Structure-activity relationship of N-heterocyclic carbene-Pd(II)-imidazole complexes in Suzuki-Miyaura coupling between 4-methoxyphenyl chloride and phenylboronic acid

Article abstract of DOI:10.1002/aoc.3053

A series of N-heterocyclic carbene-PdCl₂-imidazole [NHC-Pd(II)-Im] complexes were synthesized and the structure of most of them was unambiguously determined by X-ray single-crystal diffraction. The structure-activity relationship of these complexes was investigated for the Suzuki-Miyaura coupling between 4-methoxyphenyl chloride and phenylboronic acid, and the effect of the NHCs and Im moieties were fully discussed. The sterically hindered IPr-based complex showed the highest catalytic activity. Copyright

Full text of DOI:10.1002/aoc.3053

Full Paper
Received: 17 June 2013
Revised: 4 August 2013
Accepted: 6 August 2013
Published online in Wiley Online Library: 8 October 2013
(wileyonlinelibrary.com) DOI 10.1002/aoc.3053
Structure–activity relationship of
N-heterocyclic carbene–Pd(II)–imidazole
complexes in Suzuki–Miyaura coupling
between 4-methoxyphenyl chloride and
phenylboronic acid
Huan Lv, Lei Zhu, Yi-Qiang Tang and Jian-Mei Lu*
A series of N-heterocyclic carbene–PdCl2–imidazole [NHC–Pd(II)–Im] complexes were synthesized and the structure of most of
them was unambiguously determined by X-ray single-crystal diffraction. The structure–activity relationship of these
complexes was investigated for the Suzuki–Miyaura coupling between 4-methoxyphenyl chloride and phenylboronic acid,
and the effect of the NHCs and Im moieties were fully discussed. The sterically hindered IPr-based complex showed the highest
catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: N-heterocyclic carbene; palladium complex; imidazole; structure–activity relationship; Suzuki–Miyaura coupling
X-ray crystallography. All complexes show a slightly distorted
square-planar geometry of the Pd center with the two chloride
Introduction
During the past decade, N-heterocyclic carbenes (NHCs) and their
metal complexes have proven to be good catalysts for the formation
of carbon–carbon and carbon–heteroatom bonds.[1] Recently, we
developed a well-defined NHC–PdCl2–1-methylimidazole [NHC–Pd
(II)–Im] complex 1a (Scheme 1) and found it to be an effective cata-
lyst in the formation of carbon–carbon[2] and carbon–nitrogen[3]
bonds using aryl chlorides as the substrates. In addition, compared
to analogous structures with 3-chloropyridine,[1f,4] triethylamine,[5]
diethylamine[6] and other N-donors involving structures as the
‘throw-away’ ligands,[7] complex 1a showed similar catalytic activity.
To understand the effect of imidazole and NHCs, we synthesized a
number of NHC–Pd(II)–Im complexes, and their catalytic activities
in the Suzuki–Miyaura coupling between 4-methoxyphenyl chloride
2 and phenylboronic acid 3 were investigated.
ligands perpendicular to the plane of the NHC and the imidazole
trans to it (for example, see ORTEP drawing of complex 1b in Fig. 1)
(see supporting information for more details).[8] (Crystals of 1k
suitable for X-ray diffraction cannot be achieved at this stage, even
though various methods were tried in this laboratory.)
Comparison of δCcarbene and relevant bond distances are
shown in Table 1. It can be seen that the nature of the NHC in
1 has some effect on the chemical shift of the carbene carbon.
For example, the carbene carbon resonance of 1a displays a
downfield shift in the 13C NMR spectrum due to sterically encum-
bered isopropyl groups at the ortho positions of the N-phenyl
substituent compared to its methyl substituted counterparts 1c
and 1e, implying a stronger σ-donation effect. Furthermore, the
larger hindered substituents on the NHC moiety have a less trans
influence than that of the smaller substituents, which would also
account for the downfield shift of the corresponding 13C NMR of
the carbene carbon signal. Moreover, the same effect has been
previously observed in Pd(II) complexes by Bedford and co-
workers in 2010.[9] On the other hand, the imidazole moieties in
the NHC–Pd(II)–Im complexes 1 have less effect on the chemical
shift of the carbene carbon (Table 1, entry 1 vs. entries 7–11).
Results and discussion
Complexes 1 were prepared by a similar procedure to that
previously reported.[3a] Under N2 atmosphere, a mixture of an
imidazolium (or imidazolinium) salt, PdCl2, K2CO3 and imidazole
was stirred in anhydrous THF under reflux for 20 h to provide the
corresponding NHC–Pd(II)–Im complexes 1 in acceptable to good
yields (Scheme 2).
Complexes 1a–1k are both air and moisture stable, and were fully
characterized by 1H NMR, 13C NMR spectroscopy, mass spectrometry,
high-resolution mass spectrometry (HRMS) and/or elemental
analysis. Crystals of 1a–1j suitable for X-ray crystallography were
grown in a mixture of ethyl acetate and dichloromethane
(5:1), and the structures were unambiguously determined by
*
Correspondence to: Jian-Mei Lu, College of Chemistry and Materials Engineering,
Wenzhou University, Chashan University Town, Wenzhou, Zhejiang Province
325035, People’s Republic of China. E-mail: ljm@wzu.edu.cn
College of Chemistry and Materials Engineering, Wenzhou University, Chashan
University Town, Wenzhou, Zhejiang Province, 325035, People’s Republic of China
Appl. Organometal. Chem. 2014, 28, 27–31
Copyright © 2013 John Wiley & Sons, Ltd.

H. Lv et al.
The carbene carbon chemical shift was shown to be more
downfield in complex 1a compared to its analogues 1c and 1e,
due to the increasing steric bulk on the NHC moiety. This may
suggest that a more electron-deficient metal center was formed.
Table 2 compares catalytic activity of complexes 1 for the
Suzuki–Miyaura coupling between 4-methoxyphenyl chloride 2
and phenylboronic acid 3. Under the same reaction conditions,
there is a clear difference in the catalytic activity between
complexes 1a–1f, which can be only attributed to the different
NHC skeletons. The most bulky NHC-Pd(II)-Im complex 1a showed
the best catalytic activity (Table 2, entry 1), whereas complexes
1b–1f showed lower activity (Table 2, entries 2–6). This illustrates
that more σ-donating ligands on the metal center may facilitate
the oxidative addition, and the more hindered ligands may
facilitate the reductive elimination.[10] Complexes 1 with different
imidazole moieties were also tested (Table 2, entries 7–11). Similar
results were observed when complexes 1 g, 1 h and 1i were used
as the catalysts (Table 2, entries 7–9) suggesting that the imidazole
moieties in 1 have less effect on their catalytic activities.
Nevertheless, somewhat lower yields were observed when
complexes 1j and 1 k were employed (Table 2, entries 10 and 11),
which may be partially attributed to their solubility in the mixture
solvent of THF and H2O because both of them are more lipophilic
than their counterparts such as 1a, 1 g, 1 h and 1i.
iPr
Cl
iPr
N
Pd
Cl
N
N
Conclusions
N
iPr
A few NHC–Pd(II)–Im complexes have been synthesized and were
fully characterized by 1H NMR, 13C NMR, MS, HRMS and/or
elemental analysis. The structures have been confirmed by X-ray
single-crystal diffraction. The structure–activity relationship was
investigated in the Suzuki–Miyaura coupling
iPr
Scheme 1. NHC–Pd(II)–Im complex 1a.
between 4-methoxyphenyl chloride and
phenylboronic acid. The sterically bulky, unsat-
urated IPr–Pd(II) complexes demonstrated the
highest activity, while the imidazole moieties
in the complexes have less effect on the cata-
lytic activity.
R1
N
R1
N
Cl
K2CO3
THF, reflux,
20 h
R2
R2
N
N
N
N
Pd
Cl
PdCl
+
+
Cl
2
N
R1
N
R1
1
SIPr
IPr
SIXy
IMes
IXy
SIMes
Experimental
Pd Cl
N
Cl Pd Cl
N
Cl Pd Cl
Cl
Cl Pd Cl
N
Cl Pd Cl
N
Cl Pd Cl
N
General Remarks
N
N
Melting points are uncorrected. NMR spectra
were recorded at 300/500 (for 1H NMR) or 75/
N
N
N
N
N
125 MHz (for 13C NMR), respectively. H NMR
1
1b, 47%
and 13C NMR spectra recorded in CDCl3 solu-
tions were referenced to tetramethylsilane
(TMS) (0.00 ppm) and the residual solvent peak
(77.0ppm), respectively. J-values are in Hz.
Organic solvents used were dried by standard
methods. Other commercially obtained re-
agents were used without further purification.
Flash column chromatography was performed
on silica gel (300–400 mesh).
1f, 53%
1c, 65%
IPr
1e, 61%
1d, 67%
1g, 81%
IPr
IPr
IPr
Cl Pd
iPr
iPr
Cl Pd
N
Cl
Cl Pd
N
Cl
Cl
Cl Pd Cl
N
N
N
N
N
..
N
iPr iPr
IPr
N
N
Ph
Ph
nBu
1k, 93%
1h, 81%
1i, 94%
1j, 96%
General Procedure for the Synthesis of
NHC–Pd(II)–Im Complexes 1
Me
Me
iPr
iPr
Me
Me
N
N
N
N
N
N
..
..
Under N2 atmosphere,
a
mixture of
..
Me
Me
imidazolium salt (1.2 mmol), PdCl2 (1.0 mmol),
K2CO3 (1.0 mmol) and 1-methylimidazole
(4.0 mmol) was stirred in anhydrous THF
(6.0 ml) under reflux for 20 h. The solvent
was then removed under reduced pressure,
and the residue was purified by flash chroma-
tography on silica gel (CH2Cl2) to give the
pure NHC–Pd(II)–Im complex 1b as a yellow
solid (47%). The single crystal for X-ray diffrac-
tion was obtained by recrystallization from
CH2Cl2 and ethyl acetate.
iPr iPr
Me
Me
SIXy
SIPr
IXy
Me
Me
Me
Me
N
N
N
N
..
..
Me
Me
Me
Me
Me
Me
Me
IMes
Me
SIMes
Scheme 2. Synthesis of NHC–Pd(II)–Im complexes 1.
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Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 27–31

Structure–activity relationship of NHC–Pd(II)–Im complexes
Table 2. Catalytic activity of complexes 1 with the Suzuki–Miyaura
coupling between 4-methoxyphenyl chloride 2 and phenylboronic
acid 3 as the model
Cl
NHC-Pd(II)-Im 1
(1.0 mol%)
B(OH)2
K3PO4.3H2O
H2O/THF (2/1), rt, 24 h
MeO
+
OMe
2
4
3
Entrya
Complexes 1
Yield (%)b
1[2a]
2
1a
1b
1c
1d
1e
1f
91
53
50
48
70
41
84
80
86
66
55
3
4
5c
6
7
1 g
1 h
1i
8
Figure 1. ORTEP drawing of complex 1b with thermal ellipsoids at the
30% probability level and anisotropic displacement parameters. H atoms
have been omitted. Selected bond distances (Å) and angles (deg.):
Pd1―C17 = 1.962(3) Å, Pd1―N1 = 2.110(3) Å, Pd1―Cl1 = 2.301(1) Å,
Pd1―Cl2 = 2.303(1) Å, C17―Pd1―N1 = 174.97(12)°, C17―Pd1―Cl2 =
9
10
11
1j
1 k
aAll reactions were carried out using 2 (0.5 mmol), 3 (0.6 mmol), 1
(1.0 mol%), K3PO4.3H2O (2.0 equiv.) in H2O (2.0 ml) and THF
(1.0 ml) at room temperature for 24 h.
bIsolated yields.
86.74(9)°,
N1―Pd1―Cl2 = 90.28(10)°,
C17―Pd1―Cl1 = 92.52(9)°,
N1―Pd1―Cl1 = 90.66(10)°, Cl1―Pd1―Cl2 = 177.04(4)°.
Table 1. Comparison of δCcarbene and Pd―Ccarbene and Pd―N bond
distances
Entry
Complexes
δCcarbene
Pd―Ccarbene (Å)
Pd―N (Å)
671.1876; found: 671.1876. Anal. calcd for C32H44Cl2N4Pd requires
C, 57.28%; H, 6.82%; N, 8.62%; found: C, 57.27%; H, 6.82%, N, 6.83%.
Compound 1c: a yellow solid; m.p. 287 °C (decomposed). 1H NMR
(CDCl3, 500 MHz, TMS) δ 2.41 (s, 12H, 4CH3), 3.44 (s, 3H, NCH3),
6.53 (s, 1H, CH CH―NCH3 in the imidazole moiety), 7.07 (s, 2H,
CH CH), 7.18 (s, 1H, CH CH―NCH3 in the imidazole moiety), 7.21
(d, J = 7.5 Hz, 4H, 2C―CH CH―CH C in the phenyl moiety),
7.31 (t, J = 7.5 Hz, 2H, 2C―CH CH―CH C in the phenyl moiety),
7.72 (s, 1H, N CH―N in the imidazole moiety). 13C NMR
1[2a]
2
1a
1b
1c
1d
1e
1f
156.5
187.3
154.2
185.6
154.0
185.4
156.5
156.6
156.3
156.3
156.0
1.954(5)
1.962(3)
1.986(3)
1.965(2)
1.971(3)
1.957(6)
1.969(4)
1.953(4)
1.965(2)
1.964(4)
—
2.088(4)
2.110(3)
2.117(3)
2.092(2)
2.097(3)
2.089(5)
2.092(4)
2.084(4)
2.098(2)
2.091(4)
—
3
4
5[2a]
6
7
1 g
1 h
1i
8
(CDCl3, 125 MHz)
δ
19.2 (CH3), 33.9 (NCH3), 118.9
9
(N―CH CH―NCH3 in the imidazole moiety), 123.9 (CH CH),
128.5 (N―CH CH―NCH3 in the imidazole moiety), 129.3
(Ar), 136.7 (Ar), 137.7 (Ar), 138.4 (N CH―N in the imidazole
moiety), 154.2 (carbene atom). IR (neat) ν 2968, 1534, 1467,
10
11
1j
1 k
1361, 1278, 1219, 1103, 1090, 940, 773, 741, 730, 700 cmÀ1
.
Compounds 1a,[3a] 1e[3a] and 4[2a] are all known and were fully
determined according to previously reported data.
HRMS (ESI): calcd for C23H26Cl2N4NaPd [M + Na]+: 557.0465;
found: 557.0502. Anal. calcd for C23H26Cl2N4Pd requires C,
51.56%; H, 4.89%; N, 10.46%; found: C, 51.78%; H, 4.99%, N, 10.32%.
Compound 1b: a yellow solid; m.p. 270 °C (decomposed). 1H NMR
(300 MHz, CDCl3, TMS) δ 1.25 (d, J=6.6Hz, 12H, 2CH(CH3)2), 1.55 (d,
J=6.6Hz, 12H, 2CH(CH3)2), 3.45 (s, 3H, NCH3), 3.59 (hept, J=6.6Hz,
4H, 4CH(CH3)2), 4.02 (s, 4H, NCH2CH2N), 6.52 (s, 1H, CH CH―NCH3
in the imidazole moiety), 7.15 (s, 1H, CH CH―NCH3 in the imidazole
moiety), 7.27 (d, J= 6.6 Hz, 4H, 2C―CH CH―CH C in the phenyl moi-
ety), 7.38 (t, J= 6.6 Hz, 2H, 2C―CH CH―CH C in the phenyl moiety),
7.66 (s, 1H, N CH―N in the imidazole moiety). 13C NMR (CDCl3,
125 MHz) δ 24.2 (CH3), 26.8 (CH3), 28.7 (CH(CH3)2), 33.9 (NCH3), 53.8
(NCH2CH2N), 118.9 (N―CH CH―NCH3 in the imidazole moiety),
124.4 (Ar), 128.5 (N―CH CH―NCH3 in the imidazole moiety), 129.2
(Ar), 135.5 (Ar), 138.2 (N CH―N in the imidazole moiety), 147.5
(Ar), 187.3 (carbene atom). IR (neat) ν 2961, 2862, 2331, 2087, 1673,
1583, 1533, 1448, 1358, 1325, 1262, 1189, 1103, 1053, 932, 801, 753,
1
Compound 1d: a yellow solid; m.p. 256 °C (decomposed). H
NMR (CDCl3, 500 MHz TMS) δ 2.62 (s, 12H, 4CH3), 3.43 (s, 3H,
NCH3), 4.03 (s, 4H, NCH2CH2N), 6.51 (s, 1H, CH CH―NCH3 in the
imidazole moiety), 7.12 (s, 1H, CH CH―NCH3 in the imidazole
moiety), 7.17 (d, = 7.5 Hz, 4H, 2C―CH CH―CH C in the phenyl
moiety), 7.22 (t, = 7.5 Hz, 2H, 2C―CH CH―CH C in the
phenyl moiety), 7.67 (s, 1H, s, 1H, N CH―N in the imidazole
moiety). 13C NMR (CDCl3, 125 MHz)
δ 19.5 (CH3), 33.9
(NCH3), 50.9 (NCH2CH2N), 118.9 (N―CH CH―NCH3 in the
imidazole moiety), 128.4 (N―CH CH―NCH3 in the imidazole
moiety), 128.6 (Ar), 128.7 (Ar), 137.55 (Ar), 137.57 (Ar y),
138.3 (N CH―N in the imidazole moiety), 185.6 (carbene
atom). IR (neat) ν 1534, 1484, 1448, 1404, 1305, 1272, 1252,
730 cmÀ1 HRMS (ESI): calcd for C31H44Cl2N4NaPd [M + Na]+:
.
1103, 947, 775, 738, 728 cmÀ1
. HRMS (ESI): calcd for
Appl. Organometal. Chem. 2014, 28, 27–31
Copyright © 2013 John Wiley & Sons, Ltd.
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H. Lv et al.
C23H28Cl2N4NaPd [M + Na]+: 559.0621; found: 559.0590. Anal.
calcd for C23H28Cl2N4Pd requires C, 51.36%; H, 5.25%; N,
10.42%; found: C, 51.34%; H, 5.24%, N, 10.40%.
2C―CH CH―CH C in the phenyl moiety), 7.85 (s, 1H, N CH―N in
the imidazole moiety). 13C NMR (CDCl3, 125MHz) δ 23.3 (CH3), 26.2
(CH3), 28.7 (CH(CH3)2), 51.5 (NCH2Ph), 117.9 (N―CH CH―NCH2Ph in
the imidazole moiety), 124.0 (Ar), 124.9 (Ar), 127.7 (Ar), 128.5
(N―CH CH―NCH2Ph in the imidazole moiety), 128.8 (Ar), 128.9
(Ar), 130.1 (Ar), 134.7 (Ar), 135.2 (Ar), 138.0 (N CH―N in the imidazole
moiety), 146.7 (Ar), 156.3 (carbene atom). IR (neat) ν 2961, 2862, 1517,
Compound 1f: a yellow solid; m.p. 251 °C (decomposed). 1H NMR
(CDCl3, 500 MHz TMS) δ 2.30 (s, 6H, 2CH3), 2.57 (s, 12H, 4CH3), 3.44
(s, 3H, NCH3), 3.99 (s, 4H, NCH2CH2N), 6.52 (s, 1H, CH CH―NCH3 in
the imidazole moiety), 6.98 (s, 4H, CH in the phenyl moiety), 7.15
(s, 1H, CH CH―NCH3 in the imidazole moiety), 7.70 (s, 1H, N CH―N
in the imidazole moiety). 13C NMR (CDCl3, 125 MHz) δ 19.3 (CH3),
21.1 (CH3), 33.9 (NCH3), 51.0 (NCH2CH2N), 118.8 (N―CH CH―NCH3
in the imidazole moiety), 128.4 (N―CH CH―NCH3 in the imidazole
moiety), 129.4 (Ar), 135.1 (Ar), 137.1 (Ar), 138.1 (Ar), 138.4 (N CH―N
in the imidazole moiety), 185.4 (carbene atom). IR (neat) ν 1968,
1530, 1484, 1448, 1262, 1229, 1103, 945, 851, 740 cmÀ1. HRMS
(ESI): calcd for C25H32Cl2N4NaPd [M + Na]+: 587.0935; found:
587.0891. Anal. calcd for C25H32Cl2N4Pd requires C, 53.06%; H,
5.70%; N, 9.90%; found: C, 53.07%; H, 5.68%, N, 9.94%.
1454, 1341, 1103, 1083, 1056, 969, 942, 801, 755, 732, 703 cmÀ1
.
HRMS (ESI): calcd for C37H46Cl2N4NaPd [M + Na]+: 745.2034; found:
745.2031. Anal. calcd for C37H46Cl2N4Pd requires C, 61.37%; H,
6.40%; N, 7.74%; found: C, 61.35%; H, 6.68%, N, 7.17%.
Compound 1j: a yellow solid; m.p. 279 °C (decomposed). 1H
NMR (CDCl3, 300 MHz, TMS)
δ
0.86 (t, J = 7.5 Hz, 3H,
CH2CH2CH2CH3), 1.11 (d, J = 6.9 Hz, 12H, 2CH(CH3)2), 1.19–1.29
(m, 4H, CH2CH2CH2CH3), 1.47 (d, J = 6.9 Hz, 12H, 2CH(CH3)2), 3.19
(hept, J = 6.9 Hz, 4H, 4CH(CH3)2), 3.69 (t, J = 7.5 Hz, 2H,
NCH2CH2CH2CH3), 6.57 (s, 1H, CH CH―NC4H9 in the imidazole
moiety), 7.08 (s, 2H, CH CH), 7.18 (s, 1H, CH CH― NC4H9 in the
imidazole moiety), 7.32 (d, J = 7.5 Hz, 4H, 2C―CH CH―CH C in
the phenyl moiety), 7.47 (t, J = 7.5 Hz, 2H, 2C―CH CH―CH C in
the phenyl moiety), 7.72 (s, 1H, N CH―N in the imidazole moiety).
1
Compound 1 g: a yellow solid; m.p. 263 °C (decomposed). H
NMR (CDCl3, 500 MHz, TMS) δ 1.11 (d, J = 6.5 Hz, 12H, 2CH(CH3)
2), 1.27 (t, J = 7.5 Hz, 3H, CH2CH3), 1.47 (d, J = 6.5 Hz, 12H, 2CH
(CH3)2), 3.18 (hept, J = 6.5 Hz, 4H, 4CH(CH3)2), 3.75 (q, J = 7.5 Hz,
2H, NCH2CH3), 6.59 (s, 1H, CH CH―NCH2CH3 in the imidazole
moiety), 7.09 (s, 2H, CH CH), 7.17 (s, 1H, CH CH―NCH2CH3 in the
imidazole moiety), 7.33 (d, J = 8.0 Hz, 4H, 2C―CH CH―CH C in
the phenyl moiety), 7.47 (t, J = 8.0 Hz, 2H, 2C―CH CH―CH C in
the phenyl moiety), 7.72 (s, 1H, N CH―N in the imidazole moiety).
13C NMR (CDCl3, 125 MHz) δ 15.7 (CH2CH3), 23.2 (CH3), 26.2 (CH3),
28.6 (CH(CH3)2), 42.5 (NCH2CH3), 117.2 (N―CH CH―NCH2CH3
in the imidazole moiety), 123.9 (Ar), 124.8 (Ar), 128.5
(N―CH CH―NCH2CH3 in the imidazole moiety), 130.0 (Ar),
135.2 (Ar), 137.2 (N CH―N in the imidazole moiety), 146.6
(Ar), 156.5 (carbene atom). IR (neat) ν 2968, 1527, 1461, 1441,
13C NMR (75 MHz, CDCl3)
δ 13.4 (NCH2CH2CH2CH3), 19.7
(NCH2CH2CH2CH3), 23.3 (CH(CH3)2), 26.3 (CH(CH3)2), 28.7 (CH
(CH3)2), 32.5 (NCH2CH2CH2CH3), 47.5 (NCH2CH2CH2CH3), 117.7
(N―CH CH―NC4H9 in the imidazole moiety), 124.0 (Ar), 124.8
(Ar), 128.4 (N―CH CH―N C4H9 in the imidazole moiety), 130.0
(Ar), 135.3 (Ar), 137.6 (N CH―N in the imidazole moiety), 146.7
(Ar), 156.3 (carbene atom). IR (neat) ν 2954, 2915, 2855, 1520,
1457, 1404, 1345, 1109, 1086, 1053, 969, 939, 843, 801, 756, 748,
740, 733 cmÀ1. HRMS (ESI): calcd for C34H48Cl2N4NaPd [M + Na]+:
711.2190; found: 711.2158. Anal. calcd for C34H48Cl2N4Pd requires
C, 59.17%; H, 7.01%; N, 8.12%; found: C, 59.21%; H, 7.20%,
N, 7.81%.
1262, 1109, 1086, 1056, 942, 834, 799, 760, 733, 703 cmÀ1
.
HRMS (ESI): calcd for C32H44Cl2N4NaPd [M + Na]+: 683.1876;
found: 683.1872. Anal. calcd for C32H44Cl2N4Pd requires C,
58.05%; H, 6.70%; N, 8.46%; found: C, 58.32%; H, 6.90%, N, 8.28%.
Compound 1h: a yellow solid; m.p. 296 °C (decomposed). 1H NMR
(CDCl3, 500MHz, TMS) δ 1.11 (d, J= 7.0Hz, 12H, 2CH(CH3)2), 1.30
(d, J= 7.0 Hz, 6H, NCH(CH3)2), 1.47 (d, J=7.0Hz, 12H, 2CH(CH3)2),
3.19 (hept, J= 7.0 Hz, 4H, 4CH(CH3)2), 4.11 (hept, J= 7.0 Hz, 1H, NCH
(CH3)2), 6.63 (s, 1H, CH CH―NCH(CH3)2 in the imidazole moiety),
7.09 (s, 2H, CH CH), 7.17 (s, 1H, CH CH―NCH(CH3)2 in the imidazole
moiety), 7.33 (d, J= 7.5 Hz, 4H, 2C―CH CH―CH C in the phenyl
moiety), 7.47 (t, J= 7.5 Hz, 2H, 2C―CH CH―CH C in the phenyl
moiety), 7.74 (s, 1H, N CH―N in the imidazole moiety). 13C NMR
(CDCl3, 125MHz) δ 23.2 (CH3), 26.2 (CH3), 28.6 (CH(CH3)2), 49.9 (NCH
(CH3)2), 115.3 (N―CH CH―NCH(CH3)2 in the imidazole moiety),
123.9 (Ar), 124.8 (Ar), 128.4 (N―CH CH―NCH(CH3)2 in the imidazole
moiety), 130.0 (Ar), 135.2 (Ar), 136.0 (N CH―N in the imidazole
moiety), 146.6 (Ar), 156.6 (carbene atom). IR (neat) ν 2961, 2862,
1514, 1461, 1404, 1341, 1265, 1202, 1113, 1083, 1056, 940, 800, 756,
Compound 1 k: a yellow solid; m.p. 196–197 °C. 1H NMR (CDCl3,
500 MHz, TMS) δ 1.12 (d, J = 7.0 Hz, 12H, 2CH(CH3)2), 1.48 (d,
J = 7.0 Hz, 12H, 2CH(CH3)2), 3.20 (hept, J = 7.0 Hz, 4H, 4CH(CH3)2),
6.95 (s, 1H, CH CH―NPh in the imidazole moiety), 7.11 (s, 2H,
CH CH), 7.20 (d, J = 7.0 Hz, 2H, CH in the phenyl moiety), 7.32–
7.40 (m, 8H, CH in the phenyl moiety and imidazole moiety),
7.47 (t, J = 7.5 Hz, 2H, 2CH CH―CH C in the phenyl moiety), 8.10
(s, 1H, N CH―N in the imidazole moiety). 13C NMR (125 MHz, CDCl3)
δ 23.3 (CH3), 26.3 (CH3), 28.7 (CH(CH3)2), 117.3 (N―CH CH―NPh in
the imidazole moiety), 121.7 (Ar), 124.0 (Ar), 124.9 (Ar), 128.1
(N―CH CH―NPh in the imidazole moiety), 129.3 (Ar), 129.8
(Ar), 130.1 (Ar), 135.2 (Ar), 136.6 (N CH―N in the imidazole
moiety), 136.7 (Ar), 146.7 (Ar), 156.0 (carbene atom). IR (neat) ν
2961, 2862, 1511, 1461, 1302, 1262, 1202, 1056, 801, 735, 702 cm-1.
MS (ESI): 731 [M + Na]+; HRMS (ESI): calcd for C36H44Cl2N4NaPd
[M + Na]+: 731.1877; found: 731.1847.
733 cmÀ1 HRMS (ESI): calcd for C33H46Cl2N4NaPd [M + Na]+:
.
General Procedure for the Suzuki–Miyaura Coupling between
4-Methoxyphenyl Chloride 2 and Phenylboronic Acid 3
697.2033; found: 697.2013. Anal. calcd for C33H46Cl2N4Pd requires
C, 58.63%; H, 6.86%; N, 8.29%; found: C, 58.72%; H, 7.31%, N, 7.96%.
1
Compound 1i: a yellow solid; m.p. 198–199 °C. H NMR (CDCl3,
Under N2 atmosphere, phenylboronic acid 3 (0.6 mmol), NHC–Pd
(II)–Im complex 1a (1.0 mol%), K3PO4.3H2O (2.0 equiv.), H2O
(2.0 ml), and THF (1.0 ml) were added to a Schlenk reaction tube,
then 4-methoxyphenyl chloride 2 (0.5 mmol) was added. The
mixture was stirred at room temperature for 24 h. The mixture
was then extracted with EtOAc, dried over anhydrous Na2SO4
and purified by flash column chromatography to give pure prod-
uct 4 as a white solid.
500 MHz, TMS)
δ 1.11 (d, J=6.5 Hz, 12H, 2CH(CH3)2), 1.47
(d, J= 6.5Hz, 12H, 2CH(CH3)2), 3.18 (hept, J= 6.5 Hz, 4H, 4CH(CH3)2),
4.86 (s, 2H, NCH2Ph), 6.51 (s, 1H, CH CH―NCH2Ph in the imidazole
moiety), 7.04–7.06 (m, 2H, CH in the phenyl moiety), 7.09 (s, 2H,
CH CH), 7.21 (s, 1H, CH CH―NCH2Ph in the imidazole moiety), 7.27–
7.29 (m, 3H, CH in the phenyl moiety), 7.32 (d, J= 7.5 Hz, 4H,
2C―CH CH―CH C in the phenyl moiety), 7.47 (t, J= 7.5 Hz, 2H,
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Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 27–31

Structure–activity relationship of NHC–Pd(II)–Im complexes
Crystal Structure Determination of NHC–Pd(II)–Im Complexes 1
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Single-crystal data were collected on a Bruker Smart APEX CCD
diffractometer and graphite monochromated Mo-Kα radiation
(λ = 0.71073 Å) at room temperature. Structure solution and
refinement were carried out with the program package
SHELXTL-PLUS version 5.1.[11] All the non-hydrogen atoms
were refined with anisotropic displacement parameters using
full-matrix, least-squares technique.
The crystallographic data for complexes 1b–d and 1f–j have
been included in the supporting information.
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Acknowledgments
[8] CCDC-808377, -818903, -808367, -808368, -819946, -824878, 818754,
-828919 and À882158 contain the supplementary, crystallographic
data for this paper.
[9] R. B. Bedford, C. S. J. Cazin, S. J. Coles, T. Gelbrich, P. N. Horton, M. B.
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Financial support from the National Natural Science Foundation
of China (No. 21002072) is greatly acknowledged.
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Supporting Information
Additional supporting information may be found in the online
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The crystal data of compounds 1 can be obtained free of
charge from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ (fax: +44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk), reference numbers CCDC-808377,
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Appl. Organometal. Chem. 2014, 28, 27–31
Copyright © 2013 John Wiley & Sons, Ltd.
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