Iron(II) vacataporphyrins: A variable annulene conformation inside a regular porphyrin frame

Article abstract of DOI:10.1021/ic2015176

5,10,15,20-Tetraaryl-21-vacataporphyrin (1), an annulene-porphyrin hybrid containing a butadiene fragment in the macrocycle perimeter, gives paramagnetic iron(II) complexes 2. The porphyrin 1 is devoid of one donor atom of the coordination core; hence, metal ion is bound in the macrocyclic cavity by only three pyrrolic nitrogen atoms. The coordination sphere in 2-X (where X = Cl, Br, I) is completed by a halide anion. The butadiene fragment flexibility and constraints of coordination lead to two stereoisomers with the chain oriented inward (2-i-X) or outward (2-o-X) of the macrocyclic center. Axial halide subtraction (AgBF₄ addition) leads to two new forms differing in the butadiene chain configuration. The ¹H NMR spectra of all complexes show characteristics typical for high-spin iron(II) complexes of porphyrinoids. The dependence of the relaxation times T₁ versus Fe ^II???H distances (estimated by MM+ models) for three of the isomers is in accordance with the in, out, and/or zigzag geometries. The 2-o-X complex is more reactive than 2-i-X and reacts at room temperature with dioxygen to form the iron(II) 21-oxaporphyrin complex, conserving the iron(II) oxidation state. After the addition of imidazole or excess of methanol to a mixture of 2-o-X and 2-i-X, single five-coordinate complexes with out annulene configuration and two axial ligands are formed.

Full text of DOI:10.1021/ic2015176

ARTICLE
pubs.acs.org/IC
Iron(II) Vacataporphyrins: A Variable Annulene Conformation inside a
Regular Porphyrin Frame
Ewa Pacholska-Dudziak,* Aneta Gaworek, and Lechoszaw Latos-Graz_yꢀnski*
Department of Chemistry, University of Wroczaw, ul. F. Joliot-Curie 14, 50-383 Wroczaw, Poland
S Supporting Information
b
ABSTRACT: 5,10,15,20-Tetraaryl-21-vacataporphyrin (1), an annuleneꢀporphyrin hybrid
containing a butadiene fragment in the macrocycle perimeter, gives paramagnetic iron(II)
complexes 2. The porphyrin 1 is devoid of one donor atom of the coordination core; hence,
metal ion is bound in the macrocyclic cavity by only three pyrrolic nitrogen atoms. The
coordination sphere in 2-X (where X = Cl, Br, I) is completed by a halide anion. The
butadiene fragment flexibility and constraints of coordination lead to two stereoisomers with
the chain oriented inward (2-i-X) or outward (2-o-X) of the macrocyclic center. Axial halide
subtraction (AgBF4 addition) leads to two new forms differing in the butadiene chain
configuration. The 1H NMR spectra of all complexes show characteristics typical for high-
spin iron(II) complexes of porphyrinoids. The dependence of the relaxation times T1 versus
FeII H distances (estimated by MM+ models) for three of the isomers is in accordance
3 3 3
with the in, out, and/or zigzag geometries. The 2-o-X complex is more reactive than 2-i-X
and reacts at room temperature with dioxygen to form the iron(II) 21-oxaporphyrin
complex, conserving the iron(II) oxidation state. After the addition of imidazole or excess of methanol to a mixture of 2-o-X
and 2-i-X, single five-coordinate complexes with out annulene configuration and two axial ligands are formed.
Chart 1. 5,10,15,20-Tetraphenyl-21,23-ditelluraporphyrin
’ INTRODUCTION
The chemistry of iron porphyrins has been strongly stimulated by
the need to understand the functions and catalytic processes of
various biologically important heme proteins. Iron porphyrins as
functional and spectroscopic models of the active sites of hemoglo-
bins, peroxidases, cytochromes, etc., have been synthesized and
widely studied by a number of techniques. Among them, the nuclear
magnetic resonance (NMR) of paramagnetic molecules is particu-
larly useful because it provides detailed information on the electro-
nic structure of the complexes in a solution or in a protein
pocket.1ꢀ3 The iron(III) and high-spin iron(II) d orbitals with
unpaired electron(s) interact with specific molecular orbitals of a
porphyrin and increase the spin density at specific carbon and
nitrogen atoms of the complex. Consequently, the NMR signals of
the attached protons exhibit paramagnetic shifts arranging in specific
spectral patterns dependent on the iron ion configuration.4ꢀ10
The electronic structure of iron porphyrins is controlled by the
number and field strength of axial ligands and by the macrocycle
deformations.11,12 The porphyrin distortions from planarity are
commonly observed in naturally occurring heme proteins because
the deformations are induced by the protein environment.13ꢀ15
Thus, changes in the nonplanarity may provide a mechanism for
protein modulation of the biological properties. It is suggested that
the flexibility of the porphyrin ring is important in some biocata-
lytic processes, for example, involved as a key transition-state
intermediate of the active site of ferrochelatase.14ꢀ16
porphyrins, formed by the replacement of one or more nitrogen
atoms by other heteroatom(s), i.e., heteroporphyrins sometimes
demonstrate nonplanar arrangements, but generally the distortions
are much more distinct in the metalated macrocycles (for example,
thiaporphyrin complexes).18ꢀ20 A special chapter is constituted by
carbaporphyrin metal complexes, where a hydrocarbon moiety does
not form a σ bond with a metal but remains in a strongly tilted
position with a side-on coordination or weak interaction.21
Widely studied benziporphyrin and inverted porphyrin complexes
provide good illustrations.22,23 Searching for borders of porphyrin
flexibility leads to a unique core-modified porphyrin, with a severely
distorted basic porphyrin framework, i.e., ditelluraporphyrin
Nonplanar porphyrin conformations are accomplished by the
introduction of sterically demanding residues in the porphyrin core
or at the periphery (alkylation and arylation), as well as the
coordination of metal ions of maladjusted size.17 Core-modified
Received: July 18, 2011
Published: September 27, 2011
r
2011 American Chemical Society
10956
dx.doi.org/10.1021/ic2015176 Inorg. Chem. 2011, 50, 10956–10965
|

Inorganic Chemistry
ARTICLE
Chart 2. 5,10,15,20-Tetraaryl-21-vacata- and 21,23-
divacataporphyrins
Scheme 1. Synthesis of the Iron Vacataporphyrin Complexes
(Chart 1), with one tellurophene moiety rotated and pointing with
the tellurium atom outward.24 This sort of tilt and possible rotation
was discovered also in p-benziporphyrin and naphthiporphyrin.25ꢀ27
A significant skeleton flexibility was also reached by a different
sort of core modifications: subtraction of successive nitrogen
atoms of the porphyrin core. According to the commonly accepted
[18]annulene model of porphyrin aromaticity, the two NH
moieties may be treated as bridging linkers of diaza[18]annulene,
making the porphyrin macrocycle rigid, contrary to a nonbridged
[18]annulene. Hybrid annuleneꢀporphyrin molecules were
synthesized, i.e., partially bridged diazaannulenes, preserving their
aromaticity and a porphyrin-like skeleton in general, however
showing much larger flexibility than regular porphyrins. Two steps
of bridge removal have led to 21-vacataporphyrin28 and 21,23-
divacataporphyrin (dideazaporphyrin)29,30 (Chart 2). The first
molecule shows elasticity only after metal ion insertion, but for the
second macrocycle, its flexibility results in the existence of another,
minor conformer, different from the main form in the configura-
tion of the two (bridge-devoid) annulene moieties.30
21-Vacataporphyrin reveals a unique structural flexibility trig-
gered by the coordination of cadmium(II), zinc(II), nickel(II),
and particularly palladium(II).31ꢀ33 The structural rearrange-
ments of the annulene fragment lead to two general modes of
interaction between the palladium ion and annulene moiety: σ
coordination through a deprotonated, trigonally hybridized car-
bon atom (C2) of the butadiene segment and η2-type interaction
involving the C2ꢀC3 unit of the butadiene part. The coordinated
vacataporphyrin acquires H€uckel or extremely rare M€obius topol-
ogies, readily reflected by the spectroscopic properties. Palladium
vacataporphyrin complexes reveal H€uckel aromaticity or M€obius
antiaromaticity of a [18]annulene 18π-electron circuit, applying
the butadiene fragment as a topology selector.32
Figure 1. UVꢀvis spectraof1 (black line) and 2-Br(red line) in toluene.
reaction yields a similar complex, 2-I, with axially bound iodide
(Scheme 1). The products are stable in oxygen-free solutions.
The porphyrinoid ligand with three nitrogen donors, if shaped as
presented in Scheme 1, is tridendate. Still, there is a fourth equatorial
site: the “vacated 21-position” within the porphyrin plane, fenced by
the annulene moiety. A bond formation between the central ion
and the C1ꢀC2ꢀC3ꢀC4 chain would require configuration
changes, which were observed in already published vacataporphyrin
complexes.31,32 The halide ligand makes, therefore, the firm fourth
donor. In fact, this ligand is not expected to occupy the axial position
of the square-pyramid structure but, in analogy to known vacata-
porphyrin complexes, may be rather directed toward the annulene
side, affording the coordinating environment of iron(II).
Here we introduce vacataporphyrin as a ligand for iron(II) and
1
study the system by means of H NMR, profitting from the
paramagnetic properties of the complexes to gain a complemen-
tary characterization of the isomerism. The deazaporphyrin ligand
isprobed byiron(II) asa paramagnetic sensor, and the influence of
one nitrogen absence on the spin delocalization is examined. Thus,
we report the synthesis of iron(II) vacataporphyrin complexes and
their isomerism and unusual reactivity toward dioxygen.
The electronic absorption spectrum of 2-Br is shown in Figure 1,
together with the spectrum of the free ligand 1. A metalloporphyrin-
like pattern is clearly present with a distinct Soret-like band (443 nm)
and a set of bands in the Q region. The spectral pattern resembles
that of analogous cadmium, zinc, and palladium complexes.31,32
’ RESULTS AND DISCUSSION
Synthesis. 5,20-Diphenyl-10,15-bis(4-methoxyphenyl)-21-
vacataporphyrin (1)28 reacts readily with iron(II) chloride or bro-
mide in boiling tetrahydrofuran (THF) to give paramagnetic high-
spin iron(II) vacataporphyrin complexes 2-Cl or 2-Br, respectively.
The absence of oxygen is crucial for the reaction accomplishment
(for the product purity). The macrocyclic ligand is monoanionic,
and one halide ligand is required to form a neutral complex. If iron
pentacarbonyl and iodine are used instead of a metal salt, the
1
1H NMR of 2. The H NMR spectrum of a representative
spectrum of the iron vacataporphyrin complex 2-Cl in toluene-d8 is
shown in Figure 2. The selected spectral parameters of all three
complexes 2-X (X = Cl, Br, I) are gathered in Table 1. The spectra
show characteristics typical for high-spin iron(II) porphyrins and,
10957
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
more closely, core-modified porphyrin analogues. Each spectrum
displays nine paramagnetically shifted signals outside the diamag-
netic region, which largely fall in the region from +75 to ꢀ30 ppm,
but one peak is distinctly shifted up to ꢀ163 to ꢀ220 ppm -
(depending on the axial halide). Taking into consideration the
symmetry of the vacataporphyrin ligand and the predicted 2-fold
symmetry of the formed complex (Cs), we expect only five strongly
shifted signals for 2: three pyrrole and two annulene resonances. A
careful integration indicates that the signals are differentiated by
their intensities into two sets, assigned to two isomeric forms of 2.
Similar isomers were detected for diamagnetic vacataporphyrin
complexes with cadmium(II) and zinc(II) and for paramagnetic
complexes with nickel(II).31 The first set of five signals, marked in
red, is assigned (in the T1 experiment, see below) to a form denoted
as 2-o with a typical porphyrin-like perimeter, i.e., with an out
configuration of the butadiene (annulene) fragment (Scheme 2).
All of the β-pyrrolic and 2,3-butadiene protons are shifted down-
field. On the low frequency side of the spectrum, a single strongly
shifted broad signal is present [ꢀ163 (2-I) to ꢀ220 ppm (2-Cl) in
298 K], assigned to the inner 1,4-H protons. The second set of
signals (green) comes from form 2-i, with the butadiene fragment
strongly bent in. For this form, four signals with large paramagnetic
shifts were readily detected. The missing fifth signal of 1,4-H was
eventually identified in the inversionꢀrecovery experiment in the
diamagnetic region (ꢀ0.93 ppm for 2-i-Cl) and, independently, in
the 2H NMR spectrum of specifically deuterated 2-Br-dx and 2-I-dx
complexes (Table 1).
Signal Assignment: Deuteration and T1 Studies. The assign-
ment of signals for each form of 2-X was done on the basis of a
1
detailed H NMR signal intensity comparison of specifically
deuterated compounds and T1 relaxation time analysis. 2D
NOESY and COSY experiments were helpful in a few favorable
cases only. The deuterated ligand 1-dx was synthesized as pub-
lished before,31 and the degree of deuteration (x) varied much
depending on the reaction conditions. In every case, deuteration
was attained not only at the 1 and 4 positions of deuterium
substitution as expected but also at the β-pyrrole positions as well
and in a very diverse level (14ꢀ77%) at the 2,3-carbon atoms of
the butadiene chain. Eventually, the degree of deuteration for each
position was precisely determined for each sample by integration
1
of the H NMR signals of a free ligand and was the basis for
β-pyrrole and butadiene signal assignment.
Scheme 2. Conformational Rearrangement of Two Isomers
of Complexes 2-X (X = Cl, Br, I)
Figure 2. 1H NMR spectra (300 K, 600 MHz, toluene-d8) of (A) 2-Cl
(isomer out marked in red and isomer in in green) (B and C) the
diamagnetic region. Spectra were acquired by an inversionꢀrecovery
technique, with delay times τ = 2 ms for part B and τ = 100 ms for part C;
Ar denotes the 4-methoxyphenyl group.
1
Table 1. H NMR Chemical Shifts for 2-Cl, 2-Br, and 2-I, Including meso-Aryl Signals for 2-Cl (Data in Toluene-d8 Solutions, at
300 K, Except for Footnotes a and b)
isomer 2-o
isomer 2-i
butadiene
pyrroles
7,18-H
butadiene
2,3-H
pyrroles
7,18-H
1,4-H
2,3-H
12,13-H
8,17-H
1,4-H
12,13-H
8,17-H
2-Cl
2-Br
2-I
ꢀ220.05
ꢀ195.29
ꢀ163.13
25.98
24.79
23.26
75.19
75.74
75.61
53.47
58.89
65.11
15.26
17.33
20.15
ꢀ0.93
3.90a
3.83b
76.15
71.33
65.11
33.07
35.05
37.40
ꢀ28.33
ꢀ29.86
ꢀ31.06
44.64
47.38
52.93
aryl 2-o-Cl
aryl 2-i-Cl
ortho
meta
para
9.35
OCH3
ortho
meta
para
9.62
OCH3
3.41
phenyl
13.32
ꢀ0.24
ꢀ2.53
10.94
10.70
3.38
11.03
13.76
2.81
8.82
8.20
4.87
4-methoxy-phenyl
4.07
a Detected in 1,4-deuterated 2-Br in 300 K (benzene) in a 2H NMR experiment. b Detected in 1,4-deuterated 2-I in 350 K (toluene) in a 2H NMR
experiment.
10958
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
Table 2. Relaxation Times T1 for 2-Cl Measured by an
InversionꢀRecovery Technique
T1 (ms)a
proton name
2-o-Cl
2-i-Cl
0.75
1,4-H
0.14
2,3-H
8.6
0.17
pyrrole 8,17
pyrrole 7,18
pyrrole 12,13
o-Ph
4.6
6.9
11.9
4.8
4.4
3.6
4 < T1 < 7
6.7; 6.7
6.0
Figure 3. 2H NMR spectrum (77 MHz, toluene, 350 K) of 2-I. Partially
deuterated pyrrole positions (7, 8, 17, and 18) give signals of smaller intensity.
o-Ar
6.5; 6.6
27.5
m-Ph
∼25
The 2H NMR spectrum (Figure 3) measured for the deuter-
m-Ar
31.0; 15 < T1 < 60
39.0; 37.6
52.1
p-Ph
75.1
ated complex 2-Idx allowed for the unambiguous identification of
1
OCH3
132.9
115.6
1,4-H signals, particularly eluding for the in form. H NMR of
2-Idx measured at different temperatures allowed assignment of
the porphyrin perimeter signals.
a All data for 298 K, toluene-d8, 600 MHz.
The assignment of two sets of signals to respective structures
2-o-Cl and 2-i-Cl was done on the basis of the relaxation times.
For 2-Br and 2-I, the assignments followed those for 2-Cl. We
considered the significant line broadening of resonances of
annulene protons, 1,4-H and 2,3-H, expressing short T2 (T2*)
relaxation times, caused by the proximity of the paramagnetic
iron(II) center. The 1H NMR pattern with one such broad signal
was assigned to the geometry of 2-o-X with 1,4-H pointing
toward iron(II), whereas the second set of resonances with two
broad peaks was attributed to 2-i-X, where both 1,4-H and 2,3-H
of a strongly bent butadiene moiety are expected to relax rapidly.
For semiquantitative analysis, T1 relaxation times were chosen
because they are independent of exchange effects, contrary to T2.
Assuming that dipolar relaxation dominates over contact relaxa-
tion, as is the common situation for iron porphyrins, the inverse
of relaxation times T1 is proportional to τc/r6, where τc is the
rotational correlation time of a molecule and r is the distance
between the (relaxing) nucleus (here a proton) and a paramag-
netic metal center [iron(II)]. Simply
Figure 4. Dependencies T1 on the Fe H distance in logarythmic
scales for 2-o-Cl (left) and 2-i-Cl (right).
3 3 3
T1 ∼ r6
where the proportionality constant is equal for all of the protons of
one molecule. The T1 relaxation times were measured for 2-Cl by
the inversionꢀrecovery experiments in toluene-d8 at three differ-
ent temperatures. The data for 298 K are gathered in Table 2.
The values fall into distinct ranges: (1) below 1 ms for the
crucial 1,4-H of both forms and 2,3-H for 2-i-Cl, being in the
iron(II) proximity; (2) 4ꢀ12 ms for β-pyrrolic, 2,3-H of 2-o-Cl,
and o-aryl protons; (3) 25ꢀ40 ms for m-aryl protons; (4) 50ꢀ75
ms for p-phenyl groups; (5) above 100 ms for methoxyl groups.
The above equation leads to a linear dependence between T1 and
r in a bilogarithmic scale, with the slope equal to 6. Figure 4 shows
the T1 dependences on r for both 2-o-Cl and 2-i-Cl. The r values
are obtained from MM+ models (Figure 5) and are averaged for
Figure 5. MM+ models of 2-o-Cl and 2-i-Cl (in side views, aryl groups
omitted for clarity).
relaxation mechanisms operating (which is consistent with the
presumed domination of the dipolar relaxation).
1
T1 data analysis, together with 2D COSY and NOESY spectra,
allowed assignment of all of the aryl signals (Figure 1C and
Table 1). The 5,20-meso-phenyls of each form give one set of
orthoꢀmetaꢀpara signals, proving the fast rotation of the rings.
On the contrary, both ortho and meta protons of 10,15-meso-
methoxyphenyls are differentiated (at 300 K), distinguishing
between the “up” and “down” side of the macrocycle.
protons equivalent in the H NMR spectrum. The fit is suffi-
ciently accurate to confirm the proposed conformations.
Strikingly, the NMR features of the 2,3-H signal of 2-o-Cl are
similar to those of β-pyrrole resonances regarding the chemical
shift (26 ppm), half-width (50 Hz), and relaxation time T1 (8.6
ms, all for toluene-d8, 298 K). For this “β-butadiene” position,
the nitrogen donor atom seems to be unnecessary for the
10959
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
The large negative chemical shifts of 1,4-protons of 2-o-X
(ꢀ163 to ꢀ220 ppm at 298 K, depending on the axial ligand)
are without precedence for iron(II) porphyrins. Very large but
positive isotropic shifts were recorded for the inner protons of the
CꢀH groups of iron(II) carbaporphyrin complexes. For several
complexes of carbaporphyrinoids, the rings with internal carbon
atoms are sharply bent from a porphyrin plane, allowing side-on
interaction of a central ion with the inner CꢀH fragment. The
uniquely large positive isotropic shift of the inner hydrogen atom
[over 1000 ppm, for an iron(II) inverted porphyrin] is a diagnostic
sign of FeII CꢀH agostic interaction.34ꢀ37 The geometric rela-
3 3 3
Figure 6. 1H NMR of 2-I in chloroform-d after 8 h at 330 K. Solid
circles denote 2-I and empty circles growing peaks of 2-Cl. Isomer out is
in red and in in green. Arrows represent EXSY peaks in the NOESY
spectrum; impurities are marked by asterisks: 3-I and 3-Cl.
tionship of iron(II) and CꢀH is, however, essentially different
from that of 2-o-X.
The paramagnetic shifts of 2-o-X and 2-i-X are generally in the
range typical for high-spin iron(II) core-modified porphyrins, i.e.,
carbaporphyrins, heteroporphyrins, inverted, N-substituted por-
phyrins, and can be explained by a model typically applied to these
compounds.34ꢀ39 In the case of a high-spin iron(II) center,
(dxy)2(dxzdyz)2(dz2)1(dx2ꢀy2)1, both σ and π routes of spin-density
delocalization can operate. The contact shift predominates for the
resonances of protons in β positions, yielding their downfield
shifts. The typical delocalization pathways involve delocalization
through a σ framework by way of a σ donation to the half-occupied
iron(II) dx2ꢀy2 orbital. The differentiation of paramagnetic shifts
for 2-X is characteristic for the above-mentioned porphyrinoids
and markedly larger than that in porphyrins of higher symmetry
and may be accounted for by specific π-delocalization mechanisms
discussed in detail for iron(III) porphyrins.40,41
Conformational Rearrangements of 2-X. The relative intensity
of the signals of the 2-o-X and 2-i-X forms depends on an axial ligand,
the solvent, and the temperature, but, in general, it is not simply a
function of these parameters. The ratio varies to some extent from
one synthesis to another and from one sample to another.
The controlled and reproducible conversion of form in to
form out is achieved by heating a sample (a mixture of out and in
isomers) in toluene, above 340 K. Up from this temperature, the
ratio [out]:[in] is a function of the temperature and is deter-
mined by an anionic ligand. Thus, only at higher temperatures
does isomerization occur at a reasonable rate and is thermo-
dynamic equilibrium reached. The mechanism possibly involves
axial ligand dissociation because axial ligand exchange also is
observed only at higher temperatures (see below).
In an NMR experiment, a sample of 2-I was dissolved in
toluene-d8 and 1H NMR spectra were measured in the tempera-
ture range of 200ꢀ370 K with parameters chosen to correctly
record the intensities (D1 = 1ꢀ0.3 s and SW = 220 ppm). The
ratio of [2-o-I]:[2-i-I] (K) was calculated from integration of
nonoverlapping signals after a baseline correction. In the tempera-
ture range of 200ꢀ320 K, the molar ratio [2-o-I]:[2-i-I], equal for
an exemplary sample to 0.95:1, was not affected by the tempera-
ture changes even in longer periods of time (24 h). Heating the
solution to 340 K and above induced the ratio changes, and the
relative concentration of the out form increased from K = 0.95:1 to
1.15:1 at 340 K and finally to 1.30:1 at 370 K. Upon cooling of the
solution, the ratio went back to 1.15:1 (at 340 K) and stopped
there, suggesting that the conformational exchange was practically
frozen at this temperature. In contrast to 2-I, the preference for
the 2-i-X form at higher temperature has been observed for 2-Br
(K = 0.9) and 2-Cl (K = 0.7, values at 360 K in toluene-d8).
Axial Ligand Exchange. Another dynamic process was de-
tected in a solution of the complex, that is, an axial ligand
exchange, traced easily by 1H NMR spectroscopy. For 2-I
dissolved in chloroform-d at elevated temperature (330 K),
replacement of axial iodide with chloride, originating from the
solvent, CDCl3, was observed. The reaction proceeds for both
out and in forms, although the latter reacts more rapidly. After
8 h at 330 K, 28% of 2-o-I converted into 2-o-Cl and 38% of 2-i-I
converted into 2-i-Cl. The calculation was based on the assump-
tion that the axial ligand exchange is much faster than out a in
isomerization. In fact, during this experiment, the overall
[out]:[in] ratio was practically constant (39% of isomer in
before the reaction and 41% after 8 h). Moreover, at 330 K
out a in transformation was not observed in toluene-d8.
The NOESY spectrum measured at 330 K for the mixture of
2-I and 2-Cl in chloroform-d showed EXSY cross-peaks (mixing
times 0.01 and 0.02 s) between the respective signals of 2-o-I and
2-o-Cl, likewise 2-i-I and 2-i-Cl (Figure 6). The exchange
correlations between forms out and in were not detected.
Conformational Rearrangements of 2-BF4. The previously
published31,32 and aforementioned results indicate that flexibility
seems to be an immanent quality of the vacataporphyrin ligand
and that some tendencies are general for several metal ions.
There are at least six possible reasonable conformational forms of
metal(II) vacataporphyrin complexes,32 and their relative ener-
gies (and energy barriers), depending on specific ions, may be
calculated, whereas their physical accessibility has to be found for
each case. That is to say, in and out forms were detected for most
of the studied metals, i.e., cadmium(II), nickel(II), zinc(II), and,
as shown above, iron(II). Their relative concentrations can be
modulated by the temperature or light irradiation. Axial chloride
subtraction from the palladium(II) vacataporphyrin complex
resulted in profound conformational changes of the macrocycle,
including the formation of an antiaromatic 18π-electron species
with a M€obius strip delocalization pathway. Prompted by the
latter studies, we have examined a similar reaction procedure for
iron(II) complexes (expecting M€obius isomers or at least new
isomers) to analyze the paramagnetic analogues. Consequently,
the 1H NMR monitored titrations of 2-Cl, 2-Br, and 2-I with a
AgBF4 solution were done, resulting in the identification of two
new sets of peaks (Figure 7B), attributed to new forms of iron(II)
vacataporphyrin. Their spectral patterns are independent from
an axial halide in starting complexes.
The first set of signals (purple triangles in Figure 7B) is
composed of five resonances of equal intensity, within the
iron(II) vacataporphyrin chemical shift range, with differentiated
half-widths. This set of signals, denoted as 2-S (for symmetric), is
ꢀ
attributed to a complex of 2-fold symmetry, with BF4 as the
counterion. The axial coordination of water was excluded
because a reaction conducted in strictly water-free conditions
10960
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
in a drybox did not suppress the formation of 2-S. The T1
relaxation times of the five peaks are differentiated, falling,
however, exactly in the range of 2-o-Cl and 2-i-Cl T1 values.
Three values (11.5, 9.6, and 7.5 ms) fit in the range observed for
β-pyrrole or “β-annulene” protons, and the other two are much
shorter but are not similar (1.4 and 0.2 ms), suggesting their
proximity to the paramagnetic ion and attributed to 1,4-H and
2,3-H. Independently, an experiment with a specifically deuter-
ated complex allowed assignment of the signal with T1 = 1.4 ms
to 1,4-H. Evidently, the T1 values are similar to those of 2-i-Cl
with the 2,3-H proton closer to iron(II) than 1,4-H. Among
possible iron(II) vacataporphyrin stereoisomers consistent with
2-S spectral characteristics, one can construct at least three (2-i+
corresponding to the 2-i-Cl form and 2m+ and 2m0+ of M€obius
topology) that match steric constraints imposed by T1 data
(Scheme 3). The dependence of T1 vs r (the Fe H distances
3 3 3
are estimated by appropriate MM+ models; see the Supporting
Information) in logarithmic scales gives a fairly linear graph for
each considered geometry, ruling out a definitive assignment of
the structure based upon the available spectroscopic data.
The second 1H NMR pattern, denoted as 2-A (for asymmetric),
consisting of 10 signals of equal intensity (blue squares, Figure 7B)
is placed in a much wider window (+115 to ꢀ60 ppm) and
provides evidence for full asymmetry of this form. The signal
count is assigned to six pyrrole and four butadiene protons. Two
signals at both borders of the spectrum are distinctly broader
than others, suggesting the proximity of the respective protons
to the paramagnetic center. The T1 relaxation times of all
10 resonances are much shorter than those for all other forms
(3 ms for three signals, ∼1 ms for seven signals, and below 1 ms
for the two broadest signals). The asymmetric isomers (2-a+,
+
2-a0 ), which may explain the observed 10-peak NMR pattern,
are shown in Scheme 4. The presence of two significantly broad
butadiene resonances favors the structure 2-a+ with two protons
(2,4-H) closer to the iron(II) center. There are two hypothetical
structures with C2ꢀFeII σ-bond formation: with or without
C2ꢀH2 bond dissociation (structures 2-C and 2-C0, Scheme 4).
The first possibility (Csp2-M) was observed for palladium vaca-
taporphyrin complexes, but in the case of iron(II), the observa-
tion of 10 peaks excludes formation of 2C. In any case of FeꢀC
σ-bond formation, the products of demetalation proceeded with
deuterated acid, DCl (in D2O), should give a free ligand
selectively deuterated at C2. In fact, demetalation proceeded
smoothly and quantitatively, but a monodeuterated product was
never detected, excluding the σ-C coordination.
Figure 7. 1H NMR (600 MHz, toluene-d8, 300 K) spectra: (A) 2-Br;
(B) [2+][BF4ꢀ], 2-Br after the addition of approximately 2 equiv of
AgBF4; (C) same solution after filtration under unaerobic conditions
and Et4NBr (excess) addition. Annotations: p = pyrrole, red circle, 2-o-
Br; green circle, 2-i-Br; blue square, 2-A-BF4; purple triangle, 2-S-BF4.
The ratio of new forms, [2-S]:[2-A], changes from one sample
to another, but it is not dependent on the initial relative
concentration of [2-o-X]:[2-i-X]. The formation of a 2-S/2-A
mixture from 2-o-X/2-i-X is reversible because Et4NCl or Et4NBr
addition to 2-S/2-A (after removal of the solid byproduct, AgX)
Scheme 3. Isomers of the Vacataporphyrin Complexes of 2-Fold Symmetry
Scheme 4. Asymmetric Isomers of the Iron(II) Vacataporphyrin Complexes
10961
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
recovers 2-o-X/2-i-X but in a ratio different from the initial one.
Methanol-d4 addition transforms the 2-S/2-A mixture into a five-
coordinate 2-o-(MeOD)2+ complex (see below).
A solution of 2-S/2-A is not stable in air or at higher
temperature. Its oxidation with dry dioxygen gives an iron(II)
21-oxaporphyrin complex (identified after Et4NCl addition) and
free ligand 1 (see below).
an exemplary nitrogen ligand: imidazole. In the course of
titration, a difference in the reactivity of the isomers toward the
nitrogen ligand became evident. The first portions of imidazole
reacted with 2-o-I and the signals of 2-o slightly moved, while the
signals of 2-i-I were not disturbed. This may be interpreted as the
formation of five-coordinate 2-o-I-Im with two different axial
ligands, which remains in fast equilibrium with 2-o-I. After the
addition of 0.7 equiv of imidazole, new signals appeared,
attributed to [2-o-Im2]+, which grow at the expense of signals
of a 2-o-I-Im a 2-o-I mixture and, after these are almost
consumed, at the expense of 2-i-I.
Five-Coordinate Iron(II) Vacataporphyrin Complexes. The
addition of an excess of methanol-d4 (50% v/v) to a toluene
sample of2 beinga mixtureof isomers, out/inor S/A, converts the
initial forms into a single five-coordinate bis(alcohol) cationic
complex [2-(MeOD)2]+. The 1H NMR spectrum of the 2-o-Cl/
2-i-Cl sample (toluene-d8) measured immediately (about 3 min)
after methanol-d4 addition showed the presence of a small
percentage of the in form, but after 15 min, the only form present
in the solution was [2-o-(MeOD)2]+ (Figure 8B). As expected, an
excess of the solvent acting as a ligand and saturating the axial
positions favors the form out, where the butadiene moiety does
not block the second axial coordinating site of the iron ion. The
out conformation of the annulenic part of the vacataporphyrin
ligand is preserved when the solvents are evaporated to dryness,
and the remaining solid is dissolved in toluene-d8. The original
axial ligand (chloride) replaced methanol, and identical chemical
shifts were registered like for the original toluene solution of 2-o-
Cl (excluding any axial ligand exchange) and almost pure isomer
out was obtained (Figure 8C and Scheme 5).
The NMR pattern of [2-o-Im2]+ signals, with four vacatapor-
phyrinsignals shifted downfield in the range 70ꢀ25ppm, is similar
to that of the bis(alcohol) complex attributed to the out form. For
[2-o-Im2]+, the 1,4-H resonance strongly upfield shifted was
detected at ꢀ118.3 ppm. Paramagnetically shifted protons of
coordinated imidazole were easily assigned by the reaction with
D2O (N1ꢀH was exchanged to N1ꢀD) and with specifically
deuterated imidazole (imidazole-1,2-d2). The 4-H imidazole signal
has not been detected probably because of its large width. The
relative intensity of the imidazole and porphyrin signals is con-
sistent with the above bis(imidazole) complex stoichiometry.
Oxygenation of 2-o-X to Iron(II) 21-Oxaporphyrin. The 1H
NMR samples (toluene-d8) of 2-X prepared in dry and oxygen-
free atmospheres of a glovebox are stable for weeks at the low
temperature of a freezer (about ꢀ18 °C). When the solution is
exposed to dry dioxygen at 300 K, 2-o-X undergoes slowly
(hours) an unprecedented oxygenation, yielding the iron(II) 21-
To study in detail the axial ligand exchange and formation of
five-coordinate complexes, 1H NMR titration of 2-I was done for
1
oxaporphyrin complex characterized previously in detail by H
NMR38 3-X (Scheme 6). Regarding solely the porphyrin’s
building blocks, a butadiene unit is oxidized to a furan ring
without a change of the porphyrin perimeter. In fact, the reaction
is, in some sense, reverse to the synthesis of vacataporphyrin,
achieved by extrusion of tellurium from 21-telluraporphyrin.28
1
The H NMR experiment following the reaction of 2-I with
dioxygen is presented in Figure 9. As demonstrated by a char-
acteristic spectroscopic pattern (blue dots, Figure 9 B), the iron-
(II) oxidation state has been conserved in the course of the
Scheme 6. Oxygenation of 2-o-X
Figure 8. 1H NMR spectra (300 K) of (A) [2-o-(Im)2]+ in toluene-d8,
imidazole partially deuterated at NH, (B) [2-o-(MeOD)2]+ in methanol-
d4/toluene-d8 (1:1, v/v), and (C) 2-o-Cl in toluene-d8. Traces of 2-i-Cl
are marked by green circles; impurity 3-Cl is marked by asterisks.
Scheme 5. Formation of Five-Coordinate Vacataporphyrin Complexes
10962
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
macrocyclic transformation. The resulting iron(II) 21-oxapor-
phyrin is known to stabilize low oxidation states of iron, and
3-X is air-stable. While 2-o-I is gradually consumed in the reaction,
2-i-I remains unchanged (Figure 9B) provided that the reaction is
carried out at temperatures below 330 K to prevent any out a in
isomerization. After 8 h (at 300 K), the solution contains only 2-i-I
and 3-I (Figure 9C). Heating this sample for a few minutes at
370 K restored the equilibrium concentration of 2-i-I (Figure 9D).
Integration of the signals of 2-o-I, 2-i-I (used here as an intensity
standard), and 3-I through the experiment shows a significant
difference between the ratio [2-o-I]:[2-i-I] in the initial sample and
the ratio [3-I]:[2-i-I] in the final solution and indicates that the yield
of the 2-o-I f 3-I transformation is far from quantitative. The
important side products are the free ligand 1 and μ-oxo dimer of
iron(III) oxaporphyrin4(Chart3),38 marked by * and # in Figure 9C.
Attempts to trap any intermediates at low temperature
(200ꢀ240 K) were unsuccessful because the reaction is relatively
slow and the intermediates must have very low concentrations. A
facile formation of 4 (which is not formed from 3-X just under O2)
gives, however, some suggestions of possible intermediates, pre-
organized to form μ-oxo dimer 4. One of the conceivable
mechanisms of the transformation of 2-o-X to 3-X is presented
in Scheme 7. The first step, activating the inert O2 molecule, is
probably its binding to the iron(II) ion, sterically possible only for
the 2-o-X isomer with one side of the macrocycle plane available
for oxygen attack. In the more inert 2-i-X form, one side of
the complex is blocked by an axial halide X and the opposite by
the bent butadiene chain. The second step, the formation of
a ꢀOꢀOꢀ bridge between iron(II) and C2, is relevant to a
mechanism proposed for the conversion of verdoheme to
biliverdin.42 The following processes are ꢀOꢀOꢀ cleavage and
intramolecular oxidation. The activated CꢀH bonds are C1ꢀH1
and C4ꢀH4, the closest to the bound oxygen molecule for the
out conformation.
The reaction mixture after demetalation with concentrated
hydrochloric acid (stirring for 30 min at room temperature), was
searched for other oxidation products, like 2-hydroxy- or 2-
oxovacataporphyrin, but none was detected by 1H NMR or mass
spectrometry. In fact, the products of demetalation were neu-
tralized with triethylamine and identified as a surprisingly clean
mixture of vacataporphyrin free base and 21-oxaporphyrin.
Conclusions. An annuleneꢀporphyrin hybrid, vacatapor-
phyrin, is a porphyrin devoid of one nitrogen or, in other words,
having a four-carbon chain in the macrocyclic perimeter in place
of one pyrrole ring. It acts as a versatile ligand, binding a variety of
transition-metal ions. Here the high-spin iron(II) center allowed
us to study the conformational changes of the vacataporphyrin
perimeter by means of relaxation time (T1) studies and 1H NMR
paramagnetic shifts. The results gave us another argument that
the flexibility of the annulene fragment is an immanent quality of
vacataporphyrin and may be controlled by the axial ligand
addition or subtraction and temperature.
Figure 9. 1H NMR spectra (600 MHz, 300 K, toluene-d8) of (A) 2-I,
(B) the sample after 3 h in a dry oxygen atomosphere (3-I is marked with
blue dots), (C) the sample after 8 h (*, the NH signal of 1; #, signals of μ-
oxo dimer 4); (D) the sample from part C after 5 min in 370 K. Labeling:
red dots, 2-o-I; green dots, 2-i-I; blue dots, 3-I.
Chart 3. Iron(III) Oxaporphyrin μ-Oxo Dimer
Originally, two isomers have been detected for the vacatapor-
phyrin iron(II) complex with one axial halide anion, differing in
the configuration of the annulene fragment, which acquires
Scheme 7. Proposed Mechanism of 2-o-X Oxidationa
a Aryl substituents are not presented for clarity.
10963
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
planar (isomer out) or bent (isomer in) geometry. On the other
hand, axial halide subtraction allowed us to observe two more
isomeric forms of iron(II) vacataporphyrin with a BF4ꢀ counter-
ion differentiated by conformation of the butadiene linker.
Moreover, there is a significant difference in the reactivity of
the isomers, connected with the different accessibilities of the
iron center for a reagent. Solely, the isomer out reacts with
dioxygen, which leads iron(II) 21-oxaporphyrin. The mechanism
of the reaction involves the peculiar incorporation of an oxygen
atom in the butadiene fragment to form a furan ring. The
intramolecular reactivity toward dioxygen bears some impor-
tance for the initial stages of verdoheme clevage in the course of
coupled oxidation of heme.
were added, and the solution was refluxed under nitrogen for about 20
min. The solvent was distilled off, still under nitrogen. The flask with the
dry residue was immediately introduced to the glovebox, and 1H NMR
samples were prepared by extracting the solid with toluene-d8 or CDCl3
and filtering the suspension through glass wool directly to an NMR tube.
1H NMR for 2-o-I (500 MHz, toluene-d8, 298 K): δ 75.2 (2H, pyrr
12,13), 64.5 (2H, pyrr 7,18), 23.1 (2H, vac 2,3), 20.3 (2H, pyrr 8,17),
ꢀ162.5 (2H, vac 1,4). 1H NMR for 2-i-I (500 MHz, toluene-d8, 298 K):
δ 64.5 (2H, vac 2,3), 52.7 (2H, pyrr 8,17), 37.2 (2H, pyrr 12,13), ꢀ30.9
(2H, pyrr 7,18). HRMS (ESI). Calcd for [M ꢀ I]+ (C46H36N3O255Fe+):
m/z 716.1999. Found: m/z 716.1992. UVꢀvis (toluene; λmax, nm): 443
(4.4), 617 (sh), 657 (3.7), 714 (3.6).
2-BF4. A sample of 2-Cl (or 2-Br or 2-I) in an NMR tube was titrated
with a saturated toluene-d8 solution of AgBF4 under NMR control at
300 K. When the formation of 2-BF4 was complete according to 1H NMR,
the sample was transferred to a glovebox, AgX was filtered off, and the
clear sample was used for further studies.
’ EXPERIMENTAL SECTION
1H NMR for 2-A-BF4 (600 MHz, toluene-d8, 300 K): δ 113.1, 72.9,
Solvents and Reagents. Chloroform-d was passed through basic
Al2O3. All of the NMR solvents (toluene, toluene-d8, chloroform-d, and
methanol-d4) were deoxygenated by a freezeꢀpumpꢀthaw technique.
THF was distilled under dinitrogen over sodium/benzophenone.
Imidazole-1,2-d2 was prepared according to the reported method.43
Vacataporphyrin [5,20-diphenyl-10,15-bis(4-metoxyphenyl)-21-
vacataporphyrin] has been obtained according to the previously de-
scribed procedures.31 The deuterated ligand 1-dx was synthesized as
published before,31 and the degree of deuteration (x) varied much
depending on the reaction conditions, mainly the reaction time (Table
S2 in the Supporting Information). The reaction time was optimized to
maximize the yield for two available DCl concentrations: a higher
concentration of DCl (35% in D2O) required shorter reaction time
(50ꢀ60 min) and yielded a ligand with a generally lower degree of
deuteration. A higher deuterium substitution level was obtained for
longer reaction time, 1 h 30 min, applied for 20% DCl.
1
62.1, 48.6, 39.0, 34.5, 28.0, 14.3, ꢀ55.1. H NMR for 2-S-BF4 (600
MHz, toluene-d8, 300 K): δ 76.4 (1H, 2,3-H), 44.4 (1H, pyrr), 38.1 (1H,
pyrr), 32.9 (1H, 1,4-H), 11.9 (1H, pyrr).
MM+ Models. In the minimization procedure, we have used the
standard MM+ parametrization of the HyperChem program with the
exception of the iron coordination surroundings, where we have
imposed the constraints reflecting the high-spin state of the iron(II)
ion applying the respective data determined previously for iron(II) 21-
thiaporphyrin.19
Instrumentation. NMR spectra were recorded on Bruker Avance
500 MHz and Bruker Avance III 600 MHz spectrometers. UVꢀvis
electronic spectra were recorded on a Varian Cary 50 Bio spectrometer.
Mass spectra were recorded on a Bruker micrOTOF-Q spectrometer
using the electrospray ionization (ESI) technique.
2-Cl: Vacataporphyrin 128,31 (13 mg, 0.020 mmol) was dissolved in
freshly distilled THF (15 mL), and nitrogen was bubbled through the
’ ASSOCIATED CONTENT
solution for 20 min. FeCl2 4H2O (11 mg, 0.057 mmol) was added, and
3
S
Supporting Information.Dependencies T1 on the Fe
H
b
3 3 3
the solution was refluxed under nitrogen for about 20 min. The color
changed from peach-red to bright green, and the solvent was distilled off,
still under nitrogen. The flask with the dry residue was immediately
1
distance in logarythmic scales, H NMR chemical shifts, and
percentage of deuteration of different sites of ligand 1. This
material is available free of charge via the Internet at http://pubs.
acs.org.
1
introduced to the glovebox, and H NMR samples were prepared by
extracting the solid with toluene-d8 and filtering the suspension through
glass wool directly to an NMR tube.
1H NMR for 2-o-Cl (500 MHz, toluene-d8, 298 K): δ 75.2 (2H, pyrr
12,13), 53.4 (2H, pyrr 7,18), 26.0 (2H, vac 2,3), 15.4 (2H, pyrr 8,17), 13.3
(4H, o-Ph), 10.9 (4H, m-Ph), 10.7 (2H, m-Ar), 9.4 (2H, p-Ph), 4.1 (6H,
OCH3), 3.4 (2H, m-Ar), ꢀ0.2 (2H, o-Ar), ꢀ2.5 (2H, o-Ar), ꢀ220.2 (2H,
vac 1,4). 1H NMR for 2-i-Cl (500 MHz, toluene-d8, 298 K): δ 75.2 (2H,
vac 2,3), 44.7 (2H, pyrr 8,17), 33.1 (2H, pyrr 12,13), 13.8 (2H, o-Ar), 11.0
(4H, o-Ph), 9.6 (2H, p-Ph), 8.8 (4H, m-Ph), 8.2 (2H, m-Ar), 4.9 (2H,
m-Ar), 3.4 (6H, OCH3), 2.8 (2H, o-Ar); ꢀ28.4 (2H, pyrr 7,18). HRMS
(ESI). Calcd for [M ꢀ Cl]+ (C46H36N3O255Fe+): m/z 716.2011. Found:
m/z 716.1992. UVꢀvis [toluene; λmax, nm (log ε)]: 443 (4.4), 550 (3.3),
617 (sh), 651 (3.6), 711 (3.5);
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: lechoslaw.latos-grazynski@chem.uni.wroc.pl (L.L.-G.),
ewa.dudziak@chem.uni.wroc.pl (E.P.-D.). Tel: +48 71 3757256.
Fax: +48 71 3282348. Homepage: http://llg.chem.uni.wroc.pl/.
’ ACKNOWLEDGMENT
Financial support from the Ministry of Science and Higher
Education (Grant N204 013536) is kindly acknowledged.
2-Br was synthesized in the same manner using FeBr2 instead of
1
FeCl2 4H2O. H NMR for 2-o-Br (500 MHz, toluene-d8, 298 K): δ
3
76.0 (2H, pyrr 12,13), 59.0 (2H, pyrr 7,18), 25.0 (2H, vac 2,3), 17.5 (2H,
pyrr 8,17), ꢀ193.0 (2H, vac 1,4). 1H NMR for 2-i-Br (500 MHz,
toluene-d8, 298 K): δ 71.7 (2H, vac 2,3), 47.5 (2H, pyrr 8,17), 35.1 (2H,
pyrr 12,13), ꢀ30.0 (2H, pyrr 7,18). HRMS (ESI). Calcd for [M ꢀ Br]+
(C46H36N3O255Fe+): m/z 716.1999. Found: m/z 716.1992. UVꢀvis
(toluene, λmax, nm): 443 (4.4), 617 (sh), 655 (3.7), 714 (3.8).
’ REFERENCES
(1) Bertini, I.; Luchinat, C.; Parigi, G.; Pierattelli, R. Dalton Trans.
2008, 3782–3790.
(2) Rivera, M.; Zeng, Y. J. Inorg. Biochem. 2005, 99, 337–354.
(3) Turano, P. Heme Acquisition by Hemophores: A lesson from
NMR. In Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M.,
Guilard, R., Eds.; World Scientific: Singapore: 2010; pp 339ꢀ365.
(4) Bertini, I.; Turano, P.; Vila, A. J. Chem. Rev. 1993, 93, 2833–2932.
(5) Bertini, I.; Luchinat, C. Coord. Chem. Rev. 1996, 150, 29–75.
2-I. Vacataporphyrin 1 (25 mg; 0.038 mmol) was dissolved in freshly
distilled THF (15 mL), and nitrogen was bubbled through the solution
for 20 min. Fe(CO)5 (37 mg, 0.19 mmol) and I2 (10 mg, 0.079 mmol)44
10964
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965

Inorganic Chemistry
ARTICLE
(6) Goff, H. M. Nuclear Magnetic Resonance of Iron Porphyrins. In
Iron Porphyrins; Lever, A., Ed.; Addison-Wesley: Reading, MA, 1983; pp
237ꢀ281.
(36) Myꢀsliborski, R.; Rachlewicz, K.; Latos-Graz_yꢀnski, L. Inorg.
Chem. 2006, 45, 7828–7834.
(37) Hung, C.-H.; Chang, F.-C.; Lin, C.-Y.; Rachlewicz, K.; Stepieꢀn,
)
(7) Walker, F. A. ProtonNMRandEPRSpectroscopyof Paramagnetic
Metalloporphyrins. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000; pp 81ꢀ183.
(8) Walker, F. A. Chem. Rev. 2004, 104, 589–616.
M.; Latos-Graz_yꢀnski, L.; Lee, G.-H.; Peng, S.-M. Inorg. Chem. 2004,
43, 4118–4120.
(38) Pawlicki, M.; Latos-Graz_ynꢀski, L. Inorg. Chem. 2002, 41, 5866.
(39) Balch, A. L.; Chan, Y.-W.; La Mar, G. N.; Latos-Graz_yꢀnski, L.;
Renner, M. W. Inorg. Chem. 1985, 24, 1437.
(40) Cheng, R.-J.; Chen, P.-Y.; Lovell, T.; Liu, T.; Noodleman, L.;
Case, D. A. J. Am. Chem. Soc. 2003, 125, 6774–6783.
(41) Wojaczyꢀnski, J.; Latos-Graz_yꢀnski, L.; Hrycyk, W.; Pacholska, E.;
Rachlewicz, K.; Szterenberg, L. Inorg. Chem. 1996, 35, 6861–6872.
(42) Ortiz de Montellano, P. R. Acc. Chem. Res. 1998, 31, 543–549.
(43) Vaugh, J. D.; Mugharbi, Z.; Wu, E. C. J. Org. Chem. 1970,
35, 1141–1145.
(9) Nakamura, M.; Ohgo, Y.; Ikezaki, A. Electronic and Magnetic
Structures of Iron Porphyrin Complexes. In Handbook of Porphyrin
Science; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; World Scientific:
Singapore, 2010; pp 1ꢀ146.
(10) Walker, F. A. NMR and EPR Spectroscopy of Paramagnetic
Metalloporphyrins and Heme Proteins. In Handbook of Porphyrin
Science; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; World Scientific:
Singapore, 2010; pp 1ꢀ337.
(11) Nakamura, M. Coord. Chem. Rev. 2006, 250, 2271–2294.
(12) Ohgo, Y.; Hoshino, A.; Okamura, T.; Uekusa, H.; Hashizume,
E.; Ikezaki, A.; Nakamura, M. Inorg. Chem. 2007, 46, 8193–8207.
(13) Jentzen, W.; Ma, J.-G.; Shelnutt, J. A. Biophys. J. 1998, 74,
753–763.
(44) Rachlewicz, K.; Latos-Graz_yꢀnski, L.; Vogel, E. Inorg. Chem.
2000, 39, 3247.
(14) Ma, J.-G.; Zhang, J.; Franco, R.; Jia, S.-L.; Moura, I.; Moura, J. J. G.;
Kroneck, P. M. H.; Shelnutt, J. A. Biochemistry 1998, 37, 12431–12442.
(15) Shelnutt, J. A.; Song, X.-Z.; Ma, J.-G.; Jia, S.-L.; Jentzen, W.;
Medforth, C. J. Chem. Soc. Rev. 1998, 27, 31–41.
(16) Ma, J.-G.; Leberge, M.; Song, X.-Z.; Jentzen, W.; Jia, S.-L.;
Zhang, J.; Vanderkooi, J. M.; Shelnutt, J. A. Biochemistry 1998,
37, 5118–5128.
(17) Senge, M. O. Highly Substituted Porphyrins. The Porphyrin
Handbook; Academic Press: San Diego, CA, 2000; p 239.
(18) Latos-Graz_yꢀnski, L.; Lisowski, J.; Olmstead, M. M.; Balch, A. L.
J. Am. Chem. Soc. 1987, 109, 4428–4429.
(19) Latos-Graz_yꢀnski, L.; Lisowski, J.; Olmstead, M. M.; Balch, A. L.
Inorg. Chem. 1989, 28, 1183–1188.
(20) Hung, C.-H.; Ou, C.-K.; Lee, G.-H.; Peng, S.-M. Inorg. Chem.
2001, 40, 6845–6847.
(21) Pawlicki, M.; Latos-Graz_yꢀnski, L. Carbaporphyrinoids—
Synthesis and Coordination Properties 203. In Handbook of Porphyrin
Science: with Applications to Chemistry, Physics, Materials Science, Engi-
neering, Biology and Medicine; Kalish, H., Smith, K. M., Guilard, R., Eds.;
World Scientific Publishing: Singapore, 2010; pp 104ꢀ192.
(22) Chmielewski, P. J.; Latos-Graz_yꢀnski, L. Coord. Chem. Rev. 2005,
249, 2510–2533.
(23) Stepieꢀn, M.; Latos-Graz_yꢀnski, L. Acc. Chem. Res. 2005, 8, 88–98.
)
(24) Pacholska, E.; Latos-Graz_yꢀnski, L.; Ciunik, Z. Angew. Chem., Int.
Ed. 2001, 40, 4466–4469.
(25) Stepieꢀn, M.; Latos-Graz_yꢀnski, L. J. Am. Chem. Soc. 2002,
)
124, 3838–3839.
(26) Stepieꢀn, M.; Latos-Graz_ynꢀski, L.; Szterenberg, L. Inorg. Chem.
)
2004, 43, 6654–6662.
(27) Szyszko, B.; Latos-Graz_ynꢀski, L. Organometallics 2011, 30,
4354–4363.
(28) Pacholska, E.; Latos-Graz_ynꢀski, L.; Ciunik, Z. Chem.—Eur. J.
2002, 8, 5403–5406.
(29) Lash, T. D.; Jones, S. A.; Ferrence, G. M. J. Am. Chem. Soc. 2010,
132, 12786–12787.
(30) Pacholska-Dudziak, E.; Szterenberg, L.; Latos-Graz_yꢀnski, L.
Chem.—Eur. J. 2011, 17, 3500–3511.
(31) Pacholska-Dudziak, E.; Skonieczny, J.; Pawlicki, M.; Latos-
Graz_yꢀnski, L.; Szterenberg, L. Inorg. Chem. 2005, 44, 8794.
(32) Pacholska-Dudziak, E.; Skonieczny, J.; Pawlicki, M.;
Szterenberg, L.; Ciunik, Z.; Latos-Graz_yꢀnski, L. J. Am. Chem. Soc.
2008, 130, 6182–6195.
(33) Pacholska-Dudziak, E.; Latos-Graz_yꢀnski, L. Coord. Chem. Rev.
2009, 253, 236–248.
(34) Rachlewicz, K.; Wang, S.-L.; Peng, C.-H.; Hung, C.-H.; Latos-
Graz_yꢀnski, L. Inorg. Chem. 2003, 42, 7348–7350.
(35) Rachlewicz, K.; Gorzelaꢀnczyk, D.; Latos-Graz_yꢀnski, L. Inorg.
Chem. 2006, 45, 9742.
10965
dx.doi.org/10.1021/ic2015176 |Inorg. Chem. 2011, 50, 10956–10965