Rotaxanes of a macrocyclic ferrocenophane with dialkylammonium axle components

Article abstract of DOI:10.1039/b907417a

Octaoxa[22]ferrocenophane, 1, was synthesized and employed as the macrocyclic component of [2]rotaxanes. [2]Pseudorotaxanes composed of macrocyclic molecule 1 and dialkylammonium derivatives with a terminal vinyl group undergo end-capping via cross-metathesis of the terminal group with bulky acrylates. The [2]rotaxanes of 1 with axle components having bulky terminal groups, such as 3,5-dimethylphenyl, 9-anthryl, and ferrocenyl groups, maintain an interlocked structure in CDCl₃ solution, but they are gradually converted into a mixture of the individual components via dethreading of the end groups in polar solvents such as CD₃CN and dmso-d₆. The reaction rate varies depending on the end group and solvent. The cationic rotaxane with an anthryl end group of the axle component, [(1){AnCH ₂NH₂CH₂C₆H₄-4-OCH ₂CH₂CHCHCOOC₆H₄-4-C(C ₆H₄-4-tBu)₃}](BAr_F) (An = 9-anthryl, BAr_F = B{C₆H₃-3,5-(CF₃) ₂}₄) shows weak emission upon excitation of the anthryl group (12b, λ_em = 419 nm, quantum yield, = 0.012). The quantum yield is lower than that of the neutral rotaxane 13b ( = 0.030) formed by N-acetylation of 12b and a physical mixture of the corresponding free axle molecule, AnCH₂N(Ac)CH₂C₆H₄-4- OCH₂CH₂CHCHCOOC₆H₄-4-C(C ₆H₄-4-tBu)₃ (8), and 1 ( = 0.34). The efficiency of the quenching caused by the ferrocenylene group caused by energy transfer is affected significantly by the relative positions of the anthryl and ferrocenylene groups in the rotaxane. The rotaxane with axles having a secondary ammonium moiety has a redox potential E_1/2 = -0.03-0.02 V (vs. Ag⁺/Ag), which is lower those of than compound 1 (E_1/2 = -0.10 V) and the neutral [2]rotaxanes with the N-acetylated axle components (E_1/2 = -0.11 and -0.22 V). The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b907417a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Rotaxanes of a macrocyclic ferrocenophane with dialkylammonium
axle components†
Yuji Suzaki, Eriko Chihara, Atsuko Takagi and Kohtaro Osakada*
Received 15th April 2009, Accepted 9th September 2009
First published as an Advance Article on the web 6th October 2009
DOI: 10.1039/b907417a
Octaoxa[22]ferrocenophane, 1, was synthesized and employed as the macrocyclic component of
[2]rotaxanes. [2]Pseudorotaxanes composed of macrocyclic molecule 1 and dialkylammonium
derivatives with a terminal vinyl group undergo end-capping via cross-metathesis of the terminal group
with bulky acrylates. The [2]rotaxanes of 1 with axle components having bulky terminal groups, such as
3,5-dimethylphenyl, 9-anthryl, and ferrocenyl groups, maintain an interlocked structure in CDCl3
solution, but they are gradually converted into a mixture of the individual components via dethreading
of the end groups in polar solvents such as CD3CN and dmso-d6. The reaction rate varies depending on
the end group and solvent. The cationic rotaxane with an anthryl end group of the axle component,
=
[(1){AnCH2NH2CH2C6H4-4-OCH2CH2CH CHCOOC6H4-4-C(C6H4-4-tBu)3}](BArF) (An =
9-anthryl, BArF = B{C6H3-3,5-(CF3)2}4) shows weak emission upon excitation of the anthryl group
(12b, lem = 419 nm, quantum yield, f = 0.012). The quantum yield is lower than that of the neutral
rotaxane 13b (f = 0.030) formed by N-acetylation of 12b and a physical mixture of the corresponding
=
free axle molecule, AnCH2N(Ac)CH2C6H4-4-OCH2CH2CH CHCOOC6H4-4-C(C6H4-4-tBu)3 (8), and
1 (f = 0.34). The efficiency of the quenching caused by the ferrocenylene group caused by energy
transfer is affected significantly by the relative positions of the anthryl and ferrocenylene groups in the
rotaxane. The rotaxane with axles having a secondary ammonium moiety has a redox potential E1/2
=
-0.03–0.02 V (vs. Ag+/Ag), which is lower those of than compound 1 (E1/2 = -0.10 V) and the neutral
[2]rotaxanes with the N-acetylated axle components (E1/2 = -0.11 and -0.22 V).
The Fe(II)/Fe(III) redox of the ferrocenyl group in the axle
Introduction
component of the rotaxanes is affected by the structures and
relative positions of the axle and cyclic components.7,10,11 Recently,
we prepared a pseudorotaxane having an axle component with
a terminal ferrocenyl group12,13 and found a structures14 and
chemical properties.15 Rotaxanes with ferrocene-containing cyclic
components are still rare. Willner,16 Beer,17 and Prato18 reported
rotaxanes with ferrocenyl pendant groups in the macrocyclic
component. Ferrocenophanes,19-21 which contain a ferrocenylene
group as a part of the macrocycle, have not been employed as
components of rotaxanes. In this paper, we report the preparation
of octaoxa[22]ferrocenophane 1 (Chart 1), having a similar
structure to DB24C8, and its rotaxanes with the axle molecule
containing a dialkylammonium moiety. The rotaxanes exhibit
unique chemical and photochemical properties.
Rotaxane, composed of interlocked cyclic and axle components,
allows individual motion of the component molecules with
restrictions on the direction and degree of the movement in the
interlocked structure.1 The design of the functional groups in
either or both of the components enables changes in relative
positions of the component molecules of the rotaxane upon
chemical transformation. Typically, a chemical reaction of the
functional group in the axle component induces a change in
the interaction between the components and causes shifts of the
macrocyclic component along the axle molecule.2 This unique
stimulus-response behaviour of the functionalized rotaxanes is
applied to molecular shuttles,3 molecular muscles,4 molecular
bulbs,5 and the transportation of a droplet on a solid surface
covered with rotaxanes.6
The ferrocenyl group is employed as a terminal blocking
group of the axle component of many rotaxanes. [24]Crown-8-
ethers,7,8 cyclodextrins,9,10 and viologens11 were reported to form
rotaxanes with the axle molecules containing ferrocenyl stoppers.
Chemical Resources Laboratory R1-3, Tokyo Institute of Technol-
ogy, 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
† Electronic supplementary information (ESI) available: Experimental
section including characterization data for compounds. CCDC reference
number 724381. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b907417a
Chart 1
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Results and discussion
Synthesis and dethreading reaction of rotaxanes
Scheme
1 summarizes the procedure for preparation of
octaoxa[22]ferrocenenophane 1. Tosylation of Fe{C5H4-
(OCH2CH2)3OH}2 and cyclizative condensation of the resultant
Fe{C5H4(OCH2CH2)3OTs}2 (Ts
=
SO2C6H4-4-Me) with o-
catechol under dilute conditions ([Fe{C5H4(OCH2CH2)3-
OTs}2]0 = [o-catechol]0 = 5 mM) yield 1 in high isolated yield.
Compound 1 was characterized by 1H and 13C{ H} NMR
1
spectroscopy and comparison of the data with oxa[n]ferroceno-
phanes (n = 4, 7, 10, 13, 16) and related ferrocenylene derivatives.22
1
13C{ H} NMR signals due to the CH carbons of the ferrocenylene
group are observed at d 56.1 and 62.1, and the quaternary
carbon signal at d 127.6 is broadened. Slow evaporation of an
acetone/methanol solution of 1 and KBPh4 caused separation
of [K(1)]BPh4 as single crystals, which were analyzed by X-ray
crystallography. Fig. 1 shows the molecular structure of the
cationic part of [K(1)]BPh4 obtained by X-ray crystallography.
The distance between K(1) and oxygen atoms of 1 (O(1)–O(8))
Chart 2
1
=
4-OCH2CH2CH CH2](BArF) (R = C6H4-4-OC6H4-4-C(C6H4-
˚
is in the range of 2.736(2)–2.927(2) A. The two cyclopentadienyl
4-tBu)3 (2), An (3), Fc (4)) (An
=
9-anthryl, Fc
=
ligands are in eclipsed positions. The dihedral angle between
Fe(C5H4)(C5H5), BArF
=
B{C6H3-3,5-(CF3)2}4). [(C6H3-3,5-
C(5)–O(1) and C(25)–O(8) bonds is 45◦.
=
Me2)CH2NH2CH2C6H4-4-OCH2CH2CH CH2](BArF) (5) was
=
prepared from NH2CH2C6H4-4-OCH2CH2CH CH2 and (C6H3-
3,5-Me2)COCl.7 Compounds
7
and
8
with amide groups
were also prepared to compare their properties with those
of the rotaxanes containing neutral molecules as the axle
components (vide infra). N-acetylation of [AnCH2NH2CH2C6H4-
=
4-OCH2CH2CH CH2](Cl), followed by cross-metathesis
reaction23 of the vinyl group of AnCH2N(Ac)CH2C6H4-
=
4-OCH2CH2CH CH2 (6) with aryl acrylate catalyzed by
=
(H2IMes)(PCy3)Cl2Ru CHPh (H2IMes = N,N-bis(mesityl)-4,5-
dihydroimidazol-2-ylidene) led to the amide derivatives.
Dissolution of 1 and 3 in CDCl3 forms an equilibrated mixture
of 1, 3, and their [2]pseudorotaxane 10, as shown in Scheme 2. Fast
atom bombardment mass spectrometry (FABMS) reveals a peak at
m/z = 924, which corresponds to the cationic [2]pseudorotaxane.
The 1H NMR spectrum of the CDCl3 solution formed by mixing 1
and 3 at a concentration of 5 mM for each compound contains the
signals of the alkylammonium group of 10 at d 5.08–5.24 (NCH2),
5.64 (NCH2), and 7.09 (NH2). The signals of 3 (d 4.33 (NCH2), 5.27
(NCH2), 6.89 (NH2)) were almost negligible. [2]Pseudorotaxane 11
was formed from 1 and [NH2(CH2Ph)2](BArF) (9) in CDCl3 and
showed a FABMS peak at the predicted position (m/z = 754).
Scheme 1 Synthesis of 1.
-
Fig. 1 Molecular structure of [K(1)]BPh4. Hydrogen atoms and BPh4
have been omitted for clarity.
Chart 2 lists the compounds used as the axle components.
Condensation of a primary amine with an aromatic aldehyde
and further reduction of the imine produced with NaBH4
(or LiAlH4) form the dialkylamine with a bulky terminal
group. Protonation of the amines produces the corresponding
secondary dialkylammonium compounds [R1CH2NH2CH2C6H4-
Scheme 2 Pseudorotaxane formation.
Scheme 3 shows a summary of the preparation of the
[2]rotaxanes of 1 and DB24C8 with the dialkylammonium
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Table 1 Structure and yield of rotaxanes 12a–12i
Compound
Isolated yield
88%
12a
12b
12c
12d
12e
12f
65%
42%
64%
50%
44%
Scheme 3 Synthesis of [2]rotaxanes. See Table 1 for structures of 12a–12i.
12g
12h
12i
53%
52%
88%
group and conversion of the cationic [2]rotaxanes into the
neutral ones via acetylation of the axle component. The Ru-
carbene-complex-catalyzed cross-metathesis reaction of 2 with
=
CH2 CHCOOC6H4-4-C(C6H4-4-tBu)3 in the presence of 1 (1 =
=
0.11 mmol, 2 = 0.10 mmol, CH2 CHCOOC6H4-4-C(C6H4-4-
tBu)3 = 0.20 mmol) forms [2]rotaxane [(1)(R1CH2NH2CH2C6H4-
2
1
=
4-OCH2CH2CH CHCOOR )](BArF) (R = C6H4-4-OC6H4-4-
C(C6H4-4-tBu)3, R2 = C6H4-4-C(C6H4-4-tBu)3) (12a) in 88%
isolated yield. The FABMS peak (m/z = 1858) agrees with the
1
molecular weight of the rotaxane. The H NMR signals of the
vinylene hydrogen atoms of the axle component show a large
coupling constant (J(HH) = 16 Hz), indicating the selective
formation of the selective formation of the trans linkage by
1
cross-metathesis. The H NMR signals of the NCH2 hydrogen
atoms were observed at a lower magnetic field (d 4.51–4.58)
than those of 2 (d 4.04, 4.06), which is ascribed to the
C–H ◊ ◊ ◊ O hydrogen bonds between the axle and the macrocyclic
component.24 Cyclopentadienyl ligands of the cyclic component
formation and end-capping of the terminal vinyl group via cross-
metathesis produce [2]rotaxanes 12b–12i in 42–88% isolated yields,
as summarized in Table 1.
Acetylation of the ammonium groups of 12a, 12b, and 12c with
Ac2O in MeCN forms neutral rotaxanes 13a (38%), 13b (81%),
and 13c (84%), respectively (Scheme 3).25 The IR peaks of 13a at
1653 cm-1 and of 13b at 1651 cm-1 are assigned to vibration of the
1
show four independent 13C{ H} NMR signals for the CH carbons
with equal intensity (d 56.1, 56.4, 62.8, 62.8). This result provides
additional evidence for formation of a rotaxane that contains 1 as
the cyclic component. Similar reactions involving pseudorotaxane
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amide groups. The 1H NMR spectrum of 13b shows the signals of
the vinylene hydrogen atoms (d 6.43, 7.63) at lower magnetic field
positions than those of 12b (d 6.18, 7.24–7.28), which is ascribed
to shuttling of the macrocyclic component of 13a–13c along the
axle component. A similar reaction using rotaxane 12d does not
give 13d but yields a mixture of 1 and 7 in 84 and 86% yields,
respectively .
Rotaxanes 12a–12i and 13a–13c maintain the interlocked
structures in CDCl3 at room temperature, but dissolution of 12b,
12d, and 12e in polar solvents (dmso-d6, CD3CN) or heating the
solution in these solvents causes dethreading, as shown in eqn
(1). Dissolving 12b in CD3CN or dmso-d6 at 25 ◦C converts
the rotaxane gradually into a mixture of the cyclic compound
1 and the dialkylammonium compound [AnCH2NH2CH2C6H4-
Fig. 2 (A) Profile and (B) first-order plots of the dethreading reaction
of 12d in (a) CD3CN (45 ◦C), (b) CD3CN (60 ◦C), (c) CD3CN (70 ◦C),
(d) CD3CN (75 ◦C), and (e) dmso-d6 (20 ◦C).
=
4-OCH2CH2CH CHCOOC6H4-4-C(C6H4-4-tBu)3](BArF) (14).
◦
The dethreading of 12d in dmso-d6 takes place rapidly at 20 C,
and the 1H NMR and FABMS spectra after the reaction indicate
quantitative formation of 1 and 15. This behaviour is contrasted
with that of 12g, composed of the same axle component and
DB24C8, which does not undergo dethreading, probably due to
the smaller cavity size and the less flexible structure of DB24C8
compared with 1. Fig. 2 shows profile and first-order plots of the
dethreading reaction of 12d. The reaction in dmso-d6 is completed
within 12 min at 20 ◦C (kobs = 4.9(5) ¥ 10-3 s-1), while heating the
CD3CN solution of 12d causes dethreading at lower rates (kobs
=
1.0(1)◦¥ 10-5 s-1 at 45 ◦C, 3.5(3) ¥ 10-5 s-1 at 60 ◦C, 8.9(4) ¥ 10-5 s-1
at 70 C and 1.9(3) ¥ 10-4 s-1 at 75 ◦C). Kinetic parameters of the
reaction in CD3CN were determined as DG‡(318 K) = 1.1(1) ¥
102 kJ mol-1, DH‡ = 79(5) kJ mol-1, and DS‡ = -91(14) J mol-1 K-1
Fig. 3 (A) Profile and (B) first-order plots of the dethreading reaction of
12e in (a) CD3CN (25 ◦C), (b) dmso-d6 (25 ◦C), (c) dmso-d6 (35 ◦C) and
(d) dmso-d6 (45 ◦C).
from the temperature dependence of kobs
.
12e: 72(1) kJ mol-1 in dmso-d6) are smaller than those of the
dethreading reaction of the rotaxane composed of DB24C8 and
the axle molecule with tBu end groups (DH‡ = 85–100 kJ mol-1,
DS‡ = -9 to -79 J mol-1K-1). The large negative activation
enthalpy for the latter reaction was ascribed to the less favorable
conformational change during the slippage of DB24C8 over the
end groups.26
Table 2 shows a summary of the results of the kinetic study
of the reactions. Dethreading reactions of 12a and 13a are not
observed in CD3CN or in dmso-d6 during 4 d at 25 ◦C, probably
because of the sterically bulky C(C6H4-4-tBu)3 end groups of the
axle components. Rotaxane 12b undergoes dethreading in both
solvents but more slowly than 12d and 12e. The dethreading of
13b, having the same end group as 12b, does not occur at all at
25 ◦C and requires heating for 20 h at 60 ◦C, although interaction
between the two components of 13b is weaker than the hydrogen
bonding between the axle and cyclic components of 12b.
(1)
A plausible mechanism of the dethreading reaction is shown
in Scheme 4. Initial activation of hydrogen bonds between oxygen
atoms in the cyclic component and NH2+ and CH2 hydrogen atoms
in the axle and sliding of the macrocycle to a neutral part of the axle
component form an intermediate. It is enhanced by coordination
The dethreading reaction of 12e in dmso-d6 (kobs = 2.7(2) ¥
10-5 s-1 at 25 ◦C) is much slower than that of 12d (kobs = 4.9(5) ¥
10-3 s-1 at 20 ◦C), and complete consumption of the rotaxane
requires 4 h even at 45 ◦C (kobs = 1.9(1) ¥ 10-4 s-1), as shown
in Fig. 3. Kinetic parameters of the reaction were determined as
DG‡(318 K) = 1.0(1) ¥ 102 kJ mol-1, DH‡ = 72(1) kJ mol-1, and
DS‡ = -90(2) J mol-1K-1 in dmso-d6. The dethreading reaction in
+
of the polar solvent molecules to the NH2 group. Subsequent
slippage of the macrocyclic component over R1 or R2 end group
leads to the dethreading. Dissolving the rotaxanes 12b, 12d, and
12e in dmso-d6 or in CD3CN does not show the 1H NMR signals
assigned to the intermediate rotaxanes for dethreading, which
indicates a pre-equilibration involving coordination of solvent to
◦
CD3CN (kobs = 3.9(7) ¥ 10-6 s-1 at 45 C) is slower than that in
dmso-d6. Observed DH‡ values (12d: 79(5) kJ mol-1 in CD3CN,
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CD3CN (DG‡(318 K) = 1.1(1) ¥ 102 kJ mol-1, DH‡ = 79(5) kJ mol-1,
and DS‡ = -91(14) J mol-1K-1) suggests a similar transition state
for dethreading in this study.
Table 2 Kinetic rate constants, kobs, of the dethreading reaction of
rotaxanesa
Compound
12a
Solvent
T/◦C
k
obs/s-1
b
b
Photochemical and electrochemical properties
CD3CN
dmso-d6
CD3CN
dmso-d6
CD3CN
dmso-d6
CD3CN
dmso-d6
dmso-d6
dmso-d6
25
25
25
25
45
20
45
25
25
25
25
25
25
25
c
12b
1.3(3) ¥ 10-7
4.3(2) ¥ 10-6
1.0(1) ¥ 10-5
4.9(5) ¥ 10-3
3.9(7) ¥ 10-6
Fluorescence resonance energy transfer (FRET) was reported for
the organic rotaxanes containing cumarines, naphthalenes, and
anthracenes because of close contact of the fluorescent group
in one component with the functional group with lower energy
orbitals in the other within the rotaxane framework.27–29 Combi-
nation of the energy transfer in the rotaxane with the molecular
shuttling was applied to clear switching for the fluorescence.28,29
Typically, a Ru(bpy)3 unit in the axle component of a rotax-
ane changes its optical properties depending on the distance
from the functional groups in the cyclic component. Ferrocene
derivatives act as a fluorescent quencher of photoexcited organic
species,30 and they serve as the electron acceptor from viologen,11
bis(phenanthroline)copper,31 and the photoexcited state of C60
within the rotaxane framework.8,18 We conducted TD-DFT cal-
culations of the triplet energy level of [AnCH2NH2CH2Ph]+ and
AnCH2N(Ac)CH2Ph, respective model compounds of 2 and 8, to
elucidate details of interaction between the functional groups in
the rotaxanes in Table 1. The energies between the orbitals, 14 300
and 14 100 cm-1, are consistent with the energy transfer reaction
rather than the electron transfer (vide infra). Table 3 shows sum-
mary of the absorption and fluorescent properties of the rotaxanes
and the component molecules. The rotaxanes 12b–12i, 13b and
13c, and the axle compounds and their precursors 3 and 6–8 show
the characteristic absorption due to the 9-anthryl terminal group
at lmax = 366–372 nm with molar absorption coefficient of e =
6900–13 200 M-1cm-1. Excitation at respective lmax(absorption),
corresponding to p–p* transitions of the anthryl group, causes
emission at wavelength lower than 400 nm. Compound 1 shows
weak absorption due to ferrocene at lmax = 437 nm and is not
12d
12e
2.7(2) ¥ 10-5
b
12g
12i
13a
b
CD3CNc
c
b
b
dmso-d6
CD3CNc
dmso-d6
b,d
b,e
13b
a [Compound]0 = 5.0 mM. b Dethreading is not observed (1H NMR
spectrum of rotaxane solution does not change for 4 d). c A part of the
rotaxane remains undissolved. d Complete dethreading was observed after
heating for 8 h at 60 ◦C. e Complete dethreading was observed after heating
for 20 h at 60 ◦C.
Table 3 Photochemical data on compounds
Absorptiona
max/nm
Emissionb
max/nm
c
Compound
l
e/M-1cm-1
l
f
1
437d
371
368
368
368
372
373
372
366
367
372
366
366
368
369
372
368
366
60d
—
—
0.56
3
7600
10 200
9400
10 700
6900
7100
7000
8800
8900
7100
11 200
13 200
9800
9600
7100
11 400
7800
8400
423
418
418
418
419
414
420
417
414
424
415
414
418
418
422
418
418
416
6
0.309
0.337
0.344
0.012
0.0043
0.043
0.0010
0.024
0.73
0.0008
0.0046
0.030
0.097
0.34
7
8
12b
12c
12d
12e
12f
12g
12h
12i
13b
13c
1 + 3
1 + 8
Scheme 4 Plausible mechanism of dethreading reaction.
NH2 and the shuttling of the crown ether, which is fast on the
NMR timescale.
Stoddart et al. reported that the dethreading reaction
of rotaxane composed of dibenzometaphenylene[25]crown-
8-ether (DMP25C8) and [tBuC6H4-4-CH2NH2CH2C6H4-4-
CH2PPh3](PF6)2 was the passing of the crown ether over the end
group (DG‡(298 K) = 109 kJ mol-1, DH‡ = 66 kJ mol-1, and DS‡ =
-146 J mol-1K-1 in CD3CN). The large negative DS‡ value was
ascribed to the limited conformations possible for the crown ether
to pass over the end group and the solvation of polar solvent
during the shuttling of the macrocyclic component.26a Similar
thermodynamic parameters of the dethreading reaction of 12d in
0.33
0.0047
0.24
=
CH2 CHCO2An
CH2 CHCO2CH2An 367
=
a [Compound] = 1.0 ¥ 10-2 mM, CHCl3, 25 ◦C. b [Compound] = 2.0 ¥
10-3 mM, CHCl3, 25 ◦C, lex = lmax(absorption). c Quantum yield. d [1] =
1.0 mM, CHCl3, 25 ◦C.
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Table 4 Electrochemical data on ferrocene compoundsa
responsible for the emission of the rotaxanes. Addition of 1 to
a solution of 3 decreases emission intensity of 3 from f = 0.56
to f = 0.34. This change can be attributed to quenching of the
fluorescence of the anthryl group by the ferrocenyl end group,
which absorbs in a lower energy region than the emission.30,32
The ferrocenylene group of the rotaxanes 12b–12f and 13b–13c
quenches the fluorescence of the 9-anthryl stopper of the axle
molecule. Fig. 4(A) shows the UV-vis spectra of CHCl3 solutions
of 8, 12b, 13b, and 13c for comparison which show characteristic
structural bands of the anthracene chromophoric unit with similar
intensities. Emission spectra of the compounds upon excitation at
the corresponding wavelength of maximum absorption (Fig. 4(B))
differ among these compounds. Intensity of emission of 8 (f =
0.344) is significantly higher than that of rotaxane 13b (f = 0.030)
and an equimolar mixture of 1 and 8 showed an emission spectrum
with a quantum yield (f = 0.33) similar to that of 8 (f = 0.344). The
quantum yield of fluorescence of the cationic rotaxane 12b (f =
0.012) is lower than that of neutral rotaxane 13b (f = 0.030). The
degree of quenching is less significant in rotaxane 13c (f = 0.097)
having longer axle component. A similar decrease in emission
from the anthryl unit was observed in rotaxanes 12d (f = 0.043),
12e (f = 0.0010), 12f (f = 0.024), and 12h (f = 0.0008), which
are compared with those of CH2CHCO2An (f = 0.0047) and
CH2CHCO2CH2An (f = 0.24). The decrease in emission from the
anthracene unit is not observed for 12g (lmax = 424 nm, f = 0.73),
which has DB24C8 as its macrocyclic component.
Compound
E
pa/V
Epc/V
E1/2 (DE)b/V
1
-0.07
0.02
0.32
0.11
0.01
-0.07
0.02
0.05, 0.37
-0.13
-0.10
0.25
-0.10
-0.07
-0.17
-0.05
-0.03, 0.29
-0.10 (0.06)
-0.04 (0.12)
0.29 (0.07)
0.05 (0.12)
-0.03 (0.08)
-0.12 (0.10)
-0.02 (0.06)
0.01, 0.33
1c
4
12ac
12b
12cc
12d
12ed
(0.08, 0.08)
0.02, 0.34
12fd
0.05, 0.37
-0.02, 0.30
(0.07, 0.07)
0.27 (0.06)
-0.03 (0.10)
-0.11 (0.09)
-0.22 (0.11)
0.11 (0.07)
12h
0.30
0.02
-0.06
-0.16
0.14
0.24
13ac
-0.08
-0.15
-0.27
0.07
13b
13c
Ferrocene
a Electrochemical results are obtained by cyclic voltammetry in MeCN
containing nBu4NPF6 as the electrolyte. Potentials are referenced to
Ag+/Ag. Sweep rate: 0.10 V s-1. b DE = Epa - Epc. c In CH2Cl2. d Two-
steps redox.
of 3 by mixing with 1 is attributed to partial formation of
[2]pseudorotaxane 10 in solution and an intrarotaxane energy
transfer reaction. The association constant for the formation
of pseudorotaxane 10 is estimated to be 6 ¥ 105 M-1 at 25 ◦C
by fluorescent spectroscopy on the basis of assumptions that
pseudorotaxane 10 is non-luminescent owing to intrarotaxane
quenching.32
The redox potentials of the ferrocene-containing compounds
are summarized in Table 4. Redox peaks of the ferrocenylene unit
in the macrocyclic molecule of the cationic rotaxanes (12b, 12d–
12f) were observed at higher potentials (E1/2 = -0.03 to +0.02 V,
vs. Ag+/Ag) than those of the neutral rotaxane (E1/2 = -0.03 (13a),
-0.11 (13b) V) and of 1 (E1/2 = -0.10 V) in MeCN. Fe(II)/Fe(III)
redox in the ferrocenylmethylammonium group of 4, 12e, 12f, and
12h was observed in the range of E1/2 = +0.27 to +0.34 V. The
redox peak positions of terminal ferrocenyl groups in 12e, 12f,
and 12h were similar to those reported for ferrocene containing
[2]- and [3]rotaxanes.15 Fig. 5 shows cyclic voltammograms of 1,
4, and 12e. Two redox peaks of 12e are observed, as shown in
Fig. 5(C). Both oxidations (E1/2 = 0.01, 0.33 V) were observed
at higher potentials than in 1 and 4. The redox potential of 12e
does not change significantly (Epc: 0.046 0.004, 0.366 0.006 V,
Epa: 0.029 0.004, 0.288 0.003 V) in the range of scan rates
from 0.01 to 1.0 V s-1. These shifts in oxidation potential of the
second ferrocene unit are attributed to the positive charge of the
ferrocenium ion formed by the initial electrochemical oxidation,
similarly to other supramolecular systems.35,36
Fig. 4 (A) UV-vis spectra ([compound] = 1.0 ¥ 10-2 mM) and (B) emission
spectra ([compound] = 2.0 ¥ 10-3 mM, lex = lmax(absorption)) of CHCl3
solution of (a) 8, (b) 13c, (c) 13b, and (d) 12b.
The interlocked structure of 12b fixes the distance between
the ferrocenyl and anthryl groups within the range of effective
quenching. Previous studies revealed the quenching pathway of the
excited anthracene with the ferrocene group via dominant energy
transfer mechanisms30,33 rather than electron transfer reactions.34
Herkstroester and Kikuchi suggest that ferrocene behaves as a
non-luminescent energy acceptor, at least when the organic triplet
energy level is higher than 15 000 1000 cm-1, while a triplet with
a level lower than 13 000 cm-1 would be quenched by another
pathway, such as electron transfer reaction. The quenching of
fluorescence by the rotaxanes in this study may be attributed to
the energy transfer reaction from the photoexcited anthryl group
to the ferrocenylene unit in 1 rather than to an electron transfer
reaction. The quenching of rotaxane 12b is more efficient than
that of 13b and 13c because of strong hydrogen bonds between
the macrocyclic component and the ammonium moiety of 12b
and of the closer position of the anthryl and ferrocenylene groups
in the former rotaxane than in the latter. The partial quenching
Conclusions
In this paper, we present the synthesis and properties of ro-
taxanes containing macrocyclic compound 1 equipped with a
ferrocenylene group. The compound of 1 with a slightly larger
ring size and more flexible conformation than DB24C8 allows
dethreading of the rotaxane having anthryl and ferrocenyl end
groups in the polar solvents. The ferrocenylene group in the cyclic
component of rotaxane works as a quencher of fluorescence from
the excited anthryl group in the axle component. The efficiency
9886 | Dalton Trans., 2009, 9881–9891
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tered, and evaporated to give crude product as yellow oil. Purifica-
tion by SiO2 column chromatography (eluent: hexane–AcOEt 1 : 1)
give Fe{C5H4(OCH2CH2)3OTs}2 as yellow oil (0.27 g, 0.34 mmol,
87%) (found: C 53.52, H 5.84, S 7.77. C36H46O12S2Fe(H2O) requires
C 53.46, H 5.98, S 7.93%). dH(300 MHz; CDCl3; r.t.) 2.43 (6 H, s,
CH3), 3.60 (8 H, m, CH2), 3.68 (8 H, m, CH2), 3.80-4.45 (8 H,
C5H4), 3.93 (4 H, m, CH2), 4.15 (4 H, m, CH2), 7.33 (4 H, d, J =
8 Hz, C6H4) and 7.78 (4 H, d, J = 8 Hz, C6H4). dC(100 MHz;
CDCl3; r.t.) 21.5 (CH3), 55.4 (C5H4), 63.1 (C5H4), 68.5 (CH2),
69.1 (CH2), 69.5 (CH2), 69.7 (CH2), 70.4 (CH2), 70.5 (CH2), 127.7
(C6H4), 129.6 (C6H4), 132.7 (C6H4) and 144.6 (C6H4). The signal
of quaternary carbon of C5H4 ligand was not observed clearly
probably due to overlapping with the signal at 127.7 ppm. Rf 0.20
(hexane–AcOEt 1 : 1).
Compound 1
A DMF solution (36 cm3) containing Fe{C5H4(OCH2CH2)3OTs}2
(0.22 g, 0.28 mmol) and ortho-catechol (31 mg, 0.28 mmol) was
added dropwise to the DMF suspension (18 cm3) of Cs2CO3
(0.91 g, 2.8 mmol) at 80 ◦C for 1 h. The resulting solution was
stirred for 3 d at 80 ◦C followed by evaporation. The obtained
brown oil was dissolved in CH2Cl2 and the solution was washed
with saturated NH4Cl (aq). The separated organic phase was dried
over MgSO4, filtered and evaporated to form yellow oil. The crude
product was purified by SiO2 column chromatography (eluent:
hexane/AcOEt 1:1) and HPLC (eluent: CHCl3) to give 1 was
brown oil (0.13 g, 0.23 mmol, 82%) (found: C 59.79, H 6.98.
C28H36FeO8(H2O)0.5 requires C 59.48, H 6.60%). dH(300 MHz;
CDCl3; r.t.) 3.70–7.85 (12 H, m, CH2), 3.86 (4 H, br s, C5H4), 3.91
(4 H, m, CH2), 4.01 (4 H, m, CH2), 4.13 (4 H, br, C5H4), 4.17 (4
H, m, CH2) and 6.91 (4 H, C6H4). dH(100 MHz; CDCl3; r.t.) 56.1
(C5H4), 62.1 (C5H4), 69.3 (CH2), 69.9 (CH2), 69.9 (2 C, CH2), 70.8
(CH2), 71.0 (CH2), 114.7 (C6H4), 121.5 (C6H4), 127.6 (C5H4) and
149.0 (C6H4); m/z (FAB) 556 (M+. C28H36FeO8 requires 556); Rf
0.25 (hexane–AcOEt = 1 : 1).
Fig. 5 Cyclic voltammograms of (A) 1, (B) 4, and (C) 12e in MeCN
(1.0 mM) containing 0.10 M nBu4NPF6.
of the quenching varies depending on the co-conformation of the
component molecules of the rotaxane.
Experimental
General
Dried solvents were purchased from Kanto Chemical Co., Inc.
1
1
1
NMR spectra (1H, 13C{ H}, H-1H COSY, 13C{ H}-1H COSY,
DEPT, NOESY) were recorded on Varian MERCURY300 and
JEOL EX-400 spectrometers. Fe{C5H4(OCH2CH2)3OH}2,36
37
=
H2NCH2C6H4OCH2CH2CH CH2,
(C6H4-4-tBu)3CC6H4-4-
OH,38 3,5-dimethylphenyl acrylate,39 NaBArF (BArF
=
B{C6H3(CF3)2-3,5}4),40 [NH2(CH2Ph)2](BArF),41 and [FcCH2-
15
=
NH2C6H4OCH2CH2CH CH2](Cl)
were prepared by the
literature method. Other chemicals were commercially available.
Cyclic voltammetry (CV) was measured in MeCN solution
containing 0.10 mM nBu4NPF6 with ALS Electrochemical
Analyzer Model-600A. The measurement was carried out in a
standard one-compartment cell equipped with Ag+/Ag reference
electrode a platinum-wire counter electrode and a platinum-disk
working electrode (ID: 1.6 mm). The absorption spectra were
recorded using a JASCO V-530 UV-vis spectrometer as 1.0 ¥
10-5 M solution in MeCN. Photoluminescence spectra were
recorded as 2.0 ¥ 10-6 M solutions in MeCN. Quantum yields
were estimated by comparison of standard solution of quinine
sulfate (1.0 M, f = 0.546). Fast atom bombardment mass
spectrum (FABMS) was obtained from JEOL JMS-700 (matrix,
2-nitrophenyloctylether). Elemental analyses were carried out
with a Yanaco MT-5 CHN autorecorder.
[(C6H4-4-tBu)3CC6H4-4-OC6H4-4-CH2NH2CH2C6H4-4-
=
OCH2CH2CH CH2](BArF) (2)
To an Et2O (7.0 cm3) solution of [(C6H4-4-tBu)3CC6H4-4-
=
OC6H4-4-CH2NH2CH2C6H4-4-OCH2CH2CH CH2](Cl) (0.24 g,
0.30 mmol) was added NaBArF (0.27 g, 0.30 mmol), and the
mixture was stirred for 11 h at room temperature. The precipitated
salt was removed by filtration. Evaporation of filtrate gave 2 as
a white solid, which was washed with hexane and dried under
reduced pressure (0.44 g, 0.27 mmol, 90%) (found: C 63.37, H
4.81, N 0.87. C87H76BF24NO2(H2O)0.5 requires C 63.59, H 4.72, N
0.85%). dH(300 MHz; CDCl3; r.t.) 1.31 (27 H, s, CH3), 2.54 (2 H,
=
dt, J = 7 and 7 Hz, CH2CH CH2), 3.99 (2 H, t, J = 7 Hz, OCH2),
4.04 (2 H, s, NCH2), 4.06 (2 H, s, NCH2), 5.12 (1 H, dd, J = 10
=
and 2 Hz, cis-CH CH2), 5.17 (1 H, dd, J = 17 and 2 Hz, trans-
Fe{C5H4(OCH2CH2)3OTs}2 (Ts = SO2C6H4Me-4)
=
=
CH CH2), 5.87 (1 H, ddt, J = 17, 10 and 7 Hz, CH CH2), 6.90–
6.93 (4 H, C6H4), 7.05–7.12 (4 H, C6H4), 7.10 (6 H, d, J = 8 Hz,
tBuC6H4), 7.18 (2 H, d, J = 9 Hz, C6H4), 7.23–7.28 (2 H, C6H4),
7.26 (6 H, d, J = 8 Hz, tBuC6H4), 7.53 (4 H, s, para-C6H3) and 7.72
(8 H, br s, ortho-C6H3). dC(100 MHz; CDCl3; r.t.) 31.4 (CH3), 33.4
NaOH (0.10 g, 2.5 mmol) and TsCl (0.20 g, 1.0 mmol) was
added to a solution (THF–H2O = 1.0 cm3 : 0.1 cm3) of
Fe{C5H4(OCH2CH2)3OH}2 (0.19 g, 0.39 mmol) at room tem-
perature. The solution was stirred for 14 h at room temperature
followed by addition of water and extraction of the product with
CH2Cl2. The separated organic phase was dried over MgSO4, fil-
=
(CH2CH CH2), 34.4 (C(CH3)3), 51.8 (NCH2), 52.1 (NCH2), 63.4
(C( BuC6H4)3), 67.5 (OCH2), 116.0, 117.4 (CH2CH CH2), 117.5
t
=
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(para-C6H3), 118.4, 119.1 119.2, 121.4, 124.1 (tBuC6H4), 124.5 (q,
CF3, J(CF) 271), 128.4–129.3 (m, CCF3), 130.6 (tBuC6H4), 130.8,
132.9, 133.7, 134.7 (ortho-C6H3), 143.6, 144.1, 148.6, 152.8, 160.3,
161.1, 161.5 (q, CB, J(CB) = 50 Hz).
7.09 (2 H, d, J = 8 Hz, C6H4), 7.52 (4 H, s, para-C6H3) and 7.70 (8
H, br s, ortho-C6H3). dC(100 MHz; CDCl3; r.t.) 33.4 (OCH2CH2),
54.0 (NCH2), 56.2 (NCH2), 67.5 (OCH2), 69.4 (C5H5), 70.3 (C5H4),
=
71.0 (C5H4), 72.7 (ipso-C5H4), 115.9 (C6H4), 117.4 ( CH2), 117.5
(para-C6H3), 119.4, 124.5 (quintet, J(FC) = 271 Hz, CF3), 128.8
=
(quintet, J(FC) = 35 Hz, CCF3), 131.2 (C6H4), 133.7 (CH CH2),
=
[AnCH2NH2C6H4OCH2CH2CH CH2](BArF) (3)
134.7 (ortho-C6H3), 160.8 (C6H4) and 161.8 (quintet, J(BC) =
=
=
AnCH NC6H4OCH2CH2CH CH2 (0.50 g, 1.4 mmol) was dis-
solved in MeOH (10 cm3) at room temperature. NaBH4 (0.42 g,
11 mmol) was added to the solution in one portion and the mixture
was stirred for 11 h at room temperature. After quenching the mix-
ture with 4 M HCl (aq) (30 cm3) and further stirring for 1 h caused
50 Hz, BC).
[(C6H3-3,5-Me2)-CH2NH2CH2C6H4-4-
=
OCH2CH2CH CH2](BArF) (5)
the separation of [AnCH2NH2C6H4OCH2CH2CH CH2](Cl) as a
To
a
methanol solution (10 cm3) of (C6H3-3,5-Me2)-
=
=
yellow solid from the solution. The solid product was collected
by filtration, washed (Et2O, water), and dried under reduced
pressure (0.38 g, 0.94 mmol, 67%). To an Et2O (15 cm3) suspension
CH2NHCH2C6H4-4-OCH2CH2CH CH2 (1.6 g, 5.0 mmol) was
added 4 M HCl (aq) (30 cm3). The stirring the mixture for 1 h
at room temperature causes separation of crude product from the
solution. The solid product was collected by filtration and washed
with Et2O and dried under reduced pressure to give [(C6H3-3,5-
=
of obtained [AnCH2NH2C6H4OCH2CH2CH CH2](Cl) (0.26 g,
0.64 mmol) was added NaBArF (0.57 g, 0.64 mmol), and the
mixture was stirred for 14 h at room temperature. The precipitated
salt was removed by filtration. Evaporation of the filtrate gave
crude 3 as yellow oil, which is extracted with Et2O and CH2Cl2,
followed by evaporation to dryness. The product was extracted
again with CH2Cl2 and the solution was filtered, evaporated.
The crude product was washed with hexane to give 3 as pale-
yellow solid (0.69 g, 0.56 mmol, 88%) (found: C 55.87, H 3.41, N
1.22. C58H38BF24NO(H2O) requires C 55.74, H 3.23, N 1.12%).
dH(300 MHz; CDCl3; r.t.) 2.58 (2 H, dt, J = 7 and 7 Hz,
OCH2CH2), 4.05 (2 H, t, J = 7 Hz, OCH2), 4.33 (2 H, m,
=
Me2)-CH2NH2CH2C6H4-4-OCH2CH2CH CH2](Cl) as a white
solid (0.28 g, 0.84 mmol, 84%). dH(300 MHz; CDCl3; r.t.) 2.29
=
(6 H, s, CH3), 2.47 (2 H, dt, J = 7 and 7 Hz, CH2CH CH2), 3.76
=
(4 H, m, NCH2), 3.87 (2 H, t, OCH2), 5.08–5.17 (2 H, CH CH2),
=
5.84 (1 H, ddt, J = 17, 11 and 7 Hz, CH CH2), 6.85 (2 H, d,
J = 9 Hz, C6H4), 6.95 (1 H, s, para-C6H3), 7.09 (2 H, s, ortho-
C6H3), 7.40 (2 H, d, J = 9 Hz, C6H4) and 10.06 (2 H, br s, NH2).
=
dC(100 MHz; CDCl3; r.t.) 21.3 (CH3), 33.5 (CH2CH CH2), 48.1
=
(NCH2), 48.4 (NCH2), 67.1 (OCH2), 114.8, 117.0 (CH2CH CH2),
122.0, 127.9, 129.8, 130.8, 131.8, 134.1, 138.6 and 159.4. To an
Et2O (15 cm3) solution of [(C6H3-3,5-Me2)-CH2NH2CH2C6H4-4-
=
NH2CH2C6H4), 5.14 (1 H, d, J = 11 Hz, CH2), 5.18 (1 H, d,
=
=
J = 17 Hz, CH2), 5.27 (2 H, m, NH2CH2An), 5.89 (1 H, ddt,
OCH2CH2CH CH2](Cl) (0.20 g, 0.64 mmol) was added NaBArF
=
J = 17, 11 and 7 Hz, CH CH2), 6.89 (2 H, br s, NH2), 7.02 (2 H, d,
(0.57 g, 0.64 mmol), and the mixture was stirred for 12 h at
room temperature. The precipitated salt was removed by filtration.
Evaporation of filtrate gave 5 as a white solid which was washed
with hexane and dried under reduced pressure (0.25 g, 0.22 mmol,
34%) (found: C 52.97, H 3.58, N 1.20. C52H38BF24NO(H2O)
requires C 53.03, H 3.42, N 1.19%). dH(300 MHz; CDCl3; r.t.) 2.28
J = 8 Hz, C6H4), 7.26 (2 H, d, J = 8 Hz, C6H4), 7.49 (4 H, s, para-
C6H3), 7.46–7.61 (4 H, H2-An, H3-An), 7.68 (2 H, H1-An), 7.71
(8 H, br s, ortho-C6H3), 8.12 (2 H, dd, J = 9 and 2 Hz, H4-An) and
8.67 (1 H, s, H10-An). dC(100 MHz; CDCl3; r.t.) 33.4 (OCH2CH2),
44.4 (NCH2An), 53.5 (NCH2C6H4), 67.7 (OCH2), 116.4 (C6H4),
=
=
117.2, 117.4 ( CH2), 117.5 (para-C6H3), 119.0, 119.5 (C1-An),
(6 H, s, CH3), 2.55 (2 H, dt, J = 7 and 7 Hz, CH2CH CH2), 3.99 (2
124.5 (quintet, J(FC) = 271 Hz, CF3), 126.0 (C2-An or C3-An),
128.8 (quintet, J(FC) = 29 Hz, CF3C), 129.5 (C2-An or C3-An),
130.0, 130.7 (C4-An), 130.9 (C6H4), 131.2, 132.5 (C10-An), 133.7
H, t, OCH2), 4.02 (2 H, m, NCH2), 4.06 (2 H, m, NCH2), 5.10–5.20
=
=
(2 H, CH CH2), 5.87 (1 H, ddt, J = 17, 11 and 7 Hz, CH CH2),
6.81 (2 H, d, J = 9 Hz, C6H4), 7.11 (2 H, d, J = 9 Hz, C6H4),
7.13 (1 H, s, para-C6H3(CF3)2), 7.52 (4 H, s, para-C6H3(CF3)2) and
7.70 (8 H, m, ortho-C6H3). dC(100 MHz; CDCl3; r.t.) 21.0 (CH3),
=
(CH CH2), 134.8 (ortho-C6H3), 161.5 (C6H4) and 161.5 (quintet,
J(BC) = 50 Hz, BC). dF(282 MHz; CDCl3; r.t.) -62.7 (CF3).
=
33.4 (CH2CH CH2), 52.3 (NCH2), 52.4 (NCH2), 67.5 (OCH2),
116.0, 117.3 (CH2CH CH2), 117.5 (para-C6H3), 120.4, 124.5 (q,
J(FC) = 271 Hz, CF3), 126.5, 127.8, 128.8 (q, J(FC) = 31 Hz,
CCF3), 130.7, 132.9, 1337, 134.7, 140.4, 161.1, 161.6 (q, J(BC) =
50 Hz, BC).
=
=
[FcCH2NH2C6H4OCH2CH2CH CH2](BArF) (4)
To an Et2O (15 cm3) suspension of [FcCH2NH2C6H4OCH2-
=
CH2CH CH2](Cl) (0.26 g, 0.64 mmol) was added NaBArF (0.57 g,
0.64 mmol), and the mixture was stirred for 11 h at room
temperature. The precipitated salt was removed by filtration.
Evaporation of the filtrate gave crude 4 as yellow oil, which is
extracted with Et2O and CH2Cl2, followed by evaporation to
dryness to give 4 as pale-yellow oil (0.72 g, 0.58 mmol, 71%)
(found: C 52.83, H 3.58, N 1.16. C54H38BF24NO(H2O)2 requires
C 53.18, H 3.47, N 1.15%). dH(400 MHz; CDCl3; r.t.) 2.52 (2 H,
dt, J = 7 and 6 Hz, OCH2CH2), 3.97 (2 H, t, J = 6 Hz, OCH2),
4.02 (2 H, br s, C5H4), 4.03 (2 H, br s, C5H4), 4.15 (5 H, s, C5H5),
4.18 (2 H, m, NCH2), 4.31 (2 H, m, NCH2), 5.09 (2 H, d, J =
=
AnCH2N(Ac)CH2C6H4-4-OCH2CH2CH CH2 (6)
=
To
a solution of [AnCH2NH2CH2C6H4-4-OCH2CH2CH
CH2](Cl) (1.5 g, 3.8 mmol) in MeCN (150 cm3) were added Et3N
(2.5 cm3, 19 mmol) and acetic anhydride (1.8 cm◦3, 19 mmol),
and the reaction mixture was stirred for 12 h at 60 C. After the
removal of the solvent by evaporation, the product was dissolved
in CH2Cl2 and the organic layer was washed with water, dried
over MgSO4. Removal of solvent by evaporation gave 6 as yellow
solid, which was washed with hexane and dried under reduced
pressure (1.5 g, 3.5 mmol, 94%) (found: C 81.17, H 6.69, N 3.37.
=
=
10 Hz, CH2), 5.11 (2 H, d, J = 17 Hz, CH2), 5.85 (1 H, ddt,
=
J = 17, 10 and 7 Hz, CH CH2), 6.90 (2 H, d, J = 9 Hz, C6H4),
9888 | Dalton Trans., 2009, 9881–9891
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=
C28H27NO2(H2O)0.25 requires C 81.23, H 6.69, N 3.38%). n(KBr
NCH2An), 6.18 (1 H, d, J = 16 Hz, CH2CH CH), 6.84 (4
disk; r.t.)/cm-1 1640 (C O). dH(300 MHz; CDCl3; r.t.) 2.21 (3
H, m, NCH2C6H4), 7.01 (2 H, d, J = 9 Hz, C6H4(tBuC6H4)3),
=
=
H, s, CH3), 2.57 (2 H, dt, J = 7 and 7 Hz, CH2CH CH2), 4.03
7.10 (6 H, tBuC6H4), 7.21–7.26 (9 H, tBuC6H4, C6H4(tBuC6H4)3,
CH2CH CH), 7.38–7.48 (4 H, 2H-An, 3H-An), 8.00 (2 H, dd,
=
(2 H, t, J = 7 Hz, OCH2), 4.07 (2 H, m, NCH2), 5.13 (1 H, dd,
=
J = 17 and 2 Hz, CH2CH CH2), 5.72 (2 H, m, NCH2), 5.94 (1
J = 9 Hz and 2, 4H-An), 8.10 (2 H, d, J = 9 Hz, 1H-An) and 8.45
=
H, ddt, J = 17, 11 and 7 Hz, CH CH2), 6.84 (4 H, C6H4), 7.37–
(1 H, s, 10H-An). dC(75.5 MHz; CDCl3; r.t.) 22.0 (COCH3), 31.4
=
7.48 (4 H, 2H-An, 3H-An), 7.99–8.10 (4 H, 1H-An, 4H-An) and
(C(CH3)3), 32.3 (CH2CH CH), 34.4 (C(CH3)3), 39.2 (NCH2An),
8.45 (1 H, s, H10-An). dC(75.5 MHz; CDCl3; r.t.) 21.8 (CH3), 33.6
48.7 (NCH2C6H4), 63.4 (C(tBuC6H4)3), 65.9 (OCH2), 114.8
t
=
=
(CH2CH CH2), 39.0 (NCH2), 48.5 (NCH2), 67.2 (OCH2), 114.8,
(NCH2C6H4), 119.9 (C6H4( BuC6H4)3), 122.8 (CH2CH CH),
117.1, 124.3, 125.0, 126.3, 127.0, 127.5, 128.2, 128.3, 129.0, 131.2,
124.1 (tBuC6H4), 124.3 (1C-An), 125.0 (2C-An or 3C-An), 126.3
(2C-An or 3C-An), 127.0 (NCH2C6H4), 127.8, 128.2 (10C-
=
131.4, 134.4, 158.1 (C6H4) and 171.1 (C O).
An), 128.9, 129.0 (4C-An), 130.6 (tBuC6H4), 131.2, 131.4, 132.1
t
=
(C6H4( BuC6H4)3), 143.6, 144.7, 146.7 (CH2CH CH), 148.4,
=
AnCH2N(Ac)CH2C6H4-4-OCH2CH2CH CHCOOC6H3-3,5-
Me2 (7)
=
=
157.7, 164.4 (NC O) and 171.0 (C( O)O); Rf 0.31 (CH2Cl2).
A mixture of 5 (0.41 g, 1.0 mmol) and 3,5-dimethylphenyl
acrylate (0.35 g, 2.0 mmol) was dissolved in CH2Cl2
(5.0 cm3), followed by addition of a Ru–carbene complex
=
Pseudorotaxane [(1)(AnCH2NH2C6H4OCH2CH2CH CH2)]-
(BArF) (10)
1H NMR spectrum was obtained from CDCl3 solution (0.7 cm3)
containing 1 (3.5 ¥ 10-3 mmol) and 3 (3.5 ¥ 10-3 mmol).
dH(300 MHz, CDCl3, r.t.) 2.53 (2 H, dt, J = 7 and 7 Hz,
=
((H2IMes)(PCy3)Cl2Ru CHPh, H2IMes = N,N-bis(mesityl)-4,5-
dihydroimidazol-2-ylidene) (42 mg, 5.0 ¥ 10-2 mmol). The mixture
was refluxed for 11 h and the solvent was removed by evaporation
to give crude 7, which was purified by SiO2 column chromatog-
raphy (eluent: hexane–CH2Cl2 1 : 1) (0.26 g, 0.47 mmol, 47%)
(found: C 79.60, H 6.47, N 2.49. C37H35NO4 requires C 79.69,
=
CH2CH CH2), 3.25–4.23 (34 H, OCH2, C5H4), 5.08–5.24 (4 H,
=
NCH2, CH2CH CH2), 5.64 (2 H, br s, NCH2), 5.71 (2 H, m, C6H4-
=
Crown), 5.87 (1 H, ddt, J = 17, 11 and 7 Hz, CH2CH CH2), 6.53
(2 H, m, C6H4-Crown), 6.95 (2 H, J = 9 Hz, C6H4-Axle), 7.09 (2
H, br s, NH2), 7.42–7.58 (6 H, H2-An, H3-An, C6H4-Axle), 7.52
(4 H, s, para-C6H3), 7.71 (8 H, br s, ortho-C6H3), 7.83 (2 H, d, J =
8 Hz, An), 8.11 (1 H, s, H10-An) and 8.41 (2 H, d, J = 9 Hz, An).
m/z (FAB) 924 ([M - BArF]+. C54H62FeNO9 requires 924).
H 6.33, N 2.51%). n(KBr disk; r.t.)/cm-1 1646 and 1728 (C O).
=
dH(300 MHz; CDCl3; r.t.) 2.22 (3 H, s, COCH3), 2.32 (6 H, s,
=
C6H3(CH3)2), 2.79 (2 H, ddt, J = 7, 6 and 2 Hz, CH2CH CH),
4.08 (2 H, m, NCH2C6H4), 4.14 (2 H, t, J = 6 Hz, OCH2), 5.73
=
(2 H, m, NCH2An), 6.19 (1 H, dt, J = 16 and 2 Hz, CH2CH CH),
6.75 (2 H, m, ortho-C6H3), 6.85 (4 H, m, C6H4), 6.89 (1 H, m,
Spectrofluorimetric determination of association constant of the
reaction of 1 and 3 to form 10
=
para-C6H3), 7.26 (1 H, dt, J = 16 and 7 Hz, CH2CH CH), 7.39–
7.48 (4 H, 2H-An, 3H-An), 8.00 (2 H, m, 4H-An), 8.11 (2 H, d,
J = 8 Hz, 1H-An), 8.45 (1 H, s, H10-An). dC(100 MHz; CDCl3;
The association constant Kobs for formation of pseudorotaxane
10 was estimated by analyzing the fluorescence intensity of
10 as a function of the concentration. Pseudorotaxane 10 was
assumed to be non-luminescent due to intrarotaxane quenching.
Intermolecular quenching between 1 and 3 was not considered.
The intensity read at the maximum of anthracene band was fitted
to [10] = Iobs/I0[10]0. Kobs satisfies usual 1 : 1 binding expressed in
eqn (2).
=
r.t.) 21.3 (COCH3), 21.9 (C6H3(CH3)2), 32.2 (CH2CH CH), 39.2
(NCH2An), 48.6 (NCH2C6H4), 65.9 (OCH2), 114.8 (C6H4), 119.1
=
(ortho-C6H4), 122.8 (CH2CH CH), 124.3 (1C-An), 124.9 (2C-An
or 3C-An), 126.3 (2C-An or 3C-An), 127.0 (C6H4 or para-C6H3),
127.5 (C6H4 or para-C6H3), 127.8, 128.2 (10C-An), 128.8, 129.0
=
(3C-An), 131.2, 131.4, 139.2, 146.6 (CH2CH CH), 150.4, 157.7
=
=
(C6H4), 164.7 (NC O) and 171.0 (C O); Rf 0.16 (CH2Cl2).
Kobs = [10]/{([1]0 - [10])([3]0 - [10])}
(2)
=
AnCH2N(Ac)CH2C6H4-4-OCH2CH2CH CHCOOC6H4-4-
C(C6H4-4-tBu)3 (8)
Pseudorotaxane [(1){NH2(CH2Ph)2}](BArF) (11)
=
6 (0.20 g, 0.50 mmol) and CH2 CHCOOC6H4-4-C(C6H4-
4-tBu)3 (0.56 g, 1.0 mmol) was dissolved in CH2Cl2
The 1H NMR spectrum was obtained from CDCl3 solution
(0.7 cm3) containing 1 (7.0 ¥ 10-3 mmol) and 9 (7.0 ¥ 10-3 mmol).
dH(300 MHz; CDCl3; r.t.) 3.28 (4 H, br s, OCH2), 3.47 (12 H, br s,
OCH2), 3.94–4.10 (12 H), 4.29 (4 H, br s, C5H4), 4.98 (4 H, br s,
NCH2), 6.63 (2 H, m, C6H4-Crown), 6.69 (2 H, m, C6H4-Crown),
7.24 (4 H, br s, C6H4-Axle), 7.53 (4 H, s, C6H3(CF3)2), 7.71 (2 H,
br s, NH2) and 7.72 (8 H, s, C6H3(CF3)2). m/z (FAB) 754 ([M -
BArF]+. C42H52FeNO8 requires 754).
(2.5 cm3), followed by addition of a Ru–carbene complex
=
((H2IMes)(PCy3)Cl2Ru CHPh, H2IMes = N,N-bis(mesityl)-4,5-
dihydroimidazol-2-ylidene) (21 mg, 2.5 ¥ 10-2 mmol). The mixture
was refluxed for 54 h. The reaction mixture was partitioned by
addition of water and CH2Cl2. The separated organic phase was
washed with water, dried over MgSO4, filtered, and evaporated
to give 8 as a white solid which was purified by SiO2 column
chromatography (eluent: CH2Cl2) (0.27 g, 0.29 mmol, 57%)
(found: C 84.16, H 7.56, N 1.56. C66H69NO4 requires C 84.31,
[{(C6H4-4-tBu)3CC6H4-4-OC6H4-4-CH2NH2CH2C6H4-4-OCH2-
H 7.40, N 1.49%). n(KBr disk; r.t.)/cm-1 1651 and 1740 (C O).
dH(300 MHz; CDCl3; r.t.) 1.30 (27 H, s, C(CH3)3), 2.22 (3 H, s,
=
=
CH2CH CHCOOC6H4-4-C(C6H4-4-tBu)3}(1)](BArF) (12a)
=
COCH3), 2.79 (2 H, dt, J = 7 and 7 Hz, CH2CH CH), 4.09 (2
Compounds 2 (163 mg, 0.10 mmol) and 1 (61 mg, 0.11 mmol)
H, s, NCH2C6H4), 4.14 (2 H, t, J = 6 Hz, OCH2), 5.73 (2 H, s,
were dissolved in CH2Cl2 (2.0 cm3), followed by addition of
This journal is
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Dalton Trans., 2009, 9881–9891 | 9889
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=
CH2 CHCOOC6H4-4-C(C6H4-4-tBu)3 (111 mg, 0.20 mmol) and
to 13a from corresponding rotaxanes, 12b and 12c. See Electronic
Supplementary Information (ESI) for more detail.†
=
a Ru–carbene complex ((H2IMes)(PCy3)Cl2Ru CHPh) (4.2 mg,
5.0 ¥ 10-3 mmol). The mixture was refluxed for 14 h and the
solvent was removed by evaporation to give brown oil. The crude
product was purified by preparative HPLC (CHCl3) to give 12a
(160 mg, 0.088 mmol, 88%) (found: C 66.39, H 5.95, N 0.54.
C153H154BF24FeNO12(H2O) requires C 66.21, H 5.81, N 0.50%).
dH(300 MHz; CDCl3; r.t.) 1.31 (54 H, s, CH3), 2.73 (2 H, dt,
Reaction of Ac2O with 12d
To a solution of 12d (0.14 g, 0.073 mmol) in MeCN (3.0 cm3) were
added Et3N (5.6 ¥ 10-2 cm3, 0.40 mmol) and acetic anhydride
(3.8 ¥ 10-2 cm3, 0.40 mmol), and the reaction mixture was
stirred for 14 h at room temperature. After the removal of
the solvent by evaporation, the products were isolated by SiO2
column chromatography (hexane–AcOEt 1 : 1) to give 1 (34 mg,
0.061 mmol, 84%, Rf 0.10, hexane–AcOEt 1 : 1) and 7 (35 mg,
0.063 mmol, 86%, Rf 0.18, hexane–AcOEt 1 : 1).
=
J = 6 and 6 Hz, CH2CH CH2), 3.42–4.30 (34 H, OCH2-Axle,
CH2-Crown, C5H4), 4.51–4.58 (4 H, m, NCH2), 6.16 (1 H, d,
=
J = 16 Hz, CH2CH CH), 6.68 (2 H, m, C6H4-Crown), 6.74 (2
H, d, J = 9 Hz, C6H4-Axle), 6.83 (2 H, d, J = 9 Hz, C6H4-
Axle), 6.87–6.91 (4 H, C6H4-Crown, C6H4-Axle), 7.01 (2 H, d,
t
J = 8 Hz, C6H4-Axle), 7.10 (6 H, d, J = 9 Hz, BuC6H4), 7.11
t
t
Dethreading reaction of rotaxanes
(6 H, d, J = 8 Hz, BuC6H4), 7.19–7.32 (21 H, BuC6H4, C6H4-
=
Axle, CH2CH CH), 7.55 (4 H, s, para-C6H3), 7.65 (2 H, br s,
To an NMR tube was charged a CD3CN (or dmso-d6) solution
(0.6 cm3) of rotaxane, 12a, 12b, 12d, 12e, 12g, 12i, 13a, 13b, (3.0 ¥
10-3 mmol) and 2-chloro-2-methylpropane, which was used as
internal standard. The NMR tube was heated in a thermostat
NH2) and 7.74 (8 H, br s, ortho-C6H3). dC(100 MHz; CDCl3; r.t.)
31.4 (CH3), 31.4 (CH3), 32.0 (CH2CH CH2), 34.3 (C(CH3)3), 51.8
=
(NCH2), 52.1 (NCH2), 56.1 (C5H4), 56.4 (C5H4), 62.8 (2C, C5H4),
63.3 (C(tBuC6H4)3), 63.4 (C(tBuC6H4)3), 65.7 (OCH2-Axle), 68.3
(CH2-Crown), 68.9 (CH2-Crown), 69.8 (CH2-Crown), 70.2 (CH2-
Crown), 70.6 (CH2-Crown), 71.2 (CH2-Crown), 112.1 (C6H4-
Crown), 114.5 (C6H4-Axle), 117.4 (para-C6H3), 117.8 (C6H4-
1
bath and stored when not being actively monitored. H NMR
spectra were checked occasionally and reaction was monitored
by comparison of peak area ratio between rotaxane and internal
standard. After reaction, the solvent was removed by evaporation
and the residue was checked by FABMS measurement.
Axle), 118.3 (C6H4-Axle), 119.9 (C6H4-Axle), 119.9 (C6H4-Axle),
t
=
122.0 (C6H4-Axle), 122.9 (CH2CH CH2), 124.1 ( BuC6H4), 124.1
(tBuC6H4), 124.5 (q, J(CF) = 271 Hz, CF3), 124.5 (q, J(CF) =
31 Hz, CCF3), 125.2, 130.6 (tBuC6H4), 130.6 (tBuC6H4), 130.7
(C6H4-Axle), 130.7 (C6H4-Axle), 132.1 (C6H4-Axle), 132.7 (C6H4-
Axle), 134.7 (ortho-C6H3), 143.2, 143.6, 143.6, 144.8, 146.4, 146.6
Crystal structure determination
Crystals of [K(1)]BPh4 suitable for X-ray diffraction study were
obtained by recrystallization from an acetone/methanol solution
of 1 and KBPh4 (found: C 67.97, H 6.25. C52H56O8FeKB requires
C 68.28, H 6.17%). All measurements were made on a Rigaku
AFC7R diffractometer with graphite monochromated MoKa
radiation and a rotating anode generator. Data were analyzed
by assuming disorder between C(21) and C(22).
=
(CH2CH CH2), 148.3, 148.4, 148.6, 153.6, 158.5, 159.4, 161.6 (q,
=
J(CB) = 50 Hz, CB) and 164.5 (C O). m/z (FAB) 1858 ([M -
BArF]+. C121H142FeNO12 requires 1858). Rotaxanes 12b–12i were
synthesized similarly to 12a from corresponding crown ether and
olefins. See Electronic Supplementary Information (ESI) for more
detail.†
Crystal data
C52H56O8BFeK, M = 914.76, monoclinic, a = 13.846(2), b =
[(1){(C6H4-4-tBu)3CC6H4-4-OC6H4-4-CH2N(Ac)CH2C6H4-4-
3
˚
˚
22.065(4), c = 14.893(3) A, U = 4545(2) A , T = 113 K, space
group P21/n (no. 14), Z = 4, 32 533 reflections were measured,
10 119 unique (Rint = 0.021), which were used in all calculations.
The final Rw was 0.0624 (I > 2s(I)).
=
OCH2CH2CH CHCOOC6H4-4-C(C6H4-4-tBu)3}] (13a)
To a solution of 12a (0.22 g, 0.080 mmol) in MeCN (3.0 cm3) were
added Et3N (5.6 ¥ 10-2 cm3, 0.40 mmol) and acetic anhydride (3.8 ¥
10-2 cm3, 0.40 mmol), and the reaction mixture was stirred for 14 h
at room temperature. After the removal of the solvent by evapo-
ration, the product was purified by SiO2 column chromatography
(eluent: hexane–AcOEt 1 : 1), preparative HPLC (eluent: CHCl3),
and SiO2 column chromatography (eluent: hexane–AcOEt 2 : 1)
to give 13a as a yellow solid (82 mg, 3.0 ¥ 10-2 mmol, 38%) (found:
C 75.52, H 7.16, N 0.80. C123H143FeNO13(CHCl3)0.5 requires C
Acknowledgements
This work was supported by Grant-in-Aid for Scientific Research
for Young Scientists from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (19750044) and by a Global
COE Program “Education and Research Center for Emergence
of New Molecular Chemistry”. We thank Tomohito Ide for the
theoretical calculation of the triplet level of the model compounds.
75.72, H 7.38, N 0.71%). n(KBr disk; r.t.)/cm-1 1653, 1734 (C O).
=
dH(300 MHz; CDCl3; r.t.) 1.32 (54 H, s, C(CH3)3), 2.21 (3 H, m,
=
COCH3), 3.14 (2 H, m, CH2CH CH), 3.50–4.60 (38 H, C5H4,
=
CH2-Crown, NCH2), 6.41 (1 H, d, J = 16 Hz, CH2CH CH),
References
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9890 | Dalton Trans., 2009, 9881–9891
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
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