Synthesis, structures and electrochemistry of two Schiff base compounds bearing phenylferrocene

Article abstract of DOI:10.1016/j.inoche.2004.09.024

Two novel ferrocene derivatives, FcL₁ and FcL₂, were prepared and characterized. The X-ray crystal structure of FcL₁ was also described. The electrochemical studies reveal that oxidation of the substituents on the ferrocen

Full text of DOI:10.1016/j.inoche.2004.09.024

Inorganic Chemistry Communications 8 (2005) 44–47
www.elsevier.com/locate/inoche
Synthesis, structures and electrochemistry of two Schiff
base compounds bearing phenylferrocene
*
Bao-Xian Ye , Yan Xu, Fei Wang, Yong Fu, Mao-Ping Song
Department of Chemistry, Zhengzhou University, Zhengzhou, 450052, PR China
Received 23 July 2004; accepted 9 September 2004
Available online 8 December 2004
Abstract
Two novel ferrocene derivatives, FcL1 and FcL2, were prepared and characterized. The X-ray crystal structure of FcL1 was also
described. The electrochemical studies reveal that oxidation of the substituents on the ferrocene moiety leads to an electrode pas-
sivation process.
ꢀ 2004 Published by Elsevier B.V.
Keywords: Ferrocenyl Schiff base derivatives; Synthesis; Crystal structure; Electrochemical property
Since its discovery [1,2], ferrocene and its derivatives
are among the most thoroughly studied compounds in
organometallic chemistry. Of particular interest is the
redox chemistry of the iron center [3,4] and the structure
[5,6]. Ferrocene/ferrocenium (Fc/Fc+) itself represents a
strictly reversible one-electron redox couple. However,
substituents on the ferrocene moiety would influence
the redox behavior by changing energy level of the
HOMO [7], so the reversibility may be significantly
lowed [8]. Schiff bases are condensation products of
arylamines and carbonyl compounds; these compounds
are quite stable and represent versatile intermediates for
preparation of a number of important compounds.
Incorporation of ferrocene moiety into Schiff bases im-
parts the chemical and physicochemical properties
which are absent or little manifested in the parent sub-
stance. Related analogues have been investigated
[9,10], but we were surprised that there has been limited
study of their electrochemistry character.
In this paper, we report synthesis of two Schiff base
compounds bearing phenylferrocene (Scheme 1), FcL1
[N-(2-hydroxybenzylidene)-3-ferrocenylaniline]
and
[N-(2-hydroxybenzylidene)-4-ferrocenylaniline],
FcL2
and these compounds were characterized by IR, 1H
NMR, UV–Vis, elemental analysis and cyclic voltamme-
try. IR spectra were measured on a Perkin–Elmer FTIR-
1
1750 spectrometer. H NMR spectra were recorded at
room temperature on a Bruker DPX spectrometer 400
MHz, Chemical shifts are denoted in d units (ppm) rel-
ative to Me4Si as internal standard. UV–Vis spectra
were recorded on a Unicoꢁ UV-2102 PC spectrometer.
Electrochemical experiments were performed in dry ace-
tonitrile with CHI 650A electrochemical analyzer using
a conventional three-electrode system.
The compounds 3-ferrocenylaniline and 4-ferroceny-
laniline were prepared according to procedures reported
in the literature [11]. 3-Ferrocenylaniline (0.277 g, 1
mmol) was dissolved in 20 ml of absolute ethyl alcohol
on heating and mixed with salicylal (0.135 g, 1.1 mmol),
and the mixture was refluxed until the peaks of amino
disappeared according to the IR spectrum. The precipi-
tated yellow material was filtered off after cooling down,
and then the product was washed with cooled ethanol,
*
Corresponding author. Tel.: +371 7766159; fax: +371 7763220.
E-mail addresses: yebx@zzu.edu.cn (B.-X. Ye), wf2003@zzu.edu.cn
(F. Wang).
1387-7003/$ - see front matter ꢀ 2004 Published by Elsevier B.V.
doi:10.1016/j.inoche.2004.09.024

B.-X. Ye et al. / Inorganic Chemistry Communications 8 (2005) 44–47
45
NH2
R
R
O2N
N2Cl
NO2
R
Sn
Fe
Fe
Fe
HCl
HO
OH
R
N
C
H
CHO
Fe
:
:
L2 R=
L1 R=
Scheme 1.
and dried on the vacuum apparatus. Yield: 81% (0.31 g);
Analytical data for the compound FcL1: Yellow solid;
m.p. 144–145 ꢂC; UV–Vis (CH3CN) kmax: 279.0 nm
(emax = 2.09 · 104 L/mol cm), 339.0 nm (emax = 1.34 ·
104 L/mol cm); IR (KBr, cmÀ1): 3369.75 (m-OH),
1616.78 (–C@N), 1103.92 and 999.73 (Fc), 1283.29 (m-
Ar–N);1H NMR (CDCl3, d ppm): 4.072 (s, 5H, –Fc),
4.353 (s, 2H, –Fc), 4.687 (s, 2H, –Fc), 6.9–7.4 (m, 8H,
H–Ar,), 8.617 (s, 1H, –ArOH); Anal. Calc. for
C23H19FeNO: C, 72.44; H, 4.98; N, 3.67. Found: C,
72.63; H, 5.14; N, 3.77. Compound FcL2 was prepared
according to a similar procedure used for compound
FcL1, replacing 3-ferrocenylaniline by 4-ferrocenylani-
line. Yield: 76% (0.28 g). Analytical data for the com-
pound FcL2: Yellow solid, m.p. 171–172 ꢂC; UV–Vis
(CH3CN) kmax: 277.4 nm (emax = 1.60 · 104 L/mol cm),
350.0 nm (kmax = 1.98 · 104 L/mol cm); IR (KBr,
cmÀ1): 3445.63 (m-OH), 1623.35 (–C@N), 1104.21 and
1000.01 (Fc), 1277.45 (m-Ar–N);1H NMR (CDCl3, 400
MHz) ppm: 4.062 (s, 5H, –Fc), 4.354 (s, 2H, –Fc),
4.671 (s, 2H, –Fc), 6.9–7.6 (m, 8H, H–Ar), 8.687 (s,
1H, –ArOH); Anal. Calc. for C23H19FeNO: C, 72.44;
H, 4.98; N, 3.67. Found: C, 72.53; H, 5.01; N, 3.80.
The X-ray crystal structure of FcL1 was also pre-
sented. All measurements were made on a Rigaku
RAXIS-IV imaging plate area detector with graphite
˚
monochromated Mo Ka radiation (k = 0.71073 A).
Temperature 291(2) K, I > 2r reflections were 4280.
The data were corrected for Lorentz and polarization ef-
fects. The crystal structure of compound FcL1 is shown
in Fig. 1. It belongs to monoclinic system P2 (1)/c space
group, a = 1.0130(2) nm, a = 90ꢂ, b = 0.77015(15) nm,
d = 93.51(3)ꢂ, c = 2.3386(5) nm, c = 90ꢂ. The final R fac-
tor was 0.0964, Rw = 0.2436. Fe–Cring distances range
Fig. 1. The molecular structure of compound FcL1.

46
B.-X. Ye et al. / Inorganic Chemistry Communications 8 (2005) 44–47
GC electrode, which is attributed to the Fc/Fc+ redox
process. It is interesting to find that the formal potential
(E0), taken as the average of Epa and Epc, of these com-
pounds show a gradual increase in the order 3-ferroce-
nylaniline ꢀ 4-ferrocenylaniline < ferrocene < FcL2 ꢀ
FcL1, suggesting that the electron withdrawing imine
group substantially in FcL1 and FcL2 significantly influ-
ence the redox potential of the iron center. At the same
time, the formal potential of FcL1 and FcL2, 3-ferroce-
nylaniline and 4-ferrocenylaniline are very close, which
indicate ferrocene subunit in both case are in the equiv-
alent environment. For two novel ferrocene derivatives
and related compounds, the values of the diffusion coef-
ficient (D) obtained confirm this concept that the D val-
ues decreases as an increase in the molecular weight of
the compound and the size of the molecules. According
to Nicholson formula [13], the standard rate constant of
the electrode reaction (ks) values of compounds are also
calculated, shown in Table 1.
˚
from 2.004(12) to 2.048(9) A and intracyclopentadienyl
˚
C–C bond lengths lie in the range 1.361(19)–1.45(2) A,
and C–C–C angles (average 108.03(45)ꢂ) are very similar
to those reported in the literature [12]. The bond lengths
and angles within the phenyl group are unexceptional.
The mean deviations from planes C1 to C5 (1), C6 to
˚
C10 (2) are 0.089, 0.041 A, respectively. The cyclopenta-
dienyl rings in ferrocenyl fragment are planar and nearly
parallel with a dihedral angle of 1.1ꢂ. It is clear from the
structure that the phenyl ring is almost coplanar to the
cyclopentadienyl ring plane to which it is attached; their
dihedral angle (planes C11–C16 and C6–C10) is 8.5ꢂ and
the dihedral angle of two phenyl rings is 49.8ꢂ. The phe-
nyl ring is bonded with cyclopentadienyl ring at a dis-
˚
tance of 1.473(12) A (C10–C11). The torsion angle is
170.3(9)ꢂ for C15–N1–C17–C18. The intramolecular
hydrogen bond originates from hydroxy with imine
forming
a
six membered ring. N1Á Á ÁO1 = 2.606,
˚
HÁ Á ÁN1 = 1.678 A, N1–H1Á Á ÁO1 = 143.41ꢂ. Obviously,
the N–HÁ Á ÁO interactions are strong. The imine C@N
Moreover, though not seen in Table 1, FcL1 and
FcL2 also exhibit an irreversible anodic process at
higher potential values, which is obviously assigned
to the oxidation of hydroxybenzylidene. The impor-
tant feature of CVs was the pronounced shape change
between the first and second scans (Fig. 2(A)). The
currents for the second scan in Fig. 2(A) were much
˚
distance is 1.269(13) A.
The electrochemical parameters for two compounds
and related compounds obtained from the CV are sum-
marized in Table 1. The cyclic voltammetric behavior of
these compounds show one pair of well-defined and sta-
ble redox waves in the potential range of 0.0–1.0 V at the
Table 1
Electrochemical data of FcL1, FcL2 and related compounds
Compound
CV data
Kinetics data
Epa (V)
Epc (V)
DEp (mV)
E0 (V)
D0 · 105 (cm2/s)
ks · 102 (cm/s)
CV
CA
Ferrocene
0.473
0.405
0.409
0.522
0.528
0.400
0.334
0.337
0.450
0.455
73
71
72
72
73
0.437
0.370
0.373
0.485
0.492
2.38
1.42
1.51
1.02
1.10
2.40
1.45
1.47
1.10
1.18
2.35
1.82
1.85
1.56
1.62
3-Ferrocenylaniline
4-Ferrocenylaniline
FcL1
FcL2
(a) All potentials are referred to the saturated calomel electrode (SCE) in CH3CN solution, m = 100 mV/s.
(b) DEp = (Epa À Epc), E0 = (Epa + Epc)/2.
(c) CV:D was computed from normalized peak currents data using CV relationships; CA:D was computed from i–t data using Cottrell relationships.
Fig. 2. (A) Consecutive CVs of 5 · 10À4 mol/L FcL1 at a GC electrode in 0.1 M TBAP acetonitrile from 0.0 to 1.6 V. (B) CVs of 5 · 10À3 mol/L
ferricyanide in aqueous KCl (0.1 mol/L) at the GC electrode: (a) following five cycles through the oxidation process of FcL1, and at a clean GC
electrode; (b) m = 100 mV/s.

B.-X. Ye et al. / Inorganic Chemistry Communications 8 (2005) 44–47
47
lower than those of the first scans. The disappearance
Acknowledgements
of the irreversible peak and the decrease of electro-
chemical reversibility for Fc/Fc+ after the first scan
suggested a rapid and efficient passivation of the GC
surface similar to that following the electrochemical
oxidation of phenol [14,15]. As with phenol, the oxi-
dized product of the electrode reaction at higher po-
tential undergoes a following chemical reaction to
produce a passivating, non-conducting film on the
electrode surface. It is clear also from the magnitude
of the currents on the second and subsequent poten-
tial cycles that complete passivation of the electrode
surface has not occurred. Electrode surface passivation
was also tested by probing the electrochemistry of the
ferri/ferrocyanide couple on electrodes that has been
repeatedly cycled through the oxidation of compounds
FcL1 and FcL2. Fig. 2(B) shows CVs of ferricyanide
at clean GC electrodes as well as at those which
had been used for repetitive oxidative cycling of the
target compounds. In both cases there is severe atten-
uation of the electrochemical detection of the probe
redox ion, indicating deposition of an electropolymer-
ized layer.
Our work was generously supported by the National
Natural Science Foundation of China (No. 20475050).
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