Palladium-catalyzed aminations of aryl halides with phosphine- functionalized imidazolium ligands

Article abstract of DOI:10.1039/b714892e

A series of 1-(2-diphenylphosphinoferrocenyl)ethyl-3-substituted imidazolium iodides [3-substituent = methyl (1a); isopropyl (1b); tert-butyl (1c); 1-adenosyl (1d); cyclohexyl (1e); 2,6-dimethylphenyl (1f); 2,4,6-trimethylphenyl (1g); 2,6-diisopropylphenyl (1h)] have been prepared and evaluated as ligands in the palladium-catalyzed aminations of aryl halides with various amines. The scope of the coupling process was carried out for various aryl bromides and chlorides with the catalysts generated in situ from a mixture of Pd(OAc)₂ and 1 in the presence of a base. NaO^tBu was found the choice of base in combination with dioxane, toluene, or DME as solvent, although NaOH or Cs₂CO₃ promoted the coupling of 4-bromotoluene with morpholine in moderate conversion. The steric hindrance from the 3-substituent of imidazolium in the hybrid-bidentate chelating system was found to be only beneficial to the substrates without ortho-substituents. The more sterically hindered 1d or 1h promoted the coupling of bromobenzene with morpholine in nearly quantitative conversion with 0.2 mol% of palladium loading in the presence of NaO^tBu at 110°C, and 94% of conversion was afforded with the less sterical demanding 1a for a longer time. However, for the substrates with ortho-substituents, higher conversions were achieved with 1a. The Pd(OAc)₂/1d catalytic system was also active for deactivated aryl chloride, and 71% isolated yield for the desired product was realized for coupling of 4-chloroanisole with morpholine at 2 mol% of catalyst loading. The developed catalyst system has been applied successfully to the synthesis of a key building block for a type of functional polymers. The Royal Society of Chemistry.

Full text of DOI:10.1039/b714892e

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www.rsc.org/dalton | Dalton Transactions
Palladium-catalyzed aminations of aryl halides with phosphine-functionalized
imidazolium ligands†
Ji-cheng Shi,*a,b Pengyu Yang,b Qingsong Tonga and Li Jiaa
Received 27th September 2007, Accepted 21st November 2007
First published as an Advance Article on the web 14th December 2007
DOI: 10.1039/b714892e
A series of 1-(2-diphenylphosphinoferrocenyl)ethyl-3-substituted imidazolium iodides [3-substituent =
methyl (1a); isopropyl (1b); tert-butyl (1c); 1-adenosyl (1d); cyclohexyl (1e); 2,6-dimethylphenyl (1f);
2,4,6-trimethylphenyl (1g); 2,6-diisopropylphenyl (1h)] have been prepared and evaluated as ligands in
the palladium-catalyzed aminations of aryl halides with various amines. The scope of the coupling
process was carried out for various aryl bromides and chlorides with the catalysts generated in situ from
a mixture of Pd(OAc)2 and 1 in the presence of a base. NaOtBu was found the choice of base in
combination with dioxane, toluene, or DME as solvent, although NaOH or Cs2CO3 promoted the
coupling of 4-bromotoluene with morpholine in moderate conversion. The steric hindrance from the
3-substituent of imidazolium in the hybrid-bidentate chelating system was found to be only beneficial to
the substrates without ortho-substituents. The more sterically hindered 1d or 1h promoted the coupling
of bromobenzene with morpholine in nearly quantitative conversion with 0.2 mol% of palladium
loading in the presence of NaOtBu at 110 ◦C, and 94% of conversion was afforded with the less sterical
demanding 1a for a longer time. However, for the substrates with ortho-substituents, higher conversions
were achieved with 1a. The Pd(OAc)2/1d catalytic system was also active for deactivated aryl chloride,
and 71% isolated yield for the desired product was realized for coupling of 4-chloroanisole with
morpholine at 2 mol% of catalyst loading. The developed catalyst system has been applied successfully
to the synthesis of a key building block for a type of functional polymers.
the stability of the catalyst which may exclude the side pathway of
Introduction
b-H elimination. Hybrid bidentate phosphine/NHC ligands have
been explored in the Heck6g and the Suzuki–Miyaura6h reactions
and found to be effective.
Recently, the chemistry of N-heterocyclic carbenes (NHCs) and
their transition-metal complexes has received much attention
because these carbenes impact significantly on the catalytic
performances of their ligating complexes for several organic
transformations.1 Exploring various NHCs as supporting ligands
in transition-metal catalyzed reactions,2 including asymmetric
syntheses,3 has been one of the current focuses in catalysis.
For palladium-catalyzed cross-coupling reactions, monodentate
NHCs with high steric demands as supporting ligands have
allowed to employ deactivated aryl chlorides as substrates under
mild reaction conditions.4 The large steric demand of monodentate
NHCs realises the possibility of a 12-electron Pd(0) species as a
genuine catalyst and the readily available coordination sites of
such a 12-e species greatly facilitates the oxidative addition of
palladium to aryl chlorides. After oxidative addition of the 12e
species with aryl halides, the catalytic species in the following
steps should involve three-coordinate palladium complexes which
are believed to be beneficial for reductive elimination.5 Bidentate
ligands containing NHCs have found widespread applications.6
Theoretical calculations indicated that certain bidentate chelating
ligands could favor the oxidative-addition process7 and improve
In the palladium-catalyzed cross-coupling, the optimal bite
angle (ca. 102◦) induced by the chelating ligand plays a crucial role
on the activity and selectivity.8 Chung and co-workers found that
the bite angle of an NHC/phosphine Rh complex derived from
1-(2-diphenylphosphinoferrocen◦yl)ethyl-3-methylimidazolium io-
dide (1a, see Scheme 1) is 97.2 .9 This value of the bite angle,
close to 102◦, has prompted us to evaluate the performance of
this type of diphenylphosphinoferrocenyl-functionalized NHCs
in palladium-catalyzed Suzuki–Miyaura cross-coupling reactions.
The Pd(OAc)2/1d catalyst system exhibits high efficiency and
stability, indicated by the up to 20 000 turnover numbers (TONs)
for coupling 4-bromotoluene with phenylboronic acid.10
aCollege of Chemistry and Materials Science, Fujian Normal University,
Fuzhou, 350007, China. E-mail: jchshi@fjnu.edu.cn
bDalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian,
Liaoning, 116023, China
† Electronic supplementary information (ESI) available: Experimental
procedures and spectroscopic details for characterization of compounds.
See DOI: 10.1039/b714892e
Scheme 1 Phosphine-functionalized imidazolium salts 1.
938 | Dalton Trans., 2008, 938–945
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The N-aryl moiety is often observed in natural products and
pharmaceutical and medicinal compounds,11 as well as being an
important functional unit in materials.12 Remarkable advances
have been achieved in palladium-catalyzed aminations of aryl
halides or halide equivalents.13 Since the phosphine-functionalized
imidazolium salts 1 have been effective in the palladium-catalyzed
Suzuki–Miyaura reaction,10 it would be of interest to explore
their potential in the aminations of aryl halides. There have
been no reports applying phosphine-functionalized N-heterocyclic
carbenes in palladium-catalyzed amination reactions so far.
Scheme 2 Synthesis of complexes 3.
in complexes 3f and 3h, indicating the successful deprotonation of
the salts into the carbenes. The HRMS data for 3f and 3h were in
good agreement with their elemental compositions and suggested
that they are monomeric palladium complexes.
Results and discussion
Since the isolated yields for the palladium complexes are
moderate and their activities for Suzuki–Miyaura cross-coupling
reactions were found to be comparable to those generated in situ,10
we decided to take advantage of generating the catalysts in situ in
evaluating their catalytic performance.
Preparation of phosphinoferrocenyl-functionalized imidazolium
salts
Sinc◦e the bite angle of the rhodium(I) complex derived from 1a is
97.2 ,9 it is reasonable to predict the bite angle of the palladium(II)
complex derived from 1 would be close to this value since
they are both d8 with square-planar structure. Steric hindrance
around the palladium center contributes to the catalytic activity
when using unactivated aryl chlorides as substrates.4 However,
the rigid steric bulkiness may disfavor the couplings between
the substrates with ortho-substituents. Recently, Glorius and co-
workers introduced the notion of the flexible steric bulkiness,
which could be varied: to be large to meet steric hindrance
required for the high activity of catalyst; to be small to favor
the couplings with sterically hindered substrates.4b Therefore,
a series of 1-(2-diphenylphosphinoferrocenyl)ethyl-3-substituted
imidazolium iodides with different size of 3-substituents were
synthesized to reveal steric effects in the hybrid phosphine/NHC
system for palladium-catalyzed amination. From the readily
available racemic ferrocenyl derivative 2 the desired phosphine-
functionalized imidazolium salts 1 were prepared via the substitu-
tion reaction of the OAc group with imidazoles in 79–87% yields
(Scheme 1). The imidazolium salts, which are stable under nitrogen
Effect of the base on the amination of 4-bromotoluene with
morpholine
A survey of bases for the palladium-catalyzed amination of 4-
bromotoluene with morpholine using 1d as ligand, which shows
high activity combined with Pd(OAc)2 for Suzuku–Miyaura cross-
couplings,10 is provided in Table 1. The catalytic reactions were
all set up on the benchtop and the solid components were
weighed in the air. Cs2CO3, which is a highly effective base
for the Pd(OAc)2/1d-catalyzed Suzuki–Miyaura coupling of aryl
bromides with phenylboronic acid, showed moderate activity for
amination of 4-bromotoluene and morpholine (Table 1, entry 1).
A remarkable increasing in activity was observed with NaOtBu as
base: >99% conversion of 4-bromotoluene with 94% isolated yield
◦
was achieved within 1 h with 1 mol% catalyst loading at 110 C
(Table 1, entry 2). The performances of NaOH and K3PO4 as bases
for the phosphine-functionalized NHC ligands are also moderate,
1
but slowly oxidized in air in solution, were characterized by H,
Table 1 Effect of the base on the rate of the Pd(OAc)2/1d catalyzed
13C and 31P NMR spectroscopy and HRMS or elemental analysis.
aminations of 4-bromotoluene with morpholinea
1
A singlet 31P{ H} NMR peak observed around d −26 for 1 is
expected for diphenylferrocenylphosphines and consistent with
the known compound 1a.9 The carbenic protons of 1 observed in
the range of d 9.2–10.2 reflect the high acidity of the 2-proton of
the imidazolium ions.
Syntheses of phosphine/NHC palladium complexes
The free carbene route has been used to prepare the phos-
phine/NHC rhodium complex derived from the imidazolium salt
1a.9 We then tried another protocol to enrich the coordination
chemistry of the phosphine/NHC bidentate ligands, e.g. the silver
carbene transfer path, to attain the square-planar complex.14
Treating the salt 1f or 1h with half of equiv. of Ag2O in
dichloromethane for 2 h at room temperature, and then adding
Pd(NCMe)2Cl2 directly to the mixture led to the palladium
complexes 3f and 3h in 34 and 41% yields, respectively (Scheme 2).
Entry
Base
t/h
Yieldb (%)
1
2
3c
4
5
6
7
Cs2CO3
NaOtBu
NaOtBu
K2CO3
NaOH
K3PO4
KF
16
1
2
16
16
16
16
32 (22)
99 (94)
99 (93)
18
41 (28)
30
<5
1
Compared to the ligand, the 31P{ H} NMR peaks for 3f and 3h
a General conditions: 5 mmol of 4-bromotoluene, 1.2 equiv. of morpholine,
1.5 equiv. of base, 10 mL of dioxane, 1 mol% of Pd(OAc)2/1d (1 : 1). b GLC
conversion calibrated via internal standard. Isolated yields in parentheses.
c Toluene used as solvent.
were shifted downfield to d 8.0 and 7.7, respectively, as expected
1
upon metal coordination. The H NMR signals at d 9.91 and
10.22 for H-2 of imidazolium 1f and 1h, respectively, disappeared
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Table 3 Comparison of the catalysts generated in situ with isolated
and other inorganic bases such as K2CO3 and KF resulted in
lower yields. The choice of base for the hybrid phosphine/NHC
as ligand in the palladium-catalyzed aminations of aryl halides is
consistent with literature work on other ligands such as bidentate
phosphines,15 monodentate phosphines,16 and mono-NHCs.4,17
samples for the amination of 4-bromotoluene with morphinea
Entry
Catalyst
t/h
Yieldb (%)
1
2
3
4
Pd(OAc)2/1fc
24
16
12
12
98 (93)
>99 (94)
>99 (95)
>99 (97)
Pd(OAc)2/1hc
3f
3h
Influence of the imidazolium salts on the amination of
bromobenzene with morpholine
a General conditions: 5 mmol of 4-bromotoluene, 1.2 equiv. of morpholine,
1.5 equiv. of NaOtBu, 10 mL of dioxane, 0.2 mol% of catalyst. b GLC
conversion calibrated via internal standard. Isolated yields in parentheses.
c Pd(OAc)2/1 (1 : 1).
An investigation of the activity of the synthesized phosphine-
functionalized imidazolium salts was carried out with NaOtBu
as base and Pd(OAc)2 as palladium source at 110 ◦C. Since 1
mol% of palladium loading resulted in complete conversion of
4-bromotoluene in the amination with morpholine within 1 h,
catalyst loading was decreased to 0.2 mol% for differentiating
the substituent size effects. The results are summarized in Table 2.
The phosphine-functionalized imidazolium salts 1 are comparably
effective ligands in the above reaction conditions for amination
of bromobenzene with morpholine, although 1c, 1d, 1g and
1h are a little better. The results indicate: (1) the large bite
angle created by the ferrocenyl backbone and the electronic
properties of the coordinating atoms play an importance role in
the catalytic performance of the hybrid phosphine/NHC systems
1 as supporting ligands for the palladium-catalyzed coupling of
4-bromobenzene with morpholine; (2) high steric demand of the
system 1 also benefits the aminations of the aryl bromides without
ortho-substituents such as 4-bromotoluene or bromobenzene with
morpholine in a minor way. Herein it should pointed out that
much better results have been obtained so far by the groups of
Hartwig,15 Buchwald,17 Beller,5a Nolan,18 etc.
with the catalysts generated in situ for the aminations of aryl
bromides with amines. Two steps are needed for preparing the
complexes 3 with moderate isolated yields, so further evaluation
of the synthesized phosphine/NHC system as supporting ligands
was carried out with the advantage of generating catalysts in situ.
Extended scope and application of aminations of aryl bromides
As shown in Table 4, the procedure employing the catalyst system
Pd(OAc)2/1d is effective in aminations of aryl bromides with
various amines. For amination of bromobenzene with morpholine
the catalyst loading could be further decreased to 0.1 mol% and
the reaction was complete within 24 h with 95% isolated yield
for the desired product (Table 4, entry 2). The catalyst system
Pd(OAc)2/1d is also applicable to heteroaryl bromides. Using
2-bromopyridine and morpholine as substrates leads to a 94%
isolated yield at 0.2% loading of catalyst (entry 10). The weakly
binding effect from heterocyclic nitrogen to depress the coupling
reactions was not observed for the catalyst system Pd(OAc)2/1d
as well for another case (entry 11).18 The catalytic system is very
effective for cyclic secondary amines: deactivated aryl bromide
could be used as substrate (entry 9) and double arylation of
piperazine could be achieved with an excess of aryl bromide
(entry 6) in 88% yield at 0.5 mol% loading of catalyst. Entry
5 shows the catalyst system could couple an acyclic secondary
amine with an aryl bromide in high yield. Primary alkylamine
coupling with aryl bromide required a longer time, but 83–87%
yields of the desired products were still realized with 2 equiv. of
amines and at 1 mol% loading of catalyst (entries 7 and 8). The
catalyst system Pd(OAc)2/1d is not suitable for coupling aniline
with aryl bromides. The supporting ligand 1d is effective, however,
in combination with Pd2(dba)3 at higher reaction temperature and
1% loading of catalyst (entries 12 and 13).
Amination with the prepared palladium complexes
Although no differences were observed for palladium-catalyzed
Suzuki–Miyaura cross-coupling reactions using the catalysts gen-
erated in situ or the prepared palladium complexes 3,10 we were
still interested in the situation in the Hartwig–Buchwald amination
reactions. Under the same reaction conditions as indicated above,
the amination of 4-bromotoluene with morpholine with the
palladium complexes was complete in 12 h (Table 3, entries 3 and
4). Considering the induction time and the probable experimental
error, the prepared palladium complexes 3 are also comparable
Table 2 Influence of imidazolium salts on Pd(OAc)2-catalyzed amination
of 4-bromotoluene with morpholinea
Entry
Ligand
t/h
Yieldb (%)
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
1g
1h
1d
1d
24
24
16
16
24
24
16
16
16
18
94 (88)
96 (89)
99 (93)
99 (96)
96 (91)
98 (93)
99 (95)
99 (94)
99 (94)
98 (92)
Aminations of aryl chlorides
Aryl chlorides are attractive coupling partners because they are
widely available and inexpensive. With the optimal conditions for
amination of aryl bromides, the catalyst systems were tested using
aryl chlorides with morpholine. 2-Chloropyridine couples with
morpholine smoothly in 94% yield in 16 h at 1 mol% of loading
of Pd(OAc)2/1d (Table 5, entry 4). Activated aryl chloride as
substrate leads to a 87% isolated yield (entry 3). This system is
also applicable to deactivated aryl chlorides in higher (2 mol%)
catalyst loading and only minimal dehalogenation products were
observed. However, no activity of the present system was found
8
9c
10d
a General conditions: 5 mmol of bromobenzene, 1.2 equiv. of morpholine,
1.5 equiv. of NaOtBu, 10 mL of dioxane, 0.2 mol% of Pd(OAc)2/1 (1 :
1). b GLC conversion calibrated via internal standard. Isolated yields in
parentheses. c Toluene used as solvent. d DME used as solvent.
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Table 4 Pd(OAc)2/1d-catalyzed aminations of aryl bromides with aminesa
Entry
1
ArBr
Amine
Product
Pd (mol%)
0.2
t/h
Yield (%)
96
6
2
4
5
6
0.1
0.5
0.5
0.5
24
6
95
93
92
88
6
6
7
1
16
87a
8
9
1b
1
16
16
16
83
89
94
10
1
11
0.2
16
71
12
13
2b
2b
24c
24c
58
70
a General conditions: 1 mmol of ArBr; 1.2 equiv. of amine; 1.5 equiv. of NaOtBu; 2 mL of dioxane; Pd(OAc)2/1d (1 : 1), 110 ◦C (oil bath). b Pd2(dba)3 was
used as the palladium source; toluene as solvent. c 120 ◦C.
for aryl tosylates as an aryl halide equivalent or for indole and
imidazole as amine (data not shown).
flexible steric demand has been introduced in the ligand design for
coupling reactions.4b We suspect that the effect from the steric re-
pulsion becomes more obvious in the chelating system and carried
out experiments to compare the catalytic performance between the
ligand 1a with the smallest 3-substituent and 1d with the largest
one for palladium-catalyzed aminations of ortho-substituted aryl
halides. Table 6 shows that the performance of 1d is indeed worse
than that of 1a. In the case of aryl bromide with two ortho-
substituents, the effect becomes more profound (Table 6, entry 4).
Aminations of aryl halides with ortho-substituents
For the present phosphine/NHC chelating ligands, it has been
found that increasing steric demand of substituents on the
imidazole provides little benefit for the catalytic activities of their
supported palladium catalysts for coupling the aryl bromides with-
out ortho-substituents such as 4-bromotoluene and bromobenzene
with morpholine. The bite angles and election character of the
ligating atoms are likely the major factors for the catalytic activity.
For coupling aryl halides with ortho-substituents, the steric
demand of ligands may retard reaction owing to steric repulsion
between the substrate and the catalyst. Therefore a notion of a
Synthesis of a building block
Aryl piperazines are an important type of medicinal compounds
and have been pursued through palladium-catalyzed amination
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Table 5 Pd(OAc)2/1d-catalyzed amination of aryl chlorides with morphinea
Entry
1b
ArCl
Product
Pd (mol%)
2
T/◦C
t/h
Yield (%)
79c
120
24
2b
3
2
1
1
120
110
110
24
16
16
71d
87
4
94
a General conditions: 1 mmol of ArCl; 1.2 mmol of morphine; 1.5 mmol of NaOtBu; 2 mL of dioxane; Pd/1d (1 : 1). b 1.5 Equiv. of amine; 2.0 equiv. of
NaOtBu. c Pd2(dba)3 was used as the palladium source; toluene as solvent. d 2% of the dehalogenation product was observed.
Table 6 Palladium catalyzed amination aryl halides with ortho-substituents with supporting ligands 1a and 1da
Entry
1
ArX
Product
Ligand
Yield b,c (%)
1a
1d
>99 (93)
96 (91)
2
3
4
1a
1d
>99 (91)
91 (87)
1a
1d
>99 (90)
83 (81)
1a
1d
84 (72)
62 (46)
5
6
1a
1d
>99 (90)
94 (83)
1a
1d
>99 (89)
97 (84)
a General conditions: 1 mmol of ArX; 1.2 equiv. of amine; 1.5 equiv. of NaOtBu; 2 mL of dioxane; 2 mol% Pd(OAc)2; Pd(OAc)2/1 (1 : 1); 16 h; 110 ◦C.
b GLC conversion calibrated via internal standard. Isolated yield in parentheses. c Around 3% of the dehalogenation product was observed.
reactions.19 The present catalytic system is effective for preparing
aryl piperazines. We are pursuing a new type of imidazoliun
polymer and have designed the building block 5. Imidazolium
salts are important compounds as ligands and reaction media.
The ratio of aryl bromide to piperazine determines the
mono- or di-arylation of piperazine (see Scheme 3). We were
pleased that the present catalyst system worked well to reach the
building block in 78% yield with 0.5 mol% of catalyst loading.
942 | Dalton Trans., 2008, 938–945
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Scheme 3 Arylation of piperazine.
together with NaI (3.0 mmol, 450 mg) in ethanol (10 mL) and
the mixture was stirred at 25 ◦C for 4 h. After evaporating the
solvent the crude product was chromatographed on a silica gel
column by a eluting first with hexane–ethyl acetate (5 : 1), then
with CH2Cl2–MeOH (95 : 5) to give a orange solid (529 mg, 87%
Conclusions
In summary, diphenylferrocenylphospine-functionalized imida-
zolium salts are effective ligands for palladium-catalyzed Hartwig–
Buchwald aminations involving aryl bromides and aryl chlorides.
The Pd(OAc)2–1–NaOtBu system was found to be very efficient
for amination of aryl bromides with a variety of primary and
secondary cyclic and acyclic alkyl amines. The bulkiness of the 3-
substituents on the imidazole-ring of the hybrid phosphine/NHC
chelating ligands was found to benefit the coupling of aryl
halides without ortho-substituents, but retard those with ortho-
substituents. This is an interesting clarification for palladium-
catalyzed coupling reactions supported by chelating ligands. The
developed system has been successfully applied to the synthesis of
a new building block for a functional polymer.
1
yield). H NMR (400 MHz, CDCl3): d 1.31 (t, J = 7.6 Hz, 6H),
2.07 (d, J = 7.2 Hz, 3H), 3.89 (s, 1H), 4.01 (s, 5H), 4.42–4.47 (m,
2H), 4.96 (s, 1H), 5.99–6.02 (m, 1H), 6.69–6.75 (m, 3H), 6.87 (s,
1H), 6.99–7.08 (m, 3H), 7.31–7.42 (m, 5H), 9.59 (s, 1H). 31P NMR
(162 MHz, CDCl3): d −27.7 (s). 13C NMR (100 MHz, CDCl3): d
21.5, 22.4, 22.7, 29.5, 52.7, 56.2, 56.3, 70.0, 70.2, 70.9, 72.7, 90.1,
118.3, 119.5, 128.0, 128.2, 128.3, 129.6, 131.4, 131.6, 134.2, 134.7,
134.9, 135.5, 138.8. HRMS (ESI) m/z: calc. for C30H32FeN2P:
507.1652 [M+ − I]; found: 507.1646.
3-(tert-Butyl)-1-[(2-diphenylphosphinoferrocenyl)ethyl]-3H-imida-
1
zolium iodide (1c). Yield: 81%. H NMR (400 MHz, CDCl3):
Experimental
d 1.36 (s, 9H), 2.14 (d, J = 2.5 Hz, 3H), 3.98 (s, 1H), 4.04 (s,
5H), 4.54 (s, 1H), 5.04 (s, 1H), 6.23 (m, 1H), 6.75 (m, 2H), 6.85
(s, 1H), 7.05–7.13 (m, 4H), 7.37–7.41 (m, 3H), 7.47 (s, 2H), 9.52
(s, 1H). 31P NMR (162 MHz, CDCl3): d −25.7 (s). 13C NMR
(100 MHz, CDCl3): d 21.4, 29.7, 56.1, 60.2, 70.3, 70.8, 71.1, 72.8,
90.1, 90.4, 118.9, 119.5, 128.2, 128.3, 129.9, 131.2, 131.4, 133.5,
134.9, 135.1. Anal. Calc. for C31H34FeIN2P: C, 57.43; H, 5.28; N,
4.32. Found: C, 57.21; H, 5.66; N, 3.88%. HRMS (ESI) m/z: calc.
for C31H34FeN2P: 521.1809 [M+ − I]; found: 521.1804.
General considerations
All amines, aryl bromides and chlorides (Aldrich or Acros) were
used as received. 3-Methyl-1-[(2-diphenylphosphinoferrocenyl)-
ethyl]-3H-imidazolium iodide (1a) was prepared accord-
ing to the literature method.9 Palladium acetate and tris-
(dibenzylideneactone)dipalladium(0) were purchased from Strem
Chemical Company. 1,4-Dioxane, toluene and THF were distilled
under nitrogen from sodium benzophenone ketyl prior to use.
Cs2CO3, K2CO3, KF, NaOBut, K3PO4 and NaOH were used as
received. All reactions and manipulations involving air- and/or
moisture-sensitive compounds were carried out using standard
Schlenk techniques under nitrogen. NMR spectra were recorded
on a BRUKER DRX 400 MHz or Varian INOVA 400 MHz (1H
400 MHz; 13C 100 MHz; 31P 162 MHz) spectrometers. Elemental
analyses were obtained on an Elementar Vario EI analyzer.
High-resolution mass spectra (HRMS, ESI) were obtained on a
Micromass Q-Tof Micro (Micromass Inc., Manchester, England).
3-(1-Admantyl)-1-[(2-diphenylphosphinoferrocenyl)ethyl]-3H-
imidazolium iodide (1d). Yield: 82%. 1H NMR (400 MHz,
CDCl3): d 1.62 (s, 6H), 1.79 (s, 6H), 2.13 (d, J = 7.2 Hz, 6H),
3.94 (s, 1H), 4.01 (s, 5H), 4.49 (s, 1H), 4.98 (s, 1H), 6.16 (m, 1H),
6.70 (t, J = 7.0 Hz, 2H), 6.96 (s, 1H), 7.02–7.09 (m, 4H), 7.34–7.36
(m, 3H), 7.44–7.47 (m, 3H), 9.32 (s, 1H). 31P NMR (162 MHz,
CDCl3): d −26.75 (s). 13C NMR (100 MHz, CDCl3): d 21.3, 29.2,
35.1, 42.0, 56.2, 60.3, 70.1, 70.3, 72.7, 90.6, 117.9, 119.3, 128.0,
128.1, 128.3, 129.8, 131.2, 131.4, 133.0, 135.0, 135.2. HRMS (ESI)
m/z: calc. for C37H40FeN2P: 599.2279 [M+ − I]; found: 599.2272.
Synthesis
3-(Isopropyl)-1-[(2-diphenylphosphinoferrocenyl)ethyl]-3H-imida-
zolium iodide (1b). Representative procedure: Under nitrogen,
6.0 mL of CH3CN and 3.0 mL of H2O was added to a Schlenk
tube charged with racemic PPFOAc 2 (1.2 mmol, 550 mg)
and 1-methyl-1H-imidazole (1.5 mmol, 186 mg). The mixture
was allowed to stir at 25 ◦C for 3 days to give a clear orange
solution. After addition of benzene (10 mL) the organic phase was
separated and concentrated in vacuum. The residue was dissolved
3-(2,6-Dimethylphenyl)-1-[(2-diphenylphosphinoferrocenyl)ethyl]-
3H-imidazolium iodide (1f). Yield: 85%. H NMR (400 MHz,
1
CDCl3): d 1.96 (s, 6H), 2.15 (d, J = 7.2 Hz, 3H), 3.90 (s, 5H), 4.13
(s, 1H), 4.51 (s, 1H), 4.95 (s, 1H), 6.56 (m, 1H), 6.72–6.77 (m, 3H),
6.99–7.01 (m, 5H), 7.11–7.17 (m, 3H), 7.30–7.32 (m, 3H), 7.52
(t, J = 7.2 Hz, 2H), 9.91 (s, 1H). 31P NMR (162 MHz, CDCl3):
d −26.9 (s). HRMS (ESI) m/z: calc. for C35H34FeN2P: 569.1809
[M+ − I]; found: 569.1801.
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3-(2,4,6-Trimethylphenyl)-1-[(2-diphenylphosphinoferrocenyl)-
ethyl]-3H-imidazolium iodide (1g). Yield: 84%. 1H NMR
(400 MHz, CDCl3): d 1.96 (s, 6H), 2.15 (d, J = 7.2 Hz, 3H),
4.04 (s, 5H), 4.25 (s, 1H), 4.67 (s, 1H), 5.15 (s, 1H), 6.68–6.93 (m,
5H), 7.11–7.17 (m, 3H), 7.44–7.46 (m, 3H), 7.68 (t, J = 7.2 Hz,
2H), 10.08 (s, 1H). 31P NMR (162 MHz, CDCl3): d −25.7 (s).
HRMS (ESI) m/z: calc. for C36H34FeN2P: 583.1966 [M+ − I];
found: 583.1970.
under nitrogen. The mixture was stirred at 50 ◦C for 0.5 h.
After cooling to room temperature, the aryl halide and amine
were added, and the vial was placed in an oil bath. The reaction
was monitored by GLC. After cooling to room temperature, the
reaction mixture was filtered through a layer of Celite with the aid
of ethyl acetate. The filtrate was concentrated in vacuum and the
crude product was purified chromatographically and the products
were identified by 1H NMR.
3-(2,6-Diisopropylphenyl)-1-[(2-diphenylphosphinoferrocenyl)-
ethyl]-3H-imidazolium iodide (1h). Yield: 80%. 1H NMR
(400 MHz, CDCl3): d 0.72 (d, J = 6.4 Hz, 3H), 0.97 (d, J =
6.8 Hz, 3H), 1.07 (d, J = 6.8 Hz, 3H), 1.22 (d, J = 6.8 Hz,
3H), 1.68 (sept, J = 6.6 Hz, 1H), 2.07 (sept, J = 6.8 Hz, 1H),
2.21 (d, J = 6.4 Hz, 3H), 3.92 (s, 5H), 4.21 (s, 1H), 4.56 (s, 1H),
5.01 (s, 1H), 6.78–6.84 (m, 4H), 7.11–7.27 (m, 6H), 7.41–7.45 (m,
4H), 7.69 (m, 2H), 10.22 (s, 1H). 31P NMR (162 MHz, CDCl3): d
−25.5 (s). 13C NMR (100 MHz, CDCl3): d 22.9, 23.6, 24.0, 24.2,
24.6, 28.0, 28.2, 28.5, 56.5, 69.7, 70.4, 71.3, 73.4, 89.3, 89.6, 120.3,
123.6, 124.3, 124.4, 127.3, 127.8, 128.2, 129.7, 131.1, 131.2, 131.5,
135.4, 135.6, 136.2, 137.3, 140.7, 145.1. HRMS (ESI) m/z: calc.
for C39H42FeN2P: 625.2435 [M+ − I]; found: 625.2429.
Acknowledgements
The National Natural Science Foundation of China (20473089),
and Fujian Normal University are gratefully acknowledged for
support of this research.
Notes and references
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Synthesis of the palladium complex 3f. The imidazolium salt 1f
(320 mg, 0.46 mmol) and Ag2O (63.6 mg, 0.27 mmol) suspended in
CH2Cl2 solution (20 mL) was stirred for 2 h at room temperature.
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1
MeOH (95 : 5) to give an orange solid (117 mg, 34% yield). H
NMR (400 MHz, CD2Cl2): d 1.97 (s, 3H), 2.08 (d, J = 6.8 Hz, 3H),
2.93 (dd, J1 = 6.8 Hz, J2 = 14.0 Hz, 1H), 3.66 (s, 5H), 4.04 (s, 1H),
4.31 (s, 1H), 4.42 (s, 1H), 4.60 (s, 1H), 6.23 (m, 1H), 6.75 (m, 2H),
6.85 (s, 1H), 6.54–7.29 (m, 8H), 7.41 (s, 3H), 7.50–7.55 (m, 2H),
7.91 (m, 2H). 31P NMR (162 MHz, CD2Cl2): d 8.0 (s). 13C NMR
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90.1, 90.4, 118.9, 119.5, 128.2, 128.3, 129.9, 131.2, 131.4, 133.5,
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N, 3.76. Found: C, 56.25; H, 4.66; N, 3.28%. HRMS (ESI) m/z:
calc. for C35H33ClFeN2PPd: 709.0454 [M+ − Cl]; found: 709.0480.
Synthesis of the palladium complex 3h. Yield: 41%. 1H NMR
(400 MHz, CD2Cl2): d 0.39 (d, J = 6.4 Hz, 3H), 0.58 (d, J =
6.8 Hz, 3H), 1.08 (d, J = 6.8 Hz, 3H), 1.37 (d, J = 6.8 Hz, 3H),
2.15–2.10 (m, 4H), 2.66 (m, 1H), 3.60 (s, 5H), 4.37 (s, 1H), 4.43
(s, 1H), 4.63 (s, 1H), 6.52 (m, 1H), 7.01–7.58 (m, 12H), 8.12–
8.17 (m, 2H). 31P NMR (162 MHz, CD2Cl2): d 7.7 (s). 13C NMR
(100 MHz, CD2Cl2): d 92.2, 115.0, 123.6, 124.4, 127.5, 127.6,
128.0, 128.1, 128.6, 129.7, 130.4, 130.6, 132.0, 134.5, 134.6, 135.4,
135.5, 135.7, 139.4, 143.9, 147.2, 157.6. HRMS (ESI) m/z: calc.
for C39H41ClFeN2PPd: 765.1080 [M+ − Cl]; found: 765.1089.
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944 | Dalton Trans., 2008, 938–945
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