First used of Alkylbenzimidazole-Cobalt(II) complexes as a catalyst for the N-Alkylation of amines with alcohols under solvent-free medium

Article abstract of DOI:10.1016/j.jorganchem.2020.121285

In this study, alkylbenzimidazole-cobalt(II)-catalyzed direct N-alkylation reactions of amines with alcohols derivatives have been investigated under solvent-free medium. For this purpose, a series of cobalt(II) complexes bearing N-alkylbenzimidazole complexes have been synthesized and novel complexes fully characterized by elemental analysis, FT-IR, ¹H NMR and, ¹³C{¹H} NMR spectroscopies. Also, the structure of the complex 2a has been confirmed by X-ray crystallography. Generally, the N-alkylating reaction is usually performed in toluene with various metal complexes including cobalt. In this catalytic study of complexes, 2a-c has carried out in without solvent and alcohol acted both as solvent and reactant. Conversion and selectivity of amine products according to imine products for alkylation reactions have been seen high yield in medium solvent-free relative to in toluene.

Full text of DOI:10.1016/j.jorganchem.2020.121285

Journal of Organometallic Chemistry 918 (2020) 121285
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
First used of Alkylbenzimidazole-Cobalt(II) complexes as a catalyst for
the N-Alkylation of amines with alcohols under solvent-free medium
,
b
,
c
d
e
b, c
Neslihan S¸ ahin a , Ilkay Yıldırım , Namık Ozdemir , Nevin Gürbüz
Ismail Ozdemir
,
_
€
b, c, *
_
€
a University of Cumhuriyet Faculty of Education, Department of Basic Education, 58140, Sivas, Turkey
University of Inonü Faculty of Science and Art, Department of Chemistry, University, 44280 Malatya, Turkey
University of Inonü Catalysis Research and Application Center, 44280, Malatya, Turkey
d University of Biruni, Vocational School, Department of Radiotherapy, 34010 Istanbul, Turkey
e University of Ondokuz Mayıs Department of Mathematics and Science Education, Faculty of Education, 55139, Samsun, Turkey
b
_
€
c
_
€
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, alkylbenzimidazole-cobalt(II)-catalyzed direct N-alkylation reactions of amines with al-
cohols derivatives have been investigated under solvent-free medium. For this purpose, a series of
cobalt(II) complexes bearing N-alkylbenzimidazole complexes have been synthesized and novel com-
plexes fully characterized by elemental analysis, FT-IR, 1H NMR and, 13C{1H} NMR spectroscopies. Also,
the structure of the complex 2a has been confirmed by X-ray crystallography. Generally, the N-alkylating
reaction is usually performed in toluene with various metal complexes including cobalt. In this catalytic
study of complexes, 2a-c has carried out in without solvent and alcohol acted both as solvent and
reactant. Conversion and selectivity of amine products according to imine products for alkylation re-
actions have been seen high yield in medium solvent-free relative to in toluene.
Received 31 January 2020
Received in revised form
24 February 2020
Accepted 6 April 2020
Available online 21 April 2020
Keywords:
N-alkylbenzimidazole
Cobalt
N-alkylation
Crystal structure
Solvent-free
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
of an amine with an alcohol was reported firstly in 1981 [22]. In this
process, alcohols are first dehydrogenated to form aldehydes, fol-
Alkylated amines are fundamental organic chemicals that play
an important role as building blocks in many organic synthesis
reactions and have extensive applications in drug molecules, ag-
rochemicals, polymer materials, and synthetic industries [1e6].
Synthesis of these compounds, which have such diverse and vital
uses, is an important area of interest in synthetic chemistry.
Traditional methods of obtaining these compounds are the
hydroamination of alkenes or alkynes and the amination of aryl
halides, the reaction of amines with alkyl halides, reductive ami-
nation of aldehydes or carboxylic acids [7e21]. But, because of
these reactions have disadvantages such as poor yield and selec-
tivity, a large amount of inorganic waste and atom uneconomy, a
utilitarian method has attracted attention that it is called
“hydrogen borrowing chemistry” or “hydrogen auto-transfer
chemistry”. This method based on metal-catalyzed N-alkylation
lowed by the condensation of the resulting aldehydes with nucle-
ophilic agents, which affords imine intermediates that are further
hydrogenated by metal hydride species generated in the step of the
dehydrogenation of alcohols to give alkylated products (Scheme 1).
After the first use of RhH(PPh3)4] many useful homogeneous
catalysts based on ruthenium, iron, iridium, palladium, copper, and
manganese have been synthesized [22e28]. Although some of
these metal precursors are almost ten-fold more expensive than
cobalt precursors, cobalt-based catalysts were reported only a few
studies until this time for the N-alkylation reaction. If we examine
them, firstly, Kempe and co-workers described a new Co-PNP
pincer complex that stabilized by a PN5P ligand (triazine back-
bone) which was highly active for the alkylation of aromatic amines
in 2015 [29] (Fig. 1a). In later years, Zhang employed cobalt(II)
catalyst based on a pincer PNP ligand for the efficient N-alkylation
of both aromatic and aliphatic amines with alcohols [30] (Fig.1b). In
another study, Zeng and Zhang presented selective alkylation of
amines with amines to synthesize a large variety of secondary
amines using the same cobalt catalyst [31] (Fig. 1b). Kirchner and
_
€
* Corresponding author. University of Inonü Faculty of Science and Art, Depart-
ment of Chemistry, University, 44280 Malatya, Turkey.
_
€
E-mail address: ismail.ozdemir@inonu.edu.tr (I. Ozdemir).
https://doi.org/10.1016/j.jorganchem.2020.121285
0022-328X/© 2020 Elsevier B.V. All rights reserved.

2
N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
dimethylsulfoxide and halogenated solvents such as chloroform,
dichloromethane but insoluble in petroleum ether, diethyl ether.
At the elemental analysis, for all compounds (2a-c), experi-
mental elemental analysis values of all compounds are compatible
with the theoretical ones.
In keeping with the a distorted tetrahedral geometry of the
cobalt(II) atom, complexes 2a-c exhibited paramagnetic behavior.
We noted that signals number of hydrogen atoms of the complexes
was missing in the 1H NMR spectrum in the range 0e12 ppm. Also,
no NMR signals of carbon atoms of the complexes could be seen in
the range 0e200 ppm in the 13C{1H}NMR spectrum. Cobalt com-
plexes (2a-c) have paramagnetic properties due to 3d configuration
of cobalt(II) since signals of the aromatic protons appear as broad
singlet and shifted downfield region up to 15.00 ppm according to
ligands (1a-c). Also, aliphatic protons appear as broad singlet and
shifted upfield region down to 1.00 ppm according to ligands (1a-
c). The position and sharpness of the 1H NMR resonances clearly
demonstrate the paramagnetic nature of the complex, indicative of
a Co(II) complex.
Scheme 1. The general mechanism for alkylation of amines with alcohols through the
Hydrogen Borrowing strategy.
In the infrared spectrum of complexes 2a-c, strong peaks at
1509, 1516 and 1516 are assigned to C]N vibrations, respectively.
These NMR and FT-IR values are in agreement with reported data
for N-coordinated cobalt(II) complexes in literatüre [41,44]. See the
Supplementary data for print out of the elemental analysis, and
spectrums of 1H, 13C{1H} NMR and FT-IR.
Fig. 1. Efficient cobalt-based catalysts for the alkylation of amines with alcohols.
co-workers described the efficient alkylation of amines with alco-
hols catalyzed by Co(II) complexes which are stabilized by an
anionic PCP ligand based on the 1,3-diaminobenzene scaffold [32]
(Fig. 1c). Balaraman described alkylation of aromatic amines by
alcohols catalyzed by in-situ reaction using CoCl2$6H2O and tri-
phenylphosphine as a ligand [33].
2.2. Description of the crystal structure
The molecular structure of 2a with the atom-labelling scheme is
shown in Fig. 2, while selected bond distances and angles are listed
in Table 1.
Benzimidazoles have attracted much attention due to their us-
age in many applications in coordination-, medicinal- and
supramolecular-chemistry. Because of having high thermal stabil-
ity, good catalytic performance and superior optical properties,
metal complexes with benzimidazole ligands are important
[34e39]. The cobalt complexes are easy to synthesize and simple to
activate. They can be synthesized quantitatively on a multigram
scale and are air-stable as crystalline materials for months.
In only a few examples available in the literature, toluene has al-
ways been used as the solvent for the catalytic reaction medium.
Herein,wereportforthefirst time cobaltcatalyzed the N-alkylationof
amines with alcohols via the “hydrogen-borrowing” under solvent-
free medium. Also, N-alkylbenzimidazole coordinated-cobalt cata-
lyst was used the first time for the N-alkylation reaction in this study.
The complex consists of two 1-allyl-1H-benzo[d]imidazole
ligand with a CoII metal center and two chlorine ligands. The CoII
ion is four-coordinated and adopts a distorted tetrahedral geometry
involving two nitrogen atoms from the two benzimidazole ligands
and two chlorine atoms, with the CleCoeCl angle [115.33(3)ꢀ] be-
ing significantly larger than the CleCoeN angles [average
109.33(5)ꢀ] and the NeCoeN angle [110.02(6)ꢀ]. The four-
coordinate geometry index for the complex, t4 [48], is 0.94. In the
case of ideal square-planar geometry, the t4 value is equal to zero,
while it becomes unity for a perfect tetrahedral geometry. As a
result, the value of t4 confirms the slightly distorted tetrahedral
environment of the cobalt atom.
The CoeN bond distances [2.0041(15) and 2.0147(15) Å] are
somewhat longer than the sum of the individual covalent radii of
the cobalt and nitrogen atoms (1.97 Å), while the CoeCl bond dis-
tances [2.2440(6) and 2.2274(6) Å] are slightly smaller than the
sum of the covalent individual radii of the cobalt and chlorine
atoms (2.28 Å) [49]. The internal NeCeN ring angles at the carbene
centers are 112.98(19) and 113.76(18)ꢀ. Bond lengths and angles
around the cobalt atom are consistent with the similar structures
with a chromophore group CoCl2N2 [50e55]. The benzimidazole
rings are almost perpendicular to each other with a dihedral angle
of 89.95(7)ꢀ.
2. Result and discussion
2.1. Synthesis and characterization of N-alkyl benzimidazole cobalt
(II) complexes
Nitrogen-containing heterocyclic ligands have attracted atten-
tion in the fields of coordination chemistry, homogeneous catalysis
and organic synthesis due to organometallic complexes bearing
nitrogen donor ligands by a majority show high reactivities. Co(II)
complexes bearing benzimidazole ligand were synthesized reac-
tion of N-alkylbenzimidazoles with CoCl2$6H2O in very good yields
and complexes 2a-c were characterized by elemental analysis, 1H
NMR, 13C{1H} NMR, and FT-IR spectroscopies. Besides, suitable
crystals of 2a were obtained and the structure of 2a was charac-
terized by X-ray crystallography studies. The general synthesis
pathway for N-alkybenzimidazole cobalt(II) complexes (2a-c) was
summarized in Scheme 2.
2.3. The catalytic activity of complexes 2a-c in N-alkylation
reaction of aniline with benzyl alcohol
Complexes 2a-c were studied in the N-alkylation reaction of
aniline with benzyl alcohol. At the end of the reaction, two products
may be formed, namely, amines (A) or imines (B). To determine
optimum conditions for the catalytic system, we have carried out
the N-alkylation of aniline with benzyl alcohol using as base KOtBu
in toluene for 24 h at 120 ꢀC as a model reaction which catalyzed
with 2c based on literature [32] (Table 2). To see the catalytic role of
The Co(II) complexes (2a-d) with blue color are air and moisture
stable in the solid-state and soluble in dimethylformamide,

N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
3
Scheme 2. Synthesis of the N-alkylbenzimidazole cobalt(II) complexes.
Fig. 2. The molecule of 2a, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
Table 1
Table 2
Selected geometric parameters for 2a.
Optimization studies of N-alkylation reaction of aniline with benzyl alcohol cata-
lyzed by complex 2ca.
Bond lengths (Å)
Co1eCl1
Co1eCl2
Co1eN1
Co1eN3
2.2440(6)
2.2274(6)
2.0041(15)
2.0147(15)
N1eC1
N2eC1
N3eC11
N4eC11
1.319(2)
1.338(3)
1.311(3)
1.338(2)
Bond angles (ꢀ)
Cl1eCo1eCl2
Cl1eCo1eN1
Cl1eCo1eN3
Cl2eCo1eN1
115.33(3)
106.82(5)
104.28(5)
108.46(5)
Cl2eCo1eN3
N1eCo1eN3
N1eC1eN2
N3eC11eN4
111.75(5)
110.02(6)
112.98(19)
113.76(18)
Entry
Base
Temperature
Conversion (Yield A: B%)
1
2
3
4
5
6
KOtBub
KOtBuc
KOtBu
120
120
120
100
120
120
0
26(61/39)
43(69/31)
21(63/37)
75(96/4)
51(93/7)
KOtBu
KOtBud
KOtBuc,d
the cobalt catalyst, experiment without complex was performed
and the reaction did not give any product (Table 2, entry 1). Under
the same conditions, when 1.5 mol % 2c was loaded, the conversion
was % 21 (Table 2, entry 2), when 2.5 mol % 2c was loaded, the
conversion was 43% (Table 2, entry 3). Reducing the temperature of
reaction to 100 ꢀC, reaction resulted in a conversion of 21% (Table 2,
entry 4). In the experiments at the same reaction conditions to see
if it affects the yield of the reaction solvent-free medium, surpris-
ingly, we found that the solvent-free medium increased the
a
Reaction conditions: Complexes 2c (0.025 mmol, 2.5 mol %), benzyl alcohol
(1.5 mmol), aniline (1 mmol), base (1 mmol), toluene (2 mL), 24 h. The conversions
and selectivities were determined by GC for which the calibrations were based on
decane.
b
Without 2c.
1,5% of 2c.
Without solvent.
c
d

4
N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
efficiency of reaction and selectivity of the amine with 75% (Table 2,
entry 5). As a result of the optimization experiments, it was found
that the optimal environment for this reaction is solvent-free me-
dium, 120 ꢀC, 24 h and using KOtBu base and % 2.5 mol catalyst.
Based optimal conditions were applied to examine the substrate
scope of the N-alkylation between various amines with alcohol
derivatives using N-alkylbenzimidazole cobalt(II) complexes as
catalyst (2a-c) at solvent-free medium and results are summarized
Table 3 and Table 4. Also, when referring to conversion and yield
throughout the text it is meant the amine product (A).
60e75% compared to other alcohols. (Table 3, entry 3). Among the
complexes, complex 2c yielded the highest conversion. From the
reaction of benzyl alcohols with p-(threefloromethyl)benzylaniline
was obtained amine products in good conversions at around %
60e70 for all alcohol derivatives for the 2a and 2c (Table 3, entry
5e8). p-Methoxyaniline was converted to the corresponding amine
in excellent yield (%85) with benzyl alcohol loading 2c (Table 3,
entry 9). The reaction involving 2,4-dimethylaniline resulted in
amine product in only moderate yield, due to the steric effect of an
o-methyl group (Table 3, entries 13e16). In general, the complex 2b
gave low yields and 2c provided the highest yield for all N-alkyl-
ation reactions. The activity of 2c may be attributed to the presence
of electron donating-oxygen in the alkyl group bound to the ni-
trogen. Therefore, the presence of benzimidazole ligands bearing a
Under the optimal condition, N-alkylation reaction data among
anilines with benzyl alcohols were showed in Table 3. On the N-
alkylation reaction between various alcohol with the aniline, p-
methoxybenzylalcohol gave the highest conversion at around
Table 3
N-alkylation of anilines with benzyl alcohols.a.
Entry
Amine
Alcohol
[Co] Conversion (Yield A: B%)
2a
2b
2c
1
2
3
4
42(55/45)
46(61/39)
75(96/4)
58(95/5)
60(100/0)
12(100/0)
42(86/14)
61(77/23)
47(100/0)
66(91/9)
75(100/0)
56(100/0)
5
6
7
8
60(97/3)
64(98/2)
68(100/0)
69(100/0)
33(100/0)
39(97/3)
60(97/3)
56(100/0)
63(100/0)
57(100/0)
41(100/0)
46(100/0)
9
74(100/0)
76(100/0)
77(100/0)
36(100/0)
61(77/23)
36(80/20)
49(68/32)
12(100/0)
87(100/0)
67(100/0)
68(91/9)
10
11
12
45(100/0)
13
14
15
16
43(100/0)
56(100/0)
55(100/0)
49(100/0)
6(67/33)
7(57/43)
22(100/0)
12(100/0)
22(31/69)
48(72/28)
59(100/0)
44(100/0)
a
Reaction conditions: Complexes 2a-c (0.025 mmol, 2.5 mol %), arylmethyl alcohol (1.5 mmol), heterocyclic amine (1 mmol), KOtBu (1 mmol), 120 ꢀC, 24 h. The conversions
and selectivities were determined by GC for which the calibrations were based on decane.

N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
5
Table 4
N-alkylation of 2-pyridyl amine with arylmethyl alcohols.a.
3. Experimental
3.1. Materials and methods
All experiments were performed under argon in flame-dried
glassware using standard Schlenk line techniques. All reagents
were purchased from Sigma Aldrich Co. (Dorset, UK). The solvents
used were purified by distillation over the drying agents indicated
and were transferred under Argon. Elemental analyses were done
Entry
Alcohol
[Co] Conversion (Yield A: B%)
_
€
by Inonü University Scientific and Technology Center. Melting
points were determined using the Electrothermal 9100 melting
point detection apparatus in capillary tubes and the melting points
are reported as uncorrected values. Fourier transform infrared (FT-
IR) spectra were recorded in the range of 400e4000 cmꢁ1 on Per-
kinElmer Spectrum 100 FT-IR. 1H NMR and 13C{1H} NMR spectra
were taken using a Bruker As 400 Mercury spectrometer operating
at 400 MHz (1H), 100 MHz (13C) in CDCl3 with tetramethylsilane as
the internal reference. 1H peaks are labeled as singlet (s). Chemical
shifts and coupling constants are reported in ppm and in Hz,
respectively. Catalytic reactions were observed on an Agilent
6890 N GC system by GC-FID with an HP-5 column of 30 m length,
2a
2b
2c
1
2
3
4
50(100/0)
73(100/0)
60(100/0)
53(100/0)
69(100/0)
50(100/0)
69 (100/0)
71(100/0)
52(100/0)
61(100/0)
78(100/0)
67(100/0)
5
6
5(100/0)
8(100/0)
10(100/0)
63(100/0)
0.32 mm diameter and 0.25 mm film thickness. Column chroma-
61(100/0)
54(100/0)
tography was performed using silica gel 60 (70e230 mesh). All the
measurements were taken at room temperature for freshly pre-
pared solutions.
a
Reaction conditions: Complexes 2a-c (0.025 mmol, 2.5 mol %), heteroaromatic
alcohol (1.5 mmol), 2-pyridyl amine (1 mmol), KOtBu (1 mmol), 120 ꢀC, 24 h. The
conversions and selectivities were determined by GC for which the calibrations
were based on decane.
3.2. General procedure for the preparation of the N-
alkylbenzimidazole cobaltII) complexes
All compounds were sythesized according to literature [40,41].
Benzimidazole (10 mmol) was added to a solution of NaH
(10 mmol) in dry THF (30 mL), the mixture was stirred for 1 h at
room temperature and corresponding alkyl halides (10.1 mmol)
was added dropwise and heated for 24 h at 60 ꢀC. Then, the THF
was removed under the vacuum. Dichloromethane (50 mL) was
added upon to solid. The mixture was filtered and the obtained
clear solution was concentrated under vacuum. Then the solution
was distillated and 1-alkylbenzimidazoles (1a-c) were obtained. A
solution of CoCl2$6H2O (0.10 mmol) in methanol (5 mL) was care-
fully added to a solution of 1a-c (0.20 mmol) in chloroform (5 mL)
to give two layers. Blue crystals were obtained after a few days. The
solid (2a-c) was filtered and washed with diethyl ether (3 ꢂ 10 mL)
and dried under vacuum.
different donating group such as ether side chains on the metal
may radically increase the catalytic performance of the catalyst. The
chelating nature of these ligands promotes production of highly
stable complexes. The hemilabile part of such ligands is capable of
reversible dissociation to produce vacant coordination sites,
allowing complexation of substrates during the catalytic cycle.
Although 3,4-dimethoxybenzylalcohol have electron-donating
methoxy groups, due to sterically hindered of the o-methoxy
group, it yielded the lowest conversion among the alcohols (Table 3,
entries 4, 8, 12, 16).
A heteroaromatic amine such as a 2-pyridyl amine was also
efficiently alkylated with alcohol derivatives under optimal condi-
tions. Except for furfuryl alcohol, 2-pyridyl amine was converted to
amine products with all other alcohols in good conversion at
around 50e80% using 2a-c catalysts (Table 4, entries 1e4, 6).
In the literature, CoCl2$6H2O and PPh3 were used as in-situ for
the N-alkylation reaction of benzyl alcohol and 4-methoxy ani-
line at 130 ꢀC and 5% catalyst for 48 h and a yield of 73% was
obtained. For the same reaction in our study, we obtained 87%
yield with 2.5% 2c catalyst for 24 h h. While for the N-alkylation
reaction of 4-methoxybenzyl alcohol and aniline at the same
condition, reaction yield was 66% in the literature, in our study,
reaction yield was 75% for 2c catalyst [33]. By comparison re-
ported for related Co catalysts, in the present catalytic system
using N-alklybenzimidazole cobalt(II) complexes are more eco-
nomic due to solvent-free medium, higher efficiency and the
cheapness of cobalt precursor [29e33]. The use of organic sol-
vents as re-action media for hydrogenation reactions is very
common. However, the practical use of organic solvents is limited
due to the production of environmental waste and high energy
consumption of the subsequent separation of the reaction mix-
tures. Thus, compared with diluted reaction, the solvent-free
reaction is more efficient for scale-up and saves cost for solvent
purification and recycling [56,57].
3.2.1. 1-Allylbenzimidazole, 1a [42]
Yield: 76%; liquid product; FT-IR n(CN): 1615 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
d
¼ 7.93 (s, 1H, NCHN), 7.84 (t, 1H, NC6H4N,
3J ¼ 4 Hz),7.40 (t, 1H, NC6H4N, 3J ¼ 4 Hz), 7.32 (d, 2H, NC6H4N,
3J ¼ 4 Hz), 6.03 (quint, 1H, NCH2CHCH2, 3J ¼ 8 Hz), 5.32 (d, 1H,
NCH2CHCH2, 3J ¼ 8 Hz), 5.22 (d, 1H, NCH2CHCH2, 3J ¼ 16 Hz), 4.80 (s
br, 2H, NCH2CHCH2). 13C{1H} NMR (100 MHz, CDCl3):
(NCHN),142.9,140.9,133.8,131.9,123.0,122.2,120.3,118.7 and 110.0
(NC6H4N and NCH2CHCH2), 47.4 (NCH2CHCH2). Anal. Calcd for
d
¼ 143.8
C10H10N2: C, 75.92; H, 6.37; N, 17.71. Found: C, 75.84; H, 6.29; N:
17.62.
3.2.2. 1-(2-Methylallyl)benzimidazole, 1b [43]
Yield: 78%; mp: 50e51 ꢀC; FT-IR n(CN): 1615 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
d
¼ 7.92 (s, 1H, NCHN), 7.84 (t, 1H, NC6H4N,
3J ¼ 4 Hz), 7.39 (t, 1H, NC6H4N, 3J ¼ 4 Hz), 7.31 (d, 2H, NC6H4N,
3J ¼ 4 Hz), 5.02 (s, 1H, NCH2C(CH3)CH2), 4.85 (s, 1H, NCH2C(CH3)
CH2), 4.71 (s, 2H, NCH2C(CH3)CH2), 1.73 (s, 2H, NCH2C(CH3)CH2). 13
C
{1H} NMR (100 MHz, CDCl3):
d
¼ 143.8 (NCHN), 143.3, 139.5, 134.0,
123.0, 122.2, 120.4, 114.0 and 110.1 (NC6H4N and NCH2C(CH3)CH2),
51.11 (NCH2C(CH3)CH2), 19.8 NCH2C(CH3)CH2). Anal. Calcd for

6
N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
Table 5
Crystal data and structure refinement parameters for 2a.
CCDC depository
1915723
Color/shape
Blue/prism
[CoCl2(C10H10N2)2]
446.23
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
296
0.71073 Mo K
a
Triclinic
P1 (No. 2)
Unit cell parameters
a, b, c (Å)
9.9921(6), 10.4927(6), 10.9233(7)
100.999(5), 108.449(5), 90.875(5)
1062.90(12)
2
1.394
a
,
b
,
g
(ꢀ)
Volume (Å3)
Z
Dcalc. (g/cm3)
m
(mmꢁ1
)
1.070
Absorption correction
Tmin., Tmax.
F000
Integration
0.6038, 0.7926
458
Crystal size (mm3)
Diffractometer/measurement method
Index ranges
0.67 ꢂ 0.33 ꢂ 0.28
STOE IPDS II/rotation (u scan)
ꢁ13 ꢃ h ꢃ 13, ꢁ13 ꢃ k ꢃ 14, ꢁ14 ꢃ l ꢃ 14
q
range for data collection (ꢀ)
2.156 ꢃ
q
ꢃ 28.435
Reflections collected
Independent/observed reflections
Rint.
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
16624
5326/3810
0.038
Full-matrix least-squares on F2
5326/0/244
0.921
Final R indices [I > 2
R indices (all data)
s(I)]
R1 ¼ 0.0344, wR2 ¼ 0.0745
R1 ¼ 0.0569, wR2 ¼ 0.0807
0.28, ꢁ0.26
Drmax.,
Drmin. (e/Å3)
C11H12N2: C, 76.71; H, 7.02; N, 16.27. Found: C, 76.63; H, 7.11; N:
16.21.
3.2.6. Dichloro-bis[1-(2-vinyloxyethyl)benzimidazole]cobalt(II), 2c
[44]
Yield: 79%, mp: 141e142 ꢀC; FT-IR n(CN): 1516 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
d
¼ 15.32 s br, 4H, arom. CH), 6.94 (s, 2H, arom.
3.2.3. 1-(2-Vinyloxyethyl)benzimidazole, 1d [44]
CH), 6.62 (s, 4H, arom. CH), 5.57 (s br, 2H, NCH2CH2OCHCH2), 4.62
(s, 2H, NCH2CH2OCHCH2), 4.18 (s, 2H, NCH2CH2OCHCH2), 3.12 (s br,
2H, NCH2CH2OCHCH2), 1.24 (s, 1H, NCH2CH2OCHCH2), 1.03 (s, 1H,
Yield: 79%; mp: 49e50 ꢀC. FT-IR n(CN): 1611 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
d
¼ 7.99 (s, 1H, NCHN), 7.84 (d, 1H, NC6H4N,
3J ¼ 8 Hz), 7.44 (d, 1H, NC6H4N, 3J ¼ 8 Hz), 7.34e7.29 (m, 2H,
NC6H4N), 6.42 (dd, 1H, OCHCH2, 3J ¼ 8 Hz, 2J ¼ 8 Hz), 4.45 (t, 2H,
NCH2CH2O, 3J ¼ 4 Hz), 4.19 (d, 1H, OCHCH2, 3J ¼ 16 Hz), 4.06e4.03
(m, 3H, OCHCH2 and NCH2CH2O). 13C{1H} NMR (100 MHz, CDCl3):
NCH2CH2OCHCH2). 13C{1H} NMR (100 MHz, CDCl3):
d
¼ 89.7 and
152.9. Anal. Calcd for C22H24Cl2N4O2Co: C: 52.19; H: 4.78; N: 11.07.
Found C: 51.95; H: 4.94 N: 11.33.
d
¼ 150.9 (OCHCH2), 143.7 (NCHN), 133.7, 123.1, 122.3, 120.4, 115.6
and 109.5 (NC6H4N), 87.6 (NCH2CH2OCHCH2), 65.8
(NCH2CH2OCHCH2), 44.2 (NCH2CH2OCHCH2). Anal. Calcd for
11H12N2O: C, 70.19; H, 6.43; N, 14.88. Found C: C, 70.11; H, 6.52; N:
3.3. General procedure for the N-Alkylation of aniline with alcohols
Under the optimized reaction conditions, in a Schlenk tube, a
mixture of aniline derivative (1.0 mmol), excess of alcohol deriva-
tive (1.5 mmol), KOtBu (1.0 mmol) and Co catalyst (2a-c)
(0.025 mmol, 2.5 mol %) were stirred at 120 ꢀC for 24 h under argon
atmosphere. After cooling to room temperature, CH2Cl2 (2 mL) was
added to the crude mixture. The obtained mixture was passed
through a pad of short silica gel and the filtrate was analyzed by GC-
MS.
C
14.81.
3.2.4. Dichloro-bis(1-allylbenzimidazole)cobalt(II), 2a
Yield: 91%, mp: 201e202 ꢀC; FT-IR n(CN): 1509 cmꢁ1 1H NMR
;
(400 MHz, CDCl3):
d
¼ 15.33 (s, 4H, arom. CH), 9.23 (s, 2H, arom.
CH), 7.23 (s, 2H, arom. CH), 6.61 (s, 2H, arom. CH), 6.47 (s, 2H, arom.
CH), 5.16 (s, 2H, NCH2CHCH2), 2.98 (s, 2H, NCH2CHCH2), 1.37 (s, 2H,
NCH2CHCH2). Anal. Calcd for C20H20Cl2N4Co: C: 53.83; H: 4.52; N:
12.56. Found C: 53.86; H: 4.69; N: 12.71.
3.4. Crystal structure of complex 2a
Intensity data of 2a were collected on a STOE IPDS II diffrac-
tometer at room temperature using graphite-monochromated Mo
3.2.5. Dichloro-bis[1-(2-methylallyl)benzimidazole]cobalt(II), 2b
Ka radiation by applying the u-scan method. Data collection and
Yield: 88%; mp: 224e225 ꢀC; FT-IR n(CN): 1516 cmꢁ1
;
1H NMR
cell refinement were carried out using X-AREA while data reduc-
tion was applied using X-RED32 [45]. The structure was solved by a
dual-space algorithm using SHELXT-2018 and refined with full-
matrix least-squares calculations on F2 using SHELXL-2018 [46]
implemented in WinGX [47] program suit. All H atoms were located
in difference electron-density map and then treated as riding atoms
in geometrically idealized positions, with CeH distances of 0.93
(400 MHz, CDCl3):
d
¼ 14.80 (s br, 4H, arom. CH), 7.19 (s, 1H, arom.
CH), 6.04 (s, 2H, arom. CH), 5.76 (s, 2H, NCH2C(CH3)CH2), 5.15 (s, 2H,
NCH2C(CH3)CH2), 3.03 (s, 6H, NCH2C(CH3)CH2), 2.86 (s, 2H,
NCH2C(CH3)CH2), 1.21 (s br, 2H, NCH2C(CH3)CH2). Anal. Calcd for
C
22H24Cl2N4Co: C: 55.71; H: 5.10; N: 11.81. Found C: 54.99; H: 5.25;
N: 11.78.

N. S¸ ahin et al. / Journal of Organometallic Chemistry 918 (2020) 121285
7
[8] J.F. Hartwig, Pure Appl. Chem. 76 (2004) 507.
[9] T.E. Müller, M. Beller, Chem. Rev. 98 (1998) 675.
[10] M. Beller, J. Seayad, A. Tillack, H. Jiao, Angew. Chem. Int. Ed. 43 (2004) 3368.
[11] R. Severin, S. Doye, Chem. Soc. Rev. 36 (2007) 1407.
[12] A.M. Beauchemin, J. Moran, M.E. Lebrun, C. Seguin, E. Dimitrijevic, L. Zhang,
S.I. Gorelsky, Angew. Chem. Int. Ed. 47 (2008) 1410.
(aromatic CH and terminal CH2) and 0.97 Å (CH2), and with Uiso(H)
values of 1.2Ueq(C). The crystallographic data and refinement pa-
rameters are summarized in Table 5. The molecular graphic was
created by using ORTEP-3 [47].
[13] A.S. Guram, R.A. Rennels, S.L. Buchwald, Angew. Chem. Int. Ed. 34 (1995) 1348.
[14] S. Shekhar, P. Ryberg, J.F. Hartwig, J.S. Mathew, D.G. Blackmond, E.R. Strieter,
S.L. Buchwald, J. Am. Chem. Soc. 128 (2006) 3584.
4. Conclusion
[15] O. Navarro, N. Marion, J. Mei, S.P. Nolan, Chem. Eur J. 12 (2006) 5142.
[16] J.F. Hartwig, Synlett 2006 (2006) 1283.
[17] X. Li, E.A. Mintz, X.R. Bu, O. Zehnder, C. Bosshard, P. Günter, Tetrahedron 56
(2000) 5785.
[18] B.G. Das, P. Ghorai, Chem. Commun. 48 (2012) 8276.
[19] I. Sorribes, K. Junge, M. Beller, J. Am. Chem. Soc. 136 (2014) 14314.
[20] M. Zhang, H. Yang, Y. Zhang, C. Zhu, W. Li, Y. Cheng, H. Hu, Chem. Commun. 47
(2011) 6605.
[21] S. Liang, P. Monsen, G.B. Hammond, B. Xu, Org. Chem. Fron. 3 (2016) 505.
[22] R. Grigg, T.R.B. Mitchell, S. Sutthivaiyakit, N. Tongpenyai, J. Chem. Soc., Chem.
Commun. 12 (1981) 611.
[23] W. Lv, B. Xiong, H. Jiang, M. Zhang, Adv. Synth. Catal. 359 (7) (2017) 1202.
[24] M. Bala, P.K. Verma, U. Sharma, N. Kumar, B. Singh, Green Chem. 15 (6) (2013)
1687.
[25] Y.H. Chang, Y. Nakajima, F. Ozawa, Organometallics 32 (7) (2013) 2210.
[26] T.T. Dang, B. Ramalingam, S.P. Shan, A.M. Seayad, ACS Catal. 3 (11) (2013)
2536.
As a result, three N-alkylbenzimidazole cobalt(II) complexes
(2a-c), including two new compounds, were synthesized. The
structure of complexes 2a was confirmed by X-ray crystallography.
All complexes were investigated catalytic activities on alkylation
reaction of amines with alcohol derivatives. For the first time in the
literature, N-alkylbenzimidazole complexes were on alkylation re-
action of amines with alcohol derivatives performed under the
solvent-free medium. It was found that in the solvent-free medium
is more efficient and selective compared with a solvent medium
such as toluene by using complexes 2a-c as catalysts. Cobalt is
almost ten-fold cheaper than other metals such as ruthenium,
palladium, iridium, and cobalt complexes are easy to synthesize
and simple to activate. They can be synthesized quantitatively on a
multigram scale and are air-stable as crystalline materials for
[27] J. He, K. Yamaguchi, N. Mizuno, Chem. Lett. 39 (11) (2010) 1182.
[28] M. Huang, Y. Li, Y. Li, J. Liu, S. Shu, Y. Liu, Z. Ke, Chem. Commun. 55 (44) (2019)
6213.
months. As
a result, cobalt-based compounds appear to be
€
[29] S. Rosler, M. Ertl, T. Irrgang, R. Kempe, Angew. Chem. Int. Ed. 54 (50) (2015)
economical for N-alkylation reaction.
15046.
[30] G. Zhang, Z. Yin, S. Zheng, Org. Lett. 18 (2) (2015) 300.
[31] Z. Yin, H. Zeng, J. Wu, S. Zheng, G. Zhang, ACS Catal. 6 (10) (2016) 6546.
[32] M. Mastalir, G. Tomsu, E. Pittenauer, G. Allmaier, K. Kirchner, Org. Lett. 18 (14)
(2016) 3462.
[33] S.P. Midya, A. Mondal, A. Begum, E. Balaraman, Synthesis 49 (17) (2017) 3957.
[34] X. Ma, X. Li, Y.E. Cha, L.P. Jin, Cryst. Growth Des. 12 (2012) 5227.
[35] V.C.O. Njar, A.M.H. Brodie, J. Med. Chem. 58 (2015) 2077.
[36] C.H. Chen, W.S. Huang, M.Y. Lai, W.C. Tsao, J.T. Lin, Y.H. Wu, T.H. Ke, L.Y. Chen,
C.C. Wu, Adv. Funct. Mater. 19 (2009) 2661.
Appendix A. Supplementary data
CCDC 1915723 contains the supplementary crystallographic
data for the compound reported in this article. These data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: þ44 1223 336 033, e-mail: deposit@
ccdc.cam.ac.uk, https://www.ccdc.cam.ac.uk/structures/].
[37] M.R. Maurya, A. Kumar, M. Ebel, D. Rehder, Inorg. Chem. 45 (2006) 5924.
€
[38] O. Dayan, M. Tercan, N. Ozdemir, J. Mol. Struct. 1123 (2016) 35.
[39] Q.Y. Yu, B.X. Lei, J.M. Liu, Y. Shen, L.M. Xiao, R.L. Qiu, D.B. Kuang, C.Y. Su, Inorg.
Chim. Acta. 392 (2012) 388.
[40] E. Üstün, A. Ozgür, K.A. Cos¸ kun, S. Demir, I. Ozdemir, Y. Tutar, J. Coord. Chem.
69 (22) (2016) 3384.
[41] C.X. An, X.L. Han, P.B. Wang, Z.H. Zhang, H.K. Zhang, Z.J. Fan, Trans. Met. Chem.
Declaration of interests
€
_
€
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.
33 (7) (2008) 835.
[42] F.E. Hahn, C. Holtgrewe, T. Pape, M. Martin, E. Sola, Oro LA Organometallics 24
(2005) 2203.
€
[43] J.J. Weemers, F.D. Sypaseuth, P.S. Bauerlein, W.N. Van Der Graaff, I.A. Filot,
Acknowledgement
M. Lutz, C. Müller, Eur. J. Org Chem. 2 (2014) 350.
[44] H. Küçükbay, S. Günal, E. Orhan, R. Durmaz, Asian J. Chem. 22 (9) (2010) 7376.
[45] Stoe & Cie, X-AREA Version 1.18 and X-RED32 Version 1.04, Stoe & Cie,
Darmstadt, Germany, 2002.
This study was supported by Ondokuz Mayıs University (Project
No: PYO. FEN.1906.19.001).
[46] G.M. Sheldrick, Acta Crystallogr. C 71 (2015) 3.
[47] L.J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849.
[48] L.D. Yang, R. Powell, R.P. Houser, Dalton Trans. 9 (2007) 955.
[49] B. Cordero, V. Gomez, A.E. Platero-Prats, M. Reves, J. Echeverria, E. Cremades,
F. Barragan, S. Alvarez, Dalton Trans. 21 (2008) 2832.
[50] [a] F.F. Jian, K.F. Wang, Liq. Cryst. 35 (2008) 1415;
[b] F. Jian, H. Xiao, P. Sun, U. Mukhopadhyay, I. Bernal, J. Coord. Chem. 57
(2004) 923.
Appendix B. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jorganchem.2020.121285.
[51] C.Y. Li, L. Li, T.L. Hu, J. Inorg. Organomet. Polym. Mater. 21 (2011) 682.
[52] S.B. Zhou, C.C. Du, X.F. Wang, Y.Z. Han, J.L. Dong, D.Z. Wang, J. Chem. Crys-
tallogr. 47 (2017) 215.
[53] Y. Shan, M.E. Cadiz, P.L. Sanchez, S.D. Huang, Acta Crystallogr. C 55 (1999)
1262.
[54] F. Jian, H. Wang, H. Xiao, Struct. Chem. 15 (2004) 277.
[55] R. Zhuang, F. Jian, K. Wang, J. Mol. Struct. 938 (2009) 254.
[56] S. Shao, W. Dong, X. Li, H. Zhang, R. Xiao, Y. Cai, J. Clean. Prod. 250 (2020)
119459.
[57] Q. Deng, J. Xu, P. Han, L. Pan, L. Wang, X. Zhang, J.J. Zou, Fuel Process. Technol.
48 (2016) 361.
References
[1] G. Guillena, D.J. Ramon, M. Yus, Chem. Rev. 110 (3) (2009) 1611.
[2] B.R. Brown, The Organic Chemistry of Aliphatic Nitrogen Compounds, vol. 28,
Oxford University Press, 1994.
[3] J.W. Grate, GC Frye in Sensors Update, vol. 2, 1996.
[4] H. Baltes, W. Gopel, J. Hesse (Eds.), Wiley-VCH, Weinheim, 1996, pp. 10e20.
€
[5] Z. Rappoport (Ed.), The Chemistry of Anilines, vol. 1, Wiley Interscience, New
York, 2007.
[6] J.L. McGuire (Ed.), Pharmaceuticals: Classes, Therapeutic Agents, Areas of
Application, 1ꢁ4, Wiley-VCH, Weinheim, 2000.
[7] M.B. Nobis, Angew. Chem. Int. Ed. 40 (2001) 3983.