Oxidation and Oxygenation of Iron Complexes of 2-Aza-21-carbaporphyrin

Article abstract of DOI:10.1021/ja039792y

Oxidation and oxygenation of (HCTPPH)Fe^IIBr an iron(II) complex of 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin (CTPPH)H₂ have been followed by ¹H and ²H NMR spectroscopy. Addition of I₂ or Br₂ to the solution of (HCTPPH)Fe^IIBr in the absence of dioxygen results in one-electron oxidation yielding [(HCTPPH)Fe^IIIBr]⁺. One electron oxidation with dioxygen, accompanied by deprotonation of a C(21)H fragment and formation of an Fe-C(21) bond, produces an intermediate-spin, five-coordinate iron(III) complex (HCTPP)Fe^IIIBr. In the subsequent step an insertion of the oxygen atom into the preformed Fe^III-C(21) bond has been detected to produce [(CTPPO)Fe^IIIBr]^-. Protonation at the N(2) atom affords (HCTPPO)Fe^IIIBr. The considered mechanism of (HCTPPH)Fe ^IIBr oxygenation involves the insertion of dioxygen into the Fe-C bond. The ¹H NMR and ²H NMR spectra of paramagnetic iron(III) complexes were examined. Functional group assignments have been made with use of selective deuteration. The characteristic patterns of pyrrole and 2-NH resonances have been found diagnostic of the ground electronic state of iron and the donor nature localized at C(21) center as exemplified by the ¹H NMR spectrum of intermediate-spin (HCTPP)Fe^IIIBr:β -H 7.2, -10.6, -19.2, -20.6, -23.2, -24.9, -43.2; 2-NH -76.6 (ppm, 298 K). The structures of two compounds (HCTPP)Fe^IIIBr and (HCTPPO)Fe ^IIIBr, were determined by X-ray diffraction studies. In the first case, the iron(III) is five-coordinate with bonds to three pyrrole nitrogen atoms (Fe-N distances: 1.985(8), 2.045(7), 2.023(8) A), and the pyrrolic trigonal carbon (Fe-C: 1.981(8) A). The iron(III) of (HCTPPO)Fe ^IIIBr forms bonds to three pyrrole nitrogen atoms (Fe-N distances 2.104(5), 2.046(5), 2.102(5) A). The Fe-O 2.041(5) A and Fe-C(21) 2.192(5) A distances suggests a direct interaction between the iron center and the π electron density on the carbonyl group in a η ² fashion.

Full text of DOI:10.1021/ja039792y

Published on Web 03/13/2004
Oxidation and Oxygenation of Iron Complexes of
2-Aza-21-carbaporphyrin
Krystyna Rachlewicz,† Sian-Ling Wang,‡ Jia-Ling Ko,‡ Chen-Hsiung Hung,‡* and
Lechosław Latos-Graz˘ yn´ski†*
Contribution from the Department of Chemistry, UniVersity of Wrocław, 14 F. Joliot-Curie St.,
Wrocław 50 383, Poland, and Department of Chemistry, National Changhua UniVersity of
Education, Changhua, 50058 Taiwan
Received November 25, 2003; E-mail: llg@wchuwr.chem.uni.wroc.pl; chhung@cc.ncue.edu.tw
Abstract: Oxidation and oxygenation of (HCTPPH)FeIIBr an iron(II) complex of 2-aza-5,10,15,20-tetraphenyl-
1
2
21-carbaporphyrin (CTPPH)H2 have been followed by H and H NMR spectroscopy. Addition of I2 or Br2
to the solution of (HCTPPH)FeIIBr in the absence of dioxygen results in one-electron oxidation yielding
[(HCTPPH)FeIIIBr]+. One electron oxidation with dioxygen, accompanied by deprotonation of a C(21)H
fragment and formation of an Fe-C(21) bond, produces an intermediate-spin, five-coordinate iron(III)
complex (HCTPP)FeIIIBr. In the subsequent step an insertion of the oxygen atom into the preformed FeIII-
C(21) bond has been detected to produce [(CTPPO)FeIIIBr]-. Protonation at the N(2) atom affords
(HCTPPO)FeIIIBr. The considered mechanism of (HCTPPH)FeIIBr oxygenation involves the insertion of
dioxygen into the Fe-C bond. The 1H NMR and 2H NMR spectra of paramagnetic iron(III) complexes were
examined. Functional group assignments have been made with use of selective deuteration. The
characteristic patterns of pyrrole and 2-NH resonances have been found diagnostic of the ground electronic
1
state of iron and the donor nature localized at C(21) center as exemplified by the H NMR spectrum of
intermediate-spin (HCTPP)FeIIIBr: â-H 7.2, -10.6, -19.2, -20.6, -23.2, -24.9, -43.2; 2-NH -76.6 (ppm,
298 K). The structures of two compounds (HCTPP)FeIIIBr and (HCTPPO)FeIIIBr, were determined by X-ray
diffraction studies. In the first case, the iron(III) is five-coordinate with bonds to three pyrrole nitrogen atoms
(Fe-N distances: 1.985(8), 2.045(7), 2.023(8) Å), and the pyrrolic trigonal carbon (Fe-C: 1.981(8) Å).
The iron(III) of (HCTPPO)FeIIIBr forms bonds to three pyrrole nitrogen atoms (Fe-N distances 2.104(5),
2.046(5), 2.102(5) Å). The Fe-O 2.041(5) Å and Fe-C(21) 2.192(5) Å distances suggests a direct interaction
between the iron center and the π electron density on the carbonyl group in a η2 fashion.
(III),11,14,15 copper(II),16,17 copper(III),18 palladium(II),19 anti-
mony(V),20 silver(III),17,21 manganese(II) and manganese(III),22,23
Introduction
Inverted (N-confused) porphyrin 5,10,15,20-tetraaryl-2-aza-
21-carbaporphyrin (CTPPH)H2 and its derivatives1-3 revealed
a remarkable tendency to stabilize peculiar organometallic
compounds,4-6 containing diamagnetic nickel(II),1,7-11 para-
magnetic nickel(II) with one or two Ni-C bonds,12,13 nickel-
zinc(II),16,24 iron,25,26 rhodium(I),27 and platinum.28 An ac-
companying involvement of the perimeter nitrogen atom which
results in the outer coordination has been detected for iron-
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1996, 118, 5690.
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(15) Xiao, Z.; Patrick, B. O.; Dolphin, D. Inorg. Chem. 2003, 42, 8125.
(16) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Schmidt, I. Inorg. Chem. 2000,
39, 5475.
† University of Wrocław.
‡ National Changhua University of Education.
(1) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.; Głowiak, T.
Angew. Chem., Int. Ed. Engl. 1994, 33, 779.
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Org. Lett. 2003, 5, 1293.
(2) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767.
(3) We will use the symbol CTPP to denote the trianion obtained from the
inverted porphyrin by abstraction of all pyrrolic NH proton and the C-bound
H(21) hydrogen. The groups attached to the N(2) atom will be indicated
by a prefix in italic and the group attached to C(21) will appear as a suffix
in italic. A similar methods will be used to form acronyms for other
carbaporphynoids.
(18) Maeda, H.; Ishikawa, Y.; Matsuda, T.; Osuka, A.; Furuta, H. J. Am. Chem.
Soc. 2003, 125, 11822.
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Metalloporphyrins; In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: New York, 2000; pp 361-416.
(5) Furuta, H.; Maeda, H.; Osuka, A. Chem. Commun. 2002, 1795.
(6) Harvey, J. D.; Ziegler, C. J. Coord. Chem. ReV. 2003, 247, 1.
(7) Chmielewski, P. J.; Latos-Graz˘yn´ski, L. J. Chem. Soc., Perkin Trans.2 1995,
503.
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9
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J. AM. CHEM. SOC. 2004, 126, 4420-4431
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2-Aza-21-carbaporphyrin
A R T I C L E S
(II),26 palladium(II),19 and platinum(II) complexes.28 The related
carbaporphyrinoid, i.e., the pyrrole append O-confused oxa-
carbaporphyrin gave three structurally related organometallic
complexes with nickel(II), palladium(II) and silver(III) in which
the metal ions are bound by three pyrrolic nitrogens and a
Chart 1. Selected Coordination Modes of Monomeric 2-Aza-21-
carbaporphyrin Complexes
trigonally hybridized C(21) atom of the O-confused furan.29
A
stable aromatic silver(III) complex of the O-confused oxapor-
phyrin derivative substituted at the tetrahedral C(3) positions
by ethoxy and pyrrole moieties was also reported.29
The ability of carbaporphyrinoids to coordinate metal ions
and to form metal-carbon bonds extends beyond the family of
N- or O-confused porphyrins.4,5,30-33 6,11,16,21-Tetraphenyl-
benziporphyrin (TPmBPH)H gave organometallic complexes
with palladium(II) and platinum(II), (TPmBP)PdII and (TPmBP)-
PtII.30 The metal ion is bound in the macrocyclic cavity by three
pyrrolic nitrogens and a trigonal carbon of the benzene ring. A
hydroxyl derivative of 8,9,13,14,18,19-hexaalkylbenziporphyrin,
i.e., 8,19-dimethyl-9,13,14,18-tetraethyl-2-oxybenziporphyrin
(OBPH)H2,34 coordinates palladium(II) to form the four-
coordinate anionic complex [(OBP)PdII]- with the retention of
macrocyclic aromaticity and coordination via a carbon σ-do-
nor.31 Subsequently, the palladium(II) complexes of core modi-
fied oxybenziporphyrin,33 nickel(II), palladium(II) and platinum-
(II) azuliporphyrins,35,36 and silver(III) benzocarbaporphyrin
were investigated.37 5,10,15,20-Tetraphenyl-p-benziporphyrin
(TPpBPH2)H - isomeric to 6,11,16,21-tetraphenyl-m-benzi-
porphyrin - with the benzene ring linked at para positions
formed a complex with cadmium(II) to reveal an unprecedented
η2 Cd(II)-arene interaction.32
Considering the coordination modes, established until now
for carbacyclic fragments containing one carbon atom in the
coordination core of carbaporphyrinoids, four fundamental types
can be identified as represented here by monomeric N-confused
porphyrin complexes (Chart 1).4,5 The first one involves the
replacement of the hydrogen atom by metal ions to yield a M-C
σ-bond. The donor carbon atom is trigonally hybridized and
metal ion is located in the porphyrin plane. Alternatively, the
carbacyclic fragment is bound to metal via a pyramidal carbon
in the η1-fashion. The third mode, i.e., the side-on arrangement
of the metal ion with respect to the planar carbacyclic moiety,
preserves the basic structural features of the interacting ring
including the trigonal sp2 hybridization of the carbon cen-
ter.12,22,24,26,38
Chart 2. Iron(II) 2-Aza-5,10,15,20-tetraphenyl-21-carbaporphyrin
This uncommon type of a metal ion-inverted pyrrole ring
interaction is reflected in 1H NMR studies by an unprecedented
isotropic shift (812 pm at 298 K) of the engaged H(21).39 An
agostic interaction has also been suggested for manganese
N-inverted porphyrin complexes.22 A dimeric iron(II) N-
confused porphyrin, [(CTPPH)FeII]2 was obtained from the
anaerobic reaction of (HCTPPH)FeIIBr with NaSePh. Under
aerobic conditions, a µ-hydroxo bridged iron(III) dimer,
[(CTPPO)FeIII]2OH‚Na(THF)2, was obtained with Na+ bridging
the outer-N atoms. Oxygenation occurred at the inner core
pyrrolic carbon to form a novel (CTPPOH)H2 porphyrinic ring.26
The present contribution concerns with chemical oxidation
and/or oxygenation of high-spin iron(II) complex (HCTPPH)-
1
2
FeIIBr 1. Particular emphasis has been placed on H and H
NMR studies as a source of insight into the electronic and
molecular structure of these low symmetry iron(n) carbapor-
phyrinoids and as potential means for detecting intermediate
species formed in the course of chemical processes. Their
behavior with respect of iron-carbon bond reactivity can be
compared to that of the related and much more intensively
studied iron porphyrin and iron porphyrin aryl complexes,40-42
which are of considerable interest in bioinorganic chemistry.
Iron(II) inverted porphyrin complexes (HCTPPH)FeIIBr 1
(Chart 2) and (HCTPPH)FeII(SC7H7) present the conformation
with the side-on position of the iron with respect to the inverted
pyrrole plane.25 The Fe‚‚‚C(21) distances are longer than the
regular iron-carbon bonds but shorter than the sum of van der
Waals radii. The solid-state geometry of the FeII‚‚‚{C(21)-
H(21)} fragment in (HCTPPH)FeIIBr and particularly the
Fe‚‚‚H(21) distance of 1.971 Å implied an agostic interaction.
Results and Discussion
NMR Studies of Paramagnetic Iron(n) Complexes of
2-Aza-21-carbaporphyrin. The 1H NMR data of paramagnetic
(29) Pawlicki, M.; Latos-Graz˘yn´ski, L. Chem.Eur. J. 2003, 9, 4650.
(30) Ste¸pien´, M.; Latos-Graz˘yn´ski, L. Chem. Eur. J. 2001, 7, 5113.
(31) Ste¸pien´, M.; Latos-Graz˘yn´ski, L.; Lash, T. D.; Szterenberg, L. Inorg. Chem.
2001, 40, 6892-6900.
(38) Furuta, H.; Ishizuka, T.; Osuka, A. Inorg. Chem. Commun. 2003, 6, 398.
(39) Rachlewicz, K.; Wang, S.-L.; Peng, C.-H.; Hung, C. H.; Latos-Graz˘yn´ski,
L. Inorg. Chem. 2003, 42, 7348.
(32) Ste¸pien´, M.; Latos-Graz˘yn´ski, L. J. Am. Chem. Soc. 2002, 124, 3838-
3839.
(33) Venkatraman, S.; Anand, V. G.; Pushpan, S. K.; Sankar, J.; Chandrashekar,
T. K. Chem. Commun. 2002, 462.
(40) Arasasingham, R. D.; Balch, A. L.; Cornman, C. R.; Latos-Graz˘yn´ski, L.
J. Am. Chem. Soc. 1989, 111, 4357.
(34) Lash, T. D. Angew. Chem., Int. Ed. Engl. 1995, 34, 2533.
(35) Graham, S. R.; Ferrence, G. M.; Lash, T. D. Chem. Commun. 2002, 894.
(36) Lash, T. D.; Colby, D.; Graham, S. L.; Ferrence, G. M.; Szczepura, L. F.
Inorg. Chem. 2003, 42, 7326.
(41) Arasasingham, R. D.; Balch, A. L.; Hart, R. H.; Latos-Graz˘yn´ski, L. J.
Am. Chem. Soc. 1990, 112, 7566.
(42) Guilard, R.; van Caemelbecke, E.; Tabard, A.; Kadish, K. M. Synthesis,
Spectroscopy and Electrochemical Properties of Porphyrins with Metal-
Carbon; In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard,
R., Eds. Academic Press: San Diego, CA, 2000; pp 295-345.
(37) Muckey, M. A.; Szczepura, L. F.; Ferrence, G. M.; Lash, T. D. Inorg.
Chem. 2002, 41, 4840.
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A R T I C L E S
Rachlewicz et al.
Figure 1. NMR spectra of iron inverted porphyrins: A, (HCTPPH)FeIIBr
1 (1H NMR, dichloromethane-d2, 298 K); B, (HCTPP)FeIIIBr 2 (1H NMR,
dichloromethane-d2, 298 K); C (HCTPP-d7)FeIIIBr (2H NMR, dichlo-
romethane, 298 K).
Figure 2. NMR spectra of 3: A, [(CTPPO)FeIIIBr]- 3 (1H NMR,
dichloromethane-d2, 298 K); B, [(CTPPO-d7)FeIIIBr]- (2H NMR, dichlo-
romethane, 298 K). Inset A′ presents the meso-phenyl region (223 K). Peak
labels in this and in following figures: pyrr-pyrrole resonances, o, m,
p-resonances of ortho, meta, para hydrogens of meso-phenyl rings, * the
decomposition product.
iron(n) inverted porphyrins (n ) II,III), have been analyzed
considering their C1 symmetry as determined previously in the
crystal structures of (HCTPPH)FeIIBr 1.25 There are seven
distinct â-H pyrrole positions for (HCTPPH)FeIIBr 1, a 2-NH
position analogous to 2-CH of the regular porphyrin and four
different meso sites. It may be anticipated that the ortho and
meta positions on each meso-aryl ring will be distinguishable.
Four para, eight ortho and eight meta resonances may therefore
be expected for iron(n) 2-aza-5,10,15,20-tetraphenyl-21-car-
baporphyrin complexes since the two opposite sides of the
porphyrin are not equivalent. In the case of fast rotation, the
number of ortho and meta resonances reduces to four each. On
the other hand, four ortho, four meta and four para phenyl
resonances are expected once two porphyrin sides are identical
(e.g., six-coordinate complexes).
Respective 1H and 2H NMR spectra for (HCTPPH)FeIIBr and
its oxidation/oxygenation transformation products are presented
in Figures 1-6. The spectral parameters have been gathered in
Table 1. Resonance assignments, which are given above selected
peaks, have been made on the basis of relative intensities, line
widths, and site specific deuteration. As the spectroscopic
analysis is primarily based on patterns of pyrrole resonances
the 2H NMR spectra of iron(n) inverted porphyrins are directly
shown in each essential case. The plots of the temperature
dependence of the chemical shifts which are typical for given
electronic state of iron inverted porphyrin are shown in the
Supporting Information (Figures 1S-5S)
1
changes in H NMR spectra. The resonances of (HCTPPH)-
FeIIBr (Figure 1, Trace A) have decreased in intensity and new
resonances, assigned to as (HCTPP)FeIIIBr 2, have grown
gradually (Figure 1, Trace B).
The total and selective conversion of 1 to 2 requires 12 h at
203 K but only 0.5 h at 298 K. In these experimental conditions
we did not detected any intermediate, which could precede 2
in the reaction route. The spectral changes, similar to those
shown in Figure 1, have also been detected when dioxygen is
added to the solution of (HCTPPH)FeIIBr in other solvents
including chloroform-d, methanol-d4, toluene-d8, DMF-d7, and
DMSO-d6. The pyrrole resonances of 2 are spread in the upfield
7.2 to -80.0 ppm region (298 K, dichloromethane-d2). The most
upfield located resonance at -76.6 ppm has been identified as
corresponding to 2-NH position as is absent in 2H NMR
spectrum of (HCTPP-d7)FeIIIBr but it is present in 1H NMR of
the same sample (Figure 1). The new species is stable in solution
providing the dioxygen has been removed by freezing-thawing
technique. Eventually, 2 has been isolated in the solid state and
characterized by X-ray crystallography (see below).
The magnetic moment of (HCTPP)FeIIIBr 2 as measured by
the Evans technique,43 in a chloroform-d solution at 298 K
equals 4.2 ( 0.1 µB. This value corresponds to the intermediate-
spin state S ) 3/2 of iron(III).44-46 The signs and magnitudes
Dioxygen Addition. Addition of dioxygen to dichlo-
romethane-d2 solution of (HCTPPH)FeIIBr 1 produces marked
(43) Evans, D. F. J.; James, T. A. J. Chem. Soc., Dalton Trans. 1979, 723.
(44) Evans, D. R.; Reed, C. R. J. Am. Chem. Soc. 2000, 122, 4660.
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2-Aza-21-carbaporphyrin
A R T I C L E S
Figure 4. NMR spectra of iron(III) inverted porphyrin: A, [(HCTPPH)-
FeIIIBr]+ 5 (1H NMR, dichloromethane-d2, 298 K); B, [(HCTPPD-d7)FeIII-
Br]+ (2H NMR, dichloromethane, 298 K). Inset A′ presents the meso-phenyl
region (223 K).
Figure 3. NMR spectra of: A, (HCTPPO)FeIIIBr 4 (1H NMR, dichlo-
romethane-d2, 223 K); B, (HCTPPO-d7)FeIIIBr (2H NMR, dichloromethane,
223 K). Inset A′ presents the meso-phenyl region (223 K).
that of the conjugated base 3, allowing the conclusion that the
process involves the ligand protonation (vide infra) without
changes of the ground electronic state of the metal ion. The
final, stable product of oxygenation 4 was isolated and
characterized by X-ray crystallography providing independent
insight into the oxygenation/oxidation route (vide infra).
Reaction of (HCTPPH)FeIIBr with Other Oxidizing Re-
agents. The anaerobic addition of 5 equiv. iodine to the solution
of (HCTPPH)FeIIBr 1 results exclusively in formation of
of the isotropic shifts of 2 are consistent with such a ground
electronic state as well. The value of µ ) 4.9 ( 0.1 µB has
been determined for samples of high-spin iron(II) of (HCTPPH)-
FeIIBr 1, which have been directly used to produce samples of
2 applied in magnetic moment measurements (see the Experi-
mental section).
1
The subsequent changes in the H NMR spectrum, caused
by the permanent presence of dioxygen, have been followed
systematically in the period of 12 h at 298 K. A set of seven
downfield shifted pyrrole resonances, spread at the 110-30 ppm
region (Figure 2), have been assigned to the high-spin derivative
[(CTPPO)FeIIIBr]- 3. The 2-NH resonance has not been
detected. Compound 3 is formed by insertion of oxygen atom
into the preformed Fe-C(21) bond of 2. The magnetic moment
of [(CTPPO)FeIIIBr]- 3 is 5.6 ( 0.1 µB at 298 K. This value is
typical of that of high-spin iron(III) porphyrins and it is
1
[(HCTPPH)FeIIIBr]+ 5 as confirmed by the distinct H NMR
spectrum (Figure 4).
Iodine reacts only as the one-electron oxidizing agent and
the formed iodide anion does not enter the coordination sphere
of the metal ion (as a sixth ligand or replacing the already
coordinated bromide). Significantly, a titration of (HCTPP)-
FeIIIBr 2 with trifluoroacetic acid, followed by 1H NMR resulted
in generation of [(HCTPPH)FeIIIBr]+ 5 using an independent
route according to eq 1
1
consistent with H NMR features of 3.
The species 3 can be converted into the related high-spin
derivative (HCTPPO)FeIIIBr 4 after addition of the acid (TFA)
as shown in Figure 3. The species 4 presents the seven pyrrole
resonances. The 2-NH resonance has been detected at low
temperatures only (-25 ppm, 223 K). The protonation is
reversible (e.g., an addition of collidine reverses the course of
this reaction yielding 3). The pattern and shift values resemble
(HCTPP)FeIIIBr + H+ / [(HCTPPH)FeIIIBr]+ (1)
This process has a precedent. Previously the reversible proto-
nation of the inner carbon of nickel(II) or copper(II) inverted
porphyrin complexes was reported.8,16 The pyrrole resonances
of [(HCTPPH)FeIIIBr]+ 5 are spread in the 100 to -40 ppm
region reflecting the intrinsic asymmetry of the ligand and the
high-spin state of the metal ion. The most upfield resonance
has been identified as corresponding to 2-NH position as it
absent in 2H NMR spectrum of [(HCTPPD-d7)FeIIIBr]+ 5, where
(45) Simonato, J.-P.; Pe´caut, J.; Le Pape, L.; Oddou, J.-L.; Jeandey, C.; Shang,
M.; Scheidt, W. R.; Wojaczyn´ski, J.; Wołowiec, S.; Latos-Graz˘yn´ski, L.;
Marchon, J.-C. Inorg. Chem. 2000, 39, 3978.
(46) Rachlewicz, K.; Latos-Graz˘yn´ski, L.; Vogel, E.; Ciunik, Z.; Jerzykiewicz,
L. Inorg. Chem. 2002, 41, 1979.
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A R T I C L E S
Rachlewicz et al.
ably, the accompanying upfield resonance belongs to the same
pyrrole (3-H) as the peculiar upfield position of these resonances
may reflect the specific location of the inverted pyrrole with
respect to the metal ion.12 An effort has been made to locate
1
the H(21) resonance of [(HCTPPH)FeIIIBr]+ in H NMR or
D(21) of [(HCTPPD-d7)FeIIIBr]+ in 2H NMR similarly as it has
been done for the iron(II) derivative.39 The substantially larger
broadening of all perimeter â-H pyrrole resonances has been
seen for [(HCTPPH)FeIIIBr]+ 5 in comparison to (HCTPPH)-
FeIIBr 1. Presuming that the similar relation of line width due
to the analogous structures and mechanisms of spin delocal-
ization holds for the H(21) position for [(HCTPPH)FeIIIBr]+ 5
and (HCTPPH)FeIIBr 1 the predicted line width of H(21) is well
in excess of reasonably observed lines in the conditions of our
experiment.
A careful titration of (HCTPPH)FeIIBr 1 with Br2 has been
carried out in strictly anaerobic conditions. The effect of addition
of less than 1 equiv of bromine to a solution of (HCTPPH)-
1
FeIIBr is shown in the H NMR spectrum (Trace B of Figure
5). Separate resonances of (HCTPP)FeIIIBr 2, assigned previ-
ously once dioxygen reacted with 1, are readily detected (Figure
5, Traces B and C). Simultaneous broadening of (HCTPPH)-
FeIIBr 1 resonances and their gradual relocation in the course
of titration have also been noticed. Eventually, the originally
broadened lines resembling the spectrum of (HCTPPH)FeIIBr
transform into the characteristic set of resonances assigned to
[(HCTPPH)FeIIIBr]+ 5, (Figure 5, Trace D), i.e., to the product
of one-electron, metal-centered oxidation of (HCTPPH)FeIIBr
1. Thus, in the course of this one-electron oxidation two iron-
(III) products 2 an 5 have been formed as accounted for by the
1H NMR spectrum (Figure 5, Traces C and D). Separate
Figure 5. 1H NMR spectra of [(HCTPPH)FeIIBr] (dichloromethane-d2, 298
K) after addition of Br2: A, 0 equiv; B, 0.5 equiv; C, 0.7 equiv; D, 1. equiv;
E, 1.5 equiv; F, 2 equiv. The peak labels refer to pyrrole resonances of
dominating species as follows: B, [(HCTPP)FeIIIBr] 2; D, [(HCTPPH)-
FeIIIBr]+ 5, F, [(HCTPPBr)FeIIIBr]+ 6.
resonances of (HCTPPH)FeIIBr 1 and [(HCTPPH)FeIIIBr]+
5
could not be detected in the course of titration with bromine.
Instead, an averaged pattern has been observed. Thus, the rate
of electron exchange between these two species is fast on the
1H NMR time scale suggesting that relatively modest structural
changes occur in the course of the redox process. Addition of
further portions of the titrant to the solution containing (HCT-
PP)FeIIIBr and [(HCTPPH)FeIIIBr]+ produces the spectrum
shown in Trace F of Figure 5. At this stage, resonances of 2
and 5 diminished to the point where they are no longer observed
but the resonances of the new compound 6 have grown. The
1H NMR patterns of 5 and 6 are consistent with the high-spin
ground electronic state. The multiplicity of meso-phenyl reso-
nances of 5 and 6 reflects the unequivalency of two carbapor-
phyrins sides due to a five-coordination and side-on arrangement
of the inverted pyrrole fragments. The species 6 has also been
formed once the strongly oxidizing reagent phenoxatine hexachlo-
roantimonate reacted with (HCTPPH)FeIIBr 1 (anaerobic condi-
tions) or (HCTPP)FeIIIBr 2 (aerobic conditions). In these
experimental conditions, [(HCTPPH)FeIIIBr]+ 5 undergoes
substitution at C(21) to form [(HCTPPBr)FeIIIBr]+ 6. This
substitution has been confirmed by mass spectrometry. The mass
spectra has been measured directly for the sample of 6 obtained
1
Figure 6. 1H NMR spectrum of [(HCTPP)FeIII(1-MeIm)2]+ 7 (dichlo-
romethane-d2, 298 K, 10 equiv of 1-MeIm added). The solvent impurity in
region of pyrrole resonances marked with *.
in the H NMR course of titration with Br2. In the conditions
of our experiment (ES), the most intense peak m/z ) 694.5
corresponds to the demetalation product of 6, i.e., -(HCTPPBr)-
H2. Previously, it was documented that the C(21) atom of
inverted porphyrin are susceptible to substitution reactions.
the ligand is deuterated in all pyrrolic positions, but it was
present in 1H NMR collected for [(HCTPPH)FeIIIBr]+. Presum-
9
4424 J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004

2-Aza-21-carbaporphyrin
A R T I C L E S
Table 1. 1H NMR Chemical Shifts of Iron(II) of 2-Aza-21-carbaporphyrin and Its Oxidation and Oxygenation Product
chemical shiftsa
compound
pyrrole
2-NH
(HCTPPH)FeIIBr
1
2
3
4
5
6
7
44.8, 43.7, 43.7, 31.7, 31,7, 8.4, 0.78
-8.0
(HCTPP)FeIIIBr
7.2, -10.6, -19.2, -20.6, -23.2, -24.9, -43,2
106.3, 82.2, 69.4, 68.5, 53.5, 48.1, 37.5
117.3, 80.0, 76.8, 69.1, 59,1, 31,3, 29.3
115.2, 112.9, 107.9, 91.5, 50.7, 35.9, -32.8
108.7, 104.4, 90.5, 76.9, 58.0, 46.1, -58.6
1.3, -2.3, -3.7, -4.1, -4.95, -8.5, -11.5
-76.6
[(CTPPO)FeIIIBr]-
[(HCTPPO)FeIIIBr
[(HCTPPH)FeIIIBr]+
[(HCTPPBr)FeIIIBr]+
[(HCTPP)FeIII(1-MeIm)]2
-25.0b
-31.2
-39.7
-42.6
+
a δ/ppm, at 298 K unless marked differently. b at 223 K, all measurements in dichloromethane-d2.
Examples reported to date include alkylation,7,10,12,47 halogena-
tion,48,49 nitration,50 or cyanation.51
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
(HCTPP)FeIIIBr 2 and (HCTPPO)FeIIIBr 4
As described above, the reaction of (HCTPPH)FeIIBr 1 with
dioxygen ends up with formation of [(CTPPO)FeIIIBr]- 3.
Significantly, we have found that the conversion of [(HCTPP-
Br)FeIIIBr]+ 6 into [(CTPPO)FeIIIBr]- 3 has taken place,
presumably by nucleophilic substitution featuring water as
nucleophile, once the 1H NMR sample of [(HCTPPBr)FeIIIBr]+
6 was kept in dichloromethane-d2 saturated with D2O.
Titration of (HCTPP)FeIIIBr with 1-MeIm. Coordination
of nitrogen base has been of interest because of possible
correlations between the ground electronic state, coordination
2
4
Fe-Br1
2.443(2)
1.985(8)
2.045(7)
2.023(8)
1.981(8)
2.3906(12)
2.104(5)
2.046(5)
2.102(5)
2.192(6)
2.041(5)
1.299(7)
1.470(9)
1.463(9)
1.401(8)
1.311(8)
1.393(8)
1.374(8)
1.400(9)
94.62 (19)
78.6(4)
Fe-N22
Fe-N23
Fe-N24
Fe-C21
Fe-O1
O1-C21
C1-C21
1.435(1)
1.393(1)
C4-C21
C1-N2
1.407(11)
1.341(11)
1.421(11)
1.420(12)
1.376(13)
N2-C3
C3-C4
1
mode and H NMR spectroscopic patterns of iron(n) carbap-
C4-C5
orphyrins.
C1-C20
Br1-Fe-C21
Fe-O1-C21
O1-C21-Fe
C1-N2-C3
N2-C3-C4
C3-C4-C21
C4-C21-C1
C21-C1-N2
100.0(2)
Addition of 1-methylimidazole to a solution of (HCTPP)-
FeIIIBr 2 in dichloromethane results in its conversion to a six-
coordinate low-spin complex [(HCTPP)FeIII(1-MeIm)2]+ 7. The
65.9(3)
110.7(9)
107.4(1)
109.1(9)
106.3(8)
106.5(1)
108.7(6)
113.7(6)
105.1(6)
104.7(6)
107.3(6)
1
representative H NMR spectrum is shown in Figure 6. The
characteristic set of eight upfield shifted resonances (â-H, 2-NH,
and 3-H) of 2 spread at the 7.2 to -76.6 region, have been
replaced by an analogous set assigned to [(HCTPP)FeIII-
(1-MeIm)2]+ 7 which demonstrate markedly smaller paramag-
netic shifts. These resonances are accompanied by sets of upfield
shifted ortho and para meso phenyl proton resonances and
downfield shifted meta protons. The observation of 1-MeIm
resonances and their relative intensity with respect to â-H
resonances presents convincing evidence for the presence of
two axial ligands. In general the spectroscopic data are consistent
with the low-spin ground electronic state of [(HCTPP)FeIII(1-
MeIm)2]+.52
X-ray Structures of (HCTPP)FeIIIBr 2 and (HCTPPO)-
FeIIIBr 4. Once the conditions were determined, an attempt was
1
made to crystallize some of the species detected by H NMR
spectroscopy. The respective structures and essential structural
parameters are shown at Figures 7-10 and in Table 2. In each
case the identity of the crystallized compound has been
Figure 7. Perspective drawing (with 35% probability ellipsoid) of
(HCTPP)FeIIIBr 2.
1
confirmed by the H NMR spectroscopy to eliminate a pos-
sibility of any substantial chemical changes in the course of
crystallization.
Compound 2 crystallized in the monoclinic space group P21/n
with four molecules in the unit cell. The crystal structure of
(HCTPP)FeIIIBr 2 has a planar porphyrin ring (Figure 7). The
averaged deviation of 24 core-atoms from a plane defined by
three pyrrolic nitrogens and the inner core carbon is 0.077 Å.
The iron sits 0.336 Å above the plane. A non bonded contact
with distance of 2.822 Å between axial bromide and peripheral
N-H of the neighboring carbaporphyrin ring agrees with the
assignments of atoms on the inverted pyrrole ring. Consequently,
the shortest distance of 1.981(8) Å among the four bonds of
iron and inner coordination sphere atoms has been assigned as
Fe-C bond. Nevertheless, the distance of 1.981(8) Å for Fe-C
bond in 2 is comparable to 1.955(3) Å for the Fe-C distance
of low-spin five-coordinate phenyl(meso-tetraphenylporphyri-
(47) Schmidt, I.; Chmielewski, P. J. Chem. Commun. 2002, 92.
(48) Furuta, H.; Ishizuka, T.; Osuka, A.; Ogawa, T. J. Am. Chem. Soc. 1999,
121, 2945.
(49) Furuta, H.; Ishizuka, T.; Osuka, A.; Ogawa, T. J. Am. Chem. Soc. 2000,
122, 5748.
(50) Ishikawa, Y.; Yoshida, I.; Akaiwa, K.; Koguchi, E.; Sasaki, T.; Furuta, H.
Chem. Lett. 1997, 453.
(51) Xiao, Z.; Patrick, B. O.; Dolphin, D. Chem. Commun. 2003, 1062.
(52) Walker, F. A. Proton NMR and EPR Spectroscopy of Paramagnetic
Metalloporphyrins; In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds. Academic Press: San Diego, CA, 2000; pp 81-
183.
9
J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004 4425

A R T I C L E S
Rachlewicz et al.
Figure 8. Perspective drawing (with 35% probability ellipsoid) of
(HCTPPO)FeIIIBr 4.
Figure 9. The deviations of atoms (in 0.001 Å) from the mean-plane
defined by three coordination sphere pyrrolic nitrogens of (HCTPPO)FeIII-
Br 4.
nato)iron(III).53 The applicable Fe-C(pyrrole) bond distance
equals 1.962(2) Å as determined for the dinuclear compound
produced in reaction of Fe2CO9 with heterocyclic imines and
N-methyl-pyrrole carbaldehyde [µ2-η3-CH3N-CH2-CdCH-
CHdCH-NCH3]Fe2(CO)6 but the pyrrolic ring is also involved
in interaction with the adjacent Fe(CO3) unit.54,55 The averaged
bond distance of 2.018(8) Å for the three Fe-Np bonds in 2 is
shorter than corresponding averaged distance 2.096(8) Å for
(HCTPPH)FeIIBr 1.25 Interestingly, the average Fe-Np distance
in 2 is shorter than 2.070 Å Fe-N bond lengths of iron(III)
porphyrin complexes with high-spin electronic state but is
comparable to Fe-Np bond lengths of intermediate-spin iron(III)
porphyrins 1.997 Å.45,56
The structure of 4 determined in an X-ray diffraction study
is shown in Figure 8.
The crystal structure of 4 has a monoclinic space group C2/c
with eight molecules in the unit cell. The peripheral nitrogen
and carbon on the inverted pyrrole ring were refined as mutually
disordered. Identical coordinates and thermal-parameters were
used for the refinements of overlapping carbon and nitrogen.
The carbaporphyrin ring of 4 exhibits a nonplanar geometry
with the inverted pyrrole ring tilted away from the porphyrin
plane which resembles the geometry of (HCTPPH)FeIIBr 1.25
The torsion angles between the inverted pyrrole ring and
neighboring pyrrole rings are 31.8° (N22) and 28.2° (N24). The
porphyrin core as a whole exhibits saddle shape distortion with
a mean deviation of 0.226 Å from the plane defined by three
pyrrolic nitrogens. The alternate sign of deviations of the
neighboring pyrrole rings are consistent with the saddle distor-
tion (Figure 9).
The iron lies 0.309 Å above the N3 plane. An oxygen atom
is inserted into the Fe-C bond and is nearly coplanar to the
inverted pyrrole ring with deviations of 0.411 and 0.272 Å from
the averaged inverted pyrrole plane and the plane defined by
C1, C21, and C4, respectively.
Interestingly, the distances and angles surrounding inverted
pyrrole ring and oxygen for 4 can be compared to the dimeric
complex, [(CTPPO)FeIII]2OH‚Na(THF)2. The comparison sug-
gest the preference for different tautomers of the equatorial
Figure 10. Comparison of coordination modes of [(CTPPOFeIII)]2OH‚
Na(THF)2 (left) and (HCTPPO)FeIIIBr 4. (right).
ligand in these two complexes.26 As depicted in Figure 10, the
CdO distance of 1.299(7) Å in 4 is shorter than 1.336(5) Å
found in the dimeric complex and closer to CdO distances for
dioxoporphodimethane type complexes 1.223(6).57,58 The C-O
distance 1.336(5) Å is typical of phenoxide ligands,59 and
pyrrolic alkoxide fragment (1.300-1.360 Å) of cyclic iron(III)
trimer.60 The bond distances from inner carbon to neighboring
pyrrolic carbons (C(21)-C(1) and C(21)-C(4) of 1.470(9) and
1.463(9) Å in 4 are both longer than corresponding distances
in the dimeric [(CTPPO)FeIII]2OH‚Na(THF)2 complex which
is consistent with a keto-like structure. The IR measurements
have been carried out for the solid sample of 4. A stretching
CO band appeared at 1706.4 cm-1, which confirmed the
presence of carbonyl group.
Moreover, the Fe-C(21) distance of 2.199(7) Å for 4 is
significantly shorter than 2.296(5) Å detected for [(CTPPO)-
FeIII]2OH‚Na(THF)2.26 The Fe-O(1) distance 2.041(5) Å is
significantly longer that the Fe-O distances (1.873-1.886 Å)
found for cyclic iron(III) 2-hydroxyporphyrin trimer where the
pyrrolic alkoxide coordination was described.60 Thus, a direct
(53) Dopplet, P. Inorg. Chem. 1984, 23, 4009.
(54) Imhof, W. J. Organomet. Chem. 1997, 533, 31.
(55) Imhof, W. J. Organomet. Chem. 1997, 541, 109.
(56) Scheidt, W. R.; Gouterman, M. In Iron Porphyrin, Part I.; Lever, A. B.
P., Gray, H. B., Eds.; Addison-Wesley, Inc.: Reeding, 2003; pp 111-
122.
(57) Senge, M. O.; Smith, K. M. Z. Naturforsch. 1992, 47, 837.
(58) Balch, A. L.; Olmstead, M. M.; Phillips, S. L. Inorg. Chem. 1993, 32,
3931.
(59) Ste¸pien´, M.; Latos-Graz˘yn´ski, L. Inorg. Chem. 2003, 42, 6183.
(60) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Olmstead, M. M.; Balch, A. L. Inorg.
Chem. 1997, 36, 4548.
9
4426 J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004

2-Aza-21-carbaporphyrin
A R T I C L E S
Scheme 1. Oxidation of (HCTPPH)FeIIBr
Scheme 2. Substitution
finally in formation of the CdO fragment (Scheme 2). Analo-
gously, the reaction of benzocarbaporphyrin with aqueous ferric
chloride (ferric bromide) afforded in a regioselective process
the corresponding 21-chlorobenzocarbaporphyrin (21-bromoben-
zocarbaporphyrin).61 The species 3 and its conjugated acid 4
contain a ligand which is an 2-aza-21-carbaporphyrin derivative
with the oxygen atom located on the inner carbon-N-confused
porphyrin C-oxide. Originally, such a ligand has been detected
in the dimeric product of [(CTPPH)FeII]2 oxygenation although
in different tautomeric form,26 and in oxidation of (HCTPP)-
NiII with OsO4.15 In this work, the species 3 and 4 have been
generated in the course of oxygenation of 2 as discussed below.
In the course of our NMR and X-ray studies on oxidation
and oxygenation of iron(II) 2-aza-21-carbaporphyrin we have
trapped two essential steps of the process (Scheme 3). The
formation of 2 requires a one-electron oxidation. In the case
where dioxygen is the oxidant the formation of a superoxide is
implied.41 One electron oxidation is accompanied by deproto-
nation of C(21)-H and resembles the process shown in Scheme
1. The next step requires an insertion of the oxygen atom into
the FeIII-C bond to obtain 3 and eventually its conjugated acid
4. The coordination of iron(III) favors the resonance structure
4A, where the carbaporphyrinoids acts as a trianionic ligand.
Thus, in absence of some acid in excess the 2-NH proton of 4
dissociates readily to form 3.
As matter of fact the reaction of 2 to produce 4 resembles
the reaction of dioxygen with low-spin, five-coordinate com-
plexes, (P)FeIIIAr (P, porphyrin dianion; Ar, aryl group) which
produced (P)FeIIIOAr.41 Thus, for oxygenation of 2 one can
consider a course of the reaction (Scheme 4), which involves
an initial insertion of dioxygen into the Fe-C bond to form a
transient form T-1 (alternatively the four-center transition state
T-1′ can be considered). The peroxide intermediate is expected
to be extremely short-lived. Thus, the insertion step should be
followed by rapid homo- or heterolysis of the peroxide moiety.
Only the heterolytic route leading to T-2 has been shown in
Scheme 4. Thus two reactive centers, which are locked in the
cage created by the restrains of macrocycle, are generated. The
CO fragment coordinates to the metal ion. The reaction with
the surrounding solvents converts highly oxidized iron center
into iron(III). Likely, the oxygen atom is transferred to solvent
interaction between the iron center and the π electron density
on the C(21)dO carbonyl group is evident. The projection of
the iron(III) ion onto the C(21)-O bond lies close to its center
as readily reflected by the appropriate angles Fe-C(21)-O
65.9(3)° and Fe-O-C(21) 78.6(4)°. Thus, the metal ion
interacts with the CdO fragment in a η2 fashion. Recently, such
a coordination mode was reported by Dolphin and co-workers
for nickel(III) complex N-confused porphyrin inner C-oxide.15
Noticeably, the angles between phenyl rings and porphyrin
core are significantly affected by the geometry of pyrrole rings.
The phenyl rings neighboring to tilted inverted pyrrole ring give
dihedral angles of 42.1(2) and 43.4(3)° to the plane defined by
three internal pyrrolic nitrogens. These dihedral angles are
smaller than 64.3(2) and 51.0(2)° for two phenyl rings inside
the tripyrrolic unit of the carbaporphyrin core.
Oxidation/Oxygenation Mechanisms. The NMR study ac-
companied by crystallographic data demonstrates that (HCTP-
PH)FeIIBr undergoes oxidation and oxygenation which result a
series of paramagnetic complexes. These species are most
1
readily detected by H NMR spectroscopy. To account for the
detected 1H NMR spectroscopic pattern in the presence of
dioxygen we have considered the following phenomena: one
electron oxidation of (HCTPPH)FeIIBr 1 to form [(HCTPPH)-
FeIIIBr]+ 5, protonation/deprotonation at the C(21) carbon atom,
and oxygenation at the C(21) carbon atom to produce the CO
fragment, which coordinates to the iron(III) central ion. In
addition, changes of the unpaired spin density distribution due
to the axial ligation and protonation of N(2) nitrogen atom have
been considered. Finally, we have detected that the substitution
of the H(21) with the bromine atom plays an essential role once
dibromine has been applied in excess as the oxidizing agent.
The process of one-electron oxidation is likely to proceed as
shown in Scheme 1. Depending on the choice of oxidizing agent
a preference for 5 (I2) or 2 (O2) has been observed. Only in the
course of oxidation with Br2 two iron(III) inverted porphyrin
complexes (2 and 5) remained in the detected acid-base
equilibrium in the presence of iron(II) complex. Once formed
the species 2 can be converted into 5 by addition of acid.
Addition of Br2 to the solution containing [(HCTPP)FeIIIBr]
2 and [(HCTPPH)FeIIIBr]+ 5 results in bromination at C(21)
yielding [(HCTPPBr)FeIIIBr]+ 6 in accord with typical inverted
porphyrin reactivity.7 The subsequent reaction with water results
(61) Lash, T. D.; Muckey, M. A.; Hayes, M. J.; Liu, D.; Spence, J. D.; Ferrence,
G. M. J. Org. Chem. 2003, 68, 8558.
9
J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004 4427

A R T I C L E S
Rachlewicz et al.
Scheme 3. Oxygenation
m-CPBA, a typical donor of an oxygen atom, to the solution of
(HCTPP)FeIIIBr 2 affords 4 as well. In our opinion, there is a
significant parallel between the reaction of 2 with m-CPBA to
yield 4 and the reaction of (TMP)FeIIICl with m-CPBA to
produce iron(III) porphyrin N-oxide.65-68
Electronic Structure of Iron(n) Inverted Porphyrinss1H
1
NMR Studies. Generally, H NMR spectroscopy was shown
to be a definitive method for detecting and characterizing iron(n)
porphyrins (n ) I-IV),52 and lower symmetry derivatives
modified at the coordination core: iron(n) N-substituted por-
phyrins (n ) II-IV),52,69-73 iron(II) 21-thiaporphyrin,74 and
iron(n) 21-oxaporphyrin (n ) I-III).75 The hyperfine shift
patterns, that were recorded for iron porphyrins52,76 are sensitive
to the iron oxidation, spin and ligation states. The intermediate
iron porphyrins, acting in dioxygen activation of oxygen atom
transfer, have been trapped by NMR spectroscopy.40,77-79 The
fundamental spectroscopic features have been preserved in iron
complexes of core modified porphyrins (N-CH3, O, S, N-C-
Fe) providing that spin/electronic state are identical.52,69-75,80
1
The H NMR spectra of iron(n) inverted porphyrins display
characteristics that clearly reveal the lowering of symmetry.
Thus, the spread of regular â-H resonances are markedly larger
than for more symmetrical counterparts. Nevertheless, the
pattern of chemical shifts for these iron(III) inverted porphyrins
resembles that of iron(n) porphyrins and of core modified
iron(n) porphyrins. An average chemical shift of the perimeter
resonances as determined at 298 K has been considered here as
a suitable parameter to characterize the ground electronic/spin
state of iron(n) inverted porphyrins. Thus the average shifts for
six regular pyrroles have been examined for 1, 5, and 6 where
a side-on location of the metal ion with respect to the N-confused
pyrrole ring has been determined. The chemical shift values of
all downfield resonances for 3 and 4 have been included to
calculate the arithmetic mean. In two cases: 7 and 2, where all
internal donors including the C(21) atom are involved in regular
coordination, the shifts of eight upfield resonances including
2-NH contributed to the average. These values decrease in a
series 5, 85.3 (79.3); 6, 80.8 (62.6); 4, 66.1 (87.7); 3, 64.4 (68.5);
1, 24.1 (52.8); 7, -9.5 (43.9); 2, -26.4 (83.8) (in ppm at 298
K, in parentheses the spread of chemical shifts included in mean
values are given). Actually, the average shift values of 3, 4, 5,
and 6 approach those found for high-spin iron(III) tetraarylpor-
Scheme 4. Suggested Oxygenation Mechanism
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4428 J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004

2-Aza-21-carbaporphyrin
A R T I C L E S
phyrins,52 iron(III) â-substituted tetraarylporphyrin81 and
iron(III) N-methyltetraarylporphyrin (the average value for
regular pyrrole rings).70 The average chemical shift of 1 is
consistent with that found for high-spin iron(II) tetraarylpor-
phyrins, iron(II) N-methyltetraarylporphyrin, and iron(II) 21-
thia-tetraarylporphyrin.52,69,74 Finally, the upfield positions, seen
for 2 and 7, are clearly consistent with the intermediate- and
low-spin states respectively considering the asymmetric iron-
(III) porphyrins as the reference molecules.45,46,52,72,80
inverted porphyrin. The dominance of the π-spin transfer
2
2
mechanism has been taken as a direct evidence that dx -y is
not populated in 2 and 7. Thus, the ground state can be related
to the following models of the electronic configuration: inter-
2
1
1
1
0
2
2
2
mediate-spin (dxy) (dxz) (dyz) (dz ) (dx -y ) for 2 and low-spin
2
3
0
0
2
2
2
(dxy) (dxzdyz) (dz ) (dx -y
) for 7. The intermediate S ) 3/2
ground electronic state is characterized by the upfield shift
similarly as the low spin one as the identical delocalization path
is operating.45 The â-H shift value is expected to be large as
there are two π-symmetry unpaired electrons in the S ) 3/2
state in comparison to one for S ) 1/2 as clearly exemplified
the 2 and 7 couple.80
In the high-spin ion(III) complexes 5 and 6 the distinct low
field positions of â-H resonances assigned to the regular pyrroles
accompanied by the sign alternations detected for ortho-H, meta-
H, para-H of meso-aryls respectively provide an evidence for
the domination of contact contribution in isotropic shifts. Thus
the paramagnetic shifts of 5 and 6 can be explained by a model
typically applied to regular iron porphyrins and iron N-
substituted porphyrins. In the case of a high-spin iron(III)
Conclusion
An insertion of the oxygen atom into the M-C bond (a
carbon atom built into the aromatic moiety) is quite rare.41,83-91
In particular, the dioxygen addition to (P)FeIIIAr yielded the
phenoxide complexes, (P)FeIIIOAr as the principle products.41,92
The corresponding alkyl complexes (P)FeIIIR (P, porphyrin
dianion; R, alkyl group) reacted with dioxygen to form intially
µ-peroxo complexes (P)FeIIIOOR trapped in low temperatures.
This intermediates decomposed to (P)FeIIIOH and an aldehyde,
ketone or alcohol when R was a primary, secondary, or tertiary
alkyl group.40
1
1
1
1
1
2
2
2
centers(dxy) (dxz) (dyz) (dz ) (dx -y ) sboth σ and π routes of
spin density delocalization operate.52,81,82 Typical delocalization
pathways involve delocalization through a σ-framework by way
1
2
2
of σ-donation to the half occupied (dx -y ) iron(III) orbital.
Additionally the π-delocalization locates a considerable amount
of spin density at â-C, â-H, and meso positions.41,52,70,72,75,81
1
Actually the variation of the â-H positions in the H NMR
spectrum may be accounted for by specific π-delocalization
The results reported here demonstrate that dioxygen reacts
cleanly with iron(II) 2-aza-21-carbaporphyrin to form the
corresponding five-coordinate intermediate-spin iron(III) com-
plexes and eventually, 2-aza-21-carbaporphyrin gains the oxo
functionality. No direct evidence for the formation of intermedi-
ates in the oxygenation process has been found. An oxygenation
mechanism has been considered which involves the insertion
of dioxygen molecule into the Fe-C bond to form a transient
Fe-O-O-C(21) peroxide. A rapid O-O bond cleavage results
in a unique situation where two reactive centers are locked in
the macrocyclic cage as a consequence of restraints imposed
by the ligand structure. Further investigations of the iron
carbaporphyrinoid complexes are expected to afford an insight
into the reactivity of a metal-carbon bond as specifically tuned
carbaporphyrins can be expected to stabilize intermediates of
the oxygenation process.
mechanisms.81,82
In principle, the â-H isotropic shifts of 3 could be explained
by the similar spin delocalization mechanism as described for
5 and 6. However, once the oxygen has been introduced into
the coordination core an additional spin delocalization mech-
anism has been found to be instrumental. This new delocaliza-
tion route is remarkably effective. The sign of spin densities at
meso positions of 5 and 6 is identical as for (TPP)FeIIICl,52
which results in the upfield position of ortho-H and para-H
resonances and, respectively, the downfield shifts for meta
protons. Significantly, the reversed signs of the meso spin
densities for 3 and 4 have been determined as reflected by the
reversed shift signs of meso-aryl resonances. (Figures 4-6, Table
1S and 2Sssee the Supporting Information). In qualitative terms
one can readily assume that the unique (CO)‚‚‚Fe route provides
the negative spin π density meso carbons of 3 and 4. A detailed
analysis requires a more advanced description of electronic
structure for 3 and 4.
Experimental Section
Materials. Inverted porphyrin (CTPPH)H2 and its iron(II)
complexes (HCTPPH)FeIIBr have been obtained by already
described methods.25,93 The deuterated derivatives have been
synthesized using pyrrole-d5 or benzaldehyde-d6 in condensa-
tion.12 Chloroform-d used in 1H NMR was deacidified by
passing down a basic alumina column. Toluene-d8, dichlo-
Another characteristic feature of the iron(III) complexes 5
and 6 is the localized effect of the N-confused pyrrole ring. For
5 and 6 one pyrrole and 2-NH resonances are clearly distinct
from the other six and show a considerable upfield shift. The
logical conclusion is that the side-on-location of the iron(III)
with respect to the pyrrole ring primarily affects spin transfer
to the modified pyrrole ring. The inverted pyrrole reflects the
features of side-on interaction described for heteroporphyrins.4,12
In addition one can expect some contribution of an agostic
interaction as discussed previously for 1.39
(83) Grigor, B. A.; Neilson, A. J. Organomet. Chem. 1977, 129, C17.
(84) Kamaraj, K.; Bandyopadhyay, D. J. Am. Chem. Soc. 1997, 119, 8099.
(85) Wadhwani, P.; Mukherjee, M.; Bandyopadhyay, D. J. Am. Chem. Soc. 2001,
123, 12 430.
(86) Ryabov, A. D. Synthesis 1985, 233.
(87) Mahapatra, A. K.; Bandyopadhyay, D.; Bandyopadhyay, P.; Chakravorty,
A. Inorg. Chem. 1986, 25, 2214.
The isotropic shift pattern for â-H pyrrole of 2 and 7 reflects
the extensive spin delocalization into π molecular orbitals of
(88) Sinha, C.; Bandyopadhyay, D.; Chakravorty, A. Inorg. Chem. 1988, 27,
1173.
(89) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakravorty, A. Organometallics
1991, 10, 1135.
(80) Balch, A. L.; Cheng, R.-J.; La Mar, G. N.; Latos-Graz˘yn´ski, L. Inorg. Chem.
1985, 24, 2651.
(90) Marsella, A.; Agapakis, S.; Pinna, F.; Strukul, G. Organometallics 1992,
11, 3578.
(81) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L.; Hrycyk, W.; Pacholska, E.; Rachlewicz,
K.; Szterenberg, L. Inorg. Chem. 1996, 35, 6861.
(91) Valk, J.-M.; Boersma, J.; van Koten, G. Organometallics 1996, 15, 1996.
(92) Balch, A. L.; Hart, R. H.; Latos-Graz˘yn´ski, L. Inorg. Chem. 1990, 29, 3253.
(93) Geier, G. R., III.; Haynes, D. M.; Lindsey, J. S. Org. Lett. 1999, 1, 1455.
(82) Cheng, R.-J.; Chen, P.-Y.; Lovell, T.; Liu, T.; Noodleman, L.; Case, D. A.
J. Am. Chem. Soc. 2003, 125, 6774.
9
J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004 4429

A R T I C L E S
Rachlewicz et al.
Table 3. Summary of Crystallographic Data (HCTPP)FeIIIBr 2 and
(HCTPPO)FeIIIBr 4
romethane-d2, chloroform-d, DMSO-d6, DMF-d7 were degassed
by freezing-pumping-thawing method and stored in a dry
glovebox.
2
4
1H NMR Studies and Low-Temperature Studies. The
solution of (HCTPPH)FeIIBr in a deuterated solvent was
prepared under purified nitrogen in a glovebox. The sample
concentration 1 in the solvent of choice were on the order 2-5
mM Thus, typically a sample ca. 1-2 mg of 1 was dissolved
in 0.5 mL of deuterated solvent. The solution was directly placed
into an 1H NMR tube and sealed with a septum cap. In titration
experiments, a solution of the appropriate nitrogen base or
oxidizing reagent in the deuterated, deoxygenated solvent was
gradually added to the sample through a 10-µL microsyringe.
Usually, an appropriate mass of an applied reagent was dissolved
to give an approximately 0.25 M solution. It typically required
2-5 µL of the solution to be added to the NMR tube containing
iron inverted porphyrin to cause a detectable conversion. A
stepwise addition of dioxygen was carried out by titration with
the deuterated solvent saturated with dioxygen.
empirical formula
formula weight
temperature
crystal system
C44H28BrFeN4
748.46
298(2) K
monoclinic
P21/n
10.288(2)
15.757(3)
20.811(4)
90.000(4)°
3373.5(11)
4
C51H36BrFeN4O
856.60
150(2) K
monoclinic
C2/c
33.229(4)
13.2249(15)
18.102(2)
94.060(2)°.
7935.0(15)
8
space group
a, Å
b, Å
c, Å
b
V, Å3
Z
D
calcd, g‚cm-3
1.474
1.434
absorption coefficient
θ range
1.671 mm-1
1.62 to 25.08°
-11 to 12, -18
to 17, -22 to 24
17738
1.433 mm-1
1.23 to 27.52°.
-30 to 43, -16
to 17, -22 to 23
24572
hkl ranges
reflections collected
independent reflections 5961 [R(int) ) 0.1215] 9062 [R(int) ) 0.0914]
parameters
451
0.583
498
1.034
0.0510/0.1043
0.1616/0.1606
0.900/-0.660
goodness-of-fit on F2
R1/wR2 [I > 2sigma(I)]a 0.0449/0.0910
In the case of low-temperature studies, the sample was
removed from the glovebox and cooled to 195 K in the ethanol
bath which was chilled by the addition of sufficient amount of
liquid nitrogen to reach 195 K. Dioxygen was introduced into
the sample through the syringe needle. The sample was shaken
in the cold bath and transferred to the precooled NMR probe
R1/wR2 (all data)
0.2401/0.1586
0.268/0.366
max/min peak (e.Å-3
)
a R1 ) Σ||Fo| - |Fc||/Σ|Fo|. wR2 ) [Σ[w(Fo - Fc )2/Σ[w(Fo )2]}1/2
.
2
2
2
Isolation of (HCTPP)FeIIIBr 2 and (HCTPPO)FeIIIBr 4.
(HCTPP)FeIIIBr 2. In a round-bottom flask, (HCTPPH)FeIIBr
(100 mg, 0.133 mmol) was dissolved in 30 mL of anhydrous
CH2Cl2. The solution was exposed to air for one minute. The
green solution was then capped and stirred at room temperature.
The progress of the reaction was monitored by UV-vis
spectroscopy and the reaction was stopped when the peak at
461 nm completely disappeared. After solvent removal under
vacuum the product was placed in the inner atmosphere drybox.
The solid was recrystallized from THF/hexane under anaerobic
condition to obtain crystals suitable for X-ray analysis. The yield
of this reaction is near quantitative. Anal. Calcd for FeBrN4-
C44H28‚0.1THF‚0.3CH2Cl2: N, 7.17; C, 68.73; H, 3.79.
1
and the progress of the reaction was followed by H NMR
spectroscopy.
2H NMR Studies. The samples used in 2H NMR experiments
1
have been prepared similarly as for H NMR starting from
(HCTPPD-d7)FeIIBr and using regular solvents.
Solution Magnetic Moment Measurements.43 The magnetic
susceptibility data carried out for five samples in the concentra-
tion range 2.7 mg/mL to 3.6 mg/mL. The measurements were
carried out in chloroform-d using methylene chloride as an
internal reference. After the completion of Evans method
measurement on (HCTPPH)FeIIBr 1, the solution was exposed
1
briefly to dioxygen and the H NMR spectra were recorded to
trace the progress of the reaction. The measurements of
(HCTPP)FeIIIBr 2 were made when no (HCTPPH)FeIIBr 1 and
[(CTPPO)FeIIIBr]- 3 IIBr were observable in 1H NMR spectra.
The measurements gave the following magnetic moments: 4.87
( 0.10 µB for (HCTPPH)FeIIBr and 4.19 ( 0.10 µB
for (HCTPP)FeIIIBr. The solution magnetic moment of
[(CTPPO)FeIIIBr]- 3 (5.6 ( 0.1 µB) was also determined starting
from the separately synthesized compound (HCTPPO)FeIIIBr
4. Diamagnetic correction of ligand was made using the value
of 409 × 10-6 cgs emu/mol calculated from Pascal’s constants.
Instrumentation. 1H NMR (300 and 500 MHz) spectra were
measured on Bruker AMX 300 and Bruker Avance 500
spectrometers. The peaks were referenced against the residual
resonances of the deuterated solvents. The 2H NMR spectra were
collected using a Bruker Avance 500 instrument operating at
76.77 MHz. A spectral width of 200 ppm was typical and 16 K
points was used. A pulse delay of 50 ms was applied. The
Found: N, 6.59; C, 68.80; H, 3.28. UV-vis (CH2Cl2) [λmax
,
nm (log ꢀ, M-1 cm-1)]: 337 (4.51), 361 (4.50), 416 (4.48),
564 (4.09), 692 (3.49), 887 (3.60).
(HCTPPO)FeIIIBr 4. (HCTPPH)FeIIBr (50 mg, 0.067 mmol)
was dissolved in 30 mL of anhydrous CH2Cl2. The solution
was bubbled with oxygen for one minute. The green solution
was then capped and stirred at room temperature for 12 h. The
progress of the reaction was monitored by UV-vis spectroscopy
and the reaction was stopped when the Soret band shifted to
390 nm and Q band of the starting (HCTPPH)FeIIBr disap-
peared. After solvent removal under vacuum the product was
placed in the inner atmosphere drybox. The crude solid was
dissolved in 3 mL of CH2Cl2 and a slow addition of hexane
precipitated the desired product. Yield: 39 mg (76%). The
crystals suitable for X-ray analysis were obtained from a slow
diffusion of hexane into a toluene solution of 4. Anal. Calcd
for FeBrN4C44H28O: N, 7.33; C, 69.13; H, 3.69. Found: N,
7.35; C, 68.81; H, 3.97. UV-vis (CH2Cl2) [λmax, nm (log ꢀ,
M-1 cm-1)]: 390 (4.76), 572 (3.99, sh), 670 (3.82, sh).
2
residual H NMR resonances of the solvents were used as a
secondary reference.
The mass spectra were obtained on the Finnigan MAT TSQ
700 spectrometer by means of ESI method. UV-vis spectra
were recorded on the Hewlett-Packard 8435 diode-array spec-
trophotometer. IR spectra were measured on the FTIR-IFS 113
V Bruker spectrometer.
Crystallography Studies. The crystal of (HCTPP)FeIIIBr 2
were obtained from a slow diffusion of n-hexane into a THF
solution of 2 under anaerobic conditions. The crystal of
(HCTPPO)FeIIIBr 4 were obtained from a slow diffusion of
9
4430 J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004

2-Aza-21-carbaporphyrin
A R T I C L E S
n-hexane into a toluene solution of 4 under anaerobic conditions.
The summary of crystallographic data is given in Table 3.
Each crystal was attached to the tip of a glass capillary and
mounted on a Bruker SMART 1000 CCD diffractometer for
data collection using graphite-monochromated MoKR (λ )
0.710 73 Å) radiation. All non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were placed in ideal
positions and refined as riding atoms with relative isotropic
displacement parameters. The N2 and C3 of compound 4 were
refined as mutually disorder with 50% occupancy on each site.
The coordinates and thermal parameters were defined equated
on the two atoms sharing the same site. In the crystal lattice,
there are two independent toluene sites with half occupancy on
each site. The atoms on the phenyl ring of the disordered
toluenes were constrained to regular hexagonals and refined
isotropically.
Acknowledgment. This work was supported at the University
of Wrocław by the State Committee for Scientific Research
KBN of Poland (Grant 4 T09A 147 22) (L.L.-G.) and by the
National Science Council of Taiwan (C.-H.H.).
Supporting Information Available: Crystallographic data for
2 and 4 (CIF), the figure showing packing and intermolecular
interactions in the crystal lattice of (HCTPPO)FeIIIBr 4, VT
NMR data for 2, 3, 4, 5, 6, tables of chemical shifts of meso-
phenyl resonances for 3, 4, 5, and 6. This material is available
free of charge via the Internet at http://pubs.acs.org.
JA039792Y
9
J. AM. CHEM. SOC. VOL. 126, NO. 13, 2004 4431