H44F12HgN4O8P2
Fw
937.10
Monoclinic
C2/c
1260.14
Triclinic
P¯
1283.39
Monoclinic
C2/c
Cryst syst
Space group
a /Å
15.398(2)
21.286(3)
12.480(1)
90.0(0)
112.2(5)
90.0(0)
3785.8(9)
4
13.557(1)
13.676(1)
15.681(1)
79.7(5)
76.1(1)
68.3(0)
2609.8(3)
2
21.023(4)
12.719(3)
18.421(5)
90.0(0)
100.6(7)
90.0(0)
4840(2)
4
b /Å
c /Å
./deg
ꢁ/deg
ꢂ/deg
V /Å3
Z
Dcalcd, Mg/m3
Abs coeff, mm-1
F(000)
1.644
1.604
1.761
6.216
3.101
3.351
1824
1245
2544
Cryst size, mm
ꢃmin, ꢃmax, deg
T /K
0.18 × 0.17 × 0.16
1.72, 25.01
173(2)
0.17 × 0.15 × 0.14
1.344, 25.01
296(2)
0.15 × 0.14 × 0.13
1.88, 25.01
173(2)
No. of data collected
No. of unique data
No. of refined params
Goodness-of-fit on F2a
Final R indicesb [I >
9476
13495
12096
3343
9154
4249
222
696
336
1.059
1.029
1.059
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21(I)]
R1
0.0336
0.0861
0.0491
0.1248
0.0414
0.0884
wR2
R indices (all data)
R1
wR2
2
0.0382
0.0891
0.0681
0.1372
0.0512
0.0930
aGOF = [ꢀw(Fo - Fc2)2/(n - p)]1/2, where n is the number of reflection and p is the number of
2 2 1/2
parameters refined. bR1 = ꢀ(||Fo| - |Fc||)/ꢀ|Fo|; wR2 = [ꢀ[w(Fo2 - Fc2)2 ]/ꢀw(Fo ) ] .
Conclusion
In
1,8-bis[3‘-(N-R-azoliumyl)propoxy]-9,10-anthraquinone
L1H2(PF6)2-L2H2(PF6)2 (R = ethyl or picolyl, azoliumyl = imidazoliumyl or
summary,
three
bis-azolium
salts
hexafluorophosphate
benzimidazoliumyl)
and
1,3-bis[8‘-(3‘‘-(N-ethyl-imidazoliumyl)propoxy)anthraquinon-l-yloxy]propane
hexafluorophosphate (L3H2(PF6)2), as well as their three macrometallocycle
N-heterocyclic carbene mercury(II) complexes [L1‘HgBr2] (1), [L2Hg](PF6)2 (3) and
[L3Hg](PF6)2 (3) were prepared and characterized by 1H NMR, 13C NMR
spectroscopy and X-ray crystallography. In the crystal packings of 1-3, 1D polymeric
chains, 2D supramolecular layers and 3D supramolecular frameworks are formed via
hydrogen bonds and ŒđđđŒ interactions. Additionally, the catalytic activity of L1-Pd(II)
complex in situ in Suzuki-Miyaura reactions was studied. The results show that this
catalytic system is efficient to Suzuki-Miyaura reactions. Further studies on new
organometallic compounds from these ligands and analogous ligands are underway.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China (No. 21572159) and Youth Fund of Tianjin Normal University (52XQ1402)
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Software of Graphics:
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A Table of Contents Entry:
NHC Ag(I), Hg(II) complexes were prepared and characterized, and catalytic
activities of NHC Pd(II) complex in Suzuki-Miyaura was investigated.
1