M. Bassetti et al. / Journal of Organometallic Chemistry 593–594 (2000) 292–298
297
butenynyl complex; (iv) formal s-bond metathesis at
the Ruꢂalkenyl bond with a molecule of free alkyne to
form the enyne product and regenerate the catalytic
acetylide species [3,7,10]. Any of these possible species
from the ruthenium complexes of this study are evi-
dently highly reactive and escape direct observation.
More simple pictures, implying insertion of the alkyne
into the Ruꢂacetylide bond [4] or direct attack of a free
alkyne molecule to the acetylide fragment, followed by
reductive coupling of the butenynyl complex, would be
consistent with the lack of observable intermediates, as
it is often the case. These matters will be addressed
through more specific mechanistic experiments.
SiMe4 or 85% H3PO4 as standards. GLC Analyses were
performed on a Varian 3400 gas chromatograph (OV1
capillary column, 25 m×0.25 mm). GC-MS analyses
were obtained on a HP5890 GC (OV1 capillary
column, 12 m×0.2 mm) coupled with a HP5970 MSD.
Low resolution mass spectra (FAB, m-nitrobenzyl alco-
hol) were obtained with a VG-Quattro Instrument, at
the Universita` di Tor Vergata, Roma.
5.1. (E)-1,4-Diphenylbut-1-en-3-yne
A
vial
containing
complex
5,
[Ru(h5-
C9H7)(CꢀCPh)(PPh3)2] (0.27 g, 0.32 mmol), pheny-
lacetylene (0.97 g, 9.5 mmol) and toluene (3 ml), was
sealed and heated at 120°C for 48 h. After evaporation
of the solvent and of unreacted alkyne, the residue was
washed with hexane (5×3 ml), while crashing the
mixture in a ultrasonic bath, in order to separate the
organic products from insoluble material. The organic
extracts, containing the enyne products and PPh3, were
chromatographed over silica (250 g) using petroleum
ether as eluant to obtain a mixture of E (65%) and Z
(34%) 1,4-diphenylbut-1-en-3-yne as the first band (0.24
g, 1.21 mmol, 25% yield). The E isomer separates out of
the reaction mixture by crystallization from di-
ethylether–hexane (−20°C), or from hexane at room
temperature (98% purity). The isomeric mixture (168
mg) can be chromatographed further (silica, petroleum
ether) to yield a band of essentially the Z component
(36 mg, 93%), a second band of both isomers, and a
third band of essentially the E component (46 mg,
96%).
4. Conclusions
The activity of indenyl ruthenium complexes in the
dimerization and polimerization of terminal alkynes is
reported, as well as another case of indenyl effect in
catalysis. The role of phosphine is that of tuning
chemioselectivity (dimers–polymers) and stereoselectiv-
ity (E/Z) by steric effects and electron donation. The
one pot preparation of both geometric isomers of 1,4-
diphenylbut-1-en-3-yne is accessible through a process
of atom economy.
5. Experimental
The indenyl ruthenium complexes 1, 3, 4 [13], 2, 5–7
[27], 8, [28] and the cyclopentadienyl complex 9 [29]
have been prepared as described in the literature. The
reactions were carried out in toluene, which was dis-
tilled over potassium–benzophenone under nitrogen.
Hexane and petroleum ether (40–70°C) were distilled
before use. Silica Gel 60 (0.063–0.200 mm) was used
for chromatography. In a typical run, the alkyne (0.90
mmol) and the ruthenium complex (0.023–0.025
mmol), in 0.50 ml of toluene, or of toluene-d8, were
sealed in a vial, or in a 5 mm NMR tube, under argon,
and heated at the chosen temperature. The vials were
opened, the appropriate amount of bibenzyl (ca. 20 mg)
was added, and the reaction mixture analyzed by GLC
or GC-MS. In the gas chromatographic method, the
moles of products were determined by the use a conver-
sion factor for phenylacetylene (0.50) and for the eny-
nes (0.90) with respect to the internal standard
bibenzyl. In the NMR method, the conversion was
determined by integration of the peaks due to pheny-
lacetylene (l=2.74) and to 1,4-diphenylbut-1-en-3-yne
(E isomer: l=6.22, d, JHꢂH=16.3 Hz; Z isomer: l=
5.75, d, JHꢂH=11.9 Hz) with respect to the multiplet of
toluene-l8 at l 2.09 (PhMe), as internal standard.
NMR spectra were recorded on a Bruker AC300
instrument at 300 MHz (1H) or 121.5 MHz (31P) using
5.2. (Z)-1,4-Diphenylbut-1-en-3-yne
A vial containing complex 4, [Ru(h5-C9H7)H(PPh3)2]
(0.15 g, 0.20 mmol), phenylacetylene (0.97 g, 9.5 mmol)
and toluene (3 ml), was sealed and heated at 120°C for
24 h. The crude reaction mixture was washed with
hexane, and the extracts were chromatographed, as
above. The first fraction yields 253 mg of Z enyne (97%
by gc, 25% yield). A second band is eluted containing
177 mg of the isomers in comparable quantities (total
yield 44%).
Acknowledgements
Financial support for travel from NATO (Collabora-
tive Research Grant 950794), and CNR–CSIC (Pro-
gram of Scientific Cooperation), are acknowledged.
References
[1] B.M. Trost, M.T. Sorum, C. Chan, A.E. Harms, G. Ruhter, J.
Am. Chem. Soc. 119 (1997) 698 and references therein.