Creation of nanoscale oxaarenecyclynes and their C60 complexes

Article abstract of DOI:10.1016/S0040-4039(02)00539-7

Novel nanoscale oxaarenecyclynes (3 and 4) consisting of diethynylbenzene and ether units were synthesized, which form supramolecular complexes with C₆₀.

Full text of DOI:10.1016/S0040-4039(02)00539-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 3277–3280
Creation of nanoscale oxaarenecyclynes and their C60 complexes
Yoshihiro Yamaguchi,a Shigeya Kobayashi,a Nobuhiro Amita,a Tateaki Wakamiya,a
Yoshio Matsubara,a Kunihisa Sugimotob and Zen-ichi Yoshidaa,*
aFaculty of Science and Engineering, Kinki University, 3-4-1 Kowakae, Higashi-Osaka, 577-8502, Japan
bX-Ray Research Laboratory, Rigaku Corporation, 3-9-12 Matsubara, Akishima, Tokyo, 196-8666, Japan
Received 15 February 2002; revised 11 March 2002; accepted 15 March 2002
Abstract—Novel nanoscale oxaarenecyclynes (3 and 4) consisting of diethynylbenzene and ether units were synthesized, which
form supramolecular complexes with C60. © 2002 Elsevier Science Ltd. All rights reserved.
Geometrically-controlled and shape-persistent macrocy-
cles have attracted much attention. Among them,
macrocycles having binding sites inside or outside the
cavity are known.1 However, those which contain bind-
ing sites as a macrocyclic ring member are novel and
interesting, because they could be useful for examining
the problem of recognition of a rigid spherical substrate
(e.g. C60) by rigid macrocycles. As such macrocycles, we
have designed a novel family of cyclynes (1) consisting
of diethynylbenzene and ether units, and reported the
synthesis and novel Ag+-induced cyclization of a simple
member 2 (m-, n=2).2
oxaarenecyclyne-related macrocycles, some investiga-
tions have been made.4–6
O
O
O
O
O
O
1.1 nm
1.3 nm
O
O
4
3
For the synthesis of 3 and 4, we chose the strategy
involving Sonogashira Pd coupling7 as the key step,
because employment of the Williamson synthesis in the
final step of the synthetic route provided low product
yield.2
O
O
O
O
n-1
1
2
Thus, iodoaniline (5a: m-, 5b: p-) was converted to a
triazene derivative 6, which had a propargyl alcohol
unit introduced by the Pd coupling. The obtained 6 by
the reaction with propargyl bromide, led to 7 which is
a key compound in this synthetic route. Protection of
the terminal acetylene group by the TMS group, fol-
lowed by conversion of the triazene group into an
iodo-group8 afforded 8, which is another key com-
pound in this synthetic route, in good yield. The Pd
coupling reaction between 7 and 8 provided compound
9, which was converted to 10 by alkaline hydrolysis on
one hand, and to 11 by iodination of the triazene group
on the other hand. Treatment of 10 and 11 in the same
manner (Sonogashira Pd coupling, iodination and desi-
lylation) as described above afforded the precursor
compound 12. The intramolecular cyclization of 12a or
The nanoscale oxaarenecyclynes 3 (m-, n=4) and 4 (p-,
n=4) having a large cavity of this family, in which four
oxygen atoms (n-donor) and four benzene rings (p-
donor) are alternately arranged, are expected to form
supramolecular complexes with
a large spherical
molecule such as C60 based on Yoshida’s concept,
which regards C60 as a transition metal-like superatom,3
and AM1 calculation. We report here synthesis of 3
and 4 and the formation of supramolecular complexes
with C60. Regarding complex formation of C60 with
Keywords: coupling reaction; fullerenes; macrocycles; molecular
recognition.
* Corresponding author. Tel.: +81-6-6721-2332 (ext. 4121); fax: +81-
6-6723-2721; e-mail: yamaguch@chem.kindai.ac.jp
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00539-7

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Y. Yamaguchi et al. / Tetrahedron Letters 43 (2002) 3277–3280
derivative prepared by the catalytic hydrogenation of 3
and 4 showed a reasonable molecular ion peak. In this
manner, the macrocyclic structure of 3 and 4 was
confirmed by spectral data. Finally, the structure of 4
was determined by single-crystal X-ray analysis (Fig.
1).10 As shown in Fig. 1, 4 is not coplanar and has a
small bond angle strain at CꢀCꢁCꢀC (175.2–179.1°)
12b under high-dilution reaction conditions provided
the desired nano oxaarencyclyne 3 or 4 in medium yield
(3; 31.4%, 4; 35.6%) (Scheme 1).
The observed simple signals of 1H and 13C NMR
spectra9 for 3 and 4 support their symmetrical struc-
ture. The MS spectra9 of the corresponding saturated
N3Et2
c
O
7a: 85.0%
7b: 85.3%
7a, b
H
a, b
f
O
O
N3Et2
NH2
I
6a: 100%.
6b: 93.7%
9a: 80.1%
9b: 79.4%
TMS
5a: m-
5b: p-
OH
I
N3Et2
6a, b
c, d, e
9a, b
O
8a: 44.4%
8b: 71.3%
8a, b
TMS
g
O
O
10a: 100%
10b: 100%
O
H
10a, b
N3Et2
f, e, h
i
9a, b
3
4
O
O
12a: 54.8%
12b: 68.3%
(31.4%) (35.6%)
I
H
O
e
O
O
11a: 92.8%
11b: 90.6%
12a, b
TMS
11a, b
I
Scheme 1. (a) i. 6 M HCl, NaNO2, (ii) Et2NH, K2CO3, MeCN–H2O; (b) propargyl alcohol, Pd(Ph3P)4, CuI, pyrrolidine; (c)
n
propargyl bromide, KOH, 18-crown-6, THF; (d) BuLi, TMSCl, THF; (e) I2, MeI; (f) Pd(dba)2, Ph3P, CuI, Et3N; (g) 1 M KOH,
MeOH; (h) 1 M KOH, MeOH–CHCl3; (i) Pd(dba)2, Ph3P, CuI, Et3N–THF.
Figure 1. ORTEP drawing of 4 (a, front view; b, side view) including two benzene molecules (solvent). Ellipsoids are drawn at
50% probability.

Y. Yamaguchi et al. / Tetrahedron Letters 43 (2002) 3277–3280
3279
and CꢀOꢀC (114.3 and 111.2°). Interestingly,
4
included two benzene (the solvent used for recrystalliza-
tion) molecules in the cavity, suggesting that the cavity
of oxaarenecyclyne is hydrophobic.11
The diagonal OꢀO distances of 4 obtained from its
crystal structure incorporating two benzene molecules
,
in the cavity are 13.4 and 20.3 A, respectively. Taking
the van der Waals radius of the oxygen atom (1.4 A)
,
into consideration, the cavity size of 4 is estimated as
,
,
10.6 and 17.5 A, respectively (13.4 A from MM-2
calculation). On the other hand, the cavity size of 3
obtained from its MM2-optimized structure is esti-
,
mated as 11.5 A. Therefore, 3 and 4 have sufficient
cavity size for including C60 with almost 10 A in van
,
der Waals diameter. Furthermore, as mentioned above,
both 3 and 4 have four n- or p-donor groups, respec-
tively, which can interact well with four equatorial
double bond carbons of C60. Thus, nano oxaarenecycly-
nes 3 and 4, despite their rigid framework, seem to
incorporate C60 (rigid substrate) to form the
supramolecular complexes, provided under appropriate
conditions.
Figure 2. Absorption spectra of C60 (1.05×10−4 mol dm−3) in
the presence of oxaarenecyclyne 3 in toluene. Concentrations
of 3: 0.00, 0.21, 0.42, 0.63, 0.84, 1.05 (×10−4 mol dm−3) from
the bottom. The inset shows the magnification of absorption
spectra between 400 and 500 nm.
The formation of supramolecular complexes of C60 with
3 and 4 was confirmed by the following experiments:
The color change from purple to reddish-brown was
observed only upon refluxing the toluene solution of
C60 and 3 (or 4) (molar ratio; 1:1) for 45 min. The
absorption spectra measurements were made for the
solution after cooling to 298 K. As shown in Figs. 2
and 3, the intensity of the C60 absorption band in the
400–550 nm region increased with concentration of 3
(or 4). This is ascribed to the formation of the
oxaarenecyclyne (3 or 4)-C60 complex in solution.12 The
complex formation was not observed at ambient tem-
perature. Job’s plot13 and isosbestic point (3: 607 nm, 4:
608 nm) between C60 and the receptor (3 or 4), pro-
vided evidence for a 1:1 complex formation. The forma-
tion constant of the complexes at 298
K was
determined by spectroscopic titration method (3 for
C60: 3.41 1.51×103 dm3 mol−1, 4 for C60: 5.43 0.37×103
dm3 mol−1) (Figs. 2 and 3).14 Both constants for m- and
p-cyclynes are of the same order, but the latter is
slightly larger than the former. The AM1 heat of
complex formation15 is 2.23 kcal/mol for the 3-C60
complex, and 0.59 kcal/mol for the 4-C60 complex,
reflecting the difference in distance between the receptor
oxygen atoms and the C60 molecular surface in both
complexes.
Figure 3. Absorption spectra of C60 (1.03×10−4 mol dm−3) in
the presence of oxaarenecyclyne 4 in toluene. Concentrations
of 4: 0.00, 0.21, 0.41, 0.62, 0.82, 1.03 (×10−4 mol dm−3) from
the bottom. The inset shows the magnification of absorption
spectra between 400 and 500 nm.
Therefore, the larger formation constant for the 4-C60
complex could be ascribed to its larger entropy (free-
dom) effect. The MM2/AM1 structure for both com-
plexes (see Figs. 2 and 3) supports this interpretation.
LUMO coefficients at the apical position for Saturn-
type C60 complexes with 3 and 4 become larger than
those of C60, suggesting the increase in reactivity of C60
of the Saturn-type C60 complexes. Investigation on
novel functions emerging from the supramolecular
complex of C60 with 3 and 4 is currently in progress.
The result will be published in due course.
Acknowledgements
We are grateful to JSPS for financial support of this
research (JSPS-RFTF 9711601).

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Y. Yamaguchi et al. / Tetrahedron Letters 43 (2002) 3277–3280
References
16 H); 13C NMR (75.4 MHz, CDCl3), l 58.1, 86.5, 86.6,
122.6, 131.6; IR (KBr, cm−1) 2894, 2846, 2231, 1508,
1496, 1442, 1363, 1346, 1257, 1241, 1081, 1033, 1020, 970,
883, 835, 655, 545.
1. (a) Morrison, D. L.; Ho¨ger, S. J. Chem. Soc., Chem.
Commun. 1996, 2313–2314; (b) Anderson, H. L.; Sanders,
J. K. M. J. Chem. Soc., Chem. Commun. 1989, 1714–
1715; (c) Mackeay, L. G.; Anderson, H. L.; Sanders, J.
K. M. J. Chem. Soc., Chem. Commun. 1992, 43–44; (d)
Anderson, S.; Neidlein, U.; Gramlich, V.; Diedrich, F.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1596–1597.
2. Yamaguchi, Y.; Kobayashi, S.; Wakamiya, T.; Matsub-
ara, Y.; Yoshida, Z. J. Am. Chem. Soc. 2000, 122,
7404–7405.
3. Yoshida, Z. Presented at The IUPAC Third International
Symposium on Functional Dyes, July 16–21, 1995, Santa
Cruz, USA, Opening Lecture, and at Japan–Northern
Baltic Symposium on Synthetic Chemistry, June 25–26,
1996, Helsinki, Finland, Abstracts PL18.
The saturated derivative of 3: 1H NMR (300 MHz,
CDCl3), l 1.89 (tt, J=6.6, 7.2 Hz, 8H), 2.67 (t, J=7.2
Hz, 8H), 3.39 (t, J=6.6 Hz, 8H), 6.98 (s, 2H), 7.00 (d,
J=7.2 Hz, 4H), 7.18 (t, J=7.2 Hz, 2H); HRMS (EI, 70
eV) calcd 704.4805, found 704.4732.
The saturated derivative of 4: 1H NMR (300 MHz,
CDCl3), l 1.87 (tt, J=6.5, 7.5 Hz, 16H), 2.67 (t, J=7.5
Hz, 16H), 3.37 (t, J=6.5 Hz, 16H), 7.09 (s, 16H); 13C
NMR (75.4 MHz, CDCl3), l 31.2, 31.8, 69.6, 128.4,
139.3; HRMS (EI, 70 eV) calcd 704.4805, found
704.4750.
10. Crystal data for 4·2C6H6: C60H44O4, M=829.01, mono-
clinic, P21/n, a=15.343(4), b=5.8076(12), c=26.216(6)
3
,
,
4. Fuji and co-workers have reported oxacalix[3]arenes to
form a sitting the center-type complex with C60: Tsubaki,
K.; Tanaka, K.; Kinoshita, T.; Fuji, K. J. Chem. Soc.,
Chem. Commun. 1998, 859–860.
A, i=104.925(5)°, V=2257.2(8) A , Z=2, Dcalcd=1.220
g/cm3, R=0.048, RW=0.074, Rigaku Mercury, 26018
measured reflections, Mo Ka, 5161 unique (Rint=0.060),
312 variables [I>−10.00|(I)].
5. We have also reported complexation of C60 with
nanoscale crown ether derivatives: Yoshida, Z.; Matsub-
ara, Y.; Yamaguchi, Y. Japan Society for the Promotion
of Science 116 Committee Report 1999, 51, 203–206.
6. Oda and co-workers have reported the synthesis of arene-
cyclynes (Kawase, T.; Ueda, N.; Tanaka, K.; Seirai, Y.;
Oda, M. Tetrahedron Lett. 2001, 42, 5509–5511) and the
formation of an inclusion complex with C60 (private
communication).
The X-ray structures of 3, 3-C60 complex and 4-C60
complex are not established yet, because of difficulty in
obtaining single crystals for X-ray analysis.
11. Oxaarenecyclynes 3 and 4 did not show concentration
1
dependence in the H NMR spectra in CDCl3 (10−2–10−4
M), indicating that these did not tend to self-associate.
12. Significant shifts in 1H and 13C NMR spectra were not
observed for the supramolecular complexes of C60 with 3
or 4.
7. For a review, see: Sonogashira, K. In Comprehensive
Organic Synthesis; Trost, B. M.; Fleming, I., Eds.; Perga-
mon: Oxford, 1991; Vol. 3, pp. 521–549.
13. (a) Rabie, U. M.; Patal, B. P.; Crabtree, R. H. Inorg.
Chem. 1996, 36, 2236; (b) Zimmerman, S. C.; Wu, W.;
Zeng, Z. J. Am. Chem. Soc. 1991, 113, 196.
8. Wu, Z.; Moore, J. S. Tetrahedron Lett. 1994, 35, 5539–
5542.
9. 3: H NMR (300 MHz, CDCl3), l 4.53 (s, 16H), 7.26 (t,
14. The absorption spectra measurements for Job’s plot and
the determination of each complex formation constant
were made for the solution after refluxing for 45 min
followed by cooling to 298 K.
15. The AM1 heat of formation is adopted instead of the
experimental one because the convergent experimental
values are difficult to get owing to high complexation
temperature.
1
J=7.6 Hz, 4H), 7.39 (d, J=7.6 Hz, 8H), 7.56 (bs, 4H);
13C NMR (75.4 MHz, CDCl3), l 57.3, 85.0, 86.0, 122.8,
128.4, 131.7, 135.1; IR (KBr, cm−1) 2921, 2852, 2233,
1477, 1355, 1203, 1074, 1035, 887, 794, 682, 557.
1
4: H NMR (300 MHz, CDCl3), l 4.54 (s, 16H), 7.33 (3,