N-Substituted 2-aza-[3]-ferrocenophanes. New synthesis using RuCl2(PPh3)3 catalyzed condensation, structure, and electrochemical behavior

Article abstract of DOI:10.1016/S0022-328X(99)00114-X

The reactions of 1,1′-ferrocenedimethanol with arylamine and with alkylamine in the presence of RuCl₂(PPh₃)₃ catalyst led to condensation of CH₂OH and NH groups to afford N-alkyl-(or N-aryl-)2-aza-[3]-ferrocenop

Full text of DOI:10.1016/S0022-328X(99)00114-X

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 584 (1999) 213–216
Priority Communication
N-Substituted 2-aza-[3]-ferrocenophanes. New synthesis using
RuCl2(PPh3)3 catalyzed condensation, structure, and
electrochemical behavior
Isao Yamaguchi, Tatsuaki Sakano, Hidetake Ishii, Kohtaro Osakada *,
Takakazu Yamamoto 1
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
Received 26 January 1999; received in revised form 23 February 1999
Abstract
The reactions of 1,1%-ferrocenedimethanol with arylamine and with alkylamine in the presence of RuCl2(PPh3)3 catalyst led to
1
condensation of CH2OH and NH groups to afford N-alkyl-(or N-aryl-)2-aza-[3]-ferrocenophanes. The H- and 13C-NMR spectra
and crystallography of N-(4-butylphenyl)-2-aza-[3]-ferrocenophane showed the proposed structure. Electrochemical oxidation of
the N-aryl- and N-alkyl-2-aza-[3]-ferrocenophane was studied. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Ferrocenophane; Ruthenium; Condensation; Electrochemistry
several reactions, starting from oxoferrocenophane and
were revealed to be unstable at room temperature (r.t.)
[2]. Reaction of 1,1%-ferrocenedimethanol with aryl iso-
cyanate gave N-aryl-2-aza-[3]-ferrocenophane but often
in very low yields (7% for phenyl isocyanate) [3]. N-
Methyl-2-aza-[3]-ferrocenophane was recently prepared
by Plenio et al. in 35% yield from condensation of
methylamine with [1,1%-ferrocenediylbis(methylene)]-
bis(pyridinium) tosylate [4]. The above preparation
methods, however, often suffer from insufficient yields
and lack in the generality of product structures.
Recent progress in synthetic organic reactions using
Groups 8–10 metal complexes as catalysts have en-
abled condensation of primary alcohols with amines to
form C–N bonds under relatively mild conditions [5,6].
Extension of this reaction to primary amine and 1,1%-
ferrocenedimethanol would provide a general prepara-
tion method for N-alkyl-(or N-aryl)-2-aza-[3]-
ferrocenophanes. In this paper we reported results of
the reaction using aliphatic and aromatic amines to
afford N-substituted-2-aza-[3]-ferrocenophanes as well
as their structures and properties.
1. Introduction
Ferrocene and its derivatives are of various kinds of
use in synthetic organic chemistry and material science,
owing to stable coordination of the cyclopentadienyl
(Cp) ligands, possible induction of chirality in the
molecules, and reversible redox behavior of the metal
center [1]. Introduction of functional groups onto Cp
ligands of ferrocene leads to the synthesis of a number
of new reagents, ligands for transition metal complexes,
and polymers containing ferrocene derivative in the
repeating unit. Ferrocenophanes with bivalve-like struc-
tures are expected to show unique chemical properties
owing to functionality of the side arm. There has been
a lesser number of studies carried out on structure and
properties of aza-[n]-ferrocenophanes than on other
ferrocenophanes in spite of the rich functionality of the
side arm. 2-Aza-[4]-ferrocenophanes were prepared by
* Corresponding author. Fax: +81-45-924-5276.
1 Also corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00114-X

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I. Yamaguchi et al. / Journal of Organometallic Chemistry 584 (1999) 213–216
Table 1
Preparation of N-alkyl (or aryl)-2-aza-[3]-ferrocenophanes a
Amine
Product
Yield (%)
Analysis (%) b
C
H
N
4-Butylaniline
4-t-Butylaniline
4-Hydroxyaniline
Hexylamine
1
2
3
4
5
63
58
56
40
70
73.87
(73.54)
72.89
(73.54)
67.73
(67.72)
69.46
(69.36)
72.66
6.73
(7.01)
6.85
(7.01)
5.37
(5.36)
8.10
3.89
(3.90)
3.85
(3.90)
3.39
(4.42)
4.50
(7.95)
5.68
(4.25)
4.02
Benzylamine
(71.94)
(6.04)
(4.42)
a The reactions were carried out by heating of the NMP solution for 24 h at 180°C under a nitrogen or argon atmosphere.
b Required values are in parentheses.
picts cyclic voltammograms of 1 and 4 in MeCN solu-
2. Results and discussion
tions. Two reversible peaks (I and II) are observed at
Heating of an NMP solution of 1,1%-fer-
rocenedimethanol and 4-butylaniline in the presence of
RuCl2(PPh3)3 catalyst gave N-(4-butylphenyl)-2-aza-[3]-
ferrocenophane in 63% yield (Eq. 1).
E1/2=0.10 and 0.72 V, respectively, for 1, whereas 4
exhibits the peaks (III and IV) at E1/2=0.03 and 0.35
V. The first oxidation and reduction are close to that of
ferrocene and assigned to redox between the ferrocene
and ferricenium cation. The second peaks are assigned
to oxidation of the ammonium salt formed via protona-
tion of the nitrogen atom. Scheme 1 summarizes a
plausible mechanism for the oxidation of the N-substi-
tuted-2-aza-[3]-ferrocenophanes. The intermediate (A%),
formed via initial oxidation of the FeII center of ferro-
cenophane and intramolecular electron transfer (i), un-
dergoes further oxidation of the FeII center
(1)
Similar reactions with 4-t-butylaniline, 4-hydroxyani-
line, hexylamine, and benzylamine afforded the corre-
sponding N-substituted 2-aza-[3]-ferrocenophanes as
summarized in Table 1. Yields of the isolated products
are moderate to high, and not lowered by the presence
of the OH-p group in preparation of 3. The complexes
were characterized by NMR spectroscopy and elemen-
tal analyses. The 1H- and 13C{1H}-NMR spectra of
1–5 show the signals at l 2.8–3.9 (1H) and l 46–48
(13C) due to the CH2 group attached to the nitrogen
atom and to the Cp rings. Fig. 1 depicts the molecular
structure of 1 determined by X-ray crystallography.
The unit cell contains two crystallographically indepen-
dent molecules which have similar structures to each
other. The two Cp rings are at almost staggered posi-
tions, similar to the previously reported structures of
[3]-ferrocenophanes [7,8]. N–C(aryl) bond distances
Fig. 1. ORTEP drawing of N-(4-butylphenyl)-2-aza-[3]-ferrocenophane
(1) with 50% thermal ellipsoidal level. One of the two crystallograph-
,
(1.400(6) and 1.396(6) A) are significantly shorter than
,
ically independent molecules is shown. Selected bond distances (A)
and angles (°): Fe–C1 2.010(4), Fe–C2 2.042(4), Fe–C3 2.062(5),
Fe–C4 2.051(5), Fe–C5 2.036(5), Fe–C6 2.009(4), Fe–C7 2.032(4),
Fe–C8 2.065(5), Fe–C9 2.053(4), Fe–C10 2.036(4), C1–C11
1.519(6), C6–C12 1.514(6), N1–C11 1.467(6), N1–C12 1.464(6), N1–
C13 1.400(6), C11–N1–C12 113.8(4), C11–N1–C13 120.7(4), C12–
N1–C13 119.6(4), N1–C11–C1 115.4(4), N1–C12–C6 115.1(3).
those of N–CH2 bonds (1.467(6), 1.464(6), 1.464(6),
,
and 1.462(6) A), suggesting conjugation of the phenyl
rings and the nitrogen atom.
The obtained ferrocenophanes are air and thermally
stable, but electrochemically easily oxidized. Fig. 2 de-

I. Yamaguchi et al. / Journal of Organometallic Chemistry 584 (1999) 213–216
215
ous kinds of N-alkyl and N-aryl-2-aza-[3]-ferro-
cenophanes including that containing the reactive OH
group. The rigid structure and unique electrochemical
properties suggest their potential utility as a new
material.
3. Experimental
3.1. Preparation of N-substituted-2-aza-[3]-
ferrocenophanes.
To an NMP (3 cm3) solution of RuCl2(PPh3)3 (67
mg, 0.070 mmol) was added 4-butylaniline (298 mg,
2.0 mmol) and then 1,1%-ferrocenedimethanol (492 mg,
2.0 mmol) at r.t. under a nitrogen atmosphere. The
solution was heated for 24 h at 180°C and then kept
at r.t. overnight. The product was purified by column
chromatography (silica gel, hexane: ethyl acetate, 1:1)
and recrystallized from a chloroform–methanol mix-
ture to afford 1 as orange crystals (226 mg, 63%).
lH(CDCl3) 0.93 (3H, t, CH3, J=8 Hz), 1.38 (2H, tq,
CH2, J=7–8 Hz), 1.59 (2H, tt, CH2, J=8 Hz), 2.54
(2H, t, CH2–C6H4, J=8 Hz), 3.80 (4H, s, CH2N),
4.06 and 4.18 (4H, s, C5H4), 6.93 and 7.07 (4H, d,
C6H4, J=8 Hz); lC(CDCl3) 14.0 (CH3), 22.4
(CH2CH3), 33.9 and 34.6 (CH2), 46.9 (CH2N), 69.1
and 70.0 (CH in C5H4), 84.6 (C–CH2N), 114.7, 129.2,
132.3 and 147.9.
Fig. 2. Cyclic voltammograms for the oxidation of 2.5×10−3
M
solutions of (a) 1 and (b) 4 in acetonitrile containing 0.10 M NEt4BF4
at 0.05 V s−1 and 25°C.
accompanied by reduction and protonation at the ni-
trogen with a radical cation character (ii) to afford
the two electron oxidation product (B). Similar two-
step electrochemical oxidation of cationic N,N-
dimethyl-2-aza-[3]-ferrocenophane was reported to
occur at a higher potential than N-methyl-2-aza-[3]-
ferrocenophane [4,9]. The proton in (ii) may come
from water impurities contained in the solvent or the
ammonium salt.
Compounds 2–5 were prepared analogously. 2 was
purified by recrystallization from CHCl3–MeOH.
NMR data for 2: lH(CDCl3) 1.32 (9H, s, CH3), 3.81
(4H, s, CH2N), 4.07 and 4.19 (4H, s, C5H4), 6.93 and
7.23 (4H, d, C6H4, J=9 Hz); lC(CDCl3) 31.5 (CH3),
33.8 (CCH3), 47.0 (CH2N), 69.1 and 70.0 (CH in
C5H4 group), 84.7 (C–CH2N), 114.4, 126.1, 140.6 and
147.7. NMR data for 3: lH(CDCl3) 3.69 (4H, s,
CH2N), 4.08 and 4.18 (4H, s, C5H4), 4.38 (1H, s,
OH), 6.80 and 6.93 (4H, d, C6H4, J=5 Hz). NMR
data for 4: lH(CDCl3) 0.92 (3H, t, CH3, J=7 Hz),
1.36 (6H, br, CH2CH2CH2CH3), 1.59 (2H,
CH2(CH2)3CH3, quintet, J=10 Hz), 2.68 (2H, t,
CH2(CH2)4CH3, J=7 Hz), 2.88 (4H, s, CH2N), 4.07
and 4.08 (4H, s, C5H4); lC(CDCl3) 14.1 (CH3), 22.7
(CH2CH3), 27.2 (CH2CH2CH3), 27.6 (CH2(CH2)2-
CH3), 31.8 (CH2(CH2)3CH3), 52.2 (Cp–CH2N), 57.8
(CH2(CH2)4CH3), 69.0 and 69.8 (CH in Cp group),
83.9 (C–CH2N). NMR data for 5: lH(CDCl3) 2.91
(2H, s, NCH2Ph), 3.86 (4H, s, CpCH2N), 4.07 and
4.12 (4H, s, C5H4), 7.27 (2H, d, ortho-, J=6 Hz),
7.36 (2H, t, meta-, J=6 and 7 Hz), 7.44 (1H, t,
para-, J=7 Hz).
The difference in the first and second oxidation po-
tentials of 1 is larger than that of 4. Plenio et al.
found a wide range of oxidation potentials for vari-
ous ferrocene derivatives containing ammonium
groups and assigned the Fe–N nonbonding distances
as a primary factor [4]. However, the above results
indicate that the kind of N-substituent is also to be
considered and that the second oxidation potential
can be controlled by change of the substituent.
In summary we have demonstrated a new prepara-
tion method of N-substituted-2-aza-[3]-ferroceno-
phanes. The reaction is applied to syntheses of vari-
3.2. X-ray structure determination of 1
Data were collected at 23°C on a Rigaku AFC-5R
Scheme 1.

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I. Yamaguchi et al. / Journal of Organometallic Chemistry 584 (1999) 213–216
automated diffractometer and monochromatic Mo–
Acknowledgements
,
Ka radiation (u=0.71073 A). The structure was
This work was financially supported by a Grant-in-
Aid for Scientific Research from the Ministry of Edu-
cation, Science, Sports and Culture, Japan.
solved by a direct method. All nonhydrogen atoms
were refined anisotropically. For the hydrogen atoms
the riding model was used. Crystal data for 1:
(
C22H25NFe, Mr=359.29, triclinic, space group P1
,
(no. 2), a=12.803(4), b=13.020(4), c=12.764(4) A,
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3
A , Z=4, Dcalc. =1.368 g cm−3, v=8.66 cm−1, 8375
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