10.1002/chem.201900236
Chemistry - A European Journal
FULL PAPER
2872 (m), 1960 (w), 1894 (w), 1824 (w), 1589 (w), 1484 (w), 1427 (s),
1262 (w), 1185 (w), 1113 (s), 1052 (m), 1030 (m), 1002 (s), 954 (bs),
912 (s), 744 (m), 701 (s), 578 (m), 525 (s), 486 (m). UV/vis
Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft (LI
714/10-1 and “Unifying Concepts in Catalysis”) as well as the
Humboldt-Universität zu Berlin for financial support.
λ
max(THF)/nm (ε/cm-1 mol-1 L): 371 (38), 462 (26). HR-ESI-MS [M–
4∙THF–2K++O]–: [C48H40CrO6Si4O]–: calcd. 893.1340, found 893.1370.
As a measurement under completely inert conditions is not possible only
a partially oxidized species can be detected. Elemental analysis, found:
H 3.7, C 48.9 %, calcd. for C48H40CrO6Si4K2+3∙KCl: H 3.4, C 49.0 %. Due
to the solubility of KCl in THF it was not possible to obtain a completely
KCl free sample.
Keywords: alkali metal • superoxide• chromium • siloxide •
Lewis acids
Synthesis of compound 7
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room temperature. After adding 0.5 equivalents CrCl3∙3THF (44.9 mg,
0.12 mmol) the resulting green solution was stirred overnight and filtered.
Subsequently the solvent was removed under reduced pressure. The
green solid residue was washed with hexane and dried. Green crystals of
6 (120 mg, 0.1 mmol, 84 %) suitable for single crystal X-ray diffraction
analysis were grown by layering a saturated THF solution of the product
with hexane.
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IR ῡmax/cm-1 (KBr ): 3065(m), 3046 (m), 2998 (m), 2975 (m), 2878 (m),
1960 (w), 1890 (w), 1825 (w), 1630 (w), 1590 (w), 1485 (w), 1457 (w),
1427 (s), 1261 (w), 1186 (w), 1111 (s), 1034 (s), 1013 (s), 994 (s),
967 (bs), 890 (w), 743 (m), 712 (s), 701 (s), 528 (s), 480 (w), 442 (m).
UV/vis λmax(THF)/nm: 450, 605, 783 nm, UV/vis λmax(KBr)/nm: 438,
598, 807 nm. HR-ESI-MS [M–4∙THF–Cl]+: [C48H40CrO6Si4Li2]+: calcd.
890.1622, found 890.1623. Elemental analysis found: H 5.8, C 61.1,
calcd. for C64H72CrO10Si4Li2Cl1+LiCl: H 5.8, C 61.2. Due to the solubility
of LiCl in THF it was not possible to obtain a completely LiCl free sample.
[3]
General procedure for the preparation of 5 and 6
1 (solid) or 3 (THF solution) were exposed to dioxygen at –80 °C. The
solid was dissolved in pre-cooled EtCN. Solutions of 5 and 6 were
subsequently layered with pre–cooled hexane and stored at –80 °C.
Crystals suitable for X-ray diffraction analysis could be isolated after 10
days. Due to the temperature and light sensitivity of the samples a
determination of the yield could not be done and further analysis was
limited.
[4]
(5): UV/vis λmax(THF)/nm (ε/cm-1 mol-1 L), 0 °C: 319 (1460), 508 (72),
712 (222). UV/vis
696 (115).
HR-ESI-MS [M+1e]–:
λ
max(EtCN)/nm (ε/cm-1 mol-1 L), 0 °C: 309 (940),
[5]
[6]
[7]
[8]
[9]
[C68H80CrNa2O1118O2Si4]–
calcd.
1319.3984, found 1319.2469. (6): UV/vis λmax(EtCN)/nm (ε/cm-1 mol-
1 L), –80 °C: 306 (800), 487 (80), 685 (120). rRaman: 16O2 : 1130 nm.
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Synthesis of TEMPO–H
TEMPO (5.02 g, 32 mmol) was dissolved in a 1:1 mixture of degassed
acetone and water (70 mL). Sodium dithionite (9.5 g, 55 mmol) was
added and the reaction mixture was stirred for 10 min. After removal of
the acetone, the reaction mixture was extracted with dry diethylether and
transferred onto dried MgSO4. The solution was collected via filtration
and the solvent was removed. The product (3.80 g, 24 mmol, 75 %) was
purified via sublimation and stored under inert conditions at –30 °C. The
product purity was analyzed by means of EPR.
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Radical concentration < 1 %.
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