Novel dimerization, alkoxylation, and sulfidation of olefins catalyzed by RuCl3·nH2O

Article abstract of DOI:10.1246/cl.2004.728

Novel ruthenium-catalyzed reactions that employ ruthenium trichloride n-hydrate (RuCl₃·nH₂O) were investigated and dimerization, alkoxylation and sulfidation of olefins were noted. Adducts of Markovnikov type and anti-Markovnikov type were obtained in a stereospecific manner and in good yield, depending on the type of olefins used as the starting materials. (Graph Presented).

Full text of DOI:10.1246/cl.2004.728

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Chemistry Letters Vol.33, No.6 (2004)
Novel Dimerization, Alkoxylation, and Sulfidation of Olefins Catalyzed by RuCl3ÁnH2O
Mitsuteru Higashimura, Keita Imamura, Yukiko Yokogawa, and Tsutomu SakakibaraÃ
Department of BioScience, Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065
(Received March 8, 2004; CL-040260)
Novel ruthenium-catalyzed reactions that employ ruthenium
fluxed under N2 for 24 h. The reaction mixture was monitored by
TLC. After filtration and solvent-evaporation, the residue was
purified by SiO2 column chromatography to give ꢀ-methylstyr-
ene dimer 1 in excellent yield. When the solvent was replaced
with THF, dimer 2 was obtained in good yield (Scheme 1). Indan
type dimers were named type I and all other dimers were named
type II. Styrene derivatives were also allowed to react with
RuCl3ÁnH2O, and gave the corresponding dimers in THF. In
benzene, however, it polymerized. Table 1 shows the results of
dimerization of olefins. Type I and II dimers can be classified
as Markovnikov-type adducts. The classification of Markovni-
kov-type and anti-Markovnikov-type is the same as that for ad-
dition of halogenated acid to olefins: The hydrogen of intermedi-
ate Ru–H bonds to carbon on which more hydrogens are present,
and ruthenium bonds to carbon in which less hydrogens are pres-
ent.
trichloride n-hydrate (RuCl3ÁnH2O) were investigated and dime-
rization, alkoxylation and sulfidation of olefins were noted. Ad-
ducts of Markovnikov type and anti-Markovnikov type were ob-
tained in a stereospecific manner and in good yield, depending
on the type of olefins used as the starting materials.
In recent years, various catalytic reactions of ruthenium
compounds have been developed. Generally speaking, most of
interest is focused on the unique carbon–carbon bond formation
to contribute to organic synthesis. One of most common reac-
tions is olefin metathesis. Since the discovery of Grubbs cata-
lysts, those catalysts and their preparation have been the focus
of many investigators.1 First off, olefin metathesis was studied
by using of simple olefins, and nowadays it expands to the use
of dienes and enones.2–5 More recently, it is reported that ruthe-
nium catalyzes cyclization reactions of dienes, in which isomer
selectivity is excellent.3 Some other reactions are also investigat-
ed.6–12 These reactions are interesting as atom-economy reaction
to minimize waste production.13 However, in many cases, the
necessity and role of such metal ligands in reaction mechanisms
are not clearly elucidated. Therefore, we have investigated novel
ruthenium-catalyzed reactions employing RuCl3ÁnH2O as com-
mercially available and more economical catalyst, instead of ex-
pensive or complex catalysts requiring some work-up for prepa-
ration, wherein we have gotten some interesting and significant
information.
Ruthenium-catalyzed reactions of enones with olefins were
studied and discussed on their selectivities.5 We also examined
the reaction of conjugate enones (Scheme 1). Although their re-
activity was relatively low, compared with that of simple olefins,
formation of anti-Markovnikov type dimer 3 was exclusively ob-
served along with small amount of unidentified trimer.14
O
N(CH )
3 2
RuCl nH O
3
2
(H C) N
3
2
solv.:CH ClCH Cl
2
2
O
(H C) N
3
2
3 (17%)
anti-Markovnikov-type
O
Scheme 1. Dimerization of N,N-dimethylacrylamide.
Table 1. Dimerization of olefins
Alcohol is sometimes employed as a solvent for ruthenium-
2mol%
RuCl3 nH2O
2mol%
RuCl3 nH2O
catalyzed reactions. Therefore we carried out the reactions in the
presence of EtOH. The reactions gave alkoxylated adducts al-
most as sole product.
THF
benzene
1 (94%)
2 (78%)
Markovnikov-type
[Type II]
Table 2 shows the results of alkoxylation. Olefins reacted
with primary alcohols and diols to give alkoxylated products
in moderate to good yields. However, they did not react with ter-
tiary alcohols or phenol. The products obtained in these reactions
were Markovnikov-type, whereas products in the addition of al-
cohols to conjugate enones were anti-Markovnikov-type, which
showing the coincidence with the result in olefin dimerization
above mentioned.
Furthermore, a reaction of methyl vinyl ether with
mercaptoethanol was conducted. As expected, sulfidated product
was obtained in excellent yield. In case of Table 2, Entries 3 and
5, we obtained the products which olefins or enones reacted with
both hydroxy group (–OH) and mercapto group (–SH). It is un-
derstandable that the reactivity of mercapto group (–SH) should
be much greater than that of hydroxy group (–OH). When ethan-
ditiol was used, not one but two mercapto groups reacted with
olefins and enones.
Markovnikov-type
[Type I]
Dimer
Entry
Olefin
Yield/%
R
65
83
81
70
R=H
CH3
OCH3
Cl
a)
1
2
type
type
R
R
b)
CH2
64
solvent: a) THF b) benzene.
Our initial attempt at this investigation began with ꢀ-meth-
ylstyrene as a substrate. A mixture of ꢀ-methylstyrene
(10 mmol) and 2 mol % RuCl3ÁnH2O in benzene (10 mL) was re-
We do not have any confirmed information on the initial ac-
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.6 (2004)
729
Table 2. Alkoxylation of olefins and enones
N
O
N
R2
O
O
R1
Ru
H
RuCl3 nH2O
R2
R1
Hydrometallation
Markovnikov-type
O
N
OH
solv.:CH2ClCH2Cl
O
β
-H elimination
R1
O
N
O
R1
N
O
R2
O
anti Markovnikov-type
H
H
Olefin or enone
Yield/%
68
Entry
1
Alcohol
Carbometallation
O
Ru
N
O
O
N
OH
Scheme 3. Proposed catalytic cycle for N,N-dimethyacryl-
amide dimer.
O
a)
90
O
O
2
3
OH
Anti-Markovnikov
type
Markovnikov
OH
99
Reductive Elimination
Ru
HS
type
R
O
O
O
O
65
90
R
2 R"CH2OH
O
OH
SH
R'
R
4
5
R"CHO
R
HO
HO
H
O
O
Ru
H
a) solv.: THF
O
Ru
R
Ru
R'
R
H
tive species of ruthenium catalyst in the present reactions. How-
ever, the formation of initial ruthenium hydride (Ru–H)15 might
be suggested from the structure of isolated products and from
lots of precedence of similar reactions. The proposed reaction
mechanism is outlined in Scheme 2–4. After the initial coordina-
tion of olefin onto ruthenium hydride species followed by 1,2-
hydrometallation of Markovnikov-type, carbometallation of sec-
ond olefin takes place, followed either by ꢀ-elimination of ruthe-
nium (formation of type II products) or by oxidative cyclization
into aromatic C–H bond (formation of type I product), as shown
in Scheme 3. In the case of conjugate enones, anti-Markovnikov-
type products are formed, because oxygen of the carbonyl group
may affect the coordination of enones to Ru–H (Scheme 4).
Scheme 4 shows a proposed mechanism of alkoxylation. Ruthe-
nium hydride could be formed from alkoxylated ruthenium,16,17
and subsequent hydrometallation and reductive elimination take
place in the same manner as of dimerization. It is possible that
sulfidation occurs in the same manner.
R
O
O
Hydrometallation
Ru
O
Hydrometallation
Ru
H
R'
Scheme 4. Proposed catalytic cycle for alkoxylation.
on the starting material. We are interested in reactions of olefins
with optically active substances, which are currently in progress.
References and Notes
1
2
3
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4
5
6
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8
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CH
H
3
9
Ru
β
-H
Reductive
elimination
elimination
Hydrometallation
Type
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Type
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CH
CH
3
H
2
Ru
Ru
H
CH
H
3
Ru
H
H
Ru
ortho C−H
insertion
Oxidative
cyclization
13 B. M. Trost, Angew. Chem., Int. Ed. Engl., 34, 259 (1995).
14 Because of the low yield, the structure is not identified yet.
15 ꢁ-Chloro-ꢀ-methylstyrene was formed in a considerable yield
when equimolar amounts of RuCl3ÁnH2O and ꢀ-methylstyrene
were used. The result may show that at least in part, Ru–H was pro-
duced by the addition of Ru–Cl to olefin, and afterwards ꢁ-elimina-
tion.
16 R. V. Hoffman, Tetrahedron Lett., 15, 2415 (1974).
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H C
3
Scheme 2. Proposed catalytic cycle for styrene dimer.
In summary, we discovered novel catalytic reactions in
which two kinds of olefin dimers, Markovnikov type and anti-
Markovnikov type, were obtained regioselectively and in good
yield. Alcohols and thiols also reacted with olefins and gave
two types of adducts. The type of adduct obtained depended
Published on the web (Advance View) May 17, 2004; DOI 10.1246/cl.2004.728