Iron nitrosyl "natural" porphyrinates: Does the porphyrin matter?

Article abstract of DOI:10.1021/ic500086k

The synthesis and spectroscopic characterization of three five-coordinate nitrosyliron(II) complexes, [Fe(Porph)(NO)], are reported. These three nitrosyl derivatives, where Porph represents protoporphyrin IX dimethyl ester, mesoporphyrin IX dimethyl ester

Full text of DOI:10.1021/ic500086k

Article
pubs.acs.org/IC
Iron Nitrosyl “Natural” Porphyrinates: Does the Porphyrin Matter?
Graeme R. A. Wyllie,‡,# Nathan J. Silvernail,‡,# Allen G. Oliver,‡ Charles E. Schulz,§
and W. Robert Scheidt*,‡
‡Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
§Department of Physics, Knox College, Galesburg, Illinois 61401, United States
S
* Supporting Information
ABSTRACT: The synthesis and spectroscopic characterization of three five-
coordinate nitrosyliron(II) complexes, [Fe(Porph)(NO)], are reported. These
three nitrosyl derivatives, where Porph represents protoporphyrin IX dimethyl
ester, mesoporphyrin IX dimethyl ester, or deuteroporphyrin IX dimethyl
ester, display notable differences in their properties relative to the symmetrical
synthetic porphyrins such as OEP and TPP. The N−O stretching frequencies
are in the range of 1651−1660 cm−1, frequencies that are lower than those of
synthetic porphyrin derivatives. Mossbauer spectra obtained in both zero and
̈
applied magnetic field show that the quadrupole splitting values are slightly
larger than those of known synthetic porphyrins. The electronic structures of
these naturally occurring porphyrin derivatives are thus seen to be consistently different from those of the synthetic derivatives,
the presumed consequence of the asymmetric peripheral substituent pattern. The molecular structure of [Fe(PPIX-DME)(NO)]
has been determined by X-ray crystallography. Although disorder of the axial nitrosyl ligand limits the structural quality, this
derivative appears to show the same subtle structural features as previously characterized five-coordinate nitrosyls.
Further studies focused on preparing a series of additional
five-coordinate (nitrosyl)iron(II) porphyrinate derivatives that
vary in the nature and the position of the β-pyrrolic- and meso-
substituents. Characterization of derivatives of a β-oxochlorin
and the asymmetrically substituted 2,3,12,13-tetrabromo-
5,10,15,20-tetraphenylporphyrin revealed the same tilt/asym-
metry pattern observed in the [Fe(OEP)(NO)] derivatives.21
To date there is only one structure reported for a naturally
occurring porphyrin derivative, that of [Fe(DPIX-DME)-
(NO)].23 This structure displayed the same off-axis tilting as
previously observed in the synthetic porphyrins, with the tilt
direction lying in the direction of the two pyrrole rings bearing
the propionate groups.
However, despite these similarities, physical characterization
of these naturally occurring porphyrin derivatives showed some
significant differences from the synthetic porphyrins. Initial
investigation of the vibrational spectra of nitrosyl iron
derivatives utilizing nuclear resonance vibrational spectroscopy
(all taken as powder spectra) showed that the in-plane
components of the iron vibrational spectra were surprisingly
sensitive to the nature of the peripheral groups. Even changing
only two substituents in the trio of naturally occurring
porphyrins (protoporphyrin IX, deuteroporphyrin IX, and
mesoporphyrin IX, shown in Scheme 1) had observable effects
on the in-plane vibrational spectra.24
INTRODUCTION
■
It has been just over two decades since the role of nitric oxide
(NO) as an essential biological signaling agent was recognized
and which led to its selection as Science’s molecule of the year in
1992.1 NO is now recognized for its importance in blood
pressure regulation, as a neurotransmitter, as well as a (toxic)
defense mechanism in neutrophils and macrophages.2−13
Iron(II) porphyrinates are one of the critical biological
targets of NO, and extensive work has characterized the iron
nitrosyl unit in a range of synthetic porphyrin model complexes
[Fe(Porph)(NO)].14−16 However, information from early
crystallographic studies was limited due to severe problems
with disorder of the NO ligand.17−19 It was only with the report
of two ordered crystalline polymorphs of the five-coordinate
(nitrosyl)iron(II) porphyrinate derivative [Fe(OEP)(NO)]20
that hitherto unobserved structural trends became apparent,
trends that have been since observed in a number of other
iron(II) nitrosyl porphyrinates.16,21 In these structures, the
FeN5 coordination group shows substantial deviation from an
ideal symmetric coordination, with a significant off-axis tilt of
the Fe−N(NO) bond vector and an apparently correlated
asymmetry in the equatorial Fe−Np bond distances. This
equatorial asymmetry pattern is displayed wherein the two Fe−
Np bonds closest to the tilted Fe−N(NO) axial vector are
effectively identical but significantly shorter than the other two
Fe−Np bonds, which are also effectively equal to each other.
The tilting/asymmetry pattern has also been observed in a
cobalt system, although the deviations from ideal axial
symmetry are smaller.22
To further investigate the differences between the naturally
occurring and synthetic porphyrins, we report the synthesis of
Received: January 14, 2014
Published: March 12, 2014
© 2014 American Chemical Society
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Article
for the structure determination. The crystalline sample was placed in
inert oil, mounted on a glass pin, and transferred to the cold gas stream
of the diffractometer. Crystal data were collected at 100 K. The
structure was solved by direct methods and refined against F2 using
SHELXL;27 subsequent difference Fourier syntheses led to the
location of all remaining non-hydrogen atoms. For the structure
refinement, all data were used, including negative intensities.
Scheme 1. Diagrams Giving the Structure for (a)
Protoporphyrin IX Dimethyl Ester, (b) Mesoporphyrin IX
Dimethyl Ester, (c) Deuteroporphyrin IX Dimethyl Ester
The asymmetric unit contains one independent porphyrin molecule
and one not quite fully occupied chloroform solvate. Unfortunately,
the structure is somewhat marred by disorder; most significantly, the
oxygen atom of the nitrosyl ligand is found in two distinct locations
with occupancies of 0.66(2) and 0.34(2). The carbonyl group of one
of the propionate ester side arms is also disordered with two positions
for the CO moiety. The chloroform solvate molecule was also found
to be disordered with two different orientations of the solvate,
centered on the same carbon atom position. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were idealized with the
standard SHELXL idealization methods. Brief crystallographic
information is given in Table 1. Complete crystallographic details,
atomic coordinates, anisotropic thermal parameters, and hydrogen
atom coordinates are given in the Supporting Information.
[Fe(Porph)(NO)] derivatives based on the trio of naturally
occurring porphyrins. These derivatives have been character-
ized by UV−vis, IR, and EPR spectroscopy. In addition, the
three derivatives have been characterized by Mossbauer
̈
spectroscopy in zero and applied magnetic field. After
significant effort, single crystals of [Fe(PPIX-DME)(NO)]
have been obtained, and the X-ray structure has been
determined. Unfortunately, the axial NO ligand displays some
disorder.
Table 1. Brief Crystallographic Data and Data Collection
Parameters
formula
C36.91H36.88Cl2.68FeN5O5
781.14
FW, amu
a, Å
10.6098(6)
11.0454(6)
15.5814(9)
101.428(3)
97.149(3)
EXPERIMENTAL SECTION
■
b, Å
General Information. All reactions and manipulations of the
iron(II) porphyrin derivatives were carried out under argon using a
double-manifold vacuum line, Schlenkware, and cannula techniques.
Dichloromethane, chloroform, methanol, and hexanes were distilled
under argon over CaH2, magnesium turnings, and sodium/
benzophenone, respectively. The free bases, protoporphyrin IX
dimethyl ester, deuteroporphyrin IX dimethyl ester, and mesopor-
phyrin IX dimethyl ester, were purchased from Frontier Scientific.
Nitric oxide (Mittler Specialty Gases) was purified by fractional
distillation through a trap containing 4A molecular sieves bathed in a
dry ice/ethanol slurry.25
Synthetic Information. Iron(II) chloride was purchased from
Acros. Insertion of iron into H2(PPIX-DME), H2(DPIX-DME), or
H2(MPIX-DME) was accomplished by the reaction of the free base
and iron(II) chloride in DMF.26 The desired five-coordinate
[Fe(Porph)(NO)] derivative was obtained by reductive nitrosylation.
Chloroporphyrinatoiron(III) compounds were reductively nitro-
sylated17 under argon, and all solvents used were degassed by sparging
with argon for 5 min. Liquid−liquid diffusion crystallization was done
with chloroform solutions and with methanol as the counter solvent in
40 cm × 7 mm glass tubes, sealed with rubber septa. Crystals were
typically harvested after about 10 days and washed with methanol.
Crystals of [Fe(PPIX-DME)(NO)] and [Fe(DPIX-DME)(NO)] were
thus obtained. The obtained crystals of [Fe(DPIX-DME)(NO)] are a
new polymorphic form. Unfortunately, the crystal structure determi-
nation of the new DPIX-DME derivative was only partly successful;
the successful PPIX-DME determination is reported herein.
c, Å
α, deg
β, deg
γ, deg
V, Å3
94.792(3)
1764.84(17)
space group
Z
Dc, g/cm3
P1
̅
2
1.469
808
F(000)
μ, mm−1
0.682
Mo Kα, λ
100(2)
radiation
̅ = 0.71073 Å
temperature, K
final R indices [I > 2σ(I)]
final R indices (all data)
R1 = 0.0832, wR2 = 0.2166
R1 = 0.1037, wR2 = 0.2408
RESULTS
■
The synthesis and spectroscopic characterization for three five-
coordinate nitrosyl porphyrinates have been successfully carried
out. The porphyrinate species are all related to protoporphyrin
IX or heme b. Protoporphyrin IX has two vinyl groups at the 3
and 7 positions of the porphine nucleus. These are often noted,
trivially, as the 2, 4 positions. The two vinyl groups are reduced
to ethyl groups in the mesoporphyrin IX species and converted
to hydrogen atoms in the deuteroporphyrin derivative. The
other six peripheral substituents remain unchanged (3,8,12,18-
tetramethyl and 13,17-dipropionate, cf. Scheme 1). The two
acidic propionate side chains are often esterified for synthetic
convenience. Methyl esters have been used in the studies
reported here. The UV−vis, IR, and EPR data are summarized
in Table 2.
Spectral Data. All three complexes were characterized by UV−vis,
IR, EPR, and Mossbauer spectroscopies. UV−vis spectra were
̈
recorded in chloroform solution on a Perkin-Elmer Lambda 19
spectrometer. IR spectra were recorded on a Perkin-Elmer model 883
as KBr pellets. EPR spectra were recorded at 77 K with an X-band
Varian E-12 spectrometer. Frozen solution spectra were obtained in
dichloromethane glasses. Mossbauer measurements were performed
̈
on a constant acceleration spectrometer at 4.2 K in zero field and at
4.2 K in 4 and 9 T fields using a superconducting magnet system
(Knox College).
The three nitrosyl complexes have been characterized by
Mossbauer spectroscopy in zero and applied magnetic field; all
samples were found to be consistent with the presence of a
single species. The spectra of all three are sharp, slightly
X-ray Structure Determination. Single crystal experiments on
[Fe(PPIX-DME)(NO)] were carried out on a Bruker Apex II system
̈
with graphite-monochromated Mo Kα radiation (λ
̅ = 0.71073 Å). A
dark-red crystal with the dimensions 0.44 × 0.35 × 0.09 mm3 was used
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Table 2. UV-vis, IR, and EPR Data for [Fe(PPIX-DME)(NO)], [Fe(DPIX-DME)(NO)], [Fe(MPIX-DME)(NO)], and Related
Complexes
complex
UV−vis, nm
ν(NO), cm−1
ν(CO), cm−1
g1
g2
g3
A (G)
ref
a
a
a
b
b
c
c
c
f
c
c
c
f
c
c
c
f
c
[Fe(PPIX-DME)(NO)]
[Fe(DPIX-DME)(NO)]
[Fe(MPIX-DME)(NO)]
[Fe(OEP)(NO)]
395, 480, 543, 568
388, 473, 530, 555
390, 478, 525, 560
389, 479, 529, 554
1660
1740
2.10
2.11
2.10
2.06
2.06
2.06
2.00
2.01
2.01
17
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21, 28
b
b
c
1651
1735
16
b
b
c
1658
1738
16
de
,
be
,
f
1673
NA
2.11
2.04
2.06
2.01
2.01
18
ag
,
hi
bg
,
i
i
i
i
[Fe(TPP)(NO)]
405, 537, 606
1700 , , 1670
NA
2.103
17
17, 29
a
b
c
d
e
f
CHCl3 solution. KBr pellet. Frozen CH2Cl2 glass at 77 K. CH2Cl2 solution. Data taken from ref 21. Data measured on doped single crystal, ref
g
h
i
28. Data from ref 17. Nujol mull. Data from ref 29.
asymmetric, quadrupole doublets; the zero field spectrum of
[Fe(PPIX-DME)(NO)] is shown in Figure 1.
DISCUSSION
■
A major issue for these nitrosyl derivatives of the naturally
occurring porphyrins is whether they have significantly different
properties from those based on synthetic porphyrins. The N−
O stretching frequency of the three are seen to be significantly
lower than those of the synthetic species (Table 2). Since
Maxwell and Caughey30 and especially Yoshimura31 had shown
that the N−O stretching frequency in [Fe(PPIX-DME)(NO]
was sensitive to environment, we compare values for all species
measured in as close as possible the same conditions. Values for
the three new porphyrin species are seen to be lower than those
for either the TPP or OEP derivatives. Given the ν(NO)
sensitivity to environment shown by [Fe(PPIX-DME)(NO)],
we thought that these lower NO stretching frequencies might
be reflected in interactions between the NO and the polar
propionate side chains. A careful examination of the crystalline
packing environments of [Fe(PPIX-DME)(NO)] (reported
here) and [Fe(MPIX-DME)(NO)]23 show no such inter-
actions. We conclude that the peripheral groups of the naturally
occurring porphyrins have a real effect on the NO stretching
frequency.
Figure 1. The zero field Mossbauer spectrum of [Fe(PPIX-
DME)(NO)] at 4.2 K.
̈
The molecular structure of [Fe(PPIX-DME)(NO)] has been
determined at 100 K. As noted in the experimental section,
there are some modest disorder issues, but the major features of
the molecule are clear. A thermal ellipsoid plot of the
[Fe(PPIX-DME)(NO)] molecule is given in Figure 2, and a
fully labeled diagram with all atom names is given in Figure S1,
Supporting Information.
Gas phase spectra of the NO complex of protoporphyrin IX
itself, although protonated on one vinyl group, shows ν(NO) of
1720 cm−1.32 The ν(NO) of the iron(III) species also shows a
higher value of than those reported in KBr pellet or in
solution.33
Although the data are limited, an effect stemming from the
peripheral group substituents on the Mossbauer parameters is
̈
also observed. Values of the Mossbauer parameters for all three
̈
derivatives are given in Table 3. There are only limited
Mossbauer data available for other nitrosyls and one previous
̈
study in applied magnetic field; these data are also given in
Table 3. The Mossbauer parameters for the nitrosyl derivatives
̈
show slightly greater quadrupole splitting and isomer shift
values in the natural porphyrins compared to TTP and OEP.
The increased isomer shift results from greater population of
the valence orbitals which, through the resulting screening of
the nuclear charge, causes a reduced s-electron density at the
nucleus. An increased valence electron population must occur
among orbitals that make a positive contribution to the electric
2
2
field gradient: dxy, dx −y , px, py in order to result in a
corresponding increase in the (positive) quadrupole splitting.
This is probably the result of the asymmetric peripheral
substitution pattern. The spectroscopic data are thus consistent
with a modest difference in the electronic structures of the
natural heme derivatives relative to those of the synthetic
hemes.
Figure 2. Thermal ellipsoid plot of the [Fe(PPIX-DME)(NO)]
molecule. Ellipsoids are plotted at the 50% probability level. Hydrogen
atoms have been omitted for clarity. The porphyrin ring appears to be
pivoting around a point between N2 and N3, that leads to the
extended ellipsoids in only a part of the ring.
Lang and Marshall37,38 reported Mossbauer spectra for a
̈
number of liganded hemoglobin derivatives including a nitrosyl
derivative; their observed NO spectrum showed a broad
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Table 3. Mossbauer Data for [Fe(Porph)(NO)] Complexes
Article
̈
ab
,
a
c
d
d
d
complex
ΔEq
δ
η
Axx/gnβn
−5.3
Ayy/gnβn
−15.7
Azz/gnβn
ref
e
f
[Fe(PPIX-DME)(NO)]
[Fe(PPIX-DME)(NO)]
+1.39
+1.38
+1.43
+1.48
+1.24
1.24
0.40
0.37
0.39
0.38
0.35
0.35
0.37
0.35
0.37
0.15
10.5
this work
34
e
[Fe(MPIX-DME)(NO)]
0.23
0.22
0.32
−3.0
−8.8
−25
−14.2
−16.4
−10
10.0
11.0
13.2
this work
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35
e
[Fe(DPIX-DME)(NO)]
e
[Fe(TPP)(NO)]
e
[Fe(TPP)(NO)]
this work
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36
e
[Fe(OEP)(NO)]
1.27
f
[Fe(OEP)(NO)]
1.26
f
[Fe(OEP)(NO)]
1.22
34
a
b
c
d
e
f
Value in mm/s. + sign determined experimentally. Asymmetry parameter. Value in T. Measured at 4.2 K. Measured at 100 K.
Table 4. Structural Parameters for [Fe(Porph)(NO)] Complexes
a
b
bc
,
bd
,
b
b
ae
,
af
,
complex
Fe−N−O
<Fe−Np >
ΔFe(Ct)
ΔFe(N4)
Fe−N
N−O
orientation
tilt
ref
g
g
g
[Fe(PPIX-DME)(NO)]
[Fe(DPIX-DME)(NO)]
[Fe(OEP)(NO)] (A)
[Fe(OEP)(NO)] (B)
143.4(6)
1.998(9)
0.29
0.26
0.29
0.27
0.20
0.37
0.32
0.29
0.26
0.35
0.37
0.31
0.26
0.26
0.28
0.28
0.20
0.31
0.30
0.28
0.26
i
1.719(4)
1.723(3)
1.722(2)
1.7307(7)
1.739(6)
1.734(8)
1.726(9)
1.691(11)
1.7320(13)
1.713(4)
1.714(4)
1.140(8)
1.187(4)
1.167(3)
1.1677(11)
1.163(5)
1.119(11)
1.144(12)
1.145(16)
1.1696(19)
1.149(5)
1.142(5)
1.155(5)
36
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23
143.1(3)
144.4(2)
142.74(8)
144.4(5)
147.9(8)
146.9(9)
145(1)
2.005(21)
2.004(15)
2.010(12)
1.999(4)
2.01(3)
35.0
37.9
40.2
44.3
0.0
6.2
6.5
8.2
6.3
5.6
7.1
21
21
h
[Fe(TPP)(NO)]
39
[Fe(TPPBr4)(NO)] (A′)
[Fe(TPPBr4)(NO)] (A″)
[Fe(TPPBr4)(NO)] (B)
[Fe(oxoOEC)(NO)]
21
2.00(2)
0.0
21
1.95(3)
18.4
40.9
∼0
∼0
39.6
21
143.11(15)
146.3(4)
146.6(5)
2.009(9)
1.991(8)
1.993(5)
1.932(9)
7.1
21
[Fe(3,5-MeBAFP)(NO)] (A)
[Fe(3,5-MeBAFP)(NO)] (B)
i
40
i
i
40
[Fe(OETAP)(NO)]
143.7(4)
i
1.721(4)
7.6
36
a
b
c
d
Value in degrees. Value in Å. Iron atom displacement from 24-atom mean plane. Iron atom displacement from four nitrogen atom plane.
e
f
g
Minimum dihedral angle between Fe−N−O and Np−Fe−N(NO) planes. Deviation from normal to 24-atom mean plane. Major NO oxygen
h
i
atom. Triclinic form, 33 K. Not reported.
quadrupole doublet, and the investigators did not give values
for the isomer shift and quadrupole splitting constant.
DME)(NO)] (with a single NO orientation). This orientation
of the NO, with its projection onto the porphyrin plane
approximately midway between a pair of equatorial Fe−Np
bonds, is the most common orientation.
The porphyrin core conformation in [Fe(PPIX-DME)(NO)]
is shown in the formal diagram of Figure 3 and is seen to be
The structural parameters of a number of five-coordinate
nitrosyl derivatives are provided in Table 4. Previous structure
determinations of heme nitrosyls have revealed a number of
distinct structural features. The resolution of these subtle
features requires high-quality single crystals and the extensive
and accurate data provided by modern area detector
diffractometers. Prominent among these features are an off-
axis tilt of the Fe−NO bond and a correlated asymmetry in the
equatorial Fe−Np bonds. These features seemed to be
accentuated in the structure of [Fe(DPIX-DME)(NO)] relative
to the synthetic porphyrins. The crystallization and structure
determination of the protoporphyrin derivative was undertaken
to see if indeed these differences were as large in that derivative
as well. Unfortunately the structure of [Fe(PPIX-DME)(NO)]
is disordered, especially in the axial NO ligand that obscures
and limits the statistical significance of any comparisons of
equatorial asymmetry and off-axis NO tilt.
The structural parameters found for [Fe(PPIX-DME)(NO)]
can be compared with those of [Fe(DPIX-DME)(NO)] and
other derivatives found in Table 4. Despite the disorder that
would obscure the off-axis tilt and equatorial asymmetry, the
geometrical parameters of [Fe(PPIX-DME)(NO)] are com-
parable to all other nitrosyls. This includes most parameters of
the FeNO group other than the (unresolvable) off-axis tilt,
which clearly must be greater than 2.5° and likely much larger.
Interestingly, the orientation of the major FeNO group (Figure
2) is between the pyrrole groups bearing the propionate side
chains, the same orientation as that found for [Fe(DPIX-
Figure 3. Formal diagram of [Fe(PPIX-DME)(NO] showing the
displacements of each atom from the 24-atom mean plane in units of
0.01 Å. Positive values of the displacement are toward the NO ligand.
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Article
ruffled. Although the core conformation of the deuteropor-
phyrin analogue is also ruffled, it is less so. There does not
appear to be a consistent pattern of ring conformations in the
nitrosyls listed in Table 4.
One interesting solid-state packing feature is the formation of
pairwise interacting molecules as shown in Figure 4. This
ASSOCIATED CONTENT
* Supporting Information
Figure S1 is the thermal ellipsoid diagram giving the complete
■
S
atom naming scheme. Figures S2−S4 give the experimental and
fitted Mossbauer data. Tables S1−S6 give complete crystallo-
̈
graphic details, atomic coordinates, bond distances and angles,
anisotropic temperature factors, and fixed hydrogen atom
positions for [Fe(PPIX-DME)(NO)]. A crystallographic
information file (CIF) is also available. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: scheidt.1@nd.edu.
■
Author Contributions
#G.R.A.W. and N.J.S. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Institutes of Health for support of this
research under Grant GM-38401 to W.R.S.
REFERENCES
Figure 4. Diagram illustrating the solid-state interactions for (a)
[Fe(DPIX-DME)(NO)] and (b) [Fe(PPIX-DME)(NO)]. Both top-
down and side-on views are given.
■
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complexes. The pairs of molecules are related by inversion
symmetry, and thus the two porphyrin rings are precisely
parallel. Both top-down and side-on views of the two systems
are shown along with some metrics of the interactions. The two
complexes have somewhat different lateral shifts for the two
overlapped rings. The lateral shift for [Fe(PPIX-DME)(NO)]
is 3.27 Å, which puts it into the Group I class according to the
classification scheme of Scheidt and Lee.41 The ring overlap in
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of 2.30 Å, putting this complex in the Class S group. The lateral
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than those observed in two different crystalline forms of the
[Fe(OEP)(NO)]+ cation.42,43 In those two derivatives, the very
strong pairwise interaction leads to lateral shifts of the two rings
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protoporphyrin IX dimethyl ester; DPIX-DME, dianion of deuter-
oporphyrin IX dimethyl ester; MPIX-DME, dianion of mesoporphyrin
IX dimethyl ester; Porph, dianion of a generalized porphyrin; OEP,
dianion of octaethylporphyrin; TPP, dianion of meso-tetraphenylpor-
phyrin; TPPBr4, dianion of 2,3,12,13-tetrabromo-5,10,15,20-tetraphe-
nylporphyrin; oxoOEC, dianion of (oxooctaethylchlorin),
3,3,7,8,12,13,17,18-octaethyl-(3 H)-porphin-2-onato(2-); OETAP,
dianion of octaethyltetraazaporphyrin; 3,5-MeBAFP, dianion of 3,5-
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SUMMARY
■
The spectroscopic properties (UV−vis, IR, EPR, and
Mossbauer) of the nitrosyliron(II) derivatives of proto-,
̈
deutero- and mesoporphyrin dimethyl esters are reported.
These are similar to those of synthetic porphyrin derivatives but
are consistent with small differences in electronic structure.
These are the presumed result of the asymmetric peripheral
substituents compared to the synthetic porphyrins. The
molecular structure of [Fe(PPIX-DME)(NO)] has been
determined and compared with that previously reported for
the deuteroporphyrin analogue. Unfortunately, the determi-
nation of the magnitude of equatorial Fe−Np asymmetry and
the off-axis tilt could not be made owing to the NO axial ligand
disorder.
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