Inorganic Chemistry
Forum Article
9
{
{
Fe(NO) } dinuclear DNIC 1 with THF bound to the
the addition of 5 equiv of NO and 14.3 ± 4.5 and 84.0 ± 8.1% yields
2
9
28b
for the addition of 10 equiv of NO), respectively. The headspace gas
Fe(NO) } unit with an EPR g value of 2.013 (THF). It is
2
−
1
9
detected by GC and IR vN−N 2223 cm (THF) was characterized as
presumed that the {Fe(NO) } unit of DNIC 1 serves as an
electron-buffering reservoir to accommodate electron redis-
tribution, and the {Fe(NO) } unit acts as an electron-transfer
channel to drive exogeneous ·NO coordination. In addition,
the regeneration of DNIC 1 through synthesis cycle (complex
→ 3 → 4 → 5 → 1), and alternatively, through synthesis
2
N O. On the basis of the IR spectrum (v 1762 m, 1701 s, 1682 sh,
2
NO
−
1
10
1650 s cm ) of complex 1, it cannot be ruled out that a trace of
residual complex 1 remained in the reaction solution. Attempts to
isolate the trace of residual complex 1 were not successful. However,
ESI-MS results show the presence of thermodynamically stable
complex [Fe (NO) (μ-bdmap) ]. Alternatively, complex 1 (0.225 g,
2
1
2
4
2
2
cycle (complex 1 → 2 → 5 → 1), modulated by the key κ -
0.5 mmol), potassium nitrite (43 mg, 0.5 mmol), and ferrocenium
−
N,O-[NO] -bridged intermediate A, highlights that species A
hexafluorophosphate ([Cp Fe][PF ]) (165 mg, 0.5 mmol) prepared
2
6
acts as a relay intermediate for NO reduction to N O via both
the hyponitrite formation pathway and the NO disproportio-
nation pathway (Scheme 2).
in a Schlenk tube were added to THF (5 mL) at 0 °C, leading to the
formation of complex 3 (0.179 g, 85%). The THF solution of
complex 3 layered with n-hexane (10 mL) was kept at −20 °C for 1
week, leading to dark-brown crystals suitable for X-ray crystallog-
2
−
1
raphy. IR ν 1759 s, 1694 s cm (THF); 1763 sh, 1751 s, 1677 s
NO
EXPERIMENTAL SECTION
Manipulations, reactions, and transfers were conducted under a pure
nitrogen atmosphere according to Schlenk techniques or in a glovebox
−1
■
cm (KBr). The EPR spectrum shows an isotropic signal of g = 2.020
(solid) at 77 K. Absorption spectrum (THF) [λmax, nm (ε, M
−
1
−
1
cm )]: 535 (417), 615 (294), 760 (226) at 30 °C; 790 (261) at −80
(
N atmosphere). Solvents were purified and distilled under nitrogen
2
°C. Magnetic susceptibility (solid state (2−300 K): μ = 2.75 (300
B
−
1
by utilizing suitable reagents (acetonitrile from CaH −P O ; diethyl
K), μ = 0.53 (2 K), and calcd for g = 2.030 and J = −45.3 ± 0.5 cm
2
2
5
B
ether/n-hexane/tetrahydrofuran (THF) from sodium benzophenone)
(antiferromagnetically coupled). Anal. Calcd. for C H Fe N O : C,
7 17 2 7 7
and stored in dried, N -filled flasks over 4 Å molecular sieves.
19.88; H, 4.05; N, 23.18. Found: C, 20.12; H, 3.96; N, 22.92.
2
Reagents 1,3-bis(dimethylamino)-2-propanol (Hbdmap) (97%
Quantification of Released N O upon Complex 1 Reacted
2
(
(
Sigma-Aldrich)), triflate acid, ferrocenium hexafluorophosphate
with Various Amounts of NO. N O was quantified on a Shimadzu
2
[Cp Fe][PF ]) (Sigma-Aldrich), and bis(triphenylphosphoranyl-
GC-2030 gas chromatography equipped with a BID detector and
ShinCarbon ST (100/120 mesh) columns filled with poly(dimethyl)-
siloxane (Rtx-1). Helium was adopted as a carrier gas to conduct
sample separation. The oven temperature was kept at 40 °C and then
increased to 240 °C (rate 20 °C/min), and the detector was heated to
2
6
idene)ammonium chloride ([PPN][Cl], Fluka) were used as received.
Complexes [Fe(CO) (NO) ] and {[Fe(NO) ] (μ-bdmap) } (bdmap
2
2
2
2
2
=
1,3-bis(dimethylamino)-2-propanoate) were synthesized on the
28b
basis of previous reports. Nitric oxide gas (10% NO + 90% N ) was
2
purified by passage through a column of Ascarite (8−20 mesh)
purchased from Sigma. Infrared spectra (IR) were recorded on a
PerkinElmer-Frontier with sealed solution cells (0.1 mm, KBr
windows). UV−vis spectra were recorded on an Agilent 8453
2
80 °C. The identification and quantification of N O were achieved
2
by utilizing a gastight syringe to acquire 0.1 mL of sample headspace
28b,35,77
gas and injected into GC.
The calibration curves were derived
by the injection of various amounts of NO ((10% NO + 90% N ; 2.2,
2
spectrophotometer equipped with an UNICOKU liquid N cryostat.
2
4.5, 6.8, 11.2, and 22.4 mL) and pure N O (0.10, 0.15, 0.20, 0.30, and
2
1
H NMR spectra were obtained on a Varian Unity-500 MHz
0.50 mL) into a vial (65 mL) containing 2 mL of THF. The
spectrometer. N O quantification was performed on a Shimadzu GC-
2
calibration curve was plotted in Figure S2. Quantification of the
2
030 gas chromatograph equipped with a barrier-discharge ionization
released N O is based on gas chromatography with a retention time of
2
detector (BID). Analyses of carbon, hydrogen, and nitrogen were
obtained with a CHN analyzer (Elementar Vario EL III CHN-OS
Rapid).
8.14 min. Each vial (65 mL) containing THF solution (2 mL) of
complex 1 (4.5 mg, 0.01 mmol) was added to 1 equiv of NO(g) (2.2
mL, (10% NO + 90%N )), 2 equiv of NO (4.5 mL), 3 equiv of NO
2
Preparation of [Fe(NO) (μ-bdmap)Fe(NO) (THF)] (1). Freshly
2
2
(6.8 mL), 5 equiv of NO (11.2 mL), and 10 equiv of NO (22.4 mL),
individually. The reaction solution was stirred for 3 h, and then the
prepared complex [Fe(NO) (μ-bdmap)Fe(NO) (THF)] (1) was
2
2
2
8b
synthesized according to published procedures.
701 s, 1682 sh, 1650 s cm (THF); 1749 s, 1676 s, 1659 s, 1636 s
cm (KBr). Absorption spectrum (THF) [λmax, nm (ε, M cm )]:
40 (1090), 755 (1650). EPR spectra show an isotropic signal with g
2.013 (THF) and g = 2.016 (solid) at 77 K, respectively. The THF
solution of complex 1 layered with n-hexane (10 mL) was kept at −20
C for 1 week, leading to dark-green crystals of [Fe(NO) (μ-
IR νNO 1762 m,
headspace gas (0.1 mL) was injected into the GC for N O detection.
−
1
2
1
The average amounts of generated N O are displayed in Figure 1b
−
1
−1
−1
2
with yields of 23.2 ± 3.54% (injection of 1 equiv of NO), 46.7 ± 9.0%
5
=
(injection of 2 equiv of NO), 75.8 ± 11.8% (injection of 3 equiv of
NO), 84.5 ± 7.2% (injection of 5 equiv of NO), and 87.5 ± 3.5%
(
injection of 10 equiv of NO) of N O.
2
°
2
Preparation of [Fe (NO) (μ-bdmap)(μ-OCH )] (4) Derived
2
4
3
bdmap)Fe(NO) ] characterized by single-crystal X-ray diffraction, as
2
from the Reaction of Complex 3 and Sodium Methoxide.
shown in Figure 5a.
Complex 3 (84 mg, 0.2 mmol) and [Na][OMe] (10.8 mg, 0.2 mmol)
were added to a Schlenk tube containing 3 mL of THF under an N2
atmosphere and stirred for 2 h. The resulting brown solution was
4
Preparation of {[Fe (NO) (μ-bdmap)] (κ -N O )} (2). Complex
2
4
2
2
2
4
{
[Fe (NO) (μ-bdmap)] (κ -N O )} (2) was synthesized according
2
4
2
2
2
2
8b
to the published procedures.
IR 1744 s, 1721 s, 1669 s, 1644 s
filtered through Celite to remove the insoluble solid (NaNO ), and
2
−
−1
2
(νNO), 1087 s (νN−O ([N O ] )) cm (KBr).
2
2
the brown filtrate was then dried under vacuum to obtain bright-
brown solid [Fe (NO) (μ-bdmap)(μ-OCH )] (4) (isolated yield 72
Addition of Various Quantities of NO(g) to a THF Solution
2
4
3
of Complex 1 Yielding Complex 2 and [Fe (NO) (μ-bdmap)(μ-
2
4
mg (88.2%)). The residual (NaNO ) was extracted with anaerobic
NO )] (3) along with N O. Nitric oxide (74 mL (NO 10% + N
2
2
2
2
water and was quantified by a Griess test (yield 74.2%). The THF
solution of complex 4 was layered with n-hexane (15 mL) at −20 °C
for 1 week to produce dark-brown crystals suitable for X-ray
9
0%), 0.3 mmol) was injected into the freshly prepared THF solution
(
2 mL) of complex 1 (45 mg (0.1 mmol) stored in a 65 mL vial) by
syringe, and the mixture solution was stirred for 3 h at ambient
temperature. The mixture solution was then filtered to collect
insoluble complex 2 (7.9 mg, yield 19.3 ± 8.7% based on complex 1),
and the brown filtrate was then dried under vacuum to obtain dark-
brown solid [Fe (NO) (μ-bdmap)(μ-NO )] (3) (32.2 mg, 76.2 ±
−
1
crystallography. IR ν 1743 sh, 1730 s, 1668 s cm (THF); 1716
NO
−
1
−1
s, 1637 s cm (KBr). Absorption spectrum (THF) [λmax, nm (ε, M
cm )]: 548 (430), 620 (300), and 825 (216). The EPR spectrum
−
1
shows an isotropic signal with g = 2.036 (solid) at 77 K. Magnetic
2
4
2
10.2% based on complex 1). In a similar fashion, upon addition of 1
susceptibility (solid state (2−300 K): μ
K)) and calcd for g = 2.035 and J = −172.57 ± 4.87 cm
(antiferromagnetically coupled). Anal. Calcd. for C H Fe N O : C,
B B
= 2.23 (300 K), μ = 0.89 (2
−
1
equiv of NO to complex 1, complexes 2 and 3 were obtained in yields
of 71.8 ± 7.7 and 25.4 ± 6.9% (47.0 ± 9.1 and 48.6 ± 9.7% yields for
the addition of 2 equiv of NO; 14.7 ± 6.3 and 82.7 ± 9.8% yields for
8
20
2
6
6
23.55; H, 4.94; N, 20.60. Found: C, 23.85; H, 4.97; N, 19.98.
K
Inorg. Chem. XXXX, XXX, XXX−XXX
Wu, Wun-Yan
