Preparation of alkanechalcogenolate- And benzenechalcogenolate-bridged diruthenium complexes and their catalytic activity toward propargylation of acetone with propargylic alcohol

Article abstract of DOI:10.1021/om049475f

Various alkanechalcogenolate (SR, SeR, TeR)and benzenechalcogenolate (SPh, SePh, TePh)-bridged diruthenium complexes have been newly prepared, and their catalytic activity toward the propargylation of acetone with propargylic alcohol has been investigated

Full text of DOI:10.1021/om049475f

5100
Organometallics 2004, 23, 5100-5103
P r ep a r a tion of Alk a n ech a lcogen ola te- a n d
Ben zen ech a lcogen ola te-Br id ged Dir u th en iu m Com p lexes
a n d Th eir Ca ta lytic Activity tow a r d P r op a r gyla tion of
Aceton e w ith P r op a r gylic Alcoh ol
Yoshiaki Nishibayashi,*,† Hiroaki Imajima,† Gen Onodera,† Youichi Inada,†
Masanobu Hidai,‡ and Sakae Uemura*,†
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering,
Kyoto University, Kyoto 615-8510, J apan, and Department of Materials Science and
Technology, Faculty of Industrial Science and Technology, Tokyo University of Science,
Chiba 278-8510, J apan
Received J uly 14, 2004
Sch em e 1
Summary: Various alkanechalcogenolate (SR, SeR, TeR)-
and benzenechalcogenolate (SPh, SePh, TePh)-bridged
diruthenium complexes have been newly prepared, and
their catalytic activity toward the propargylation of
acetone with propargylic alcohol has been investigated
for comparison. Ab initio molecular orbital calculations
of syn and anti methanechalcogenolate-bridged, propane-
2-selenolate-bridged, and benzenethiolate-bridged diru-
thenium complexes have been carried out to explain the
reason for favorable formation of either isomer.
In tr od u ction
We have recently found that the efficient ruthenium-
catalyzed propargylic substitution reactions of propar-
gylic alcohols with various heteroatom- and carbon-
centered nucleophiles gave the corresponding pro-
pargylated products in high yields with complete regi-
oselectivity.1 It is noteworthy that the reactions are
catalyzed by thiolate-bridged diruthenium complexes
such as [Cp*RuCl(µ2-SR)]2 (Cp* ) η5-C5Me5; R ) Me,
could be formed in two stereoisomeric forms, syn and
anti, the ratio depending greatly on the kind of organic
group on chalcogen as well as that of chalcogen atoms.
This finding prompted us to investigate a whole aspect
of the preparation and catalytic reactivity of a variety
of organochalcogenolate-bridged diruthenium com-
plexes, supported by an unambiguous X-ray structural
determination of the new complexes prepared. We
describe here in detail the preparation of a variety of
syn and anti alkanechalcogenolate- and benzenechal-
cogenolate-bridged diruthenium complexes together
with the result of ab initio molecular orbital calculations
on the stability of some complexes and also the result
of the propargylation of acetone with propargylic alcohol
catalyzed by these diruthenium complexes.
i
nPr, Pr) and [Cp*RuCl(µ2-SMe)2RuCp*(OH2)]OTf (OTf
) OSO2CF3), but not by various monoruthenium com-
plexes.2 More recently, we have prepared a series of
methanechalcogenolate-bridged diruthenium complexes
and compared their catalytic activities toward propar-
gylic substitution reactions.3 As a result, it was revealed
that thiolate- and selenolate-bridged diruthenium com-
plexes were quite effective as catalysts, while telluro-
late-bridged complexes did not show any catalytic
activity.3 During these investigations we came across
the phenomenon that these diruthenium complexes
Resu lts a n d Discu ssion
[Cp*RuCl(µ2-SeMe)]2 (syn-2a )3 was isolated in 54%
yield from the reaction of the tetranuclear ruthenium-
(II) complex [Cp*Ru(µ3-Cl)]4 with dimethyl diselenide
in tetrahydrofuran (THF) at room temperature for 20
h. By careful examination of the filtrate after recrys-
tallization of syn-2a , the presence of another diruthe-
nium complex was disclosed, and it was actually isolated
in 16% yield. This was revealed to be the
anti methaneselenolate-bridged diruthenium complex
[Cp*RuCl(µ2-SeMe)]2 (anti-2a) by X-ray analysis (Scheme
1). The ORTEP drawing of anti-2a is shown in Figure
1, which clearly shows the presence of the doubly
bridged µ2-SeMe moieties and that of the two Cp*
groups and two chloride ligands in a trans configuration
relative to one another. Similarly, methanethiolate- and
methanetellurolate-bridged diruthenium complexes,
[Cp*RuCl(µ2-SMe)]2 (syn-1a ) and [Cp*RuCl(µ2-TeMe)]2
* To whom correspondence should be addressed. E-mail: ynishiba@
scl.kyoto-u.ac.jp (Y.N.), uemura@scl.kyoto-u.ac.jp (S.U.).
† Kyoto University.
‡ Tokyo University of Science.
(1) (a) Nishibayashi, Y.; Wakiji, I.; Hidai, M. J . Am. Chem. Soc. 2000,
122, 11019. (b) Nishibayashi, Y.; Wakiji, I.; Ishii, Y.; Uemura, S.; Hidai,
M. J . Am. Chem. Soc. 2001, 123, 3393. (c) Inada, Y.; Nishibayashi, Y.;
Hidai, M.; Uemura, S. J . Am. Chem. Soc. 2002, 124, 15172. (d)
Nishibayashi, Y.; Onodera, G.; Inada, Y.; Hidai, M.; Uemura, S.
Organometallics 2003, 22, 873.
(2) (a) The thiolate-bridged diruthenium complexes have been found
to provide unique bimetallic reaction sites for activation and trans-
formation of various terminal alkynes; see: Nishibayashi, Y.; Yama-
nashi, M.; Wakiji, I.; Hidai, M. Angew. Chem., Int. Ed. 2000, 39, 2909
and references therein. (b) The methanethiolate-bridged diruthenium
complex [Cp*RuCl(µ2-SMe)2RuCp*Cl] (syn-1a ) is commercially avail-
able from Wako Pure Chemical Industries (J apan) as met-DIRUX
(methanethiolate-bridged diruthenium complex) (No. 130-14581).
(3) Nishibayashi, Y.; Imajima, H.; Onodera, G.; Hidai, M.; Uemura,
S. Organometallics 2004, 23, 26.
10.1021/om049475f CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/17/2004

Notes
Organometallics, Vol. 23, No. 21, 2004 5101
Sch em e 2
Sch em e 3
F igu r e 1. Crystal structure of anti-[Cp*RuCl(µ2-SeMe)]2
(anti-2a ) with 50% probability ellipsoids.
(syn-3a ), were prepared by using dimethyl disulfide and
dimethyl ditelluride in 71% and 83% isolated yields,
respectively (Scheme 1).3 In these cases the preparation
of a very minor amount of another diruthenium com-
plex, which was thought to be the anti isomer, was
detected but could not be isolated. It has been previously
confirmed that no isomerization occurred between these
isomers when a mixture of syn and anti thiolate-bridged
diruthenium complexes was heated at 60 °C for 5 h.1d
When the reactions of the tetranuclear ruthenium-
(II) complex [Cp*Ru(µ3-Cl)]4 with other dialkyl dichal-
cogenides were carried out under similar reaction
conditions, the corresponding alkanechalcogenolate-
bridged diruthenium complexes [Cp*RuCl(µ2-YR)]2 were
obtained in good to high isolated yields, the yields of
the complexes being shown in Scheme 1. In contrast to
the formation of syn alkanethiolate (syn-1b,4 syn-1c,
syn-1d )-, syn alkanetellurolate (syn-3b)-, and syn pro-
pane-2-selenolate (syn-2d )-bridged diruthenium com-
plexes, only the anti isomer was formed in the cases of
ethaneselenolate- and n-propaneselenolate-bridged diru-
thenium complexes (anti-2b and anti-2c). The ORTEP
drawings of anti-2b, syn-3b, anti-2c, and syn-2d are
shown in the Supporting Information (Figures S2-S5,
respectively).
intramolecular distances between the two ruthenium
atoms (2.84-3.06 Å) correspond to a Ru-Ru single bond
(2.71-3.02 Å).6 The Ru-Ru bond distances of the
cationic complexes were slightly shorter than those of
the neutral complexes. The selected bond lengths and
angles for these complexes are shown in the Supporting
Information (Table S11). The orientations of the chal-
cogenolate substituents are almost the same in all cases.
Although the preparation of ferrocenechalcogenolate-
bridged diruthenium complexes [Cp*RuCl(µ2-YFc)]2 (Y
) S, Se, Te; Fc ) ferrocenyl) has already been reported
by our group,7 other arenechalcogenolate-bridged diru-
thenium complexes [Cp*RuCl(µ2-YAr)]2 (Y ) S, Se, Te;
Ar ) aryl) have not yet been prepared until now.
Treatment of the tetranuclear ruthenium(II) complex
[Cp*Ru(µ3-Cl)]4 with diphenyl disulfide and diselenide
in THF at room temperature for 20 h gave the ben-
zenethiolate- and benzeneselenolate-bridged diruthe-
nium complexes [Cp*RuCl(µ2-YPh)]2 (1e (Y ) S) and 2e
(Y ) Se)) in 65% and 73% isolated yields, where the
formation of only anti isomers was observed, in sharp
contrast to the alkanethiolate case (Scheme 3). The
molecular structures of the complex (anti-1e and anti-
2e) were unambiguously confirmed by X-ray analysis,
and ORTEP drawings are shown in the Supporting
Information (Figures S8 and S9). In the reaction with
diphenyl ditelluride, the corresponding benzenetelluro-
late-bridged diruthenium complex [Cp*RuCl(µ2-TePh)]2
(anti-3e) was formed in only 23% isolated yield, together
with the diruthenium complex [Cp*Ru(µ2-TePh)3RuCp*]-
Cl8 (24% isolated yield), although the molecular struc-
tures of these complexes could not be determined by
X-ray analysis (Scheme 3).
Treatment of the neutral alkanechalcogenolate-
bridged diruthenium complexes obtained thus far with
an equimolar amount of silver triflate (AgOTf)1c,d,5 in
THF at room temperature for 1 h gave the correspond-
ing cationic alkanechalcogenolate-bridged diruthenium
complexes [Cp*RuCl(µ2-YR)2RuCp*(OH2)]OTf (Y ) S,
i
Se, Te; R ) Me,3 Et, nPr, Pr) in high yields with
complete stereoselectivity (Scheme 2). For instance, the
reaction of either syn-2a or anti-2a with AgOTf gave
the same cationic complex, [Cp*RuCl(µ2-SeMe)2RuCp*-
(OH2)]OTf (syn-2a ′), in 89% or 77% isolated yield,
respectively, as a single isomer. Although anhydrous
solvents were used, the cationic complexes contain a
water molecule as a ligand, probably due to adventitious
water in the solvents. Similarly, starting from either
the syn or anti isomer of either diruthenium complex,
only the cationic syn isomer was obtained in all cases,
in which only the molecular structures of syn-2b′ and
syn-2d′ were unambiguously determined by X-ray analy-
sis (Supporting Information, Figures S6 and S7). The
Interestingly, treatment of the neutral benzenethi-
olate-bridged diruthenium complex (anti-1e) with an
(6) Gao, Y.; J ennings, M. C.; Puddephatt, R. J .; J enkins, H. A.
Organometallics 2001, 20, 3500 and references therein.
(7) Matsuzaka, H.; Qu¨, J .-P.; Ogino, T.; Nishio, M.; Nishibayashi,
Y.; Ishii, Y.; Uemura, S.; Hidai, M. J . Chem. Soc., Dalton Trans. 1996,
4307.
(8) (a) A similar benzenethiolate-bridged complex, [Cp*Ru(µ2-SPh)3-
RuCp*]Cl, has already been reported; Dev, S.; Imagawa, K.; Mizobe,
Y.; Cheng, G.; Wakatsuki, Y.; Yamazaki, H.; Hidai, M. Organometallics
1989, 8, 1232. (b) Matsuzaka, H.; Ogino, T.; Nishio, M.; Hidai, M.;
Nishibayashi, Y.; Uemura, S. J . Chem. Soc., Chem. Commun. 1994,
223.
(4) Hashizume, K.; Mizobe, Y.; Hidai, M. Organometallics 1996, 15,
3303.
(5) Matsuzaka, H.; Takagi, Y.; Hidai, M. Organometallics 1994, 13,
13.

5102 Organometallics, Vol. 23, No. 21, 2004
Notes
F igu r e 2. Molecular structures of [Cp*RuCl(µ2-SMe)]2 (1a ), [Cp*RuCl(µ2-SeMe)]2 (2a ), [Cp*RuCl(µ2-TeMe)]2 (3a ), [Cp*RuCl-
(µ2-SeiPr)]2 (2d ), and [Cp*RuCl(µ2-SPh)]2 (1e).
Sch em e 4
configuration of benzenechalcogenolate moieties (Scheme
4), similar to the corresponding cationic syn complexes
produced in the reactions of the corresponding fer-
rocenechalcogenolate-bridged diruthenium complexes
with AgOTf.7
Ab initio molecular orbital calculations of the meth-
anechalcogenolate-bridged, propane-2-selenolate-bridged,
and benzenethiolate-bridged diruthenium complexes
(1a , 2a , 3a , 2d , and 1e) were carried out to find the
reason for the favorable formation of either syn or anti
isomers. As shown in Figure 2, the structural optimiza-
tions gave quite similar geometries to those of X-ray
analysis. The energies of all complexes were obtained
by the single-point enegy calculations for optimized
geometries. Figure 2 shows the relative energy differ-
ences for syn and anti methanechalcogenolate-bridged
diruthenium complexes (1a , 2a , and 3a ), propane-2-
selenolate-bridged diruthenium complexes (2d ), and
benzenethiolate-bridged diruthenium complexes (1e). In
general, syn methanechalcogenolate-bridged diruthe-
nium complexes (syn-1a , syn-2a , and syn-3a ) are more
stable than the corresponding anti complexes (anti-1a ,
anti-2a , and anti-3a ), the calculated energy differences
between syn and anti complexes being 3.69, 2.08, and
2.28 kcal/mol, respectively. Steric repulsion between the
Cp* ring and the bridged alkane moiety of the anti
complex is considered to be the reason the syn complex
is more stable than the anti complex. In contrast, the
anti benzenethiolate-bridged diruthenium complex (anti-
equimolar amount of AgOTf in THF at room tempera-
ture for 1 h gave the corresponding cationic benzenethi-
olate-bridged diruthenium complex [Cp*Ru(µ2-Cl)(µ2-
SPh)2RuCp*]OTf (1e′) in 96% isolated yield as a single
isomer (Scheme 4). The molecular structure of the
complex (1e′) was unambiguously determined by X-ray
analysis, and an ORTEP drawing is shown in the
Supporting Information (Figure S10). The dinuclear
structure of 1e′ is bridged by one chloride moiety and
two benzenethiolate moieties, the latter of which are
present in a cis configuration. The Ru-Ru bond distance
of 1e′ is apparently shorter than those of other cationic
alkanethiolate-bridged diruthenium complexes. Simi-
larly, the corresponding cationic benzeneselenolate-
and benzenetellurolate-bridged diruthenium complexes
[Cp*RuCl(µ2-YPh)2RuCp*]OTf (2e′ (Y ) Se) and 3e′ (Y
) Te)) were obtained in 95% and 88% isolated yields,
respectively, but their molecular structures are not the
same as that of 1e′ and considered to have a syn

Notes
Organometallics, Vol. 23, No. 21, 2004 5103
Ta ble 1. P r op a r gyla tion of Aceton e w ith 4 Usin g a
Dir u th en iu m Com p lex a s Ca ta lysta
Sch em e 5
yield
yield
run
R
Y
complex (%)b run
R
Y
complex (%)b
1
2
3
4
5
6
7
8
9
Me
S
syn-1a
88
95
0
15c Me
S
syn-1a ′ 93d,e
Me Se syn-2a
Me Se anti-2a
Me Te syn-3a
16c Me Se syn-2a ′ 95d,e
produced by the reactions of the cationic chalcogenola-
tebridged diruthenium complexes with propargylic al-
cohol, and they reacted with nucleophiles to give the
corresponding propargylic-substituted products in good
yields.3 In sharp contrast, the formation of the alle-
nylidene complexes was not observed in the reactions
of anti alkanechalcogenolate-bridged diruthenium com-
plexes with propargylic alcohols such as 4 and 1,1-di-
p-tolyl-2-propyn-1-ol in the presence of NH4BF4 (Scheme
5). Similarly, we have also confirmed no formation of
the corresponding allenylidene complexes by the reac-
tions of anti benzenechalcogenolate-bridged diruthe-
nium complexes with propargylic alcohol in the presence
of NH4BF4. These results indicate that the reason the
anti diruthenium complexes showed no or only low
catalytic activity is the difficulty of formation of the
allenylidene intermediates in the reactions with prop-
argylic alcohols due to steric repulsion between the Cp*
ring of the complex and the substituents of allenylidene
ligand, as shown in Scheme 5. As another possibility,
the different abilities of the two isomers for dissociation
of a chloride ligand in the solvent in the presence of
NH4BF4 may be considered. The fact that some anti
alkaneselenolate-bridged diruthenium complexes show
a low catalytic activity may indicate some isomerization
from anti isomer to syn isomer during the reaction
between anti diruthenium complexes and propargylic
alcohols.1d As to the alkanetellurolate-bridged diruthe-
nium complexes, the difficulty of charge transfer in the
tellurolate-bridged diruthenium complexes may cor-
respond to their quite low catalytic activity, as the
charge transfer may be considered to be one of the
important factors for the catalytic alkylation, one Ru
moiety working as an electron pool or a mobile ligand
to another Ru moiety.3,12
17c Me Te syn-3a ′
0d,e
syn-1b′ 90
Se syn-2b′ 89
Te syn-3b
syn-1c′ 94
0
18c Et
19c Et
20c Et
21c nPr
S
Et
S
syn-1b
90
50
0
84
32
84
61
0
Et
Se anti-2b
Te syn-3b
5
Et
S
nPr
S
syn-1c
22c nPr Se syn-2c′ 90
nPr Se anti-2c
23c iPr
24c iPr Se syn-2d ′ 92
S
syn-1d ′ 93
10 iPr
11 iPr Se syn-2d
12 Ph anti-1e
S
syn-1d
25c Ph
S
1e′
0
0
0
S
26c Ph Se syn-2e
27c Ph Te syn-3e
13 Ph Se anti-2e
14 Ph Te anti-3e
0
0
a
All the reactions of propargylic alcohol (4; 0.60 mmol) with
acetone (36 mL) in the presence of complex (0.03 mmol) and
b
NH4BF4 (0.06 mmol) at reflux for 3 h. Isolated yield of 5.
c Without NH4BF4. Complex (2.5 mol %) was used. e GLC yield
d
of 5.
1e) is more stable than the corresponding syn complex,
the calculated energy difference between syn and anti
complexes being 5.25 kcal/mol. Experimental results of
the formation of these complexes are consistent with the
density functional calculations. The reason the forma-
tion of two isomers was observed in the case of meth-
aneselenolate-bridged diruthenium complexes (2a ) is
considered to be due to the relatively lower energy
difference between syn and anti complexes. In fact, the
syn propaneselenolate-bridged diruthenium complex
syn-2d is more stable than the corresponding anti
complex, the calculated energy difference between syn
and anti complexes being 14.3 kcal/mol. This is consis-
tent with the experimental result of only syn complex
formation. Thus, the thermodynamic stability of the
complexes is the most important factor in determining
the stereoselectivity of the complexes formed in the reac-
tions of the tetranuclear ruthenium(II) complex [Cp*Ru-
(µ3-Cl)]4 with dialkyl and diphenyl dichalcogenides.
Next, the catalytic reactivity of various chalcogeno-
late-bridged diruthenium complexes toward the prop-
argylation1b,d,3 of acetone with propargylic alcohol was
investigated for comparison. Treatment of 1-phenyl-2-
propyn-1-ol (4) with acetone in the presence of the
chalcogenolate-bridged diruthenium complex (5 mol %)
and NH4BF4 (10 mol %) at reflux temperature for 3 h
afforded the corresponding alkylated product, 4-phenyl-
5-hexyn-2-one (5). As a result, only the syn alkanethi-
olate- and alkaneselenolate-bridged diruthenium com-
plexes show a catalytic activity for the propargylation
of acetone, while syn alkanetellurolate- and anti ben-
zenechalcogenolate-bridged diruthenium complexes do
not show such catalytic activity (Table 1). Detailed
results and discussion are given in the Supporting
Information.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedure and crystallographic data of anti-2a , anti-2b, syn-3b,
anti-2c, syn-2d , syn-2b′, syn-2d ′, anti-1e, anti-2e, and 1e′ and
detailed results of the catalytic reactions. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM049475F
(9) (a) Nishibayashi, Y.; Inada, Y.; Hidai, M.; Uemura, S. J . Am.
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Previous results of stoichiometric and catalytic reac-
tions indicate that the propargylic substitution reactions
proceeded via allenylidene9-11 intermediates, where
only one of the two Ru atoms works as a reactive site
throughout the catalytic reaction.1a,b,d,3 In fact, we have
already found that the allenylidene complexes were
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2002, 124, 7181.