Organometallics
Article
acrylonitrile. After 24 h, the resulting solution was evaporated to
dryness at reduced pressure. The residue was washed with diethyl
ether three times and dried under vacuum. Complex 1b (0.31 g, 0.35
mmol) was obtained as a brown crystalline powder in 90% yield. The
crystals of 1b, suitable for X-ray analysis, were obtained by a saturated
acetone solution layered with diethyl ether: 1H NMR (400 MHz,
CD2Cl2) δ 5.756−6.106 (m, 6H), 2.950 (q, 4H), 1.970 (t, 6H), 1.454
(s, 30H); IR (film; cm−1) 2963, 2924, 2241, 1381, 1055, 838, 557.
Anal. Calcd for C30H46F12Fe2N2P2S2: C, 40.02; H, 5.15; N, 3.11; S,
7.12. Found: C, 40.07; H, 5.21; N, 3.09; S, 7.07. Analogous complexes
1c−1l were obtained similarly in 80−90% yields. The spectra of these
complexes are shown in the Supporting Information.
does not originate from the solvent. These results indicate that
the proton source and oxygen source of the μ-amidate-N,O
bridge stem from the water ligand.
CONCLUSION
■
In summary, thiolate-bridged diiron complex [Cp*Fe(μ-
SEt)MeCN]2[PF6]2 (1a) reacted readily with different nitriles,
yielding [Cp*Fe(μ-SEt)RCN]2[PF6]2 (1). Complexes 1 can
realize the hydration of the nitrile ligand in ambient conditions.
Simultaneously, [Cp*Fe(μ-SEt)2(μ-η1:η1-NH(O)CR)FeCp*]-
[PF6] (2) were successfully isolated as intermediates during the
hydration process. Treatment of 2 with HBF4·Et2O in the
presence of nitriles delivered corresponding amides 3. At the
same time, the structural features of the [Fe2S2] scaffold were
retained. These results indicated that the hydration of nitriles
was accomplished by cooperative interaction on diiron centers.
Further studies on the catalytic hydration of nitriles and
activation of other small molecules at diiron sites are underway.
[Cp*Fe(μ-SEt)2(μ-η1:η1-NH(O)CR)FeCp*][PF6] (2a, R = Me). A
solution of 1a (0.317 g, 0.36 mmol) in acetone/water (8 mL/2 mL) at
room temperature was treated with 1 equiv if Et3N (52 μL, 0.36
mmol). After 2 h, the resulting yellow-green solution was evaporated
to dryness at reduced pressure. The residue was washed with 5 mL of
diethyl ether and extracted with dichloromethane to obtain a yellow-
green solution of 2a. Green crystalline powder 2a (0.245 g, 0.32 mmol,
89%) was isolated after the dichloromethane was removed in vacuo.
The crystals of 2a, suitable for X-ray analysis, were obtained by a
saturated dichloromethane solution layered with diethyl ether: 1H
NMR (400 MHz, CD2Cl2) δ 1.890 (t, 6H), 1.751 (q, 4H), 1.420 (s,
15H), 1.341 (s, 3H), 1.310 (s, 15H), the proton signal of N−H group
was not detected; IR (film; cm−1) 3365, 2964, 2927, 1731, 1561, 1471,
1226, 1023, 842, 557; ESI-HRMS calcd for [2a − PF6]+ 562.1564;
found 562.1567. Anal. Calcd for C26H44F6Fe2NOPS2: C, 44.14; H,
6.27; O, 2.26; N, 1.98; S, 9.07. Found: C, 44.19; H, 6.22; O, 2.32; N,
1.92; S, 9.02. According to the same procedure, 2b−2l were also
obtained in 70−93% yields. The spectra of these complexes are shown
in the Supporting Information.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were routinely carried out
under an argon atmosphere, using standard Schlenk-line techniques.
All organic solvents and Et3N were dried and distilled over an
appropriate drying agent under argon. Complex [Cp*Fe(μ-SEt)-
MeCN]2[PF6]2 was prepared according to the literature.9d NH4PF6
(Aldrich), organonitriles (Aldrich), and HBF4·Et2O (Aldrich) were
used without further purification.
Spectroscopic Measurements. The 1H NMR spectra were
recorded on a Bruker 400 Ultra Shield spectrometer. Infrared spectra
were recorded on a NEXVSTM FT-IR spectrometer. Elemental
analyses were performed on a Vario EL analyzer. ESI-MS were
recorded on a UPLC/Q-ToF microspectrometer. The UV−vis
absorption spectra measurement was performed on a PerkinElmer
Lambda 35 spectrophotometer.
Chromatographic Conditions. HPLC separation was achieved
on an ACCELA high-performance liquid chromatograph (HPLC)
system, which consisted of an ACCELA 1250 pump and an ACCELA
autosampler. A Click Mal column (150 mm × 4.6 mm i.d., 5 μm,
Acchrom Co. Ltd., China) was used in the experiment with the mobile
phase of 95/5 (v/v) acetonitrile/CH3COONH4 (5 mM). Eluent flow
rate was set at 200 μL/min, and the column was kept at ambient
temperature. The injection volume was 1 μL.
Mass Spectrometry. Product monitoring was achieved using a
TSQ Quantum Ultra mass spectrometer (Thermo Scientific, San Jose,
CA) equipped with a heated electrospray ionization source (HESI).
Optimization of the precursor ion, product ion, and collision energy
was carried out via direct injection of the urea standard solution at a
flow rate of 10 μL/min into the mass spectrometer. The instrument
was operated in positive ionization mode and selective reaction
monitoring with m/z between 61.2 and 44.5, CE of 17, and T lens of
63. The MS source conditions were as follows: capillary voltage of
3000 V, vaporizer temperature of 250 °C, capillary temperature of 300
°C, sheath gas pressure of 35, and aux gas pressure of 10. Xcalibur 2.2
software (Thermo) was used for instrument control, data acquisition,
and processing.
X-ray Crystallography. The data for complexes 1b, 1g, 2a, 2b,
and 2e were obtained on a Bruker SMART APEX CCD diffractometer
with graphite monochromated Mo Kα radiation (λ = 0.71073 Å).
Empirical absorption corrections were performed using the SADABS
program.19 Structures were solved by direct methods and refined by
full-matrix least-squares based on all data using F2 using SHELX97.20
Anisotropic thermal displacement coefficients were determined for all
non-hydrogen atoms. Hydrogen atoms were placed at idealized
positions and refined with fixed isotropic displacement parameters.
[Cp*Fe(μ-SEt)RCN]2[PF6]2 (1b, R = CHCH2). A solution of
complex [Cp*Fe(μ-SEt)MeCN]2[PF6]2 (1a, 0.33 g, 0.39 mmol) in 10
mL of acetone at room temperature was treated with 10 equiv of
[Cp*2Fe2(μ-SEt)2(μ-η1:η1-NDC(O)Me)][PF6] (2a-D). Using a
procedure similar to that used for 2a, 2a-D was synthesized using
D2O: yield 88%; ESI-HRMS calcd for [2a-D − PF6]+ 563.1595; found
563.1605. Anal. Calcd for C26H43DF6Fe2NOPS2: C, 44.08; H, 6.40; O,
2.26; N, 1.98; S, 9.05. Found: C, 44.15; H, 6.45; O, 2.20; N, 1.92; S,
9.15.
[Cp*2Fe2(μ-SEt)2(μ-η1:η1-NHC(18O)Me)][PF6] (2a-18O). Using a
procedure similar to that used for 2a, 2a-18O was synthesized using
H218O: yield 87%; ESI-HRMS calcd for [2a-18O − PF6]+ 564.1606;
found 564.1605. Anal. Calcd for C26H44F6Fe2N18OPS2: C, 44.02; H,
6.25; O, 2.54; N, 1.97; S, 9.04. Found: C, 44.14; H, 6.36; O, 2.44; N,
1.93; S, 9.13.
Reaction of 2a with HBF4·Et2O in the Presence of
Acetonitrile. To a stirred solution of 2a (0.153 g, 0.2 mmol) in 2
mL of acetone were added HBF4·Et2O (40.0 μL, 0.2 mmol) and
acetonitrile (0.6 mmol) at ambient temperature via a microsyringe,
followed by stirring for 2 h. The resulting brown solution was
evaporated to dryness at reduced pressure. The dark-brown residue
was extracted with Et2O to obtain a brown crystalline powder
[Cp*Fe(μ-SEt)RCN]2[PF6][BF4] (1a′, R = Me) in 90% yield. After
the solvent was removed in vacuo, the white solid acetamide (3a) was
obtained in 87% yield. Analytically pure acetamides 3b and 3d−3l
were also obtained in 74−91% yields. 3a: 1H NMR (400 MHz,
CDCl3) δ 6.281 (br, 1H), 6.111 (br, 1H), 2.010 (s, 3H). Anal. Calcd
for C2H5NO: C, 40.67; H, 8.53; N, 23.71; O, 27.09. Found: C, 40.75;
H, 8.59; N, 23.78; O, 27.18. 3b: 1H NMR (400 MHz, CDCl3) δ 6.321
(d, 1H), 6.242 (d, 1H), 5.817 (m, 1H). Anal. Calcd for C3H5NO: C,
40.67; H, 8.53; N, 23.71; O, 27.09. Found: C, 40.75; H, 8.59; N, 23.78;
O, 27.16. 3c: Anal. Calcd for CH4N2O: C, 20.00; H, 6.71; N, 46.65; O,
1
26.64. Found: C, 20.10; H, 6.78; N, 46.72; O, 26.72. 3d: H NMR
(400 MHz, CDCl3) δ 6.913 (br, 2H), 3.064 (br, 6H). Anal. Calcd for
C3H8N2O: C, 40.90; H, 9.15; N, 31.79; O, 18.16. Found: C, 40.97; H,
1
9.21; N, 31.87; O, 18.22. 3e: H NMR (400 MHz, CDCl3) δ 5.991
(br, 2H), 3.404 (q, 4H), 1.254 (t, 6H). Anal. Calcd for C5H12N2O: C,
51.70; H, 10.41; N, 24.12; O, 13.77. Found: C, 51.76; H, 10.48; N,
1
24.18; O, 13.85. 3f: H NMR (400 MHz, CDCl3) δ 7.220−7.360 (m,
10H), 5.580 (br, 2H), 4.460 (s, 4H). Anal. Calcd for C15H16N2O: C,
74.97; H, 6.71; N, 11.66; O, 6.66. Found: C, 74.91; H, 6.77; N, 11.60;
1
O, 6.62. 3g: H NMR (400 MHz, CDCl3) δ 7.816 (d, 2H), 7.530 (t,
3575
Organometallics 2015, 34, 3571−3576