End-capping of pseudo[2]rotaxane composed of alkyl(ferrocenylmethyl) ammonium and dibenzo[24]crown-8 via cross metathesis reactions

Article abstract of DOI:10.1246/cl.2006.374

Pseudo[2]rotaxane, having dialkylammonium with a ferrocenyl stopper and a vinyl group as the axis component, underwent cross-metathesis reaction with acrylate esters to form ferrocene-containing [2]rotaxanes. Copyright

Full text of DOI:10.1246/cl.2006.374

374
Chemistry Letters Vol.35, No.4 (2006)
End-capping of Pseudo[2]rotaxane Composed of Alkyl(ferrocenylmethyl)ammonium
and Dibenzo[24]crown-8 via Cross Metathesis Reactions
Yuji Suzaki and Kohtaro Osakadaꢀ
Chemical Resources Laboratory R1-3, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503
(Received December 12, 2005; CL-051519; E-mail: kosakada@res.titech.ac.jp)
Pseudo[2]rotaxane, having dialkylammonium with a ferro-
cenyl stopper and a vinyl group as the axis component, under-
went cross-metathesis reaction with acrylate esters to form ferro-
cene-containing [2]rotaxanes.
(PF6
)
(PF6
)
O O
O O
O
O
O
O
N
N
+
O H2
H2
O
O
Fe
Fe
CD3CN
20 oC
X
X
O O
O O
Rotaxanes have attracted increasing attention because of
their interlocked structures as well as their unique physical and
chemical properties.1,2 Since ferrocene derivatives undergo
one-electron redox reaction reversibly,3 they are employed as
materials to construct the host–guest systems and rotaxanes that
function as the stimulus response system driven by the electro-
chemical reaction of the ferrocene center.4,5 Recently, we report-
ed that electrochemical oxidation of aminomethylferrocene de-
rivatives in the presence of TEMPOH (1-hydroxy-2,2,6,6-tetra-
methylpiperidine) and DB24C8 (dibenzo[24]crown-8) produced
the pseudo[2]rotaxanes that contain ferrocenomethylammonium
as the axis component.6 Suitable end-capping reactions of these
pseudo[2]rotaxanes would fix the interlocked structure and form
the corresponding [2]rotaxanes with bulky stoppers at both ends
of the axis molecule, as shown in Scheme 1. Bond forming reac-
tions, such as cycloaddition of azide to alkyne and esterification
of acid anhydride with alcohol, were used for end-capping,
because they form a new bond between the axis molecule and
bulky stopper molecule efficiently under mild conditions.7 Cross
metathesis between the vinyl group and acrylate was recently
reported to proceed selectively in the presence of the Ru catalyst.
In this paper, we report end-capping of a ferrocene-containing
[2]rotaxane via the Ru-catalyzed cross metathesis reaction.8,9
Scheme 2 shows the preparation of pseudo[2]rotaxanes with
a ferrocenyl stopper and a vinyl group. 1a and 1b are prepared
from ferrocenecarboxaldehyde and benzylamines containing
an olefin group.6,10 Dissolution of an equimolar mixture of 1a
and DB24C8 in CD3CN (10 mM for each compound) forms
pseudo[2]rotaxane 2a. 1H NMR signals of NCH2 hydrogens
(ꢀ 4.37, 4.50) were observed at lower magnetic field positions
than the corresponding signals of 1a (ꢀ 4.02, 4.04), suggesting
C–HꢁꢁꢁO interaction between the NCH2 group and DB24C8,
while the signals of vinyl hydrogen of 1a and 2a overlapped with
each other. A mixture of 1b and DB24C8 in CD3CN also forms
pseudo[2]rotaxane, 2b. The 1H NMR signals of vinyl hydrogens
of 2b (ꢀ 5.22, 5.67, 6.58) shifted to higher magnetic field posi-
DB24C8
(1a)
(2a)
X =
X =
O
O
(1b)
(2b)
Scheme 2. Formation of pseudorotaxane 2a and 2b in CD3CN.
tions than the corresponding signals of 1b (ꢀ 5.33, 5.86, 6.77),
because of the shielding effect by aromatic groups of
DB24C8. The formation of 2a and 2b was confirmed also from
the electrospray ionization mass spectrometry (ESIMS). Slow
diffusion of Et2O to a CH2Cl2 solution of 1b and DB24C8 leads
to growth of the crystals of 2b. X-ray analysis of 2b revealed the
pseudo[2]rotaxane structure; NH2 and CH2 groups of the axis
molecule show the presence of Nþ–HꢁꢁꢁO and C–HꢁꢁꢁO hydrogen
˚
˚
bonds (H1–O4, 2.36 A and H13–O6, 2.35 A) (Figure 1). Close
contact is observed between an aromatic ring of DB24C8 and
11
˚
the axis (C24–C1, 3.92(2) A). Precise ratios between 1a (or
1b) and 2a (or 2b) in CDCl3 were not determined due to the
low solubility of 1a (or 1b), although the solutions in CD3CN
contain equilibrated mixtures of these compounds in a 36/64
(or 43/57) ratio at 20 ꢂC. A cross metathesis reaction of an axis
molecule 1a and 3,5-dimethylphenyl acrylate using Ru catalyst9
in the presence of DB24C8 gives [2]rotaxane 3, which is isolated
in 72% yield (Scheme 3).12,13 The trans configuration of the
C=C double bond was determined from the 1H NMR spectrum,
which shows a large coupling constant of vinylene hydrogens
(J ¼ 15 Hz). High trans selectivity in the cross metathesis reac-
tions of terminal olefins with ethyl acrylate was reported.14
A
similar reaction using ferrocenyl acrylate15 gives [2]rotaxane 4
having two ferrocenyl groups as the stopper. A reaction using
1b and 3,5-dimethylphenyl acrylate did not form [2]rotaxane
Fe1
O3
O2
O1
H2
O4
H12
N1
H13
H1
O8
O6
O5
O7
(i)
+
+
C24
(ii)
C1
Scheme 1. End-capping method for synthesis of [2]rotaxane.
Figure 1. ORTEP drawing of cationic component of 2b.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.4 (2006)
375
´
Kaifer, J. Am. Chem. Soc. 2001, 123, 11148. d) B. Gonzalez,
I. Cuadrado, B. Alonso, C. M. Casado, M. Moran, A. E. Kaifer,
Organometallics 2002, 21, 3544.
N. Kihara, M. Hashimoto, T. Takata, Org. Lett. 2004, 6, 1693.
a) M. Horie, Y. Suzaki, K. Osakada, J. Am. Chem. Soc. 2004,
126, 3684. b) M. Horie, Y. Suzaki, K. Osakada, Inorg. Chem.
2005, 44, 5844.
´
O O
O
O
O
+
+
1a
5
6
R
O
O
O
O O
DB24C8
Me
R =
Fe
,
7
8
a) P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer,
C. Schiavo, N. Spencer, J. F. Stoddart, P. A. Tasker, A. J. P.
White, D. J. Williams, Chem.—Eur. J. 1996, 2, 709. b) H.
Kawasaki, N. Kihara, T. Takata, Chem. Lett. 1999, 1015.
Formation of rotaxane via metathesis of symmetrical olefins:
a) J. S. Hannam, T. J. Kidd, D. A. Leigh, A. J. Wilson, Org.
Lett. 2003, 5, 1907. b) A. F. M. Kilbinger, S. J. Cantrill,
A. W. Waltman, M. W. Day, R. H. Grubbs, Angew. Chem.,
Int. Ed. 2003, 42, 3281.
a) T. M. Trnka, R. H. Grubbs, Acc. Chem. Res. 2001, 34, 18.
b) R. H. Grubbs, T. M. Trnka, M. S. Sanfoed, in Transition
Metal-Carbene Complexes in Olefin Metathesis and Related
Reactions, ed. by A. Yamamoto, H. Kurosawa, Current
Methods in Inorganic Chemistry, 2002, Vol. 3, Chap. 4.
Me
)
N
N
Cl
Ru
(PF6
Me
O O
N
Cl
Ph
PCy3
O
O
O
O
R
(5 mol%)
H2
Fe
O
O
O O
CH2Cl2
reflux, 15 h
R =
Fe
(4, 35%)
9
,
Me
(3, 72%)
Scheme 3. Syntheses of [2]rotaxanes via cross metathesis.
10 X.-Z. Zhu, C.-F. Chen, J. Am. Chem. Soc. 2005, 127, 13158.
11 Crystal data for 2b: C44H54F6FeNO8P, fw ¼ 925:72, mono-
due to steric congestion around the vinyl group by DB24C8
of 2b.
˚
clinic, space group P21/a (No. 14), a ¼ 38:521ð4Þ A, b ¼
The cyclic voltammogram of 3 in MeCN shows reversible
redox reaction at E1=2 ¼ 0:47 V (vs Agþ/Ag, scan rate ¼
0:1 V sꢃ1). The electrochemical oxidation and reduction of 3
are reversible in the range of scan rates 0.01–0.25 V sꢃ1. The
redox potential is the same as that of 1a (E1=2 ¼ 0:47 V,
scan rate ¼ 0:1 V sꢃ1). This result indicates that DB24C8 in 3
interacts more strongly with the ammonium group of the axis
molecule than that of neutral [2]rotaxane composed of a ferro-
cene-containing axis molecule and DB24C8.5
In summary, we have demonstrated that cross metathesis
reaction can be an efficient method for the preparation of
[2]rotaxanes. Studies of reactions to obtain higher order rotax-
anes are in progress.
ꢂ
˚
˚
10:253ð2Þ A, c ¼ 11:378ð1Þ A, ꢁ ¼ 96:222ð8Þ , V ¼ 4467ð1Þ
A , Z ¼ 4, Dcalcd ¼ 1:376 g cmꢃ3, No. of unique reflections =
3
˚
3536 (I > 3ꢂðIÞ), R ¼ 0:058, Rw ¼ 0:091. Crystallographic
data reported in this manuscript have been deposited with
Cambridge Crystallographic Data Centre as supplementary
publication No. CCDC-292617. Copies of the data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; fax: +44
1223 336033; or e-mail: deposit@ccdc.cam.ac.uk).
12 1a (52 mg, 0.1 mmol) was dissolved in 2 mL of CH2Cl2 con-
taining DB24C8 (54 mg, 0.12 mmol) followed by addition of
3,5-dimethylphenyl acrylate (35 mg, 0.2 mmol) and Ru cata-
lyst (4.2 mg, 5 ꢄ 10ꢃ3 mmol). The mixture was refluxed for
15 h and solvent was removed by evaporation to form brown
oil. The reprecipitation of crude product from CH2Cl2/Et2O
(2.5 mL/30 mL) gave brown solid which was collected, wash-
ed with Et2O (10 mL ꢄ 2) and dried under reduced pressure to
give 3 (80 mg, 0.072 mmol, 72%).
13 Data for 3: 1H NMR (300 MHz, CDCl3, rt): ꢀ 2.29 (s, 6H, Me),
2.73 (br, 2H, CH2CH=CH), 3.41–3.85 (16H, CH2-DB24C8),
4.01–4.50 (21H, NCH2, C5H5, C5H4, OCH2-Axis, CH2-
DB24C8), 4.60 (br, 2H, NCH2), 6.13 (d, 1H, C(=O)CH,
J ¼ 15 Hz), 6.70–6.72 (4H, C6H4-Axis, C6H3), 6.85 (s, 1H,
C6H3), 6.88–6.97 (8H, C6H4-DB24C8), 7.23 (1H, CH2CH),
7.34 (br, 2H, C6H4-Axis), 7.35 (br, 2H, NH2). 13C{1H} NMR
(100 MHz, CDCl3, rt): ꢀ 21.3 (Me), 32.1 (CHCH2), 47.7
(NCH2), 51.6 (NCH2), 65.9 (OCH2), 68.5 (CH2-DB24C8),
68.8 (C5H5), 69.4 (C5H4), 69.7 (C5H4), 70.3 (CH2-DB24C8),
70.8 (CH2-DB24C8), 113.0, 114.5, 119.1, 121.8, 122.7,
124.4, 127.4, 131.0, 139.1, 147.0, 147.6, 150.5, 159.0, 164.8
(C=O). C5H4-ipso is not observed due to the low intensity.
IR (KBr): ꢃ 3162 (N–H), 3073 (N–H), 1734 (C=O), 841 (P–
F), 558 (P–F) cmꢃ1. ESIMS: Anal. Calcd for C55H66O11NFe:
972.4 Found: m=z ¼ 972:5 [M ꢃ PF6]þ. For NMR spectra of
the rotaxanes, see Supporting Information.
This work was supported by Grant-in-Aid for Scientific Re-
search from the Ministry of Education, Culture, Sports, Science
and Technology, Japan and by a 21st Century COE Program
‘‘Creation of Molecular Diversity and Development of Function-
alities.’’ Y. S. acknowledges scholarship by Japan Society for the
Promotion of Science. We are grateful to Prof. Munetaka Akita
of our institute for ESIMS measurements.
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Published on the web (Advance View) March 11, 2006; DOI 10.1246/cl.2006.374