A versatile rigid binucleating ligand for Rh2(μ-Cl) 2 moieties (see abstract)

Article abstract of DOI:10.1016/S0022-328X(03)00204-3

A rigid non-deforming "MCl₂M" binucleating ligand [7,8-μ-S(4′-C₆H₃(CH₃)) S-C₂B₉H₁₀]^- able to held the two rhodium atoms in a cooperative distance has been synthesized. The original two bridging chlorides are retained in [Rh₂ (C₅Me₅)₂Cl₂{7,8-μ-S (4′-C₆H₃(CH₃))S-C₂ B₉H₁₀}]⁺. Hydrogenation of 1-hexene is 10 times faster with [Rh₂(C₅Me₅) ₂Cl₂{7,8-μ-S(4′-C₆H₃ (CH₃))S-C₂B₉H₁₀}]⁺ than with [Rh₂(C₅Me₅)₂ Cl₄]. A hydrogenation mechanism has been proposed which assumes that [Rh₂(C₅Me₅)₂ (Cl)(H){7,8-μ-S(4′-C₆H₃(CH₃)) S-C₂B₉H₁₀}]⁺ is the first generated species in the process.

Full text of DOI:10.1016/S0022-328X(03)00204-3

Journal of Organometallic Chemistry 680 (2003) 89Á99
/
www.elsevier.com/locate/jorganchem
A versatile rigid binucleating ligand for Rh2(m-Cl)2 moieties: its
application as a catalyst in hydrogenation and cyclopropanation
Crystal structure of [Rh(C5Me5)Cl{7,8-m-S(4?-C6H3(CH3))S-
C2B9H10}][7,8-m-S(4?-C6H3(CH3))S-C2B9H10]×
/
THF
Francesc Teixidor a, Ma Rosa Cirera a, Clara Vinas a,*, Raikko Kivekas b,
˜
¨
Reijo Sillanpaa c, Albert Demonceau d
¨ ¨
a Institut de Cie`ncia de Materials de Barcelona (CSIC), Campus UAB, E-08193 Bellaterra, Spain
b Department of Chemistry, University of Helsinki, Box 55, FIN-00014 Helsinki, Finland
c Department of Chemistry, University of Jyvaskyla, FIN-351 Jyvaskyla, Finland
¨
¨
¨
¨
d Laboratory of Macromolecular Chemistry and Organic Catalysis, C.E.R.M. University of Lie`ge, Sart-Tilman (B.6a), B-4000 Lie`ge, Belgium
Received 3 March 2003; received in revised form 21 March 2003; accepted 22 March 2003
In the occasion of the 75th anniversary of a master in Boron Chemistry for his outstanding research capacity and to pioneer Boron in application
areas
Abstract
A rigid non-deforming ‘‘MCl2M’’ binucleating ligand [7,8-m-S(4?-C6H3(CH3))S-C2B9H10]ꢀ able to held the two rhodium atoms in
a cooperative distance has been synthesized. The original two bridging chlorides are retained in [Rh2(C5Me5)2Cl2{7,8-m-S(4?-
C6H3(CH3))S-C2B9H10}]ꢁ. Hydrogenation of 1-hexene is 10 times faster with [Rh2(C5Me5)2Cl2{7,8-m-S(4?-C6H3(CH3))S-
C2B9H10}]ꢁ than with [Rh2(C5Me5)2Cl4].
A
hydrogenation mechanism has been proposed which assumes that
[Rh2(C5Me5)2(Cl)(H){7,8-m-S(4?-C6H3(CH3))S-C2B9H10}]ꢁ is the first generated species in the process.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Metallacarboranes; Catalysis; Hydrogenation; Cyclopropanation; Rhodium compounds
1. Introduction
a century since polyethylene’s commercialization, poly-
olefins remain highly technology-driven [4].
The discovery that metallic complexes could be used
as catalyst precursors in homogeneous hydrogenation,
isomerization, hydrosilylation, and hydroformylation
reactions permitted a great development of organome-
tallic and coordination chemistry [1]. Catalysis is very
relevant to obtain optically active compounds of interest
to industrial chemistry such as pharmaceutical, alimen-
tary, essences, and other [2]. On the other hand,
polyolefins are the fastest growing segment of the
polymer industry [3]. Although it has been almost half
Nevertheless, in spite of the high number of known
catalytic systems, the use of metallacarboranes as
catalyst precursors is very limited until now [5]. The
use of rhodacarboranes as homogeneous catalysts for
the hydrogenation and isomerization of alkenes in mild
conditions of pressure and temperature was first re-
ported by Hawthorne and coworkers [6Á10]. Rhoda-
/
and ruthenacarborane complexes containing nido-
monothio and nido-monophosphino were found to be
exceptionally effective for the hydrogenation of alkenes
[11]. Metallacarboranes were also found to be stereo-
selective in the hydrogenation of methacycline to
doxycycline [11c,12]. Additionally, closo- and exo-nido
ruthena and rhodacarboranes have been studied as
catalyst precursors in the cyclopropanation of olefins
* Corresponding author. Tel.: ꢁ
5729.
E-mail addresses: teixidor@icmab.es (F. Teixidor), clara@icmab.es
(C. Vinas).
/
34-3-580-1853; fax: ꢁ34-3-580-
/
˜
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00204-3

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F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á99
/
have shown much less catalytic activity which was
interpreted as if the dinuclear complexes generate
vacancies more easily than the mononuclear complexes
[25].
Up to now, no hints were found indicative of the
formation of binuclear complexes containing [7,8-m-
S(R)S-7,8-C2B9H10]ꢀ ligands with ligand to metal ratio
of 1:2. However, a geometry study of a series of [7,8-m-
S(R)S-7,8-C2B9H10]ꢀ ligands pointed out that the
˚
Fig. 1. 7,8-Dithioether-7,8-dicarba-nido-undecarborate(-1) ligands
ꢀ
average Sꢀ ꢀ ꢀS distance was 3.18 A [26]. This value is
[7,8-m-S(R)S-7,8-C2B9H10
] .
relatively close to the Mꢀ ꢀ ꢀM distance in ‘‘MCl2M’’
binuclear fragments where Cl are bridging elements, e.g.
in [Rh2(C5Me5)2Cl4], the Rhꢀ ꢀ ꢀRh distance is 3.7191(6)
with ethyl diazoacetate (EtDA) and no great differences
in their activities have been observed [13].
˚
A [27]. This brought about the possibility of producing
Ligand derivatives of 7,8-dithio-7,8-dicarba-nido-un-
decaborate(-1) [7,8-m-S(R)S-C2B9H10]ꢀ, where R is a
flexible alkyl spacer joining the two sulfur atoms, have
been thoroughly studied in our group [14]. Variations in
the length of the 7,8-m-S(R)S moiety, see Fig. 1, have led
to distinct properties on the resulting complexes. A
relevant characteristic of these [7,8-m-S(R)S-7,8-
C2B9H10]ꢀ ligands is the enhanced bonding capacity
of the thioether groups as compared to organic
thioether. This enhancement is interpreted as if the
negative charge of the cluster partly resides on the
thioether [11e,15]. An example is the ready substitution
of Clꢀ by these ligands from a metal’s coordination
sphere [16], contrary to organic dithioether ligands that
require the previous removal of the chloride ligand by
precipitating agents like AgPF6 [17].
binuclear bihalogen-bridged complexes with a third
bridging moiety. In this work we report on the synthesis
and bridging capacity of the first rigid and non-
deforming ‘‘MCl2M’’ binucleating anionic ligand. Inter-
estingly, minimum distortions are created with regard to
the ancient complex [Rh2(C5Me5)2Cl4] both with
‘‘MX2M’’ surroundings.
2. Results and discussion
Ligands [7,8-m-S(R)S-7,8-C2B9H10]ꢀ with flexible -
S(R)S- spacers have always shown a tendency to chelate
to metal as is represented in Fig. 1; consequently,
L:Mꢂ1:1 ratios were always obtained mostly produ-
/
cing mononuclear complexes. Thus, although the Sꢀ ꢀ ꢀS
distance and the -S(R)S- anionic character were ade-
quate for binucleation, the flexible -S(R)S- did not help
for it. We have previously described the reaction of this
type of ligands [7,8-m-S(R)S-7,8-C2B9H10]ꢀ with
[Rh2(C5Me5)2Cl4] and only monomeric species of the
type [Rh(C5Me5)Cl(7,8-m-S(R)S-7,8-C2B9H10)] were ob-
tained [28].
On the other hand, ligand substitution reactions on
pentamethylcyclopentadienyl-rhodium complexes are of
considerable importance [18], especially in view of the
utility of these complexes for many reaction types [19].
Examples of mixed thioetherÁcyclopentadienyl Rh(III)
/
complexes are, however, scarce and up to now no
structural details have been reported in the literature.
Binuclear complexes with a close metal to metal
contact can be traced back to 1975 when Muetterties
[20] proposed analogies between metal clusters and
metal surfaces and speculated that molecular metal
clusters could be found to be catalysts with novel
properties. However, the anticipated evidence of cata-
lysis by metal clusters has not emerged, which brought
about the search for binuclear metal complexes with a
possible metal to metal cooperation [21]. Two model
types may be considered: (1) the direct contact with a
bond between the two metals and (2) the bridge contact
with two monoatomic bridging elements between the
two metals. The [Rh2(OAc)4] complex which is very
active in the catalytic cyclopropanation process [22] is
one relevant example of the first type. The complex
[Rh2(C5Me5)2Cl4] [23,27] which has been proven to be a
good hydrogenation catalyst [24] is one example of the
second type. The dinuclear nature influence of these
compounds in catalysis has been proven by comparison
with similar Rh(III) mononuclear complexes. These
2.1. Designing the new disubstituted ligand
The alternative way to force binucleation was to
produce a ligand with a rigid -S(R)S- spacer. A tolyl
spacer connected to the two sulfur atoms of the o-
carborane fragment, as it is shown in Fig. 2, was
designed. Although we have not considered optical
resolution in this work, the methyl group on the
aromatic ring was included to provide chirality.
Neither 1,2-m-S(4?-C6H3(CH3))S-C2B10H10 (1) nor
its nido derivative [7,8-m-S(4?-C6H3(CH3))S-C2B9H10]ꢀ
([2]ꢀ) had previously been synthesized. Due to the
aromatic nature of the organic group in the -S(R)S-
spacer, the methods previously utilized for alkyl -S(R)S-
spacers were not valid anymore and a new synthetic
method was required. Reaction of the bis(chlorosulfe-
nyl) derivative of 3,4-dimercaptotoluene with dilithiated
o-carborane in diethyl ether led to compound 1 in a 70%
yield.

F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á
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91
Fig. 2. Synthesis of [7,8-m-S(4?-C6H3(Me))S-7,8-C2B9H10)]ꢀ ([2]ꢀ).
Partial degradation, formal removal of Bꢁ, of
compound 1 was readily accomplished by reaction
with KOH in boiling ethanol [29]. The desired
dithioether nido derivative [7,8-m-S(4?-C6H3(CH3))S-
C2B9H10]ꢀ, [2]ꢀ, was isolated as [N(CH3)4][2] in 95%
yield after the addition of [NMe4]Cl. The synthetic
procedure leading to this [2]ꢀ is schematically indicated
in Fig. 2. A racemic mixture was obtained. Indeed, [2]ꢀ
is a racemate but no attempts were made for the
isolation of the two enantiomers.
Fig. 3. The more stable conformers for [2]ꢀ
.
2.2. Characterization of closo 1,2-m-S(4?-
C6H3(CH3))S-C2B10H10 and nido [7,8-m-S(4?-
C6H3(CH3))S-C2B9H10]ꢀ species
2.3. Reactivity of the new dithioether ligand to Rh(III)
complexes
A n(BÃ
/
H) stretching frequency at 2610 cmꢀ1, typical
for a closo compound, was observed for 1. The
A conformational analysis on [2]ꢀ by semiempirical
methods was performed [30], indicating that the mole-
cule presented two minima corresponding to two con-
formers. These two were equally possible since their
energies were almost identical. They are represented in
Fig. 3. Conformer B is very similar to the coordination
motif for mononuclear chelation but conformer A had
never been observed before.
The binuclear compound [Rh2(C5Me5)2Cl4] was uti-
lized as the source of an ‘‘RhCl2Rh’’ moiety with the
hope that the structural characteristics of this core
would be preserved at the final product.
The reaction of [NMe4][2] with [Rh2(C5Me5)2Cl4] in
ethanol at reflux for 4 h yielded 3 as an orange solid.
Reactions of [Rh2(C5Me5)2Cl4] with chelating organic
dithioethers (e.g. 1,4-dithiacyclohexane, 2,5-dithiahex-
ane) have been described before [17], but the direct
synthesis was not possible. It required the preparation of
tris-solvent complexes [Rh(C5Me5)(sol)3]2ꢁ by the reac-
tion of [Rh2(C5Me5)2Cl4] with AgPF6 in the presence of
resonances of the 11B{1H}-NMR integrating 2:4:4 in
the range ꢀ
/
3/ꢀ10 ppm also support the closo nature of
/
the cluster. The H-, H{11B}-, 13C{1H}-NMR spectra,
and elemental analysis were in agreement with the
proposed formula.
1
1
The nido ligand [2]ꢀ was characterized by elemental
1
1
analysis, H-, H{11B}-, 13C{1H}-, 11B-, and 11B{1H}-
NMR. Partial degradation was clearly proven by the
appearance of a 1H{11B} resonance at ꢀ
/
2.4 ppm
attributed to the endohedral open-face hydrogen. Ad-
ditionally, a n(BÃ
H) stretching frequency at 2530 cmꢀ1
is a clear indication of the nido structure. The 2:1:4:1:1
pattern in the 11B{1H}-NMR in the range ꢀ
8/ꢀ44 ppm
/
/
/
is consistent with the cluster partial degradation. The
1H{11B}-NMR spectrum of [N(CH3)4][2] displayed, in
addition to the tetramethylammonium protons, a singlet
signal at 2.2 ppm and a multiplet at 7.3 ppm in a ratio of
1:1 attributed to the methyl and aromatic hydrogens,
respectively. The number and positions of the carbon
signals are in agreement with the proposed formula.

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F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á99
/
Fig. 4. Synthesis of [Rh2(C5Me5)2Cl2(2)]ꢁ
.
weakly binding ligands like MeCN, py or THF. For
ligand [2]ꢀ reported here there is an easy replacement of
the chloride ligands from the Rh(III) coordination
sphere.
Reaction of [NMe4][2] with [Rh2(C5Me5)2Cl4] in
ethanol in the ratio 2:1 or 1:1 invariably produced the
same compound (see Fig. 4). The spectroscopic data and
elemental analysis shed some light onto the structure of
the compound 3. The IR spectra display a n(BÃ
/
H)
stretching frequency at 2530 cmꢀ1 that corroborates the
nido cluster structure of the complex. The 11B{1H}-
NMR spectra displayed a 2:2:1:4:5:1:1:1:1 pattern,
which indicated the presence of two non-equivalent
[2]ꢀ units in the molecule. The 1H{11B}-NMR, in
agreement with the 11B{1H}-NMR, also displayed two
BHB resonances at ꢀ
/
1.21 and ꢀ2.43 ppm, which also
/
proved the non-equivalency of the two cages. Some
resonances of the 11B{1H}-NMR of the complex
matched well with those of [2]ꢀ. Furthermore, the
1H{11B}-NMR BHB resonance at ꢀ
/
2.40 ppm in [2]ꢀ
corresponded well with this at ꢀ
/
2.43 ppm in 3. The tolyl
methyl resonance also supported this conclusion since
two distinct methyl resonances were found in 3 at 2.28
and 2.42 ppm. The methyl resonance in [2]ꢀ appears at
2.26 ppm. The elemental analysis supported the stoi-
chiometry [Rh(C5Me5)Cl(2)][2] for compound 3 which
would imply the presence of two [2]ꢀ ligands. All this
indicated that one of the ligands was coordinated to
metal while, most probably, the second one was free. To
unambiguously ascertain the structure of 3, good quality
X-ray crystals were grown in ethanol and THF. The
molecular structure is indicated in Fig. 5. It consists of a
binuclear cation [Rh2(C5Me5)2Cl2(2)]ꢁ incorporating
only one [2]ꢀ ligand compensated by a second anion
[2]ꢀ.
2.4. Description of the structure of 3×
/THF
The structure of 3×
/
THF is made of the cationic
complex [Rh2(C5Me5)2Cl2(2)]ꢁ that consists of the di-
m-dichlorobridged dirhodium moiety connected to the
dithioethercarborane anion and two C5Me5ꢀ anions, a
free dithioethercarborane monoanion, and THF solvent
(see Fig. 5). In the cation, the dithioethercarborane anion
Fig. 5. (a) Simplified perspective drawing (only the important atoms
are labeled) of [Rh2(C5Me5)2Cl2(2)]ꢁ. Disordered C5Me5 with minor
occupancy, coordinated to Rh(2), has been omitted for clarity.
Skeletons of C5Me5 have been drawn with thin lines (thermal ellipsoids
are at 20% level). (b) Perspective drawing of [2]ꢀ with the labeling
scheme (thermal ellipsoids are at 20% level).
bridges the metals via two RhÃ
and two chloride anions fulfill the coordination demands
of the rhodium cations. The structure is similar to the
/
S bonds, and two C5Me5ꢀ

F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á
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93
Table 1
Cyclopropanation of alkenes with EtDA a
better, had enhanced the catalytic capacity of
[Rh2(C5Me5)2Cl4].
Olefin
Cyclopropanation yield (%) (cis/trans or endo/exo ratio)
[Rh2(C5Me5)2Cl2(2)] [Rh2(C5Me5)2Cl4] [Rh2(C5H5)2Cl4]
[2]
3. Catalytic reactions
Styrene
Styrene
49 (0.67)
66 (0.65)
6 (1.1)
11 (0.97)
55 (0.69)
60 (0.66)
3.1. Hydrogenation of alkenes
(100 8C)
4-Methyl-
styrene
Catalytic hydrogenation tests on 1-hexene were per-
formed with [Rh2(C5Me5)2Cl2(2)][2] and were compared
with data from [Rh2(C5Me5)2Cl4] obtained under the
same conditions and setup. Precursor [Rh2(C5Me5)2-
Cl2(2)][2] hydrogenated 1-hexene 10 times faster than its
core equivalent [Rh2(C5Me5)2Cl4].
We interpret this data considering that in
[Rh2(C5Me5)2Cl4] a process leading to a mononuclear
species is invoked in the hydrogenation mechanism [34].
This is not required for [Rh2(C5Me5)2Cl2(2)]ꢁ due to the
extra [2]ꢀ bridging fragment.
56 (0.45)
51 (0.50)
28 (0.66)
21 (0.52)
4 (0.75)
5 (0.61)
3 (0.90)
53 (0.54)
57 (0.51)
33 (1.0)
4-Chloro-
styrene
a-Methyl-
styrene
1-Octene
2
4 (0.52)
3 (0.70)
10 (0.68)
Cyclooctene 12 (0.75)
Cyclooctene 18 (0.72)
(100 8C)
1
13 (0.79)
Reaction conditions: catalyst, 0.0075 mmol; olefin, 20 mmol; EtDA,
1 mmol diluted by the olefin up to 1 ml; addition time, 4 h;
temperature, 60 8C.
As an illustration of the possibilities of this and related
compounds, we have tentatively produced the mechanism
indicated in Fig. 6 which makes use of the geometrical
characteristics of [Rh2(C5Me5)2Cl2(2)]ꢁ. To simplify the
drawing, the carborane cage has been indicated only
once. Through the cycle the ‘‘Rh2’’ moiety never splits,
which would happen if the bridging dithioether carborane
was not present. This is why for [Rh2(C5Me5)2Cl4] and
similar binuclear complexes the proposed mechanism
always flows through mononuclear complexes. The
migration of the hydrogen from one metal to the olefin
on the second metal provides an easy route to the alkyl
formation. The Rhꢀ ꢀ ꢀRh proximity allows the ‘‘bridging’’
chlorides or hydrides to jump from one metal to another
to compensate the charge. The created vacancies would
be fulfilled by solvent molecules or additional alkene
substrates. Through the whole mechanism the oxidation
state of Rh(III) remains unaltered.
simple dithioether complex of the dinuclear Rh(III) [31].
In both compounds the main bonding parameters around
Rh(III) are very similar (Table 1 for 3).
Important structural features in the cation are the
˚
Rhꢀ ꢀ ꢀRh distance of 3.6142(10) A and the dihedral angle
of 14.90(12)8 defined by Rh(1)Cl(1)Cl(2) and
Rh(2)Cl(1)Cl(2), and the cis orientation of the two
(C5Me5)ꢀ ligands. In [Rh2(C5Me5)2Cl4] [27] the orienta-
tion of the (C5Me5)ꢀ ligands is trans and the
Rh(1)Cl(1)Rh(2)Cl(2) ring is planar. In [Rh2(C5Me5)2-
Cl2(2)]ꢁ the observed deviation of the Rh2Cl2Rh core
from planarity and movement of the Cl atoms apart
from the dithiocarborane ligand, probably arises from
steric crowding between the Rh centers and the dithio-
carborane ligand. The two ‘‘RhClRh’’ fragments in the
cation are highly different, one Cl is on the C2B3 open
face while the second is on the benzene ring; therefore, a
different reactivity is expected for both bridging chlor-
ides.
In this mechanism, the first step consists the uptake of
H2 to produce a mixed hydride chloride bridge. Thus, it
was convenient to synthesize [Rh2(C5Me5)2(H)(Cl)(2)]ꢁ,
the first step in the cycle, and to check its catalytic
capacity to support the proposed mechanism.
The conformers of [2]ꢀ in the complex and the anion
are different and correspond to the two minima found in
the conformational analysis of [2]ꢀ. Conformer A in
Fig. 3 coordinates the ‘‘RhCl2Rh’’ core, while confor-
The direct reaction of [Rh2(C5Me5)2Cl2(2)]ꢁ with a
hydride source was not performed due to the existence of
the acidic BHB group in [2]ꢀ. Instead, the reaction of
[(Rh2(C5Me5)2Cl3(H)] with [2]ꢀ was done in ethanol. The
result was [Rh2(C5Me5)2Cl(H)(2)][2]. The 11B{1H}-NMR
displayeda2:2:1:4:5:1:1:1:1pattern, very similar to that of
[Rh2(C5Me5)2Cl2(2)][2]. The 1H{11B}-NMR at the nega-
˚
mer B is the anion. The Sꢀ ꢀ ꢀS distance (3.326(3) A) in the
coordinated anion is longer than the one in the
˚
uncoordinated species (3.174(4) A).
Binuclear complexes have been claimed to be of
particular interest due to the metal atoms’ cooperative
effect as a consequence of the short Mꢀ ꢀ ꢀM distance [32].
The molecular structure of [Rh2(C5Me5)2Cl2(2)]ꢁ has
proven little distortion of the ‘‘RhCl2Rh’’ core with
regard to the starting [Rh2(C5Me5)2Cl4] complex. This
last had been proven to be active in the hydro-
genation of alkenes [33], so it was interesting to know
if [Rh2(C5Me5)2Cl2(2)][2] had preserved or, even
tivezone displayed three resonances at ꢀ
2.43 ppm with integration 0.3:0.7:1 and one triplet at ꢀ
12.16 ppm (1J(Rh,H)ꢂ
25 Hz) integrating 1. The
resonances at ꢀ2.43 correspond to the anion’s BHB,
while signals at ꢀ 1.24 ppm correspond to the
/
0.99, ꢀ
/
1.24, and
ꢀ
/
/
/
/
/
0.99 and ꢀ
/
BHB resonances of the coordinated [2]ꢀ considering the
two possible isomers shown in Fig. 7. Based on the BHB
resonances, the most abundant isomer is thought to be the

94
F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á99
/
Fig. 6. Proposed catalytic system for the hydrogenation of terminal alkenes with [Rh2(C5Me5)2Cl2(2)][2].
one with Cl closer to the C2B3 open face (ii) in Fig. 7. The
RhHRh resonances of both isomers appear at the same
position, which means that the C2B3 interaction with
RhHRh is negligible. The Me tolyl resonance also
supported the stoichiometry [Rh2(C5Me5)2Cl(H)(2)][2]
since two distinct Me resonances were found in the
complex at 2.2 ppm for the free ligand and at 2.4 ppm for
the coordinated one. Thus, ligand [2]ꢀ is able to hold both
Rh atoms in different surroundings.
the enhanced efficiency in the hydrogenation of 1-
hexene, which has been taken as a probe for these
studies.
As mentioned, one of the main characteristics of [2]ꢀ
is its capacity to bind the ‘‘RhCl2Rh’’ cores altering very
little the initial structural parameters. The ‘‘RhCl2Rh’’
cores for [Rh2(C5Me5)2Cl4] [27] and [Rh2(C5Me5)2
Cl2(2)][2] are very similar, e.g. Rhꢀ ꢀ ꢀRh distances of
˚
3.6142(10) and 3.614 A, respectively. The dihedral angle
defined by Rh(1)Cl(1)Cl(2) and Rh(2)Cl(1)Cl(2) are
0.008 and 14.90(12)8, respectively. The rigid bridging
nature of [2]ꢀ and the strong coordinating capacity of
these thioether groups make [2]ꢀ a suitable anionic
ligand to test Mꢀ ꢀ ꢀM cooperative effect. Work is now
underway to study reactivity of [2]ꢀ in front other
‘‘M2X2’’ binuclear complexes.
Thus, under the same experimental conditions, con-
versions of 6.2, 63.5, and 100% from 1-hexene to hexane
have been found for [Rh2(C5Me5)2Cl4], [Rh2(C5Me5)2
Cl2(2)][2], and [Rh2(C5Me5)2Cl(H)(2)][2], respectively. In
all situations the 11B{1H}-NMR of the resulting com-
plex after performing catalysis was comparable to the
original starting material. The 100% conversion found
for [Rh2(C5Me5)2Cl(H)(2)][2] supports the participation
of this species in the catalytic cycle.
All three catalyst precursors basically contain the
same core ‘‘RhClXRh’’. The last two incorporate a third
bridging element, the ‘‘[2]ꢀ’’, which possibly prevents
the metal centers to move apart, facilitating an Mꢀ ꢀ ꢀM
cooperative effect. This is claimed to be the reason for
3.2. Carbene reactions
The catalytic activity of [Rh2(C5Me5)2Cl2(2)][2] in
cyclopropanation of alkenes with EtDA was also
investigated Eq. (1).
Fig. 7. Isomers of [Rh2(C5Me5)2Cl(H)(2)][2].

F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á
/99
95
(1)
Under typical reaction conditions, EtDA was used in
excess of alkene. To enhance selectivity (i.e. cyclopro-
panes versus coupling products (diethyl maleate and
diethyl fumarate)), EtDA was added slowly via a pump
syringe to a solution of alkene and catalyst. The results
from several runs with different olefins are summarized
in Table 1. The yields are based on EtDA and the
remaining balance of EtDA is always converted to
coupling products. For sake of comparison,
[Rh2(C5Me5)2Cl4] and [Rh2(C5H5)2Cl4] were also inves-
tigated under the same experimental conditions.
Due to our interest in the mechanistic chemistry of
metal-mediated carbenoid transfer [38], we followed the
reaction of [Rh2(C5Me5)2Cl2(2)][2] and [Rh2(C5H5)2Cl4]
with EtDA by NMR at low temperatures. 10 equivalent
of EtDA was added to a solution of the rhodium
complex (10ꢀ2 mmol) in toluene-d8 at 253 K. 1H-
NMR spectra were acquired at 10 8C intervals from
253 to 343 K. No intermediates, viz. a rhodiumÁcarbene
/
complex, were detected. The spectra until room tem-
perature (303 K) were that of EtDA and the rhodium
complex. At 333 K after 2 h, the reaction was complete
with maleate and fumarate as the only products.
Throughout the reaction, no appreciable amounts of
an intermediate were accumulated to allow its detection.
From Table 1 it is clear that [Rh2(C5Me5)2Cl2(2)][2] is
much more active than [Rh2(C5Me5)2Cl4]. With styre-
nics, the former afforded cyclopropyl esters in moderate
yields (ca. 50%), whereas the latter gave very poor yields
(:5%). The substrate selectivity indicates that activated
/
olefins such as styrene are more reactive than non-
activated substrates such as 1-octene and cyclooctene. In
addition, substituting the para position of styrene by
either electron-donating (CH3) or electron-withdrawing
groups (Cl) did not affect the yields. Disubstituted
arylalkenes (a-methylstyrene) resulted in poorer yields
in comparison to styrene, a monosubstituted olefin.
Likewise, cyclooctene gave lower yields than 1-octene.
4. Experimental
4.1. Instrumentation
Elemental analyses were performed using a Carlo
Erba EA1108 microanalyzer. IR spectra were recorded
with KBr pellets on a Nicolet 710 FT spectrophot-
Interestingly, [Rh2(C5Me5)2Cl2(2)][2] also tolerates OÃ
/
H
1
ometer. The H-NMR (300.13 MHz), 11B-NMR (96.29
functionality. For example, allyl alcohol was reacted
with EtDA and, in addition to the expected cyclopro-
MHz), and 13C{1H}-NMR (75.47 MHz) spectra were
performed on a Bruker ARX 300 instrument equipped
with the appropriate decoupling accessories. All NMR
measurements were performed at 22 8C. The 11B-NMR
panation, OÃ/H insertion took place (Eq. (2), Table 2).
The catalytic reactions exhibited no significant stereo-
selectivity in the cyclopropyl ester product, which is
expected for most catalysts that lack bulky ligands [35],
rhodium and iron porphyrin catalysts being the excep-
tions [36,37]. In all cases, the thermodynamically more
stable trans (exo) cyclopropane was the major isomer.
chemical shifts are referenced to external BF3×
/OEt2,
while the 1H and 13C are referenced to SiMe4. Chemical
shifts are reported in units of parts per million (ppm).
According to the IUPAC convention, positive values of
the chemical shifts are to high frequency. All coupling
constant values are reported in Hertz. Catalytic hydro-
genations were conducted in a 35-ml autoclave built at
the workshop facility of the Universitat Auto`noma de
Barcelona. The autoclave was equipped with a water
jacket, a rupture disk, a manometer, and sample and gas
inlets. GC analyses were performed with a Shimadzu
GC-15A instrument using an SPB-1 capillary column
(Supelco; 30 m in length, 0.25 mm inner diameter, and 1
mm thickness stationary phase).
Table 2
Reaction of EtDA with allyl alcohol
Complex
Yields (%)
Cyclopropanation
OÃH insertion
/
[Rh2(C5Me5)2Cl2(2)][2]
[Rh2(C5Me5)2Cl4]
16
15
27
43
Reaction conditions are the same as in Table 1.

96
F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á99
/
(2)
4.2. Materials
(4.5 ml, 6.9 mmol, 1.4 M) was added. After stirring for
30 min at the ice water temperature, the mixture was
allowed to stir at room temperature for 30 min and then
cooled again (ice water). The contents of the first flask
were syringed into the carborane solution. After stirring
for 1 h at the ice water temperature and 1 h at room
temperature the solid was filtered and the solvent
evaporated. Purification by column chromatography
(silica gel, 66% hexane/H2CCl2) yielded analytically
pure 1 after solvent evaporation as a white solid. Yield:
Unless otherwise noted, all manipulations were car-
ried out under dinitrogen atmosphere using standard
vacuum line techniques. Ethyl ether and THF were
distilled from sodium benzophenone prior to use and the
rest of the solvents were of reagent grade quality and
were used without further purification. Methylene
chloride and carbon tetrachloride were distilled from
CaCl2 prior to use. 1-Hexene (Aldrich) was freshly
distilled from CaH2 prior to use. The rest of the solvents
were of reagent grade quality and were used without
further purification. o-Carborane (Dexsil Chemical
Corp.), a 1.6 M solution of n-BuLi in hexane, and 3,4-
dimercaptotoluene (Aldrich) were used as received. All
organic and inorganic salts were of analytical reagent
grade and were used as received. All reagents for olefin
cyclopropanation were obtained from Acros and Al-
0.72 g (70%). 1H-NMR (CDCl3): dꢂ
10H, BÃH), 2.38 (s, 3H, Ã
CH3), 7.20 (d, 1H, 2J(H,H)ꢂ
8, Caryl H), 7.26 (s, Caryl 8,
H), 7.55 (d, 1H, 2J(H,H)ꢂ
Caryl 2.19 (br s, BÃ
H); H{11B}-NMR (CDCl3): dꢂ
H), 2.33 (br s, BÃH), 2.38 (s, 3H, ÃCH3), 2.54 (br s,
8, Caryl H), 7.26 (s, 1H,
H), 7.55 (d, 1H, 2J(H,H)ꢂ H); 11B-NMR
8, Caryl
(CDCl3): dꢂ 154, 2B), ꢀ8.4 (d,
3.7 (d, 1J(B,H)ꢂ
1J(B,H)ꢂ 10.0 (d, 1J(B,H)ꢂ
154, 4B), ꢀ 144, 4B);
13C{1H}-NMR (CDCl3): dꢂ
20.7 (s, ÃCH3), 130.2,
130.6, 131.0, 141.8 (s, Ã
Caryl); IR (KBr), n(cmꢀ1):
H); C9H16B10S2 (296.46)*Calc.: C, 36.46; H,
/
0.00ꢀ
/
2.80 (br,
/
/
/
Ã
/
Ã
/
/
1
Ã
/
/
/
/
/
2
BÃ
/
H), 7.20 (d, 1H, J(H,H)ꢂ
/
Ã
/
Caryl
Ã
/
/
Ã
/
/
ꢀ
/
/
/
drich.
The
starting
rhodium
compounds
/
/
/
[Rh2(C5Me5)2Cl4] and [Rh2(C5Me5)2Cl3(H)] were
synthesized according to the literature procedure [39].
/
/
/
2610 (BÃ
/
/
5.44; S, 21.63; Found: C, 36.79; H, 5.33; S, 21.35%.
4.3. Synthesis of 1,2-m-S(4?-C6H3(CH3))S-C2B10H10
(1)
4.4. Synthesis of [N(CH3)4][7,8-m-S(4?-
C6H3(CH3))S-C2B9H10] ([N(CH3)4][2])
To a three-necked round-bottomed flask (50 ml) fitted
with a dinitrogen inlet/outlet containing deoxygenated
dry methylene chloride (10 ml) and N-chlorosuccinimide
(0.93 g, 3.47 mmol) was added a solution of 3,4-
dimercaptotoluene (0.54 g, 3.47 mmol) in methylene
chloride (10 ml). After stirring for 30 min at room
temperature the solid was filtered. The solvent was
evaporated and 20 ml of dry CCl4 was added. Insolubles
were separated by filtering through celite. The solvent
was evaporated and 30 ml of dry ethyl ether was added.
To a round identical flask containing deoxygenated dry
ethyl ether (100 ml) was added o-carborane (0.50 g, 3.47
mmol). The solution was cooled (ice water) and n-BuLi
Partial degradation of 1 was achieved following the
general procedure described in the literature [29]. Yield:
1
0.6 g (95%); H-NMR ((CD3)2CO): dꢂ
/
ꢀ
/
2.40 (br, 1H,
H), 2.26 (s, 3H, ÃCH3),
3.40 (s, 12H, N(CH3)4), 6.98 (d, 1H, 2J(H,H)ꢂ
8, Caryl
H), 7.10 (s, 1H, Caryl 8,
H), 7.13 (d, 1H, 2J(H,H)ꢂ
Caryl 2.40 (s,
H); 1H{11B}-NMR ((CD3)2CO): dꢂ
1H, BÃHÃB), 0.21 (br s, BÃH), 0.73 (br s, BÃH), 1.30
(br s, BÃH), 1.47 (br s, BÃH), 2.14 (br s, BÃH), 2.26 (s,
3H, ÃCH3), 3.40 (s, 12H, N(CH3)4), 6.98 (d, 1H,
2J(H,H)ꢂ
8, Caryl H), 7.10 (s, 1H, Caryl H), 7.13 (d,
BÃ
/
HÃ
/
B), 0.00ꢀ
/
2.80 (br, 9H, BÃ
/
/
/
Ã
/
Ã
/
/
Ã
/
/
ꢀ
/
/
/
/
/
/
/
/
/
/
Ã
/
Ã
/

F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á
/99
97
1H, 2J(H,H)ꢂ
/
8, Caryl
8.6 (d, J(B,H)ꢂ139, 2B), ꢀ
1B), ꢀ 143, 4B), ꢀ
17.3 (d, 1J(B,H)ꢂ
193, 1B), ꢀ34.8 (d, J(B,H)ꢂ
145, 1B); 13C{1H}-NMR
((CD3)2CO): dꢂ20.1 (s, ÃCH3), 55.2 (s, N(CH3)4),
127.6, 129.1, 129.8, 136.2, 136.8, 143.9 (s, ÃCaryl); IR
H); C13H28NB9S2 (359.79)*
Ã
/
H); 11B-NMR ((CD3)2CO): dꢂ
/
Table 3
Selected bond lengths (A) and angles (8) for 3×
1
1
˚
/THF
ꢀ
/
/
/
12.4 (d, J(B,H)ꢂ
/
165,
/
/
/
32.4 (d, 1J(B,H)ꢂ
/
˚
Bond lengths (A)
1
/
/
Rh(1)Ã
Rh(1)Ã
Rh(2)Ã
Rh(2)Ã
Rh(1)Ã
Rh(2)Ã
/
Cl(1)
Cl(2)
Cl(1)
Cl(2)
S(1)
2.4425(18)
2.4273(19)
2.4415(19)
2.420(2)
2.424(2)
2.428(2)
1.812(7)
1.781(7)
1.799(7)
1.767(8)
1.796(8)
1.759(9)
1.803(9)
1.751(10)
1.529(9)
1.565(11)
/
/
/
/
/
(KBr), n(cmꢀ1): 2530 (BÃ
Calc.: C, 43.40; H, 7.84; N, 3.89; S, 17.82; Found: C,
/
/
/
/
/S(2)
43.47; H, 7.84; N, 3.79; S, 17.70%.
S(1)Ã
S(1)Ã
S(2)Ã
S(2)Ã
S(3)Ã
S(3)Ã
S(4)Ã
S(4)Ã
C(7)Ã
C(47)Ã
/
C(7)
/C(12)
/C(8)
4.5. Synthesis of [Rh2(C5Me5)2Cl2(2)][2] (3)
/
C(13)
C(47)
C(52)
C(48)
C(53)
/
/
Deoxygenated boiling ethanol (9 ml) containing
[Rh2(C5Me5)2Cl4] (50 mg, 0.08 mmol) and
[N(CH3)4][2] (58 mg, 0.16 mmol) was boiled for 4 h.
By filtering the warm mixture an orange solid was
isolated. The solid was washed with water, warm
ethanol, and ethyl ether to yield an analytically pure
1
solid. Yield: 75 mg (84%). H-NMR ((CD3)2CO): dꢂ
/
/
/C(8)
/
C(48)
Bond angles (8)
Cl(1)Ã
Cl(1)Ã
Cl(2)Ã
Cl(1)Ã
Cl(2)Ã
Rh(1)Ã
Rh(1)Ã
C(12)ÃS(1)Ã
C(7)ÃS(1)Ã
C(8)ÃS(2)Ã
C(13)Ã
C(12)Ã
C(13)Ã
C(52)Ã
C(53)Ã
/
Rh(1)Ã
Rh(1)Ã
Rh(1)Ã
Rh(2)Ã
Rh(2)Ã
Cl(1)Ã
Cl(2)Ã
/
Cl(2)
S(1)
82.89(6)
93.86(7)
92.42(7)
83.05(6)
92.42(7)
95.46(6)
96.42(7)
108.8(2)
112.5(2)
113.4(2)
108.7(3)
103.8(3)
104.2(3)
99.2(4)
/
/
/
ꢀ
/
2.43 (br, 1H, BÃ
0.00ꢀ2.50 (br, 18H, BÃ
(s, 3H, ÃCH3), 2.42 (s, 3H, Ã
2J(H,H)ꢂ
8, Caryl H), 7.10 (s, 1H, Caryl
1H, J(H,H)ꢂ8, Caryl
Caryl H), 7.53 (s, 1H, Caryl
8, Caryl
H); 11B-NMR ((CD3)2CO): dꢂ
1J(B,H)ꢂ 14.1 (d, 1J(B,H)ꢂ
137), 12.6,
17.3 (d, J(B,H)ꢂ145, 5B), ꢀ31.5, ꢀ32.4, ꢀ
35.6; IR (KBr), 2530
n(cmꢀ1):
(BÃ
C38H62B18Cl2Rh2S4 (1118.46)*Calc.: C, 40.81; H,
/
HÃ
H), 1.81 (s, 15H, C*Ã
CH3), 6.98 (d, 1H,
H), 7.13 (d,
/
B), ꢀ
/
1.21 (br, 1H, BÃ
/
HÃ
/
B),
/
/
S(1)
Cl(2)
S(2)
/
/
/
/
/
CH3), 2.28
/
/
/
/
/
/
Rh(2)
Rh(2)
/
Ã
/
Ã
/
/
/
2
2
/
Ã
/
H), 7.43 (d, 1H, J(H,H)ꢂ
H), 7.56 (d, 1H, 2J(H,H)ꢂ
7.3, ꢀ8.6 (d,
138),
34.8,
H);
/
8,
/
/
Rh(1)
Ã
/
Ã
/
/
/
/
Rh(1)
Rh(2)
Ã
/
/
ꢀ
/
/
/
/
/
S(2)Ã
S(1)Ã
S(2)Ã
S(3)Ã
S(4)Ã
/
Rh(2)
/
ꢀ
/
ꢀ
/
/
1
/
/C(7)
ꢀ
/
/
/
/
/
/
/C(8)
ꢀ
/
/
/
/C(47)
/
/
/C(48)
100.7(4)
5.59; S, 11.46; Found: C, 40.60; H, 5.27; S, 11.37%. A
red crystal suitable for X-ray analysis was grown from
THF and ethanol.
4.7. X-ray diffraction study
Single-crystal data collection for 3×
formed at ambient temperature on a Rigaku AFC5S
diffractometer using graphite monochromatized MoÁ
Ka radiation and v/2u scan mode (2umax 508). An
/
THF was per-
4.6. Synthesis of [Rh2(C5Me5)2Cl(H)(2)][2] (4)
/
ꢂ
/
Deoxygenated boiling ethanol (10 ml) containing
[Rh2(C5Me5)2Cl3(H)] (48 mg, 0.08 mmol) and
[N(CH3)4][2] (58 mg, 0.16 mmol) was refluxed for 4 h.
By filtering the warm mixture a red solid was separated.
This was washed with warm ethanol and ethyl ether to
empirical absorption correction was performed (c
scans). The structure was solved by direct methods
and refined on F2 by the SHELX-97 program package
[40]. The Cp* ion coordinated to Rh(2) is disordered
assuming two orientations. The disordered Cp* ion was
refined as idealized rigid group. The partially occupied
C atoms of the disordered Cp* group were refined with
isotropic but rest of the non-hydrogen atoms with
anisotropic thermal displacement parameters. Hydrogen
atoms were treated as riding atoms using the SHELX-97
default parameters. Oxygen atom of the THF solvent
could not be very reliably identified. Selected bond
lengths and angles are listed in Table 3 and crystal-
lographic data are presented in Table 4.
yield an analytically pure solid. Yield: 48 mg (55%). 1H-
1
NMR ((CD3)2CO): dꢂ
RhÃHÃRh), ꢀ2.43 (br, 1H, BÃ
BÃHÃB), ꢀ0.99 (br, 0.3H, BÃHÃ
CH3), 2.21 (s, 3H, ÃCH3), 2.45 and 2.50 (s, 3H, Ã
6.98 (d, 1H, J(H,H)ꢂ8, Caryl H), 7.10 (s, 1H, Caryl
H), 7.13 (d, 1H, J(H,H)ꢂ8, Caryl H), 7.43 (d, 0.7H,
2J(H,H)ꢂ
8, Caryl H), 7.53 (s, 0.7H, Caryl H), 7.56 (d,
0.7H, J(H,H)ꢂ8, Caryl H), 7.66 (s, 0.6H, Caryl H),
7.70 (s, 0.3H, Caryl
H); 11B{1H}-NMR ((CD3)2CO):
dꢂ 7.5, ꢀ8.6, ꢀ12.3, ꢀ14.0, ꢀ17.3, ꢀ31.5, ꢀ32.5,
34.8, ꢀ H), 1155
37.1; IR (KBr), n(cmꢀ1): 2530 (BÃ
(RhÃHÃRh); C38H63B18ClRh2S4 (1084.02)*Calc.: C,
/
ꢀ
/
12.16 (t, J(Rh,H)ꢂ
/
25, 1H,
1.24 (br, 0.7H,
B), 1.81 (s, 15H, C*Ã
CH3),
/
/
/
/
HÃ
/
B), ꢀ
/
/
/
/
/
/
/
/
/
2
/
Ã
/
Ã
/
2
/
Ã
/
/
Ã
/
Ã
/
2
/
Ã
/
Ã
/
Ã
/
/
ꢀ
/
/
/
/
/
/
/
ꢀ
/
/
/
4.8. General procedure for the hydrogenation of 1-hexene
/
/
/
42.10; H, 5.86; S, 11.83; Found: C, 41.82; H, 5.55; S,
11.56%.
To a Schlenk flask containing 10 ml of THF was
/
added 1ꢃ
10ꢀ5 mmol of rhodium complex, after the

98
F. Teixidor et al. / Journal of Organometallic Chemistry 680 (2003) 89Á99
/
Table 4
with the Cambridge Crystallographic Data Centre,
CCDC No. 100559 for 3×THF. Copies of the data can
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: ꢁ44-
1223-336033; e-mail: deposit@ccdc.cam.uk or www:
http://www.ccdc.cam.ac.uk).
Crystallographic data for 3×THF
/
/
Empirical formula
Formula weight
Temperature (8 C)
C42H70B18Cl2ORh2S4
1190.52
21
/
˚
Wavelength (A)
0.71069
Triclinic
¯
P1 (No. 2)
Crystal system
Space group
Unit cell dimensions
/
˚
a (A)
11.985(3)
20.361(3)
11.881(3)
91.887(17)
101.90(2)
89.032(15)
2835.3(11)
2
Acknowledgements
˚
b (A)
˚
c (A)
This work was supported by MCyT (Project MAT01-
1575) and Generalitat de Catalunya (2001/SGR/00337).
M.R.C. thanks the Ministerio de Educacio´n y Cultura
for a grant.
a (8)
b (8)
g (8)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
m (cmꢀ1
Number of reflections collected
)
1.395
8.57
)
10 479
9960
References
Number of unique reflections
Rint
0.0324
1216
1.039
F(0 0 0)
Goodness-of-fit on F2
[1] (a) M.C. Simpson, D.J. Cole-Hamilton, Coord. Chem. Rev. 155
(1996) 163;
a
R1 [I ꢀ
wR2 [I ꢀ
/
2s(I)]
0.0564
0.1380
(b) A. Togni, L.M. Venanzi, Angew. Chem. Int. Ed. Engl. 33
(1994) 497;
b
/
2s(I)]
(c) A.K. Gosh, T. Mathiavanan, J. Cappiello, Tetrahedron
Asymmetry 9 (1998) 1;
a
R1ꢂ
wR2ꢂ
/
ajjFojꢀ
/
jFcjj/ajFoj.
b
2 1/2
/
[aw(j
/ / / /
Fo2
jꢀ
j
Fc2/j)2]/[awj
/
Fo2
/
j ]
.
(d) A.M.d’A. Rocha Gonsalves, M.M. Pereira, J. Mol. Catal. 113
(1996) 209;
dissolution of the solid 3ꢃ
added (when Et3N was used, 1.8ꢃ
/
10ꢀ2 mmol of 1-hexene were
(e) M. Bougauchi, S. Watanabe, T. Arai, H. Sasai, M. Shibasa-
shaki, J. Am. Chem. Soc. 119 (1997) 2329;
/
10ꢀ2 mmol was
added to the same Schlenk). Meanwhile, the autoclave
had been evacuated and fitted with hoses supplying
(f) M. Rakowski, Dubois, Chem. Rev. 89 (1989) 1.;
(g) J.C. Bayo´n, C. Claver, A.M. Masdeu-Bulto´, Coord. Chem.
Rev. 193 (1999) 73.
water maintained at the desired temperature (Tꢂ25 8C)
/
[2] (a) B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis
with Organometallic Complexes: A Comprehensive Handbook 2,
vol. 1 and 2, VCH, Weinheim, 2002;
from the constant-temperature bath and the gas inlet
had been connected to the H2 line. Then, the mixture of
the Schlenk was rapidly transferred to the autoclave
through the sample inlet via syringe, the gas inlet was
opened, and the system was pressurized to 12 bar of H2.
The magnetic stirring was started and the timing counter
reset. From the addition of the alkene to the reset of the
timing counter no more than 3 min passed. After 1.5 h,
the autoclave was vented and dismantled, and the
composition of the solution was analyzed by capillary
GC.
(b) E.J. Corey, C.J. Helal, Angew. Chem. Int. Ed. Engl. 37 (1998)
1986;
(c) G.W. Parshall, S.D. Ittel, Homogeneous Catalysis. The
Applications and Chemistry of Catalysis by Soluble Transition
Metals Complexes, 2nd ed., Wiley/Interscience, New York, 1992;
(d) A.N. Collins, G.N. Sheldrake, J. Crosby, Chirality in
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