Alkylation of cyclic amines with alcohols catalyzed by Ru(II) complexes bearing N-Heterocyclic carbenes

Article abstract of DOI:10.1016/j.tet.2017.09.027

This paper includes the synthesis of 2-(1,3-dioxane-2-yl)ethyl substituted benzimidazole substituted N-heterocyclic carbenes precursors and their ruthenium complexes. Synthesized compounds were characterized by elemental analysis and NMR spectroscopy. All complexes have been tested in the alkylation of pyrrolidine and morpholine with alcohols, showing an excellent activity in this reaction.

Full text of DOI:10.1016/j.tet.2017.09.027

Accepted Manuscript
Alkylation of cyclic amines with alcohols catalyzed by Ru(II) complexes bearing N-
Heterocyclic carbenes
Öznur Doğan Ulu, Nevin Gürbüz, İsmail Özdemir
PII:
S0040-4020(17)30956-0
10.1016/j.tet.2017.09.027
TET 28978
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 16 June 2017
Revised Date: 24 August 2017
Accepted Date: 14 September 2017
Please cite this article as: Ulu ÖDoğ, Gürbüz N, Özdemir İ, Alkylation of cyclic amines with alcohols
catalyzed by Ru(II) complexes bearing N-Heterocyclic carbenes, Tetrahedron (2017), doi: 10.1016/
j.tet.2017.09.027.
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ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Alkylation of Cyclic Amines with Alcohols Catalyzed by Ru(II) Complexes Bearing
N-Heterocyclic Carbenes
Öznur Doğan Ulu,a Nevin Gürbüza,b and İsmail Özdemira,b
a İnönü University, Catalysis, Research and Application Center, 44280 Malatya, Turkey
b İnönü University Faculty of Science and Arts, Department of Chemistry, 44280 Malatya, Turkey
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
This paper includes the synthesis of 2-(1,3-dioxane-2-yl)ethyl substituted benzimidazole
substituted N-heterocyclic carbenes precursors and their ruthenium complexes. Synthesised
compounds were characterized by elemental analysis and NMR spectroscopy. All complexes
have been tested in the alkylation of pyrrolidine and morpholine with alcohols, showing an
excellent activity in this reaction.
Available online
Keywords:
N-Heterocyclic carbene
Ruthenium
Alkylation
2009 Elsevier Ltd. All rights reserved
.
Cyclic amine
1. Introduction
activation,27 olefin metathesis,28 transfer hydrogenation,29
hydrosilylation30 and cycloproponation.31 The first application
of alkylation of catalyzed by Ir-NHC complexes using the
borrowing hydrogen method, highlighted the activity of these
ligands.32 This reaction has been successfully catalyzed by
diverse Ir-NHC complexes33, but has lately been validated for
Ru-NHC catalysis.34
N-heterocyclic carbenes (NHCs) are ubiquitous ligands in
chemistry.1 Due to their bonding properties and being stable to
air and moisture relative to similar ligands, NHCs are named as
unique ligands and their transition metal complexes are
successfully applied in organometallic chemistry2, catalysis3
and medicinal chemistry.4
To the best of our knowledge, the studies of using Ru-NHC
complexes in the alkylation of amines with alcohols are rare in
the literature. Recently our group has investigated ruthenium-
carbene complexes, in situ prepared catalyst system in the
alkylation of amines with alcohols.35 In current work, the new
benzimidazolium salts containing 2-(1,3-dioxane-2-yl)ethyl
that are precursors to these NHC ligands are readily
synthesized and the subsequent formation of complexes of Ag-
NHC has proved facile. The reaction of the Ag-NHC
complexes with [RuCl2(p-cymene)]2 in dichloromethane
afforded the Ru-NHC complexes (2a-g). The obtained Ru-
Amines are one of the most important compounds for the
chemical industry and find successful application in
pharmaceuticals, natural products, agrochemicals or food
additives.5 Therefore, a number of efficient methods like
Buchwald-Hartwig6,
Ullmann
reactions7,
reductive
elimination8 or hydroamination9 are used for synthesis of
amines. Although these methods are efficient, the formation of
side products and waste represents a drawback. In recent years,
to solve these problems an exclusive method for the direct
coupling of alcohols with amines has been used known as the
borrowing hydrogen method.10 Using alcohols as the alkylating
agent and the formation of water as a stoichiometric by-
product are the basic features of this reaction. Grigg11 and
Watanabe12 reported the N-alkylation of amines with alcohols
in 1980s. Grigg and co-workers described the reaction of
different alkyl amines with alcohols catalyzed by rhodium
catalyst. Similarly, Watanabe reported the N-alkylation of
aniline with primary alcohols catalyzed by Ru catalyst. After
these, a number of reports deal with N-alkylation of amines
using metal complexes especially based on ruthenium13-19 and
iridium.20-24 Ru-NHC complexes have long been used in many
research areas such as catalysis and photochemistry.25,26 They
are also efficient catalysts in numerous reactions including C-H
1
NHC complexes were characterized by H and 13C NMR, IR
and elemental analysis. These complexes are efficient catalyst
for alkylation of cyclic amines with diverse alcohols.
Corresponding author. Tel.: +90-422-377-3700; fax: +90-422-341-0212; e-mail: ismail.ozdemir@inonu.edu.tr

2
Tetrahedron
ACCEPTED MANUSCRIPT
Scheme 1. The synthesis of benzimidazolium salts.
2. Results and Discussion
Preparation of benzimidazolium salts
Dialkylbenzimidazolium salts, (1a-g) were prepared according to
proposed structure; the imino carbon appeared as a typical singlet
in the 1H-decoupled mode at 143.3, 143.4, 153.7 and 152.3 ppm,
respectively for benzimidazolium salts 1a-c and 1g. The 1H NMR
spectra of the benzimidazolium salts further supported the
assigned structures; the resonances for C(2)-H were observed as
sharp singlets at 11.32, 9.97, 10.38 and 11.36 ppm characteristic
of NCHN proton, respectively for 1a-c and 1g. The IR data for
benzimidazolium salts 1a-g clearly indicate the presence of the –
C=N– group with a ν(C=N) vibration at 1568, 1567, 1562 and
1566 cm-1, respectively for 1a-c and 1g. These values are in good
agreement with the previously reported results.33,35,36
known methods by the reaction of 1-alkylbenzimidazole with 2-
o
(2-bromoethyl)1,3-dioxane in dimethylformamide at 80 C, and
isolated in 84-90% yields.32,36 The structure of benzimidazolium
salts (1a-1g) was showed in Scheme 1. The salts are air- and
moisture stable both in the solid state and in solution and soluble
in chlorinated
solvents, alcohols and water. The
benzimidazolium salts (1a-g) were isolated as solids in very good
yields and fully characterized by 1H and 13C NMR, and IR
spectroscopy, elemental analyses, and their melting points were
determined. 13C NMR chemical shifts were consistent with the
Scheme 2. The synthesis of Ru-NHC complexes.

Analysis
the reactions by GC-MS showed that the
Preparation of ruthenium-carbene complexeAs 2Ca-Cg EPTED MANUSCoRf IPT
N-alkylation and N-C(3)-dialkylation products were formed in all
The procedure involving Ag-NHC carbene is probably one of the
most general methods, because it generates an air stable
intermediate under mild reaction-conditions, thus allowing an
easy access to a wide range of transition metal complexes. The
ruthenium complexes were prepared according to the Ag(I)-NHC
transfer method. The silver complexes were synthesized
according to the general method described by Wang and Lin.37
The silver carbene complexes, which should subsequently serve
as a carbene-transfer agent, were synthesized by the reaction of
Ag2O with 2 equiv. of salts (1a-1g) in CH2Cl2 at ambient
temperature. The non-isolated Ag-NHC complexes were
converted into the red brown monocarbene Ru-NHC complexes
(2a-2g) in dark condition at room temperature (Scheme 2). The
air and moisture-stable ruthenium carbene complexes (2a-2g)
were soluble in solvents such as dichloromethane, chloroform,
toluene, and tetrahydrofuran and insoluble in non-polar solvents.
Ru-NHC complexes were characterized by NMR, FT-IR and
elemental analysis. Ruthenium complexes exhibit a characteristic
υ(NCN) band typically at 1468, 1485, 1465, 1471, 1470, 1466 and
1469 cm-1 respectively for 2a-2g. 13C chemical shifts provide a
useful diagnostic tool for this type of metal carbene complexes.
The chemical shifts for the carbene carbon atom are located in
the 189-190 ppm range, and are similar to those found in other
ruthenium-carbene complexes. These complexes show typical
spectroscopic signatures, which are in line with those recently
reported for other [RuCl2(NHC)(arene)] complexes.29
of the reactions involving benzyl alcohol and pyrrolidine but in
varying ratios (Table 1, entries 1-7). For example, when 2a was
used as catalyst N- and C(3)-dialkylation product was observed
in 41/59 ratio (Table 1, entry 1), whereas in the case of 2e and 2g
N-alkylation was favored (Table 1, entries 5 and 7). These
reaction conditions were applied to the coupling of pyrrolidine
with various alcohols (Table 1). Benzylic alcohols with either
electron-donating or electron withdrawing substituents on the
aromatic ring reacted smoothly with pyrrolidine. Complex 2e
was shown to be selective towards N-alkylation of pyrrolidine
with p-methylbenzyl alcohol (Table 1, entry 12). Complex 2d
was shown to be selective towards N- and C(3)-dialkylation of
pyrrolidine with p-metylbenzyl alcohol (Table 1, entry 11).
However in the case of p-methoxybenzyl alcohol only N-
alkylation product was obtained in 75-88% conversion for
complexes 2b-2d and 2f-2g (Table 1, entries 16-18 and 20-21).
Whereas the complex 2a was used the N-alkylation product was
observed in 79/21 ratio (Table 1, entry 15).
Table 1. N-C(3) alkylation of pyrrolidine with benzyl alcohol
derivatives.a
Catalytic Alkylation and Dialkylation of Cyclic Amines with
Alcohols
Conv.
(%)
80
a
(%)
41
b
(%)
59
39
18
38
0
A one-step process for the simultaneous alkylation of both the N
atom and the unactivated C(3) carbon of secondary amines
corresponding to a formal sp3C-H activation was unknown until
Bruneau et al. reported the N- and C(3)-dialkylation of saturated
cyclic amines in the presence of ruthenium precatalysts equipped
with a phosphinesulfonate ligand acting as a P,O chelate.38
Recently our research group has investigated catalytic activity of
Ru-NHC complexes in similiar reaction.35b In this work, Ru
complexes (2a-g) featuring dioxane moieties, which upon
hydrolysis generates an aldehyde as a potential internal hydrogen
acceptor, were evaluated to explore their activities in the
alkylation of cyclic amines. The presence of an NHC ligand and
a second different donating group on the metal can radically alter
the catalytic properties. Also, the chelating nature of these
ligands results in the production of highly stable complexes.
NHCs are known to be compatible with a wide set of electron
donor nitrogen-, oxygen-, arene-containing functionalities.39 The
hemilable arm in such ligands is capable of reversible
dissociation to produce vacant coordination sites allowing
complexation of substrates during the catalytic cycle. At the same
time the strong donor carbene moiety remains connected to the
metal center.
Entry
Alcohol
Ru-NHC
1
2
2a
2b
2c
2d
2e
2f
95
61
3
91
82
4
91
62
OH
5
91
100
98
6
96
2
7
2g
2a
2b
2c
2d
2e
2f
96
100
31
0
8
67
69
48
34
93
0
9
71
52
10
11
12
13
14
15
16
17
18
19
20
21
87
66
100
89
7
OH
100
62
63
38
8
2g
2a
2b
2c
2d
2e
2f
100
73
92
The alkylation of pyrrolidine with benzyl alcohol was
investigated as a model reaction (Table 1). All reactions were
carried out with 1.0 mol% catalyst loading in toluene under an
argon atmosphere, by using a 1:2.5 amine/alcohol ratio in the
presence of D-(+)-camphorsulfonic acid (CSA) (40 mol %)
corresponding to the conditions from the present literature.35b, 38
The reaction was not successful in the absence of catalyst. When
the [RuCl2(p-cymene)]2 was used as the catalyst alkylation
product of pyrrolidine with benzyl alcohol was obtained in <5%
conversion. Moderate to high conversions (63-100%) of the
corresponding amines were observed by GC analysis for the
reactions of pyrrolidine and benzyl alcohol derivatives. The
results are summarized in Table 1.
79
21
0
77
100
100
100
82
92
0
MeO
87
0
OH
73
18
0
88
100
2g
75
100
0
aReagents and conditions: Pyrrolidine (1.0 mmol); alcohol (2.5 mmol); CSA
(40 mol%); Ru-NHC (1 mol%); toluene (1 mL); 120 oC, 16 h; a and b
determined from GC.

4
Tetrahedron
high selectivity. In contrast with pyrrolidine, we observed that
Morpholine and its derivatives are one suchAveCrsCatiElePbTuilEdiDng MANUSCRIPT
block intermediate and find a multitude of pharmaceutical
application as catalysts and physiologically active agents.
Therefore, alkylation of morpholine was then explored.
Morpholine was also alkylated to the corresponding tertiary
amines along with C(3)-alkylated product within 16 h in 83-
100% conversion. Typical results are shown in Table 2. When
complexes 2f and 2g were used products were obtained in 100%
conversion (Table 2, entries 6,7,14, 20,21). N- and C(3)-
dialkylation product was observed as minor product in all of the
reactions conducted using benzyl alcohol and morpholine (Table
2, entries 1-7).
N-alkylation of morpholine with p-methylbenzyl alcohol
occurred with high selectivity. For example when 2d was used as
catalyst N-alkylation product of morpholine p-methylbenzyl
alcohol was obtained in 98% selectivity (Table 2, entry 11),
pyrrolidine N- and C(3)-dialkylation product was obtained in
93% yield (Table 1, entry 11). Also we can say that there is no
significant difference for the other complexes on the catalytic
activity of the alkylation of morpholine and pyrollidine with
benzyl alcohol and p-methoxybenzyl alcohol. Among the tested
complexes, 2e, 2f and 2g are highly efficient in the N-alkylation
of morpholine.
Table 2 . N-C(3)-alkylation of morpholine with benzyl alcohol
3. Conclusion
derivatives.a
From readily available starting materials, such as 1,3-
dialkylbenzimidazolium salts, seven [RuCl2(p-cymene)(1,3-
dialkyl-benzimidazolidin-2-ylidene)] complexes (2a-g) have been
prepared by transmetallation with Ag-NHC complexes. The
efficiency of complexes 2a-g as catalyst precursors for the
alkylation of cyclic amines has been established. The Ru-NHC
complexes are very efficient to promote the catalytic reaction
affording N-alkylation or N- and C(3)-dialkylation of cyclic
amines from alcohols and secondary amines. We could show that
the selectivity of the reaction strongly depends on the nature of
the alcohol substrate. We can say that there is no significant
difference between complexes in ref 35b and these complexes on
the catalytic activity of the alkylation of morpholine and
pyrrolidine with derivative of benzyl alcohol. Here, although the
Conv.
(%)
93
a
(%)
82
87
87
84
100
97
98
79
82
84
98
100
81
98
90
98
96
97
80
100
94
b
(%)
18
13
13
16
0
Entry
Alcohol
Ru-NHC
1
2
2a
2b
2c
2d
2e
2f
93
3
98
conversion is not 100%, the selectivity is high. We are currently
investigating the scope and applications of these complexes as
catalysts for other borrowing hydrogen type reactions.
4
99
OH
5
94
6
100
100
83
3
Experimental Section
7
2g
2a
2b
2c
2d
2e
2f
2
All reactions for the preparation benzimidazolium salts (1) and
ruthenium-(NHC) complexes (2) were carried out under argon in
flame-dried glassware using standard Schlenk techniques.
Chemicals and solvents were purchased from Sigma–Aldrich and
Merck. The solvents used were purified by distillation over the
drying agents indicated and were transferred under Ar: Et2O
(Na/K alloy), CH2Cl2 (P4O10), hexane, toluene (Na). Melting
points were determined in glass capillaries under air with an
Electrothermal-9200 melting point apparatus. FT-IR spectra
were recorded as KBr pellets in the range 400-4000 cm-1 on a
ATI UNICAM 1000 spectrometer. 1H NMR and 13C NMR
8
21
18
16
2
9
86
10
11
12
13
14
15
16
17
18
19
20
21
98
100
94
OH
0
95
19
2
2g
2a
2b
2c
2d
2e
2f
100
90
10
2
spectra were recorded using
a Varian AS 400 Merkur
spectrometer operating at 300 MHz (1H), 75 MHz (13C) in CDCl3
and DMSO-d6 with tetramethylsilane as an internal reference. All
catalytic reactions were monitored on a Agilent 6890N GC and
Schimadzu 2010 Plus GC-MS system by GC-FID with a HP-5
column of 30 m length, 0.32 mm diameter and 0.25 ꢀm film
thickness. Column chromatography was performed using silica
gel 60 (70-230 mesh). Elemental analyses were performed by
İnönu University Scientific and Technology Center.
93
98
4
MeO
98
3
OH
87
20
0
100
100
2g
6
aReagents and conditions: Morpholine (1.0 mmol); alcohol (2.5 mmol); CSA
(40 mol%); Ru-NHC (1 mol%); toluene (1 mL); 120 oC, 16 h; a and b
determined from GC, dodecane was used as internal standard.
General method for the preparation of benzimidazolium salts
(1a-g)
To a solution of 1-alkylbenzimidazole (1 mol) in DMF (5 mL)
was slowly added 2-(2-bromoethyl)1,3-dioxane (1 mmol) and
the resulting mixture was stirred at room temperature for 5 h.
Diethyl ether (10 mL) was added to obtain a white crystalline
solid, which was filtered off. The solid was washed with diethyl
ether (3 x 10 mL) dried under vacuum and the crude product was
recrystallized from ethanol / diethylether.
We observed that N-alkylation of morpholine occurred with high
selectivity. For example, when 2a was used as catalyst N-
alkylation product of morpholine with benzyl alcohol was
obtained in 82% selectivity (Table 2, entry 1). However in the
case of pyrrolidine N- and C(3)-dialkylation product was
obtained in 59% yield (Table 1, entry 1). Under the reaction
conditions p-methylbenzyl, and p-methoxybenzyl alcohol reacted
cleanly with morpholine and produced N-alkylation products in

1-(Benzyl)-3-[2-(1,3-dioxane-2-yl)ethyl)]benzimidazolium
bromide, 1a
dioxane); 50.2 (NCH2CH2-1,3-dioxane); 57.3 (4-(C(CH3)3)C6H4-
CH2); 66.7 (NCH2CH2-1,3-dioxane-4,6-CH2); 99.2 (NCH2CH2-
1,3-dioxane-2-CH); 113.7, 126.3, 126.9, 127.1, 128.1, 129.6,
130.1, 131.1, 131.4 and 143.5 (C6H4 and 4-(C(CH3)3)C6H4);
152.3 (NCHN). Anal Calc. for C24H31BrN2O2: C: 62.74; H: 6.80;
N: 6.10 Found: C: 62.77; H: 6.83; N: 6.08.
ACCEPTED MANUSCRIPT
o
1
Yield: 3.38 g (% 84); ν(CN) = 1568 cm,-1 m.p.:153-154 C. H
NMR (300 MHz, CDCl3): δ: 1.84 (m, 2H, NCH2CH2-1,3-
dioxane-5-CH2); 2.28 (m, 2H, NCH2CH2-1,3-dioxane); 3.86 (m,
4H, NCH2CH2-1,3-dioxane-4,6-CH2); 4.78 (m, 2H, NCH2CH2-
1,3-dioxane-2-CH); 5.90 (s, 2H, C6H5-CH2); 7.26-7.75 (m, 9H,
C6H5-CH2, C6H4); 11.32 (NCHN). 13C NMR (75 MHz, CDCl3): δ
25.3 (NCH2CH2-1,3-dioxane-5-CH2); 33.8 (NCH2CH2-1,3-
dioxane); 42.3 (NCH2CH2-1,3-dioxane); 51.1 (s, 2H, C6H5-CH2),
66.7 (NCH2CH2-1,3-dioxane-4,6-CH2); 99.1 (NCH2CH2-1,3-
dioxane-2-CH); 113.2, 113.7, 126.9, 127.0, 128.2, 129.1, 129.3,
131.1, 131.5, 133.1 (C6H5-CH2, C6H4); 143.3 (NCHN). Anal
Calc. for C20H22O2N2Br: C: 59.71 H: 5.51; N: 6.96. Found: C:
59.70; H: 5.52; N: 6.94%.
General method for the synthesis of Ru(II)-NHC complexes
2a-2g
A solution of benzimidazolium salt (1.0 mmol), Ag2O (0.5
mmol), and activated 4 Å molecular sieves in dichloromethane
(30 mL) was stirred room temperature for 24 h. The reaction
mixture was filtered through Celite, and the solvent was removed
under reduced pressure. The prepared Ag-NHC was reacted with
[RuCl2(p-cymene)]2 in the dark, and the mixture was allowed to
stir for 24 h at room temperature. The solution was filtered
through Celite, and the solvent was removed under vacuum to
afford the product as a red-brown powder. The crude product was
recrystallized from dichloromethane/diethyl ether (1:2) at room
temperature.
1-(3-Methylbenzyl)-3-[2-(1,3-dioxane-2-
yl)ethyl]benzimidazolium bromide, 1b
o
Yield: 3.74 g (% 90); ν(CN) = 1567 cm,-1 m.p.:160-161 C. 1H
NMR (300 MHz, DMSO-d6): δ 2.17 (m, 2H, NCH2CH2-1,3-
dioxane); 2.30 (s, 3H, (3-CH3)C6H4-CH2); 2.51 (m, 2H,
NCH2CH2-1,3-dioxane-5-CH2); 3.86 ve 3.64 (m, 4H, NCH2CH2-
1,3-dioxane-4,6-CH2); 4.62 (t, J = 6.6 Hz 2H, NCH2CH2-1,3-
dioxane); 4.69 (t,1H, J = 4.5, NCH2CH2-1,3-dioxane-2-CH);
7.28-8.08 (m, 8H, (3-CH3)C6H4-CH2, C6H4); 5.74 (s, 2H, (3-
CH3)C6H4-CH2); 9.97 (NCHN). 13C NMR (75 MHz, DMSO-d6):
δ 21.4 ((3-CH3)C6H5-CH2); 25.5 (NCH2CH2-1,3-dioxane-5-CH2);
33.6 (NCH2CH2-1,3-dioxane); 42.8 (NCH2CH2-1,3-dioxane);
50.2 ((3-CH3)C6H5-CH2); 66.5 (NCH2CH2-1,3-dioxane-4,6-CH2);
99.5 (NCH2CH2-1,3-dioxane-2-CH), 114.2, 114.3, 125.7, 127.0,
127.1, 129.2, 129.4, 129.8, 131.2, 131.7, 134.5, 138.8, 143.4 ((3-
CH3)C6H4-CH2, C6H4); 143.4 (NCHN). Anal Calc. for
C21H24O2N2Br: C: 60.58; H: 5.81; N: 6.73. Found: C: 60.56; H:
5.79; N: 6.71.
Dichloro-[1-(benzyl)-3-(2-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II),
2a
Yield: 0.2 g (65%); ν(CN) = 1468 cm,-1 m.p.:185-186 oC. 1H NMR
(300 MHz, CDCl3): δ 1.24 (d, 6H, J= 6.9 Hz, (CH3)2CH-
C6H4CH3); 1.98 (s, 3H, (CH3)2CH-C6H4CH3); 3.86 (m, 4H,
NCH2CH2-1,3-dioxane-4,6-CH2); 2.08 (m, 2H, NCH2CH2
NCH2CH2-1,3-dioxane-5-CH2); 2.17 (m, 2H, NCH2CH2-1,3-
dioxane); 2.99 (m, 1H, (CH3)2CH-C6H4CH3); 4.15; 4.73; 5.31 (d,
4H, J = 6.0 Hz, (CH3)2CH-C6H4CH3); 4.84 (t, J = 4,8, 2H,
NCH2CH2-1,3-dioxane), 4,97 (m, 1H, NCH2CH2-1,3-dioxane-2-
CH); 5.76 (s, 2H, C6H5-CH2); 7.01-7.62 (m, 9H, C6H5-CH2,
C6H4). 13C NMR (75 MHz, CDCl3): δ 18.6 ((CH3)2CH-
C6H4CH3); 18.8 ((CH3)2CH-C6H4CH3); 25.9 (NCH2CH2-1,3-
dioxane-5-CH2); 30.6 ((CH3)2CH-C6H4CH3); 35.6 (NCH2CH2-
1,3-dioxane); 45.5 (NCH2CH2-1,3-dioxane); 52.6 (s, 2H, C6H5-
CH2); 66.9 (NCH2CH2-1,3-dioxane-4,6-CH2); 83.6; 87.0
1-(2,3,5,6-Tetramethylbenzyl)-3-[2-(1,3-dioxane-2-
yl)ethyl]benzimidazolium bromide, 1c
o
Yield: 4.08 g (% 89); ν(CN) = 1562 cm,-1 m.p.:215-216 C. 1H
(CH3)2CH-C6H4CH3);
99.2
(NCH2CH2-1,3-dioxane-2-CH);
NMR (300 MHz, CDCl3): δ
1.80 (m, 2H, NCH2CH2-1,3-
100.3, 108.5, 111.2, 111.5, 122.9, 123.1, 126.0, 126.1, 127.4,
128.8, 135.0, 135.7 137.6 (C6H5-CH2, C6H4); 190.4 (Ru-Ccarbene).
Anal. Calc. for C30H36O2Cl2N2Ru: C: 57.32; H: 5.77; N: 4.46.
Found: C: 57.30; H: 5.78; N: 4.44.
dioxane-5-CH2); 2.25 (s, 12H, 2,3,5,6-(CH3)4C6H); 2.94 (m, 2H,
NCH2CH2-1,3-dioxane); 3.83 (m, 4H, NCH2CH2-1,3-dioxane-
4,6-CH2); 4.83 (m, 3H, NCH2CH2-1,3-dioxane-2-CH); 5.81 (s,
2H, 2,3,5,6-(CH3)4C6H-CH2); 7.07 (s, 1H, 2,3,5,6-(CH3)4C6H);
7.28-8.00 (m, 4H, C6H4); 10.38 (s, 1H, NCHN),. 13C NMR (75
MHz, CDCl3): δ 15.3 (2,3,5,6-(CH3)4C6H2); 25.4 (NCH2CH2-1,3-
dioxane-5-CH2); 47.9 (NCH2CH2-1,3-dioxane); 54.7 (NCH2CH2-
1,3-dioxane), 56.8 (2,3,5,6-(CH3)4C6H2-CH2), 60.9 (NCH2CH2-
Dichloro-[1-(3-methylbenzyl)-3-(2-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II),
2b
Yield: 0.25g (78%); ν(CN) = 1485 cm,-1 m.p.: 194-195 C. H
NMR (300 MHz, CDCl3): δ 1.27 (d, 6H, J = 7.2 Hz, (CH3)2CH-
C6H4CH3); 2,0 (s, 3H, (CH3)2CH-C6H4CH3); 2.01(s, 3H, (3-
CH3)C6H4-CH2); 2.15 (m, 2H, NCH2CH2-1,3-dioxane-5-CH2);
2.31 (m, 2H, NCH2CH2-1,3-dioxane); 2.93 (m, 1H, (CH3)2CH-
C6H4CH3); 3.85 (m, 4H, NCH2CH2-1,3-dioxane-4,6-CH2); 4.72
(m, 2H, NCH2CH2-1,3-dioxane); 4,84 (t,1H, J = 4.8, NCH2CH2-
1,3-dioxane-2-CH), 4.85; 5.30; 5.68 (d, 4H, J = Hz, (CH3)2CH-
C6H4CH3); 5,63 (s, 2H, (3-CH3)C6H4-CH2); 6.51-7.63 (m, 8H, (3-
CH3)C6H4-CH2, C6H4). 13C NMR (75 MHz, CDCl3): δ 18.5
o
1
1,3-dioxane-4,6-CH2);
106.9 (NCH2CH2-1,3-dioxane-2-CH);
113.7, 127.2, 128.2, 131.8, 138.4, 138.8, 143.9 (C6H4 and 2,3,5,6-
(CH3)4C6H2); 153.7 (NCHN). Anal Calc. for C24H30BrN2O2:
C:62.88; H: 6.60; N: 6.11 Found: C: 62.79; H: 6.51; N: 6.02.
The benzimidazolium salts 1d-1f were synthesized according to
published procedure.36
1-(4-terbutylbenzyl)-3-[2-(1,3-dioxane-2-
yl)ethyl]benzimidazolium bromide, 1g
((CH3)2CH-C6H4CH3);
((CH3)2CH-C6H4CH3); 25.8 (NCH2CH2-1,3-dioxane-5-CH2);
30.6 ((CH3)2CH-C6H4CH3); 35.6 (NCH2CH2-1,3-dioxane); 45.54
21.5
((3-CH3)C6H4-CH2);
21.8
o
1
Yield: 3.7 g (% 80); ν(CN)
=
1566 cm,-1 m.p.:142-143 C. H
NMR (300 MHz, CDCl3): δ 1.26 (s, 9H, 4-(C(CH3)3)C6H4); 1.86
(m, 2H, NCH2CH2-1,3-dioxane-5-CH2); 2.96 (m, 2H, NCH2CH2-
1,3-dioxane); 3.86 (m, 4H, NCH2CH2-1,3-dioxane-4,6-CH2);
4.78 (t, 2H, J= 6.6 Hz, NCH2CH2-1,3-dioxane); 4.83 (t, 1H, J =
(NCH2CH2-1,3-dioxane); 52.5
((3-CH3)C6H4-CH2); 66.8
(NCH2CH2-1,3-dioxane-4,6-CH2); 83.6; 85.9 (CH3)2CH-
C6H4CH3); 99.4 (NCH2CH2-1,3-dioxane-2-CH); 87.1;100.4;
108.5; 111.2; 111.6, 122.9, 123.1, 126.8, 128.2, 128.7, 134.9,
135.8, 137.6 138.6, ((3-CH3)C6H4-CH2, C6H4); 190.2 (Ru-
Ccarbene). Anal. Calc. for C31H38O2Cl2N2Ru: C: 57.94; H: 5.96; N:
4.36. Found: C: 57.91; H: 5.95; N: 4.34.
4.2 Hz, NCH2CH2-1,3-dioxane-2-CH);
5.85 (s, 2H, 4-
(C(CH3)3)C6H4-CH2); 7.37-7.75 (m, 8H, C6H4 and 4-
(C(CH3)3)C6H4); 11.36 (s, 1H, NCHN),. 13C NMR (75 MHz,
CDCl3): δ
25.4 (NCH2CH2-1,3-dioxane-5-CH2); 31.2 (4-
(C(CH3)3)C6H4); 34.6 (4-(C(CH3)3)C6H4); 42.6 (NCH2CH2-1,3-

6
Tetrahedron
Dichloro-[1-(2,3,5,6-tetramethylbenzyl)-3-(2-(1,3-dioxane-2-
86.1, 87.3 (CH3)2CH-C6H4CH3); 99.4 (NCH2CH2-1,3-dioxane-2-
ACCEPTED MANUSCRIPT
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II),
CH),
103.7, 111.2, 133.0, 134.7, 137.2, 153.5 ((3,4,5-
2c
(OCH3)3C6H2-CH2), 109.2, 111.7, 123.1, 134.9 (C6H4); 190.41
(Ru-Ccarbene). Anal. Calc. for C33H42O5RuCl2N2: C: 55.99; H:
6.71; N: 373. Found: C: 55.96; H: 6.68; N: 3.67.
Yield: 0.29g (85%); ν(CN) = 1465 cm,-1 m.p.: 303-304 C. H
NMR (300 MHz, CDCl3): δ 1.34 (d, 6H, J = 7.2 Hz,
(CH3)2CHC6H4CH3); 1.77 (s, 3H, (CH3)2CH-C6H4CH3); 2.01 (m,
2H, NCH2CH2-1,3-dioxane-5-CH2); 2.19 and 2.30 (s, 12H,
2,3,5,6-(CH3)4C6H2); 2.17 (m, 2H, NCH2CH2-1,3-dioxane); 3.06
(m, 1H, (CH3)2CH-C6H4CH3); 3.86 (m, 4H, NCH2CH2-1,3-
dioxane-4,6-CH2); 4.84 (m, 3H, NCH2CH2-1,3-dioxane-2-CH);
4.16; 5.36 (d, 4H, J= 3.6 Hz, (CH3)2CH-C6H4CH3); 5.63 (s, 2H,
2,3,5,6-(CH3)4C6H2-CH2); 6.10 (s, 1H, 2,3,5,6-(CH3)4C6H1);
6.79-7.50 (m, 4H, C6H4). 13C NMR (75 MHz, CDCl3): δ 16.1
o
1
Dichloro-[1-(methoxyethyl)-3-(-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II), 2f
o
1
Yield: 0.19 g (65%); ν(CN) = 1466 cm,-1 m.p.:173-174 C. H
NMR (300 MHz, CDCl3): δ 2.12 (m, 2H, NCH2CH2-1,3-dioxane-
5-CH2); 2.28 (q, 2H, J = 5.7 Hz, NCH2CH2-1,3-dioxane); 3.31 (s,
3H, NCH2CH2OCH3); 3.97 (m, 4H, NCH2CH2-1,3-dioxane-4,6-
CH2); 4.73 (t, 2H, J = 6.3 Hz, NCH2CH2OCH3); 4.86 (m, 3H,
NCH2CH2-1,3-dioxane-2-CH); 4.94 (t, 2H,
J = 6.3 Hz,
(2,3,5,6-(CH3)4C6H2);
18.7
((CH3)2CH-C6H4CH3);
20.6
NCH2CH2OCH3); 7.31-7.73 (m, 4H, C6H4). 13C NMR (75 MHz,
CDCl3): δ 25.4 (NCH2CH2-1,3-dioxane-5-CH2); 35.1 (NCH2CH2-
((CH3)2CH-C6H4CH3); 25.8 (NCH2CH2-1,3-dioxane-5-CH2);
30.9 ((CH3)2CH-C6H4CH3); 35.8 (NCH2CH2-1,3-dioxane); 45.4
(NCH2CH2-1,3-dioxane); 51.7 (2,3,5,6-(CH3)4C6H2-CH2), 66.9
(NCH2CH2-1,3-dioxane-4,6-CH2); 98.9 (NCH2CH2-1,3-dioxane-
2-CH), 83.9; 98.9 (CH3)2CH-C6H4CH3); 100.3, 108.1, 110.7,
111.6, 122.3, 122.6, 131.9, 132.0, 135.0, 135.6 (C6H4 and 2,3,5,6-
1,3-dioxane);
45.0
(NCH2CH2-1,3-dioxane);
48.2
(NCH2CH2OCH3); 59.8 (NCH2CH2OCH3); 67.1 (NCH2CH2-1,3-
dioxane-4,6-CH2); 70.7 (NCH2CH2OCH3); 97.6 (NCH2CH2-1,3-
dioxane-2-CH); 112.8, 126.7, 131.0, 133.8 (C6H4); 190.0 (Ru-
Ccarbene). Anal. Calc. for C26H35O3RuCl2N2: C: 52.44; H: 5.92; N:
4.70. Found: C: 52.41; H: 5.89; N: 4.68.
(CH3)4C6H2);
188.8
(Ru-Ccarbene).
Anal.
Calc.
for
C34H44O2Cl2N2Ru: C: 60.32; H: 7.31; N: 3.91. Found: C: 60.28;
H: 7.27; N: 3.85.
Dichloro-[1-(4-terbutylbenzyl)-3-(2-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II),
2g
Dichloro-[1-(2,4,6-trimethylbenzyl)-3-(2-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p-cymene)ruthenium(II),
2d
o
Yield: 0.27 g (77% ); ν(CN) = 1469 cm,-1 m.p.: 199-200 C. 1H
Yield: 0.24 g (71%); ν(CN) = 1471 cm,-1 m.p.: 287-288 C. H
NMR (300 MHz, CDCl3): δ 1.33 (d, 6H, J= 6.9 Hz, (CH3)2CH-
C6H4CH3); 1.88 (s, 3H, (CH3)2CH-C6H4CH3); 2.09 (m, 2H,
NCH2CH2-1,3-dioxane-5-CH2); 2.11 (s, 6H, 2,6-(CH3)3C6H2),
2.22 (m, 2H, NCH2CH2-1,3-dioxane); 2.29 (s, 3H, 4-
(CH3)3C6H2), 3.03 (m, 1H, (CH3)2CH-C6H4CH3); 3.85 (m, 4H,
NCH2CH2-1,3-dioxane-4,6-CH2); 4.84 (m, 3H, NCH2CH2-1,3-
dioxane-2-CH); 4.16; 4.71; 5.32 (d, 4H, J = 6.0 Hz, (CH3)2CH-
C6H4CH3); 5.62 (s, 2H, 2,4,6-(CH3)3C6H2-CH2), 6.39 (s, 2H,
2,4,6-(CH3)3C6H2); 6.83-7.53 (m, 4H, C6H4). 13C NMR (75 MHz,
o
1
NMR (300 MHz, CDCl3): δ 1.31 (s, 9H, 4-(C(CH3)3)C6H4); 1.80
(m, 2H, NCH2CH2-1,3-dioxane-5-CH2); 2.85 (m, 2H, NCH2CH2-
1,3-dioxane); 3.93 (m, 4H, NCH2CH2-1,3-dioxane-4,6-CH2);
4.69 (t, 2H, J = 6.3 Hz, NCH2CH2-1,3-dioxane); 4.91 (t, 1H, J =
5.4 Hz, NCH2CH2-1,3-dioxane-2-CH);
(C(CH3)3)C6H4-CH2); 7.48-7.81 (m, 8H, C6H4 and 4-
(C(CH3)3)C6H4). 13C NMR (75 MHz, CDCl3):
24.9
(NCH2CH2-1,3-dioxane-5-CH2); 31.7 (4-(C(CH3)3)C6H4); 35.0
(4-(C(CH3)3)C6H4); 43.7 (NCH2CH2-1,3-dioxane); 52.4
5.96 (s, 2H, 4-
δ
(NCH2CH2-1,3-dioxane); 58.3 (4-(C(CH3)3)C6H4-CH2); 67.5
(NCH2CH2-1,3-dioxane-4,6-CH2); 98.2 (NCH2CH2-1,3-dioxane-
2-CH); 112.1, 125.9, 127.2, 127.9, 128.8, 129.1, 130.7, 131.8,
132.5, 142.6 (C6H4 and 2,3,5,6-(CH3)4C6H2); 191.3 (Ru-Ccarbene).
Anal Calc. for C34H43O3RuCl2N2: C: 58.36; H: 6.19; N: 4.00
Found: C: 58.32; H: 6.17; N: 4.03.
CDCl3):
δ
18.7 ((CH3)2CH-C6H4CH3); 18.9 ((CH3)2CH-
C6H4CH3); 20.4 (2,6-(CH3)3C6H2); 20.9 (4-(CH3)3C6H2); 25.8
(NCH2CH2-1,3-dioxane-5-CH2); 30.9 ((CH3)2CH-C6H4CH3);
35.9 (NCH2CH2-1,3-dioxane); 45.3 (NCH2CH2-1,3-dioxane);
50.5 (2,4,6-(CH3)3C6H2); 66.9 (NCH2CH2-1,3-dioxane-4,6-CH2);
83.8, 86.2 (CH3)2CH-C6H4CH3); 98.8 (NCH2CH2-1,3-dioxane-2-
CH); 98.7, 100.1, 108.3, 109.0, 110.8, 111.3, 122.5, 122.7, 129.0,
129.5, 130.2, 134.9, 135.2, 137.4, 138.3 (2,4,6-(CH3)C6H2,
C6H4); 188.9 (Ru-Ccarbene). Anal. Calc. for C33H42O2Cl2N2Ru: C:
59.82; H: 7.17; N: 3.99. Found: C: 59.78; H: 7.10; N: 3.90.
General Procedure for Catalytic N-Alkylation and N- and
C(3) dialkylation of Cyclic Amines with Alcohols. As
described in reference 35b and 38, to a stirred solution of cyclic
1 mL toluene was added D-(+)-
camphorsulfonic acid (40 mol %). After stirring for 1 min,
alcohol (2.5 mmol) and Ru-NHC (1 mol%) were added and
amine (1 mmol) in
Dichloro-[1-(3,4,5-trimethoxybenzyl)-3-(2-(1,3-dioxane-2-
yl)ethyl)benzimidazole-2-ylidene](p- cymene)ruthenium(II) ,
2e
o
stirred at 120 C for 16 h. The reaction mixture was quenched in
toluene and filtered through a short pad of SiO2. The filtrate was
subjected to GC and GC-MS. All data reported are an average of
at least two runs and, dodecane was used as internal standard.
Yield: 0.25 g (70%); ν(CN) = 1470 cm,-1 m.p.:150-151 C. H
NMR (300 MHz, CDCl3): δ 1.26 (d, 6H, J = 6.9 Hz, (CH3)2CH-
C6H4CH3); 1.73 (s, 3H, (CH3)2CH-C6H4CH3); 2.02 (m, 2H,
NCH2CH2-1,3-dioxane-5-CH2); 2.21 (q, 2H, , J = 5.4 Hz,
NCH2CH2-1,3-dioxane); 2.96 (h, 1H, J= 6.9 Hz, (CH3)2CH-
C6H4CH3); 3.71 (s, 6H, 3,5-(OCH3)3C6H2); 3.81 (s, 3H, 4-
(OCH3)3C6H2); 3.89 (m, 4H, NCH2CH2-1,3-dioxane-4,6-CH2);
4.75 (m, 3H, NCH2CH2-1,3-dioxane-2-CH); 5.31 (s, 2H, 3,4,5-
(OCH3)3C6H2-CH2), 6.38 (s, 2H, 3,4,5-(OCH3)3C6H2); 4.98, 5.02,
5.42 and 5.83 (d, 4H, J = 4.8 Hz, (CH3)2CH-C6H4CH3); 7.10-7.62
(m, 4H, C6H4). 13C NMR (75 MHz, CDCl3): δ 18.7 ((CH3)2CH-
C6H4CH3); 21.9 ((CH3)2CH-C6H4CH3); 25.8 (NCH2CH2-1,3-
dioxane-5-CH2); 30.7 ((CH3)2CH-C6H4CH3); 35.6 (NCH2CH2-
1,3-dioxane); 45.4 (NCH2CH2-1,3-dioxane); 53.5 (3,4,5-
(OCH3)3C6H2-CH2); 56.3 (3,5-(OCH3)3C6H2); 60.9 (4-
(OCH3)3C6H266.9 (NCH2CH2-1,3-dioxane-4,6-CH2), 82.1; 83.1,
o
1
Acknowledgment
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBİTAK (112T303).
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