Journal of the American Chemical Society
Article
Synthesis of N-Methyl-N′,N″-bis(2-pyridylmethyl)-1,4,7-tria-
zacyclononane (MePy2tacn). 1,4-Bis(2-pyridylmethyl)-1,4,7-triaza-
cyclononane (0.34 g, 1.09 mmol) was dissolved in formaldehyde 37%
(3 mL), 98% formic acid (3 mL), and water (2.5 mL), and the
resulting yellow solution was refluxed for 30 h. After cooling to room
temperature, 3 mL of HCl was added, and the mixture was left stirring
for 10 min. The solvent was removed under vacuum, and a small
amount of water (10 mL) was added to the resulting residue. The
solution was brought to pH 14 by the addition of NaOH (4 M). After
stirring for 20 min, the aqueous phase was extracted with CH2Cl2 (3 ×
50 mL). The combined organic phases were dried over anhydrous
MgSO4, and the solvent was removed under reduced pressure. The
resulting residue was treated with n-hexane (75 mL) and stirred for 12
h. The solvent was decanted and removed under reduced pressure to
Kinetic Studies. The required amount of 2 (625 μL of a 1.6 mM
solution of 2 in CH3CN obtained by direct oxidation of 1 with PhIO)
was diluted in deaerated Milli-Q water (1.67 mL), then the desired
quantity of photosensitizer (dissolved in CH3CN:H2O 1:3) and/or
sulfide (XPhSMe, dissolved in CH3CN) was added. Finally, the
appropriate amounts of CH3CN and H2O were added to reach a
CH3CN/H2O ratio of 1:3 and an initial concentration of 2 of 0.4 mM.
The progress of the reaction was monitored by UV/vis spectroscopy at
25 °C.
Identification and Quantification of Sulfoxides. Reaction of 2
with sulfides (XPhSMe) caused a decay of its characteristic absorption
band (λmax = 715 nm). After full decay of this band, an internal
standard was added to the solution (trimethoxybenze or biphenyl),
and the amount of formed sulfoxide was quantified by 1H NMR
spectroscopy or gas chromatography.
1
yield 0.162 g of a colorless oil (0.50 mmol, 46%). H NMR (CDCl3,
300 MHz, 300 K) δ, ppm: 8.50 (d, 2H, PyHα), 7.64 (dt, 2H, PyHγ),
7.49 (d, 2H, PyHβ), 7.10 (dd, 2H, PyHβ′), 3.82 (s, 4H, CH2-Py),
2.90−2.82 (m, 8H, N−CH2), 2.74 (s, 4H, N−CH2), 2.34 (s, 3H,
CH3). The analysis is consistent with the previously reported synthesis
of MePy2tacn.48
ASSOCIATED CONTENT
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S
* Supporting Information
NMR and Mossbauer spectra of 1, EPR and Mossbauer spectra
̈
̈
of [FeIII(OH)(MePy2tacn)](OTf)2, NMR spectrum of 2, UV/
vis control experiments, quantification of sulfoxide products,
analysis of the final iron species, Hammett plots, and
photophysical experiments. This material is available free of
Synthesis of [FeII(CH3CN)(MePy2tacn)](OTf)2 (1). To a vial
containing MePy2tacn (150 mg, 0.46 mmol) dissolved in THF (1 mL)
was added dropwise
a THF solution (1 mL) of Fe-
(CH3CN)2(CF3SO3)2 (200 mg, 0.46 mmol). After stirring for 3 h,
the resulting red solid was filtered, washed with Et2O (3 × 2 mL), and
dried under vacuum. Recrystallization of the red solid by Et2O
diffusion into a saturated CH2Cl2/CH3CN solution yielded dark red
single crystals (198 mg, 60%) suitable for diffraction analysis. 1H NMR
(CD3CN, 400 MHz, 273 K) δ, ppm: 8.90 (d, J = 5.6 Hz, 1H, PyH),
7.94 (td, J = 7.6 Hz, J′ = 1.2 Hz, 1H, PyH), 7.81 (td, J = 7.6 Hz, J′ =
1.2 Hz, 1H, PyH), 7.61 (d, J = 7.6 Hz, 1H, PyH), 7.56 (t, J = 6.6 Hz,
1H, PyH), 7.52 (d, J = 7.6 Hz, 1H, PyH), 7.29 (d, J = 5.2 Hz, 1H,
PyH), 7.18 (t, J = 6.4 Hz, 1H, PyH), 4.72 (d, J = 16 Hz, 1H, CH2-Py),
4.58 (d, J = 15.6 Hz, 1H, CH2Py), 4.54 (d, J = 16 Hz, 1H, CH2Py),
4.06 (d, J = 16.4 Hz, 1H, CH2Py), 3.5−2.9 (m, 10H, N−CH2), 2.60−
2.59 (m, 1H, N−CH2), 2.59 (s, 3H, CH3), 1.61 (td, J = 13.2 Hz, J′ =
6.4 Hz, 1H, N−CH2). 13C NMR (CD3CN, 100 MHz, 273 K) δ, ppm:
166.07, PyC), 166.03 (1C, PyC), 157.42 (1C, PyC), 154.39 (1C,
PyC), 137.57 (1C, PyC), 137.42 (1C, PyC), 125.09 (1C, PyC), 125.06
(1C, PyC), 122.60 (1C, PyC), 122.15 (1C, PyC), 68.07 (1C, Py-CH2),
67.01 (1C, Py-CH2), 61.05 (1C, N-CH2), 60.38 (1C, N-CH2), 60.18
(2C, N-CH2), 59.01(1C, N-CH2), 58.20 (1C, N-CH2), 49.38 (1C,
CH3). ESI-MS (m/z): [M − CH3CN − CF3SO3]+ = 530.2 (100%),
[M − CH3CN − 2CF3SO3]2+ = 190.5 (26%). Anal. Calcd. (%) for
C23H30F6FeN6O6S2·1/2H2O (729.43): C, 37.87; H, 4.28; N, 11.52; S,
8.79. Found: C, 37.99; H, 4.31; H, 11.41; S, 8.67.
AUTHOR INFORMATION
Corresponding Author
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We acknowledge the European Commission for projects FP7-
PEOPLE-2011-CIG-303522 (A.C.), FP7-PEOPLE-2010-ERG-
268445 (J.L.-F.), FP7-PEOPLE-CIG-303522 (M.G.B.), and
ERC-009StG-239910 (M.C.); the Spanish Ministry of Science
for Projects CTQ2012-37420-C02-01/BQU (M.C.),
CSD2010-00065 (M.C.), and CTQ2011-27758 (J.P.P.);
Generalitat de Catalunya for an ICREA Academia Award and
Project 2009-SGR637 (M.C.); and Generalitat Valenciana for
Project ACOMP/2013/008 (J.P.P.). The Spanish Ministry of
́
Science is acknowledged for a Ramon y Cajal contract to A.C.
Preparation of [FeIV(O)(MePy2tacn)]2+ (2) with PhIO. In an
anaerobic glovebox, 1 (2.3 mg, 3.9 × 10−3 mmol) and PhIO (14 mg,
6.4 × 10−2 mmol) were mixed in CH3CN (2 mL). The resulting
solution was vigorously stirred 10−12 min. Removal of unreacted
PhIO was achieved by filtration, which afforded a pale green solution
of compound 2. The yield of the reaction was estimated according to
and J.L.-F. J.M.L. acknowledges the support, in part, of Labex
ARCANE (ANR-11-LABX-0003-01). The work at the
University of Minnesota was supported by the US National
Science Foundation (Grant CHE1058248 to L.Q.) and the Dr.
Venkateswarlu Pothapragada and Family Fellowship (to M.P.).
XAS data were collected at beamline 9-3 of the Stanford
Synchrotron Radiation Lightsource supported by the US-NIH
and US-DOE. We thank Catexel for a generous gift of tritosyl-
1,4,7-triazacyclononane.
the amount of FeIV determined by Mossbauer spectroscopy by
̈
preparation of a 50% 57Fe-enriched sample of compound 2. Yield:
1
82%. H NMR (CD3CN, 400 MHz, 300 K) δ, ppm: 46.46 (s, 1H,
PyHβ), 13.34 (s, 1H, PyHγ), 11.22 (s, 1H, PyHγ), 2.05 (s, 1H, PyHβ),
−1.36 (s, 1H, PyHβ), −13.27 (s, 1H, PyHβ). ESI-MS (m/z): [M −
CF3SO3]+ = 546.1 (100%), [M − 2CF3SO3]2+ = 198.5 (5%). UV/vis
(CH3CN/H2O 1:3): λmax = 715 nm, ε = 240 M−1 cm−1
REFERENCES
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Preparation of [FeIV(O)(MePy2tacn)]2+ (2) under Photo-
catalytic Conditions. In an anaerobic glovebox, a solution of 1
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vis cuvette. Addition of 5 mol % of [Ru(bpy)3]Cl2 (0.05 μmol, 100 μL
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ratio CH3CN/H2O 1:3, 0.4 mM in 1). Irradiation at 447 nm caused
immediate changes in the UV/vis spectrum that led to the formation
of 2, as evidenced by the appearance of its characteristic band at 715
nm (see Figure 5).
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dx.doi.org/10.1021/ja412059c | J. Am. Chem. Soc. 2014, 136, 4624−4633