S
1
Supplemental Information for
A
Trans
-
Hyponitrite Intermediate in the Reductive Coupling and Deoxygenation of
Nitric Oxide by a Tricopper
-
Lewis Acid Complex
Davide Lionetti
, Graham de Ruiter,
and Theodor Agapie*
Division of Chemistry and Chemical Engineeri
ng, California Institute of Technology, 1200 East California
Boulevard, MC 127
-
72, Pasadena, California 91125, United States
Contents
Experimental Section
S
1
General Considerations
S
1
Synthesis of
2
S
2
Synthesis of 4
S
2
Synth
esis of 5
S
3
Protocol for Gas Analysis in Reactions of 2 with Acids
S
3
Figure
S1
.
1
H NMR spectrum of
2
in CD
3
CN.
S
4
Figure
S2
.
1
H NMR spectrum of
4
in CD
3
CN.
S
5
Figure
S3
.
1
H NMR spectrum of
5
in CD
3
CN.
S
5
Figure
S4
.
IR Spectra
of
2
a
nd
15
N
-
2
S
6
Figure
S5
.
Gas
-
phase IR spectra for N
2
O detection
S
6
Figure
S6
.
Summary of GC
-
MS data for reactions of
15
N
-
labeled
complex
2
with pyridinium triflate
S
7
Crystallographic Information
S
7
Refinement Details
S
8
Table
S
1
.
Crys
tal and Refinement Data
S
8
Special Refinement Details for 2
S
9
Figure
S7
.
Solid
-
state structure of complex
2
S
9
Special Refinement Details for 4
S
10
Figure
S8
.
Solid
-
state structure of complex
4
S
10
Figure
S9
.
Preliminary sol
id
-
state structure of complex
5
S1
1
Figure S10.
UV
-
Visible spectrum of reaction of
1
with N
2
O
S1
1
Figure S11.
EPR spectrum of
2
S1
2
Figure S12
. FTIR spectrum of purified nitric oxide
S12
Figure S13
.
1
H NMR spectrum of
3
with 1 equiv. NO
in CD
3
CN.
S13
Crystallographic Tables
S2
-
S5
S
1
4
References
S2
3
Experimental Section
General Considerations
Unless indicated otherwise, reactions performed under inert atmosphere were
carried out in oven
-
dried glassware in a glovebox under a nit
rogen atmosphere.
Anhydrous tetrahydrofuran (THF) was purchased from Aldrich in 18 L Pure
-
Pac
TM
containers. Anhydrous diethyl ether, acetonitrile, and THF were purified by
sparging with nitrogen for 15 minutes and then passing under nitrogen pressure
throu
gh a column of activated A2 alumina (Zapp’s).
Propionitrile was dried over
S
2
calcium
hydride and vacuum transferred over molecular sieves.
CD
3
CN was
purchased from Cambridge Isotope Laboratories, dried over calcium hydride,
degassed by three freeze
-
pump
-
thaw
cycles, and vacuum
-
transferred prior to use.
1
H NMR spectra were recorded on a Varian 300 MHz instrument, with shifts
reported relative to the residual solvent peak.
19
F NMR spectra were recorded on a
Varian 300 MHz instrument, with shifts reported relati
ve to the internal lock
signal. Electrospray ionization mass spectrometry (ESI
-
MS) was performed in the
positive ion mode using a LCQ ion trap mass spectrometer (Thermo) at the
California Institute of Technology Mass Spectrometry Facility. The ATR
-
IR
measu
rements were recorded on a Bruker APLHA ATR
-
IR spectrometer at 2 cm
-
1
resolution using the OPUS software package.
The gas
-
phase IR measurements
were recorded on a
Bio
-
Rad Excalibur Series spectrometer using a custom
-
made
Schlenk cell fitted with KBr window
s (pathlength = 10 cm).
GC
-
MS
analysis was
performed
on an Agilent 6890 gas chromatogram equipped with an Agilent 5793
mass
-
selective detector
and an Agilent 19091S
-
433 column, using a 1.0 mL/min
flow (He) and a 50
°C
oven temperature.
UV
-
Vis spectra were
collected on a
Varian 50Bio spectrophotometer using a Schlenk
-
adapted 1 cm quartz cuvette.
Low
-
temperature UV
-
Vis spectra were obtained using a Varian dip
-
probe
(661.202
-
UV, 10 mm) and a custom
-
made glass vessel E
lemental analyses were
performed by Midwest
Microlab, LLC. (Indianapolis, IN).
The EPR spectrum of
2
was obtained on an X
-
band EPR spectrometer and simulated using the EasySpin
package for Matlab.
1
Unless indicated otherwise, all commercial chemicals were
used as received. Nitric oxide was purchased from Aldrich.
15
NO was purchased
from Cambridge Isotope Laboratories
Complexes
1
and
3
were prepared according
to previously published procedures.
2
Identical
1
H
-
NMR spectra
were obtained with
purified nitric oxide (NO), which
was
purified
by careful distillation from
pentane/liquid nitrogen at
-
115
°
C
(Figure S12)
; according to
a modification of a
procedure reported by Karlin and co
-
workers.
3
In short, on a high
-
vacuum
manifold, nitric oxide was frozen in a 1L schlenk
-
tube at
-
196
°
C, and
heated to
-
115
°
C in a pentane/liquid nitrogen bath. Once distillation commences, it is
important to keep the distillation time short (< 30 sec.) in order to prevent N
2
O
contamination. The evolved gas was collected in a trap cooled at
-
196
°
C. This
procedu
re was repeated three times, and the purified nitric oxide was stored in a
500 mL
glass bulb, fitted with Teflon valve, at reduced pressure
.
Synthesis of 2.
In a Schlenk tube, a solution of
1
(0.212 g, 0.1
07 mmol) in EtCN (8 mL) was
degassed by three fre
eze
-
pump
-
thaw cycles. The solution was cooled to
-
78 °C in a
dry ice/acetone bath, and nitric oxide (43.5 mL, 54 mmHg,
0.1
24 mmol, 1.2 equiv)
was added to the vessel via a volumetric gas bulb. The golden yellow solution
changed to dark yellow
-
green in ~15
minutes. The solution was stirred at
-
78 °C
for 6 hours, then warmed to room temperature. The solvent was removed
in vacuo
,
and the residue was washed with THF and filtered through a pad of Celite. The
green
-
yellow solid was extracted with acetonitrile. Va
por diffusion of diethyl ether
into an acetonitrile solution of this product yielded crystalline
2
as green urchins,
S
3
which were mechanically separated from other precipitates (0.055 g, 27% yield
based on [YCu
3
]).
1
H NMR (CD
3
CN, 300 MHz):
δ
8.63 (br), 8.42
(br), 7.87 (br
overlapped), 7.75 (br overlapped), 7.40 (br), 7.26 (br), 6.88 (br overlapped), 6.72
(br overlapped), 3.6 (br overlapped), 3.35 (br overlapped), 2.09 (br) ppm.
19
F NMR
(CD
3
CN):
δ
−
78.96 ppm.
UV
-
Vis (CH
3
CN)
λ
max
[
ε
(M
-
1
×
cm
-
1
)]:
229 nm
(1.74
×
10
5
), 369 nm (3.56
×
10
4
), 706 (3.11
×
10
2
).
Anal. Calcd. For
C
144
H
144
Cu
6
F
18
N
28
O
26
S
6
Y
2
: C, 45.80; H, 3.84; N, 10.39. Found: C. 46.00; H, 3.91;
N, 10.27.
Synthesis of 4
.
In a Schlenk tube, a solution of
3
(0.
5585
g,
0.927
mm
ol) in EtCN (8 mL) was
degassed by three freeze
-
pump
-
thaw cycles. The solution was cooled to
-
78 °C in a
dry ice/acetone bath, and nitric oxide (
234
mL,
362
mmHg,
4.64
mmol,
5
equiv
.
)
was added to the vessel via a volumetric gas bulb. The
dark
yellow solut
ion
changed to
green
-
blue
in ~
1 hour
. The solution was stirred at
-
78 °C for 6 hours,
then warmed to room temperature. The solvent was removed
in vacuo
. The
residue
was
triturated with THF and the green solution (which contained mostly desired
product) was
filtered through
a pad of Celite.
The material remaining on the Celite
filter was extracted with acetonitrile, and the solvent was removed
in vacuo
to give
the nitrite product
4
as a green
-
blue powder (0.369 g, 61%). Single
-
crystals of
4
suitable for X
-
ra
y diffraction studies were obtained via vapor
diffusion of diethyl
ether into an acetonitrile solution of
4
.
1
H NMR (CD
3
CN, 300 MHz):
δ
9.80
(br),
7.95
(br
overlapped
), 7.
49
(br overlapped),
3.58
(br),
1.14 (br) ppm
.
19
F NMR
(CD
3
CN):
δ
−
79.08
ppm.
Anal. Ca
lcd. For C
26
H
31
CuF
3
N
4
O
6
S: C, 48.18; H, 4.82;
N, 8.64. Found: C. 48.07; H, 4.74; N, 8.42.
Note; addition of 1 equiv. of NO to
complex
3
gave a mixture of complex
3
and
4
as judged by
1
H NMR spectroscopy
(Figure S13).
Synthesis of 5.
In a Schlenk vessel, a
solution of
1
(0.3024 g, 0.163 mmol) in 1:1 THF/EtCN was
cooled to
-
78 °C. NO was bubbled through the solution via syringe needle for 1
min, during which the solution turned from yellow to dark green/brown. After
stirring at
-
78 °C for 4 hours, the solutio
n was warmed to room temperature, and
precipitation of a brown solid was observed. In the glovebox, the suspension was
filtered through Celite, and the brown residue extracted with fresh CH
3
CN. The
solvent was removed
in vacuo
to give the product as a brow
n powder (0.241 g,
74%).
Single
-
crystals suitable for X
-
ray diffraction studies were obtained via vapor
diffusion of diethyl ether into an acetonitrile solution
of
5
.
1
H NMR (CD
3
CN, 300
MHz):
δ
10.0
(br
overlapped
),
9.4
(br
overlapped
),
3.4
(br)
ppm
.
19
F N
MR
(CD
3
CN):
δ
−
7
8.80
ppm.
Anal. Calcd. For C
72
H
72
Cu
3
F
9
N
16
O
18
S
3
Y
: C, 4
3
.
32
; H,
3.64
; N,
11.23
. Found: C.
43.29
; H,
3.76
; N,
11.29
.
Protocol for Gas Analysis in Reactions of
2
with Acids.
Gas
-
phase IR:
a Schlenk tube was charged with a solution of
2
in CH
3
C
N. On a
Schlenk line, the solution was frozen in LN
2
. Under positive N
2
pressure, fresh
CH
3
CN was layered on top of the frozen solution via syringe and frozen, after
S
4
which a CH
3
CN solution of pyridinium triflate (6 equiv.) was added and also
frozen. The Sc
hlenk tube was sealed, and the solution was thawed and stirred at
room temperature for three hours. On a high
-
vacuum line, N
2
was removed from
the solution via three freeze
-
pump
-
thaw cycles (the solution was frozen in LN
2
to
keep any N
2
O produced condensed
). The volatiles in the reaction vessel were than
vacuum transferred through a trap cooled to
-
78 °C (to condense CH
3
CN) and into
a liquid nitrogen
-
cooled Schlenk flask (to condense N
2
O). The flask containing the
gaseous products was then connected to an e
vacuated gas IR cell fitted with two
greased joint connections. The gases in the Schlenk flask were allowed to expand
into the cell and IR spectra were recorded.
Headspace analysis by GC
-
MS: in the glovebox,
a
10 mL
Schlenk
flask
was
charged with a soluti
on of
2
in CH
3
CN. On a Schlenk line, the solution was
degassed and placed under an argon atmosphere. The solution was frozen in a dry
ice/acetone bath. Under
positive
Ar
pressure
,
fresh
CH
3
CN
sparged with Ar
was
layered on top of the frozen solution via sy
ringe and
frozen
,
after which a CH
3
CN
solution of pyridinium triflate (6 equiv.)
sparged with Ar
was added
via syringe
and also frozen. The Schlenk tube was sealed
with a rubber septum
, and the
solution was thawed and stirred at room temperature
. To analyz
e the headspace, a
gastight microsyringe purged with Ar was used to extract a headspace sample (~5
μ
L) and inject it into the GC
-
MS instrument.
Figure
S
1
.
1
H NMR spectrum of
2
obtained from commercially available nitric
oxide (top) and purified nitric oxide (bottom), recorded
in CD
3
CN.
S
5
Figu
re
S
2
.
1
H NMR spectrum of
4
in CD
3
CN.
Figure
S
3
.
1
H NMR spectrum of
5
in CD
3
CN.
S
6
Figure
S
4
.
Solid
-
state ATR
-
IR spectra of
2
prepared from natural abundance NO
(red)
and
15
NO (blue). The N
–
O asymmetric stretch regio
n is highlighted in the
inset.
Figure
S5
.
Red: gas
-
phase IR spectrum of an authentic sample of N
2
O. Blue: gas
-
phase IR spectrum of the products of the reaction of
2
(natural abundance NO)
with pyridinium triflate. Green: gas
-
phase IR spectrum of the pro
ducts of the
reaction of
2
(
15
NO) with pyridinium triflate.
S
7
Figure S
6
.
GC
-
MS data for reactions of
15
N
-
labeled complex
2
with pyridinium
triflate
at 24 h (black) and 96 h (red)
. Labels represent assignment of m/z peaks.
Peaks at m/z=28 and m/z=3
2
are due
to introduction of air into the GC line during
sample injection (as shown by their presence in the Ar blank).
Note: peak at m/z=30
(
14
NO) in authentic
14
N
2
O sample due to fragmentation of N
2
O under mass
spectrometry conditions.
Likewise, the peak at m/z=3
1 (
15
NO) observed after 24 h is
due to fragmentation of
15
N
2
O under the MS conditions, indicating that release of
15
N
2
O is already occurring at this time point.
Crystallographic Information
Refinement details
Crystals were mounted on a nylon loop using P
aratone oil under a nitrogen
stream. Low temperature (100 K) X
-
ray data were obtained on a Bruker APEXII
CCD based diffractometer (Mo sealed X
-
ray tube, K
α
= 0.71073 Å). All
diffractometer manipulations, including data collection, integration and scaling
were carried out using the Bruker APEXII software.
4
Absorption corrections were
applied using SADABS.
5
Space groups were determined on the basis of systema
tic
absences and intensity statistics and the structures were solved by direct methods
using
XS
6
(incorporated into SHELXTL) and refined by full
-
matrix least squares
on F
2
. All non
-
hydrogen atoms were refined using anisotropic displacement
parameters. Hydr
ogen atoms were placed in idealized positions and refined using a
riding model. The structures were refined (weighted least squares refinement on
F
2
) to convergence.
It should be noted that due to the size of
2
, its crystal included
solvent accessible void
s, which tended to contain disordered solvent. These
S
8
disordered solvent molecules were largely responsible for the alerts generated by
the checkCIF protocol.
Table
S1
.
Crystal and refinement data.
a
R1 =
Σ
||F
o
|
-
|F
c
|| /
Σ
|F
o
|
b
wR2 = [
Σ
[w(F
o
2
-
F
c
2
)
2
] /
Σ
[w(F
o
2
)
2
] ]
1/2
c
GOOF
= S
= [
Σ
[w(F
o
2
-
F
c
2
)
2
] / (n
-
p) ]
1/2
2
4
CCDC #
142594
3
1425942
empirical formula
C
162
H
179
Cu
6
F
18
N
33
O
28
S
6
Y
2
C
26
H
31
CuF
3
N
4
O
6
S
formu
la wt
4129.79
648.15
T (K)
100
100.0
a, Å
13.8507(13)
20.569(2)
b, Å
16.8194(17)
15.5906(15)
c, Å
21.214(2)
18.3755(18)
α
, deg
105.556(3)
90
β
, deg
105.602(3)
104.318(3)
γ
, deg
94.915(3)
90
V, Å
3
4518.7(8)
5709.7(10)
Z
1
8
cryst syst
triclinic
monoclinic
space group
P
-
1
C2/c
ρ
calcd
, g/cm
3
1.518
1.508
2
θ
range, deg
4.384 to 55.028
5.226 to 79.504
μ
, mm
-
1
1.490
0.905
abs corr
Multi
-
scan
Multi
-
scan
GOOF
c
1.038
1.032
R1,
a
wR2
b
(I > 2
σ
(I))
0.0533, 0.1447
0.0421, 0.1018
S
9
Special Refinement Details for 2
The structure of
2
displayed disorder in a handful of outer
-
sphere components.
One of the triflate anions was disordered over two positions with ~80:20
occupancy. Due to the c
onsiderable size of the complex, large solvent voids
existed that required modelling of highly disordered solvent molecules. A diethyl
ether molecule was modelled fully (including H atoms) but not refined
anisotropically. An acetonitrile molecule residing
on a special position was
satisfactorily modelled using the EADP and EXYZ commands to account for the
disorder of the N atom over two position. H atoms were included but this molecule
was also not refined anisotropically.
Figure
S7
.
Full solid
-
state str
ucture of complex
2
. Both components of the
disordered outer
-
sphere triflate moiety are included. Hydrogen atoms omitted for
clarity.
Thermal
ellipsoids
shown
at
the
50%
probability
level.