S
1
Supporting Information for
A Thermodynamic Model for Redox
-
Dependent Binding of
Carbon Monoxide at Site
-
Differentiated, High Spin Iron
Clusters
Charles H. Arnett, Matthew J. Chalkley and
Theodor Agapie*
Division of Chemistry and Chemical Engineering,
California Institute of Technology, Pasadena,
California 91125, United States
Table of Contents
Experimental and Synthetic Details
............................................................
.........
..2
-
3
Synthetic Procedures
..............................................................................
.........
.
4
-
6
Spectra
l Characterization
........................................................................
.......
..
7
-
1
5
Variable Temperature UV
-
Vis Spectroscopy
...................................................
.....
..1
6
-
1
8
Variable Temperature IR Spectroscopy
.........................................................
...
...1
9
-
21
Variable Temperature NMR Spectroscopy and Thermodynamic Measurements
............
....
.
22
-
4
5
Electroche
mistry
.......................................................................................
...
4
6
-
53
Magnetic Measurements
...........................................................................
...
...
54
-
55
EPR Spectroscopy
....................................................................................
....
...
56
Mössbauer Spectroscopy
..............................................................................
..
57
-
78
X
-
ray Crystallography
..............................................................................
..
...
79
-
85
Summary Tables
....................................................................................
.
.....
86
-
93
References
.........
........................................................................................
93
-
9
5
S
2
Experimental and Synthetic Details
General Considerations
All reactions were performed at room temperature in a nitrogen filled M. Braun
glovebox or using
standard Schlenk techniques unless otherwise specified. Glassware was oven dried at 140
o
C for at
least two hours prior to use, and allowed to cool under vacuum. PhIm
-
H
was prepared according
to a literature procedure,
1
dried over calcium hydride, and distilled at 130
o
C under vacuum.
LFe
3
(OAc)
3
was prepared according to a literature procedure
2
and purified by recrystallization.
[Fc]
[
OTf
]
3
and
Na[BAr
F
24
]
4
were prepared according to literature procedures.
[Fc
*
]
[
OTf
]
was
prepared by oxidation of Fc
*
with [Fc]
[
OTf
]
in dichloromethane followed by crystallization from
dichloromethane/pentane.
[Cp
2
Co][OTf] was prepared by oxidation of Cp
2
Co with AgOTf.
All
other
reagents were obtained commercially unless otherwise noted and typically stored over
activate
d 4 Å molecular sieves. Tetrahydrofuran
was
dried using sodium/benzophenone ketyl,
degassed with three freeze
-
pump
-
thaw cycles, vacuum transferred, and stored over 3 Å molecular
sieves prior to use. Dichloromethane, diethyl ether, benzene, acetonitrile, he
xanes, and pentane
were dried by sparging with nitrogen for at least 15 minutes, then passing through a column of
activated A2 alumina under positive nitrogen pressure.
Acetone and acetone
-
d
6
were dried using
calcium sulfate (Drierite), degassed with three freeze
-
pump
-
thaw cycles, vacuum transferred, and
stored over
3 Å molecular sieves prior to use
. Dichloromethane
-
d
2
was
dried over calcium hydride,
degassed by three freeze
-
pump
-
thaw cycles,
and vacuum transferred prior to use.
Chlorobenzene
-
d
5
was degassed by three
-
pump
-
thaw cycles and dried over
3 Å molecular sieves prior to use
.
1
H
and
19
F NMR spectra were recorded on a Varian 300
or 400
MHz spectrometer. All chemical shifts
(
δ
) are reporte
d in ppm, and coupling constants (
J
) are in hertz. The
1
H
-
NMR
spectra
were
referenced using residual H impurity in the deuterated solvent, whereas the
19
F chemical shifts are
reported relative to the
internal lock signal.
UV
-
Vis spectra were recorded on a
Varian Cary Bio
50 spectrophotometer. Infrared (ATR
-
IR) spectra were recorded on a Bru
ker ALPHA ATR
-
IR
spectrometer
.
Solution ATR
-
IR spectra were recorded on a Mettler Toledo iC10 ReactIR
.
Elemental analyses were performed at Caltech.
Physical Methods
Mössbauer Measurements
. Zero field
57
Fe Mössbauer spectra were recorded in constant
acceleration on a spectrometer from See Co (Edina, MN) equipped with an SVT
-
400 cryostat
(Janis, Wilmington, WA). The quoted isomer shifts are relative to the centroid of t
he spectrum of
α
-
Fe foil at room temperature.
Unless otherwise noted, s
amples were prepared by grinding
polycrystalline (20
-
50
mg) into a fine powder and pressed into a homogenous pellet with boron
nitride in a cup fitted with a screw cap. The data were fi
tted to Lorentzian lineshapes using the
program WMOSS (www.wmoss.org).
EPR Spectroscopy.
X
-
band EPR spectra were
collected on a Bruker EMX spectrometer
equipped with a He flow cryostat
. Samples of
3
were
prepar
ed as frozen glasses in
4:5
propionitrile/but
y
r
onitrile
(2
mM
). Spectra were collected with microwave
powers ranging from
2
mW to 8 mW with modulation amplitudes of 4 G
aus
s.
Variable temperature s
pectr
a
were
plotted
with SpinCount (Prof. Michael Hendrich).
Magnetic Measurements
.
Magnetic measurements
for
3
were conducted
with a
Quantum
Design
MPMS3
SQUID
Magnetometer
at the University of California, Los Angeles
.
A
polycrystalline sample of
3
was
wrapped
in plastic film
and placed in a gelatin capsule. The capsule
was
then
inserted
into a plastic straw. Magnetization data at 100 K from 0 to 4 T were collected to
S
3
confirm the absence of ferromagnetic impurities. Direct current variable temperature magnetic
susceptibility measurements were collected between 1.8 and 300 K with a 0.1 T f
ield. Reduced
magnetization data was collected between 1.8 and 9 K at field
s
between 1 and 7 T. Magnetic
susceptibility data was corrected for diamagnetism of the sample, estimated using Pascal’s
constants. Magnetic susceptibility data was simulated with j
ulX
(Prof. Eckhard Bill) and
reduced
magnetization data was simulated with PHI
.
5
Electrochemical Measurements
. CVs
were recorded with a Pine Instrument Company
AFCBP1 bipotentiostat using the AfterMath software package. All measurements were performed
in a three electrode cell, which consisted of (1) a glassy carbon working electrode, (2) a Pt wire
counter electrode,
and (3) a Ag wire reference electrode.
Dry
solvent
that contained 0.1 M
n
Bu
4
NPF
6
was employed as the electrolyte solution for all electrochemical measurements.
All
electrochemical measurements were performed at room temperature in an M.
Braun nitrogen filled
glovebox
or in specialized glassware on the Schlenk line
.
The ferrocene/ferrocenium (Fc/Fc
+
)
redox couple was used
as an internal standard
for all measurements.
X
-
ray Crystallography
.
For compounds
1
-
2
,
4
-
5
,
3
-
(CO)
2
and
5
-
CO
low
-
tempe
rature
(100 K) diffraction data
(
φ
-
and
ω
-
scans) were collected on a Bruker AXS D8 VENTURE KAPPA
diffractometer coupled
to a PHOTON 100 CMOS detector with Mo K
α
radiation (
λ
= 0.71073 Å)
or with Cu K
α
(
λ
=
1.54178 Å). For compound
3
,
low
-
temperature (100 K) diffraction data (
φ
-
and
ω
-
scans) were
collected on a Bruker AXS KAPPA APEX II diffractometer coupled to an APEX II
CCD
detector
with graphite monochromated Mo K
α
radiation (
λ
= 0.71073 Å). All diffractometer
manipulations, including
data collection, integration, and scaling were carried out using the
Bruker
APEXII software.
6
Absorption corrections were applied using SADABS.
7
Structures were
solved
by direct methods using SHELXS
8
and refined against
F
2 on all data by full
-
matrix least
squares
with SHELXL
-
2014
9
interfaced with Olex2
-
1.2.8
10
and using
established refinement techniques.
All non
-
hydrogen atoms
were refined anisotropically
, except heavily disordered solvent in some
cases
. All hydrogen atoms were included into the model at
geometrically
calculated positions and
refined using a riding model. The isotropic displacement parameters of
all hydrogen atoms were
fixed to 1.2 times the
U
value of the atoms they are linked to (1.5 times
for methyl groups). All
disordered atoms were re
fined with the help of similarity restraints on the
1,2
-
and 1,3
-
distances
and displacement parameters as well as enhanced rigid bond restraints for
anisotropic displacement
parameters
. Due to the size of
the
compounds
, most
crystals included solvent acces
sible voids,
which tended to contain disordered solvent. In most
cases, this disorder could be modeled
satisfactorily
.
Furthermore, the long
-
range order of these
crystals and amount of high angle data
was in some cases not ideal, due to desolvation of the
crystals and/or solvent disorder.
DFT Calculations
Gaussian09 was used for all calculations.
11
Geometry optimizations for 3
-
methylpyrazolate and 1
-
methylimidazolate were performed with the BP86 functional with a double
-
ζ
basis set and one set
of polarization functions (6
-
31G+(d,p))
. Initial ge
ometries were taken from the X
-
ray crystal
structures of [LFe
3
O(PhPz)
3
Fe][OTf]
2
and [LFe
3
O(PhIm)
3
Fe][OTf]
2
(
3
), respectively, by
removing all atoms except for one of the bridging ligands and exchanging the aryl substituent for
a methyl group.
Single point
energy calculations were
then
performed with t
he B3LYP functional,
also with the 6
-
31G+(d,p) basis set. Molecular orbitals were visualized with Gaussview.
S
4
S
ynthetic Procedures
LFe
3
(OTf)
3
,
(1
)
. Trimethylsilyl triflate (4.10 mL, 22.65 mmol, 10 equiv.)
was added
dropwise to a suspension of LFe
3
(OAc)
3
(2.72 g, 2.26 mmol, 1 equiv.) in dichloromethane (80
mL), affording a golden yellow solution. After stirring for 30 minutes, the volatiles were removed
in vacuo affording LFe
3
(OTf)
3
as a pale yellow solid
.
The material can be triturated with
dichloromethane t
o remove most of the
impurities. After trituration,
LFe
3
(OTf)
3
is collected on a
course frit as a light yellow solid (2.59 g, 78% yield). Crystals suitable for X
-
ray diffraction were
grown by diffusion o
f diethyl ether into a concentrated dichloromethane solution of the compound.
W
e have
not
been
able to
obtain a satisfactory elemental analysis for
LFe
3
(OTf)
3
, possibly due to
its extreme air and moisture sensitivity. However, structural analysis confirms
its identity, which
is satisfactory for its use as a precursor to
2
.
1
H NMR (300 M
Hz, CD
2
Cl
2
)
δ
112.96 (s), 97.06 (s),
84.67 (s), 45.45 (s), 37.18 (s), 35.38 (s), 26.25 (s), 16.68 (s), 7.84 (s), 3.81 (s),
-
2.35 (b),
-
3.16 (s),
-
7.32 (s).
19
F NMR (300 M
Hz,
CD
2
Cl
2
)
δ
–
41.79 (b). UV
-
Vis (CH
2
Cl
2
) [
ε
(M
-
1
cm
-
1
)]: 372 nm
(2.91 x 10
3
).
[
LFe
3
O(PhIm
-
H
)
3
]
[
OTf
]
3
,
(
2
)
. A solution of PhIm (838 mg, 5.82 mmol, 3.3 equiv.) in
tetrahydrofuran (13 mL) was added dropwise to a stirring suspension of LFe
3
(OTf)
3
(2.59 g, 1.76
mmol, 1.0 equiv.) in tetrahydrofuran (43 mL). The resulting orange solution was allowed to stir
for one hour, at which point a suspension of PhIO (388 mg, 1.76 mmol, 1.0 equiv.) in
tetrahydrofuran (20 mL) was added. The solution immediately
darkened and a dark brown
precipitate form
ed gradually. After stirring
overnight
, the precipitate was collected on a bed of
Celite, washed with additional tetrahydrofuran, and then eluted with dichloromethane. The
volatiles were removed under reduced
pressure to afford [LFe
3
O(PhIm
-
H
)
3
]
[
OTf
]
3
as a dark brown
solid (3.02 g, 97% yield). Crystals suitable for X
-
ray diffraction were grown by diffusion of diethyl
ether into a concentrated dichloromethane solution of the compound.
Unfortunately, we have not
b
een able to obtain satisfactory elemental
analysis for this compound.
1
H NMR (300 M
Hz,
CD
2
Cl
2
)
δ
103.79 (b), 100.89 (b), 98.12 (b), 82.04 (s), 78.36 (b), 68.19 (s), 66.99 (s), 66.58 (s),
59.35 (s), 51.73 (s), 49.32 (s), 48.89 (s), 47.62 (s), 46.74 (s), 45.
35 (s), 44.51 (s), 42.11 (b), 18.16
(b), 17.02 (s), 15.14 (b), 14.04 (b), 13.31 (s), 12.80 (b), 11.88 (s), 10.69 (s), 9.19 (b), 8.36 (b), 7.93
(s), 6.61 (s), 4.81 (s), 4.40 (s), 2.90 (s), 1.13 (b),
-
2.88 (b),
-
6.15 (b).
19
F NMR (300 M
Hz, CD
2
Cl
2
)
δ
-
9.21
(3F),
-
77.58 (6F). UV
-
Vis (CH
2
Cl
2
) [
ε
(M
-
1
cm
-
1
)]: 408 nm (2.60 x 10
3
), 531 nm (7.74 x
10
2
).
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
, (
3
)
. In a 20 mL scintillation vial charged with a stir bar and
wrapped in foil, [LFe
3
O(PhIm
-
H
)
3
]
[
OTf
]
3
(1.06 g, 0.55 mmol, 1.0 equiv.) and PhIm (87.1 mg,
0.60
mmol, 1.1 equiv.) were suspended in 5 mL of tetrahydrofuran and frozen
in a
cold well along
with a solution of Na[N(SiMe
3
)
2
] (334 mg, 1.83 mmol, 3.3
equiv.) in 1.5 mL of tetrahydrofuran.
Upon suffici
ent thawing for the mixture to begin stirring, the Na[N(SiMe
3
)
2
] solution was added
dropwise in the dark. After stirring for 1 hour, the solution was frozen in
the
cold well. Upon
sufficient thawing for the mixture to begin stirring, a thawing slurry of Fe
Cl
2
(80.2 mg, 0.64 mmol,
1.2
equiv.) in 3.5 mL of tetrahydrofuran was added dropwise. After stirring for 22 hours, the
mixture was filtered over a bed of Celite and the precipitate was eluted with dichloromethane. The
volatiles were removed under reduced p
ressure to afford [LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
as a dark brown
solid (230 mg, 23
% yield). Crystals suitable for X
-
ray diffraction were grown by layering a dilute
solution of the compound with diethyl ether at
-
35
o
C.
1
H
NMR (300 M
Hz, CD
2
Cl
2
)
δ
117.34 (b),
76.82 (
s), 74.75 (s), 70.70 (b), 51.84 (s), 47.54 (s), 47.08 (s), 20.98 (b), 20.40 (s), 14.68 (s), 12.89
(s), 12.42 (s), 7.25 (s), 6.34 (s), 5.52 (s), 4.93 (s), 4.60 (s), 3.32 (s), 2.99 (s), 2.42 (s), 1.05 (s),
-
S
5
4.58 (b),
-
6.98 (s).
19
F NMR (300 M
Hz, CD
2
Cl
2
)
δ
-
78.32. UV
-
Vis (CH
2
Cl
2
) [
ε
(M
-
1
cm
-
1
)]: 252
nm (9.56 x 10
4
), 464 nm (1.04 x 10
4
). ESI
-
MS (m/z): 762 ([LFe
3
O(PhIm)
3
Fe]
2+
) Anal.
Calcd (%)
for C
86
H
60
F
6
Fe
4
N
12
O
10
S
2
: C, 56.66; H, 3.32; N, 9.22. Found: C, 56.38; H, 3.40; N, 9.09.
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
3
(4
).
In
a 20 mL scintillation vial charged with a stir bar, a
dichloromethane solution of [Fc]
[
OTf
]
(26.8 mg, 0.08 mmol, 1.0 equiv.) was added dropwise to a
stirring solution of [LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
(145.9 mg, 0.08 mmol, 1.0 equiv.) in 2 mL of
dichloromethane.
A
fter 30 minutes, the volatiles were removed under reduced pressure and the
pink purple residue was triturated with diethyl ether. The suspension was filtered over Celite and
the remaining pink
-
purple powder was washed with additional diethyl ether before e
luting with
dichloromethane. The volatiles were removed under reduced pressure to afford
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
3
as a pink
-
purple solid (110 mg, 70% yield). Crystals suitable for X
-
ray
diffraction were obtained by diffusion of diethyl ether into a dilute solution of
4
in
dichloromethane.
1
H NMR (400 M
Hz, CD
2
Cl
2
)
δ
139.84 (b), 101.61 (b), 87.16 (s), 65.70 (s), 63.96
(s), 57.17 (s), 32.93 (b), 14.58 (s), 12.39 (s), 11.70 (s), 10.99 (s), 6.33 (s), 4.97 (b), 3.99 (s),
-
2.30
(b),
-
12.29 (b)
.
19
F NMR (300 M
Hz, CD
2
Cl
2
)
δ
-
78.53
.
UV
-
Vis (CH
2
Cl
2
) [
ε
(M
-
1
cm
-
1
)]: 379
nm
(
8.88
x 10
3
), 494 nm (8.37
x 10
3
). Anal. Calcd (%) for C
87
H
60
F
9
Fe
4
N
12
O
13
S
3
: C, 52.9
9; H, 3.07;
N, 8.52. Found: C, 52.65; H, 3.17; N, 8.46
.
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
,
(5
)
.
(A) By reduction of
3
:
In a 20 mL scintillation vial charged
with a stir bar, a
dichloromethane solution of Cp
2
Co (10.6 mg
, 0.056 mmol, 1.0
equiv.) was added
d
ropwise to a stirring solution
of [LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
(102 m
g, 0.056 mmol, 1.0 equiv.) in 3
mL of
dichloromethane
.
After one hour, t
he volatiles were removed under reduced pressure an
d
the dark purple residue was
then triturated in dimethoxyethane
(DME)
overnight. The purple
precipitate was collected on a bed of Celite
, washed with additional
DME,
and then eluted with
dichloromethane. The volatiles were removed under reduced pressure to afford
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
as a dark purple solid (69.5 mg, 74% yield).
Crystals suitable for X
-
ray
diffraction were obtained by diffusion of diethyl e
ther into a dilute solution of
5
in 1:1
dichloromethane:acetonitrile.
(B) By oxidation of
6
: To a suspension of [LFe
3
O(PhIm)
3
Fe] (
31.5
mg, 0.021 mmol) in tetrahydrofuran (1 mL) was added a suspension of [Cp
2
Co][OTf] (10.5 mg,
0.031 mmol, 1.5 equiv.). The mixture immediately changes color from blue to purple. After stirring
for 45 minutes, the mixture was concentrated under vacuum. Th
e
1
H
-
NMR spectrum (CD
2
Cl
2
) of
the crude product mixture revealed clean re
-
generation of
5
.
1
H NMR (300 M
Hz, CD
2
Cl
2
)
δ
101.23
(b), 57.39 (s), 56.72 (s), 40.91 (b), 38.06 (s), 36.00 (s), 31.58 (s), 24.16 (s), 13.54 (s), 12.66 (s),
11.92 (s), 8.26 (s), 7.22 (s),
-
4.45 (b).
19
F NM
R (300 M
Hz, CD
2
Cl
2
)
δ
-
78.89.
UV
-
Vis (CH
2
Cl
2
) [
ε
(M
-
1
cm
-
1
)]: 413 nm (4.28 x 10
2
), 513 nm
(3.39 x 10
3
). Anal. Calcd (%) for C
85
H
60
F
3
Fe
4
N
12
O
7
S:
C, 60.99; H, 3.61; N, 10.04. Found: C, 60.14; H, 3.66; N, 10.51.
[LFe
3
O(PhIm)
3
Fe] (6
).
A solution of naphthalene (32.6 mg, 0.25 mmol,
5.0
equiv.) in 8
mL of tetrahydrofuran was added dropwise to a
suspension of sodium metal
in 10 mL of
tetrahydrofuran
(45 mg, 1.96
mmol, 39.2
equiv.), affording a dark green solution.
After stirring for
two hours, the solution was filtered over Celite and added dropwise to a stirring solution of
[LFe
3
O(PhIm)
3
Fe]
[
OTf
]
(86.1 mg, 0.05 mmol, 1.0 equiv.) and Na[BAr
F
24
] (4
5.
6 mg, 0.05
mmol
,
1.0
equiv.). After stirri
ng overnight, the precipitate was
collected on a fine frit and washed with
additional tetrahydrofuran (2x5 mL), affording [LFe
3
O(PhIm)
3
Fe] as a metallic blue
powder (50.5
mg
, 66
% yield).
We have not been able to obtain satisfactory elemental analysis for
6
, likely due
to its air sensitivity.
[LFe
3
O(PhIm)
3
Fe(CO)] (6
-
CO).
A suspension of [LFe
3
O(PhIm)
3
Fe]
(27.5 mg, 0.018
mmol)
in 2.7 mL of tetrahydrofuran was transferred to 20 mL Schlenk tube. The suspension was
S
6
degassed by three freeze
-
pump
-
thaw cycles and an atmosphere of CO was admitted at room
temperature. After stirring for five ho
urs, an IR spectrum of the
green suspension
was collected.
The mixture was then frozen, evacuated once, and exposed to N
2
(without thawing). After stirring
for two hours or overnight, only the vibrational feature assigned to [LFe
3
O(PhIm)
3
Fe(CO)] was
observed
(
ν
CO
= 1899 cm
-
1
)
. The green precipitate
was collected by filtration
at the 2
-
3 hr. time
point to minimize CO loss
(20 mg, 72
%).
[LFe
3
O(PhIm)
3
Fe][OTf]
4
(7).
For
1
H
-
NMR
:
A solution of [LFe
3
O(PhIm)
3
Fe][OTf]
3
(
4
, 18 mg)
was prepared in 0.7 mL CD
2
Cl
2
. An aliquot (0.35 mL) was added to a J Young
tube and the solution
was frozen in the cold well. A solution of [N(C
6
H
4
Br
-
4)
3
][OTf] (7 mg) was prepared in 2 mL of
CD
2
Cl
2
. An aliquot (0.2 mL) of this [N(C
6
H
4
Br
-
4)
3
][OTf] solution was added to the frozen
solution of
4
and mixed thawing, affording a dark o
range
-
brown solution and a considerable
amount of a dark precipitate.
1
H
-
NMR spectra were collected at 298 K, 223 K and 198 K which
confirmed the formation of one (or more) new species. The tube was then degassed by three freeze
-
pump
-
thaw cycles and CO (1
atm.) was admitted at 293 K.
1
H
-
NMR spectra collected under an
atmosphere of CO matched those under N
2
, demonstrating that CO does not bind the dissolved,
NMR
-
active fraction of the material. Subsequently, the tube was degassed by three freeze
-
pump
-
thaw cy
cles. A solution of ferrocene (5.7 mg) was prepared in 0.2 mL CD
2
Cl
2
. Addition of an
aliquot (0.12 mL) of this ferrocene solution to the degassed tube cleanly returns
4
, suggesting that
the oxidized product(s) retains the core geometry of
4
and most likely
corresponds to the all
-
ferric
cluster [LFe
3
O(PhIm)
3
Fe][OTf]
4
(
7
), though more detailed characterization of this compound has
not been possible to date. It is possible that triflate binds the apical Fe
III
of
[LFe
3
O(PhIm)
3
Fe][OTf]
4
(
7
), which could also
suppress CO binding.
For UV
-
Vi
s: A solution of [LFe
3
O(PhIm)
3
Fe][OTf]
3
(
4
, 7.2 mg) was prepared in
dichloromethane (19 mL). A 50 μM solution was prepared by diluting 2.5 mL of this stock solution
to 10 mL with dichloromethane. A 3 mL aliquot of this 50 μM
solution was charged into a Kontes
-
valve sealed cuvette. A solution of
[N(C
6
H
4
Br
-
4)
3
][OTf]
(8.4 mg) was prepared in 5 mL of
dichloromethane. To the stirring solution of
4
in the cuvette was added a 0.1 mL aliquot of the
[N(C
6
H
4
Br
-
4)
3
][OTf]
stock
solution
(1.5
equiv.).
The
UV
-
Vis
spectrum
of
[LFe
3
O(PhIm)
3
Fe][OTf]
4
(
7
) was then recorded under N
2
between 198 and 298
K. Then the sample
was degassed by three freeze
-
pump
-
thaw cycles and CO (1 atm.) was admitted at room
temperature. The UV
-
Vis spe
ctrum of
[LFe
3
O(PhIm)
3
Fe][OTf]
4
(
7
) was then recorded under CO
b
etween 198 and 298
. Other than a loss in signal intensity
(presumably due to a small amount of
decomposition of
7
), there is no difference in the VT behavior under N
2
or CO.
S
7
S
pectral Characterization
Figure S1
.
1
H NMR (300 MHz) of LFe
3
(OTf)
3
(1)
in CD
2
Cl
2
Figure S2
.
19
F NMR (300 MHz) of LFe
3
(OTf)
3
(1)
in CD
2
Cl
2
S
8
Figure S3
.
1
H NMR
(300 MHz) of [LFe
3
O(PhIm
-
H
)
3
]
[
OTf
]
3
(2)
in CD
2
Cl
2
Figure S4
.
19
F NMR (300 MHz) of [LFe
3
O(PhIm
-
H
)
3
]
[
OTf
]
3
(2)
in CD
2
Cl
2
. We attribute the
presence of two triflate signals to dissociation of one PhIm
-
H ligand and triflate
binding to the
cluster in solution.
S
9
Figure S5
.
1
H NMR (300 MHz) of [LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
(3)
in CD
2
Cl
2
Figure S6
.
19
F NMR (300 MHz) of [LFe
3
O(PhIm)
3
Fe]
[
OTf
]
2
(3)
in CD
2
Cl
2