A R T I C L E S
Hsieh and Darensbourg
with molecular sieves under N2 before experiments. The known
complex Fe(CO)2(NO)2 and the NO trapping agent [(bme-dach)Fe]2
were synthesized using published procedures.25,35 The following
materials were reagent-grade and used as purchased from Sigma-
Aldrich: sodium thiophenolate, sodium tert-butoxide, 1,3-bis(2,4,6-
trimethylphenyl)imidazolium chloride, nitrosyl tetrafluoroborate, and
tri-p-tolylphosphine.
N2. The resulting solution was stirried for 30 min and then added
by cannula under a positive pressure of N2 at ambient temperature
to a freshly prepared THF solution of Fe(CO)2(NO)2 (0.50 mmol).35
The mixture was stirred for an additional 1 h and monitored by IR
spectroscopy to confirm completion of the reaction. The solution
was filtered through Celite to remove precipitated NaCl and dried
under vacuum to yield spectroscopically pure product 2 (yield:
0.21 g, 92%). Dark-brown crystals suitable for X-ray analysis were
grown by slow evaporation of a diethyl ether solution of complex
2 at -35 °C. IR (THF, cm-1): ν(CO) 1986 (s); ν(NO) 1744 (s),
1702 (vs). 1H NMR (CD3CN): δ 7.41 (s, NCH), 7.06 (s, m-CH3 of
Mes), 2.32 (s, p-CH3), 2.04 (s, o-CH3). Anal. Found (Calcd for
C22H24FeN4O3): C, 58.74 (59.09); H, 5.72 (5.77); N, 13.15 (13.32).
Synthesis of [(IMes)Fe(NO)3][BF4] (1). A diethyl ether solution
of complex 2 (0.23 g, 0.50 mmol), freshly prepared as described
above, was transferred by cannula to a 50 mL Schlenk flask loaded
with [NO]BF4 (0.058 g, 0.50 mmol) at ambient temperature. The
heterogeneous mixture was stirred overnight at RT and filtered to
remove the solution from the precipitate. The green solid thus
obtained was dissolved in THF; its IR spectrum indicated the
formation of complex 1. The green solid was washed successively
with pentane (3 × 10 mL) to further remove impurities (yield:
0.19 g, 72%). Recrystallization in THF/pentane at -35 °C afforded
crystals of complex 1 suitable for X-ray crystallographic study. IR
(THF, cm-1): ν(NO) 1932 (s), 1831 (s), 1804 (vs). ATR-IR (solid,
1
Physical Measurements. H NMR spectra were measured on a
Unity+ 300 MHz superconducting NMR instrument. Solution IR
spectra were recorded on a Bruker Tensor 27 FTIR spectrometer using
0.1 mm KBr sealed cells. All of the electrochemical analyses were
done using a Bioanalytical Systems 100 electrochemical workstation
with a glassy carbon working electrode and a platinum wire auxiliary
electrode. All voltammograms were obtained using a standard three-
electrode cell under an Ar atmosphere at room temperature. All samples
in THF were run at a concentration of 2 mM with [n-Bu4N][BF4] as
the supporting electrolyte (100 mM), and potentials are reported relative
to the Fc/Fc+ couple as 0.00 V. The rest potential for complex 1 was
found to be +0.056 V. Elemental analyses were performed by Atlantic
Microlab, Inc. (Norcross, GA).
X-band EPR measurements were performed using a Bruker EMX
spectrometer equipped with an ER4102ST cavity and an Oxford
Instruments ESR900 cryostat. The microwave frequency was
measured with a Hewlett-Packard 5352B electronic counter. X-band
spectra of complex 3 in THF solution were collected with
microwave powers of 0.2012 and 0.02012 mW and frequencies of
9.487 and 9.4730 GHz at 295 and 77 K, respectively, and a modu-
lation amplitude of 10 G at 100 kHz.
1
cm-1): ν(NO) 1916 (s), 1823 (vs), 1799 (vs). H NMR (CD3CN):
δ 7.42 (s, NCH), 7.20 (s, m-CH3 of Mes), 2.39 (s, p-CH3), 2.11(s,
o-CH3). Anal. Found (Calcd for C21H24BF4FeN5O3): C, 47.37
(47.31); H, 5.08 (4.87); N, 12.53 (12.20).
ESI-MS analysis was performed using an API QStar Pulsar, MDS
Sciex (Toronto, ON) quadrupole-TOF hybrid mass spectrometer. Gas
chromatography-mass spectrometry was performed on an Ultra Trace
GC attached to a DSQII quadruple mass spectrometer (Thermo
Electron Corporation (Austin, TX). The mass spectrometer was
operated in electron impact ionization mode at 70 eV electron energy.
X-ray Crystal Structure Analyses. A Bausch and Lomb 10×
microscope was used to identify suitable crystals of the same habit.
Each crystal was coated in paratone, affixed to a Nylon loop, and
placed under streaming nitrogen (110 K) in a Bruker SMART 1000
CCD or SMART Apex CCD diffractometer (for details, see the
CIFs in the Supporting Information). The space groups were
determined on the basis of systematic absences and intensity
statistics. The structures were solved by direct methods and refined
by full-matrix least-squares on F2. Anisotropic displacement pa-
rameters were determined for all non-hydrogen atoms. Hydrogen
atoms were placed at idealized positions and refined with fixed
isotropic displacement parameters. The following is a list of
programs used: data collection and cell refinement, SMART WNT/
2000, version 5.632,36 or APEX2;37 data reductions, SAINTPLUS,
version 6.63;38 absorption correction, SADABS;39 structural solu-
tions, SHELXS-97;40 structural refinement, SHELXL-97;41 graphics
and publication materials, Mercury, version 2.3.42
Synthesis of [(IMes)Fe(SPh)(NO)2] (3). Complex 1 (0.27 g, 0.50
mmol) was dissolved in 10 mL of THF, and the solution was cooled
to 0 °C. To this solution was added via cannula a precooled solution
of NaSPh (0.067 g, 0.50 mmol) in 10 mL of THF. The reaction
mixture was stirred at 0 °C for 5 min, after which IR monitoring
indicated that no starting material remained. The solution was
filtered through Celite and dried under vacuum to yield spectro-
scopically pure product 3 (yield: 0.23 g, 85%). Deep-purple crystals
suitable for X-ray analysis were grown by slow evaporation of a
diethyl ether solution of complex 3 at -35 °C. IR (THF, cm-1):
ν(NO) 1763 (s), 1715 (vs). Anal. Found (Calcd for C27H29FeN4O2S):
C, 61.87 (61.88); H, 5.21 (5.55); N, 11.40 (11.08).
NO Capture by the NO Trapping Agent upon Reaction of
Complex 1 and NaSPh. Inside the glovebox, solid complex 1 (0.11
g, 0.20 mmol) and NaSPh (0.027 g, 0.20 mmol) were put in a vial,
which was then placed in a larger tube containing a MeOH solution
(8 mL) of [(bme-dach)Fe]2 (0.055 g, 0.10 mmol). The tube was
capped with a well-sealed septum and cooled to 0 °C. THF solvent
was then added to the inner vial of the reaction mixture by syringe.
The reaction system was slowly warmed to room temperature and
stirred for 8 h. The outer MeOH solution was collected and the
solvent removed under vacuum. The residue was redissolved in 15
mL of CH2Cl2 and filtered through Celite. A band at 1647 (s) cm-1
indicated the formation of the complex (bme-dach)Fe(NO).26 The
green filtrate was concentrated to 5 mL under vacuum, and addition
of 30 mL of pentane resulted in the precipitation of the green solid
(bme-dach)Fe(NO) (yield: 0.05 g, 82%). The IR spectrum of the
contents of the inner vial showed ν(NO) bands at 1763 and 1715
cm-1, indicating the presence of complex 3.
Direct Mixing of Complex 1 and the NO Trapping Agent
without NaSPh. Complex 1 (0.11 g, 0.20 mmol) and [(bme-
dach)Fe]2 (0.055 g, 0.10 mmol) were loaded into a septum-sealed
50 mL Schlenk flask, and 10 mL THF solvent was added by syringe.
The reaction mixture was stirred for 10 min; its IR spectrum (THF
solution) contained ν(NO) bands at 1795 (s), 1763 (s), and 1740
(vs) cm-1 (Figure S9 in the Supporting Information). Addition of
diethyl ether to the THF solution yielded a dark-brown precipitate,
which was washed successively with diethyl ether (3 × 20 mL) to
further remove impurities (yield: 0.09 g, 87%). Recrystallization
in THF/pentane/diethyl ether at -35 °C afforded crystals of
Synthesis of [(IMes)Fe(CO)(NO)2] (2). 1,3-Bis(2,4,6-trimeth-
ylphenyl)imidazolium chloride (0.17 g, 0.50 mmol) and NaOtBu
(0.048 g, 0.50 mmol) were combined and dissolved in THF under
(35) McBride, D. W.; Stafford, S. L.; Stone, F. G. A. Inorg. Chem. 1962,
1, 386–388.
(36) SMART: Program for Data Collection on Area Detectors, version
5.632; Bruker AXS Inc.: Madison, WI, 2005.
(37) APEX2, version 2009.7-0; Bruker AXS Inc.: Madison, WI, 2007.
(38) SAINTPLUS: Program for Reduction of Area Detector Data, version
6.63; Bruker AXS Inc.: Madison, WI, 2007.
(39) Sheldrick, G. M. SADABS: Program for Absorption Correction of Area
Detector Frames; Bruker AXS Inc.: Madison, WI, 2001.
(40) Sheldrick, G. M. SHELXS-97: Program for Crystal Structure Solution;
Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
(41) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Refine-
ment; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
(42) Mercury: Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl.
Crystallogr. 2006, 39, 453–457.
9
14124 J. AM. CHEM. SOC. VOL. 132, NO. 40, 2010
Hsieh, Chung-Hung
