Acid controlled alkyne dimerisation initiated by a Ru-carbene precursor

Article abstract of DOI:10.1016/S0022-328X(02)01722-9

The Grubb's catalyst Cl₂(PR₃)₂Ru=CHPh (1) is an excellent precursor for the dimerisation of terminal alkynes. Thermal treatment and addition of two equivalents of phenylacetylene to complex 1 generates a new Ru-vinylidene (3). Complex 3 catalyses a selective product formation for trans-tail-to-tail enynes. Addition of acetic acid enhances the yield and the reaction rate dramatically and a reversed stereoselectivity for the formation of Z-isomers is obtained. The stereoselectivity can be easily tuned by addition of acetic acid. The influence of the acid on the reaction pathway has been revealed. A simple one-pot preparation of tail-totail enynes is established.

Full text of DOI:10.1016/S0022-328X(02)01722-9

Journal of Organometallic Chemistry 659 (2002) 159Á164
/
www.elsevier.com/locate/jorganchem
Acid controlled alkyne dimerisation initiated by a RuÁ
/
carbene
precursor
a
Karen Melis , Dirk De Vos , Pierre Jacobs , Francis Verpoort *
b
b
a,
a
Department of Inorganic and Physical Chemistry, Division of Organometallic Chemistry and Catalysis, Ghent University, Krijgslaan 281 (S-3), 9000
Ghent, Belgium
Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Heverlee, Belgium
b
Received 31 May 2002; received in revised form 15 July 2002; accepted 15 July 2002
Abstract
The Grubb’s catalyst Cl
2
(PR
3
)
2
RuÄ
/
CHPh (1) is an excellent precursor for the dimerisation of terminal alkynes. Thermal
vinylidene (3). Complex 3 catalyses
treatment and addition of two equivalents of phenylacetylene to complex 1 generates a new RuÁ
/
a selective product formation for trans-tail-to-tail enynes. Addition of acetic acid enhances the yield and the reaction rate
dramatically and a reversed stereoselectivity for the formation of Z-isomers is obtained. The stereoselectivity can be easily tuned by
addition of acetic acid. The influence of the acid on the reaction pathway has been revealed. A simple one-pot preparation of tail-to-
tail enynes is established. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Homogeneous catalysis; Dimerisation; Ruthenium; Carbene ligands; Vinylidene ligands
1
. Introduction
Metal vinylidenes (MÄ
in a regio- and stereoselective manner. Enol esters are
useful intermediates for carbonÁcarbon and carbonÁ
heteroatom bond formation. They have been used for
the selective generation of enolates, acylation of car-
bonyl compounds and O- and N-acylation under mild
/
/
/
CÄ
/
CHR) have emerged as
useful precursors with an unusual reactivity for a variety
of organic reactions of industrial importance [1]. The
direct simple formation of metal vinylidene intermedi-
ates from commercially available terminal alkynes and a
metal complex made the transfer from stoichiometric to
catalytic reactions possible. Based on the fundamental
mechanism metal vinylidenes are involved in catalytic
conditions [8Á
rearrangement of the vinylidene ligand ([M]Ä
to an alkylidene moiety ([M]ÄCHR) in the presence of
an olefin [12Á14]. This enlarges the application field of
/11]. Another important feature is the
/
CÄCHR)
/
/
/
vinylidenes to valuable, easy accessible precursors for
selective cross-metathesis, ring-closing metathesis and
ring opening metathesis polymerisation (ROMP). A
reactions of the type: dimerisation of alkynes, [2ꢀ2]
/
cycloaddition, nucleophilic addition to alkynes and
radical cycloaromatisation. Direct coupling of 1-al-
kynes, i.e. dimerisation, represents an easy route to
unsaturated dimeric species, in particular 1,3- and 1,4-
disubstituted enynes [2]. These are valuable precursors
for the synthesis of natural products as well as interest-
well-known stable, well-defined metalÁ
plex for olefin metathesis is the Grubb’s ‘first genera-
tion’ catalyst (Cl (PR ) RuÄCHPh) [15,16]. The wide
alkylidene is derived from its
activity, stability and functional group tolerance [17Á
0]. The catalyst remains active in the presence of a
/
alkylidene com-
/
2
3 2
spread use of the RuÁ
/
/
2
ing building blocks for further organic modifications [3Á
]. Nucleophilic addition of carboxylic acids to terminal
alkynes, also known as vinylation, produces enol esters
/
variety of functional groups like carbonyls, amides and
alkohols. However, the thermolytic decomposition is a
major drawback and limits the use in many challenging
reactions [21]. The alkylidene decomposition proceeds
predominantly via a second order reaction pathway
requiring phosphine dissociation. The nature of the
inorganic decomposition products still remains uniden-
7
*
Corresponding author. Tel.: ꢀ
983
E-mail address: francis.verpoort@rug.ac.be (F. Verpoort).
/
32-9-264-4436; fax: ꢀ32-9-264-
/
4
0
022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 7 2 2 - 9

160
K. Melis et al. / Journal of Organometallic Chemistry 659 (2002) 159Á164
/
tified. Here, we describe the generation of a RuÁ
vinylidene precursor, from thermal treatment of
Cl (PR ) RuÄCHPh with phenylacetylene, for the di-
merisation of terminal alkynes.
/
addition of phenylacetylene results in full conversion to
CHPh. (v) Preferentially tail-to-tail en-
ynes are formed.
On the basis of this spectroscopic data a mechanistic
hypothesis for the Ru-catalysed dimerisation of pheny-
lacetylene is depicted in Scheme 1.
PhCÅ
/
CÃ
/
CHÄ
/
/
2
3 2
2
. Results and discussion
.1. Thermal treatment of Cl (PCy ) RuÄ
Thermal treatment of the Grubb’s catalyst or complex
results in an unidentified Ru-compound (complex 2)
1
2
/
CHPh
2
3 2
(I). Addition of two equivalent phenylacetylene is
needed to fully transform complex 2 into the vinylidene
complex 3 (II). The reaction of 3 reacts with further
alkyne to form the alkynyl (alkyne) complex 4 (III). The
formation of complex 4 is consistent with the insertion
The thermal treatment of Cl (PCy ) RuÄCHPh (com-
/
2
3 2
plex 1) at 110 8C in toluene results in a decomposition
of the carbene ligand. Grubbs et al. performed similar
reactions at 55 8C [21]. They established that the
decomposition proceeds via a second order reaction
pathway requiring phosphine dissociation. The organic
product was determined as stilbene, but the inorganic
compound remained unidentified. Our attempts to
monitor the thermal decomposition products of com-
plex 1 show the disappearance of the carbene ligand,
of PhCÅ/CH. The mechanism of insertion involves
decoordination of a phosphine ligand. This thesis is
supported by the following experiment: a 1- to 2-fold
excess PCy3 is added to the reaction mixture. The
addition of an increasing amount of phosphine inhibited
the reaction completely. Only traces of PhCÅ
/
CÃ
/
CHÄ
/
1
31
CHPh are detected. The decoordination of one phos-
phine ligand plays a pivotal role in the initiation process.
Once complex 4 has rearranged into an alkynyl (vinyl-
since H- and P{H}-NMR analysis show no signal at
0.02 and 36.6 ppm, respectively, after the thermal
treatment at 110 8C.
2
3
1
idene) complex 5, the PhCÅ
formed via CÃC bond formation between the a-carbon
of vinylidene and the alkynylligand (IVÁV). The PhCÅ
CÃCÄCHPh ligand in 6 will partially dissociate from
/
CÃ
/
CÄ/CHPh ligand may be
P{H}-NMR shows two types of PCy groups (dꢁ
/
3
31 and 47 ppm). No evidence is found for a dissociation
equilibrium of a phosphine ligand taking place at the
/
/
/
metal center since no free PCy is detected. The signal at
3
/
/
3
1 ppm remains unidentified. Isolation and crystal-
the Ru-center with generation of a carbanion. This
lisation of the inorganic compound was unsuccessful,
so the nature of the inorganic complex 2 still remains
undetermined.
carbanion will then accept hydrogen from the generated
ꢀ
HPCy3 and will be eliminated as tail-to-tail enynes
(VI). The free co-ordination places are immediately
occupied by a newly incoming alkyne and PCy ligand,
3
2
.2. Reactivity of complex 1 with PhCÅ
/CH: generation
with generation of a highly unstable Ru-complex 7.
Subsequent rearrangement of complex 7 regenerates the
original alkynyl intermediate 3 (VII).
of a RuÁvinylidene
/
A solution of complex 1 and one equivalent pheny-
lacetylene is treated at reflux of toluene for 60 min. A
rapid colour change from purple to red-brown occurs.
The optimal temperature to promote the reaction
process is 110 8C. The reaction is performed at 20, 40,
60, 80 and 110 8C and yielded, respectively, 0, 17, 27, 37
3
1
P{H}-NMR reveal a new type of co-ordinated PCy3
and 92%. It is known from literature that the addition of
the second 1-alkyne only proceeds at elevated tempera-
tures [22].
(
dꢁ53 ppm) and some free phosphine. A RuÁvinyli-
/
/
dene complex 3 is formed. Complete formation of
complex 3 is not yet achieved, since the signal of
complex 2 still remains present. Subsequent addition
of another equivalent phenylacetylene at 110 8C results
Vinylideneruthenium (II) precursors of the type
RuCl (Ä
/
CÄ
/
CHR)L2 (Rꢁ
/
t-Bu; LꢁPCy , PiPr ) are
/
2
3 3
known to serve as good catalyst precursors for the
in a quantitative conversion of complex 2 to the RuÄ
/
CÄ
a
/
1
CHPh (3) after 1 h. C{H}-NMR determines the C
3
ROMP of cyclic alkenes and ring closing metathesis
(
RCM) of a,v-dienes, a,v-enynes and dienynes. In the
presence of an olefin the RuÁvinylidene is transformed
into the active species, i.e. a RuÁalkylidene complex.
and C of the RuÁvinylidene 3 at 341.4 and 118.3 ppm,
/
b
respectively. Analysing the time evolution of NMR
spectra of the reaction between complex 1 and a 10-
/
/
For this reason, complex 3 was treated with a 10-fold
excess of diethyl diallylmalonate (Scheme 2).
After 1 h at 110 8C, a conversion of 51% into the
corresponding cyclic alkene is reached. No other reac-
tion products than the ring-closed product were de-
fold excess of PhCÅ
All PhCÅCH is consumed in 1 h to produce PhCÅ
CHÄCHPh. (ii) Free PCy is detected by P{H}-NMR.
iii) No new phosphorus containing species, next to the
signals of complex 1 (36.6), 2 (47) and 3 (53 ppm), are
detected during the transformation from complex 1 to
complex 2 and subsequently to complex 3. (iv) Extra
/
CH provided following evidence, (i)
/
/
CÃ
/
3
1
/
3
(
tected. This result also confirms that complex 3 is a RuÁ
/
vinylidene.

K. Melis et al. / Journal of Organometallic Chemistry 659 (2002) 159Á
/
164
161
Scheme 1. Proposed mechanism for the dimerisation of phenylacetylene.
2
.3. Catalytic alkyne dimerisation and vinylation
vs. 5 h) and the yield increased to 92%. Surprisingly only
% of the endproducts consists of enol esters. The major
5
Complex 1 is tested for the dimerisation of phenyla-
adducts are enynes (95%) with a regioselectivity for tail-
to-tail adducts and a reversed stereoselectivity for cis-
substitution.
cetylene in normal catalytic conditions: alkyneÁ
/cat-
alystꢁ100/1. After 5 h the reaction yield reaches a
/
plateau. Only 21.4% of the 1-alkyne are converted, with
a high regioselectivity for tail-to-tail adducts (92%), with
2.4. Influence of acetic acid on the catalytic reaction
process
9
0% trans substitution.
The nucleophilic addition of a carboxylic acid or
vinylation proceeds via a similar fundamental mechan-
ism as the dimerisation (Scheme 3).
Both catalytic reaction pathways are initiated by a
Detailed NMR studies were conducted to determine
the role of the acid functionality. The acid has no direct
influence on the catalyst, since no covalent or coordi-
native bond between the acid and the transition metal is
detected.
The influence of the carboxylic acid on the terminal
alkyne was examined by two different experiments. In
the first experiment, the catalytic reaction was per-
formed at different dilution levels of acetic acid. The
metalÁvinylidene intermediate. In both cases Ru-com-
/
plexes are known as excellent catalysts. This tempted us
to test the activity of complex 1 for the vinylation.
Complex 1 was treated at 110 8C with 100 equivalent of
phenylacetylene and 100 equivalent of acetic acid. The
time for completion of the reaction is significantly
decreased compared with that of the dimerisation (3.5
ratio of catalystÁ
/
alkyneÁacid was altered from 1/100/1
/
Scheme 2. RCM of diethyl diallylmalonate catalysed by complex 3.

162
K. Melis et al. / Journal of Organometallic Chemistry 659 (2002) 159Á
/
164
Scheme 3. Dimerisation and vinylation of terminal alkynes.
to 1/100/200, only changing the concentration of the
acetic acid (Fig. 1).
The optimal ratio for the catalytic reaction is cat-
phenylacetylene solution (1/100). The reaction is per-
formed at 110 8C in a sealed NMR tube. At several
time intervals, H-NMR analysis is conducted. After 3 h
of reaction 97% of the phenylacetylene is converted into
1
alystÁ
/
phenylacetyleneÁ
/
acetic acidꢁ/1/100/100. At lower
concentration of acetic acid, the reaction rate is slower
and the obtained yield is decreased. The same observa-
tion is made when the molar amount of acid exceeds the
amount of phenylacetylene (1/100/200). The acid seems
the dimeric products (PhCÅ
/
CÃ
/
CHÄ
/
CDPh) and a signal
due to CH COOH at 12.4 ppm appears. This is
3
confirmed by GCÁ
mentation pattern characteristic to PhCÅ
CDPh. The same results are obtained with
phenylacetyleneÁCH COODÁcatalyst ratio equal to
/MS analysis, which shows a defrag-
/
CÃCHÄ
/
/
to promote the reaction when the ratio alkyneÁ
/acid is
a
equimolar. The acid does not influence the reaction
catalytically, but has effect on the reaction on a
stoechiometric level.
/
/
3
10/10/1. These data confirm that the acid influences
the reaction stoechiometrically.
In the second experiment, 100 equivalents of labelled
The combined two experiments clearly prove a direct
influence of acetic acid on the reaction pathway. Acetic
acetic acid (CH COOD) were added to a catalystÁ
/
3
Fig. 1. Dependence for the dimerisation of phenylacetylene on the concetration of acetic acid. Yield as determined with Raman spectroscopy and
1
H-NMR analysis. The experimental error for all reactions is smaller than 4%.

K. Melis et al. / Journal of Organometallic Chemistry 659 (2002) 159Á
/
164
163
acid seems to act as a proton donor for the reaction
ꢀ
process. HPCy3 (pK ꢁ
/
9.06) acts as a weaker acid
compared with acetic acid (pK ꢁ4.75). Acetic acid now
acts as the proton donor. The hydrogen needed to free
CHPh ligand from the Ru-complex is
a
/
a
the PhCÅ
/
CÃ
/
CHÄ
/
ꢀ
now donated by the acetic acid instead of HPCy . The
influence of the acid on the reaction pathway is depicted
in Scheme 4.
3
Addition of acetic acid to the reaction mixture results
in a reversed stereoselectivity for the formation of Z-
isomers. In analogy to the article of Sevin et al. the
product distribution can be explained by the following
hypothesis [23].
Fig. 2. Dependence of product formation on acetic acid.
When no acetic acid is added, no stabilisation of the
carbanion via the COOH-group is possible. The only
stabilisation is derived from the Ru-center. The attack
of the incoming alkyne can occur via both sides, leading
to E- and Z-isomer. The formation of the thermody-
namic stable E-isomer is preferred.
This surprising feature of the acid combined with the
catalytic activity of complex 1 at elevated temperature,
provides a very fast and regioselective catalytic environ-
ment for the dimerisation of phenylacetylene.
1
)
Considering the high thermal conditions for the
dimerisation reaction (110 8C) and the thermal
instability of the alkenyl ruthenium compound 6,
the formation and release of a vinyl carbanion from
the intermediate may be expected. The resonance-
stabilised molecule should have a V-shaped inter-
mediate, resulting in an unsymmetrical environment
on the sp-hybridized carbanion centre. This geome-
try facilitates the attack of the proton from the less
hindered side, thus leading to the formation of the
less stable Z-isomer (Fig. 2, A).
3
. Conclusion
2
)
)
Displacement of the sigma bonds to the ruthenium
atom generates an unsymmetrical structure. The
attack of the carboxylic acid shows no preference
for either side. The dimerisation leads to formation
of both the E- and Z-isomer (Fig. 2, B).
Combination of both suggests that it is possible that
the generated carbanion remains within the ruthe-
nium complex and is stabilised equally well by the
ruthenium atom. Again, the attack of the carboxylic
acid leads to the formation of Z-isomers (Fig. 2, C).
A new and unexpected route towards the dimerisation
of phenylacetylene is revealed. Thermal treatment of the
alkylidene Cl (PCy ) RuÄCHPh (1) at 110 8C and
subsequent addition of two equivalent of phenylacety-
lene leads to the formation of a RuÁvinylidene complex
. The RuÁvinylidene catalyses the selective tail-to-tail
/
2
3 2
3
/
3
/
addition of phenylacetylene with an additional prefer-
ence for trans-isomers. Addition of acetic acid, in a
stoechiometrical ratio, enhances the reaction rate and
yield dramatically. Instead of the decoordinated phos-
phine, the acid acts as a proton donor. Adding acetic
acid results in a reversed stereoselectivity towards the
formation of Z-isomers. The acid seems to stabilise the
released carbanion and generate an unsymmetrical
structure, which leads to preferential Z-adducts.
4. Experimental
4.1. General remarks
All reactions were performed under inert atmosphere
using Schlenck techniques. NMR spectra were recorded
on a Varian Unity 300 MHz spectrometer. GCÁMS
/
TM
analysis were performed on a GC (column SPB -5ꢁ
0 mꢂ0.25 mmꢂ0.25 mm film thickness, carrier gas:
He, 100 kPa, detectorꢁFID, gas chromatographꢁ
Varian 4600) and MS (Finnigan MAT ITD). Toluene-
/
3
/
/
/
/
Scheme 4. Influence of acetic acid on the reaction pathway.

164
K. Melis et al. / Journal of Organometallic Chemistry 659 (2002) 159Á164
/
d8 (obtained from Acros) and toluene were dried over
Na. Cl (PR ) RuÄCHPh (obtained from Strem Chemi-
cals), phenylacetylene, CH COOH and CH COOD
(obtained from Acros) were used without further
purification.
CHPh) 5.84 (d, Jꢁ
/
12.0 Hz, Ä
/
CHCÅ
/
C); GCÁ
/
MSꢁm/
/
ꢀ
/
zꢁ
trans-PhÃ
MHz, 25 8C, ppm) d 8.10Á
16.6 Hz, ÄCHPh) 6.33 (d, Jꢁ
GCÁMSꢁm/zꢁ
/204 [M ].
2
3 2
1
/
CHÄ
/
CHCÅ
/
CPh: H-NMR (tol-d , 300
8
3
3
/
6.80 (m, Ph) 7.04 (d, Jꢁ
/
/
/
16.6 Hz, ÄCHCÅC);
/
/
ꢀ
/
/
/204 [M ].
4
.1.1. Ru Complex 2
Cl (PR ) RuÄCHPh was heated at 110 8C in toluene
for 60 min. H-NMR (tol-d , 300 MHz, 25 8C, ppm): d
/
4.2.2. Head-to-tail adduct
1
2
3 2
1
H-NMR (tol-d , 300 MHz, 25 8C, ppm) d 8.10Á
/
6.80
8
8
1
3
1
.95Á
/
1.20 (m, PCy3). C{H}-NMR (tol-d , 75 MHz,
(m, Ph) 5.37 (s, Ä
/
CH ) 4.92 (s, Ä
/
CH ); GCÁ
/
MSꢁm/
/
8
2
2
ꢀ
2
5 8C, ppm): d 35.76, 30.34, 28.1, 27.02 (all m, PCy3).
zꢁ205 [M ].
/
3
1
P{H}-NMR (tol-d , 129 MHz, 25 8C, ppm): d 46.9,
8
3
0.68.
Acknowledgements
4
.1.2. Ru Complex 3
To Ru-complex (2) two equivalents of phenylacety-
K.M. is indebted to the Bijzonder Onderzoeksfonds
(BOF) of Ghent University for a research grand. We are
indebted to Fonds voor Wetenschappelijk Onderzoek-
Vlaanderen (FWO) for a research grand (D.D.V., P.J.,
F.V.). Financial support by The Research funds of
Ghent University is gratefully acknowledged.
lene were added. The reaction was stirred at 110 8C for
1
1
h. H-NMR (tol-d , 300 MHz, 25 8C, ppm): d 7.99Á
/
8
7
.21 (m, H of Ph), 5.34 (s, RuÄ
/
CÄ
/
CHPh), 2.20Á1.39(m,
/
1
3
PCy3). C{H}-NMR (tol-d , 75 MHz, 25 8C, ppm): d
8
3
41.4 (RuÄ
of Ph), 118.80 (RuÄ
5.62, 34.03, 30.68, 27.73 (PCy3). P{H}-NMR (tol-
d8, 129 MHz, 25 8C, ppm): d 52.92.
Dimerisation of phenylacetylene catalysed by the
Cl (PR ) RuÄCHPh precursor: A solution of the
CHPh (0.032 mmol) in
/
C Ä
/
CHPh), 132.72, 131.76, 130.85, 123.26 (C
/
CÄCHPh), 37.48, 37.13, 36.34,
/
3
1
2
References
[
1] C. Bruneau, P. Dixneuf, Acc. Chem. Res. 32 (1999) 311.
2] B. Trost, M. Sorum, C. Chan, A. Harms, G. R u¨ ther, J. Am.
Chem. Soc. 119 (1997) 698 (and references therein).
3] B. Trost, C. Chan, G. Ruther, J. Am. Chem. Soc. 109 (1987) 3486.
4] T. Kusumoto, K. Nishide, T. Hiyama, Bull. Chem. Soc. Jpn. 63
(1990) 1947.
/
2
3 2
[
Grubb’s catalyst Cl (PR ) RuÄ
toluene (3 ml) is treated at 110 8C for 1 h. Hundred
equivalent phenylacetylene (3.20 mmol) are added and
/
2
3 2
[
[
the reaction mixture is stirred at 110 8C. The reaction is
1
[5] J. Oshita, K. Furumori, A. Matsuguchi, M. Ishikawa, J. Org.
Chem. 55 (1990) 3277.
monitored by H-NMR and GCÁ
/MS.
Reaction of phenylacetylene and CH COOH cata-
3
[
[
6] B. Trost, G. Kottirsc, J. Am. Chem. Soc. 112 (1990) 2816.
7] G. Lee, B. Tobias, J. Holmes, D. Harcourt, M. Garst, J. Am.
Chem. Soc. 112 (1990) 9330.
lysed by the Cl (PR ) RuÄ
/
CHPh precursor. A solution
CHPh (0.032
2
3 2
of the Grubb’s catalyst Cl (PR ) RuÄ
/
2
3 2
mmol) in toluene (3 ml) is treated at 110 8C for 1 h.
Hundred equivalents phenylacetylene (3.2 mmol) and
[8] H. House, D. Crumrine, A. Teranishi, H. Olmstead, J. Am.
Chem. Soc. 95 (1973) 3310.
[9] E. Rothman, G. Moore, Tetrahedron Lett. (1969) 2553.
1
00 equivalent acetic acid (3.2 mmol) are added and the
[
[
10] Z. Kabouche, C. Bruneau, P. Dixneuf, J. Chem. Soc. Perkin
Trans. (1991) 1197.
11] T. Opstal, F. Verpoort, Synlett 6 (2002) 935.
reaction mixture is stirred at 110 8C. The reaction is
1
monitored by H-NMR and GCÁ
/MS.
Reaction of phenylacetylene and CH COOD cata-
3
[12] H. Katayama, H. Urushima, F. Osawa, J. Organomet. Chem. 606
2000) 16.
(
lysed by Cl (PR ) RuÄ
/
CHPh precursor: In a glove box,
2
3 2
[
[
[
13] I. Del Rio, G. van Koten, Tetrahedron Lett. 40 (1999) 1401.
14] J. Louie, R. Grubbs, Angew. Chem. Int. Ed. Engl. 40 (2001) 247.
15] P. Schwab, R. Grubbs, J. Ziller, J. Am. Chem. Soc. 118 (1996)
100.
a 5 mm Wilmad NMR tube is charged with Grubb’s
catalyst (0.056 mmol, 0.046 g) and phenylacetylene (0.56
mmol, 0.057 g) and toluene-d8 (1 ml). The reaction
mixture is treated at 110 8C for 60 min. Acetic acid-d
[16] E. Dias, S. Nguyen, R. Grubbs, J. Am. Chem. Soc. 119 (1997)
887.
3
17] K. Ivin, J. Mol. Catal. A Chem. 133 (1998) 1.
18] M. Schuster, S. Blechert, Angew. Chem. Int. Ed. Engl. 36 (1997)
(
0.56 mmol, 0.034 g) is added to the solution and the
[
[
sealed NMR tube was kept at 110 8C. Product forma-
2
1
tion and H-exchange is monitored by H-NMR and
GCÁMS.
2036.
19] K. Melis, D. De Vos, P. Jacobs, F. Verpoort, J. Mol. Catal. A
Chem. 169 (2001) 47.
/
[
[
[
[
20] B. De Clerq, F. Verpoort, J. Mol. Catal. A Chem. 170 (2002) 67.
21] M. Ulman, R. Grubbs, J. Org. Chem. 64 (1999) 7202.
22] C. Banchini, P. Frediani, D. Masi, M. Peruzzini, F. Zanobini,
Organometallics 13 (1994) 4616.
4
4
2
.2. Spectroscopic data for dimeric products
.2.1. Tail-to-tail adducts
cis-PhÃCHÄCHCÅCPh: H-NMR (tol-d , 300 MHz,
5 8C, ppm) d 8.10Á6.80 (m, Ph) 6.48 (d, Jꢁ
1
/
/
/
8
[23] N. Balcioglu, I. Uraz, C. Bozkurt, F. Sevin, Polyhedron 16 (1997)
/
/
12.0 Hz, Ä
/
327.