A tubular macrocycle from covalently linked anthracenes and meta-phenylene spacers

Article abstract of DOI:10.1039/c2cc31383a

A novel tubular macrocycle containing four anthracene panels covalently linked by meta-phenylene spacers was synthesized. The tube is approximately 1 nm long with anthracene panels delimiting a columnar cavity with a diameter of ～1 nm and exhibits strong blue fluorescence.

Full text of DOI:10.1039/c2cc31383a

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Showcasing research from Dr Michito Yoshizawa’s
group, Chemical Resources Laboratory, Tokyo Institute
of Technology, Japan
A tubular macrocycle from covalently linked anthracenes and
meta-phenylene spacers
K. Hagiwara et al. report that a novel tubular macrocycle containing
four anthracene panels covalently linked by meta-phenylene
spacers is synthesized by sequential cross-coupling reactions.
The tube is approximately 1 nm long with anthracene panels
delimiting a columnar cavity with a diameter of ~1 nm and exhibits
strong blue fluorescence.
See Michito Yoshizawa et al.,
Chem. Commun., 2012, 48, 7678.
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COMMUNICATION
A tubular macrocycle from covalently linked anthracenes and
meta-phenylene spacersw
Keita Hagiwara, Yoshihisa Sei, Munetaka Akita and Michito Yoshizawa*
Received 24th February 2012, Accepted 29th March 2012
DOI: 10.1039/c2cc31383a
A novel tubular macrocycle containing four anthracene panels
covalently linked by meta-phenylene spacers was synthesized.
The tube is approximately 1 nm long with anthracene panels
delimiting a columnar cavity with a diameter of B1 nm and
exhibits strong blue fluorescence.
Inspired by the sophisticated shapes and advantageous properties
of single-walled carbon nanotubes (SWNTs),1 formed from
extended rolls of aromatic sheets, much attention has been
paid to the covalent synthesis of macrocyclic2–5 and tubular6,7
architectures composed of aromatic rings. As the size and
surface area of the aromatic rings imbedded within the macro-
Fig. 1 (a) Cartoon representation of a tetra-anthracene nanotube
cycle or ‘‘molecular nanotube’’ increase, the spatial and electronic
properties of a more tubular cavity are expected to approach
those of extended SWNTs. However, the majority of macro-
cycles are composed of small aromatic rings, e.g., benzene and
naphthalene rings (except for a few porphyrin-based macro-
cycles),8 and/or ethynylene units. Tubular macrocycles with
extended aromatic surfaces still present a significant synthetic
challenge due to ring strain and steric hindrance.9 Here we
report the preparation of molecular nanotube 1 with four
anthracene panels covalently linked by meta-phenylene spacers
(Fig. 1). X-ray crystallographic analysis reveals that the aromatic
tube is approximately 1 nm long with anthracene panels delimiting
a columnar cavity with a diameter of B 1 nm. Nanotube 1
shows strong blue fluorescence from the anthracene panels.
We employed anthracene as a large aromatic panel for the
synthesis of novel tubular macrocycles because anthracene
subunits are imbedded within the framework of SWNTs. To
construct a tubular structure with anthracene surfaces,10 we
first designed half-tube shaped 2 with two anthracene rings
connected by a phenylene spacer at the meta position and two
meta-functionalized phenyl groups (X = triflate (–OTf) and
pinacol boronate (–Bpin)) bound to the anthracene rings
(Fig. 2). The steric interactions between ortho-substituents
on the phenylene–anthryl and anthryl–phenyl bonds of 2 force
and (b) chemical structure of molecular nanotube 1 containing four
anthracene panels (R1 = R2 = –OCH2CH2OCH3).
adjacent aromatic rings to adopt orthogonal conformations
(Fig. 2). As a result, half-tube 2 presents a rigid curved
structure and the dimerization of two half-tubes can generate
rigid tubular macrocycle 1 with extended anthrylene p-surfaces.11
To synthesize tubular macrocycle 1, we prepared methoxy-
methoxy (MOM)-protected half-tube 2MOM for the facile
transformation into appropriately functionalized half-tubes
2OTf and 2Bpin, ready for dimerization via cross-coupling
reactions (Scheme 1). The Negishi coupling of 1,3-dibromo-
4,6-dimethoxybenzene and 9-anthrylzinc chloride in the
presence of PdCl2(PhCN)2/P(t-Bu)3 catalyst provided a bent
anthracene dimer precursor which gave 3 after selective
Chemical Resources Laboratory, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
E-mail: yoshizawa.m.ac@m.titech.ac.jp; Fax: +81-45-924-5230;
Tel: +81-45-924-5284
w Electronic supplementary information (ESI) available: Experimental
procedures, and physical and crystal data. CCDC 866637. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2cc31383a
Fig. 2 Chemical structure of half-tube 2 (R1 = R2 = –OCH2CH2OCH3,
X = methoxymethoxy (–MOM), triflate (–OTf), and pinacol boronate
(–Bpin)) and the optimized structure by DFT calculation (B3LYP/6-31G*
level; R1 = –OCH2CH2OCH3, R2 = X = –H).
c
7678 Chem. Commun., 2012, 48, 7678–7680
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Fig. 3 1H NMR spectra (400 MHz, CDCl3, rt) of (a) nanotube 1 and
Scheme 1 Preparation of tubular macrocycle 1. Reagents and conditions:
(a) 3-(2-methoxyethoxy)-5-(methoxymethoxy)phenylboronic acid pinacol
ester, PdCl2(PhCN)2, P(t-Bu)3, K3PO4, DMF, 80 1C; (b) 1. HCl, THF,
MeOH, rt; 2. Triflic anhydride, pyridine, 0 1C to rt; (c) bis(pinacolato)-
diboron, PdCl2(PPh3)2, NaOAc, DMF, 80 1C; (d) Pd(PPh3)4, K3PO4,
DMF, 80 1C.
(b) triflate-capped half-tube 2OTf.
The 13C NMR spectrum of 1 showed only twenty-four signals
due to the higher symmetry. The identity of 1 was further
confirmed by MALDI-TOF MS and HR MS (ESI) with promi-
nent peaks at m/z = 1753.45 [M]+ and 1886.6444 [M + Cs]+,
respectively. The rigid tubular structure shows moderate
solubility in organic solvents (e.g., CH2Cl2, acetone, and THF)
due to the pendant methoxyethoxy groups.
bromination of the anthracene rings and conversion of the
methoxy groups into 2-methoxyethoxy groups through sequential
demethylation and etherification protocols.10 The Suzuki–
Miyaura coupling of brominated anthracene dimer 3 with
MOM-protected (2-methoxyethoxy)phenylboronic acid pinacol
ester afforded half-tube 2MOM in 68% yield.12 Acid-promoted
deprotection of MOM groups of 2MOM led to a dihydroxy
derivative. The half-tube was converted stepwise into triflate-
capped half-tube 2OTf (96% yield) and Bpin-capped half-tube
2Bpin (38% yield) by the sequential treatments with triflic
The structure of molecular nanotube 1 was unambiguously
determined by single-crystal X-ray analysis. Pale-yellow single
crystals were obtained by the slow evaporation of a CHCl3
solution of 10 (an analogue of 1 where R1 = –OCH2CH2OCH3
and R2 = –OCH3)14 at room temperature for 5 d. X-ray
crystallographic analysis showed that the four anthracene
rings linked by the m-phenylene and m-biphenylene spacers
form the expected tubular structure in a slightly distorted D2h
symmetry with a length of B1 nm (Fig. 4).14,17 The dihedral
angles between the anthryl and phenyl rings of 10 are in the
range of 60.0–88.81. The four parallel anthracene surfaces define
the large cavity of nanotube 10 with inner distances of 1.1 nm
and 0.9 nm diagonal between the opposing m-biphenylene
Hi atoms and m-phenylene Hb atoms, respectively. Two well-
ordered CHCl3 molecules were located within the cavity
(Fig. 4c). In the crystal packing, the nanotubes are all lined
up in the same direction without infinite channels (Fig. S40,
ESIw).14
anhydride and bis(pinacolato)diboron.13 Half-tubes 2MOM
OTf, and 2Bpin were fully characterized by NMR spectroscopy
and mass spectrometry (MS).14
,
2
Tetra-anthracene nanotube 1 was synthesized by Suzuki–
Miyaura coupling of half-tubes 2OTf and 2Bpin (Scheme 1).14
Nanotube 1 was successfully isolated as a pale yellow solid
in 4% yield after purification by column chromatography
on silica gel followed by gel permeation chromatography
(GPC).15 The 1H NMR spectrum of 1 showed nine peaks
(Ha–h) in the aromatic region and six peaks (HA–F) in the
aliphatic region which were assigned to the anthrylene and
phenylene rings and the peripheral methoxyethoxy groups,
respectively (Fig. 3), as confirmed by COSY and NOESY
analyses. The spectrum of 1 is in striking contrast to that of
half-tubes 2OTf and 2Bpin; in the 1H NMR of 2OTf, two sets of
peaks derived from the phenyl ring (Hg–h and HD–F) were
observed in a 1 : 1 ratio (Fig. 3b). Both of the half-tubes exist
as a mixture of three atropisomers due to hindered rotation
around the anthryl–phenyl bonds.16 The upfield shift of
the inner m-phenylene signal of 1 (Hb; Dd = ꢀ0.25 ppm)
agrees with the formation of a discrete tubular structure.
The UV-vis spectrum of nanotube 1 in CH2Cl2 exhibited the
typical p–p* transition bands of the anthracene panels
(Fig. 5a). The emission spectrum of 1 displayed a broad band
in the range from 390 to 550 nm (lmax = 420 nm; Fig. 5b) and
the absolute quantum yield (FF) was found to be 70% (Fig. 5c).
The emission properties of 1 are similar to those of half-tubes
2OTf (lmax = 422 nm, FF = 72%) and 2Bpin (lmax = 419 nm,
FF = 70%) and reveal that the close proximity does not lessen
the emissivity of the anthracene moieties, presumably due to
the geometry of the enforced orthogonal conformations.
c
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Next Generation World-Leading Researchers’’ and the Tokyo
Institute of Technology via ‘‘Challenging Research Award’’,
and also MEXT (Japan) via Grants-in-Aid for Scientific
Research on Innovative Areas ‘‘Coordination Programming’’.
Notes and references
1 (a) S. Iijima, Nature, 1991, 354, 56–58; (b) S. Iijima and
T. Ichihashi, Nature, 1993, 363, 603–605; (c) D. S. Bethune,
C. H. Klang, M. S. de Vries, G. Gorman, R. Savoy, J. Vazquez
and R. Beyers, Nature, 1993, 363, 605–607; (d) Carbon Nanotubes:
Synthesis Properties and Applications, ed. M. Dresselhaus,
G. Dresselhaus and P. Avouris, Springer, Berlin, 2001.
2 (a) C. Grave and A. D. Schluter, Eur. J. Org. Chem., 2002,
¨
3075–3098; (b) Y. Yamaguchi and Z. Yoshida, Chem.–Eur. J.,
2003, 9, 5430–5440; (c) S. Hoger, Chem.–Eur. J., 2004, 10,
¨
1320–1329; (d) W. Zhang and J. S. Moore, Angew. Chem.,
Int. Ed., 2006, 45, 4416–4439; (e) M. Iyoda, J. Yamakawa and
M. J. Rahmanh, Angew. Chem., Int. Ed., 2011, 50, 10522–10553.
3 (a) T. Kawase, H. R. Darabi and M. Oda, Angew. Chem., Int. Ed.
Engl., 1996, 35, 2664–2666; (b) T. Kawase and M. Oda, Pure Appl.
Chem., 2006, 78, 831–839.
4 Arylene macrocycles: (a) G. R. Newkome and H.-W. Lee, J. Am.
Chem. Soc., 1983, 105, 5956–5957; (b) D. J. Cram, T. Kaneda,
R. C. Helgeson, S. B. Brown, C. B. Knobler, E. F. Maverick and
K. N. Trueblood, J. Am. Chem. Soc., 1985, 107, 3645–3657;
(c) V. Hensel and A. D. Schluter, Chem.–Eur. J., 1999, 5,
¨
2000, 3483–3487; (e) J. Kromer, I. Rios-Carreras, G. Fuhrmann,
¨
421–429; (d) U. Lehmann and A. D. Schluter, Eur. J. Org. Chem.,
¨
C. Musch, M. Wunderlin, T. Debaerdemaeker, E. Mena-Osteritz
Fig. 4 X-ray crystal structure of 10. (a) Top and (b) side views of the
space-filling model. (c) Two CHCl3 molecules (space-filling model)
occupying the cavity of 10 (stick model).
and P. Bauerle, Angew. Chem., Int. Ed., 2000, 39, 3481–3486;
¨
(f) Y. Miyake, M. Wu, M. J. Rahmanh and M. Iyoda, Chem.
Commun., 2005, 411–413; (g) Y. Miyake, M. Wu, M. J. Rahmanh,
Y. Kuwatani and M. Iyoda, J. Org. Chem., 2006, 71, 6110–6117.
5 (a) R. Jasti, J. Bhattacharjee, J. B. Neaton and C. R. Bertozzi,
J. Am. Chem. Soc., 2008, 130, 17646–17647; (b) H. Takaba,
H. Omachi, Y. Yamamoto, J. Bouffard and K. Itami, Angew.
Chem., Int. Ed., 2009, 48, 6112–6116; (c) S. Yamago, Y. Watanabe
and T. Iwamoto, Angew. Chem., Int. Ed., 2010, 49, 757–759;
(d) A. Yagi, Y. Segawa and K. Itami, J. Am. Chem. Soc., 2012,
134, 2962–2965.
6 (a) B. Esser, F. Rominger and R. Gleiter, J. Am. Chem. Soc., 2008,
130, 6716–6717; (b) B. Esser, A. Bandyopadhyay, F. Rominger and
R. Gleiter, Chem.–Eur. J., 2009, 15, 3368–3379.
7 (a) E. Nakamura, K. Tahara, Y. Matsuo and M. Sawamura,
J. Am. Chem. Soc., 2003, 125, 2834–2835; (b) Y. Matsuo,
K. Tahara, M. Sawamura and E. Nakamura, J. Am. Chem. Soc.,
2004, 126, 8725–8734.
8 J. Song, N. Aratani, H. Shinokubo and A. Osuka, J. Am. Chem.
Soc., 2010, 132, 16356–16357.
Fig. 5 (a) UV-vis (CH2Cl2, 5 mM, rt) and (b) fluorescence (degassed
CH2Cl2, lex = 378 nm, rt) spectra of 1 (red line) and 2OTf (blue line).
(c) Blue emission from 1 and 2OTf in CH2Cl2 under UV irradiation
(lex = 365 nm) at rt.
9 S. Hitosugi, W. Nakanishi, T. Yamasaki and H. Isobe, Nat.
Commun., 2011, 2, 492.
In conclusion, we successfully prepared tubular macrocycle 1
with covalently linked anthracene panels and m-phenylene spacers
by dimerization of semi-rigid half-tube precursors using palladium
catalyzed cross-coupling protocols. The novel nanotube is fully
aromatic and rigid with a large cavity (0.8 nm ꢁ 1.0 nm ꢁ B1 nm)
defined by extended aromatic surfaces, which is in sharp
contrast to the previous macrocycles.2–5,11 The tube exhibited
strong blue fluorescence in a high quantum yield. Tubular
nanostructures that delimit a one-dimensional space have
potential applications for the selective inclusion, isolation, or
transportation of ions and molecules. The robust tubular
macrocycle described here presents a well-defined cavity with
an exterior surface, which can be rapidly modified to introduce
new functionality. We are currently exploring host–guest
interactions within nanotube 1 with the particular aim of
developing unique fluorescent sensors and materials.
10 (a) N. Kishi, Z. Li, K. Yoza, M. Akita and M. Yoshizawa, J. Am.
Chem. Soc., 2011, 133, 11438–11441; (b) Z. Li, N. Kishi,
K. Hasegawa, M. Akita and M. Yoshizawa, Chem. Commun.,
2011, 47, 8605–8607.
11 An ethynylene macrocycle with three anthracene rings: K. Miki,
M. Fujita, Y. Inoue, Y. Senda, T. Kowada and K. Ohe, J. Org.
Chem., 2010, 75, 3537–3540.
12 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457–2483.
13 Palladium-catalyzed borylation of aryl halides: T. Ishiyama,
M. Murata and N. Miyaura, J. Org. Chem., 1995, 60, 7508–7510.
14 See the ESIw.
15 Oligomeric species including six or more anthracene rings were
mainly formed.
16 Interconversion between the atropisomers is slow on the NMR
time scale even at 80 1C, as revealed by VT NMR analysis.
17 X-ray crystal data of 10ꢂ4CHCl3: C112H92Cl12O12, Mr = 2055.26,
%
Triclinic, P1, a = 9.2507(13) A, b = 15.609(2) A, c = 17.265(2) A,
a = 95.404(2)1, b = 102.159(2)1, g = 90.147(2)1, V = 2425.7(6) A3,
Z = 1, rcalcd = 1.407 g cmꢀ3, F(000) = 1064, T = 90(2) K,
reflections collected/unique 11 489/8368 (Rint = 0.0152), R1 = 0.0881
(I > 2s(I)), wR2 = 0.2598, GOF 1.057. CCDC 866637 contains the
supplementary crystallographic data.
This work was financially supported by the Japan Society
for the Promotion of Science (JSPS) via ‘‘Funding Program for
c
7680 Chem. Commun., 2012, 48, 7678–7680
This journal is The Royal Society of Chemistry 2012