Axial ligand exchange of iron(III) tetramesitylporphyrin phenolate complexes

Article abstract of DOI:10.1039/a902636c

The axial ligand of a series of iron(III) 5,10,15,20-tetramesitylporphyrin phenolate complexes was found to exchange with added carboxylic acids and alcohols. The rates of axial ligand exchange with carboxylic acids were found to be dependent on acidity of the carboxylic acid, basicity of the phenolate, and the steric bulk of both the carboxylic acid and the phenolate axial ligand. The rates of axial ligand exchange with alcohols were found to be dependent on the nucleophilicity of the alcohol, leaving group ability of the phenolate, and the steric bulk of both the alcohol and the phenolate axial ligand. Different mechanisms for ligand exchange are proposed for carboxylic acids and alcohols. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a902636c

View Article Online / Journal Homepage / Table of Contents for this issue
Axial ligand exchange of iron(III) tetramesitylporphyrin phenolate
complexes
Michael W. Nee*a and John R. Lindsay Smithb
a Department of Chemistry, Oberlin College, Oberlin, OH 44074, USA
b Department of Chemistry, University of York, Heslington, York, UK YO10 5DD
Received 1st April 1999, Accepted 6th August 1999
The axial ligand of a series of iron() 5,10,15,20-tetramesitylporphyrin phenolate complexes was found to exchange
with added carboxylic acids and alcohols. The rates of axial ligand exchange with carboxylic acids were found to be
dependent on acidity of the carboxylic acid, basicity of the phenolate, and the steric bulk of both the carboxylic acid
and the phenolate axial ligand. The rates of axial ligand exchange with alcohols were found to be dependent on the
nucleophilicity of the alcohol, leaving group ability of the phenolate, and the steric bulk of both the alcohol and the
phenolate axial ligand. Different mechanisms for ligand exchange are proposed for carboxylic acids and alcohols.
group, by treating Fe(TMP)X with ozone, an oxidant whose
Introduction
reduced form, dioxygen, is a poor ligand. Paeng et al.10 reported
Iron porphyrins play central roles in a number of enzymes and
proteins. These heme proteins serve a wide range of functions
resonance Raman evidence for the presence of trans halide
ligands even in the presence of mCPBA and methanol.
and the nature of the axial ligand on the iron is thought to play
As part of a study in our laboratories on the structure
a key role in controlling the properties of the heme proteins. Of
particular interest are the oxidizing enzymes peroxidases, cyto-
chrome P-450s, and catalases for which high-valent oxoiron()
porphyrin π-cation radical species are thought to be active oxid-
and chemistry of oxoiron() 5,10,15,20-tetramesitylporphyrin
π-cation radical species, generated from a series of iron()
tetramesitylporphyrin phenolates [Fe(TMP)(OAr)], the fate of
the phenolate axial ligand was brought into question and it
ation intermediates.1–3 In the case of peroxidases and heme
was important to determine whether the phenolate ligand was
catalases the well characterized oxoiron() porphyrin π-cation
replaced on the iron() porphyrin prior to formation of the
radical is called compound I. While the active intermediate in
oxoiron() porphyrin π-cation radical. The question of ligand
exchange in iron() porphyrins is more difficult to study. Axial
cytochrome P-450s has not directly been observed, a compound
I species also has been proposed.4 Despite the involvement of
ligand exchange studies of iron porphyrins have focused pri-
similar active intermediates, these three classes of heme
marily on neutral nitrogen ligands such as imidazoles. To our
enzymes catalyse different reactions. Peroxidases catalyse the
oxidation of organic and inorganic compounds by peroxides,
cytochrome P-450s the transfer of a single oxygen atom from
dioxygen to organic substrates and catalases the dispropor-
knowledge, only one study on the kinetics of anionic ligand
exchange of iron() porphyrins has been reported. Uno et al.11
studied the reaction of iron() 2,3,7,8,12,13,17,18-octaethyl-
porphyrin methoxide [Fe(OEP)(OMe)] with a series of phenols,
tionation of hydrogen peroxide to water and dioxygen. The
carboxylic acids, and thiols. Equilibrium constants were meas-
diverse functions of these classes of enzymes are thought to be
ured for the reaction of phenols and carboxylic acids with
in part related to the different proximal ligands on the heme
[Fe(OEP)(OMe)], while thiols were found to react irreversibly.
prosthetic group in the active site of these enzymes. Peroxidases
have a proximal imidazole from a histidine, cytochrome P-450s
have a thiolate ligand from a cysteine and heme catalases have a
In the present study we have investigated the ligand exchange
reaction of a series of iron() tetramesitylporphyrin phenolate
complexes with carboxylic acids and alcohols and report on the
phenolate from a tyrosine.
mechanism of this exchange.
Synthetic iron porphyrins have proved useful as chemical
models for the above heme proteins. However, most of these
studies have used iron porphyrins with axial ligands which
could dissociate from the metal centre, consequently the role
and identity of the axial ligand on the catalysts is often subject
to question. Groves et al. reported the characterization of the
active species generated from iron() 5,10,15,20-tetramesityl-
porphyrin chloride [Fe(TMP)Cl] and 3-chloroperoxybenzoic
acid (mCPBA) as an oxoiron() porphyrin π-cation radical5
and assumed that the axial chloride ligand of Fe(TMP)Cl was
replaced by the carboxylate anion of the reduced peroxyacid in
a dichloromethane–methanol mixture.6 There, however, are
conflicting views on the nature of the axial ligand trans to the
oxo group and even whether there is a trans ligand. Trautwein
et al.,7 based on Mössbauer evidence, concluded that there is
no ligand trans to the oxo group. Kitagawa and co-workers8
proposed methanol coordinates in place of the chloride ion
based on resonance Raman studies. Gross and co-workers9
generated the oxoiron() porphyrin π-cation radical, in non-
co-ordinating solvents with different ligands trans to the oxo
Results and discussion
Iron() 5,10,15,20-tetramesitylporphyrin phenolate complexes
undergo axial ligand exchange with added carboxylic acids or
alcohols. As was observed with the reaction of carboxylic
acids and phenols with [Fe(OEP)(OMe)],11 there is an equi-
librium between the phenolate complexes and the carboxylate
or alkoxide complexes.
Carboxylic acids
The addition of carboxylic acids to solutions of all of the
phenolate complexes in CH2Cl2 at 25 ЊC results in an equi-
librium being established between the iron() tetramesityl-
porphyrin carboxylate and the iron() tetramesitylporphyrin
phenolate complexes. The equilibrium favours the carboxylate
complex with all [Fe(TMP)(OAr)] complexes except that of the
4-nitrophenolate. However, the reaction of the iron() tetra-
mesitylporphyrin 4-trifluoromethylphenolate complex with 160
J. Chem. Soc., Dalton Trans., 1999, 3373–3377
This journal is © The Royal Society of Chemistry 1999
3373

View Article Online
Table 1 Pseudo-first order rate constants (sϪ1) for axial ligand exchange of [Fe(TMP)(OAr)] with carboxylic acids in dichloromethane at 25.0 ЊC
Phenolate ligand substituent(s) (phenol pKa)
Acid (pKa)
2,4,6-Me3 (10.9)
4-CH3O (10.2)
H (10.0)
4-CF3 (8.7)
BrCH2CO2H (2.7)
2.1 × 10Ϫ3
9.0 × 10Ϫ4
3.5 × 10Ϫ3
7.5 × 10Ϫ4
6.9 × 10Ϫ4
1.6 × 10Ϫ4
2.7 × 10Ϫ4
2.6 × 10Ϫ4
>2 × 10Ϫ1
1.8 × 10Ϫ1
1.6 × 10Ϫ1
2.2 × 10Ϫ1
1.9 × 10Ϫ1
8.2 × 10Ϫ2
6.4 × 10Ϫ2
4.1 × 10Ϫ2
1.9 × 10Ϫ2
4.0 × 10Ϫ3
>2 × 10Ϫ1
1.7 × 10Ϫ1
1.7 × 10Ϫ1
2.3 × 10Ϫ1
1.3 × 10Ϫ1
5.6 × 10Ϫ2
6.0 × 10Ϫ2
2.8 × 10Ϫ2
1.6 × 10Ϫ2
2.9 × 10Ϫ3
1.4 × 10Ϫ1
5.0 × 10Ϫ2
6.6 × 10Ϫ2
5.4 × 10Ϫ2
4.0 × 10Ϫ2
2.2 × 10Ϫ2
1.9 × 10Ϫ2
1.2 × 10Ϫ2
7.2 × 10Ϫ3
9.7 × 10Ϫ4
CH3CH(Br)CO2H (2.9)
2,6-(CH3)2C6H3CO2H (3.2)
3-ClC6H4CO2H (3.8)
4-NO2C6H4CH2CO2H (3.8)
C6H5CH2CO2H (4.3)
CH3CO2H (4.8)
CH3CH2CO2H (4.9)
(CH3)2CHCO2H (4.8)
(CH3)3CCO2H (5.0)
Fig. 2 Plots of Ϫlog(ligand exchange rate in CH2Cl2 at 25 ЊC) versus
the difference in the pKa of the carboxylic acid and the pKa of the
conjugate acid of the phenolate ligand. ᭹, [Fe(TMP)(OC6H2Me3-
2,4,6)]; ᭺, [Fe(TMP)(OC6H4OMe-4)]; ᮀ, [Fe(TMP)(OPh)]; and ᭝,
[Fe(TMP)(OC6H4CF3-4)]. The lines represent least squares fits of each
data set: (a) sterically unhindered carboxylic acids and 2,4,6-trimethyl-
phenolate, (b) 2,2-dimethylpropanoic acid with unhindered phenolate
ligands, (c) 2-methylpropanoic acid with unhindered phenolate lig-
ands, and (d) sterically unhindered carboxylic acids with unhindered
phenolate ligands.
Fig. 1 The UV-visible changes for the reaction of [Fe(TMP)(OC6H2-
Me3-2,4,6)], 7.6 × 10Ϫ6 M, and 2-bromopropanoic acid, 1.3 × 10Ϫ3 M,
in CH2Cl2 at 25 ЊC. Spectra recorded every 300 s.
equivalents of propanoic acid is effectively stopped by the
addition of 140 equivalents of 4-trifluoromethylphenol. When
a strong carboxylic acid, such as 2-bromopropanoic acid, and a
complex with a relatively basic phenolate ligand, such as the
4-methoxyphenolate complex, are combined in a 1:1 molar
ratio, the 2-bromopropanoate complex is formed essentially
quantitatively. The equilibria and kinetics were measured by
UV-visible spectroscopy by monitoring the spectral changes
between 300 and 800 nm with time. The spectral changes
observed for a typical kinetic run, the reaction of iron()
tetramesitylporphyrin 2,4,6-trimethylphenolate and 2-bromo-
propanoic acid, are shown in Fig. 1.
The kinetics of the exchange of phenolate ligand by carb-
oxylate was studied with a large excess (160-fold) of carboxylic
acid. Under these conditions the reverse reaction should be
unimportant and as expected the reactions show pseudo-first
order kinetics. As confirmation for this conclusion the addition
of 10 equivalents of 4-trifluoromethylphenol to the reaction of
the iron() tetramesitylporphyrin 4-trifluoromethylphenolate
complex and 2-bromoethanoic acid has no effect on the rate of
formation of the carboxylate complex. The pseudo-first order
rates of axial ligand exchange for the complexes of four
phenolate ligands, 2,4,6-trimethylphenolate, 4-methoxyphenol-
ate, phenolate and 4-trifluoromethylphenolate, with a series of
carboxylic acids were measured in dichloromethane at 478 nm
and are listed in Table 1. Kinetics measurements at other wave-
lengths gave comparable rates.
carboxylic acids and the sterically hindered phenolate ligand,
2,4,6-trimethylphenolate; (b) the sterically hindered carboxylic
acid, 2,2-dimethylpropanoic acid, with unhindered phenolate
ligands; (c) the sterically hindered carboxylic acid, 2-methyl-
propanoic acid, with unhindered phenolate ligands; and (d)
sterically unhindered carboxylic acids with unhindered phenol-
ate ligands. The slopes from the least-squares fit for each set are
approximately the same, suggesting that there is a general trend
where the more acidic the carboxylic acid or the more basic the
phenolate ion, the faster is the rate of the exchange. Overlayed
on this acidity effect is a steric effect, either bulky carboxylic
acids or phenolate ligands, which results in the differentiation
of the carboxylic acid/phenolate ligand sets. Thus the iron()
tetramesitylporphyrin 2,4,6-trimethylphenolate undergoes
exchange about 100 times slower than the other three phenolate
complexes and the exchange with 2,2-dimethylpropanoic acid
is about 10 times slower than with less bulky carboxylic
acids. Close inspection of the results from the “unhindered”
carboxylic acids and phenolate ligands reveals that the reac-
tions of 2-methylpropanoic acid are slightly slower than those
of the remainder of the less bulky carboxylic acids.
It is interesting that 2,6-dimethylbenzoic acid, which might
be expected to exchange at a slower rate than its pKa predicts,
actually exchanges at a rate which suggests that the methyl
groups do not hinder the exchange. Molecular modelling indi-
cates that the carboxylic acid group of 2,6-dimethylbenzoic acid
A plot of Ϫlog(rate constant) in dichloromethane versus the
difference in the pKa of the carboxylic acid and of the conjugate
acid of the phenolate ligand is shown in Fig. 2. The results fall
into four main sets: the reaction of (a) sterically unhindered
3374
J. Chem. Soc., Dalton Trans., 1999, 3373–3377

View Article Online
Table 2 Gas phase acidities
is slightly twisted out of the plane of the aromatic ring whilst in
2,2-dimethylpropanoic acid methyl groups extend above and
below the plane of the carboxylic group, suggesting that steric
effects on the ligand exchange are most pronounced for groups
out of the plane of the carboxylic group.
Acid
D Ϫ EAa/kJ molϪ1
4-Nitrophenol
31b
75
77
2-Bromoethanoic acid
3-Chlorobenzoic acid
2-Bromopropanoic acid
4-Trifluoromethylphenyl
2-Phenylethanoic acid
2,2-Dimethylpropanoic acid
2-Methylpropanoic acid
Propanoic acid
Ethanoic acid
Phenol
4-Methoxyphenyl
2,2,2-Trifluoroethanol
2-Methyl-2-propanol
2-Propanol
These kinetic results are consistent with a mechanism where
there is a fast pre-equilibrium protonation step, followed by the
formation of a six-co-ordinate complex, and the loss of the
protonated phenolate ligand (Scheme 1). The difference in acid-
84
88b
104
117
122
128
133
139
143
191
232
236
244
256
Ethanol
Methanol
a Difference between the bond dissociation energy D(A–H) and the
electron affinity EA(A). b Estimated value, see text.
and phosphorus acids, including alcohols and some phenols.
Table 2 lists the gas phase acidities of most of the carboxylic
acids, phenols and alcohols used in this study. They were
reported on different scales, however there were at least several
common acids allowing the acidities to be compared on a
common scale (the values are probably only accurate to 5 kJ
molϪ1). The value for 4-nitrophenol was not measured directly
because the sample decomposed under the measurement condi-
tions. However, because of the good linear correlation between
the gas phase and aqueous phase acidities of other substituted
phenols, the gas phase acidity of 4-nitrophenol was estimated
by Kebarle to be greater than that of any of the carboxylic acids
used in this study. In a similar manner, we have estimated the
gas phase acidity of 4-trifluoromethylphenol from its aqueous
acidity.
It is clear that the acidity of phenols is greatly enhanced in
the gas phase relative to carboxylic acids and that in the gas
phase phenols have comparable acidities to carboxylic acids. It
is a reasonable assumption that the acidities of carboxylic acids
and phenols in dichloromethane will be closer to the gas phase
rather than the aqueous phase values. Furthermore the data
predict that for most of the carboxylic acids the equilibrium
between the 4-nitrophenolate complex and the carboxylate
complexes will favour the former species.
Scheme 1 Mechanism for the exchange of axial phenolate ligands
with carboxylic acids.
ity between the carboxylic acid and the phenol affects the first
equilibrium, the protonation step. Bulky phenolate ligands or
carboxylic acids affect the second equilibrium, the formation of
a six-co-ordinate complex. In the five-co-ordinate iron porphy-
rin complex the metal is out of the plane of the porphyrin ring
and therefore the steric effects between the axial ligand and the
porphyrin ring are minimized. However, the six-co-ordinate
iron porphyrin complex has the metal in the same plane as the
porphyrin ring and the distance between the porphyrin ring and
both of the axial ligands is less than in the five-co-ordinate
complex. Therefore bulky phenolate ligands or carboxylic acids
will disfavour formation of the six-co-ordinate complex.
In contrast to the phenolate complexes described above, the
4-nitrophenolate complex, even with a 160-fold excess of carb-
oxylic acid, is not completely converted into the corresponding
carboxylate complex, except with the most acidic carboxylic
acids.
In the exchange reaction with different oxygen ligands the
forward rate of exchange is dependent (in part) on the acidity
of the oxygen acid, RCO2H, and the basicity of the oxygen
axial ligand on the porphyrin, OAr, eqn. (i). Conversely, the rate
Alcohols
The reactions of alcohols with the iron() tetramesitylporphy-
rin phenolates are much slower than those with carboxylic acids
and required elevated temperatures (60 ЊC in toluene) and a
large excess of alcohol [(2–6) × 104-fold] to obtain rates com-
parable to those of the acids. The reactions were followed by
monitoring the decrease in the Soret band absorbance (417 nm)
of the phenolate complexes and the rate constants are given in
Table 3.
The alcohol exchange reactions show two major differences
from those of the carboxylic acids. First, for a given alcohol the
order of ease of ligand exchange with a series of phenolate
complexes is 4-nitrophenolate > 4-trifluoromethylphenolate >
phenolate ≈ 4-methoxyphenolate ӷ 2,4,6-trimethylphenolate.
This order is different from that observed with carboxylic
acids; indeed for unhindered phenolates the order of reactivity
is reversed. Secondly, the order of reactivity of a series of
alcohols with a given phenolate complex (4-nitrophenolate)
K
[Fe(TMP)(OAr)] ϩ RCO2H
[Fe(TMP)(O2CR)] ϩ ArOH (i)
of the reverse exchange is dependent on the acidity of ArOH
and the basicity of RCO2 . If we assume that the Fe–O bond
Ϫ
is ionic, then pK ≈ pKa(RCO2H) Ϫ pKa(ArOH). Based on the
aqueous acidities of the species involved, it would be expected
that the equilibrium constant should favour the carboxylate
complex for all combinations of carboxylic acids and phenol-
ates, including 4-nitrophenolate. Since this is not the case it is
likely that the aqueous acidities are not good estimates of the
relative acidities of carboxylic acids and phenols in a non-polar
solvent such as dichloromethane. Gas phase acidities may
provide a better measure of the relative acidities in non-polar
solvents.
Kebarle and co-workers have measured the gas phase acidi-
ties of a series of substituted phenols and benzoic acids12 and
aliphatic carboxylic acids.13 Bartmess et al.14 measured the gas
phase acidities of a range of oxygen, nitrogen, carbon, sulfur
is
CH3OH > CH3CH2OH > (CH3)2CHOH > CF3CH2OH >
(CH3)3COH. This is not unexpected since the gas phase acidi-
ties suggest that the alcohols are not strong enough acids to
protonate the phenolate ligands. These results are consistent
J. Chem. Soc., Dalton Trans., 1999, 3373–3377
3375

View Article Online
Table 3 Pseudo-first order rate constants (sϪ1) for ligand exchange rates of alcohols with [Fe(TMP)(OAr)] in dichloromethane at 60.0 ЊC
Phenolate ligand substituent(s) (phenol pKa)
Alcohol
2,4,6-Me3 (10.9)
4-CH3O (10.2)
H (10.0)
4-CF3 (8.7)
4-NO2 (7.2)
CH3OH
3 × 10Ϫ4
2 × 10Ϫ3
2 × 10Ϫ3
3 × 10Ϫ3
8 × 10Ϫ3
5 × 10Ϫ3
2 × 10Ϫ3
8 × 10Ϫ4
1 × 10Ϫ4
CH3CH2OH
(CH3)2CHOH
CF3CH2OH
(CH3)3COH
Scheme 2 Mechanism for the exchange of axial phenolate ligands with alcohols.
with a mechanism where the phenolates are displaced by a dir-
ect nucleophilic attack by the alcohol (Scheme 2) where the rate
depends on the nucleophilicities and the bulk of the alcohol
and the leaving group ability of the phenolate.
Ultraviolet-visible spectroscopy
The UV-vis spectra and kinetics were measured on a Hewlett-
Packard 8453 Diode Array spectrophotometer equipped with a
thermostatted cell holder. The kinetics with carboxylic acids
were studied at 25.0 ЊC with [Fe(TMP)(OAr)] = 7.7 × 10Ϫ6
M
and [carboxylic acid] = 1.3 × 10Ϫ3 M, and with alcohols at
60.0 ЊC in toluene with [Fe(TMP)(OAr)] = 7.7 × 10Ϫ6 M and
[alcohol] = 0.17–0.40 M.
Experimental
Materials
The iron() tetramesitylporphyrin carboxylate complexes
were found to undergo slow photochemical decomposition in
dichloromethane to form [Fe(TMP)Cl], probably by photo-
chemically induced homolytic cleavage of the iron–oxygen
bond to give iron() tetramesitylporphyrin and a carboxyl rad-
ical.17 The latter can then undergo unimolecular decomposition
to a carbon radical and carbon dioxide. Chloride ion must
then be formed by a reaction of the carbon radical with
dichloromethane and subsequent decomposition of the
dichloromethyl radical. The diode array light source initiates
this photochemical decomposition. Use of a 300 nm cut-off
filter significantly reduces the rate of photochemical decom-
position of the carboxylate complex. Reactions in toluene
do not undergo this decomposition presumably because the
toluene absorbs strongly below 280 nm.
Dichloromethane and toluene were refluxed over calcium
hydride then distilled. Methanol and ethanol were refluxed
over the corresponding magnesium alkoxide then distilled.
Tetrahydrofuran was refluxed over sodium and distilled
from the ketyl of benzophenone. Benzene was refluxed over
sodium and distilled. 5,10,15,20-Tetramesitylporphyrin
(H2TMP) was prepared by the method of Lindsey and co-
workers.15 Iron() tetramesitylporphyrin chloride [Fe(TMP)Cl]
was prepared by refluxing H2TMP in acetic acid containing
iron() chloride.16
Iron(III)
tetramesitylporphyrin
2,4,6-trimethylphenolate
solution of 2,4,6-tri-
[Fe(TMP)(OC6H2Me3-2,4,6)]. To
a
methylphenol (0.0689 g, 5.06 × 10Ϫ4 mol) in dry THF (10 cm3)
was added sodium (0.0112 g, 4.87 × 10Ϫ4 mol) and the mixture
allowed to react until all of the sodium had been consumed. A
portion of the phenolate solution (5 cm3) was then added to a
solution of [Fe(TMP)Cl] (0.0942 g, 1.08 × 10Ϫ4 mol) in dry
benzene. The mixture was refluxed for 2 h and the progress of
the reaction monitored by UV-Vis spectroscopy. At the end
of the reaction the solvent was removed under vacuum and the
resulting residue redissolved in dichloromethane, washed with
water, dried (Na2SO4), and evaporated to dryness. The crude
product was recrystallized from hot cyclohexane to give purple
crystals of [Fe(TMP)(OC6H2Me3-2,4,6)] (0.0945 g, 90%)
(Found: C, 79.90; H, 6.82. C65H63FeN4O requires C, 80.31; H,
6.53%).
References
1 H. B. Dunford, Adv. Inorg. Biochem., 1982, 4, 41.
2 Y. Watanabe and J. T. Groves, in The Enzymes, ed. D. S. Sigman,
Academic Press, San Diego, CA, 1992, vol. 20, pp. 405–452.
3 G. R. Schonbaum and B. Chance, in The Enzymes, ed. P. D. Boyer,
Academic Press, New York, 1976, vol. 20, pp. 405–452.
4 T. L. Poulos, Adv. Inorg. Biochem., 1988, 7, 1.
5 J. T. Groves, R. C. Haushalter, M. Nakamura, T. E. Nemo and
B. J. Evans, J. Am. Chem. Soc., 1981, 103, 2884.
6 J. T. Groves and Y. Watanabe, J. Am. Chem. Soc., 1986, 108, 7834;
1988, 110, 8443.
7 A. X. Trautwein, E. Bill, E. L. Bominaar and H. Winkler, Struct.
Bonding (Berlin), 1991, 78, 1.
8 S. Hashimoto, Y. Mizutani, Y. Tatsuno and T. Kitagawa, J. Am.
Chem. Soc., 1991, 113, 6542.
9 Z. Gross and S. Nimri, Inorg. Chem., 1994, 33, 1731; J. Am. Chem.
Soc., 1995, 117, 8021; K. Czarnecki, S. Nimri, Z. Gross, L. M.
Proniewicz and J. R. Kincaid, J. Am. Chem. Soc., 1996, 118, 2929;
Z. Gross, S. Nimri, C. M. Barzilay and L. Simkhovich, J. Biol. Inorg.
Chem., 1997, 2, 492.
10 K.-J. Paeng, D.-H. Shin and I. R. Paeng, Inorg. Chem., 1997, 36,
2901.
Other iron() tetramesitylporphyrin phenolate complexes
were prepared in a similar manner: iron() tetramesitylporphy-
rin 4-methoxyphenolate [Fe(TMP)(OC6H4OMe-4)] (Found:
C, 78.80; H, 6.56. C63H59FeN4O2 requires C, 78.82; H, 6.19%);
iron() tetramesitylporphyrin phenolate [Fe(TMP)(OPh)]
(Found: C, 80.07; H, 6.18. C62H57FeN4O requires C, 80.07; H,
6.18%); iron() tetramesitylporphyrin 4-trifluoromethylphenol-
ate [Fe(TMP)(OC6H4CF3-4)] (Found: C, 76.09; H, 6.19. C69H68-
F3FeN4O requires C, 76.58; H, 6.33%); iron() tetramesityl-
porphyrin 4-nitrophenolate [Fe(TMP)(OC6H4NO2-4)] (Found:
C, 76.47; H, 5.81. C62H56FeN5O3 requires C, 76.38; H, 5.79%).
11 T. Uno, K. Hatano, Y. Nishimura and Y. Arata, Inorg. Chem., 1990,
29, 2803.
12 T. B. McMahon and P. Kebarle, J. Am. Chem. Soc., 1977, 99, 2222.
3376
J. Chem. Soc., Dalton Trans., 1999, 3373–3377

View Article Online
13 G. Caldwell, R. Renneboog and P. Kebarle, Can. J. Chem., 1989, 67,
16 C. K. Chang, R. K. DiNello and D. Dolphin, Inorg. Synth., 1980,
611.
20, 147.
14 J. E. Bartmess, J. A. Scott and R. T. McIver, Jr., J. Am. Chem. Soc.,
1979, 101, 6046.
17 B. C. Gilbert, G. R. Hodges, J. R. Lindsay Smith, P. MacFaul and
P. Taylor, J. Mol. Catal. A-Chem., 1997, 117, 249 and refs. therein.
15 R. W. Wagner, D. S. Lawrence and J. S. Lindsey, Tetrahedron Lett.,
1987, 28, 3069.
Paper 9/02636C
J. Chem. Soc., Dalton Trans., 1999, 3373–3377
3377