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NMR (150 MHz, CDCl3), d: 14.3, 22.9, 29.6, 29.9, 30.5, 30.7, 31.8, Rigaku's ‘CrystalStructure’ crystallographic soware package
56.3, 68.9, 69.2, 114.3, 115.8, 116.4, 128.3, 129.0, 129.2, 129.4, except for renement, which was performed using SHELXL-
129.6, 149.8, 150.9. HRMS (ESI/QTOF) m/z: calcd for [M + H+]: 2017/1. The crystallographic data for all structures reported in
1486.7575 (for C53H59O10Br8); found 1486.7526.
this paper have been deposited at the Cambridge Crystallo-
Pillar-4a. White solid (560 mg, 19%). Mp 125–126 ꢀC. 1H graphic Data Centre as supplementary publications (CCDC
NMR (600 MHz, CDCl3) d: 3.53 (t, J ¼ 6 Hz, 8H), 3.71–3.72 (m, 1880766–1880769).
12H), 3.75 (s, 6H), 3.81–3.82 (m, 10H), 4.11–4.15 (m, 8H), 6.78
(d, J ¼ 10.8 Hz, 4H), 6.83–6.84 (m, 6H). 13C NMR (150 MHz,
1H NMR titrations
CDCl3), d: 29.8, 30.3, 56.0, 56.3, 68.9, 114.1, 114.5, 115.9, 128.1,
A 0.5 mL sample of the OMA guest solutions was prepared at
a concentration of 8.4 mM in chloroform-d. A sample of the host
solutions (2 mL) was prepared at a concentration of 0.1 M in
a chloroform-d solvent. All titration experiments were carried
128.3, 128.7, 129.3, 129.4, 149.9, 150.9. HRMS: (m/z): calcd for
[M + Na+]: 1324.8871 (for C51H56O10Br6Na); found 1324.8835.
Pillar-4b. White solid (350 mg, 12%). Mp 130–131 ꢀC. 1H
NMR (600 MHz, CDCl3) d: 3.55–3.59 (m, 12H), 3.75–3.76 (m,
12H), 3.83–3.84 (m, 10H), 4.12–4.21 (m, 12H), 6.80 (d, J ¼ 8.4 Hz,
4H), 6.86–6.87 (m, 6H). 13C NMR (150 MHz, CDCl3), d: 29.2, 29.7,
29.9, 30.4, 30.5, 56.3, 68.9, 69.3, 114.4, 115.9, 116.6, 128.3, 128.4,
129.1, 129.4, 129.6, 149.9, 150.0, 150.9. HRMS (ESI/QTOF) m/z:
calcd for [M + Na+]: 1324.8871 (for C51H56O10Br6 Na); found
1324.8856.
1
out in an NMR tube at 298 K, and H-NMR spectra were recor-
ded upon successive addition of aliquots of the stock solution of
the appropriate host with a syringe. The 1H-NMR spectral
changes were tted to 1 : 1 binding isotherms by nonlinear
least-squares treatment using Microso Excel to determine the
association constant, Ka.24
Pillar-3a. Yield (590 mg, 20%). Mp 124–125 ꢀC. 1H NMR (600
MHz, CDCl3) d: 3.53 (t, J ¼ 6 Hz, 8H), 3.71–3.72 (m, 12H), 3.75 (s,
6H), 3.81–3.82 (m, 10H), 4.11–4.15 (m, 8H), 6.78 (d, J ¼ 10.8 Hz,
4H), 6.83–6.84 (m, 6H). 13C NMR (150 MHz, CDCl3), d: 29.8, 30.3,
56.0, 56.3, 68.9, 114.1, 114.5, 115.9, 128.1, 128.3, 128.7, 129.3,
129.4, 149.9, 150.9. HRMS: (m/z): calcd for [M + Na+]: 1141.0348
(for C49H54O10Br4 Na); found 1141.0392.
Conclusions
In conclusion, constitutional isomers of tetra-and hexabromo-
functionalized pillar[5]arenes were synthesized by co-
cyclization from hydroquinone derivatives of 1,4-dimethox-
ybenzene and 1,4-bis(2-bromoethoxy)benzene with para-
formaldehyde in presence of BF3$OEt2. Separation of the
constitutional brominated-pillar[5]arene isomers by column
chromatography was attempted, the yields of the regioisomers
dependent on nature and the monomer mole feed ratio. The
1,4-dimethoxybenzene monomer 1 is more reactive relative to
1,4-bis(2-bromoethoxy)benzene toward the electrophilic
condensation reaction. HPLC analysis of the crude pillararene
mixture, revealed that the isomeric distribution of tetra-and
hexabromo-functionalized pilla[5]arene were 3 : 1 and 3 : 2
respectively. Characterization of the prepared and isolated
constitutional isomers revealed that they exhibited different
melting points, NMR spectra, crystal structures, and stacking
patterns in the solid state. The binding study carried out for
pillar[5]arane constitutional isomers with OMA guest indicate
that the association constant of complexation was affected by
the spatial arrangement of the substituents on the pillararene
rim. Our future work will focus on the modication and appli-
cation of the synthesized brominated-functionalized pillar[5]
arenes isomers in the receptor design.
1
Pillar-3b. Yield (206 mg, 7%). Mp 133–134 ꢀC. H NMR (600
MHz, CDCl3) d: 3.48 (t, J ¼ 6 Hz, 4H), 3.54 (t, J ¼ 6 Hz, 4H), 3.71
(s, 6H), 3.74–3.75 (m, 12H), 3.80–3.83 (m, 10H), 4.07 (t, J ¼ 6 Hz,
4H), 4.16 (t, J ¼ 6 Hz, 4H), 6.77 (s, 2H), 6.83–6.84 (m, 8H). 13C
NMR (150 MHz, CDCl3), d: 29.6, 29.8, 30.2, 56.1, 56.3, 68.9, 69.3,
114.1, 114.2, 114.4, 115.9, 116.6, 127.9, 128.4, 128.7, 128.9,
129.7, 149.8, 150.1, 150.9. HRMS (ESI/QTOF) m/z: calcd for [M +
Na+]: 1141.0348 (for C49H54O10Br4Na); found 1141.0374.
1
ꢀ
Pillar-2. Yield (440 mg, 15%). Mp 117–118 C H NMR (600
MHz, CDCl3) d: 3.47 (t, J ¼ 6 Hz, 4H), 3.67 (s, 6H), 3.71–3.72 (m,
18H), 3.80–3.81 (m, 10H), 4.08 (t, J ¼ 6 Hz, 4H), 6.76–6.82 (m,
10H). 13C NMR (150 MHz, CDCl3), d: 29.7, 30.1, 53.3, 55.9, 56.3,
68.9, 114.0, 114.2, 115.9, 128.0, 128.3, 128.8, 129.3, 149.9, 150.9,
151.0.
Pillar-1. Yield (236 mg, 8%). The NMR and mass spectral
details are consistent with those reported in the literature.1 1H
NMR (600 MHz, CDCl3) d: 3.72 (s, 30H), 3.76 (s, 10H), 6.83 (s,
10H). 13C NMR (150 MHz, CDCl3), d: 29.5, 55.4, 128.1, 133.6,
150.4.
Preparation of single crystals for X-ray diffraction
Conflicts of interest
Single crystals of the synthesized pillar[5]arenes and their
inclusion complexes were grown using either the slow solvent
evaporation method or by the diffusion method using
dichloromethane and n-hexane or acetonitrile. The single
crystal data collections were made on Rigaku R-AXIS RAPID II
There are no conicts to declare.
Acknowledgements
diffractometer by ltered Mo-Ka radiation. The data were The support received from the Kuwait Foundation of Advance-
collected under liquid nitrogen (Oxford cryosystems). ‘Crystal- ment Science (KFAS), made available through research grant no.
clear’ soware package was employed to generate hkl and p4p PR17-14SC-07, in addition to the facilities of RSPU (grant no.
les. The structure was then solved by direct methods using GS01/01, GS01/03, and GS03/08) is gratefully acknowledged.
13818 | RSC Adv., 2019, 9, 13814–13819
This journal is © The Royal Society of Chemistry 2019