Ruthenium(II)-(p-cymene)-N-Heterocyclic Carbene Complexes for the N-Alkylation of Amine Using the Green Hydrogen Borrowing Methodology

Article abstract of DOI:10.1002/ejic.201701479

Six ruthenium(II) complexes with the general molecular formula [RuCl₂(NHC)(η⁶-p-cymene)] (NHC = N-heterocyclic carbene) were synthesized by the transmetalation method from [RuCl₂(η⁶-p-cymene)]₂ and silver(I)-NHC complexes. All complexes were fully characterized by analytical and spectral methods (FT-IR, elemental analysis and ¹H and ¹³C NMR). The solid-state structure of one of the ruthenium complexes [dichloro-{1-[2-(2-ethoxyphenoxy)ethyl]-3-(3,5-dimethylbenzyl)benzimidazol-2-ylidene}(p-cymene) ruthenium(II)] has been established by single-crystal X-ray diffraction study, which revealed that the ruthenium atom adopt a classical piano-stool coordination geometry. Under the optimised conditions, these ruthenium complexes were found to be efficient catalysts for N-alkylation of aniline with arylmethyl alcohols using the hydrogen borrowing strategy, which is a cost-effective and environmentally attractive reaction for the preparation of N-alkylated amines.

Full text of DOI:10.1002/ejic.201701479

A Journal of
Accepted Article
Title: Ruthenium(II)-(p-cymene)-N-Heterocyclic Carbene Complexes
for the N-Alkylation of Amine Using the Green Hydrogen
Borrowing Methodology
Authors: İsmail Özdemir, Murat Kaloğlu, Nevin Gürbüz, and David
Semeril
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201701479
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10.1002/ejic.201701479
European Journal of Inorganic Chemistry
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Ruthenium(II)-(p-cymene)-N-Heterocyclic Carbene Complexes for
the N-Alkylation of Amine Using the Green Hydrogen Borrowing
Methodology
Murat Kaloğlu,[a,b] Nevin Gürbüz,[a,b] David Sémeril[c] and İsmail Özdemir*[a,b]
Dedication ((optional))
methods have been developed for the catalytically synthesis of
secondary or tertiary amines, including Buchwald-Hartwig [4],
Ullmann [5], hydroamination [6] and hydroaminovinylation [7]. In
this context, the creation of C-N bonds from primary or
secondary amines and alcohols as alkylating agent using the
“hydrogen borrowing” or “hydrogen auto-transfer” methodology
has more recently attracted attention (Figure 1b) [8]. In this one-
pot reaction, the alcohol is dehydrogenated in situ to give the
corresponding aldehyde or ketone by the catalyst, which
"borrows" hydrogen from the substrate. Subsequent
condensation with the amine and final rehydrogenation leads to
alkylated amine. This transformation is highly atom economical
and environmentally friendly, since water was produced as the
only by-product.
Abstract: Six ruthenium(II) complexes with the general molecular
formula [RuCl2(NHC)(η6-p-cymene)] (NHC = N-heterocyclic carbene)
were synthesized by the transmetalation method from [RuCl2(η6-p-
cymene)]2 and silver(I)-NHC complexes. All complexes were fully
characterized by analytical and spectral methods (FT-IR, elemental
1
analysis and H and 13C NMR). The solid-state structure of one of
the ruthenium complexes {dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-
(3,5-dimethylbenzyl)benzimidazol-2-ylidene](p-cymene)
ruthenium(II)} has been established by single-crystal X-ray diffraction
study, which revealed that the ruthenium atom adopt a classical
piano-stool coordination geometry. Under the optimised conditions,
these ruthenium complexes were found to be efficient catalysts for
N-alkylation of aniline with arylmethyl alcohols using the hydrogen
borrowing strategy, which is a cost-effective and environmentally
attractive reaction for the preparation of N-alkylated amines.
Introduction
Alkyl amines are widely used in both the bulk and fine chemical
industries as biologically active compounds, agrochemicals,
functionalized materials and dyes [1]. Due to the importance of
these products, alkylation of primary amines to secondary or
tertiary amines is one of the most fundamental and important
reactions in organic chemistry [2]. Alkylated amines are
traditionally synthesized by using alkylating agents, such as alkyl
halides in the presence of stoichiometric amounts of inorganic
bases. However, these procedures are often associated with
environmental problems, such as the toxic nature of alkylating
agents. In addition, these reactions generate equimolar amounts
of wasteful salts as by-products (Figure 1a) [3]. Thus, valuable
Figure 1. (a) Traditional approach using alkyl halides and (b) hydrogen
borrowing strategy for C-N bond formation.
[a] Department of Chemistry, Faculty of Science and Art, İnönü University,
44280 Malatya, Turkey
E-mail: ismail.ozdemir@inonu.edu.tr
https://www.inonu.edu.tr/
At the beginning of the 1980s, pioneering reports dealing
with the rhodium and ruthenium catalysed N-alkylation of amines
by alcohols were described independently by the groups of
Grigg ([RhH(PPh3)4]) [9], Watanabe ([RuCl2(PPh3)3]) [10] and
[b] Catalysis Research and Application Center, İnönü University.
44280 Malatya, Turkey
[c] Laboratoire de Chimie Inorganique Moléculaire et Catalyse, Institut de
Chimie UMR 7177 CNRS, Université de Strasbourg, 4 rue Blaise
Pascal,
Murahashi
([RuH2(PPh3)4])
[11].
These
first
reports
67008 Strasbourg cedex, France
demonstrated that noble metals such as rhodium, ruthenium
could catalyse the hydrogen borrowing reaction, but with a lack
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201701479
European Journal of Inorganic Chemistry
FULL PAPER
of selectivity, formation of both secondary and tertiary amines,
due to the harsh catalytic conditions. Then new catalysts were
developed to carry out this reaction under milder conditions,
especially lower temperature [12]. Recent of applications
catalysed by mainly ruthenium- or iridium-based complexes
have been described by the groups of Williams [13], Fujita [14],
Crabtree [15], Peris [16], Beller [17], Zhao [18], Wang [19],and
from other groups [20].
Results and Discussion
Preparation of Ruthenium(II) Complexes
The synthesis of ruthenium complexes 1a-f required that of the
benzimidazolium salts 3a-f, respectively (Scheme 1). The two
new benzimidazolium salts 3a and 3b were obtained by
alkylation (RBr; R = CH2-C6H3-3,5-(CH3)2 and CH2-C6-(CH3)5) of
benzimidazole 2 in 87 and 83 % isolated yield, respectively. The
salts 3a and 3b were fully characterised by elemental analysis,
1H and 13C NMR and infrared spectroscopies (Table 1). The FT-
IR spectra of the free ligands showed a broad band at 1572 and
1556 cm-1, which corresponds to the -C=N- bond vibration of 3a
and 3b, respectively. The signal of the NCHN proton appears in
the expected range, at  = 11.42 and 10.33 ppm for 3a and 3b,
respectively. Their 13C NMR spectra display the characteristic
singlet at 143.1 and 142.1 ppm for the NCHN carbon for 3a and
3b, respectively [24, 25]. The silver complexes 4a and 4b were
synthesized according to the general method described by
Wang and Lin [26] by reacting the corresponding
benzimidazolium salts with Ag2O in dichloromethane under dark
condition at room temperature for 24 h. The spectroscopic data
are similar to those found for other silver(I)-NHC complexes [24,
27]. The two silver(I) complexes exhibit a characteristic v(NCN)
band at 1442 and 1451 cm-1 for 4a and 4b, respectively. In their
1H NMR spectra, the NCHN protons were disappeared upon
complexation with silver. As previously mentioned by several
authors [28], the Ag-C atom was not observed by 13C NMR
spectroscopy in complexes 4a and 4b. Note that,
benzimidazolium salts 3c-f and their corresponding silver
complexes 4c-f were conveniently prepared according to a
method reported earlier [24].
Over the last 20 years, N-heterocyclic carbenes (NHCs)
have become an ubiquitous alternative to phosphine ligands in
homogeneous catalysis [21] in particularly in association with
ruthenium salts [22], which have been reported to be active
catalysts for the N-alkylation of amines with alcohols by
hydrogen borrowing strategy [23].
In a recent study we have reported the synthesis of
benzimidazolium salts and their silver(I) complexes, which were
tested as potential antimicrobial agents [24]. In the present
article, we now described the synthesis and characterization of
two benzimidazolium salts and six novel ruthenium(II)
complexes of the general formula [RuCl2(NHC)(η6-p-cymene)]
1a-f (Figure 2). These complexes were tested in N-alkylation of
aniline with arylmethyl alcohols using the hydrogen borrowing
strategy.
The ruthenium(II) arene complexes 1a-f were obtained in
57-70 % yields by transmetalation of the corresponding silver
adducts 4a-f and [RuCl2(p-cymene)]2 (Scheme 1). The air- and
moisture-stable ruthenium complexes are brown in colour and
soluble in common chlorinated organic solvents. They are found
to be diamagnetic and they were fully characterised by
elemental analysis, 1H and 13C NMR and infrared spectroscopies
(Table 1). Their FT-IR data each show a band at 1450-1454 cm-1
(v(NCN)) and their 13C NMR spectra each display a singlet in the
range 189.9-191.5 ppm (NCN), two evidences of the formation
of a Ru-carbene bond [29].
Figure 2. Ruthenium complexes 1a-f synthesised and assessed in the present
study.
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10.1002/ejic.201701479
European Journal of Inorganic Chemistry
FULL PAPER
Scheme 1. Synthesis of ruthenium complexes 1a-f.
Table 1. Physical and spectroscopic properties of new compounds.
Compound
Formula
Isolated yield (%)
M.p. (oC)
v(CN) (cm-1)
H(2) 1H NMR (ppm)
C(2) 13C NMR (ppm)
3a
3b
4a
4b
1a
1b
1c
1d
1e
1f
C26H29BrN2O2
87
83
81
74
65
57
62
70
63
68
178-179
169-170
206-207
151-152
187-188
165-166
136-137
191-192
157-158
159-160
1572
1556
1442
1451
1452
1450
1452
1450
1454
1452
11.42
143.1
C29H35BrN2O2
10.33
142.1
C26H28AgBrN2O2
C29H34AgBrN2O2
C36H42RuCl2N2O2
C39H48RuCl2N2O2
C30H38RuCl2N2O3
C37H44RuCl2N2O2
C38H46RuCl2N2O2
C38H46RuCl2N2O2
-
-
-
-
-
-
-
-
not observed[a]
not observed[a]
191.2
189.9
190.6
190.2
189.9
191.5
[a] As previously reported by several groups [26], for compounds 4a and 4b, the characteristic C-Ag picks were not observed.
Structural Characterization of Complex 1a
Table 2. Selected bond lengths [Å] and angles [°] in complex 1aCHCl3.
The solid-state structure of the mononuclear ruthenium
complex 1a was established by a single-crystal X-ray diffraction
study (Figure 3 and Table 2). The complex crystallised with one
molecule of chloroform. The half-sandwich arene ruthenium(II)
complex adopts a classical piano-stool geometry with a typical
Ru-Ccarbene bond length (2.060(4) Å) [29].
Lengths [Å]
Angles [°]
C(1)-Ru(1)
Cl(1)-Ru(1)
Cl(2)-Ru(1)
C(1)-N(1)
C(1)-N(2)
C(8)-N(1)
C(17)-N(2)
2.060(4)
2.420(1)
2.429(1)
1.365(6)
1.365(4)
1.459(5)
1.464(6)
N(1)-C(1)-Ru(1)
N(2)-C(1)-Ru(1)
Cl(1)-Ru(1)-Cl(2)
N(1)-C(1)-N(2)
C(1)-N(1)-C(8)
C(1)-N(2)-C(17)
C(1)-Ru(1)-C(l1)
C(1)-Ru(1)-C(l2)
126.6(3)
128.2(3)
84.15(4)
105.1(3)
127.1(3)
126.5(3)
89.4(1)
87.5(1)
N-Alkylation of Aniline with Arylmethyl Alcohols
The ruthenium complexes 1a-f were evaluated as catalysts
for N-alkylation of aniline with arylmethyl alcohols. The
corresponding tests were performed in the presence of a base in
toluene at 120 °C for 24 hour. In the present catalytic conditions,
two products may be formed, namely, a N-(arylmethyl)aniline (A)
or a N-phenyl-arylmethylanimine (B) (Scheme 2).
Figure 3. ORTEP drawing illustrating the solid state structure of complex
1aCHCl3 (displacement ellipsoids are drawn at the 50 % probability level).
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10.1002/ejic.201701479
European Journal of Inorganic Chemistry
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Scheme 2. N-alkylation of aniline with arylmethyl alcohol.
To determine the optimal catalytic conditions, ruthenium
complex 1c (5 mol %) was used in the alkylation of aniline with
benzyl alcohol at 120 °C in toluene. Each experiment was
stopped after 24 h. As a control experiment, no products were
formed without the addition of ruthenium complex (Table 3, entry
1). In the first series of reactions, we determined the optimal
the conversion and the selectivity toward the formation of
compound A (Table 3, entries 4 and 5). A good compromise is
the use of 2.5 mol % of 1c, which led to a full conversion after 24
h with an A/B ratio of 80/20 (Table 3, entry 6). Operating at
lower temperature or for a shorter time reduced both the
conversion and the chemoselectivity (Table 3, entries 7 and 8).
Note that, under our catalytic conditions, only mono-alkylated
compounds were formed, no bis-alkylated derivatives were
observed.
t
base by employing either BuOK, Cs2CO3 or KOH. As can be
inferred from the results (Table 3, entries 2-4), the most efficient
base was tBuOK, which led to a full conversion with an A/B ratio
of 85/15. Reducing the catalyst loading to 1 mol % decreased
Table 3. N-alkylation of aniline with benzyl alcohol – a search for optimal catalytic conditions.[a]
Selectivity [%]
Entry
1c [mol %]
Base
Time [h]
Temp. [oC]
Yield [%]
A
B
1
2
3
4
5
6
7
8
No
5
tBuOK
Cs2CO3
KOH
24
24
24
24
24
24
16
24
120
120
120
120
120
120
120
90
0
-
-
32
71
100
70
100
80
74
89
72
85
70
80
69
73
11
28
15
30
20
31
27
5
5
tBuOK
tBuOK
tBuOK
tBuOK
tBuOK
1
2.5
2.5
2.5
[a]
Reagents and conditions: 1c, benzyl alcohol (1.0 mmol), aniline (1.1 mmol), base (2.5 mmol), toluene (3 mL). The conversions and the
selectivities were determined by GC and GC-MS analysis with the calibrations based on dodecane.
t
Under the determined optimal conditions, BuOK as base
in toluene at 120 °C for 24 h, the ruthenium complexes 1a-f (2.5
mol %) were further examined in the N-alkylation of aniline with
four arylmethyl alcohols, namely, benzyl alcohol, p-
conversions were reached for benzyl alcohol (1c), p-
tolylmethanol (1d) and (4-methoxyphenyl)methanol (1d) (Table
4, entries 3, 10 and 16). A conversion of 95 % for the more
sterically
hindered
(3,4-dimethoxyphenyl)methanol
was
tolylmethanol,
(4-methoxyphenyl)methanol
and
(3,4-
observed when ruthenium complex 1e was employed (Table 4,
entry 23). In all catalysis, high chemoselectivities toward the
formation of amines A were obtained. In fact, A/B ratios of 95/5
were measured for alkylation with benzyl alcohol and p-
tolylmethanol when complexes 1a and 1f were used,
respectively (Table 4, entries 1 and 12). For the two alcohols
bearing methoxy substituents, (4-methoxyphenyl)methanol (A/B
= 97/3) and (3,4-dimethoxyphenyl)methanol (A/B = 94/6), the
highest selectivity for the formation of amine products was
obtained with complex 1e (Table 4, entries 17 and 23).
dimethoxyphenyl)methanol (Table 4). In all tests, conversions in
arylmethyl alcohol higher than 78 % were measured. Due to the
similar nature of the NHC moieties, small differences in
reactivities were observed. Nevertheless, by comparison with
common
NHCs
such
as
the
1,3-bis(2,4,6-
presence of
trimethylphenyl)imidazolylidene
[22f],
benzimidazolylidene contributes to promote the formation of
amines A rather than imines B.
The two more efficient ruthenium precatalysts were
complexes 1c and 1d. With the latter complexes, full
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Table 4. Ruthenium-catalysed N-alkylation of aniline with arylmethyl alcohols.[a]
Selectivity[%]
Entry
[Ru] complex
Arylmethyl alcohol
Yield [%]
A
B
1
1a
1b
1c
1d
1e
1f
91
86
100
91
96
80
88
94
87
100
92
100
90
78
86
100
93
98
89
87
92
89
95
91
95
76
80
93
89
80
72
80
83
92
83
95
92
78
76
87
97
93
83
77
83
88
94
90
5
2
24
20
7
3
4
5
11
20
28
20
17
8
6
7
1a
1b
1c
1d
1e
1f
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
17
5
1a
1b
1c
1d
1e
1f
8
22
24
13
3
7
1a
1b
1c
1d
1e
1f
17
23
17
12
6
10
[a] Reagents and conditions: [Ru] (0.025 mmol, 2.5 mol %), arylmethyl alcohol (1.0 mmol), aniline (1.1 mmol), tBuOK (2.5 mmol), toluene (3 mL),
120 oC, 24 h. The conversions and the selectivities were determined by GC and GC-MS analysis with the calibrations based on dodecane.
Ruthenium complexes 1a-f were further assessed in the N-
alkylation of aniline with furfuryl alcohol or 2-thiophene methanol
(Table 5). Both alcohols were efficiently converted in 24 h when
the reactions were performed in the presence of complexes 1c
(99 % for furfuryl alcohol and 97 % for 2-thiophene methanol;
Table 5, entries 3 and 9). With the latter precatalyst, the
proportions of amines products A formed were 91 % with furfuryl
alcohol and 98 % with 2-thiophene methanol. Repeating the run
with furfuryl alcohol and complex 1f increase the
chimioselectivity toward the formation of A to 93 % (Table 5,
entry 6).
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Table 5. Ruthenium-catalysed N-alkylation of aniline with heteroaromatic alcohols.[a]
Selectivity [%]
Entry
[Ru] complex
Heteroaromatic alcohols
Yield [%]
A
B
1
2
1a
1b
1c
1d
1e
1f
100
88
99
95
95
91
92
89
97
90
91
87
88
84
91
91
80
93
78
87
98
83
95
78
12
16
9
3
4
9
5
20
7
6
7
1a
1b
1c
1d
1e
1f
22
13
2
8
9
10
11
12
17
5
22
[a]
t
Reagents and conditions: [Ru] (0.025 mmol, 2.5 mol %), heteroaromatic alcohol (1.0 mmol), aniline (1.1 mmol), BuOK (2.5 mmol), toluene (3 mL),
120 oC, 24 h. The conversions and the selectivities were determined by GC and GC-MS analysis with the calibrations based on dodecane.
mm NMR tubes. Chemical shifts (δ) and coupling constants (J) are
Conclusions
1
reported in ppm and in Hz, respectively. H NMR spectra are referenced
to residual protiated solvents (δ = 7.26 ppm for CDCl3), 13C chemical
shifts are reported relative to deuteriated solvents (δ = 77.16 ppm for
CDCl3). The catalytic solutions were analysed with an Agilent 6890N GC
and Schimadzu 2010 Plus GC-MS system by GC-FID with an HP-5
column of 30 m length, 0.32 mm diameter, and 0.25 μm film thickness.
The benzimidazolium bromides 3c-f and the silver(I) complexes 4c-f
were prepared according to literature procedures [24].
In this study, we prepared six new ruthenium complexes in
which a nitrogen atom of the N-heterocyclic carbene ligand is
substituted either with an ether or an arylmethyl chain. These
complexes were all found to be suitable for N-alkylation of
aniline with a range of alcohols including arylmethyl alcohols and
heteroaromatic alcohols. Future work will aim at exploiting the
stabilisation of active species with such ligands in catalytic
applications.
General Procedure for the Preparation of Benzimidazolium
Bromides 3a and 3b: A chloroform (10 mL) solution of 1-(2-(2-
ethoxyphenoxy)ethyl)benzimidazole (0.282 g, 1.0 mmol) and alkyl
bromide (1.0 mmol) was stirred at 60 °C for 24 h. After completion of the
reaction, the solvent was removed by vacuum and diethyl ether (15 mL)
was added to obtain a white crystalline solid, which was filtered off. The
solid was washed with Et2O (3 × 10 mL) and dried under vacuum. The
crude product was recrystallized from EtOH/Et2O mixture (1:2, v/v) and
dried under vacuum.
Experimental Section
General Methods: All reactions performed to prepare the
benzimidazolium salts and their metal complexes were carried out under
argon in flame-dried glassware using standard Schlenk techniques.
Chemicals and solvents were purchased from Sigma-Aldrich and Merck.
Dichloromethane, dimethylformamide, toluene and diethyl ether were of
anhydrous quality and were used as received. The solvents used were
purified by distillation over the drying agents indicated and were
transferred under argon. All reagents were purchased from commercial
sources and used without further purification. Microanalyses were
performed by İnönü University Scientific and Technological Research
Center (Malatya, Turkey). IR spectra were recorded on ATR unit in the
range of 400-4000 cm-1 with Perkin Elmer Spectrum 100
Spectrofotometer. Melting points were measures in open capillary tubes
with an Electrothermal-9200 melting points apparatus. Routine 1H NMR
and 13C NMR spectra were recorded using a Bruker Avance AMX
spectrometer operating at 300, 400 and 500 MHz for 1H NMR, and at 75,
100 and 125 MHz for 13C NMR in CDCl3 with tetramethylsilane as an
internal reference. The NMR studies were carried out in high-quality 5
1-(2-(2-Ethoxyphenoxy)ethyl)-3-(3,5-dimethylbenzyl)benzimidazol-
ium Bromide 3a: (0.480 g, yield 87 %) 1H NMR (300 MHz, CDCl3, 25
oC): δ = 1.33 (t, 3J = 7.0 Hz, 3H, OCH2CH3), 2.27 (s, 6H, C6H3(CH3)2),
3.95 (q, 3J = 6.9 Hz, 2H, OCH2CH3), 4.56 (t, 3J = 4.5 Hz, 2H,
NCH2CH2O), 5.25 (t, 3J = 4.4 Hz, 2H, NCH2CH2O), 5.69 (s, 2H,
NCH2C6H3(CH3)2), 6.80-6.90 (m, 4H, arom. CH, C6H4OCH2CH3), 6.97 (s,
1H, arom. CH, C6H3(CH3)2), 7.05 (s, 2H, arom. CH, C6H3(CH3)2), 7.54-
7.61 (m, 3H, arom. CH, C6H4 benzimidazol), 8.22 (d, 3J = 6.0 Hz, 1H,
arom. CH, C6H4 benzimidazol), 11.42 (s, 1H, NCHN) ppm. 13C NMR (75
o
MHz, CDCl3, 25 C): δ = 14.9 (s, OCH2CH3), 21.2 (s, C6H3(CH3)2), 47.9
(s, OCH2CH3), 51.7 (s, NCH2CH2O), 63.8 (s, NCH2CH2O), 68.2 (s,
NCH2C6H3(CH3)2), 112.7-148.7 (arom. Cs), 143.1 (s, NCHN) ppm.
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Elemental analysis calcd (%) for C26H29BrN2O2 (Mr = 481.42): C 64.87, H
6.07, N 5.82; found (%): C 64.90, H 6.10, N 5.84.
(arom. Cs and C-Ag) ppm. Elemental analysis calcd (%) for
C29H34AgBrN2O2 (Mr = 630.36): C 55.26, H 5.44, N 4.44; found (%): C
55.27, H 5.46, N 4.45.
1-(2-(2-Ethoxyphenoxy)ethyl)-3-(2,3,4,5,6-pentamethylbenzyl)benz-
imidazolium Bromide 3b: (0.435 g, yield 83 %) 1H NMR (300 MHz,
CDCl3, 25 oC): δ = 1.34 (t, 3J = 6.8 Hz, 3H, OCH2CH3), 2.26 (s, 6H,
NCH2C6(CH3)5), 2.29 (s, 6H, NCH2C6(CH3)5), 2.30 (s, 3H,
NCH2C6(CH3)5), 3.95 (q, 3J = 6.8 Hz, 2H, OCH2CH3), 4.51 (t, 3J = 4.0 Hz,
2H, NCH2CH2O), 5.33 (t, 3J = 4.0 Hz, 2H, NCH2CH2O), 5.70 (s, 2H,
NCH2C6(CH3)5), 6.81-6.94 (m, 4H, arom. CH, C6H4OCH2CH3), 7.56-7.66
(m, 3H, arom. CH, C6H4 benzimidazol), 8.30 (d, 3J = 9.0 Hz, 1H, arom.
CH, C6H4 benzimidazol), 10.33 (s, 1H, NCHN) ppm. 13C NMR (75 MHz,
General Procedure for the Preparation of the Ruthenium(II)-NHC
Complexes 1a-f: To a solution of silver (I) complex (2.0 mmol) in
anhydrous CH2Cl2 (10 mL) was added [RuCl2(p-cymene)]2 (1.0 mmol).
The reaction mixture was then stirred for 12 h at room temperature, then
was filtered through Celite. The filtrate was evaporated under vacuum,
the solid residue was washed with Et2O (3 × 5 mL), dried under vacuum
and recrystallized from CHCl3/ Et2O (1:2, v/v).
o
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(3,5-dimethylbenzyl)benz-
imidazol-2-ylidene](p-cymene) ruthenium(II) 1a: (0.919 g, yield 65 %)
1H NMR (400 MHz, CDCl3, 25 oC): δ = 1.24 (d, 3J = 7.0 Hz, 6H,
CH(CH3)2), 1.46 (t, 3J = 6.9 Hz, 3H, OCH2CH3), 2.04 (s, 3H, CH3 of p-
cymene), 2.21 (s, 6H, C6H3(CH3)2), 2.92 (hept, 3J = 7.0 Hz, 1H,
CH(CH3)2), 4.08 (q, 3J = 6.9 Hz, 2H, OCH2CH3), 4.52-4.56 (m, 2H,
NCH2CH2O), 4.97-5.04 (m, 1H, NCH2CH2O), 5.15 (d, 3J = 5.6 Hz, 2H,
arom. CH of p-cymene), 5.30-5.33 (m, 1H, NCH2CH2O), 5.40-5.44 (m,
1H, NCH2C6H3(CH3)2), 5.54-5.59 (m, 2H, arom. CH of p-cymene), 6.48-
6.52 (m, 1H, NCH2C6H3(CH3)2), 6.66 (s, 2H, arom. CH, C6H3(CH3)2),
6.80-6.91 (m, 4H, arom. CH, C6H4OCH2CH3), 6.84 (s, 1H, arom. CH,
C6H3(CH3)2), 7.03 (d, 3J = 8.0 Hz, 1H, arom. CH, C6H4 benzimidazol),
CDCl3, 25 C): δ = 14.9 (s, OCH2CH3), 17.1 (s, NCH2C6(CH3)5), 17.2 (s,
NCH2C6(CH3)5), 17.4 (s, NCH2C6(CH3)5), 47.6 (s, OCH2CH3), 48.1 (s,
NCH2CH2O), 63.8 (s, NCH2CH2O), 68.5 (s, NCH2C6(CH3)5), 112.5-148.6
(arom. Cs), 142.1 (NCHN) ppm. Elemental analysis calcd (%) for
C29H35BrN2O2 (Mr = 523.50): C 66.53, H 6.74, N 5.35; found (%): C
66.59, H 6.76, N 5.39.
General Procedure for the Preparation of the Silver(I)-NHC
Complexes 4a and 4b: A solution of benzimidazolium bromide (1.0
mmol), Ag2O (0.5 mmol) and activated 4 Å molecular sieves in anhydrous
CH2Cl2 (10 mL) was stirred at room temperature for 24 h. The reaction
mixture was then filtered through Celite and the solvent was removed
under reduced pressure. The resulting solid was washed with Et2O (3 × 5
mL) and dried under vacuum. The crude product was recrystallized from
CH2Cl2/ Et2O (1:2, v/v).
3
3
7.13 (t, J = 8.0 Hz, 1H, arom. CH, C6H4 benzimidazol), 7.24 (d, J = 8.0
Hz, 1H, arom. CH, C6H4 benzimidazol), 8.08 (d, 3J = 8.0 Hz, 1H, arom.
CH, C6H4 benzimidazol) ppm. 13C NMR (100 MHz, CDCl3, 25 oC): δ =
15.1 (s, OCH2CH3), 18.3 (s, CH3 of p-cymene), 21.3 (s, CH(CH3)2), 21.4
(s, CH(CH3)2), 21.6 (s, C6H3(CH3)2), 23.6 (s, C6H3(CH3)2), 30.7 (s,
CH(CH3)2), 50.5 (s, OCH2CH3), 52.6 (s, NCH2C6H3(CH3)2), 63.9 (s,
NCH2CH2O), 69.6 (s, NCH2CH2O), 83.1 (s, arom. CH of p-cymene), 85.0
(s, arom. CH of p-cymene), 85.1 (s, arom. CH of p-cymene), 86.4 (s,
arom. CH of p-cymene), 98.7-148.8 (arom. Cs), 191.2 (s, C-Ru) ppm.
Elemental analysis calcd (%) for C36H42RuCl2N2O2 (Mr = 706.70): C
61.18, H 5.99, N 3.96; found (%): C 61.20, H 6.02, N 3.99.
Bromo-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(3,5-dimethylbenzyl)benz-
imidazol-2-ylidene]silver(I) 4a: (0.477 g, yield 81 %) 1H NMR (400 MHz,
CDCl3, 25 oC): δ = 1.29 (t, 3J = 7.0 Hz, 3H, OCH2CH3), 2.18 (s, 6H,
C6H3(CH3)2), 3.89 (q, 3J = 7.0 Hz, 2H, OCH2CH3), 4.38 (t, 3J = 4.9 Hz,
2H, NCH2CH2O), 4.80 (t, 3J = 4.9 Hz, 2H, NCH2CH2O), 5.44 (s, 2H,
NCH2C6H3(CH3)2), 6.68-6.83 (m, 4H, arom. CH, C6H4OCH2CH3), 6.82 (s,
2H, arom. CH, C6H3(CH3)2), 6.85 (s, 1H, arom. CH, C6H3(CH3)2), 7.24-
3
7.31 (m, 3H, arom. CH, C6H4 benzimidazolylidene), 7.82 (d, J = 8.0 Hz,
1H, arom. CH, C6H4 benzimidazolylidene) ppm. 13C NMR (100 MHz,
CDCl3, 25 oC): δ = 15.0 (s, OCH2CH3), 21.3 (s, C6H3(CH3)2), 49.6 (s,
OCH2CH3), 53.5 (s, NCH2CH2O), 63.9 (s, NCH2CH2O), 69.2 (s,
NCH2C6H3(CH3)2), 111.8-148.8 (arom. Cs and C-Ag) ppm. Elemental
analysis calcd (%) for C26H28AgBrN2O2 (Mr = 588.28): C 53.08, H 4.80, N
4.76; found (%): C 53.10, H 4.82, N 4.79.
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(2,3,4,5,6-pentamethyl-
benzyl)benzimidazol-2-ylidene](p-cymene) ruthenium(II) 1b: (0.854 g,
o
3
yield 57 %) 1H NMR (400 MHz, CDCl3, 25 C): δ = 1.32 (d, J = 7.0 Hz,
3
6H, CH(CH3)2), 1.45 (t, J = 6.8 Hz, 3H, OCH2CH3), 2.15 (s, 3H, CH3 of
p-cymene), 2.18 (s, 6H, C6(CH3)5), 2.20 (s, 6H, C6(CH3)5), 2.29 (s, 3H,
3
C6(CH3)5), 3.02 (hept, 3J = 7.0 Hz, 1H, CH(CH3)2), 4.08 (q, J = 6.8 Hz,
2H, OCH2CH3), 4.46-4.56 (m, 2H, NCH2CH2O), 5.00-5.08 (m, 1H,
NCH2CH2O), 5.34-5.75 (m, 6H, NCH2CH2O, NCH2C6(CH3)5 and arom.
Bromo[1-(2-(2-ethoxyphenoxy)ethyl)-3-(2,3,4,5,6-pentamethylbenzyl)
1
CH of p-cymene), 6.13 (d, 3J
= 8.4 Hz, 1H, arom. CH, C6H4
benzimidazol-2-ylidene]silver(I) 4b: (0.466 g, yield 74 %) H NMR (400
MHz, CDCl3, 25 oC): δ = 1.33 (t, 3J = 6.9 Hz, 3H, OCH2CH3), 2.10 (s, 6H,
NCH2C6(CH3)5), 2.11 (s, 6H, NCH2C6(CH3)5), 2.14 (s, 3H,
NCH2C6(CH3)5), 3.91 (q, 3J = 6.8 Hz, 2H, OCH2CH3), 4.28 (t, 3J = 4.8 Hz,
2H, NCH2CH2O), 4.69 (t, 3J = 4.8 Hz, 2H, NCH2CH2O), 5.38 (s, 2H,
NCH2C6(CH3)5), 6.63-6.84 (m, 4H, arom. CH, C6H4OCH2CH3), 7.34-7.43
(m, 3H, arom. CH, C6H4 benzimidazolylidene), 7.86 (d, 3J = 8.0 Hz, 1H,
arom. CH, C6H4 benzimidazolylidene) ppm. 13C NMR (100 MHz, CDCl3,
25 oC): δ = 15.0 (s, OCH2CH3), 17.1 (s, NCH2C6(CH3)5), 17.2 (s,
NCH2C6(CH3)5), 17.2 (s, NCH2C6(CH3)5), 47.5 (s, OCH2CH3), 50.3 (s,
NCH2CH2O), 63.9 (s, NCH2CH2O), 69.4 (s, NCH2C6(CH3)5), 110.8-148.7
benzimidazolylidene), 6.78-6.90 (m, 6H, NCH2C6(CH3)5 and arom. CH of
C6H4 benzimidazolylidene and C6H4OCH2CH3), 7.08 (t, 1H, 3J = 8.4 Hz,
1H, arom. CH, C6H4 benzimidazolylidene), 7.87 (d, 3J = 8.4 Hz, 1H, arom.
o
CH, C6H4 benzimidazolylidene) ppm. 13C NMR (100 MHz, CDCl3, 25 C):
δ = 15.1 (s, OCH2CH3), 16.9 (s, NCH2C6(CH3)5), 17.2 (s, NCH2C6(CH3)5),
17.4 (s, NCH2C6(CH3)5), 18.6 (s, CH3 of p-cymene), 21.9 (s, CH(CH3)2),
23.5 (s, CH(CH3)2), 30.9 (s, CH(CH3)2), 50.4 (s, OCH2CH3), 52.5 (s,
NCH2C6(CH3)5), 63.9 (s, NCH2CH2O), 69.3 (s, NCH2CH2O), 84.9 (s,
arom. CH of p-cymene), 85.6 (s, arom. CH of p-cymene), 86.3 (s, arom.
This article is protected by copyright. All rights reserved.

10.1002/ejic.201701479
European Journal of Inorganic Chemistry
FULL PAPER
3
CH of p-cymene), 86.6 (s, arom. CH of p-cymene), 98.2-148.8 (arom.
Cs), 189.9 (s, C-Ru) ppm. Elemental analysis calcd (%) for
C39H48RuCl2N2O2 (Mr = 748.78): C 62.56, H 6.46, N 3.74; found (%): C
62.89, H 6.51, N 3.77.
2.16 (s, 3H, CH3 of p-cymene), 2.21 (s, 6H, C6H(CH3)4), 3.03 (hept, J =
7.0 Hz, 1H, CH(CH3)2), 4.07 (q, 3J = 7.0 Hz, 2H, OCH2CH3), 4.45-4.56
(m, 2H, NCH2CH2O), 5.00-5.07 (m, 1H, NCH2CH2O), 5.34-5.61 (m, 5H,
NCH2CH2O and arom. CH of p-cymene), 5.70-5.79 (m, 1H,
NCH2C6H(CH3)4), 6.62 (d, 3J
= 8.0 Hz, 1H, arom. CH, C6H4
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(2-methoxyethyl)benzimid-
azol-2-ylidene](p-cymene) ruthenium(II) 1c: (0.802 g, yield 62 %) 1H
benzimidazol), 6.79-6.89 (m, 6H, NCH2C6H(CH3)4 and arom. CH of
C6H4OCH2CH3 and C6H4 benzimidazol), 7.01 (s, 1H, arom. CH,
C6H(CH3)4), 7.10 (t, 3J = 8.0 Hz, 1H, arom. CH, C6H4 benzimidazol), 7.89
(d, 3J = 8.0 Hz, 1H, arom. CH, C6H4 benzimidazol) ppm. 13C NMR (100
MHz, CDCl3, 25 oC): δ = 15.1 (s, OCH2CH3), 16.2 (s, C6H(CH3)4), 18.6 (s,
CH3 of p-cymene), 20.6 (s, C6H(CH3)4), 21.9 (s, CH(CH3)2), 22.7 (s,
CH(CH3)2), 30.9 (s, CH(CH3)2), 50.3 (s, OCH2CH3), 51.9 (s,
NCH2C6H(CH3)4), 63.9 (s, NCH2CH2O), 69.4 (s, NCH2CH2O), 83.6 (s,
arom. CH of p-cymene), 85.0 (s, arom. CH of p-cymene), 85.3 (s, arom.
CH of p-cymene), 86.6 (s, arom. CH of p-cymene), 98.2-148.8 (arom.
Cs), 189.9 (s, C-Ru) ppm. Elemental analysis calcd (%) for
C38H46RuCl2N2O2 (Mr = 734.76): C 62.12, H 6.31, N 3.81; found (%): C
62.15, H 6.29, N 3.78.
3
NMR (300 MHz, CDCl3, 25 oC): δ = 1.30 (d, J = 6.9 Hz, 6H, CH(CH3)2),
3
1.50 (t, J = 7.0 Hz, 3H, OCH2CH3), 2.04 (s, 3H, CH3 of p-cymene), 3.04
(hept, 3J = 6.9 Hz, 1H, CH(CH3)2), 3.34 (s, 3H, OCH3), 3.88-3.93 (m, 2H,
3
NCH2CH2OCH3), 4.11 (q, J = 7.0 Hz, 2H, OCH2CH3), 4.45-4.60 (m, 2H,
NCH2CH2OAr), 4.68-4.77 (m, 1H, NCH2CH2OCH3), 4.87-5.00 (m, 1H,
NCH2CH2OAr), 5.03-5.13 (m, 1H, NCH2CH2OAr), 5.27-5.48 (m, 3H,
NCH2CH2OAr and arom. CH of p-cymene), 5.56-5.68 (m, 2H, arom. CH
of p-cymene), 6.84-6.93 (m, 4H, arom. CH, C6H4OCH2CH3), 7.10-7.14
(m, 2H, arom. CH, C6H4 benzimidazolylidene), 7.56-7.64 (m, 1H, arom.
CH, C6H4 benzimidazolylidene), 8.02-8.10 (m, 1H, arom. CH, C6H4
benzimidazolylidene) ppm. 13C NMR (75 MHz, CDCl3, 25 oC): δ = 15.0 (s,
OCH2CH3), 18.5 (s, CH3 of p-cymene), 22.3 (s, CH(CH3)2), 22.7 (s,
CH(CH3)2), 30.7 (s, CH(CH3)2), 50.4 (s, OCH2CH3), 58.9
(NCH2CH2OCH3), 64.0 (s, NCH2CH2OAr), 69.7 (s, NCH2CH2OCH3), 69.7
(s, NCH2CH2OAr), 72.2 (s, NCH2CH2OCH3), 83.3 (s, arom. CH of p-
cymene), 83.7 (s, arom. CH of p-cymene), 86.6 (s, arom. CH of p-
cymene), 86.8 (s, arom. CH of p-cymene), 99.5-148.7 (arom. Cs), 190.6
(s, C-Ru) ppm. Elemental analysis calcd (%) for C30H38RuCl2N2O3 (Mr =
646.60): C 55.72, H 5.92, N 4.33; found (%): C 55.78, H 5.95, N 4.35.
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(4-tert-butylbenzyl)benz-
imidazol-2-ylidene](p-cymene) ruthenium(II) 1f: (0.998 g, yield 68 %)
1H NMR (400 MHz, CDCl3, 25 oC): δ = 1.21-1.30 (m, 6H, CH(CH3)2), 1.28
(s, 9H, C(CH3)3), 1.45 (t, 3J = 7.0 Hz, 3H, OCH2CH3), 2.04 (s, 3H, CH3 of
3
3
p-cymene), 2.89 (hept, J = 6.8 Hz, 1H, CH(CH3)2), 4.10 (q, J = 7.0 Hz,
2H, OCH2CH3), 4.54-4.56 (m, 2H, NCH2CH2O), 5.05-5.09 (m, 1H,
NCH2CH2O), 5.17-5.21 (m, 2H, arom. CH of p-cymene), 5.31-5.40 (m,
2H, arom. CH of p-cymene), 5.57-5.64 (m, 2H, NCH2CH2O and
NCH2C6H4C(CH3)3), 6.54-6.62 (m, 1H, NCH2C6H4C(CH3)3), 6.83-7.38 (m,
11H, arom. CH of NCH2C6H4C(CH3)3, C6H4OCH2CH3 and C6H4
benzimidazol), 8.04 (d, 3J = 8.4 Hz, 1H, arom. CH, C6H4 benzimidazol)
ppm. 13C NMR (100 MHz, CDCl3, 25 oC): δ = 15.1 (s, OCH2CH3), 18.4 (s,
CH3 of p-cymene), 21.7 (s, CH(CH3)2), 23.4 (s, CH(CH3)2), 30.6 (s,
CH(CH3)2), 31.3 (s, C(CH3)3), 34.5 (s, C(CH3)3), 50.4 (s, OCH2CH3), 52.3
(s, NCH2C6H4C(CH3)3), 63.9 (s, NCH2CH2O), 69.3 (s, NCH2CH2O), 83.7
(s, arom. CH of p-cymene), 85.0 (s, arom. CH of p-cymene), 85.1 (s,
arom. CH of p-cymene), 86.6 (s, arom. CH of p-cymene), 98.4-150.4
(arom. Cs), 191.5 (s, C-Ru) ppm. Elemental analysis calcd (%) for
C38H46RuCl2N2O2 (Mr = 734.76): C 62.12, H 6.31, N 3.81; found (%): C
62.20, H 6.40, N 3.85.
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(2,4,6-trimethylbenzyl)-
benzimidazol-2-ylidene](p-cymene) ruthenium(II) 1d: (1.009 g, yield
70 %) 1H NMR (400 MHz, CDCl3, 25 oC): δ = 1.31 (d, 3J = 7.0 Hz, 6H,
CH(CH3)2), 1.44 (t, 3J = 7.0 Hz, 3H, OCH2CH3), 2.11 (s, 3H, CH3 of p-
cymene), 2.12 (s, 6H, C6H2(CH3)3), 2.27 (s, 3H, C6H2(CH3)3), 3.01 (hept,
3J = 7.0 Hz, 1H, CH(CH3)2), 4.07 (q, 3J = 7.0 Hz, 2H, OCH2CH3), 4.45-
4.52 (m, 2H, NCH2CH2O), 5.01-5.12 (m, 1H, NCH2CH2O), 5.29-5.62 (m,
5H, NCH2CH2O and arom. CH of p-cymene), 5.66-5.76 (m, 1H,
NCH2C6H2(CH3)3), 6.36 (d, 3J
= 8.4 Hz, 1H, arom. CH, C6H4
benzimidazol), 6.62-6.72 (m, 1H, NCH2C6H2(CH3)3), 6.81 (s, 2H, arom.
CH, C6H2(CH3)3), 6.82-6.91 (m, 5H, arom. CH, C6H4OCH2CH3 and C6H4
benzimidazol), 7.14 (t, 3J = 8.4 Hz, 1H, arom. CH, C6H4 benzimidazol),
7.88 (d, 3J = 8.4 Hz, 1H, arom. CH, C6H4 benzimidazol) ppm. 13C NMR
o
(100 MHz, CDCl3, 25 C): δ = 15.1 (s, OCH2CH3), 18.5 (s, C6H2(CH3)3),
General Procedure for the N-Alkylation of Aniline with Alcohols: A
10 mL-Schlenk tube, under an argon atmosphere, was filled with
ruthenium complex (0.025 mmol, 2.5 mol %), alcohol derivative (1.0
20.5 (s, C6H2(CH3)3), 20.9 (s, CH3 of p-cymene), 22.3 (s, CH(CH3)2), 22.9
(s, CH(CH3)2), 30.8 (s, CH(CH3)2), 50.2 (s, OCH2CH3), 50.8 (s,
NCH2C6H2(CH3)3), 63.9 (s, NCH2CH2O), 69.3 (s, NCH2CH2O), 83.7 (s,
arom. CH of p-cymene), 84.6 (s, arom. CH of p-cymene), 85.2 (s, arom.
CH of p-cymene), 86.4 (s, arom. CH of p-cymene), 97.8-148.8 (arom.
Cs), 190.2 (s, C-Ru) ppm. Elemental analysis calcd (%) for
C37H44RuCl2N2O2 (Mr = 720.73): C 61.66, H 6.15, N 3.89; found (%): C
61.69, H 6.20, N 3.92.
t
mmol), aniline (1.1 mmol) and BuOK (2.5 mmol). Degassed toluene (3
mL) was then added and the reaction mixture was heated at 120 °C for
24 h. After cooling to room temperature, the reaction was cooled room
temperature and filtered through a short pad of SiO2 and the filtrate was
analyzed by and GC-MS with the calibrations based on decane.
X-ray Crystallographic Data: Single crystal of complex 1aCHCl3
suitable for X-ray analysis were obtained by slow diffusion of diethyl ether
into a chloroform solution of the complex 1a. Empirical formula =
C36H42RuCl2N2O2.CHCl3, Mr = 826.05 g.mol-1, crystal system = trigonal,
space group = R-3 system, a = 27.383(3), b = 27.383(3), c = 26.499(3) Å,
Dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(2,3,5,6-tetramethylbenzyl)
benzimidazol-2-ylidene](p-cymene) ruthenium(II) 1e: (0.926 g, yield
63 %) 1H NMR (400 MHz, CDCl3, 25 oC): δ = 1.32 (d, 3J = 7.0 Hz, 6H,
3
CH(CH3)2), 1.44 (t, J = 7.0 Hz, 3H, OCH2CH3), 2.10 (s, 6H, C6H(CH3)4),
This article is protected by copyright. All rights reserved.

10.1002/ejic.201701479
European Journal of Inorganic Chemistry
FULL PAPER
α = 90o,  = 90°,  = 120o, V = 17208(4) Å3, Z = 18, d = 1.435 g.cm-3, μ =
0.794 mm-1, F(000) = 7632, T = 173(2) K. The crystal size (0.160 × 0.140
× 0.100 mm) was studied with a Bruker APEX2 DUO Kappa-CCD
diffractometer using Mo-Kα radiation (λ = 0.71073 Å). The structure was
solved by using SHELXS-2013 [30], which revealed the non-hydrogen
atoms of the molecule. After anisotropic refinement, all the hydrogen
atoms were found by Fourier difference. The whole structure was refined
with SHELXL-2013 [31] by using the full-matrix least-squares technique
(use of F2; x, y, z, ij for C, Cl, N, O and Ru atoms, x, y, z in the riding
mode for hydrogen atoms); 436 variables and 6199 observations with I >
2.0σ(I); calcd. w = 1/[σ2(Fo2) + (0.0801P)2] in which P = (Fo2 + 2Fc2)/3.
Extra solvent accessible voids were detected in 1aCHCl3, therefore, a
SQUEEZE/PLATON technique [32] was applied to remove the
unidentified solvent contributions. Final results: R = 0.0526, Rw =
0.1455, Sw = 1.057 and Δρ < 0.961 e Å-3. CCDC 1580353 contains the
supplementary crystallographic data for 1a. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Crabtree, Chem. Rev. 2010, 110, 681-703; d) G. Guillena, D. J. Ramon,
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J.-B. Sortais, K. Junge, C. Darcel, M. Beller, Nat. Commun. 2016, 7,
12641; j) X. Ma, C. Su, Q. Xu, Top Curr. Chem. 2016, 374, 1-74.
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Supporting Information (see footnote on the first page of this article):
Full 1H NMR, 13C NMR and FT-IR spectra for the of benzimidazolium
bromides (3a and 3b), silver(I)-NHC complexes (4a and 4b) and
ruthenium(II)-NHC complexes (1a-f) .
Acknowledgements
This work was financially supported by the Technological and
Scientific Research Council of Turkey TÜBİTAK (112T303).
Keywords: N-Heterocyclic carbene • ruthenium • amine • N-
alkylation • hydrogen borrowing strategy
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FULL PAPER
Ruthenium(II)-(p-cymene)-N-
Heterocyclic Carbene Complexes:
Very Efficient Catalsts for The N-
Alkylation of Aniline
M. Kaloğlu, N. Gürbüz, D. Sémeril,
İ. Özdemir*
1 – 10
Ruthenium(II)-(p-cymene)-N-
Heterocyclic Carbene Complexes for
the N-Alkylation of Amine Using the
Green
Hydrogen
Borrowing
Methodology
Six ruthenium(II) complexes with the general molecular formula
[RuCl2(NHC)(η6-p-cymene)], (NHC = N-heterocyclic carbene) were synthesized.
The obtained complexes were fully characterized by analytical and spectral
methods (FT-IR, elemental analysis and 1H and 13C NMR). The solid-state structure
of one of the ruthenium complexes {dichloro-[1-(2-(2-ethoxyphenoxy)ethyl)-3-(3,5-
dimethylbenzyl)benzimidazol-2-ylidene](p-cymene)ruthenium(II)}
has
been
established by single-crystal X-ray diffraction study. The catalytic activity of the all
ruthenium(II) complexes have been evaluated in the N-alkylation of aniline using
the green hydrogen borrowing methodology
This article is protected by copyright. All rights reserved.