Synthesis and catalytic activity of chiral linker-bridged bis-N-heterocyclic carbene dipalladium complexes

Article abstract of DOI:10.3184/174751918X15293145282582

A series of new chiral-bridged N-heterocyclic carbene ligands with different substituents and their corresponding palladium complexes have been synthesised. The effect of the substituents on the catalytic activity of these Pd complexes was investigated in the Suzuki reaction of p-bromotoluene with phenylboronic acid, and the results showed that the complexes with aryl substituents performed better than those with alkyl substituents. The complex with the most sterically hindered substituent (diisopropyl on a phenyl group) performed best, and it was also an efficient catalyst for the reaction of various arylboronic acids with aryl halides having different electronic and steric properties. In addition, it was employed as a catalyst in the asymmetric Suzuki reaction, but only moderate yields of 1,1-binaphthalenes with less than 20% enantiomeric excess were obtained.

Full text of DOI:10.3184/174751918X15293145282582

320 RESEARCH PAPER
VOL. 42 JUNE, 320–325
JOURNAL OF CHEMICAL RESEARCH 2018
Synthesis and catalytic activity of chiral linker-bridged bis-N-heterocyclic
carbene dipalladium complexes
Xu Lia, Guowen Zhanga, Man Chaoa, Changsheng Caoa, Guangsheng Pangb and Yanhui Shia*
aSchool of Chemistry and Material Science and Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University,
Xuzhou, Jiangsu 221116, P.R. China
bState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, Jilin 130012, P.R. China
A series of new chiral-bridged N-heterocyclic carbene ligands with different substituents and their corresponding palladium complexes
have been synthesised. The effect of the substituents on the catalytic activity of these Pd complexes was investigated in the Suzuki
reaction of p-bromotoluene with phenylboronic acid, and the results showed that the complexes with aryl substituents performed better
than those with alkyl substituents. The complex with the most sterically hindered substituent (diisopropyl on a phenyl group) performed
best, and it was also an efficient catalyst for the reaction of various arylboronic acids with aryl halides having different electronic and steric
properties. In addition, it was employed as a catalyst in the asymmetric Suzuki reaction, but only moderate yields of 1,1-binaphthalenes
with less than 20% enantiomeric excess were obtained.
Keywords: chiral, 1,1’-bi-2-naphthol, palladium complexes, N-heterocyclic carbene, Suzuki reaction
Asymmetric catalysis is a powerful method for obtaining valuable
enantio-enriched molecules, and chiral ligands and transition
metal complexes play a major role in the transformations
entailed.1,2 N-Heterocyclic carbenes (NHCs) as a choice of
ligands have been successfully applied in many different types of
transition metal-catalysed reactions.3,4 Moreover, a great number
of chiral NHC ligand and transition metal complexes have been
synthesised and successfully used in various asymmetric catalytic
reactions.5 Among these asymmetric reactions, using a chiral
NHC as the ligand in palladium-catalysed asymmetric aryl–aryl
cross coupling reactions has become one of the most efficient
methods for constructing the axially chiral biaryl motif, which
exists in a large number of biologically active natural products,6–11
and is one of the most commonly used chiral ligands12 that include
1,1’-bi-2-naphthol (BINOL),13 2,2’-bis(diphenylphosphino)-1,1’-
binaphthyl (BINAP)14 and (R)-(+)-2-(diphenylphosphino)-2’-
methoxy-1,1’-binaphthyl (MOP)15 (Scheme 1).
Great efforts have been made with regard to the design and
synthesis of enantiopure NHC ligands and metal complexes,
leading to efficient and selective organic transformations.
Chelating bis(NHC) ligands represent a special class of
carbenes, and their metal complexes usually have improved
stability. A simple strategy for constructing a chiral bis(NHC)
ligand is through introducing a chiral linker to bridge two NHC
ligands.16,17 Herein, we report the efficient synthesis of a series
of chiral Pd-NHC complexes bridged by an S-BINOL linker,
and we have investigated the influence of ligand substituents on
the catalytic activity of these complexes in Suzuki reactions and
have also tested their application in asymmetric Suzuki–Miyaura
reactions.
bis(NHC) precursors. As shown in Scheme 2, (S)-(−)-1,1’-
bi-2-naphthol first reacted with 2-bromoethanol to give (S)-
2,2’-([1,1’-binaphthalene]-2,2’-diylbis(oxy))bis(ethan-1-ol),
which was further converted to (S)-2,2’-bis(2-chloroethoxy)-
1,1’-binaphthalene by chlorination with thionyl chloride
(Scheme 1).18 Then the bis(imidazolium) dichlorides were
synthesised through the alkylation of imidazole with (S)-2,2’-
bis(2-chloroethoxy)-1,1’-binaphthalene.19 Finally, the reaction
of bis(imidazolium) dichloride with PdCl2 in the presence of
pyridine and K2CO3 led to the formation of chiral Pd-NHC
complexes 1–6.
All compounds were characterised by multinuclear NMR
(1H, 13C), IR spectra and elemental analysis. Unfortunately, a
suitable single crystal was unavailable for X-ray structural
analysis. The spectral and analytical data for these complexes
1
were consistent with the proposed structures. In the H NMR
spectra of 1–6 in CDCl3, the characteristic peaks of the proton
of NCHN (ca. 10.52–9.60 ppm) in the NHC precursors19
were absent, indicating the formation of the Pd–Ccarbene bond.
All signals corresponding to these protons from pyridine,
naphthalene and imidazole occurred in the expected aromatic
region. As listed in Table 1, two doublet peaks at 8.97–8.68
and 7.78–7.64 parts per million (ppm) correspond to the
protons of α- and ß-pyridine, and the doublet peak at ~8.0 ppm
corresponds to the proton of 8,8’-naphthalene. The two protons
of the imidazole group occur at 6.53–6.09 and 5.79–5.55 ppm
as two singlet peaks, respectively. In addition, the two protons
of the methylene group of the ethoxy group (OCH2CH2) appear
as two multiplets due to the chiral effect, and the protons of
the methyl group appear at ~5.75 ppm as a singlet. Moreover,
all of the characteristic resonances of 1–6 appeared in the
13C NMR spectra. The peaks corresponding to pyridine,
(S)-(−)-1,1’-Bi-2-naphthol was used as a readily available
building block to introduce the chiral element into the target
OH
OH
PPh2
PPh2
PPh2
OMe
(R)-BINOL
(R)-BINAP
(R)-MOP
Scheme 1 Axially chiral biaryl ligands.
* Correspondent. E-mail: yhshi@jsnu.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2018 321
Br
OH
OH
Cl
Cl
SOCl2
HO
OH
OH
O
O
O
O
N
Pd
Cl
R
R
Cl
N
N
N
N
N
R
R
N
N
N
R
Py, K2CO3
80 °C
O
O
O
O
+
PdCl2
N
N
Cl
2
Cl
Pd
N
Cl
,
,
,
,
,
R = CH3
1
2
3
4
5
6
Scheme 2 Synthesis of chiral Pd-NHC complexes 1–6.
Table 1 NMR and rotational data for palladium complexes 1–6
1Ha
13Ca
[α]25D = 57.5
Complex
Pyridine
(α-Py, β-Py)
Naphthalene
(8,8’-CH)
Imidazole
(CH)
Ethoxy
(OCH2)
Ethoxy
(OCH2CH2)
(c 1.0, CH2Cl2)
CH3
Ccarbene
1
2
3
4
5
6
8.97, 7.78
8.96, 7.76
8.71, 7.65
8.73, 7.66
8.68, 7.64
8.73, 7.65
7.98
7.95
7.99
7.98
8.01
8.01
6.53, 5.57
6.38, 5.55
6.12, 5.67
6.09, 5.66
6.18, 5.71
6.24, 5.79
5.01–4.96
4.98–4.94
5.10–5.06
5.11–5.07
5.21–5.14
5.30–5.24
5.75
5.75
5.79
5.74
5.78
5.78
153.2
153.5
153.5
153.5
153.6
153.6
68.2, 50.1
68.2, 51.6
68.6, 50.9
68.7, 50.9
68.7, 51.0
68.7, 51.1
−56.8
−44.3
9.3
39.5
57.5
41.3
a1H and 13C NMR in CDCl3 (ppm).
naphthalene and imidazole exhibited in the aromatic region in
the range 154–113 ppm. The carbon resonances corresponding
to -OCH2CH2 appeared at ~68 and 50 ppm, and other alkyl
carbons exhibited at <60 ppm. The signal at ca. 154 ppm was
assigned to the Ccarbene–Pd resonance, providing direct evidence
of the metalation of the ligand. In addition, the optical rotation
of the chiral compounds was measured in methylene dichloride
solution, and the results are listed in Table 1. Complexes 1 and
2 are laevorotatory, whereas complexes 3–6 are dextrorotatory.
p-bromotoluene with phenylboronic acid. For economic
reasons, it is better to use the minimal amount of the expensive
Pd complex. As 0.5 mol% of 6 led to 100% conversion of
p-bromotoluene at 65 °C, using half the amount of 6 (0.25 mol%)
was tested. As shown in Table 3, entry 1, the conversion and
yield decreased dramatically with low loading of 6. However,
a good yield and conversion could be achieved by raising the
reaction temperature to 100 °C (Table 3, entry 2). Normally, the
solvent and base influence the yield of the product; therefore,
different solvents and bases were explored. For all tested bases
(Table 3, entries 2–6), KOH performed best and the other
bases provided less than 25% yields of the product. Out of all
of the solvents tested, dioxane and DMSO were relatively good
solvents for the reaction, and dioxane provided the highest yield
of the product. The other solvents gave yields of less than 40%.
To assess the scope of the reaction catalysed by 6, a variety of
aryl halides were chosen and examined in the Suzuki reaction
with phenylboronic acid and 1-naphthaleneboronic acid (Table
4). The results show that not only active aryl bromides and
iodides reacted smoothly in the reaction, but also inactive and
cheap aryl chlorides reacted well (Table 4, entries 14,15). As
expected, the yields of analogous halides follows the order:
Catalytic properties
First, we tested the catalytic activity of 1–6 in the Suzuki
reaction of p-bromotoluene with phenylboronic acid to elucidate
the influence of different substituents on the ligands (Table 2).
The reaction catalysed by 0.5 mol% of Pd-NHC was carried out
in dioxane at 65 °C for 24 h. The results (Table 2, entries 1–6)
indicated that the complexes with aryl substitutes have better
catalytic activity than those with alkyl substitutes, and complex
6, with the most sterically hindered ligand, showed the greatest
activity, with 100% conversion and 81% isolated yield.
Second, complex 6 was selected as the catalyst to examine
the influence of different conditions on the reaction of

322 JOURNAL OF CHEMICAL RESEARCH 2018
Table 2 Catalytic activities of Pd complexes 1–6 in the Suzuki reaction
Pd-NHC (0.5 mol%)
KOH, dioxane
B(OH)2 + Br
CH3
CH3
65 °C
Entrya
Catalyst (mol%)
Temp. (ºC)
Yield (%)b
Conversion (%)c
1
2
3
4
5
6
1 (0.5)
2 (0.5)
3 (0.5)
4 (0.5)
5 (0.5)
6 (0.5)
65
65
65
65
65
65
11
58
77
75
75
81
13
71
95
92
92
100
aReaction conditions: p-bromotoluene (1 mmol), phenylboronic acid (1.2 mmol), KOH (3 mmol), Pd complex (0.5 mol%), dioxane (1 mL), 65 °C, 24 h.
bIsolated yield.
cDetermined by GC with dodecane as an internal standard.
Table 3 Effect of different conditions on the Suzuki reaction catalysed by 6
6
(0.25 mol%)
base, solvent, 100 °C
Yield (%)b
B(OH)2 + Br
CH3
CH3
Entrya
1d
2
Base
KOH
KOH
Solvent
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Toluene
o-Xylene
DMF
Conversion (%)c
15
65
16
22
5
12
29
36
40
57
18
80
19
27
6
15
36
44
51
70
3
4
5
6
K3PO4
K2CO3
Na2CO3
Cs2CO3
KOH
7
8
KOH
9
KOH
10
KOH
DMSO
aReaction conditions: p-bromotoluene (1 mmol), phenylboronic acid (1.2 mmol), base (3 mmol), complex 6 (0.25 mol%), solvent (1 mL), 100 °C, 24 h.
bIsolated yield.
cDetermined by GC with dodecane as an internal standard.
d65 °C.
Experimental
iodide > bromide > chloride (Table 4, entries 1 and 15,16).
The catalyst performed well for the aryl halides bearing both
electron-withdrawing and electron-donating groups and had
good tolerance for various functional groups, including CN, Cl,
NO2, COCH3, CHO, CF3, OH, OCH3, NHCOCH3, etc. In the
case of dibromobenzene, the double coupling reaction could
occur in a one-pot process (Table 4, entry 11). Furthermore,
its application in asymmetric Suzuki coupling reactions of
1-naphthaleneboronic acid with 1-bromonaphthalene was
investigated (Table 5). Due to hindrance in the substrates, the
reaction afforded only moderate yields of 1,1-binaphthalenes,
with less than 20% enantiomeric excess (ee). The flexible
ethylene linker between NHC and BINOL is probably the
reason for the low enantioselectivity in asymmetric catalysis.
All manipulations were carried out under a nitrogen atmosphere
using standard Schlenk or glovebox techniques. Anhydrous dioxane,
toluene and o-xylene were distilled over Na, and anhydrous pyridine,
DMF and DMSO were distilled over calcium hydride under a
nitrogen atmosphere prior to use. Potassium carbonate was ground
to a fine powder prior to use. All other chemicals were obtained from
1
commercial suppliers and were used without further purification. H
and 13C NMR spectra were recorded on a Bruker AV 400 spectrometer
at room temperature and referenced to the residual signals of the
solvent. Elemental analyses were performed on a EuroVektor EA-
3000 elemental analyser. IR spectra were recorded on KBr pellets
on an FTIR-Tensor 27 spectrometer. GC-MS was performed on
an Agilent 6890-5973N system with electron ionisation (EI) mass
spectrometry. Optical rotations were measured with an Autopol IV
automatic polarimeter in methylene dichloride (CH2Cl2) solution
(1.0 M). Analytical HPLC was performed using an Agilent 1200
series chromatograph equipped with a Chiralcel OJ-H column, and the
products were identified by comparison with authentic samples. Flash
column chromatography was carried out on silica gel.
Conclusion
A variety of chiral linker-bridged bis(NHC) dipalladium
complexes with different substituents have been designed and
synthesised in good yields. The results of the Suzuki reaction
showed that Pd-NHC complexes with aryl substitutes showed
better catalytic activity than those with alkyl substitutes,
and complex 6 with the most sterically hindered substituents
performed best. It is an efficient catalyst for various arylboronic
acids and aryl halides with different electronic and steric
properties. However, in the asymmetric Suzuki reaction, only
moderate yields of 1,1-binaphthalenes with less than 20% ee
were obtained.
Palladium complex 1
To
a 50 mL round-bottom flask was added (S)-3,3’-(([1,1’-
binaphthalene]-2,2’-diylbis(oxy))bis(ethane-2,1-diyl))bis(1-methyl-
1H-imidazol-3-ium) dichloride (0.58 g, 1.0 mmol), PdCl2 (0. 354 g,
2.0 mmol) and K2CO3 (2.764 g, 20 mmol). The flask was purged with
nitrogen gas three times, and then pyridine (15 mL) was injected under
nitrogen into the mixture by means of a syringe. The reaction mixture
was heated at 80 °C for 16 h and then cooled. The solids were removed

JOURNAL OF CHEMICAL RESEARCH 2018 323
Table 4 Suzuki reaction catalysed by complex 6
6
(0.25 mol%)
+
X
dioxane, KOH, 100 °C
B(OH)2
R
R
Entry
Aryl halide
Product
Yield (%)
1
2
3
4
81
92
98
81
Br
Br
CH3
CH3
Cl
Cl
CN
Br
CN
Br
O
O
NO2
Br
NO2
5
6
64
98
Br
NO2
NO2
Br
7
98
CN
CN
O
O
Br
Br
8
9
97
63
O
H
O
H
10
11
12
13
14
92
88
84
97
34
NHCOCH3
Br
NHCOCH3
Br
Br
Br
Cl
Cl
I
Br
CF3
OH
CF3
OH
NO2
CH3
CH3
NO2
CH3
CH3
15
16
17
70
98
79
I
O
O
Br
Br
18
19
75
52
F
F
Reaction conditions: aryl halides (1 mmol), phenylboronic acid (1.2 mmol), KOH (3 mmol), complex 6 (0.5 mol%), dioxane (1 mL), 100 °C, 24 h. Isolated yield.

324 JOURNAL OF CHEMICAL RESEARCH 2018
Table 5 Asymmetric Suzuki–Miyaura coupling reactions catalysed by 6
6
(0.5 mol%)
+
Br
B(OH)2
dioxane, KOH, 100 °C
R1
R2
R1 R2
Entry
R1
H
R2
Product
Yield (%)a
ee (%)b
1
H
H
48
51
1
2
17
Me
Me
20
Me
32
3
4
5
14
2
H
Me
H
52
43
OEt
OEt
Reaction conditions: Aryl halides (0.5 mmol), 1-naphthaleneboronic acid (0.6 mmol), KOH (1.5 mmol), Pd
complex 6 (0.25 mol%, 0.00125 mmol), dioxane (1 mL), 100 °C, 24 h.
aIsolated yield.
bDetermined by HPLC.
by filtration over Celite and washed with dichloromethane (DCM).
to yield complex 2: Yellow solid; Yield 0.79 g (72%);1H NMR (400 MHz,
CDCl3): δ (ppm) 8.96 (d, J = 5.2 Hz, 4H, α-Py), 7.95 (d, J = 8.8 Hz, 2H,
ArH), 7.88 (d, J = 8.4 Hz, 2H, ArH), 7.76 (t, J = 7.6 Hz, 2H, β-Py), 7.45
(d, J = 8.8 Hz, 2H, ArH), 7.37–7.32 (m, 6H, γ-Py, ArH), 7.23 (t, J =7.4 Hz,
2H, ArH), 7.14 (d, J = 8.4 Hz, 2H, ArH), 6.38 (s, 2H, Himidazole), 5.55 (s, 2H,
The filtrate was concentrated under vacuum to leave crude solids that
crystallised from ether/DCM to give the product 1: Yellow solid; yield
0.84 g (83%); 1H NMR (400 MHz, CDCl3): δ (ppm) 8.97 (d, J = 5.6 Hz,
4H, α-Py), 7.98 (d, J = 8.8 Hz, 2H, ArH), 7.88 (d, J = 8.4 Hz, 2H, ArH), 7.78
(t, J = 7.6 Hz, 2H, β-Py), 7.41 (d, J = 9.2 Hz, 2H, ArH), 7.36 (t, J = 6.6 Hz,
6H, ArH, γ-Py), 7.26 (d, J = 15.2 Hz, 2H, ArH), 7.19 (d, J = 8.8 Hz, 2H,
ArH), 6.53 (s, 2H, Himidazole), 5.57 (s, 2H, Himidazole), 5.01–4.96 (m, 2H,
OCH2), 4.48–4.40 (m, 4H, CH2), 4.21–4.15 (m, 2H, CH2), 4.00 (s, 6H,
CH3); 13C NMR (100 MHz, CDCl3): δ (ppm) 153.2, 151.1, 147.0, 138.1,
133.9, 129.7, 129.2, 128.0, 126.8, 125.3, 124.4, 123.9, 122.9, 122.3, 119.1,
113.1, 68.2, 50.1, 37.5; IR (KBr) (νmax/cm−1): 3446, 1592, 1508, 1472,
1456, 1448, 1263, 1243, 1220, 1089, 1071, 810, 757, 689; Anal. calcd for
C42H42Cl4N6O2Pd2 (1017.47 g mol−1): C, 49.58; H, 4.16; N, 8.26; found: C,
49.42; H, 4.03; N, 8.46%; [α]25D = −56.8 (c 1.0, DCM).
H
imidazole), 4.98–4.94 (m, 2H, OCH2), 4.86–4.81 (m, 2H, CH2), 4.63–4.55 (s,
4H, CH2), 1.95 (s, 18H, CH3); 13C NMR (100 MHz, CDCl3): δ (ppm) 153.5,
151.4, 144.3, 137.9, 134.0, 129.4, 129.2, 127.8, 126.6, 125.5, 124.4, 123.8,
122.5, 119.6, 119.2, 114.4, 68.2, 58.7, 51.6, 32.0; IR (KBr) (νmax/cm−1): 3482,
1592, 1508, 1447, 1418, 1262, 1238, 1217, 1149, 1089, 1071, 810, 756, 691;
Anal. calcd for C48H54Cl4N6O2Pd2 (1101.63 g mol−1): C, 52.33; H, 4.94; N,
7.63; found: C, 52.17; H, 4.59; N, 7.85%; [α]25D = −44.3 (c 1.0, DCM).
Palladium complex 3
A procedure analogous to that for 1 was used to synthesise this complex
from (S)-3,3’-(([1,1’-binaphthalene]-2,2’-diylbis(oxy))bis-(ethane-2,1-
diyl))bis(1-(2,6-dimethylphenyl)-1H-imidazol-3-ium) dichloride to
yield complex 3; Yellow solid; yield 0.93 g (78%); 1H NMR (400 MHz,
CDCl3): δ (ppm) 8.71 (d, J = 5.2 Hz, 4H, α-Py), 7.99 (d, J = 8.8 Hz, 2H,
ArH), 7.88 (d, J = 8.0 Hz, 2H, ArH), 7.65 (t, J = 7.6 Hz, 2H, β-Py), 7.49
Palladium complex 2
A procedure analogous to that for 1 was used to synthesise this complex
from
(S)-3,3’-(([1,1’-binaphthalene]-2,2’-diylbis(oxy))bis-(ethane-2,1-
diyl))bis(1-(tert-butyl)-1H-imidazol-3-ium) dichloride (0.66 g, 1 mmol)

JOURNAL OF CHEMICAL RESEARCH 2018 325
(d, J = 9.2 Hz, 2H, ArH), 7.35–7.27 (m, 4H, ArH), 7.23–7.14 (m, 12H,
γ-Py, ArH), 6.12 (s, 2H, Himidazole), 5.67 (s, 2H, Himidazole), 5.10–5.06
(m, 2H, OCH2), 4.72–4.64 (m, 6H, CH2), 2.18 (s, 6H, CH3), 2.09 (s,
6H, CH3); 13C NMR (100 MHz, CDCl3): δ (ppm) 153.5, 151.2, 149.4,
137.7, 137.0, 136.7, 136.6, 134.0, 129.6, 129.3, 129.2, 128.3, 127.8,
126.7, 125.4, 124.1, 123.9, 123.1, 122.7, 119.7, 114.4, 68.6, 50.9, 19.0;
IR (KBr) (νmax/cm−1): 3483, 1592, 1508, 1476, 1448, 1417, 1263, 1244,
1220, 1089, 1071, 776, 757, 730, 694; Anal. calcd for C56H54Cl4N6O2Pd2
(1197.72 g mol−1): C, 56.16; H, 4.54; N, 7.02; found: C, 56.03; H, 4.52;
N, 7.15%; [α]25D = 9.3 (c 1.0, DCM).
12H, CH3), 0.94 (dd, J = 23.6 Hz, 6.8 Hz, 12H, CH3); 13C NMR
(100 MHz, CDCl3): δ (ppm) 153.6, 151.2, 150.4, 146.9, 137.7, 134.2,
134.0, 130.1, 129.6, 129.3, 127.9, 126.8, 125.4, 124.7, 124.2, 124.0,
123.9, 122.2, 119.6, 114.6, 68.7, 51.1, 28.2, 26.5, 23.1; IR (KBr) (νmax
/
cm−1): 3461, 1592, 1468, 1448, 1418, 1262, 1241, 1219, 1071, 1059, 806,
758, 695; Anal. calcd for C64H70Cl4N6O2Pd2 (1309.93 g mol−1): C, 58.68;
H, 5.39; N, 6.42; found: C, 58.46; H, 5.13; N, 6.51%; [α]25 = 41.3 (c
D
1.0, DCM).
Acknowledgements
We are grateful for financial support from the National
Natural Science Foundation of China (NSFC 21571087),
the Major Projects of Natural Science Research in Jiangsu
Province (15KJA150004), the PAPD and TAPP of Jiangsu
Higher Education Institutions, the Research & Practice
Innovation Program of Jiangsu Province for Undergraduate and
Postgraduate Students (KYCX17_1582, 201710320086Y and
HXKY2017008) and the State Key Laboratory of Inorganic
Synthesis and Preparative Chemistry at Jilin University
(2016-01).
Palladium complex 4
A procedure analogous to that for 1 was used to synthesis this complex
from (S)-3,3’-(([1,1’-binaphthalene]-2,2’-diylbis(oxy))bis(ethane-2,1-
diyl))bis(1-mesityl-1H-imidazol-3-ium) dichloride to yield complex 4:
Yellow solid; yield 1.04 g (85%); 1H NMR (400 MHz, CDCl3): δ (ppm)
8.73 (d, J = 6.0 Hz, 4H, α-Py), 7.98 (d, J = 8.8 Hz, 2H, ArH), 7.87 (d,
J = 8.0 Hz, 2H, ArH), 7.66 (t, J = 7.6 Hz, 2H, β-Py), 7.49 (d, J = 9.2 Hz,
2H, ArH), 7.32 (t, J = 7.4 Hz, 2H, ArH), 7.24–7.15 (m, 8H, γ-Py,
ArH), 6.95 (s, 4H, ArH), 6.09 (s, 2H, Himidazole), 5.66 (s, 2H, Himidazole),
5.11–5.07 (m, 2H, OCH2), 4.70–4.63 (m, 6H, CH2), 2.33 (s, 6H, CH3),
2.13 (s, 6H, CH3), 2.05 (s, 6H, CH3); 13C NMR (100 MHz, CDCl3): δ
(ppm) 153.5, 151.2, 149.3, 138.9, 137.7, 136.3, 136.2, 134.5, 134.0,
129.5, 129.3, 129.0, 127.8, 126.7, 125.4, 124.1, 123.9, 123.0, 122.9, 119.7,
114.5, 68.7, 50.9, 21.1, 18.9; IR (KBr) (νmax/cm−1): 3649, 1592, 1508,
1487, 1448, 1418, 1262, 1244, 1220, 1091, 1071, 757, 731, 694; Anal.
calcd for C58H58Cl4N6O2Pd2 (1225.77 g mol−1): C, 56.83; H, 4.77; N,
6.86; found: C, 56.66; H, 4.48; N, 7.04%; [α]25D = 39.5 (c 1.0, DCM).
Received 18 April 2018; accepted 7 June 2018
Paper JCR1805388
https://doi.org/10.3184/174751918X15293145282582
Published online: 24 June 2018
References
Palladium complex 5
1
2
E.C. Swift and E.R. Jarvo, Tetrahedron, 2013, 69, 5799.
A.H. Cherney, N.T. Kadunce and S.E. Reisman, Chem. Rev., 2015, 115,
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A procedure analogous to that for 1 was used to synthesise this
complex from (S)-3,3’- 3,3’-(([1,1’-binaphthalene]-2,2’-diylbis(oxy))
bis(ethane-2,1-diyl))bis(1-(2,6-diethylphenyl)-1H-imidazol-3-
ium) dichloride to yield complex 5: Yellow solid; yield 1.03 g (82%);
1H NMR (400 MHz, CDCl3): δ (ppm) 8.68 (d, J = 9.6 Hz, 4H, α-Py),
8.01 (d, J = 9.2 Hz, 2H, ArH), 7.88 (d, J = 8.0 Hz, 2H, ArH), 7.64 (t,
J = 7.6 Hz, 2H, β-Py), 7.52 (d, J = 9.2 Hz, 2H, ArH), 7.41 (t, J = 7.6 Hz,
2H, ArH), 7.32 (t, J = 7.6 Hz, 2H, ArH), 7.23–7.19 (m, 12H, γ-Py, ArH),
6.18 (s, 2H, Himidazole), 5.71 (s, 2H, Himidazole), 5.21–5.14 (m, 2H, OCH2),
4.65–4.62 (m, 6H, CH2), 2.69–2.58 (m, 4H, CH2), 2.31–2.15 (m, 4H,
CH2), 1.13–1.06 (m, 12H, CH3); 13C NMR (100 MHz, CDCl3): δ (ppm)
153.6, 151.2, 150.1, 142.0, 142.0, 137.7, 135.7, 134.1, 129.7, 129.6, 127.9,
126.7, 126.0, 125.4, 124.2, 124.0, 123.6, 122.7, 114.6, 68.7, 51.0, 24.4,
24.3, 14.7, 14.6; IR (KBr) (νmax/cm−1): 3649, 1541, 1508, 1466, 1458,
1448, 1418, 1263, 1241, 1219, 1071, 810, 756, 731, 694; Anal. calcd for
C60H62Cl4N6O2Pd2 (1253.83 g mol−1): C, 57.48; H, 4.98; N, 6.70; found:
C, 57.26; H, 4.68; N, 6.93%; [α]25D = 57.5 (c 1.0, DCM).
3
4
5
6
7
8
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Palladium complex 6
A procedure analogous to that for 1 was used to synthesise this
complex
from
(S)-3,3’-(([1,1’-binaphthalene]-2,2’-diylbis(oxy))
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Chem. Res., 2011, 35, 471.
bis(ethane-2,1-diyl))bis(1-(2,6-diisopropylphenyl)-1H-imidazol-3-
ium) dichloride to yield complex 6: Yellow solid; yield: 1.09 g (83%);
1H NMR (400 MHz, CDCl3): δ (ppm) 8.73 (d, J = 4.8 Hz, 4H, α-Py),
8.01 (d, J = 9.2 Hz, 2H, ArH), 7.88 (d, J = 8.0 Hz, 2H, ArH), 7.65 (t,
J = 7.6 Hz, 2H, β-Py), 7.53 (d, J = 9.2 Hz, 2H, ArH), 7.46–7.42 (m,
2H, ArH), 7.33–7.26 (m, 6H, ArH), 7.23–7.21 (m, 8H, γ-Py, ArH),
6.24 (s, 2H, Himidazole), 5.79 (s, 2H, Himidazole), 5.30–5.24 (m, 2H, OCH2),
4.69–4.62 (m, 6H, CH2), 2.73–2.67 (m, 4H, CH), 1.34 (d, J = 6.8 Hz,