Synthesis and Characterization of a New Series of Nickel(II) meso-Tetrakis (polyfluorophenyl)porphyrins Functionalized by Pyrrole Groups and Their Electropolymerized Films

Article abstract of DOI:10.1021/ic9510268

A new series of nickel(II) meso-tetrakis(polyfluorophenyl)porphyrins functionalized by pyrrole groups have been synthesized. Each new complex was isolated and characterized by ¹H NMR, ¹⁹F NMR, IR, UV-visible spectroscopy, and mass spectrometry as well as electrochemistry. This is the first example of polyfluorinated substituted porphyrins where the four possible compounds have been obtained by functionalization of the parafluorine substituents of the nickel (II) meso-tetrakis(pentafluorophenyl)porphyrin. This functionalization has allowed the preparation for the first time of polyfluorinated metalloporphyrin films by oxidative electropolymerization. Electrochemical stability studies of these polymeric films have shown better stability for films derived from the monomer having four pyrrole groups because of their high degree of cross-linking degree. A large difference of electroactive solute permeation has been found in the polymeric films which have been obtained by electropolymerization of monomers for which one pyrrole group has been substituted compared to those for which four pyrrole groups have been substituted. This could be related to quite rigid polymer structures for tetrasubstituted polymer films and molecular sieving properties of monosubstituted polymer films. The spectroelectrochemistry of a polymeric film on an OTE has established that the two-electron-oxidized species are stable in the film; likewise the singly and doubly electroreduced species are stable and are more likely ligand-centered.

Full text of DOI:10.1021/ic9510268

Inorg. Chem. 1996, 35, 2659-2664
2659
Synthesis and Characterization of a New Series of Nickel(II) meso-Tetrakis
(polyfluorophenyl)porphyrins Functionalized by Pyrrole Groups and Their
Electropolymerized Films
Maria A. Carvalho de Medeiros, Serge Cosnier,* Alain Deronzier,* and Jean-Claude Moutet
Laboratoire d’Electrochimie Organique et de Photochimie Re´dox (URA CNRS 1210), Universite´ Joseph
Fourier Grenoble 1, BP 53, 38041 Grenoble Cedex 9, France
ReceiVed August 4, 1995X
A new series of nickel(II) meso-tetrakis(polyfluorophenyl)porphyrins functionalized by pyrrole groups have been
synthesized. Each new complex was isolated and characterized by 1H NMR, 19F NMR, IR, UV-visible
spectroscopy, and mass spectrometry as well as electrochemistry. This is the first example of polyfluorinated
substituted porphyrins where the four possible compounds have been obtained by functionalization of the para-
fluorine substituents of the nickel(II) meso-tetrakis(pentafluorophenyl)porphyrin. This functionalization has allowed
the preparation for the first time of polyfluorinated metalloporphyrin films by oxidative electropolymerization.
Electrochemical stability studies of these polymeric films have shown better stability for films derived from the
monomer having four pyrrole groups because of their high degree of cross-linking degree. A large difference of
electroactive solute permeation has been found in the polymeric films which have been obtained by
electropolymerization of monomers for which one pyrrole group has been substituted compared to those for
which four pyrrole groups have been substituted. This could be related to quite rigid polymer structures for
tetrasubstituted polymer films and molecular sieving properties of monosubstituted polymer films. The
spectroelectrochemistry of a polymeric film on an OTE has established that the two-electron-oxidized species are
stable in the film; likewise the singly and doubly electroreduced species are stable and are more likely ligand-
centered.
Introduction
Numerous studies on metalloporphyrin catalysis have dem-
onstrated that polyhalogenated metalloporphyrins are robust
catalysts for alkane hydroxylation and olefin epoxidation.1-5
The catalyst stability, in particular, is markedly enhanced via
substitution of the metalloporphyrin macrocycle by electron-
withdrawing pentafluorophenyl groups.2-8 Current interest is
also in supported metalloporphyrins which is directed toward
developing oxidation catalysts that combine the versatility of
2
homogeneous metalloporphyrins
with the advantages of
heterogeneous systems. In this connection, production and
application of modified electrodes by films of polymers contain-
ing metalloporphyrins have been developed.9,10 For instance,
we recently reported the application to electrocatalytic biomi-
metic oxidation of drugs of a series of poly(pyrrole-manganese
tetraphenylporphyrin)-modified electrodes.11 In that context, it
would be useful to elaborate modified electrodes containing
X Abstract published in AdVance ACS Abstracts, April 1, 1996.
(1) Traylor, P. S.; Dolphin, D.; Traylor, T. G. J. Chem. Soc., Chem.
Commun. 1984, 279.
(2) Recent reviews on metalloporphyrins catalysis: (a) Meunier, B. Chem.
ReV. 1992, 92, 1411. (b) Mansuy, D. Coord. Chem. ReV. 1993, 125,
129.
(3) Castellino, A. J.; Bruice, T. C. J. Am. Chem. Soc. 1988, 110, 158.
(4) Nappa, M. J.; Tolman, C. A. Inorg. Chem. 1985, 24, 4711.
(5) Battioni, P.; Renaud, J. P.; Bartoli, J. F.; Reina-Artiles, M.; Fort, M.;
Mansuy, D. J. Am. Chem. Soc. 1988, 110, 8462.
(6) Chang, C. K.; Ebina, F. J. Chem. Soc., Chem. Commun. 1981, 778.
(7) Traylor, T. G.; Kim, C.; Richards, J. L.; Xu, F.; Perrin, C. L. J. Am.
Chem. Soc. 1995, 117, 3468 and references cited therein.
(8) Komuro, M.; Nagatsu, Y.; Higuchi, T.; Hirobe, M. Tetrahedron Lett.
1992, 33, 4949.
Figure 1. Structures of the 1a-d compounds.
polyhalogenated metalloporphyrins. Thus we describe herein
the synthesis and properties of a new series of nickel(II) meso-
tetrakis(polyfluorophenyl) porphyrins functionalized by pyrrole-
containing groups (R1) (Figure 1) and their electropolymerized
(9) Bedioui, F.; Devynck, J.; Bied-Charreton, C. Acc. Chem. Res. 1995,
28, 30.
(10) Deronzier, A.; Moutet, J.-C. Acc. Chem. Res. 1989, 22, 249; Coord.
Chem. ReV. in press.
(11) Cauquis, G.; Cosnier, S.; Deronzier, A.; Galland, B.; Limosin, D.;
Moutet, J.-C.; Bizot, J.; Deprez, D.; Pulicani, J.-P. J. Electroanal.
Chem. Interfacial Electrochem. 1993, 352, 181.
0020-1669/96/1335-2659$12.00/0 © 1996 American Chemical Society

2660 Inorganic Chemistry, Vol. 35, No. 9, 1996
Carvalho de Medeiros et al.
films. By extending a synthetic procedure previously reported
by Traylor et al.12 for polyfluorinated porphyrins (or their Zn
(II) and Fe (III) complexes), we were able to synthesize and
for the first time separate and characterize the four possible
compounds obtained by functionalization of the para-fluorine
atoms of nickel(II) meso-tetrakis(pentafluorophenyl)porphyrin.
Here a pyrrole alcoholate was used as nucleophile. As will be
demonstrated in this paper, the polymeric films obtained from
the electropolymerization of 1a-d monomers have different
electrochemical properties and exhibit large differences in
permeation according to their degree of cross-linking.
Experimental Section
Materials. The following solvents and common laboratory chemi-
cals employed in the preparation of the compounds were reagent grade
and were used without further purification: deuterated chloroform
(CDCl3, Aldrich), dichloromethane (HPLC grade, SDS), tetrachloro-
1,4-benzoquinone (p-chloranil, Aldrich), 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ, Aldrich), pentafluorobenzaldehyde (Janssen
Chimica), boron trifluoride etherate (BF3‚Et2O, Aldrich), nickel(II)
acetate tetrahydrate (Ni(C2H3O2)2‚4H2O, Janssen Chimica), 3-amino-
1-propanol (Janssen Chimica), 2,5-dimethoxytetrahydrofuran (Janssen
Chimica). Tetrahydrofuran (THF) was purchased from SDS and
distilled from lithium aluminum hydride (Fluka). Cyclohexane was
obtained from Janssen Chimica and distilled before use. Pyrrole
(Aldrich) was distilled at atmospheric pressure before use. The
porphyrins were chromatographed on a silica gel column (70-230
mesh, Matrex).
Physical Measurements. NMR spectra were obtained on a Bruker
AC 200 MHz FT-NMR spectrometer using CDCl3 as solvent. 1H and
19F NMR spectra were quoted as δ (ppm) vs tetramethylsilane (TMS)
and CFCl3, respectively.
UV-visible spectra were collected by use of a Cary 1 UV-vis
spectrophotometer interfaced with an Epson Ax 2e PC computer. The
measurements were made in standard 1 mm quartz cuvettes.
Infrared (IR) spectra were recorded by use of a Nicolet Impact 400
FT-IR spectrophotometer interfaced with a PC computer. IR measure-
ments were made either in KBr pellets or in a demountable cell with
KBr plates.
Fast atom bombardment (FAB) mass spectra were obtained on a
AIE Kratos MS 50 mass spectrometer fitted with an Ion Tech Ltd.
gun at the mass spectrometry service UJF-CNRS, CERMAV, Grenoble,
France. A standard FAB source was used, and m-nitrobenzyl alcohol
(NBA) was the liquid matrix.
Elemental analyses were performed by Service Central
d’AnalysessCNRS, Vernaison, France.
Synthesis and Purification. (a) 5,10,15,20-Tetrakis(pentafluo-
rophenyl)porphyrin (H2F20TPP) was synthesized via the condensation
of pyrrole and pentafluorobenzaldehyde according to the method
reported by Lindsey13,14 using either DDQ or p-chloranil (3 equiv (per
porphyrinogen)) as the oxidant. The yield obtained was ca. 30%, which
agreed with that published recently15 with 1 mM BF3‚Et2O as catalyst.
H2F20TPP was characterized by 1H and 19F NMR spectroscopy (Table
1).
(b) NiF20TPP. The nickel(II) complex of H2F20TPP was prepared
1
using the method reported by Kadish16 and was characterized by H
and 19F NMR spectroscopy (Table 1).
Mass spectral data (C44H8F20N4Ni): calculated MW 1031.23; m/e
of parent peak at 1030. UV-visible data [λmax, nm (10-4ꢀ, M-1 cm-1)],
CH3CN: 399 (20.1), 521(1.44), 555 (1.23). IR (KBr): 1064, 1080
cm-1
.
(12) Battioni, P.; Brigaud, O.; Desvaux, H.; Mansuy, D.; Traylor, T. G.
Tetrahedron Lett. 1991, 32, 2893.
(13) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827.
(14) Lindsey, J. S.; Wagner, R. W. J. Org. Chem. 1989, 54, 828.
(15) La, T.; Richards, R.; Miskelly, G. M. Inorg. Chem. 1994, 33, 3159.
(16) Kadish, K. M.; Aroullo-McAdams, C.; Han, B. C.; Franzen, M. M. J.
Am. Chem. Soc. 1990, 112, 8364.

Nickel(II) meso-Tetrakis(polyfluorophenyl)porphyrins
Inorganic Chemistry, Vol. 35, No. 9, 1996 2661
(c) 1-(3-Hydroxypropyl)pyrrole. This compound was prepared as
described previously17 and was characterized by 1H NMR spectroscopy
(Table 1).
(diameter 5 mm) polished with 1 µm diamond paste. All potentials
were referred to the Ag/Ag+ (10 mM in CH3CN + 0.1 M TBAP)
reference electrode. The counter electrode was platinum gauze.
Typical nickel(II) porphyrin concentrations for cyclic voltammetry were
in the range 10-3-10-4 M.
Apparent surface coverages of immobilized species (Γ) were
determined from the charge under the two-electron-oxidation peaks of
the metalloporphyrin.
Spectroelectrochemistry. UV-visible spectroelectrochemistry mea-
surements on films were made using a conventional sandwich-type cell18
in a drybox under an argon atmosphere. Spectral changes were
monitored by a Hewlett-Packard HP 8452A diode array spectropho-
tometer interfaced with a Compaq 286 computer. The optically
transparent conductive electrode (OTE) (diameter 1.1 cm) was doped
with indium tin oxide (ITO) (Balthracon Z20 from Balzers).
(d) 1a-d Monomers. The synthesis of the 1a-d monomers which
contain one, two, three, and four 3-(pyrrol-1-yl)propyloxy groups (R1),
respectively, covalently linked to the macrocycle by the substitution
of the para-F atoms of NiF20TPP was accomplished by the following
procedure: initially 1-(3-hydroxypropyl)pyrrole (1.7 × 10-3 mol) was
refluxed in THF (10 mL) with Na (1.7 × 10-2 mol) for 6 h in a drybox
(Ar atmosphere). The solution was cooled to ca. 20 °C, and then 2
equiv of this solution (3.8 × 10-4 M) was reacted with 1 equiv of
NiF20TPP (1.9 × 10-4 mol) in refluxing THF (10 mL) overnight in a
drybox (Ar atmosphere). The solvent was evaporated, and then the
product was washed with H2O and extracted with CH2Cl2. The extract
was dried over anhydrous Na2SO4 and filtered, and the solvent was
removed via rotary evaporation. The crude product was then chro-
matographed by using a silica gel column with a 1:1 cyclohexane/
CH2Cl2 mixture as eluting solvent. The first of the five major bands
which eluted was red-purple and was identified as unreacted NiF20-
TPP. The other bands were also red-purple. The second band was
collected, and after a second chromatographic procedure using a silica
gel column with a 1:1 cyclohexane/CH2Cl2 mixture as eluting solvent,
the product obtained, after solvent evaporation, was identified as the
1a compound corresponding to the monosubstitution of a para-F atom
of NiF20TPP by a 3-(pyrrol-1-yl)propyloxy group (R1) (ca. 20% yield).
1a Monomer. UV-visible data [λmax, nm (ꢀ x 10-4, M-1 cm-1)],
CH3CN: 400 (19.7), 521 (1.4), 555 (1.21). Mass spectral data (C51H18-
F19N5ONi): calculated MW 1136.39; m/e of parent peak at 1136. IR
Results and Discussion
Synthesis and Characterization. meso-Tetrakis(pentafluo-
rophenyl)porphyrin was synthesized using the methodology
reported by Lindsey13,14 with yield and purity in accordance
with recent results.15 This approach gives a better yield than
that reported by Longo.19 The regiospecific substitution of
fluorine by pyrrole-containing groups (R1) was accomplished,
and confirmed by 1H and 19F NMR, IR, mass spectra,
electrochemistry, and elemental analysis. These data showed
consistency with the calculated molecular weights for all
assigned structures of the 1a-d compounds (Figure 1). 1H and
19F NMR spectral data for this new series of nickel(II)
porphyrins are summarized in Table 1. It should be noted that
all proton NMR spectra show integration ratios consistent with
these assigned structures. The results reveal that the reaction
of a pyrrole alcoholate group (R1) with NiF20TPP occurs by a
substitution of the most reactive F atom (para-position) of an
electron-withdrawing pentafluorophenyl group in accordance
with that published previously for other nucleophiles.12 19F
NMR spectra of all complexes are shown in Figure 2. The
ortho-fluorine atoms are the most downfield and appear at ca.
-137 ppm for an ortho-F in an unsubstituted pentafluorophenyl
group and at ca. -139 ppm for an ortho-F in an aryl group
substituted by a pyrrole-containing group (R1). The resonance
recorded at ca. -152 ppm (triplet signal) is attributed to the
para-F of each group. The resonances for the meta-F atoms
are the most upfield and appear at ca. -162 ppm for meta-F
atoms in the unsubstituted aryl group and at ca. -157 ppm for
those in a substituted aryl group (see Table 1). The relative
intensities of integration of these signals are in agreement with
the structures attributed to 1a-d. The monosubstituted 1a
compound (Figure 2B) gives a ratio of 6:2:3:2:6 for ortho-F in
the unsubstituted aryl groups, ortho-F in the substituted aryl
group, para-F in the unsubstituted aryl groups, meta-F in the
substituted aryl group, and meta-F in the unsubstituted aryl
groups, respectively, and likewise 4:4:2:4:4 (Figure 2C) for the
1b disubstituted and 2:6:1:6:2 (Figure 2D) for the 1c trisubsti-
tuted compound. The tetrasubstituted 1d compound appears
at lower fields than that recorded for NiF20TPP (Figure 2A).
Similar phenomena were previously published by Kadish16 for
other electron-donating substituents.
(KBr): 1064, 1084, 1283 cm-1
.
The third major band was collected, and after a purification procedure
similar to that for the second band, the product obtained was identified
as the 1b compound with disubstitution of the para-F atoms by pyrrole-
containing groups (R1) (ca. 10% yield). It should noted that this band
probably corresponds to a mixture of the two possible isomers (see
Figure 1).
1b Monomer. UV-visible data [λmax, nm (ꢀ x 10-4, M-1 cm-1)],
CH3CN: 400 (19.1), 521 (1.37), 555 (1.17). Mass spectral data (C58H28-
F18N6O2Ni): calculated MW 1241.56; m/e of parent peak 1242. IR
(KBr): 1067, 1084, 1283 cm-1
.
The fourth band was collected, and after a purification procedure
similar to that used for the second band, the product obtained was
identified as the 1c compound with trisubstitution of the para-F atoms
by pyrrole-containing groups (R1) (ca. 17% yield).
1c Monomer. UV-visible data [λmax, nm (ꢀ x 10-4, M-1 cm-1)],
CH3CN: 400 (18.7), 521 (1.34), 555 (1.14). Mass spectral data (C65H38-
F17N7O3Ni): calculated MW 1346.73; m/e of parent peak 1346. IR
(KBr): 1069, 1086, 1283 cm-1
.
Finally, the fifth band was collected, and after a purification
procedure similar to that for the second band, the product obtained
was identified as the 1d compound with tetrasubstitution of the para-F
atoms by pyrrole-containing groups (R1) (ca. 25% yield).
1d Monomer. UV-visible data [λmax, nm (ꢀ x 10-4, M-1 cm-1)],
CH3CN: 401 (18.3), 521 (1.3), 555 (0.98). Mass spectral data (C72H48-
F16N8O4Ni): calculated MW 1451.88; m/e of parent peak 1452. Anal.
Calcd for 1d: C, 60.25; H, 3.64; F, 19.35. Found: C, 59.91; H, 3.57;
F, 19.36. IR (KBr): 1069, 1086, 1283 cm-1
.
Electrochemistry. All electrochemical experiments were performed
with a Princeton Applied Research Model 173 potentiostat equipped
with a Model 179 digital coulometer and a Model 175 universal
programmer. A Sefram TGM 164 X-Y recorder was used for plotting
cyclic voltammograms. All experiments were run at room temperature
in a drybox under an argon atmosphere with a normal three-electrode
configuration. Acetonitrile (Rathburn, HPLC grade) was used as
received. Tetrabutylammonium perchlorate (TBAP) (Fluka puriss) was
recrystallized from ethyl acetate/cyclohexane and vacuum-dried at 80
°C 3 days before use. The working electrode was a glassy carbon disk
Redox Behavior of Monomers 1a-d. The cyclic voltam-
mograms of NiF20TPP, 1a and 1d monomers recorded in CH3-
CN + 0.1 M TBAP, are shown in Figure 3 and a summary of
reduction and oxidation potentials of the 1a-d complexes is
given in Table 2. Upon reductive scanning, the voltammograms
(17) Carpio, H.; Galeazzi, E.; Greenhouse, R.; Guzman, A.; Velarde, E.;
Antonio, Y.; Franco, F.; Leon, A.; Perez, V.; Salas, R.; Valdes, D.;
Ackrell, J.; Cho, D.; Gallegra, P.; Halpern, O.; Koehler, R.; Maddox,
M. L.; Muchouwski, J. M.; Prince, A.; Tegg, D.; Thurber, T. C.; Van
Horn, A. R.; Wren, D. Can. J. Chem. 1982, 60, 2295.
(18) Cosnier, S.; Deronzier, A.; Moutet, J.-C. J. Phys. Chem. 1985, 89,
4895.
(19) Longo, F. R.; Finarelli, M. G.; Kim, J. B. J. Heterocycl. Chem. 1969,
6, 927.

2662 Inorganic Chemistry, Vol. 35, No. 9, 1996
Carvalho de Medeiros et al.
Figure 3. Cyclic voltammograms recorded at a glassy carbon electrode
(diameter 5 mm) of (A) NiTFPP, (B) 1a monomer, and (C) 1d monomer
in CH3CN + 0.1 M TBAP. Scan rate ) 0.1 V s-1
.
Table 2. Half-Wave Potentials (E1/2) for the 1a-d Complexes in
CH3CN with 0.1 M TBAP (Scan Rate ) 0.1 V s-1
E1/2a, V (vs Ag/10 mM Ag+)
)
complex
redn 2
redn 1
oxidnc ∆E1/2red,b V
NiF20TPP
-1.72
-1.74
-1.76
-1.78
-1.80
-1.18
-1.20
-1.22
-1.24
-1.26
1.03
1.02
1.01
1.00
0.99
0.54
0.54
0.54
0.54
0.54
Figure 2. 19F NMR spectra of (A) NiTFPP, (B) 1a monomer, (C) 1b
monomer, (D) 1c monomer, and (E) 1d monomer in CDCl3 (δ (ppm)
vs CFCl3).
monomer 1a
monomer 1b
monomer 1c
monomer 1d
a E1/2 ) (Ep + Ep )/2 where Ep and Epc are the positive and negative
show two reversible one-electron-peak systems for all com-
plexes. It should be noted that the difference between the first
and second reduction potentials is constant (∆E1/2 ) 0.54 V)
whatever the complexes and may be compared to the 0.44 (
0.04 V separation observed for the reduction at the π-ring system
of porphyrin complexes yielding π-anion radicals (P0/•-) and
dianions (P•-/2-).20 Thus, as previously described for other
nickel(II) porphyrins, these reductions could be assigned at
ambient temperature to the reduction of the porphyrin ring,
rather than reduction to Ni(I).15,21-23 Upon oxidative scanning,
the voltammogram for NiF20TPP (Figure 3A) exhibits a revers-
ible two-electron-peak system, as established by the ratio of
the peak intensities due to the metalloporphyrin oxidation and
a
c
a
peaks potentials, measured on the first scan. b ∆E1/2 ) difference
between first and second reduction potentials. c Since polymerization
accompanies oxidation of these metalloporphyrins, E1/2 values for
oxidations are not readily obtained.
chain induces a slight negative potential shift of the P0/•- and
P
•-/2- couples. A less evident slight shift was observed for the
two-electron-oxidation system of the nickel(II) porphyrins, since
polymerization accompanies oxidation of these porphyrins. The
cyclic voltammograms of the polymerizable complexes (Figure
3B,C) reveal in the positive region one irreversible oxidation
peak. The anodic peak ip1a is abnormally high while its
associated cathodic peak ip2c is low. This behavior is due to the
catalytic oxidation of the pyrrole groups by the oxidized forms
of the nickel porphyrins25 since N-alkylpyrroles are oxidized
around 1.0 V.10 In addition, Figure 3C shows that this catalytic
effect increases with the number of pyrrole-containing groups
to the one-electron reduction of the metalloporphyrin (i1pa/ip2c
)
2.02). This oxidation corresponds probably to the oxidation of
the porphyrin ring (π-cation radical and dication) as reported
previously for oxidation of (para-Cl) TPPNi in CH2Cl2 + 0.1
M TBAP24 at ambient temperature, rather than oxidation to Ni-
(III). It should be noted that, as expected, the replacement of
highly-electron-withdrawing para-F atoms by a propyl ether
(R1) in the monomer, as established by the ratio between i1
pa
(anodic peak current for the two-electron porphyrin oxidation)
and i2pc (cathodic peak current for the P0/•- porphyrin system).
The ratio of i1pa/ip2c increased from 3.1 (1a monomer) to 8.7 (1d
(20) Kadish, K. M. Phys. Bioinorg. Chem. Ser. 1986, 34, 435.
(21) Nahor, G. S.; Neta, P.; Hambright, P.; Robinson, L. R.; Harriman, A.
J. Phys. Chem. 1990, 94, 6659.
monomer) at a scan rate of 0.1 V s-1
.
Electropolymerization and Redox Behavior of the Modi-
(22) Kadish, K. M.; Franzen, M. M.; Han, B. C.; Araullo-McAdams, C.;
Sazou, D. J. Am. Chem. Soc. 1991, 113, 512.
fied Electrodes. Repeatedly scanning the potential over the
(23) Bettelheim, A.; White, B. A.; Raybuck, S. A.; Murray, R. W. Inorg.
Chem. 1987, 26, 1009.
(24) Chang, D.; Malinski, T.; Ulman, A.; Kadish, K. M. Inorg. Chem. 1984,
23, 817.
(25) (a) Deronzier, A.; Latour, J.-M. J. Electroanal. Chem. Interfacial
Electrochem. 1987, 224, 295. (b) Deronzier, A.; Devaux, R.; Limosin,
D.; Latour, J.-M. J. Electroanal. Chem. Interfacial Electrochem. 1992,
324, 325.

Nickel(II) meso-Tetrakis(polyfluorophenyl)porphyrins
Inorganic Chemistry, Vol. 35, No. 9, 1996 2663
Figure 5. Cyclic voltammograms (A) of a C/poly-1d electrode
(diameter 5 mm) obtained by oxidative electropolymerization at 0.75
V (Γ1d ) 5.0 × 10-9 mol cm-2) and (B) of a C/poly-1a electrode (Γ1a
) 5.0 × 10-9 mol cm-2) obtained by a procedure similar to that for
(A) in CH3CN + 0.1 M TBAP. Scan rate ) 0.1 V s-1; at controlled
potential (Eapp ) 0.75 V).
Figure 4. (A) Oxidative electropolymerization of monomer 1a by
repeated potential scans between -2.2 and +1.3 V at a glassy carbon
electrode (diameter 5 mm) in CH3CN + 0.1 M TBAP. Scan rate ) 0.1
V s-1. (B) Cyclic voltammogram of a C/poly-1a electrode in CH3CN
Table 3. Half-Wave Potentials (E1/2) for the C/poly-1a-d Modified
Electrodes in CH3CN with 0.1 M TBAP (Scan Rate ) 0.1 V s-1
E1/2,a V (vs Ag/10 mM Ag+)
)
+ 0.1 M TBAP (Γ1a ) 8 × 10-9 mol cm-2). Scan rate ) 0.1 V s-1
scan range -2.1 to +1.3 V.
;
complex
red (2)
red (1)
ox
poly-1a
poly-1b
poly-1c
poly-1d
-1.76
-1.78
-1.80
-1.82
-1.21
-1.23
-1.26
-1.28
1.01
1.00
0.98
0.97
range from -2.1 to +1.5 V results in a continuous increase in
the size of the cyclic voltammetric peaks as shown in Figure
4A. This indicates the formation of an electropolymerized film
on the electrode surface as a consequence of the pyrrole
oxidation. After a period of scanning (10 cycles, Figure 4A),
the glassy carbon electrode covered by a dark blue and adherent
thin polymeric film of poly-1a was transferred with thorough
rinsing to a CH3CN + 0.1 M TBAP solution free of monomer.
The cyclic voltammogram of this modified electrode exhibited
the regular electroactivity of the immobilized nickel(II) por-
phyrin characterized by a reversible two-electron-oxidation wave
(E1/2 ) 1.01 V) and two successive one-electron-reduction
waves (E1/2(P0/•-) ) -1.21 V and E1/2(P•-/2-) ) -1.76 V)
(Figure 4B) as judged by the relative charges under the different
peak systems. The regular polypyrrole wave was not observed
owing the high positive potential used to elaborate the polymer.
As previously described for other functionalized polypyrrole
films having no polypyrrole electrochemical feature,26 the
intense prepeak arising at the foot of the first reduction wave
disappears on the second scan if the potential scan range is
restricted to the negative region (Figure 4B) but is fully restored
after a sweep in the positive region up to the oxidation of the
macrocycle. This prepeak is a consequence of the resistivity
of the film due to the destruction of the regular polypyrrole
conductivity.26 Modified electrodes have also been prepared
by controlled-potential oxidation at 0.75 V. For instance, the
oxidative electropolymerization of 1d affords a modified
electrode (Γ1d ) 5.3 × 10-9 mol cm-2) which shows clearly
the reversible oxidation of the polypyrrole matrix (E1/2 ) 0.32
V with an anodic-cathodic peak potential separation (∆Ep)
equal to 0.04 V, V ) 0.1 V s-1) in the positive part of the cyclic
a E1/2 ) (Ep + Ep )/2, where Ep and Epc are the positive and negative
peaks potentials.
a
c
a
voltammogram (Figure 5A). This voltammogram exhibits also
a reversible one-electron-peak system (E1/2 ) -1.28 V, ∆Ep
) 0.03 V, V ) 0.1 V s-1) corresponding to the P0/.- couple.
Figure 5B shows the cyclic voltammogram of the C/poly-1a
electrode (Γ1a ) 5.0 × 10-9 mol cm-2), which depicts an
electrochemical behavior similar to that of poly-1d film. The
cyclic voltammetric data for the poly-1a_d films are summarized
in Table 3. It should be noted that the negative region of the
cyclic voltammograms (Figures 5A,B) is limited to the first
reversible one-electron-peak system but the second reversible
one-electron-peak system was also observed likewise in Figure
4B (see Table 3). Although the two modified electrodes contain
similar amounts of polymerized nickel(II) porphyrins, the
polypyrrole response for poly-1d is obviously more markedly
evident than that for poly-1a. The electropolymerization yields
were determined by dividing the charge under the one-electron
reduction peak of the nickel porphyrin in the film by the charge
passed during the electropolymerization and multiplying by
2.33n (n being the number of pyrrole groups linked to the
macrocycle).27 It appears that the electropolymerization yield
depends strongly on the number of electropolymerizable groups.
The best result was obtained with the poly-1d film (20%) while
the yield for the poly-1a film was found to be equal to 8%. In
(27) The 2.33 factor used here corresponds to the number of electrons
involved in the electropolymerization of the pyrrole (2 electrons
molecule-1) plus that for the electrooxidation of the polypyrrole chain
(0.33 electron molecule-1).10
(26) Cosnier, S.; Deronzier, A.; Roland, J.-F. J. Electroanal. Chem.
Interfacial Electrochem. 1990, 280, 133.

2664 Inorganic Chemistry, Vol. 35, No. 9, 1996
Carvalho de Medeiros et al.
addition, the electrochemical stability of these poly-1a and poly-
1d modified electrodes was investigated by repeatedly scanning
the electrode potential at 0.1 V s-1 over the oxidation wave. A
slow decrease in the intensity current of the peaks (35% and
20%) was observed after 65 cycles with the poly-1a (mono-
substituted) and the poly-1d (tetrasubstituted) films, respectively.
The better redox stability of the poly-1d film could be related
to a high degree of cross-linking for this polymer due to the
presence of four pyrrole-containing groups (R1) on the macro-
cycle.
without application of potential, as for the 1a monomer in
solution, presents the expected three absorption bands at 400,
521, and 555 nm. The visible spectrum of the electrooxidation
at 1.4 V of a poly-1a film on an OTE indicates that the main
absorption band of the doubly oxidized form of the film changes
from 400 to 334 nm. This behavior could be due to the fact
that the oxidation is more likely localized on the metallopor-
phyrin ring at room temperature.29 Morever, similar spectral
evolution was recently reported by Gray and co-workers30 for
the double-oxidized species of nonplanar zinc(II) tetrakis-
(pentafluorophenyl)porphyrin in CH2Cl2 solution. The spectra
of the singly and doubly reduced forms at -1.4 and -1.9 V,
respectively, exhibit a significant decrease of the main absorp-
tion band at 400 nm. Furthermore, the electroreduction of the
poly-1a film induces the appearance of broad bands between
600 and 700 nm. This suggests that the one- and two-electron
reductions are more likely localized on the immobilized
metalloporphyrin rings.22
Electroactive Solute Permeation in the Polymeric Films.
Since the ferrocene and polypyrrole electrochemical responses
are close together, the permeation measurements were performed
at polymeric films without the polypyrrole feature to avoid
mixing of the two signals. Thus, the destruction of the
polypyrrole response by overoxidation was accomplished by
repeatedly scanning the potential in range from 0 to 1.5 V.26
The permeation rate (PE) is expressed as the ratio of the current
peaks for direct oxidations of ferrocene (Fc) or bis(pentameth-
ylcyclopentadienyl)iron (DmFc) at the modified electrodes and
at a bare glassy carbon electrode.28 The permeation measure-
ments were performed in 2 mM solutions of Fc and DmFc in
CH3CN + 0.1 M TBAP. The cyclic voltammograms for
permeant Fc at a bare electrode and at a poly-1a electrode (Γ1a
) 5 × 10-9 mol cm-2) show that the current peaks for direct
oxidation of Fc are nearly identical in both voltammetric curves
(PE ≈ 1.0). A similar permeation measurement with this poly-
1a film was accomplished utilizing DmFc as permeant and the
signal was not attenuated (PE ≈ 1.0), showing no molecular
size discrimination of poly-1a film toward either solute in
contact with it (molecular sieving property). The same experi-
ment was repeated with the poly-1d film exhibiting a similar
apparent surface coverage (Γ1d ) 5 × 10-9 mol cm-2). The
response was largely attenuated for permeant Fc (PE ) 0.22),
and no signal was detected for the bulky DmFc, showing
molecular size discrimination of poly-1d films in relation to
the structure containing one pyrrole-containing group (1a),
which could lead to construction of a linear chain, and that
conformed with four pyrrole-containing groups (1d), which
could allow a strong cross-linking structure.
Conclusions
We have synthesized and characterized a new series of nickel-
(II) meso-tetrakis (polyfluorophenyl)porphyrins functionalized
by pyrrole-containg groups. It should be noted that this is the
first example of polyfluorinated substituted porphyrins where
the four possible compounds were obtained by functionalization
of the para-fluorine substituents of the aryl groups. The
electropolymerization of these nickel(II) porphyrins (1a-d)
allows the easy obtention of films exhibiting the regular
electroactivity of N-substituted polypyrroles as well as the
spectroscopic and electrochemical features of the nickel(II)
porphyrins. The investigation of the redox stability and
permeability of the metalloporphyrin films has illustrated the
influence of the cross-linking degree of the polymeric structure.
Application of this kind of electrode material based on other
metals like Fe and Mn for biomimetic oxidations and biosen-
soring is now under investigation.
Acknowledgment. M.A.C.d.M. gratefully acknowledges
CAPES (Coordenac¸ao de Aperfeic¸oamento de Pessoal de Nivel
Superior)sFoundation of EducationsBrazil for a Ph.D.
scholarship.
Spectroelectrochemistry of the Films. Only results for
poly-1a are presented here. Poly-1a film was grown on an OTE
doped with ITO by controlled-potential oxidation at 0.75 V and
transferred with thorough rinsing to a pure CH3CN + 0.1 M
TBAP solution. The initial visible spectrum for poly-1a film
IC9510268
(29) (a) Fajer, J.; Borg, D. C.; Forman, A.; Dolphin, D.; Felton, R. H. J.
Am. Chem. Soc. 1970, 92, 3451. (b) Seth, J.; Palaniappan, V.; Bocian,
D. F. Inorg. Chem. 1995, 34, 2201 and references cited therein.
(30) Hodge, J. A.; Hill, M. G.; Gray, H. B. Inorg. Chem. 1995, 34, 809.
(28) Cosnier, S.; Deronzier, A.; Roland, J.-F. J. Electroanal. Chem.
Interfacial Electrochem. 1991, 310, 71.