Ruthenium-mediated cyclotrimerization of alkynes utilizing the cationic complex [RuCp(CH3CN)3]PF6

Article abstract of DOI:10.1016/S0022-328X(03)00783-6

The substitutionally labile cationic complex [RuCp(CH₃CN) ₃]⁺ (as the PF₆^- salt) was tested with respect to its ability to catalyze the cyclotrimerization of terminal alkynes and diynes to afford benz

Full text of DOI:10.1016/S0022-328X(03)00783-6

Journal of Organometallic Chemistry 682 (2003) 204ꢂ211
/
www.elsevier.com/locate/jorganchem
Ruthenium-mediated cyclotrimerization of alkynes utilizing the
cationic complex [RuCp(CH3CN)3]PF6
Eva Ruba a, Roland Schmid a, Karl Kirchner a,*, Maria Jose´ Calhorda b,c
¨
a Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
b ITQB, Av. da Repu´blica, EAN, Apart. 127, 2781-901 Oeiras, Portugal
c Departamento de Qu´ımica e Bioqu´ımica, Faculdade de Cieˆncias, Universidade de Lisboa, 1749-016 Lisboa, Portugal
Received 27 February 2003; received in revised form 27 June 2003; accepted 27 June 2003
Abstract
The substitutionally labile cationic complex [RuCp(CH3CN)3]ꢀ (as the PF6ꢁ salt) was tested with respect to its ability to catalyze
the cyclotrimerization of terminal alkynes and diynes to afford benzene derivatives. Whereas [RuCp(CH3CN)3]ꢀ is in fact
promoting the catalytic cyclotrimerization of alkynes, the formation of stable and inert sandwich complexes of the type [RuCp(h6-
arene)]ꢀ deactivates the catalyst and thus quenches the catalytic cycle. All new sandwich complexes were isolated and characterized
spectroscopically. A proposal for a plausible catalytic cycle including possible degradation pathways of the catalyst is presented
based on DFT calculations. As key intermediates several novel carbene complexes have been identified including metallacyclo-
pentatriene and metallaheptatetraene species.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Alkynes; Cyclotrimerization; Arene Complexes; DFT calculations
1. Introduction
The transition-metal mediated [2ꢀ
mental results has been accumulated containing vast and
widely diversified information. Nevertheless, in order to
systematize the manifold observations further experi-
mental data and theoretical studies are of vital impor-
tance [10]. Important issues to be addressed are: What
intermediates are involved, e.g. metallacyclopenta-
dienes, metallacyclopentatrienes, metallaheptatrienes,
or metallanorbornadienes? What is the origin of the
chemo- and regioselectivity, and what determines
whether sometimes five- [11] and four-membered rings,
/
2ꢀ2] cycloaddi-
/
tion of alkynes is a very efficient method to synthesize
functionalized arene systems [1]. Particularly appealing
is the intrinsic atom-economical nature of these reac-
tions, although the chemo- and regioselectivity still
remains a problem. These transformations occur both
in stoichiometric and catalytic fashion depending on the
transition metal complexes. In the first case, the arene
ring frequently remains coordinated to the metal frag-
ment. Recent stoichiometric examples include alkyne
coupling reactions mediated by (h2-propene)Ti(O-i-Pr)2
[2], [Cp*Fe(CH3CN)3]ꢀ [3], and ZrCp2(C4Et4) [4].
Metal-catalyzed cyclotrimerizations have also been
reported using, for instance, the complexes CpCo(CO)2
[5], Ni(acac)2/PPh3 [6], RhCl2(PPh3)3 [7], (h5-
C9H7)Ru(cod)Cl [8], CpRu(cod)Cl, and Cp*Ru(cod)Cl
[9] as precatalysts. Accordingly, a large body of experi-
instead of six membered rings are formed, i.e. why [2ꢀ
/
2ꢀ1] and [2ꢀ2] cycloadditions take place? In the
/
/
present work we focus, experimentally and theoretically,
on the reaction of [CpRu(CH3CN)3]ꢀ (1) with terminal
alkynes and diynes. Despite the fact that the CH3CN
ligands of [RuCp(CH3CN)3]ꢀ are substitutionally labile
[12], one cannot a priori surmise that this complex is not
suitable for promoting the cyclotrimerization of alkynes
in catalytic fashion due to facile arene coordination, a
process requiring the dissociation of all three CH3CN
ligands. It has been shown [13] that as soon as one
CH3CN ligand is replaced by another ligand such as CO
or PR3, the exchange rate of the remaining two CH3CN
* Corresponding author. Tel.:
5880115499.
ꢀ
/
43-1-5880115341; fax:
ꢀ/43-1-
E-mail address: kkirch@mail.zserv.tuwien.ac.at (K. Kirchner).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00783-6

E. Ruba et al. / Journal of Organometallic Chemistry 682 (2003) 204ꢂ
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211
205
¨
ligands drops by several orders of magnitude. Moreover,
it may be noted that complex 1 is active also with respect
in Table 1. With the terminal alkynes HCꢀ
/
CBun, HCꢀ
/
CCH2Ph, and HCꢀCCOOEt, isomeric mixtures of
/
to alkeneꢂ
/
alkyne and alkyneꢂ
/
alkyne coupling [14,15]
cyclotrimerization products viz 1,2,4- and 1,3,5-substi-
tuted benzenes I and II were isolated in low to medium
and the cyclization of yne-enones [16].
yields. Only in the case of HCꢀ
/
CCOOEt the yield was as
CC6H9, on
high as about 85%. With HCꢀCPh and HCꢀ
/
/
the other hand, surprisingly no cyclotrimerization
products were formed at all. It is interesting to note
that the two possible isomers were exclusively obtained
in a 3:1 ratio which may be explained by the inter-
mediates shown in Scheme 1. This finding may also
suggest that there is no steric or electronic preference for
any of these pathways. A detailed mechanistic study
based on DFT/B3LYP calculations is presented in the
following section.
In a fashion similar to terminal alkynes, also the
diynes 1,6-heptadiyne and 1,7-hexadiyne afforded cyclo-
trimierzation products isolated as mixtures of the dimers
III and IV in moderate to medium yields (Table 1). With
most alkynes, complex 1 reacted to give sandwich
2. Results and discussion
2.1. Reactions of [RuCp(CH3CN)3]PF6 (1) with
terminal alkynes and diynes
Treatment of 1 with an excess of terminal alkynes
HCꢀ
/
CR (Rꢃn-Bu, CH2Ph, COOEt, Ph, C6H9) at
/
80 8C afforded on work-up a mixture of both organic
cyclotrimerization products as well as metal complexes
of the type [RuCp(h6-C6H3R3)]PF6 containing h6-co-
ordinated arene ligands.
The organic products could be separated by extrac-
tion with Et2O with the product distribution determined
1
by H-NMR spectroscopy. The results are summarized
Table 1
Cyclotrimerization of alkynes mediated by complex 1

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¨
Scheme 1.
complexes [RuCp(h6-C6H3R3)]PF6 in high yields (Table
CCOOEt no metal complex
formation has been observed. All complexes were
several conversions such as in cyclotrimerizations, but
surprisingly no representative of Ru is known. Oxidative
coupling of the acetylene ligands in B results in the
formation the coordinatively saturated metallacyclopen-
tatriene C, a symmetry allowed process if Cs symmetry
is preserved. Location of the transition state TSBC for
this reaction revealed a moderate activation barrier of
10.0 kcal molꢁ1. The detailed structures of B, C, and the
transition state TSBC are shown in Fig. 2. As the
reaction proceeds, the new CÁ Á ÁC bond starts to form
noted by the decrease in the CÁ Á ÁC distance from 2.787
1). Only in the case of HCꢀ
/
1
characterized by H- and 13C{1H}-NMR spectroscopy.
The complexes with Rꢃn-Bu and CH2Ph were 3:1
/
mixtures of the 1,2,4- and the 1,3,5-substituted arene
complexes 2a, 2b, 3a, and 3b and could not separated.
With HCꢀ
/
CPh and HCꢀ
CC6H9 exclusively the h6-
1,2,4-substituted benzene complexes 2c and 2b were
/
1
formed. The H-NMR spectrum typically showed one
characteristic signal for the three protons of the h6-
coordinated 1,3,5-substituted benzene and two doublets
and one singlet for the protons of the 1,2,4-substituted
product in the range of 6.3 to 5.9 ppm. The signal of the
protons of the Cp ligand gives rise to a singlet between
5.4 and 5.2 ppm. In the 13C{1H}-NMR spectra the
coordinated benzene ligand exhibits characteristic reso-
nances in the range of 100 to 80 ppm.
˚
in B to 2.106 in TSBC, to reach 1.390 A in species C,
characteristic of a CꢁC bond. At the same time, the two
acetylene groups must reorient themselves, so that two
of the RuꢂC bonds become stronger (distances decrease
from 2.252 (B), via 2.104 TSBC to 1.946 (C), and the
/
/
˚
other two weaker (2.240, 2.368, 2.883 A, respectively).
These changes occur smoothly. The transition state
occupies an intermediate position, lying closer to the
bisacetylene complex than to the metallacycle. Note that
2.2. Theoretical study. Formation of benzene and benzene
complexes
the Caꢂ
triple bond character (1.243 compared to 1.270 A in the
starting structure B), while CbꢂCb? is still away from a
/
Cb distances are still rather short exhibiting
˚
/
A general pathway for the conversion of the labile
tris-acetonitrile complex [CpRu(NCCH)3]ꢀ (1) (the
model with NCH will be called A), into benzene
complex H and free benzene is schematically shown in
Scheme 2 as a result of DFT/B3LYP [17] calculations
using Gaussian98 [18]. The potential energy surface (in
kcal molꢁ1) for a catalytic cycle including possible side
reactions is given in Fig. 1.
˚
bonding distance (2.106 A). The calculated structure C
compares well with the X-ray structures of the related
species containing CpRuBr and RuCp* fragments [19].
The metallacyclopentatriene C readily adds a third
acetylene molecule to give the metallacyclopentadiene D
(Fig. 3). In the absence of a-substituents there are no
severe steric restrictions for an incoming third alkyne,
since the nitrile co-ligand is a sterically little demanding
molecule. This is in contrast to related RuCp systems
containing the more bulky PR3 or SbR3 co-ligands
where no catalytic activity towards cyclotrimerization
has been observed [20]. A comparison of the optimized
The first step consists of the substitution of acetoni-
trile by acetylene which by experiment is known to
proceed via a dissociative mechanism [12], leading to the
bis-acetylene complex B. The associative alternative for
which the coordination of acetylene is accompanied by
h50h3 ring slippage to preserve the 18-electron count
/
geometry of C with that of D shows that the Cꢂ
/
C and
Ruꢂ
/
C bond distances within the metallacycle are very
can be excluded. The overall substitution reaction is
endothermic by 10.2 kcal molꢁ1 (Fig. 1). Bis-acetylene
complexes have been proposed as intermediates in
different and coordination of a third alkyne severely
perturbs the metallacycle framework. In contrast to

E. Ruba et al. / Journal of Organometallic Chemistry 682 (2003) 204ꢂ
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207
¨
Scheme 2.
Fig. 1. Profile of the B3LYP potential energy surfaces for the formation of benzene catalyzed by the ruthenium bisacetylene complex B and
formation of the benzene complex H.

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¨
Chart 1.
˚
Fig. 2. Relevant distances (A) in the optimized B3LYP geometries of
the ruthenium bisacetylene complex B, the metallacyclotpentatriene C,
termediates [21] in cyclotrimerization reactions of
alkynes referred to as Schore’s mechanism [1b]. How-
and the transition state TSBC
.
ever, as the reaction proceeds and the new Cꢂ
starts to form, the RuꢂCa bond which is directly
involved in the CꢂC coupling process increases from
2.124 in D to 2.134 in TSDE and 2.240 A in E but is not
being cleaved, while the other one decreases from 2.077
/
C bond
complex C the Cꢂ
shortꢂlongꢂshort pattern with the Caꢂ
CbꢂCb? bonds being 1.350, 1.348, and 1.444 A, respec-
tively, while the RuꢂC distances are elongated being
2.077 and 2.124 A. Energetically, D lies 4.8 kcal mol
lower in energy than C and free acetylene. The activa-
tion energy required for this addition is rather small
being merely 4.3 kcal molꢁ1. Complex D undergoes
/
C bond distances of D exhibit a
/
/
/
/
Cb, Ca?ꢂCb? and
/
/
˚
/
˚
/
ꢁ1
˚
˚
to 2.071 and 1.959 A, respectively. The detailed struc-
tures of D, E, and the transition states TSCD and TSDE
are given in Fig. 3.
It is very important to note, however, that the
transformation of D to E via TSDE is difficult if C and
subsequently facile Cꢂ
/
C bond coupling to give the novel
bicyclic carbene complex E releasing thereby 24.8 kcal
molꢁ1. The transition state for this process, TSDE, is
very similar to the structure of D coupled with the long
D bear a-substituents since after Caꢂ
/
Cacetylene coupling
the substituent (in the model system a hydrogen atom,
complex E) is pointing towards the Cp ligand giving rise
to repulsive interactions (Fig. 3). In fact, as has been
shown [9], the catalytic cyclotrimerizations of alkynes by
RuCp(COD)Cl takes place only if one of the alkynes to
be coupled is a 1,6-diyne.
˚
2.161 A Caꢂ
/Cacetylene bond distance indicating that the
transition state structure occurs quite early along the
reaction coordinate. The only noticeable change from D
is rotation of the acetylene ligand by ca. 58. Energeti-
cally this transition state lies merely 0.1 kcal molꢁ1
higher in energy than D (Fig. 2). Complex E contains an
unusual five- and four-membered bicyclic ring system
Another intermediate to be envisaged in the forma-
tion of arenes is the metallanorbornadiene M (Chart 1).
For the present system we were unable, however, to
locate neither a stationary point for L nor M. Notwith-
standing this, even if L and M had been located at the
density functional level, the reductive elimination carry-
ing both a metallacycloheptatriene and a metallanor-
bornadiene to benzene is actually symmetry forbidden
thus implying a prohibitively large activation barrier.
with one short and two long Ruꢂ
and 2.067 A). It is very important to mention that
addition of a third alkyne to form D does not result in a
/
C bonds (1.959, 2.240,
˚
classical insertion of an alkyne into the RuꢂCa single
/
bond of D to give the coordinatively unsaturated
metallacycloheptatriene L as shown in Chart 1. Metal-
lacycloheptatrienes are indeed frequently proposed in-
˚
Fig. 3. Relevant distances (A) in the optimized B3LYP geometries of complexes D, E, F, G and the transition states TSCD, TSDE, TSEF, and TSFG
.

E. Ruba et al. / Journal of Organometallic Chemistry 682 (2003) 204ꢂ
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209
¨
Similar results have been reported recently for the
related CoCp system [10b].
Complex E rearranges easily via transition state TSDE
to afford the novel metallacycle F. In the course of this
easily formed upon release of HCN from G. This
reaction is exothermic by 17.5 kcal. The detailed
structures of J, K, and the transition states TSJK and
TSKH are given in Fig. 4. Accordingly, the two most
likely reactions to form the arene complex H may
originate from D and/or G via dissociation of HCN.
process the internal Ruꢂ
/
C single is cleaved. This
reaction requires merely 1.0 kcal molꢁ1 activation
energy and is energetically very favorable releasing
12.9 kcal molꢁ1. Complex F features an unusual non-
planar asymmetric seven-membered metallacyclic moi-
3. Conclusion
˚
C bonds (1.971 and 1.915 A).
C bond distances within the metallacycle are
ety with two short Ruꢂ
/
We have shown here that [RuCp(CH3CN)3]ꢀ indeed
promotes the catalytic cyclotrimerization of alkynes, but
not in a selective manner with 1,2,4- as well as 1,3,5-
trisubstituted arenes formed in most cases. However, in
the course of the catalytic process several pathways to
form stable and inert sandwich complexes of the type
[RuCp(h6-arene)]ꢀ become readily available. In this
way the catalytically active intermediates are consumed
and the catalytic cycle is gradually quenched. Therefore,
The Cꢂ
/
˚
very similar ranging from 1.392 to 1.402 A. In simplified
F may be described as a metallacycloheptatetraene
species.
The final intermediate in the catalytic cycle of Scheme
2 is complex G featuring a weakly bound h3-coordi-
nated benzene ligand. The release of the resonance
stabilization energy upon arene formation combines
with the construction of two new carbon carbon s-
bonds releasing 64.0 kcal molꢁ1. The arene ligand is
although active in various other Cꢂ
/
C bond coupling
reactions, involving even alkynes, [RuCp(CH3CN)3]ꢀ is
an unsuitable catalyst for the cyclotrimerization of
alkynes. The formation of arene complexes may be
prevented under photochemical conditions, since the
arene ligands in [RuCp(h6-arene)]ꢀ are known to be
photo-labile [23].
only weakly coordinated noting the two rather long
˚
Ruꢂ
/
C bonds (2.733 and 2.727 A). This reaction is
unusual, however, since a new Cꢂ/C bond is formed via a
reductive elimination process involving a biscarbene
complex, a species that contains two metal carbon
double bonds. In the course of this reductive elimination
the carbon carbon distance decreases from 2.774 in F to
˚
2.323 in TSFG eventually to 1.416 A in G.
Completing the catalytic cycle in Scheme 2 requires
displacement of the arene ligand in G by a pair of
alkynes ligands. Thermodynamically, the barrier to
overcome this process is the Ru-arene binding energy
4. Experimental
4.1. General information
which appears to be small (weak Ruꢂ
/
C bonds). The
All manipulations were performed under an inert
atmosphere of argon by using Schlenk techniques. All
chemicals were standard reagent grade and used without
further purification. The solvents were purified accord-
ing to standard procedures [22]. The deuterated solvents
energetic consequences of the displacement of benzene
by two alkynes to give benzene and B is exothermic by
25.7 kcal molꢁ1 showing that arene displacement is
thermodynamically accessible (Fig. 1).
˚
were purchased from Aldrich and dried over 4 A
molecular sieves. [RuCp(CH3CN)3]PF6 (1) [23] was
prepared according to the literature. 1H-, and
Experimentally it has been found that the formation
of arene complexes gradually quenches the catalytic
cycle of Scheme 2 due the formation of sandwich
complexes of type H. This process requires at some
stage the liberation of HCN for which several dissocia-
tion scenarios are conceivable. If HCN dissociates
already from C, metallacycle I is formed (Fig. 1). This
reaction is endothermic by 18.0 kcal and not very likely.
On the other hand, if HCN is liberated from D, the
metallacyclopentadiene acetylene complex J is formed.
This reaction is only moderately endothermic by 4.8 kcal
molꢁ1. Once formed, J rearranges quite easily to afford
the cyclic biscarbene K and eventually via TSKH to give
the sandwich complex H. The activation energies to
convert J into K and K into H are rather small being 3.0
and 1.5 kcal molꢁ1, respectively. The small kinetic
barrier may be attributed to the large thermodynamic
driving force associated with the conversion of K into H
releasing 91.7 kcal molꢁ1. Finally, complex H may be
˚
Fig. 4. Relevant distances (A) in the optimized B3LYP geometries of
complexes J, K, H and the transition states TSJK and TSKH
.

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¨
13C{1H}-NMR spectra were recorded on Bruker
AVANCE-250 spectrometer and were referenced to
SiMe4.
103.9 (3C, h6-Bz), 89.0, 86.6, 86.3 (3C, h6-Bz), 83.5 (s,
5C, Cp).
4.2.4. [RuCp(h6-C6H3(1,2,4-C6H9)3)]PF6 (2d)
Only one isomer and no cyclotrimerization products
1
have been observed. Yield: 26 mg (90%). H-NMR (d,
4.2. Reactions of [RuCp(CH3CN)3]PF6 (1) with
alkynes
3
CDCl3, 20 8C): 6.41 (m, 1H, C6H9), 6.35 (d, JHH
ꢃ6.5
/
In a typical procedure, 100 ml of HCꢀ
/
CR (Rꢃ/n-Bu,
Hz, 1H, h6-Bz), 6.13 (d, 3JHH
ꢃ
6.5 Hz, 1H, h6-Bz), 6.05
/
CH2Ph, COOEt, Ph, C6H9) and 1,6-heptadiyne and 1,7-
octadiyne) were added to a solution of 1 (20 mg, 0.046
mmol) in 3 ml CH3NO2. The solution was heated to
80 8C for 24 h. After that time the reaction mixture was
evaporated to dryness under vacuum and the products
were extracted with Et2O. The solvent was again
removed under vacuum affording mixtures of coupling
products. The product distribution was determined by
NMR spectroscopy. The residues, which were insoluble
in Et2O, were filtrated, dried under vacuum and
characterized by NMR spectroscopy.
(s, 1H, h6-Bz), 5.94 (m, 2H, C6H9), 5.29 (s, 5H, Cp),
2.32-1.48 (m, 24H, C6H9). 13C{1H}-NMR (d, CDCl3,
20 8C): 133.4, 133.2, 133.0, 132.6, 133.4 (6C, C6H9),
108.4, 108.3, 105.4 (3C, h6-Bz), 86.0, 82.7, 81.5 (3C, h6-
Bz), 80.9 (5C, Cp), 30.6, 30.3, 27.1, 26.2, 26.0, 22.9, 22.6,
21.8, 21.7, 21.6 (12C, C6H9).
4.2.5. [RuCp(h6-C14H16]PF6 (2e)
Yield: 19 mg (83%). 1H-NMR (d, CDCl3, 20 8C): 6.32
(s, 1H, h6-C6H3), 6.27 (d, 3JHH
ꢃ
6.0 Hz, h6-C6H3), 5.99
/
3
(d, JHH
ꢃ
/
6.0 Hz, h6-C6H3), 5.29 (s, 5H, Cp), 2.90 (t,
3JHH
ꢃ
/
7.5 Hz, 4H, CH2), 2.73 (t, JHH
ꢃ
/
7.5 Hz, 2H,
2.4 Hz, 2H, CH2),
7.4 Hz, 2H, CH2), 2.02 (t, 4JHH
2.4 Hz,
3
4.2.1. [RuCp(h6-C6H3(n-Bu)3)]PF6 (2a, 3a)
CH2), 2.23 (dt, 3JHH
2.09 (t, 3JHH
ꢃ
/
7.0 Hz, 3JHH
ꢃ
/
The residue is a mixture of 1,2,4- and the 1,3,5-
substituted benzene complexes at a ratio of 3:1. The two
compounds were not separated. Yield: 23 mg (88%). 1H-
NMR (d, CDCl3, 20 8C): 6.19 (s, 3H, h6-Bzsym), 6.05 (s,
1H, h6-Bzasym), 6.00 (s, 1H, h6-Bzasym), 5.98 (s, 1H, h6-
Bzasym), 5.24 (s, 5H, Cpsym), 5.23 (s, 5H, Cpasym), 2.72-
2.36 (m, 6H, CH2), 1.71-1.27 (m, 12H, CH2), 1.06-0.83
(m, 9H, CH3). 13C{1H}-NMR (d, CDCl3, 20 8C): 106.8
(1C, h6-Bzasym), 106.5 (s, 1C, h6-Bzasym), 106.0 (3C, h6-
Bzsym), 105.3 (h6-Bzasym), 88.1 (3C, h6-Bzsym), 87.0 (1C,
h6-Bzasym), 86.7 (1C, h6-Bzasym), 86.0 (1C, h6-Bzasym),
81.6 (5C, Cpsymꢀasym), 34.5, 34.3, 34.2, 34.1, 34.0, 31.9,
31.6, 23.3, 23.2, 22.9, 22.8 (Bun), 14.0 (CH3).
ꢃ
/
ꢃ
/
1H, CCH), 1.85 (m, 2H, CH2). 13C{1H}-NMR (d,
CDCl3, 20 8C): 109.1, 108.3, 104.7 (3C, h6-Bz), 85.2,
83.7, 82.1 (3C, h6-Bz), 81.2 (5C, Cp), 70.2, 65.6 (2C,
CCH), 35.5, 34.6, 33.2, 31.2, 30.9, 24.6, 17.7 (6C, CH2).
4.2.6. [RuCp(h6-C16H20)]PF6 (2f) and [RuCp(h6-
C24H30)]PF6 (2g)
The compounds 2f and 2g could not separated, but
their ratio was determined by NMR spectroscopy and is
1
7:4 (2f:2g). Yield: 23 mg (89%). H-NMR (d, CDCl3,
20 8C): 7.04-6.83 (m, 3H, Bz (non-coord., trimer)), 6.25-
5.99 (m, 3H, Bz (coord., dimerꢀ
/
trimer)), 5.30 (s, 5H,
Cp(dimer)), 5.25 (s, 5H, Cp (trimer)), 2.88-2.69 (m, 4H,
3
CH2), 2.64-2.43 (m, 2H, CH2), 2.27 (dt, JHH
4.2.2. [RuCp(h6-C6H3(CH2Ph)3)]PF6 (2b, 3b)
The residue is a mixture of 1,2,4- and the 1,3,5-
substituted benzene complexes at a ratio of 3:1. The two
compounds were not separated. Yield: 26 mg (86%). 1H-
NMR (d, acetone-d6, 20 8C): 7.59-7.00 (m, 15H, Ph),
6.34-5.99 (m, 3H, Bz), 5.34 (s, 5H, Cp), 4.20-3.80 (m,
6H, CH2). 13C{1H}-NMR (d, acetone-d6, 20 8C): 139.4,
138.4, 138.3 (3C, Ph), 129.5, 129.4, 129.2, 129.1, 128.9,
128.7, 127.6, 127.5 (15C, Ph), 106.0, 104.9, 104.4 (3C,
h6-Bz), 88.4, 86.9, 85.8 (3C, h6-Bz), 81.9 (5C, Cp), 39.4,
37.3, 36.9 (3C, CH2).
ꢃ
/6.6 Hz,
4
4JHH
ꢃ
/
2.6 Hz, 2H, CH2 (dimer)), 2.00 (t, JHH 2.6
ꢃ
/
Hz, CH (dimer)), 1.92-1.50 (m, 12H, CH2). 13C{1H}-
NMR (d, CDCl3, 20 8C): 138.6, 136.2, 132.4 (3C, Bz
(non-coord., trimer)), 129.5, 129.4, 124.3 (3C, Bz (non-
coord., Trimer)), 112.8, 103.3, 102.7 (3C, Bz (coord.,
dimerꢀ
/
trimer)), 87.3, 86.5, 85.4 (3C, Bz (coord.,
dimerꢀ
/
trimer)), 81.4 (5C, Cp, dimer), 81.2 (5C, Cp,
trimer), 78.5, 69.3 (2C, CCH), 30.9, 30.1, 22.5, 19.5,
18.4, 14.1 (8C, CH2 (dimerꢀtrimer).
/
4.3. Computational techniques
4.2.3. [RuCp(h6-C6H3(1,2,4-Ph)3)]PF6 (2c)
Only one isomer and no cyclotrimerization products
All calculations were performed using the Gaussian98
software package [18] on the Silicon Graphics Cray
Origin 2000 of the Vienna University of Technology.
The geometry and energy of the model complexes and
the transition states were optimized at the B3LYP level
[17] with the Stuttgart/Dresden ECP (sdd) basis set [25]
to describe the electrons of the ruthenium atom. For all
1
have been observed [24]. Yield: 23 mg (80%). H-NMR
(d, CD3CN, 20 8C): 7.76 (m, 2H, Ph), 7.50 (m, 4H, Ph),
7.40-7.12 (m, 9H, Ph), 6.79 (s, 1H, h6-Bz), 6.76 (d,
JHH
ꢃ
/
6.0 Hz, 1H, h6-Bz), 6.53 (d, JHH
ꢃ6.0 Hz, 1H,
/
h6-Bz), 5.36 (s, 5H, Cp). 13C{1H}-NMR (d, CD3CN,
20 8C): 134.8, 133.9, 133.8, 130.7, 130.1, 129.8, 129.6,
129.5, 129.0, 128.9, 128.8, 128.2 (18C, Ph), 106.1, 106.0,
other atoms the 6ꢂ31g** basis set was employed [26].
/

E. Ruba et al. / Journal of Organometallic Chemistry 682 (2003) 204ꢂ
/
211
211
¨
[14] B.M. Trost, F.D. Toste, Tetrahedron Lett. 40 (1999) 7739.
Frequency calculations were performed to confirm the
nature of the stationary points, yielding one imaginary
frequency for the transition states and none for the
minima. Each transition state was further confirmed by
following its vibrational mode downhill on both sides,
and obtaining the minima presented on the reactions
energy profile. All geometries were optimized without
constraints (C1 symmetry) and the energies were zero
point corrected.
[15] B.M. Trost, M.T. Rudd, J. Am. Chem. Soc. 124 (2002) 4178.
[16] B.M. Trost, R.E. Brown, F.D. Toste, J. Am. Chem. Soc. 122
(2000) 5877.
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(c) C. Lee, W. Yang, G. Parr, Phys. Rev. B 37 (1988) 785.
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Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, Jr.,
R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D.
Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q.
Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghava-
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Acknowledgements
Financial support by the ‘Fonds zur Forderung der
¨
wissenschaftlichen Forschung’ (project no. P14681-
CHE) is gratefully acknowledged.
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