Inorganic Chemistry
Article
1, 2a, 2b, 2d, and 2e (Scheme 1) and Ph3CSNO were synthesized
according to literature procedures.6a,11,13 All organic chemicals were
purchased from Sigma-Aldrich and used as received. Metal salts were
purchased from Strem Chemicals and used as received.
for X-ray diffraction studies were grown by vapor diffusion of diethyl
ether into an acetonitrile solution of 2c. The 1H NMR spectrum
matched that previously published.19 1H NMR (600 MHz, CD3CN, δ
ppm): 8.25 (5-H), 7.13 (2′-H), 6.83 (3′-H), 5.05 (br, 2-H), 3.90 (4-
Me), 3.87 (6-Me), 2.24 (4′-Me). Anal. Calcd for C95H87Fe4N3P2S13O:
C, 58.37; H, 4.31; N, 2.06. Found: C, 58.34; H, 4.47; N, 1.82. ESI-MS
(MeCN, m/z): 339.2 ([Ph4P]+, calcd 339.1), 1678.7 ([M − Ph4P]−,
calcd 1678.9), 669.6 ([M − 2(Ph4P)]2−, calcd 669.4). FTIR (KBr,
cm−1): 2906 (w), 2055 (s, νazide), 1585 (w), 1488 (w), 1435 (s), 1377
(w), 1336 (w), 1258 (w), 1185 (w), 1107 (s), 1079 (s), 1028 (w), 996
(w), 954 (w), 872 (w), 801 (w), 751 (w), 722 (s), 688 (s), 526 (s).
Synthesis of (Ph4P)2[Fe4S4(LS3)(S2CNEt2)], 2f. In a 25 mL
Erlenmeyer flask, 1 (104.6 mg, 52 μmol) and NaS2CNEt2 (10.0 mg,
58.4 μmol) were combined. The solid mixture was dissolved in
acetonitrile (8 mL) and stirred. After 4 h, the crude reaction solution
was filtered through glass microfiber filter paper into a 125 mL
Erlenmeyer flask. The filtrate was stripped to dryness and redissolved
in acetonitrile (3 mL). The solution was layered with diethyl ether
(120 mL) and placed in a −30 °C freezer overnight to afford a
precipitate, which was collected on an F-grade frit and washed with
diethyl ether (3 × 10 mL) to yield 83.8 mg (38.9 μmol, 74.8%) of
black microcrystalline material. Crystals suitable for X-ray diffraction
studies were grown by vapor diffusion of diethyl ether into a N,N-
Physical Measurements. NMR spectra were recorded on a
Bruker Avance spectrometer operating at 600 MHz at ambient
temperature and referenced to residual signals in the deuterated
solvent. Low-resolution electrospray ionization mass spectrometry
(ESI-MS) spectra were obtained with an Agilent 1100 series LC/MSD
mass spectrometer using degassed acetonitrile as the carrier solvent.
FTIR spectra were recorded on a Thermo Nicolet Avatar 360
spectrometer running the OMNIC software package; solid samples
were pressed into KBr disks, and solution samples were prepared in an
airtight Graseby-Specac solution cell with CaF2 windows and 0.1 mm
spacers. In situ IR spectra were recorded on a ReactIR iC 10
instrument from Mettler Toledo equipped with a 1-in.-diameter, 30-
reflection silicon ATR (SiComp) probe. In a typical experiment, the
instrument was blanked with CH2Cl2 and the sample, at concen-
trations ranging from 15 to 30 mM. At the first data collection time
point, NO(g) or a 30 mM CH2Cl2 solution of Ph3CSNO was added to
the anaerobic sample compartment through a rubber septum via a
gastight syringe. Samples for 57Fe Mossbauer studies were prepared by
̈
grinding a solid sample with Apiezon-N grease. These 57Fe Mossbauer
̈
1
samples were placed in an 80 K cryostat during measurement. A 57Co/
Rh source was moved at a constant acceleration at room temperature
against the absorber sample. All isomer shift (δ) and quadrupole
splitting (ΔEQ) values are reported with respect to 57Fe-enriched
metallic iron foil that was used for velocity calibration. The displayed
spectrum was folded to enhance the signal-to-noise ratio. Fits of the
data were calculated by the WMOSS plot-and-fit program, version
2.5.14 Samples for EPR data were prepared in 2-methyltetrahydrofuran.
X-band EPR spectra were recorded on a Bruker EMX EPR
spectrometer at ambient or liquid-nitrogen temperature using a quartz
finger dewar. Electrochemical measurements were performed at
ambient temperature in a glovebox on a VersaSTAT3 Princeton
Applied Research potentiostat running the V3-Studio electrochemical
analysis software. A three-electrode setup was employed comprising a
glassy carbon working electrode, a platinum wire auxiliary electrode,
and a Ag(s)/Ag+(s) silver wire pseudoreference electrode. Triply
recrystallized (Bu4N)PF6 was used as the supporting electrolyte. All
electrochemical data were referenced internally to the Fc/Fc+ couple at
0.00 V.
dimethylformamide solution of 2f. The H NMR spectrum matched
the published one.11c 1H NMR (600 MHz, CD3CN, δ ppm): 8.26 (5-
H), 7.20 (2′-H), 7.01 (CH2), 6.74 (3′-H), 4.89 (br, 2-H), 3.88 (6-Me),
3.64 (4-Me), 2.27 (4′-Me), 1.27 (CH3). Anal. Calcd for
C104H95Fe4NP2S15·2Et2O: C, 59.17; H, 5.10; N, 0.62. Found: C,
59.42; H, 5.15; N, 0.53. ESI-MS (MeCN, m/z): 339.4 ([Ph4P]+, calcd
339.1), 1446.0 ([M − 2(Ph4P)]−, calcd 1445.8). FTIR (KBr, cm−1):
2908 (w), 1585 (w), 1524 (w), 1483 (s), 1435 (s), 1375 (w), 1354
(w), 1266 (w), 1210 (w), 1139 (w), 1107 (s), 1078 (s), 1014 (w), 996
(w), 955 (w), 800 (w), 752 (w), 722 (s), 688 (s), 506 (s). 57Fe
Mossbauer (80 K, δ mm/s, ΔE mm/s, Γ mm/s, area %): (site 1)
̈
Q
0.71(2), 2.06(2), 0.31(2), 20; (site 2) 0.46(2), 1.12(2), 0.34(2), 80.
NO(g) Reactions. In a 20 mL vial, 1 or 2a−2f (20.8 μmol) was
dissolved in methylene chloride (6 mL), and the vial was sealed with a
rubber septum. A total of 1 equiv of NO(g) (500 μL, 16.35 μmol) was
then injected via a gastight syringe into the reaction vial. The reaction
was stirred for 2 h and subsequently poured into pentane (120 mL)
and stirred for 10 min. The mixture was filtered over Celite, and the
residual solid was extracted with methylene chloride (50 mL). After
solvent removal, the remaining solid was characterized by ESI-MS and
CH2Cl2 solution FTIR. Formation of [Fe4S4(NO)4]−, 4, and
[Fe4S3(NO)7]−, RBA, was observed.
X-ray Data Collection and Structure Solution and Refine-
ment. Crystals of 2c·4MeCN·Et2O·0.5H2O, 2f·2.5Et2O, and
(Cp*2Fe)4 suitable for X-ray diffraction were mounted in Paratone
N oil and frozen under a nitrogen cold stream maintained at 100 K by
a KRYO-FLEX low-temperature apparatus. Data were collected on a
Bruker APEX CCD X-ray diffractometer with Mo Kα radiation (λ =
0.71073 Å) controlled by the APEX2 software package.15 Empirical
absorption corrections were calculated with SADABS.16 The structures
were solved by direct methods with refinement by full-matrix least
squares based on F2 using SHELXTL-97.17 All non-hydrogen atoms
were located and refined anisotropically. Hydrogen atoms were
assigned to idealized positions and given thermal parameters equal to
either 1.5 (methyl hydrogen atoms) or 1.2 (nonmethyl hydrogen
atoms) times the thermal parameters of the atoms to which they were
attached. Figures were generated using the Olex2 Graphical User
Interface.18 See Table 1 for crystallographic data and refinement
details.
Synthesis of (Ph4P)2[Fe4S4(LS3)N3], 2c. In a 25 mL Erlenmeyer
flask, 1 (47.2 mg, 23.5 μmol) and NaN3 (7.2 mg, 111 μmol) were
combined. The mixture were dissolved in acetonitrile (14 mL) and
then stirred at ambient temperature. After 18 h, the crude reaction
solution was filtered through glass microfiber filter paper into a 125
mL Erlenmeyer flask. The filtrate was stripped to dryness and the
resulting solid dissolved in acetonitrile (3 mL). The solution was
layered with diethyl ether (45 mL) and placed in a −30 °C freezer
overnight to afford a precipitate, which was collected on an F-grade frit
and washed with diethyl ether (3 × 10 mL) to yield 29.3 mg (14.5
μmol, 58.2%) of blue-black microcrystalline material. Crystals suitable
Ph3CSNO Reactions. In a 20 mL vial, 1 or 2a−2f (16.35 μmol)
were dissolved in methylene chloride (6 mL), and the vial was sealed
with a rubber septum. In a 5 mL vial, 1, 2, 4, or 8 equiv of Ph3CSNO
(16.35, 32.7, 65.4, and 130.8 μmol, respectively) was dissolved in
methylene chloride (5 mL) and instantly injected via syringe into the
reaction vial. Throughout the course of the reaction, 40−60 μL
aliquots were taken to monitor the reaction by solution IR. After no
further growth of the bands in the region between 1600 and 1850
cm−1 was observed (2−6 h), the reaction mixture was poured into
pentane (120 mL) and stirred for 10 min. The mixture was filtered
over Celite. The filtrate was analyzed by gas chromatography−mass
spectrometry (GC−MS) to reveal the formation of (Ph3CS)2 and by
1H NMR spectroscopy in CD3CN to show the presence of the LS3
ligand. The solid remaining on the Celite was extracted with
methylene chloride (50 mL). After solvent removal, the remaining
solid was characterized by ESI-MS, Mossbauer, CH Cl solution FTIR,
̈
2
2
and KBr solid-state FTIR. If up to 4 equiv of Ph3CSNO were used, the
isolated nitrosated product was 4. When 8 equiv of Ph3CSNO were
used, the isolated product was RBA.
Synthesis of [(C5Me5)2Fe][Fe4S4(NO)4], (Cp*2Fe)[4]. In a 20 mL
vial, 1 (32.9 mg, 16.4 μmol) and TlPF6 (28.4 mg, 81.3 μmol) were
dissolved in methylene chloride (6 mL). The reaction vial was sealed
with a septum. In a 5 mL vial, Ph3CSNO (20.0 mg, 65.4 μmol) was
dissolved in methylene chloride (5 mL) and instantly injected via
syringe into the reaction vial. After 2 h, the reaction mixture was
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dx.doi.org/10.1021/ic500586g | Inorg. Chem. 2014, 53, 5311−5320