1
Supp
orting
Information for
Highly Activated Terminal Carbon Monoxide Ligand in
an
Iron
-
Sulfur Cluster Model of FeMoc
o
Linh N. V. Le
1
,
Justin
P. Joyce
2
, Serena DeBeer
2
,
*
and
Theodor Agapie
1
*
1
Division of Chemistry and Chemical Engineering,
California Institute of Technology, Pasadena,
California 91125, United States
2
Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34
-
36, 45470 Mülheim an der
Ruhr, Germany
*To whom correspondence may be addressed.
Email:
agapie@caltech.edu
serena.debeer@cec.mpg.de
Table of Contents:
A)
Synthetic details
and characterization
2
1.
General considerations
2
2.
Procedures
2
Synthesis of
2
-
t
Bu
2
Synthesis of
2
-
Xyl
3
Synthe
s
is of
3
3
Synthesis of
4
4
Synthesis of
4
-
K
5
Synthesis of
4
-
K(18
-
crown
-
6)
5
Synthesis of
5
6
Reaction of
1
with 1 atm CO
6
3.
NMR spectra
8
4.
Support for assignment of
3
17
5.
Physical methods
1
9
M
ö
s
sbauer spectroscopy
1
9
Ele
c
trochemical measurements
2
3
Additiona
l
IR spectra
2
6
Evans method for
4
30
EPR spectroscopy
30
B)
Crystallographic information
3
7
C)
Computational details
4
7
D)
References
5
6
2
A)
Synthetic
detail
s
and characterization
:
1.
General considerations
:
All reactions were performed at
room temperature in a N
2
-
filled MBraun glovebox or using
standard Schlenk techniques unless otherwise specified. Glassware was oven
-
dried at 140 °C for at
least 2 h prior to use and allowed to cool under vacuum.
1
was
prepared acc
ording to literature
procedures
.
1
Diethyl ether, benzene, tetrahydrofuran (THF), and pentane were dried by sparging
with N
2
for at least 15 min and then passing through a column of activated A2 alumina under
positive N
2
pressure, and stored over 3 Å molecular sieves prior to use.
1
H spectra were recorded
on a Varian 300 MHz spectrometer.
D
euterated benzene (C
6
D
6
) w
as
purchased from Cambridge
Isotope Laboratories, dried over sodium/benzophenone ketyl, degassed by three freeze
–
pump
–
thaw cycles, and vacuum
-
transferred prior to use.
IR spectra
were obtained as
either
solution
samples using a
KBr
window cell on a Thermo Scientific Nicolet 6700 FT
-
IR
spectrometer
or
thin
films formed by evaporation of solutions using
a Bruker Alpha Platinum ATR spectrometer with
OPUS software in a glovebox under an N
2
atmosphere.
2.
Procedures:
Synthesis of
2
-
t
Bu
. In a glovebox,
1
(
300
.0 mg, 0.
20
6
mmol, 1 eq
uiv
) was dissolved in
THF
(15
mL)
.
To this solution,
t
BuNC
(
70
μ
L
,
0.
619
mmol,
3
eq
uiv
) was added to the reaction
using a
microsyringe. The reaction was stirred at room temperature for 20 h, after which the volatiles were
removed
in vacuo
. The crude material was used without further purification.
Yield:
317
mg
(
quant
).
X
-
ray quality crystals of
2
-
t
Bu
were grown by first washing the crude material with
pentane and Et
2
O, extracting the product into C
6
H
6
and diffusing HMDSO
into a concentrated
C
6
H
6
solution for several days.
1
H NMR (400 MHz, THF
-
h
8
, solvent suppression) δ 12.91, 7.28,
6.89, 6.1
4, 5.56, 5.13, 0.42,
-
1.57,
-
2.77,
-
2.95,
-
3.35,
-
3.76,
-
4.98,
-
6.36
.
Anal. calcd (%)
C
65
H
115
BFe
3
N
13
S
3
W
(M
r
= 1
537
.
09
): C, 5
0
.
7
9; H, 7.
54
; N,
11
.8
5
. Found: C, 5
0
.
55
; H,
8
.
44
; N,
11
.
54
.
3
Synthesis of
2
-
Xyl
. In a glovebox,
1
(
21
0
.0 mg, 0.
144
mmol, 1 eq
uiv
)
and XylNC
(
56.8 mg
, 0.
433
mmol,
3
eq
uiv
)
were combined in
THF
(5 mL)
.
The reaction was stirred at room temperature for
20 h, after which the volatiles were removed
in vacuo
. The crude material was
triturated
three
times with Et
2
O
and
washed with Et
2
O.
The solid was redissolved in a minimal amount of THF,
filtered and crystallized by THF/pentane vapor diffusion
.
Yield:
195
mg (
85%
).
X
-
ray quality
crystals were grown by diffusing
Et
2
O
into a concentrated solu
tion
of
2
-
Xyl
in THF
.
1
H NMR (400
MHz,
THF
-
h
8
, solvent suppression
) δ
15.53, 11.59, 11.10, 9.63, 7.26, 6.99, 6.45, 6.01, 5.54, 0.24,
-
0.66,
-
1.80,
-
1.86,
-
2.77,
-
3.36.
Anal. calcd (%
)
C
69
H
115
BFe
3
N
13
S
3
W
(M
r
= 1
5
85
.
14
): C, 5
2
.
28
; H,
7.
31
; N,
11
.
49
.
Found: C, 5
1
.
24
; H,
7
.
35
; N,
1
2
.
4
4
.
Synthesis of
3
.
In a glovebox,
crude
2
-
t
Bu
(
3
00.0
mg, 0.1
95
mmol
)
was added to a Schlenk tube
and dissolved in THF
(6 mL)
. The tube was capped, taken out of the box and heated in an oil bath
at 70 °C for 16 h
. T
he tube
must be closed while heated to give
3
(***NOTE: heating a closed
system can lead to an explosion, so make sure the amount of solvent is much smaller than the flask
volume and that the reaction does not boil)
. The tube was then cooled, brought back into
the box
and the solvent removed
in vacuo
. The resultant solid was triturated in pentane, washed with
pentane and Et
2
O, then redissolved in THF and crystallized b
y THF/pentane vapor
diffusion
to
yield X
-
ray quality crystals
. Yield: 1
48
mg (5
1
%).
The mother liquor still contains some
3
although less pure, but it can be used to prepare
4
.
1
H NMR (400 MHz,
THF
-
h
8
, solvent
suppression
) δ 14.89, 8.24, 6.91, 6.43, 5.16, 1.31, 1.07, 0.84, 0.59, 0.02,
-
0.58,
-
3.17,
-
3.48,
-
4.48
.
Anal. calcd (%)
C
61
H
106
BFe
3
N
13
S
3
W
·THF
(M
r
= 1
552
.
0
8
): C, 5
0
.
30
; H, 7.
40
; N,
11
.
73
. Found: C,
5
0
.
17
; H,
7
.80
; N,
1
1
.
0
4
.
4
Synthesis of
4
. In a glovebox,
3
(
132.0
mg, 0.08
9
mmol
) was
added to a Schlenk tube and
dissolved in
THF
(5
mL
)
.
The tube was capped and degassed by three freeze
-
pump
-
thaw cycles on
a Schlenk line. Then, the headspace of the tube was pressurized with 1 atm CO. The tube was
capped again and inverted over a period of 5 minutes, after which
the solution changed from
green
-
brown to red
-
brown.
NMR spectroscopy
typically indicates the complete consumption of
3
at this point. The volatiles were removed
in vacuo
and the tube was
brought back into the box. The
resultant solid was washed with Et
2
O then redissolved in THF to crystallize by THF/pentane vapor
diffusion.
Yield:
94.2
mg (83
%).
X
-
ray quality crystals can be grown by
washing the crude
material with C
6
H
6
, followed by
vapor diffusion of Et
2
O into a concentrated solution of
4
in THF
.
1
H NMR (400 MHz, THF
-
h
8
, solvent suppression)
δ 10.18, 8.48, 7.24, 6.91, 6.81, 5.81, 5.58, 1.40,
1.23, 1.10, 1.06, 0.83,
-
0.28,
-
1.58,
-
3.73
.
Anal. calcd (%)
C
47
H
78
BFe
3
N
11
OS
3
W
(M
r
= 1
271
.
58
):
C, 4
4
.
39
; H, 6.
1
8; N, 1
2
.
12
. Found: C, 4
4
.
49
; H, 6.
91
; N, 1
1
.1
5
.
Synthesis of
4
with
13
CO
. In a glovebox,
3
(
20.0
mg, 0.0
13
mmol
) was
added to a
20 mL
Schlenk
tube
with a stir bar
and
dissolved in
THF
(2
mL
)
.
The tube was capped and degassed by three
freeze
-
pump
-
thaw cycles on a Schlenk line
,
capped tightly,
then connected to
one end of a glass
solvent transfer bridge
(as small as possible to minimize the amount of unused
13
CO)
, which
is
connected to the Schlenk line
. The other end of the tube was connected to a
13
CO flask (~1 atm in
500 mL)
.
T
he
system was evacuated
, then the
solution was frozen in liquid nitrogen to prevent
solvent contamination to the
13
CO flask. The
n, the
transfer bridge
was
closed to vacuum
(similarly
to a solvent vacuum transfer)
, and the
13
CO
flask was opened to fill the system with
13
CO
. The
reaction
tube was
opened
for about 5 minutes
to fill the headspace
with
13
CO while still frozen,
then
capped again and
thawed while stirring vigorously.
T
he solution changed from green
-
brown
to red
-
brown
after about 10 minutes
.
The
tube was left to stir for 2 h, after which
t
he volatiles were
removed
in vacuo
and the tube was brought back into the box. The resultant solid was washed with
Et
2
O then redi
ssolved in THF to crystallize by THF/pentane vapor diffusion.
Yield:
7.1
mg (
41
%).
NMR
data are identical to
4
prepared from regular CO.
5
Synthesis of
4
-
K
. In a glovebox,
4
(
20.0
mg, 0.0
16
mmol
, 1 equiv
)
was
dissolved in THF
(2 mL)
in
a 20 mL scintillation vial with a pre
-
reduced Teflon stir bar to form a dark red
-
brown solution and
cooled to
-
78 °C in the cold well. To this solution was added
KC
8
(
2
.
5
mg, 0.0
19
mmol, 1
.2
equiv)
or potassium
naphthalenide (
0.15
7
mL,
0.1 M in THF,
0.016 mmol, 1 equiv)
and the dark
green
-
brown reaction was stirred at
-
78 °C. After 2 h, the solution was filtered through Celite and the
solvent removed
in vacuo
. The resultant solid was washed with Et
2
O, then redissolved in THF and
crystallized by THF/pentane vapor diffusion. Yield:
19
mg (
88
%). X
-
ray quality crystals were
grown by vapor diffusion of
Et
2
O into a concentrated solution of
4
-
K
in THF.
1
H NMR (400 MHz,
THF
-
h
8
, solvent suppression) δ 15.24, 14.71, 10.86, 8.88, 6.43, 6.12, 5.13, 2.83, 2.42, 1.04, 0.79,
0.10,
-
0.42,
-
3.31,
-
8.89,
-
12.96.
Anal. calcd (%)
C
47
H
78
BFe
3
N
11
OS
3
W
K·THF
(M
r
= 1
382
.
79
): C,
44
.
3
0
; H,
6
.
27
; N,
1
1
.
1
4
. Found: C,
44
.
82
; H,
6.
30
; N,
1
0
.
96
.
The
13
CO
-
labeled version was
prepared
identically from
13
CO
-
labeled
4
for IR spectroscopy.
Synthesis of
4
-
K(18
-
crown
-
6)
. In a glovebox,
4
(
12
.
8
mg, 0.01
0
mmol, 1 equiv
)
was dissolved in
THF
(2 mL)
in a 20 mL scintillation vial with a pre
-
reduced Teflon stir bar to form a dark red
-
brown solution and cooled to
-
78 °C in the cold well. To this solution was added
excess
KC
8
(
2.3
mg, 0.0
20
mmol,
2
equiv)
and the dark green
-
brown reaction was stirred at
-
78 °C. After 2 h,
IR
spectroscopy indicated the disappearance of the starting material,
and
excess 18
-
crown
-
6 (
5.
4
mg,
0.020 mmol, 2 equiv) was added to the reaction. The solution was stirred
at
-
78 °C
for another 2 h
before
taking an aliquot for IR spect
roscopy and
concentrated under vacuum, then filtered through
Celite and
crystallized by THF/pentane vapor diffusion. Yield: 1
0
mg (
64
%). X
-
ray quality
crystals were grown by vapor diffusion of Et
2
O into a concentrated solution of
4
-
K
(18
-
crown
-
6)
in
DME
.
1
H NMR (400 MHz,
THF
-
h
8
, solvent suppression) δ 19.10, 11.39, 9.07, 6.44, 6.04, 5.41,
2.94, 2.54, 1.07, 0.84, 0.10,
-
0.64,
-
3.82,
-
9.78,
-
14.87.
Anal. calcd (%)
C
59
H
102
BFe
3
KN
11
O
7
S
3
W
(M
r
= 1
575
.
00
): C,
44
.
99
; H,
6
.
53
; N,
9
.
78
. Found: C,
4
3
.
14
; H,
6.3
1
; N,
9
.
57
.
The
13
CO
-
labeled
version was prepared identically from
13
CO
-
labeled
4
.
6
The reaction was also carried out identically using [2.2.2]cryptand
instead of 18
-
crown
-
6 for IR
spectroscopy, which shows the same C
-
O stretch.
The following clusters were not discussed in the main text but were also prepared/isolated
to
provide more support for structural assignment or reactivity pattern.
Synthesis of
5
. In a glovebox,
2
-
Xyl
(
52.1
mg, 0.033 mmol, 1 equiv
)
was dissolved in THF (2 mL)
in a 20 mL scintillation vial with a stir bar to form a dark green
-
brown solution and cooled to
-
78
°C in the cold well. To this solution was added AgOTf (8.4 mg, 0.033 mmol, 1 equiv) and the dark
red
-
brown reaction was stirred
at
-
78 °C. After 2 h, the solution was filtered through Celite and the
solvent removed
in vacuo
. The resultant solid was washed with Et
2
O, then redissolved in THF and
crystallized by THF/pentane vapor diffusion. Yield: 40 mg (70%). X
-
ray quality crystals were
grown by vapor diffusion of
i
Pr
2
O into a concentrated solution of
5
in THF
.
1
H NMR (400 MHz,
THF
-
h
8
, solvent suppression) δ 13.29, 11.09, 10.22, 7.33, 6.97, 6.38, 5.88, 5.75, 4.99, 1.08, 0.38,
-
0.27,
-
1.10,
-
1.88
.
Anal. calcd (%)
C
70
H
115
BFe
3
N
13
S
4
F
3
O
3
W
(M
r
= 1
734
.
20
): C,
48
.
48
; H,
6
.
68
; N,
10
.
50
. Found: C,
48
.
71
; H,
6.60
; N,
12
.
91
.
Reaction of
1
with 1 atm CO
.
Treatment of
1
with 1 atm CO results in a complex reaction mixture
by
1
H NMR spectroscopy (see SI)
, but one product could be characterized by crystallography.
In a
glovebox,
1
(20.
0
m
g,
0
.
014 mmol) was dissolved in THF (0.7 mL) and transferred to a J. Young
NMR tube
.
The tube was capped and degassed by three freeze
-
pump
-
thaw cycles on a Schlenk
line. Then, the headspace of the tube was pressurized with 1 atm CO. The tube was capped again
and inverted over a period of 5 minutes, after which NMR spectroscopy indicated th
e complete
consumption of
1
and the appearance of new peaks between
-
2 and
-
12 ppm
.
Th
e tube was brought
back into the glovebox and the solvent was removed
in vacuo
to yield a dark film. The film was
7
washed with pentane and the product was extracted into Et
2
O and filtered through a pad of Celite
before the solvent was removed
in vacuo
. The resultant material was redissolved in a minimal
amount of Et
2
O and placed at
-
35 °C for several days to yield X
-
ray quality crystals
, whose
structure is determined to be
6
. Despite multiple trials, only a few crystals of
6
were observed each
time, which precludes bulk characterization
.
For all the reactions
that result in products that can be isolated and characterized, spectroscopic
yields were also measured by NMR spectroscopy. Each reaction was carried out on a small scale
,
and a
known amount of an
internal standard (4
-
phenylbenzaldehyde or cobaltocene)
was added at
the end of the reaction mixture without working up. Separately, a known amount of the same
internal standard was added to a known amount of purified material.
Comparison of the
integrations between a pair of non
-
overlapping peaks
(one each for the standard and the analyte)
in
both
cases allows for the determination of reaction yield
s
by NMR spectroscopy. The table below
displays the results.
Table S1: Measured NMR spectroscopic yields for reactions
Product
Spectroscopic yield/%
Isolated yield/%
Standard
2
-
t
Bu
98
Quant
4
-
phenylbenzaldehyde
2
-
Xyl
94
85
4
-
phenylbenzaldehyde
3
61
51
4
-
phenylbenzaldehyde
4
87
83
4
-
phenylbenzaldehyde
4
-
K
90
88
cobaltocene
4
-
K(18
-
crown
-
6)
92
64
cobaltocene
5
93
70
4
-
phenylbenzaldehyde
8
3.
NMR spectra
:
Figure S
1
:
1
H NMR spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
1
(top) and
1
+ CO
(
1
atm
)
after mixing for 5 min (bottom)
. The peaks corresponding to the starting material disappears
and new peaks appear within the
-
2 to
-
12 ppm region, assigned to
6
(structure below as
determined by X
-
ray crystallography).
1
1
+ CO
(
1 atm
)
after 5 min
9
Figure S
2
:
1
H NMR spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
2
-
t
Bu
. Solvent peak
s
are
indicated by asterisk
s
(*).
*
*
10
Figure S
3
:
1
H NMR
spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
2
-
Xyl
. Solvent peak
s
are
indicated by asterisk
s
(*).
*
*
11
Figure S
4
:
1
H NMR spectrum (
4
00
MHz,
THF
-
h
8
, solvent suppression
) of
3
. Solvent peak
s
are
indicated by asterisks (*).
*
*
*
12
Figure S
5
:
1
H NMR spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
4
. Solvent peak
s
are
indicated by asterisk
s
(*).
*
*
13
Figure S
6
:
1
H NMR
spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
4
-
K
. Solvent peak
s
are
indicated by asterisk
s
(*).
*
*
14
Figure S
7
:
1
H NMR spectrum (
4
00 MHz,
THF
-
h
8
, solvent suppression
) of
4
-
K
(18
-
crown
-
6)
.
Solvent peak
s
are
indicated by asterisk
s
(*).
*
*
15
Figure S
8
:
1
H NMR spectrum (400
MHz,
THF
-
h
8
, solvent suppression
)
of
5
. Solvent peaks are
indicated by asterisks (*).
*
*