Acyclic palladium(II)-N-heterocyclic carbene metallacrown ether complexes: Synthesis, structure and catalytic activity

Article abstract of DOI:10.1002/cjoc.201100596

Novel acyclic Pd(II)-N-heterocyclic carbene (NHC) metallacrown ethers 5a, 5b have been synthesized. Reaction of the imidazolium salts bearing a long polyether chain with Ag₂O afforded Ag-NHC complexes, which then reacted as carbene transfer age

Full text of DOI:10.1002/cjoc.201100596

FULL PAPER
DOI: 10.1002/cjoc.201100596
Acyclic Palladium(II)-N-heterocyclic Carbene Metallacrown
Ether Complexes: Synthesis, Structure and Catalytic Activity
Zhang, Weixia(张维熙)
Zhang, Xiaoqina,b(张孝琴)
Luo, Meiming*,a(罗美明)
a Key Laboratory of Green Chemistry & Technology of Ministry of Education, College of Chemistry,
Sichuan University, Chengdu, Sichuan 610064, China
b Department of Chemistry, Luzhou Medical College, Luzhou, Sichuan 646000, China
Novel acyclic Pd(II)-N-heterocyclic carbene (NHC) metallacrown ethers 5a, 5b have been synthesized. Reac-
tion of the imidazolium salts bearing a long polyether chain with Ag2O afforded Ag-NHC complexes, which then
reacted as carbene transfer agent with PdCl2(MeCN)2 to give the desired acyclic Pd(II)-NHC metallacrown ether
1
complexes 5a and 5b. The H NMR and 13C NMR spectra show 5a and 5b exist as mixtures of cis and trans iso-
mers in solution. The trans isomer of 5a was characterized by X-ray diffraction, which clearly demonstrated two
pseudo-crown ether cavities in trans-5a. Pd(II)-NHC complexes 5a and 5b have been shown to be highly effective
in the Suzuki-Miyaura reactions of a variety of aryl bromides in neat water without the need of inert gas protection.
Keywords palladium, N-heterocyclic carbene, carbene ligands, acyclic metallacrown ether, C—C coupling
Introduction
matic residue are located at the end of the polyether
chain,[19-22] overall organization is enhanced.[23] In these
acyclic crown ethers, the flexible polyether units provide
basic requirement for complexation and aromatic groups
control the structure elements,[24] such as π-electron,
steric influence, hydrophobic interaction or donor groups
in ortho position of aromatic residue.[25-27] Hence, acyclic
crown ethers with aromatic end groups fill the gap be-
tween linear oligoethylene glycol methyl ether and the
common crown ether.[24] Nevertheless, very few exam-
ples appending acyclic crown ether to NHC ligands have
appeared,[28-32] and NHC transition metal-complexes
which have acyclic crown ether with aromatic donor end
groups in the molecule are unprecedented to date. We
hereby present the synthesis and characterization of
acyclic Pd-NHC metallacrown ethers with aromatic do-
nor end groups. Their application as catalysts for
N-Heterocyclic carbenes (NHCs) in recent years have
been employed with considerable success in coordination
chemistry and various catalytic transformations.[1-3] Sub-
stitution of phosphine donor in phosphine metallacrown
ether, which combines the two features of transition
metal complex and crown ether in the same molecule,[4-7]
with NHCs has led to several examples of NHC metal-
lacrwon ether. For example, Cavell et al. prepared an
oxoether-bridged Ag-containing dimetallacrown rings of
smaller size.[8] Rogers et al. reported a mercury(II) car-
bene complex containing a three-ether spacer which re-
vealed the possibility of a carbene extraction mecha-
nism.[9-11] Zhang et al. described bidentate NHC-bridged
dinuclear Ag(I), Au(I) and Cu(I) cationic metallacrown
ethers.[12-14] These publications were mainly focused on
the synthesis and characterization. Nielsen et al. reported
a Pd(II)-NHC complex containing one ether spacer Suzuki-Miyaura coupling in neat water is also described.
which was an active catalyst for Heck reaction in the
presence of n-Bu4NBr.[15] We reported Pd(II)-NHC met-
Results and Discussion
allacrown ether complexes which were shown to be ef-
fective catalysts for the Suzuki-Miyaura reaction.[16]
Ligand and metal complex synthesis
Acyclic crown ether which has more flexible poly-
The synthetic route to desired acyclic Pd-NHC met-
allacrown ether 5 is shown in Scheme 1. Compound 1
was prepared by the classical method from catechol and
1,2-bis(2-chloroethoxy)ethane.[33] Reaction of 1 with
2-chloroethanol using the same procedure gave com-
pound 2. Chlorination of 2 with thionyl chloride was
ether chain compared to common crown ether can easily
adopt itself to different ions. Flexibility of the acyclic
nature allows acyclic crown ether to engage in multiple
bridging and helical binding modes when are not possi-
ble with crown ethers.[17,18] When aromatic groups, espe-
cially those with donor groups in ortho position of aro-
*
E-mail: luomm@scu.edu.cn
Received November 18, 2011; accepted February 2, 2012; published online XXXX, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201100596 or from the author.
Chin. J. Chem. 2012, XX, 1—6
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1

Zhang, Zhang & Luo
FULL PAPER
Scheme 1 Synthesis of acyclic Pd(II)-NHC metallacrown ether
O
O
O
O
O
O
ClCH2CH2OH
NaOH
N
NR
O
O
SOCl2, pyridine
benzene, 80 oC
O
O
O
O
HO
toluene, reflux
O
t-BuOH
reflux, 24 h
HO
O
HO
OH
1
Cl
OH
3
2
O
O
O
O
R
N
Cl
N
N
O
O
O
O
O
O
O
OH
O
(1) Ag2O, CH2Cl2, r.t., 2 h
(2) PdCl2(MeCN)2, r.t., 2 h
Cl
HO
O
OH
O
O
N
R
Cl
N R
N
5a (R = mesityl)
5b (R = 2,6-diisopropylphenyl)
4a (R = mesityl)
4b (R = 2,6-diisopropylphenyl)
1
optimized to give 3 in good isolated yield. Compound 3 and 5b are also observed. The H NMR spectra indicate
was subsequently treated with substituted imidazoles to that the two isomers of 5a are present in a ca. 1∶1.15
1
give the corresponding imidazolium salt 4. In the H ratio and the two isomers of 5b in a ca. 1∶1.35 ratio.
NMR spectra, characteristic signals of the imidazolium Similar cis-trans isomer equilibrium mixtures of
salt NC(H)N protons were observed at δ 10.28 and 10.11. Pd-NHC complex in solution had been described in lit-
These values fall in the range observed for related imi- erature.[37,41-44]
dazolium salts.[34-36]
The pale yellow crystals of the trans isomer (trans-5a)
The choice of base for the synthesis of palladium of complex 5a suitable for an X-ray diffraction study
complex 5 was found to be crucial. Attempts to prepare were obtained by evaporating slowly its CH2Cl2/hexane
the palladium complexes by in situ deprotonation of 4 solution at room temperature. Slowly precipitation of the
with external strong base followed by reaction with trans isomer during evaporation of solvents presumably
PdCl2 or Pd(OAc)2 were unsuccessful. Transmetalation helps to drive the equilibrium between the cis and trans
has proved to be a promising procedure[16,37,38] to obtain isomers to trans-5a. The molecular structure of complex
metal-NHC complexes, which typically involves treat- trans-5a is depicted in Figure 1.[45] The two NHC ligands
ment of the imidazolium salt with silver oxide to form are coordinated to palladium in a trans-positioned fash-
the Ag-NHC complex, followed by transmetalation to a ion, with the palladium-carbene distances of Pd—C10＝
species such as [PdCl2(MeCN)2] to give the metal- 2.024 Å and Pd—C10'＝2.024 Å which are very similar
carbene complexes. We then turned to the synthesis of 5 to the Pd—Ccarbene bond distances found for complexes
by transmetalation from the corresponding Ag-NHC with two trans-positioned imidazolin-2-ylidene donor
complexes. Although it was clearly observed that the groups.[41-44] X-ray diffraction analysis of trans-5a re-
reactions of imidazolium salt 4 with silver oxide oc- veals the square-planar arrangement of the ligands at the
curred when the dark reaction mixture turned pale, the metal center, with a C10-Pd-C10' angle of 180.00° and a
corresponding pure Ag-NHC complex was not isolated. Cl1-Pd-Cl1' angle of 180.00°. The two NHC planes are
We found it best to add PdCl2(MeCN)2 directly to the parallel to each other and approximately orthogonal to
Ag-NHC solutions after filtering off the unreacted silver the coordination plane. These definitely result from the
oxide and insoluble residues. The addition of space group symmetry of P-1.
[PdCl2(MeCN)2] immediately gave a white precipitate of
It is noteworthy that the X-ray single crystal diffrac-
silver chloride and the desired product in good isolated tion analysis of trans-5a reveals clearly the formation of
yield. The formation of 5 was confirmed by the appear- the pseudo-crown ether cavity at each ethylene glycol
ance of the signals around δ 170 which are characteristic chain, with a water molecule inside the cavity. In the
resonances for palladium carbene complexes in the 13C cavity, weak hydrogen bonds are found between the pro-
NMR spectra.[39,40] The appearance of two carbenoid tons of water and the oxygen of acyclic crown ether
carbon signals in the 13C NMR spectra of 5a and 5b in- [Ow—H1w…O1, Ow—H1w…O2, Ow—H2w…O4].
dicate that they exist as a mixture of cis and trans iso- The hydrogen bonds between the acidic proton of the
mers in solution. Two sets of resonances corresponding phenolic hydroxyl and oxygen of water [O6—H6…Ow]
to the cis and trans isomers in the 1H NMR spectra of 5a are also observed. The distances[46] between donor
2
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Chin. J. Chem. 2012, XX, 1—6

Acyclic Palladium(II)-N-heterocyclic Carbene Metallacrown Ether Complexes
Figure 1 Molecular structure of complex trans-5a•2H2O. Hydrogen atoms have been omitted for clarity; thermal ellipsoids are drawn at
the 20% probability level. Selected interatomic distances (Å) and angles (°): Pd—C10＝2.024, Pd—C10'＝2.024, Pd—Cl1＝2.3075,
Pd—Cl1'＝2.3075, C10-Pd-C10'＝180.00°, Cl-Pd-Cl'＝180.00°.
and acceptor of these hydrogen bonds are similar to the Table 1 Effect of base on the Suzuki-Miyaura cross-coupling of
length of known hydrogen bonds.[47-51] We presume that 4-bromoanisole with phenylboronic acida
the adventitious water may come from air and/or the
CH2Cl2/hexane solution and stabilize the pseudo-crown
cavity resulting in the formation of single crystal of
trans-5a.
catalyst
PhB(OH)2
MeO
Ph
MeO
Br
+
base, water
reflux, 24 h
Entry
1c
Base
Yieldb/%
TON
Application as catalyst
KOBu-t
KOBu-t
K3PO4
KOH
86
91
86000
91000
83000
63000
33000
32000
79000
64000
0
Water which is abundant, non-toxic, inexpensive and
nonflammable can undoubtedly be considered as the
cleanest solvent for chemical reaction.[52] Much effort has
recently been directed towards using water as solvent for
organic and organometallic reactions. The palladium-
catalyzed Suzuki-Miyaura reaction, which involves the
coupling of aryl halides and arylboronic acids, has be-
come one of the most powerful and convenient synthetic
tools for the synthesis of biaryl compounds. Intensive
research efforts are being directed to perform the
Suzuki-Miyaura coupling either via aqueous biphasic
catalysis or in neat water.[32,53-65]
2
3
83
4
63
5
K2CO3
Na2CO3
NaOMe
NaOH
Cs2CO3
Et3N
33
6
32
7
79
8
64
9
trace
60
10
60000
a
Reaction conditions: 0.25 mmol of 4-bromoanisole, 0.5 mmol of
The acyclic Pd-NHC metallacrown ethers 5a and 5b
are thermally stable and inert toward air and moisture in
the solid state. The application of them as catalysts was
then examined by catalyzing the Suzuki-Miyaura reac-
tions under aerobic and aqueous conditions. Based on our
recent experience,[16] the catalytic activities of 5a and 5b
were firstly tested at a catalyst loading of 0.001 mol% in
neat water. It is well known that the base can improve the
reaction efficiency for some catalytic system. Subse-
quently, the reaction was investigated in the presence of
different bases. As summarized in Table 1, the reaction
conditions involving KOBu-t appeared to be superior to
the others. K2CO3, Na2CO3 and Cs2CO3 were less effec-
tive, and K3PO4, NaOMe, NaOH and Et3N gave moder-
ate yields. We found 5a and 5b showed high activity in
the coupling reaction of 4-bromoanisole with phenyl-
phenylboronic acid, 0.5 mmol of base, 10 μL of 5b as catalyst in
dioxane (0.25 mmol/L), 1.0 mL of water, 100 ℃, 24 h, under air.
Isolated by silica gel column chromatography and based on
4-bromoanisole. c 5a as catalyst.
b
boronic acid under the optimized reaction conditions, and
5b was slightly superior to 5a.
The above optimized conditions were used to exam-
ine the representative range of aryl bromides for the re-
action. The results are summarized in Table 2. A variety
of aryl bromides and arylboronic acids containing both
electron-donating (methoxyl, methyl) and electron-
withdrawing substitutents (fluoro, nitro, formyl, acetyl,
trifluoromethyl) tolerated well the reaction conditions,
affording the corresponding biaryl products in good to
excellent yields. It is noteworthy that all cross-couplings
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3

Zhang, Zhang & Luo
FULL PAPER
listed in Table 1 and Table 2 were carried out in air, and dioxaoctane (1)[33] was prepared according to literature
no visible palladium black formation was observed dur- procedure. All other reagents are commercially available
ing the catalytic process. Though various catalysts have and were used without further purification. 1H (400 MHz,
been developed for the Suzuki-Miyaura reactions, very 600 MHz) and 13C (100 MHz, 150 MHz) NMR spectra
few examples[32,58-63] can be used at a low catalyst load- were recorded using Bruker instruments. Chemical shifts
ing of 0.001 mol% in neat water without the need of inert are reported relative to TMS as an internal standard. All
gas protection.
NMR spectra were acquired at room temperature.
GC-MS were recorded on an Agilent Technologies
Table 2 Catalytic Suzuki-Miyaura cross-coupling reactions of 6890-5973N. Mass spectra were obtained by using
aryl bromides with arylboronic acidsa
Bruker Daltonics Data Analysis 3.2. Elemental analyses
were performed on a Carlo Erba-1106 instrument.
catalyst 5b
KOBu-t, H2O, 100 oC
Ar1-Ar2
Ar1-X
Ar2-B(OH)2
+
1-Hydroxy-15-(2-hydroxyphenyl)-4,5-dibenzo-3,6,
9,12,15-pentaoxapentadecane (2)[66] To a solution of
dissolved 1,8-bis(2-hydroxyphenoxy)-3,6-dioxa-octane
(1) (9.00 g, 27 mmol) and sodium hydroxide (2.75 g, 67
mmol) in butanol (60 mL) was added dropwise in 15 min
2-chloroethanol (2.50 mL, 37.5 mmol), and the mixture
was refluxed for 24 h. The solvent was removed under
vacuum. The resultant oil was dissolved in CH2Cl2,
washed with aqueous sodium hydroxide and water, and
dried over Na2SO4. The product was purified by flash
chromatography on silica gel (ethyl acetate/petroleum
ether, V∶V＝3∶1) to give a yellow oil. Yield: 6.5 g
Entry
Ar1
Ar2
Catalyst/mol%
Yieldb/%
1
3-MeOPhBr
4-CF3PhBr
Ph
Ph
0.005
0.005
0.001
0.001
0.001
0.001
0.005
0.005
0.001
0.001
0.001
96
80
83
97
98
86
84
93
96
93
95
2
3
3-NO2PhBr
4-MeCOPhBr
4-CHOPhBr
4-MeOPhBr
4-MeOPhBr
3-MeOPhBr
3-NO2PhBr
4-MeOPhBr
4-MeOPhBr
Ph
4
Ph
5
Ph
6
4-CF3Ph
3-NO2Ph
4-MePh
4-MePh
4-MePh
4-FPh
7
8
1
(64%). H NMR (400 MHz, CDCl3) δ: 6.83—6.91 (m,
9
7H, Ar-H), 6.77—6.79 (m, 1H, Ar-H) 4.14—4.18 (m, 4H,
OCH2CH2O), 4.09—4.11 (m, 2H, OCH2CH2O), 3.91—
3.93 (m, 2H, OCH2CH2O), 3.82—3.89 (m, 6H, OCH2-
CH2O), 3.74—3.77 (m, 2H, OCH2CH2O); 13C NMR
(100 MHz, CDCl3) δ: 149.2, 149.1, 147.2, 146.1, 122.5,
122.2, 121.9, 119.7, 115.7, 115.3, 115.1, 114.0, 71.6, 70.8,
69.9, 69.7, 69.5, 68.8, 61.2; HRMS (MALDI) calcd for
C20H26O7 ([M＋Na]＋) 401.1576, found 401.1527.
10
11
a
Reaction conditions: 0.25 mmol of aryl bromide, 0.5 mmol of
arylboronic acid, 0.5 mmol of KOBu-t, 10 μL of 5b in dioxane
(0.25 mmol/L), 1.0 mL of water, 100 ℃, under air. The reactions
b
were monitored by TLC. Isolated by silica gel column chroma-
tography and based on aryl bromides.
1-Chloro-15-(2-hydroxyphenyl)-4,5-dibenzo-3,9,
12,15-pentaoxapentadecane (3) To a solution of 2
(0.700 g, 1.85 mmol) in dry benzene (15 mL) were added
Conclusions
In summary, we have synthesized and characterized thionyl chloride (0.34 mL, 4.6 mmol) and pyridine (0.3
two novel acyclic Pd(II)-NHC metallocrown ethers (5a, mL, 3.7 mmol). The mixture was refluxed for 8 h and
5b) from the corresponding imidazolium salts by trans- poured into water after cooling. The solution was ex-
metallation. NMR spectra indicated that 5a and 5b ex- tracted three times with ethyl acetate. The organic phase
isted as mixtures of cis and trans isomers in solution. The was dried over Na2SO4. The product was purified by
molecular structure of trans-5a was successfully deter- flash chromatography on silica gel (ethyl acetate/petro-
mined by X-ray structural analysis which clearly showed leum ether, V∶V＝1∶1) to a give yellow oil. Yield:
the formation of the pseudo-crown ether cavity at each 0.68 g (93%). 1H NMR (400 MHz, CDCl3) δ: 6.90—6.95
ethylene glycol chain, with a water molecule inside the (m, 7H, Ar-H), 6.77—6.81 (m, 1H, Ar-H), 4.24—4.28 (m,
cavity. Complexes 5a and 5b have been shown to be 2H, OCH2), 4.15—4.20 (m, 4H, OCH2), 3.88—3.90 (m,
highly effective in the Suzuki-Miyaura reactions of a 2H, OCH2), 3.79—3.84 (m, 6H, OCH2), 3.76—3.73 (m,
variety of aryl bromides and arylboronic acids in neat 2H, ClCH2); 13C NMR (100 MHz, CDCl3) δ: 149.2,
water without the need of inert gas protection. Typically 148.2, 147.5, 146.0, 122.9, 122.5, 121.7, 119.8, 115.8,
the use of 0.001—0.005 mol% of Pd catalyst gave the 115.7, 115.2, 114.8, 70.8, 70.7, 69.9, 69.8, 69.7, 69.6,
biaryl products in good to excellent yields.
68.9, 42.1; HRMS (MALDI) calcd for C20H25ClO6
([M＋K]＋) 435.0977, found 435.0981.
1-(3-Mesitylimidazolium)-15-(2-hydroxyphenyl)-4,
5-dibenzo-3,6,9,12,15-pentaoxapentadecane chloride
Experimental
General
(4a)
A solution of 3 (0.317 g, 0.8 mmol) and
1-mesitylimidazole (0.446 g, 2.4 mmol) in xylene (1 mL)
was heated to 150 ℃ for 50 h. After removal of the
solvent, the residue was washed with ethyl acetate to
give a yellow oil. Yield: 0.4 g (95%). 1H NMR (400 MHz,
Unless otherwise noted, all manipulations were per-
formed under an argon atmosphere using standard
Schlenk techniques. All solvents were dried according to
standard procedures. 1,8-Bis(2-hydroxyphenoxy)-3,6-
4
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Chin. J. Chem. 2012, XX, 1—6

Acyclic Palladium(II)-N-heterocyclic Carbene Metallacrown Ether Complexes
CDCl3) δ: 10.28 (s, 1H, NCHN), 8.48 (s, 1H, imi-H), imi-Hb), 6.63 (d, J＝1.6 Hz, 2H, imi-Ha), 5.07—5.09 (m,
7.12 (s, 1H, imi-H), 6.89—6.96 (m, 9H, Ar-H), 6.71 (d, 4H, NCH2aCH2O), 4.67—4.69 (m, 4H, NCH2bCH2O),
J＝2.4 Hz, 1H, Ar-H), 5.29—5.30 (m, 2H, NCH2CH2O), 4.55—4.57 (m, 4H, NCH2CH2aO), 4.24—4.26 (m, 4H,
4.51—4.53 (m, 2H, OCH2CH2N), 4.15—4.17 (m, 2H, NCH2CH2bO), 4.09 — 4.18 (m, 16H, OCH2CH2O),
OCH2CH2O), 4.04—4.07 (m, 2H, OCH2CH2O), 3.78— 3.87—3.90 (m, 8H, OCH2CH2O), 3.73—3.80 (m, 24H,
3.83 (m, 4H, OCH2CH2O), 3.65 — 3.72 (m, 4H, OCH2CH2O), 2.46 (s, 6H, CH3a), 2.29 (s, 6H, CH3b),
OCH2CH2O), 2.33 (s, 3H, CH3), 1.97 (s, 6H, CH3); 13C 2.17 (s, 12H, CH3b), 1.88 (s, 12H, CH3a); 13C NMR (100
NMR (100 MHz, CDCl3) δ: 148.4, 147.7, 147.4, 142.9, MHz, CDCl3) δ: 171.7 (NCNb), 170.0 (NCNa) (Ccarbene),
141.1, 138.4, 134.3, 130.8, 129.7, 125.2, 123.6, 122.7, 148.7, 148.5, 148.4, 148.3, 147.5, 146.1, 138.4, 137.5,
122.5, 122.4, 121.9, 121.1, 114.9, 113.6, 70.5, 70.1, 69.8, 136.7, 135.9, 135.5, 128.8, 128.6, 123.0, 122.8, 122.5,
69.5, 69.3, 68.3, 67.9, 49.9, 21.1, 17.4; HRMS (ESI) 122.4, 122.0, 121.9, 121.3, 119.8, 115.8, 114.8, 114.4,
calcd for C32H39ClN2O6 ([M－Cl]＋) 547.2803, found 114.2, 113.9, 70.6, 69.9, 69.7, 69.4, 69.2, 68.9, 68.7, 68.4,
547.2789.
50.6, 50.3, 21.3, 21.1, 18.9, 18.5; HRMS (MALDI) calcd
1-[3-(2,6-Diisopropylphenyl)imidazolium]-15-(2-hy- for C64H76Cl2N4O12Pd (M＋) 1268.3872, found 1268.3927.
droxyphenyl)-4,5-dibenzo-3,6,9,12,15-pentaoxapenta- Anal. calcd for C64H76Cl2N4O12Pd: C 60.50, H 6.03, N
decane chloride (4b) A solution of 3 (0.635 g, 1.6 4.41; found C 60.39, H 5.92, N 4.56.
mmol) and 1-(2,6-diisopropyl)phenylimidazole (0.925 g,
[Pd{1-(3-(2,6-diisopropylphenyl)imidazolin-2-
4.0 mmol) in xylene (1 mL) was heated to 150 ℃ for 60 yliden-1-yl-)-15-(2-hydroxyphenyl)-4,5-dibenzo-3,6,9,
h. Then addition of ethyl acetate resulted in precipitation 12,15-pentaoxapentadecane}2Cl2] (5b) Yield: 0.12 g
(50%). 1H NMR [400 MHz, CDCl3; two isomers in a ca.
of a white powder, which was collected and washed with
ethyl acetate (5 mL×3) to afford the product. Yield: 0.96
g (97%). H NMR (400 MHz, CDCl3) δ: 10.11 (s, 1H,
1∶1.35 ratio (a∶b)] δ: 7.47—7.27 (m, 12H, Ar-H,
imi-H), 7.06 (d, J＝7.6 Hz, 4H, Ar-H), 6.87—6.89 (m,
26H, Ar-H), 6.74—6.79 (m, 8H, Ar-H, imi-Hb), 6.66 (s,
1
NCHN), 8.61 (s, 1H, imi-H), 7.51 (t, J＝7.8 Hz, 1H,
Ar-H), 7.27 (d, J＝3.2 Hz, 1H, Ar-H), 7.12 (t, J＝1.8 Hz,
1H, imi-H), 6.82—6.96 (m, 8H, Ar-H), 6.12—6.76 (m,
1H, Ar-H), 5.28—5.30 (m, 2H, NCH2CH2O), 4.49—4.51
(m, 2H, NCH2CH2O), 4.12—4.14 (m, 2H, OCH2CH2O),
4.06—4.08 (m, 2H, OCH2CH2O), 3.76—3.79 (m, 4H,
OCH2CH2O), 3.70—3.71 (m, 4H, OCH2CH2O), 2.21—
2.24 [m, 2H, (CH3)2CH], 1.11 (d, J＝6.4 Hz, 6H, CH3),
1.05 (d, J＝6.4 Hz, 6H, CH3); 13C NMR (100 MHz,
CDCl3) δ: 148.5, 147.9, 147.5, 146.1, 145.6, 138.7, 131.7,
130.4, 125.5, 124.5, 123.2, 123.0, 122.5, 121.9, 119.7,
116.3, 115.5, 115.0, 113.8, 70.5, 70.3, 69.8, 69.6, 68.4,
67.9, 50.1, 28.6, 24.4, 24.0; HRMS (ESI) calcd for
C35H45ClN2O6 ([M－Cl]＋) 589.3121, found 589.3088.
[Pd{1-(3-arylimidazolin-2-yliden-1-yl)-15-(2-hy-
droxyphenyl)-4,5-dibenzo-3,6,9,12,15-pentaoxapenta-
decane}2Cl2] (5) A mixture of imidazolium salt 4 (0.40
mmol) and silver(I) oxide (48.3 mg, 0.21 mmol) in 5 mL
of CH2Cl2 was stirred at room temperature for 2 h. The
reaction mixture was filtered and washed with CH2Cl2 (5
mL×2). The combined filtrate was reduced to 5 mL un-
der vacuum. [PdCl2(MeCN)2] (25.8 mg, 0.10 mmol) in
CH2Cl2 (3 mL) was added to the resulting solution and
stirred at room temperature for 2 h. The reaction mixture
was filtered and washed with CH2Cl2 (5 mL×2). The
combined solution was evaporated under reduced pres-
sure to leave a raw product, which was purified by flash
chromatography on silica gel (CH2Cl2) to give a yellow
solid.
2H, imi-Ha), 5.25—5.27 (m, 4H, NCH2(a b)CH2O), 4.62
＋
—4.66 (m, 8H, NCH2(a b)CH2O, NCH2CH2(a b)O), 4.10
＋
＋
—4.16 (m, 20H, OCH2CH2O), 3.87—3.90 (m, 8H,
OCH2CH2O), 3.72—3.80 (m, 24H, OCH2CH2O), 2.85—
2.55 [m, 8H, (CH3)2CH(a+b)], 1.31 (d, J＝6.4 Hz, 12H,
CH3(a+b)), 0.85—0.91 (m, 36H, CH3(a b)); 13C NMR (100
＋
MHz, DMSO-d6) δ: 171.6 (NCNa), 170.9 (NCNb)
(Ccarbene), 148.8, 148.7, 148.6, 147.4, 147.2, 147.0, 146.2,
135.9, 135.3, 129.9, 124.9, 124.8, 123.7, 123.5, 122.8,
122.0, 121.8, 119.7, 116.2, 115.3, 114.7, 70.4, 69.7, 69.5,
68.9, 68.6, 50.4, 50.3, 28.2, 27.8, 26.8, 26.4, 23.1, 22.8;
HRMS (MALDI) calcd for C70H88Cl2N4O12Pd (M+)
1352.4811, found 1352.4842. Anal. calcd for C70H88-
Cl2N4O12Pd: C 61.06, H 6.55, N 4.14; found C 61.08, H
6.48, N 4.68.
X-ray crystal structure determination and refinement
X-ray single-crystal diffraction data for trans-5a
were collected on an Enraf-Nonius CAD-4 diffractome-
ter at 294(2) K with Mo Kα radiation (λ＝0.71073 Å)
by ω/2θ scan mode. The structures were solved with
direct methods using SHELXS-97 and refined by full-
matrix least-squares refinement on F2 with SHELXL-97.
All atoms except hydrogen atoms were refined with
anisotropic displacement parameters. In general, hydro-
gen atoms were fixed at calculated positions, and their
positions were refined by a riding model.
General procedure for the Suzuki-Miyaura cross-
coupling reaction
[Pd{1-(3-mesitylimidazolin-2-yliden-1-yl-)-15-(2-hy-
droxyphenyl)-4,5-dibenzo-3,6,9,12,15-pentaoxapenta-
1
decane}2Cl2] (5a) Yield: 0.15 g (21%). H NMR [400
In a typical run, aryl bromide (0.25 mmol), aryl-
MHz, CDCl3; two isomers in a ca. 1∶1.15 ratio (a∶b)] boronic acid (0.50 mmol), KOBu-t (0.50 mmol), and
δ: 7.48 (d, J＝1.6 Hz, 2H, imi-Ha), 7.36 (d, J＝2.0 Hz, Pd-NHC metallacrown ether complex 5b in dioxane (10
2H, imi-Hb), 6.95 (s, 4H, Ar-H), 6.85—6.89 (m, 30H, μL, 0.0025 μmol) were charged in a reaction tube with a
Ar-H), 6.78—6.79 (m, 6H, Ar-H), 6.67 (d, J＝2.0 Hz, 2H, stirring bar. Water (1 mL) was then added to the mixture
Chin. J. Chem. 2012, XX, 1—6
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
5

Zhang, Zhang & Luo
FULL PAPER
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1
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Acknowledgement
This work was supported by the Natural Science
Foundation of China (Nos. 21021001, 21072134) and
Program for Changjiang Scholars and Innovative Re-
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(Pang B.; Qin, X.)
6
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