Preparation of porphyrin-stoppered rotaxane aiming at immobilization on substrate

Article abstract of DOI:10.1246/cl.2002.174

The porphyrin-stoppered rotaxane was prepared from dibenzo-24-crown-8 (DB24C8) and the secondary ammonium ion derivative end-capped by the axial coordination of rhodium(III) tetra-(3,5-di-tert-butylphenyl) porphyrin [TBPP Rh(III) C1]. This rotaxane molecule was designed aiming at the immobilization on a substrate and the analysis of the physicochemical properties as a single molecule.

Full text of DOI:10.1246/cl.2002.174

174
Chemistry Letters 2002
Preparation of Porphyrin-stoppered Rotaxane Aiming at Immobilization on Substrate
Masumi Asakawaꢀ, Taichi Ikeday, Nobuhiko Yuiy, and Toshimi Shimizuꢀ
Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology,
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565
ySchool of Materials Science, Japan Advanced Institute of Science and Technology,
1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292
(Received November 26, 2001;CL-011192)
The porphyrin-stoppered rotaxane was prepared from
dibenzo-24-crown-8 (DB24C8) and the secondary ammonium
ion derivative end-capped by the axial coordination of rhodiu-
m(III) tetra-(3,5-di-tert-butylphenyl) porphyrin [TBPP Rh(III)
Cl]. This rotaxane molecule was designed aiming at the
immobilization on a substrate and the analysis of the physico-
chemical properties as a single molecule.
The interlocked molecules, e.g. rotaxane in which a cyclic
molecule is threaded on a linear compound capped with bulky end
groups, has attracted much attention as a candidate for the
molecular devices in nanotechnology.1 The molecular devices
should be immobilized on a substrate in practical use. The
immobilization of the functional interlocked molecules by
Langmuir-Blodgett technique or self-assembled monolayer on
the gold surface has been demonstrated.2 The property of the
immobilized molecules may be different from the real properties
of the single molecule. This is because the functional molecules
should be affected by the surrounding molecules. The character-
istic of the rotaxane molecule is the rotational and translational
motions of a cyclic molecule against a linear component.
Therefore, the immobilization of the rotaxane molecule in the
isolated state is an important subject to minimize the steric
hindrance of the surrounding molecule.
Recently, some research groups reported the STM observa-
tion of the immobilized porphyrin derivatives on a substrate.3 It
was found that porphyrin ring of TBPP stands on the noble metal
surface by using four 3,5-di-tert-butylphenyl groups as the legs.
Since the porphyrin ring occupies much room on the substrate, the
coordinated rotaxane molecule on TBPP should be in the isolated
state. From CPK model, it was confirmed that the cross-sectional
areas of TBPP and DB24C8 are almost same. The STM
observation of the isolated rotaxane molecule should accelerate
the analysis of the physicochemical properties of the rotaxane as a
single molecule and clarify the feasibility of the rotaxane
molecule as a molecular device.
Scheme 1. Synthesis of axis molecule for porphyrin-stoppered
rotaxane. Aromatic carbons of 5 was numbered from C1 to C11.
elemental analysis.4 5 is the guest molecule for DB24C8 (6) and
the axial ligand for TBPP Rh(III) Cl (8) simultaneously.
TBPP was synthesized from 3,5-di-tert-butylbenzaldehyde
and pyrrole (see elsewhere).5 8 was prepared by the reaction of
TBPP with [Rh(CO)2Cl2]2.6
Prior to the preparation of the porphyrin-stoppered rotaxane,
the inclusion complexation between 5 and 6 was examined (7 in
Scheme 2). The secondary amino group was converted to the
ammonium salt (5þ) by the addition of trifluoroacetic acid. It was
confirmed that the peaks assigned to the protons around the
secondary ammonium ion group shifted towards down-field by
the mixing of 5þ and 6.7 This result suggests that the 5þ forms an
inclusion complex with 6.8 The chemical shift change towards
down-field is attributed to the anisotropic shielding of DB24C8
aromatic rings. The stability constant of the complex was
estimated to be ca. 3000 LÁmolÀ1 from the peak integrals of 1H
NMR spectrum (concentration: 1:2 Â 10À3 molÁLÀ1).
In this letter, we report the preparation of the porphyrin-
stoppered rotaxane aiming at the immobilization of the
interlocked molecules on a substrate.
The molecule 5 was synthesized in conventional chemistry
(Scheme 1). 3 was synthesized by reductive amination of 4-tert-
benzaldehyde with 4-methoxycarbonylbenzylamine hydrochlor-
ide. The secondary amino group was protected by Boc group, then
the ester was hydrolyzed to yield 4. The condensation reaction
between 4 and 4-aminopyridine by 1-ethyl-3-(3-dimethylamino-
propyl)carbodiimide hydrochloride (WSC) and the deprotecton
of secondary amino group yield 5. Total yield was 50%. The
synthesis of 5 was confirmed by 1H, 13C NMR, FAB-MS and the
The porphyrin-stoppered rotaxane (9) could be obtained
easily from 7 and 8.9 After purification, the yield of the rotaxane
was 70%. The preparation of the rotaxane was confirmed by 1H
NMR and FAB-MS spectrum.10 The 1H NMR peaks of 9 appears
in higher field than those of 7. This is due to the diamagnetic ring
current of the porphyrin ring. The intensity of the anisotropic
shielding effect by the porphyrin ring depends on the distance
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
175
References and Notes
1
a) ‘‘Molecular Catenanes, Rotaxanes and Knots,’’ ed. by J.-P.
Sauvage and C. O. D-. Buchecker, John Wiley & Sons, New York
(1999). b) S. J. Cantrill, A. R. Pease, and J. F. Stoddart, Dalton,
2000, 3715. c) C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K.
Beverly, J. Sampaio, F. M. Raymo, J. F. Stoddart, and J. R. Heath,
Science, 289, 1172 (2000).
2
3
4
a) M. Asakawa, M. Higuchi, G. Mattersteig, T. Nakamura, A. R.
Pease, F. M. Raymo, T. Shimizu, and J. F. Stoddart, Adv. Mat., 12,
1099 (2000). b) C. D. Nadai, C. M. Whelan, C. Perollier, G.
Clarkson, D. A. Leigh, R. Caudano, and P. Rudolf, Surf. Sci., 454,
112 (2000).
a) P. J. Thomas, N. Berovic, P. Laitenberger, R. E. Palmer, N.
Bampos, and J. K. M. Sanders, Chem. Phys. Lett., 294, 229 (1998).
b) J. K. Gimzewski and C. Joachim, Science, 283, 1683 (1999). c)
M. Furukawa, H. Tanaka, K. Sugiura, Y. Sakata, and T. Kawai,
Surf. Sci., 445, L58 (2000).
Data for 5: white solid. 1H NMR (CDCl3, 600 MHz, 298 K) ꢀ 1.31
(s, 9H, C(CH3)3), 1.77 (br, CH2NHCH2), 3.77 (s, 2H, C4-CH2),
3.88 (s, 2H, C5-CH2), 7.25 (d, J ¼ 8:1 Hz, 2H, C3H), 7.35 (d,
J ¼ 8:1 Hz, 2H, C2H), 7.47 (d, J ¼ 8:1 Hz, 2H, C6H), 7.60 (d,
J ¼ 6:2 Hz, 2H, C10H), 7.82 (d, J ¼ 8:1 Hz, 2H, C7H), 8.16 (br,
CONH), 8.51 (d, J ¼ 6:2 Hz, 2H, C11H). 13C NMR (CDCl3,
600 MHz, 298 K): ꢀ ¼ 31:36 (C(CH3)3), 34.48 (C(CH3)3), 52.66,
52.87 (CH2NHCH2), 113.81 (C10), 125.39 (C2), 127.29 (C7),
127.83 (C3), 128.32 (C6), 133.62 (C8), 136.87 (C4), 145.12 (C5),
145.50 (C1), 150.10 (C9), 150.77 (C11), 166.03 (C ¼ O). MS (FAB)
found: m=z 374. Calcd for C24H27N3O: Mþ, 374. Anal. Calcd for
C
75.26;H, 7.37;N, 10.66%.
H. Tamiaki, S. Suzuki, and K. Maruyama, Bull. Chem. Soc. Jpn., 66,
2633 (1933).
24H27N3O 0.5H2O: C, 75.36;H, 7.38;N, 10.99%. Found: C,
Scheme 2. Preparation of porphyrin-stoppered rotaxane.
5
6
a) H. Ogishi, J. Setsume, T. Omura, and Z. Yoshida, J. Am. Chem.
Soc., 97, 6461 (1975). b) Data for 8: purple solid. 1H NMR (CDCl3,
600 MHz, 298 K) ꢀ1.51 (s, 36H, C(CH3)3), 7.77 (s, 4H, Py), 8.06 (s,
4H, Py), 8.15 (s, 4H, Ar), 9.00 (s, 8H, Ar). MS (FAB) found: m=z
from the porphyrin ring.6a For instance, the peak assigned to C11H
shifts towards up-field drastically (Áꢀ ¼ 8:53 À 0:75 ¼
7:78 ppm). On the other hand, the peak assigned to tert-butyl
group of 5þ, which are the most far from the porphyrin ring, shifts
slightly (Áꢀ ¼ 0:11 ppm). The peaks of DB24C8 also shift
towards up-field (Áꢀ ¼ ca. 0.22 ppm). The intensity of the
anisotropic shielding effect on DB24C8 is almost same for that on
the methylene protons of the axis (C4-CH2) (Áꢀ ¼ 0:23 ppm).
This result suggests that DB24C8 locate around the methylene
group of 5þ.
The absorption maxima of the Soret and Q bands of 8 shifted
towards longer wavelength by the formation of 9. This result is
consistent with that for the axial coordination of pyridine
derivatives to 8.
Recently, some groups reported the porphyrin-stoppered
rotaxanes.11 In these studies, the end capping reaction by the axial
coordination of porphyrin derivatives is thermodynamically
unstable. In our study, the coordination of 7 to 8 is quite stable.
No dissociated species could be observed by 1H NMR spectrum
even if it heated to 323 K.
1200. Calcd for C76H92ClN4Rh: Mþ, 1200. UV-vis (CHCl3): ꢁmax
:
425, 535, 569 nm.
7
Data for 7: 1H NMR (CDCl3, 600 MHz, 298 K) ꢀ 1.25 (s, 9H,
C(CH3)3), 3.39 (m, 8H, CH2 of 6), 3.73 (m, 8H, CH2 of 6), 4.09 (m,
8H, CH2 of 6), 4.43 (m, 2H, C4-CH2), 4.74 (m, 2H, C5-CH2), 6.75
(m, 4H, Ar of 6), 6.87 (m, 4H, Ar of 6), 7.15 (d, J ¼ 7:3 Hz, 2H,
C3H), 7.24 (d, J ¼ 7:3 Hz, 2H, C2H), 7.47 (d, J ¼ 8:1 Hz, 2H,
C6H), 7.67 (br, 2H, CH2NH2CH2), 7.89 (d, J ¼ 8:4 Hz, 2H, C10H),
8.39 (d, J ¼ 8:1 Hz, 2H, C7H), 8.53 (d, J ¼ 8:4 Hz, 2H, C11H),
10.88 (s, 1H, CONH).
8
9
a) P. R. Ashton, P. T. Glink, J. F. Stoddart, P. A. Tasker, A. J. P.
White, and D. J. Williams, Chem. Eur. J., 2, 729 (1996). b) H.
Kawasaki, N. Kihara, and T. Takata, Chem. Lett., 1999, 1015.
6 (6:4 Â 10À5 mol) was dissolved in 1.6 mL of CHCl3 solution
containing 5 (3:2 Â 10À5 mol). TFA (1:9 Â 10À4 mol) was added,
and then 8 (3:2 Â 10À5 mol) was dissolved in the solution. After
complete dissolution of 8, the product was immediately purified by
GPC (Sephadex LH20, solvent: MeOH). Moreover, the product was
purified by SiO2 column (solvent: CH2Cl2 then MeOH).
10 Data for 9: purple solid. 1H NMR (CDCl3, 600 MHz, 298 K) ꢀ 0.75
(d, J ¼ 7:7 Hz, 2H, C11H), 1.14 (s, 9H, C(CH3)3 of 5), 1.44 (m, 72H,
4 Â C(CH3)3 of 8), 3.16 (m, 8H, CH2 of 6), 3.52 (m, 8H, CH2 of 6),
3.87 (m, 8H, CH2 of 6) 4.20 (m, 2H, C4-CH2), 4.42 (m, 2H, C5-
CH2), 5.71 (d, J ¼ 7:7 Hz, 2H, C10H), 6.54 (m, 4H, Ar of 6), 6.64
(m, 4H, Ar of 6), 6.95 (d, J ¼ 8:4 Hz, 2H, C3H), 7.05 (d, J ¼ 8:4 Hz,
2H, C6H), 7.07 (d, J ¼ 8:4 Hz, 2H, C2H), 7.38 (d, J ¼ 8:4 Hz, 2H,
C7H), 7.39 (br, 2H, CH2NH2CH2), 7.67 (s, 4H, Ar of 8), 7.96 (s, 4H,
Py of 8), 8.09 (s, 4H, Py of 8), 8.85 (s, 8H, Ar of 8), 10.29 (br, 1H,
CONH). MS (FAB) found: m=z 2021. Calcd for
The preparation of the porphyrin-stoppered rotaxane mono-
layer on a substrate and the observation of the physicochemical
properties of the rotaxane as a single molecule are now in
progress.
This study was supported by Industrial Technology Research
Grant Program in ’00 from the New Energy and Industrial
Technology Development Organization (NEDO) of Japan.
C
124H151ClN7O9Rh: Mþ, 2021.
11 a) K. Chichak, M. C. Walsh, and N. R. Branda, Chem. Commun.,
2000, 847. b) M. J. Gunter, N. Bampos, K. D. Johnstone, and J. K.
M. Sanders, New J. Chem., 25, 166 (2001).
This paper is dedicated to Professor Teruaki Mukaiyama on
the occasion of his 75th birthday.