Concise synthesis of 3D π-extended polyphenylene cylinders

Article abstract of DOI:10.1002/anie.201309104

The synthesis of structurally well-defined, monodisperse carbon nanotube (CNT) sidewall segments poses a challenge in materials science. The synthesis of polyphenylene cylinders that comprise typical benzene connectivity to resemble precursors of [9,9] an

Full text of DOI:10.1002/anie.201309104

Angewandte
Chemie
DOI: 10.1002/anie.201309104
Carbon Nanostructures
Concise Synthesis of 3D p-Extended Polyphenylene Cylinders**
Florian E. Golling, Martin Quernheim, Manfred Wagner, Tomohiko Nishiuchi,* and
Klaus Mꢀllen*
Abstract: The synthesis of structurally well-defined, mono-
disperse carbon nanotube (CNT) sidewall segments poses
a challenge in materials science. The synthesis of polypheny-
lene cylinders that comprise typical benzene connectivity to
resemble precursors of [9,9] and [15,15] CNTs is now
reported, and the products were characterized by X-ray
crystallography. To investigate the oxidative cyclodehydroge-
nation of ring-strained molecules as a final step towards
a bottom-up synthesis of CNT sidewall segments, phenylene-
extended cyclic p-hexaphenylbenzene trimers ([3]CHPB) were
prepared, and NMR studies revealed a strain-induced 1,2-
phenyl shift. It was further shown that an increase in ring size
leads to selectively dehydrogenated macrocycles. Larger
homologues are envisioned to give smooth condensation
reactions toward graphenic sidewalls and should be used in
the future as seeds for CNT formation.
which lead to bent arenes, as they induce non-planarity.[10]
A different concept to obtain curvature, and thus 3D
materials, is based on cyclic molecules, such as cyclo-para-
phenylenes (CPPs).[11] These macrocycles are envisioned as
precursors for a 3D p extension towards length- and diame-
ter-defined CNTs.[12] Thus far, template-mediated growth of
CNTs from opened C60 and CPP precursors has been achieved
on quartz and sapphire surfaces, yielding tubes with narrow
diameter distributions.[13] Still, the synthetic bottom-up 3D
design that yields monodisperse, soluble, and short tubular
CNT sidewall segments remains challenging.[14]
To achieve a p extension of CPPs, a 3D-arranged cyclic p-
hexaphenylbenzene trimer ([3]CHPB) was introduced by our
group as a synthetic approach towards length-defined arm-
chair CNTs. As oxidative cyclodehydrogenation is known to
be a powerful reaction for the synthesis of linear, planar, and
nonplanar structures (3D), its applicability to highly strained
macrocycles was investigated.[15] Nevertheless, the nine-mem-
bered [3]CHPB did not undergo clean and selective cyclo-
dehydrogenation to give the corresponding cyclic p-hexa-
peri-benzocoronene ([3]CHBC). For a bottom-up synthesis
towards CNTs, two modes of extending the [3]CHPB are
necessary: the extension of the circumference and the
introduction of additional phenyl rings to form cylindrical
CNT precursors (Scheme 1).
T
he extension of hexa-peri-benzocoronene (HBC) into the
third dimension (3D) to form a cylindrical structure, is a key
step towards the synthesis of size-defined carbon nanotube
(CNT) segments. As one of the fundamental polycyclic
aromatic hydrocarbons (PAHs), HBC[1] has garnered increas-
ing interest since the advent of graphene.[2] Starting from
polyphenylene precursors, the HBC motif has been widely
used for the synthesis of one- (1D) and two-dimensional (2D)
structures, such as nanoribbons[3] and disc-shaped nanogra-
phenes (NGs).[4] These graphenic structures are of great
interest because of their electronic properties, which sensi-
tively depend on the size and shape (armchair or zigzag) of
the molecules. Oxidative cyclodehydrogenation is generally
used to transform twisted polyphenylenes into fused and
planar target structures.[5] This approach allows the synthesis
of compounds with different sizes and edge structures,[6] and
also affords five-,[7] seven-,[8] and eight-membered rings,[9]
Herein, we describe the synthesis of the cylinders 2 and 4,
which are based on 9- and 15-membered p-phenylene rings, as
precursors for [9,9] and [15,15] CNTs. To investigate the
[*] F. E. Golling, M. Quernheim, Dr. M. Wagner, Dr. T. Nishiuchi,[+]
Prof. Dr. K. Mꢀllen
Max Planck Institute for Polymer Research
Ackermannweg 10, 55128 Mainz (Germany)
E-mail: muellen@mpip-mainz.mpg.de
F. E. Golling
Graduate School Materials Science in Mainz
Staudinger Weg 9, 55128 Mainz (Germany)
[+] Current address: Department of Chemistry
Graduate School of Science, Osaka University
1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
[**] This work was supported by the EU (FP 7 256617 MOLESOL). We
thank Dr. Schollmeyer, University of Mainz, for X-ray crystal
structure analysis. F.E.G. thanks the Graduate School MAINZ for
a scholarship.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201309104.
Scheme 1. Concept of the size extension of 1: cylinder 2 and extended
[3]CHPB 3.
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Figure 1. X-ray crystal structure of 4. ORTEP drawing (left) and wire-
frame model (right). Ellipsoids set at 50% probability. Hydrogen
atoms and solvent molecules were omitted for clarity (see the
Supporting Information). The CPP rings are depicted in red.
To extend cylinder 4 from a 9- to the 15-membered ring 2,
six additional terphenyl units were introduced (Scheme 2).
Therefore, 7 was terphenylated through a Suzuki coupling to
give the kinked precursor 10 in two steps (see the Supporting
Information). Analogous to the synthesis of 4, oxidative
coupling and subsequent reductive aromatization afforded
the trimeric macrocycle 2 in similar yields.
Single crystals of 4 were grown from a CH2Cl2/acetonitrile
solution. X-ray analysis[17] revealed an ellipsoid structure with
a length of 13.0 ꢀ and a width of 11.8 ꢀ (Figure 1). The
dihedral angles vary between 428 and an astonishing 848. To
the best of our knowledge, these values are unprecedented, as
the maximum dihedral angles for [9]CPP[11g] and [3]CHPB
trimer 1 are 448 and 678, respectively. These large dihedral
angles induce, either directly or in neighboring positions,
strong twists of single phenyl units with a maximum internal
dihedral angle (Cipso-Cortho-Cortho-Cipso) of 8.28 (see the Sup-
porting Information). A quinoidal character, as reported for
[9]CPP, was not observed for compound 4, owing to the
previously described large dihedral angles between adjacent
phenyl rings. The outlined physical properties support the
presence of a highly strained macrocycle.
Scheme 2. Reagents and conditions: a) [Ni(cod)2], 1,5-cyclooctadiene,
2,2’-bipyridine, DMF, toluene, THF, 808C, 16 h or tBuLi, CuCN,
Et2O·duroquinone, ꢀ788C, 30 min!RT, 2 h; b) sodium naphthalide,
THF, ꢀ788C, 1 h. cod=1,5-cyclooctadiene, DMF=N,N-dimethylform-
amide, THF=tetrahydrofuran.
oxidative cyclodehydrogenation of strained cycles in detail,
the two less complex and extended [3]CHPB macrocycles 3a
and 3b were synthesized, which consist of 15- and 21-
membered CPPs.
For the synthesis of the p-extended [3]CHPBs 3a and 3b,
the key intermediates 6a and 6b were subjected to the
Yamamoto conditions (Scheme 2). The reactions primarily
afforded the cyclic trimer 8a and 8b, owing to the kinking
angle of the precursor.[15] Linear tetramers and pentamers
were also observed as side products. For 4, however,
Yamamoto coupling of 7 did not give the desired macro-
cycle 9, but rather resulted in the dehalogenation of the
kinked starting material 7, which was caused by the steric
demand of the ortho-phenyl substituents. The synthetic
challenge was overcome with an oxidative coupling via
a Lipshutz cuprate intermediate that gave macrocycle 9,
which contains a 15-membered phenylene ring.[16] As men-
tioned before, the kinking angle of substrate 7 leads to the
preferred formation of a cyclic trimer. A subsequent reduc-
tive aromatization with sodium naphthalide in THF furnished
the macrocycles 3a and 3b and the sterically demanding
cylinder 4, which resembles a phenylene-based [9,9] CNT
precursor segment.
Figure 2. UV/Vis (c) and fluorescence (b) spectra for 3a,b
(CH2Cl2), 2, and 4 (hexanes).
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The strain of the cylinders can also be deduced from the
UV/Vis spectra (Figure 2). The absorption maxima of 2 and 4
are hypsochromically shifted to 260 nm, whereas the absorp-
tion maxima of [3]CHPB macrocycles and CPPs are found at
320 nm and 340 nm, respectively.[11a] This can be explained by
the distortion between phenyl rings in the CPP base, which
leads to a reduction in p conjugation.[18] The emission maxima
of 2, 3a, and 3b appeared at 410–420 nm, the emission
maximum of 4 was bathochromically shifted to 435 nm. In the
excited state, however, the large ring strain and the distortion
of these CPP scaffolds are released by partial planarization of
neighboring phenyl rings, which results in large Stokes
shifts.[19] This effect was especially pronounced for the small
cylinder 4.
Cyclodehydrogenation of cylinders 2 and 4 under oxida-
tive conditions resulted in mixtures of dehydrogenated
products, which indicates partial formation of cyclic graphe-
noid structures. To investigate the oxidative dehydrogenation
for molecules with different degrees of ring strain, we
designed structures 3a and 3b. Circumferences that are
larger than that of compound 1 were obtained by introducing
six and twelve additional phenylene rings, respectively, to
obtain HPB units that are embedded into a CPP with reduced
ring strain.
The less distorted and less strained macrocycles 3a and 3b
were subjected to cyclodehydrogenation with different oxi-
dants, such as CF3SO3H with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ), Sc(OTf)3/DDQ (Tf = trifluorometh-
anesulfonyl), phenyliodonium bis(trifluoroacetate) (PIFA)
with BF3·Et2O, or FeCl3.[20] The addition of FeCl3 at room
temperature gave the best results and led to highly dehydro-
genated compounds without any chlorinated side products.
Rather than the expected [3]CHBCs 5a and 5b, we obtained
compounds with an extra loss of two (5b’), four, and six (5a’;
see the Supporting Information) hydrogen atoms (Scheme
3a,b). For a better understanding of these findings, the model
compound 11 was synthesized, which could be selectively
converted into the expected target compound 12 by oxidative
cyclodehydrogenation (Scheme 3c). In previous studies, a 1,2-
phenyl shift was observed for the cyclodehydrogenation of
PAHs toward NGs, which resulted in a higher degree of
dehydrogenation.[21]
Scheme 3. a) Cyclodehydrogenation reaction of 3b; b) 1,2-phenyl shift;
c) cyclodehydrogenation of model compound 11.
These findings show that an increase in ring size can lead to
selectively dehydrogenated macrocycles.
In summary, we have presented the bottom-up synthesis
of the two polyphenylene cylinders 2 and 4. As the sidewalls
are comprised of accordingly joined benzene rings, they
represent precursors of [9,9] and [15,15] CNTs. For macro-
cycle 4, a single-crystal structure could be obtained, which
revealed a strongly bent cycle. To investigate the oxidative
cyclodehydrogenation in the presence of ring strain, the less
complex 3D-arranged [3]CHPBs 3a and 3b were designed.
Detailed NMR studies revealed that a 1,2-phenyl shift had
occurred during the reaction to give 5’. These results show
that strained macrocycles can undergo oxidative cyclodehy-
drogenation to potentially access defined CNT segments.
Future challenges include the synthesis of larger homologues
with smooth condensation reactions towards graphenic walls
and the use of the products as seeds for carbon-nanotube
formation.
In the following discussion we focus on 5b’, as several
structural isomers were found in the product mixture of 5a’.
The ion peak at m/z 3143.4757 that was obtained by matrix-
assisted laser desorption/ionization time-of-flight (MALDI-
TOF) mass spectrometry revealed an additional loss of two
hydrogen atoms for 5b’, compared to the expected compound
5b, which suggests that a 1,2-phenyl shift has occurred
(Scheme 3). Detailed NMR studies confirmed the 1,2-
phenyl shift for 5b’. The appearance of two AB systems at
1
9.79 ppm and 9.62 ppm in the H NMR spectrum, supported
Received: October 18, 2013
Published online: January 22, 2014
by further 2D NMR studies, is consistent with the structure of
5b’ (see the Supporting Information).
These results suggest that ring strain was relieved upon
cyclodehydrogenation by a 1,2-phenyl shift to give the
rearranged macrocycle 5b’. Furthermore, we could demon-
strate that the increase of the CPP circumference from a 15-
to a 21-membered ring afforded 5b’ as a single compound.
Keywords: carbon nanotubes · cyclodehydrogenation ·
cyclo-para-phenylene · macrocycles · polycycles
.
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Org. Chem. 2012, 77, 5857 – 5860; i) J. Xia, R. Jasti, Angew.
Chem. 2012, 124, 2524 – 2526; Angew. Chem. Int. Ed. 2012, 51,
2474 – 2476; j) A. Yagi, Y. Segawa, K. Itami, J. Am. Chem. Soc.
2012, 134, 2962 – 2965; k) S. Hitosugi, T. Yamasaki, H. Isobe, J.
Am. Chem. Soc. 2012, 134, 12442 – 12445; l) S. Hitosugi, W.
Nakanishi, H. Isobe, Chem. Asian J. 2012, 7, 1550 – 1552; m) T.
Matsuno, S. Kamata, S. Hitosugi, H. Isobe, Chem. Sci. 2013, 4,
3179 – 3183; n) H. Isobe, S. Hitosugi, T. Yamasaki, R. Iizuka,
Chem. Sci. 2013, 4, 1293 – 1297.
[1] a) M. D. Watson, A. Fechtenkçtter, K. Mꢁllen, Chem. Rev. 2001,
101, 1267 – 1300; b) J. P. Hill, W. Jin, A. Kosaka, T. Fukushima,
H. Ichihara, T. Shimomura, K. Ito, T. Hashizume, N. Ishii, T.
Aida, Science 2004, 304, 1481 – 1483; c) W. Pisula, X. Feng, K.
Mꢁllen, Chem. Mater. 2010, 22, 554 – 567.
[2] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang,
S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science 2004, 306,
666 – 669.
[3] a) V. S. Iyer, K. Yoshimura, V. Enkelmann, R. Epsch, J. P. Rabe,
K. Mꢁllen, Angew. Chem. 1998, 110, 2843 – 2846; Angew. Chem.
Int. Ed. 1998, 37, 2696 – 2699; b) L. Dçssel, L. Gherghel, X. L.
Feng, K. Mꢁllen, Angew. Chem. 2011, 123, 2588 – 2591; Angew.
Chem. Int. Ed. 2011, 50, 2540 – 2543; c) Y. Fogel, L. Zhi, A.
Rouhanipour, D. Andrienko, H. J. Rꢂder, K. Mꢁllen, Macro-
molecules 2009, 42, 6878 – 6884; d) M. G. Schwab, A. Narita, Y.
Hernandez, T. Balandina, K. S. Mali, S. De Feyter, X. Feng, K.
Mꢁllen, J. Am. Chem. Soc. 2012, 134, 18169 – 18172.
[4] a) V. S. Iyer, M. Wehmeier, J. D. Brand, M. A. Keegstra, K.
Mꢁllen, Angew. Chem. 1997, 109, 1676 – 1679; Angew. Chem. Int.
Ed. Engl. 1997, 36, 1604 – 1607; b) S. M. Draper, D. J. Gregg, R.
Madathil, J. Am. Chem. Soc. 2002, 124, 3486 – 3487; c) D.
Wasserfallen, M. Kastler, W. Pisula, W. A. Hofer, Y. Fogel, Z.
Wang, K. Mꢁllen, J. Am. Chem. Soc. 2006, 128, 1334 – 1339; d) X.
Feng, V. Marcon, W. Pisula, M. R. Hansen, J. Kirkpatrick, F.
Grozema, D. Andrienko, K. Kremer, K. Mꢁllen, Nat. Mater.
2009, 8, 421 – 426.
[12] a) Fragments of Fullerenes and Carbon Nanotubes (Eds.: M. A.
Petrukhina, L. T. Scott), Wiley, Hoboken, 2011; b) R. L. Via-
vattene, F. D. Greene, L. D. Cheung, R. Majeste, L. M. Trefonas,
J. Am. Chem. Soc. 1974, 96, 4342 – 4343; c) F. H. Kohnke,
A. M. Z. Slawin, J. F. Stoddart, D. J. Williams, Angew. Chem.
1987, 99, 941 – 943; Angew. Chem. Int. Ed. Engl. 1987, 26, 892 –
894; d) A. Godt, V. Enkelmann, A.-D. Schlꢁter, Angew. Chem.
1989, 101, 1704 – 1706; Angew. Chem. Int. Ed. Engl. 1989, 28,
1680 – 1682; e) S. Kammermeier, P. G. Jones, R. Herges, Angew.
Chem. 1996, 108, 2834 – 2836; Angew. Chem. Int. Ed. Engl. 1996,
35, 2669 – 2671; f) R. Jasti, C. R. Bertozzi, Chem. Phys. Lett.
2010, 494, 1 – 7; g) H.-B. Li, A. J. Page, S. Irle, K. Morokuma, J.
Am. Chem. Soc. 2012, 134, 15887 – 15896.
[13] a) X. Yu, J. Zhang, W. Choi, J.-Y. Choi, J. M. Kim, L. Gan, Z. Liu,
Nano Lett. 2010, 10, 3343 – 3349; b) H. Omachi, T. Nakayama, E.
Takahashi, Y. Segawa, K. Itami, Nat. Chem. 2013, 5, 572 – 576.
[14] a) L. T. Scott, E. A. Jackson, Q. Zhang, B. D. Steinberg, M.
Bancu, B. Li, J. Am. Chem. Soc. 2012, 134, 107 – 110; b) E. H.
Fort, P. M. Donovan, L. T. Scott, J. Am. Chem. Soc. 2009, 131,
16006 – 16007.
[5] a) A. A. O. Sarhan, C. Bolm, Chem. Soc. Rev. 2009, 38, 2730 –
2744; b) M. Grzybowski, K. Skonieczny, H. Butenschçn, D. T.
Gryko, Angew. Chem. 2013, 125, 10084 – 10115; Angew. Chem.
Int. Ed. 2013, 52, 9900 – 9930.
[15] T. Nishiuchi, X. Feng, V. Enkelmann, M. Wagner, K. Mꢁllen,
Chem. Eur. J. 2012, 18, 16621 – 16625.
[6] M. Kastler, J. Schmidt, W. Pisula, D. Sebastiani, K. Mꢁllen, J.
Am. Chem. Soc. 2006, 128, 9526 – 9534.
[16] Y. Miyake, M. Wu, M. J. Rahman, M. Iyoda, Chem. Commun.
2005, 411 – 413.
[7] Y. Avlasevich, C. Kohl, K. Mꢁllen, J. Mater. Chem. 2006, 16,
1053 – 1057.
[8] K. Kawasumi, Q. Zhang, Y. Segawa, L. T. Scott, K. Itami, Nat.
Chem. 2013, 5, 739 – 744.
[17] CCDC 966737 (4) and 966738 (9) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[9] Y. Sakamoto, T. Suzuki, J. Am. Chem. Soc. 2013, 135, 14074 –
14077.
[18] a) D. Sundholm, S. Taubert, F. Pichierri, Phys. Chem. Chem.
Phys. 2010, 12, 2751 – 2757; b) T. Nishihara, Y. Segawa, K. Itami,
Y. Kanemitsu, J. Phys. Chem. Lett. 2012, 3, 3125 – 3128.
[19] M. Fujitsuka, D. W. Cho, T. Iwamoto, S. Yamago, T. Majima,
Phys. Chem. Chem. Phys. 2012, 14, 14585 – 14588.
[20] a) R. Scholl, C. Seer, Justus Liebigs Ann. Chem. 1912, 394, 111 –
177; b) P. Rempala, J. Kroulꢃk, B. T. King, J. Org. Chem. 2006, 71,
5067 – 5081; c) L. Zhai, R. Shukla, R. Rathore, Org. Lett. 2009,
11, 3474 – 3477; d) D. J. Jones, B. Purushothaman, S. Ji, A. B.
Holmes, W. W. H. Wong, Chem. Commun. 2012, 48, 8066 – 8068;
e) A. Konishi, Y. Hirao, K. Matsumoto, H. Kurata, R. Kishi, Y.
Shigeta, M. Nakano, K. Tokunaga, K. Kamada, T. Kubo, J. Am.
Chem. Soc. 2013, 135, 1430 – 1437; f) A. Konishi, Y. Hirao, K.
Matsumoto, H. Kurata, T. Kubo, Chem. Lett. 2013, 42, 592 – 594.
[21] K. Yoshimura, L. Przybilla, S. Ito, J. D. Brand, M. Wehmeir, H. J.
Rꢂder, K. Mꢁllen, Macromol. Chem. Phys. 2001, 202, 215 – 222.
[10] a) Y.-T. Wu, J. S. Siegel, Chem. Rev. 2006, 106, 4843 – 4867;
b) V. M. Tsefrikas, L. T. Scott, Chem. Rev. 2006, 106, 4868 – 4884.
[11] a) R. Jasti, J. Bhattacharjee, J. B. Neaton, C. R. Bertozzi, J. Am.
Chem. Soc. 2008, 130, 17646 – 17647; b) H. Takaba, H. Omachi,
Y. Yamamoto, J. Bouffard, K. Itami, Angew. Chem. 2009, 121,
6228 – 6232; Angew. Chem. Int. Ed. 2009, 48, 6112 – 6116; c) H.
Omachi, S. Matsuura, Y. Segawa, K. Itami, Angew. Chem. 2010,
122, 10400 – 10403; Angew. Chem. Int. Ed. 2010, 49, 10202 –
10205; d) S. Yamago, Y. Watanabe, T. Iwamoto, Angew. Chem.
2010, 122, 769 – 771; Angew. Chem. Int. Ed. 2010, 49, 757 – 759;
e) S. Hitosugi, W. Nakanishi, T. Yamasaki, H. Isobe, Nat.
Commun. 2011, 2, 492; f) T. Iwamoto, Y. Watanabe, Y. Saka-
moto, T. Suzuki, S. Yamago, J. Am. Chem. Soc. 2011, 133, 8354 –
8361; g) Y. Segawa, P. Senel, S. Matsuura, H. Omachi, K. Itami,
Chem. Lett. 2011, 40, 423 – 425; h) T. J. Sisto, X. Tian, R. Jasti, J.
1528
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