One-step synthesis of a cyclic 2,17-dioxo[3,3](4,4′) biphenylophane and first preparation of a microporous polymer network from a macrocyclic precursor by cyclotrimerization

Article abstract of DOI:10.1039/c5cc01654a

One-step synthesis of a cyclic 2,17-dioxo[3,3](4,4′)biphenylophane (MC) was achieved in high yield; its structure was verified by single crystal X-ray analysis. As a first example, a microporous polymer network was formed from macrocycle MC via acid-catal

Full text of DOI:10.1039/c5cc01654a

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DOI: 10.1039/C5CC01654A.
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One-step Synthesis of a Cyclic 2,17-Dioxo[3,3](4,4’)
biphenylophane and First Preparation of a
Microporous Polymer Network from a Macrocyclic
Precursor by Cyclotrimerization
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Suman Kalyan Samanta,a* Eduard Preis,a Christian W. Lehmann,b Richard Goddard,b
DOI: 10.1039/x0xx00000x
Saientan Bag,c Prabal K. Maiti,c Gunther Brunklausd and Ullrich Scherfa
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observed for this class of MPNs.9 In this report, we for the first time
One-step synthesis of a cyclic 2,17-dioxo[3,3](4,4’)biphenylo-
phane (MC) was achieved in high yield; its structure was
verified by single crystal X-ray analysis. As a first example, a
microporous polymer network was formed from macrocycle
MC via acid-catalysed cyclotrimerization yielding a BET
surface area of ca. 570 m2/g.
use a macrocycle (Scheme 1) as building block for the design of
microporous polymer networks via acid-catalysed cyclotrimerization
protocol. Another example for the incorporation of macrocyclic
precursors into an organic cage framework (OCF) following a so-
called “cage-to-framework” approach was published recently.10 In a
related research area supramolecular polymerization of metallacyclic
precursors has been described.11 In addition, supramolecular organic
frameworks12 as well as metal organic frameworks13 containing
macrocyclic building blocks were also developed. Our macrocyclic
precursor was prepared with a simple one-step procedure via
dimerization of an aromatic di-bromo compound.
Microporous polymer networks (MPNs) are fully organic, covalently
crosslinked, porous architectures that are attractive due to their high
surface areas.1 Such MPNs can be prepared under affordable,
transition-metal-free conditions.2 MPNs often possess functional
groups such as extended π-conjugated segments and coordinating
sites that make these networks attractive candidates for specialized
fields of application, such as energy transfer/storage, gas storage/gas
separation or heterogeneous catalysis.3 Therefore, research into
MPNs is challenging, especially towards novel advanced materials
that combine microporosity with other useful functions.
Up to now, the highest specific surface area for a MPN, as
determined by the Brunauer-Emmett-Teller (BET) method is 5640
m2 g-1, which was achieved for a polymer network obtained by Qiu,
Zhu et al. from Ni(0)-mediated Yamamoto coupling of tetra(4-
bromo-phenyl)methane.4 Thomas et al. reported cyclotrimerization
of aromatic dinitriles under ionothermal conditions (molten zinc
chloride at high temperature), producing triazine-based covalent
polymer frameworks with BET surface areas (SBET) of up to 2475 m2
g-1.5 Côté, Yaghi et al. reported cyclotrimerization of diboronic acids
leading to the formation of boroxine-based crystalline covalent
frameworks with SBET values up to 1590 m2 g-1.6 Recently, cyclo-
trimerization of bifunctional diketo-s-indacene derivatives was
successfully achieved.7 The resulting products yielded BET surface
areas of up to 1650 m2 g-1 under metal free conditions (using
methane sulfonic acid as condensing agent) compared to 1165 m2 g-1
in the case of condensation with TiCl4 as Lewis acid. Kaskel et al.
reported a related acid-catalyzed cyclotrimerization of bifunctional
acetyl derivatives forming MPNs with SBET values of 895 m2 g-1
(using SiCl4) and 832 m2 g-1 (using p-toluene sulfonic acid).8
Notably, a rather high SBET value of up to 2250 m2/g was obtained
for microporous polymer networks prepared in a metal-free poly-
hydroxymethylation procedure which is among the highest values
Scheme 1. One-step synthesis of the cyclic 2,17-dioxo[3,3](4,4’)
biphenylophane (MC), including a favourable, folded conformation
of the monocoupled, dimeric intermediate for ring closure.
The synthesis of macrocycles from α,ω-difunctionalized precursors
is generally challenging due to the competition between cyclic and
linear chain products. Also, by maintaining high dilution condition
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often low yields of cyclic products are obtained. However, if the macrocycle resembles the one extracted from a single crystal
macrocycles are prepared in a simple one-step, single-pot process, diffraction analysis (Fig. 1 and Fig. S3, ESI†). Hereby, the crystal
the achieved yields typically benefit over multistep syntheses result, shows an anti-orientation of the two carbonyl moieties while
particularly in terms of total reaction time.14 The amount of macro- theoretical calculations predict similar energies for both anti- or syn-
cycle formation is highly dependent on the conformation of the oriented carbonyl groups. The crystal belongs to space group C 2/c
intermediate that is present after the first coupling step. Favourably, with unit cell parameters a = 31.067(15) Å, b = 13.835(6) Å, and c =
the intermediate adopts a conformation for which the intermolecular 15.670(7) Å, cell volume V = 6724(5) Å3 and a monoclinic angle of
macrocyclization easily occurs. Herein, we describe the one-step β = 93.25(1)o. The long axes of the two biphenyl moieties are
synthesis of 2,17-dioxo[3,3](4,4’)biphenylophane macrocycle (MC) arranged parallel while the biphenyl dihedral angle is about 36o and
in a two-fold, Ni(0)-mediated Yamamoto coupling procedure. The the through space π-π stacking distance ca. 3.5 Å (see ESI† for
structure of the macrocycle was verified by single crystal X-ray crystal structure analysis). In the UV-vis spectrum of MC we
analysis, while the conformation of the mono-coupled intermediate observed a slight, about 10 nm red-shift of the absorption maximum
was investigated by theoretical calculations. The macrocycle was (260 nm) compared to biphenyl as model compound, accompanied
further used for the synthesis of a microporous polymer network, the by a weak low energy shoulder at ca. 315 nm, possibly reflecting
first MPN that is based on a macrocyclic precursor, yielding a BET ground state interactions of the two biphenyls (Fig. 2).16
surface area of up to 570 m2/g.
Interestingly, the fluorescence maximum shows a noticeable 103 nm
The macrocycle MC was obtained in a single-step Yamamoto bathochromic shift for MC if compared to the isolated biphenyl
coupling as described in Scheme 1 (also Experimental Section, chromophore, likely as a result of the formation of π-stacked
ESI†). Slow addition of the dibromo compound 1,3-bis(4- aggregates. The fluorescence quantum efficiency of MC in
bromophenyl)-propan-2-one into the solution containing the Ni(0) dichloromethane was estimated to be 25% with respect to biphenyl
reagent under high dilution conditions leads to the formation of the as standard (18% in cyclohexane17).
dimer along with linear, acyclic byproducts (Fig. S1, ESI†).
Although formation of the macrocycle is less favoured, a yield of
30% could be achieved in this instance. In a literature report, the
UV_MC
UV_Biphenyl
Fl._MC
250 nm 260 nm 312 nm
415 nm
same macrocycle was isolated in only <1% yield in a multistep
sequence.15
Fl._Biphenyl
Top view
Side view
200
250
300
350
400
450
500
550
Wavelength (nm)
Fig. 2 Normalized UV-vis and fluorescence spectra of the macro-
cycle MC and biphenyl (as a comparison) recorded in dichloro-
methane (λext.: 245 nm for MC and 235 nm for biphenyl).
Axial view
Cyclotrimerization of either indan-1-one18 or indan-1,3-dione7, 18a,
under formation of truxene cores can be accomplished by either
19
Fig. 1 Single crystal X-ray structure of the macrocycle MC protic (such as sulfuric acid, methanesulfonic acid (MSA), p-
including the geometry of the single molecules and packing in the toluenesulfonic acid, polyphosphoric acid etc.) or Lewis acids (such
unit cell.
as titanium tetrachloride (TiCl4), boron tribromide, molten zinc
chloride etc.). Using such a protocol, the formation of microporous
The presence of linear by-products indicates that the reaction takes polymer networks (MPNs) was achieved from bifunctional s-
place in a stepwise manner where a linear dimer is initially formed, indacene derivatives7 or bifunctional acetyl compounds8 with high
which can adopt a variety of different conformations. Cyclisation is specific BET surface areas. Considering these literature results, a
favoured for the folded conformation FD for which the two bromo cyclotrimerization reaction was also tested for our new macrocycle
end groups are prearranged for macrocyclization. Theoretical MC with protic acids (MSA) or Lewis acids (TiCl4), respectively
calculations were performed to predict the total energies of probable (Experimental Section, ESI†). Notably, dark colored rather insoluble
conformations of the linear dimer. Among the calculated geometries, products could be obtained in both cases.
two conformations ((i) and (ii), Fig. S2, ESI†) with a folded
Scheme 2 depicts the (idealized) structure of the resulting cross-
structure possess lower energy if compared to a linear, non-folded linked polymer network. Within the network, the macrocyclic
arrangement. Somewhat different to FD, for the minimum energy building blocks of the MPN can adopt an anti- (Site-II) or syn- (Site-
conformation (i), one 4-bromobenzyl moiety is parallel to the axis of I) structure regarding the -CH2- links. With respect to the newly
the biphenyl unit while the other 4-bromobenzyl group is arranged formed hexa-substituted benzene cores, a symmetric arrangement of
perpendicularly to the biphenyl axis perhaps to avoid steric repulsion the substituents is assumed, thus minimizing steric expulsion. The
and to reduce the dipole moment. Generally, however, linear FT-IR spectrum of the macrocycle MC exhibits a strong C=O
conformations of the open-chain dimer show higher energies (Table stretching band at 1690 cm-1. However, in the polymer network the
S1, ESI†) thus indicating that folded conformations are preferred. intensity of the band strongly decreases and is shifted to 1708 cm-1
Calculations of transition state geometry resulted in a conformation (representing keto end-groups) along with a new band generated at
that is similar to FD. Moreover, the optimized geometry of the 1600 cm-1 due to a C=C stretching transition of the hexa-substituted
2 | J. Name., 2012, 00, 1-3
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benzene cores (Fig. S4, ESI†).20 13C{1H} CPMAS NMR analysis of particle voids.8 A BET surface area of 568 m2 g-1 was calculated for
the polymer network obtained under metal-free condition (using
MSA), while SBET value of 245 m2 g-1 was achieved by condensation
with TiCl4 accompanied by total pore volumes of 0.85 cm3 g-1 and
0.23 cm3 g-1, respectively. Gas adsorption studies were performed
with H2, CO2 and CH4 (Table 1 and Fig. S7, ESI†) and in each case
the amount of gas adsorbed is higher for the MPN generated under
metal-free conditions. A lower BET surface area as well as lower gas
adsorption values for the condensation product with TiCl4 could be
due to the presence of catalyst traces that block a certain part of the
micropores. Thus, TGA under air showed a residue of 26.6% for the
TiCl4-condensation product at 950 °C compared to only 1.9% for the
MSA-condensation product (Fig. S8, ESI†).
the MPNs confirmed the presence of aromatic units (100160 ppm)
and –CH2– linkers (2560 ppm). In addition a small fraction of keto
terminal groups (170210 ppm) is also present (Fig. S5, ESI†). The
MPNs obtained with either MSA or TiCl4 were thermally stable up
to 200 oC (TGA, Fig. S6, ESI†). Although, MC shows intrinsic
fluorescence at 415 nm (Fig. 2), the resulting π-conjugated polymer
networks did not exhibit any fluorescence.
In conclusion, the dimeric, biphenyl-based macrocycle MC was
generated with high yield of up to 30% in a simple one-step, Ni(0)-
mediated Yamamoto coupling. The structure of the macrocycle was
confirmed by single crystal analysis. Theoretical calculations point
to a folded conformation of the acyclic dimer, thus supporting the
formation of the macrocycle. Acid-catalysed cyclotrimerization was
successfully applied for the condensation of MC into a microporous
polymer network (MPN). The microporous network display BET
surface areas of up to 570 m2/g for the product synthesized under
metal-free acid conditions (with MSA).
SKS gratefully acknowledges the Alexander von Humboldt
Scheme 2. Synthesis of microporous polymer network through acid
catalyzed cyclotrimerization of macrocycle MC and idealized
structure of the resulting crosslinked polymer network.
Foundation for
a post-doctoral research fellowship. We
acknowledge the Synchrotron Light Source ANKA (KIT,
Karlsruhe) for provision of instruments at their beamlines and
thank Dr. Gernot Buth for his support at the SCD beamline
600
MPN@MSA
MPN@TiCl4
500
Notes and references
Macromolecular Chemistry Group and Institute for Polymer
a
400
300
200
100
0
Technology, Wuppertal University, Gauss-Strasse 20, 42119 Wuppertal,
Germany. E-mail: sksiisc@gmail.com, scherf@uni-wuppertal.de
b
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1,
45470 Mülheim an der Ruhr, Germany.
c
Center for Condensed Matter Theory, Department of Physics, Indian
Institute of Science, Bangalore 560 012, India.
0.0
0.2
0.4
0.6
0.8
1.0
d
Westfälische Wilhelms-Universität, Institut für Physikalische Chemie,
p/p0
Corrensstr. 28/30 48149 Münster, Germany.
Fig. 3 BET nitrogen sorption isotherms for the microporous polymer
networks (filled symbols represent adsorption and empty symbols
represent desorption branches).
†
Electronic Supplementary Information (ESI) available: Experimental
Section, Supporting Figures and Tables and also the single crystal X-ray
structure analysis of MC. See DOI: 10.1039/c000000x/
CCDC 1050402 contains the supplementary crystallographic data for
MC
.
These data can be obtained free of charge via
Table 1. BET surface areas and corresponding gas adsorption data
for the MPNs generated with MSA and TiCl4.
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336-033; or E-Mail: deposit@ccdc.cam.ac.uk).
Total
pore
volume
(cm3/g)
Surface
area
(m2/g)
H2 uptake
cm3/g
CO2 uptake
cm3/g
CH4 uptake
cm3/g
(wt%)
(wt%)
(wt%)
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