Asymmetric Alkene Epoxidation
J . Org. Chem., Vol. 63, No. 22, 1998 7725
collected on a frit, washed with ice-cold water followed by
diethyl ether, and dried in vacuo. Yield: 65%. Anal. Calcd
for C37H39N7Cl4O4Ru: C, 50.01; H, 4.42; N, 11.03. Found: C,
49.75; H, 4.66; N, 10.98. FAB-MS m/z: 790 (M - ClO4)+.
E°(RuIII/II) ) 0.46 V versus Cp2Fe+/0 in 0.1M n-Bu4NPF6
acetonitrile solution. UV-vis (in MeOH) λmax/nm (ꢀmax/cm-1
M-1): 285 (43 300), 317 (42 600), 482 (5300).
dard was added to the organic filtrate, and an aliquot was
taken for analysis by GC or H NMR for product identification
1
and quantification. The ee of chiral epoxides was determined
either by GC analysis using chiral columns [Cyclodex-B (J &W
Scientific, 30 m × 0.25 mm i.d., 0.25-µm thickness), Chiraldex
G-TA (Astec, 30 m × 0.32 mm i.d., 0.125-µm thickness)], or
by1H NMR analysis using the chiral shift reagent (-)-tris[3-
(heptafluoropropylhydroxymethylene)-d-camphorato]europium-
(III), Eu(hfc)3. The cis-trans-epoxide ratios for the cis-â-
deuteriostyrene oxidations were evaluated from the integration
ratio of the appropriate proton resonance: cis-â-deuteriosty-
rene oxide (δH ) 3.18 ppm) and trans-â-deuteriostyrene oxide
(δH ) 2.80 ppm).
[Ru II(P P z*)(bp y)(H2O)](OTf)2. A mixture of [RuII(PPz*)-
(bpy)Cl]ClO4 (0.12 mmol, 100 mg) and silver trifluoromethane-
sulfonate (1.1 equiv) in an acetone/water mixture (25 mL, 1:1
v/v) was heated at reflux for 30 min. After being cooled to
room temperature, the red solution was filtered to remove the
insoluble silver chloride. The complex was isolated by pre-
cipitation with an aqueous ammonium trifluoromethane-
sulfonate solution. Recrystallization was performed by dis-
solving the crude product in a minimum amount of hot water;
the red solution was kept in a refrigerator (5 °C) overnight.
The red microcrystalline solids deposited were collected by
filtration and dried in vacuo. Yield: 80%. Anal. Calcd for
C39H43N7O7F6S2Ru: C, 46.80; H, 4.33; N, 9.79. Found: C,
45.86; H, 4.50; N, 9.69. 1H NMR (300 MHz, CD3CN): δ -0.07
(s, 3H), 0.08 (s, 3H), 0.13 (s, 3H), 0.22 (m, 1H), 0.60 (s, 3H),
0.75 (s, 3H), 0.81 (s, 3H), 0.87 (m, 1H), 1.19 (m, 1H), 1.29 (m,
1H), 1.50 (m, 1H), 1.75 (m, 1H), 1.90 (m, 1H), 2.08 (m, 1H),
2.83 (d, 2H, J ) 3.6 Hz), 7.17 (m, 1H), 7.43 (d, 1H, J ) 5.3
Hz), 7.75 (d, 1H, J ) 4.2 Hz), 7.77 (d, 1H, J ) 4.1 Hz), 7.85
(m, 2H), 8.25 (m, 4H), 8.41 (d, 1H, J ) 8.1 Hz), 8.61 (d, 1H, J
) 8.1 Hz), 9.77 (d, 1H, J ) 5.5 Hz). UV-vis (in H2O/MeOH,
1:1 v/v) λmax/nm (ꢀmax/cm-1 M-1): 286 (46 500), 324 (26 800),
375 (3870), 446 (5140).
Characterizations of complexes 2a ,19b 2b,12 and 2c13 have
already been reported elsewhere.
[Ru II(P P z*)(bp y)(MeCN)](ClO4)2 (2d ). Anal. Calcd for
C
39H44N8O8Cl2Ru: C, 50.65; H, 4.80; N, 12.12. Found: C,
49.64; H, 4.75; N, 11.76. 1H NMR (300 MHz, CD3CN): δ -0.06
(s, 3H), 0.09 (s, 3H), 0.13 (s, 3H), 0.25 (m, 1H), 0.59 (s, 3H),
0.75 (s, 3H), 0.81 (s, 3H), 0.85 (m, 1H), 1.19 (m, 1H), 1.30 (m,
1H), 1.50 (m, 1H), 1.75 (m, 1H), 1.90 (m, 1H), 2.06 (m, 1H),
2.82 (d, 2H, J ) 3.4 Hz), 7.18 (m, 1H), 7.43 (d, 1H, J ) 4.9
Hz), 7.93 (m, 4H), 8.28 (m, 2H), 8.48 (s, 1H), 8.51 (s, 1H), 8.53
(d, 1H, J ) 7.9 Hz), 8.76 (d, J ) 8.1 Hz), 9.82 (d, 1H, J ) 5.4
Hz). IR (Nujol): 2256 cm-1 (νCtN). UV-vis (in MeCN) λmax
/
nm (ꢀmax/cm-1 M-1): 285 (44 700), 317 (28 400), 424 (5730).
FAB-MS m/z: 826 (M - ClO4)+.
[Ru II(P P z*)(6,6′-Cl2-bpy)(MeCN)](ClO4)2 (2e). Anal. Cal-
cd for C39H42N8O8Cl4Ru: C, 47.14; H, 4.26; N, 11.28. Found:
C, 48.16; H, 4.34; N, 11.62. 1H NMR (300 MHz, CD3CN): δ
0.13 (s, 3H), 0.15 (s, 3H), 0.35 (s, 3H), 0.52 (s, 3H), 0.69 (m,
1H), 0.83 (s, 3H), 0.84 (s, 3H), 0.97 (m, 1H), 1.30 (m, 1H), 1.70
(m, 2H), 2.82 (d, 1H, J ) 4.0 Hz), 2.95 (d, 1H, J ) 4.1 Hz),
7.32 (m, 1H), 7.59 (d, 1H, J ) 8.1 Hz), 7.67 (d, 1H, J ) 7.9
Hz), 7.85 (m, 1H), 8.05 (m, 1H), 8.15 (s, 1H), 8.25 (m, 2H),
8.34 (m, 1H), 8.37 (s, 1H), 8.52 (m, 1H). UV-vis (in MeCN)
[Ru II(P P z*)(6,6′-Cl2-bp y)(H2O)](OTf)2. The same proce-
dure as for the preparation of [RuII(PPz*)(bpy)(H2O)](OTf)2 was
adopted here. Anal. Calcd for C39H41N7O7Cl2F6S2Ru: C,
1
43.78; H, 3.87; N, 9.17. Found: C, 43.33; H, 3.99; N, 8.94. H
NMR (270 MHz, CD3CN): δ 0.14 (s, 3H), 0.15 (s, 3H), 0.34 (s,
3H), 0.51 (s, 3H), 0.68 (m, 1H), 0.84 (s, 3H), 0.85 (s, 3H), 0.97
(m, 1H), 1.32 (m, 1H), (1.69 (m, 2H), 2.81 (d, 1H, J ) 3.9 Hz),
2.96 (d, 1H, J ) 4.1 Hz), 7.30 (m, 1H), 7.61 (d, 1H, J ) 8.3
Hz), 7.68 (d, 1H, J ) 7.8 Hz), 7.84 (m, 1H), 8.06 (m, 1H), 8.17
(s, 1H), 8.24 (m, 2H), 8.33 (m, 1H), 8.39 (s, 1H), 8.51 (m, 1H).
UV-vis (in H2O/MeOH, 1:1 v/v) λmax/nm (ꢀmax/cm-1 M-1): 286
(44 500), 317 (42 900), 469 (5400).
[Ru IV(P P z*)(bp y)O](ClO4)2 (1d ). To an ice-cooled solution
of [RuII(PPz*)(bpy)(H2O)](OTf)2 (0.10 mmol, 100 mg) in deion-
ized water (50 mL) was added an ammonium cerium(IV)
nitrate solution (200 mg in 5 mL of water), causing an
immediate color change from red to yellow. The titled complex
was isolated as a yellow solid by adding a saturated sodium
perchlorate solution. The product was collected on a frit,
washed with a small amount of cold water, and then dried in
vacuo. Yield: 70%. Anal. Calcd for C37H41N7O9Cl2Ru: C,
49.39; H, 4.59; N, 10.90. Found: C, 49.18; H, 4.68; N, 10.73.
Magnetic moment µeff (room temperature) ) 2.91µB. UV-vis
(in MeCN) λmax/nm (ꢀmax/cm-1 M-1): 287 (45 100). IR (Nujol
mull): 788 cm-1 (νRudO).
[Ru IV(P P z*)(6,6′-Cl2-bp y)O](ClO4)2 (1e). The same pro-
cedure as for the preparation of [RuIV(PPz*)(bpy)O](ClO4)2 was
adopted here. Yield: 45%. Anal. Calcd for C37H39N7O9Cl4Ru:
C, 45.88; H, 4.06; N, 10.12. Found: C, 45.75; H, 3.98; N, 9.82.
Magnetic moment µeff (room temperature) ) 2.89 µB. UV-vis
(in MeCN) λmax/nm (ꢀmax/cm-1 M-1): 287 (44 900). IR (Nujol
mull): 792 cm-1 (νRudO). Caution: Metal perchlorate salts are
potentially explosive and must be handled in small quantities
with proper safety precautions.
Gen er a l P r oced u r es for th e Stoich iom etr ic Oxid a tion
of Alk en es by Oxor u th en iu m (IV) Com p lexes a n d th e
Isola tion of [Ru II(L1)(L2)(MeCN)](ClO4)2 Com p lexes. The
ruthenium oxidant (50 µmol) was added to an acetonitrile
solution (4 mL) containing alkene (1-2 mmol) in a 25-mL
round-bottom flask under a nitrogen atmosphere. The solution
mixture was stirred for 12 h at room temperature. [RuII(L1)-
(L2)(MeCN)](ClO4)2 was isolated by precipitation using diethyl
ether (>95% yield) and recrysrallized by the slow diffusion of
diethyl ether into an acetonitrile solution. An internal stan-
λ
max/nm (ꢀmax/cm-1 M-1): 284 (40 900), 311 (41 200), 446 (5980).
FAB-MS m/z: 895 (M - ClO4)+.
Kin etic Stu d ies for Alk en e Oxid a tion s by Oxor u th e-
n iu m (IV) Com p lexes. Kinetic experiments were performed
on a diode array UV-vis spectrophotometer interfaced with
an IBM-compatible PC. The measurements were made in
standard 1.0 cm quartz cuvettes. The solution temperature
during kinetic experiments was maintained to within (0.2 °C
using a circulating water bath. The oxidation of alkenes by
the oxoruthenium(IV) complexes was followed by monitoring
the growth of the MLCT band of [RuII(L1)(L2)(MeCN)](ClO4)2
(2) under the condition that the concentration of alkenes was
at least 100-fold in excess of the ruthenium oxidants. Pseudo-
first-order rate constants, kobs, were obtained by nonlinear
least-squares fits of (Af - At) to time (t) according to the
equation:
(Af - At) ) (Af - Ai) exp(-kobs t)
where Ai and Af are the initial and final absorbances, respec-
tively, and At is the absorbance at time t. Kinetic data over 4
half-lives (t1/2) were used for the least-squares fitting. Second-
order rate constants, k2, were obtained from the linear fit of
the kobs values to the alkene concentrations.
Activation enthalpy (∆Hq) and activation entropy (∆Sq) were
calculated from the linear plot of ln(k2/T) versus (1/T) according
to the Eyring equation:
ln(k2/T) ) ln(R/NA h) + ∆Sq/R - ∆Hq/RT
where T is the temperature in Kelvin scale (K), NA is
Avogadro’s number, R is the universal gas constant, and h is
Planck’s constant.
Ack n ow led gm en t. We acknowledge support by The
University of Hong Kong and the Hong Kong Research
Grants Council. We are also thankful to Dr. Wing-Chi
Cheng for his contribution at the early stage of this work