Ru(II)-NHC catalysed N-Alkylation of amines with alcohols under solvent-free conditions

Article abstract of DOI:10.1016/j.ica.2021.120294

The reaction of [RuCl₂(p-cymene)]₂ with in situ prepared Ag-N-heterocyclic carbene (NHC) complexes yields a series of [RuCl₂(p-cymene)(NHC)] complexes (2). All of the complexes have been characterised by elemental analysis, and ¹H NMR and ¹³C NMR spectroscopies. These complexes have been tested for the N-alkylation of aromatic amines with arylmethyl alcohols under neat conditions in the presence of KOtBu at 120 °C. Compounds (2) are stable and have high catalytic/selective activity for the N-alkylation reactions of primary amines to afford secondary amines.

Full text of DOI:10.1016/j.ica.2021.120294

Inorganica Chimica Acta 520 (2021) 120294
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Ru(II)-NHC catalysed N-Alkylation of amines with alcohols under
solvent-free conditions
a
a
,
,
,c
Emine Ozge Karaca , Zieneb Imene Dehimat b, Sedat Yasara c, Nevin Gürbüza
,
¨
¸
b
d
a,c,*
¨
˙
Dahmane Tebbani , Bekir Çetinkaya , Ismail Ozdemir
a
¨
Catalysis Research and Application Center, Inonü University, 44280 Malatya, Turkey
b Laboratory of Natural Products of Plant Origin and Organic Synthesis, Department of Chemistry, Faculty of Exact Sciences, University of Constantine 1, 25000
Constantine, Algeria
c
¨
Department of Chemistry, Faculty of Science and Art, Inonü University, 44280 Malatya, Turkey
d Department of Chemistry, Ege University, 35100 Izmir, Turkey
A R T I C L E I N F O
A B S T R A C T
The reaction of [RuCl2(p-cymene)]2 with in situ prepared Ag-N-heterocyclic carbene (NHC) complexes yields a
series of [RuCl2(p-cymene)(NHC)] complexes (2). All of the complexes have been characterised by elemental
analysis, and 1H NMR and 13C NMR spectroscopies. These complexes have been tested for the N-alkylation of
aromatic amines with arylmethyl alcohols under neat conditions in the presence of KOtBu at 120 ◦C. Compounds
(2) are stable and have high catalytic/selective activity for the N-alkylation reactions of primary amines to afford
secondary amines.
Dedicated to Professor Maurizio Peruzzini on
the occasion of his 65th birthday and contri-
bution to the transition metal chemistry.
Keywords:
Amine
Hydrogen auto-transfer method
N-alkylation
Ru(II)-NHC
1. Introduction
generally low in the N-alkylation with alkyl halides because the nucle-
ophilicity of amines is increased by the N-alkylation, resulting in the
N-Heterocyclic carbenes have been used in recent years as an alter-
native to phosphine ligands in organometallic chemistry for homoge-
neous catalyst synthesis [1]. Unlike phosphine ligands, NHC ligands are
formation of undesired tertiary amines and alkylammonium halides as
byproducts [9–11].
More environmentally benign outcomes are obtained by metal-
catalysed N-alkylation of primary amines with either alcohols or
amines. These methods all have advantages and disadvantages, and
there is still room for improvement [12]. The advantage of the proced-
ure in comparison with the N-alkylation with alkyl halides is the high
selectivity to the desired. However, these systems have disadvantages
such as the recovery and reuse of expensive catalysts and/or the indis-
pensable use of cocatalysts such as bases and stabilising ligands.
The borrowing hydrogen (BH) or the hydrogen auto-transfer method
is a tandem process, where alcohols are dehydrogenated followed by
base-mediated condensation of the resulting carbonyls with an amine
nucleophile; subsequently the imine intermediate product is reduced.
This procedure can be carried out under milder conditions at atmo-
spheric pressures as it does not require additional hydrogen. It has many
advantages over conventional methods when it comes to selectivity,
cost, efficiency, and environmental considerations: only water emerges
more desirable because they have good σ-donor properties, low toxicity
and can be more easily synthesised. The tunable character of NHCs al-
lows easy control of the electronic and steric properties at the metal
centre. As a result, NHC complexes have emerged as versatile tools in
homogenous catalysis. N-Heterocyclic carbenes play a key role in the
–
– –
catalytic form of organic synthesis such as C H activation, C C, C O,
–
and C N bond formation [2–6].
Amines are extensively used as pharmaceuticals and synthetic in-
termediates [7,8]. They can be synthesised by various stoichiometric
and catalytic methods. The stoichiometric methods produce large
amounts of waste. Furthermore, N-alkylation with alkyl halides and
reactions containing strong reducing agents are particularly unfriendly
to the environment, as these materials are highly toxic. Many of the
reported methods (both catalytic and non-catalytic) have drawbacks
with selectivity. The selectivity to the desired secondary amines is
* Corresponding author.
¨
˙
E-mail address: ismail.ozdemir@inonu.edu.tr (I. Ozdemir).
https://doi.org/10.1016/j.ica.2021.120294
Received 28 September 2020; Received in revised form 4 February 2021; Accepted 8 February 2021
Available online 16 February 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

¨
E.O. Karaca et al.
Inorganica Chimica Acta 520 (2021) 120294
as a by-product [13]. All of these features make this method attractive
for environmentally friendly and green chemistry. It is important from
both industrial and academic points of view to improve selectivity and
productivity by developing new and effective catalysts.
The new [RuCl2(p-cymene)(NHC)] complexes (2a-2d) were pre-
pared using a two-step process by transmetalling the respective silver-
NHC derivatives (Scheme 1). Without isolation, the silver-NHC com-
plexes were used in situ. Then, adding [RuCl2(p-cymene)]2 to the
mixture gave orange-brown complexes with good yields (70–78%).
Ruthenium carbene complexes (2a-2d) are soluble in solvents such as
chloroform, dichloromethane; and tetrahydrofuran, but not in nonpolar
Grigg [14] and Watanabe [15] initially performed Ru-catalysed N-
alkylation. More recently, better catalytic systems have been reported:
these homogenous catalysts for alcohol amination are based on com-
plexes of Ru, Ir, Fe, Co, Mn, Cu, Pd, Ni and Cr containing different li-
gands [16–29]. In the past several years, we have synthesised several
NHC complexes bearing symmetrical or unsymmetrical benzyl groups
with various alkyl substituents on the benzene ring. Their diverse
structures could tune the properties of the corresponding complexes
[30,31]. The incorporation of alkyl-substituents in the NHC ligand
provides soluble catalyst complexes. Also, the electron-donating ability
of the ligands greatly affects the redox potential of the transition metal
complex and influences the reactivity of the metal centre. In this work,
Ru(II) complexes 2 based on the imidazole/ benzimidazole skeleton was
synthesised and the catalytic properties for BH were investigated.
solvents. The structure of 2a-2d complexes was confirmed by 1H and 13
C
NMR pectra. The characteristic downfield signals for the NCHN protons
of the corresponding salts 1a-1d disappeared in the 1H NMR spectra of
complexes 2a-2d. The aromatic protons of benzimidazole were seen as a
multiplet at δ between 6.19 and 7.38 ppm in the 1H NMR spectrum. –CH-
Protons of p-cymene group on all complexes (2a-2d) are seen as heptets
in the range from 2.58 to 2.91 ppm. Methylic protons of isobutyl group
on p-cymene resonated between 1.13, 1.14, 1.22 and 1.25 as doublets
while methyl protons on p-cymene were detected as singlets at 2.06,
1.89 and 1.90 ppm. The proton signals of adamantyl groups were
observed at 1.60–1.89 ppm. The complexes exhibit 13C chemical shifts of
carbene carbon at 174.3, 189.0, 191.4 and 190.2 ppm, respectively. The
data are close to those reported for other Ru-NHC complexes [31].
2. Results and discussions
In this study, we used imidazolium and benzimidazolium salts (1)
containing 4-(1-adamantylbenzyl substituent(s), which are readily syn-
thesised precursors to these NHC ligands. The subsequent formation of
Ag-NHC complexes has proved simple. The in situ reaction of the Ag-
NHC complexes with [RuCl2(p-cymene)]2 in dichloromethane afforded
Ru-NHC complexes (2a-2d). The obtained Ru-NHC complexes were
characterised by elemental analysis, 1H NMR and 13C NMR spectros-
copies. These complexes are effective precatalysts for the alkylation of
aromatic amines with different alcohols, in neat conditions.
2.4. The N-alkylation of amines with alcohols
Secondary amines can be synthesised by many different methods.
Reactions for their synthesis include the alkylation of amines with alkyl
halides [37–39], the direct reductive amination of ketones and alde-
hydes [40] and the hydroamination of unsaturated hydrocarbons with
amines [41,42]. These methods generally require environmentally
harmful organic solvents, alkyl halides and/or stoichiometric quantities
of reducing agents. In recent decades, much attention has focused on the
use of inexpensive and low toxicity alcohols as the alkylation reagent
[43]. The N-alkylation of amines with alcohols presents a green method
for the synthesis of substituted amines that have substantial importance
in synthetic applications. Ru- and Ir catalysed amine alkylation by
alcohol has been previously reported by several groups [13].
2.1. Preparation of imidazolium salt, 1a
The known compound 4-(1-adamantylbenzyl) bromide [32] was
heated with 1-methylimidazole to obtain 1a. 1-Methyl-3-(4-adamantyl-
benzyl)imidazolium bromide (1a) is air and moisture stable. 1a is sol-
uble in chlorinated solvents, alcohols, and water. The spectral properties
of the imidazolium salt are similar to those of other reported imidazo-
lium salts [33]. In the 1H NMR spectrum of 1a, the NCHN proton appears
as a singlet at 10.41. The signal of benzylic and aromatic hydrogens of
adamantyl group appeared at 7.21–7.37 ppm. Protons of imidazole
CH=CH appear as singlets at 5.45 and 5.47 ppm. The other signals of
adamantyl group appear as singlet 1.74 and 2.02 ppm and quartet 1.66
ppm. The signal of methyl group as singlet 4.03 ppm.
Here, we used the optimised conditions for the catalytic reaction,
which were determined in our previous works [30a,31]. In a standard
experiment, KOtBu (1 mmol), aromatic amine (1 mmol), alcohol de-
rivative (1.5 mmol), and the Ru-NHC complex 2a-2d (0.025 mmol) were
added to the Schlenk tube under an inert atmosphere. The sealed
Schlenk tube was stirred at 120 ◦C for 24 h. The reaction mixture was
cooled to room temperature at the end of the reaction, before CH2Cl2 (2
mL) was added, and filtered through a short SiO2 pad. The filtrate was
analysed by GC. The yields were based on the corresponding aniline. The
reactions were performed at a molar ratio of 1:0.025:1 aniline/pre-
catalyst /base (S/C/base). It is worth noting that when the excess of
benzyl alcohol (5 mmol) is used, only the secondary amine is formed in
the catalytic reaction.
2.2. Preparation of benzimidazolium salts
According to the literature [32,34], ligand precursors (1b-1d) were
synthesised by quaternisation of 1-(4-adamantylbenzyl)-benzimidazole
in DMF with corresponding benzyl bromides in a nearly quantitative
yield, 88–90%. The salts are stable in solid-state. All salts are soluble in
chlorinated solvents, alcohols, and water. The NCHN protons appear in
the 1H NMR range of 1b-1d at 11.40, 11.76 and 10.82 ppm, respectively,
and these downfield signals confirm the formation of the benzimidazo-
The N-alkylation of aniline, 2,4-dimethyl aniline, 4-(trifluoromethyl)
aniline with the alcohols (benzyl alcohol, 4-methybenzyl alcohol, 4-
methoxybenzyl alcohol, furfuryl alcohol, and 3,4-dimethoxybenzyl
alcohol) was investigated using 2a-d precatalysts to obtain the second-
ary amines under reaction conditions. Table 1 summarises the N-alkyl-
ation of arylamines with benzyl alcohols. When the reaction of aniline
with benzyl alcohol was performed by the complex 2a-2d, N-benzyla-
niline was obtained as a major product (Table 1, entry 1). For example,
when complex 2a was used as the precatalyst, 93% conversion with an
amine/imine ratio of 98/2 was observed. Examination of the table
shows that conversions are relatively low in the case of sterically hin-
dered 2,4-dimethylaniline (Table 1, entries 6–10). We obtained the
corresponding N-benzyl-2,4-dimethylaniline with 60–100% selectivity
in 48–98% conversions (Table 1, entries 6–10). In this reaction when 2b
complex was used as the precatalyst, 96% conversion with an amine/
imine ratio of 83/17 was observed (Table 1, entry 6). Alkylation re-
actions with arylmethyl alcohols, bearing electron-donating methyl and
methoxy groups resulted in high conversion mainly amine was obtained
1
lium salts. The H NMR shifts of 1b-1d are identical to those of other
characterised benzimidazolium salts [35].
2.3. Preparation of ruthenium-carbene complexes 2a-2d
NHC complexes are prepared using a variety of methods. One of the
most useful approaches in this regard is transmetalation with Ag-NHC
complexes. The use of silver-carbene complexes as a carbene transfer
agent avoids complicated working difficulties. Transmetalation re-
actions can often be conducted under aerobic conditions; this method
can be successfully extended to metals such as Cu, Au, Pd, Ni, Pt, Rh, Ru
and Ir [36].
2

¨
E.O. Karaca et al.
Inorganica Chimica Acta 520 (2021) 120294
Cl
Ru
Cl
N
N
N
N
Ag Br
N
N
Br-
2a
1a
1/2 Ag2O / DCM
- H2O
1/2 [RuCl2(p-cymene)]2
- AgBr
R
R
R
R'
R'
R'
R'
R'
R'
N
N
N
Cl
Ru
Cl
N
Br-
Ag Br
N
N
2b-2d
1b-1d
2b R' = CH3 R= 3,5-Dimethyl
2c R' = H
2d R' = H
R = 4-tert-Butyl
R = 2,3,4,5,6-Pentamethyl
Scheme 1. Synthesis of [RuCl2(p-cymene)(NHC)] complexes.
(Table 1, entries 2–4) and complex 2a was the most efficient precatalyst.
When 4-methylbenzyl alcohol is used as an alkylating agent, N-(4-
methylbenzyl)aniline could be obtained in high conversion (Table 1,
entry 2). When 2a complex was used as the precatalyst, full conversion
with mono-alkylated N-alkylaniline was formed selectively.
adamantyl substituent at the C-4 positions of the benzyl rings, was
synthesized. N-Heterocyclic carbene based ruthenium(p-cymene) com-
plexes 2a-2d were prepared in situ by reacting Ag(I)-NHC complexes
with [RuCl2(p-cymene)]2 in dichloromethane at room temperature. The
catalytic activity of the resulting Ru(II) complexes was evaluated in the
alkylation of aniline derivatives via arylmethyl alcohols. We thought
that Ru-NHC complexes would be the better catalyst due to the steric
hindrance of the adamantyl group. But the catalytic results of N-alkyl-
ation reactions are not so different than others in our previous work.
Substitution of the aromatic rings at the C-4 position of the NHC ligand
did not reveal a notable enhancement of the catalytic reactions.
The amine with an electron-withdrawing group like -CF3 has been
almost converted to an N-alkylated product (up to 100%) with aryl-
methyl alcohols using 2a-2d as a precatalyst (Table 1, entries 11–14).
The electron-donating substituents like Me and OMe on both benzyl
alcohol and aniline have significantly improved the selectivity of mono-
alkylated amine products under the same conditions. All of the reactions
using 3,4-dimethoxybenzyl alcohol resulted in the selective formation of
mono-alkylated aniline in high conversions (Table 1, entry 4). When the
reaction was carried out in the presence of 2a as the precatalyst, full
conversion was obtained with mono-alkylated N-alkylaniline formed
selectively. The results are similar to those of other aniline derivatives.
Similar trends for the other Ru(II) systems carrying NHC ligands have
been reported [30a]. When the furfuryl alcohol was used as an alky-
lating agent, aniline and 2,4-dimethyl aniline gave corresponding mono-
alkylated amine with 100% selectivity for all complexes 2a-d (Table 1,
entries 5, 10). In all of the reactions N-(2-furufurilmethyl)aniline was
obtained as a major product, and very low imine formation ratio
(selectivity of imine < 5%) was observed (Table 1, entries 15, 20).
The N-alkylation of 2-aminopyridine with the same alcohols (benzyl
alcohol, 4-methybenzyl alcohol, 4-methoxybenzyl alcohol, furfuryl
alcohol and 3,4-dimethoxybenzyl alcohol) was also investigated by
using 2a-d precatalysts to obtain N-alkylated amines under the same
conditions. 2-(N-Alkylamino)pyridines were obtained in good to excel-
lent selectivity in the presence of 2.5 mol% precatalysts. Also, under
these catalytic conditions, the heteroaromatic moiety in 2-aminopyri-
dine has also been well tolerated. 2-Aminopyridine was efficiently
alkylated with 4-methybenzyl alcohol for all complexes 2a-d with 100%
selectivity (Table 1, entry 17). The reaction of 2-aminopyridine with
benzyl alcohol, 4-methoxybenzyl alcohol, furfuryl alcohol and 3,4-dime-
thoxybenzyl alcohol also gave corresponding products in conversions
from 95 to 100%.
4. Experimental section
4.1. Materials
All reactions were performed using normal Schlenk techniques under
argon in flame-dried glassware. 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).
4.2. Apparatus and instruments
Schlenk line technique was used for performing all the synthesis and
catalytic reactions. 1H NMR and 13C NMR spectra were recorded using a
Bruker Avance AMX spectrometer operating at 400 MHz (1H), 100 MHz
(
13C) in CDCl3 and DMSO‑d6 with tetramethylsilane as an internal
reference. The NMR studies were carried out in high-quality 5 mm NMR
tubes. Signals are quoted in parts per million as δ a downfield from
tetramethylsilane (δ = 0.00) as an internal standard. Coupling constants
(J values) are given in hertz. NMR multiplicities are abbreviated as
follows: s = singlet, d = doublet, t = triplet, m = multiplet signal.
Elemental analyses were performed by LECO CHNS-932 elementary
chemical analyzer. For the measurement of catalytic results (conversion
and yield), Shimadzu GC 2025 with the specification of GC-FID sensor,
column of RX-5 ms which have 30 m length, 0.25 mm diameter and 0.25
µM film thickness was used. Column chromatography was performed
using silica gel 60 (70–230 mesh). Solvent ratios are given as v/v.
3. Conclusion
A
series of imidazolium/benzimidazolium salts, with the 1-
3

¨
E.O. Karaca et al.
Inorganica Chimica Acta 520 (2021) 120294
Table 1
N-alkylation of arylamine derivatives with different aryl methyl alcoholsa.
2a-d, KOtBu
Ar NH
Ar NH2
+
R
Ar N
+
OH
R
R
A
B
Entry
Ar-NH2
Alcohol
[Ru]
Conversionb (Yield A:B%)
2a
2b
2c
2d
1
2
3
4
93 (98/2)
99(81/19)
96(89/7)
98(71/29)
NH2
OH
100(100/-)85c
98(90/10)
94(72/28)
99(65/35)
98(95/5)
98(76/34)
89(100/-)
94(100/-)
96(100/0)
86(91/9)
91(100/-)
OH
O
OH
100(100/-)
O
O
OH
5
100(100/-)
100(100/-)
97(100/-)
89(100/-)
O
OH
6
7
8
9
94(60/40)
91(77/22)
74(100/-)
90(90/10)
96(83/17)
96(89/11)
80(100/-)
98(96/4)
96 (80/20)
78(95/5)
81(98/2)
88(91/9)
87(74/26)
92(86/14)
87(72/28)
91(92/8)
H3C
NH2
CH3
OH
OH
O
OH
O
O
OH
10
48(100/-)
72(100/-)
61(100/-)
76(100/-)
O
OH
11
12
13
14
93(100/-)
98(51/46)
94(98/2)
98(72/28)
96(100/-)
100(100/-)
96(80/20)
94(94/6)
98 (80/20)
99(95/5)
87(100/-)
92(90/10)
97(92/8)
96(91/9)
F3C
NH2
OH
OH
89(77/33)
98(75/25)
O
OH
O
O
OH
15
88(97/3)
88(99/1)
79(100/-)
92(100/-)
O
OH
16
17
18
19
98(100/-)80c
100(100/-)
100(100/-)
100(93/7)
99(93/7)
100(100/-)
100(100/-)
99(98/2)
98(100/-)
100(100/-)
99(98/2)
OH
N
NH2
100(100/-)
100(100/-)
100(100/-)
OH
O
OH
96(96/4)
100(92/8)
O
O
OH
20
95(96/4)
99(100/-)
96(100/0)
97(100/-)
O
OH
aReaction conditions: Complexes 2a-d (0.025 mmol, 2.5 mol %), arylmethyl alcohol (1.5 mmol), aromatic amine (1 mmol), KOtBu (1 mmol), 120 ◦C, 24 h. The
conversions and the selectivities were determined by GC and dodecane were used as in internal standard. bRefers to arylamine’s conversion to secondary amine and
imine. cIsolated yield.
4

¨
E.O. Karaca et al.
Inorganica Chimica Acta 520 (2021) 120294
4.3. Synthesis
C6H2(CH3)2–5,6], 6.92[s, 2H, CH2C6H3(CH3)2–3,5], 7.04 [d, 2H, J = 8
Hz, CH2C6H4Ad], 7.33 [d, 2H, J = 8 Hz, CH2C6H4Ad]. 13C NMR (100
MHz, CDCl3, 25 ◦C): δ = 17.9, 20.2, 21.5 [(CH3)2CHC6H4CH3-p], 28.9
4.3.1. Preparation of 4-benzyladamantyl bromide
4-(1-Adamantylbenzyl bromide was synthesized according to the
literature [32].
[CH2C6H3(CH3)2–3,5],
30.4,
36.1,
36.7
[CAd],
43.2
[CH2C6H3(CH3)2–3,5], 52.1, [CH2C6H3(CH3)2–3,5], 52.2 [NCH2Ar],
96.9, 106.9, 111.7, 123.5, 125.5, 128.9, 132.2, 134.4, 135.0, 138.1,
150.6 [C6H2(CH3)2–5,6, CH2C6H3(CH3)2–3,5, CH2C6H4Ad and
(CH3)2CHC6H4CH3-p], 189.0 [Ru-Ccarb]. Anal. Calc. for C45H54N2RuCI2:
C, 55.82; H, 5.50; N, 2.83. Found: C, 55.79; H, 5.58; N, 2.97%.
4.3.2. 1-Methyl-3-[4-(1-adamantyl]benzylimidazolium bromide, 1a
Imidazolium salt 1a was prepared accordingly known methods [33].
A solution of 1-methylimidazole (10 mmol) and 4-(1-adamantyl)benzyl
bromide (10 mmol) in DMF (5 mL) was heated to 80 ◦C for 2 days. The
solution was allowed to cool room temperature and the participants
were treated with diethyl ether and washed with it. Solid was solved in
DCM, and white solid crystals were obtained by addition of diethyl
ether. Yield: 90%. 1H NMR (400 MHz, CDCl3, 25 ◦C): δ = 1.66 [q, 6H, J
= 8 Hz, HAd], 1.74 [s, 6H, HAd], 2.02 [s, 3H, HAd], 4.03 [s, 3H, NCH3],
5.45 [CH2C6H4Ad], 7.21 and 7.29 [s, 2H, NCHCHN], 7.23–7.37 [m, 4H
CH2C6H4Ad], 10.41 [s, 1H, NCHN].13C NMR (100 MHz, DMSO‑d6, 25
◦C): δ = 29.9 [NCH3], 30.7, 31.5, 33.7, 41.6, 42.9, 49.4 [CAd], 50.8
[CH2C6H4Ad], 125.3 [s, 2H, NCHCHN], 128.8, 134.8 [CH2C6H4Ad],
151.2 [NCHN]. Anal. Calc. for C21H27N2Br: C, 65.11; H, 7.03; N, 4.46.
Found: C, 65.28; H, 7.24; N, 4.30%.
4.3.5. Dichloro-[1-(4-Adamantylbenzyl)-3-(4-tert-butylbenzyl)
benzimidazol-2-ylidene](p-cymene) ruthenium(II), 2c
Yield: 76%. 1H NMR (400 MHz, CDCl3, 25 ◦C): δ = 1.14 [d, 6H J = 4
Hz (CH3)2CHC6H4CH3-p], 1.31 [s, 12H, HAd], 1.31 [s, 9H,
CH2C6H4(CH3)3], 1.77 [d, 6H, J = 8 Hz, CH2C6H4C(CH3)3], 1.89 [s, 3H
(CH3)2CHC6H4CH3-p], 2.77 [hept, 1H, J = 4 Hz, (CH3)2CHC6H4CH3-p],
5.07 and 5.35 [s, 4H, (CH3)2CHC6H4CH3-p], 6.59–7.38 [m, 16H,
CH2C6H4Ad, CH2C6H4Ad, C6H4, CH2C6H4C(CH3)3 and CH2C6H4C
(CH3)3]. 13C NMR (100 MHz, CDCl3, 25 ◦C): δ = 18.2, 22.9, 28.8
[(CH3)2CHC6H4CH3-p], 31.4, 34.6, 36.1 [CH2C6H3(CH3)3], 36.7, 43.1,
43.2 [CAd], 52.6 [NCH2Ar], 84.6, 85.5, 97.3, 107.2, 111.8, 122.1,
125.4,134.4, 135.6, 150.7 [C6H4, CH2C6H4C(CH3)3, CH2C6H4Ad and
(CH3)2CHC6H4CH3-p], 191.4 [Ru-Ccarb]. Anal. Calc. for C45H54N2RuCI2:
C, 55.82; H,5.50; N, 2.83. Found: C, 55.79; H, 5.62; N, 2.98%.
The following salt precursors were synthesized according to the
literature [32]:
1-[4-(1-Adamantyl)benzyl]-3-(3,5-dimethylbenzyl)-5,6-dime-
thylbenzimidazolium bromide, 1b
4.3.6. Dichloro-[1-(4-adamantylbenzyl)-3-(2,3,4,5,6-pentamethylbenzyl)
benzimidazol-2-ylidene](p-cymene) ruthenium(II), 2d
1-[4-(1-Adamantyl)benzyl]-3-(4-tert-butylbenzyl)benzimidazolium
bromide, 1c
Yield: 72%. 1H NMR (400 MHz, CDCl3, 25 ◦C): δ = 1.25 [m, 6H
(CH3)2CHC6H4CH3-p], 1.58 [s, 6H, HAd], 1.76 [d, 6H, J = 16 Hz, HAd],
1.89 [s, 3H (CH3)2CHC6H4CH3-p], 1.89, 2.07, 2.32 [s, 15H,
CH2C6(CH3)5], 2.83 [hept, 1H, J = 4 Hz, (CH3)2CHC6H4CH3-p],
5.26–5.58 [m, 4H, (CH3)2CHC6H4CH3-p], 6.19–7.32 [m, 12H,
CH2C6H4Ad, CH2C6H4Ad, C6H4, CH2C6(CH3)5] 13C NMR (100 MHz,
CDCl3, 25 ◦C): δ = 15.8, 17.3, 18.4 [(CH3)2CHC6H4CH3-p], 28.9, 30.9,
36.1, 36.7, 36.8 [CH2C6(CH3)5], 43.1, 43.2 [CAd], 52.6 [NCH2Ar], 96.4,
106.9, 111.9, 122.5, 125.4, 126.3, 128.9, 129.3, 134.7, 135.6, 150.6
[C6H4, CH2C6(CH3)5, CH2C6H4Ad and (CH3)2CHC6H4CH3-p], 190.2 [Ru-
Ccarb]. Anal. Calc. for C46H56N2RuCI2: C, 56.23; H, 5.62; N, 2.79. Found:
C, 56.39; H, 5.67; N, 2.93%.
1-[4-(1-Adamantyl)benzyl]-3-(2,3,4,5,6-pentamethylbenzyl)benzi-
midazolium bromide, 1d
4.3.3. Dichloro-[1-methyl-3-(4-adamantylbenzyl)imidazol-2-ylidene](p-
cymene) ruthenium(II), 2a
Ag2O (0.54 mmol) was added to a solution of 1a (1.08 mmol) in
dichloromethane (25 mL) under an atmosphere of argon. The mixture
was stirred for 24 h at room temperature, covered with aluminum foil,
and then filtered through celite to remove the formed AgBr. [RuCl2(p-
cymene)]2 (0.43 mmol) was added to the colorless solution, and the
reaction mixture was stirred for 24 h at room temperature. The resulting
mixture was filtered through celite, and the solvent was removed under
vacuum to afford the product. The crude product was recrystallized from
dichloromethane:diethyl ether (1:2) at room temperature. The orange-
brown crystals were filtered off, washed with diethyl ether (3 × 10
mL) and dried under vacuum. Yield: 78%. 1H NMR (400 MHz, CDCl3, 25
◦C): δ = 1.22 [d, 6H, J = 8 Hz, (CH3)2CHC6H4CH3-p], 1.62 [s, 3H, HAd],
1.77 [q, 6H, J = 8 Hz, HAd], 1.89 [s, 6H, HAd], 2.06 [s, 3H
(CH3)2CHC6H4CH3-p], 2.91 [hept, 1H, J = 8 Hz, (CH3)2CHC6H4CH3-p],
4.06 [s, 3H, NCH3], 5.30–5.58 [m, 4H, (CH3)2CHC6H4CH3-p], 5.64 [s,
2H, CH2C6H4Ad], 6.87 [d, 1H, J = 4 Hz, NCHCHN], 6.98 [d, 1H, J = 4
Hz, NCHCHN], 7.19 [d, 2H, J = 8 Hz, CH2C6H4Ad], 7.34 [d, 2H, J = 8
CRediT authorship contribution statement
¨
Emine Ozge Karaca: Investigation. Zieneb Imene Dehimat:
Investigation. Sedat Yas¸ar: Investigation. Nevin Gürbüz: Investigation,
Visualization. Dahmane Tebbani: Supervision. Bekir Çetinkaya:
˙
¨
Writing - review & editing. Ismail Ozdemir: Resources, Writing -
original draft, Writing - review & editing.
Declaration of Competing Interest
13
◦
Hz, CH2C6H4Ad]. C NMR (100 MHz, CDCl3, 25 C): δ = 18.7, 28.9,
30.8 [(CH3)2CHC6H4CH3-p], 36.1, 36.7, 39.8 [CAd], 43.2 [NCH3], 54.7
[CH2C6H4Ad], 98.9, 108.4, 123.1, 125.3, 127.3, 134.6, 151.2
[CH2C6H4Ad and (CH3)2CHC6H4CH3-p], 123.7 [NCHCHN], 174.4 [Ru-
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
C
carb]. Anal. Calc. for C31H40N2RuCI2: C, 47.59; H, 4.99; N, 3.47. Found:
Appendix A. Supplementary data
C, 47.41; H,4.83; N, 3.59%.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120294.
4.3.4. Dichloro-[1-(4-Adamantylbenzyl)-3-(3,5-dimethylbenzyl)-5,6-
dimethylbenzimidazol-2-ylidene](p-cymene) ruthenium(II), 2b
Yield: 70%. 1H NMR (400 MHz, CDCl3, 25 ◦C): δ = 1.13 [d, 6H, J = 8
Hz (CH3)2CHC6H4CH3-p], 1.60–1.80 [m, 12H, HAd], 1.90 [s, 3H
(CH3)2CHC6H4CH3-p], 2.09 [s, 9H, HAd and CH2C6H3(CH3)2–3,5], 2.21
[s, 3H, C6H3(CH3)2–5,6], 2.31 [s, 3H, C6H2(CH3)2–5,6] 2.58 [hept, 1H, J
= 4 Hz, (CH3)2CHC6H4CH3-p], 4.99–5.27 [m, 4H, (CH3)2CHC6H4CH3-p],
5.58–5.64 [m, 2H, CH2C6H3(CH3)2–3,5], 6.50–6.56 [m, 2H,
CH2C6H4Ad], 6.61[s, 2H, CH2C6H3(CH3)2–3,5], 6.84 [s, 2H,
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6