Iron(II) Corrole Anions

Article abstract of DOI:10.1021/acs.inorgchem.9b02209

Reduction of [Fe(TPC)(THF)] (TPC = trianion of 5,10,15-Triphenylcorrole) with KC8 generates the iron(II) corrole anion, K(THF)2[FeII(TPC)] (3a). Compound 3a represents the first example of an isolated and crystallographically characterized corrole complex of divalent iron. The compound adopts an intermediate-spin state (S = 1), displaying square-planar geometry about the iron atom. All-electron density functional theory (OLYP and B3LYP) calculations with STO-TZP basis sets indicate two essentially equienergetic d electron configurations, dxy2dz22dxz1dyz1 (occupation 1) and dxy2dz21dxz1dyz2 (occupation 2), as likely contenders for the ground state of [FeII(TPC)]-, with the optimized geometry of the former in slightly better agreement with the low-Temperature X-ray structure. Solutions of 3a react with carbon monoxide to afford the low-spin (S = 0) complex, [Fe(TPC)(CO)]-, whereas introduction of oxygen at-78 °C leads to a putative O2 adduct, [Fe(TPC)(O2)]-, which decays rapidly even at low temperatures. Treatment of 3a with organic electrophiles results in formal oxidative addition to give both iron(III) and iron(IV) corrole species. With iodomethane, [Fe(TPC)Me] is produced, illustrating the first instance of alkyl ligand coordination in an iron corrole complex.

Full text of DOI:10.1021/acs.inorgchem.9b02209

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Iron(II) Corrole Anions
†
‡,§
†
‡
Kenneth P. Caulfield, Jeanet Conradie,
Hadi D. Arman, Abhik Ghosh,
,
†
and Zachary J. Tonzetich*
†
Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States
Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway
‡
§
Department of Chemistry, University of the Free State, P.O. Box 339, 9300 Bloemfontein, Republic of South Africa
S Supporting Information
*
ABSTRACT: Reduction of [Fe(TPC)(THF)] (TPC = trianion
of 5,10,15-triphenylcorrole) with KC8 generates the iron(II)
II
corrole anion, K(THF) [Fe (TPC)] (3a). Compound 3a
2
represents the first example of an isolated and crystallographically
characterized corrole complex of divalent iron. The compound
adopts an intermediate-spin state (S = 1), displaying square-planar
geometry about the iron atom. All-electron density functional
theory (OLYP and B3LYP) calculations with STO-TZP basis sets
indicate two essentially equienergetic d electron configurations,
2
2
1
1
2
1
2
1
2
2
z
d d d d (occupation 1) and d d d d (occupation 2),
xy
xz yz
xy
z
xz yz
II
−
as likely contenders for the ground state of [Fe (TPC)] , with the optimized geometry of the former in slightly better
agreement with the low-temperature X-ray structure. Solutions of 3a react with carbon monoxide to afford the low-spin (S = 0)
−
−
complex, [Fe(TPC)(CO)] , whereas introduction of oxygen at −78 °C leads to a putative O adduct, [Fe(TPC)(O )] , which
2
2
decays rapidly even at low temperatures. Treatment of 3a with organic electrophiles results in formal oxidative addition to give
both iron(III) and iron(IV) corrole species. With iodomethane, [Fe(TPC)Me] is produced, illustrating the first instance of alkyl
ligand coordination in an iron corrole complex.
INTRODUCTION
given the importance of the divalent oxidation state in the
14
■
chemistry of related iron porphyrins and the noted
electrocatalytic activity of iron corroles for small molecule
Iron corrole complexes have provided fascinating case studies
in transition metal−ligand covalence, in light of the potential
redox non-innocence of the corrole macrocycle. This feature
is most apparent for the family of formally iron(IV) complexes
of the form [Fe(cor)X], which in most instances are better
regarded as possessing an intermediate-spin iron(III) metal
15
1
,2
reduction. In contrast to iron, the 2+ oxidation state of
cobalt in corrole complexes has attracted more attention,
16−19
although no solid-state structures exist for such species.
Questions concerning the interplay of ligand and metal
redox states in reduced iron corroles and the potential
similarity of its reactivity to that of porphyrin analogues
motivated us to examine these compounds in greater detail.
Moreover, given the formally trianionic nature of the corrole
ligand, we hypothesized that iron(II) corrole complexes would
display enhanced reactivity in reductive processes over their
porphyrin counterparts. In this work, we describe the
preparation, structure, and reactivity of divalent iron corroles.
Notably, the compounds behave in ways quite unique from
those of related iron(II) porphyrin systems.
3
−6
center bound to a corrole radical dianion.
By contrast, the
lower oxidation states of iron corroles have received
comparatively little attention. Iron(III) corroles have been
described in some detail, but their preparative means can be
variable and dependent on both the substitution pattern of the
7
−10
corrole ligand and the presence of coordinating solvents.
Even more scarce are reports of iron(II) corroles, which are
very rare. Murakami first observed evidence of divalent iron
corroles in work examining the oxygenation of olefins with
iron(III) and cobalt(III) complexes of 2,3,17,18-tetramethyl-
,8,12,13-tetraethylcorrolate. Subsequent work by Kadish
and co-workers identified the iron(II) complex of octaethyl-
1
1
7
RESULTS AND DISCUSSION
■
Iron(III). Trivalent iron complexes of several substituted
corrolate electrochemically, but no spectroscopic features were
1
2
corrole ligands can be prepared by direct metalation with
reported. A later publication by Gross in 2002 described the
20
II
−
II
−
iron(II). Although such a strategy is often successful, the
propensity of certain iron(III) corroles to undergo further
in situ generation of [Fe (TPFC)] and [Fe (TDCC)]
TPFC = trianion of 5,10,15-tris(pentafluororphenyl)corrole,
[
21
oxidation in the presence of air, coupled with the variable
and TDCC = trianion of 5,10,15-tris(2,6-dichlorophenyl)-
corrole], but no further studies concerning the electronic or
molecular structure of iron(II) corroles have appeared in the
Received: July 23, 2019
1
3
literature since. Such a dearth of information is surprising
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b02209
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Inorganic Chemistry
Scheme 1. Preparation and Reactivity of [Fe (TPC)(L)]
Article
III
Figure 1. Thermal ellipsoid (50%) drawing of 2·CH CN. The disordered position of the CH CN ligand has been omitted for the sake of clarity.
3
3
Selected bond distances (angstroms) and angles (degrees): Fe(1)−N(1), 1.8993(19); Fe(1)−N(2), 1.9041(18); Fe(1)−N(3), 1.8717(19);
Fe(1)−N(4), 1.8779(19); Fe(1)−N(5), 2.177(2); Fe−corrole = 0.256(2).
22
nature of axial solvent coordination, prompted us to pursue
benzene-d produced an effective magnetic moment of 4.1
6
a reduction strategy from [Fe(TPC)Cl] (1). Treatment of 1
± 0.2 μ , as expected for a quartet ground state and in line
B
21,22
with KC in tetrahydrofuran afforded the iron(III) triphe-
with prior reports of ferric corroles.
Addition of 5 equiv of
8
III
nylcorrole complex, [Fe (TPC)(THF)] [2·THF (Scheme
)], in good yields. Compound 2·THF is soluble in
pyridine to 2·CH CN resulted in liberation of free acetonitrile
3
1
1
and formation of 2·py as judged by H NMR (Scheme 1).
Much like that of 2·CH CN, the NMR spectrum of 2·py
hydrocarbon solvents, facilitating its purification from the
chloride adduct (vide infra). Attempts to obtain crystals of 2·
THF suitable for X-ray diffraction were unsuccessful, but
crystallization from acetonitrile afforded the corresponding
3
demonstrates apparent C2v symmetry consistent with either
rapid pyridine dissociation/association or formation of a bis-
solvento adduct. We favor the former scenario on the basis of
solvento complex, 2·CH CN. The solid-state structure of 2·
the five-coordinate nature of 2·CH CN. This behavior differs
3
3
CH CN is shown in Figure 1. The metric parameters of iron
from that found by Gross and co-workers for iron(III) corrole
complexes containing electron-withdrawing substituents in the
meso-aryl rings. In such cases, six-coordinate bis-solvento
3
are similar to those of other five-coordinate ferric corrole
species with the iron atom residing 0.256 Å above the best-fit
8
1
plane defined by the corrole macrocycle. H nuclear magnetic
iron(III) complexes were observed with both Et O and
2
8
,23
resonance (NMR) spectra of 2·THF and 2·CH CN in
pyridine ligation.
3
benzene-d6 are similar, although not identical, with both
molecules demonstrating apparent C2v symmetry consistent
with fluxional binding of THF or acetonitrile at room
temperature (see the Supporting Information). Solution
In contrast to reactions involving KC , reduction of 1 with
8
Cp Co produced a new iron(III) species that we assign as the
2
anionic chloride adduct, (Cp Co)[Fe(TPC)Cl] (2·Cl). This
2
1
assignment is based on the H NMR features of 2·Cl, which
magnetic susceptibility measurements of 2·CH CN in
demonstrate a doubling of the resonances assigned to the
3
B
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Article
Figure 2. Cyclic voltammograms of 2·CH CN (2 mM) in acetonitrile at a glassy carbon electrode. The scan rate is 50 mV/s, and the supporting
3
electrolyte is 0.1 M Bu NPF . Each scan was initiated from the open circuit potential.
4
6
Scheme 2. Oxygen Reactivity of 3a
ortho and meta hydrogen atoms of the phenyl rings consistent
with loss of C2v symmetry (see the Supporting Information).
With samples of pure 2·CH CN in hand, we next
3
investigated its electrochemistry. Previous work has exten-
25
sively characterized the redox events of iron corroles.
Therefore, unlike 2·THF and 2·CH CN, the axial chloride
3
However, in the case of triaryl corroles, most prior treatments
have examined complexes of the type [Fe(cor)X] as opposed
ligand of 2·Cl must remain bound in solution. Despite
differences in their NMR features, electronic absorption
III
to [Fe (cor)], thereby incurring the additional complication
spectra of 2·L (L = THF, CH CN, or Cl) are nearly
3
provided by the axial nonsolvent ligand. Cyclic voltammo-
identical. As a further confirmation of the nature of 2·Cl, we
grams for anodic and cathodic sweeps of 2·CH CN are
3
attempted its independent synthesis from Bu NCl. Gratify-
4
displayed in Figure 2. The compound shows a total of five
quasi-reversible events between 1.5 and −2.5 V (vs ferrocene/
ferrocenium), with additional irreversible events visible at
lower potentials. In agreement with previous work, the events
at E values of −0.03 and −0.95 V are assigned to the
ingly, treatment of 2·CH CN with Bu NCl in acetonitrile-d
3
4
3
generated a new species with resonances identical to those
observed for 2·Cl as prepared from 1 and Cp Co. Related
2
ionic iron(III) corrolates similar to 2·Cl possessing axial
1
/2
22,24
3
−
2−•
12
anionic ligands have been described.
Much like 2·Cl, these
corr /corr and Fe(III)/Fe(II) couples, respectively.
species also display NMR resonances consistent with a loss of
top-bottom symmetry.
Iron(II). The well-behaved nature of the Fe(III)/Fe(II)
couple in [Fe(TPC)] prompted us to examine its chemical
C
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Article
reduction. Reaction of 2·THF or 2·CH CN in tetrahydrofuran
meso-phenyl groups indicating C2v symmetry in solution (see
the Supporting Information).
3
with stoichiometric quantities of KC afforded the iron(II)
8
corrolate, K(THF) [Fe(TPC)] (3a, eq 1), after crystallization
The crystal structure of 3a is displayed in Figure 4. The
complex exists as a coordination polymer in the solid state
2
with THF-solvated potassium cations bridging two [Fe-
−
(
TPC)] units through the faces of their pyrrole rings. We
also obtained the crystal structure of (Bu N)[Fe(TPC)] (3b),
4
which displays bond metrics similar to those of 3a and no
close contacts between the anion and cation (see the
Supporting Information). Unlike those of 2·CH CN, the
3
iron atoms of 3a and 3b are essentially coplanar with the
corrole ligand showing minimal deviation from the best-fit
plane defined by the macrocycle. The structures of 3a and 3b
are most similar to that of the Mn(III) corrole complex,
from a THF/pentane mixture. The use of stoichiometric
quantities of KC as opposed to excess is critical to avoid
8
13
forming over-reduction products. Solutions of compound 3a
are deep forest green and yield a solution magnetic moment
(
(
7,13-dimethyl-2,3,8,12,17,18-hexaethylcorrolato)manganese-
III), which similarly displays a square-planar geometry about
of 2.9 ± 0.2 μ , consistent with a triplet ground state (S = 1).
B
The electronic absorption spectrum of the complex in
tetrahydrofuran (Figure 3) features a split Soret band near
the metal atom and minimal deviation from the plane of the
26
macrocycle. To the best of our knowledge, 3a and 3b
represent the first example of a crystallographically charac-
terized four-coordinate iron corrole.
In line with the modest reduction potential of 2·CH CN
3
(
E1/2 = −0.95 V), reaction with weaker reductants such as
−
hydrosulfide ion (HS ) was also found to generate
II
−
[
Fe (TPC)] . In this case, however, >3 equiv of Bu NSH
4
was required to completely transform 2·CH CN to (Bu N)-
3
4
[
Fe(TPC)] (3b) as judged by ultraviolet−visible (UV−vis)
−
spectroscopy. No evidence for further binding of HS to
II
−
[
Fe (TPC)] was evident by UV−vis or NMR spectroscopy,
demonstrating a reluctance to associate with simple Lewis
bases. Such behavior stands in contrast to that of porphyrin
analogues, which readily bind both solvent molecules and
27−29
other Lewis bases, including hydrosulfide.
Despite the lack of reactivity with HS , compound 3a was
found to bind carbon monoxide to afford the monocarbonyl
−
II
−
1
complex, [Fe (TPC)(CO)] (4, eq 2). The H NMR
Figure 3. Electronic absorption spectrum of 3a in tetrahydrofuran.
4
30 nm and a prominent multifaceted Q peak at 625 nm in
agreement with that found by Gross and co-workers for both
−
−
13
1
[Fe(TDCC)] and [Fe(TPFC)] . The H NMR spectrum
of 3a in acetonitrile-d displays a total of six resonances for the
3
Figure 4. Thermal ellipsoid (50%) drawing of the anion of 3a. Only one of the two crystallographically independent molecular ions is shown. The
K(THF)2+ cation has been omitted for the sake of clarity. Selected bond distances (angstroms): Fe(1)−N(1), 1.896(4); Fe(1)−N(2), 1.895(4);
Fe(1)−N(3), 1.870(4); Fe(1)−N(4), 1.881(4); Fe−corrole, 0.079(2).
D
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Inorganic Chemistry
Article
features unique from those of 2·THF (Figure 5). We propose
−
that this new species is the oxygen adduct, [Fe(TPC)(O )]
2
16,18
(
5), by analogy with related cobalt(II) systems.
Solutions
of 5 evolve rapidly to 2·THF upon warming and were even
observed to convert slowly to 2·THF at −78 °C (see the inset
of Figure 5). Inclusion of PPh to solutions of 5 resulted in
3
formation of OPPh upon warming, although no evidence of
3
oxygenation was observed at low temperatures. In contrast to
PPh , dihydroanthracene (DHA) failed to react with solutions
3
of 5, even upon being warmed to room temperature. These
observations suggest that 5 decays to 2·THF, presumably by
−
−
loss of superoxide (O ). The subsequent reactivity of O
2
2
generated from decomposition of 5 may then account for the
observed oxygenation of PPh . In no instance, however, was
3
3
0
evidence of formation of a ferryl-type species found.
Therefore, it appears that 3a is less efficient at oxygen
activation than its porphyrin counterparts.
Figure 5. Electronic absorption spectra of 3a in THF at −78 °C
before (green) and immediately after (black) addition of molecular
oxygen. The red trace corresponds to 2·THF formed by warming the
Despite the lack of efficient oxygen activation displayed by
3
a, the compound did prove to be reactive toward organic
electrophiles. Treatment of 3a with 4-iodotoluene in
acetonitrile-d resulted in the formation of 2·CH CN with
solution of 3a and O followed by recooling to −78 °C. The inset
2
displays the Soret region with gray traces demonstrating the slow
decay of 5 at low temperatures.
3
3
concomitant production of 4,4′-dimethylbiphenyl as judged by
NMR and UV−vis spectroscopy (Scheme 3). By contrast, a
spectrum of 4 in acetonitrile-d displays sharp resonances
3
similar reaction of 3a with CH I led to formation of a new
between 0 and 10 ppm consistent with a change to the S = 0
3
iron corrole complex that we assign as the organometallic
Fe(IV)-methyl species [6 (Scheme 3)]. Compound 6 was
spin state (see the Supporting Information). The infrared (IR)
−
1
absorption for the CO ligand of 4 occurs at 1894 cm in
tetrahydrofuran, and its UV−vis features are similar to those
observed to precipitate from acetonitrile-d solutions con-
3
−
13
sistent with its formulation as a neutral species incapable of
reported previously for [Fe(TDCC)(CO)] . Attempts to
isolate 4 were hampered by facile dissociation of CO upon
solvent removal.
further solvent coordination (as opposed to 2·L). Moreover,
the NMR features of 6 in benzene-d are similar to those of
6
Reactivity of 3. Given the rich oxygenation chemistry
displayed by divalent iron porphyrins, we were curious about
the behavior of 3a with molecular oxygen. Room-temperature
other Fe(IV) triphenylcorrole complexes containing carbon-
3
,31
based ligands.
Unfortunately, compound 6 proved to be
challenging to isolate in bulk due to its spontaneous
decomposition to 2·L after several hours in solution. However,
we were able to obtain single crystals that were suitable for X-
ray diffraction. The solid-state structure of 6 is depicted in
Figure 6. The bond metrics about iron are similar to those of
[Fe(TTC)Ph] (TTC = 5,10,15-tritolylcorrolate) with an Fe−
treatment of solutions of 3a with O in THF rapidly generated
2
2
(
·THF as judged by UV−vis and NMR spectroscopy
Scheme 2). Prolonged exposure resulted in formation of
the bridging oxo complex, [Fe (TPC) (μ-O)], for which we
2
2
have obtained the crystal structure (see the Supporting
31
Information). Upon cooling to −78 °C, solutions of 3a were
CH bond length of 2.006(3) Å. Taken together, the
3
found to react with O to afford a new species with UV−vis
reactivity of 3a with 4-iodotoluene and CH I demonstrates a
2
3
Figure 6. Thermal ellipsoid (50%) drawing of 6. Selected bond distances (angstroms): Fe(1)−C(37), 2.006(3); Fe(1)−N(1), 1.865(2); Fe(1)−
N(2), 1.886(2); Fe(1)−N(3), 1.892(2); Fe(1)−N(4), 1.860(2); Fe−corrole, 0.206(2).
E
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Scheme 3. Reactivity of 3a with Organic Electrophiles
for comparison, similar calculations were also carried out for
2
·CH CN and 6. Judicious use was made of group theory to
3
investigate the relative energies of alternative metal d orbital
occupancies. Toward that end, we used C symmetry for
2
II
−
[
Fe (TPC)] , which is rigorously correct, and C symmetry
s
for 2·CH CN and 6, which is a minor simplification; in
3
II
−
addition, we also optimized [Fe (TPC)] with a C2v
symmetry constraint, which allowed for an investigation of
an even wider range of electron occupancies.
The results for 2·CH CN provide a good starting point for
3
3
our discussion. Both functionals clearly indicated an S = /
2
2
1
1
1
2
ground state with a d d d d electronic configuration
xy
z
xz yz
(
where the z direction approximately corresponds to the
direction of the axial Fe−N bond) and ∼90% of the electronic
spin density concentrated on the iron center (Figure 7).
II
−
Interestingly for [Fe (TPC)] (Figure 8), both functionals
indicated two plausible contenders for the ground state,
2
xy
2
1
1
2
corresponding to the d d d d
(occupation 1) and
d d d d (occupation 2) configurations. Thus, for gas-
z
xz yz
2
1
1
2
2
xy
z
xz yz
phase electronic energies, B3LYP indicated occupation 1 as
the ground state, with occupation 2 ∼0.1 eV higher in energy;
in contrast, OLYP indicated occupation 2 as the ground state,
with occupation 1 only 0.05 eV higher. The energy difference
between the two configurations is so small that the relative
ordering is likely to be easily reversed as a function of thermal
effects, solvation, counterions, crystal-packing forces, and/or
other environmental effects. For 6 (Figure 9), nearly the
entire spin density was found to be concentrated on the Fe;
the small amount of negative spin density on the methyl
carbon atom (−0.044) is consistent with a largely covalent
•
Fe−C σ-bond with only a small amount of H C character.
3
Furthermore, the characteristic spin density profile, resembling
a stack of two circular cheeses, is clearly indicative of a
2
1
1
d d d occupation. Qualitatively, the spin density results
xy xz yz
for 6 are similar to those of [Fe(cor)Ph] complexes and
3
,31,32
support an Fe(IV) formalism for the compound.
An interesting question is whether a comparison of DFT
II
−
and experimental data for [Fe (TPC)] might permit an
assignment of the latter to one theoretically studied d orbital
occupancy or the other. Figure 8 does indicate subtle
differences in corrole skeletal spin populations between
occupations 1 and 2, especially for C7, C8, C12, and C13.
Due to the paramagnetism of 3a and 3b, however, the
hydrogens at these positions have not all been unequivocally
assigned, which frustrates our goal of exploiting NMR contact
shifts as a probe of d orbital occupancy. Figure 8 also indicates
subtle differences in corrole skeletal bond distances between
3
Figure 7. Selected calculated results for S = / 2·CH CN: (top)
2
3
3
B3LYP spin density plot (contour of 0.005 e/Å ), (middle) selected
Mulliken spin populations (blue, underlined) and bond distances for
OLYP, and (bottom) the same for B3LYP.
propensity for oxidative addition with single-electron transfer
being preferred in the case of the aryl iodide and an S 2-like
N
process occurring for methyl iodide.
Electronic Structure and DFT Calculations. To
the two occupations. Here, the optimized N−C
α
distances
II
−
establish the electronic structure of [Fe (TPC)] with greater
certainty, DFT calculations were carried out with the OLYP
and B3LYP exchange-correlation functionals and all-electron
Slater-type triple-ζ plus double polarization (TZ2P) basis sets;
appear to be in slightly better agreement with experiment for
2
2
1
1
2
occupation 1 (dxy d d dyz ) than for occupation 2.
z
xz
2
Incidentally, because of the double occupancy of the dz
orbital, occupation 1 is naturally also a nucleophile and can
F
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Article
II
−
3
Figure 8. Selected calculated results for two S = 1 occupations of [Fe (TPC)] . The spin density plots (middle, contour of 0.005 e/Å ) are
shown for only B3LYP. Selected Mulliken spin populations (blue, underlined) and bond distances (black) are shown for both OLYP and B3LYP.
react directly with CH I via an S 2 pathway. This last
argument, however, does not prove that occupation 1 is the
ground state; it could just as well be a reactive intermediate.
indicate two near-equienergetic d orbital occupancies,
3
N
2
2
1
1
2
1
1
2
2
2
d d
d d (occupation 1) and d d d d (occupation
xy
z
xz yz
xy
z xz yz
2), as plausible contenders for the ground state, with the
optimized geometry of the former in slightly better agreement
with the low-temperature X-ray structure of the complex.
Reaction of the iron(II) corrolate with molecular oxygen gives
rise to a putative oxygen adduct, which decays rapidly with
loss of superoxide to generate the corresponding iron(III)
corrole. Treatment with organic electrophiles results in
oxidative addition-type processes. In the case of methyl
iodide, an iron(IV)-methyl complex is produced, which
CONCLUSIONS
■
In this work, we have described the first isolation of a divalent
II
−
iron corrole complex, [Fe (TPC)] . The iron(II) corrolate is
four-coordinate in the solid state and demonstrates a
reluctance to coordinate axial solvent molecules. The complex
adopts an intermediate spin state (S = 1) but becomes low-
spin upon binding of carbon monoxide. DFT calculations
G
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with a path length of 0.10 mm). UV−vis spectra were recorded on a
Cary-60 spectrophotometer in airtight Teflon-capped quartz cells.
For low-temperature data acquisition, a custom-made cuvette was
employed. Cyclic voltammetry was performed in the glovebox at 23
°
C on a CH Instruments 620D electrochemical workstation. A three-
electrode setup was employed comprising a glassy carbon working
electrode, a platinum wire auxiliary electrode, and a Ag/AgCl quasi-
reference electrode. Triply recrystallized Bu NPF was used as the
4
6
supporting electrolyte. All electrochemical data were referenced
internally to the ferrocene/ferrocenium couple at 0.00 V. Solution
magnetic susceptibility measurements were determined by the Evans
method without a solvent correction using reported diamagnetic
33
corrections. Elemental analyses were performed by the CENTC
facility at the University of Rochester.
Materials. [Fe(TPC)Cl] and KC were prepared according to
8
34,35
literature procedures.
All other reagents were purchased from
chemical suppliers and used as received.
X-ray Crystallography. Crystals suitable for X-ray diffraction
were mounted, using Paratone oil, onto a nylon loop. All data were
collected at 98(2) K using a Rigaku AFC12/Saturn 724 CCD
instrument fitted with Mo Kα radiation (λ = 0.71075 Å). Low-
temperature data collection was accomplished with a nitrogen cold
stream maintained by an X-Stream low-temperature apparatus. Data
collection and unit cell refinement were performed using
36
CrystalClear software. Data processing and absorption correction,
giving minimum and maximum transmission factors, were accom-
3
7
38
plished with CrysAlisPro and SCALE3 ABSPACK, respectively.
39
40
2
The structures, using Olex2, were determined with the ShelXT
structure solution program using direct methods and refined (on F )
with the ShelXL refinement package using the full-matrix, least-
41
squares techniques. All non-hydrogen atoms were refined with
anisotropic displacement parameters. All hydrogen atom positions
were determined by geometry and refined by a riding model. In the
case of 6, the PLATON SQUEEZE command was used to remove a
severely disordered acetonitrile molecule from the asymmetric unit.
DFT Calculations. All structures were fully optimized with the
4
2−44
43,45−47
B3LYP
and OLYP
functionals using all-electron STO-
48,49
TZP basis sets, as implemented in the ADF program. Grimme’s
D3 dispersion correction and solvation with dichloromethane in
COSMO (Conductor-like Screening Model)
50
51−55
did not have an
appreciable effect on the energetics, structures, or spin density
profiles. Accordingly, only gas-phase dispersion-free results have been
quoted in the discussion above.
Group theory was employed to study different d orbital
Figure 9. Selected calculated results for S = 1 6: (top) B3LYP spin
density plot (contour of 0.005 e/Å ), (middle) selected Mulliken
spin populations (blue, underlined) and bond distances for OLYP,
and (bottom) the same for B3LYP.
II
−
configurations for the complexes examined. For [Fe (TPC)] (C ),
3
2
all-electron α/β occupancies for the two irreducible representations
are as follows: occupation 1, α 79/78 β 72/71; occupation 2, α 79/
7
7 β 72/72.
III
[
Fe (TPC)(L)] (2·L). To a round-bottom flask were added 486 mg
(
0.79 mmol) of 1 and 117 mg (0.87 mmol) of KC . The solids were
represents the first example of a tetravalent iron corrole
complex bearing an alkyl ligand. In total, the chemistry of
divalent iron has been shown to differ markedly in reactions
with O2 and organic electrophiles when in a corrole
environment versus that of a porphyrin.
8
dissolved in 125 mL of tetrahydrofuran, and the resulting mixture
was stirred for 18 h at room temperature, during which time it took
on a wine-red color. After this time, the mixture was filtered to
remove insoluble byproducts (KCl and graphite). The resulting
filtrate was evaporated to dryness to give a crude solid, which was
exhaustively extracted into warm hexanes (∼50 °C). Removal of the
hexanes in vacuo afforded 2·THF as 347 mg (76% as the THF
adduct) of a dark red-purple solid. Analytically pure crystals of 2·
EXPERIMENTAL SECTION
■
General Comments. Manipulations of air- and moisture-
sensitive materials were performed under an atmosphere of nitrogen
gas using standard Schlenk techniques or in a Vacuum Atmospheres
glovebox under an atmosphere of purified nitrogen. Tetrahydrofuran,
diethyl ether, pentane, dichloromethane, and toluene were purified
by being sparged with argon and passage through two columns
CH CN suitable for X-ray diffraction were obtained by slow cooling
3
of a warm (60 °C), saturated acetonitrile solution at room
temperature. The following characterization data apply to 2·
1
CH
CN: μeff = 4.1(2) μ
;
B
H NMR (300 MHz, C
D
6
) δ 12.2
3
6
(3H), 10.2 (4H), 9.96 (2H), 9.77 (4H), 6.97 (2H), 4.65 (1H), 3.9
(2H), −0.3 (2H), −58.6 (2H), −72.1 (2H). Anal. Calcd for
C H FeN : C, 75.49; H, 4.22; N, 11.29. Found: C, 73.74; H, 3.86;
packed with 4 Å molecular sieves. Benzene-d was dried over sodium
6
ketyl and vacuum-distilled prior to use. Acetonitrile-d was stored
3
39 26
5
1
over 4 Å molecular sieves prior to use. H NMR spectra were
recorded on Varian spectrometer operating at 300 or 500 MHz ( H)
N, 11.30. Repeated analyses returned slightly low values for C.
1
K(THF) [Fe(TPC)] (3a). A round-bottom flask was charged with
2
and referenced to the residual proton resonance of the solvent.
Fourier transform IR spectra were recorded with a ThermoNicolet iS
167 mg (0.26 mmol) of 2·THF and 40 mL of tetrahydrofuran. To
the resulting solution was added 36 mg (0.27 mmol) of KC as a
8
1
0 spectrophotometer in a solution transmission cell (KBr windows
solid in one portion. Upon addition of the KC , the solution
8
H
DOI: 10.1021/acs.inorgchem.9b02209
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
immediately became green. The mixture was allowed to stir overnight
at room temperature. After this time, the mixture was filtered through
Celite to remove graphite. All volatiles were removed in vacuo, and
the resulting dark residue was rinsed repeatedly with warm (50 °C)
hexanes to remove unreacted 2·THF. Once the hexane washes were
nearly colorless, the remaining solid was extracted into 4 mL of
tetrahydrofuran, layered with heptane, and set aside at −30 °C. After
AUTHOR INFORMATION
■
Corresponding Author
E-mail: zachary.tonzetich@utsa.edu.
*
ORCID
Jeanet Conradie: 0000-0002-8120-6830
Abhik Ghosh: 0000-0003-1161-6364
Zachary J. Tonzetich: 0000-0001-7010-8007
∼24 h, the desired material precipitated as 173 mg (88%) of purple
1
crystals suitable for X-ray diffraction: μ = 2.9(2) μ ; H NMR (300
eff
B
MHz, CD CN) δ 23.8 (4H), 13.26 (2H), 12.80 (4H), 10.58 (2H),
3
Notes
9
.24 (1H), 8.33 (2H), 3.71 (THF 8H), 1.84 (THF 8H), −16.9
The authors declare no competing financial interest.
(
2H), −31.6 (2H), −90.0 (2H). Anal. Calcd for C H FeKN O : C,
4
5
39
4
2
7
0.86; H, 5.15; N, 7.35. Found: C, 70.42; H, 4.66; N, 7.63.
Procedure for Reaction of 3a with CO To Generate 4. In an
ACKNOWLEDGMENTS
■
NMR tube, 13.1 mg (17 μmol) of 3a was dissolved in 0.7 mL of
The authors thank the Welch Foundation (Grant AX-1772 to
ZJT), the Research Council of Norway (Grant 262229 to
A.G.), and the South African National Research Fund (Grant
acetonitrile-d . The tube was capped with a rubber septum and CO
3
gas was injected directly. The tube was inverted several times to
1
ensure dissolution of CO, and the H NMR spectrum was recorded
9
6111 to J.C.) for financial support. NMR facilities at the
directly. For the purpose of UV−vis and IR spectroscopy, solutions
University of Texas at San Antonio are supported by a grant
from the National Science Foundation (NSF) (CHE-
1625963). The CENTC Elemental Analysis Facility is
supported by NSF (CHE-0650456).
of 3a in THF were prepared in a similar fashion at concentrations of
1
2
2 μM and 15 mM, respectively, and then treated with CO: H
NMR (300 MHz, CD CN) δ 8.98 (d, 2H), 8.70 (d, 2H), 8.43 (app
3
d, 4H), 8.26 (app d, 4H), 8.16 (m, 2H), 7.81−7.69 (m, 9H); IR
1
(
THF) 1894 cm− (ν ).
CO
Procedure for Reaction of 3a with O To Generate 5. A 4.4
2
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briefly swirled to encourage dissolution of the oxygen, a color change
was observed, indicating formation of 5. Spectra were then recorded
at the desired time interval. To observe complete formation of 2·
THF, the contents of the cell were allowed to warm to room
temperature. The cell was then recooled to acquire the spectrum of
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