Reaction of an oxoiron(IV) complex with nitrogen monoxide: Oxygen atom or oxide(1-) ion transfer?

Article abstract of DOI:10.1021/ic2007205

Reaction of [FeO(tmc)(OAc)]⁺ with the free radical nitrogen monoxide afforded a mixture of two Fe^II complexes, [Fe(tmc)(OAc)]⁺ and [Fe(tmc)(ONO)]⁺ (where tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and AcO^- = acetate anion). The amount of nitrite produced in this reaction (ca. 1 equiv with respect to Fe) was determined by ESI mass spectrometry after addition of ¹⁵N-enriched NaNO₂. In contrast to oxygen atom transfer to PPh₃, the NO reaction of [FeO(tmc)(OAc)]⁺ proceeds through an Fe^III intermediate that was identified by UV-vis-NIR spectroscopy and ESI mass spectrometry and whose decay is dependent on the concentration of methanol. The observations are consistent with a mechanism involving oxide(1-) ion transfer from [FeO(tmc)(OAc)]⁺ toNOto form an Fe^III complex andNO₂^-, followed by reduction of the Fe^III complex. Competitive binding of AcO^- and NO₂^- to Fe^II then leads to an equilibrium mixture of two Fe^II(tmc) complexes. Evidence for the incorporation of oxygen from the oxoiron(IV) complex into NO₂^- was obtained from an ¹⁸O-labeling experiment. The reported reaction serves as a synthetic example of the NO reactivity of biological oxoiron(IV) species, which has been proposed to have physiological functions such as inhibition of oxidative damage, enhancement of peroxidase activity, and NO scavenging.

Full text of DOI:10.1021/ic2007205

ARTICLE
pubs.acs.org/IC
Reaction of an Oxoiron(IV) Complex with Nitrogen Monoxide: Oxygen
Atom or Oxide(•1ꢀ) Ion Transfer?
Travis M. Owen and Jan-Uwe Rohde*
Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
S Supporting Information
b
þ
ABSTRACT: Reaction of [FeO(tmc)(OAc)] with the free radical nitro-
II
þ
gen monoxide afforded a mixture of two Fe complexes, [Fe(tmc)(OAc)]
and [Fe(tmc)(ONO)] (where tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetra-
azacyclotetradecane and AcO = acetate anion). The amount of nitrite
þ
ꢀ
produced in this reaction (ca. 1 equiv with respect to Fe) was determined by
1
5
ESI mass spectrometry after addition of N-enriched NaNO . In contrast
2
þ
to oxygen atom transfer to PPh , the NO reaction of [FeO(tmc)(OAc)]
3
III
proceeds through an Fe intermediate that was identified by UVꢀvisꢀNIR
spectroscopy and ESI mass spectrometry and whose decay is dependent on
the concentration of methanol. The observations are consistent with a mechanism involving oxide(•1ꢀ) ion transfer from
þ
III
ꢀ
III
[
FeO(tmc)(OAc)] to NO to form an Fe complex and NO , followed by reduction of the Fe complex. Competitive binding of
2
II II
ꢀ
ꢀ
AcO and NO to Fe then leads to an equilibrium mixture of two Fe (tmc) complexes. Evidence for the incorporation of oxygen
2
ꢀ
18
from the oxoiron(IV) complex into NO2 was obtained from an O-labeling experiment. The reported reaction serves as a
synthetic example of the NO reactivity of biological oxoiron(IV) species, which has been proposed to have physiological functions
such as inhibition of oxidative damage, enhancement of peroxidase activity, and NO scavenging.
’
INTRODUCTION
Lastly, the possibility of a direct reaction between the ferryl group
of cytochrome bd and NO has been discussed in the context of
inhibition of this oxidase by NO.
Reactions of the free radical nitrogen monoxide with metalꢀ
8
oxygen species of metalloproteins have been recognized as me-
chanisms relevant to NO metabolism and detoxification in vivo.
For example, oxygenated metalloproteins such as oxyhemoglobin
and oxymyoglobin react rapidly with NO, causing dioxygenation to
While synthetic precedent exists for the chemistry of super-
oxometal complexes and NO showing conversion of NO into
peroxynitrite and subsequently into nitrate, nitrite, and/or
9
ꢀ12
1
nitrogen dioxide,
knowledge of the fundamental reactivity
nitrate. The reaction of NO with the ferryl state of these and
between oxometal complexes and NO is limited. Studies with Cr
related proteins is of interest, as well. Studies with several globins
and Mn complexes suggested that the reactions of oxometal
have shown that NO can efficiently and rapidly reduce the high-
1
0,13,14
III
species with NO are very fast.
For example, the first step in
valent state to the Fe state under concomitant formation of
IV 2þ
2,3
the NO reaction of aqueous Cr O (aq) is too fast to be
observed spectrophotometrically, but Cr (ONO) (aq) is
believed to be the primary product based on its decay kinetics.
innocuous nitrite. It has been suggested that the role of NO could
be that of an antioxidant of oxoiron(IV) and oxoiron(IV) protein
III
2þ
1
0
2
ꢀ4
radical species to inhibit oxidative damage.
transformation of NO into nitrite mediated by ferryl globins may be
Conversely, the
In another case, photolysis of the macrocyclic ligand complex
III
þ
2,3
trans-[Cr ([14]aneN )(ONO) ] generated a transient spe-
4 2
IV
important as a mechanism for NO scavenging and detoxification.
cies, proposed to be the corresponding Cr O complex, which
Nitrogen monoxide may then be viewed as a substrate for globins
13,15
3
underwent rapid recombination with NO.
oxoiron(IV) porphyrin π-cation radicals, [Fe O(tpfpp) ]
The reactions of
displaying peroxidase activity.
IV
þ• þ
In reactions of NO with the compounds I of peroxidase
IV
þ• þ 15
and [Fe O(ppIX) ] , with NO were studied in the gas
enzymes, reduction occurs in two one-electron steps via com-
16
III
5,6
phase. These reactions were proposed to proceed through
oxygen atom transfer, because the corresponding iron(III) por-
phyrins, which are two oxidizing equivalents below the oxoiron-
(IV) porphyrin π-cation radicals, were detected as primary
pound II to the Fe state. At low NO levels, NO increases the
activity of some peroxidases, and this effect has been linked to the
ability of NO to accelerate the reduction of compound II to the
III
Fe state, which is the rate-limiting step in the catalytic cycles of
16
6
products. Consequently, NO was inferred as the product of
2
these enzymes. Similar to the interaction between NO and ferryl
oxidation of NO. In contrast, the reaction of electrochemically
globins, the idea of a bidirectional relationship between NO and
peroxidases has been put forward where NO affects peroxidase
6
catalysis and compound I functions as a sink for NO. Also
catalase has been reported to consume NO in the presence of
Received: April 7, 2011
Published: April 28, 2011
7
H O , presumably by reaction of NO with catalase compound I.
2
2
r 2011 American Chemical Society
5283
dx.doi.org/10.1021/ic2007205
|Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
ARTICLE
IV
Generation of [Fe O(tmc)(OTf)]OTf, 2ꢀOTf(OTf), and
generated oxoiron(IV) and oxomanganese(IV) porphyrins with
NO in aqueous solution yielded nitrite.
In the reverse direction, some oxo complexes and NO were
17
IV
[Fe O(tmc)(OAc)]OTf, 2ꢀOAc(OTf). Method A. For the purpose
of investigating the reaction of 2ꢀOAc with NO, the preparation of
produced irreversibly by thermal or photoinduced dissociation of
2ꢀOTf and 2ꢀOAc was carried out in an N
2
atmosphere. A 1 mM
1
8
III
III
solution of 1ꢀOTf(OTf) (0.002 mmol) in 2.0 mL of nitromethane was
placed in a 1-cm UVꢀvis cuvette and precooled to ꢀ20 °C. Upon
addition of 0.050 mL of a solution of iodosylbenzene (0.002 mmol) in
methanol (anhydrous, 99%), 2ꢀOTf formed within 5 min. ESI(þ) MS
nitrito complexes of Mn and Cr and by oxygen atom
1
9
III
transfer from NO to a Cr complex. Other examples of reac-
2
tions related to NO reactivity of oxo complexes are nitrogen
atom transfer reactions from nitrido complexes to NO, which
þ
þ
20
(MeNO ) m/z: M calcd for C H F FeN O S ({2ꢀOTf} ), 477.14;
þ þ þ
2
15 32
3
4 4
have been reported to liberate N O.
2
found, 477.1 (M ), 461.2 ({M ꢀ O} ), 257.3 ({tmc þ H} ). UVꢀvis
We report here the reaction of an oxoiron(IV) complex,
Fe O(tmc)(OAc)] , with NO. While the equatorial coordi-
IV
þ 15
(MeNO ) λ , nm (ε): 825 (230).
2
max
[
Subsequently, a solution of 0.002 mmol of tetraethylammonium
acetate in 0.050 mL of nitromethane was added to the solution of
nation of the Fe center by the macrocyclic ligand offers a
IV
stabilizing environment for the Fe dO group, the acetate anion
2
2
ꢀOTf in nitromethane at ꢀ20 °C. The formation of 2ꢀOAc from
was chosen as the sixth ligand to discourage direct interaction
between NO and the Fe center. The reaction described here
complements the established reactivity modes of oxoiron(IV)
complexes, which include oxygen atom transfer to organic
substrates and other iron complexes, hydrogen-atom abstraction,
ꢀOTf was indicated by a decrease of intensity at λ = 825 nm and the
appearance of a new peak at λ = 995 nm over a period of ca. 1 h. ESI(þ)
þ
þ
þ
þ
MS (MeNO
2
) m/z: M calcd for C16
H
35FeN
4
O
3
({2ꢀOAc} ),
þ
3
87.21; found, 387.0 (M ), 371.3 ({M ꢀ O} ), 257.3 ({tmc þ H} ).
UVꢀvis (MeNO ) λ , nm (ε): 825 (120), 995 (100).
21
2
max
electron transfer, and hydride transfer.
For the conversion of 2ꢀOTf into 2ꢀOAc by incremental addition
of NEt
4
AcO, a 1 mM solution of 2ꢀOTf (0.002 mmol) in 2.0 mL of
nitromethane was prepared in a 1-cm UVꢀvis cuvette at ꢀ20 °C as
’
EXPERIMENTAL SECTION
described above. Volume increments of 0.015 mL of a 33 mM solution of
ꢀ
4
4
NEt AcO (5 10 mmol) in nitromethane were added in 2-min
intervals to the solution of the Fe complex up to a total of 1.5 molar equiv
Materials. All reagents and solvents were purchased from commer-
cial sources and were used as received, unless noted otherwise. Acet-
onitrile, dichloromethane, and diethyl ether were deoxygenated by
3
of NEt AcO (with respect to Fe).
4
Method B. Upon addition of 0.150 mL of a solution of (diacet-
oxyiodo)benzene (0.006 mmol) in nitromethane to a 1 mM solution of
sparging with N and purified by passage through two packed columns
2
of molecular sieves under an N pressure (MBraun solvent purification
2
1
ꢀOTf(OTf) (0.002 mmol) in 2.0 mL of nitromethane at 20 °C, 2ꢀ
system). Nitromethane was refluxed over CaH
sphere, distilled, and passed through a column of basic Al
2
under an Ar atmo-
2
2
OTf formed within 30 s. UVꢀvis (MeNO ) λ , nm (ε): 825 (230).
2
O
3
.
Pre-
2
max
1
9
Samples for F NMR spectroscopy were prepared at a concentration of
paration and handling of air- and moisture-sensitive materials were
carried out under an inert gas atmosphere by using standard Schlenk and
vacuum line techniques or a glovebox. Nitrogen monoxide was prepared
1
9
1
0 mM in CD
[FeO(tmc){OS(O)
3
NO
2
.
F NMR (282.4 MHz, CD
3
NO
ꢀ
3 3
SO ). For comparison,
2
, δ): ꢀ77.5
þ
(
2
CF
3
}] ), ꢀ79.2 (CF
1
9
2
3
F NMR of 1ꢀOTf(OTf) (282.4 MHz, CD NO , δ): ꢀ0.6 ([Fe-
by reaction of concentrated hydrochloric acid with sodium nitrite. The
gas mixture produced was passed through a 50-cm column of KOH
3
2
þ
ꢀ
(
tmc){OS(O)
2
CF
3
}] ), ꢀ79.3 (CF
3 3
SO ).
Addition of a solution of 0.002 mmol of NEt
4
AcO in 0.050 mL of
pellets, a 2-m stainless steel coil cooled to ꢀ94 °C (acetoneꢀliquid N
2
),
nitromethane to this solution caused conversion of 2ꢀOTf into 2ꢀOAc
and a bubbler charged with a concentrated aqueous NaOH solution for
removal of unwanted nitrogen oxides; the gas was dried by passing it
1
9
(
ca. 30 s). UVꢀvis (MeNO ) λ , nm (ε): 832 (120), 1005 (110).
F
2
max
ꢀ
22
NMR (282.4 MHz, CD NO , δ): ꢀ79.4 (CF SO ).
through a short column (ca. 20 cm) of KOH pellets. (Caution:
3
2
3
3
15
Reaction of 2ꢀOAc with Triphenylphosphine. A 1 mM
solution of 2ꢀOAc (0.002 mmol) in 2.0 mL of nitromethane was
prepared in a UVꢀvis cuvette at ꢀ20 °C as described above (method A),
cooled to ꢀ25 °C, and treated with a solution of 0.020 mmol of tri-
phenylphosphine in 0.35 mL of nitromethane. The half-life of the
reaction was ca. 10 min. The product solution was subjected to ESI
2
Nitrogen monoxide is a toxic gas.) Fe(OTf) 2MeCN was synthe-
3
24
sized by a modified literature method from anhydrous FeCl
2
and
trimethylsilyl trifluoromethanesulfonate in acetonitrile and recrystal-
25
lized from acetonitrileꢀdiethyl ether. The ligand 1,4,8,11-tetramethyl-
1
5,26
II
27
1
(
,4,8,11-tetraazacyclotetradecane,
[Fe (tmc)(OTf)]OTf [1ꢀOTf-
28
OTf), stored under an N atmosphere], and iodosylbenzene were
2
prepared following published procedures. (Caution: Iodosylbenzene is
mass spectrometry. ESI(þ) MS (MeNO
2
) m/z calcd for C16
H
35Fe-
([Fe (tmc)(OAc)] , {1ꢀOAc} ), 371.21; found, 371.4 ({1ꢀ
þ
II
þ
þ
potentially explosive, if dried extensively, and should be handled with
4 2
N O
29
18
2
18
15
15
care. ) Isotope-enriched H
O (98% O) and Na NO
2
(98% N)
OAc} ). The product solution was evaporated to dryness, and the
3
1
31
were purchased from Cambridge Isotope Laboratories, Andover, MA.
residue was dissolved in CDCl
3
for P NMR spectroscopy. P NMR
), ꢀ5.4 (PPh ).
Physical Methods. UVꢀvisible spectra were recorded on an HP
(121.5 MHz, CDCl , δ): 29.0 (OPPh
3
3
3
8
453A diode array spectrophotometer (Agilent Technologies) with
Reaction of 2ꢀOAc with NO. A 1 mM solution of 2ꢀOAc (0.002
mmol) in 2.0 mL of nitromethane was prepared as described above
(method A) in a UVꢀvis cuvette at ꢀ20 °C and then cooled to ꢀ25 °C.
A total of 5 mL of NO(g) was purged via gastight syringe through this
solution (<5 s), and the reaction was monitored by UVꢀvisible spec-
troscopy. (The solubility of NO in nitromethane is not known but may be
similar to that in other organic solvents, which is in the range of ca.
samples maintained at the desired temperature using a cryostat/heater
from Unisoku Scientific Instruments. For solutions containing both
nitromethane and methanol, the same solvent mixture was used for the
background sample. NMR spectra were recorded on a Bruker Avance
19
31
DPX 300 spectrometer at ambient temperature. F and P chemical
shifts are reported in parts per million (ppm) and were referenced to an
1
9
30
external standard [CFCl
0
3
(δ = 0 ppm) for F NMR and H
3
PO
4
(85%,
10ꢀ20 mM at ꢀ25 °C. Here, the actual concentration of dissolved NO
31
ppm) for P NMR spectra]. Mass spectral data were acquired on a
will likely be below the solubility limit.) After complete disappearance of
quadrupole ion trap ThermoFinnigan LCQ Deca mass spectrometer
using an electrospray ionization source. Analysis by GCꢀMS was
performed on a TRACE GC 2000 gas chromatograph (column, TRACE
TR-1) coupled with a single quadrupole ThermoFinnigan Voyager mass
spectrometer.
the characteristic bands of 2ꢀOAc, the solution was purged for 10 min
with Ar to remove excess NO. ESI(þ) MS (MeNO ) m/z calcd for
2
þ
II
C
16
H
35FeN
O
4 2
({1ꢀOAc} ), 371.21; C14
H
32FeN O
5 2
([Fe (tmc)-
þ
þ
þ
(ONO)] , {1ꢀONO} ), 358.19; found, 371.3 ({1ꢀOAc} ), 358.1
þ
þ
þ
({1ꢀONO} ), 328.1 ({1ꢀONO ꢀ NO} ), 257.3 ({tmc þ H} ).
5
284
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
ARTICLE
a
Mass spectra of samples withdrawn from the reaction solution within
Chart 1. Structures of 1ꢀX and 2ꢀX
1
.5 min of the initiation of the reaction showed additional peaks: ESI(þ)
III þ
2
MS (MeNO ) m/z: 492.1 ([Fe (tmc)(OMe)(OTf)] ), 402.2
III
þ
II
þ
(
(
(
[Fe (tmc)(OMe)(OAc)] ), 343.3 ([Fe (tmc)(OMe)] ), 171.7
III
2þ
III
[Fe (tmc)(OMe)] ). Relative abundance of Fe ions, 10ꢀ25%
t = 1.5 min), <5% (1 h), not observed (4 h). For samples prepared using
deuterated methanol (CD
3
OD, 99.8% D), ESI(þ) MS (MeNO
2
) m/z:
495.2, 405.2, 346.4, 173.2.
Comparison of Self-Decay and NO Reaction of 2ꢀOAc. A
a
ꢀ
ꢀ
ꢀ
2
X = TfO , AcO , NO
.
1
mM solution of 2ꢀOAc in nitromethane was prepared at ꢀ20 °C, as
described above (method A), and then warmed to 20 °C. The half-life of
1
8
the decay, as determined by UVꢀvisible spectroscopy, was ca. 25 min.
Isotope Labeling Experiments. For the generation of O-
þ
IV 18
þ
18
ESI(þ) MS (MeNO
2
) m/z calcd for C16
71.21; found, 371.3 ({1ꢀOAc} ), 257.3 ({tmc þ H} ).
H
35FeN
4
O
2
({1ꢀOAc} ),
enriched [Fe ( O)(tmc)(OAc)] , [ O]-2ꢀOAc, a solution of iodo-
þ
þ
18 18
3
sylbenzene in methanol was treated with 10 equiv of H O (98% O)
2
1
8
In a separate experiment, a solution of 2ꢀOAc was prepared
for 30 min at 20 °C. The generation of [ O]-2ꢀOAc at ꢀ20 °C and
at ꢀ20 °C, warmed to 20 °C, and immediately purged with 5 mL of
NO(g) (<5 s). After complete disappearance of the characteristic bands
of 2ꢀOAc (<10 s), the solution was purged for 10 min with Ar to
remove excess NO and subjected to ESI mass spectrometry. The mass
spectrum displayed peaks identical to those observed for the reaction of
subsequent reaction with NO at ꢀ25 °C were carried out as described
1
8
above for 2ꢀOAc. To determine the extent of O incorporation, the
isotope distribution patterns observed by ESI mass spectrometry for
þ
þ
{2ꢀOAc} and {1ꢀONO} , respectively, were simulated using the
1
6
18
18
patterns calculated for the O and O isotopologues. For 2ꢀOAc,
O
2
ꢀOAc with NO at ꢀ25 °C.
incorporation was in the range of 52ꢀ72% (based on the peaks at m/z =
ꢀ
16
þ
18
þ
Quantification of NO Formed in the Reaction of 2ꢀOAc
387.0 and 389.0 for {[ O]-2ꢀOAc} and {[ O]-2ꢀOAc} , respec-
18
2
with NO. The reaction of 2ꢀOAc with NO at ꢀ25 °C was carried out
tively). For 1ꢀONO, O incorporation was in the range of 6ꢀ18%
16 16 þ
1
5
as described above. After removal of excess NO, a solution of Na NO
2
(based on the peaks at m/z = 358.1 and 360.1 for {1ꢀ ON O} and
18 16 þ 18
15
(
0.002 mmol, 98% N) in 0.015 mL of methanol was added as a
{1ꢀ ON O} , respectively). The retention of O in 1ꢀONO from
2ꢀOAc was 12ꢀ25% (average of six trials, 18%). When the reaction of
unlabeled 2ꢀOAc with NO was carried out in the presence of 10 equiv
15
2
standard to the product solution at 20 °C (1 equiv of Na NO with
respect to Fe). Following an equilibration time of 1 h, the solution was
subjected to ESI mass spectrometry. The isotope distribution pattern
1
8
18
of H
observed.
2
O, no incorporation of O into 2ꢀOAc or 1ꢀONO was
þ
of {1ꢀONO} was simulated using the patterns calculated
na
þ
14
þ
for {1ꢀO NO} and a mixture of {1ꢀO NO} (2%) and
15
þ
{
1ꢀO NO} (98%) (na, natural abundance). In six trials, the ratio
’
RESULTS AND DISCUSSION
na
ꢀ
15
ꢀ
of NO produced to N-enriched NO2 added (and thus to Fe)
2
ranged from 1.03:1 to 1.49:1 [average, 1.32(18)]. [Because 0.27(6)
Generation and Characterization of Oxoiron(IV) Complexes.
The complex [Fe O(tmc)(OAc)] , 2ꢀOAc (Chart 1), was
þ
ꢀ
IV
þ
equiv of NO
2
(with respect to Fe) was found in solutions of 1ꢀOAc
ꢀ
II
treated with an excess of NO (vide infra), the average amount of NO
2
generated by oxidation of [Fe (tmc)(OTf)] , 1ꢀOTf, and sub-
produced from the NO reaction of 2ꢀOAc was estimated as 1.05(19)
sequent ligand substitution in a manner similar to that reported for
ꢀ
IV
equiv of NO
2
(with respect to Fe).] The validity of this method was
the corresponding trifluoroacetato complex, [Fe O(tmc){OC-
þ 31
tested on two series of authentic samples consisting of (a) equimolar
(
O)CF }] . Reaction of 1ꢀOTf with iodosylbenzene in the
3
1
5
amounts of 1ꢀOTf(OTf) and Na NO
2
and varying amounts of
weakly coordinating solvent nitromethane at ꢀ20 °C produced
na
Na NO (0.25ꢀ1.5 equiv) and (b) equimolar amounts of 1ꢀOTf-
IV
þ
2
[
Fe O(tmc)(OTf)] , 2ꢀOTf, which was converted into 2ꢀOAc
15
na
(
(
OTf), NEt
4
AcO and Na NO
2
na
and varying amounts of Na NO
2
by exchange of the triflato ligand with acetate. Both 2ꢀOTf and
ꢀ
15
ꢀ
0.25ꢀ1.5 equiv). The ratio of NO
2
to N-enriched NO
2
[i.e.,
2
ꢀOAc exhibit absorption bands in the near-IR region character-
na
þ
14
þ
ratio of {1ꢀO NO} to a mixture of {1ꢀO NO} (2%) and
IV
2þ/þ
ꢀ1
31
istic of [Fe O(tmc)(L/X)]
complexes [2ꢀOTf, λ
=
15
þ
max
{
1ꢀO NO} (98%)] determined from the observed intensity ratio
ꢀ1
8
M
25 nm (ε = 230 M cm ); 2ꢀOAc, λ = 825 (ε = 120
3
max
was typically slightly overestimated (<20%).
ꢀ1
ꢀ1
ꢀ
cm ) and 995 nm (100)]. As shown by incremental
3
The amount of NO
2
present in solutions of NO in MeNO
2
ꢀ
addition of NEt AcO, 1 equiv of acetate is required for the
4
MeOH was estimated as follows. A mixture of 2.0 mL of nitromethane
and 0.050 mL of methanol was purged with 5 mL of NO(g) and, after
standing for 30 min, purged for 10 min with Ar to remove excess NO. To
this solution were added a solution of 0.002 mmol of 1ꢀOTf(OTf)
conversion of 2ꢀOTf into 2ꢀOAc in nitromethane (Figure 1).
The complexes also were identified by peaks at m/z = 477
(
2ꢀOTf) and 387 (2ꢀOAc) in their ESI mass spectra.
15
The coordination of the triflate anion to the Fe centers in
2
in 2.0 mL of nitromethane and a solution of Na NO (0.002 mmol,
15
1ꢀOTf and 2ꢀOTf in solution and its dissociation upon addi-
9
8% N) in 0.015 mL of methanol. Analysis of the isotope distribution
19
þ
tion of NEt AcO were investigated by F NMR spectroscopy.
4
pattern of {1ꢀONO} by ESI mass spectrometry indicated that
na
ꢀ
na
ꢀ
For this purpose, 2ꢀOTf was generated by oxidation of 1ꢀOTf
typically less than 0.1 mM NO2 was present (<0.2 equiv of NO2
15
2ꢀ
with PhI(OAc) , because 2ꢀOTf exhibits greater stability under
2
with respect to N-enriched NO and Fe added).
Similarly, the possible formation of NO
19
ꢀ
these conditions. The F NMR spectrum of 1ꢀOTf(OTf) in
3 2
2
from the reaction of 1ꢀ
CD NO displays two resonance signals at δ = ꢀ0.6 and ꢀ79.3
OAc with NO was tested. A solution of 0.002 mmol of 1ꢀOTf(OTf)
ꢀ
ppm, where the latter is attributed to the free CF SO anion
and 0.002 mmol of NEt
4
AcO in 2.0 mL of nitromethane and 0.050 mL
3
3
ꢀ
II
and the former to CF SO3 bound to the high-spin Fe center.
of methanol was purged with 5 mL of NO(g) and, after standing for 30
min, purged for 10 min with Ar to remove excess NO. To this solution
3
On the basis of the relative intensities of these two peaks, the
1
5
15
was added a solution of Na NO (0.002 mmol, 98% N) in 0.015 mL
resonance signal at δ = ꢀ0.6 ppm accounts for ca. 40% of the
2
þ
ꢀ
of methanol. Analysis of the isotope distribution pattern of {1ꢀONO}
CF
3
SO
3
present (i.e., ca. 0.8 equiv with respect to Fe). This
II
na
ꢀ
by ESI mass spectrometry showed that 0.27(6) equiv of NO
2
was
indicates that ca. 80% of the Fe (tmc) is present in the form
15
ꢀ
present (with respect to N-enriched NO2 and Fe).
of 1ꢀOTf, whereas the remainder corresponds to a complex
5
285
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
ARTICLE
Figure 1. Conversion of 1 mM 2ꢀOTf (bold green line) into 2ꢀOAc
Figure 2. Reaction of 1 mM 2ꢀOAc (bold black line) with 10 equiv of
(
bold black line) in nitromethane by addition of NEt AcO in increments
PPh in nitromethane at ꢀ25 °C as monitored by electronic absorption
4
3
of 0.25 equiv at ꢀ20 °C as monitored by electronic absorption
spectroscopy (path length, 1 cm). Inset: Corresponding changes of
absorbance at 825 nm (green squares).
spectroscopy (path length, 1 cm). Inset: Time course of the reaction (λ
= 825 nm).
ꢀ
without coordinated CF SO , presumably the solvento com-
3
3
II
2þ
19
plex [Fe (tmc){ON(O)CD }] . Similarly, two F resonance
3
signals were observed for 2ꢀOTf(OTf), δ = ꢀ77.5 and ꢀ79.2
ꢀ
ppm. Here, the peak at δ = ꢀ77.5 ppm is attributed to CF SO
3
3
IV
bound to the Fe center and accounts for ca. 30% of the
CF SO present. Thus, ca. 60% of the Fe in CD NO solution
ꢀ
3
3
3
2
IV
corresponds to 2ꢀOTf and 40% to [Fe O(tmc){ON(O)-
2
þ
IV
2þ
CD }]
or perhaps [Fe O(tmc)] . Upon addition of
3
NEt AcO to the solution of 2ꢀOTf(OTf), the resonance signal
4
ꢀ
of coordinated CF SO
disappeared, while that of free
3
3
ꢀ
CF SO became more intense and sharper (δ = ꢀ79.4 ppm).
3
3
ꢀ
3
These observations confirm the displacement of the CF SO
3
ꢀ
ligand in 2ꢀOTf by AcO to afford 2ꢀOAc.
19
To explain the different F chemical shifts for the triflato
ligands in 1ꢀOTf and 2ꢀOTf, several factors must be consid-
ered. First, coordination of the triflate ion to a Lewis-acidic metal
Figure 3. Reaction of 1 mM 2ꢀOAc (bold black line) in nitromethane
with NO at ꢀ25 °C (reaction solution after ca. 1 min, bold red line), as
monitored by electronic absorption spectroscopy (path length, 1 cm). Inset:
Time course of the reaction [λ = 825 (black line) and 470 nm (red line)].
19
center can be expected to cause a downfield shift of the F reso-
19
nance relative to that of free triflate. Second, the F resonances
in 1ꢀOTf and 2ꢀOTf may be subject to a hyperfine shift due to
the presence of a paramagnetic metal center. By comparison with
indicated by the disappearance of the near-IR features associated
with 2ꢀOAc (Figure 2). No intermediate was detected in this
reaction.
þ
32
related S = 2 [Fe(tmc)X] complexes, the Fe dz2 orbital in
1
ꢀOTf is singly occupied (orientation of z axis defined by FeꢀO
bond), so a direct σ contact likely is the predominant mechanism
for delocalization of unpaired spin density into triflato ligand
molecular orbitals. (A π-contact contribution arising from the
IV
þ
II
þ
½
Fe OðtmcÞðOAcÞꢁ þ PPh3 f ½Fe ðtmcÞðOAcÞꢁ þ OPPh3
ð1Þ
singly occupied dxz and d orbitals should be negligible due to
yz
insignificant, if any, FeꢀOTf π bonding.) Complex 2ꢀOTf, on
19
Under the same conditions, 2ꢀOAc reacted rapidly with an
the other hand, should lack a σ-contact contribution to the
F
excess of NO. Experiments with different amounts of NO
revealed that a large excess is required for complete decomposi-
tion of 2ꢀOAc. As shown in Figure 3, spectral changes were also
observed between 400 and 600 nm. These changes suggest the
formation of an intermediate, which reached maximum accumu-
lation within 1 min. An isosbestic point close to 600 nm persisted
for about the same time frame (Figure 3 and Figure S1 in the
Supporting Information). When a smaller excess of NO was
used, 2ꢀOAc decayed only partially, followed by tailing of the
time trace at 825 nm (Figure S2 in the Supporting Information).
The dependence of the total absorbance change at 825 nm on
the concentration of NO is consistent with an equilibrium
process in the first reaction step, while the continuing slow decay
in experiments with a smaller excess of NO can be explained by
chemical shift, because its Fe dz orbital is vacant (S = 1).
2
Furthermore, the oxo ligand being a strong (σ þ π) donor
IV
ligand may be expected to attenuate the Lewis acidity of the Fe
center and weaken the FeꢀOTf interaction. This is indeed
observed as the equilibrium of triflate-bound and dissociated
forms is further shifted toward the dissociated form for 2ꢀOTf
than for 1ꢀOTf. The differences in hyperfine shift contributions
and FeꢀOTf binding between 1ꢀOTf and 2ꢀOTf may account
for the large shift difference of ca. 77 ppm.
IV
þ
Reactivity of [Fe O(tmc)(OAc)] , 2ꢀOAc. The principal
oxygen atom transfer reactivity of 2ꢀOAc was established by
II
þ
reaction with PPh affording [Fe (tmc)(OAc)] (1ꢀOAc) and
3
OPPh (eq 1). When a solution of 1 mM 2ꢀOAc was reacted
3
with 10 equiv of PPh at ꢀ25 °C, the half-life was ca. 10 min, as
3
5
286
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
ARTICLE
III
II
removal of the unstable intermediate from the equilibrium
mixture.
Analysis of the product solution by ESI mass spectrometry
followed by reduction of the Fe center to Fe (Scheme 1). The
absorbance increase and decrease in the 400ꢀ600 nm region
III
may then be related to the accumulation and decay of the Fe
revealed peaks at m/z = 358 and 371, whose masses and isotope
distribution patterns are consistent with [Fe (tmc)(ONO)]
intermediate. Indeed, analysis of the reaction mixture by ESI
mass spectrometry at earlier reaction times indicated the pre-
II
þ
III
III
(
1ꢀONO) and 1ꢀOAc, respectively. Both features also were
sence of Fe (tmc) complexes that are derived from [Fe -
þ
III
observed in the mass spectrum of an authentic sample prepared
(tmc)(OAc)(ONO)] by solvent exchange, i.e., [Fe (tmc)-
III
þ
þ
from equimolar amounts of 1ꢀOTf(OTf), NEt AcO, and
(OAc)(OMe)] and [Fe (tmc)(OTf)(OMe)] . These species
dissipated over time. When deuterated methanol was used, the
peaks associated with these ions shifted accordingly (cf. the
Experimental Section). The fact that the putative [Fe (tmc)-
(OAc)(ONO)] complex was not directly detected is not
4
ꢀ
NaNO , demonstrating competitive binding of AcO and
NO2 to the Fe center. Consistent with the F NMR spectro-
2
ꢀ
II
19
II
III
scopic data for 1ꢀOTf (vide supra) and [Fe (tmc){OC-
þ 31
II
þ
(
O)CF }] , the Fe center is expected to be coordinated by
3
ꢀ
only one apical ligand. To quantify the yield of NO , we added
surprising as it likely is a consequence of steric constraints
imposed by the tetradentate tmc ligand. Fe(tmc) complexes
with two axial ligands are only known where at least one of the
2
1
5
Na NO to the product solution prior to mass spectrometric
2
15
analysis and utilized the peak arising from 1ꢀO NO as refer-
II
15
ꢀ
2ꢀ
ence. Because the ratio of Fe (tmc): NO was known, the
two axial ligands is either a monatomic (e.g., O ) or a linearly
2
ꢀ
ꢀ
27,31,32,38
yield of NO2 from the reaction of 2ꢀOAc with NO could be
coordinated diatomic ligand (e.g., NO, OH ).
Since the
calculated from the intensity ratio of the peaks associated with
nitrite ion is bent and expected to form at the sterically more
hindered coordination site, dissociation may be favored.
1
4
15
1
ꢀO NO (m/z = 358) and 1ꢀO NO (m/z = 359). The
III
þ
results from six trials indicate that approximately 1 equiv of
Whether the [Fe (tmc)X(OMe)] ions are the predominant
ꢀ
33
III
NO2 (with respect to Fe) was produced (Figure 4). Taken
intermediate species in solution or are only formed from [Fe -
(tmc)(OAc)(ONO)] and methanol during the mass spectro-
þ
together, the observations reveal that the reaction of 2ꢀOAc
IV
II
with NO caused reduction of the Fe center to Fe and
metry experiment cannot be answered at this time.
ꢀ
III
produced NO2
.
The apparent instability of the Fe state is peculiar but must
A plausible mechanism entails attack of NO on the oxo ligand
be viewed in the light of the almost complete absence of
III
þ
III
of 2ꢀOAc to give [Fe (tmc)(OAc)(ONO)] or its dissociated
Fe (tmc) complexes from the literature. There is only one
form, [Fe (tmc)(OAc)] þ NO2ꢀ (net O ion transfer),
III
2þ
•ꢀ
III
report of an isolated Fe(tmc) complex with a formal Fe
38
center. We also note that the self-decay of 2ꢀOAc yields the
II
III
Fe complex 1ꢀOAc rather than an Fe complex (cf. the
Experimental Section). In the reaction of 2ꢀOAc with NO,
III
methanol must be involved in the decay of the Fe intermediate,
because its decay was decelerated with decreasing concentration
of methanol. The decay of 2ꢀOAc was not affected (Figure S3 in
the Supporting Information).
Because of the presence of NO and methanol, we have
considered the possibility that reductive nitrosylation (and
III
solvolysis) of the Fe intermediate takes place, which would
II
result in the formation of an Fe complex and methyl nitrite
3
9ꢀ41
ꢀ
(
eq 2).
In addition, NO2 is known to catalyze the reduc-
35,41
tive nitrosylation of some Fe complexes (eqs 3 and 4).
To assess the relevance of reductive nitrosylation here, we
have attempted to determine whether MeONO was produced.
GCꢀMS analysis of the product mixture for MeONO is
complicated by solvent interference, so we have opted to analyze
the headspace of samples prepared with deuterated methanol.
Figure 4. Electrospray ionization mass spectrum of the products of the
reaction of 2ꢀOAc with NO in nitromethane followed by addition of 1
15
15
No significant increase in CD ONO concentration was observed
3
equiv of Na NO (98% N). Inset: Expanded views of the features
2
þ
þ
compared to samples of NO in the same solvent system
attributed to {1ꢀONO} and {1ꢀOAc} (bottom, black lines) and
but without 2ꢀOAc. In contrast, the CD ONO concentra-
their calculated isotope distribution patterns (top, red lines). For
3
þ
tion increased upon addition of O to samples of NO in
{
1ꢀONO} , the simulated data represent the isotope distribution
2
na
þ
pattern calculated for a mixture of {1ꢀO NO} (50%), {1ꢀ
MeNO ꢀCD OD. This increase correlated with the increase
2
3
1
4
þ
15
þ
O NO} (1%), and {1ꢀO NO} (49%).
in nitrite yield, consistent with chemistry ensuing from
a
Scheme 1. Reaction of 2ꢀOAc with NO
a
—Fe— = Fe(tmc).
5
287
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
ARTICLE
36
oxidation of NO to NO2.
that NO (or N O ) is formed (eqs 3 and 5). Oxygen exchange
2
2 3
would then take place between NO and NO via N O (eq 6). In
2
2 3
½
Fe ðtmcÞðOAcÞꢁ2þ þ NO þ MeOH f ½Fe ðtmcÞðOAcÞꢁ
III
II
þ
the presence of methanol, however, the chemistry in eqs 3 and 5
inadvertently leads to formation of MeONO (eq 4), but this was
not observed.
þ
þ MeONO þ H
ð2Þ
½
Fe ðtmcÞðOAcÞꢁ þ NO þ NO2 f ½Fe ðtmcÞðOAcÞꢁþ
III
2þ
ꢀ
II
’
CONCLUSION
þ N2O3
ð3Þ
The reaction of an oxoiron(IV) complex, 2ꢀOAc, with the
ꢀ
N2O3 þ MeOH f NO2ꢀ þ MeONO þ Hþ
ð4Þ
free radical NO is rapid and produces NO2 , which has been
identified in the form of a nitritoiron(II) complex, 1ꢀONO. This
reaction is considerably faster than oxygen atom transfer from
Alternatively, a two-electron pathway with oxygen atom
transfer from 2ꢀOAc to NO would produce 1ꢀOAc and NO
2
ꢀOAc to PPh and differs from the latter reaction in the for-
3
2
III
mation of an intermediate, presumably an Fe complex. Two
possible mechanistic scenarios for the reaction between the
Fe O complex and NO involve (i) O ion transfer to afford
an Fe complex and NO2 , followed by reduction of the Fe
complex (Scheme 1), or (ii) oxygen atom transfer to afford an
Fe complex and NO , which is converted into NO and
(
eq 5). Nitrite along with MeONO could be formed from equili-
bration of NO and NO with N O and methanolysis (eqs 6
2
2 3
IV
•ꢀ
and 4). This mechanism cannot be ruled out on the basis of the
Fe products, 1ꢀOAc and 1ꢀONO. It is incompatible, however,
with the lack of MeONO formation and the dependence of the
III
ꢀ
III
II
ꢀ
2
III
decay rate of the Fe intermediate on the concentration of
2
MeONO via formation of N O and methanolysis (eqs 5, 6,
methanol.
2 3
18
and 4). While an O-labeling study provides evidence for the
incorporation of oxygen from the Fe O group into the NO
product, the observation of an intermediate Fe complex, the
dependence of its decay on the concentration of methanol, and
the lack of MeONO formation support an O• ion transfer
mechanism. An outer-sphere electron transfer from NO to
IV
ꢀ
IV
þ
II
þ
2
½
Fe OðtmcÞðOAcÞꢁ þ NO f ½Fe ðtmcÞðOAcÞꢁ þ NO2
ð5Þ
III
ꢀ
NO2 þ NO h N2O3
ð6Þ
2
ꢀOAc may also be considered, but this seems unlikely due to
As a third alternative, a mechanism initiated by outer-sphere
unfavorable electron-transfer properties and redox potentials and
electron transfer from NO to 2ꢀOAc would likely be unfavor-
must be ruled out because it would produce MeONO and not
ꢀ
able due to the slow electron-transfer properties of related
NO
2
. In addition to expanding the fundamental chemistry of
21b
þ
oxoiron(IV) complexes and the high NO/NO redox poten-
oxoiron(IV) complexes, the reaction described here serves as a
synthetic example of the NO reactivity of biological ferryl species,
such as those in myoglobin, hemoglobin, and peroxidase
enzymes.
4
0,41
tial.
This mechanism would yield MeONO upon trapping of
þ
ꢀ
NO by MeOH and no NO2 (in the absence of H O).
2
Isotope Labeling Study. Further insights into the mechanism
ꢀ
18
by which NO2 is formed were sought from an O-labeling
18
study. When the reaction was carried out with O-enriched 2ꢀ
18
’ ASSOCIATED CONTENT
OAc, ca. 20% of the O was incorporated into 1ꢀONO,
demonstrating that the oxoiron(IV) unit is capable of transfer-
S
Supporting Information. Spectral changes and time
ꢀ
b
ring its oxygen to NO to afford NO2 . In contrast, the reaction of
courses for the reaction of 2ꢀOAc with NO (Figures S1ꢀS3,
PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
18
unlabeled 2ꢀOAc with NO in the presence of H O did not
2
18
lead to incorporation of O into 2ꢀOAc or the nitrite product.
1
8
18
The low O incorporation into 1ꢀONO from O-enriched 2ꢀ
OAc indicates that isotope scrambling had occurred. A possible
mechanism accounting for loss of labeled O atoms involves
’
AUTHOR INFORMATION
III
linkage isomerization of the nitrito ligand in [Fe (tmc)(OAc)-
Corresponding Author
*E-mail: jan-uwe-rohde@uiowa.edu.
1
8
þ
(
ONO)] and reversible NꢀO bond cleavage. This process
18
generates unlabeled 2ꢀOAc (and N O), which in turn reacts
ꢀ
with unlabeled NO to produce unlabeled NO2 (eqs 7 and 8).
’
ACKNOWLEDGMENT
III 18
III
18
IV
18
LnFe ꢀ ONO h LnFe ꢀON O h LnFe dO þ N O
This research was supported by the University of Iowa.
ð7Þ
IV
III
III
ꢀ
2
’ REFERENCES
L Fe dO þ NO h L Fe ꢀONO h L Fe þ NO
ð8Þ
n
n
n
(1) (a) Gardner, P. R. J. Inorg. Biochem. 2005, 99, 247. (b) Gardner,
P. R.; Gardner, A. M.; Brashear, W. T.; Suzuki, T.; Hvitved, A. N.;
Setchell, K. D. R.; Olson, J. S. J. Inorg. Biochem. 2006, 100, 542. (c) Yukl,
E. T.; de Vries, S.; Mo €e nne-Loccoz, P. J. Am. Chem. Soc. 2009, 131, 7234.
A similar mechanism has previously been described for a
nitratooxoruthenium(IV) complex that was formed by oxygen
ꢀ
atom transfer from a dioxoruthenium(VI) complex to NO . On
2
(
d) Su, J.; Groves, J. T. J. Am. Chem. Soc. 2009, 131, 12979. (e) Su, J.;
Groves, J. T. Inorg. Chem. 2010, 49, 6317.
2) (a) Herold, S.; Rehmann, F.-J. K. J. Biol. Inorg. Chem. 2001,
IV 18
18
þ
2
the basis of isotope scrambling, the L Ru ( O)( ONO )
n
complex was proposed to undergo linkage isomerization of the
(
4
2
nitrato ligand followed by reversible NꢀO bond cleavage.
6, 543. (b) Herold, S.; Rehmann, F.-J. K. Free Radical Biol. Med. 2003,
34, 531. (c) Herold, S.; Puppo, A. J. Biol. Inorg. Chem. 2005, 10, 946.
Another scrambling mechanism would be possible in the event
5
288
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289

Inorganic Chemistry
3) (a) Ascenzi, P.; De Marinis, E.; Coletta, M.; Visca, P. Biochem.
Biophys. Res. Commun. 2008, 373, 197. (b) De Marinis, E.; Casella, L.;
Ciaccio, C.; Coletta, M.; Visca, P.; Ascenzi, P. IUBMB Life 2009, 61, 62.
ARTICLE
(
(23) Holleman, A. F.; Wiberg, E.; Wiberg, N. Inorganic Chemistry,
101st ed.; Walter de Gruyter: Berlin, Germany, 2001.
(24) Hagen, K. S. Inorg. Chem. 2000, 39, 5867.
(4) (a) Bruckdorfer, K. R.; Dee, G.; Jacobs, M.; Rice-Evans, C. A.
(25) Arnold, J.; Hoffman, C. G.; Dawson, D. Y.; Hollander, F. J.
Biochem. Soc. Trans. 1990, 18, 285. (b) Dee, G.; Rice-Evans, C.;
Obeyesekera, S.; Meraji, S.; Jacobs, M.; Bruckdorfer, K. R. FEBS Lett.
Organometallics 1993, 12, 3645.
(26) Royal, G.; Dahaoui-Gindrey, V.; Dahaoui, S.; Tabard, A.;
Guilard, R.; Pullumbi, P.; Lecomte, C. Eur. J. Org. Chem. 1998, 1971.
(27) Rohde, J.-U.; In, J.-H.; Lim, M. H.; Brennessel, W. W.; Bukowski,
M. R.; Stubna, A.; M €u nck, E.; Nam, W.; Que, L., Jr. Science 2003,
299, 1037.
(28) Saltzman, H.; Sharefkin, J. G. In Organic Syntheses; Wiley &
Sons: New York, 1973; Collect. Vol. V, pp 658ꢀ659.
(29) McQuaid, K. M.; Pettus, T. R. R. Synlett 2004, 2403.
(30) Young, C. L. IUPAC Solubility Data Ser. 1981, 8, 336.
(31) Rohde, J.-U.; Que, L., Jr. Angew. Chem., Int. Ed. 2005, 44, 2255.
(32) Hodges, K. D.; Wollmann, R. G.; Barefield, E. K.; Hendrickson,
D. N. Inorg. Chem. 1977, 16, 2746.
1
991, 294, 38. (c) Gorbunov, N. V.; Osipov, A. N.; Day, B. W.;
Zayas-Rivera, B.; Kagan, V. E.; Elsayed, N. M. Biochemistry 1995,
4, 6689. (d) Osipov, A. N.; Gorbunov, N. V.; Day, B. W.; Elsayed,
N. M.; Kagan, V. E. Methods Enzymol. 1996, 268, 193.
5) Glover, R. E.; Koshkin, V.; Dunford, H. B.; Mason, R. P. Nitric
Oxide 1999, 3, 439.
6) (a) Abu-Soud, H. M.; Hazen, S. L. J. Biol. Chem. 2000, 275, 5425.
b) Abu-Soud, H. M.; Hazen, S. L. J. Biol. Chem. 2000, 275, 37524. (c)
3
(
(
(
Abu-Soud, H. M.; Khassawneh, M. Y.; Sohn, J.-T.; Murray, P.; Haxhiu,
M. A.; Hazen, S. L. Biochemistry 2001, 40, 11866.
(
7) Brunelli, L.; Yermilov, V.; Beckman, J. S. Free Radical Biol. Med.
001, 30, 709.
8) Borisov, V. B.; Forte, E.; Sarti, P.; Brunori, M.; Konstantinov,
A. A.; Giuffr ꢀe , A. FEBS Lett. 2006, 580, 4823.
9) (a) Wick, P. K.; Kissner, R.; Koppenol, W. H. Helv. Chim. Acta
000, 83, 748. (b) Wick, P. K.; Kissner, R.; Koppenol, W. H. Helv. Chim.
Acta 2001, 84, 3057. (c) Herold, S.; Koppenol, W. H. Coord. Chem. Rev.
ꢀ
ꢀ
2
(33) We have also probed other sources of NO2 . First, NO2 has
(
been reported to be commonly present in aqueous NO solu-
1
0,11,34,35
36
tions
due to oxidation of NO by trace amounts of O
2
.
Here,
(
solutions of NO in MeNO
2
ꢀMeOH were found to contain less than
37
ꢀ
2
0.1 mM NO2 . Second, a number of transition metal complexes are
ꢀ
known to produce NO
2
by disproportionation of NO. When
2
005, 249, 499.
10) Nemes, A.; Pestovsky, O.; Bakac, A. J. Am. Chem. Soc. 2002,
24, 421.
solutions of 1ꢀOAc, which was identified as a product of the reaction
(
of 2ꢀOAc with NO, were treated with an excess of NO, we found ca. 0.3
ꢀ
ꢀ
2
1
equiv of NO (with respect to Fe). Thus, these two sources of NO
2
ꢀ
(11) Pestovsky, O.; Bakac, A. J. Am. Chem. Soc. 2002, 124, 1698.
12) (a) Maiti, D.; Lee, D.-H.; Narducci Sarjeant, A. A.; Pau,
play a minor role in the formation of NO
2
here but likely are res-
ꢀ
(
ponsible for the observation of NO
2
in excess of 1 equiv (cf. the
M. Y. M.; Solomon, E. I.; Gaoutchenova, K.; Sundermeyer, J.; Karlin,
K. D. J. Am. Chem. Soc. 2008, 130, 6700. (b) Schopfer, M. P.; Mondal, B.;
Lee, D.-H.; Sarjeant, A. A. N.; Karlin, K. D. J. Am. Chem. Soc. 2009,
Experimental Section for details).
(34) Wolak, M.; Stochel, G.; Hamza, M.; van Eldik, R. Inorg. Chem.
2000, 39, 2018.
1
31, 11304. (c) Park, G. Y.; Deepalatha, S.; Puiu, S. C.; Lee, D.-H.;
(35) (a) Fernandez, B. O.; Lorkovic, I. M.; Ford, P. C. Inorg. Chem.
2003, 42, 2. (b) Fernandez, B. O.; Lorkovic, I. M.; Ford, P. C. Inorg.
Chem. 2004, 43, 5393.
Mondal, B.; Narducci Sarjeant, A. A.; del Rio, D.; Pau, M. Y. M.;
Solomon, E. I.; Karlin, K. D. J. Biol. Inorg. Chem. 2009, 14, 1301.
(
13) (a) De Leo, M.; Ford, P. C. J. Am. Chem. Soc. 1999, 121, 1980.
b) DeLeo, M. A.; Ford, P. C. Coord. Chem. Rev. 2000, 208, 47.
14) Sharpe, M. A.; Ollosson, R.; Stewart, V. C.; Clark, J. B. Biochem.
J. 2002, 366, 97.
15) Abbreviations: [14]aneN
or cyclam; H ppIX, 7,12-diethenyl-3,8,13,17-tetramethyl-21H,23H-
porphine-2,18-dipropanoic acid or protoporphyrin IX; H tpfpp, 5,10,15,
(36) (a) Awad, H. H.; Stanbury, D. M. Int. J. Chem. Kinet. 1993,
25, 375. (b) Ford, P. C.; Wink, D. A.; Stanbury, D. M. FEBS Lett. 1993,
326, 1.
(37) (a) Franz, K. J.; Lippard, S. J. J. Am. Chem. Soc. 1998, 120, 9034.
(b) Franz, K. J.; Lippard, S. J. J. Am. Chem. Soc. 1999, 121, 10504.
(c) Ford, P. C.; Lorkovic, I. M. Chem. Rev. 2002, 102, 993.
(38) Hodges, K. D.; Wollmann, R. G.; Kessel, S. L.; Hendrickson,
D. N.; Van Derveer, D. G.; Barefield, E. K. J. Am. Chem. Soc. 1979,
101, 906.
(39) (a) Gwost, D.; Caulton, K. G. J. Chem. Soc., Chem. Commun.
1973, 64. (b) Gwost, D.; Caulton, K. G. Inorg. Chem. 1973, 12, 2095.
(c) Wayland, B. B.; Olson, L. W. J. Chem. Soc., Chem. Commun. 1973,
897. (d) Wayland, B. B.; Olson, L. W. J. Am. Chem. Soc. 1974, 96, 6037.
(40) Tran, D.; Skelton, B. W.; White, A. H.; Laverman, L. E.; Ford,
P. C. Inorg. Chem. 1998, 37, 2505.
(
(
(
4
, 1,4,8,11-tetraazacyclotetradecane
2
2
2
0-tetrakis(2,3,4,5,6-pentafluorophenyl)-21H,23H-porphine; TfOH
=CF SO H), trifluoromethanesulfonic or triflic acid; tmc, 1,4,8,
1-tetramethyl-1,4,8,11-tetraazacyclotetradecane.
16) (a) Crestoni, M. E.; Fornarini, S. Inorg. Chem. 2005, 44, 5379.
b) Crestoni, M. E.; Fornarini, S. Inorg. Chem. 2007, 46, 9018. (c)
(
3
3
1
(
(
Chiavarino, B.; Cipollini, R.; Crestoni, M. E.; Fornarini, S.; Lanucara, F.;
Lapi, A. J. Am. Chem. Soc. 2008, 130, 3208.
(
17) (a) Lei, J.; Trofimova, N. S.; Ikeda, O. Chem. Lett. 2003, 32, 610.
b) Lei, J.; Ju, H.; Ikeda, O. J. Electroanal. Chem. 2004, 567, 331. (c)
Trofimova, N. S.; Safronov, A. Y.; Ikeda, O. Electrochim. Acta 2005,
0, 4637.
18) (a) Suslick, K. S.; Watson, R. A. Inorg. Chem. 1991, 30, 912. (b)
Suslick, K. S.; Bautista, J. F.; Watson, R. A. J. Am. Chem. Soc. 1991,
13, 6111. (c) Yamaji, M.; Hama, Y.; Miyazaki, Y.; Hoshino, M. Inorg.
Chem. 1992, 31, 932.
19) Crestoni, M. E.; Fornarini, S.; Lanucara, F.; Warren, J. J.; Mayer,
J. M. J. Am. Chem. Soc. 2010, 132, 4336.
20) (a) McCarthy, M. R.; Crevier, T. J.; Bennett, B.; Dehestani, A.;
(
(41) Ford, P. C.; Fernandez, B. O.; Lim, M. D. Chem. Rev. 2005,
105, 2439.
(42) Man, W.-L.; Lam, W. W. Y.; Wong, W.-Y.; Lau, T.-C. J. Am.
5
(
Chem. Soc. 2006, 128, 14669.
1
(
(
Mayer, J. M. J. Am. Chem. Soc. 2000, 122, 12391. (b) Walstrom, A.; Pink,
M.; Fan, H.; Tomaszewski, J.; Caulton, K. G. Inorg. Chem. 2007, 46,
7
704.
21) (a) Nam, W. Acc. Chem. Res. 2007, 40, 522. (b) Lee, Y.-M.;
Kotani, H.; Suenobu, T.; Nam, W.; Fukuzumi, S. J. Am. Chem. Soc. 2008,
30, 434. (c) Fukuzumi, S.; Kotani, H.; Lee, Y.-M.; Nam, W. J. Am. Chem.
Soc. 2008, 130, 15134.
22) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemi-
cals, 5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.
(
1
(
5
289
dx.doi.org/10.1021/ic2007205 |Inorg. Chem. 2011, 50, 5283–5289