meso substituent effects on the geometric and electronic structures of high-spin and low-spin iron(III) complexes of mono-meso-substituted octaethylporphyrins

Article abstract of DOI:10.1021/ic011034q

Introduction of a single meso substituent into ClFe^III(OEP) or K[(NC)₂Fe(OEP)] results in significant changes in the geometric and/or spectroscopic properties of these complexes. The mono-meso-substituted iron(III) complexes ClFe^III(meso-Ph-OEP), ClFe^III(meso-n-Bu-OEP), ClFe^III(meso-MeO-OEP), ClFe^III(meso-Cl-OEP), ClFe^III(meso-NC-OEP), ClFe^III(meso-HC(O)-OEP), and ClFe^III(meso-O₂N-OEP) have been isolated and characterized by their UV/vis and paramagnetically shifted ¹H NMR spectra. The structures of both ClFe^III(meso-Ph-OEP) and ClFe^III(meso-NC-OEP) have been determined by X-ray crystallography. Both molecules have five-coordinate structures typical for high-spin (S = 5/2) iron(III) complexes. However, the porphyrins themselves no longer have the domed shape seen in ClFe^III(OEP), and the N₄ coordination environment possesses a slight rectangular distortion. These high-spin, mono-meso-substituted iron(III) complexes display ¹H NMR spectra in chloroform-d solution which indicate that the conformational changes seen in the solid-state structures are altered by normal molecular motion to produce spectra consistent with C_s molecular symmetry. In pyridine solution the high-spin six-coordinate complexes {(py)-ClFe^III(meso-R-OEP)} form. In methanol solution in the presence of excess potassium cyanide, the low-spin six-coordinate complexes K[(NC)₂Fe^III(meso-R-OEP)] form. The ¹H NMR spectra of these show that electron-donating substituents produce an upfield relocation of the meso-proton chemical shifts. This relocation is interpreted in terms of increased contribution from the less common (d_xz,d_yz)⁴(d_xy)¹ ground electronic state as the meso substituent becomes more electron donating.

Full text of DOI:10.1021/ic011034q

Inorg. Chem. 2002, 41, 989−997
meso Substituent Effects on the Geometric and Electronic Structures of
High-Spin and Low-Spin Iron(III) Complexes of Mono-meso-Substituted
Octaethylporphyrins
,‡
Heather Kalish,† Jason E. Camp,† Marcin Ste¸pien´,‡ Lechosław Latos-Graz3yn´ski,*
,‡,§
Marilyn M. Olmstead,† and Alan L. Balch*
Departments of Chemistry, UniVersity of California, DaVis, California 95616 and
UniVersity of Wrocław, Wrocław, Poland
Received October 8, 2001
III
Introduction of a single meso substituent into ClFe (OEP) or K[(NC)2Fe(OEP)] results in significant changes in the
geometric and/or spectroscopic properties of these complexes. The mono-meso-substituted iron(III) complexes
III
III
III
III
III
ClFe (meso-Ph-OEP), ClFe (meso-n-Bu-OEP), ClFe (meso-MeO-OEP), ClFe (meso-Cl-OEP), ClFe (meso-NC-
III
III
OEP), ClFe (meso-HC(O)-OEP), and ClFe (meso-O N-OEP) have been isolated and characterized by their UV/
vis and paramagnetically shifted 1H NMR spectra. The structures of both ClFe (meso-Ph-OEP) and ClFe (meso-
2
III
III
NC-OEP) have been determined by X-ray crystallography. Both molecules have five-coordinate structures typical
5
for high-spin (S ) /2) iron(III) complexes. However, the porphyrins themselves no longer have the domed shape
III
seen in ClFe (OEP), and the N coordination environment possesses a slight rectangular distortion. These high-
4
spin, mono-meso-substituted iron(III) complexes display 1H NMR spectra in chloroform-d solution which indicate
that the conformational changes seen in the solid-state structures are altered by normal molecular motion to produce
spectra consistent with C molecular symmetry. In pyridine solution the high-spin six-coordinate complexes {(py)-
s
III
ClFe (meso-R-OEP)} form. In methanol solution in the presence of excess potassium cyanide, the low-spin six-
III
coordinate complexes K[(NC)2Fe (meso-R-OEP)] form. The 1H NMR spectra of these show that electron-donating
substituents produce an upfield relocation of the meso-proton chemical shifts. This relocation is interpreted in
terms of increased contribution from the less common (dxz,d )4(d )1 ground electronic state as the meso substituent
yz
xy
becomes more electron donating.
Introduction
binding to or oxidation of the iron ion.1,5 Mono-meso-methyl
hemes undergo oxidation by heme oxygenase, which specif-
ically attacks the methylated meso position with remarkable
specificity.6,7 meso-Nitroetioheme with its nitro group pro-
truding above and below the heme plane has been used to
probe the available space for heme seating in myoglobin and
for observing steric factors that may be involved in directing
the regiospecificity of heme cleavage.8 Treatment of low-
spin (S ) 0) (py)2FeII(meso-R-OEP) with hydrogen peroxide
results in replacement of the unique R substituent or attack
at the meso-H sites in a reaction whose specificity depends
on the specific R substituent present.9 The pattern of
Naturally occurring hemes have hydrogen atoms at their
meso positions. Substitution of one of those protons by a
different functional group can have a marked effect on the
electronic structure and reactivity of the heme. For example,
(py)2Fe(OEPO), shown in Chart 1, has an unusual electronic
structure that arises from the delocalization of electrons
between the metal and ligand.1-4 In solution, (py)2Fe(OEPO)
is also unusually sensitive toward dioxygen, which causes
degradation through ring opening of the porphyrin rather than
† University of California.
‡ University of Wrocław.
§ E-mail: albalch@ucdavis.edu.
(5) St Claire, T. N.; Balch, A. L. Inorg. Chem. 1999, 38, 684.
(6) Torpey, J.; Lee, D. A.; Smith, K. M.; Ortiz de Montellano, P. R. J.
Am. Chem. Soc. 1996, 118, 9172.
(7) Torpey, J.; Ortiz de Montellano, P. R. J. Biol. Chem. 1996, 271, 26067.
(8) Wang, J.-T.; Li, Y.; Ma, D.; Kalish, H.; Balch, A. L.; La Mar, G. N.
J. Am. Chem. Soc. 2001, 123, 8080.
(1) Balch, A. L. Coord. Chem. ReV. 2000, 200-202, 349.
(2) Morishima, I.; Fujii, H.; Shiro, Y. J. Am. Chem. Soc. 1986, 108, 3858.
(3) Morishima, I.; Shiro, Y.; Hiroshi, F. Inorg. Chem. 1995, 34, 1528.
(4) Balch, A. L.; Koerner, R.; Latos-Graz˘yn´ski, L.; Noll, B. C. J. Am.
Chem. Soc. 1996, 118, 2760.
10.1021/ic011034q CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/31/2002
Inorganic Chemistry, Vol. 41, No. 4, 2002 989

Kalish et al.
Chart 1
Figure 1. Perspective view of ClFeIII(meso-Ph-OEP) showing 50% thermal
contours.
reactivity in this hydrogen peroxide induced reaction indi-
cates that the attacking reagent is nucleophilic.
The environment of the meso sites in hemes has been
recognized to be sterically constricted.10 With highly sub-
stituted porphyrins such as 2,3,7,8,12,13,17,18-octaethyl-
5,10,15,20-tetraphenylporphyrin (H2OETPP), severe geo-
metric distortions of the porphyrin from planarity can occur.
For example, five-coordinate ClFeIII(OETPP) shows a pro-
nounced saddle-shaped distortion in its geometric struc-
ture.11,12 Its electronic structure involves some degree of spin
Figure 2. Perspective view of ClFeIII(meso-CN-OEP) showing 50%
thermal contours.
5
3
determined by X-ray crystallography. Figures 1 and 2 show
drawings of each of the two molecules. While the structure
of ClFeIII(meso-Ph-OEP) is fully ordered, the structure of
ClFeIII(meso-NC-OEP) is disordered with regard to the
position of the cyano group. In the major orientation (with
a 0.92 site occupancy) shown in Figure 2, the cyano group
is attached to C5, while in the minor orientation (0.08 site
occupancy) the cyano group is attached to C20. Selected
interatomic distances and angles for both ClFeIII(meso-Ph-
OEP) and ClFeIII(meso-NC-OEP) are given in Table 1, where
they can be compared to those of ClFeIII(OEP) (in C60‚ClFeIII-
(OEP)‚CHCl3),13 ClFeIII(meso-O2N-OEP),14 and ClFeIII(meso-
CH3COO-OEP).15
admixture of the S ) /2 and /2 forms, although there is
3
some controversy about the magnitude of the S )
/
2
contribution.11,12
This article is concerned with the characterization of the
geometric and electronic structures of a range of mono-meso-
substituted octaethylporphyrin complexes of Fe(III). Does
the introduction of a single meso substituent into octaeth-
ylporphyrin alter the geometry of the resulting hemes and
produce changes in their electronic structures? The work
reported here is part of a project designed to investigate the
effects of a non-hydrogen substituent at the meso position
of a heme on the reactivity of these modified hemes.
Results and Discussion
Both molecules shown in Figures 1 and 2 have five-
coordinate structures typical for high-spin (S ) 5/2) iron(III)
complexes. The Fe-N bond lengths fall near the range
(2.060-2.087 Å) found for this class of heme complexes.16
Additionally, the distances of the iron atom from the N4 plane
in each complex is in the range (0.39-0.54 Å) seen for other
high-spin, five-coordinate iron(III) porphyrin complexes. The
Fe-Cl distances are also normal in length.
The mono-meso-substituted porphyrins were prepared by
known routes and iron inserted to produce ClFeIII(meso-R-
OEP) as outlined in the Experimental Section. The UV/vis
spectra of these complexes, which are given in the Experi-
mental Section, are compatible with high-spin, five-
coordinate structures for these complexes.
Crystallographic Characterization of ClFeIII(meso-Ph-
OEP) and ClFeIII(meso-NC-OEP). The structures of both
ClFeIII(meso-Ph-OEP) and ClFeIII(meso-NC-OEP) have been
While aspects of the iron coordination in these unsym-
metrically substituted porphyrins are normal, the porphyrins
themselves show interesting variations in their structures. The
(9) Kalish, H. R.; Camp, J. E.; Stepien´, M.; Latos-Graz˘yn´ski, L.; Balch,
A. L. J. Am. Chem. Soc. 2001, 123, 11719.
(10) Woodward, R. B. Angew. Chem. 1960, 72, 651.
(11) Cheng, R.-J.; Chen, P.-Y.; Gau, P.-R.; Chen, C.-C.; Peng, S.-M. J.
Am. Chem. Soc. 1997, 119, 2563.
(12) Schu¨nemann, V.; Gerdan, M.; Trautwein, A. X.; Haoudi, N.; Mandon,
D.; Fisher, J.; Weiss, R.; Tabard, A.; Guilard, R. Angew. Chem., Int.
Ed. 1999, 38, 3181.
(13) Olmstead, M. M.; Costa, D. A.; Maitra, K.; Noll, B. C.; Phillips, S.
L.; Van Calcar, P. M.; Balch, A. L. J. Am. Chem. Soc. 1999, 121,
7090.
(14) Senge, M. Personal communication, CCD file, TOYSAB.
(15) Balch, A. L.; Latos-Graz˘yn´ski, L.; Noll, B. C.; Olmstead, M. M.;
Zovinka, E. P. Inorg. Chem. 1992, 31, 2248.
(16) Scheidt, R. W.; Reed, C. A. Chem. ReV. 1981, 81, 543.
990 Inorganic Chemistry, Vol. 41, No. 4, 2002

Fe(III) Complexes of Octaethylporphyrins
Table 1. Selected Interatomic Distances and Angles
ClFeIII(meso-Ph-OEP)
ClFeIII(meso-CN-OEP)
ClFeIII(OEP)a
Distances (Å)
ClFeIII(meso-O2N-OEP)b
ClFeIII(meso-CH3COO-OEP)c
Fe-N1
Fe-N2
Fe-N3
Fe-N4
Fe-Cl
Fe-N4
2.044(5)
2.055(5)
2.056(5)
2.060(4)
2.2175(16)
0.455
2.0728(14)
2.0705(14)
2.0661(14)
2.0638(14)
2.2341(5)
0.463
2.073(8)
2.069
2.079
2.067
2.068
2.209
0.448
2.073(5)
2.060(4)
2.075(4)
2.066(4)
2.236(2)
0.462
2.235(9)
0.492
Angles (deg)
N1-Fe-N2
N2-Fe-N3
N3-Fe-N4
N1-Fe-N4
N1-Fe-N3
N2-Fe-N4
Cl-Fe-N1
Cl-Fe-N2
Cl-Fe-N3
Cl-Fe-N4
85.78(18)
88.43(18)
85.17(18)
88.95(18)
153.90(18)
153.96(17)
103.53(13)
103.16(13)
102.57(13)
102.86(13)
85.71(6)
88.37(5)
86.43(6)
86.7(4)
86.8
88.0
87.2
87.9(2)
86.2(1)
88.1(2)
88.39(6)
87.3
86.2(2)
154.42(6)
154.74(6)
105.05(4)
103.42(4)
100.53(4)
101.83(4)
152.6(6)
103.7(3)
156.4
153.6
103.9
106.2
99.7
154.9(2)
153.4(2)
101.1(1)
102.4(1)
103.9(1)
104.2(1)
110.0
a Data from: Olmstead, M. M.; Costa, D. A.; Maitra, K.; Noll, B. C.; Phillips, S. L.; Van Calcar, P. M.; Balch, A. L. J. Am. Chem. Soc. 1999, 121, 7090.
b Data from: Senge, M. Personal communication, CCD file, TOYSAB. c Data from: Balch, A. L.; Latos-Graz˘yn´ski, L.; Noll, B. C.; Olmstead, M. M.;
Zovinka, E. P. Inorg. Chem. 1992, 31, 2248.
presence of a unique meso substituent alters the geometry
of the ligating N4 group from nearly square in ClFeIII(OEP)
to slightly rectangular in the meso-substituted complexes.
This is best appreciated by comparing the nonbonded
N‚‚‚N distances between cis pairs of nitrogen atoms. In
ClFeIII(OEP) there are two unique N‚‚‚N distances which
are nearly equal, 2.848 and 2.847 Å. In ClFeIII(meso-
Ph-OEP) the N1‚‚‚N2 and N3‚‚‚N4 distances (2.818 and
2.828 Å, respectively) are shorter than the N2‚‚‚N3 and
N1‚‚‚N4 distances (2.883 and 2.884 Å). In ClFeIII(meso-
NC-OEP) and ClFeIII(meso-CH3COO-OEP) similar compres-
sions and elongations occur. For ClFeIII(meso-NC-OEP) the
N1‚‚‚N2 and N3‚‚‚N4 distances are 2.790 and 2.785 Å, while
the N2‚‚‚N3 and N1‚‚‚N4 distances are 2.867 and 2.876 Å.
In ClFeIII(meso-CH3COO-OEP) the distances corresponding
to the N1‚‚‚N2 and N3‚‚‚N4 separations in the structures
reported here are 2.827 and 2.828 Å and the distances
corresponding to the N2‚‚‚N3 and N1‚‚‚N4 separations are
longer: 2.870 and 2.880 Å. For ClFeIII(meso-O2N-OEP)
disorder produces substantial distribution of the nitro group
between two sites (two-thirds at a site equivalent to C5 and
one-third at a site equivalent to C20) that blurs any effect of
this sort.
The presence of the unique meso substituent also changes
the porphyrin conformation from the domed conformation
Figure 3. Diagrams showing the out-of-plane displacements of the
porphyrin core atoms from the mean plane of the porphyrin. The unique
meso substituents are attached to the meso carbon atoms denoted by arrows.
seen in ClFeIII(OEP) and in the monoclinic form of ClFeIII-
(TPP)17 to differently distorted forms. Porphyrin distortions
from planarity follow the low-frequency normal vibrational
modes of the porphyrin and involve sad, ruf, dom, waV(x),
these solids assumes a somewhat different conformation.
waV(y), and pro deformations.18,19 Figure 3 shows the out-
In comparison to ClFeIII(OEP), the porphyrin core of
of-plane displacements (in units of 0.01 Å) of the core atoms
ClFeIII(meso-Ph-OEP) is less domed. In ClFeIII(meso-
for five related iron porphyrins: ClFeIII(OEP), ClFeIII(meso-
NC-OEP) the porphyrin core assumes a ruf conformation,
Ph-OEP), ClFeIII(meso-NC-OEP), ClFeIII(meso-O2N-OEP),
while ClFeIII(meso-O2N-OEP) displays a predominant saddle
and ClFeIII(meso-CH3COO-OEP). Each of the porphyrins in
conformation. Finally, ClFeIII(meso-CH3COO-OEP) shows
a weaker saddle distortion. These observations complement
the recent work of Scheidt, Shelnut, and co-workers who
have shown that one molecule, (Cl3CCO2)FeIII(OEP), can
adopt five diverse conformations in the crystalline state.20
(17) Scheidt, W. R.; Finnegan, M. G. Acta Crystallogr. 1989, C45, 1214.
(18) Jentzen, W.; Song, X.-Z.; Shelnutt, J. A. J. Phys. Chem. B 1997, 101,
1684.
(19) Shelnutt, J. A.; Song, X.-Z.; Ma, J.-G.; Jia, S.-L.; Jentzen, W.;
Medforth, C. J. Chem. Soc. ReV. 1998, 27, 31.
Inorganic Chemistry, Vol. 41, No. 4, 2002 991

Kalish et al.
Chart 2
1H NMR Spectra of ClFeIII(meso-R-OEP). The 1H NMR
spectrum of ClFeIII(OEP) in chloroform-d at 298 K consists
of a single meso resonance at -55.5 ppm, a doublet for the
diastereotopic methylene resonances at 41.6 and 43.7 ppm,
and a singlet at 1.5 ppm for the methyl resonances, which is
consistent with an earlier study.21 The temperature depen-
dence of the spectrum almost follows the Curie law (see
1
Supplementary Figure S1). The H NMR spectra of com-
plexes of the ClFeIII(meso-R-OEP) type are similar to that
of ClFeIII(OEP) but reflect the effects of lower symmetry.
As seen in Chart 2,22 with idealized Cs symmetry
ClFeIII(meso-R-OEP) has four distinct types of ethyl groups
and two types of meso protons. Since the chloride ligand
protrudes from one side of the porphyrin plane, the methylene
groups are all diastereotopic. Thus, the symmetry of
ClFeIII(meso-R-OEP) dictates that there should be two meso
resonances in a 2:1 intensity ratio, eight equally intense
methylene resonances, and four equally intense methyl
resonances for five-coordinate complexes. Figure 4 shows
the spectrum of ClFeIII(meso-Cl-OEP). (Similar data for
ClFeIII(meso-NC-OEP) are shown in Supplementary Figure
S2.) Trace B presents an overview of the spectrum. The two
types of meso protons produce two broad resonances with a
1:2 intensity ratio in the upfield region, while the methylene
protons produce eight resolved resonances of equal intensity
in the downfield region. This region is expanded in trace C
of Figure 4. Although symmetry dictates that there should
be four methyl resonances, there are only three resonances
in a 1:2:1 intensity ratio due to accidental overlap of two
resonances.
The 1H NMR spectra of the other complexes of this type
have related features. Data for ClFeIII(meso-R-OEP) are
collected in Table 2. Figure 5 presents a comparison of the
upfield portions of the spectra which contain the resonances
of the meso protons. While the spectrum of ClFeIII(OEP)
shows only a single meso resonance, the mono-meso-
substituted complexessClFeIII(meso-Ph-OEP), ClFeIII(meso-
Cl-OEP), ClFeIII(meso-NC-OEP), and ClFeIII(meso-O2N-
OEP)sshow two resonances in a 2:1 intensity ratio in this
region, as expected from their structures. The spectra of
ClFeIII(meso-n-Bu-OEP), ClFeIII(meso-HC(dO)-OEP), and
ClFeIII(meso-MeO-OEP) show additional weak resonances
1
Figure 4. 500 MHz H NMR spectra of ClFeIII(meso-Cl-OEP) at 25 °C.
Resonances are labeled Hb&d and Hg for the meso protons, M for methyl
protons, and m for the methylene protons. Trace A shows the spectrum in
pyridine-d5, B shows the spectrum in chloroform-d, C shows the region of
the methyl resonances taken under inversion recovery conditions, and D
shows an expansion of the methylene region.
in this region. The added resonances result from the presence
of a less abundant, rotomeric isomer. With such five-
coordinate complexes, the meso-n-Bu, meso-HC(O), and
meso-MeO substituents can exist in two forms with the
substituent protruding on either the same side or the opposite
side from the axial chloride ligand. The constricted environ-
ment at this meso site restricts rotation of these groups about
the C-C(meso) and O-C(meso) bonds. Similar features have
been previously observed in the 1H NMR spectrum of ClFeIII-
(meso-MeC(dO)O-OEP).15
Figure 6 shows the downfield methylene region of the
spectra of these complexes. The spectrum of ClFeIII(OEP)
shows two equally intense resonances in this region. These
two resonances are due to the two inequivalent protons of
each of the eight symmetrically equivalent methylene groups
of the molecule. The spectra of ClFeIII(meso-NC-OEP) and
ClFeIII(meso-Cl-OEP) show eight equally intense resonances
in this region, as expected on the basis of symmetry. The
spectra of ClFeIII(meso-Ph-OEP) and ClFeIII(meso-O2N-OEP)
are less well resolved, while the spectra of ClFeIII(meso-n-
Bu-OEP), ClFeIII(meso-MeO-OEP), and ClFeIII(meso-HC-
(dO)-OEP) show overlapping of the eight resonances of the
major isomer and additional smaller peaks due to the
presence of a second rotomeric isomer. Note that similar
small peaks are also seen in the upfield meso region for these
complexes.
(20) Neal, T. J.; Cheng, B.; Ma, J.-G.; Shelnut, J. A.; Schultz, C. E.; Scheidt,
W. R. Inorg. Chim. Acta 1999, 291, 49.
(21) Morishima, I.; Kitagawa, S.; Matsuki, E.; Inubushi, T. J. Am. Chem.
Soc. 1980, 102, 2429.
(22) In this chart we use the conventional axis system that is generally
employed for metalloporphyrins.
992 Inorganic Chemistry, Vol. 41, No. 4, 2002

Fe(III) Complexes of Octaethylporphyrins
Table 2. Chemical Shifts in ppm for ClFeIII(meso-R-OEP) at 298 Ka,b
ClFeIII(meso-R-OEP) in chloroform-d3
ClFeIII(meso-R-OEP) in pyridine-d5
meso
meso
substituent
methylene
methyl
cis
trans
methylene
cis
trans
H
butyl
43.7 (8), 41.6 (8)
47.3, 42.2
38.6, 37.3
36.7, 36.3
35.1, 53.2 i
43.9 i, 33.3 i
32.6 i
1.5
6.7
6.5
5.9
-55.5
-57.9
-66.2 i
44.4 (8), 41.6 (8)
46.92, 41.39 (2)
38.93, 38.08
37.19, 36.50
34.83
-34.2
-50.70
-74.7
-78.1 i
-63.51
phenyl
chloro
42.4 (2), 41.9
40.4, 39.3 (2)
38.9, 37.6
46.6, 44.5
42.2, 40.8
39.7, 38.4
36.6, 35.6
45.8, 43.8
41.6, 40.2
39.1, 37.9
36.1, 35.1
46.9, 45.7
44.7, 43.5
42.4, 39.7
39.4, 38.8
47.6, 44.2
43.1 (2), 42.3
39.2, 37.9 (2)
6.5
6.2
-65.9
-63.7
-58.5
-60.7
42.61, 42.16
41.81, 40.83
40.23 (3), 37.62
46.43, 45.67
42.97, 42.09
40.42 (2), 36.67
35.32
-39.53
-27.32
-29.98
-18.24
6.5
6.3
1.7
chloro (axial Br)
cyano
6.1
5.9
-62.9
-39.8
-57.3
-63
-59.9
-25.3
-44.4
-75
46.6, 45.8
-26.8
-17.9
10.97
-3.05
43.1, 42.2
40.5 (2), 36.8
35.4
6.7
6.4
49.24, 47.92
45.24, 44.52
43.12 (2), 38.36
37.32
49.13, 44.67 (2)
43.20, 42.09
40.03, 37.37
35.58
43.88, 42.83
42.02 (2), 40.79
38.71, 37.24
36.56, 47.52 i
41.61 i, 39.95 i
19.44
nitro
6.7
6.4
not seen
methoxy
43.7, 43.4
42.1 (2), 39.9
38.0, 37.7
36.3
49.1 i, 41.2 i
39.3 i
44.6, 43.5 (2)
42.5, 41.3
40.7, 40.2
39.9, 37.8 i
34.2 i
6.7
6.4
5.9
-48.63
-34.41 i
-56.97
-46.01 i
formyl
6.5
6.3
5.6
-51.5
-55.6 i
-42.3
-43.9 i
46.09, 44.30
44.03, 42.30 (2)
41.94, 40.34
38.06, 43.61 i
40.91 i, 34.83 i
-16.20
-35.56 i
-6.17
1 All resonances are of intensity 1 unless indicated in parentheses. 2 Resonances labeled i correspond to the minor isomer.
resonance does show a pronounced downfield shift relative
to the corresponding spectrum seen in chloroform-d. More
importantly, the temperature dependence of the meso reso-
nance no longer obeys the Curie law. Figure 7 compares
the temperature dependence of the position of the meso
resonance of ClFeIII(OEP) in pyridine-d5 solution with its
behavior in chloroform-d solution in a plot of the observed
chemical shift versus the temperature. The anti-Curie be-
havior of ClFeIII(OEP) in pyridine solution is ascribed to the
formation of six-coordinate (py)ClFeIII(OEP) via the equi-
librium shown in eq 1. Previous reports have shown that
ClFeIII(meso-R-OEP) + py h (py)ClFeIII(meso-R-OEP)
(1)
Figure 5. Upfield (meso) portion of the 500 MHz 1H NMR spectra of
ClFeIII(meso-R-OEP) at 25 °C in chloroform-d.
the meso resonances of FeIII porphyrins are sensitive to the
axial ligation, with five-coordinate complexes producing
upfield meso resonances and six-coordinate complexes
producing downfield-shifted meso resonances.23-25 Conse-
quently, the data in Figure 7 are consistent with the influence
of the equilibrium shown in eq 1 on the position of the meso
Since a number of studies on the chemical reactivity of
these iron porphyrins have been conducted in pyridine
solution, the 1H NMR spectra of ClFeIII(OEP) and
ClFeIII(meso-R-OEP) have been examined in pyridine-d5
1
solution. As seen in Table 2, the H NMR spectrum of
(23) Morishima, I.; Shiro, Y.; Wakino, T. J. Am. Chem. Soc. 1985, 107,
1063.
(24) Zobrist, A.; La Mar, G. N. J. Am. Chem. Soc. 1978, 100, 1944.
(25) Budd, D. L.; La Mar, G. N.; Langry, K. C.; Smith, K. M.; Nayyir-
Mazhir, R. J. Am. Chem. Soc. 1979, 101, 6091.
ClFeIII(OEP) in pyridine resembles the spectrum obtained
in chloroform with an upfield meso resonance and two
methylene resonances in the downfield region. The meso
Inorganic Chemistry, Vol. 41, No. 4, 2002 993

Kalish et al.
Table 3. Chemical Shifts in ppm for K[(NC)2FeIII(meso-R-OEP)] in
Methanol-d4 at 298 K
meso
meso
substituent
substituent
peak
methylene
trans
cis
butyl
methoxy
11.52
12.40
between 6.34 and 5.82 -10.46
-17.15
-10.74
7.47, 7.18
6.50, 6.36
8.36, 7.92
6.42, 6.11
-7.49
-3.50
-0.17
chloro
phenyl
none
-10.31
-7.57
8.47 ortho 7.65, 7.21
8.11 meta 6.72, 5.95
7.68 para
nitro
none
9.23, 8.05
5.78, 4.98
9.23, 8.96
6.13, 5.96
10.05, 8.15
7.90, 6.00
7.35
4.23
5.85
5.50
3.32a
-0.56
2.23
cyano
none
11.88
3.32a
formyl
3.10
hydrogen
3.32a
a There is only a single meso-proton resonance.
Figure 6. Downfield (methylene) portion of the 500 MHz 1H NMR spectra
of ClFeIII(meso-R-OEP) at 25 °C in chloroform-d. Resonance assignments
follow those used in Figure 4.
Figure 8. 500 MHz 1H NMR spectra of (A) K[(NC)2FeIII(meso-Ph-OEP)]
and (B) K[(NC)2FeIII(meso-NC-OEP)] in methanol-d4 at 298 K. The inset
shows an expansion of the 9-7 ppm region of the spectrum of K[(NC)2FeIII-
(meso-Ph-OEP)], where the phenyl resonances occur.
also been examined (see Table 2). In both solvents the spectra
of ClFeIII(meso-Cl-OEP) and BrFeIII(meso-Cl-OEP) show
differences in the chemical shift values for all resonances.
This observation is consistent with the axial halide ligands
retaining their positions in the coordination sphere of both
complexes and in both solvents. In pyridine solution the meso
resonances for all complexes have undergone a downfield
shift in comparison to their positions in chloroform solution
(see Table 2). We attribute this downfield shift to the
existence of an equilibrium between five-coordinate ClFeIII-
(meso-R-OEP) and six-coordinate (py)ClFeIII(meso-R-OEP),
as shown in eq 1. The temperature dependence of these
spectra is also consistent with this hypothesis. Thus, for
ClFeIII(meso-Cl-OEP) the meso resonances shift from -27.32
and -18.24 ppm at 298 K to -9.5 and 32 ppm at 243 K.
1H NMR Spectra of K[(NC)2FeIII(meso-R-OEP)]. Ad-
dition of potassium cyanide in methanol-d4 to solutions of
ClFeIII(meso-R-OEP) in methanol-d4 produces solutions of
the low-spin complexes K[(NC)2FeIII(meso-R-OEP)]. Data
from the 1H NMR spectra of these complexes are presented
Figure 7. Curie plot (chemical shift versus 1/T) of the meso resonances
for ClFeIII(OEP) in chloroform-d and pyridine-d5 solutions.
resonances, with the equilibrium favoring the six-coordinate
adduct at low temperature for entropic reasons. This is a
dynamic equilibrium which results in observing resonances
which represent the average of the five- and six-coordinate
forms.
As seen in trace A of Figure 4, the spectrum of ClFeIII-
(meso-Cl-OEP) in pyridine-d5 resembles that obtained in
chloroform-d, shown in trace B. In both solvents there are
eight methylene resonances. Consequently, the two sides of
the porphyrin plane are different and the chloride ligand must
remain bound. To confirm this conclusion, the spectra of
BrFeIII(meso-Cl-OEP) in chloroform-d and pyridine-d5 have
1
in Table 3. Figure 8 shows representative H NMR spec-
tra for solutions of K[(NC)2FeIII(meso-NC-OEP)] and
K[(NC)2FeIII(meso-Ph-OEP)] at 298 K. As expected on the
994 Inorganic Chemistry, Vol. 41, No. 4, 2002

Fe(III) Complexes of Octaethylporphyrins
formation seen in ClFeIII(OEP). However, each meso sub-
stituent produces a somewhat different structural change.
Nevertheless, it is interesting to note that, for the most part,
the mono-meso-substituted complexes show smaller out-of-
plane atom displacements for the porphyrin core atoms than
is observed for the unsubstituted parent, ClFeIII(OEP).
Comparison of the 1H NMR spectra of the high-spin, five-
coordinate iron(III) complexes shown in Figure 4 shows that
meso substitution produces a significant effect on the
chemical shifts of the meso resonances with electron-
withdrawing groups shifting these resonances, and particu-
larly the Hm′ resonance, in a downfield fashion. These
downfield relocations of the meso resonances can be quite
substantial, as seen in Figure 5. Related work on the effects
of â-substitution on the pyrrole rings has shown that
substitution has a marked effect upon the chemical shift of
the adjacent proton within the same pyrrole ring.23 In that
case, the adjacent pyrrole proton undergoes a downfield shift
as the neighboring substituent becomes more electron
withdrawing.26 On the other hand, the chemical shifts of the
methylene protons of ClFeIII(meso-R-OEP) show a much
smaller effect from the meso substituent. These resonances
are found in the 35-55 ppm region. The methyl protons are
also found to resonate in the narrow window from 0 to 10
ppm.
1
Figure 9. Representative drawings of the 500 MHz H NMR spectra of
K[(NC)2FeIII(meso-R-OEP)], showing the location of the two meso-H
resonances. For clarity none of the other resonances are shown in these
diagrams.
basis of symmetry, the spectrum of each complex consists
of four equally intense methylene resonances in the 10-5
ppm region and four equally intense methyl resonances in
the 2-0 ppm region. The two types of meso protons produce
two resonances in a 2:1 intensity ratio, but the observed
chemical shifts of these are markedly affected by the unique
meso substituent, R. For K[(NC)2FeIII(meso-Ph-OEP)] the
meso resonances are found upfield at -0.17 and -7.57 ppm,
whereas for K[(NC)2FeIII(meso-NC-OEP)] they occur down-
field at 7.95 and 2.23 ppm. Additionally the spectrum of
K[(NC)2FeIII(meso-Ph-OEP)] contains resonances in the
9-7.5 ppm region that are due to the meso-phenyl substitu-
ent, as seen in inset A. The small hyperfine shifts of these
phenyl protons indicate that the dipolar contribution is
negligible.
Figure 9 shows the remarkable variation in the chemical
shifts of the meso resonances in the seven complexes
K[(NC)2FeIII(meso-R-OEP)], where R is butyl, methoxy,
chloro, phenyl, formyl, nitro, and cyano in methanol-d4 at
298 K. It is clear that the chemical shifts of the meso
resonances undergo a marked upfield relocation as the
π-donating character of the unique meso substituent in-
creases.
The typical spin delocalization pathways for high-spin
iron(III) porphyrins produce resonances for the â-pyrrole
((TPP)FeIIIX) or R-CH2 ((OEP)FeIIICl) protons that are
strongly shifted downfield. This downfield shift is a result
of the σ-contact contribution due to the delocalization through
the σ-framework by way of σ-donation to the half-occupied
2
2
dx -y iron(III) orbital. Additionally, π-delocalization places
a considerable amount of spin density at the meso positions.
The mechanism is identified as Fe to porphyrin π back-
bonding and involves the empty 4e(π*) orbitals of the
porphyrin with a large contribution from the 2pz meso-carbon
atomic orbitals.39 The π-spin density delocalized further on
produces sign alternation of the contact shift measured for
the meso-phenyl resonances and is reflected by a large upfield
shift of the meso protons of (OEP)FeIIICl. We have noticed
previously that the contact shift of high-spin iron(III) meso-
substituted tetraphenylporphyrins may result from the si-
multaneous delocalization in σ orbitals as well as in both
filled 3e(π) and vacant 4e(π*) molecular orbitals.26
It seems that in (meso-R-OEP)FeIIICl the contribution of
the 4e(π*) related orbitals is systematically varied so that
the amount of the π spin density is lowered as the substituent
becomes more electron withdrawing. The originally degener-
ate 4e(π*) orbitals are split because of the symmetry
lowering. The relative amount of spin density located on
these orbitals is reversed once we go from the 5-Bu
substituent to the 5-CN substituent. The relocations of the
meso-H resonances seen in Table 2 are simply a reflection
of the different pattern of the orbital in question that is
produced by the introduction of a unique substituent at one
meso position.
Discussion
The results presented here indicate that the introduction
of a single substituent at one of the meso positions of
octaethylporphyrin can produce significant changes in the
structure and/or spectroscopic features of the resulting iron-
(III) complexes.
High-Spin Complexes. In terms of structure as seen in
Figure 3, the introduction of one meso substituent alters the
conformation of the porphyrin ligand for high-spin, five-
coordinate iron(III) complexes away from the domed con-
(26) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Hrycyk, W.; Pacholska, E.;
Rachlewicz, K.; Szterenberg, L. Inorg. Chem. 1996, 35, 6861.
Inorganic Chemistry, Vol. 41, No. 4, 2002 995

Kalish et al.
The 1H NMR spectra of pyridine solutions of ClFeIII(OEP)
and ClFeIII(meso-R-OEP) are indicative of the formation of
high-spin, six-coordinate complexes, {(py)ClFeIII(OEP)} and
{(py)ClFeIII(meso-R-OEP)}, in which pyridine is added to
the coordination site trans to the axial halide. Such mixed-
ligand complexes of iron(III) porphyrins are uncommon, but
a few well-characterized examples have been isolated and
crystallized, including high-spin {(py)(SCN)FeIII(OEPO)}.27,28
Generally, reactions of pyridine and substituted pyridines
with ClFeIIIP results in the formation of low-spin, six-
coordinate [(py)2FeIIIP]+.29,30 In the work described here,
pyridine, a relatively nonpolar solvent, was used, and under
these conditions, ionization of the axial halide does not occur.
Rather the high-spin, six-coordinate {(py)ClFeIII(meso-R-
OEP)} forms.
Low-Spin Complexes. The spectroscopic results for the
low-spin cyano complexes K[(NC)2FeIII(meso-R-OEP)] show
marked differences which relate to their electronic structures.
Low-spin Fe(III) complexes of 4-fold symmetric porphyrins
such as H2TPP and H2OEP can exist in two different
electronic states: the common (dxy)2(dxz,dyz)3 state and the
less common (dxz,dyz)4(dxy)1 state. However, an increasing
number of examples of the less common (dxz,dyz)4(dxy)1 state
have come to light recently.31-38 For the lower symmetry
complexes K[(NC)2FeIII(meso-R-OEP)], where one meso
position is unique, the situation is more complex, and the
ground state of K[(NC)2FeIII(meso-R-OEP)] combines the
features of both ground states with the composition for any
one complex controlled by the nature of the meso-R
substituent. Although we employ the conventional porphyrin-
based axis system shown in Chart 2, in the lower symmetry
of K[(NC)2FeIII(meso-R-OEP)], the dxz and dyz orbitals are
no longer strictly degenerate. Nevertheless, we will continue
to use the conventional labels (dxy)2(dxz,dyz)3 and (dxz,dyz)4-
(dxy)1 for the two limiting ground-state electronic structures
for these low-spin complexes.
with the presumption that one deals with similar distortion
of geometry due to the meso substitution. Thus, the most
electron donating substituents produce the largest upfield
shifts. As a matter of fact, the trend resembles that observed
for the high-spin derivative (see above). The gradual nature
of the upfield shift probably reflects an incremental change
in separation of the energies of the spin-containing orbitals,
dxy, dxz, and dyz. The likely dominating factor is the occupancy
of the iron dxy orbital as the meso substituent becomes more
electron donating. The electron-donating substituent can
stabilize the dxz and dyz orbitals relative to the dxy orbital by
facilitating M-to-L back-donation in the out-of-plane π
system. Thus, in the series of complexes studied here, there
is a gradual increase in the contribution of the dxy orbital
relative to the dxz and dyz orbitals to the electronic structure
as the unique meso substituent becomes more electron
donating. As a result, the meso resonances (Hm and Hm′)
relocate in an upfield direction. The upfield meso-proton shift
seen for iron porphyrins with the (dxz,dyz)4(dxy)1 ground state
arises from the presence of spin in the a2u-like porphyrin
orbital, which has principal contributions at the meso
positions and little or no contribution at the pyrrole â
positions.39
Complexes with the (dxz,dyz)4(dxy)1 electronic state that
involve (OEP)2- as the ligand are rare, but [(t-BuNC)2FeIII-
(OEP)]+ is one example which is reported to have a nearly
1
pure (dxz,dyz)4(dxy)1 electronic ground state.31 The H NMR
spectrum of [(t-BuNC)2FeIII(OEP)]+ shows that the meso-
protons are shifted relatively far upfield (δ -37 ppm at 303
K).31 The crystallographic structure of this complex shows
that the porphyrin is significantly ruffled. This ruffling allows
mixing of the porphyrin π orbitals with the spin-containing
dxy iron orbital and places spin in the porphyrin 3a2u, π-type
orbital, which has large electron density at the meso positions.
Thus, the structural distortion results in transfer of spin from
the half occupied, in-plane dxy orbital to the out-of-plane
porphyrin π orbital.
The marked upfield shift of the meso-proton resonances
of of K[(NC)2FeIII(meso-R-OEP)] seen in Figure 9 is related
to the electronic chaacteristics of the unique meso substituent
A similar path for spin density transfer can operate in the
K[(NC)2FeIII(meso-R-OEP)] series. However, in this series
the nature of the meso-R substituent strongly influences the
pattern of the modified porphyrin a2u-like orbital, as reflected
by the relative amount of spin density at the meso positions.
Some preference for added spin density at the Hm positions
is observed as the contribution from the (dxz,dyz)4(dxy)1 state
is increased, since the Hm protons, rather than the Hm′ protons,
experience the larger upfield relocation as the meso sub-
stituent becomes electron donating.
Thus, this work has revealed an important meso effect on
the structure of low-spin iron(III) porphyrins: the presence
of a single electron-donating meso substituent favors the
(dxz,dyz)4(dxy)1 state when that substituent is electron donating.
Factors consistent with this meso effect have also been
observed in work on meso-tetraalkylporphyrins which readily
accommodate the less common (dxz,dyz)4(dxy)1 electronic
state.40 In particular, comparative studies have shown that
(27) Adams, K. M.; Rasmussen, P. G.; Scheidt, W. R.; Hatano, K. Inorg.
Chem. 1979, 18, 1892.
(28) Scheidt, W. R.; Lee, Y. J.; Geiger, D. K.; Taylor, K.; Hatano, K. J.
Am. Chem. Soc. 1982, 104, 3367.
(29) Walker, F. A.; Lo, M.; Ree, M. T. J. Am. Chem. Soc. 1976, 98, 5552.
(30) Satterlee, J. D.; LaMar, G. N.; Frye, J. S. J. Am. Chem. Soc. 1976,
98, 7275.
(31) Safo, M. K.; Walker, F. A.; Raitsimring, A. M.; Walters, W. P.; Dolata,
D. P.; Debrunner, P. G.; Scheidt, W. R. J. Am. Chem. Soc. 1994, 116,
7760.
(32) Guillemot, M.; Simonneaux, G. J. Chem. Soc., Chem. Commun. 1995,
2093.
(33) Walker, F. A.; Nasri, H.; Turowska-Tyrk, I.; Mohanrao, K.; Watson,
C. T.; Shokhirev, N. V.; Debrunner, P. G.; Scheidt, W. R. J. Am.
Chem. Soc. 1996, 118, 12109.
(34) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Glowiak, T. Inorg. Chem. 1997,
36, 6299.
(35) Nakamure, M.; Ikeute, T.; Fujii, H.; Yoshimure, T. J. Am. Chem. Soc.
1997, 119, 6284.
(36) Wolowiec, S.; Latos-Graz˘yn´ski, L.; Mazzanti, M.; Marcon, J.-C. Inorg.
Chem. 1997, 36, 5761.
(37) Wolowiec, S.; Latos-Graz˘yn´ski, L.; Toronto, D.; Marcon, J.-C. Inorg.
Chem. 1998, 37, 724.
(38) Simonneaux, G.; Schu¨nemann, V.; Morice, C.; Carel, L.; Toupet, L.;
Winkler, H.; Trautwein, A. X.; Walker, F. A. J. Am. Chem. Soc. 2000,
122, 4366.
(39) Walker, F. A. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 5, p
81.
996 Inorganic Chemistry, Vol. 41, No. 4, 2002

Fe(III) Complexes of Octaethylporphyrins
the (dxz,dyz)4(dxy)1 electronic state is stabilized by various
porphyrin ligands in the following order: octaethyl-meso-
tetraphenylporphyrin e octamethyl-meso-tetraphenylporphy-
rin e meso-tetraphenylporphyrin < meso-tetra-n-propylpor-
phyin, meso-tetracyclopropylporphyrin < meso-tetraisopropyl-
porphyrin.41
In addition to the marked shifts of the meso-proton
resonances in these low-spin complexes, the introduction of
a unique meso substituent also alters the pattern of the pyrrole
methylene protons. As seen in Table 3, the spread of the
methylene resonances (as given as the difference in chemical
shifts of the most upfield and most downfield methylene
resonance) decreases as the meso substituent becomes more
electron-donating. Also, there is an upfield relocation of the
methylene resonances as the meso substituent becomes more
electron donating.
Table 4. Crystallographic Data
ClFeIII(meso-Ph-OEP) ClFeIII(meso-CN-OEP)
formula
fw
C42H48ClFeN4
700.14
C37H43ClFe3N5
649.06
a, Å
b, Å
c, Å
9.975(2)
13.454(3)
14.799(3)
113.590(4)
95.736(5)
105.215(5)
1708.5(6)
2
12.6033(5)
13.6049(5)
19.8435(8)
90
103.8230(10)
90
R, deg
â, deg
γ, deg
V, Å3
3304.0(2)
4
Z
cryst syst
space group
T, K
triclinic
P1h
90(2)
monoclinic
P21/c
90(2)
λ, Å
0.710 73 (Mo KR)
0.710 73 (Mo KR)
F, g/cm3
µ, mm-1
max and min transmissn
R1 (obsd data)a
wR2 (all data, F2
refinement)b
1.361
1.305
0.557
0.99-0.90
0.066
0.571
0.96-0.88
0.041
0.170
0.108
Experimental Section
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, observed data (>4σFo). b wR2 ) [∑[w(Fo
2
Materials. Octaethylporphyrin and iron(III) octaethylporphyrin
chloride were purchased from Mid Century. The mono-meso-
substituted porphyrins meso-NO2-H2OEP,42 meso-NC-H2OEP,43
meso-Cl-H2OEP,44 meso-MeO-H2OEP,45 meso-HC(O)-H2OEP,46
meso-Ph-H2OEP,47 and meso-n-Bu-H2OEP47 were prepared as
described previously.
2
2
- Fc )2]/∑[w(Fo )2]]1/2, all data.
A saturated solution of potassium cyanide in methanol-d4 was added
to the solution of the iron complex. The color of the solution went
from a dark brown to bright red or greenish brown upon addition
of the cyanide solution. The progress of the reaction was followed
1
Formation of High-Spin ClFeIII(meso-R-OEP). Iron was
inserted by a standard procedure48 to yield the five-coordinate chloro
complexes ClFeIII(meso-R-OEP), which were isolated as dark green-
brown crystals. UV/vis spectra in chloroform (λmax, nm (ꢀ, M-1
cm-1)): ClFeIII(meso-Ph-OEP), 386 (7.7 × 104), 510 (8.2 × 103),
540 (3.1 × 103), 642 (3.7 × 103); ClFeIII(meso-n-Bu-OEP), 390
(4.4 × 104), 514 (5.0 × 103), 544 (4.4 × 103), 646 (2.0 × 103);
ClFeIII(meso-MeO-OEP), 386 (7.0 × 104), 508 (7.9 × 103), 538
(6.1 × 103), 640 (3.1 × 103); ClFeIII(meso-Cl-OEP), 388 (7.7 ×
104), 512 (8.5 × 103), 542 (6.8 × 103), 646 (3.7 × 103); ClFeIII-
(meso-HC(dO)-OEP), 384(8.7 × 104), 508 (8.4 × 103), 538 (8.2
× 103), 638 (4.4 × 103); ClFeIII(meso-NC-OEP), 384 (8.2 × 104),
484 (6.9 × 103), 570 (7.2 × 103), 678 (2.5 × 1033); ClFeIII(meso-
O2N-OEP), 378 (8.4 × 104), 508 (9.1 × 1033), 538 (8.6 × 103),
640 (4.3 × 103).
by H NMR spectroscopy.
X-ray Data Collection for ClFeIII(meso-Ph-OEP) and
ClFeIII(meso-NC-OEP). Crystals were obtained by slow diffusion
of n-hexane into a chloroform solution of the appropriate complex.
The crystals were coated with a light hydrocarbon oil and mounted
in the 90 K dinitrogen stream of a Bruker SMART 1000 diffrac-
tometer equipped with a CRYO Industries low-temperature ap-
paratus. Intensity data were collected using graphite-monochromated
Mo KR radiation. Crystal data are given in Table 4.
Solution and Structure Refinement. Scattering factors and
correction for anomalous dispersion were taken from a standard
source.49 An absorption correction was applied to each structure.50
The solutions of the structures were determined by direct methods
with SHELXS-97 and subsequent cycles of least-squares refinement
on F2 with SHELXL-97.
1
Formation of Low-Spin K[(NC)2FeIII(meso-R-OEP)]. At room
temperature a methanol-d4 solution of ClFeIII(meso-R-OEP) (2-3
mol) was placed in an NMR tube and sealed with a rubber septum.
Instrumentation. H NMR spectra were recorded on a Bruker
Avance 500 FT spectrometer (1H frequency is 500.13 MHz). The
spectra were recorded over a 100 kHz bandwidth with 64K data
points and a 5-ms 90° pulse. For a typical spectrum between 500
and 1000 transients were accumulated with a 50 µs delay time.
The residual 1H resonances of the solvents were used as a secondary
reference.
(40) Ikeue, T.; Ohgo, Y.; Saitoh, T.; Nakamura, M.; Fujii, H.; Yokoyama,
M. J. Am. Chem. Soc. 2000, 122, 4068.
(41) Ikeue, T.; Ohgo, Y.; Saitoh, T.; Yamaguchi, T.; Nakamura, M. Inorg.
Chem 2001, 40, 3423.
(42) Bonnett, R.; Stephenson, G. F. J. Org. Chem. 1965, 30, 2791.
(43) Johnson, A. W.; Oldfield, D. J. Chem. Soc. C 1966, 794.
(44) Bonnett, R.; Gale, A. D.; Stephenson, G. F. J. Chem. Soc. C 1966,
1600.
(45) Barnett, G. H.; Hudson, M. F.; McCombie, S. W.; Smith, K. M. J.
Chem. Soc., Perkin Trans. 1 1973, 691.
(46) Inhoffen, H. H.; Furhop, J. H.; Voit, A.; Brockman, H. Ann. Chem.
1966, 695, 133.
(47) Kalisch, W. W.; Senge, M. O. Angew. Chem., Int. Ed. 1998, 37, 1107.
(48) Adler, A. D.; Longo, F. R.; Kampas, F. J. Inorg. Nucl. Chem. 1970,
32, 2443.
Acknowledgment. We thank the NIH (Grant GM-26226,
A.L.B.) and the Foundation for Polish Science (L.L.-G) for
financial support, the NSF (Grant OSTI 97-24412) for partial
funding of the 500 MHz NMR spectrometer, and Sigma Xi
for Grants in Aid of Research to H.K.
Supporting Information Available: Supplementary figures S1
and S2 and X-ray crystallographic files in CIF format for ClFeIII-
(meso-Ph-OEP) and ClFeIII(meso-NC-OEP). This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
(49) International Tables for Crystallography; Kluwer Academic: Dor-
drecht, The Netherlands, 1992.
(50) Sheldrick, G. M. SADABS 2.0, 2000.
IC011034Q
Inorganic Chemistry, Vol. 41, No. 4, 2002 997