Methylidynetricobalt nonacarbonyl catalyzed cyclotrimerization of alkynes

Article abstract of DOI:10.1039/b111179e

A cobalt carbonyl cluster, methylidynetricobalt nonacarbonyl, catalyzed inter- and intramolecular cyclotrimerization of alkynes producing substituted benzene derivatives in good to excellent yields.

Full text of DOI:10.1039/b111179e

Methylidynetricobalt nonacarbonyl catalyzed cyclotrimerization of
alkynes
Takumichi Sugihara,* Akihito Wakabayashi, Yasuko Nagai, Hiroko Takao, Hiroshi Imagawa and
Mugio Nishizawa
Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514,
Japan. E-mail: taku@ph.bunri-u.ac.jp; Fax: +81-88-655-3051; Tel: +81-88+622-9611
Received (in Cambridge, UK) 7th December 2001, Accepted 31st January 2002
First published as an Advance Article on the web 21st February 2002
Table 1 Cyclization of oct-4-yne (7) catalyzed by various cobalt carbonyl
A cobalt carbonyl cluster, methylidynetricobalt nonacarbo-
nyl, catalyzed inter- and intramolecular cyclotrimerization
of alkynes producing substituted benzene derivatives in good
to excellent yields.
complexes.a
Alkylidynetricobalt nonacarbonyl clusters1,2 are easily prepared
by reaction of dicobalt octacarbonyl with trihaloalkanes and are
more stable against auto-oxidation than the parent dicobalt
octacarbonyl. Since the clusters can be also synthesized by
heating a solution of terminal alkyne-dicobalt hexacarbonyls,3,4
the clusters are more thermally stable than the structurally
similar alkyne-dicobalt hexacarbonyls. We recently reported
that one of the clusters, methylidynetricobalt nonacarbonyl
(1a), catalyzed the Pauson–Khand reaction of phenylacetylene
(2) with norbornene to give 3.5,6 When the reaction with allyl
ether 4 was carried out, the desired cyclopentenone 6 was not
obtained, but 1,2,4-triphenylbenzene (5) was produced in good
yield even under 7 atm of CO atmosphere (Scheme 1).
Whereas some of the clusters, benzylidyne- and ethylidyne-
tricobalt nonacarbonyl, were known to catalyze the [2 + 2 +
2]-cyclotrimerization of alkynes producing substituted ben-
zenes,4,7 the reaction conditions were vigorous and the turnover
number was not satisfactory compared with the result shown in
Scheme 1. The present results suggest that the alkylidyne unit of
the clusters might greatly influence the catalytic activity in the
reaction. To confirm this, oct-4-yne (7) was chosen as the
substrate and we investigated the catalytic activity of various
alkylidynetricobalt nonacarbonyls (1). The results are shown in
Table 1.
Entry
Catalyst
Yield of 8 (%)
3
1
2
3
4
5
6
7
8
9
Co3(CO)9(m -CH)
1a
1b
1c
1d
1e
1f
1g
9
10
92
13
21
19
11
42
38
8
3
Co3(CO)9(m -CMe)
3
Co3(CO)9(m -CPh)
3
Co3(CO)9(m -CCOOEt)
3
Co3(CO)9(m -CCl)
3
Co3(CO)9(m -CBr)
3
[Co3(CO)9(m -C)]2
Co2(CO)8
Co4(CO)12
47
a All reactions were carried out in 0.3 M solution in toluene under argon
atmosphere.
methylidynetricobalt nonacarbonyl (1b), (1c), and (1d), the
cyclization was slow and the yield of 8 was moderate as
reported in the literature (Entries 2–4).4 Whereas the cyclization
did not proceed smoothly in the presence of 1e (Entry 5), the
cluster with a bromomethylidyne-unit (1f) catalyzed the
cyclization (Entry 6). While it is known that treatment of 1f in
refluxing toluene gave 1g,9 1g itself also catalyzed the
cyclization (Entry 7). The catalytic activity of the clusters was
greatly influenced by the nature of the substituent on the carbon
unit. The thermally stable clusters, such as 1b–e were not good
catalysts, and the structurally simple 1a was the most efficient
among the thermally unstable ones, such as 1a, 1f, and 1g.
Binary cobalt carbonyl complexes, such as dicobalt octacarbo-
nyl 9 and tetracobalt dodecacarbonyl 10, also catalyzed the
cyclization (Entries 8 and 9), although the catalytic activity was
much less than 1a.
When methylidynetricobalt nonacarbonyl (1a)8 was used as a
catalyst, the cyclization proceeded smoothly to give hexa(n-
propyl)benzene (8) in an excellent yield (Entry 1). In the
presence of ethylidyne-, benzylidyne-, and ethoxycarbonyl-
An interesting feature of the present method was that the
cyclization could be carried out at a lower temperature and the
catalyst 1a was recovered (Scheme 2). The result suggested that
not the decomposition products but the cluster 1a itself was
transformed into the active catalysts, such as the coordinatively
unsaturated complexes, under the conditions and also that 1a
was the catalyst resting state.
The method was also applied to various substrates (Scheme
3). When conjugated diyne 11 was used as the substrate,
Scheme 1
Scheme 2
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CHEM. COMMUN., 2002, 576–577
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Scheme 4
cyclotrimerization of alkynes. Polynuclear organotransition
metal complexes are considered to have a tendency to accept
coordination of an alkyne more preferably than that of an
alkene.10 The present results may support this consideration.
This work is supported in part by grants from the Asahi Glass
Foundation and the Ministry of Education, Science, Sports, and
Culture, Japan. TS gratefully thanks Professor Masahiko
Yamaguchi at Graduate School of Pharmaceutical Sciences,
Tohoku University, Japan for helpful discussions.
Notes and references
1 For reviews, see: (a) B. R. Penfold and B. H. Robinson, Acc. Chem.
Res., 1973, 6, 73; (b) D. Seyferth, Adv. Organomet. Chem., 1976, 14, 97;
(c) R. D. W. Kemmitt and D. R. Russell in Comprehensive Organome-
tallic Chemistry, Vol. 5, eds. G. Wilkinson, F. G. A. Stone and E. W.
Abel, Pergamon Press, Oxford, 1982, p. 1.
2 (a) G. Bor, B. Marko and L. Marko, Acta Chim. Acad. Sci. Hung., 1961,
27, 395; (b) W. T. Dent, L. A. Duncanson, R. G. Guy, H. W. B. Reed and
B. L. Shaw, Proc. Chem. Soc., London, 1961, 169; (c) D. Seyferth, J. E.
Hallgren and P. L. K. Hung, J. Organomet. Chem., 1973, 50, 265.
3 (a) R. Markby, I. Wender, R. A. Friedel, F. A. Cotton and H. W.
Sternberg, J. Am. Chem. Soc., 1958, 80, 6529; (b) W. Hübel and U.
Krüerke, Chem. Indust., 1960, 1264.
4 R. S. Dickson and G. R. Tailby, Aust. J. Chem., 1970, 23, 229.
5 T. Sugihara and M. Yamaguchi, J. Am. Chem. Soc., 1998, 120,
10782.
Scheme 3
6 T. Sugihara, M. Yamaguchi and M. Nishizawa, Chem. Eur. J., 2001, 7,
1589.
1,3,5-triphenyl substituted benzene derivative 12 was produced
and the 1,2,4-triphenyl substituted one was not detected at all.
The regioselectivity in the cyclization seemed to be controlled
by both electronic and steric factors of the substituents. Diynes
13–15, triynes 19–21, and tetraynes 25 and 26, were also
cyclized in the presence of 2 mol% of 1a, although a longer
reaction time was required. Cocyclization between diyne 14 and
phenylacetylene (2) also proceeded nicely to give the desired 29
in a good yield.
As we reported previously, methylidynetricobalt nonacarbo-
nyl (1a) also nicely catalyzed the intramolecular Pauson–Khand
reaction under CO atmosphere.5,6 When the substrate has the
possibility to proceed both the cyclotrimerization of alkynes and
the Pauson–Khand reaction, which process is favorable? The
answer is shown in Scheme 4. The cyclization of 30 under 20
atm of CO atmosphere, which was suitable for the Pauson–
Khand reaction, gave neither the cyclopentenone 32 nor the
pentacyclic compound 33, but the substituted benzene deriva-
tive 31. This result suggested that the intramolecular cyclo-
trimerization of alkynes was much faster than the intra-
molecular Pauson–Khand reaction and the intermolecular
7 For some recent reviews of cyclotrimerization of alkynes mediated and
catalyzed by organotransition metals, see: (a) P. M. Maitlis, Acc. Chem.
Res., 1976, 9, 93; (b) K. P. C. Vollhardt, Acc. Chem. Res., 1977, 10, 1;
(c) K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl., 1984, 23, 539; (d)
N. E. Shore, Chem. Rev., 1988, 88, 1081; (e) N. E. Shore in
Complehensive Organic Synthesis, Vol. 5, eds. B. M. Trost, I. Fleming
and L. A. Paquette, Pergamon, New York, 1991, p. 1129; (f) D. B.
Grotijahn in Comprehensive Organometallic Chemistry II, Vol. 12, eds.
E. W. Abel, F. G. A. Stone, G. Wilkinson and L. S. Hegedus, Pergamon,
New York, 1995, p. 741; (g) M. Lautens, W. Klute and W. Tam, Chem.
Rev., 1996, 96, 49.
8 Methylidynetricobalt nonacarbonyl (1a) was easily prepared by reaction
of dicobalt octacarbonyl (cheap transition metal complex) with
bromoform in 80% yield and was purified by silica gel column
chromatography (eluted with n-hexane; open-air). The cluster was quite
stable at ambient temperatures and could be used as a catalyst with no
problems after storing for more than four years at 0 °C. See also ref.
2.
9 G. Allegra, R. Ercoli and E. M. Peronai, J. Chem. Soc., Chem. Commun.,
1966, 549.
10 R. S. Dickson and P. J. Fraser, Adv. Organomet. Chem., 1974, 12,
323.
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