Kinetic and Thermodynamic Studies of Iron(III) and Iron(IV)σ -Bonded Porphyrins. Formation and Reactivity of [(OEP)Fe(R)]n+, Where OEP Is the Dianion of Octaethylporphyrin (n = 0, 1, 2, 3) and R = C6H5, 3,4,5-C6F3H2, 2,4,6-C6F32, C6F4H, or C6F5

Article abstract of DOI:10.1021/ic9714706

A series of high- and low-spin iron(III) phenyl and fluorophenyl octaethylporphyrin complexes are characterized by their electrochemical and spectroscopic properties in nonaqueous media. The investigated compounds are represented as (OEP)Fe(R), where R = C₆H₅, 3,4,5-C₆F₃H₂, 2,4,6-C₆F₃H₂, C₆F₄H, or C₆F₅ and OEP is the dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin. The two C₆F₃H₂ complexes are of special interest in that these isomers differ in the spin state of the iron(III). Electrochemical studies indicate that three one-electron oxidations are seen for all of the (OEP)Fe(R) derivatives which were investigated both at room and low temperature under conditions where migration of the σ-bonded ligand does not occur on the time scale of the experiment. The first one-electron oxidation of each compound leads to an Fe(IV) porphyrin, and this is followed by a migration of the axial group from the iron center to one of the four nitrogen atoms independent of the nature of the axial group or the iron(III) spin state. The kinetics were examined to evaluate the migration rate constants in the presence and absence of pyridine as a sixth axial ligand. The results of this study show that the stronger the electron donor ability of the R group, the faster the migration rate in the case of the five-coordinate species. However, an increase in charge density at the metal center by axial coordination of pyridine retards the migration rate and this result is interpreted in terms of a rate determining electron transfer step from R to Fe(IV) of the singly oxidized species prior to the migration. Our results also show that the spin state of the iron(TII) octaethylporphyrin is not a key factor which governs the migration of the axial ligand of the electrooxidized species. For the first time, an overall mechanism is proposed to explain the migration reaction in the σ-bonded iron porphyrin complexes.

Full text of DOI:10.1021/ic9714706

Inorg. Chem. 1998, 37, 1759-1766
1759
Kinetic and Thermodynamic Studies of Iron(III) and Iron(IV) σ-Bonded Porphyrins.
Formation and Reactivity of [(OEP)Fe(R)]n+, Where OEP Is the Dianion of
Octaethylporphyrin (n ) 0, 1, 2, 3) and R ) C6H5, 3,4,5-C6F3H2, 2,4,6-C6F3H2, C6F4H, or
C6F5
Karl M. Kadish,*,1a Eric Van Caemelbecke,1a Elena Gueletii,1a Shunichi Fukuzumi,*,1b
Kenichi Miyamoto,1b Tomoyoshi Suenobu,1b Alain Tabard,1c and Roger Guilard*,1c
Department of Chemistry, University of Houston, Houston, Texas 77204-5641, Department of Applied
Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan, and LIMSAG,
UMR 5633, Universite´ de Bourgogne, Faculte´ des Sciences “Gabriel”, 6 Boulevard Gabriel,
21000 Dijon, France
ReceiVed NoVember 19, 1997
A series of high- and low-spin iron(III) phenyl and fluorophenyl octaethylporphyrin complexes are characterized
by their electrochemical and spectroscopic properties in nonaqueous media. The investigated compounds are
represented as (OEP)Fe(R), where R ) C6H5, 3,4,5-C6F3H2, 2,4,6-C6F3H2, C6F4H, or C6F5 and OEP is the dianion
of 2,3,7,8,12,13,17,18-octaethylporphyrin. The two C6F3H2 complexes are of special interest in that these isomers
differ in the spin state of the iron(III). Electrochemical studies indicate that three one-electron oxidations are
seen for all of the (OEP)Fe(R) derivatives which were investigated both at room and low temperature under
conditions where migration of the σ-bonded ligand does not occur on the time scale of the experiment. The first
one-electron oxidation of each compound leads to an Fe(IV) porphyrin, and this is followed by a migration of the
axial group from the iron center to one of the four nitrogen atoms independent of the nature of the axial group
or the iron(III) spin state. The kinetics were examined to evaluate the migration rate constants in the presence
and absence of pyridine as a sixth axial ligand. The results of this study show that the stronger the electron
donor ability of the R group, the faster the migration rate in the case of the five-coordinate species. However,
an increase in charge density at the metal center by axial coordination of pyridine retards the migration rate and
this result is interpreted in terms of a rate determining electron transfer step from R to Fe(IV) of the singly
oxidized species prior to the migration. Our results also show that the spin state of the iron(III) octaethylporphyrin
is not a key factor which governs the migration of the axial ligand of the electrooxidized species. For the first
time, an overall mechanism is proposed to explain the migration reaction in the σ-bonded iron porphyrin complexes.
Introduction
To understand the reactivity and role of these organoiron
species in biological systems, a number of iron porphyrins
Organoiron derivatives have been identified as intermediates
in several biological processes, including lipoxygenation cata-
lyzed by lipoxygenase enzymes2 and heme inactivation in
hemoglobin, myoglobin, cytochrome P-450, and catalase.3-7
These transient species are unstable and undergo a migration
of the σ-bonded axial ligand from the heme iron to one of the
four porphyrin ring nitrogens leading to the formation of
N-substituted hemes.8
possessing σ-bonded alkyl or aryl axial ligands have been
synthesized and characterized over the last 15 years.9-33 Our
(9) Lexa, D.; Save´ant, J.-M. J. Am. Chem. Soc. 1982, 104, 3503-3504.
(10) Ogoshi, H.; Sugimoto, H.; Yoshida, Z.-I.; Kobayashi, H.; Sakai, H.;
Maeda, Y. J. Organomet. Chem. 1982, 234, 185-195.
(11) Mansuy, D.; Fontecave, M.; Battioni, J.-P. J. Chem. Soc., Chem.
Commun. 1982, 317-319.
(12) Mansuy, D.; Battioni, J.-P. J. Chem. Soc., Chem. Commun. 1982, 638-
639.
(1) (a) University of Houston. (b) Osaka University. (c) Universite´ de
Bourgogne.
(13) Mansuy, D.; Battioni, J.-P.; Dupre, D.; Sartori, E. J. Am. Chem. Soc.
1982, 104, 6159-6161.
(2) Corey, E. J.; Wright, S. W.; Matsuda, S. P. T. J. Am. Chem. Soc.
1989, 111, 1452-1455.
(14) Kunze, K. L.; Ortiz de Montellano, P. R. J. Am. Chem. Soc. 1983,
105, 1380-1381.
(3) Ortiz de Montellano, P. R.; Kunze, K. L.; Augusto, O. J. Am. Chem.
Soc. 1982, 104, 3545-3546.
(15) Battioni, P.; Mahy, J.-P.; Gillet, G.; Mansuy, D. J. Am. Chem. Soc.
1983, 105, 1399-1401.
(4) Ortiz de Montellano, P. R.; Kerr, D. E. Biochemistry 1985, 24, 1147-
(16) Cocolios, P.; Lagrange, G.; Guilard, R. J. Organomet. Chem. 1983,
253, 65-79.
1152.
(5) Ortiz de Montellano, P. R.; Reich, N. O. In Cytochrome P-450; Ortiz
de Montellano, P. R., Ed.; Plenum Press: New York, 1986; pp 273-
314.
(6) Ortiz de Montellano, P. R. Acc. Chem. Res. 1987, 20, 289-294.
(7) Guilard, R.; Kadish, K. M. Chem. ReV. 1988, 88, 1121-1146.
(8) Lavallee, D. K. The Chemistry and Biochemistry of N-Substituted
Porphyrins, 1st ed.; VCH Publishers: New York, 1987; p 313.
(17) Cocolios, P.; Laviron, E.; Guilard, R. J. Organomet. Chem. 1982, 228,
C39-C42.
(18) Lanc¸on, D.; Cocolios, P.; Guilard, R.; Kadish, K. M. J. Am. Chem.
Soc. 1984, 106, 4472-4478.
(19) Lanc¸on, D.; Cocolios, P.; Guilard, R.; Kadish, K. M. Organometallics
1984, 3, 1164-1170.
(20) Doppelt, P. Inorg. Chem. 1984, 23, 4009-4011.
S0020-1669(97)01470-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/31/1998

1760 Inorganic Chemistry, Vol. 37, No. 8, 1998
Kadish et al.
own laboratories have concentrated, in large part, on the
synthesis and characterization of σ-bonded iron porphyrins
containing phenyl or perfluorophenyl groups of the type C6H5,
C6F5, or C6F4H.16-19,34-39 A migration of the σ-bonded axial
ligand has been shown to occur upon the chemical or electro-
chemical oxidation of some synthetic σ-bonded iron(III)
porphyrins,3,7,13,22,34,36-38 but the exact conditions leading to the
occurrence or absence of a migration reaction has yet to be
completely understood.
The first electrochemical studies of (OEP)Fe(R) and (TPP)-
Fe(R)18,40 showed that a migration of the σ-bonded R group
was initiated by a one-electron oxidation but seemed to occur
only for compounds containing a specific σ-bonded ligand and/
or iron(III) spin state.34,41 Electrogenerated [(OEP)Fe(C6H5)]+
and [(TPP)Fe(C6H5)]+ were shown to undergo an axial ligand
migration, but this reaction was not observed on the cyclic
voltammetry time scale for the same singly oxidized porphyrins
containing σ-bonded C6F5 or C6F4H groups. This difference
in reactivity between [(P)Fe(C6H5)]+ and the perfluorophenyl
derivatives, [(P)Fe(C6F4H)]+ and [(P)Fe(C6F5)]+, was first
attributed to a difference in iron(III) spin state of the neutral
compounds and/or a difference in the site of electron transfer
of the singly oxidized species. The low-spin compounds
containing C6H5 were proposed to be oxidized at the metal
center, while the high-spin compounds containing C6F4H or C6F5
were proposed to be oxidized at the conjugated porphyrin π
ring system. However, a more recent electrochemical study of
(OETPP)Fe(C6H5), (OETPP)Fe(C6F5), and (OETPP)Fe(C6F4H)39,40
indicates this analysis to be much too simplified since all three
OETPP derivatives contain low-spin iron(III) and none of the
[(OETPP)Fe(R)]+ complexes undergoes a migration, despite the
unequivocal formation of iron(IV) in singly oxidized [(OETPP)-
Fe(C6H5)]+.39 This result seems to clearly indicate that the
iron(III) spin state is not a key factor governing the axial ligand
migration of oxidized σ-bonded Fe(III) porphyrins.
Two additional results emerge from the electrochemical study
of (OETPP)Fe(R).39 The first is that doubly oxidized [(OETPP)-
FeIV(C6H5)]2+ undergoes a slow migration reaction to give [(N-
C6H5OETPP)FeIII]2+, and the second is that three well-defined
one-electron oxidations are observed for the initial σ-bonded
complex by cyclic voltammetry at high scan rates or low
temperatures in benzonitrile containing 0.1 M tetrabutylammo-
nium perchlorate (TBAP). The three oxidations are consistent
with formation of an iron(IV) porphyrin followed by an iron(IV)
porphyrin π cation radical and dication, and these latter two
reactions at the porphyrin π ring system should also have been
observed after the facile formation of [(OEP)FeIV(C6H5)]+ and
[(TPP)FeIV(C6H5)]+ in benzonitrile containing 0.1 M TBAP.18
To explore this possibility, and to look for the expected third
oxidation of other (P)Fe(R) derivatives, we have now systemati-
cally investigated the redox properties of five σ-bonded por-
phyrins in the OEP series under experimental conditions where
a third oxidation might be observed at very positive potentials.
We have also more closely examined the reactivity of the singly
oxidized porphyrins on time scales longer than those of cyclic
voltammetry and provide the first kinetic measurements for rate
constants involving the conversion of [(OEP)Fe(R)]+ to [(N-
ROEP)Fe]+.
(21) Balch, A. L.; Renner, M. W. Inorg. Chem. 1986, 25, 303-307.
(22) Balch, A. L.; Renner, M. W. J. Am. Chem. Soc. 1986, 108, 2603-
2608.
The investigated porphyrins are represented as (OEP)Fe(R),
where R ) C6H5, 3,4,5-C6F3H2, 2,4,6-C6F3H2, C6F4H, or C6F5.
The two (OEP)Fe(C6F3H2) isomers differ in the degree of steric
hindrance between the axial ligand and the porphyrin macrocycle
as well as in spin state of the Fe(III). The 3,4,5-C6F3H2
derivative contains low-spin iron(III), and the 2,4,6-C6F3H2
derivative contains high-spin iron(III) as shown in Chart 1.
(23) Clarke, D. A.; Dolphin, D.; Grigg, R.; Johnson, A. W.; Pinnock, H.
A. J. Chem. Soc. C 1968, 881-885.
(24) Lexa, D.; Mispelter, J.; Save´ant, J.-M. J. Am. Chem. Soc. 1981, 103,
6806-6812.
(25) Lexa, D.; Save´ant, J.-M.; Battioni, J.-P.; Lange, M.; Mansuy, D. Angew.
Chem., Int. Ed. Engl. 1981, 20, 578-579.
(26) Reed, C. A.; Mashiko, T.; Bentley, S. P.; Kastner, M. E.; Scheidt, W.
R.; Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979, 101, 2948-
2958.
(27) Balch, A. L.; Hart, R. L.; Latos-Grazynski, L.; Traylor, T. G. J. Am.
Chem. Soc. 1990, 112, 7382-7388.
Experimental Section
(28) Arasasingham, R. D.; Balch, A. L.; Hart, R. L.; Latos-Grazynski, L.
J. Am. Chem. Soc. 1990, 112, 7566-7571.
Chemicals. Benzonitrile (PhCN) was obtained from Aldrich
Chemical Co. and distilled over P2O5 under vacuum prior to use.
Absolute dichloromethane (CH2Cl2) over molecular sieves (Fluka
Chemika) and anhydrous pyridine (Aldrich) were used without further
purification. Tetra-n-butylammonium perchlorate (TBAP) was pur-
chased from Sigma Chemical Co., recrystallized from ethyl alcohol,
and dried under vacuum at 40 °C for at least 1 week prior to use. 2,3-
Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) was obtained com-
mercially and used without further treatment.
Synthesis of (OEP)Fe(R). The five investigated aryl σ-bonded iron
porphyrins were prepared by reacting the corresponding aryl Grignard
reagent with (OEP)FeCl according to literature procedures.18,34 The
synthesis of (OEP)Fe(R), where R ) C6H5, C6F4H, or C6F5, has already
been reported in the literature.34 The (OEP)Fe(R) derivatives, where
R ) 3,4,5- and 2,4,6-C6F3H2, have not previously been reported, and
a description of their physicochemical properties is given below.
(OEP)Fe(3,4,5-C6F3H2). UV-visible (CH2Cl2) λmax, nm (10-3 ꢀ,
M-1 cm-1): 390 (63), 531 (8), 554 (8). 1H NMR (C6D6 from SiMe4
at 300 K) δ, ppm: 8.14, -0.06 (16H, R-CH2), -1.30 (24 H, â-CH3),
-77.90 (2 H, o-Haxial ligand), 5.84 (4 H, meso-H). 19F NMR (using CFCl3
as external reference at 294 K) δ, ppm: -120.8, -194.9 in C5D5N,
-92.9, -206.5 in C6D6 (Faxial ligand). Mass spectrum (DEI): M•+, m/z
719 (66); [M - C6F3H2]+, m/z 588 (100). Anal. Calcd for C42H46N4F3-
Fe: C, 70.09; H, 6.44; N, 7.78. Found: C, 69.2; H, 6.7; N, 8.1.
(OEP)Fe(2,4,6-C6F3H2). UV-vis (CH2Cl2) λmax, nm (10-3 ꢀ, M-1
cm-1): 365 (58), 510(6), 537(6), 642(2). 1H NMR (C6D6 from SiMe4
at 300 K) δ, ppm: 38.9, 37.5 (16 H, R-CH2), 5.5 (24 H, â-CH3), -47.5
(29) Arasasingham, R. D.; Balch, A. L.; Cornman, C. R.; Latos-Grazynski,
L. J. Am. Chem. Soc. 1989, 111, 4357-4363.
(30) Arasasingham, R. D.; Balch, A. L.; Latos-Grazynski, L. J. Am. Chem.
Soc. 1987, 109, 5846-5847.
(31) Li, Z.; Goff, H. M. Inorg. Chem. 1992, 31, 1547-1548.
(32) Shin, K.; Yu, B.-S.; Goff, H. M. Inorg. Chem. 1990, 29, 889-890.
(33) Arafa, I. M.; Shin, K.; Goff, H. M. J. Am. Chem. Soc. 1988, 110,
5228-5229.
(34) Guilard, R.; Boisselier-Cocolios, B.; Tabard, A.; Cocolios, P.; Simonet,
B.; Kadish, K. M. Inorg. Chem. 1985, 24, 2509-2520.
(35) Kadish, K. M.; Tabard, A.; Lee, W.; Liu, Y. H.; Ratti, C.; Guilard, R.
Inorg. Chem. 1991, 30, 1542-1549.
(36) Kadish, K. M.; D’ Souza, F.; Van Caemelbecke, E.; Tabard, A.;
Guilard, R. In Proceedings of the Fifth International Symposium on
Redox Mechanisms and Interfacial Properties of Molecules of Biologi-
cal Importance; Shultz, F. A., Taniguchi, I., Eds.; The Electrochemical
Society, Inc.: Princeton, NJ, 1993; Vol. 93-II, pp 125-134.
(37) Kadish, K. M.; D’Souza, F.; Van Caemelbecke, E.; Villard, A.; Lee,
J.-D.; Tabard, A.; Guilard, R. Inorg. Chem. 1993, 32, 4179-4185.
(38) Kadish, K. M.; Van Caemelbecke, E.; D’Souza, F.; Medforth, C. J.;
Smith, K. M.; Tabard, A.; Guilard, R. Organometallics 1993, 12,
2411-2413.
(39) Kadish, K. M.; Van Caemelbecke, E.; D’Souza, F.; Medforth, C. J.;
Smith, K. M.; Tabard, A.; Guilard, R. Inorg. Chem. 1995, 34, 2984-
2989.
(40) Notation used: P, any porphyrin; OEP2-, dianion of octaethylpor-
phyrin; TPP2-, dianion of tetraphenylporphyrin; OETPP2-, dianion
of octaethyltetraphenylporphyrin.
(41) Guilard, R.; Lecomte, C.; Kadish, K. M. Struct. Bonding 1987, 64,
205-268.

Studies of Iron(III) and Iron(IV) σ-Bonded Porphyrins
Inorganic Chemistry, Vol. 37, No. 8, 1998 1761
Chart 1
axial ligand, with the number and positions of the fluorine atoms
on the R group determining the spin state of the initial Fe(III)
complex. The spin state of iron(III) porphyrins is known to
depend on the ligand field strength of the fifth or sixth axial
ligand,44 and a conversion from low-spin Fe(III) to high-spin
Fe(III) is observed upon going from (OEP)Fe(C6H5) to either
one of the two perfluorophenylporphyrins, (OEP)Fe(C6F5) or
(OEP)Fe(C6F4H).34
A change in the position of the fluorine atoms from the meta
to the ortho positions of the σ-bonded aryl group on (OEP)Fe-
(C6F3H2) will also induce a change in the iron(III) spin state as
1
indicated by H NMR spectra. (OEP)Fe(3,4,5-C6F3H2) is in a
1
low-spin state (S ) /2). In contrast, (OEP)Fe(2,4,6-C6F3H2)
(4 H, meso-H). 19F NMR (in C5D5N using CFCl3 as external reference
at 294 K) δ, ppm: -53.1, -82.8 (Faxial ligand). Mass spectrum (DEI):
M•+, m/z 719 (28); [M - C6F3H2]+, m/z 588 (100). Anal. Calcd for
C42H46N4F3Fe: C, 70.09; H, 6.44; N, 7.78. Found: C, 71.2; H, 6.9;
N, 7.9.
contains high-spin Fe(III) (S ) 5/2) and exhibits two typical ESR
signals at g ) 5.85 and 2.06 in toluene at 4 K. However, as
expected, the two compounds are in a low-spin state when a
pyridine ligand is six-coordinated to the iron center. This is
unambiguously shown by the 19F NMR chemical shifts in
C5D5N.35
The room-temperature UV-visible spectra of (OEP)Fe(R)
support the NMR-based assignments of spin state in the case
of the two C6F3H2 derivatives. The spectrum of low-spin
(OEP)Fe(3,4,5-C6F3H2) is similar to that of low-spin (OEP)-
Fe(C6H5),16 while the spectrum of high-spin (OEP)Fe(2,4,6-
C6F3H2) is comparable to that of high-spin (OEP)Fe(C6F4H)34
(see Table 1). The differences in electronic properties between
the axial ligands of (OEP)Fe(3,4,5-C6F3H2) and (OEP)Fe(2,4,6-
C6F3H2) are smaller than the differences in electronic properties
between the axial ligands of (OEP)Fe(C6H5) and (OEP)Fe-
(C6F5).45,46 Thus, the fact that two different spin states are seen
for (OEP)Fe(3,4,5-C6F3H2) and (OEP)Fe(2,4,6-C6F3H2) indi-
cates that the iron spin state in the (OEP)Fe(R) is quite
dependent on the nature of the axial ligands.
Electrochemistry of (OEP)Fe(R) in CH2Cl2. Figure 1
illustrates cyclic voltammograms for oxidation and reduction
of the five (OEP)Fe(R) derivatives in CH2Cl2 containing 0.2
M TBAP at -50 °C. Each σ-bonded porphyrin undergoes one
reversible reduction and three reversible oxidations at potentials
between E1/2 ) -0.86 and +1.83V vs SCE. Two of the
compounds (R ) C6F4H, C6F5) also show a second irreversible
reduction at Epc ≈ -1.80V. Previous electrochemical studies
of (OEP)Fe(R) were carried out only in PhCN at room
temperature, and the first one-electron reduction was invariably
accompanied by a loss of the σ-bonded ligand under these
experimental conditions.34 The low-temperature cyclic voltam-
mograms in Figure 1 therefore provide the first reversible E1/2
values for reduction of an (OEP)Fe(R) complex with C6F4H
and C6F5 axial ligands.
The most significant feature of Figure 1 is that all five
σ-bonded porphyrins undergo three one-electron oxidations, and
this can only be accounted for by one of the three reactions
being assigned to an Fe(III)/Fe(IV) transition and the other two
to an oxidation of the conjugated porphyrin macrocycle. As
will be demonstrated in the following sections, the first one-
electron oxidation of (OEP)Fe(R) invariably results in the
formation of an Fe(IV) complex while the latter two reactions
are proposed to involve an electron abstraction from the
porphyrin π ring system.
Instrumentation. 1H and 19F NMR spectra were recorded at 500
MHz on a Bruker Avance DRX and at 200 MHz on a Bruker AC 200
spectrometers at the CSMUB (“Centre de Spectrome´trie Mole´culaire
de l’Universite´ de Bourgogne”). ESR spectra were recorded in toluene
on a Bruker ESP 300 spectrometer equipped with an Oxford Instrument
Cryostat. The g values were measured with respect to diphenyl-
picrylhydrazyl (g ) 2.0036 ( 0.0003). Electronic absorption spectra
were recorded on a Varian Cary 5 spectrophotometer. Mass spectra
were obtained with a Kratos Concept 32S spectrometer, and the data
were collected and processed using a Sun 3/80 workstation.
Cyclic voltammetry was carried out with an an EG&G Princeton
Applied Research model 173 Potentiostat/Galvanostat coupled with an
EG&G PARC model 175 Universal Progammer. Current-voltage
curves were recorded on an EG&G Princeton Applied Research model
RE-0151 X-Y recorder. A three-electrode system was used and
consisted of a glassy carbon button or a platinum working electrode, a
platinum wire counter electrode, and a saturated calomel reference
electrode (SCE). The reference electrode was separated from the bulk
of the solution by a fritted-glass bridge filled with the solvent/supporting
electrolyte mixture. All potentials are referenced to the SCE.
Spectroelectrochemical experiments were performed at a platinum
thin-layer electrode whose design is described in the literature.42 The
potentials were applied and monitored with an EG&G Princeton Applied
Research model 173 potentiostat. Time-resolved UV-visible spectra
were recorded with a Hewlett-Packard model 8453 diode array
spectrophotometer.
Kinetic Measurements. The chemical oxidation of (OEP)Fe(R)
(R ) C6H5, 3,4,5-C6F3H2, 2,4,6-C6F3H2, C6F4H) was accomplished by
adding an aliquot (50 µL) of DDQ (3.0 × 10-2 M) in CH2Cl2 to a
quartz cuvette (10 mm i.d.) which contained (OEP)Fe(R) (1.2 × 10-4
M) and TBAP (0.2 M) in deaerated CH2Cl2 (3.0 mL). The UV-visible
spectral changes associated with the initial electron transfer from (OEP)-
Fe(R) to DDQ and the subsequent migration of the σ-bonded ligand
from the singly oxidized porphyrin were monitored in the dark at 298
K using a Hewlett-Packard model 8452A or 8453 diode array
spectrophotometer. Similar experiments were carried out in the case
of (OEP)Fe(R)(py).
Theoretical Calculations. The HOMO energy level calculations
of phenyl and perfluorophenyl anions, i.e., C6H5-, 3,4,5-C6F3H2-, 2,4,6-
C6F3H2-, 2,3,5,6-C6F4H-, and C6F5-, were performed using the
MOPAC program (Ver. 6) which is incorporated in the MOLMOLIS
program by Daikin Industries, Ltd. The PM3 Hamiltonian was used
for the semiempirical MO calculations.43 Final geometries and energet-
ics were obtained by optimizing the total molecular energy with respect
to all structural variables.
The half-wave potentials for each process in Figure 1 are
summarized in Table 2 under different experimental conditions,
Results and Discussion
Spectroscopic Characterization of (OEP)Fe(R). The five
investigated (OEP)Fe(R) derivatives vary in the nature of the
(44) (a) Scheidt, W. R.; Lee, Y. J. Struct. Bonding 1987, 64, 1-70. (b)
Palmer, G. In Iron Porphyrins; Lever, A. B. P., Gray, H. B., Eds.;
Addison-Wesley: Reading, MA, 1983; Vol. II, pp 43-88.
(45) Adcock, W.; Khor, T.-C. J. Am. Chem. Soc. 1978, 100, 7799-7810.
(46) Hansch, C.; Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165-195.
(42) Lin, X. Q.; Kadish, K. M. Anal. Chem. 1985, 57, 1498-1501.
(43) Stewart, J. J. P. J. Comput. Chem. 1989, 10, 209-221.

1762 Inorganic Chemistry, Vol. 37, No. 8, 1998
Kadish et al.
Table 1. UV-Visible Data of (OEP)Fe(R) and [(OEP)Fe(R)]+ in CH2Cl2, 0.2 M TBAP
λ
max, nm (ꢀ × 10-3, M-1 cm-1
)
Soret bands
visible bands
compound
R
spin statea
(OEP)Fe(R)
C6H5
ls
ls
hs
hs
c
c
c
391 (62)
390 (63)
521 (6)
531 (8)
510 (6)
510 (6)
498 (sh)
499 (sh)
500 (sh)
500 (sh)
552 (7)
554 (8)
537 (6)
536 (5)
525 (7)
531 (13)
535 (23)
531 (18)
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
365 (58)
367 (63)
642 (2)
646 (2)
-
626 (0.6)
641 (0.4)
641 (0.4)
[(OEP)Fe(R)]+
C6H5
389 (57)
391 (49)
b
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
374 (59)
374 (59)
c
a Assignment of spin state based on NMR spectra (ls, low spin; hs, high spin) at room temperature. b Spectrum of unstable product obtained after
10 s of electrolysis. c Spin state has not been assigned.
Figure 1. Low-temperature (-50 °C) cyclic voltammograms of (OEP)Fe(R) derivatives in CH2Cl2 containing 0.2 M TBAP.
and the four electrode reactions are proposed to occur as shown
in eqs 1-4. The given iron oxidation state assignments are
These data indicate that both the first oxidation and the first
reduction of (OEP)Fe(R) are strongly dependent upon the
number and the position of the fluorine atoms on the axial
ligand, and this is consistent with the metal-centered electron-
transfer reactions shown in eqs 1 and 4. However, it is
important to note that the relationship between E1/2 and electron
donor properties of the σ-bonded axial ligand do not follow a
simple relationship with the number of F atoms, independent
of Fe(III) spin state, as was previously suggested.39 This is
discussed in later sections of the manuscript.
UV-Visible Characterization of [(OEP)Fe(R)]+. Metal-
centered electrode reactions of metalloporphyrins are generally
accompanied by only small changes in the porphyrin Soret band,
while ring-centered reactions are often characterized by a large
decrease in the Soret band intensity due to loss of the ring
conjugation.47 The best examples in the case of σ-bonded
porphyrins are given by the conversion of (OETPP)M(C6H5)
to [(OETPP)M(C6H5)]+ where M ) Fe or In in PhCN.39 The
one-electron oxidation of (OETPP)Fe(C6H5) involves an Fe(III)/
(OEP)FeIII(R) a [(OEP)FeIV(R)]+ + e-
[(OEP)FeIV(R)]+ a [(OEP)FeIV(R)]2+ + e-
[(OEP)FeIV(R)]2+ a [(OEP)FeIV(R)]3+ + e-
(OEP)FeIII(R) + e- a [(OEP)FeII(R)]-
(1)
(2)
(3)
(4)
consistent with previous analysis of the (OEP)Fe(C6H5) electrode
reactions18 and differ only by the presence of a third oxidation
(Reaction 3) which is not observable in PhCN due to the more
limited anodic potential range of this solvent. The potentials
for the first reduction of (OEP)Fe(R) (Reaction 4) vary from
E1/2 ) - 0.86 V for (OEP)Fe(C6H5) to - 0.63 V for (OEP)-
Fe(C6F5) and a similar positive shift is seen upon going from
the first oxidation of (OEP)Fe(C6H5) (E1/2 ) +0.47 V) to the
(47) Felton, R. H. In The Porphyrins; Dolphin, D., Ed.; Academic: New
York, 1978; Vol. V, pp 53-125.
first oxidation of (OEP)Fe(C6F5) (E1/2
) +0.80 V).

Studies of Iron(III) and Iron(IV) σ-Bonded Porphyrins
Inorganic Chemistry, Vol. 37, No. 8, 1998 1763
Table 2. Half-Wave Potentials (V vs SCE) for Oxidation and Reduction of (OEP)Fe(R) in Solvents Containing 0.2 M TBAP
-50 °C
CH2Cl2/pyra
room temperature
initial Fe(III)
spin state (RT)
electrode reaction
1st oxidation
axial ligand, R
CH2Cl2
CH2Cl2
PhCN
C6H5
ls
ls
hs
hs
hs
ls
0.47
0.62
0.68
0.76
0.80
1.27
1.28
1.14
1.10
1.11
1.68
1.70
1.73
1.83
1.83
0.31
0.49
0.57
0.73
0.45
0.64
0.73
0.81
-
0.48b
0.66
0.76
0.79c
0.87c
1.30b
1.31
1.19
1.14c
1.18c
-
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
C6F5
C6H5
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
C6F5
C6H5
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
C6F5
C6H5
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
2nd oxidation
3rd oxidation
1st reduction
-
ls
1.31
1.23
1.22
-
hs
hs
hs
ls
-
ls
-
-
hs
hs
hs
ls
-
-
-
-
-
-
-0.86
-0.70
-0.74
-0.65
-0.63
ls
hs
hs
hs
C6F5
a [py] ) 0.12 M. b Data from: Lanc¸on, D.; Cocolios, P.; Guilard, R.; Kadish, K. M. J. Am. Chem. Soc. 1984, 106, 4472-4478. c Data from:
Guilard, R.; Boisselier-Cocolios, B.; Tabard, A.; Cocolios, P.; Simonet, B.; Kadish, K. M. Inorg. Chem. 1985, 24, 2509-2520.
Fe(IV) reaction, and, as expected, the singly oxidized iron
porphyrin shows only a 9 nm shift in the position of the Soret
band and no loss in Soret band intensity. This contrasts with
the oxidation of (OETPP)In(C6H5) where a porphyrin π cation
radical is generated, leading to a UV-visible spectrum whose
Soret band has virtually disappeared.39
The UV-visible spectra of singly oxidized [(OEP)Fe(R)]+
also provide strong indirect evidence for the site of electron
abstraction. The spectral data for each neutral and singly
oxidized porphyrin are summarized in Table 1. As seen in this
table, only relatively small changes occur upon going from
(OEP)Fe(R) to [(OEP)Fe(R)]+ independent of the initial Fe(III)
spin state or the number of F atoms on the σ-bonded axial ligand.
For example, the two low-spin derivatives, (OEP)Fe(C6H5) and
(OEP)Fe(3,4,5-C6F3H2), have a Soret band close to 390 nm both
in their neutral and singly oxidized states. The two high-spin
porphyrins have a Soret band at around 366 nm in the neutral
state and 374 nm in the singly oxidized state. Most importantly,
the spectral features of [(OEP)Fe(R)]+ are almost identical for
all of the singly oxidized compounds (Table 1), and this can
only be interpreted in terms of the same metal oxidation state
assignment, i.e., FeIV in [(OEP)Fe(R)]+.
The spectroscopic data discussed above indicate that all five
investigated (OEP)Fe(R) derivatives are oxidized at the metal
center to generate Fe(IV) as previously shown for (OEP)Fe-
(C6H5).18 The reversible half-wave potentials for these metal-
centered reactions are fairly insensitive to the nature of the
solvent (PhCN or CH2Cl2) or solution temperature between 25
and -50 °C in CH2Cl2 (see Table 2), but they do depend
strongly on the nature of the axial ligand of the initial Fe(III)
complex. This is not the case for electrode reactions involving
the conjugated porphyrin macrocycle. Indeed, the second
oxidation (Figure 2) and third oxidation of (OEP)Fe(R), as well
as the first oxidation of (OEP)In(R) and (OEP)Tl(R) (R ) C6H5,
C6F4H, C6F5),48,49 all involve the porphyrin π ring system but
have E1/2 values which do not vary significantly with the nature
of the axial ligand.
Figure 2. Relationship between E1/2 for the second oxidation of (OEP)-
Fe(C6FxHy) and the number of fluorine atoms on the axial ligand.
In the first electrochemical study of (OEP)Fe(R),34 it was
pointed out that an overall 390 mV difference in half-wave
potentials is observed between the same oxidations or reductions
of (OEP)Fe(C6H5) and (OEP)Fe(C6F5) in PhCN. The perfluoro-
phenyl species were harder to oxidize and easier to reduce by
approximately 80 mV per added electron-withdrawing F group
upon going from (OEP)Fe(C6H5) to (OEP)Fe(C6F5), and this
was attributed to a purely inductive effect of the σ-bonded axial
ligand. A similar potential difference is observed in CH2Cl2 at
room temperature, but smaller values of 330 mV (oxidation)
or 230 mV (reduction) are seen in CH2Cl2 at low temperature.
However, an analysis of the data for all five compounds clearly
shows that only a part of the difference between E1/2 for
reduction of (OEP)Fe(C6H5) and (OEP)Fe(C6F5) is due to the
inductive effect of the F groups with the remainder being due
to the specific high- or low-spin state of the Fe(III) ion in (OEP)-
Fe(R).
The key compounds which lead to this conclusion are (OEP)-
Fe(3,4,5-C6F3H2), which is low spin, and (OEP)Fe(2,4,6-
C6F3H2), which is high spin. As seen in Table 2 and Figure 3,
high-spin (OEP)Fe(2,4,6-C6F3H2) is both harder to oxidize and
harder to reduce (by 60-100 mV) than the low-spin (OEP)-
Fe(3,4,5-C6F3H2) derivative. This difference cannot be simply
(48) Kadish, K. M.; Boisselier-Cocolios, B.; Cocolios, P.; Guilard, R. Inorg.
Chem. 1985, 24, 2139-2147.
(49) Kadish, K. M.; Tabard, A.; Zrineh, A.; Ferhat, M.; Guilard, R. Inorg.
Chem. 1987, 26, 2459-2466.

1764 Inorganic Chemistry, Vol. 37, No. 8, 1998
Kadish et al.
Figure 4. UV-visible spectral changes observed upon addition of 5.0
× 10-4 M DDQ to a CH2Cl2 solution containing (OEP)Fe(3,4,5-C6F3H2)
(1.2 × 10-4 M) and 0.2 M TBAP at 298K; t ) 0, 60, 135, 325, 520,
840, and 2930 s.
Table 3. Rate Constants for R Group Migration of [(OEP)Fe(R)]+
and [(OEP)Fe(R)(py)]+ in CH2Cl2 Containing 0.2 M TBAP at 298
K
axial ligand, R
group
kmig, s-1 a
[(OEP)Fe(R)]+
[(OEP)Fe(R)(py)]+ c
b
Ip
C6H5
2.06
2.97
3.35
3.68
2.8 × 10-2
4.6 × 10-3
1.7 × 10-4
1.3 × 10-4
1.2 × 10-3
5.9 × 10-4
no migration
no migration
Figure 3. Dependence of E1/2 for first oxidation and first reduction of
(OEP)Fe(C6FxHy) on the number of fluorine atoms of the σ-bonded
axial ligand.
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
a Rate constants good to (5%. b The ionization potentials, Ip, were
calculated by using the PM3 method. c Measured in CH2Cl2 containing
0.2 M TBAP and 0.12 M pyridine.
related to a difference in inductive effects of the fluorine atoms
between the two compounds since a purely inductive effect
would shift the half-wave potentials for oxidation and reduction
in the same direction, which is clearly not the case.
of (OEP)Fe(3,4,5-C6F3H2), the migration rate constant was
determined by simultaneously monitoring a decay in the peak
at 531 nm and the rise of a new band at ca. 586 nm (see Figure
4). The migration rate obeys first-order kinetics, and this is also
the case for the other three singly oxidized porphyrins whose
migration rate constants (kmig) at 298 K are summarized in Table
3. As seen in this table, the kmig values vary by 2 orders of
magnitude among the four investigated Fe(IV) complexes in
CH2Cl2 and increase with increasing electron donor ability of
the R group. For example, kmig ) 1.3 × 10-4 s-1 for [(OEP)-
Fe(C6F4H)]+ and 2.8 × 10-2 s-1 for [(OEP)Fe(C6H5)]+ in
CH2Cl2. The migration rate constants and half-wave potentials
are both dependent on the donor properties of the σ-bonded
axial ligand, and a good correlation therefore exists between
these values and the ionization potential of the anionic axial
ligand. This correlation is shown in Figure 5.
Kinetics and Mechanism of R Group Migration from
[(OEP)Fe(R)]+. The first published reports of phenyl group
migration from electrogenerated [(TPP)Fe(C6H5)]+ or [(OEP)-
Fe(C6H5)]+ related this reaction to the presence of an Fe(IV)
oxidation state which was initially postulated on the basis of
UV-visible and electrochemical data19 and later proven on the
basis of NMR spectra for several singly oxidized σ-bonded
derivatives.22 At the same time, the stability of [(P)Fe(C6F5)]+-
and [(P)Fe(C6F4H)]+ was explained34 in terms of a different
site of electron transfer, i.e., the formation of an Fe(III)
porphyrin π cation radical in the singly oxidized species. More
extensive results, now described in this present paper, clearly
point to the generation of an Fe(IV) oxidation state in all of the
investigated [(OEP)Fe(R)]+ derivatives, independent of iron spin
state, and this leads to the conclusion that a migration reaction
might actually occur for [(P)Fe(C6F5)]+ and [(P)Fe(C6F4H)]+
on longer time scales than those previously studied.
To investigate this possibility, we measured the rate constant
for migration of C6H5 in [(OEP)Fe(C6H5)]+ and also monitored
the much slower time-dependent changes in UV-visible spectra
of the other [(OEP)Fe(R)]+ complexes after the chemical or
electrochemical oxidation of (OEP)Fe(R). Of special impor-
tance was an investigation of the two [(OEP)Fe(C6F3H2)]+
complexes since the 3,4,5-C6F3H2 derivative contains low-spin
Fe(III) and the 2,4,6-C6F3H2 species contains high-spin Fe(III).
Surprisingly, both C6F3H2 complexes, as well as [(OEP)Fe-
(C6F4H)]+, undergo a metal-to-nitrogen migration of the σ-bond-
ed axial ligand, and the resulting spectral data in the case of
[(OEP)Fe(3,4,5-C6F3H2)]+ is shown in Figure 4.
The effect of pyridine on the migration rate constant was also
examined in the present paper since earlier studies of (OEP)-
Fe(C6H5)(py) had indicated a stabilization of the oxidized
complex by pyridine and a slowing down of the migration rate
in PhCN/py mixtures.19 No other (OEP)Fe(R)(py) complexes
have since been investigated as to a migration reaction after
electrooxidation, and the known35 spin state conversion upon
5
1
going from S ) /2, (OEP)Fe(C6F4H) to S ) /2, (OEP)Fe-
(C6F4H)(py) was therefore of interest in terms of relating the
iron(III) spin state in (OEP)Fe(R)(py) to the presence or absence
of a migration reaction in the electrooxidized species.
The eight compounds which were kinetically investigated are
represented by (OEP)Fe(R) and (OEP)Fe(R)(py), where R )
C6H5, 3,4,5-C6F3H2, 2,4,6-C6F3H2, and C6F4H, and the resulting
kinetic data are listed in Table 3. The kmig decreases by 2 orders
of magnitude upon going from [(OEP)Fe(C6H5)]+ to [(OEP)-
Fe(C6F4H)]+, by about 1 order of magnitude upon going from
[(OEP)Fe(C6H5)]+ to [(OEP)Fe(C6H5)(py)]+, and by a factor
The axial ligand migration rates for [(OEP)Fe(R)]+ were
determined by monitoring the time-dependent spectral changes
as [(N-ROEP)Fe]+ is formed after the one-electron oxidation
of (OEP)Fe(R) in CH2Cl2 containing 0.2 M TBAP. In the case

Studies of Iron(III) and Iron(IV) σ-Bonded Porphyrins
Inorganic Chemistry, Vol. 37, No. 8, 1998 1765
Scheme 1
Table 4. Pyridine Binding Constants (Kf) for Neutral and Singly
Oxidized (OEP)Fe(R) Complexes in CH2Cl2
log Kf
axial ligand, R
(OEP)Fe(R)(py)
[(OEP)Fe(R)(py)]+
C6H5
1.9
2.6
1.4
1.5
3.7
4.2
4.1
4.5
3,4,5-C6F3H2
2,4,6-C6F3H2
C6F4H
of the E1/2 values for oxidation, and a similar shift in E1/2 is
observed upon coordination of pyridine to form (OEP)Fe(R)-
(py) (see Table 2). This shift in potential is due to an increase
in charge density on the iron center of the neutral complex from
which the electron is removed. However, once the oxidation
has occurred and [(OEP)FeIV(R)]+ is generated, an increase in
the donor ability of the R group will accelerate the migration
rate while an increased electron donation from the pyridine axial
ligand to the iron(IV) center will decelerate the migration rate
(see Table 3). Such an opposite effect on the migration rate
constants suggests a rate-determining intramolecular electron
transfer from R to Fe(IV) as a first step in the metal to nitrogen
migration of [(OEP)Fe(R)]+. This is shown in Scheme 1.
The stronger the electron donor ability of R, the faster is the
intramolecular electron transfer from R to Fe(IV). In contrast,
the intramolecular electron transfer from the axial ligand, R, to
the Fe(IV) center of (OEP)Fe(R)(py) is slowed upon coordina-
tion of pyridine which will increase the charge density at the
Fe(IV) center. The effect of pyridine coordination is largest
for the σ-bonded complex with the strongest electron-withdraw-
ing σ-bonded axial ligand, i.e., for (OEP)Fe(C6F4H), a com-
pound which undergoes a slow migration in CH2Cl2 but not in
CH2Cl2/pyridine mixtures where [(OEP)Fe(C6F4H)(py)]+ ap-
pears to be stable.
Evidence for the Formation of Fe(II) in Singly Reduced
(OEP)Fe(R). Evidence for formation of Fe(II) after the first
one electron reduction of (OEP)Fe(R) is based largely on the
electrochemical data which differs substantially from that of
other (OEP)M(R) complexes, with M ) Al, In, Ga, or Tl, which
are known to undergo reduction at the conjugated macrocycle
to give porphyrin π anion radicals. These differences are best
shown by examining the dependence of E1/2 for the first
reduction of (OEP)M(R) on both the electronegativity of the
central metal ion and the donor properties of the axial ligand.
This comparison is illustrated in Figure 6a which shows that
the first reduction of (OEP)M(C6H5) is virtually independent
of the central metal ion when M ) Al, In, Ga, or Tl. These
four main group complexes are all reduced to π anion radicals
at half-wave potentials of -1.40 to -1.44 V vs SCE as
Figure 5. Relationships between (a) E1/2 for oxidation of (OEP)Fe-
(C6FxHy) and (b) the axial ligand migration rate constant and the
calculated ionization potential of the phenyl and perfluorophenyl anions
(see Experimental Section for calculation of Ip).
of 2 upon going from [(OEP)Fe(C6H5)(py)]+ to [(OEP)Fe(3,4,5-
C6F3H2)(py)]+. No migration reaction at all can be detected in
the case of [(OEP)Fe(2,4,6-C6F3H2)(py)]+ or [(OEP)Fe(C6F4H)-
(py)]+, the two compounds which have the weakest electron-
donating σ-bonded R groups. It is especially important to note
that both low-spin six-coordinated compounds contain high-
spin iron(III) prior to coordination with pyridine. The relevant
ligand-binding reaction of the neutral and singly oxidized
porphyrins are shown in eqs 5 and 6, and a summary of the log
K values as determined in CH2Cl2 is given in Table 4.
(OEP)FeIII(R) + py a (OEP)FeIII(R)(py)
(5)
[(OEP)FeIV(R)]+ + py a [(OEP)FeIV(R)(py)]+ (6)
An increased electron donation from the σ-bonded R group
to the iron center of (OEP)Fe(R) will result in a negative shift

1766 Inorganic Chemistry, Vol. 37, No. 8, 1998
Kadish et al.
Figure 6. Dependence of the first reduction potential (a) of (OEP)M(C6H5) on the central metal electronegativity of the complex, where M ) Fe,
Al, Ga, In, or Tl, and (b) of (OEP)M(C6FxHy) on the number of fluorine atoms of the axial ligand for complexes where M ) Fe or In and x + y
) 5.
compared to the first reduction of (OEP)Fe(C6H5) which is
reduced at the central metal ion and has an E1/2 of -0.86 V
under the same experimental conditions even though the Fe(III)
electronegativity is similar to that of Ga(III).
investigated compounds undergo three oxidations independent
of the axial ligand and that all compounds are oxidized to an
Fe(IV) state in the first one-electron transfer step. The first
kinetic measurements for rate constants involving the conversion
of the singly oxidized species, [(OEP]Fe(R)]+ or [(OEP)Fe(R)-
(py)]+ to [(N-ROEP)Fe]+, definitively show that the donor
ability of the R group accelerates the migration rate while an
increased electron donation from the pyridine axial ligand
decelerates the migration rate. Consequently, it is proposed that
the rate determining intramolecular electron transfer from R to
the Fe(IV) center of [(OEP)Fe(R)]+ is the first step in the metal-
to-nitrogen migration of the singly oxidized compound.
The reductions of (OEP)M(R) are also virtually independent
of the axial ligand when this electrode reaction occurs at the
conjugated macrocycle as is the case for the main group
complexes. For example, the (OEP)In(R) derivatives show only
a 2 mV shift in potentials between E1/2 for the reduction of
(OEP)In(C6H5) and (OEP)In(C6F5) in CH2Cl2 and this ∆E1/2
can be compared to a 230 mV shift between the E1/2 for
reduction of (OEP)Fe(C6H5) and (OEP)Fe(C6F5) under the same
experimental conditions (see Figure 6b). Again, the difference
in behavior between the two series of compounds is attributed
to a difference in the site of electron transfer, i.e., formation of
a porphyrin π radical, [(OEP•)MIII(R)]-, for the main group
derivatives and a metal-reduced complex, [(OEP)FeII(R)]-, for
the iron complexes.
Acknowledgment. The support of the CNRS and the Robert
A. Welch Foundation (K.M.K., E-680) is gratefully acknowl-
edged.
Supporting Information Available: Three figures showing the
UV-visible spectra (CH2Cl2, 0.2 M TBAP) of low-spin (OEP)Fe(3,4,5-
C6F3H2), high-spin (OEP)Fe(2,4,6-C6F3H2), and [(OEP)Fe(R)]+ com-
plexes and the changes in absorbance bands at λ ) 531 nm due to the
loss of [(OEP)Fe(3,4,5-C6F3H2)]+ and λ ) 586 nm due to the formation
of [(N-3,4,5-C6F3H2OEP)Fe]+ after the one-electron oxidation of (OEP)-
Fe(3,4,5-C6F3H2) (1.0 × 10-4 M) by DDQ in deaerated CH2Cl2
containing 0.2 M TBAP at 298 K (4 pages). Ordering information is
given on any current masthead page.
Conclusion
This study presents the first overall mechanism to explain
the migration reactions of oxidized σ-bonded iron porphyrins
which have been identified as intermediates in several biological
processes. The data in this paper clearly demonstrate that
neither the iron(III) spin state nor the ligand field strength of
the σ-bonded axial ligand are in themselves key factors in the
occurrence of this reaction. It is shown that all of the
IC9714706