Inorganic Chemistry
Forum Article
has a more substantial effect on the rate of substrate activation
dichloromethane in a sealed 1 cm quartz cuvette with an Agilent Cary
1
+
0
6
0 UV−vis spectrophotometer. CV experiments were recorded with a
(
6-V O vs 4-V O ; 64-fold increase in the reaction time
6 6 6 6
Bio-Logic SP200 potentiostat/galvanostat and the EC-Lab software
suite. All measurements were performed in a three-electrode system
cell configuration that consisted of a glassy carbon (ø = 3.0 mm) as
due to the redox potential). Overall, these investigations
confirm that remote redox changes within the metal oxide
assembly play a significant role in the surface activity of these
materials.
the working electrode (CH Instruments, USA), platinum wire as the
counter electrode (CH Instruments, USA), and Ag/Ag+ as the
nonaqueous reference electrode with 0.01 M AgNO in 0.05 M
3
n
CONCLUSION
[ Bu N][PF ] in dichloromethane (BASi, USA). All electrochemical
4
6
■
In this work, we have demonstrated that NOx− (x = 2, 3)
reduction is significantly influenced by the charge state of
oxygen-deficient POV-alkoxide clusters. While the oxidation
state of remote vanadyl ions clearly plays a role in dictating the
rate and extent to which OAT reactions proceed, our
investigations have revealed that two additional factors can
influence OAT with these polynuclear assemblies: (1) the
steric bulk imparted on the active metal center by surrounding
surface ligands and (2) electrostatic interactions between the
substrate and cluster. The former is evident in comparing the
reaction time required for oxyanion reduction via complex 1-
measurements were performed at room temperature in a dinitrogen-
filled drybox. Anhydrous dichloromethane (DCM) that contained
n
[
Bu N][PF ] was used as the electrolyte solution.
4 6
Capture of Nitric Oxide by CoTPP. To probe whether nitric
n
oxide was produced in nitrite reduction with [V O (OC H ) ] (n =
6
6
2
5 12
1−, 0, 1+), CoTPP was added to the reaction mixture. CoTPP, a NO
complexation agent, exhibits a highly characteristic shift in the
position of the absorption band (λ
dichloromethane) following NO coordination.
= 528 nm in
A calibration
CoTPP,initial
4
3−45,61
curve, collected in dichloromethane by Symes and co-workers, was
used to qualitatively measure the amount of NO-ligated CoTPP
43
1
formed. H NMR measurements were taken in CDCl to further
3
assess (NO)CoTPP formation via the growth of new resonances at
8.91, 8.17, and 7.74 ppm, which match the previously reported spectra
1−
V O
to that of the anionic, methoxide-bridged POV-
6
6
1
−
61
alkoxide cluster, ([V O (OCH ) ] ), which reveals that
for the NO-ligated CoTPP complex. Control experiments: Six 20
6
6
3 12
1
−
increasing the steric bulk results in enhanced oxyanion
coordination. Similarly, the dramatic increase of the reaction
time required for NO2− reduction in the case of the
mL scintillation vials were charged with (1) CoTPP and 1-V O
,
6
6
0
1+
(2) CoTPP and 4-V O , (3) CoTPP and 6-V O , (4) CoTPP and
6 6 6 6
-V O7 , (5) CoTPP and 7-V O , and (6) CoTPP and 9-V O
1−
0
1+
5
6 6 6 6 7
1
−
each in 6 mL of tetrahydrofuran. The reactions mixtures were stirred
for 24 h at 21 and 50 °C, after which 0.01 mL was removed and
diluted with 10 mL anhydrous dichloromethane. Electronic
band of CoTPP and that of each reaction mixture (Figure S9).
General Reaction Procedure for NO Trapping Using CoTPP.
In a glovebox, a 20 mL scintillation vial or 15 mL pressure vessel was
monoanionic POV-alkoxide cluster (1-V O6 ), relative to
6
that of the neutral and cationic species, reveals that
electrostatic repulsion between the most-reduced cluster and
substrate significantly influences the rate of OAT. The factors
that have emerged from our structure−function investigations
reveal design strategies that might improve the reactivity of
metal oxide materials in small-molecule activation schematics.
Future work analyzing OAT chemistry with these reduced,
vanadium oxide assemblies will focus on the study of OAT
from neutral substrates in order to decouple the influence of
ion-pairing interactions from that of the change in the remote
metal oxidation state.
n
charged with [V O (OC H ) ] (n = −1, 0, 1+) and 8 mL of
6
6
2
5 12
n
tetrahydrofuran. CoTPP (1 equiv) and [ Bu N]NO (1 equiv) were
4 2
added to the solution as solids. The reaction mixture was stirred at (1)
1
−
0
2
°
1 °C for 24 h (1-V O ), (2) 50 °C for 24 h (4-V O ), and (3) 50
6 6 6 6
1+
C for 24 h (6-V O6 ), after which 0.01 mL was removed from the
6
reaction mixture and diluted with 10 mL of anhydrous dichloro-
methane. Electronic absorbance spectroscopy was used to measure
the shift in the wavelength following NO complexation to CoTPP
(λCoTPP,initial = 528 nm in dichloromethane).
EXPERIMENTAL SECTION
■
1
−
n
1−
(
1) 1-V O6
+ [ Bu N]NO . 1-V O
(0.010 g, 0.009 mol),
2
General Considerations. All manipulations were carried out in
the absence of water and dioxygen using standard Schlenk techniques
or in a UniLab MBraun inert-atmosphere drybox under a dinitrogen
atmosphere except where specified otherwise. All glassware was oven-
dried for a minimum of 3 h and cooled in an evacuated antechamber
prior to use in the drybox. All solvents were dried and deoxygenated
on a Glass Contour System (Pure Process Technology, LLC) and
stored over activated 3 Å molecular sieves purchased from Fisher
6
4
2
6
6
n
CoTPP (0.006 g, 0.009 mol), and [ Bu N]NO (0.003 g, 0.009 mol).
H NMR (400 MHz, CDCl ): δ 27.24 (fwhh = 466 Hz), 8.91 (fwhh =
4
1
3
3
2 Hz), 8.17 (fwhh = 40 Hz), 7.74 (fwhh = 40 Hz), −1.91 (fwhh =
224 Hz). UV−vis (CH Cl ): 538 nm.
2
2
0
n
0
(
2) 4-V O + [ Bu N]NO . 4-V O (0.028 g, 0.029 mol),
6 6 4 2 6 6
n
CoTPP (0.019 g, 0.029 mol), and [ Bu N]NO (0.008 g, 0.029 mol).
4
2
1
H NMR (400 MHz, CDCl ): δ 26.81 (fwhh = 1364 Hz), 15.93
3
1
−
34
Scientific prior to use. [CoCp ]V O (OC H ) (1-V O6 ),
(fwhh = 108 Hz), 13.14 (fwhh = 80 Hz), 9.94 (fwhh = 32 Hz), 9.74
(fwhh = 32 Hz), 8.91 (fwhh = 20 Hz), 8.17 (fwhh = 28 Hz), 7.74
2
6
6
2
5
12
6
0
0
32
1+
[
V O (OC H ) ] (4-V O ), and [V O (OC H ) ] (6-
6 6 2 5 12 6 6 6 6 2 5 12
33
1
+
V O
6
)
6
were prepared according to previously published
(fwhh = 28 Hz), −2.09 (fwhh = 432 Hz). UV−vis (CH
2
Cl
(0.019 g, 0.017 mol),
N]NO (0.005 g, 0.018 mol).
H NMR (400 MHz, CDCl ): δ 23.98 (fwhh = 1252 Hz), 8.91 (fwhh
3
2
): 538 nm.
1+
n
1+
procedures. Tetrabutylammonium nitrite and nitrate were purchased
from Sigma-Aldrich and stored in the drybox over P O . 5,10,15,20-
Tetraphenyl-21H,23H-porphinecobalt(II) (CoTPP), silver triflate,
(3) 6-V
6
O
6
+ [ Bu N]NO . 6-V O
4 2 6 6
n
CoTPP (0.012 g, 0.018 mol), and [ Bu
2
5
4
2
1
and cobaltocene (CoCp ) were purchased from Sigma-Aldrich and
= 20 Hz), 8.17 (fwhh = 528 Hz), 7.74 (fwhh = 24 Hz), −1.64 (fwhh
2
used as received.
= 328 Hz). UV−vis (CH Cl ): 538 nm.
2
2
1
1−
All H NMR spectra were recorded at 400 MHz on a Bruker DPX-
00 MHz spectrometer locked on the signal of deuterated solvents.
Nitrite Reduction with [CoCp ][V O (OC H ) ] (1-V O ). In
2 6 6 2 5 12 6 6
1
−
4
a glovebox, a 20 mL scintillation vial was charged with 1-V O
6 6
n
All chemical shifts were reported relative to the peak of a residual H
(0.010 g, 0.009 mmol) and 8 mL of tetrahydrofuran. [ Bu N]NO
4 2
signal in deuterated solvents. Acetonitrile (CD CN) and chloroform
(0.003 g, 0.009 mmol, 1 equiv) was added to the solution as a solid.
3
(
CDCl ) were purchased from Cambridge Isotope Laboratories,
The reaction mixture was stirred for 30 min at 21 °C, after which the
3
2
−
degassed by three freeze−pump−thaw cycles, and stored in the
drybox over activated 3 Å molecular sieves. IR (Fourier transform and
attenuated total relectance) spectra of complexes were recorded on a
Shimadzu IRAffinity-1 Fourier transform infrared spectrophotometer
volatiles were removed under vacuum to yield a mixture of 2-V O
6 7
1
−
1
and 3-V O NO . H NMR (400 MHz, CD CN): δ 26.47 (2-
V O ; fwhh = 928 Hz), 16.10 (3-V O NO ; fwhh = 352 Hz), 5.66
6
6
3
2
−
1−
6
7
6
6
(fwhh = 56 Hz), 3.06 (fwhh = 68 Hz), 1.58, 1.33, 0.96, −0.20 (3-
−
1
1−
2−
and are reported in wavenumbers (cm ). Electronic absorption
measurements were recorded at room temperature in anhydrous
V O NO ; fwhh = 132 Hz), −2.05 (2-V O ; fwhh = 260 Hz). FT-
6
6
6
7
−1
IR (ATR, cm ): 1053 (O−C H ), 932 (VO). UV−vis (CH Cl ):
2
5
2
2
G
Inorg. Chem. XXXX, XXX, XXX−XXX
Petel, Brittney E.
