Chemical and electrochemical formation of pseudorotaxanes composed of alkyl(ferrocenylmethyl)ammmonium and dibenzo[24]crown-8

Article abstract of DOI:10.1021/ic050215f

Protonation of p-xylylaminomethylferrocene (1) and n- hexylaminomethylferrocene (2) by HCl and NH₄PF₆ forms the ferrocenylmethyl(alkyl)ammonium salt. Inclusion of the compounds by dibenzo[24]crown-8 (DB24C8) produces [2]pseudorotaxanes, [(DB24C8)(1-H)] ⁺(PF₆) and [(DB24C8)(2-H)]⁺(PF₆), respectively. X-ray diffraction of the former product indicates an interlocked structure composed of the axis and the macrocyclic molecule. Intermolecular N-H...O and C-H...O interactions and stacking of the aromatic planes are observed. [(DB24C8)(1-H)]⁺(PF₆), in the solid state, is characterized by IR spectroscopy and elemental analyses. A similar reaction of 1,1′-bis(p-xylylaminomethyl)ferrocene (3) forms a mixture of [2] and [3]pseudorotaxanes, [(DB24C8)(3-H₂)]²⁺(PF ₆)₂ and [(DB24C8)₂(3-H₂)] ²⁺(PF₆)₂. The latter product having two DB24C8 molecules is isolated and characterized by X-ray crystallography. Formation of these pseudorotaxanes in a CD₃CN solution is evidenced by ¹H NMR and mass spectrometry. Electrochemical oxidation of 1-3 at 0.4 V (vs Ag⁺/Ag) in the presence of TEMPOH (1-hydroxy-2,2,6,6- tetramethylpiperidine) and DB24C8 affords the corresponding pseudorotaxanes. The ESR spectrum of the reaction mixture indicates the formation of a TEMPO radical in high yield. Details of the conversion of the dialkylamino group of the ligand to the dialkylammonium group are investigated by using a flow electrolysis method linked to spectroscopic measurements. The proposed mechanism for the reaction involves the ferrocenium species, formed by initial oxidation, which undergoes electron transfer from nitrogen to the Fe(III) center, producing a cation radical at the nitrogen. Transfer of hydrogen from TEMPOH to the cation radical and inclusion of the resulting dialkylammonium species by DB24C8 yields the pseudorotaxanes.

Full text of DOI:10.1021/ic050215f

Inorg. Chem. 2005, 44, 5844−5853
Chemical and Electrochemical Formation of Pseudorotaxanes
Composed of Alkyl(ferrocenylmethyl)ammmonium and
Dibenzo[24]crown-8
Masaki Horie,† Yuji Suzaki, and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
Received February 9, 2005
Protonation of p-xylylaminomethylferrocene (1) and n-hexylaminomethylferrocene (2) by HCl and NH4PF6 forms
the ferrocenylmethyl(alkyl)ammonium salt. Inclusion of the compounds by dibenzo[24]crown-8 (DB24C8) produces
[2]pseudorotaxanes, [(DB24C8)(1
product indicates an interlocked structure composed of the axis and the macrocyclic molecule. Intermolecular
‚‚‚O and C ‚‚‚O interactions and stacking of the aromatic planes are observed. [(DB24C8)(1
H)]+(PF6), in
the solid state, is characterized by IR spectroscopy and elemental analyses. A similar reaction of 1,1 -bis(p-
xylylaminomethyl)ferrocene (3) forms a mixture of [2] and [3]pseudorotaxanes, [(DB24C8)(3
H2)]2+(PF6)2 and
[(DB24C8)2(3
H2)]2+(PF6)2. The latter product having two DB24C8 molecules is isolated and characterized by X-ray
crystallography. Formation of these pseudorotaxanes in a CD3CN solution is evidenced by 1H NMR and mass
spectrometry. Electrochemical oxidation of 1
3 at 0.4 V (vs Ag+/Ag) in the presence of TEMPOH (1-hydroxy-
− −
H)]+(PF6) and [(DB24C8)(2 H)]+(PF6), respectively. X-ray diffraction of the former
N
−H
−H
−
′
−
−
−
2,2,6,6-tetramethylpiperidine) and DB24C8 affords the corresponding pseudorotaxanes. The ESR spectrum of the
reaction mixture indicates the formation of a TEMPO radical in high yield. Details of the conversion of the dialkylamino
group of the ligand to the dialkylammonium group are investigated by using a flow electrolysis method linked to
spectroscopic measurements. The proposed mechanism for the reaction involves the ferrocenium species, formed
by initial oxidation, which undergoes electron transfer from nitrogen to the Fe(III) center, producing a cation radical
at the nitrogen. Transfer of hydrogen from TEMPOH to the cation radical and inclusion of the resulting
dialkylammonium species by DB24C8 yields the pseudorotaxanes.
Introduction
these compounds. Anthraquinone substituted by two ferro-
cenyl groups was reported to undergo electrochemical
oxidation, which accompanies change of the absorption
spectra.2 Ferrocene having an azo or azobenzene group at
the ligand changes the optical properties depending on the
valence of the Fe center.3 Inclusion of ferrocene and
ferrocenium by macrocyclic molecules such as cyclodextrins4
show different binding constants from each other.5 Supramo-
lecular systems that cause decomplexation-recomplexation
of a guest molecule are proposed on the basis of the above
A number of functionalized ferrocenes have been prepared
by introduction of the organic groups to the η5-cyclopenta-
dienyl ligands of ferrocene.1 The ferrocene derivatives,
containing π-conjugated groups in the substituents of the
ligand, exhibit both redox of the Fe center and optical
properties of the organic group. Smooth electronic com-
munication between the metal and the ligand would enable
the cooperative electrochemical and optical performance of
* To whom correspondence should be addressed. Fax: +81-45-924-
5224. E-mail: kosakada@res.titech.ac.jp.
(2) Murata, M.; Yamada, M.; Fujita, T.; Kojima, K.; Kurihara, M.; Kubo,
K.; Kobayashi, Y.; Nishihara, H. J. Am. Chem. Soc. 2001, 123, 12903-
12904.
(3) (a) Kurihara, M.; Matsuda, T.; Hirooka, A.; Yutaka, T.; Nishihara, H.
J. Am. Chem. Soc. 2000, 122, 12373-12374. (b) Kurihara, M.;
Hirooka, A.; Kume, S.; Sugimoto, M.; Nishihara, H. J. Am. Chem.
Soc. 2002, 124, 8800-8801.
(4) Harada, A.; Takahashi, S. J. Chem. Soc., Chem. Commun. 1984, 645-
646.
† Present address: Supramolecular Science Laboratory, The Institute of
Physical and Chemical Research (RIKEN) 2-1 Hirosawa, Wako, Saitama
351-0198, Japan.
(1) (a) Ferrocenes; Togni, A., Hayashi, T., Eds.; VCH: New York, 1995.
(b) Nguyen, P.; Gomez-Elipe, P.; Manners, I. Chem. ReV. 1999, 99,
1515-1548. (c) Colacot, T. J. Chem. ReV. 2003, 103, 3101-3118,
and references therein.
5844 Inorganic Chemistry, Vol. 44, No. 16, 2005
10.1021/ic050215f CCC: $30.25
© 2005 American Chemical Society
Published on Web 07/08/2005

Chemical and Electrochemical Formation of Pseudorotaxanes
Scheme 1
results. A pseudorotaxane composed of a ferrocene deriva-
tive, having long chains at the cyclopentadienyl ligands, and
cationic paraquat-type macrocycles extrude the ferrocene-
containing guest upon electrochemical oxidation.6 Analogous
dethreading-rethreading of the axis molecule in a pseudo-
rotaxane is controlled by pH change of the solution.7
Rotaxanes that change positions of the cyclic molecules by
external stimulus such as change of pH, electrochemical
reaction, and photoirradiation are called molecular shuttles.8,9
An electrochemically driven molecular shuttle was recently
prepared by using the ferrocene-containing molecule as the
axis molecule.10 Application of molecular shuttles, proposed
by several research groups, covers photoinduced high-speed
switching in solution,11 field effect transistors (FET),12 and
molecular memory in the thin films.13
We recently reported that 2-aza[3]ferreocenophanes having
an azobenzene group undergo reversible multistep electro-
chemical oxidation and reduction14 and proposed electron
transfer between the Fe and N atoms at the oxidized state to
account for the electrochemical reaction.15 This electronic
communication between the metal and the ligand provides
a cationic nitrogen center which would be included by crown
ethers to form rotaxanes.16 In this paper, we report the
preparation of pseudorotaxanes containing a ferrocene-
substituted ammonium axis from chemical and electrochemi-
cal reactions. A part of the work was reported in a
preliminarily form.17
Results and Discussions
Preparation of Pseudorotaxanes and Their Character-
ization. Scheme 1 summarizes preparation of the amino-
methylferrocene derivatives. p-Methylbenzylaminomethyl-
ferrocene (1) and n-hexylaminomethylferrocene (2) are
obtained by condensation of ferrocenecarboxaldehyde with
the primary amines followed by NaBH4 reduction of the
formed imines. Analogous reaction of 1,1′-ferrocenedicar-
boxaldehyde yields 1,1′-bis(p-xylylaminomethyl)ferrocene
(3). Treatment of 1-3 with HCl(aq) and NH4PF6 produces
the ferrocene with a dialkylammonium group as the ligand
and a PF6 counteranion, [1-H]+(PF6), [2-H]+(PF6), and
[3-H2]2+(PF6)2, as shown in Scheme 2.
(5) (a) Isnin, R.; Salam, C.; Kaifer, A. E. J. Org. Chem. 1991, 56, 35-
41. (b) Liu, J.; Alvarez, J.; Ong, W.; Roma´n, E.; Kaifer, A. E. J. Am.
Chem. Soc. 2001, 123, 11148-11154. (c) Gonza´lez, B.; Cuadrado,
I.; Alonso, B.; Casado, C. M.; Mora´n, M.; Kaifer, A. E. Organome-
tallics 2002, 21, 3544-3551.
(6) Balzani, V.; Becher, J.; Credi, A.; Nielsen, M. B.; Raymo, F. M.;
Stoddart, J. F.; Talarico, A. M.; Venturi, M. J. Org. Chem. 2000, 65,
1947-1956.
(7) Ashton, P. R.; Ballardini, R.; Balzani, V.; Fyfe, M. C. T.; Gandolfi,
M. T.; Mart´ınez-D´ıaz, M.-V.; Morosini, M.; Schiavo C.; Shibata, K.;
Stoddart, J. F.; White, A. J. P.; Williams, D. J. Chem. Eur. J. 1998,
4, 2332-2341.
(8) (a) Anelli, P. L.; Spencer, N.; Stoddart, J. F. J. Am. Chem. Soc. 1991,
113, 5131-5133. (b) Bissell, R. A.; Co´rdova, E.; Kaifer, A. E.;
Stoddart, J. F. Nature 1994, 369, 133-137. (c) Balzani, V.; Credi,
A.; Mattersteig, G.; Matthews, O. A.; Raymo, F. M.; Stoddart, J. F.;
Venturi, M.; White, A. J. P.; Williams, D. J. J. Org. Chem. 2000, 65,
1924-1936. (d) Altieri, A.; Gatti, F. G.; Kay, E. R.; Leigh, D. A.;
Martel, D.; Paolucci, F.; Slawin, A. M. Z.; Wong, J. K. Y. J. Am.
Chem. Soc. 2003, 125, 8644-8654.
(9) (a) Ashton, P. R.; Ballardini, R.; Balzani, V.; Baxter, I.; Credi, A.;
Fyfe, M. C. T.; Gandolfi, M. T.; Go´mez-Lo´pez, M.; Mart´ınez-D´ıaz,
M.-V.; Piersanti, A.; Spencer. N.; Stoddart, J. F.; Venturi, M.; White,
A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1998, 120, 11932-11942.
(b) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.; Na-
kashima, N. J. Am. Chem. Soc. 1997, 119, 7605-7606. (c) Bottari,
G.; Leigh, D. A.; Pe´rez, E. M. J. Am. Chem. Soc. 2003, 125, 13360-
13361. (d) Pe´rez, E. M.; Dryden, D. T. F.; Leigh, D. A.; Teobaldi,
G.; Zerbetto, F. J. Am. Chem. Soc. 2004, 126, 12210-12211.
(10) Kihara, N.; Hashimoto, M.; Takata, T. Org. Lett. 2004, 6, 1693-
1696.
(11) Brouwer, A. M.; Frochot, C.; Gatti, F. G.; Leigh, D. A.; Mottier, L.;
Paolucci, F.; Roffia, S.; Wurpel, G. W. H. Science 2001, 291, 2124-
2128.
(12) (a) Joachim, C.; Gimzewski, J. K.; Aviram, A. Nature 2000, 408, 541-
548. (b) Cavallini, M.; Biscarini, F.; Leo´n, S.; Zerbetto, F.; Bottari,
G.; Leigh, D. A. Science 2003, 299, 531.
Slow addition of Et2O to a CH2Cl2 solution of [1-H]+-
(PF6) and DB24C8 leads to separation of [(DB24C8)(1-
H)]+(PF6) as crystals, as shown in Scheme 3. [(DB24C8)(3-
H2)]2+(PF6)2 is isolated similarly by addition of Pr2O to a
CH2Cl2/acetone solution of [3-H2]2+(PF6)2 and DB24C8.
The obtained [2] and [3]pseudorotaxanes are characterized
by X-ray crystallography and IR spectroscopy. Figure 1
exhibits molecular structures of the [2] and [3]pseudorotax-
anes. [(DB24C8)(1-H)]+(PF6) has an interlocked structure
with [1-H]+ threading into the pore of DB24C8.
The NH2 and CH2 groups of the axis show short contacts
with the oxygen atoms of DB24C8 (NH‚‚‚O, 2.18 Å and
CH‚‚‚O, 2.35 Å), suggesting the presence of N+-H‚‚‚O and
C-H‚‚‚O interactions between the axis and cyclic molecules.
The aromatic planes of the axis and cyclic molecules are
stacked with each other with a distance between planes of
(13) Collier, C. P.; Wong, E. W.; Belohradsky, M.; Raymo, F. M.; Stoddart,
J. F.; Kuekes, P. J.; Williams, R. S.; Heath, J. R. Science 1999, 285,
391-394.
(16) For recent reviews of ammonium-crown ether rotaxane, see: (a)
Raymo, F. M.; Stoddart, J. F. Chem. ReV. 1999, 99, 1643-1663. (b)
Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. Angew. Chem.,
Int. Ed. 2000, 39, 3348-3391. (c) Balzani, V.; Venturi, M.; Credi, A.
Molecular DeVices and Machines - A Journey into the Nano World;
Wiley-VCH: Weinheim, 2003.
(14) (a) Horie, M.; Sakano, T.; Osakada, K.; Nakao, H. Organometallics
2004, 23, 18-20. (b) Sakano, T.; Horie, M.; Osakada, K.; Nakao, H.
Eur. J. Inorg. Chem. 2005, 4, 644-652.
(15) Sakano, T.; Horie, M.; Osakada, K.; Nakao, H. Bull. Chem. Soc. Jpn.
2001, 74, 2059-2065.
(17) Horie, M.; Suzaki, Y.; Osakada, K. J. Am. Chem. Soc. 2004, 126,
3684-3685.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5845

Horie et al.
Scheme 2
Scheme 3
3.34 Å. [(DB24C8)2(3-H2)]2+(PF6)2 contains two DB24C8
molecules which include the cationic groups attached to the
cyclopentadienyl ligands. The bulky pseudorotaxane groups
are oriented to avoid steric repulsion.
Figure 2 compares the IR spectra of [(DB24C8)(1-H)]+-
(PF6), [1-H]+(PF6), DB24C8, and a mixture of [1-H]+(PF6)
and DB24C8. Peaks due to asymmetric and symmetric
vibration of the NH2 group of [1-H]+(PF6) are observed at
3266 and 3233 cm-1, respectively.
The νN-H positions of [(DB24C8)(1-H)]+(PF6) are shifted
to lower wavenumber by 100 cm-1 (νN-H ) 3166 cm-1) and
166 cm-1 (νN-H ) 3067 cm-1) from that of [1-H]+(PF6),
respectively, indicating weaker N-H bonds of the pseudo-
rotaxane than those in the free axis molecule due to N+-
H‚‚‚O hydrogen bonds.
Thermal properties of the rotaxanes and the pseudorotax-
anes in the solid state are of interest, although the number
of the studies on this subject is small.18 TGA (thermal
gravimetric analysis) of [(DB24C8)(1-H)]+(PF6) shows 5%
weight loss at 237 °C, which is between those of [1-H]+-
(PF6) (217 °C) and DB24C8 (309 °C) (Figure 3).
An equimolar mixture of [1-H]+(PF6) and DB24C8
undergoes similar weight decrease, suggesting that [(DB24C8)-
(1-H)]+(PF6) is dissociated to DB24C8 and [1-H]+(PF6)
on heating in the solid state. DSC (differential scanning
calorimetric) measurement of [(DB24C8)(1-H)]+(PF6) shows
endothermic and exothermic peaks at 125 °C on heating and
114 °C on cooling, respectively. The differential enthalpy
of the phase transition is ∆H ) 1.8 kcal mol-1 at 125 °C.
The temperature of this phase transition of [(DB24C8)(1-
H)]+(PF6) differs from those of [1-H]+(PF6) (Tend ) 188
°C) and of DB24C8 (Tend ) 104 °C, Texo ) 79 °C).
Dissolution of an equimolar mixture of [1-H]+(PF6) and
DB24C8 in CD3CN (10 mM for each compound) gives rise
1
to the H NMR peaks of CH2N hydrogens of [(DB24C8)-
(1-H)]+(PF6) at 4.37 and 4.53 ppm and those of [1-H]+-
(PF6) at 4.04 and 4.06 ppm. Chemical exchange between
the pseudorotaxane and its free axis should take place in the
solution, although it is slower than the NMR time scale.
Downfield shifts of the CH2N hydrogen peaks were reported
for pseudorotaxanes composed of DB24C8 and dibenzylam-
monium cations.19 The ratio of [1-H]+(PF6) to [(DB24C8)-
(1-H)]+(PF6) is determined to be 49:51 from the peak
intensity of the cyclopentadienyl hydrogens. Formation of
[(DB24C8)(2-H)]+(PF6) from [2-H]+(PF6) and DB24C8
in CD3CN (10 mM for each compound) is confirmed by the
1H NMR spectroscopy. The CH2N hydrogen signal of
[2-H]+(PF6) (2.90 ppm) is at a higher-field position than
the corresponding hydrogens of [(DB24C8)(2-H)]+(PF6)
(18) Gibson, H. W.; Liu, S.; Lecavalier, P.; Wu, C.; Shen, Y. X. J. Am.
Chem. Soc. 1995, 117, 852-874.
5846 Inorganic Chemistry, Vol. 44, No. 16, 2005

Chemical and Electrochemical Formation of Pseudorotaxanes
Figure 4. 1H NMR spectra in CD3CN at room temperature (300 MHz).
(a) [3-H2]2+(PF6)2, (b) a mixture of [3-H2]2+(PF6)2 and DB24C8 in a 1:1
molar ratio (10 mM for each compound), and (c) a mixture of [3-H2]2+
(PF6)2 (10 mM) and DB24C8 (50 mM) in a 1:5 molar ratio.
-
the 1H NMR spectrum of [3-H2]2+(PF6)2 which exhibits the
cyclopentadienyl hydrogens at 4.41 and 4.32 ppm and CH2-
N+ hydrogens at 4.01-4.09 ppm.
Figure 1. ORTEP drawing of (a) [(DB24C8)(1-H)]+(PF6) and (b)
[(DB24C8)2(3-H2)]2+(PF6)2 with 30% ellipsoidal plotting. PF6- anions are
omitted. Positions of the hydrogen atoms are obtained by calculation.
1
The H NMR spectrum of a mixture of DB24C8 and
[3-H2]2+(PF6)2 (10 mM for each compound) (Figure 4(b))
exhibits the signals of the CH2-N+ hydrogens at lower-field
positions than those of the axis molecule (4.56, 4.48, 4.38,
and 4.21 ppm). The signals at 4.48 and 4.21 ppm are assigned
to [(DB24C8)2(3-H2)]2+(PF6)2, while the signals at 4.56 and
4.38 ppm are due to [(DB24C8)(3-H2)]2+(PF6)2. The
spectrum of a solution of DB24C8 (50 mM) and [3-H2]2+-
(PF6)2 (10 mM) displays two signals for the CH2-N+
hydrogens (4.48 and 4.21 ppm) (Figure 4(c)). The signal at
3.96 ppm observed in Figure 4(b) and (c) is due to
cyclopentadienyl hydrogens of [(DB24C8)2(3-H2)]2+(PF6)2,
while Figure 4(b) shows the signals of [(DB24C8)(3-H2)]2+-
(PF6)2 at 4.56 and 4.38 ppm. The ratio among [3-H2]2+-
(PF6)2, [(DB24C8)(3-H2)]2+(PF6)2, and [(DB24C8)2(3-
H2)]2+(PF6)2 is determined to be 4.0:4.2:1.1 from the peak-
area ratio of Cp hydrogens.
Figure 2. IR spectra of (a) [(DB24C8)(1-H)]+(PF6), (b) mixture of
[1-H]+(PF6) and DB24C8, (c) [1-H]+(PF6), and (d) DB24C8.
The cyclic voltammogram of [(DB24C8)(1-H)]+(PF6) in
CH3CN shows reversible redox at E1/2 ) 0.23 V (vs Ag+/
Ag). [(DB24C8)(1-H)]+(PF6) up to 0.4 V does not show
any other oxidation reaction. The positive charge of the
pseudorotaxane renders the potential at a more positive
position than 1.5,20,21 The redox potential is the same as that
of [1-H]+(PF6). It is contrasted with the observed shielding
(19) (a) Ashton, P. R.; Campbell, P. J.; Chrystal, E. J. T.; Glinke, P. T.;
Menzer, S.; Philp, D.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.;
Williams, D. J. Angew. Chem., Int. Ed. Engl. 1995, 1865-1869. (b)
Ashton, P. R.; Chrystal, E. J. T.; Glink, P. T.; Menzer, S.; Schiavo,
C.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.; White, A. J. P.; Williams,
D. J. Chem. Eur. J. 1996, 2, 709-728. (c) Ashton, P. R.; Fyfe, M. C.
T.; Hickingbottom, S. K.; Stoddart, J. F.; White, A. J. P.; Williams,
D. J. J. Chem. Soc., Perkin Trans. 2 1998, 2117-2128. (d) Chang,
T.; Heiss, A. M.; Cantrill, S. J.; Fyfe, M. C. T.; Pease, A. R.; Rowan,
S. J.; Stoddart, J. F.; Williams, D. J. Org. Lett. 2000, 2, 2943-2946.
(e) Williams, A. R.; Northrop, B. H.; Houk, K. N.; Stoddart, J. F.;
Williams, D. J. Chem. Eur. J. 2004, 10, 5406-5421.
Figure 3. TGA curves of (a) [(DB24C8)(1-H)]+(PF6), (b) [1-H]+(PF6),
(c) DB24C8, and (d) an equimolar mixture of [1-H]+(PF6) and DB24C8.
Heating rate ) 10 °C min-1
.
(3.32 ppm). The ratio of [2-H]+(PF6) and [(DB24C8)(2-
H)]+(PF6) is 1.0:1.0 in the solution.
Mixing [3-H2]2+(PF6)2 and DB24C8 in CD3CN forms [2]
and [3]pseudorotaxanes whose ratio depends on the ratio of
the axis and cyclic molecules employed. Figure 4(a) shows
(20) (a) Alvarez, J.; Kaifer, A. E. Organometallics 1999, 18, 5733-5734.
(b) Alvarez, J.; Ren, T.; Kaifer, A. E. Organometallics 2001, 20,
3543-3549.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5847

Horie et al.
Scheme 4
effect of the macrocyclic component in the interlocked
structure of the rotaxane composed of a ferrocene-containing
axis molecule and DB24C8.10
Formation of Pseudorotaxane Induced by Electro-
chemical Oxidation. Electrochemical oxidation of 1 and 2
at 0.4 V (vs Ag+/Ag) in the presence of DB24C8 and
TEMPOH produces the [2]pseudorotaxanes composed of the
ferrocene derivative, with the dialkylammonium group and
DB24C8, as shown in Scheme 4.
subsequent addition of TEMPOH. The three peaks are
assigned to the TEMPO radical by comparison with the
standard sample (Figure 6(b)). The intensity of the produced
TEMPO radical is determined as 92% of the initially charged
TEMPOH.22 The solution without electrochemical oxidation
gives the signal with a much smaller intensity (Figure 6(c)).
Formation of the pseudorotaxanes indicates that the
electrochemical oxidation in the presence of TEMPOH
A mixture of the [2] and [3]pseudorotaxanes, [(DB24C8)-
(3-H)]+ and [(DB24C8)2(3-H2)]2+, is obtained from the
oxidation of 3 at the same potential in the presence of
TEMPOH and DB24C8. A CH3CN solution of a mixture of
1, n-Bu4NPF6, DB24C8, and TEMPOH does not produce a
pseudorotaxane without electrochemical oxidation.
Figure 5(a) depicts the FAB mass spectrum after electro-
chemical oxidation of 1 at 0.4 V in the presence of DB24C8
and TEMPOH.
A peak at m/z ) 768 is assigned to the cationic part of
[(DB24C8)(1-H)]+(PF6). Flow electrolysis of 2 in the
presence of TEMPOH and DB24C8 at 0.4 V leads to the
formation of [(DB24C8)(2-H)]+, which shows a peak at m/z
) 748 in the mass spectrum (Figure 5(b)). The CH3CN
solution after flow electrolysis of 3 in the presence of
TEMPOH and DB24C8 at 0.4 V shows the FAB mass peak
at m/z ) 674 corresponding to the dicationic [3]pseudo-
rotaxane, [(DB24C8)2(3-H2)]2+ and that at m/z ) 901 due
to the monocationic [2]pseudorotaxane, [(DB24C8)(3-H)]+
(Figure 5(c)). These reactions convert TEMPOH into the
TEMPO radical. Figure 6(a) displays the ESR spectrum of
the solution, obtained by electrochemical oxidation of 1 and
Figure 5. FAB mass spectra of (a) [(DB24C8)(1-H)]+, (b) [(DB24C8)-
(2-H)]+, and (c) [(DB24C8)(3-H)]+ and[(DB24C8)2(3-H2)]2+. The
pseudorotaxanes formed by the electrochemical oxidation of the axis
molecules at 0.4 V by using of flow electrolysis system are applied to
measurement. A mixture of glycerol and m-nitrobenzyl alcohol was used
as the matrix. Peaks with asterisks are due to the compounds used as the
matrixes.
(21) (a) Menger, F. M.; Sherrod, M. J. J. Am. Chem. Soc. 1988, 110, 8606-
8611. (b) Matsue, T.; Evans, D. H.; Osa, T.; Kobayashi, N. J. Am.
Chem. Soc. 1985, 107, 3411-3417.
5848 Inorganic Chemistry, Vol. 44, No. 16, 2005

Chemical and Electrochemical Formation of Pseudorotaxanes
Figure 6. ESR spectra of (a) 1 (1.0 mM) and n-Bu4NPF6 (1.0 mM) after
flow electrolysis at 0.4 V and addition of TEMPOH (1.0 mM), (b) TEMPO
(1.0 mM), and (c) a mixture of 1 (1.0 mM), n-Bu4NPF6 (1.0 mM) and
TEMPOH (1.0 mM). g ) 2.0059.
induces protonation of the dialkylamino group of 1-3 to
afford the ferrocene derivatives with the dialkylammonium
group at the ligands. The reactions without addition of
TEMPOH take place much more slowly but produce similar
products. Electrochemical and spectroscopic measurements
of the reaction mixtures are conducted in order to elucidate
the detailed mechanism of the protonation. Cyclic and linear
sweep voltammograms during the electrochemical oxidation
of 1 (2.0 mM) indicate that the quantitative one-electron
oxidation at 0.40 V (vs Ag+/Ag) converts the ferrocenylene
group into ferrocenium in >98% yield.23 The presence of
DB24C8 does not influence this reaction at all.9a
Figure 7. 1H NMR spectra of (a) [1-H]+(PF6) (electrochemically
hydrogenated), (b) [1-H]+(PF6) (chemically protonated), and (c) 1 in CD3-
CN (300 MHz).
The products of flow electrolysis of 1 (2.0 mM) in the
presence of H2O (2.0 mM) and n-Bu4NPF6 at 0.4 V were
analyzed by 1H NMR and absorption spectra. The 1H NMR
signals of the CH2-N+ hydrogens (4.04 and 4.06 ppm) are
at the same positions as those of [1-H]+(PF6) prepared by
protonation of 1, as shown in Figure 7(a) and (b).
Figure 8. Absorption spectra of 1 in the presence of DB24C8 in a CH3-
CN solution of 10 mM n-Bu4NPF6. [1]0 ) 2.0 mM, [DB24C8]0 ) 4.0 mM.
Spectra measured immediately after the electrolysis at (a) -0.4 (vs Ag+/
Ag), (b) 0, (c) 0.05, (d) 0.1, and (e) 0.40 V.
The other peak positions are identical to each other except
for the peaks of the electrolyte in the electrochemically
prepared [1-H]+(PF6). Addition of DB24C8 to the product
yields the pseudorotaxane [(DB24C8)(1-H)]+, which gives
Scheme 5
1
rise to the H NMR signals at 4.37 and 4.53 ppm.
The absorption spectra of the solution during the electro-
chemical oxidation without addition of TEMPOH show
immediate formation of a peak at 630 nm and its gradual
decrease. Scheme 5 displays a plausible pathway of the
reaction converting 1 into [1-H]+. Initial electrochemical
oxidation of the Fe center takes place rapidly to form a
ferrocenium intermediate (i). Subsequent electron transfer
from nitrogen to Fe(III) and intermolecular hydrogen transfer
from other compounds afford the product (ii). Since TEM-
POH is a good source of hydrogen radical, reaction (ii) is
accelerated by addition of TEMPOH.
Figure 8 shows the spectra of the solution soon after
electrochemical oxidation of a mixture of 1 and DB24C8
(1:2 molar ratio) at constant potentials (-0.4-1.0 V).
The peak at 630 nm, whose intensity increases with an
increase of the applied potential, Eapp, is assigned to the
ferrocenium ion on the basis of the characteristic peak
position.24 Applying of the Nernst equation (Eapp ) E° +
(22) (a) Keana, J. F. W. Chem. ReV. 1978, 78, 37-64. (b) Roth, J. P.;
Yoder, J. C.; Won, T.-J.; Mayer, J. M. Science 2001, 294, 2524-
2526.
(24) Winter, R. F.; Wolmersha¨user, G. J. Organomet. Chem. 1998, 570,
201-218.
(23) Nakao, H.; Hayashi, H.; Okita, K. Anal. Sci. 2001, 17, 545-549.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5849

Horie et al.
Scheme 6
Figure 9. Pseudo-first-order plots of consumption of ferricinium ion of 1
in the presence of DB24C8 of (a) 0 (kobsd ) 3.4 × 10-4 s-1), (b) 2.0 (kobsd
) 4.6 × 10-4 s-1), (c) 5 (kobsd ) 1.5 × 10-3 s-1), (d) 10 (kobsd ) 2.6 ×
10-3 s-1), (e) 20 (kobsd ) 4.4 × 10-3 s-1), and (f) 20 mM with H2O (kobsd
) 4.4 × 10-3 s-1). Change in the observed rate constants depending on
the DB24C8 concentration is in inset.
(RT/nF) ln([Ox]/[Red]), E° ) the formal oxidation potential),
by assuming an equilibrium between the oxidized and
reduced species, gave E° ) 0.10 V and n ) 0.5. The n value,
which is much smaller that expected for one-electron
oxidation (1.0), indicates that a irreversible chemical reaction
of the oxidized species also takes place at this potential.
The above solutions undergo gradual decrease in the peak
intensity at 630 nm, while addition of TEMPOH to the
solution (2.0 mM) results in disappearance of the peak within
2 s. These reactions correspond to the conversion of the
ferrocenium into the ferrocene bonded to the dialkylammo-
nium group (Scheme 5(ii)). Figure 9 displays first-order plots
of decrease in the peak intensity at various concentrations
of DB24C8 in the absence of TEMPOH. The observed rate
constants, kobsd, vary from 3.4 × 10-4 ([DB24C8]0 ) 0 mM)
to 4.4 × 10-3 s-1 ([DB24C8]0 ) 20 mM).
ammonium cation and a TEMPO radical. The formed
dialkylammonium group undergoes inclusion by DB24C8
immediately to afford the pseudorotaxane (ii). In the absence
of TEMPOH, the intermediate B is hydrogenated by the CH2
group of DB24C8 much more slowly than the reaction with
TEMPOH to produce the ferrocene-containing dialkylam-
monium group. Since the mass spectra of the pseudorotax-
anes formed by the reactions without TEMPOH give rise to
the peak composed of the axis molecule and DB24C8, the
cyclic compound whose hydrogen is abstracted does not form
the rotaxane with the cationic axis molecule. Enhancement
of the reaction by [15]crown-5 indicates that the hydrogen
transfer from the crown ether to the nitrogen cation radical
does not require inclusion of the cyclic compound to the
cation radical species. The reaction without addition of
TEMPOH and DB24C8 causes intramolecular C-H hydro-
gen abstraction from the aminomethyl cation radical to
produce the imminium [-CHdN+-] cation (m/z ) 319
observed by FAB mass spectroscopy).
In summary, we synthesized new [2] and [3]pseudorotax-
anes containing ferrocenyl groups on the axis molecule and
DB24C8 and identified them well in the solid state and in
solution. Electrochemical oxidation coupled with the transfer
of a hydrogen atom from a hydrogen source such as
TEMPOH provides the pseudorotaxanes with DB24C8.
Electron transfer between the Fe and N atoms plays an
important role for formation of the dialkylammonium from
the dialkylamine group.
Increase of the concentration of DB24C8 increases the
observed rate constants, indicating that DB24C8 enhances
the conversion of the ferrocenium with dialkylamine group
into the ferrocene having a dialkylammonium group. The
reaction in the presence of [15]crown-5 (20 mM) instead of
DB24C8 proceeds with kobsd ) 2.4 × 10-3 s-1, which is
larger than that for the reaction without addition of the crown
ethers (3.4 × 10-4 s-1). Thus, the crown ether with a too-
small cavity to include the dialkylammonium group also
enhances the reaction.
Scheme 6 summarizes the mechanism that accounts for
the above results for electrochemical oxidation of 1 into
[1-H]+(PF6) and its pseudorotaxane. One-electron oxidation
of 1 forms the ferrocenium species A containing an Fe(III)
center, as shown in (i). A is in fast equilibrium with B, having
an Fe(II) center and a cation radical at the N atom via
electron transfer between the Fe and N atoms.
Similar electron transfer between N and Fe(III) atoms of
aminoalkylferrocenium species is proposed to explain the
electrochemical behavior of 2-aza[3]ferrocenophanes and
oligoferrocenes with Fe-CH2-NR-CH2-Fe groups.15,20
The absorption spectrum in Figure 8(e) shows a similar peak
intensity for [Fe(Cp)2]+(PF6) (approximately 86%), indicating
that the equilibrium is shifted to the formation of A with
the Fe(III) center. TEMPOH transfers a hydrogen radical to
the cation radical at the nitrogen of B to produce a secondary
Experimental Section
General Methods. 125 and 1,1′-ferrocenedicarboxaldehyde26
were prepared according to the literature methods. DB24C8 and
ferrocenecarboxaldehyde were purchased from Tokyo Kasei Kogyo
Co., Ltd. and Strem Chemicals. 1H and 13C{1H} NMR spectra were
recorded on JEOL EX-400 and Varian Mercury 300 spectrometers.
The chemical shifts were referenced with the solvent peaks (CHCl3,
δΗ ) 7.24; CD2HCN, δΗ ) 1.93; CDCl3, δC ) 77.0; and CD3CN,
(25) Hess, A.; Brosch, O.; Weyhermu¨ller, T.; Metzler-Nolte, N. J.
Organomet. Chem. 1999, 589, 75-84.
(26) Bastin, S.; Agbossou-Niedercorn, F.; Brocard, J.; Pelinski, L. Tetra-
hedron: Asymmetry 2001, 12, 2399-2408.
5850 Inorganic Chemistry, Vol. 44, No. 16, 2005

Chemical and Electrochemical Formation of Pseudorotaxanes
δC ) 1.30). IR spectra were recorded on Shimadzu FT/IR-8100
spectrometers. Elemental analyses were carried out with a Yanaco
MT-5 CHN autorecorder. Melting point determinations were carried
out with a Yanagimoto Seisakusho Micro Melting Point Apparatus.
TGA and DSC analyses were conducted on Seiko TG/DTA6200R
and DSC6200S, respectively. FAB mass spectra were obtained with
JEOL JMS-700 using glycerol or m-nitrobenzyl alcohol as the
matrix. ESR spectra were recorded on a JEOL RE3X spectrometer.
Cyclic voltammetry (CV) was measured in CH3CN solutions
containing 10 mM n-Bu4NPF6 with ALS electrochemical analyzer
Model-600A. The measurement was carried out in a standard one-
compartment cell under inert gas equipped with a Ag+/Ag reference
electrode, a platinum-wire counter electrode, and a platinum-disk
working electrode (ID, 1.6 mm). A combination of flow through
Figure 10. ORTEP drawing of 1,1′-bis(p-xylyliminomethyl)ferrocene with
50% ellipsoidal plotting.
an electrolysis cell, a peristaltic pump SMP-11 at 0.7 mL min-1
,
69.4 (CH2, C5H4 or CdN), 71.3 (CH2, C5H4 or CdN), 81.4 (CH2,
C5H4 or CdN), 127.9 (C6H4), 129.1 (C6H4), 136.3 (C6H4), 136.4
(C6H4), 161.1 (C6H4). mp: 113-116 °C. Figure 10 shows the
molecular structure determined by X-ray crystallography.
and a JASCO V-530 UV/VIS spectrometer was used for the linear
sweep voltammetry and the spectroelectrochemical measurements
in situ.23
Preparation of 1,1′-Bis(p-xylylaminomethyl)ferrocene (3).
1,1′-Bis(p-xylyliminomethyl)ferrocene (1.42 g, 3.17 mmol) was
dissolved in a THF/MeOH solution (THF/MeOH ) 50 mL:50 mL).
NaBH4 (360 mg, 9.52 mmol) was added to the solution and stirred
for 2 h at room temperature. An extra portion of NaBH4 (360 mg,
9.52 mmol) was added to the reaction mixture, which was stirred
for further 24 h, before being quenched with 1 N HCl (100 mL).
Evaporation of the solvent gave the remaining solid, which was
partitioned between 2 N KOH and CH2Cl2. The organic extract
was dried over MgSO4 then filtered and concentrated under reduced
pressure to give 3 as brown oil (1.42 g, 99%). Anal. Calcd. for
C28H32N2Fe: C, 74.33; H, 7.13; N, 6.19. Found: C, 74.07; H, 7.39;
Preparation of (n-Hexylamino)methylferrocene (2). A toluene
solution (80 mL) containing ferrocenecarboxaldehyde (2.13 g, 10.0
mmol) and n-hexylamine (1.02 g, 10.1 mmol) was stirred for 24 h
at 80 °C in the presence of MS4A (4 Å molecular sieves). MS4A
was removed by filtration, and the filtrate was evaporated to give
n-hexyliminomethylferrocene as a brown oil which is used without
further purification [1H NMR spectrum (300 MHz, CDCl3, r. t.):
δ 0.92 (m, 3H, CH3), 1.32-1.35* (6H, CH2), 1.65 (m, 2H, CH2),
3.46 (2H, NCH2), 4.19 (s, 5H, C5H5), 4.36 (s, 2H, C5H4), 4.64 (s,
2H, C5H4), 8.11 (s, 1H, NCH). 13C{1H} NMR spectrum (75.5 MHz,
CDCl3, r. t.): δ 14.0 (CH3), 22.5 (CH2), 26.9 (CH2), 30.8 (CH2),
31.6 (CH2), 61.9 (NCH2), 68.2 (C5H4 or C5H5), 68.9 (C5H4 or C5H5),
70.1 (C5H4 or C5H5), 80.7 (C5H4), 160.4 (NCH).]. The above
product was dissolved in THF/MeOH (50 mL:50 mL) at room
temperature. NaBH4 (766 mg, 20.5 mmol) was added to the
solution, and the mixture was stirred for 2 h at room temperature.
An extra portion of NaBH4 (720 mg, 19.0 mmol) was added to the
reaction mixture. Stirring was continued for 12 h before the product
being quenched with 1 N HCl (100 mL). After evaporation of the
solvent, the remaining solid was partitioned between 2 N KOH
and CH2Cl2. The organic extract was dried over MgSO4, filtered,
and concentrated under reduced pressure to give 2 as a brown oil
(2.31 g, 7.75 mmol, 78%). Anal. Calcd. For C17H25NFe: C, 68.24;
1
N, 5.91. H NMR (300 MHz, CDCl3, r. t.): δ 2.33 (s, 6H, CH3),
3.47 (s, 4H, CH2), 3.74 (s, 4H, CH2), 4.03 (m, 4H, C5H4), 4.10 (m,
4H, C5H4), 7.12 (d, 4H, o-C6H4 or m-C6H4, J (HH) ) 8 Hz), 7.20
(t, 4H, o-C6H4 or m-C6H4, J(HH) ) 8 Hz). 13C{1H} NMR (75.5
MHz, CDCl3, r. t.): δ 21.0 (CH3), 47.8 (CH2), 52.9 (CH2), 68.1
(C5H4), 68.6 (C5H4), 86.9 (C5H4), 127.9 (C6H4), 129.0 (C6H4), 136.3
(C6H4), 137.1 (C6H4).
Preparation of [1-H]+(PF6). A suspension of 1 (362 mg, 1.13
mmol) in 6 N HCl (40 mL) was stirred for 12 h at room temperature.
Evaporation of the solvent gave [1-H]+Cl, which was washed with
water. To a suspension of [1-H]+Cl in acetone (50 mL) was added
NH4PF6 (1.63 g, 10 mmol), and the mixture was stirred for 4 h at
room temperature. The precipitate was removed by filtration.
Evaporation of the filtrate gave [1-H]+(PF6) as a yellow solid (408
mg, 0.877 mmol, 78%). Anal. Calcd. for C19H22NF6FeP: C, 49.06;
1
H, 8.42; N, 4.68. Found: C, 68.76; H, 8.07; N, 4.61. H NMR
spectrum (300 MHz, CDCl3, r. t.): δ 0.86 (t, 3H, CH3, J (HH) )
7 Hz), 1.26-1.28* (6H, CH2), 1.46 (m, 2H, CH2), 2.60 (t, 2H,
NCH2, J (HH) ) 8 Hz), 3.48 (s, 2H, NCH2), 4.08 (m, 2H, C5H4),
4.10 (s, 5H, C5H5), 4.16 (m, 2H, C5H4). 13C{1H} NMR spectrum
(75.5 MHz, CDCl3, r. t.): δ 14.0 (CH3), 22.6 (CH2), 27.1 (CH2),
30.0 (CH2), 31.8 (CH2), 49.1 (NCH2), 49.7 (NCH2), 67.7 (C5H4 or
C5H5), 68.2-68.4* (2C, C5H4 or C5H5), 68.4 (C5H4 or C5H5). The
peaks with asterisks are overlapped significantly with other signals.
1
H, 4.77; N, 3.01. Found: C, 48.98; H, 4.65; N, 3.02. H NMR
(300 MHz, CD3CN, r. t.): δ 2.34 (s, 3H, CH3), 4.04 (br, 2H, CH2),
4.06 (br, 2H, CH2), 4.21 (s, 5H, C5H5), 4.28 (m, 2H, C5H4), 4.37
(m, 2H, C5H4), 7.25 (d, 2H, C6H4, J (HH) ) 8 Hz), 7.30 (d, 2H,
C6H4, J (HH) ) 8 Hz). 13C{1H} NMR spectrum (75.5 MHz, CD3-
CN, r. t.): δ 21.3 (CH3), 48.7 (CH2), 51.6 (CH2), 70.1 (C5H5 or
C5H4), 70.7 (C5H5 or C5H4), 71.7 (C5H5 or C5H4), 76.5 (C5H5 or
C5H4), 128.4 (C6H4), 130.6 (C6H4), 131.0 (C6H4), 140.6 (C6H4).
IR spectrum (KBr): ν (N-H), 3266 and 3233 cm-1. mp: 189-
192 °C (decomp).
Preparation of [2-H]+(PF6). A suspension of 2 (740 mg, 2.47
mmol) in 6 N HCl (60 mL) was stirred for 12 h at room temperature.
Evaporation of the solvent gave [2-H]+Cl, which was washed with
water. To a suspension of [2-H]+Cl in acetone (50 mL) was added
NH4PF6 (1.63 g, 10 mmol), and the mixture was stirred for 4 h at
room temperature. The precipitate was removed by filtration, and
the evaporation of the filtrate gave [2-H]+(PF6) as a yellow solid
(395 mg, 0.887 mmol, 36%). Anal. Calcd. for C17H26NF6FeP: C,
Preparation of 1,1′-Bis(p-xylylaminomethyl)ferrocene (Fc-
imine). A solution of 1,1′-ferrocenedicarboxaldehyde (1.21 g, 5.00
mmol) and p-methylbenzylamine (1.21 g, 9.99 mmol) in toluene
(80 mL) was stirred for 3 days at 80 °C in the presence of MS4A.
MS4A was removed by the filtration, and the filtrate was evaporated
to give Fc-imine as a redbrick solid, which was purified by
recrystallization from Et2O (1.63 g, 3.64 mmol, 73%). Anal. Calcd.
for C28H28N2Fe: C, 75.00; H, 6.29; N, 6.25. Found: C, 74.60; H,
1
6.48; N, 6.04. H NMR (300 MHz, CD3CN, r. t.): δ 2.31 (s, 6H,
CH3), 4.33 (m, 4H, C5H4), 4.54 (s, 4H, CH2), 4.63 (m, 4H, C5H4),
7.14 (t, 4H, o-C6H4 or m-C6H4, J (HH) ) 8 Hz), 7.16 (t, 4H, o-C6H4
or m-C6H4, J (HH) ) 8 Hz), 8.06 (s, 2H, CH). 13C{1H} NMR (75.5
MHz, CD3CN, r. t.): δ 21.0 (CH3), 65.0 (CH2, C5H4 or CdN),
Inorganic Chemistry, Vol. 44, No. 16, 2005 5851

Horie et al.
Table 1. Crystal Data and Details of Structure Refinement of [(DB24C8)(1-H)]+(PF6) and [(DB24C8)2(3-H2)]2+(PF6)2 and
1,1′-Bis(p-xylyliminomethyl)ferrocene (Fc-imine)
compound
formula
mol wt
cryst syst
space group
a/Å
b/Å
c/Å
[(DB24C8)(1-H)]+(PF6)
[(DB24C8)2(3-H2)]2+(PF6)2(H2O)2
Fc-imine
C43H54F6FeNO8P
913.71
C76H102FeN2P2F12O18
1677.42
triclinic
P1h (No. 2)
10.568(7)
18.641(12)
22.41(2)
78.21(3)
82.02(3)
69.27(2)
4032(5)
2
C28H28FeN2
448.39
triclinic
P1h (No. 2)
10.1889(13)
11.050(3)
19.460(2)
87.09(3)
98.43(2)
89.02(2)
2135.1(7)
2
monoclinic
P21/c (No. 14)
5.9651(11)
13.627(2)
27.819(8)
R/deg
â/deg
102.955(12)
γ/deg
V/Å3
2203.7(8)
4
7.02
944.00
1.351
0.5 × 0.2 × 0.2
4909
3355
308
0.037
0.050
1.00
Z
µ (Mo KR)/cm-1
F(000)
4.69
956.00
1.421
3.22
1760.00
1.382
D c/g cm-1
crystal size/mm
unique reflns
used reflns [I g 3.0σ (I)]
no. of variables
R
0.5 × 0.2 × 0.15
0.3 × 0.1 × 0.1
8838
16527
5174
595
0.063
0.090
6515
1088
0.111
0.138
Rw
GOF
0.95
1.34
1
45.86; H, 5.89; N, 3.15. Found: C, 45.98; H, 6.03; N, 3.20. H
NMR (300 MHz, CD3CN, r. t.): δ 0.88 (t, 3H, CH3, J (HH) ) 7
Hz), 1.28-1.32* (6H, CH2), 1.57 (m, 2H, CH2), 2.90 (m, 2H, NCH2-
CH2), 3.97 (s, 2H, NCH2C5H4), 4.20 (s, 5H, C5H5), 4.27 (m, 2H,
C5H4), 4.35 (m, 2H, C5H4), 6.41 (br, 2H, NH2). 13C{1H} NMR (75.5
MHz, CD3CN, r. t.): δ 14.2 (CH3), 23.0 (CH2), 26.3 (CH2), 26.5
(CH2), 31.7 (CH2), 48.2 (NCH2), 48.7 (NCH2), 69.9 (C5H5 or C5H4),
70.5 (C5H5 or C5H4), 71.3 (C5H5 or C5H4), 76.6 (C5H5 or C5H4).
The peak with asterisk is overlapped significantly with other signals.
mp: 193-196 °C (decomp).
mmol, or [2-H]+(PF6), 3.1 mg, 0.0070 mmol). The sample was
placed in an NMR spectrometer. The 1H NMR spectra were
recorded at 30 °C. The molar ratio of DB24C8 and ammonium
salts was determined by comparison of the peak area of methylene
hydrogens.
1H NMR of [(DB24C8)(1-H)]+(PF6) (300 MHz, CD3CN, r. t.):
δ 2.14 (s, 3H, CH3), 3.60-4.20* (OCH2, C5H5, C5H4, 33H), 4.37
(m, 2H, NCH2), 4.53 (m, 2H, NCH2), 6.85-6.64* (10H, C6H4, o-
1
or m-C6H4 (DB24C8)), 7.14 (2H, o- or m-C6H4 (DB24C8)). H
NMR of [(DB24C8)(2-H)]+(PF6) (400 MHz, CD3CN, 30 °C): δ
0.89 (t, 3H, CH3, J (HH) ) 1 Hz), 1.03-1.11* (4H, CH2), 1.29-
1.38* (2H, CH2), 1.40 (m, 2H, CH2), 3.32 (m, 2H, NCH2), 3.60-
4.35* (35H, C5H5, OCH2), 6.88-6.98* (8H, C6H4). FABMS: m/z
) 748 [M - PF6]+. The peaks with asterisks are overlapped
significantly with other signals.
Preparation of [3-H2]2+(PF6)2. A heterogeneous solution of
1,1′-bis(p-xylylaminomethyl)ferrocene (3) (460 mg, 1.02 mmol) in
6 N HCl (50 mL) was stirred for 13 h at room temperature.
Evaporation of the solvent gave [3-H2]2+Cl2 that was washed with
water. [3-H2]2+Cl2 was suspended in an acetone solution (50 mL)
of NH4PF6 (1.65 g, 10 mmol), and the suspension was stirred for
4 h at room temperature. The precipitate was removed by the
filtration and the evaporation of the filtrate gave [3-H2]2+(PF6)2
as a yellow solid (523 mg, 0.703 mmol, 69%). Anal. Calcd. for
C28H34NF12Fe2P2: C, 45.18; H, 4.60; N, 3.76. Found: C, 45.40;
[2] and [3]Pseudorotaxane Formation in CD3CN. DB24C8
(3.1 mg, 0.0069 mmol) and [3-H2]2+(PF6)2 (5.2 mg, 0.0070 mmol)
were dissolved in CD3CN (0.7 mL) in an NMR tube. The molar
ratio of [3-H2]2+(PF6)2, [(DB24C8)(3-H2)]2+(PF6)2, and [(DB24C8)2-
(3-H2)]2+(PF6)2 in the reaction mixture was determined to be 4.0:
4.2:1.1 by the 1H NMR spectrum (CH2 peak area ratio). Evaporation
of the solvent left a red solid whose FABMS spectrum showed the
peaks of the [2] and [3]pseudorotaxanes. The solution from DB24C8
(3.1 mg, 0.0069 mmol) and [3-H2]2+(PF6)2 (15.7 mg, 0.0035 mmol)
in CD3CN (0.7 mL) contained [3]pseudorotaxane, [(DB24C8)2(3-
1
H, 4.53; N, 3.76. H NMR (300 MHz, CD3CN, r. t.): δ 2.35 (s,
6H, CH3), 4.03 (m, 4H, CH2), 4.07 (m, 4H, CH2), 4.32 (m, 4H,
C5H4), 4.41 (m, 4H, C5H4,), 6.78 (br, 4H, NH2), 7.27 (m, 4H, o-C6H4
or m-C6H4), 7.29 (m, 4H, o-C6H4 or m-C6H4). 13C{1H} NMR (75.5
MHz, CD3CN, r. t.): δ 21.3 (CH3), 48.3 (CH2), 51.8 (CH2), 71.7
(br, C5H4), 72.6 (br, C5H4), 77.5 (C5H4), 128.5 (C6H4), 130.6 (C6H4),
131.0 (C6H4), 140.8 (C6H4). 13C{1H} NMR (100 MHz, CD3CN,
60 °C): δ 21.4 (CH3), 48.7 (CH2), 52.2 (CH2), 72.1 (C5H4), 72.7
(C5H4), 77.9 (C5H4), 128.7 (C6H4), 130.9 (C6H4), 131.1 (C6H4),
141.1 (C6H4). mp: 197-200 °C (decomp).
1
H2)]2+(PF6)2, only. H NMR of [(DB24C8)(3-H2)]2+(PF6)2 (400
MHz, CD3CN, r. t.): δ 2.15 (s, 3H, CH3), 2.34-2.36* (3H, CH3),
3.53-4.25* (32H, C5H4, NCH2, OCH2), 4.21 (m, 2H, C5H4), 4.27
(m, 2H, C5H4), 4.38 (m, 2H, NCH2), 4.56 (m, 2H, NCH2), 6.87-
6.92* (12H, C6H4), 7.14 (2H, C6H4 (DB24C8), J(HH) ) 8 Hz),
7.26-7.29* (4H, C6H4 (DB24C8)). NH2 was not observed.
Isolation of [(DB24C8)(1-H)]+(PF6). Yellow crystals of pseu-
dorotaxane [(DB24C8)(1-H)]+(PF6) were obtained by vapor dif-
fusion of Et2O into a solution of [1-H]+(PF6) (58.3 mg) and
DB24C8 (46.5 mg) in CH2Cl2 (2 mL) in 72% yield. [(DB24C8)-
(1-H)]+(PF6) was obtained in 72% yield. Anal. Calcd. for C43H54-
NF6FeP: C, 56.52; H, 5.96; N, 1.53. Found: C, 56.37; H, 5.80; N,
1.53. IR (KBr): ν(N-H), 3067 and 3166 cm-1. FABMS: m/z )
768 [M - PF6]+.
1
FABMS: m/z ) 1047 [M - PF6]+. H NMR of [(DB24C8)2(3-
H2)]2+(PF6)2 (400 MHz, CD3CN, r. t.): δ 2.16 (s, 6H, CH3), 3.53-
4.11*(68H, C5H4, OCH2), 3.96 (m, C5H4, 4H), 4.21 (m, NCH2, 4H),
4.48 (m, NCH2, 4H), 6.86-6.93* (20H, C6H4), 7.14 (br, 4H, NH2),
7.15 (4H, C6H4 (DB24C8), J (HH) ) 8 Hz). FABMS: m/z ) 1496
[M - PF6]+, 901 [M - 2(PF6)]+. The peaks with asterisks are
overlapped significantly with other signals.
[2]Pseudorotaxane Formation in CD3CN. In an NMR tube was
charged a CD3CN solution (0.7 mL) of DB24C8 (3.1 mg, 0.0069
mmol) and the ammonium salts ([1-H]+(PF6) 3.3 mg, 0.0070
Spectroscopic Measurement of Electrochemical Formation
of [2]Pseudorotaxane. A typical kinetic experiment is as follows.
A CH3CN solution of 1 (2.0 mM) containing n-Bu4NPF6 (0.1 M)
5852 Inorganic Chemistry, Vol. 44, No. 16, 2005

Chemical and Electrochemical Formation of Pseudorotaxanes
was electrochemically oxidized at 0.4 V (vs Ag+/Ag) by using flow
electrolysis system and was soon collected to a 1 cm × 1 cm quartz
cell. After addition of DB24C8 (0, 4, 10, 20, or 40 mM) to the
solution, the absorption spectra were measured every 3 min.
Crystal Structure Analysis. Crystals of [(DB24C8)(1-H)]+-
(PF6), [(DB24C8)2(3-H2)]2+(PF6)2, and 1,1′-bis{(4-xylyl)imino-
methyl}ferrocene suitable for X-ray diffraction study were obtained
by recrystallization from CH2Cl2/Et2O, CH2Cl2/acetone/n-Pr2O, and
Et2O, respectively, and mounted in glass capillary tubes. The data
were collected to a maximum 2θ value of 55.0°. A total of 720
oscillation images were collected. A sweep of data was done using
ω scans from -110.0° to 70.0° in 0.5° steps, at ø ) 45.0° and φ
) 0.0°. The detector swing angle was -20.42°. A second sweep
was performed using ω scans from -110.0° to 70.0° in 0.5° step,
at ø ) 45.0° and φ ) 90.0°. The crystal-to-detector distance was
44.84 mm. Readout was performed in the 0.070 mm pixel mode.
Calculations were carried out by using a program package Crystal
Structure for Windows.27 The structure was solved by direct
methods and expanded using Fourier techniques. A full-matrix least-
squares refinement was used for the nonhydrogen atoms withaniso-
tropic thermal parameters. Crystal data and detailed results of
refinement are summarized in Table 1.
Acknowledgment. This work was financially supported
by a Grant-in-aid for Scientific Research from the Ministry
of Education, Culture, Sport, Science, and Technology Japan,
and by The 21st Century COE Program “Creation of
Molecular Diversity and Development of Functionalities”.
We are grateful to Assistant Prof. Atsushi Mori of our
institute for FABMS measurement.
Supporting Information Available: Crystallographic data have
been deposited at the CCDC, 12 Union Road, Cambridge CB21EZ,
UK and copies can be obtained on request, free of charge, by
quoting the publication citation and the deposition numbers, 235382,
257706, and 257707.
IC050215F
(27) Crystal Structure 3.6.0: Crystal analysis package, Rigaku and Rigaku/
MSC (2000-2004).
Inorganic Chemistry, Vol. 44, No. 16, 2005 5853