Inorganic Chemistry
Article
mmol), K2CO3 (0.35 g, 2.5 mmol), and KI (0.08 g, 0.5 mmol) in
CH3CN (35 mL) under a N2 atmosphere. The reaction mixture was
refluxed for 24 h. The resulting solution was filtered, and then the
filtrate was dried under vacuum. The crude solid was dissolved in a 10
M NaOH (20 mL) solution and then extracted with dichloromethane
(3 × 20 mL). The combined organic phase was dried over Na2SO4
and evaporated to dryness to yield a brown solid. Yield: 0.15 g (65%).
1H NMR (300 MHz, CDCl3, 298 K): δ 7.30 (t, 2H), 7.29−7.17 (m,
Synthesis of [(L3)FeII (OTf)6] (1T). Solid FeII(OTf)2·2CH3CN (0.44
3
g, 1.0 mmol) was added to a solution of the L3 ligand (0.41 g, 0.33
mmol) in dichloromethane (5 mL), and the mixture was vigorously
stirred for 12 h under an inert atmosphere. The resulting solution was
filtered, and then the filtrate was dried under vacuum. The crude solid
thus obtained was triturated with diethyl ether (5 mL) to obtain a
yellow solid. Yield: 0.44
g (58%). Anal. Cald. for
C87H96F18Fe3N12O18S6 (2298.31 g/mol): C, 45.44; H, 4.21; N,
7.31. Found: C, 45.12; H, 4.40; N, 6.87. IR (cm−1): 3406(br),
2361(m), 2339(m), 1606(m), 1578(w), 1464(m), 1283(vs),
1250(vs), 1167(s), 638(s), 517(m). 1H NMR (500 MHz, 298 K,
CDCl3): δ 63.3, 53.8, 51.1, 14.6, 11.9, 7.3, 3.7, 3.3, 2.2, 1.2, −28.8,
−56.9.
12H), 6.95 (d, 2H), 3.66 (s, 4H), 3.55 (s, 4H), 2.65 (s, 4H), 2.49 (s,
6H). ESI-MS (positive-ion mode, acetonitrile): m/z 451.28 ([M +
H]+), 473.27 ([M + Na]+).
Synthesis of N1,N1′-[1,4-Phenylenebis(methylene)]bis[N2-benzyl-
N1,N2-bis[(6-methylpyridin-2-yl)methyl]ethane-1,2-diamine] (L2).
To a mixture of LNH (0.36 g, 1.0 mmol), K2CO3 (0.70 g, 5.0
mmol), and KI (0.17 g, 1.0 mmol) in CH3CN (30 mL) was added
α,α′-dibromo-p-xylene (0.13 g, 0.5 mmol) under a N2 atmosphere.
The reaction mixture was refluxed for 48 h. The resulting solution was
filtered, and then the filtrate was dried under vacuum. The crude solid
was dissolved in a 10 M NaOH (20 mL) solution and then extracted
with dichloromethane (3 × 20 mL). The combined organic extract
was dried over Na2SO4 and evaporated to dryness to yield a brown
Catalytic Reactions. All experiments reported in this work were
performed in the presence of air. In a typical reaction, H2O2 (0.02
mmol, 10 equiv relative to iron in the catalyst; 30% aqueous solution
dissolved in 0.5 mL of CH3CN) was added at 298 K via a syringe
pump over 20 min to a vigorously stirred CH3CN solution (1.0 mL)
containing the iron catalyst (0.002 mmol) and substrate. In the
presence Sc(OTf)3, H2O2 (10 equiv) was slowly added for over a
period of 5 min at 273 K. The reaction mixture was stirred for another
15 min at 273 K and then 15 min at 298 K after the complete addition
of H2O2. At the end of the reaction, the organic products were
esterified by acetic anhydride (1.0 mL), together with 1-
methylimidazole (0.1 mL) for cyclohexane oxidation. After ester-
ification, the resulting solution was passed through a 15 cm silica
column (60−120 mesh size) using ethyl acetate/diethyl ether as the
eluent. The combined organic phase was then analyzed by GC−MS.
Quantification of the oxidized products was performed using standard
calibration curves with authentic compounds and naphthalene as the
standard. Naphthalene was added to the mixture after the reaction but
prior to separation through the column.
1
solid. Yield: 0.25 g (61%). H NMR (300 MHz, CDCl3, 298 K): δ
7.43 (q, 4H), 7.28 (m, 3H), 7.22 (t, 5H), 7.18 (m, 2H), 7.16 (s, 4H),
6.93 (t, 4H), 3.66 (s, 4H), 3.65 (s, 4H), 3.55 (s, 4H), 3.52 (s, 4H),
2.66 (s, 8H), 2.48 (s, 12H). ESI-MS (positive ion mode, acetonitrile):
m/z 823.51 ([M + H]+), 845.49 ([M + Na]+).
Synthesis of N1,N1′,N1″-[(2,4,6-Trimethylbenzene-1,3,5-triyl)tris-
(methylene)]tris[N2-benzyl-N1,N2-bis[(6-methylpyridin-2-yl)-
methyl]ethane-1,2-diamine] (L3). To a mixture of LNH (0.36 mg, 1.0
mmol), K2CO3 (0.70 g, 5.0 mmol), and KI (0.17 g, 1.0 mmol) in
CH3CN (30 mL) was added 1,3,5-tris(bromomethyl)-2,4,6-trime-
thylbenzene (131 mg, 0.33 mmol) under a N2 atmosphere. The
reaction mixture was refluxed for 48 h. The resulting solution was
filtered, and then the filtrate was dried under vacuum. The crude solid
was dissolved in a 10 M NaOH (20 mL) solution and then extracted
with dichloromethane (3 × 20 mL). The combined organic extract
was dried over Na2SO4 and evaporated to dryness to yield a brown
In the case of the catalytic oxidation of alkanes except cyclohexane,
the iron complex at the end of the reaction was decomposed by the
addition of 1.0 mL of a 1.0 M H2SO4 solution. The organic products
were extracted by diethyl ether, and the organic layer was dried over
anhydrous sodium sulfate. The organic products were then analyzed
by a comparison of their GC retention times and GC−MS of the
authentic compounds.
1
liquid. Yield: 0.20 g (49%). H NMR (300 MHz, CDCl3, 298 K): δ
7.42 (t, 6H), 7.18 (m, 15H), 6.93 (t, 6H), 6.84 (d, 6H), 3.58 (s, 6H),
3.54 (s, 6H), 3.49 (s, 6H), 3.44 (s, 6H), 2.61 (s, 12H), 2.48 (s, 9H),
2.42 (s, 9H), 2.29 (s, 9H). ESI-MS (positive-ion mode, acetonitrile):
m/z 1237.78 ([M + H]+).
Isotope Labeling Experiments. In an experiment with H218O,
40 μL of H218O (1000 equiv relative to iron) was added to the
mixture of the iron complex (0.002 mmol), adamantane (0.1 mmol),
and Sc(OTf)3 (0.02 mmol) in CH3CN (1.0 mL) in air. Then a 30%
aqueous solution of H2O2 (0.02 mmol) in 0.5 mL of CH3CN was
added to the resulting mixture via a syringe pump over a period of 20
min. The reaction mixture was stirred for an additional 15 min at 298
K. After completion of the reaction, the iron complex was
decomposed by the addition of 1.0 mL of a 1.0 M H2SO4 solution.
The organic products were extracted by diethyl ether, and the organic
layer was dried over anhydrous sodium sulfate. The organic products
were then analyzed by GC−MS.
Synthesis of [(6-Me2-Bn-BPMEN)FeII(OTf)2] (1). Solid FeII(OTf)2·
2CH3CN (0.22 g, 0.5 mmol) was added to a solution of the 6-Me2-
Bn-BPMEN ligand (0.23 g, 0.5 mmol) in dichloromethane (5 mL),
and the mixture was vigorously stirred for 12 h under an inert
atmosphere. The resulting solution was filtered, and then the filtrate
was dried under vacuum. The crude solid thus obtained was triturated
with diethyl ether (5 mL) to obtain a brown solid. X-ray-quality single
crystals were obtained from a solvent mixture of dichloromethane and
n-hexane. Yield: 0.32 g (72%). Anal. Calcd for C32H34F6FeN4O6S2·
CH2Cl2 (888.07 g/mol): C, 44.56; H, 4.08; N, 6.30. Found: C, 44.98;
H, 4.24; N, 6.33. IR (cm−1): 3429(br), 2926(m), 2854(w), 1745(w),
1645(w), 1609(w), 1464(m), 1286(vs), 1244(vs), 1225 (s), 1167 (s),
1030(vs), 706(w), 638(s), 519(w). 1H NMR (500 MHz, 298 K,
CDCl3): δ 71.2, 64.7, 61.9, 54.1, 47.9, 14.0, 7.4, 4.2, 3.7, 2.5, 1.2,
−28.5, −60.5.
KIE Experiments. To a mixture of iron (0.002 mmol) and
Sc(OTf)3 (0.02 mmol) in CH3CN (1.0 mL) was added 1:1
cyclohexane/cyclohexane-d12 in air. Then a 30% aqueous solution
of H2O2 (0.02 mmol) in 0.5 mL of CH3CN was added to the
resulting mixture via a syringe pump over a period of 20 min. The
reaction mixture was stirred for an additional 15 min at 298 K. After
the reaction, the organic products were esterified by acetic anhydride
(1.0 mL), together with 1-methylimidazole (0.1 mL), for cyclohexane
oxidation. After esterification, the solution was then passed through a
15 cm silica column (60−120 mesh size) using ethyl acetate/diethyl
ether as the eluent. The combined organic phase was then analyzed by
GC−MS.
X-ray Crystallographic Data Collection, Refinement, and
Solution of Structures. Single-crystal X-ray diffraction data for 1 at
120 K (Table S1) using Mo Kα (λ = 0.7107 Å) radiation on a
SMART-APEX diffractometer equipped with a CCD area detector.
Data collection, data reduction, structure solution, and refinement
were carried out using the software package of APEX II.79 The
structure was solved by direct methods and subsequent Fourier
Synthesis of [(L2)FeII (OTf)4] (1D). Solid FeII(OTf)2·2CH3CN
2
(0.44 g, 1.0 mmol) was added to a solution of the L2 ligand (0.41 g,
0.5 mmol) in dichloromethane (5 mL), and the mixture was
vigorously stirred for 12 h under an inert atmosphere. The resulting
solution was filtered, and then the filtrate was dried under vacuum.
The crude solid thus obtained was triturated with diethyl ether (5
mL) to obtain a brown solid. Yield: 0.51 g (67%). Anal. Calcd for
C58H62F12Fe2N8O12S4 (1530.19 g/mol): C, 45.50; H, 4.08; N, 7.32.
Found: C, 44.96; H, 4.02; N, 7.11. IR (cm−1): 3409(br), 2926(m),
2361(s), 2339(m), 1608(m), 1578(w), 1466(m), 1284(vs), 1246(vs),
1
1167(s), 1030(vs), 638 (s), 517(m). H NMR (500 MHz, 298 K,
CDCl3): δ 70.0, 63.6, 61.0, 53.6, 47.6, 13.8, 7.3, 3.7, 3.4, 1.2, −28.3,
−59.4.
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Inorg. Chem. 2021, 60, 5969−5979