Experimental and theoretical investigation of intramolecular cooperativity in cyclic benzene trimer motif

Article abstract of DOI:10.1039/C8RA06647G

A series of new symmetrical tripodal molecules 1a-4b with a central benzene scaffold substituted with methyl/ethyl groups and three benzimidazolyl units having a bithiophene/biphenyl/5-alkylthiophene motif at the 2-position via a-CH₂-unit were

Full text of DOI:10.1039/C8RA06647G

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Experimental and theoretical investigation of
intramolecular cooperativity in cyclic benzene
Cite this: RSC Adv., 2019, 9, 753
trimer motif†
a
b
b
Chakka Kiran Kumar, ‡ Shankar Deval Sathiyashivan,‡ Dhanraj T. Masram,*
a
a
K. V. Jovan Jose* and Malaichamy Sathiyendiran
*
A series of new symmetrical tripodal molecules 1a–4b with a central benzene scaffold substituted with
methyl/ethyl groups and three benzimidazolyl units having a bithiophene/biphenyl/5-alkylthiophene
motif at the 2-position via a –CH
MS, and NMR spectroscopy. NMR spectral data reveal that all molecules adopt a cyclic benzene trimer
CBT) using three benzimidazolyl units. Intramolecular cooperative edge-to-face C–H/p interactions
2
– unit were synthesized and characterized by elemental analysis, HR-
(
stabilize the CBT motif in solution and are strong in ethyl substituted molecules (1b–4b) compared to
methyl substituted (1a–4a) ones. However, the strength of the CBT unit in the tripodal molecule is
1
independent of the length of the substituent at the 2-position of the benzimidazolyl unit. The relative H
NMR chemical shift calculated at the MPW1PW91/6-311+G(d,p) level of theory corroborates the
experimental values, and the calculations predict the distribution of the structures into syn isomers. The
relative change in the NMR chemical shift is justified by the relative change in the magnitude of the
Received 7th August 2018
Accepted 18th December 2018
(
3,+3) critical point (CP) in the molecular electrostatic potential (MESP) topography. Also, a linear
DOI: 10.1039/c8ra06647g
correlation of the intramolecular C–H/p interactions evaluated at M062X/6-311+G(d,p) with the relative
rsc.li/rsc-advances
NMR chemical shift suggest the latter as a measure of intramolecular cooperativity.
state are not noticed or reported. However, reports on molecules
Introduction
possessing the CBT motif both in solution and the solid state
7
Cooperative noncovalent interactions are vital for determining has started to appear recently. We found a simple strategy to
1,2
the structure and properties of molecules and materials.
Among the several interactions, O–H/O, O–H/N, N–H/N, N– central spacer and aryl/heteroaryl ring substituted benzimida-
engineer CBT motif in a tripodal molecule which consists of
8
8
H/O, C–H/O, C–H/p hydrogen bonding interactions and zolyl cores. Our earlier studies reveal that both alkyl group on
p/p aromatic stacking interactions, cooperative edge-to-face the central benzene spacer and the aromatic group at 2-position
C–H/p interactions between the aromatic units provide of benzimidazolyl core are necessary to arrange the tripodal
3
a signicant contribution in stabilizing molecular structure.
molecules with benzimidazolyl based CBT motif. Up to now,
The cyclic benzene trimer (CBT) motif, i.e., three benzene units furan, thiophene, phenyl, pyridyl, methoxy groups substituted
arranged in a cyclic manner, is the smallest cyclic cluster phenyl are used as a steric group at 2-position of benzimidazolyl
stabilized through cooperative C–H/p interactions in various unit, to force the tripodal molecule to adopt CBT motif. To
aromatic clusters and is the basic building unit for higher order understand the stability of the CBT motif, we engineered the
1,4
aromatic clusters. Due to its importance, the cooperative tripodal molecule by increasing the length of heteroaryl/aryl
edge-to-face C–H/p interactions in the CBT motif are studied and alkylthiophene at 2-position of benzimidazolyl unit (Fig. 1).
5
theoretically. The non-additive behavior of the C–H/p inter-
Herein, a series of 2-substituted bithiophene, biphenyl and
1
4
actions within CBT motifs adds to the intramolecular cooper- alkylthiophene benzimidazoles (L –L ) and tripodal molecules
ativity. Several complexes possessing CBT motif in the solid 1a–4b were prepared and characterized by elemental analysis,
6
high-resolution mass spectrometry (HR-MS) and NMR spectro-
scopic methods. Though there are experimental and theoretical
a
School of Chemistry, University of Hyderabad, India. E-mail: msathi@uohyd.ac.in; works on cooperative interactions, quantitative intramolecular
jovanjose@uohyd.ac.in
b
9–17
cooperativity measurements are scarce in the literature.
Department of Chemistry, University of Delhi, India. E-mail: dtmasram@chemistry.
Therefore, theoretically, it is challenging and interesting to
come up with a scheme to partition the CBT motifs to calculate
the intramolecular interactions and to correlate with experi-
mental relative NMR chemical shis.
du.ac.in
†
Electronic supplementary information (ESI) available: NMR spectra and
1
4
theoretical data of L –L and 1a–4b. See DOI: 10.1039/c8ra06647g
Both authors contributed equally.
‡
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1
1
Fig. 2 Partial H NMR spectra of L , 1a and 1b in d
6
-DMSO solvent.
shied compared to 1a (Fig. 2). This data indicates that 1b has
8
a stronger CBT motif compared to 1a.
1
The H NMR spectrum of molecule 2a showed no signicant
shi for H and H protons of benzimidazolyl, whereas, H and
H displayed an upeld shi compared to those in L (Fig. S1 in
ESI†). The biphenyl protons (H –H ) of 2a displayed no signif-
icant shi compared to L . Thus, 2a adopt a strong CBT motif
with syn-conformation similar to 1a. The H NMR spectrum of
molecule 2b displays similar pattern as in 2a, except H and H
4
5
6
7
2
b
e
Fig. 1 Tripodal molecules 1a–4b.
2
1
6
7
Results and discussion
Preparations
protons of benzimidazolyl unit. Latter showed an upeld shi
of d 0.73 ppm and d 1.25 ppm relative to L , respectively (Fig. 3).
2
1
0
This data indicates that 2b also adopt a syn-conformation, but
a stronger CBT motif than 2a. Molecules 3 and 4, possessing
alkylthiophene units display H NMR pattern similar to those of
0
2
-(2,2 -Bithiophen-5-yl)benzimidazole (L ), 2-(1,1 -biphenyl-4-yl)
2
3
benzimidazole (L ), 2-(5-hexylthiophen-2-yl)benzimidazole (L )
and 2-(5-octylthiophen-2-yl)benzimidazole (L ) were synthe-
sized by the reaction of o-phenylenediamine with correspond-
1
4
1
–2 (Fig. S3 and S4 in ESI†).
1
8c
n
H NMR data indicate that modulating ve-membered het-
ing aldehydes. Subsequent treatment of L with 1,3,5-
tris(bromomethyl)mesitylene or 1,3,5-tris(bromomethyl)-2,4,6-
triethylbenzene in THF by using NaH as base yield tripodal
molecules 1a–4b. All the benzimidazoles and the tripodal
molecules (1a–4b) are air and moisture stable and soluble in
organic solvents. Elemental analysis, HR-MS and NMR spec-
troscopic methods were used for characterizing the molecules.
All the ligands and the tripodal molecules display molecular ion
eroaryl units to six-membered aromatic or alkyl substituted ve-
membered heteroaryl at 2-position of benzimidazolyl unit does
not alter the strength of edge-to-face interactions (CBT motif) in
8
the tripodal molecules (Fig. S4 and S5 in ESI†). This data
supports that increasing the length of alkyl chain on thiophene
at 2-position of benzimidazolyl unit does not inuence the
nature of edge-to-face C–H/p interactions in the CBT motif as
8
c
+
observed in previously studied molecules. However, alkyl
substituted molecules (3–4) possess stronger CBT motif than
aryl substituted molecules (1–2).
peaks (m/z for [M + H] ) those match the theoretical values (vide
infra experimental section).
NMR studies
1
4
6
NMR spectra of L –L and 1a–4b were recorded in d -DMSO
solvent (Fig. S7–S32 in ESI†). Molecule 1a displays a single set of
chemical resonances for all protons. A new peak at d 5.6 ppm
and 6 : 27 methylene : aromatic protons ratio conrms the
6
7
formation of 1a (Fig. 2). The chemical resonances for H and H
protons of benzimidazolyl were signicantly upeld shied
1
4
5
compare to those in L (Fig. 2 and 3). H and H protons of
a
e
benzimidazolyl and bithiophene protons (H –H ) either remain
in the same position or downeld shied relative to L . These
1
data reveal that 1a adopts a syn-conformer with strong CBT
motif with three benzimidazolyl units, and all bithiophene
units are pointing away from each other. The NMR spectrum of
ethyl substituted molecule 1b shows a similar pattern like that
1
4
7
Fig. 3 The relative H-NMR chemical shift (in ppm) of H –H protons
6
7
1
4
of 1a, except for H and H protons, which are broad and upeld (Mol ¼ 1a–4b and L ¼ L –L ).
754 | RSC Adv., 2019, 9, 753–760
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Fig. 4 Molecular structures of 1a, 1b, 2a and 2b evaluated at MPW1PW91/6-311+G(d,p) level of theory and basis function showing the cyclic
benzene trimer (CBT) between three benzene rings of benzimidazolyl units.
Molecular modelling
performed with the optimized geometries at MPW1PW91/6-
3
3
11G(d,p). The calculated intramolecular energies at M062X/6-
11+G(d,p) [MPW1PW91/6-311+G(d,p)] levels of theory and
To further understand the geometry as well as intramolecular
interactions for 1a–1b and 2a–2b, DFT calculations were per-
18
basis function are reported in Table 1. The calculated intra-
molecular C–H/p interaction energy between benzene C–H
with neighboring benzene p-electron cloud in the CBT core
indicates that the intramolecular interaction energy is higher
for ethyl substituted molecules (1b and 2b) than methyl
substituted ones (1a and 2a).
formed with Gaussian09 suite of packages at MPW1PW91/6-
11G(d,p) level of theory and basis function. All four mole-
3
cules adopt an edge-to-face syn-conformation, i.e., CBT motif
with three benzene rings of benzimidazolyl units (Fig. 4). The
7
geometrical distance between H to the center of benzene ring
in benzimidazolyl unit is shorter in ethyl substituted molecules
The relative magnitude of the NMR chemical shi of 1a, 1b,
˚
˚
(
3.55 A for 1b and 3.53 A for 2b) compared to methyl substituted
2a and 2b in DMSO solvent were calculated relative to the
˚
˚
(
3.66 A for 1a and 3.60 A for 2a) molecules.
1
2
20
6
ligands (L and L ) using SMD solvent model (Table 2). The H
and H protons of benzimidazolyl unit shows a higher upeld
We have followed the scheme depicted in Fig. S6 in ESI† for
7
19
calculating the intramolecular C–H/p interaction energies,
ꢀ1
Table 1 Fragment energies, total energy (Hartrees) and intramolecular energies (kcal mol ) at M062X [MPW1PW91]/6-311+G(d,p) levels of
theory and basis function calculated for 1a, 1b, 2a and 2b, as per the scheme depicted in Fig. S6 in ESI
Mol
F
1
F
2
F
3
E
Total
E
3F ꢀ3F +F
E
Intra-hydrogen
1
2
3
1a
1b
2a
2b
ꢀ3392.63315
ꢀ3510.52082
ꢀ2109.61118
ꢀ2227.49869
ꢀ1871.33900
ꢀ1989.22580
ꢀ1229.82792
ꢀ1347.71468
ꢀ350.04673
ꢀ467.93282
ꢀ350.046850
ꢀ467.93286
ꢀ4913.92920
ꢀ5031.81789
ꢀ2989.39661
ꢀ3107.28491
ꢀ4913.92731
ꢀ5031.81585
ꢀ2989.39443
ꢀ3107.28271
ꢀ1.18[ꢀ0.10]
ꢀ1.28[ꢀ0.12]
ꢀ1.37[ꢀ0.04]
ꢀ1.38[ꢀ0.05]
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1
Table 2 Experimental and theoretical [MPW1PW91/6-311+G(d,p)] relative H chemical shift (in ppm) of 1a, 1b, 2a and 2b with the corresponding
1
2
ligand (L –L ) in d
6
-DMSO solvent
4
5
6
7
a
b
c
d
e
Mol
H
H
H
H
H
H
H
H
H
1a
1b
2a
2b
ꢀ0.03 [ꢀ0.02]
ꢀ0.04 [ꢀ0.01]
0.01 [0.00]
ꢀ0.02 [0.00]
0.08 [0.01]
0.06 [0.06]
0.11 [0.39]
0.09 [0.07]
0.53 [0.79]
0.79 [1.04]
0.55 [0.94]
0.73 [1.16]
1.22 [1.25]
0.00 [0.05]
0.00 [ꢀ0.11]
ꢀ0.03 [ꢀ0.13]
0.09 [ꢀ0.01]
0.06 [ꢀ0.09]
ꢀ0.02 [ꢀ0.05]
ꢀ0.05 [ꢀ0.05]
0.04 [ 0.06]
0.02 [ꢀ0.06]
0.08 [ꢀ0.02]
0.00 [ 0.02]
1.29 [1.42] ꢀ0.09 [0.00]
0.07 [ꢀ0.02] ꢀ0.01 [ 0.02]
1.24 [1.47]
1.26 [1.53]
0.43 [ꢀ0.02]
0.01 [0.03]
0.00 [0.05]
0.02 [ꢀ0.04]
0.38 [0.20]
ꢀ0.01 [ꢀ0.04]
Fig. 5 MESP topography distribution of 1a, 1b, 2a and 2b evaluated at MPW1PW91/6-311+G(d,p) level of theory and basis set. The consecutive
contours are separated by 0.02 a.u.
4
5
a
e
shi, while the remaining H –H protons and H –H protons of the benzene trimer motifs shows an increase in the electronic
bithiophene/biphenyl unit are unaffected on the formation of contribution in this region. Also, the magnitude of the MESP
the cyclic-trimer motifs (Table 2). The theoretical results (3,+3) CP indicates the formation of a stable intramolecular CBT
corroborated well with the experiment. To justify the relative motif.
NMR chemical shi and to quantify the cooperative C–H/p
interaction, the molecular electrostatic potential (MESP)
topography is calculated and is dened at a point r, as the
Conclusions
21
amount of energy required to bring a unit positive charge from Bithiophene, biphenyl, alkylthiophene based benzimidazoles
22–24
1
4
innity to that point.
MESP contours in the plane passing (L –L ), new tripodal molecules (1–4) possessing these benzi-
through the center of the benzene rings are depicted in Fig. 5. midazolyl units and benzene spacer with methyl/ethyl group
The (3,+3) MESP critical point at the center of the cyclic trimer were prepared and characterized. These molecules adopt
ring indicates the formation of CBT motif in 1a, 1b, 2a, and 2b. a strong CBT motif in solution. A stronger edge-to-face intra-
The MESP minimum is more negative for ethyl substituted molecular C–H/p interactions is observed in ethyl substituted
molecules (ꢀ0.024 a.u for 1b and ꢀ0.030 a.u. for 2b) than molecules (1b–4b) than the corresponding methyl ones (1a–4a)
methyl substituted ones (ꢀ0.020 a.u for 1a and ꢀ0.027 a.u. for in solution. A similar formation of strong CBT motif stabilized
2a). An increase in the negative value of the MESP value within by cooperative edge-to-face interactions in molecules (1–2) in
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DMSO solution is observed by using DFT calculations. Also, the NMR (100 MHz, d
6
-DMSO, ppm): d 151.36, 141.83, 139.70,
formation of CBT is explained by intramolecular cooperative 129.52, 129.43, 128.46, 128.40, 127.64, 127.51, 127.17 and
1
energy, relative H NMR chemical shi and (3,+3) critical point 122.72 (aromatic and biphenyl). HR-MS (m/z): calc. for C H N
1
9
15
2
+
in MESP topology in molecules (1–2). The results indicate that (M + H) : 271.1235; found 271.1239. Anal. calc. for C H N : C,
1
9
14 2
increasing the length of aromatic units or alkyl chain on thio- 84.42; H, 5.22; N, 10.36 found: C, 84.32; H, 5.15, N, 10.36.
3
phene and benzene group at 2-position of benzimidazolyl unit
2-(5-Hexylthiophen-2-yl)benzimidazole (L ). Yellow solid
is not enough to break the CBT motif, stabilized by the coop- product (2.6 g, 98%) was prepared from 5-hexylthiophene-2-
erative edge-to-face C–H/p interactions, in solution. There- carboxaldehyde (1.81 g, 9.23 mmol), o-phenylenediamine
1
fore, this quantitative study may facilitate crystal engineering of (1.0 g, 9.25 mmol) and NaHSO
3
(2.88 g, 27.67 mmol). H NMR
molecules with CBT motifs for desired properties.
(500 MHz, d -DMSO, ppm): d 12.82 (1H, br s, NH), 7.63 (1H, d,
6
a
4,7
J
H
¼ 3.6 Hz, H ), 7.52 (2H, br s, H ), 7.17 (2H, q, JHH ¼ 3.0 Hz,
HH
5
,6
b
), 6.94 (1H, d, J ¼ 3.6 Hz, H ), 2.83 (2H, t, J ¼ 7.5 Hz,
HH
HH
Experimental section
General experimental methods
thio–CH
2
–), 1.68–1.62 (2H, quint, JHH ¼ 7.4 Hz, thio–C–CH
2
–),
).
3
, ppm): d 149.65, 148.07, 138.94,
1
.36–1.25 (6H, m, –(CH
C NMR (100 MHz, CDCl
2
)
3
–), 0.87 (3H, t, JHH ¼ 7.05 Hz, –C–CH
3
1
3
Biphenyl-4-carboxaldehyde, NaHSO3, o-phenylenediamine,
NaH,
1,3,5-tris(bromomethyl)mesitylene
and
1,3,5- 130.25, 127.18, 125.28, 122.73, 114.84 (aromatic and thio-
tris(bromomethyl)-2,4,6-triethyl- benzene were purchased from phene), 31.50, 31.40, 30.19, 28.67, 22.54 and 14.06 (hexyl). HR-
0
+
commercial sources and used as received. 2,2 -Bithiophene-5- MS (m/z): calc. for C17
carboxaldehyde, 5-hexylthiophene-2-carboxaldehyde, and 5- 285.1429. Anal. calc. for C17
octylthiophene-2-carboxaldehyde were prepared from previ- 11.27 found: C, 71.68; H, 7.15; N, 9.76; S, 11.41.
H
N
S (M + H) : 285.1425, found,
H N S: C, 71.79; H, 7.09; N, 9.85; S,
20 2
21
2
25
4
ously reported methods. All solvents were purchased from
2-(5-Octylthiophen-2-yl)benzimidazole (L ). Yellow solid
commercial sources and distilled prior to use. All reactions were product (2.1 g, 85%) was prepared from 5-octylthiophene-2-
carried out in an inert atmosphere. NMR spectra were recorded carboxaldehyde (1.80 g, 8.0 mmol), o-phenylenediamine
1
on Bruker Avance III 400 and 500 MHz instruments. The (865 mg, 8.0 mmol) and NaHSO
chemical shis (d) were reported in parts per million (ppm) (500 MHz, d
3
(2.5 g, 24.0 mmol). H NMR
6
a
-DMSO, ppm): d 12.83 (1H, br, NH), 7.64 (1H, d, JHH
4,7
relative to the residual solvent signal. HR-MS were recorded on ¼ 3.7 Hz, H ), 7.52 (2H, br s, H ), 7.17 (2H, q, JHH ¼ 3.0 Hz,
5
,6
b
a Bruker maXis mass spectrometer. Elemental analysis was
performed on a Flash EA series 1112 CHNS analyzer.
H
), 6.94 (1H, d, JHH ¼ 3.7 Hz, H ), 2.83 (2H, t, JHH ¼ 7.5 Hz,
thio–CH
–), 1.65 (2H, quint, JHH ¼ 7.4 Hz, thio–C–CH
–), 1.36–
2
2
1
4
13
General procedure for the synthesis of ligands (L –L ). A 1.25 (10H, m, –(CH
2
)
5
–), 0.85 (3H, t, JHH ¼ 7.0 Hz, –CH
3
).
C
stirred solution of o-phenylenediamine (1 equiv.), aldehyde (1 NMR (100 MHz, CDCl
3
, ppm): d 149.71, 147.71, 130.21, 126.67,
ꢁ
equiv.) and NaHSO (3 equiv.) in DMF were heated at 80 C for 125.21, 122.81 (aromatic and thiophene), 31.84, 31.48, 30.22,
3
7
–8 h. The progress of the reaction was monitored by TLC. Aer 29.29, 29.20, 29.04, 22.65, 14.10 (octyl). HR-MS (m/z): calc. for
+
completion of reaction, the crude mixture was poured into ice-
cold water. The precipitated solid was ltered, washed with
water and dried under vacuum to get crude product.
C
C
19
19
H
H
25
N
N
2
S (M + H) : 313.1728; found, 313.1736. Anal. calc. for
S: C, 73.03; H, 7.74; N, 8.97; S, 10.26 found: C, 73.15; H,
24
2
7.68; N, 8.89; S, 10.28.
0
1
2
-(2,2 -Bithiophen-5-yl)benzimidazole (L ). Orange solid
General procedure for the synthesis of tripodal molecules
0
1
4
ꢁ
product (1.8 g, 93%) was prepared from 2,2 -bithiophene-5- (1–4). To a stirred solution of ligand (L –L ) in THF at 0 C, NaH
carboxaldehyde (1.37 g, 7.05 mmol), o-phenylenediamine (1.2 equiv.) was added and allowed to stir at room temperature
1
(
762 mg, 7.05 mmol) and NaHSO (2.21 g, 21.15 mmol). H NMR for 1 h. To this solution, solid tribromo compound(s) were
3
(
500 MHz, d
6
a
-DMSO, ppm): d 13.04 (1H, br, NH), 7.78 (1H, d, JHH added and stirring continued. The progress of the reaction was
e
¼
3.9 Hz, H ), 7.60 (1H, dd, JHH ¼ 5.0, 1.1 Hz, H ), 7.57 (2H, q, monitored by TLC. Aer completion of reaction, the solvent was
4
,7
c
J
HH ¼ 3.0 Hz, H ), 7.44 (1H, dd, JHH ¼ 3.5, 1.1 Hz, H ), 7.41 (1H, removed under reduced pressure and ice water was added to the
b 5,6
d, JHH ¼ 3.8 Hz, H ), 7.21 (2H, q, JHH ¼ 3.0 Hz, H ) and 7.15 resulting mixture. The precipitated solid was collected by
d
13
(
1H, dd, JHH ¼ 3.6, 1.4 Hz, H ). C NMR (125 MHz, d
6
-DMSO, ltration under vacuum, washed with hexane and air dried.
0
ppm): d 146.93, 139.14, 136.34, 132.44, 129.03, 128.15, 126.82,
1,3,5-Tris(2-(2,2 -bithiophen-5-yl)benzimidazol-1-ylmethyl)-
1
25.44, 125.31 and 122.86 (aromatic and bithiophene). HR-MS 2,4,6-trimethylbenzene (1a). Yellow solid product (436 mg, 87%)
+
1
(m/z): calc. for C H N S (M + H) : 283.0364; found, was prepared from L (424 mg, 1.5 mmol), NaH (45 mg, 2.0
1
5
11
2
2
2
2
10 2 2
83.0363. Anal. calc. for C15H N S : C, 63.80; H, 3.57; N, 9.92; S, mmol) and 1,3,5-tris(bromomethyl)mesitylene (200 mg, 0.5
1
2.71 found: C, 63.71; H, 3.51; N, 10.07; S, 22.71.
mmol). H NMR (400 MHz, d
6
-DMSO, ppm): d 7.78 (3H, d, JHH
¼
0
2
a
4
e
2
-(1,1 -Biphenyl-4-yl)benzimidazole (L ). White solid product 3.9 Hz, H ), 7.60 (6H, d, JHH ¼ 6.3 Hz, H & H ), 7.46 (3H, d, JHH
c
b
(
2.3 g, 92%) was prepared from biphenyl-4-carboxaldehyde ¼ 3.5 Hz, H ), 7.41 (3H, d, JHH ¼ 3.8 Hz, H ), 7.15–7.11 (6H, m,
5 d 6
(
1.69 g, 9.25 mmol), o-phenylenediamine (1.0 g, 9.25 mmol) H & H ), 6.68 (3H, t, JHH ¼ 7.7 Hz, H ), 6.35 (3H, d, JHH ¼ 8.3 Hz,
1
7
13
and NaHSO
3
(2.89 g, 27.75 mmol). H NMR (500 MHz, d
6
-
H ) 5.78 (6H, s, –CH
2 3
–) and 2.05 (9H, s, –CH ). C NMR (100
a
DMSO, ppm): d 8.28 (2H, dt, J ¼ 8.5, 1.8 Hz, H ), 7.88 (2H, dt, MHz, d
6
-DMSO, ppm): d 147.72, 143.17, 139.96, 138.95, 136.06,
HH
b
c
JHH ¼ 8.5, 1.8 Hz, H ), 7.78 (2H, dd, J ¼ 7.2, 1.2 Hz, H ), 7.63 136.52, 131.58, 131.24, 130.70, 129.04, 126.98, 125.65, 125.20,
HH
4
,7
d
(
(
2H, q, JHH ¼ 3.0 Hz, H ), 7.51 (2H, t, JHH ¼ 7.4 Hz, H ), 7.42 123.15, 122.40, 119.58, 111.68 (aromatic and bithiophene),
e 5,6 13
1H, t, JHH ¼ 7.3 Hz, H ), 7.23 (2H, q, JHH ¼ 3.0 Hz, H ).
C
46.56 (–CH
2
–) and 16.84 (–CH
3
). HR-MS (m/z): calc. for
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+
57 43 6 6
C H N S (M + H) : 1003.1873; found 1003.1873. Anal. calc. mmol) and 1,3,5-tris(bromomethyl)mesitylene (100 mg, 0.25
1
for C H N S : C, 68.23; H, 4.22; N, 8.38; S, 19.17 found: C, mmol). H NMR (500 MHz, d -DMSO, ppm): d 7.62 (3H, d, J
¼
¼
¼
5
7
42
6
6
6
HH
HH
HH
a
4
6
8.36; H, 4.26, N, 8.27, S, 19.05.
3.6 Hz, H ), 7.55 (3H, d, J
7.6 Hz, H ), 6.97 (3H, d, J
¼ 8.1 Hz, H ), 7.10 (3H, t, J
HH
0
5
b
1,3,5-Tris(2-(2,2 -bithiophen-5-yl)benzimidazol-1-ylmethyl)-
¼ 3.4 Hz, H ), 6.63 (3H, t, J
HH
6
7
2
,4,6-triethylbenzene (1b). Yellow solid product (492 mg, 83%) 7.6 Hz, H ), 6.29 (3H, d, JHH ¼ 8.2 Hz, H ), 5.70 (6H, s, –CH
2
–),
1
was prepared from L (480 mg, 1.7 mmol), NaH (52 mg, 2.1 2.85 (6H, t, JHH ¼ 7.4 Hz, thio–CH
1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (6H, quint, JHH ¼ 7.4 Hz, –C–CH
mmol) and –), 1.35–1.27 (18H, m, –(CH
3 3
250 mg, 0.56 mmol). H NMR (400 MHz, d ). C NMR (100 MHz, CDCl ,
2 3
–), 1.99 (9H, s, –CH ), 1.66
2
2 3
) –
1
13
(
6
-DMSO, ppm): ), 0.85 (9H, t, JHH ¼ 6.8 Hz, –C–CH
a
d 7.87 (3H, d, JHH ¼ 3.9 Hz, H ), 7.61 (6H, dd, JHH ¼ 5.2, 1.3 Hz, ppm): d 150.41, 148.58, 143.26, 138.80, 134.80, 131.19, 129.23,
4
e
c
H & H ), 7.49 (3H, dd, J ¼ 3.6, 1.2 Hz, H ), 7.44 (3H, d, J
¼
128.90, 124.96, 122.96, 122.94, 122.27, 119.97, 110.83 (aromatic
HH
HH
b
5
d
6
3
.4 Hz, H ), 7.17–7.12 (6H, m, H & H ), 6.42 (3H, br, H ), 6.28 and thiophene), 46.29 (–CH –), 17.01 (–CH ), 31.54, 31.48,
2
3
7
(
3H, br s, H ), 5.76 (6H, s, –CH –), 2.58 (6H, d, J
CH
¼ 6.8 Hz, 30.18, 28.77, 22.57 and 14.09 (hexyl). HR-MS (m/z): calc. for
2
HH
1
3
+
–
2
–CH
3
) and 0.72 (9H, s, –CH
2
–CH
3
). C NMR (125 MHz, d
6
-
C
63
H
73
N
H
6
S
N
3
(M + H) : 1009.5059; found, 1009.5054. Anal. calc.
: C, 74.96; H, 7.19; N, 8.33; S, 9.53 found C, 74.89;
DMSO, ppm): d 147.64, 145.75, 143.31, 140.07, 136.06, 135.58, for C63
72
6
S
3
1
31.06, 130.67, 129.06, 126.99, 125.69, 125.16, 122.98, 122.29, H, 7.15; N, 8.26; S, 9.70.
19.67, 112.28 (aromatic and bithiophene), 45.28 (–CH –), 23.55 1,3,5-Tris(2-(5-hexylthiophen-2-yl)benzimidazol-1-ylmethyl)-
–CH ) and 14.75 (–CH –CH ). HR-MS (m/z): calc. for 2,4,6-triethylbenzene (3b). Yellow solid product (421 mg, 88%)
C H N S (M + H) : 1045.2343; found 1045.2342. Anal. calc. was prepared from L (387 mg, 1.36 mmol), NaH (40 mg, 1.7
1
2
(
–CH
2
3
2
3
+
3
6
0
49 6 6
for C H N S : C, 68.93; H, 4.63; N, 8.04; S, 18.40 found: C, mmol)
and
1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene
6
0
48 6 6
1
6
8.83; H, 4.71; N, 8.12; S, 18.34.
(200 mg, 0.45 mmol). H NMR (500 MHz, d -DMSO, ppm):
d 7.69 (3H, d, JHH ¼ 3.2 Hz, H ), 7.56 (3H, t, JHH ¼ 6.8 Hz, H ),
6
0
a
4
1,3,5-Tris(2-(1,1 -biphenyl-4-yl)benzimidazol-1-ylmethyl)-
5 b
2
,4,6-trimethylbenzene (2a). White solid product (214 mg, 89%) 7.08 (3H, quint, JHH ¼ 6.9 Hz, H ), 7.00 (3H, s, H ), 6.45–6.39
2
6
7
was prepared from L (270 mg, 0.75 mmol), NaH (22 mg, 0.9 (3H, m, H ), 6.24–6.20 (3H, m, H ), 5.67 (6H, s, –CH
2
–), 2.87 (6H,
–), 2.46 (6H, d, JHH ¼ 1.8 Hz, –CH
), 1.72–1.63 (6H, m, –C–CH –), 1.39–1.27 (18H, m, –(CH
and 0.86–0.83 (18H, m, –CH –CH and –C–CH ). C NMR (100
mmol) and 1,3,5-tris(bromomethyl)mesitylene (100 mg, 0.25 t, JHH ¼ 7.2 Hz, thio–CH
2
2
–
1
mmol). H NMR (500 MHz, d
6
-DMSO, ppm): d 7.85 (6H, d, JHH
¼
¼
¼
¼
¼
CH
3
2
2 3
) –)
a
b
13
8
7
7
7
8
.2 Hz, H ), 7.79 (6H, d, J
.3 Hz, H ), 7.62 (3H, d, J
.6 Hz, H ), 7.40 (3H, t, J
¼ 8.2 Hz, H ), 7.74 (6H, d, J
HH
HH
2
3
3
c
4
¼ 8.0 Hz, H ), 7.50 (6H, t, J
MHz, CDCl , ppm): d 150.30, 148.26, 145.77, 143.28, 134.91,
130.62, 129.08, 128.92, 124.92, 123.16, 122.21, 119.94, 114.54
(aromatic and thiophene), 44.83 (–CH
HH
HH
3
d
e
¼ 7.3 Hz, H ), 7.12 (3H, t, J
HH
HH
5
6
.8 Hz, H ), 6.68 (3H, t, JHH ¼ 7.7 Hz, H ), 6.39 (3H, d, JHH
2 2 3
–), 23.75 (–CH –CH ),
7
13
.2 Hz, H ), 5.56 (6H, s, –CH
2
–) and 1.89 (9H, s, –CH
3
). C NMR 14.59 (–CH
2
–CH ), 31.53, 30.16, 28.6, 22.57, and 14.08 (hexyl).
3
+
(
1
1
100 MHz, d
6
-DMSO, ppm): d 154.04, 143.22, 141.63, 139.64, HR-MS (m/z): calc. for C66
38.40, 135.13, 131.56, 130.68, 129.94, 128.42, 127.24, 127.17, 1051.5525. Anal. calc. for C66
22.85, 121.97, 119.71, 111.66 (aromatic and biphenyl), 46.25 S, 9.15 found C, 75.29; H, 7.56; N, 7.91; S, 9.24.
1,3,5-Tris(2-(5-octylthiophen-2-yl)benzimidazol-1-ylmethyl)-
H
79
N
6
S
3
(M + H) : 1051.5528; found,
78 6 3
H N S : C, 75.38; H, 7.48; N, 7.99;
(–CH –) and 16.81 (–CH ). HR-MS (m/z): calc. for C H N (M +
2
3
69 55 6
+
H) : 967.4488; found, 967.4488. Anal. calc. for C H N : C, 2,4,6-trimethylbenzene (4a). Yellow solid product (486 mg, 89%)
6
9
54 6
4
8
5.68; H, 5.63; N, 8.69 found: C, 85.49; H, 5.67, N, 8.58.
was prepared from L (470 mg, 1.504 mmol), NaH (43 mg, 1.8
mmol) and 1,3,5-tris(bromomethyl)mesitylene (200 mg, 0.501
0
1,3,5-Tris(2-(1,1 -biphenyl-4-yl)benzimidazol-1-ylmethyl)-
1
a
2
,4,6-triethylbenzene (2b). White solid product (661 mg, 96%) mmol). H NMR (500 MHz, d
6
-DMSO, ppm): d 7.60 (3H, s, H ),
2
4
5
was prepared from L (551 mg, 2.04 mmol), NaH (60 mg, 2.5 7.55 (3H, d, JHH ¼ 7.6 Hz, H ), 7.09 (3H, t, JHH ¼ 6.8 Hz, H ), 6.95
b
6
mmol)
and
1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene (3H, s, H ), 6.63 (3H, t, JHH ¼ 7.6 Hz, H ), 6.29 (3H, d, JHH
¼
1
7
(300 mg, 0.68 mmol). H NMR (500 MHz, d
6
-DMSO, ppm): 7.6 Hz, H ), 5.69 (6H, s, –CH
2
–), 2.83 (6H, s, thio–CH
2
–), 1.98
a
b
d 7.90 (6H, d, JHH ¼ 8.0 Hz, H ), 7.84–7.80 (6H, m, H ), 7.76 (6H, (9H, s, –CH ), 1.65 (6H, s, –C–CH –), 1.29–1.22 (30H, m, –(CH ) –
3
2
2 5
c
4
13
d, JHH ¼ 7.6 Hz, H ), 7.65 (3H, d, J ¼ 8.0 Hz, H ), 7.51 (6H, t, ), 0.83 (9H, s, –CH3). C NMR (100 MHz, d -DMSO, ppm):
HH
6
d
e
JHH ¼ 7.5 Hz, H ), 7.44–7.41 (3H, m, H ), 7.14 (3H, t, J
¼
¼
d 149.52, 148.39, 143.09, 138.76, 135.16, 131.16, 131.44, 129.78,
129.70, 125.79, 122.81, 122.06, 119.35, 111.44 (aromatic and
thiophene), 46.37 (–CH –), 16.78 (–CH ), 31.74, 31.49, 29.85,
2 3
HH
5
6
7
8
.5 Hz, H ), 6.50 (3H, t, JHH ¼ 6.0 Hz, H ), 6.37 (3H, d, JHH
7
.0 Hz, H ), 5.55 (6H, s, –CH
2
–), 2.71–2.63 (6H, m, –CH
2
–CH
3
)
1
3
and 0.47 (9H, s, –CH
2 3 3
–CH ). C NMR (100 MHz, CDCl , ppm): 29.17, 29.11, 28.96, 22.56 and 14.36 (octyl). HR-MS (m/z): calc.
+
d 153.74, 145.40, 143.24, 142.74, 139.95, 134.65, 130.69, 130.14, for C69
H
85
N
6
S
3
(M + H) : 1093.5998; found, 1093.5991. Anal.
: C, 75.78; H, 7.74; N, 7.68; S, 8.79 found C,
1
1
29.18, 129.01, 128.04, 127.45, 127.38, 127.16, 123.30, 122.23, calc. for C69
H
84
N
6
S
3
20.11, 111.62 (aromatic and biphenyl), 44.97 (–CH –), 23.76 75.86; H, 7.68; N, 7.75; S, 8.71.
2
(
–CH –CH ) and 14.48 (–CH –CH ). HR-MS (m/z): calc. for
1,3,5-Tris(2-(5-octylthiophen-2-yl)benzimidazol-1-ylmethyl)-
2
3
2
3
+
C H N (M + H) : 1009.4958; found, 1009.4961. Anal. calc. for 2,4,6-triethylbenzene (4b). Yellow solid product (427 mg, 83%)
C
8
7
2
61
6
4
72
H
60
N
6
: C, 85.68; H, 8.33; N, 8.33 found: C, 85.76; H, 5.99, N, was prepared from L (425 mg, 1.36 mmol), NaH (40 mg, 1.7
mmol) and 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene
6
(200 mg, 0.45 mmol). H NMR (500 MHz, d -DMSO, ppm):
.33.
,3,5-Tris(2-(5-hexylthiophen-2-yl)benzimidazol-1-ylmethyl)-
,4,6-trimethylbenzene (3a). Yellow solid product (209 mg, 83%) d 7.67 (3H, d, JHH ¼ 3.4 Hz, H ), 7.57 (3H, d, JHH ¼ 8.0 Hz, H ),
1
1
a
4
2
3
5
b
was prepared from L (213 mg, 0.75 mmol), NaH (22 mg, 0.9 7.09 (3H, t, JHH ¼ 7.5 Hz, H ), 6.99 (3H, s, H ), 6.40–6.35 (3H,
758 | RSC Adv., 2019, 9, 753–760
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6
7
br s, H ), 6.21 (3H, s, H ), 5.67 (6H, s, –CH
2
–), 2.87 (6H, t, JHH
¼
¼
5 (a) T. Morimoto, H. Uno and H. Furuta, Angew. Chem., Int.
Ed., 2007, 46, 3672; (b) S. Janich, R. Frohlich, A. Wakamiya,
S. Yamaguchi and E. U. Wurthwein, Chem.–Eur. J., 2009,
15, 10457.
6 A. S. Mahadevi and G. N. Sastry, Chem. Rev., 2016, 116, 2775.
7 (a) K. Funatsu, A. Kimura, T. Imamura, A. Ichimura and
Y. Sasaki, Inorg. Chem., 1997, 36, 1625; (b)
M. Sathiyendiran, J. Y. Wu, M. Velayudham, G. H. Lee,
S. M. Peng and K. L. Lu, Chem. Commun., 2009, 3795; (c)
S. H. Lin, C. I. Yang, T. S. Kuo, M. H. Chiang, K. C. Hsu
and K. L. Lu, Dalton Trans., 2012, 41, 1448; (d) J. Zaho,
K. Peng, Y. Guo, J. Zhang, S. Chen and J. Hu, New J. Chem.,
2015, 39, 6016.
8 (a) P. Elumalai, P. Rajakannu, F. Hussain and
M. Sathiyendiran, RSC Adv., 2013, 3, 2171; (b)
S. D. Sathiyashivan, B. Shankar, P. Rajakannu, P. Vishnoi,
D. T. Masram and M. Sathiyendiran, RSC Adv., 2015, 5,
74705; (c) S. D. Sathiyashivan, C. K. Kumar, B. Shankar,
M. Sathiyendiran and D. T. Masram, RSC Adv., 2017, 7,
17297.
7
.1 Hz, thio–CH –), 2.49 (6H, s, –CH –CH ), 1.67 (6H, t, J
.7 Hz, –C–CH –), 1.30–1.23 (30H, m, –(CH ) –), 0.82 (9H, t, J
5.5 Hz, –CH ), 0.79–0.72 (9H, m, –CH –CH ). C NMR (100
3 2 3
MHz, CDCl
34.91, 130.63, 129.09, 128.91, 124.92, 123.16, 122.21, 119.94,
11.94 (aromatic and thiophene), 44.83 (–CH –), 23.78 (–CH
), 14.59 (–CH –CH ), 31.85, 31.58, 30.17, 29.22, 29.05, 22.66,
and 14.11 (octyl). HR-MS (m/z): calc. for C72
135.6467, found 1135.6458. Anal. calc. for C H N S : C,
6.14; H, 7.99; N, 7.40; S, 8.47 found C, 76.24; H, 7.89; N, 7.32; S,
.55.
2
2
3
HH
6
2
2 5
HH
1
3
¼
3
, ppm): d 150.31, 148.26, 145.76, 143.76, 143.28,
1
1
2
2
–
CH
3
2
3
+
H
91
N
6
S
3
(M + H) :
1
7
8
7
2
90 6 3
DFT calculations. Geometry optimization of 1a–1b and 2a–
b structures were performed with Gaussian 09 suite of pack-
2
18
ages at MPW1PW91/6-311G(d,p) level of theory and basis set.
The stationary points were characterized by the absence of
imaginary frequencies in the harmonic normal vibrational
mode analysis. The optimized structures at this level of theory
and basis are furnished in the Tables S1–S4 in ESI.† C–H/p
intramolecular interaction energy calculations were performed
at MPW1PW91 and M06-2X levels of theory with 6-311+G(d,p)
basis function. The relative magnitude of the NMR chemical
9 R. Ludwig, F. Weinhold and T. C. Farrar, J. Phys. Chem. A,
1997, 101, 8861.
shi in the presence of DMSO solvent was calculated relative to 10 A. S. Mahadevi, A. Rahalkar, S. R. Gadre and G. N. Sastry, J.
1
2
ligand (L –L ) evaluated with solvation model based on density
Chem. Phys., 2010, 133, 164308.
20
(
SMD) solvent model and MPW1PW91 level of theory with 6- 11 R. Wieczorek and J. J. Dannenberg, J. Am. Chem. Soc., 2004,
11+G(d,p) basis function in Gaussian 09 suite of packages.
18
3
126, 14198.
MESP of the 1a–2b molecules were evaluated with Gaussian 09 12 T. van Mourik and A. J. Dingley, J. Phys. Chem. A, 2007, 111,
suite of packages at MPW1PW91/6-311+G(d,p) level of theory
and basis set.
11350.
24
13 R. D. Parra, S. Bulusu and X. C. Zeng, J. Chem. Phys., 2005,
122, 184325.
1
1
1
4 P. Salvador, N. Kobko, R. Wieczorek and J. J. Dannenberg, J.
Am. Chem. Soc., 2004, 126, 14190.
5 K. Ohno, M. Okimura, N. Akai and Y. Katsumoto, Phys.
Chem. Chem. Phys., 2005, 7, 3005.
6 S. S. Xantheas, Chem. Phys., 2000, 258, 225.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
17 S. Shimizu and H. S. Chan, Proteins: Struct., Funct., Bioinf.,
002, 48, 15.
2
CKK thank UGC-DSKPDF, SDS thank UGC-NRC, and KVJJ thank
UGC-FRPS for funding.
1
8 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
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760 | RSC Adv., 2019, 9, 753–760
This journal is © The Royal Society of Chemistry 2019