Chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes: Synthesis, structure, and catalytic activity towards C-H activation

Article abstract of DOI:10.1039/c5ra21183b

The synthesis of novel chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes (NHCs) via direct metallation of the precursor imidazolium salts is presented. The structure has been characterized unambiguously by X-ray single crystal analysis. Catalytic activity investigation showed that the complexes catalyse the direct C-H bond arylation of (benzo)oxazoles efficiently when using ^tBuOLi as base and DMF as solvent.

Full text of DOI:10.1039/c5ra21183b

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: L. Yang, J. Yuan,
P. Mao and Q. Guo, RSC Adv., 2015, DOI: 10.1039/C5RA21183B.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

View Article Online
DOI: 10.1039/C5RA21183B
Page 1 of 8
RSC Advances
Journal Name
RSCPublishing
ARTICLE
Chelating Palladium Complexes Containing
Pyridine/pyrimidine Hydroxyalkyl Di-functionalized
N-Heterocyclic Carbenes: Synthesis, Structure, and
Catalytic Activity towards C-H Activation
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Liangru Yang,* Jinwei Yuan, Pu Mao* and Qi Guo
DOI: 10.1039/x0xx00000x
The synthesis of novel chelating palladium complexes containing pyridine/pyrimidine
hydroxyalkyl di-functionalized N-heterocyclic carbenes (NHCs) via direct metallation of the
precursor imidazolium salts is presented. The structure has been characterized unambiguously
by X-ray single crystal analysis. Catalytic activity investigation showed that the complexes
www.rsc.org/
t
catalyse the direct C-H bond arylation of (benzo)oxazoles efficiently when using BuOLi as
base and DMF as solvent.
of alkenes or ketones, dimerization of alkenes and C-H
activation of methane. Alcohol-functionalized imidazolium
Introduction
N-Heterocyclic carbenes (NHCs) have been widely used as
ancillary ligands in coordination chemistry and organic
catalysis since the successful isolation and characterization of
the first stable NHC by Arduengo et al. in 1991.1 As a class of
non-phosphine ligands and alternative to tertiary phosphines,
their unique properties such as strong -donating ability,
robustness, and sterically demanding character have been well
documented.2 Numerous NHC metal complexes have been
synthesized, characterized and applied successfully to organic
transformations, including C-C, C-hetero atom coupling,
polymerization, hydrogenation and oxidation reactions.3 As
chelating/pincer ligands might control the stability of the active
species and improve the catalytic activity, the chelating/pincer
NHC metal complexes have drawn especially much attention in
recent years.4 Chelating NHC metal complexes containing
heteroatom donors, such as P, N, O and S, have been
synthesized, characterized and employed as catalysts for
catalytic organic transformations (Fig. 1).5 The preliminary
research demonstrated that CNHC,P and CNHC,N chelating
palladium,6 iridium,7 rhodium6a,7a,7c and ruthenium8 complexes
to be highly efficient catalyst for the Heck reaction of vinyl
compounds with aryl bromides and chlorides, Suzuki-Miyaura
cross-coupling of aryl bromides and chlorides, hydrogenation
salts have been reported to afford different type of CNHC,O
chelating palladium or nickel complexes upon certain
metallation conditions, and the comparatively weak CNHC,O
chelate dissociate easily.5a Hydroxyethyl substituted CNHC,O
chelating complexes have been demonstrated to catalyse the
Heck reaction and asymmetric addition of diethylzinc to
benzaldehyde efficiently.9
Figure 1.Chelating NHC metal complexes
Our group have developed an efficient procedure to
synthesize chiral hydroxyalkyl functionalized imidazole
derivatives.10 Quaternization of the hydroxyalkyl functionalized
imidazole with halides containing N, P, et al. heteroatom would
produce di-functionalized imidazolium salts, which should be
ideal precursors for the hybrid pincer NHC ligands (NCNHCO or
PCNHCO) or chelating NHC ligands (CNHC,N or CNHC,P). Owing
to the comparatively strong stability and coordination capability
of nitrogen compounds, we prepared hetero-difunctionalized
This journal is © The Royal Society of Chemistry 2013
J. Name., 2013, 00, 1-3 | 1

View Article Online
DOI: 10.1039/C5RA21183B
RSC Advances
Page 2 of 8
ARTICLE
Journal Name
imidazolium salts through the quaternization of hydroxyalkyl toward the direct C−H bond arylation of (benzo)oxazoles.13
substituted imidazoles by 2-bromopyridine or 2- Shao and co-workers reported that 2-aryl functionalized
chloropyrimidine. Direct metallation of the hetero- (benzo)oxazoles can be obtained efficiently via direct C−H
difunctionalized imidazolium salts by Pd(OAc)2 under mild bond arylation of (benzo)oxazoles catalysed by a well-defined
reaction condition produced the CNHC,N chelating palladium imidazole coordinated NHC palladium complex.14 While to the
complexes smoothly.
best of our knowledge, the catalytic activity of chelating or
2-Aryl substituted (benzo)oxazoles are very important pincer NHC palladium complexes towards the direct C−H bond
backbones for the synthesis of natural products, arylation of (benzo)oxazoles has not been reported.
pharmaceutically active compounds, and functional materials.11
In view of the successful application of chelating palladium
Recently, the transition metal-catalysed direct C−H bond catalyst in classical C-C bond formation, while comparatively
arylation has been noticed to be a potentially more e cient and rare application in C-H activation, here we report the synthesis,
ffi
convenient alternative for the straight forward synthesis of such characterization and C-H bond activation catalytic activity
compounds.12 However, in most cases, excessive free tertiary study of a novel type of CNHC,N chelating complexes. As
phosphines were used as ligands with transition metal salts. expected, the CNHC,N chelating complexes here proved
Besides air-, thermal-, and moisture-sensitive tertiary phosphine remarkably stable toward air and moisture, and showed high
ligands and metal salts systems, Arslan and co-workers catalytic activity toward C−H bond arylation of
reported
a
mixed-halide NHC complex, (NHC)2PdX2 (benzo)oxazoles. These results underline the high potential of
(X=Cl0.7Br0.3) and established its efficient catalytic activity this class of chelating NHC complexes in catalysis.
Scheme 1. Synthesis of the ligands and chelating NHC-Pd complexes. (a) HCHO, CHOCHO, NH4Cl, MeOH, 0-60 °C; (b) 2-bromopyridine or 2-chloropyrimidine, 150 or
110 °C; (c) Pd(OAc)2, CH2Cl2, r.t., 10 h.
additional proton signals in the range of 9.08-7.18 ppm
confirmed the formation of pyridine/pyrimidine hydroxyalkyl
di-functionalized imidazolium salts.
Results and discussion
Synthesis of pyridine/pyrimidine hydroxyalkyl di-functionalized
imidazolium salts
Synthesis of chelating NHC palladium complexes
Through slight modification of the literature reports,10
The chelating NHC-Pd complexes (3a-d) were prepared
through the direct metallation of imidazolium salts (2a-b) by
imidazole alcohols
(
1a-b
)
were synthesized from the
Pd(OAc)2 in dichloromethane at room temperature (Scheme 1).
The formation of the chelating NHC palladium complexes was
observed from the studies of NMR spectra, showing the
conspicuous absence of the NCHN resonances of imidazolium
condensation reaction of amino alcohols, formaldehyde,
glyoxal, and ammonium chloride in relatively high yields
(Scheme 1). The structure was characterized by NMR and MS
analysis.
1
salts in the H NMR spectra, and the appearance of additional
Pyridine hydroxyalkyl di-functionalized imidazolium salts
signals within 160.5-149.7 ppm in the 13C NMR spectra, which
should be attributed to the new Ccarbene–Pd resonance.
Meanwhile, the resonances of the pyridine proton adjacent to
the nitrogen atom appeared at 9.44 (3a) and 9.40 (3b) ppm,
obviously downfielded compared to those of the imidazolium
salts 2a (8.68 ppm) and 2b (8.65 ppm), supporting the
coordination of pyridine to the palladium center. Similarly, in
compounds 2c-2d, the resonances of the two pyrimidine
protons adjacent to the nitrogen atom appeared as doublets at
9.08 (2c) and 9.05 (2d) ppm. While in complexes 3c-3d, those
protons appeared as two magnetically unequal signals, with one
(
2a-b) were obtained from the neat reaction of the imidazole
alcohols with excessive 2-bromopyridine at 150 °C , and
pyrimidine hydroxyalkyl di-functionalized imidazolium salts
(
2c-d) were obtained by heating the mixture of imidazole
alcohols and 2-chloropyrimidine in toluene at 110 °C (Scheme
1). The pure products were obtained by silica chromatography
and characterized by NMR and MS analysis. In imidazole
alcohols (1a-b), the resonances of NCHN protons appeared at
7.65 and 7.48 ppm, respectively. In compounds 2a-d, single
proton signals appeared within the range of 10.34-10.17 ppm,
which can be attributed to the resonances of NCHN protons,
indicated the formation of imidazolium salts. Appearances of
shifted significantly from 9.08 (2c) and 9.05 (2d) to 9.44 (3c
)
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

View Article Online
DOI: 10.1039/C5RA21183B
Page 3 of 8
Journal Name
RSC Advances
ARTICLE
t
t
and 9.42 (3d) ppm, confirming the coordination of pyrimidine tBuOLi afforded the moderate yield. BuONa, BuOK, Na2CO3,
to the palladium center. The structure of complexes 3b and 3d Li2CO3, and KOH all produced very low yields (table 1, entries
has been further characterized unambiguously by the single- 1-6). Tests of different solvents proved DMF to be the proper
crystal X-ray diffraction studies.
solvent. Reaction in DME, DMAc or dioxane produced the
Single crystals of 3b and 3d suitable for X-ray diffraction target product in a bit low yields (table 1, entries 7-10).
analysis were obtained from the slow diffusion of diethyl ether Decreasing the amount of base resulted in low yields and the
t
to concentrated dichloromethane or acetonitrile solution, highest yield was obtained when using 5.0 equiv. of BuOLi
respectively. The molecular structures were shown in Figure 2- with a catalyst loading of 2.5% (table 1, entries 11-13). Further
3, with selected bond lengths and bond angles listed in the decreasing of catalyst loading lead to low yield and no products
caption.
was obtained in the absence of NHC-Pd catalyst (table 1,
entries 14-15), implying that the introduction of the palladium
catalyst was essential for this reaction, although a metal-free
system for direct C-H bond arylation has been established
during the past years.15
Table 1 Screening of the base and solvent effect
cat.
(mol %)
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
2.5
1.0
0
Yieldsb
(%)
63
TON
entrya
solvent
base (equiv.)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
toluene
toluene
toluene
toluene
toluene
toluene
DME
tBuOLi (5.0)
tBuONa (5.0)
tBuOK (5.0)
Na2CO3 (5.0)
Li2CO3 (5.0)
KOH (5.0)
13
4.4
<1
<1
<1
2
12
16
6
11
6.4
11
35.2
27
0
Figure 2. Molecular structure of 3b (50% displacement ellipsoids). Selected bond
lengths (Å) and angles (deg): Pd(1)-C(1) 1.990(14), Pd(1)-N(1) 2.061(10), Pd(1)-
Br(1) 2.4726(12), Pd(1)-Br(2) 2.4148(15), N(2)-C(1) 1.319(16), N(3)-C(1) 1.396(18),
N(2)-C(2) 1.350(17), N(3)-C(3) 1.393(17), C(2)-C(3) 1.36(2); C(1)-Pd(1)-Br(1)
172.7(4), C(1)-Pd(1)-Br(2) 98.7(4), C(1)-Pd(1)-N(1) 78.5(5), N(1)-Pd(1)-Br(1)
94.4(3), N(1)-Pd(1)-Br(2) 170.7(3), Br(1)-Pd(1)-Br(2) 88.59(6); N(2)-C(1)-N(3)
105.7(10).
22
<5
<5
<5
10
60
80
30
55
32
55
tBuOLi (5.0)
tBuOLi (5.0)
tBuOLi (5.0)
tBuOLi (5.0)
tBuOLi (3.0)
tBuOLi (4.0)
tBuOLi (5.0)
tBuOLi (5.0)
tBuOLi (5.0)
DMF
DMAc
dioxane
DMF
DMF
DMF
In both structures, the palladium atom adopts a slightly
distorted square-planar coordination bonded to carbene,
pyridine/pyrimidine nitrogen donor and two halides, with the
five membered chelate ring exist a twisty conformation. The
hydroxyl group hangs freely, forming intermolecular hydrogen
88
27
0
DMF
DMF
bond with the halide of another molecular (ESI), although in aReaction condition: 1.0 mmol (benzo)oxazole , 0.5 mmol bromobenzene,
1.5~2.5 mmol base, 2 mL solvent, 130 °C , 24 h. b Yields determined by
some NHC palladium complexes, the hydroxyl group has been
reported to coordinate to the central palladium atom.9
HPLC.
t
Under the standard conditions, using BuOLi as base and
DMF as solvent, the catalytic activity of complexes 3a-d
towards the reaction of (benzo)oxazole with bromobenzene
were investigated (Table 2). As shown in Table 2, the
pyrimidine chelating complexes
activities than the corresponding pyridine chelating complexes
3a-b), which can be tentatively attributed to the stronger
(3c-d) displayed higher
(
basicity of pyrimidine group. For complexes having the same
chelating structure, the substituents near the hydroxyl group
also showed some effect on the catalytic activity. The
Figure 3. Molecular structure of 3d (50% displacement ellipsoids). Selected bond
lengths(Å) and angles (deg): Pd(1)-C(1) 1.972(4), Pd(1)-N(1) 2.043(3), Pd(1)-Cl(1)
2.2889(9), Pd(1)-Cl(2) 2.3502(11), N(2)-C(1) 1.354(4), N(3)-C(1) 1.336(5), N(2)-C(2)
1.381(5), N(3)-C(3) 1.404(5), C(2)-C(3) 1.343(6); C(1)-Pd(1)-Cl(1) 98.29(10), C(1)-
Pd(1)-Cl(2) 172.55(11), C(1)-Pd(1)-N(1) 79.61(14), N(1)-Pd(1)-Cl(1) 175.55(10),
N(1)-Pd(1)-Cl(2) 93.06(10), Cl(1)-Pd(1)-Cl(2) 89.12(4); N(2)-C(1)-N(3) 104.7(3).
complexes containing benzyl substituent (3b
active than those containing butyl substituent (3a 3c). In
&
3d) were more
i
&
general, complexes 3a-d all presented high catalytic efficiency
towards the C-H activation of (benzo)oxazole when using
bromobenzene as aryl source. While in literature reports, aryl
iodide is used as the aryl source for most of the Pd-catalysed
direct C–H bond functionalization of (benzo)oxazoles, or
addition of copper salt as co-catalyst is necessary to produce the
target products in moderate or high yields.16
Catalytic studies
Initially, running the reaction of (benzo)oxazole and
bromobenzene catalysed by complex 3a as a model, a brief
screening of the base, solvent, amount of base and catalyst
loading was conducted (Table 1). Among the bases tested,
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3

View Article Online
DOI: 10.1039/C5RA21183B
RSC Advances
Page 4 of 8
ARTICLE
Journal Name
5-methyl-, and 5-tert-butyl- substituted (benzo)oxazoles gave
better yields than (benzo)oxazole (Table 4, entries 9-13 and 16-
21 vs entries 1-6). While in the cases of aryl bromide with
electron-poor substituent, 5-methyl-, and 5-tert-butyl-
substituted (benzo)oxazoles gave inferior yields (Table 4,
entries 14-15 and 22-23 vs entries 7-8).
Table 2 Catalytic activity comparison of complexes 3a-d
Yieldsb
entrya
solvent
base
cat.
TOFc
TON
(%)
88
91
95
98
1
2
3
4
DMF
DMF
DMF
DMF
tBuOLi
tBuOLi
tBuOLi
tBuOLi
3a
3b
3c
3d
35.2
36.8
38
10
13
15
15
Experimental section
39.2
a Reaction condition: 1.0 mmol (benzo)oxazole, 0.5 mmol bromobenzene, 2.5
mmol tBuOLi, 0.0125 mmol 3, 2 mL DMF, 130 °C , 24 h. b Yields determined
by HPLC. c TOF (h-1) at 25% conversion.
General consideration
All solvents and chemicals were used as received or dried
with standard methods and freshly distilled prior to use if
needed. NMR spectra were recorded at 25 °C on a 400 MHz
Bruker spectrometer. Chemical shifts (in ppm, coupling
constants J in Hz) were referenced to the residual solvent
resonances. Elemental analyses were obtained from a thermo
Flash 2000. ESI-MS spectra were recorded on a Bruker Esquire
3000.
t
Using complex 3c as catalyst, BuOLi as base and DMF as
solvent, the feasibility of the complex towards the C-H
activation of (benzo)oxazole derivatives was further
investigated (Table 3). The results showed that complex 3c
presented high catalytic efficiency towards the reaction of
(benzo)oxazoles with a series of aryl bromides, producing the
target products in moderate to high yields. For instance, both
aryl bromides bearing electron-rich, -neutral, and -poor
substituents are tolerated in such conditions, and the
substituents did not show any obvious electron effect on the
reaction. In addition, 2-methyl-phenylbromide and 2,4,6-
trimethyl-phenylbromide gave inferior results (Table 4, entries
2, 6, 10, 17 and 21), maybe partially attributed to the steric
hindrance.
Synthesis of imidazole alcohols (1a-b)
L-amino alcohol (60 mmol) and ammonium chloride (60
mmol, 3.21 g) were dissolved in MeOH (120 ml), and the
mixture was put in an ice-bath. Aqueous HCHO solution (36%,
60 mmol) and aqueous CHOCHO solution (40%, 60 mmol)
were then added dropwise before the mixture being heated to
60°C for 5 h. The mixture was then cooled to room temperature
and the solvent was removed by evaporation. The residue was
dissolved in NaOH solution (150 mL, 2M), and then extracted
by CH2Cl2 (20 mL×3). The combined organic phase was dried
over anhydrous Na2SO4, filtered and concentrated successively.
Purification of the residue by flash chromatography (silica,
CH3COOEt/EtOH = 10/1, v/v) afforded the pure products.
Table 3 Reaction of (benzo)oxazoles with arylbromides
Yieldsb
(%)
entrya
(benzo)oxazoles
aryl bromides
TON
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
(benzo)oxazole
C6H5Br
2-Me-C6H4-Br
3-Me-C6H4-Br
4-Me-C6H4-Br
3,5-Me2-C6H4-Br
2,4,6-Me3-C6H4-Br
4-F-C6H4-Br
4a, 92
4b, 86
4c, 94
4d, 95
4e, 97
4f, 80
4g, 99
4h, 87
4i, 96
4j, 90
4k, 95
4l, 97
4m, 99
4n, 94
4o, 85
4p, 99
4q, 89
4r, 98
4s, 96
4t, 98
4u, 88
4v, 87
4w, 80
36.8
34.4
37.6
38
38.8
32
39.6
34.8
38.4
36
(S)-2-(1H-imidazol-1-yl)-4-methylpentan-1-ol (1a). White
1
crystals (7.57 g, 75%). Mp: 68-70 °C . H NMR (DMSO, 400
MHz):  7.65 s, 1H, CH in imidazole) 7.19 (s, 1H, CH in
imidazole ) 6.87 (s, 1H, CH in imidazole), 4.97 (t, J = 4.9 Hz,
1H, CH2OH) 4.16-4.11 (m, 1H, NCH) 3.57-3.53 (m, 2H,
CH2OH) 1.72-1.65 (m, 1H, CH2CH(CH3)2), 1.54-1.47 (m, 1H,
CH2CH(CH3)2), 1.23-1.15 (m, 1H, CH2CH(CH3)2), 0.86 (d, J =
6.6 Hz, 3H, CH2CH(CH3)2), 0.80 (d, J = 6.6 Hz, 3H,
CH2CH(CH3)2) ppm. 13C NMR (DMSO, 100 MHz)  137.4,
128.5, 118.1 65.0, 57.8, 24.5, 23.5, 22.0 ppm. MS Calcd. for
C9H16N2O, 168.1. Found: ESI-MS, m/z: 169.1 [M+H]+.
4-CF3-C6H4-Br
C6H5Br
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-Me-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
5-tBu-benzo[d]oxazole
2-Me-C6H4-Br
3-Me-C6H4-Br
4-Me-C6H4-Br
3,5-Me2-C6H4-Br
4-F-C6H4-Br
38
38.8
39.6
37.6
34
4-CF3-C6H4-Br
C6H5Br
(S)-2-(1H-imidazol-1-yl)-3-phenylpropan-1-ol (1b). White
39.6
1
2-Me-C6H4-Br
3-Me-C6H4-Br
4-Me-C6H4-Br
3,5-Me2-C6H4-Br
2,4,6-Me3-C6H4-Br
4-F-C6H4-Br
35.6 crystals (9.71 g, 80%). Mp: 74-76 °C . H NMR (DMSO, 400
39.2
38.4
39.2
35.2
34.8
32
MHz):  7.48 (s, 1H, CH in imidazole), 7.23-7.14 (m, 4H, PhH),
7.08 (d, J = 4 Hz, 2H, CH in imidazole, & PhH), 5.10 (s , 1H,
CH2OH), 4.38-4.32 (m, 1H, NCH), 3.65 (bs, 2H, CH2OH),
3.15-3.10 (m, 1H, PhCH2), 3.00-2.94 (m, 1H, PhCH2) ppm. 13C
NMR (DMSO, 100 MHz)  138.5, 137.3, 129.3, 128.7, 128.4,
126.7, 118.3, 64.0, 61.1, 37.9 ppm. MS Calcd. for C12H14N2O,
202.1. Found: ESI-MS, m/z: 203.1 [M+H]+.
4-CF3-C6H4-Br
a Reaction condition: 1.0 mmol (benzo)oxazoles, 0.5 mmol aryl bromides, 2.5
mmol tBuOLi, 0.0125 mmol 3c, 2 mL DMF, 130 °C , 24 h. b Isolated yields.
The alkyl substituents on the phenyl ring of (benzo)oxazoles
seemed to have some effect on the reaction. For examples, in
the reaction of aryl bromides bearing electron-rich substituents,
Synthesis of pyridine hydroxyalkyl di-functionalized
imidazolium bromides (2a-b)
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

View Article Online
DOI: 10.1039/C5RA21183B
Page 5 of 8
Journal Name
RSC Advances
ARTICLE
A Schlenk tube containing imidazole alcohol (1a or 1b, 5 13C NMR (100 MHz, DMSO):  160.5, 152.7, 136.3, 122.9,
mmol) and 2-bromopyridine (3 mL) was heated at 150°C for 72 122.8, 119.9, 63.4, 62.4, 38.5, 24.4, 23.2, 22.0 ppm. MS Calcd.
h. The mixture was then cooled to room temperature and added for C13H19ClN4O, 282.1. Found: ESI-MS, m/z: 247.1 [M-Cl]+.
to diethyl ether (30 mL) dropwise, leading to the formation of
(S)-1-(1-hydroxy-3-phenylpropan-2-yl)-3-(pyrimidin-2-
deep yellow precipitate, which was then collected and purified yl)-1H-imidazol-3-ium chloride (2d). Yellow crystals (1.42 g,
1
by flash chromatography (silica, CH2Cl2/EtOH = 15/1~8/1, v/v) 90 %). Mp: 128-130 °C. H NMR (400 MHz, DMSO):  10.27
to produce the pure products.
(s, 1H, CH in imidazole), 9.05 (d, 2H, J = 4.9 Hz, CH in
(
S
)-1-(1-hydroxy-4-methylpentan-2-yl)-3-(pyridin-2-yl)-
pyrimidine), 8.49 (t, 1H, J = 1.7 Hz, CH in imidazole), 8.29 (t,
1H-imidazol-3-ium bromide (2a). Viscous oil (1.42 g, 87%). 1H, J = 1.6 Hz, CH in imidazole), 7.78 (t, 1H, J = 4.9 Hz, CH
1H NMR (400 MHz, DMSO):
in pyrimidine), 7.28 (d, 4H, J = 4.4 Hz, PhH), 7.20-7.17 (m, 1H,
imidazole), 8.68-8.66 (m, 1H, CH in pyridine), 8.62 (t, J = 1.8 PhH), 5.68 (t, 1H, J = 5.4 Hz, CH2OH), 5.10-5.03 (m, 1H,
Hz, 1H, CH in imidazole), 8.26-8.22 (m, 1H, CH in pyridine), NCH), 3.91-3.80 (m, 2H, CH2OH), 3.41-3.32 (m, 2H, PhCH2)
8.21 (t, J = 1.8 Hz, 1H, CH in imidazole), 8.11 (d, J = 8.3 Hz, ppm. 13C NMR (100 MHz, DMSO):  160.5, 152.5, 136.9,
1H, CH in pyridine), 7.68-7.65 (m, 1H, CH in pyridine), 5.26 136.1, 129.4, 129.0, 127.3, 123.3, 122.9, 119.6, 65.0, 62.5, 36.0
(bs, 1H, CH2OH), 4.64-4.60 (m, 1H, NCH), 3.77-3.70 (m, 2H, ppm. MS Calcd. for C16H17ClN4O, 316.1. Found: ESI-MS, m/z:
CH2OH), 1.97-1.91 (m, 1H, CH2CH(CH3)2), 1.70-1.63 (m, 1H, 281.1 [M-Cl]+.
CH2CH(CH3)2), 1.45-1.38 (m, 1H, CH2CH(CH3)2), 0.93 (d, 3H,
Synthesis of palladium complexes (3a-d)
J = 6.5 Hz, CH2CH(CH3)2), 0.89 (d, 1H, J = 6.6 Hz,
13
CH2CH(CH3)2) ppm.
A mixture of imidazolium salt (2a, 2b, 2c or 2d, 1.0 mmol),
146.9, 141.0, 135.2, 125.7, 122.8, 120.1, 114.8, 63.5, 62.3, 38.6, Pd(OAc)2 (1.0 mmol, 0.22 g) in CH2Cl2 (10 mL) was stirred at
24.4, 23.2, 22.0 ppm. MS Calcd. for C14H20BrN3O, 325.1. room temperature for 12 h. The solvent was then evaporated
Found: ESI-MS, m/z: 246.08 [M-Br]+.
)-1-(1-hydroxy-3-phenylpropan-2-yl)-3-(pyridin-2-yl)-
and purification of the residue by column chromatography
(silica, CH2Cl2/acetone, gradient elution, 15/1~4/1, v/v)
(
S
1H-imidazol-3-ium bromide (2b). Yellow crystals (1.35 g, produced the pure palladium complexes 3a-d
75 %). Mp: 148-150 °C . H NMR (400 MHz, DMSO):  10.17
.
1
3a. Yellow solids (0.20 g, 39%). 1H NMR (400 MHz,
(s, 1H, CH in imidazole), 8.65 (d, 1H, J = 4.8 Hz, CH in DMSO):  9.44 (s, 1H, CH in pyridine), 8.46 (d, 1H, J = 2.2 Hz,
pyridine), 8.54 (t, 1H, J = 1.7 Hz, CH in imidazole), 8.24-8.20 CH in imidazole), 8.40-8.36 (m, 1H, CH in pyridine), 8.18 (d,
(m, 1H, CH in pyridine), 8.18 (t, J =1.7 Hz, 1H, CH in 1H, J = 8.2 Hz, CH in pyridine), 7.78 (d, 1H, J = 2.3 Hz, CH in
imidazole) 8.06 (d, 1H, J = 8.2 Hz, CH in pyridine), 7.66-7.63 imidazole), 7.62 (t, 1H, J = 7.0 Hz, CH in pyridine), 6.25 (bs,
(m, 1H, CH in pyridine), 7.30-7.20 (m, 5H, PhH), 5.36 (t, 1H, J 1H, NCH), 5.01 (t, 1H, J = 5.2 Hz, CH2OH), 3.70-3.60 (m, 2H,
= 5.6 Hz, CH2OH), 4.90-4.87 (m, 1H, NCH), 3.86-3.82 (m, 2H, CH2OH), 1.90-1.82 (m, 1H, CH2CH(CH3)2), 1.64-1.57 (m, 1H,
CH2OH), 3.32-3.26 (m, 2H, PhCH2) ppm. 13C NMR (100 MHz, CH2CH(CH3)2), 1.41-1.35 (m, 1H, CH2CH(CH3)2), 0.95 (d, 3H,
DMSO):  149.7, 146.7, 141.1, 136.9, 135.0, 129.4, 129.1, J = 6.5 Hz, CH2CH(CH3)2), 0.89 (d, 3H, J = 6.5 Hz,
127.3, 125.8, 123.2, 119.7, 114.7 ppm. MS Calcd. for CH2CH(CH3)2) ppm. 13C NMR (100 MHz, DMSO): 151.8,
C17H18BrN3O M+, 359.1. Found: ESI-MS, m/z: 280.1 [M-Br]+.
150.8, 143.4, 123.6, 122.6, 117.5, 112.9, 64.2, 59.3, 30.1, 24.7,
23.4, 22.8 ppm. Anal Cacld for C14H19Br2N3OPd (511.55): C,
32.87; H, 3.74; N, 8.21. Found: C, 32.68; H, 3.56; N, 8.42.
3b. Yellow solids (0.24 g, 44%). 1H NMR (400 MHz,
Synthesis of pyrimidine hydroxyalkyl di-functionalized
imidazolium chlorides (2c-d)
A Schlenk tube containing imidazole alcohol (1a or 1b, 5 DMSO):  9.40 (s, 1H, CH in pyridine), 8.42 (d, 1H, J = 1.6 Hz,
mmol), 2-chloropyrimidine (6 mmol, 0.69 g) and toluene (15 CH in imidazole), 8.37 (t, 1H, J = 8.2 Hz, CH in pyridine), 8.13
mL) was heated at 110 °C for 72 h. The mixture was then (d, 1H, J = 8.2 Hz, CH in pyridine), 7.91 (d, 1H, J = 2.0 Hz, CH
cooled to room temperature. The deep yellow precipitate in imidazole), 7.61 (t, 1H, J = 6.6 Hz, CH in pyridine), 7.34-
formed was then collected and purified by flash 7.26 (m, 4H, PhH), 7.18 (t, 1H, J = 7.3 Hz, PhH), 6.55 (bs, 1H,
chromatography (silica, CH2Cl2/EtOH = 20/1~8/1, v/v) to NCH), 5.12 (t, 1H, J = 5.0, CH2OH), 3.75-3.65 (m, 2H,
produce the pure products.
)-1-(1-hydroxy-4-methylpentan-2-yl)-3-(pyrimidin-2-
CH2OH), 3.20 (d, 2H, J = 7.9 Hz, C6H5CH2) ppm. 13C NMR
(100 MHz, DMSO):  151.7, 143.4, 137.4, 129.6, 128.8, 127.0,
(
S
yl)-1H-imidazol-3-ium chloride (2c). Yellow crystals (1.12 g, 123.7, 122.7, 117.4, 112.8, 68.9, 63.0, 56.3, 36.7 ppm. Anal
1
79 %). Mp: 184-186 °C. H NMR (400 MHz, DMSO):  10.34 Cacld for C17H17Br2N3OPd (545.56): C, 37.43; H, 3.14; N, 7.70.
(s, 1H, CH in imidazole), 9.08 (d, J = 4.9 Hz, 2H, CH in Found: C, 37.28; H, 2.97; N, 7.89.
pyrimidine), 8.55 (t, J = 1.8 Hz, 1H, CH in imidazole), 8.22 (t,
3c. Yellow solids (0.18 g, 42%). 1H NMR (400 MHz,
J = 1.7 Hz, 1H, CH in imidazole), 7.79 (t, J = 4.9 Hz, 1H, CH DMSO):  9.44 (s, 1H, CH in pyrimidine), 9.07 (s, 1H, CH in
in pyrimidine), 5.47 (t, J = 5.4 Hz, 1H, CH2OH ), 4.75-4.71 (m, pyrimidine), 8.14 (d, 1H, J = 2.3 Hz, CH in imidazole), 7.75 (d,
1H, NCH), 3.68-3.77 (m, 2H, CH2OH), 1.99-1.92 (m, 1H, 1H, J = 2.4 Hz, CH in imidazole), 7.72 (t, 1H, J = 5.3 Hz, CH
CH2CH(CH3)2), 1.67-1.60 (m, 1H, CH2CH(CH3)2), 1.43-1.36 in pyrimidine), 6.11-6.07 (m, 1H, NCH), 5.02 (t, 1H, J = 5.0 Hz,
(m, 1H, CH2CH(CH3)2), 0.93 (d,
J = 6.5 Hz, 3H, CH2OH), 3.65 (t, 2H, J = 4.6 Hz, CH2OH), 1.89-1.82 (m, 1H,
CH2CH(CH3)2), 0.88 (d, J = 6.6 Hz, 3H, CH2CH(CH3)2)) ppm. CH2CH(CH3)2), 1.62-1.55 (m, 1H, CH2CH(CH3)2), 1.39-1.34
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

View Article Online
DOI: 10.1039/C5RA21183B
RSC Advances
Page 6 of 8
ARTICLE
Journal Name
(m, 1H, CH2CH(CH3)2), 0.96 (d, 3H,
J = 6.5 Hz, the complexes catalyse the direct C-H bond arylation of
t
CH2CH(CH3)2). 0.88 (d, 3H, J = 6.6 Hz, CH2CH(CH3)2) ppm. (benzo)oxazoles efficiently when using BuOLi as base and
13C NMR (100 MHz, DMSO):  161.8, 158.6, 156.9, 151.9, DMF as solvent. The catalytic activity of this novel type of
122.5, 120.4, 117.6, 64.1, 58.8, 24.7, 23.5, 22.7 ppm. Anal NHC complexes towards other organic transformations,
Cacld for C13H18Cl2N4OPd (423.63): C, 36.86; H, 4.28; N, especially asymmetric catalysis, are currently in progress in our
13.23. Found: C, 36.69; H, 4.03; N, 13.45.
group.
3d. Yellow solids (0.18 g, 39 %). 1H NMR (400 MHz,
DMSO):  9.42 (s, 1H, CH in pyrimidine), 9.06 (s, 1H, CH in
pyrimidine), 8.12 (d, 1H, J = 2.3 Hz, CH in imidazole), 7.88 (d,
1H, J = 2.4 Hz, CH in imidazole), 7.71 (t, 1H, J = 5.8 Hz, CH
in pyrimidine), 7.34-7.26 (m, 4H, PhH), 7.19 (t, J = 7.1 Hz, 1H,
PhH), 6.45-6.35 (m, 1H, NCH), 5.14 (t, 1H, J = 5.0 Hz,
CH2OH), 3.78-3.72 (m, 1H, CH2OH), 3.69-3.64 (m, 1H,
CH2OH), 3.20 (d, 2H, J = 8.0 Hz, C6H5CH2) ppm. 13C NMR
(100 MHz, DMSO):  161.7, 158.6, 156.7, 152.0, 137.46, 129.6,
128.8, 127.0, 122.7, 120.5, 117.4, 62.6, 60.6, 36.7 ppm. Anal
Cacld for C16H16Cl2N4OPd (457.65): C, 41.99; H, 3.52; N,
12.24. Found: C, 41.78; H, 3.30; N, 12.41.
Acknowledgements
The authors are grateful to the National Natural Science
Foundation of China (No: 21172055), the Program for
Innovative Research Team from Zhengzhou (131PCXTD605),
and the Plan for Scientific Innovation Talent of Henan
University of Technology (11CXRC10) for financial support to
this work.
Notes and references
a School of Chemistry and Chemical Engineering, Henan University of
Technology, Zhengzhou 450001, P. R. China
General Procedure for the C-H activation of (benzo)oxazoles.
*Corresponding
pumao@haut.edu.cn
author.
Email
address:
lryang@haut.edu.cn;
The C-H activation of (benzo)oxazoles was conducted in a
parallel reactor. In a typical reaction, a Schlenk tube was
charged with (benzo)oxazoles (1.0 mmol), aryl bromides (0.5
Electronic Supplementary Information (ESI) available: H NMR and 13C
NMR spectra of compounds 1-4, and characterization data of the products
of the catalytic C-H activation of (benzo)oxazoles. See DOI:
1
mmol), base (2.5 mmol), NHC-Pd complex 3a
and solvent (2 mL). The mixture was stirred at 130 °C for 24 h
under Ar. After cooling, the reaction mixture was evaporated. 1. (a) A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
, 3b, 3c or 3d,
Purification of the residue by flash chromatography on silica
1991, 113, 361. (b) A. J. Arduengo III, M. Kline, J. C. Calabrese and F.
gel (hexanes/CH2Cl2 = 20:1) afforded the pure products, which
Davidson, J. Am. Chem. Soc., 1991, 113, 9704.
1
were characterized by H NMR and 13C NMR. The analytical 2. (a) M. N. Hopkinson, C. Richter, M. Schedler and F. Glorius, Nature,
data of the products were shown in the Supporting Information.
2014, 510, 485. (b) G. C. Fortman and S. P. Nolan, Chem. Soc. Rev.,
2011, 40, 5151. (c) O. Kühl, Functionalised N-Heterocyclic Carbene
Complexes; Wiley: John Wiley & Sons Ltd, 2010. (d) T. Dröge and F.
Glorius, Angew. Chem., Int. Ed., 2010, 49, 6940. (e) S. Diéz-Gonzláez,
N. Marion and S. P. Nolan, Chem. Rev. 2009, 109, 3612. (f) M.
Poyatos, J. A. Mata and E. Peris, Chem. Rev. 2009, 109, 3677. (g) F.
Glorius, N-Heterocyclic Carbenes in Transition Metal Catalysis;
Springer: Berlin, Germany, 2007. (h) S. P. Nolan, N-heterocyclic
carbenes in synthesis; Wiley-VCH: Weinheim, Germany, 2006. (i) W.
A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290.
X-ray Diffraction Studies.
The crystal data of 3b and 3d (CCDCs 1426023& 1426037)
were collected on a Xcalibur, Eos, Gemini diffractometer with
graphite monochromated Cu Kradiation ( = 1.54184 Å) and
Mo Kradiation ( = 0.71073 Å), respectively. The crystals
17
were kept at 291.15 K during data collection. Using Olex2,
the structure of 3b was solved with the Superflip18 structure
solution program using Charge Flipping and refined with the
ShelXL19 refinement package using Least Squares minimisation. 3. (a) D. Gülcemal, A. G. Gökçe, S. Gülcemal and B. Çetinkaya, RSC
The structure of 3d was solved with the ShelXS19 structure
solution program using Direct Methods and refined with the
ShelXL19 refinement package using Least Squares minimisation.
Adv., 2014,
Pang and C. Cao, RSC Adv., 2013,
Y. Wang and W.-F. Fu, RSC Adv., 2013,
4
, 26222. (b) Q. Chen, L. Lv, M. Yu, Y. Shi, Y. Li, G.
, 18359. (c) W. Yang, G.-Z. Gou,
, 6334. (d) S. Budagumpi, R.
3
3
A. Haque and A. W. Salman, Coord. Chem. Rev., 2012, 256, 1787. (e)
I. J. Lin and C. S. Vasam, Coord. Chem. Rev., 2007, 251, 642. (f) J. C.
Garrison and W. J. Youngs, Chem. Rev., 2005, 105, 3978.
Conclusions
Novel type of chelating palladium complexes containing
pyridine/pyrimidine hydroxyalkyl di-functionalized NHCs have
been synthesized via the direct metallation of the corresponding
imidazolium salts. The complexes have been characterized
unambiguously by NMR and single-crystal X-ray diffraction
studies. The X-ray structure analysis showed clearly the
formation of CNHC,N coordination chelate in the complexes, and
the hydroxyalkyl substituents hang freely. The hydroxyl group
formed intermolecular hydrogen bond with the halide of
another molecular. Catalytic activity investigation showed that
4. (a) L. Yang, X. Zhang, P. Mao, Y. Xiao, H. Bian, J. Yuan, W. Mai and
L. Qu, RSC Adv., 2015,
Geng, X.-H. Xu and Z. Jin, J. Organomet. Chem., 2013, 737, 12. (c) D.
Meyer, A. Zeller and T. Strassner, J. Organomet. Chem., 2012, 701
5, 25723. (b) Y.-J. Li, J.-L. Zhang, X.-J. Li, Y.
,
56. (d) C. del Pozo, M. Iglesias and F. Sánchez, Organometallics,
2011, 30, 2180-2188. (e) Z. Xi, B. Liu and W. Chen, J. Org. Chem.,
2008, 73, 3954. (f) Z. Xi, X. Zhang, W. Chen, S. Fu and D. Wang,
Organometallics, 2007, 26, 6636. (g) H. M. Lee, C.-C. Lee and P.-Y.
Cheng, Curr. Org. Chem., 2007, 11, 1491. (h) E. Peris and R. H.
Crabtree, Coord. Chem. Rev., 2004, 248, 2239. (i) S. Ahrens, A. Zeller,
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

View Article Online
DOI: 10.1039/C5RA21183B
Page 7 of 8
Journal Name
RSC Advances
ARTICLE
M. Taige and T. Strassner, Organometallics, 2006, 25, 5409. (j) E. 14.X.-B. Shen, Y. Zhang, W.-X. Chen, Z.-K. Xiao, T.-T. Hu and L.-X.
Mas-Marzá, M. Sanaú and E. Peris, Inorg. Chem., 2005, 44, 9961. Shao, Org. Lett., 2014, 16, 1984.
5. (a) S. Hameury, P. de Frꢀmont, P.-A. R. Breuil, H. Olivier-Bourbigou 15.(a) J. Cuthbertson, V. J. Gray and J. D. Wilden, Chem. Commun.,
and P. Braunstein, Inorg. Chem., 2014, 53, 5189. (b) S. Gu, J. Huang
and W. Chen, Chin. J. Org. Chem., 2013, 33, 715. (c) D. Yuan and H.
V. Huynh, Molecules, 2012, 17, 2491. (d) Y. Cheng and L. Sun, Chin.
J. Org. Chem., 2012, 32, 511 (e) M. Bierenstiel and E. D. Cross,
Coord. Chem. Rev., 2011, 255, 574. (f) N. Stylianides, A. A.
Danopoulos and N. Tsoureas, J. Organomet. Chem., 2005, 690, 5948.
2014, 50, 2575. (b) T. L. Chan, Y.-N. Wu, P. Y. Choy and F. Y.
Kwong, Chem.–Eur. J., 2013, 19, 15802. (c) H.-Q. Zhao, J. Shen, J.-J.
Guo, R.-J. Ye and H.-Q. Zeng, Chem. Commun., 2013, 49, 2323. (d) K.
Tanimoro, M. Ueno, K. Takeda, M. Kirihata and S. Tanimori, J. Org.
Chem., 2012, 77, 7844. (e) T. Thruong and O. Daugulis, J. Am. Chem.
Soc., 2011, 133, 4243.
(g) A. W. Waltman and R. H. Grubbs, Organometallics, 2004, 23
,
16. (a) T. J. Williams and I. J. S. Fairlamb, Tetrahedron Lett., 2013, 54,
3105.
2906. (b) X.-M. Yan, X.-R. Mao and Z.-Z. Huang, Heterocycles, 2011,
83, 1371. (c) J. Huang, J. Chan, Y. Chen, C. J. Borths, K. D. Baucom,
R. D. Larsen and M. M. Faul, J. Am. Chem. Soc., 2010, 132, 3674. (d)
D. Alagille, R. M. Baldwin and G. D. Tamagnan, Tetrahedron Lett.,
2005, 46, 1349.
6. (a) P. Gu, Q. Xu and M. Shi, Tetrahedron, 2014, 70, 7886. (b) C.-H.
Cheng, J.-R. Xu, H.-B. Song and L.-F. Tang, Transition Met. Chem.,
2014, 39, 151. (c) V. Khlebnikov, A. Meduri, H. Mueller-Bunz, T.
Montini, P. Fornasiero, E. Zangrando, B. Milani and M. Albrecht,
Organometallics, 2012, 31, 976. (d) D. Meyer, M. A. Taige, A. Zeller,
17.O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard and H.
Puschmann, J. Appl. Cryst., 2009, 42, 339.
K. Hohlfeld, S. Ahrens and T. Strassner, Organometallics, 2009, 28
,
2142. (e) C.-C. Ho, S. Chatterjee, T.-L. Wu, K.-T. Chan, Y.-W. Chang,
T.-H. Hsiao and H. M. Lee, Organometallics, 2009, 28, 2837. (f) R.
Wang, B. Twamley and J. M. Shreeve, J. Org. Chem., 2006, 71, 426.
18.(a) L. Palatinus and G. Chapuis, J. Appl. Cryst., 2007, 40, 786. (b) L.
Palatinus and A. van der Lee, J. Appl. Cryst., 2008, 41, 975. (c) L.
Palatinus, S. J. Prathapa and S. van Smaalen, J. Appl. Cryst., 2012, 45
,
(g) F. E. Hahn, M. C. Jahnke and T. Pape, Organometallics, 2006, 25
,
575.
5927. (h) H. M. Lee, P. L. Chiu and J. Y. Zeng, Inorg. Chim. Acta.,
2004, 357, 4313. (i) N. Tsoureas, A. A. Danopoulos, A. A. D. Tulloch
and M. E. Light, Organometallics, 2003, 22, 4750. (j) D. S.
McGuinness and K. J. Cavell, Organometallics, 2000, 19, 741. (k) A.
A. D. Tulloch, A. A. Danopoulos, R. P. Tooze, S. M. Cafferkey, S.
Kleinhenz and M. B. Hursthouse, Chem. Commun., 2000, 1247.
7. (a) P. Gu, J. Zhang, Q. Xu and M. Shi, Dalton Trans., 2013, 42, 13599.
(b) A. Schumacher, M. Bernasconi and A. Pfaltz, Angew. Chem. Int.
Ed., 2013, 52, 7422. (c) B. A. Messerle, M. J. Page and P. Turner,
Dalton Trans., 2006, 3927.
19.G. M. Sheldrick, Acta Cryst., 2008, A64, 112.
8. (a) Y. Cheng, H.-J. Xu, J.-F. Sun, Y.-Z. Li, X.-T. Chen and Z.-L. Xue,
Dalton Trans., 2009, 7132. (b) X.-W. Li, G.-F. Wang, F. Chen, Y.-Z.
Li, X.-T. Chen and Z.-L. Xue, Inorg. Chim. Acta., 2011, 378, 280.
9. L. Faraji, K. Jadidi and B. Notash, Tetrahedron Lett., 2014, 55, 346.
10.P. Mao, Y. Cai, Y. Xiao, L. Yang, Y. Xue and M. Song, Phosphorus,
Sulfur, and Silicon, 2010, 185, 2418.
11.(a) V. S. C. Yeh, Tetrahedron, 2004, 60, 11995. (b) C. A. Zificsak and
D. J. Hlasta, Tetrahedron, 2004, 60, 8991. (c) I. J. Turchi and M. J. S.
Dewar, Chem. Rev., 1975, 75, 389.
12.(a) D. Kim, K. Yoo, S. E. Kim, H. J. Cho, J. Lee, Y. Kim and M. Kim,
J. Org. Chem., 2015, 80, 3670. (b) F. Zhu and Z.-X Wang, Org. Lett.,
2015, 17, 1601. (c) N. Kuhl, M. N. Hopkinson, J. Wencel-Delord and
F. Glorius, Angew. Chem., Int Ed., 2012, 51, 10236. (d) K. M. Engle,
T.-S. Mei, M. Wasa and J.-Q. Yu, Acc. Chem. Res., 2012, 45, 788. (e)
P. B. Arockiam, C. Bruneau and P. H. Dixneuf, Chem. Rev., 2012, 112
5879. (f) D.-G. Yu, B.-J. Li and Z.-J. Shi, Tetrahedron, 2012, 68, 5130
(g) J. F. Hartwig, Chem. Soc. Rev., 2011, 40, 1992. (h) W. R.
Gutekunst and P. S. Baran, Chem. Soc. Rev., 2011, 40, 1976. (i) L.
,
McMurray, F. O’Hara and M. J. Gaunt, Chem. Soc. Rev., 2011, 40
,
1885. (j) C. Verrier, P. Lassalas, L. Théveau, G. Quéguiner, F.
Trécourt, F. Marsais and C. Hoarau, Beilstein J. Org. Chem., 2011, 7,
1584.
13.H. Arslan, I. Özdemįr, D. Vanderveer, S. Demįr and B. Cetįnkaya, J.
Coord. Chem., 2009, 62, 2591.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

RSC Advances
Page 8 of 8
View Article Online
DOI: 10.1039/C5RA21183B
Chelating Palladium Complexes Containing Pyridine/pyrimidine
Hydroxyalkyl Di-functionalized N-Heterocyclic Carbenes: Synthesis,
Structure, and Catalytic Activity towards C-H Activation
Liangru Yang,* Jinwei Yuan, Pu Mao,* Qi Guo
Chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized NHCs were synthesized,
characterized and tested for C-H activation of (benzo)oxazoles.