Oxygen atom insertion into iron(II) phenyl and methyl bonds: A key step for catalytic hydrocarbon functionalization

Article abstract of DOI:10.1021/om500914h

Oxy-functionalization of metal-alkyl and ?aryl bonds is a key step in potential hydrocarbon oxidation catalysis. However, well-defined examples of M-R to ROH conversion are rare, especially for first-row transition metals. CpFe(CO)(NCMe)Ph reacts with oxygen or hydrogen peroxide to produce benzoic acid. Removing CO from the CpFe(L)(L')Ph framework allows simple oxygen atom insertion into the Fe-Ph bond. CpFe(P(OCH₂)₃CEt)₂Ph reacts with Me₃NO in THF to produce PhOH in high yield when Bronsted acids are added. Studies show that light promotes P(OCH₂)₃CEt dissociation from CpFe(P(OCH₂)₃CEt)₂Ph, which facilitates the conversion to PhOH. The methyl analogue CpFe[P(OCH₂)₃CEt]₂Me reacts with oxidants to produce MeOH.

Full text of DOI:10.1021/om500914h

Article
pubs.acs.org/Organometallics
Oxygen Atom Insertion into Iron(II) Phenyl and Methyl Bonds: A Key
Step for Catalytic Hydrocarbon Functionalization
Jiajun Mei,† Daniel B. Pardue,‡ Steven E. Kalman,† T. Brent Gunnoe,*,† Thomas R. Cundari,*,‡
and Michal Sabat§
§
†Department of Chemistry and Nanoscale Materials Characterization Facility, Materials Science and Engineering Department,
University of Virginia, Charlottesville, Virginia 22904, United States
‡Department of Chemistry and Center for Advanced Scientific Computing and Modeling, University of North Texas, Denton,
Texas 76203, United States
S
* Supporting Information
ABSTRACT: Oxy-functionalization of metal−alkyl and −aryl bonds is a key
step in potential hydrocarbon oxidation catalysis. However, well-defined
examples of M−R to ROH conversion are rare, especially for first-row
transition metals. Cp*Fe(CO)(NCMe)Ph reacts with oxygen or hydrogen
peroxide to produce benzoic acid. Removing CO from the Cp*Fe(L)(L′)Ph
framework allows simple oxygen atom insertion into the Fe−Ph bond.
Cp*Fe(P(OCH2)3CEt)2Ph reacts with Me3NO in THF to produce PhOH in
high yield when Brønsted acids are added. Studies show that light promotes
P(OCH2)3CEt dissociation from Cp*Fe(P(OCH2)3CEt)2Ph, which facilitates
the conversion to PhOH. The methyl analogue Cp*Fe[P(OCH2)3CEt]2Me
reacts with oxidants to produce MeOH.
Scheme 1. Proposed Pathways for Partial Oxidation
of Hydrocarbons Involving Oxygen Atom Insertion
into a M−R Bond and 1,2-CH-Addition across a M−OR
Bond
INTRODUCTION
■
The selective catalytic oxidation of hydrocarbons is an im-
portant but challenging process.1−14 Enzymes perform C−H
oxidation via high-valent Fe−oxo complexes, which initiate net
H-atom abstraction to generate a transient radical.15−17 A C−O
bond forming “rebound” step followed by alcohol dissociation
completes the conversion.18 While progress has been made
using synthetic metal−oxo complexes that initiate H atom ab-
straction,15,19−24 successful extension to substrates possessing
C−H bond dissociation enthalpies of >100 kcal/mol (e.g., light
alkanes or arenes) is challenging.19−22 In contrast, transition
metal mediated C−H activation, defined herein as a process
where the C−H bond coordinates to the metal before being
broken, often affords activation of C−H bonds with bond dis-
sociation energies of >100 kcal/mol.5−7,12,13,25−32
One strategy for metal-mediated C−O bond formation
involves net oxygen atom insertion into metal−alkyl bonds
(Scheme 1), which can occur via a metal−oxo intermediate or a
Baeyer−Villiger-type pathway.6,33−36 The Baeyer−Villiger path-
way involves concerted C−O bond formation with Y−O
bond breaking (Scheme 1). Since the activation of C−H bonds
via 1,2-addition across M−X (X = OR, NR, NR2) bonds has
been reported,30,33,37−42 the development of catalytic cycles
is potentially viable (Scheme 1). Insertions of oxygen atoms
into M−C bonds via nonradical routes are rare, and the ma-
jority of examples involve high valent d0 metals that are inca-
pable of C−H activation.33,34,43−47 To our knowledge, O-atom
insertion into M−R bonds for non-d0 metals includes only
Ni(II), Pd(II), and one example of a two-coordinate Fe(II)
complex.45,48−50
We recently reported facile C−H activation by Cp*Fe(CO)-
(NCMe)Ph (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl).51
Having observed C−H activation, Cp*Fe(L)(L′)Ph complexes
were deemed a good starting point to pursue Fe-mediated C−O
bond formation. A computational study of metal-mediated C−O
bond formation by Cp*Fe(CO)(NCMe)R (R = Me or Ph)
indicated that O-atom insertion to form Fe−OR should be
kinetically feasible.52 Consistent with the prediction based on
theory, herein is reported the observation of conversion of Fe−R
bonds and oxidants into alcohols.
Received: September 3, 2014
Published: September 18, 2014
© 2014 American Chemical Society
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showed that the formation of Cp*Fe(CO)(NCMe)OPh
from reaction of Cp*Fe(CO)(NCMe)Ph and pyridine N-oxide
should be kinetically accessible,52 CO insertion into the Fe−Ph
bond competes with O-atom insertion. Consistent with this sug-
gestion, a computational study predicts a ΔG⧧ of 12.7 kcal/mol for
CO insertion into the Fe−Ph bond of Cp*Fe(CO)(NCMe)Ph
(Scheme 2). In contrast, the overall calculated ΔG⧧ for conversion
of Cp*Fe(CO)(NCMe)Ph and pyridine N-oxide to Cp*Fe(CO)-
(OPh) is approximately 33.1 kcal/mol. Because of the competition
of CO insertion, the reactivity with a Cp*Fe(L)2R complex without
a CO coligand was probed.
RESULTS AND DISCUSSION
■
The reaction of Cp*Fe(CO)(NCMe)Ph (1) with various
oxidants results in either decomposition or the production of
benzoic acid (eq 1 and Table 1). For some oxidants, the Cp*
The reaction of [(TMEDA)FeCl2]n (n = 1, 2) (TMEDA =
N,N,N′,N′-tetramethylethylenediamine) with P(OCH2)3CEt and
Cp*Li produces Cp*Fe[P(OCH2)3CEt]2Cl (2) in 70% isolated
yield. Complex 2 reacts with PhLi to give Cp*Fe(P(OCH2)3-
CEt)2Ph (3) in 62% isolated yield (Scheme 3). Complex 3 was
characterized by single-crystal X-ray diffraction (Scheme 3).
Under ambient light, monitoring the reaction of Cp*Fe(P-
Table 1. Reaction Conditions, Products, and Yields for the
Reactions of Cp*Fe(CO)(NCMe)Ph (1) with Various
a
Oxidants
b
c
no. oxidant T (°C) t (h) PhCOOH (%) benzene (%) fulvene (%)
1
2
3
4
5
6
7
8
O2 (15 psi) 21
24
0.5
24
1.5
60
0
20
>90
10
>90
>90
10
Me3NO
PyO
21
60
hv
21
21
21
21
1
0
(OCH2)3CEt)2Ph (3) with excess Me3NO in THF-d8 by H
PyO
0
0
15
NMR spectroscopy reveals the transformation of 3 to several
products after 4 days at room temperature. The addition of
Brønsted acid (e.g., H2O or HCl) results in the production of
PhOH in 70% yield (1H NMR) relative to 3. Phenol pro-
mCPBA
nBuN4IO4
H2O2
0.5
0.5
0.5
0
>90
10
<10
>90
0
10
60
0
<10
90
tBuOOH
24
0
1
duction has been confirmed by H NMR spectroscopy and
a
Reactions are with 3 equiv of oxidant in THF-d8 in NMR tubes.
GC-MS. The control reaction of 3 and water (THF-d8, room
temperature) produces benzene without observation of phenol.
During the reaction of 3 with Me3NO, prior to addition of acid,
the phenyl ligand of 3 is converted to a new species that has
been identified as PhOH·ONMe3 (see Experimental Section
and Supporting Information).
For the reaction of 3 with Me3NO, in addition to PhOH
production, the Cp* ligand is oxidized to 1,2,3,4-tetramethyl-
fulvene and the phosphite ligands are oxidized to phosphate,
b
Yields of products are based on integration of 1H NMR spectra
c
versus an internal standard. Fulvene = 1,2,3,4-tetramethylfulvene.
ligand is oxidized to 1,2,3,4-tetramethylfulvene (Table 1, entries
1−6). Benzene is formed in many cases (Table 1, entries 1−3
and 5−8), which is presumed to result from protonation (protic
oxidants) and/or Fe−Ph bond homolysis from an oxidized
intermediate [likely Fe(III)].53 Although previous calculations
a
Scheme 2. Calculated Free Energies for the Reaction of Cp*Fe(CO)(NCMe)Ph (1) and Pyridine N-oxide (PyO) in THF-d8
a
Numbers are free energies (kcal/mol) relative to Cp*Fe(CO)(ONMe3)Ph. Lowest energy spin states are labeled in the boxes on the top left of
structures.
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a
TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl] or 1,4-cyclo-
hexadiene. Since TEMPO is known to trap phenyl radical,55
this suggests that free phenyl radical is not formed in the
reaction of 3 with Me3NO. However, these experiments cannot
rule out a short-lived phenyl radical that rapidly recombines
with an Fe−O moiety. We also considered a pathway involving
decomposition of complex 3 in the presence of light to form
an unobserved Fe catalyst (e.g., Fe nanoparticles), which then
catalyzes the oxidation of benzene to phenol. Complex 3 and
excess Me3NO were reacted in the presence of excess benzene,
but the catalytic conversion of benzene to phenol was not ob-
served. We also performed this reaction in the presence of ex-
cess 1,4-cyclohexadiene (to provide a source of hydrogen) and,
again, did not observe catalytic production of PhOH. Thus, if
an in situ Fe catalyst for benzene oxidation is formed, it is
limited to <1 turnover. While they do not definitively eliminate
in situ formation of an Fe catalyst from consideration, these
experimental results are most consistent with a stoichiometric
oxidation reaction.
Scheme 3. Synthesis of Cp*Fe(P(OCH2)3CEt)2Ph (3)
It was hypothesized that light might promote P(OCH2)3CEt
dissociation from 3. In the dark, there is no reaction between
complex 3 and excess PMe3 (THF-d8) after 1 week at 80 °C. In
contrast, complex 3 is quantitatively converted to Cp*Fe-
(P(OCH2)3CEt)(PMe3)Ph (4) within 2 h under photolysis at
room temperature (eq 4). Under pseudo-first-order conditions
a
ORTEP drawing of 3 (50% probability ellipsoids; H atoms omitted).
Selected bond lengths (Å): Fe−C1 1.9993(2), Fe−P1 2.0854(4),
Fe−P2 2.0996(4). Selected bond angles (deg): C1−Fe−P1 92.91(4),
C1−Fe−P2 92.73(4), P1−Fe−P2 91.65(2).
as indicated by a resonance in the 31P NMR spectrum at
−8.2 ppm.54 A brown precipitate is also observed, but we have
been unable to characterize this material. Thus, the reaction
of 3 and Me3NO results in the oxidation of Cp*, both
P(OCH2)3CEt ligands, and the phenyl ligand (eq 2). When 3 is
(i.e., excess PMe3), complex 2 was treated with a series of
concentrations of PMe3 in THF-d8 under photolysis, and a first-
order rate constant for the disappearance of complex 3 was
determined for each reaction. Within deviation of the data,
a plot of kobs as a function of [PMe3] shows a zero-order
dependence on [PMe3] (Figure 1). The average kobs value is
treated with only 1 equiv of Me3NO, partial conversion of 3 to
the same products occurs.
No reaction is observed for 3 and Me3NO after 1 week in the
absence of light even upon heating at 80 °C. When photolyzed,
the reaction of 3 and Me3NO is complete within 2 h to produce
PhOH·ONMe3 (compared to 4 days in ambient light). The ad-
dition of Brønsted acid (e.g., H2O or HCl) to the reaction mix-
ture results in the formation of PhOH (eq 3). Further studies
Figure 1. Plot of kobs vs [PMe3] for the reaction of Cp*Fe(P-
(OCH2)3CEt)2Ph (3) with PMe3 showing a zero-order dependence
on [PMe3].
0.8(3) × 10−3 s−1. The large deviations in kobs are a result of
challenges associated with reproducibility using the photolysis
lamp (e.g., rate changes as a function of distance from the lamp).
As expected for an 18-electron complex, the kinetic data are con-
sistent with a dissociative ligand exchange with P(OCH2)3CEt
dissociation as the rate-limiting step.
showed that light is required for dissociation of a phosphite
ligand (see below) in the conversion of 3 and Me3NO.
We first considered a radical pathway for the net oxygen
atom insertion into the Fe−Ph bond. However, no significant
change in the product or rate is observed when the same
reaction is performed in the presence of radical traps such as
The reaction of 3 and Me3NO in THF-d8 was monitored
1
by H and 31P NMR spectroscopy under the same photolysis
conditions as the reaction of 3 and PMe3. Free P(OCH2)3CEt
is formed and then converted to OP(OCH2)3CEt, which
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oxidation of coordinated P(OCH2)3CEt to form OP(OCH2)3-
CEt, conversion of Ph−FeO to form Fe−OPh, and oxidation
of Cp* to form 1,2,3,4-tetramethylfulvene (Scheme 4).
Complex 3 is calculated to possess a singlet spin ground
state. Fe remains bonded to Cp* in an η5 fashion throughout
the reaction coordinate. Overall, the oxy-insertion product
Cp*Fe(P(OCH2)3CEt)(OPh) is calculated to be highly exer-
gonic relative to the starting materials (ΔG = −65.4 kcal/mol).
Upon dissociation of the phosphite ligand from 3, which is
found to be endergonic by 1.7 kcal/mol, a spin flip from the
singlet to a triplet occurs. The minimum energy crossing point
(MECP) for phosphine loss was calculated using Harvey’s
method.56,57 The singlet → triplet “spin flip” associated with
phosphite dissociation was calculated to be energetically de-
manding, lying ∼20 kcal/mol above complex 3, and hence
engendering a barrier that is similar to the OAT barrier (vide
infra) and consistent with the experimental proposal of rate-
determining phosphite dissociation.
Coordination of Me3NO to Cp*Fe(P(OCH2)3CEt)Ph was
calculated to stabilize the complex by 2.2 kcal/mol with ΔG =
0.5 kcal/mol compared to the starting complex 3. Another
spin flip (triplet → quintet) accompanies the transformation
of Cp*Fe(P(OCH2)3CEt)Ph → Cp*Fe(P(OCH2)3CEt)-
(ONMe3)Ph. Attempts to find phosphite/ONMe3 ligand ex-
change via an associative mechanism were not successful, and
thus, consistent with the kinetic study of P(OCH2)3CEt/PMe3
exchange (see above), the simulations imply a dissociative
mechanism.
Figure 2. Plot of concentration versus time for the starting material
and three products observed during the reaction of Cp*Fe(P-
(OCH2)3CEt)2Ph (3) with Me3NO in THF-d8 including complex 3
(green, diamonds), OP(OCH2)3CEt (black, ×), 1,2,3,4-tetrame-
thylfulvene (blue, triangles), and PhOH·ONMe3 (red, circles).
supports dissociation of P(OCH2)3CEt under photolysis as the
first step of oxygen atom insertion into the Fe−Ph bond.
Figure 2 depicts the concentration versus time plot for the
starting material 3 and the three products shown in eq 2 (based
on the integrations of 1H NMR spectra). Since oxidation of free
P(OCH2)3CEt by Me3NO occurs in the absence of photolysis,
we did not monitor the concentration of free P(OCH2)3CEt. In
the plot, in order to keep the y-scale similar for all compounds,
the concentration of OP(OCH2)3CEt is divided by 2. Using
a first-order fit for the disappearance of 3 gave kobs = 1.0(1) ×
10−3 s−1, which is almost identical to the kobs for phosphite/PMe3
exchange (see above). This is consistent with rate-limiting phos-
phite dissociation for the formation of PhOH. The generation of
PhOH·ONMe3 and 1,2,3,4-tetramethylfulvene have almost iden-
tical rates with a kobs = 0.9(1) × 10−3 s−1 as the decay of 3. The
oxidation of free P(OCH2)3CEt with Me3NO (under the same
pseudo-first-order conditions) in THF-d8 was independently
determined by 1H NMR spectroscopy at room temperature, and
kobs = 0.55(1) × 10−3 s−1 was determined (Figure 3), which is
Conversion of Cp*Fe(P(OCH2)3CEt)(ONMe3)Ph to an
FeIV−oxo Cp*Fe(P(OCH2)3CEt)(O)Ph is calculated to be ex-
ergonic (ΔG = −15.5 kcal/mol relative to 3). The transition
state for the oxygen atom transfer was calculated to be 20.0
kcal/mol above Cp*Fe(P(OCH2)3CEt)(ONMe3)Ph with a
quintet spin state. Formation of Cp*Fe(P(OCH2)3CEt)(O)Ph
entails another spin flip to a triplet upon formation of the oxo
intermediate. The Fe of Cp*Fe(P(OCH2)3CEt)(O)Ph has a
spin density of 1.315 e−, while the oxo has a 0.819 e− spin den-
sity. This suggests the oxo intermediate possesses oxyl (O−●
)
character. The spin density plot can be seen in Figure 4, show-
ing the alpha spin (orange) being shared between the oxyl and
Fe while a small amount of beta spin (purple) is on the phenyl
ligand.
Migration of the phenyl ligand to the Fe−oxo bond (Scheme 4,
blue pathway) results in a calculated free energy barrier of
16.8 kcal/mol and was found to be exergonic by 65.4 kcal/mol
upon formation of the quintet phenoxide product Cp*Fe-
(P(OCH2)3CEt)(OPh). Thus, the calculations predict that
formation of the oxo complex occurs with a more substantial
free energy of activation than the phenyl migration step. Similar
to calculations of oxy-insertion into the Fe−Ph bond of Cp*Fe-
(CO)(NCMe)Ph,52 the calculations predict that conversion of
Cp*Fe(P(OCH2)3CEt)2Ph and Me3NO to Cp*Fe(P(OCH2)3-
CEt)(OPh) is kinetically feasible.
From the oxo complex Cp*Fe(P(OCH2)3CEt)(O)Ph, the
phosphite can migrate to the oxo ligand to form phosphate
(Scheme 4, black pathway). The calculated free energy barrier
to form phosphate from Cp*Fe(P(OCH2)3CEt)(O)Ph is 11.8
kcal/mol. The formation of the phosphate product Cp*Fe-
(OP(OCH2)3CEt)Ph is 13.8 kcal/mol exergonic in relation
to the starting material Cp*Fe(P(OCH2)3CEt)2Ph. These re-
sults suggest that phosphate formation can originate from
Cp*Fe(P(OCH2)3CEt)(O)Ph or free phosphite (see above).
Figure 3. Plot of concentration versus time for the reaction of
P(OCH2)3CEt with Me3NO in THF-d8 to produce OP(OCH2)3CEt.
[P(OCH2)3CEt (diamonds), OP(OCH2)3CEt (circles)].
consistent with the observation of a low concentration of free
phosphite that is ultimately converted to phosphate. The plot in
Figure 2 shows no evidence of an induction period.
Previous computational studies of O-atom insertion into the
Fe−R bonds of Cp*Fe(CO)(NCMe)R from reactions with oxi-
dants revealed that the most favorable pathway would likely in-
volve formation of the Fe−oxo intermediate Cp*Fe(CO)(O)R
followed by migratory insertion of the hydrocarbyl ligand to
the oxo ligand.52 We extended the computational studies to
Cp*Fe(P(OCH2)3CEt)2Ph with the assumption that the ana-
logous Fe−oxo complex, Cp*Fe(P(OCH2)3CEt)(O)Ph, is an
intermediate. Density functional theory (DFT) calculations
were carried out to determine the energy barriers for the three
observed oxidation reactions following the dissociation of the
P(OCH2)3CEt and the formation of the FeO intermediate: the
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a
Scheme 4. Calculated Free Energies for the Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) and Me3NO in THF-d8
a
Numbers are free energies (kcal/mol) relative to complex 3. Lowest energy spin states are labeled in the box on the top left of structures.
Scheme 5. Proposed Pathway for the Reaction of
Cp*Fe(P(OCH2)3CEt)2Ph (3) and AgOTf
Figure 4. Spin density plot of oxo intermediate Cp*Fe(P(OCH2)3-
CEt)(O)Ph [scale: 0.33, contour value: 0.006 943].
Oxidation of Cp* was also modeled computationally
(Scheme 4, red pathway). From Cp*Fe(P(OCH2)3CEt)(O)Ph,
[Cp*Fe(P(OCH2)3CEt)2Ph]+ followed by C−C reductive
the formation of 1,2,3,4-tetramethylfulvene via H-atom transfer
to the oxo ligand was calculated to have a free energy barrier of
19.0 kcal/mol.
elimination. Consistent with this proposal, the reaction of
3 with AgOTf (OTf = trifluoromethanesulfonate), a known
single-electron oxidant in darkness, results in the formation
of Cp*Ph in quantitative yield (Scheme 5). DFT calculations
reveal that the free energy barrier for the formation of Cp*Ph
via direct C−C reductive elimination is 40.1 kcal/mol from
Fe(II) complex 3, but the calculated free energy barrier is
reduced to 19.4 kcal/mol for the cationic, formally Fe(III)
complex [Cp*Fe(P(OCH2)3CEt)2Ph]+ (Scheme 6).
In contrast to the reaction of 3 with Me3NO, the reaction of
3 with sodium periodate in a THF/H2O mixture results in the
quantitative production of 1,2,3,4,5-pentamethyl-5-phenylcy-
1
clopentadiene (Cp*Ph) after 24 h by H NMR spectroscopy
(eq 5). We considered that the formation of Cp*Ph might
result from an initial electron transfer to form the FeIII complex
Table 2 shows the yields of PhOH and Cp*Ph for the reac-
tions of 3 with a range of oxidants and solvents. The production
of PhOH requires light (either ambient or photolysis lamp);
however, Cp*Ph formation occurs in the absence of light.
These observations are consistent with light-induced dissocia-
tion of phosphite as key step in the formation of PhOH but
not Cp*Ph. Although N-oxides are not typically considered
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Scheme 6. Calculated Free Energies for the Reaction of
Cp*Fe(P(OCH2)3CEt)2Ph (3) and AgOTf in THF-d8
Table 2. Reaction Conditions and Yields for
Cp*Fe(P(OCH2)3CEt)2Ph (3) with Various Oxidants
a
a
b
c
no.
oxidant
solvent
THF
T (°C) t (h) PhOH (%) Cp*Ph (%)
1
2
3
4
5
6
7
8
9
Me3NO
Me3NO
Me3NO
21
96
2
70
70
0
10
10
THF
21 (hν)
21
CH3CN
THF
96
72
24
24
1
80
d
NMO
21
70
0
10
O2 (15 psi) CH3CN
O2 (15 psi) THF
O2 (15 psi) THF
nBU4NIO4 THF
21
90
21
15
15
25
0
20
21 (hν)
21 (hν)
21
20
4
12
NaIO4
THF/
H2O
0.5
100
10 nBU4NIO4 CH3CN
21
24
72
4
0
10
13
0
90
80
15
0
11 H2O2
12 H2O2
13 PyO
14 PyO
THF
THF
THF
THF
21
21 (hν)
21 (hν)
70
4
96
24
0
70
90
100
15 4-NO2-PyO CH3CN
16 AgOTf CH3CN
50
0
21
0.5
0
a
b
Reactions incorporate 5 equiv of oxidant in deuterated solvents. All
reactions were performed under ambient or UV light. hν is used to
show reactions performed under UV light. PhOH is not observed
c
when reactions are performed in the absence of light. Yields of pro-
1
ducts are based on integration of H NMR spectra versus an internal
d
standard. NMO = N-methylmorpholine N-oxide.
a
Numbers are free energies (kcal/mol) relative to complex 3. Lowest
energy spin states are labeled in the box on the top left of structures.
single-electron oxidants, such reactivity has precedent.58
Complex 3 reacts with Me3NO in THF to produce a high
yield of PhOH under either photolysis or ambient light (entries
1 and 2), but only the C−C coupling product is observed in
MeCN (entry 3). Although we do not have a definitive
explanation for the solvent effect, it is possible the MeCN may
promote electron transfer due to its polar nature by stabilizing
incipient charge in the transition states for the formation of
[Cp*Fe(P(OCH2)3CEt)2Ph]+. Alternatively, MeCN might
inhibit coordination of Me3NO to Fe and suppress the oxy-
insertion reaction, while the proposed mechanism for formation
of Cp*Ph does not require a vacant coordination site on Fe.
nBu4NIO4 and H2O2 also generate PhOH in THF (Table 2,
entries 8, 11, and 12). Aerobic oxidation of the Fe−Ph to form
PhOH is also observed, although the yield is low (Table 2,
entries 6 and 7). Taken together, these results suggest that
PhOH formation does not likely occur by an initial single-
electron transfer to generate an Fe(III) intermediate. Rather,
the reaction is hypothesized to occur by initial P(OCH2)3CEt/
Me3NO ligand exchange to generate Cp*Fe(P(OCH2)3CEt)-
(Me3NO)Ph, which then undergoes net O-atom transfer to the
phenyl ligand.
MeOH as the coproduct (eq 7). Table 3 shows the results of
the reactions of 5 with various oxidants.
SUMMARY AND CONCLUSIONS
■
Insertion of oxygen atoms into metal−hydrocarbyl bonds is a
key step in the development of potential catalysts for the
oxidation of hydrocarbons as shown in Scheme 1. Despite the
potential importance of such oxygen atom insertion reactions,
there are few examples of nonradical conversion of M−R bonds
and oxygen atom transfer reagents to M−OR. Herein, it is
demonstrated that Fe(II) hydrocarbyl (phenyl and methyl)
complexes undergo C−O bond formation upon reaction with
certain oxidants. The experimental observations were augmented
by computational studies that indicate Fe−oxo complexes as
viable intermediates that precede net oxo insertion into the
Fe−R bond. The reaction requires light, presumably to initiate
ligand exchange between phosphite and the oxidant. The calcula-
tions indicate that both Fe−oxo formation and the oxy-insertion
into Fe−R bonds are thermally viable processes. Although the
previous (limited) examples of O-atom insertion into M−R
We have also prepared and isolated the methyl complex
Cp*Fe(P(OCH2)3CEt)2Me (5). When treated with Me3NO
in THF, complex 5 displays analogous reactivity to 3 to pro-
1
duce MeOH, but with a lower yield (∼25%) by H NMR
spectroscopy (eq 6). The C−C reductive elimination product
1,2,3,4,5,5-hexamethylcyclopentadiene (Cp*Me) is also ob-
served when 5 reacts with Me3NO or O2 in CD3CN, with
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and analyzed by 1H NMR spectroscopy. D2O (2 μL) was added to the
reaction mixture, and the products were analyzed by H NMR spec-
troscopy and/or GC-MS.
Table 3. Reaction Conditions and Yields for Reaction of
Cp*Fe(P(OCH2)3CEt)2Me (5) with Various Oxidants
1
a
b
no.
oxidant
solvent
THF
T (°C) t (h) MeOH (%) Cp*Me (%)
Cp*Fe(P(OCH2)3CEt)2Cl (2). THF (50 mL) was cooled in a glove-
box freezer at −30 °C for 30 min. After the cooling time period,
the solution was added to a mixture of Cp*Li (1.01 g, 7.1 mmol),
[(TMEDA)FeCl2]n (n = 1, 2) (1.10 g, 4.53 mmol), and P(OCH2)3-
CEt (2.01 g, 12.3 mmol) in a round-bottom flask. The mixture was
stirred and allowed to warm to room temperature over a period of
approximately 30 min. The red-brown mixture was eluted through
silica gel on a fine-porosity frit using THF. A red-brown band was
collected, and most of the solvent was removed under vacuum.
Hexanes (50 mL) were added to form a precipitate. The red-brown
solid was collected via vacuum filtration, washed with hexanes, and dried
1
2
3
4
5
6
7
8
9
Me3NO
Me3NO
Me3NO
21
96
25
25
25
25
0
0
0
THF
21 (hν) 24
CH3CN
THF
21
21
21
21
96
96
24
24
0
c
NMO
0
O2 (15 psi) CH3CN
O2 (15 psi) THF
O2 (15 psi) THF
90
70
0
16
22
10
0
21 (hν) 24
nBu4NIO4
THF
21 (hν)
4
0
NaIO4
THF/
H2O
21
0.5
100
1
under vacuum (1.79 g, 70% yield). H NMR (300 MHz, THF-d8):
10 nBu4NIO4
11 H2O2
12 H2O2
13 PyO
CH3CN
THF
21
24
0
26
20
0
83
0
δ 4.17 (12H, s, P(OCH2)3CCH2CH3), 1.51 (15H, s, C5(CH3)5), 1.20
3
3
(4H, q, JHH = 8 Hz, P(OCH2)3CCH2CH3), 0.82 (6H, t, JHH
=
21
24
2
8 Hz, P(OCH2)3CCH2CH3). 13C NMR (201 MHz, CD3CN): δ 88.7
(P(OCH2)3CCH2CH3), 74.4 (C5(CH3)5), 35.5 (P(OCH2)3CCH2CH3),
23.7 (P(OCH2)3CCH2CH3), 9.3 (C5(CH3)5), 7.0 (P(OCH2)3-
CCH2CH3). 31P NMR (121 MHz, CD3CN): δ 163.8 (s).
THF
21 (hν)
21 (hν)
70
0
THF
4
0
14 PyO
THF
96
24
0
70
76
100
15 4-NO2-PyO CH3CN
16 AgOTf CH3CN
50
0
Cp*Fe(P(OCH2)3CEt)2Ph (3). Complex 2 (1.02 g, 1.80 mmol) was
dissolved in THF (50 mL) in a Schlenk flask. The solution was then
cooled in a 2-propanol/dry ice bath. A diethyl ether solution of PhLi
(1.8 M, 2.2 mL, 4.0 mmol) was added to the solution of 2 with stirring.
Upon addition of PhLi, the mixture turned to yellow from red-brown.
The mixture was allowed to warm to room temperature. In a glovebox,
the solution was eluted through silica gel using THF. A yellow band
was collected, and most of the solvent was removed under vacuum.
Hexanes (50 mL) were added to form a precipitate. The yellow solid
was collected via filtration, washed with hexanes, and dried under vac-
uum (0.71 g, 65% yield). Single crystals suitable for X-ray diffraction
were grown by slow diffusion of pentane into a THF solution of 3. 1H
NMR (800 MHz, CD3CN): δ 7.56 (2H, d, 3JHH = 7 Hz, phenyl ortho),
21
0.5
0
a
Reactions are performed with 5 equiv of oxidant in deuterated sol-
b
vents. Yields of products are based on integration of 1H NMR spectra
versus an internal standard. NMO = N-methylmorpholine N-oxide.
c
bonds occur with metals that will not activate C−H bonds, use of
Cp*Fe(P(OCH2)3CEt)2R complexes is promising because of the
demonstrated ability of the related Cp*Fe(CO)(NCMe)Ph to
activate C−H bonds.51 These studies establish the ability of d6
complexes to mediate O atom insertion into M−R bonds. Im-
portantly, they also point the way to new ligand motifs that avoid
(1) C−C coupling products and (2) ligand oxidation.
3
3
6.60 (2H, t, JHH = 7 Hz, phenyl meta), 6.60 (1H, t, JHH = 7 Hz,
phenyl para), 4.07 (12H, s, P(OCH2)3CCH2CH3), 1.42 (15H, s,
3
EXPERIMENTAL SECTION
C5(CH3)5), 1.15 (4H, q, JHH = 8 Hz, P(OCH2)3CCH2CH3), 0.77
■
(6H, t, JHH = 8 Hz, P(OCH2)3CCH2CH3). 13C NMR (201 MHz,
3
General Methods. Unless otherwise noted, all synthetic proce-
dures were performed under anaerobic conditions in a nitrogen-filled
glovebox or by using standard Schlenk techniques. Glovebox purity
was maintained by periodic nitrogen purges and was monitored by an
oxygen analyzer (O2 < 15 ppm for all reactions). Tetrahydrofuran was
dried by distillation from sodium/benzophenone. Diethyl ether was
distilled over CaH2. THF-d8, CD3CN, and D2O were used as received
and stored under a N2 atmosphere over 4 Å molecular sieves (except
water). 1H NMR spectra were recorded on a Varian Mercury 300 MHz,
Varian Inova 500 MHz, or Bruker 800 MHz spectrometer. 13C NMR
spectra were recorded using a Varian Mercury 300 MHz (operating
frequency 75 MHz), Varian Inova 500 MHz (operating frequency
125 MHz), or Bruker 800 MHz (operating frequency 201 MHz) spec-
trometer. 31P NMR spectra were recorded using a Varian Mercury
300 MHz (operating frequency 121 MHz) referenced against an external
CD3CN): δ 171.2 (ipso Ph, t, 2JPC = 34 Hz), 146.9, 125.2, 119.9 (Ph),
91.0 (P(OCH23)3CCH2CH3), 74.3 (C5(CH3)5), 35.5 (P(OCH2)3-
CCH2CH3, t, JPC = 15 Hz), 24.0 (P(OCH2)3CCH2CH3), 10.0
(C5(CH3)5), 7.3 (P(OCH2)3CCH2CH3). 31P NMR (121 MHz, CD3CN):
δ 167.3 (s). Anal. Calcd for C28H42O6P2Fe: C 56.78, H 7.15. Found: C
56.88, H 7.20.
Cp*Fe(P(OCH2)3CEt)2Me (5). Complex 5 was made by the same
procedure as 3 but using a MeLi solution instead of a PhLi solution
1
(65% isolated yield). H NMR (300 MHz, CD3CN): δ 4.02 (12H, s,
3
P(OCH2)3CCH2CH3), 1.53 (15H, s, C5(CH3)5), 1.13 (4H, q, JHH
=
3
8 Hz, P(OCH2)3CCH2CH3), 0.76 (6H, t, JHH = 8 Hz, P(OCH2)3-
CCH2CH3), −0.96 (3H, t, JPH = 6 Hz, CH3). 13C NMR (201 MHz,
3
CD3CN): δ 89.0 (P(OCH2)3CCH2CH3), 74.3 (C5(CH3)5), 35.3
(P(OCH2)3CCH2CH3, t, 3JPC = 15 Hz), 24.3 (P(OCH2)3CCH22CH3),
1
standard of H3PO4 (δ = 0). All H and 13C{1H} spectra are referenced
9.8 (C5(CH3)5), 7.4 (P(OCH2)3CCH2CH3), −16.5 (CH3, t, JPC
=
against residual proton signals (1H NMR) or the 13C signals of the
deuterated solvents (13C{1H} NMR). GC/MS was performed using a
Shimadzu GCMS-QP2010 Plus system with a 30 m × 0.25 mm RTx-
Qbond column with 8 μm thickness using electron impact ionization.
Photolysis experiments were performed using UV−vis radiation gen-
erated by a 450 W power supply (model #l7830, Ace Glass, Inc.)
equipped with a water-cooled 450 W 5 in. arc IMMER UV−vis lamp
(model #7825-34, Ace Glass, Inc.). All other reagents were used as pur-
chased from commercial sources. Elemental analyses were performed
by Atlantic Microlabs, Inc. [(TMEDA)FeCl2]n (n = 1, 2) and Cp*Fe-
(CO)(NCMe)Ph (1) was prepared according to the literature pro-
cedure.51,59
Reaction of Cp*Fe(CO)(NCMe)Ph (1) with Oxidants. A repre-
sentative experiment is described. Complex 1 (3.5 mg, 10 μmol) and
pyridine N-oxide (2.9 mg, 30 μmol) were dissolved in 400 μL of
THF-d8 in an NMR tube. The reaction mixture was placed in an oil
bath at 60 °C. The reaction was periodically removed from the oil bath
30 Hz). 31P NMR (121 MHz, CD3CN): δ 167.5 (s). Anal. Calcd for
C23H40O6P2Fe: C 52.21, H 7.60. Found: C 51.99, H 7.55.
Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with Me3NO. Com-
plex 3 (3 mg, 5 μmol) and Me3NO (2 mg, 25 μmol) were mixed in
∼400 μL of THF-d8 in an NMR tube under ambient light. The reac-
tion was periodically analyzed by 1H NMR spectroscopy. The reaction
was complete in 4 days. D2O (2 μL) was added to the reaction mixture,
and the products were analyzed by 1H NMR spectroscopy and GC-MS.
Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with Me3NO under
Photolysis. Complex 3 (3 mg, 5 μmol) and Me3NO (2 mg, 25 μmol)
were mixed in ∼400 μL of THF-d8 in an NMR tube. The solution
was placed in a photolysis cabinet with a Hg vapor lamp. The reaction
1
was complete within 2 h (the products were analyzed by H NMR
spectroscopy).
Attempted Catalytic Oxidation of Benzene by Cp*Fe-
(P(OCH2)3CEt)2Ph (3) with Me3NO. Complex 3 (3 mg, 5 μmol)
and Me3NO (2 mg, 25 μmol) were mixed in ∼400 μL of THF-d8 in an
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dx.doi.org/10.1021/om500914h | Organometallics 2014, 33, 5597−5605

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Article
NMR tube. Benzene (2 μL, 22 μmol) and 1,4-cyclohexadiene (2 μL,
21 μmol) were added to the solution. Me3SiSiMe3 (∼1 μL) was added
The energies quoted are free energies that were calculated at
298.15 K and 1 atm. The stationary points were defined as minima or
transition states by the presence of 0 or 1 imaginary frequency, respec-
tively, as obtained from the calculated energy Hessians. Various spin
states were studied with only results for the lowest energy spin state
reported.
1
as an internal standard for H NMR spectroscopy. The solution was
placed in a photolysis cabinet with a Hg vapor lamp. The reaction was
1
complete within 20 min (the products were analyzed by H NMR
spectroscopy).
Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with O2. Complex 3
(3.0 mg, 5.0 μmol) was dissolved in 400 μL of THF-d8. The reaction
mixture was opened to air under ambient light for 1 day and peri-
odically monitored by 1H NMR spectroscopy. The products were
ASSOCIATED CONTENT
■
S
* Supporting Information
1
analyzed by H and 13C NMR spectroscopy and GC-MS.
Kinetics plots, NMR spectra, GC/MS data, and computational
details. This material is available free of charge via the Internet
at http://pubs.acs.org.
Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with Oxidants. A
representative experiment is described. Complex 3 (6.0 mg 10.1 μmol)
and pyridine N-oxide (4.8 mg 50.0 μmol) were dissolved in 400 μL of
THF-d8 in an NMR tube. The reaction mixture was placed in an oil
bath at 70 °C. The reaction was periodically removed from the oil bath
and analyzed by 1H NMR spectroscopy. Brønsted acid (D2O or HCl)
was added to the reaction mixture, and the products were analyzed by
1H NMR spectroscopy and/or GC-MS.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail (T. B. Gunnoe): tbg7h@virginia.edu.
*E-mail (T. R. Cundari): t@unt.edu.
Kinetics for Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with
PMe3. A representative kinetic experiment is described. Complex 3
(6.0 mg 10 μmol) and 5 μL of PMe3 (3.6 mg, 50 μmol) were dissolved
in 400 μL of THF-d8. The compound OPPh3 (∼3 mg) was added as
an internal standard for 31P NMR spectroscopy. The reaction mixture
was placed in the photolysis cabinet 40 cm away from the Hg vapor
lamp (the distance is important). A 31P NMR spectrum was acquired
every 10 min. Integration of the 31P NMR peak of complex 3 gave the
variation in concentration. Similar reactions were set up for 10.0, 15.0,
and 20.0 μL of PMe3. To ensure reproducibility, every concentration
was repeated in triplicate.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors acknowledge Anna V. Sberegaeva and Prof. Andrei
N. Vedernikov (University of Maryland) for preliminary
experiments focused on aerobic oxidation. This work was
solely supported as part of the Center for Catalytic Hydro-
carbon Functionalization, an Energy Frontier Research Center
funded by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Award No. DE-
SC0001298. J.M. acknowledges Dr. Bradley McKeown for
helpful discussions.
Kinetics for Reaction of Cp*Fe(P(OCH2)3CEt)2Ph (3) with
Me3NO. A representative kinetic experiment is described. Complex 3
(0.3 mg, 0.5 μmol) and Me3NO (3.0 mg, 40 μmol) were dissolved in
500 μL of THF-d8 (Me3NO is partially dissolved and saturated in the
solution). The compound Me3SiSiMe3 (∼1 μL) was added as an
internal standard for 1H NMR spectroscopy. The reaction mixture was
placed in the photolysis cabinet 40 cm away from the Hg vapor lamp.
REFERENCES
■
(1) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 2437.
(2) Wittcoff, H. A.; Reuben, B. G.; Plotkin, J. S. Industrial Organic
Chemicals, 2nd ed.; John Wiley & Sons, 2004.
1
A H NMR spectrum was acquired every 5 min for the first 30 min
1
and every 10 min thereafter. Integration of the H NMR spectra gave
the variation in concentration of complex 3, P(OCH2)3CEt, PhOH·
ONMe3, and 1,2,3,4-tetramethylfulvene. To ensure reproducibility, each
experiment was repeated in triplicate.
(3) George, A. Olah, A. M. Hydrocarbon Chemistry, 2nd ed.; John
Wiley & Sons, 2003.
(4) Conley, B. L.; Tenn, W. J.; Young, K. J. H.; Ganesh, S.; Meier, S.;
Ziatdinov, V.; Mironov, O.; Oxgaard, J.; Gonzales, J.; Goddard, W. A.;
Periana, R. A. In Activation of Small Molecules; Wiley-VCH Verlag
GmbH & Co. KGaA, 2006; p 235.
(5) Goldberg, K. I.; Goldman, A. S. In Activation and Functionaliza-
tion of C-H Bonds; American Chemical Society, 2004.
(6) Webb, J. R.; Bolano, T.; Gunnoe, T. B. ChemSusChem 2011, 4,
37.
(7) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507.
(8) Labinger, J. A. J. Mol. Catal. A: Chem. 2004, 220, 27.
(9) Crabtree, R. H. Chem. Rev. 1985, 85, 245.
(10) Cavaliere, V. N.; Mindiola, D. J. Chem. Sci. 2012, 3, 3356.
(11) Sen, A. Acc. Chem. Res. 1998, 31, 550.
(12) Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loffler, D. G.;
Wentrcek, P. R.; Voss, G.; Masuda, T. Science 1993, 259, 340.
(13) Muehlhofer, M.; Strassner, T.; Herrmann, W. A. Angew. Chem.,
Int. Ed. 2002, 41, 1745.
(14) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879.
(15) Shu, L.; Nesheim, J. C.; Kauffmann, K.; Munck, E.; Lipscomb, J.
Kinetics for Reaction of P(OCH2)3CEt with Me3NO. A repre-
sentative kinetic experiment is described. P(OCH2)3CEt (0.3 mg, 0.5 μmol)
was dissolved in 1.6 mL of THF-d8. The compound Me3SiSiMe3
(3.0 μL) was added as an internal standard for 1H NMR spectroscopy.
Me3NO (3.0 mg, 40 μmol) was added to a screw-cap tube. A 500 μL
aliquot of the P(OCH2)3CEt solution was transferred to the Me3NO
in the tube and timed as the start of the reaction. The tube was shaken
for about 30 s to help dissolve the Me3NO (Me3NO is partially dis-
solved and saturated in the solution). The reaction mixture was then
̃
1
monitored by array H NMR spectroscopy on a 500 MHz spectro-
meter at room temperature (20.4 °C). 1H NMR spectra were acquired
every 2 min for 120 min total. Integration of the 1H NMR spectra gave
the variation in concentration of P(OCH2)3CEt. To ensure repro-
ducibility, each experiment was repeated in triplicate.
̈
Computational Methods. Density functional theory within
the Gaussian 09 package60 was used for geometry optimization and
vibrational frequency calculations. The hybrid meta-GGA functional
wB97XD61 was employed with a double-ζ basis set with pseudopoten-
tials and added d functions for group elements (e.g., CEP-31G(d)).62
This functional contains empirical dispersion terms and also long-range
corrections. Tests with a larger, all-electron basis setincluding diffuse
functions on main group elements (B3LYP/6-31+G(d))as well as
Truhlar’s M0663 functional (M06/6-31+G(d)) did not yield significantly
different calculated geometries or free energies. MECP calculations on
full models of 3 were carried out at the wB97XD/6-31+G(d) level of
theory. Calculations were carried out in the continuum SMD64 solvation
method with THF (ε = 7.58) being the solvent.
̈
D.; Que, L., Jr. Science 1997, 275, 515.
(16) Liu, K. E.; Lippard, S. J. In Advances in Inorganic Chemistry;
Sykes, A. G., Ed.; Academic Press, 1995; Vol. 42, p 263.
(17) Wallar, B. J.; Lipscomb, J. D. Chem. Rev. 1996, 96, 2625.
(18) Groves, J. T.; McClusky, G. A. J. Am. Chem. Soc. 1976, 98, 859.
(19) Gunay, A.; Theopold, K. H. Chem. Rev. 2010, 110, 1060.
(20) Liu, W.; Huang, X.; Cheng, M.-J.; Nielsen, R. J.; Goddard, W.
A.; Groves, J. T. Science 2012, 337, 1322.
(21) Chen, M. S.; White, M. C. Science 2007, 318, 783.
5604
dx.doi.org/10.1021/om500914h | Organometallics 2014, 33, 5597−5605

Organometallics
Article
(22) Bigi, M. A.; Reed, S. A.; White, M. C. J. Am. Chem. Soc. 2012,
134, 9721.
(23) Zhou, M.; Balcells, D.; Parent, A. R.; Crabtree, R. H.; Eisenstein,
O. ACS Catal. 2011, 2, 208.
(24) Qin, K.; Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H. J.
Am. Chem. Soc. 2002, 124, 14008.
(25) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471.
(26) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154.
(27) Bromberg, S. E.; Yang, H.; Asplund, M. C.; Lian, T.; McNamara,
B. K.; Kotz, K. T.; Yeston, J. S.; Wilkens, M.; Frei, H.; Bergman, R. G.;
Harris, C. B. Science 1997, 278, 260.
(28) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91.
(29) Choi, G.; Morris, J.; Brennessel, W. W.; Jones, W. D. J. Am.
Chem. Soc. 2012, 134, 9276.
(56) Harvey, J. N.; Aschi, M.; Schwarz, H.; Koch, W. Theor. Chem.
Acc. 1998, 99, 95.
(57) Harvey, J. N.; Aschi, M. Phys. Chem. Chem. Phys. 1999, 1, 5555.
(58) Sako, M.; Shimada, K.; Hirota, K.; Maki, Y. J. Am. Chem. Soc.
1986, 108, 6039.
(59) Davies, S. C.; Hughes, D. L.; Leigh, G. J.; Sanders, J. R.; de
Souza, J. S. J. Chem. Soc., Dalton Trans. 1997, 1981.
(60) Frisch, M. J.,; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; J. R. Normand, K.; Rendell, A.;
Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N.
J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;
Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
(30) Webb, J. R.; Burgess, S. A.; Cundari, T. R.; Gunnoe, T. B. Dalton
Trans. 2013, 42, 16646.
(31) Gunnoe, T. B. In Physical Inorganic Chemistry: Reactions,
Processes, and Applications; Bacak, A., Ed.; Wiley-VCH, 2010; p 495.
(32) Vetter, A. J.; Flaschenriem, C.; Jones, W. D. J. Am. Chem. Soc.
2005, 127, 12315.
(33) Conley, B. L.; Ganesh, S. K.; Gonzales, J. M.; Tenn, W. J.;
Young, K. J. H.; Oxgaard, J.; Goddard, W. A.; Periana, R. A. J. Am.
Chem. Soc. 2006, 128, 9018.
(34) Bischof, S. M.; Cheng, M.-J.; Nielsen, R. J.; Gunnoe, T. B.;
Goddard, W. A.; Periana, R. A. Organometallics 2011, 30, 2079.
(35) Gonzales, J. M.; Distasio, R.; Periana, R. A.; Goddard, W. A.;
Oxgaard, J. J. Am. Chem. Soc. 2007, 129, 15794.
̈
Dapprich, S.; Daniels, A. D.; O. Farkas, Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian, Revision B.01 ed.; Gaussian Inc:
Wallingford, CT, 2009.
(61) Grimme, S. J. Comput. Chem. 2006, 27, 1787.
(62) Stevens, W. J.; Krauss, M.; Basch, H.; Jasien, P. G. Can. J. Chem.
1992, 70, 612.
(63) Zhao, Y.; Truhlar, D. Theor. Chem. Acc. 2008, 120, 215.
(64) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B
2009, 113, 6378.
(36) Tenn, W. J.; Conley, B. L.; Hovelmann, C. H.; Ahlquist, M. r.;
̈
Nielsen, R. J.; Ess, D. H.; Oxgaard, J.; Bischof, S. M.; Goddard, W. A.;
Periana, R. A. J. Am. Chem. Soc. 2009, 131, 2466.
(37) Feng, Y.; Lail, M.; Barakat, K. A.; Cundari, T. R.; Gunnoe, T. B.;
Petersen, J. L. J. Am. Chem. Soc. 2005, 127, 14174.
(38) Tenn, W. J.; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard,
W. A.; Periana, R. A. J. Am. Chem. Soc. 2005, 127, 14172.
(39) Kloek, S. M.; Heinekey, D. M.; Goldberg, K. I. Angew. Chem.,
Int. Ed. 2007, 46, 4736.
(40) Bercaw, J. E.; Hazari, N.; Labinger, J. A. Organometallics 2009,
28, 5489.
(41) Feng, Y.; Lail, M.; Foley, N. A.; Gunnoe, T. B.; Barakat, K. A.;
Cundari, T. R.; Petersen, J. L. J. Am. Chem. Soc. 2006, 128, 7982.
(42) Cundari, T. R.; Grimes, T. V.; Gunnoe, T. B. J. Am. Chem. Soc.
2007, 129, 13172.
(43) Van Asselt, A.; Trimmer, M. S.; Henling, L. M.; Bercaw, J. E. J.
Am. Chem. Soc. 1988, 110, 8254.
(44) Brown, S. N.; Mayer, J. M. J. Am. Chem. Soc. 1996, 118, 12119.
(45) Kamaraj, K.; Bandyopadhyay, D. Organometallics 1999, 18, 438.
(46) Mei, J.; Carsch, K. M.; Freitag, C. R.; Gunnoe, T. B.; Cundari, T.
R. J. Am. Chem. Soc. 2012, 135, 424.
(47) Pouy, M. J.; Milczek, E. M.; Figg, T. M.; Otten, B. M.; Prince, B.
M.; Gunnoe, T. B.; Cundari, T. R.; Groves, J. T. J. Am. Chem. Soc.
2012, 134, 12920.
(48) Ni, C.; Power, P. P. Chem. Commun. 2009, 5543.
(49) Matsunaga, P. T.; Hillhouse, G. L.; Rheingold, A. L. J. Am.
Chem. Soc. 1993, 115, 2075.
(50) Alsters, P. L.; Boersma, J.; van Koten, G. Organometallics 1993,
12, 1629.
(51) Kalman, S. E.; Petit, A.; Gunnoe, T. B.; Ess, D. H.; Cundari, T.
R.; Sabat, M. Organometallics 2013, 32, 1797.
(52) Pardue, D. B.; Mei, J.; Cundari, T. R.; Gunnoe, T. B. Inorg.
Chem. 2014, 53, 2968.
(53) Tilset, M.; Fjeldahl, I.; Hamon, J.-R.; Hamon, P.; Toupet, L.;
Saillard, J.-Y.; Costuas, K.; Haynes, A. J. Am. Chem. Soc. 2001, 123,
9984.
(54) Mendenhall, G. D.; Kessick, R. F.; Dobrzelewski, M. J.
Photochem. 1984, 25, 227.
(55) Beckwith, A. L. J.; Bowry, V. W.; Ingold, K. U. J. Am. Chem. Soc.
1992, 114, 4983.
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