Reduction hydrogenation of imines by in situ generated rhodium NHC complexes

Article abstract of DOI:10.1016/j.molstruc.2020.128351

In this paper we examined the catalytic activity of in situ prepared bidentate azolium salt/[RhCl(COD)]₂ catalyst system in the transfer hydrogenation of imines with i-propanol to the corresponding amine. The first in situ transfer hydrogenatio

Full text of DOI:10.1016/j.molstruc.2020.128351

Journal of Molecular Structure 1216 (2020) 128351
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Reduction hydrogenation of imines by in situ generated rhodium NHC
complexes
a
a
,
,
b
a, b, *
Emine Ozge Karaca , Serpil Demir Düs¸ ünceli b, Nevin Gürbüz a , Ismail Ozdemir
€
_
€
a
_
€
Inonü University, Catalysis Researcdsh, and Application Center, 44280, Malatya, Turkey
Department of Chemistry, Faculty of Arts and Science, Inonü University, 44280, Malatya, Turkey
b
_
€
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper we examined the catalytic activity of in situ prepared bidentate azolium salt/[RhCl(COD)]2
catalyst system in the transfer hydrogenation of imines with i-propanol to the corresponding amine. The
first in situ transfer hydrogenation of imines to amines is described using [RhCl(COD)]2 with bidentate
azolium ligands. New bidentate azolium salts (1a-c, 2a-c) as NHC precursors have been synthesized and
characterized. The in situ prepared three-component bidentate azolium salts (LHX)/[RhCl(COD)]2 and t-
BuOK catalyzes quantitatively the transfer hydrogenation of imines under mild reaction conditions in i-
propanol. The results show that bidentate benzimidazolium salts were observed to be more active in
reducing imines. Moreover, the method is simple and effective against various imines.
© 2020 Elsevier B.V. All rights reserved.
Received 29 November 2019
Received in revised form
25 April 2020
Accepted 27 April 2020
Available online 30 April 2020
Keywords:
Rhodium
Bidentate azolium salt
N-heterocyclic carbene
Imine
Transfer hydrogenation
1. Introduction
In recent years, N-heterocyclic carbenes have been used as an
alternative to phosphine ligands used for homogeneous catalyst
Among all methods that can be used to reduce C ¼ O and C ¼ N,
transfer hydrogenation is an important method that has emerged
in recent years and is used as an alternative to the hydrogenation
process [1,2]. Various catalytic systems including different metal
centers and organocatalysts have been used for the transfer hy-
drogenation of imines. The most commonly used catalysts are those
containing Ir [3e5], Rh [4e6] and Ru [4,5,7] metal. In metal-
catalyzed transfer hydrogenation reactions, formic acid and i-
propanol are commonly used as hydrogen servers.
Although the transfer hydrogenation process is widely applied
in ketone reduction, the studies for transfer hydrogenation of im-
ines are very limited [1,8e11]. Contrary to the reduction of ketones,
the reduction of imines is thought to lead to some problems [12].
The most important are the; i) hydrolysis-susceptible occurrences;
ii) the presence of the cis/trans and enamine isomers making it
more difficult to control the enantioselectivity; iii) the significant
effect of N-substituents on the activity and enantioselectivity, and
iv) catalyst poisoning, resulting in imine or amine coordination of
metal.
synthesis in organometallic chemistry [13]. Phosphine compounds
are required to operate in an inert environment due to reasons such
as being sensitive to air and moisture and breaking PeC bonds at
high temperatures. In contrast to phosphine ligands, N-heterocyclic
carbene ligands are more advantageous because of their strong
s
donor properties, low toxicity, and easier synthesis. N-heterocyclic
carbenes play a key role in both catalytic and catalytic stages of
organic synthesis such as CeH activation, CeC, CeH, CeO, and CeN
bond formation through selective coordination chemistry [14e22].
N-heterocyclic carbenes have used as ligands in transfer hy-
drogenation reactions of imines. Danopoulos’s group in 2002 [23]
synthesized a pincer type Ru complex that contains two NHC motifs
and try it transfer hydrogenation of imines. After this, at the 2005
mono-NHC Ru complex prepared by William’s group [24] was also
tested with the same substrate and showed good reactivity. In
2002, Crabtree and Peris et al. [25] synthesized an air-stable
chelating bis-carbene rhodium (III) complexes and reported their
application in transfer hydrogenation of ketones and imines. Ir-
based analogs of the above-mentioned chelating bis-carbene
rhodium (III) complexes were also reported by Crabtree group in
2004 [26]. Besides the chelated bis-NHC Ir complexes, mono-
dentate triazolylidene derived NHC Ir complexes were proved to be
suitable for transfer hydrogenation of imines by the Crabtree group
_
€
* Corresponding author. Inonü University, Catalysis Researcdsh, and Application
Center, 44280, Malatya, Turkey.
_
€
E-mail address: ismail.ozdemir@inonu.edu.tr (I. Ozdemir).
https://doi.org/10.1016/j.molstruc.2020.128351
0022-2860/© 2020 Elsevier B.V. All rights reserved.

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E.O. Karaca et al. / Journal of Molecular Structure 1216 (2020) 128351
in 2007 as well [3]. Another example of NHC Ir complexes was
reported by Li’s group. They reported the first example of asym-
metric transfer hydrogenation of cyclic N-sulfonylimines using a
chiral metal carbene catalyst in 2017 [27]. The first example of Ni
catalyzed transfer hydrogenation of imines was reported by
Dchneider and Fort et al. [28] A series of Ni(0)/NHC complexes were
synthesized and tested in 2003.
To the best of our knowledge, the catalytic in situ transfer hy-
drogenation reaction of imines using metal carbene catalysts has
not been reported thus far. We have previously reported imidazo-
lidine,benzimidazole-2-ylidene-ruthenium (II) complexes and in
situ formed tetrahydropyrimidine ruthenium (II) system which
exhibits high activity [29e34]. In order to find more efficient
rhodium catalysts we have prepared a series of new bidentate
azolium salts, 1a-c, 2a-c (Scheme 1), and we now report the use of
the in situ generated catalytic system composed of [RhCl(COD)]2 as
rhodium source, 1a-c, 2a-c as carbene precursors and t-BuOK as a
base for transfer hydrogenation of aryl ketones in i-propanol for 6 h.
All synthesized compounds were characterized by 1H NMR, 13C
NMR and elemental analysis techniques the results of which sup-
port the proposed structures.
10 h) (Scheme 2).
The bidentate azolium salts were isolated as white solids in very
good yields and fully characterized by 1H and 13C NMR spectros-
copy, and elemental analyses (see Experimental section). The 1H
NMR spectra of the bidentate azolium salts further supported the
assigned structures; the resonances for acidic C (2)-H were
observed as a sharp singlet in the 9.03, 9.59, 9.63, 10.97, 10.02 and
10.39 ppm respectively for 1a-c, 2a-c. 13C NMR chemical shifts were
consistent with the proposed structure; the imino carbon appeared
as a typical singlet in the 1H-decoupled mode in the 157.1, 157.2,
157.1, 162.7, 163.0 and 163.1 ppm respectively for bidentate azolium
salts (1a-c, 2a-c). The NMR values are similar to those found for
other bidentate azolium salts [35,36]. The salts are air- and mois-
ture stable both in the solid-state and in solution.
2.2. Catalytic transfer hydrogenation of imines
Hydrogen transfer reactions of functional groups have greatly
contributed to the recent development of organic syntheses. Dur-
ing the transfer hydrogenation of ketones over the last two decades,
the reaction of imines has been little studied.
The catalytic reduction is preferred to stoichiometric reduction
for large scale industrial uses of ketones hydrogenation [37]. The
use of a solvent that can donate hydrogen overcomes these diffi-
culties. i-Propanol is a popular reactive solvent for the transfer
hydrogenation since it is easy to handle (b.p. 82 ꢀC) and is relatively
non-toxic, environmentally benign, and inexpensive. The volatile
acetone product can also be easily removed to shift an unfavorable
equilibrium. Owing to its efficiency in the transfer hydrogenation of
imine derivatives, in situ generated rhodium complexes were
further investigated by transfer hydrogenation of various imines.
We examined the catalytic activity of in situ prepared bidentate
azolium salt/[RhCl(COD)]2 catalyst system in the transfer hydro-
genation of imines with i-propanol to the corresponding amine.
Wherein i-propanol is the hydrogen source and t-BuOK presumably
enhances catalysis by promoting the formation of intermediates
2. Results and discussion
2.1. Synthesis of bidentate azolium salts
Bisimidazolidinium (1a-c) and bisbenzimidazolium (2a-c) salts
prepared according to the literature [35,36] by the reaction of 2,4-
bischloromethyl-1,3,5-trimethylbenzene with 1-alkylimidazoline/
benzimidazole. To a solution of 1-alkylimidazoline in DMF was
added slowly 2,4-bischloromethyl-1,3,5-trimethylbenzene and the
resulting mixture was stirred at 25 ꢀC for 2 h. The heating of the
resulting mixture (80 ꢀC, 6 h) allows the formation of the imida-
zolidinium salts in excellent yields (Scheme 1). Bisbenzimidazo-
lium (2a-c) salts prepared similarly from 1-alkylbenzimidazole and
2,4-bischloromethyl-1,3,5-trimethylbenzene (25 ꢀC, 5 h, and 80 ꢀC,
Scheme 1. Preparation of bidentate imidazolidinium salts.

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E.O. Karaca et al. / Journal of Molecular Structure 1216 (2020) 128351
3
Scheme 2. Preparation of bidentate benzimidazolium salts.
and deprotonation of salts. The reduction of imine to amine was
initially used as a model reaction with in situ prepared Rh(I) sys-
tems with 1a-c, 2a-c as catalysts in the transfer hydrogenation. The
RheNHC catalyst being generated in situ by mixing the corre-
sponding rhodium complexes [RhCl(COD)]2 with the bisazolium
salts (1 and 2) (Fig. 1).
In order to ensure complete formation of the active catalyst a i-
propanol solution of 0.5 mol% [RhCl(COD)]2 and 0.5 mol% 1,10-
bis(N-(3,4,5-trimethoxybenzyl)-3,3’-(2,4-dimethylene-1,3,5-
trimethylbenzene)benzimida-zolium chloride (2a) is stirred in the
presence 4 mmol t-BuOK at room temperature for 0.5 h. Then p-
methoxybenzilidene aniline (1.00 mmol) was added and was per-
formed at 80 ꢀC for 6 h. The reactions were conducted at a sub-
strate/catalyst/base (S/C/base) molar ratio of 1:0.01:4.
purity of the products was checked by GC and GC-MS and yields
were calculated according to benzylidine aniline.
Since the base facilitates the formation of a rhodium alkoxide by
abstracting the proton from i-propanol, different bases were used
_
as promoters in the transfer hydrogenation of imines. Imine was
kept as a test substrate and allowed it to react in i-propanol with
[RhCl(COD)]2/2a in the presence of different bases like NEt3, Cs2CO3,
K2CO3, NaOH, KOH, t-BuOK. With the organic base triethylamine
and potassium carbonate, we observed only poor yields (Table 1
entry 1,2). Using the inorganic base the conversion showed a de-
pendency upon the base strength. It has been observed that t-BuOK
is shown to have good conversions when compared to the Cs2CO3,
K2CO3, NaOH, and KOH in the hydrogenation reactions. When using
DBU, a strong base, results similar to KOH were obtained (Table 1,
entry 12). In the absence of a base no transfer hydrogenation of the
imines was observed (Table 1, entry 11). Also, the catalytic system
was used in the transfer hydrogenation of imine at room temper-
ature but no appreciable formation of aniline. Under the reaction
conditions [RhCl(COD)]2/2c system proved to be most effective
catalyst relative to 1a, 1b, 1c, 2a and 2b (Table 2, entry 18).
Reaction conditions: Bidentat azolium salts (1a-c, 2a-c)
(0.01 mmol), [RhCl(COD)]2 (0.005 mmol) substrate (1 mmol), i-
propanol (10 mL), t-BuOK (4 mmol), 80 ꢀC, 6 h. The purity of the
products was checked by GC and GC-MS and yields were calculated
according to imine derivatives.
Reaction conditions: 2a (0.01 mmol), [RhCl(COD)]2 (0.005 mmol)
substrate (1 mmol), i-propanol (10 mL), base (4 mmol), 80 ꢀC. The
Encouraged by the obtained in these catalytic systems we
extended our investigations to include transfer hydrogenation of
aldimine and ketimine derivatives. A variety of imines were
transformed into the corresponding amines. Typical results are
shown in Table 2. Under those conditions N-(1-diphenylethan-1-
imine) and 1-(3,4,5-trimethoxyphenyl)-N-phenylethan-1-imine
Fig. 1. Propose the structure of the in situ generated active RheNHC catalyst.

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E.O. Karaca et al. / Journal of Molecular Structure 1216 (2020) 128351
Table 1
Screening of transfer hydrogenation reaction conditions.
Entry
Base
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
NEt3
6
6
6
2
4
6
6
2
4
6
6
6
<3
5
10
6
23
46
44
14
57
82
e
K2CO3
Cs2CO3
KOH
KOH
KOH
NaOH
t-BuOK
t-BuOK
t-BuOK
e
9
10
11
12
DBU
74
Table 2
Transfer hydrogenation of imines with the catalyst system [RhCl(COD)]2/(1a-c, 2a-c)a.
Entry
Substrate
Product
LHX
Yield (%)
1
2
3
4
5
6
7
8
1a
1b
1c
2a
2b
2c
1a
1b
1c
2a
2b
2c
1a
1b
1c
2a
2b
2c
1a
1b
1c
2a
2b
2c
51
53
50
82
87
88
28
50
42
90
91
98
33
56
32
92
90
96
30
44
40
48
50
58
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
react very cleanly and in goods yields with i-propanol (Table 2,
entries 5, 6, 10e12). The presence of electron-donating (OCH3)
substituent on phenyl (Table 2, entries 10e12 and 16e18) has a
significant effect on the reduction of imines to their corresponding
amine. The maximum conversion of 1-(3,4,5-trimethoxyphenyl)-
N-phenylethan-1-imine to the corresponding amine was achieved
over a period of 6 h (Table 2, entry 12). Finally, we also investigated
to reduce of an aldimine such as a 1-(4-methylthio)phenyl-N-
phenylmethamine was also reduced under optimal conditions
(Table 2, entries 19e24). The best catalytic activity was achieved
with ligant 2c (Table 2, entry 2).
Peris et al. reported the chelating bis-carbene rhodium (II)
complexes in the transfer hydrogenation of imines. Imine de-
rivatives were reduced at reflux temperature for 10 h [25]. In 2005
Williams et al. reported dihydrideruthenium N-heterocyclic car-
bene complexes as a catalyst for the transfer hydrogenation of
imines in i-propanol at 70 ꢀC for 16 h [24]. Also, Fort et al. reported
the application of in situ generated nickel (0) carbene complexes in
the reduction of imines to the corresponding amines used Et2CH-
ONa [28]. Using catalyst system a variety of imines were reduced at
100 ꢀC in dioxane. Compared with the litherature [25] in situ pre-
pared three-component bidentate azolium salts (LHX)/
[RhCl(COD)]2/t-BuOK are active in the reduction of imines under
mild conditions with almost quantitative conversions. Under the
reaction conditions, benzimidazolium salts proved to be the most
effective catalyst relative to imidazolidinium salts. The reduction of
the imine with bidentate azolium salts was completed within 6 h in
high yields. It is evident that the NHC precursors that contain
electron-donating isopropylaminoethyl substituent (1f) are the
most effective of the salts examined.
3. Conclusions
In this paper, we have synthesized new bidentate azolium salts
as precursors of N-heterocyclic carbenes. They were associated
with [RhCl(COD)]2 to generate catalytic species. This concept for

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E.O. Karaca et al. / Journal of Molecular Structure 1216 (2020) 128351
5
making catalysts in situ opens the way for the discovery of many
new catalysts via the interaction of metal complexes and suitable
ligands. The catalytic advantages of this in situ prepared catalyst
system were investigated in the reduction of imine using i-prop-
anol and t-BuOK under mild reaction conditions. The study results
show that bidentate benzimidazolium salts are much more active
than bidentate imidazolidinium salts in reducing imines. Moreover,
the procedure is simple and effective against various imines.
Detailed investigations focusing on new metal-NHC complexes and
other applications are underway.
eCH2C6H(CH3)3CH2-); 6.88 (s, 4H, CH2C6H2(CH3)3e2,4,6); 4.77 (s,
4H, -CH2C6H(CH3)3CH2-); 4.65 (s, 4H, CH2C6H2(CH3)3e2,4,6); 3.80
and 3.65 (t, J ¼ 9.4 Hz, 8H, NCH2CH2N); 2.50 and 2.29 (s, 9H,
eCH2C6H(CH3)3CH2-); 2.26 and 2.21 (s, 18H, CH2C6H2(CH3)3e2,4,6).
13C{H}NMR (
(-CH2C6H(CH3)3CH2-);
d, CDCl3): 157.1 (NCHN), 138.7, 138.5, 131.8 and 128.7
139.6, 139.4, 130.1 and 127.3
(CH2C6H2(CH3)3e2,4,6); 49.1 (-CH2C6H(CH3)3CH2-); 48.2 and 46.6
(NCH2CH2N); 45.9 (CH2C6H2(CH3)3e2,4,6); 21.4 and 20.3
(CH2C6H2(CH3)3e2,4,6); 20.1 and 16.3 (-CH2C6H(CH3)3CH2-). Anal.
Calc. For C37H50N4Cl2: C, 71.48; H, 8.10; N, 9.01. Found C, 71.50; H,
8.08; N, 9.00.
4. Experimental section
4.2.1.2. 1,10-Bis{(N-2,3,5,6-tetramethylbenzyl)-3,3’-(2,4-dimethylene-
1,3,5-trimethylbenzene)-imidazolidinium chloride, 1b. Yield: 2.66 g;
4.1. Materials
82%. 1H NMR
(d, CDCl3): 9.59 (s, 2H, NCHN); 7.03 (s, 1H,
All reactions for the prepared compounds were carried out
under argon in flame-dried glassware using standard Schlenk
techniques. Chemicals and solvents were purchased from
SigmaeAldrich, 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).
eCH2C6H(CH3)3CH2-); 6.94 (s, 2H, CH2C6H(CH3)4e2,3,5,6); 5.07 (s,
4H, -CH2C6H(CH3)3CH2-); 4.72 (s, 4H, CH2C6H(CH3)4e2,3,5,6); 4.05
and 3.73 (t, J ¼ 9.9 Hz, 8H, NCH2CH2N); 2.55 and 2.31 and (s, 9H,
eCH2C6H(CH3)3CH2-);
2.21
and
2.19
(s,
24H,
CH2C6H(CH3)4e2,3,5,6). 13C{H}NMR (
d, CDCl3): 157.2 (NCHN), 139.6,
139.1, 131.5 and 128.7 (-CH2C6H(CH3)3CH2-); 134.5, 133.9, 132.4 and
127.6 (CH2C6H(CH3)4e2,3,5,6); 49.1 (-CH2C6H(CH3)3CH2-); 47.5 and
46.9 (NCH2CH2N); 46.7 (CH2C6H(CH3)4e2,3,5,6); 20.5 and 15.9
(CH2C6H(CH3)4e2,3,5,6); 19.9 and 16.7 (-CH2C6H(CH3)3CH2-). Anal.
Calc. For C39H54N4Cl2: C, 72.09; H, 8.38; N, 8.62. Found C, 72.15; H,
8.42; N, 8.59.
4.1.1. NMR spectroscopy
1H NMR and 13C NMR spectra were recorded using a Varian As
300 Merkur spectrometer operating at 300 MHz (1H), 75 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
d
downfield
4.2.1.3. 1,10-Bis{(N-2,3,4,5,6-pentamethylbenzyl)-3,3’-(2,4-
from tetramethylsilane ( 0.00) as an internal standard. Coupling
d
dimethylene-1,3,5-trimethylbenzene)-imidazolidinium chloride, 1c.
constants (J values) are given in hertz. NMR multiplicities are
abbreviated as follows: s ¼ singlet, d ¼ doublet, t ¼ triplet,
m ¼ multiplet signal.
Yield: 2.94 g; 87%. 1H NMR (
d, CDCl3): 9.63 (s, 2H, NCHN); 7.03 (s,
1H, eCH2C6H(CH3)3CH2-); 5.06 (s, 4H, -CH2C6H(CH3)3CH2-); 4.71 (s,
4H, CH2C6(CH3)5e2,3,4,5,6); 4.05 and 3.71 (t, J ¼ 9.9 Hz, 8H,
NCH2CH2N); 2.51 and 2.32 (s, 9H, eCH2C6H(CH3)3CH2-); 2.25, 2.21
4.1.2. Elemental analyse
and 2.19 (s, 30H, CH2C6(CH3)5e2,3,4,5,6). 13C{H}NMR (
d, CDCl3):
Elemental analyses were performed by LECO CHNS-932
elementary chemical analyser.
157.1 (NCHN), 139.4, 139.2, 131.7 and 127.6 (-CH2C6H(CH3)3CH2-);
136.1, 133.4, 133.3 and 125.9 (CH2C6(CH3)5e2,3,4,5,6); 49.1
(-CH2C6H(CH3)3CH2-); 47.5 and 47.2 (NCH2CH2N); 46.9
(CH2C6(CH3)5e2,3,4,5,6); 20.0 and 18.4 (-CH2C6H(CH3)3CH2-), 17.2,
16.9 and 16.7 (CH2C6(CH3)5e2,3,4,5,6). Anal. Calc. For C41H58N4Cl2:
C, 72.65; H, 8.62; N, 8.27. Found C, 72.69; H, 8.65; N, 8.31.
4.1.3. Gas chromatography
All reactions were monitored on an Agilent 6890 N GC system by
GC-FID with an HP-5 column of 30 m length, 0.32 mm diameter and
0.25 mm film thickness.
4.2.2. Synthesis of bidentate benzimidazolium salts
4.1.4. Gas chromatography-mass spectroscopy
All catalytic reactions were monitored on a Shimadzu 2010 Plus
GC-MS system by GC-FID with an HP-5 column of 30 m length,
4.2.2.1. General synthesis method for bisbenzimidazolidinium salts
(2a-c). To a solution of 1-alkylbenzimidazole (10 mmol) in DMF
was slowly added 2,4-bischloromethyl-1,3,5-trimethylbenzene
(5 mmol) and stirred at 25 ꢀC for 5 h. The resulting mixture was
heated at 80 ꢀC for 10 h. Diethylether (10 mL) was added to the
cooled solution to precipitate the white solid. The crude product
was filtered, washed with diethylether (3 ꢁ 5 mL) and dried in
vacuum. Recrystallized in ethanol/diethyl ether solvent mixture.
0.32 mm diameter and 0.25
mm film thickness.
4.1.5. Column chromatography
Column chromatography was performed using silica gel 60
(70e230 mesh). Solvent ratios are given as v/v.
4.2. Synthesis of bidentate imidazolidinium salts
4.2.2.2. 1,10-Bis(N-(3,4,5-trimethoxybenzyl)-3,3’-(2,4-dimethylene-
1,3,5-trimethylbenzene)-benzimidazolium chloride, 2a. Yield: 3.35 g;
4.2.1. General synthesis method for bisimidazolidinium salts (1a-c)
85%. 1H NMR (
d
, CDCl3): 10.97 (s, 2H, NCHN); 8.25 (d, J ¼ 8.4 Hz, 2H,
To the solution of 1-alkylimidazolidine (10 mmol) in DMF was
NC6H4N); 7.69e7.53 (m, 6H, NC6H4N); 7.14 (s, 1H,
eCH2C6H(CH3)3CH2-); 6.74 (s, 4H, CH2C6H2(OCH3)3-3,4,5); 5.84 and
5.80 (s, 8H, -CH2C6H(CH3)3CH2- and CH2C6H2(OCH3)3-3,4,5);3.74 and
3.73 (s, 18H, CH2C6H2(OCH3)3-3,4,5); 2.31 and 2.24 (s, 9H,
slowly
added
2,4-bischloromethyl-1,3,5-trimethylbenzene
(5 mmol) and stirred at 25 ꢀC for 2 h. The resulting mixture was
heated at 80 ꢀC for 8 h. When diethyl ether (15 mL) was added, the
resulting white crystals were filtered, washed with diethyl ether
(3 ꢁ 15 mL) and dried in vacuum. The crude product was recrys-
tallized from EtOH/Et2O.
CH2C6H(CH3)3CH2). 13C{H}NMR (
d, CDCl3): 162.7 (NCHN), 142.2,
140.9,140.3,129.3, and 127.2(-CH2C6H(CH3)3CH2-),132.0,131.8,127.7,
127.6, 114.4 and 114.0 (NC6H4N); 153.9, 138.6, 132.6 and 106.1
(CH2C6H2(OCH3)3-3,4,5); 60.9 and 56.7 (CH2C6H2(OCH3)3-3,4,5);
53.6, 51.5 and 46.8 (CH2C6H2(OCH3)3-3,4,5 and -CH2C6H(CH3)3CH2-);
20.2 and 17.2 (-CH2C6H(CH3)3CH2-). Anal. Calc. For. C45H50N4O6Cl2: C,
66.41; H, 6.19; N, 6.88. Found C, 66.45; H, 6.23; N, 6.85.
4.2.1.1. 1,10-Bis{(N-2,4,6-trimethylbenzyl)-3,3’-(2,4-dimethylene-
1,3,5-trimethylbenzene)-imidazolidinium chloride, 1a. Yield: 2.45 g;
80%. 1H NMR
(d, CDCl3): 9.03 (s, 2H, NCHN); 7.05 (s, 1H,

€
6
E.O. Karaca et al. / Journal of Molecular Structure 1216 (2020) 128351
4.2.2.3. 3,3’-(2,4-Dimethylene-1,3,5-trimethylbenzene)-1,10-bis(N-
methoxyethyl)-benzimidazolium chloride, 2b. Yield: 2.56 g; 90%. 1H
Scientific Research Council of Turkey TÜBITAK [TBAG (107T098)].
_
NMR
(d, DMSO‑d6):10.02 (s, 2H, NCHN); 8.24e8.21 (m, 2H,
Appendix A. Supplementary data
NC6H4N); 8.12e8.09 (m, 2H, NC6H4N); 7.72e7.69 (m, 4H, NC6H4N);
7.24 (s, 1H, eCH2C6H(CH3)3CH2-); 5.79 (s, 4H, -CH2C6H(CH3)3CH2-);
4.83 (s, 4H, CH2CH2OCH3); 3.12 (s, 6H, CH2CH2OCH3); 3.72 (t,
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2020.128351.
J
¼
4.8 Hz, 4H, CH2CH2OCH3); 2.29 and 2.26 (s, 9H,
eCH2C6H(CH3)3CH2-). 13C{H}NMR (
d, DMSO‑d6): 163.0 (NCHN),
References
142.7, 140.9, 140.4, 132.3 and 128.2 (-CH2C6H(CH3)3CH2-), 132.2,
132.0, 127.4, 127.2, 114.8 and 114.7 (NC6H4N); 70.2 (CH2CH2OCH3);
58.8 (CH2CH2OCH3); 47.0 (CH2CH2OCH3); 46.2 (-CH2C6H(CH3)3CH2-
); 20.2 and 16.3 (-CH2C6H(CH3)3CH2-). Anal. Calc. For
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imines
Under an inert atmosphere [RhCl(COD)]2 (0.05 mmol), bidentate
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Declaration of competing interest
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€
Emine Ozge Karaca: Conceptualization, Methodology, Investi-
gation, Writing - original draft, Writing - review & editing. Serpil
Demir Düs¸ünceli: Conceptualization, Methodology, Investigation.
Nevin Gürbüz: Conceptualization, Methodology, Investigation,
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ꢀ
Resources, Writing - original draft, Writing - original draft, Writing
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This work was financially supported by the Technological and
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