Synthesis of a Contrapositionally Substituted Cyclohexa- meta -phenylene: A Ready-to-Use Precursor for Cyclohexa- meta -phenylene-Based Materials

Article abstract of DOI:10.1055/s-0039-1690676

A contrapositionally substituted derivative of cyclohexa- meta -phenylene ([6]CMP) was synthesized by an intramolecular Yamamoto coupling reaction of an appropriate terphenyl unit containing a trimethylsilyl substituent. Iododesilylation of the trimethyls

Full text of DOI:10.1055/s-0039-1690676

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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–E
letter
A
en
I. Arshad et al.
Letter
Synlett
Synthesis of a Contrapositionally Substituted Cyclohexa-meta-
phenylene: A Ready-to-Use Precursor for Cyclohexa-meta-phenyl-
ene-Based Materials
Ifzan Arshad*a,b
Aamer Saeed*a
Diborylated 6[CMP],
Precursor for variety of CMP-based motifs
Pervaiz Ali Channara
Syeda Aaliya Shehzadic
Rana Muhammad Irfand
Any linker
O
O
O
O
linker
B
B
a Department of Chemistry, Quaid-I-Azam
University, Islamabad 45320, Pakistan
aamersaeed@yahoo.com
b CAS Key Laboratory of Materials for Ener-
gy Conversion, Department of Materials
Science and Engineering, University of
Science and Technology of China (USTC),
JinZhai Road, Hefei, Anhui Province
230026, P. R. of China
n
Polymeric Ribbons
Aryl
or
Alkyl
Halide
Aryl
or
Alkyl
Aryl
or
Alkyl
arshadmi@mail.ustc.edu.cn
c Sulaiman Bin Abdullah Aba Al-Khail-Cen-
tre for Interdisciplinary Research in Basic
Sciences (SA-CIRBS) International Islamic
University, Islamabad, Pakistan
substituted 6[CMP]s
d Department of Chemistry, Mianwali
Campus, University of Sargodha, Sar-
godha 40100, Pakistan
Received: 06.08.2019
Accepted after revision: 25.08.2019
Published online: 05.09.2019
toelectronic devices, and supramolecular chemistry.3 De-
spite the simple structure of CMPs, few groups have suc-
ceeded in one-pot or sequential syntheses of substituted
derivatives, and there have been no reports of CMPs bearing
substituents in the contra positions. Synthesis of unsubsti-
tuted and polysubstituted CMP molecules bearing trimeth-
ylsilyl, alkyl, alkoxy, or trifluoromethyl groups (Figure 1)
have been reported by Chan and Swager,4a by the Müllen
group,4b and, recently, by Isobe and co-workers.4c The Mül-
len group also demonstrated a synthesis of a phenylene-
bridged 6[CMP] as a hexa-peri-hexabenzocoronene precur-
sor.5 Given the recent interest in the design of various novel
functional materials, molecules with functionalities at se-
lective positions are needed for the design of useful materi-
als. The introduction of functional groups primed for cou-
pling reactions to CMPs would permit the preparation of
various CMP-based structures with diverse properties and
functions.
DOI: 10.1055/s-0039-1690676; Art ID: st-2019-u0412-l
Abstract A contrapositionally substituted derivative of cyclohexa-
meta-phenylene ([6]CMP) was synthesized by an intramolecular Yama-
moto coupling reaction of an appropriate terphenyl unit containing a
trimethylsilyl substituent. Iododesilylation of the trimethylsilyl groups of
the product with iodine monochloride was used to incorporate iodo
groups, an important functionality for metal-catalyzed coupling reac-
tions. The iodo groups were also converted into a (pinacolato)boryl
groups, another important functionality for coupling reactions. The di-
borylated [6]CMP is expected to be a versatile potential comonomer
and a precursor for the synthesis of CMP-based materials. The synthetic
route to the disubstituted [6]CMP included lithiation, Pd-catalyzed bor-
ylation, Suzuki coupling, and Yamamoto coupling. The structure of the
product was established by NMR spectroscopy and mass spectrometry.
Key words cyclohexaphenylene, Yamamoto coupling, borylation
[n]Cyclo-meta-phenylenes ([n]CMPs) are polycyclic aro-
matic compounds containing meta-linked benzene rings.
The first CMP was synthesized by Staab and Binnig in
1960,1 and some later work on CMP-based cation hosts was
carried by Cram and co-workers.2 During the next few de-
cades, except for a few syntheses, very little was discovered
about the chemistry of CMPs, even though their unique cy-
clic structure has potential applications in electronics, op-
Here, we report an efficient approach to a 15,45-dibory-
lated [6]CMP (Figure 2), potentially useful as precursor for
variety of architectures containing a CMP core unit. This
disubstituted [6]CMP motif might also be useful as a co-
monomer to form polymeric ribbons, and the attached pin-
acolatoboryl group might be replaced by variety of substit-
uents to provide new [6]CMP-based motifs.
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–E
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
I. Arshad et al.
(Me)3Si
Letter
Synlett
Si(Me)3
R2
R1
(Me)3Si
Si(Me)3
R1
R2
(Me)3Si
Si(Me)3
R2
R1
R
R
R
1 = Me, R2 = H
1 = R2 = Me
1 = R2 = CF3
Klaus Müllen
Hiroyuki Isobe
R1
R2
R1
R1
R3
R3
R
R
R2
R3
R1
R1
R2
R = Si(Me)3, (pinB)2
This Work
R1
=
OC12H25
R1
R2 = H, Me
R3 = –OMe
Timothy M. Swager
Figure 1 Comparison of some selected functionalized [6]CMPs
Bpin
Si
Br
Br
Si
Br
ii
O
B
Br
iii
Br
i
O
Bpin
2
Br
Br
1
O
B
O
Si
Figure 2 Structure of 15,45-diborylated [6]CMP
The 15,45-diborylated [6]CMP was synthesized in step-
wise fashion, starting from the commercially available
1,3,5-tribromobenzene. The major precursor to the macro-
cycle, (3,3′′-dibromo-1,1′:3′,1′′-terphenyl-5′-yl)(trimethyl)-
silane (3), and was prepared as shown in Scheme 1. First,
1,3,5-tribromobenzene was lithiated with tert-butyllithium
and converted into (3,5-dibromophenyl)(trimethyl)silane
(1) by treatment with chloro(trimethyl)silane.6 Treatment
of 1 with bis(pinacolato)diborane in the presence of 6 mol%
of Pd(dppf)2Cl2 [dppf = dichlorobis(1,1′-diphenylphosphi-
no)ferrocene] catalyst and KOAc afforded the diboryl deriv-
ative 2.7 Suzuki cross coupling of 2 with a fivefold amount
of 1,3-dibromobenzene at 90 °C in 3:2:1 toluene–ethanol–
water gave the m-terphenyl derivative 3.8 This large excess
of 1,3-dibromobenzene was used to prevent polymeriza-
tion of the m-terphenyl unit.
Br
Br
3
Scheme 1 Synthesis of (3,3′′-dibromo-1,1′:3′,1′′-terphenyl-5′-yl)-
(trimethyl)silane (3). Reagents and conditions: (i) BuLi, TMSCl, Et2O, –78 °C,
94%; (ii) (pinB)2, Pd(dppf)Cl2 (6 mol%), KOAc, DMF, 90 °C, 90%; (iii)
Pd(PPh3)4 (3 mol%), K2CO3, 3:2:1 toluene–EtOH–H2O, 90 °C, 81%.
to avoid polymerization of 3. Therefore, 3 was subjected to
macrocyclization under dilute conditions with bis(cyclooc-
ta-1,5-diene)nickel(0), 1,5-cyclooctadiene (cod), and 2,2′-
bipyridine at a concentration of 3 × 10–2 mol·L–1 in DMF un-
der an inert atmosphere at 90 °C for three days.9 The prod-
uct was identified by MALDI-TOF MS analysis of the crude
mixture, which indicated the presence of 4, as well as in-
completely closed species and oligomers. Column chroma-
tography was used to remove these byproducts and to iso-
late 4 in a yield of 61%.
The next and most critical step was the conversion of
the m-terphenyl unit 3 into the corresponding disubstitut-
ed cyclohexa-meta-phenylene 4 through dimerization by
using the Yamamoto coupling reaction (Scheme 2). As ex-
pected, the reaction was greatly influenced by the concen-
tration of the reaction mixture, and dilution was necessary
The structure of 4 was confirmed by high-resolution
MALDI-TOF MS (Figure 3; left) and by NMR spectroscopy
(Figure 4a). The recorded MS spectrum (blue line) agrees
with the calculated one (red line) in both the isotopic dis-
Thieme. All rights reserved. — Synlett 2019, 30, A–E

C
I. Arshad et al.
Letter
Synlett
I
Si
Si
iv
v
Br
Br
3
I
Si
4
5
O
O
O
B
B
O
6
Scheme 2 Synthesis of diborylated [6]CMP (6). Reagents and conditions: (iv) cod, 2,2′-bipyridine, [Ni(cod)2] (2 equiv), 61%; (v) ICl, 86%; (vi) (pinB)2,
Pd(dppf)Cl2 (6 mol%), KOAc, DMF, 90 °C; 58%.
1
tribution and the mass-to-charge-ratio. The H NMR spec-
trum of 4 exhibits a set of signals corresponding to only five
different types of aromatic protons, indicating a highly
symmetric structure. The trimethylsilyl groups of 4 were
converted into iodo substituents by iododesilylation with
iodine monochloride in darkness for eight hours. The re-
sulting diiodo[6]CMP 5 was a sparingly soluble white solid
that could not be characterized.
The next step was the conversion of the diiodo deriva-
tive 5 into corresponding diborylated [6]CMP 6 (Scheme 2).
High dilution was necessary to prevent polymerization re-
actions. The diiodo derivative 5 was added to (pinB)2, KOAc,
and Pd(dppf)Cl2 in DMF, and the mixture was degassed by
bubbling argon. It was then refluxed for 48 hours at
110 °C.10 The product was precipitated by addition of cold
methanol. After precipitation, MALDI-TOF MS analysis of
the crude product indicated the presence of 6. Column
chromatography was used to remove byproducts and to iso-
late 6 in a yield of 58%. The high-resolution MALDI-TOF
mass spectrum (Figure 3, right) and 1H NMR spectrum (Fig-
ure 4b) clearly confirmed the structure of the product.
In summary, we have synthesized and characterized the
diborylated cyclohexa-meta-phenylene 6, as a unique pre-
cursor that should provide smooth access to many new pol-
yaromatic structures based on [6]CMP with various substit-
uents. The diborylated [6]CMP 6 is a versatile building block
that might lead to materials with various applications and
properties, and we expect it to make a fruitful contribution
to the synthesis of CMP-based scaffolds and in the synthe-
ses of more planar molecules.
Funding Information
Figure 3 High-resolution MALDI-TOF MS spectra of structures 4 and 6
measured with tetracyanoquinodimethane (TCNQ) as a matrix. The sol-
id blue lines represent the measured mass spectra and the solid red
lines are calculated spectra based on the molecular structures.
This work was supported by the Higher Education Commission of
Pakistan.()
Thieme. All rights reserved. — Synlett 2019, 30, A–E

D
I. Arshad et al.
Letter
Synlett
Figure 4 (a) The 1H NMR spectrum of 4 in CDCl3; (b) 1H NMR spectrum of 6 in CDCl3
Supporting Information
(2) (a) Cram, D. J.; Kaneda, T.; Helgeson, R. C.; Brown, S. B.; Knobler,
C. B.; Maverick, E.; Trueblood, K. N. J. Am. Chem. Soc. 1985, 107,
3645. (b) Cram, D. J.; Carmack, R. A.; Helgeson, R. C. J. Am. Chem.
Soc. 1988, 110, 571. (c) Cram, D. J.; Lein, G. M. J. Am. Chem. Soc.
1985, 107, 3657. (d) Trueblood, K. N.; Knobler, C. B.; Maverick,
E.; Helgeson, R. C.; Brown, S. B.; Cram, D. J. J. Am. Chem. Soc.
1981, 103, 5594. (e) Cram, D. J.; Kaneda, T.; Helgeson, R. C.; Lein,
G. M. J. Am. Chem. Soc. 1979, 101, 6752.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0039-1690676.
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References and Notes
(1) (a) Staab, H. A.; Binnig, F. Tetrahedron Lett. 1964, 5, 319.
(b) Staab, H. A.; Binnig, F. Chem. Ber. 1967, 100, 293.
Thieme. All rights reserved. — Synlett 2019, 30, A–E

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Letter
Synlett
(3) (a) Xue, J. Y.; Ikemoto, K.; Takahashi, N.; Izumi, T.; Taka, H.; Kita,
H.; Sato, S.; Isobe, H. J. Org. Chem. 2014, 79, 9735. (b) Ikemoto,
K.; Yoshii, A.; Izumi, T.; Taka, H.; Kita, H.; Xue, J. Y.; Kobayashi,
R.; Sato, S.; Isobe, H. J. Org. Chem. 2016, 81, 662.
(4) (a) Chan, J. M.; Swager, T. M. Tetrahedron Lett. 2008, 49, 4912.
(b) Pisula, W.; Kastler, M.; Yang, C.; Enkelmann, V.; Müllen, K.
Chem. Asian J. 2007, 2, 51. (c) Yoshii, A.; Ikemoto, K.; Izumi, T.;
Taka, H.; Kita, H.; Sato, S.; Isobe, H. Org. Lett. 2019, 21, 2759.
(5) Dumslaff, B.; Wagner, M.; Schollmeyer, D.; Narita, A.; Müllen, K.
Chem. Eur. J. 2018, 24, 11908.
(6) Gong, L.-Z.; Hu, Q.-S.; Pu, L. J. Org. Chem. 2001, 66, 2358.
(7) Gosset, A.; Xu, Z.; Maurel, F.; Chamoreau, L. M.; Nowak, S.; Vives,
G.; Perruchot, C.; Heitz, V.; Jacquot de Rouville, H. P. New J.
Chem. 2018, 42, 4728.
(8) (3,3′′-Dibromo-[1,1′:3′,1′′-terphenyl]-5′-yl)(trimethyl)silane
(3)
(9) 15,45-Bis(trimethylsilyl)cyclohexa-meta-phenylene (4)
2,2′-bipyridine (312 mg, 2.0 mmol), cod (216 mg, 2.0 mmol),
and [Ni(cod)2] (550 mg, 2.0 mmol) were placed in a well-dried
Schlenk flask and dissolved in anhyd DMF (80 mL). The mixture
was then stirred for 30 min at 80 °C in darkness. A solution of
the dibromo compound 3 (500 mg, 1.08 mmol) in degassed
anhyd toluene (150 mL) was added quickly, and the resulting
mixture was stirred at 80 °C for 3 d. The reaction was stopped
by adding 10% aq HCl, and the organic phase was separated,
washed with H2O, dried (MgSO4) and concentrated in vacuo.
The residue was purified by column chromatography [silica gel,
PE–CH2Cl2 (20:1); Rf = 0.29] to give a colorless crystalline solid;
yield: 397 mg (61%, 0.66 mmol).
1H NMR (400 MHz, CDCl3)  = 8.34 (s, 4 H), 8.31 (s, 2 H), 7.86 (d,
J = 1.7 Hz, 4 H), 7.75 (t, J = 8.8 Hz, 8 H), 7.58 (t, J = 7.6 Hz, 4 H),
0.39 (s, 18 H).
Argon was bubbled through a solution of the diborylated deriv-
ative 2 (1 g, 2.48 mmol, 1 equiv), 1,3-dibromobenzene (2.92 g,
12.43 mmol, 5 equiv), and K2CO3 (1.46 g, 15 mmol, 5 equiv) in
3:2:1 toluene–EtOH–H2O. Pd(PPh3)4 (71 mg, 2.5 equiv) was
added, and the mixture was stirred at 90 °C for 24 h. The
organic phase was separated, washed with H2O, dried (MgSO4),
and concentrated. The residue was purified by column chroma-
tography (silica gel, hexane; Rf = 0.50) to give a colorless
powder; yield: 0.92 g (81%); mp 230 °C.
(10) 15,45-Bis(pinacolatoboryl)cyclohexa-meta-phenylene (6)
A 50 mL flask containing the diiodo compound 5 (1.0 g, 2.1
mmol), bis(pinacolato)diborane (1.42 g, 5.6 mmol), KOAc (2.06
g, 21 mmol), and Pd(dppf)Cl2 (73.2 mg, 0.1 mmol) was evacu-
ated and refilled with argon three times. DMF (30 mL) was then
transferred into the flask from a syringe under argon at r.t., and
the mixture was stirred at 110 °C for 48 h. The crude product
was purified by column chromatography [silica gel, PE–CH2Cl2
(4:1)] to give a white solid; yield: 0.8 g (58%).
1H NMR (400 MHz, CDCl3)  = 7.76 (t, J = 1.7 Hz, 2 H), 7.66 (s, 3
H), 7.56 (dd, J = 1.7, 1.1 Hz, 1 H), 7.54 (dd, J = 1.7, 1.1 Hz, 1 H),
7.52 (dd, J = 1.9, 1.0 Hz, 1 H), 7.50 (dd, J = 1.9, 1.0 Hz, 1 H), 7.33
(t, J = 7.8 Hz, 2 H), 0.36 (s, 9 H). 13C NMR (100 MHz, CDCl3):
 = 143.9, 143.0, 138.1, 133.8, 132.9, 132.0, 128.0, 127.4, 125.9,
121.5, 1.2.
1H NMR (400 MHz, CDCl3)  = 8.19 (d, J = 1.7 Hz, 6 H), 7.84 (d, J =
8.7 Hz, 4 H), 7.73 (d, J = 7.1 Hz, 8 H), 7.56 (t, J = 7.7 Hz, 4 H), 1.41
(s, 24 H).
Thieme. All rights reserved. — Synlett 2019, 30, A–E