Crystal structure and electrochemical properties of ferrocenyl aminophosphonic esters

Article abstract of DOI:10.1080/15533174.2010.492549

A series of novel compounds of aminophosphonates bearing the ferrocenyl moiety are obtained. X-ray Crystallography of 2c reveals that it belongs to monoclinic system with space group P2(1)/c, R1 = 0.0620, wR2 = 0.1516. The cyclic voltammetric behavior of these compounds show one pair of quasi-reversible and redox waves in the potential range of 0.0-1.0 V and it is controlled by diffusion. The diffusion coefficient decrease with increasing in the molecular weight of the compounds and the size of the molecules. CCDC: 679937. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2010.492549

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:386–390, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.492549
Crystal Structure and Electrochemical Properties
of Ferrocenyl Aminophosphonic Esters
Wenhao Feng, Wei Du, Chunling Ran, Huijie Lu, Yan Xu, and Yaoting Fan
Department of Chemistry, Zhengzhou University, Zhengzhou, Henan, P. R. China
More than five decades after its discovery,[10−11] ferrocene
A series of novel compounds of aminophosphonates bearing the
ferrocenyl moiety are obtained. X-ray Crystallography of 2c re-
veals that it belongs to monoclinic system with space group P2(1)/c,
R1 = 0.0620, wR2 = 0.1516. The cyclic voltammetric behavior
of these compounds show one pair of quasi-reversible and redox
waves in the potential range of 0.0–1.0 V and it is controlled by
diffusion. The diffusion coefficient decrease with increasing in the
molecular weight of the compounds and the size of the molecules.
CCDC: 679937
still evokes a great deal of research interest from scientists across
the board. Chiral and achiral ferrocenyl phosphines have been
extensively used as ligands in organic synthesis and asym-
metric catalysis for carbon–carbon, carbon–heteroatom cou-
pling, carbonylation, hydroformylation, hydrogenation, olefin
polymerization and cycloaddition.[12−14] Ferrocenyl amino
acids found their application in food chemistry as a possi-
ble substitute for phenylalanine in the commercial sweetener
aspartame.[15]
Regarding all of the above, we want to take advantage
of the properties of mixed valent phosphine bridged fer-
rocene moieties and obtain a series of novel compounds bear-
ing aminophosphonates and ferrocene moiety. We systemat-
ically investigated their electrochemical behaviors by cyclic
voltammetry (CV), chronoamperometry (CA), and chrono-
coulometry (CC). By contrast, there are few reports about
the electrochemistry of ferrocenylphosphine oxide[16−17] and
ferrocenylphosphonates.[18−19]
Keywords aminophosphonates, crystal structure, electrochemical
properties, ferrocene
INTRODUCTION
Compounds derived from the sandwich structural ferrocene
have been widely employed in electroactive polymers,[1] ther-
motropic liquid crystal,[2] and non-liner optical materials[3] be-
cause they are characterized by their ability to make metal-
centered redox systems to generate oxidized or reduced form
of different properties.[4] Experiments show that the redox po-
tential depends on the electronic effect of the ring substituent
on ferrocene. Electron-withdrawing substituents increase the
oxidation potential (decrease the reactivity towards oxidation),
while electron-donating substituent decreases the oxidation po-
tential, and thus enhances the reactivity of ferrocene.[5−6] Phos-
phines substituents on the ferrocene unit allow incorporation of a
redox-active moiety into transition metal complexes, often lead-
ing to an increase in the reactivity of the complex.[7] Coordinated
ferrocenylphosphine ligands usually exhibit simple, reversible
electrochemistry behavior arising from one-electron oxidation
of the ferrocene center, while free ferrocenylphosphine displays
complex redox properties.[8−9]
EXPERIMENTAL
X-ray Structure Determination of 2c
An orange crystal of the title compound 2c with dimensions
of 0.40 × 0.36 × 0.16 mm3 is mounted on a glass fiber. All
measurements are made on a Rigaku RAXIS-IV imaging plate
area detector with graphite monochromated Mo-Kα radiation
˚
(λ =0.71073 A). A total of 25247 reflections are collected
I > 2σ (I) reflections are 4526. The data are corrected for
Lorentz and polarization effects. The structure is solved by
direct methods, and expanded using Fourier techniques. The
non-hydrogen atoms are refined anisotropically. Hydrogen
atoms are included, but not refined. The final R factor is
0.0620, Rw = 0.1516. All calculations are performed with the
SHELXL-97 crystallographic software package.[23]
Received 2 August 2009; accepted 22 April 2010.
The authors thank Luoyang Normal College for the diffraction
measurements and Henan Province Natural Science Foundation (No.
06110214000). This work is supported by the National Natural Science
Foundation of China (No. 20771093).
Address correspondence to Yan Xu, Department of Chemistry,
Zhengzhou University, 75 University Road, Zhengzhou, Henan,
450052, P. R. China. E-mail: xuyan@zzu.edu.cn
Determination of Electrochemical Properties
Cyclic voltammetry, chronoamperometry and chrono-
coulometry studies are recorded with a CHI660B electrochem-
ical analyzer utilizing the three-electrode configuration of a Pt
386

CRYSTAL STRUCTURE AND ELECTROCHEMICAL PROPERTIES
387
O
H
N
H
C
R1
R2
O
R2
+
H
P
OEt
R1
CH
P
N
Fe
Fe
EtO
OEt
OEt
a-j
2a-j
O
,
CH2
CH2
R1
=
=
R2
R2
,
,
,
,
OH
S
a
O
e
O
b
g
c
d
O
O
R1
=
,
,
=
,
,
,
OH
O
S
j
h
i
f
SCH. 1.
working electrode, a Pt auxiliary electrode, and a commer- exhibited one-pair well-defined reduction and oxidation waves
cially available saturated calomel electrode as the reference in the potential range of 0.1–0.6 V at the Pt working electrode
electrode. The measurements are performed in acetonitrile so- (Table 3).
lution containing tetra-n-butyl-ammonium perchlorate (TBAP)
It can be seen from Table 3 that the oxidation potentials and
(0.1 mol·dm−3) as supporting electrolyte. Pure N2 gas is bubbled reduction potentials of derivates of m-ferrocenylaniline (2f, 2g,
through the electrolytic solution to remove oxygen.
2h, 2i, 2j) apparently shift to lower potentials compared with
those of the corresponding potentials of ferrocene, ferroceny-
laniline and the derivates of p-ferrocenylaniline. This might be
because derivates of p-ferrocenylaniline could form an extent ꢀ
Electrochemical Properties
The cyclic voltammogram behaviors of compounds 2 in bond, as shown in Scheme 2.
0.1mol·dm−3 TBAP acetonitrile solution were investigated at
The cyclic voltammetric diagrams of complounds 2a-j at dif-
room temperature. The CV diagrams show that compounds 2 ferent scan rates (from 50 to 400 mV·s−1) are shown in Figure 2.
FIG. 1. The molecular structure of compound 2c.

388
W. FENG ET AL.
TABLE 1
TABLE 2
◦
˚
Crystallographic data for compound 2c
Selected bond lengths(A) and angles( ) for 2c
Bond lengths Bond angles
N(1)-C(13) O(3)-P(2)-O(5)
Empirical formula
Formula weight
C28H30FeNO5P
547.35
1.387(4)
1.446(4)
1.448(3)
1.559(3)
1.584(3)
1.803(4)
1.381(4)
1.374(5)
1.355(6)
1.403(6)
1.392(6)
1.387(4)
1.446(4)
117.89(17)
115.92(17)
99.32(18)
115.13(16)
102.73(16)
103.51(19)
124.7(3)
104.3(3)
105.0(3)
124.9(3)
128.2(4)
Crystal system
Space group
Monoclinic
P2(1)/c
N(1)-C(17)
P(2)-O(3)
P(2)-O(5)
O(3)-P(2)-O(4)
O(5)-P(2)-O(4)
O(3)-P(2)-C(17)
O(5)-P(2)-C(17)
O(4)-P(2)-C(17)
C(13)-N(1)-C(17)
C(20)-O(1)-C(24)
C(21)-O(2)-C(24)
C(25)-O(4)-P(2)
C(27)-O(5)-P(2)
O(2)-C(24)-O(1)
O(4)-C(25)-C(26)
˚
a(A)
16.356(3)
11.585(2)
15.404(3)
117.92(3)
2579.1(9)
1144
1.410
293(2)
2.25 – 25.00
˚
b(A)
P(2)-O(4)
˚
c(A)
P(2)-C(17)
O(1)-C(20)
O(2)-C(21)
O(5)-C(27)
O(2)-C(24)
O(4)-C(25)
N(1)-C(13)
N(1)-C(17)
β(◦)
V(A )
3
˚
F(000)
Dcalc (mg/m3)
Temperature (K)
Theta range for data
108.7(4)
111.9(5)
collection( ◦
)
Reflections collected
Independent reflections
[R(int)]
Refinement method
Goodness-of-fit on F2
Final R indices [I >
2r(I)]
R indices (all data)
Largest difference in
peak and hole
25247
0.0330
show that the D values decrease with the increase in the molec-
ular weight of the compounds and the size of the molecules.[25]
Full-matrix least-squares on F2
1.098
R1 = 0.0620, wR2 = 0.1516
N+HR
NHR
Fe
Fe
R1 = 0.0671, wR2 = 0.1558
0.415 and –0.274
SCH. 2.
From the ipa/ipc (≈1) values of each couple, it can be seen that
the redox processes were chemically quasi-reversible processes.
Additionally, as shown in Figure3, the dependence of the cur-
rents at different scan rates on the square root of the scan rates
is linear. So the redox processes of compounds 2 are controlled
by diffusion.
RESULTS AND DISCUSSION
Synthesis
Ferrocenylaminophosphonates are synthesized according to
the following route (Scheme 1). All the Schiff bases of a-j are
synthesized by the condensation of the m-ferrocenylaniline or
In order to determine the D values of compounds 2, the CA
and CC methods were used. The relationships between the time
and the currents or the electric energies are given by Cottrell
TABLE 3
Electrochemical data for ferrocene and ferrocene derivatives
equations[24]
:
Compound
ferrocene
Epa/V Epc/V E0/V
ꢁE ipa/ ipc
nFAD1o/2Co
(πt)1/2
2nFAD1o/2Cot1/2
i(t) =
+ ic Q(t) =
+ Qdl
0.473 0.400 0.437 0.073
m-ferrocenylaniline 0.405 0.334 0.370 0.071
p-ferrocenylaniline 0.409 0.337 0.373 0.072
1.00
1.01
1.00
1.03
1.06
1.00
1.00
1.06
1.07
1.03
1.01
1.00
1.08
π1/2
where i is the current, Q is the electric energy, n is the electron
numbers involved in the redox process, F is the Faraday constant,
A is the area of the electrode, D is the diffusion coefficient, C is
the concentration of the compound, and t is time.
As depicted in Figures 4 and 5, linear trends for 2j are ob-
served from the dependence of i on t−1/2 or Q on t1/2. According
to the slope coefficients, the D value of 2j is obtained by CA
method or by CC method. In the same way, all D values of com-
pound 2a–j (Table 4.) can be obtained. Clearly, the D values ob-
tained from CA and CC are close to each other. This means that
the kinetic data measured are accurate and authentic. The results
2a
2b
2c
2d
2e
2f
2g
2h
2i
0.418 0.351 0.384 0.067
0.402 0.337 0.369 0.065
0.415 0.347 0.381 0.068
0.412 0.347 0.379 0.065
0.405 0.334 0.369 0.071
0.330 0.263 0.296 0.067
0.337 0.270 0.303 0.067
0.334 0.267 0.300 0.067
0.330 0.267 0.298 0.063
0.329 0.267 0.298 0.062
2j

CRYSTAL STRUCTURE AND ELECTROCHEMICAL PROPERTIES
389
FIG. 2. CVs of compound 2j in acetonitrile at different scan rate
(c=5×10−4mol·dm−3
)
p-ferrocenylaniline with aroma aldehyde following the known
methodology.[20] Addition of diethyl phosphite to the azome-
thine bond of Schiff bases to give the corresponding ferroceny-
laminophosphonates as we have previously reported.[21] The
addition of phosphites to Schiff bases of ferrocenecarbaldehyde
gives a racemic mixture because a chiral center is formed.
FIG. 4. The relation between i and t−1/2
.
dimensional structure with Van der Waals force. The P-C bond
[22]
˚
˚
distance is 1.803A, which is similar to average of 1.83 A.
Crystal Structure of Compound 2c
˚
The P2-O3 formed P=O bond for the distance of 1.448 A is
The crystal structure of compound 2c is illustrated in
Figure 1. The crystal data, the selected bond lengths and an-
gles are given in Tables 1 and 2.
˚
˚
shorter than that of P2-O4, P2-O5 1.584 A and 1.559 A. The
mean deviations from planes C(1)-C(5)(Cp1), C(6)-C(10) (Cp2)
˚
˚
˚
C(11)-C(16), C(18)-C(23) are 0.036A, 0.038 A, 0.023 A, 0.039
Compound 2c has two unique molecules in the symmet-
ric unit. C17 is a chiral carbon atom. In the crystals, the
two enantiomers were connected through weak hydrogen bond
˚
A. The Cp rings in ferrocenyl groups are planar and nearly par-
allel with a dihedral angle of 2.3◦(Cp1, Cp2), The dihedral angle
of Cp2-ring and phenyl ring C(11)-C(16) is 26.8◦. The dihedral
angle of the two phenyl rings C(11)-C(16), C(18)-C(23) is 55.2◦.
˚
O(2). . . H-N(1A) and O(2A). . . H-N(1) (3.013 A), forming
a approximate rectangle structure. The inner diameter was
0.540 nm × 0.262 nm. Two molecular extended three-
FIG. 3. The reaction between ipand υ1/2 of 2j.
FIG. 5. The relation between Q and t1/2
.

390
W. FENG ET AL.
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Compound
CA
CC
2a
2b
2c
2d
2e
2f
2g
2h
2i
0.80
0.84
0.82
0.83
0.82
0.81
0.85
0.82
0.85
0.82
0.80
0.82
0.81
0.82
0.80
0.80
0.84
0.85
0.84
0.81
2j
CONCLUSIONS
A series of novel aminophosphonates bearing the ferrocenyl
moiety are synthesized. The results of electrochemistry show
that these derivatives have high electroactivity. They may have
potential applications as materials for biomolecular sensors
and switches. In addition, study of the applications of these
compounds in asymmetric catalytic reactions is necessary. At
present, these applications are under way in our lab.
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SUPPLEMENTARY MATERIAL
Supplementary data Crystallographic data for the struc-
tural analyses have been deposited with the Cambridge Crys-
tallographic Data Center, CCDC-708122. 12 Union Road,
Cambridge CB2 1EZ, UK. E-mail: deposit@ccdc.cam.ac.uk.
(Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk or
www:http://www.ccdc.cam.ac.uk).
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