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7254 J. Am. Chem. Soc., Vol. 120, No. 29, 1998
Bo¨sing et al.
Using a concentrated HNO3 solution (15.67 M) the pH was set to 5-6.
After heating and stirring for 1 h at 75 °C, the mixture was allowed to
cool to ambient temperature. Finally, NH4NO3 (0.534 g, 6.67 mmol)
was added to the reaction solution and yellow needles of Na6(NH4)4-
[(MnII(H2O)3)2(WO2)2(BiW9O33)2]‚37H2O were obtained after several
hours. Yield: 2.4 g (57%). Anal. Calcd for H102N4O113Na6Mn2Bi2-
W20: H, 1.62; N, 0.89; Na, 2.19; Mn, 1.74; Bi, 6.62; W, 58.26; H2O,
12.27. Found: H, 1.51; N, 0.97; Na, 2.11; Mn, 1.98; Bi, 6.74; W,
58.11; H2O, 12.49.
Analysis Data of the Organic Products. The organic products were
identified by mass spectroscopy at 70 eV. II: m/z (%) 152 (1.1), 137
(13.9), 119 (6.8), 109 (16.2), 93 (19.5), 79 (27.4), 71 (8.5), 67 (52.6),
53 (15.8), 43 (100.0), 39 (76.3). III: m/z (%) 152 (<1), 137 (2.1),
119 (2.4), 108 (14.7), 93 (25.7), 79 (36.4), 67 (47.5), 53 (15.7), 43
(100.0), 39 (71.1). IV: m/z (%) 152 (5.4), 137 (7.0), 134 (1.7), 123
(3.7), 108 (9.6), 97 (3.7) 93 (10.1), 88 (4.8), 82 (7.3), 79 (7.0), 71
(44.8), 67 (32.4), 57 (18.6), 43 (100.0), 41 (42.3). In addition to this,
chemical ionization (CI) experiments with methanol as the reaction
gas were performed to verify the 152 m/z molecule peaks of II-IV.
In all cases the (M + H)+ peak (153 m/z) was found.
[(MnII(H2O))3(SbW9O33)2]12- (2). The first step in synthesis of 2
is the preparation of Na9[SbW9O33]‚19.5H2O.25 This compound was
prepared by the reaction of Na2WO4‚2H2O (40 g, 121 mmol) in boiling
water (80 mL) and dropwise addition of Sb2O3 (1.96 g, 6.72 mmol)
dissolved in concentrated HCl (12 M, 10 mL). The mixture was
refluxed for 1 h and was allowed to cool slowly. Colorless crystals of
Na9[SbW9O33]‚19.5H2O were formed after evaporation of one-third of
the solution volume. Yield: 28.0 g (72%). In a second step, Na9-
[SbW9O33]‚19.5H2O (4 g 1.4 mmol) was dissolved in water (8 mL)
under gentle heating. To this pale yellow mixture was given slowly a
solution of MnCl2‚4H2O (0.414 g, 2.08 mmol) in water (10 mL), leading
to an orange solution with pH 6-7. The mixture was refluxed for 1
h, and then NH4NO3 (0.673 g, 8.4 mmol) was added. After the mixture
was cooled to ambient temperature, dark orange crystals of Na11(NH4)-
[(MnII(H2O))3(SbW9O33)2]‚45H2O were obtained after several days.
Yield: 2.6 g (63%). Anal. Calcd for H100NO114Na11Mn3Sb2W18: H,
1.70; N, 0.24; Na, 4.28; Mn, 2.78; Sb, 4.12; W, 55.99; H2O, 14.62.
Found: H, 1.51; N, 0.35; Na, 4.35; Mn, 2.83; Sb, 4.25; W, 55,81;
H2O, 14.71.
1
Identification of the organic products by H NMR was done on a
Bruker 300-MHz spectrometer (CDCl3). II: δ (ppm) 1.27 (s, 3H),
1.67 (s, 3H), 2.98 (t, 1H), 4.66 (s, 2H), 1.15-2.20 (m, 7H, ring protons).
III: δ (ppm) 1.29 (s, 3H), 1.71 (s, 3H), 3.02 (t, 1H), 4.75 (s, 2H),
1.13-2.27 (m, 7H; ring protons). IV: δ (ppm) 1.20 (s, 3H), 1.66 (s,
3H), 1.86 (ddd, 1H) 3.56 (s, broad, 1H (OH)), 4.67 (s, 2H), 1.41-1.80
(m, 6H; ring protons).
UV-Visible Studies. Examination of the UV-vis spectra of
[MnII2(H2O)6(WO2)2(BiW9O33)2],10- [(MnII(H2O))3(SbW9O33)2]12-, and
[(MnII(H2O)3)2(MnII(H2O)2)2(TeW9O33)2]8- was performed on a Hewlett-
Packard 8453 diode array spectrophotometer:
First measurements (400-800 nm, under reaction conditions,
substrate/catalyst ) 1000/1, yellow (1 and 3) and orange (2) solutions,
partial evaporation of the solvent) showed no peaks in the spectra on
the basis of the 2+ oxidation states of the manganese atoms in the
catalysts before reaction.
[(MnII(H2O)3)2(MnII(H2O)2)2(TeW9O33)2]8- (3). TeO2 (0.22 g, 1.34
mmol) was dissolved under gentle heating in concentrated NaOH
solution (ca. 10 M, 1 mL) and diluted with water (10 mL) (solution 1).
Na2WO4‚2H2O (3.96 g, 12.01 mmol) was dissolved in a mixture of
water (20 mL) and concentrated HNO3 (12 M, 0.7 mL) and heated to
75 °C (solution 2). The tellurium-containing solution 1 was added
dropwise to solution 2, and Na2CO3 (0.4 g, 4.8 mmol) was supplied
simultaneously to avoid a drop in pH. To this pale yellow mixture a
solution of MnCl2‚4H2O (0.532 g, 2.68 mmol) in water (10 mL) was
given slowly leading to a deep yellow solution. The pH was set to 3
by dropwise addition of a concentrated HNO3 solution (15.67 M). After
heating and stirring for 1 h at 80 °C the mixture was filtered and allowed
to cool to ambient temperature. Yellow crystals of Na8[(MnII(H2O)3)2-
(MnII(H2O)2)2(TeW9O33)2]‚34H2O were obtained after several days.
Yield: 1.8 g (47%). Anal. Calcd for H84O108Na8Mn4Te2W18: H, 1.45;
Na, 3.18; Mn, 3.80; Te, 4.41; W, 57.23; H2O, 13.70. Found: H, 1.53;
Na, 2.98; Mn, 3.71; Te, 4.53; W, 57.37; H2O, 14.01.
Catalytic Epoxidation Procedure. Stock solutions were prepared
by dissolving Na6(NH4)4[1]‚37H2O, Na11(NH4)[2]‚45H2O or Na8[3]‚
34H2O (0.064 mmol) and methyltricaprylammonium chloride (0.64
mmol (1), 0.77 (2), and 0.52 (3)) in a water/1,2-dichloroethane mixture
(20 mL, 1:1 ratio). Under gentle heating and stirring, the color of the
organic phase turned to yellow (1 and 3) and orange (2), respectively,
whereas the aqueous phase decolorized. The organic solution was
separated and cooled. In a typical reaction, the substrate, (R)-(+)-
limonene, (40 mmol) and desired amounts of the stock solution were
dissolved in 1,2-dichloroethane (40 mL) at room temperature. The
reaction was initiated by addition of 30% hydrogen peroxide (Fluka,
purum p.a., stab., with phosphate (PO4) e 0.0002%, 80 mmol) under
atmospheric conditions and stirred, forming a biphasic system. Due
to the biphasic reaction system, product rates are a function of interfacial
area and so almost equal stirring rates (800-1000 rpm) and identical
reaction vessels were used. The epoxidation process was monitored
by gas chromatography; aliquots were taken from the organic phase of
the reaction medium (after quenching the reaction by demixing of the
organic and aqueous phase) and directly injected into the gas chro-
matograph (Finnigan MAT DANI 8521 equipped with a ITD 800 mass-
selective detector with a CP-SIL-8CB column and GC Hewlett-Packard
6890 equipped with a mass-selective detector HP 5973 with fused silica
column, respectively) to identify and quantify the organic products by
integration of peak areas; p-cymene was used as an internal standard.
In further investigations (400-800 nm, under reaction conditions,
substrate/catalyst ) 1000/1, after addition of 2 equiv of 30% aqueous
hydrogen peroxide based upon the substrate and stirring, after ca. 40
h, red color depending on the 3+ oxidation states of at least one
manganese atom in the catalysts, partial evaporation of the solvent)
distinctive peaks at 490 nm (1), 498 nm (2), and 514 nm (3) were
formed during the reactions. Several days after completion of the
epoxidations, the color of the mixtures changed slowly to yellow (1
and 3) and orange (2) again based on the 2+ oxidation states of the
manganese atoms in the catalysts leading to the original spectra of
[MnII (H2O)6(WO2)2(BiW9O33)2]10-, [(MnII(H2O))3(SbW9O33)2]12-, and
2
[(MnII(H2O)3)2(MnII(H2O)2)2(TeW9O33)2]8-
.
Measurements in the 200-400-nm range of diluted solutions of 1-3
used in the experiments described before showed a distinctive peak at
227 nm and a shoulder at ca. 270 nm. The spectrum of the quaternary
ammonium salt methyltricaprylammonium chloride in 1,2-dichloro-
ethane (5 × 10-3 M) contained two distinctive peaks at 227 and 273
nm.
Cyclic Voltammetric Measurements. Electrochemical experiments
were performed with a BAS CV-50 W appliance. Measurements of
1-3 were made in 1,2-dichloroethane solutions (1 × 10-3 M, 10 mL)
containing tetra-n-butylammonium perchlorate (0.342 g, 1 mmol) as
the supporting electrolyte and were conducted at room temperature
under an argon atmosphere. A controlled growth mercury working
electrode (Metrohm) and an Ag/AgCl reference electrode were used
for the experiments. Effective redox potentials of [MnIIMnIIIHPA]+-
[MnIIIMnIIIHPA]2+ and [MnIIMnIIHPA]-[MnIIMnIIIHPA]+: E1/2 (mV)
) ca. 640 and ca. 275 (1), ca. 480 and ca. 10 (2), ca. 840 (irreversible
process) and ca. 485 (3) with DE (mV) ) ca. 90 and ca. 110 (1), ca.
100 and ca. 180 (2), and ca. 75 (3). Redox potentials corresponding
to the formation of [MnIIMnIIHPA]-/2-: E1/2 (mV) ) ca. -80 (1), ca.
-130 (2), and ca. -140 and -580 (irreversible process) (3) with DE
(mV) ) ca. 60 (1), ca. 140 (2), and ca. 160 (3). All redox potentials
were determined from an average of the anodic and cathodic peak
potentials from various measurements. Voltage sweep rates were 750
mV/s (1), 250 mV/s (2), and 200 mV/s (3).
Infrared Spectroscopy. IR spectra of Na6(NH4)4[Mn2(H2O)6-
(WO2)2(BiW9O33)2]‚37H2O, Na11(NH4)[(MnII(H2O))3(SbW9O33)2]‚45H2O,
and Na8[(MnII(H2O)3)2(MnII(H2O)2)2(TeW9O33)2]‚34H2O were taken on
a Perkin-Elmer 683 spectrometer in a range 4000 -400 cm-1. Sodium
ammonium salt of 1 (KBr): ν˜ (cm-1) ) 937 (vs) (W-Ot); 818 (vs)
(W-Oc-W); 760 (s) (W-Oe-W); 669 (s). Sodium ammonium salt
(25) Bo¨sing, M.; Loose, I.; Pohlmann, H.; Krebs, B. Chem. Eur. J. 1997,
3, 1232-1237.