A R T I C L E S
Yip et al.
oxidations.8-11 Being isoelectronic with OsO4, RuO4 is a
powerful oxidant that cleaves the CdC bond upon reaction with
alkenes.12 Protocols for oxidative CdC cleavage using RuCl3
as a catalyst are well documented in the literature.3f,13 In 1994,
Shing and co-workers reported the RuCl3-catalyzed alkene cis-
dihydroxylation using NaIO4 as terminal oxidant.3h-j Recently,
we developed a catalytic protocol for alkene cis-dihydroxylation
using ruthenium nanoparticles as catalyst.3f Among these
reported examples, reactive cis-dioxoruthenium species have
been postulated as the key intermediate responsible for the cis-
diol formation/CdC bond cleavage. However, the reactions of
cis-dioxoruthenium complexes with alkenes to give cis-1,2-diols
remain poorly characterized. Indeed, apart from d0- and d1-
tetraoxo/trioxo complexes, limited examples on structurally
defined cis-MO2 complexes that react with alkenes to give [3
+ 2] cycloadducts are known in the literature. Previously we
prepared and structurally characterized two cis-dioxoruthenium-
(VI) complexes (Figure 1), [(Me3tacn)(CF3CO2)RuVIO2]ClO4
(1; Me3tacn ) 1,4,7-trimethyl-1,4,7-triazacyclononane),11a,c and
cis-[(Tet-Me6)RuVIO2](ClO4)2 (2; Tet-Me6 ) N,N,N′,N′-tetra-
methyl-3,6-dimethyl-3,6-diazaoctane-1,8-diamine)11d with E°
values of 1.1 V (RuVI/V) and 0.8 V (RuVI/IV) vs SCE, respec-
tively. Here we report that complex 1 oxidized alkenes to afford
cis-1,2-diols (in aqueous medium) and dialdehydes (in non-
aqueous medium) in good to excellent yields under stoichio-
Figure 1. cis-Dioxoruthenium(VI) complexes.
metric conditions. Analogous to the alkyne oxidation,11a the [3
+ 2] cycloadducts for the reactions of cyclooctene and trans-
â-methylstyrene with 1 have been isolated and structurally
characterized by X-ray crystal analyses. In this work, the
cycloaddition reaction has been examined by kinetic studies and
organic product analysis.
Results
Stoichiometric Alkene cis-Dihydroxylations by [(Me3tacn)-
(CF3CO2)RuVIO2]ClO4 (1). Treatment of cyclooctene (30
mmol) with 1 (300 µmol) in a tert-butyl alcohol-water mixture
(10:2 v/v) under an argon atmosphere at room temperature
produced cis-1,2-cyclooctanediol in 85% isolated yield (Table
1, entry 1); 1,8-octanedialdehyde (CdC bond cleavage product)
was obtained in 5% yield. Neither trans-1,2-cyclooctanediol nor
cyclooctene oxide was detected by NMR analysis of the crude
reaction mixture. The yields of the cis-1,2-diol and dialdehyde
were calculated based on the stoichiometry of Ru/cyclooctene
) 1:1. The cis-/trans-diols and 1,8-octanedialdehyde were
(7) (a) Thomas, J. A.; Davison, A. Inorg. Chim. Acta 1991, 190, 231. (b)
Pearlstein, R. M.; Davison, A. Polyhedron 1988, 7, 1981.
(8) For reviews, see: (a) Che, C.-M.; Lau, T.-C. In ComprehensiVe Coordina-
tion Chemistry II: From Biology to Nanotechnology; McCleverty, J. A.,
Meyer, T. J., Eds.; Elsevier Pergamon: Amsterdam, 2004; Vol. 5, Chapter
5.6, p 733. (b) Che, C.-M.; Yu, W.-Y. Pure Appl. Chem. 1999, 71, 281.
(c) Murahashi, S.-I.; Naota, T. In ComprehensiVe Organometallic Chemistry
II, Vol. 12; Abel, E. W., Stone, F. G. A., Wilkinson, G. W., Eds.;
Pergamon: Oxford, 1995; p 1177. (d) Che, C.-M.; Yam, V. W.-W. AdV.
Inorg. Chem. 1992, 39, 233. (e) Griffith, W. P. Chem. Soc. ReV. 1992, 21,
179. (f) Seddon, E. A.; Seddon, K. R. The Chemistry of Ruthenium;
Elsevier: Amsterdam, 1984.
1
identified by their H and 13C NMR signals with reference to
the literature data [cis-diol: δH 3.9 ppm (d, 2H, J ) 10 Hz), δC
) 73.1 ppm. trans-diol: δH 3.6 ppm (d, 2H, J ) 9.5 Hz), δC )
76.1 ppm. 1,8-octanedialdehyde: δH 9.8 ppm (t, 2H, J ) 1.5
Hz), δC ) 202.5 ppm].14 After the reaction, [(Me3tacn)2RuIII2(µ-
O)(µ-CF3CO2)2](ClO4)2 (3) was isolated in quantitative yield;
this complex has been characterized by X-ray crystal analysis
(Figure S1, Tables S1 and S2) [for more detailed characterization
of 3, including its UV-vis spectrum (Figure S2) and structure
features, see Experimental Section and Supporting Information].
The observed cis-dihydroxylation should be unique for the cis-
dioxoruthenium(VI) complex, since the analogous cyclooctene
oxidation by trans-[RuVI(N2O2)O2]ClO4 (N2O2 ) 1,12-dimethyl-
3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane)10g hav-
ing comparable E°(RuVI/IV) of 0.92 V (vs SCE, pH 1.0) afforded
cyclooctene oxide in 90% yield without any cis-1,2-diol being
detected.
The employment of aqueous tert-butyl alcohol as solvent is
critical for the cis-diol formation. When the reaction of 1 with
cyclooctene was undertaken in dry acetonitrile, 1,8-octanedi-
aldehyde was obtained in 91% yield (Table 2, entry 1); neither
cis-1,2-cyclooctanediol nor cyclooctene oxide was detected by
1H NMR analysis. However, when aqueous acetonitrile (MeCN/
H2O ) 10:1 v/v) was used as solvent, significant cis-cyclooc-
tane-1,2-diol formation (in 22% yield) was observed albeit with
1,8-octanedialdehyde being the major product (yield: 60%). In
this case, epoxide and trans-1,2-diol were not detected according
to NMR analysis of the crude reaction mixture. For oxidation
of other cycloalkenes, cleavage of the CdC bond to dialdehydes
prevailed in dry acetonitrile; details are given in later sections.
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V. W.-W.; Mak, T. C. W. J. Am. Chem. Soc. 1990, 112, 2284. (i) Dengel,
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9
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