Ferrocene-containing [2]- and [3]rotaxanes. Preparation via an end-capping cross-metathesis reaction and electrochemical properties

Article abstract of DOI:10.1039/b702785k

Cross-metathesis reactions of terminal olefins with acrylic esters catalyzed by a Ru-carbene complex ((H₂IMes)(PCy₃)Cl ₂RuCHPh, H₂IMes = N,N-bis(mesityl)-4,5-dihydroimidazol-2- ylidene) were applied to the end-capping of [2]pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and ferrocenylmethylammonium derivatives as the macrocyclic and axle components. A [3]rotaxane consisting of two DB24C8s and an axle molecule having ferrocenyl groups at both ends was obtained from the cross-metathesis reaction of two [2]pseudorotaxanes with Fe(C₅H ₄CH₂OCOCHCH₂)₂. Cyclic voltammograms of the ferrocene-containing rotaxanes show reversible redox reactions whose potentials vary depending on the presence or absence of cationic dialkylammonium groups in the vicinity of the ferrocene units. The Royal Society of Chemistry.

Full text of DOI:10.1039/b702785k

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ferrocene-containing [2]- and [3]rotaxanes. Preparation via an end-capping
cross-metathesis reaction and electrochemical properties
Yuji Suzaki and Kohtaro Osakada*
Received 22nd February 2007, Accepted 11th April 2007
First published as an Advance Article on the web 15th May 2007
DOI: 10.1039/b702785k
Cross-metathesis reactions of terminal olefins with acrylic esters catalyzed by a Ru–carbene complex
=
((H2IMes)(PCy3)Cl2Ru CHPh, H2IMes = N,N -bis(mesityl)-4,5-dihydroimidazol-2-ylidene) were
applied to the end-capping of [2]pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and
ferrocenylmethylammonium derivatives as the macrocyclic and axle components. A [3]rotaxane
consisting of two DB24C8s and an axle molecule having ferrocenyl groups at both ends was obtained
=
from the cross-metathesis reaction of two [2]pseudorotaxanes with Fe(C5H4CH2OCOCH CH2)2.
Cyclic voltammograms of the ferrocene-containing rotaxanes show reversible redox reactions whose
potentials vary depending on the presence or absence of cationic dialkylammonium groups in the
vicinity of the ferrocene units.
H2IMes = N,N -bis(mesityl)-4,5-dihydroimidazol-2-ylidene). Syn-
Introduction
thesis of [3]rotaxane by a similar procedure and the electrochem-
ical properties of these rotaxanes are also described. Part of this
work has been reported in a preliminarily form.23
Rotaxane1,2 is a mechanically interlocked supramolecule com-
posed of macrocyclic molecules threaded by a linear molecule
having bulky end groups. Pseudorotaxanes composed of
dibenzo[24]crown-8 (DB24C8) and dialkylammonium salt have
often been used as a precursor of the rotaxane due to its high
stability owing to N–H · · · O and C–H · · · O attractive interactions
between the linear and cyclic components.3 Various reactions,
such as cycloaddition of azide,4 addition of isocyanates with
amines5 and with alcohol,6 Wittig reactions,7 disulfide formation,8
ester formation,9 and acid anhydride formation,10 introduce a
bulky group at the end of the axle molecule of the pseudorotax-
anes to fix the interlocked structure. Olefin metathesis reactions
were also used for the synthesis of rotaxanes11–13 and related
Results and discussion
Scheme 1 summarizes the preparative procedure for the am-
monium salts which are employed as precursors of the axle
components of the rotaxane in this study. The dehydration reaction
of ferrocenecarboxaldehyde with p-butenoxybenzylamine forms
=
=
FcCH NCH2C6H4OCH2CH2CH CH2 (Fc = Fe(C5H4)(C5H5)).
=
Fig. 1 depicts the molecular structure of FcCH NCH2C6H4-
=
OCH2CH2CH CH2 determined by X-ray crystallography. Cy-
clopentadienyl ligands are in the eclipsed positions. Reduc-
tion of the product with NaBH4, followed by hydrolysis with
HCl and exchange of the counter anion, yields the PF6 salt
supramolecules14–16 because of efficient C C bond formation
=
under mild conditions. Recent progress in the type of catalyst used
in the metathesis reactions has enabled selective cross-metathesis
reactions of terminal alkenes with alkyl acrylates or styrene.17,18
Recently, we reported that electrochemical oxidation of
a solution containing ferrocenylmethylamine derivatives and
dibenzo[24]crown-8 (DB24C8) in the presence of 1-hydroxy-
2,2,6,6-tetramethylpiperidine (TEMPOH) formed [2]pseudoro-
taxane via formal protonation of the secondary amine group.19
Introduction of a redox active ferrocene unit to a component
of the supramolecule is of significant importance because these
supramolecules are potentially applicable to the stimulus re-
sponsive molecular materials that change optical or chemical
properties upon electrochemical reaction.20–22 A suitable end-
capping reaction would convert the pseudorotaxanes having a
ferrocenyl group into the corresponding rotaxanes.
=
[FcCH2NH2CH2C6H4OCH2CH2CH CH2](PF6) (1a). Analogous
reactions of p-vinylbenzylamine yield 1b. These compounds were
Scheme 1
In this paper, we report the synthesis of new [2]rotaxanes
via the end-capping of [2]pseudorotaxane by cross-metathesis
=
reactions using a Ru catalyst ((H2IMes)(PCy3)Cl2Ru CHPh,
Chemical Resources Laboratory R1-3, Tokyo Institute of Technology, 4259
Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan. E-mail: kosakada@res.
titech.ac.jp; Fax: +81-45-924-5224; Tel: +81-45-924-5224
=
=
Fig. 1 ORTEP plot of FcCH NCH2C6H4OCH2CH2CH CH2 with 30%
probability. Hydrogen atoms were omitted for simplicity.
2376 | Dalton Trans., 2007, 2376–2383
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1
1
characterized by H and 13C{ H} NMR and IR spectrometry as
well as elemental analyses.
Dissolution of 1a and DB24C8 in CD3CN forms [2]pseudoro-
taxane 2a as shown in Scheme 2. Formation of 2a and 2b in
the solutions was confirmed from electrospray ionization mass
spectrometry (ESIMS) which exhibited peaks due to the cationic
1
pseudorotaxanes. Fig. 2(a) and (b) show the H NMR spectra
of 1a and a mixture of 1a and DB24C8 ([1a]0 = [DB24C8]0 =
10 mM), respectively. The latter spectrum contains the signals of
the NCH2 hydrogens of the pseudorotaxane (d 4.37, 4.50) at lower
magnetic field positions than those of 1a (d 4.02, 4.04). The signals
of the aromatic hydrogens of the axle molecule of 2a are observed
at higher magnetic field positions (d 6.55, 7.17) than those of
1a (d 6.95, 7.33). The ratios of the free axle molecules and the
pseudorotaxane in these solutions were calculated to be 1a/2a =
36/64 and 1b/2b = 43/57 from comparison of the peak areas of
the phenylene hydrogen signals at 20 ◦C.24–26
Fig. 3 ORTEP plot of pseudorotaxane 2b with 30% probability. Some of
the hydrogen atoms and PF6 were omitted for simplicity.
−
Stoddart reported that the 1 : 1 complex of DB24C8 and the
dibenzylammonium cation3b,25 possess co-conformation27 where
one of the aryl rings in the axle is oriented almost parallel to one
of the catechol rings on the DB24C8. The IR spectrum of 2b shows
peaks due to asymmetric and symmetric stretching vibrations of
the NH2 group at 3156 and 3085 cm−1, which is observed at lower
wavenumber than those of 1b (3235, 3260 cm−1) due to N–H · · · O
hydrogen bonds between the axle molecule and DB24C8 in 2b.
A cross-metathesis reaction of 3,5-dimethylphenyl acrylate
(0.20 mmol) with 1a (0.10 mmol) in the presence of DB24C8
(0.12 mmol) using a Ru catalyst17 affords [2]rotaxane 3 in 72%
Scheme 2
1
isolated yield (Scheme 3). The H NMR spectrum, showing a
large coupling constant of vinylene hydrogens (J = 15 Hz),
=
indicates a trans configuration of the C C bond, similar to
the products of the other cross-metathesis reactions.18 Analogous
reaction using ferrocenylmethyl acrylate yields rotaxane 4 having
ferrocenyl groups at both ends of the axle molecule. The IR
spectra of these compounds show peaks due to N–H vibrations
(3162, 3073 cm−1 for 3 and 3166, 3092 cm−1 for 4) at similar
positions to 2b. The reaction of 3,5-dimethylphenyl acrylate with
1b in the presence of DB24C8 does not form the corresponding
[2]rotaxane. Low yields of the cross-metathesis reaction of 2b may
be ascribed to steric hindrance by DB24C8 or low reactivity of
the vinyl group attached to the aromatic ring. Acetylation of the
Fig. 2 1H NMR spectra of (a) 1a and (b) 1a and DB24C8 ([1a]0
[DB24C8]0 = 10 mM) in CD3CN. Peaks with an asterisk indicate the
signals of the complex of DB24C8 and 1a.
=
Slow addition of Et2O to a CH2Cl2 solution of 1b and DB24C8
causes separation of [2]pseudorotaxane 2b as single crystals.
Fig. 3 shows the molecular structure of 2b obtained by X-ray
crystallography. The NH2 and CH2 groups of the axle component
show short contacts with the oxygen atoms of DB24C8 (N(1)–
˚
˚
H(1) · · · O(4), 2.18 A and C(10)–H(13) · · · O(6), 2.35 A), indicating
that hydrogen bonds between them stabilize the interlocked
structure. A C–H · · · p attractive interaction is also observed
between a cyclopentadienyl hydrogen and the aromatic plane of
DB24C8; the distance between a cyclopentadienyl hydrogen and
˚
the centroid of the aromatic ring of DB24C8 is 3.07 A. An aromatic
plane of DB24C8 in 2b is close to the olefinic carbons with a
˚
distance of 4.14(2) A between C(24) and C(2). The dihedral angle
of the aryl ring of 2b and one of the catechol rings is 162◦, while
Scheme 3
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Table 1 Electrochemical data for ferrocene compoundsa
ammonium group of 3 according to Takata’s method28 forms a
neutral rotaxane 5 in 91% yield, as shown in Scheme 4. The IR
Compound
E
pa/V
Epc/V
E1/2 (DE)/V
peak of 5 at 1728 cm−1 is assigned to vibration of the C O bond
=
in the amide group. The 1H NMR spectrum of 5 shows the signal
of the vinylene hydrogens (d 6.38, 7.71) at lower magnetic field
positions than those of the corresponding signals of 3 (d 6.13,
1a
3
0.52
0.50
0.42
0.43
0.47 (0.10)
0.47 (0.07)
—
0.35 (0.08)
—
0.37 (0.07)
0.48 (0.06)
0.29 (0.07)
4b
5
0.38, 0.49 0.34, 0.43
0.39
0.31
0.45c
0.33
0.45
0.25
=
7.18). Reaction of 1a, DB24C8 and Fe(C5H4CH2OCOCH CH2)2
6
0.51c
(see Fig. 4) ([1a] = 0.10 mmol, [DB24C8] = 0.14 mmol,
=
Fe(C5H5)(C5H4CH2OCOCH CH2) 0.40
=
=
Fe(C5H4CH2OCOCH CH2)2
Ferrocene
0.51
0.32
[Fe(C5H4CH2OCOCH CH2)2] = 0.05 mmol) forms [3]rotaxane
6, having one ferrocenylene and two ferrocenyl groups in the axle
1
component, in 50% yield (Scheme 5). The 1H and 13C{ H} NMR
a Electrochemical potentials are obtained by cyclic voltammetry in MeCN
containing nBu4NPF6 as the electrolyte. Potentials are referenced to
spectra of 6 in CDCl3 indicate a symmetrical molecular structure.
Ag+/Ag. Sweep rate: 0.10 V s−1 b Two step redox behavior. c Redox peaks
.
of the Fe centers in the molecule are overlapped (see text).
compounds taken from the cyclic voltammograms are summarized
in Table 1. Fig. 5(a) shows the cyclic voltammogram of 3 in a
MeCN solution of nBu4NPF6 (0.10 M) with scan rate 0.10 V s−1.
A reversible redox peak pair of Fe(III)/Fe(II) of the ferrocenyl
group is observed at E1/2 = 0.47 V (vs. Ag+/Ag) which is similar
to 1a. The peak separation of 3, DE = Epa − Epc = 0.07 V,
however, is smaller than that of 1a (DE = 0.10 V). The cyclic
Scheme 4
=
Fig. 4 ORTEP plot of Fe(C5H4CH2OCOCH CH2)2 with 30% proba-
bility. Hydrogen atoms were omitted for clarity. Fe(1) lies on a crystallo-
graphic two fold axis. The asterisk in the atom labels indicates that these
atoms are at equivalent positions (−x, y, 1/2 − z).
The ferrocene-containing rotaxanes undergo reversible electro-
chemical oxidation and reduction. Electrochemical data for the
Fig. 5 Cyclic voltammograms of (a) 3 and (b) 4 in MeCN (1.0 mM)
containing 0.10 M nBu4NPF6.
Scheme 5
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voltammogram of 4 shows two reversible waves (Fig. 5(b)). The
peaks at higher potentials (Epa = 0.49 V, Epc = 0.43 V) are assigned
to the ferrocene unit close to the ammonium group. The neutral
rotaxane 5 shows a redox wave at a lower potential (E1/2 = 0.35 V)
than that of the cationic rotaxanes, 3, 4, and 6.29 6 shows an
apparent reversible redox due to overlapping of peaks of three Fe
centers. A linear relationship is observed between the peak currents
Ipa and Ipc and square root of scan rate below 0.25 V s−1 (Fig. 6).
Increase of the scan rate above 0.25 V s−1 causes quasi-reversible
behavior of the redox reactions.30
Syntheses
=
=
FcCH NCH2C6H4OCH2CH2CH CH2. A solution of fer-
rocenecarboxaldehyde (1.1 g, 5.0 mmol) and H2NCH2C6-
3
=
H4OCH2CH2CH CH2 (886 mg, 5.0 mmol) in toluene (100 cm )
was heated at 75 ◦C for 12 h in the presence of MS4A (molecular
˚
sieves 4 A, 1.0 g). After removal of MS4A, evaporation of the solu-
=
=
tion to dryness produced FcCH NCH2C6H4OCH2CH2CH CH2
as a brown solid which was washed with hexane (20 cm3) (1.37 g,
3.7 mmol, 74%). Anal. calc. for C22H23ONFe: C, 70.79; H, 6.21;
N, 3.75. Found: C, 70.82; H, 6.39; N, 3.66%. IR (KBr): m = 1636
−1
1
=
(C N) cm . H NMR (300 MHz, CDCl3, r. t.): d 2.52 (m, 2H,
OCH2CH2), 3.99 (t, 2H, OCH2, J = 7 Hz), 4.15 (s, 5H, C5H5),
4.35 (m, 2H, C5H4), 4.58 (s, 2H, NCH2), 4.66 (m, 2H, C5H4), 5.09
=
=
(dd, 1H, CH CH2, J = 10, 2 Hz), 5.15 (dd, 1H, CH CH2, J =
=
17, 2 Hz), 5.89 (ddt, 1H, CH CH2, J = 17, 10, 7 Hz), 6.87 (d, 2H,
C6H4, J = 8 Hz), 7.19 (d, 2H, C6H4, J = 8 Hz), 8.19 (s, 1H, NCH).
13C{ H} NMR (75.5 MHz, CDCl3, r. t.): d 33.6 (OCH2CH2), 64.4,
1
67.2, 68.6, 69.0 (C5H5), 70.4, 80.5 (C5H4), 114.6, 116.9, 129.0,
=
131.6, 134.5, 157.9, 161.7 (C N).
=
=
FcCH NCH2C6H4CH CH2. A solution of ferrocenecarbox-
aldehyde (3.6 g, 17 mmol) and p-vinylbenzylamine (2.2 g, 17 mmol)
in toluene (200 cm3) was heated at 60 ◦C for 28 h in the presence
of MS4A (4.5 g). After removal of MS4A, evaporation of the
Fig. 6 Scan rate dependence of Ipa and Ipc of the cyclic voltammograms
of 3 in MeCN (1.0 mM) containing 0.10 M nBu4NPF6.
=
=
solution to dryness produced FcCH NCH2C6H4CH CH2 as
a brown solid which was washed with hexane (50 cm3) (3.4 g,
10 mmol, 59%). Anal. calc. for C20H19NFe: C, 72.97; H, 5.82; N,
4.25. Found: C, 72.81; H, 5.70; N, 4.25%. IR (KBr): m = 1636
In summary, we have succeeded in employing Ru-catalyzed
cross-metathesis reactions of the terminal olefins (with acrylate
as the end-cap) of [2]pseudorotaxane to afford the rotaxane. The
electrochemical properties of the rotaxane with ferrocenyl groups
in the axle component are similar to that of the precursor without
the interlocked structure.
−1
1
=
(C N) cm . H NMR (300 MHz, CDCl3, r. t.): d 4.16 (s, 5H,
C5H5), 4.36 (m, 2H, C5H4), 4.63 (s, 2H, NCH2), 4.66 (m, 2H,
=
=
C5H4), 5.20 (d, 1H, CH CH2, J = 11 Hz), 5.72 (d, 1H, CH CH2,
J = 18 Hz), 6.69 (dd, 1H, CH, J = 18, 11 Hz), 7.25 (d, 2H, C6H4,
J = 8 Hz), 7.38 (d, 2H, C6H4, J = 8 Hz), 8.22 (s, 1H, NCH).
13C{ H} NMR (75.5 MHz, CDCl3, r. t.): d 64.5 (NCH2), 68.3
1
=
(C5H4), 68.8 (C5H5), 70.2 (C5H4), 80.2 (C5H4), 113.2 (CH CH2),
Experimental
=
126.0 (C6H4), 127.7 (C6H4), 135.9 (C6H4), 136.3 (CH CH2), 139.1
(C6H4), 161.8 (NCH). Assignment of these signals was supported
by 13C{ H}–1H COSY NMR spectroscopy.
General
1
Dried solvents were purchased from Kanto Chemical Co., Inc. p-
Butenoxybenzylamine,15 p-vinylbenzylamine,31 3,5-dimethylphe-
nyl acrylate,32 ferrocenylmethyl acrylate,33 and ferrocene dimetha-
nol34 were prepared by the literature method. Other chemicals were
=
=
[FcCH2NH2CH2C6H4OCH2CH2CH CH2](PF6) (1a). FcCH
=
NCH2C6H4OCH2CH2CH CH2 (1.1 g, 3.0 mmol) was dissolved in
MeOH (25 cm3) at room temperature. NaBH4 (894 mg, 24 mmol)
was added to the solution in one portion and the mixture was
stirred for 2 h at room temperature. Quenching the mixture with
4 M HCl(aq) (75 cm3) and further stirring for 30 min caused the
1
commercially available. NMR spectra (1H, 13C{ H}, 1H–1H COSY,
1
13C{ H}–1H COSY) were recorded on Varian MERCURY300
and JEOL EX-400 spectrometers. Chemical shifts were referenced
1
=
with respect to CHCl3 (d 7.24), CD2HCN (d 1.93) for H and
separation of [FcCH2NH2CH2C6H4OCH2CH2CH CH2]Cl as a
CDCl3 (d 77.0), CD3CN (d 1.30) for 13C as internal standards.
IR absorption spectra were recorded on Shimadzu FT/IR-8100
spectrometers. Cyclic voltammograms (CV) were measured in
CH3CN solution containing 0.10 M nBu4NPF6 using an ALS
Electrochemical Analyzer Model-600A. The measurements were
carried out in a standard one-compartment cell equipped with
a Ag+/Ag reference electrode, a platinum-wire counter electrode
and a platinum-disk working electrode (ID: 1.6 mm). The fast
atom bombardment mass spectra (FABMS) were obtained from
a JEOL JMS-700 (matrix, m-nitrobenzylalcohol) spectrometer.
Electrospray ionization mass spectrometry (ESIMS) was recorded
on a ThermoQuest Finnigan LCQ Duo. Elemental analyses were
carried out with a Yanaco MT-5 CHN autorecorder.
yellow solid from the solution. The solid product was washed
with Et2O (10 cm3 × 2) and dried under reduced pressure (1.1 g,
2.7 mmol, 90%). To an acetone (25 cm3) suspension of the obtained
=
[FcCH2NH2CH2C6H4OCH2CH2CH CH2]Cl (823 mg, 2.0 mmol)
was added NH4PF6 (1.7 g, 10 mmol) in acetone (25 cm3), and the
mixture was stirred for 2 h at room temperature. The precipitated
salt was removed by filtration. Evaporation of the filtrate gave 1a
as a yellow solid which was washed with water (10 cm3 × 5), and
then with Et2O (10 cm3 × 5), and dried under reduced pressure
(598 mg, 1.2 mmol, 60%). Anal. calc. for C22H23ONFe: C, 50.69;
H, 5.03; N, 2.69. Found: C, 50.69; H, 5.39; N, 2.78%. IR (KBr): m =
3260 (N–H), 3237 (N–H), 826 (P–F), 559 (P–F) cm−1. H NMR
1
(300 MHz, CD3CN, r. t.): d 2.50 (tddd, 2H, OCH2CH2, J = 7,
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7, 1, 1 Hz), 4.02 (s, 2H, NCH2), 4.04 (t, 2H, OCH2, J = 7 Hz),
overlapped with the signals of 1a and DB24C8. ESIMS: Calc. for
C46H58O9NFe: 824.3 Found: m/z = 824.1 [M − PF6]+.
4.04 (s, 2H, NCH2), 4.20 (s, 5H, C5H5), 4.27 (m, 2H, C5H4), 4.37
=
(m, 2H, C5H4), 5.08 (ddt, 1H, CH CH2, J = 10, 2, 1 Hz), 5.16
=
[(FcCH2NH2CH2C6H4CH CH2)(DB24C8)](PF6) (2b). An
=
=
(ddt, 1H, CH CH2, J = 17, 2, 1 Hz), 5.91 (ddt, 1H, CH CH2,
J = 17, 10, 7 Hz), 6.71 (brs, 2H, NH2), 6.95 (d, 2H, C6H4, J =
NMR tube was charged with 1b (3.3 mg, 6.9 × 10−3 mmol) and
DB24C8 (3.1 mg, 6.9 × 10−3 mmol) which were then dissolved
9 Hz), 7.33 (d, 2H, C6H4, J = 9 Hz). 13C{ H} NMR (100 MHz,
1
1
1
in CD3CN (0.7 cm3). H NMR showed the formation of 2b. H
NMR (300 MHz, CD3CN, 20 ◦C): d 3.59 (m, 8H, CH2-DB24C8),
3.79 (m, 8H, CH2-DB24C8), 3.93 (s, 5H, C5H5), 4.02–4.16 (m,
10H, C5H4, CH2-DB24C8), 4.18 (m, 2H, C5H4), 4.38 (m, 2H,
CD3CN, r. t.): d 34.2 (OCH2CH2), 48.5 (NCH2), 51.5 (NCH2),
68.2 (OCH2), 69.9 (C5H5), 70.5 (C5H4), 71.4 (C5H4), 76.5 (C5H4),
=
115.8 (C6H4), 117.3 (CH CH2), 123.3 (C6H4), 132.6 (C6H4), 135.7
=
(C6H4), 160.8 (CH CH2). The assignments were supported by
=
NCH2), 4.59 (m, 2H, NCH2), 5.22 (dd, 1H, CH CH2, J = 11,
13C{ H}–1H COSY NMR spectroscopy.
1
=
1 Hz), 5.67 (dd, 1H, CH CH2, J = 18, 1 Hz), 6.58 (dd, 1H,
=
=
[FcCH2NH2CH2C6H4CH CH2](PF6) (1b). FcCH NCH2-
=
CH CH2, J = 18, 11 Hz), 6.90 (m, 8H, C6H4-DB24C8), 7.14 (d,
=
C6H4CH CH2 (2.5 g, 7.6 mmol) was dissolved in MeOH
2H, C6H4, J = 8 Hz), 7.12–7.28 (br, 2H, NH2), 7.25 (d, 2H, C6H4,
J = 8 Hz). ESIMS: Calc. for C44H54O8NFe: 780.3 Found: 780.3
[M − PF6]+.
(200 cm3) at room temperature. NaBH4 (289 mg, 7.6 mmol) was
added to the solution and the mixture was stirred for 4 h at room
temperature. An extra portion of NaBH4 (290 mg, 7.6 mmol) was
added, and the mixture was stirred for a further 14 h, before being
treated with 4 M HCl(aq) (40 cm3) for 30 min. After reducing the
volume of the solution to ca. 100 cm3 by evaporation, the solid
product was partitioned between 2 M KOH(aq) (100 cm3) and
CH2Cl2 (100 cm3). The aqueous layer was separated and extracted
with CH2Cl2 (100 cm3). The combined organic extracts were
washed with water (200 cm3) and dried over MgSO4. Evaporation
Yellow crystals of 2b were obtained by recrystallization from a
CH2Cl2–Et2O solution of 1b–DB24C8 (1b–DB24C8 = 48 : 55 mg)
at room temperature (13% yield). Anal. calc. for C44H54O8NFePF6:
C, 57.09; H, 5.88; N, 1.51. Found: C, 57.18; H, 5.65; N, 1.46%. IR
(KBr): m = 3156 (N–H), 3085 (N–H), 840 (P–F) cm−1.
=
[(FcCH2NH2CH2C6H4OCH2CH2CH CHCOOC6H3-3,5-Me2)-
(DB24C8)](PF6) (3). 1a (52 mg, 0.10 mmol) was dissolved
in 2 cm3 of CH2Cl2 containing DB24C8 (54 mg, 0.12 mmol),
followed by addition of 3,5-dimethylphenyl acrylate (35 mg,
0.20 mmol) and Ru catalyst (4.2 mg, 5 × 10−3 mmol). The mixture
was refluxed for 15 h and the solvent was removed by evaporation
to form a brown oil. Reprecipitation of the crude product from
CH2Cl2–Et2O (2.5 : 30 cm3) gave a brown solid which was
collected, washed with Et2O (10 cm3 × 2) and dried under reduced
pressure to give 3 (80 mg, 0.072 mmol, 72%). Anal. calc. for
C55H66O11NF6FeP(H2O): C, 58.15; H, 6.03; N, 1.23. Found: C,
57.87; H, 6.12; N, 1.24%. IR (KBr): m = 3162 (N–H), 3073 (N–H),
=
of the solvent gave FcCH2NHCH2C6H4CH CH2 as a brown
oil (1.4 g, 4.3 mmol, 56%). A MeOH solution (40 cm3) of the
=
obtained FcCH2NHCH2C6H4CH CH2 (1.3 g, 4.0 mmol) was
treated with 4 M HCl(aq) (30 cm3) for 1 h at room temperature
to afford a yellow solid which was collected by filtration. To an
acetone (50 cm3) suspension of the solid was added NH4PF6
(3.4 g, 21 mmol) in acetone (100 cm3), and the mixture was
stirred for 1 h at room temperature. The precipitated salt was
removed by filtration and the evaporation of the filtrate gave 1b
as a yellow solid which was washed with water (20 cm3 × 10) and
then hexane (20 cm3 × 5), and dried in vacuo (1.5 g, 3.1 mmol,
78%). Anal. calc. for C20H22NFePF6: C, 50.34; H, 4.65; N, 2.94.
Found: C, 49.95; H, 4.72; N, 2.86%. IR (KBr): m = 3235 (N–H),
3260 (N–H), 847 (P–F) cm−1. 1H NMR (300 MHz, CD3CN, r. t.):
d 4.06 (s, 2H, NCH2), 4.10 (s, 2H, NCH2), 4.21 (s, 5H, C5H5), 4.28
−1
1
=
1734 (C O), 841 (P–F), 558 (P–F) cm . H NMR (300 MHz,
=
CDCl3, r. t.): d 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-axle, CH2-DB24C8), 4.60 (br, 2H, NCH2), 6.13 (d,
=
1H, C( O)CH, J = 15 Hz), 6.70–6.72 (4H, C6H4-axle, C6H3),
6.85 (s, 1H, C6H3), 6.88–6.97 (8H, C6H4-DB24C8), 7.23 (d, 1H,
=
(m, 2H, C5H4), 4.38 (m, 2H, C5H4), 5.33 (dd, 1H, CH CH2, J =
1
CH2CH), 7.34 (br, 2H, C6H4-axle), 7.35 (br, 2H, NH2). 13C{ H}
=
11, 1 Hz), 5.86 (dd, 1H, CH CH2, J = 18, 1 Hz), 6.77 (brs, 2H,
NMR (100 MHz, CDCl3, r. t.): d 21.3 (Me), 32.1 (CHCH2), 47.7
(NCH2), 51.6 (NCH2), 65.9 (OCH2-axle), 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,
NH2), 6.77 (dd, 1H, CH, J = 18, 11 Hz), 7.38 (m, 2H, C6H4), 7.51
(m, 2H, C6H4). 13C{ H} NMR (100 MHz, CD3CN, r. t.): d 48.9
1
(NCH2), 51.6 (NCH2), 70.0 (C5H5), 70.6 (C5H4), 71.5 (C5H4),
=
76.4 (C5H4), 116.2 (CH CH2), 127.7 (C6H4), 130.9 (C6H4), 131.4
=
131.0, 139.1, 147.0, 147.6, 150.5, 159.0, 164.8 (C O). C5H4-ipso
=
(C6H4), 136.9 (CH CH2), 139.9 (C6H4). Assignment of these
signals was supported by 13C{ H}–1H COSY NMR spectroscopy.
1
was not observed due to their low intensity. Assignment of these
1
1
signals was supported by H–1H and 13C{ H}–1H COSY NMR
spectroscopy. ESIMS: Calc. for C55H68O12NFe: 972.4. Found:
m/z = 972.5 [M − PF6]+.
=
[(FcCH2NH2CH2C6H4OCH2CH2CH CH2 )(DB24C8)](PF6 )
(2a). An NMR tube was charged with 1a (3.6 mg, 6.9 ×
10−3 mmol) and DB24C8 (3.1 mg, 6.9 × 10−3 mmol) which were
1
then dissolved in CD3CN (0.7 cm3). H NMR quickly showed
[(FcCH2NH2CH2C6H4OCH2CH2CH CHCOOCH2Fc)(DB24-
=
the formation of 2a. 1H NMR (300 MHz, CD3CN, 20 ◦C):
d 2.44 (tddd, 2H, OCH2CH2, J = 7, 7, 2, 2 Hz), 3.55–4.21 (30H,
C5H4, CH2-DB24C8, OCH2-axle), 3.93 (s, 5H, C5H5), 4.37 (m,
C8)](PF6) (4). 1a (52 mg, 0.10 mmol) and DB24C8 (54 mg,
0.12 mmol) was dissolved in 2 cm3 of CH2Cl2 followed by
addition of FcCH2OCOCHCH2 (54 mg, 0.20 mmol) and Ru
catalyst (4.2 mg, 5 × 10−3 mmol). The mixture was refluxed
for 15 h. Repeated recrystallization of the crude product from
CH2Cl2–Et2O gave 4 (42 mg, 0.035 mmol, 35%). Anal. calc. for
C58H68O11NFe2PF6(H2O): C, 56.64; H, 5.74; N, 1.14. Found: C,
56.80; H, 5.88; N, 1.18%. IR (KBr): m = 3166 (N–H), 3092 (N–H),
=
2H, NCH2), 4.50 (m, 2H, NCH2), 5.08† (1H, CH CH2, J =
=
10 Hz), 5.15 (ddt, 1H, CH CH2, J = 17, 2, 1 Hz), 5.89 (ddt, 1H,
=
CH CH2, J = 17, 10, 7 Hz), 6.55 (d, 2H, C6H4-axle, J = 9 Hz),
6.86–6.92† (8H, C6H4-DB24C8), 7.14 (brs, 2H, NH2), 7.17 (d,
2H, C6H4-axle, J = 9 Hz). Peaks with a dagger were significantly
2380 | Dalton Trans., 2007, 2376–2383
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Table 2 Crystallographic data and structural refinement details
=
=
=
FcCH NCH2C6H4OCH2CH2CH CH2
2b
Fe(C5H4CH2OCOCH CH2)2
Chemical formula
Molecular weight
Crystal system
Space group
C22H23FeNO
373.28
Monoclinic
P21 (no. 4)
19.257(3)
8.287(2)
5.8376(7)
95.48(1)
927.3(3)
C44H54F6FeNO8P
925.72
C18H18FeO4
354.18
Monoclinic
P21/a (no. 14)
38.521(4)
10.253(2)
11.378(1)
96.222(8)
4467(1)
Monoclinic
C2/c (no. 15)
22.261(5)
7.449(3)
11.557(3)
119.67(2)
1665.1(8)
4
˚
a/A
˚
b/A
˚
c/A
b/◦
V/A
Z
3
˚
2
4
F(000)
392.00
1.337
1936.00
1.376
736.00
0.921
Dc/g cm−1
Crystal size/mm
Unique reflections
Used reflections
No. of variables
R
0.30 × 0.20 × 0.15
0.60 × 0.30 × 0.20
0.20 × 0.15 × 0.10
2278
10267
1919
1894 [I ≥ 2.0r (I)]
250
0.074
3536 [I ≥ 3.0r (I)]
604
0.058
1439 [I ≥ 2.0r (I)]
114
0.039
Rw
0.107 [I ≥ 2.0r (I)]
0.091 [I ≥ 3.0r (I)]
0.055 [I ≥ 2.0r (I)]
Goodness of fit
Flack parameter
1.31
0.96
1.00
−0.1(2)
—
—
−1
1
=
=
1717 (C O), 841 (P–F), 558 (P–F) cm . H NMR (300 MHz,
Fe(C5H4CH2OCOCH CH2)2. To a solution of Fe(C5H4CH2-
OH)2 (246 mg, 1.0 mmol) and NEt3 (1.0 cm3) in CH2Cl2 (7.0 cm3)
was added acryloyl chloride (222 mg, 2.5 mmol) at 0 ◦C. After
stirring the mixture for 2 h at 0 ◦C, the insoluble solid was removed
by filtration. The solution was washed with an aqueous solution
of 0.1 M KOH and then with water, and dried over MgSO4.
The product was purified by chromatography on silica gel with
hexane–ethyl acetate (10 : 1) as eluent. The solvent was removed
=
CDCl3, r. t.): d 2.59 (m, 2H, CH2CH CH), 3.42–4.53 (42H, CH2-
DB24C8, C5H4, C5H5, OCH2C5H4), 3.93 (2H, OCH2CH2CH),
4.07 (2H, NCH2), 4.53 (2H, NCH2), 4.68 (2H, C5H4), 5.82 (d, 1H,
CH2CH, J = 16 Hz), 6.65 (d, 2H, C6H4, J = 8 Hz), 6.85–6.91
=
(9H, C6H4-DB24C8, C( O)H), 7.17 (brs, 2H, NH2), 7.27 (d,
2H, C6H4-axle, J = 8 Hz). Signals observed at 3.4–4.6 ppm
were overlapped significantly. Selected 13C{ H} NMR data
1
=
(100 MHz, CDCl3, r. t.): d 31.9 (CHCH2), 48.5 (NCH2), 51.7
(NCH2), 62.1, 62.2, 65.7 (OCH2), 68.4 (CH2-DB24C8), 70.3
(CH2-DB24C8), 70.8 (CH2-DB24C8), 112.8 (C6H4-DB24C8),
114.2 (C6H4-axle), 121.7, 122.6 (C6H4-DB24C8), 124.2, 130.7
at reduced pressure to give Fe(C5H4CH2OCOCH CH2)2 as a
yellow solid (87 mg, 0.25 mmol, 25%). Anal. calc. for C18H18O4Fe:
C, 61.04; H, 5.12. Found: C, 60.76; H, 4.92%. IR (KBr): m =
−1
1
=
1711 (C O) cm . H NMR (300 MHz, CDCl3, r. t.): d 4.19 (br,
=
(C6H4-axle), 144.7, 147.4, 158.8, 165.3 (C O). Some of the signals
4H, C5H4), 4.28 (br, 4H, C5H4), 4.93 (s, 4H, OCH2), 5.81 (dd,
=
=
due to the ferrocenyl groups were observed as a broad signal at
69–71 ppm. Assignment of these signals was supported by 1H–1H
1H, CH CH2, J = 10, 1 Hz), 6.09 (dd, 1H, CH CH2, J = 17,
10 Hz), 6.40 (dd, 2H, CH CH2, J = 17, 1 Hz). 13C{ H} NMR
1
=
and 13C{ H}–1H COSY NMR spectroscopy. ESIMS: Calc. for
(75.5 MHz, CDCl3, r. t.): d 62.4 (CH2), 69.3 (C5H4), 70.0 (C5H4),
1
C58H68O11NFe2: 1066.3 Found: m/z = 1066.5 [M − PF6]+.
81.9 (C5H4), 128.3, 130.9, 165.9 (C O). Fig. 4 shows the molecular
structure of Fe(C5H4CH2OCOCH CH2)2 determined by X-ray
=
=
crystallography.
=
[(FcCH2N(OAc)CH2C6H4OCH2CH2CH CHCOOC6H3 -3,5-
Me2)(DB24C8)] (5). To a solution of rotaxane 3 (112 mg,
0.10 mmol) in MeCN (4.0 cm3) were added triethylamine (70 lL,
0.50 mmol) and acetic anhydride (47 lL, 0.50 mmol), and the
reaction mixture was allowed to stand at room temperature for
26 h. The reaction mixture was diluted by CH2Cl2 (4.0 cm3),
washed with water (5.0 cm3 × 3), dried over MgSO4, filtered,
and evaporated. The crude product was purified by preparative
HPLC to give 5 (98 mg, 0.091 mmol, 91%). IR (KBr): m = 1728
=
[{(FcCH2NH2CH2C6H4OCH2CH2CH CHCOOCH2C5H4 )2 -
Fe}(DB24C8)2](PF6)2 (6). 1a (52 mg, 0.10 mmol) and DB24C8
(63 mg, 0.14 mmol) was dissolved in CH2Cl2 (2.0 cm3), followed by
addition of Fe(C5H4CH2COOCHCH2)2 (18 mg, 0.051 mmol) and
Ru catalyst (8.5 mg, 1 × 10−2 mmol). The mixture was refluxed
for 12 h and the solvent was removed by evaporation to form
a brown oil. Purification of the crude product by preparative
HPLC gave 6 (56 mg, 0.025 mmol, 50%). IR (KBr): m = 3164
−1
1
=
(C O) cm . H NMR (300 MHz, CDCl3, r. t.): d 2.03 (s, 2H,
COMe), 2.22 (s, 1H, COMe), 2.27 (s, 6H, C6H3(CH3)2), 3.13 (m,
2H, OCH2CH2-axle), 3.52–3.67 (8H, CH2-DB24C8), 3.74–3.94
(8H, CH2-DB24C8), 4.05–4.41 (23H, CH2-DB24C8, OCH2CH2-
−1
1
=
(N–H), 3081 (N–H), 1717 (C O), 843 (P–F), 558 (P–F) cm . H
NMR (300 MHz, CDCl3, r. t.): d 2.61 (m, 4H, CH2CH), 3.40–
3.61 (16H, CH2-DB24C8), 3.67–3.84 (16H, CH2-DB24C8), 3.82
(s, 10H, C5H5), 3.94 (t, 4H, CH2CH2CH, J = 6 Hz), 3.99–4.19
(32H, CH2-DB24C8, NCH2, C5H4), 4.25 (m, 4H, C5H4), 4.52 (m,
=
axle, C5H4, C5H5, NCH2), 6.38 (d, 1H, C( O)CH, J = 16 Hz), 6.60
(s, 2H, ortho-C6H3), 6.66–6.90 (13H, C6H4-DB24C8, para-C6H3,
C6H4-axle), 7.71 (dt, 1H, CH2CH, J = 16, 7 Hz). HRFABMS:
Anal. calc. for C57H67NO12Fe: 1013.4014. Found: m/z = 1013.3987
[M]+.
=
4H, NCH2), 4.91 (s, 4H, OCH2C5H4), 5.91 (d, 2H, C( O)H, J =
16 Hz), 6.64 (d, 4H, C6H4-axle, J = 8 Hz), 6.82–6.91 (16H, C6H4-
DB24C8), 7.02 (dt, 2H, CH2CH, J = 16, 7 Hz), 7.13 (br, 4H,
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NH2), 7.23–7.26† (4H, C6H4-axle). The peak with a dagger was
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Tokunaga, S. Kakuchi, K. Akasaka, N. Nishikawa, Y. Shimomura, K.
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10 Y. Suzaki and K. Osakada, Chem.–Asian J., 2006, 1, 331.
11 J. S. Hannam, T. J. Kidd, D. A. Leigh and A. J. Wilson, Org. Lett., 2003,
5, 1907; R. G. E. Coumans and J. A. A. W. Elemans, Angew. Chem.,
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and J. F. Stoddart, J. Am. Chem. Soc., 2004, 126, 9884.
12 J. A. Wisner, P. D. Beer, M. G. B. Drew and M. R. Sambrook, J. Am.
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691, 5260.
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15 X.-Z. Zhu and F.-C. Chen, J. Am. Chem. Soc., 2005, 127, 13158.
16 O. Molokanova, M. O. Vysotsky, Y. Cao, I. Thondorf and V. Bo¨hmer,
Angew. Chem., Int. Ed., 2006, 45, 8051; A. Bogdan, Y. Rudzevich, M. O.
Vysotsky and V. Bo¨hmer, Chem. Commun., 2006, 2941.
17 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34, 18; R. H.
Grubbs, T. M. Trnka and M. S. Sanford, Transition Metal–Carbene
Complexes in Olefin Metathesis and Related Reactions, in Current
Methods in Inorganic Chemistry, ed. H. Kurosawa and A. Yamamoto,
Elsevier, Amsterdam, 2002, vol. 3, ch. 4.
1
overlapping significantly with the signal of the solvent. 13C{ H}
NMR (100 MHz, CDCl3, r. t.): d 31.9 (CH2CH), 48.6 (NCH2),
51.6 (NCH2), 62.3 (OCH2C5H4), 65.8 (CH2CH2CH), 68.3 (CH2-
DB24C8), 68.8 (C5H5), 69.3 (C5H4), 69.4 (C5H4), 69.9 (C5H4),
70.0 (C5H4), 70.3 (CH2-DB24C8), 70.7 (CH2-DB24C8), 76.3
(C5H4), 82.3 (C5H4), 112.8 (C6H4-DB24C8), 114.3 (C6H4-axle),
=
121.7 (C6H4-DB24C8), 123.0 (C( O)CH), 124.2 (C6H4-axle),
130.8 (C6H4-axle), 145.4 (CH2CH), 147.6 (C6H4-DB24C8-ipso),
=
158.9 (C6H4-axle), 165.9 (C O). Assignment of these signals was
1
supported by 1H–1H and 13C{ H}–1H COSY NMR spectroscopy.
ESIMS: Calc. for C106H126N2O22Fe3: 1946.7 Found: m/z = 974.0
[M − 2(PF6)]2+.
Crystal structure determination
=
=
Crystals of FcCH NCH2C6H4OCH2CH2CH CH2, 2b, and
=
Fe(C5H4CH2OCOCH CH2)2 suitable for X-ray diffraction study
were obtained by recrystallization from Et2O, CH2Cl2–Et2O, and
CH2Cl2–Et2O respectively and mounted on a glass capillary tube.
All measurements were made on a Rigaku AFC7R diffractometer
with graphite monochromated Mo-Ka radiation and a rotating
anode generator. The data were collected using the x scan
technique to a maximum 2h value of 55.0◦. Calculations were
carried out by using a program package CrystalStructureTM for
Windows.35 Crystal data for the compounds are summarized in
Table 2.
Details of the structure of 2b (CCDC reference number 292617)
have already been published23 and the details of the structure of
2b are in the CCDC as REFCODE WECVUW.
=
CCDC reference numbers 637664 (FcCH NCH2C6H4O-
=
=
CH2CH2CH CH2) and 637665 (Fe(C5H4CH2OCOCH CH2)2).
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b702785k
18 A. K. Chatterjee, T.-L. Choi, D. P. Sanders and R. H. Grubbs, J. Am.
Chem. Soc., 2003, 125, 11360; A. K. Chatterjee, J. P. Morgan, M. Scholl
and R. H. Grubbs, J. Am. Chem. Soc., 2000, 122, 3783.
Acknowledgements
19 M. Horie, Y. Suzaki and K. Osakada, J. Am. Chem. Soc., 2004, 126,
3684; M. Horie, Y. Suzaki and K. Osakada, Inorg. Chem., 2005, 44,
5844.
20 Molecular Devices and Machines, A Journey into the Nanoworld, ed.
V. Balzani, M. Venturi and A. Credi, Wiley-VCH, Weinheim, 2003; V.
Balzani, A. Credi, F. M. Raymo and J. F. Stoddart, Angew. Chem., Int.
Ed., 2000, 39, 3348; special issue on molecular machines: P. F. Barbara,
Acc. Chem. Res., 2001, 34, 409.
This work was supported by Grants-in-Aid for Scientific Research
from the Ministry of Education, Science, Sports, and Culture,
Japan and by a 21st Century COE Program “Creation of
Molecular Diversity and Development of Functionalities”. We are
grateful to Professor Munetaka Akita of our institute for ESIMS
measurements.
21 Ferrocenes, ed. A. Togni and T. Hayashi, VCH, New York, 1995.
22 Examples of ferrocene containing rotaxanes: R. Isnin and A. E. Kaifer,
J. Am. Chem. Soc., 1991, 113, 8188; A. C. Benniston and A. Harriman,
Angew. Chem., Int. Ed. Engl., 1993, 32, 1459; L. A. God´ınez, S. Patel,
C. M. Criss and A. E. Kaifer, J. Phys. Chem., 1995, 99, 17449; V.
Balzani, J. Becher, A. Credi, M. B. Nielsen, F. M. Raymo, J. F.
Stoddart, A. M. Talarico and M. Venturi, J. Org. Chem., 2000, 65,
1947; N. Kihara, M. Hashimoto and T. Takata, Org. Lett., 2004, 6,
1693.
Notes and references
1 G. Schill, Catenanes, Rotaxanes, and Knots, Organic Chemistry, Aca-
demic Press, New York, 1971, vol. 22; Molecular Catenanes, Rotaxanes
and Knots, ed. J.-P. Sauvage and C. Dietrich-Buchecker, Wiley-VCH,
Weinheim, 1999.
2 D. B. Amabilino and J. F. Stoddart, Chem. Rev., 1995, 95, 2725; R.
Ja¨ger and F. Vo¨gtle, Angew. Chem., Int. Ed. Engl., 1997, 36, 930;
S. A. Nepogodiev and J. F. Stoddart, Chem. Rev., 1998, 98, 1959; J.-C.
Chambron and J.-P. Sauvage, Chem.–Eur. J., 1998, 4, 1362; T. J. Hubin
and D. H. Busch, Coord. Chem. Rev., 2000, 200–202, 5; T. Takata and
N. Kihara, Rev. Heteroat. Chem., 2000, 22, 197; K. Kim, Chem. Soc.
Rev., 2002, 31, 96; J.-P. Collin and J.-P. Sauvage, Chem. Lett., 2005, 34,
742; K. Osakada, T. Sakano, M. Horie and Y. Suzaki, Coord. Chem.
Rev., 2006, 250, 1012.
23 Y. Suzaki and K. Osakada, Chem. Lett., 2006, 35, 374.
24 Association constants of the reactions in Scheme 2 were estimated
as Ka-app = [2a][1a]−1[DB24C8]−1 = 4.9 × 102 M−1 and Kb-app
=
[2b][1b]−1[DB24C8]−1 = 3.1 × 102 M−1 in CD3CN at 293 K, respectively,
by a single point method (reference 25). See also reference 26 which
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