of 67
Supporting Information
Snapshots of a Migrating H-Atom: Characterization of a Reactive
Iron(III) Indenide Hydride and its Nearly Isoenergetic
Ring-Protonated Iron(I) Isomer
Marcus W. Drover, Dirk J. Schild, Paul H. Oyala, and Jonas C. Peters*
anie_201909050_sm_miscellaneous_information.pdf
S
1
Table of Contents:
I. General Considerations
S2
II. Nuclear Magnetic Spectroscopy
S2
III.
57
Fe M
ö
ssbauer Spectroscopy
S2
IV. Infrared Spectroscopy
S2
V. UV
-
VIS Spectroscopy
S2
VI. EPR
Spectroscopy
S
3
VII.
Electrochemistry
S
5
VIII. Synthetic Procedures and Spectra
S
6
IX EPR Spectroscopy data
S33
X.
Rate Data
S
5
1
X
I
. Crystallographic details
S5
3
X
II
. DFT Calculations
S5
7
X
III
.
References
S
65
S
2
I. General
Considerations
:
All experiments were carried out employing standard Schlenk techniques unde
r an atmosphere of
dry nitrogen
employing degassed,
dried solvents in a solvent purification system supplied by SG
Water, LLC. Non
-
halogenated solvents were tested w
ith a standard purple solution of sodium
benzophenone ketyl in tetrahydrofuran in order to confirm effective moisture removal.
trans
-
FeBr
2
(depe)
2
1
,
FeBr
2
(dippe)
2
, Fe(
h
6
-
toluene)(dippe),
3
Fe(Cp*)(dppe)H
4
w
ere
prepared according
to a literature procedure. All other reagents were purchased from commercial
vendors and used
without further purification unless otherwise stated.
Hydrogen Analysis
:
The headspace of reaction flasks was analyzed by gas chromatography t
o
quantify H
2
evolution with an Agilent 7890A gas chromatograph (HPPLOT U, 30 m, 0.32 mm
i.d., 30 °C isothermal, 1 mL/min flow rate, N
2
carrier gas) using a thermal conductivity detector.
II.
Nuclear Magnetic Resonance Spectroscopy
:
1
H and
13
C chemical shifts are reported in ppm relative to tetramethylsilane, using residual
solvent resonances as internal standards.
31
P chemical shifts are reported in ppm and referenced
externally to 85% aqueous H
3
PO
4
at 0 ppm.
III.
57
Fe Mössbauer Spectroscop
y:
M
ö
ssbauer spectra were recorded on a spectrometer from SEE Co. (Edina, MN) operating in the
constant acceleration mode in transmission geometry. The sample was kept in an SVT
-
400
cryostat form Janis (Wilmington, MA), using liquid N
2
as a cryogen for 80
K measurements. The
quoted isomer shifts are relative to the centroid of the spectrum of a metallic foil of
α
-
Fe at room
temperature. Solid samples were prepared by grinding solid material into a fine powder and then
mounted in to a Delrin cup fitted with
a screw cap as a boron nitride pellet. Solution samples
were transferred to a sample cup and chilled to 77 K inside of the glovebox, and quickly
removed from the glovebox and immersed in liquid N
2
until mounted in the cryostat. Data
analysis was performed
using WMOSS version 4 (www.wmoss.org) and quadrupole doublets
were fit to Lorentzian lineshapes.
5
IV.
Infrared Spectroscopy
:
Solid and thin film IR measurements were obtained on a Bruker Alpha spectrometer equipped
with a diamond ATR probe.
V. UV
-
VIS S
pectroscopy
:
UV
-
Visible spectroscopy measurements were collected with a Cary 50 UV
-
Vis
spectrophotometer using a 1 cm two
-
window quartz cell
.
S
3
VI.
EPR Spectroscopy
:
Continuous wave X
-
band EPR spectra were obtain
ed on a Bruker EMX spectrometer using
solutions prepared as frozen glasses in 2
-
MeTHF. Pulse
EPR spectroscopy: All pulse X
-
band
(9.4
-
9.7) EPR, electron nuclear double resonance (ENDOR), and hyperfine sublevel correlation
spectroscopy (
HYSCORE) experiments were acquired using a Bruker ELEXS
YS E
580 pulse
EPR spectrometer.
X
-
band ENDOR and HYSCORE experiments were performed using a Bruker
MD
-
4 X
-
band ENDOR resonator.
Temperature
control was achieved using an ER 4118HV
-
CF5
-
L Flexline Cryogen
-
Free VT cryostat manufactured by ColdEdge equipped with a
n Oxford
Instruments Mercury ITC temperature controller.
All pulse
X
-
band (
ν
9.4
-
9.7
GHz) EPR and electron nuclear double resonance (ENDOR)
experiments were aquired using a Bruker (Billerica, MA) ELEXSYS E580 pulse EPR
spectrometer equipped with a Bruk
er
MD
-
4
resonator. Temperature control was achieved using
an ER 4118HV
-
CF5
-
L Flexline Cryogen
-
Free VT cryostat manufactured by ColdEdge
(Allentown, PA) equipped with an Oxford Instruments Mercury ITC.
Pulse
X
-
band ENDOR was acquired using the Davies pulse
sequence (
π
T
$%
π
$%
T
$%
π
/
2
τ
π
echo), where
T
$%
is the delay between mw pulses and RF pulses,
π
$%
is the length
of the RF pulse and the RF frequency is randomly sampled during each pulse sequence.
X
-
band HYSCORE spectra were acquired using the 4
-
pulse sequence (
π
/
2
τ
π
/
2
t
+
π
t
,
π
/
2
echo), where
τ
is a fixed delay, while
t
+
and
t
,
are independently incremented by
Δ
t
+
and
Δ
t
,
, respectively. The time domain data was baseline
-
corrected (third
-
order
polynomial) to eliminate the exponential decay
in the echo intensity, apodized with a Hamming
window function, zero
-
filled to eight
-
fold points, and fast Fourier
-
transformed to yield the 2
-
dimensional frequency domain.
For
2
H
-
1
H difference spectra, the time domain of the HYSCORE
spectrum of the
1
H sam
ple was subtracted from that of the
2
H sample, and the same data
processing procedure detailed above was used to generate the frequency spectrum.
In general, the ENDOR spectrum for a given nucleus with spin
I
=
½
(
1
H,
31
P) coupled to the S =
½
electron spin
exhibits a doublet at frequencies
ν
±
=
1
A
2
±
ν
3
1
(1)
Where
ν
3
is the nuclear Larmor frequency and
A
is the hyperfine coupling. For nuclei with
I
1
(
2
H), an additonal splitting of the
ν
±
manifolds is produced by the nuclear quadrupole
interaction (P)
ν
±
,
7
8
=
1
ν
3
±
3P
(
2
m
=
1
)
2
1
(2)
In HYSCORE spectra, these signals manifest as cross
-
peaks or ridges in the 2
-
D frequency
spectrum which are generally symmetric about the diagonal of a given quadrant. This technique
S
4
allows hyperfine levels corresponding to the sam
e electron
-
nuclear submanifold to be
differentiated, as well as separating features from hyperfine couplings in the weak
-
coupling
regime (
|
A
|
<
2
|
ν
=
|
) in the (+,+) quadrant from those in the strong coupling regime (
|
A
|
>
2
|
ν
=
|
) in the (
,+) quadrant. The (
,
) and (
+,
) quadrants of these frequency spectra are
symmetric to the (+,+) and (
,+) quadrants, thus typically only two of the quadrants are typically
displayed in literature.
For systems with appreciable hyperfine anisotropy in frozen solutions or solids, HYSC
ORE
spectra typically do not exhibit sharp cross peaks, but show ridges that represent the sum of cross
peaks from selected orientations within the excitation bandwidth of the MW pulses at the
magnetic field position at which the spectrum is collected. The
length and curvature of these
correlation ridges can allow for the separation and estimation of the magnitude of the isotropic
and dipolar components of the hyperfine tensor, as shown in Fig. S1.
Figure S1
.
a) HYSCORE powder patterns for an
S
= 1/2,
I
= 1/2 spin system with an isotropic
hyperfine tensor A. b) HYSCORE powder patterns for an
S
= 1/2,
I
= 1/2 spin system with an
isotropic hyperfine tensor which contains isotropic (
a
CDE
) and dipolar (
T
) contributions. Blue
correlation ridges represent the
strong coupling case; red correlation ridges represent the weak
coupling case.
EPR Simulations. Simulations of all CW and pulse EPR data were achieved using the
EasySpin
6
simulation toolbox (release 5.2.21) with Matlab 2018b using the following Hamiltonian
:
S
5
H
G
=
μ
I
B
K
K
M
g
S
P
+
μ
3
g
3
B
K
K
M
I
R
+
h
S
P
U
I
R
+
h
I
R
V
I
R
(3)
In this expression, the first term corresponds to the electron Zeeman interaction term where
μ
I
is
the Bohr magneton, g is the electron spin g
-
value matrix with principle components g = [g
xx
g
yy
g
zz
], and
S
P
is the e
lectron spin operator; the second term corresponds to the nuclear Zeeman
interaction term where
μ
3
is the nuclear magneton,
g
3
is the characteristic nuclear g
-
value for
each nucleus (e.g.
1
H,
2
H
,
31
P) and
I
R
is the nuclear spin operator; the third term corr
esponds to the
electron
-
nuclear hyperfine term, where
U
is the hyperfine coupling tensor with principle
components
U
= [A
xx
, A
yy
, A
zz
]; and for nuclei with
I
1
, the final term corresponds to the
nuclear quadrupole (NQI) term which arises from the interaction of the nuclear quadrupole
moment with the local electric field gradient (efg) at the nucleus, where
V
is
the
quadrupole
coupling tensor. In the principle a
xis system (PAS),
V
is traceless and parametrized by the
quadrupole coupling constant
e
,
Qq
/
h
and the asymmetry parameter
η
such that:
V
=
[
P
\\
0
0
0
P
^^
0
0
0
P
__
`
=
e
,
Qq
/
h
4I
(
2I
1
)
b
(
1
η
)
0
0
0
(
1
+
η
)
0
0
0
2
c
(4)
where
d
e
fg
h
=
2I
(
2I
1
)
P
__
and
η
=
i
jj
k
i
ll
i
mm
. The asymmetry
parameter may have values
between 0 and 1, with 0 corresponding to an electric field gradient with axial symmetry and 1
corresponding to a fully rhombic efg.
The orientations between the hyperfine and NQI tensor principle axis systems and the g
-
matrix
refe
rence frame are define
d by the Euler angles (
α
,
β
,
γ
), with rotations performed within the zyz
convention where
α
rotates xyz counterclockwise about z
-
axis to give x'y'z',
β
rotates x'y'z
counterclockwise about y'
-
axis to give x",y",z",
γ
rotates xyz count
erclockwise about z"
-
axis to
give final frame orientation
.
VII.
Electrochemistry:
Electrochemical measurements were carried out using a CD instruments 600B electrochemical
analyzer. A freshly polished glassy carbon electrode was used as the working
electrode and a
graphite rod was used as the auxiliary electrode. Solutions (THF) of electrolyte (0.4 M tetra
-
n
-
butylammonium hexafluorophosphate) contained ferrocene (0.1 mM), to serve as an internal
reference, and analyte (0.2 mM). All reported potential
s are referenced to the
ferrocene/ferrocenium couple, [Cp
2
Fe]
+
/Cp
2
Fe.
S
6
VII
I
.
Synthetic Procedures:
Fe(
h
3
:
h
2
-
Ind
)
(depe)(Br)
(
1
)
: To a solution of
trans
-
FeBr
2
(depe)
2
(
402
mg,
0.64 mmol, 1 equiv.
) in THF at
-
78
°
C wa
s added drop
-
wise a chilled (
-
78
°
C) solution of lithium indenide (
78 mg, 0.64 mmol, 1 equiv.
). Following
addition, the resulting mixture was stirred for an additional 2 h at room
temperature, giving a clear purple solution. Subsequently, all volatiles were removed
in
-
vacuo
and the resid
ue was washed with pentane (2 x 20 mL) and Et
2
O (2 x 20 mL). The resulting
purple solid was dissolved in THF and filtered through a pad of Celite
®
. Cooling a pentane
-
layered THF solution at
35 ºC afforded
1
as
dark purple crystals (
132
mg,
45
%).
N.B.
Allo
wing
this reaction mixture to stir for longer than 2 h results in appreciable formation of Fe(Ind)
2
and
free ligand.
1
H NMR (
C
6
D
6
, 400 MHz, 298 K)
:
d
=
7.54 (m, 2H), 7.10 (m, 2H), 4.56 (br s, 1H), 4.01 (br s,
2H), 2.13 (m, 2H), 1.79 (m, 2H), 1.64 (m, 2H),
1.28 (m, 2H), 1.12 (m, 4
H), 1.01 (m, 6H), 0.77
(m, 6H).
31
P{
1
H} NMR (
C
6
D
6
, 162 MHz, 298 K)
:
d
=
92.98.
13
C NMR (THF
-
d
8
, 100 MHz,
298 K)
:
d
=
127.99, 125.39, 83.13
(
h
3
:
h
2
-
C
9
H
7
)
, 58.07
(
h
3
:
h
2
-
C
9
H
7
)
, 23.60, 21.92, 20.40, 10.13,
8.99.
CV data (1 mM, vs. Fc/Fc
+
)
:
-
0.53 V (Fe
II
/Fe
III
)
.
UV
-
VIS (
THF,
1 cm cell, 298 K)
:
l
=
529
{313 M
-
1
cm
-
1
}
, 687
{208 M
-
1
cm
-
1
}
.
Anal. Calcd
.
for C
19
H
31
BrFeP
2
(456.04): C, 49.92; H,
6.84. Found: C, 50.
40
; H,
6.96
.
P
P
Fe
Br
S
7
Figure S
2
.
1
,
1
H
NMR,
C
6
D
6
,
400
MHz, 298 K
Figure S
3
.
1
,
31
P{
1
H} NMR,
C
6
D
6
, 162 MHz, 298 K
P
P
Fe
Br
P
P
Fe
Br
S
8
Figure S
4
.
1
,
31
C
{
1
H} NMR,
THF
-
d
8
, 100
MHz, 298 K
Figure S
5
.
1
, UV
-
Visible spectrum, THF, 298 K
(
l
= 529, 687 nm)
P
P
Fe
Br
P
P
Fe
Br
S
9
Fe(
h
3
:
h
2
-
Ind
)
(depe)(H)
(
2
)
: To a solution of
1
(
21.5 mg, 0.047
mmol, 1
equiv.
) in THF at
-
78
°
C was added drop
-
wise a chilled (
-
78
°
C)
1.0 M
solution of Li[BEt
3
H] (
47.1
μ
L, 0.047 mmol, 1 equiv.
). Following addition, the
resulting mixture was stirred for an additional 10 min at
-
78
°
C and then at
room temperature for
2 h, giving a clear red solution. Subsequently, all volatiles were removed
in
-
vacuo
and the residue was dissolved in pentane (5 mL) and filtered through a pad of Celite
®
.
This was repeated three times to give
2
as a red oil (
17.5 mg, 98%
). Efforts to recry
stallize
2
were unsuccessful.
1
H NMR (
C
6
D
6
, 400 MHz, 298 K
)
:
d
= 7.39 (m, 2H), 6.81 (m, 2H), 4.73 (br s, 2H), 4.71 (m,
1H), 1.57
-
1.34 (m, 8H), 1.25 (m, 4H), 0.99 (m, 6H), 0.75 (m, 6H),
-
20.64 (t,
2
J
H,P
= 70.8 Hz
,
1
J
Fe,
H
= 10.3 Hz
).
31
P{
1
H} NMR (
C
6
D
6
, 162
MHz, 298 K)
:
d
=
106.38 (
2
J
H,P
= 70.8 Hz
,
1
J
Fe,P
= 60.3
Hz
).
13
C NMR (
C
6
D
6
, 100 MHz, 298 K)
:
d
=
126.69, 121.00
,
97.73, 80.09
(
h
3
:
h
2
-
C
9
H
7
),
62.22
(
h
3
:
h
2
-
C
9
H
7
), 27.
0
1 (m), 25.89 (dd,
J
C,P
= 21.4 Hz,
J
C,P
= 19.5 Hz)
, 2
5
.
24 (dd,
J
C,P
= 6.9 Hz,
J
C,P
=
4.89 Hz)
,
9.27, 9.14
.
IR (
thin film
, 298 K, cm
1
)
:
1851 cm
-
1
(
u
FeH
).
57
Fe Möss
bauer (
80
K,
Et
2
O
solution, mm/s)
:
d
= 0.28,
D
E
Q
= 1.61.
CV data
(1 mM, vs. Fc/Fc
+
)
:
-
0.81 V (Fe
II
/Fe
III
)
.
UV
-
VIS (
THF,
1 cm cell, 298 K)
:
l
= 396
{
498
M
-
1
cm
-
1
}
, 506
{
912
M
-
1
cm
-
1
}
.
N.B.
Given
the
physical
nature of
2
, elemental analysis was not
acquired.
Probing bimolecular H
2
loss:
To a
J.
Young
NMR tube cooled to
-
78
o
C containing a THF
-
d
8
solution
(300
μ
L)
of 4.5 mg
(12
μ
mol)
2
-
H
and 4.5 mg
(12
μ
mol)
2
-
D
(500
μ
L) was added 25.6 mg (25
μ
mol) [Fc]BAr
F
4
in 200
μ
L THF
-
d
8
. The tube was shaken and warmed to room temperature. NMR spectroscopy confirms
the presence of both H
2
and HD.
1
H NMR (
THF
-
d
8
, 400 MHz, 298 K)
:
d
=
4.50
ppm (
t,
1
J
H,D
=
42
Hz
; HD
)
, 4.55 (s, H
2
).
P
P
Fe
H
S
10
Figure S
6
.
2
,
1
H
NMR,
C
6
D
6
,
400
MHz, 298 K
Figure S
7
.
2
,
31
P{
1
H} NMR,
C
6
D
6
, 162 MHz, 298 K
P
P
Fe
H
P
P
Fe
H