Multimetallic zirconocene-based catalysis: Alkyne dimerization and cyclotrimerization reactions

Article abstract of DOI:10.1021/om8002703

Systematic exploration of zirconocene (Cp₂Zr^II) chemistry since the 1980s has offered a wide range of useful methods for organic synthesis. Many of these reactions are stoichiometric in zirconium, and even if several catalytic reactions are known, the development of catalytic zirconocene chemistry is of continuing interest. In this paper, the study of reactions catalytic in zirconium, i.e. alkyne dimerization and cyclotrimerization, is presented. These reactions are carried out by employing the recently introduced lanthanide-originated zirconocene equivalent. The use of 10 mol % of Cp ₂ZrCl₂, together with La metal or mischmetall as reductant and AlCl₃ as transmetalating agent, leads to an efficient formation of dienes from disubstituted alkynes. Under the same conditions, monosubstituted alkynes underwent cyclotrimerization reactions to afford benzene derivatives. This reaction also occurs efficiently in the absence of AlCl₃. It was postulated that the catalytic cyclotrimerization did not proceed through a typical insertion of the alkyne into the zirconacyclopentadiene intermediate. This unprecedented reaction takes place in the presence of zirconocene and lanthanide species, possibly involving a bimetallic polarization process.

Full text of DOI:10.1021/om8002703

4152
Organometallics 2008, 27, 4152–4157
Multimetallic Zirconocene-Based Catalysis: Alkyne Dimerization
and Cyclotrimerization Reactions
Antoine Joosten,† Mohamad Soueidan,‡ Cle´ment Denhez,† Dominique Harakat,†
Florence He´lion,‡ Jean-Louis Namy,*,‡ Jean-Luc Vasse,† and Jan Szymoniak*,†
Institut de Chimie Mole´culaire de Reims, CNRS (UMR 6229), UniVersite´ de Reims, 51687 Reims Cedex 2,
France, and Laboratoire de Catalyse Mole´culaire, CNRS (UMR 8182), ICMMO, Bat 420, UniVersite´
Paris-Sud, 91405 Orsay, France
ReceiVed March 27, 2008
Systematic exploration of zirconocene (Cp2ZrII) chemistry since the 1980s has offered a wide range of
useful methods for organic synthesis. Many of these reactions are stoichiometric in zirconium, and even
if several catalytic reactions are known, the development of catalytic zirconocene chemistry is of continuing
interest. In this paper, the study of reactions catalytic in zirconium, i.e. alkyne dimerization and
cyclotrimerization, is presented. These reactions are carried out by employing the recently introduced
lanthanide-originated zirconocene equivalent. The use of 10 mol % of Cp2ZrCl2, together with La metal
or mischmetall as reductant and AlCl3 as transmetalating agent, leads to an efficient formation of dienes
from disubstituted alkynes. Under the same conditions, monosubstituted alkynes underwent cyclotrim-
erization reactions to afford benzene derivatives. This reaction also occurs efficiently in the absence of
AlCl3. It was postulated that the catalytic cyclotrimerization did not proceed through a typical insertion
of the alkyne into the zirconacyclopentadiene intermediate. This unprecedented reaction takes place in
the presence of zirconocene and lanthanide species, possibly involving a bimetallic polarization process.
nesation of alkenes,5,6 bicyclization of dienes,7 and the oxidative
Introduction
addition of allyl derivatives,8 proceed through generation and
Extensive exploration of zirconocene (Cp2ZrII) chemistry in
the last two decades1 has been supported by the introduction of
practical methods for generating low-valent zirconocene species
in situ. Among them, alkene-zirconocene complexes appeared
as particularly useful reagents. The so-called Negishi reagent,
i.e. (1-butene)ZrCp2, can be generated by treatment of Cp2ZrCl2
with 2 equiv of n-BuLi at -78 °C and warming to room
temperature,2 and it has been widely used as an efficient “Cp2Zr”
equivalent.3 Similarly, (ethylene)ZrCp2 can be generated by
treatment of Cp2ZrCl2 with 2 equiv of EtMgBr.4 In addition to
a wide stoichiometric low-valent zirconocene chemistry, there
are also several zirconocene-catalyzed C-C bond-forming
reactions. Some of them, such as the Zr-catalyzed ethylmag-
carbometalative ring expansion (cyclic carbozirconation) of
zirconacyclopropanes (alkene-zirconocenes) and zirconacy-
clopropenes. The carboalumination of alkynes9 and alkenes10,11
reveal dichotomous mechanisms involving cyclic or acyclic
bimetallic carbometalation processes.12 The extensive develop-
ment of asymmetric reactions using chiral zirconocene cata-
lysts13 are noteworthy. Among them, the Zr-catalyzed asym-
metric carboalumination of alkenes has been developed by
(5) (a) Dzhemilev, U. M.; Vostrikova, O. S.; Sultanov, R. M. IzV. Akad.
Nauk SSSR, Ser. Khim. 1983, 32, 218. (b) Takahashi, T.; Seki, T.; Nitto,
Y.; Saburi, M.; Rousset, C. J.; Negishi, E. J. Am. Chem. Soc. 1991, 113,
6266. (c) Hoveyda, A. H.; Morken, J. P.; Houri, A. F.; Xu, Z. J. Am. Chem.
Soc. 1992, 114, 6692. (d) Lewis, D.; P.; Whitby, R. J.; Jones, R. V. H.
Tetrahedron 1995, 51, 4541.
* To whom correspondence should be addressed. E-mail: jan.szymoniak@
univ-reims.fr (J.S.); jelonamy@icmo.u-psud.fr (J.-L.N.).
† Universite´ de Reims.
(6) For a similar catalytic carbomagnesation of ketimines, see: (a)
Takahashi, T.; Liu, Y.; Xi, C.; Huo, S. Chem. Commun. 2001, 31. (b)
Gandon, V.; Bertus, P.; Szymoniak, J. Eur. J. Org. Chem. 2001, 3677. (c)
Gandon, V.; Bertus, P.; Szymoniak, J. Synthesis 2002, 1115.
(7) (a) Knight, K. S.; Waymouth, R. M. J. Am. Chem. Soc. 1991, 113,
6268. (b) Knight, K. S.; Wang, D.; Waymouth, R. M.; Ziller, J. J. Am.
Chem. Soc. 1994, 113, 1845. (c) Uesaka, N.; Mori, M.; Okamura, K.; Date,
T. J. Org. Chem. 1994, 59, 4542.
(8) (a) Suzuki, N.; Kondakov, D. Y.; Takahashi, T. J. Am. Chem. Soc.
1993, 115, 8485. (b) Knight, K. S.; Waymouth, R. M. Organometallics
1994, 13, 2575.
(9) (a) Van Horn, D. E.; Negishi, E. J. Am. Chem. Soc. 1978, 100, 2252.
(b) Negishi, E.; Van Horn, D. E.; Yoshida, T. J. Am. Chem. Soc. 1985,
107, 6639. (c) Negishi, E.; Kondakov, D. Y.; Choueiry, D.; Kasai, K.;
Takahashi, T. J. Am. Chem. Soc. 1996, 118, 957.
‡ Universite´ Paris-Sud.
(1) For reviews, see: (a) Negishi, E. In Titanium and Zirconium in
Organic Synthesis; Marek, I. Ed.; Wiley-VCH: Weinheim, Germany, 2002;
Chapter 1. (b) Negishi, E. Dalton Trans. 2005, 827. (c) New Aspects of
Zirconium Containing Organic Compounds In Topics in Organometallic
Chemistry; Marek, I., Ed.; Springer: Berlin, 2005; Vol. 10. (d) Metallocenes
in Regio- and Stereoselective Synthesis In Topics in Organometallic
Chemistry; Takahashi, T., Ed.; Springer: Berlin, 2005; Vol. 8. (e) Negishi,
E.; Takahashi, T. Bull. Chem. Soc. Jpn. 1998, 71, 755. (f) Negishi, E.;
Takahashi, T. Acc. Chem. Res. 1994, 27, 124.
(2) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett. 1986,
27, 2829.
(3) A free Cp2Zr has never been observed in a monomeric form, and
only stabilized Cp2Zr complexes were used; see for example: (a) Watt,
G. W.; Drummond, F. O., Jr J. Am. Chem. Soc. 1970, 92, 826. (b) Wailes,
P. C.; Weigold, H. J. Organomet. Chem. 1971, 28, 91. (c) Thanedar, S.;
Farona, M. F. J. Organomet. Chem. 1982, 235, 65. (d) Rosenthal, U.; Ohff,
A.; Michalik, M.; Go¨rls, H.; Burlakov, V. V.; Shur, V. B. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1193.
(10) (a) Kondakov, D. Y.; Negishi, E. J. Am. Chem. Soc. 1995, 117,
10771. (b) Kondakov, D. Y.; Negishi, E. J. Am. Chem. Soc. 1996, 118,
1577. (c) Negishi, E. Chem. Eur. J. 1999, 5, 411.
(11) For a similar Zr-catalyzed carboalumination of imines, see: Denhez,
C.; Vasse, J.-L.; Szymoniak, J. Synthesis 2005, 2075.
(12) For recent reviews on alkyne and alkene carboalumination, see:
(a) Negishi, E. Dalton Trans. 2005, 827. (b) Negishi, E.; Tan, Z. In Topics
in Organometallic Chemistry; Takahashi, T., Ed.; Springer: Berlin, 2005;
Vol. 8, p 139. (c) Negishi, E. Bull. Chem. Soc. Jpn. 2007, 80, 233.
(4) Takahashi, T.; Kageyama, M.; Denisov, V.; Hara, R.; Negishi, E.
Tetrahedron Lett. 1993, 34, 687.
10.1021/om8002703 CCC: $40.75
2008 American Chemical Society
Publication on Web 07/25/2008

Multimetallic Zirconocene-Based Catalysis
Organometallics, Vol. 27, No. 16, 2008 4153
Negishi14 and widely applied to the synthesis of natural
products.15 Diene cyclization was studied and applied to the
preparation of carbocycles and nitrogen heterocycles by Mori.16
Asymmetric carbomagnesation of unactivated or functionalized
alkenes was successfully developed by Hoveyda17 and Whitby.18
Although the reactions catalytic in zirconium have been
extensively studied, a number of Zr-mediated reactions remain
stoichiometric and the development of new catalytic processes
is important.
Scheme 1
We recently reported a room-temperature-based protocol for
the generation of an alkene-free zirconocene equivalent, by
reducing Cp2ZrCl2 with readily available mischmetall (an alloy
of Ce, La, Nd, and Pr).19 Ce and La (but not Nd) metal
components of mischmetall have been demonstrated to act
efficiently as reductants.19 By using this reagent, not only
reactions typical for zirconocene were carried out but also some
others: i.e., coupling of terminal alkynes as well as intermo-
lecular coupling of alkynes with imines. The mild and direct
method applied for the generation of a lanthanide-originated
Cp2Zr equivalent offers the possibility of developing new
reactions catalytic in zirconium.20 The model experiments for
such studies could involve alkyne-alkyne couplings, which are
known to proceed through zirconacyclopentadienes under sto-
ichiometric conditions.21 These dimerization reactions easily
occur in the presence of a stoichiometric amount of zirconocene.
The present work demonstrates the feasibility of such couplings
by using catalytic amounts of Cp2ZrCl2 and opens the way
toward new developments in catalytic organozirconium chemistry.
Table 1. Catalytic Dimerization of Disubstituted Alkynes
entry
R1
R2
time (h)
product (yield (%))a
1
2
3
4
5
n-Pr
Me
Ph
n-Pr
Me
n-Pr
Ph
Ph
Ph
Me3Si
7
8
48
12
1.5
2a (76)
2bb (75)
2c (31)
2db (85)
2′e (65)
a Isolated yields. b Topoisomers (10%).
Results and Discussion
zirconacyclopentadiene would be transmetalated to give a
metallacycle (Ni) or a bimetallic (Cu) intermediate (A), thus
generating Cp2ZrCl2, which in turn would be reduced to close
the catalytic cycle (Scheme 1).
By using the lanthanide-originated Cp2Zr equivalent, zir-
conacyclopentadiene complexes have already been demonstrated
to form from both internal and terminal alkynes.19 Furthermore,
zirconacyclopentadienes are known to undergo transmetalations,
especially to copper and nickel, which can be followed by
insertions or other reactions, leading to diversely functionalized
organic compounds.21 We envisioned that the alkyne coupling
might be carried out by using a catalytic amount of Cp2ZrCl2,
together with a lanthanide reductant and CuCl (2 equiv) or
NiX2(PPh3)2 (1 equiv) (X ) Cl, Br), which have been typically
used as transmetalating agents. In such cases, the initially formed
However, when Cu and Ni salts were used, no catalytic
dimerization was observed, and only complex reaction mixtures
were systematically obtained.22 Although transmetalation of
zirconocene complexes to aluminum is well-known, only a few
examples involving zirconacyclopentadienes have been re-
ported.23 In these reactions, aluminacyclopentadienes have been
postulated to form only under specific conditions (in the presence
of an aldehyde-AlCl3 adduct). Despite these limitations, in the
next experiments AlCl3 was employed. The mixture of a
catalytic amount of Cp2ZrCl2 (10 mol %) together with
powdered La metal (33 mol %) and AlCl3 (50 mol %) was
stirred until the color turned deep red (about 10 min).24 Oct-
4-yne (1a) was then added, and the reaction mixture was
warmed at 50 °C. A total conversion of 1a was observed by
GC-MS after 7 h, and (4E,6E)-5,6-dipropyldeca-4,6-diene (2a)
was obtained after a hydrolytic workup in 76% yield, ac-
companied by only a small amount (about 5%) of hexapropyl-
benzene (Table 1). Moreover, the total deuterium incorporation
at each terminal position of the diene 2a upon deuterolysis
confirms the formation of the metalacyclopentadiene intermedi-
ate. The decrease in the amount of Cp2ZrCl2 to 5 mol % made
the reaction time longer (12 h) and slightly lowered the yield
(69%). In the absence of AlCl3, the partial conversion of 1a to
2a corresponded to the amount of Cp2ZrCl2 used. The decrease
(13) For a review, see: Hoveyda, A. H. In Titanium and Zirconium in
Organic Synthesis; Marek, I., Ed.; Wiley-VCH: Weinheim, Germany, 2002;
Chapter 6.
(14) (a) Negishi, E.; Tan, Z.; Liang, B.; Novak, T. Proc. Natl. Acad.
Sci. U.S.A. 2004, 101, 5782. (b) Novak, T.; Tan, Z.; Liang, B.; Negishi, E.
J. Am. Chem. Soc. 2005, 127, 2838. (c) Tan, Z.; Huo, S.; Shi, J.; Negishi,
E. Tetrahedron: Asymmetry 2006, 17, 512.
(15) Recent articles: (a) Liang, B.; Negishi, E. Org. Lett. 2008, 10, 193.
(b) Zhu, G.; Liang, B.; Negishi, E. Org. Lett. 2008, 10, 1099. (c) Zhu, G.;
Negishi, E. Chem. Eur. J. 2008, 14, 311.
(16) (a) Yamaura, Y.; Hyakutake, M.; Mori, M. J. Am. Chem. Soc. 1997,
119, 7615. (b) Yamaura, Y.; Mori, M. Tetrahedron Lett. 1999, 40, 3221.
(17) (a) Morken, J. P.; Didiuk, M. T.; Hoveyda, A. H. J. Am. Chem.
Soc. 1993, 115, 6997. (b) Hoveyda, A. H.; Morken, J. P. J. Org. Chem.
1993, 58, 4237. (c) Didiuk, M. T.; Johannes, C. W.; Morken, J. P.; Hoveyda,
A. H. J. Am. Chem. Soc. 1995, 117, 7097.
(18) (a) Bell, L.; Whitby, R. J.; Jones, R. V. H.; Standen, M. C. H.
Tetrahedron Lett. 1996, 37, 7139. (b) Davson, G. J.; Durrant, C. A.; Kirk,
G. G.; Whitby, R. J.; Jones, R. V. H.; Standen, M. C. H. Tetrahedron Lett.
1997, 38, 2335. (c) Bell, L.; Brookings, D. C.; Davson, G. J.; Whitby, R. J.;
Jones, R. V. H.; Standen, M. C. H. Tetrahedron 1998, 54, 14617.
(19) Denhez, C.; Me´de´gan, S.; He´lion, F.; Namy, J.-L.; Vasse, J.-L.;
Szymoniak, J. Org. Lett. 2006, 8, 2945.
(20) Mischmetall and La are compatible with several functional groups;
see: Lannou, M.-I.; He´lion, F.; Namy, J.-L. Tetrahedron 2003, 59, 10551.
(21) For the formation and chemistry of zirconacyclopentadienes, see:
Takahashi, T.; Li, Y. In Titanium and Zirconium in Organic Synthesis;
Marek, I., Ed.; Wiley-VCH: Weinheim, Germany, 2002; Chapter 1.
(22) In these conditions (partial) reduction of the Cu and Ni salts very
likely takes place.
(23) (a) Xi, Z.; Li, P. Angew. Chem., Int. Ed. 2000, 39, 2950. (b) Zhao,
C.; Li, P.; Cao, X.; Xi, Z. Chem. Eur. J. 2002, 8, 4292.
(24) A change of color from yellow to red indicates the formation of
Cp2ZrII species.19

4154 Organometallics, Vol. 27, No. 16, 2008
Joosten et al.
Scheme 2
in AlCl3 up to 5 mol % resulted in the conversion of 1a to 2a
in the range of 20-30%, relative to the combined amounts of
Cp2ZrCl2 and AlCl3 involved in the reaction. These results were
in accordance with a noticeable transmetalation process, to
ensure the coupling of 1a catalytic in zirconium, as anticipated
in Scheme 1. The successful transmetalation of the intermediate
zirconacyclopentadiene with AlCl3 is noteworthy. It might
involve the AlCl3 reactivity tuning through chlorine-bridged
Cl2LaCl-AlCl3 species, similarly to the reactions in which an
aldehyde-AlCl3 adduct was involved.23
Table 2. Cyclotrimerization of Terminal Alkynes
By applying a catalytic amount of Cp2ZrCl2 together with
stoichiometric amounts of the La metal and AlCl3, other
disubstituted alkynes (1b-e) similarly reacted to afford the
corresponding tetrasubstituted dienes (2b-e) (Table 1). They
were accompanied by a small amount (e5%) of the correspond-
ing hexasubstituted benzene derivatives.
isomer ratio
product (yield (%))a
As for 1a, methylphenylacetylene (1b) was converted into
the diene 2b in the same good yield (entry 2). In contrast, the
total consumption of diphenylacetylene (1c) was obtained only
after a 48 h period, and the diene 2c was isolated in 31% yield
(entry 3).25 However, when using phenylpropylacetylene, a very
good yield was obtained (entry 4). In this case, the dissymmetric
isomer 2d was the major product formed (85% yield); it was
accompanied by two other topoisomers: i.e., (2E,4E)-3,4-
diphenylhexa-2,4-diene and (1E,3E)-2,3-dimethyl-1,4-diphe-
nylbuta-1,3-diene (10% combined yield). This marked topose-
lectivity is presumably due to steric reasons. The use of the
silylated alkyne 1e led to a rapid and totally toposelective
dimerization reaction to afford solely the diene 2′e, having
trimethylsilyl groups at the terminal C atoms (entry 5).
Trimethylsilyl-alkyne couplings are known to give selectively
R-silylated zirconacyclopentadiene intermediates.26 Similar
results were obtained by using mischmetall instead of La as
reductant. Thus, dimerization of disubstituted alkynes proved
to occur when using a catalytic amount of lanthanide-originated
zirconocene and AlCl3 as additive. A generally slow dimeriza-
tion of disubstituted dienes indicates that the Zr(II) species can
regenerate over a long reaction period to allow the closing of
the catalytic cycle. As anticipated in Scheme 1, and similarly
to some Zr-catalyzed reactions (see Introduction), the dimer-
ization would involve carbometalative ring expansion of the
zirconacyclopropene and transmetalation.
As mentioned previously, when the lanthanide-originated Cp2Zr
equivalent is applied, stoichiometric coupling of not only internal
but also terminal alkynes can be carried out.19 Therefore, we
decided to check if terminal alkynes can undergo such reactions
also in the presence of a catalytic amount of zirconium. In the
model series of experiments, phenylacetylene (3) was used as the
starting material. The experimental conditions were similar to those
employed for disubstituted alkenes, involving a catalytic amount
(5 mol %) of Cp2ZrCl2 and stoichiometric amounts of La and
AlCl3. The reaction was carried out in THF at 50 °C and monitored
by GC-MS. Alkyne 3 was completely consumed after 2 h and,
surprisingly, a mixture of 1,2,4- and 1,3,5-triphenylbenzene (4a,b
respectively, 4a:4b ) 3:2) was mainly formed, accompanied by
only a small amount of the expected diphenylbutadiene 5 (1,3-
and 1,4-isomers) (Scheme 2).
entry
R
time (h)
(a:b)
1
2
3
4
5
6
7
Ph
2
2
2
12
2
2
1.5
1.1
1.1
4 (75)
6 (80)
7 (71)
8 (80)
9 (80)
10 (73)
11 (67)
4-MeC6H4
4-MeOC6H4
1-naphthyl
4-biphenyl
n-C10H21
1.4
7.1
cyclohex-1-enyl
6
a Isolated yields.
studied extensively.27 Activated metals, as well as transition-
metal (Co, Rh, Ni, etc.) complexes have been used, but the
number of practically useful catalysts is rather limited. The
observed catalytic reaction sharply contrasts with the reported
zirconocene-mediated cyclotrimerizations, known to proceed
under stoichiometric conditions in the presence of Cu, Ni, and
Cr transmetalating agents.21,28 We noticed that compound 4 was
not formed in the presence of CuCl or NiBr2(PPh3)2 (typically
used as additives in the stoichiometric reactions), even after a
prolonged (12 h) reaction period.22
Interestingly, the cyclotrimerization reaction was noticed to
occur similarly in the absence of AlCl3. As noted previously,
the benzene derivative 4 was formed in good yield from 3. It
was also accompanied by a small amount of the diene 5,
corresponding to that of the zirconacyclopentadiene involved
in the reaction.
Other monosubstituted alkynes also reacted to afford the
corresponding trisubstituted benzene derivatives (Table 2). Thus,
alkynes bearing aryl (entries 1-5) and alkyl (entry 6) as well
as alkenyl (entry 7) groups afforded mixtures of 1,2,4- and 1,3,5-
trisubstituted benzene derivatives (4 and 6-11) in typically a
ratio of 1.1-1.5 (except in entry 7) and in good yields. In all
cases, only traces of the corresponding dienes were detected.
Similar results were obtained by using mischmetall instead of
La as reductant.
The selective preparation of benzene derivatives from dif-
ferent alkynes is of substantial synthetic interest,29 and in this
context the coupling reaction from the diyne 12 and phenyl-
acetylene 3 was next investigated. By applying the previously
established procedure, cyclic carbozirconation was first exam-
(27) (a) Schore, N. E. In ComprehensiVe Organic Synthesis; Trost, B. M.;
Fleming, I.; Paquette, L. A., Eds.; Pergamon: Oxford, U.K., 1991; Vol. 5,
p 1129. (b) Grotjahn, D. B. In ComprehensiVe Organometallic Chemistry
II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G.; Hegedus, L. S., Eds.;
Pergamon: Oxford, U.K.; 1995; Vol. 12, p 741. (c) Saito, S.; Yamamoto,
Y. Chem. ReV. 2000, 100, 2901. For a cyclotrimerization of terminal alkynes
using the CpNbCl4/Mg catalyst system, see: (d) Williams, A. C.; Sheffels,
P.; Sheehan, D.; Livinghouse, T. Organometallics 1989, 8, 1566.
(28) Takahashi, T.; Liu, Y.; Iesato, A.; Chaki, S.; Nakajima, K.; Kanno,
K. J. Am. Chem. Soc. 2005, 127, 11928.
Metal-catalyzed cyclotrimerization of alkynes (or alkynes and
nitriles) to produce substituted benzenes (or pyridines) have been
(25) A significant quantity of the reduction products, i.e. trans- and cis-
stilbene, was formed. Compound 2c was obtained in 86% yield after 4 h
when using a stoichiometric amount of Cp2ZrCl2; see also ref 6.
(26) (a) Buchwald, S. L.; Nielsen, R. B. J. Am. Chem. Soc. 1989, 111,
2870. (b) Xi, C.; Huo, S.; Afifi, T. H.; Hara, R.; Takahashi, T. Tetrahedron
Lett. 1997, 38, 4099.

Multimetallic Zirconocene-Based Catalysis
Organometallics, Vol. 27, No. 16, 2008 4155
Scheme 3
compounds 5 and 4-d3 or 5-d2 and 4 were formed from
phenylacetylene and its deuterated analogue (entries 4 and 5).
Some additional experiments were performed to gain an
insight into the reaction. When the Negishi zirconocene
equivalent was generated from Cp2ZrCl2 with 2 equiv of n-BuLi
in the presence of 1c, followed by the addition of 3 and LaCl3,
the cyclotrimerization was not observed: only diene 5 was
formed in 73% yield after hydrolysis. The same result was
obtained when the “Cp2Zr” equivalent was generated by
reducing Cp2ZrCl2 with Mg. Moreover, no cyclotrimerization
took place when generating LaCl3 from tetrachloroethane and
La32 or by using LaCl3 alone or as a mixture with La.
a
Yield related to 12.
b
Yield related to 3.
c
Yield related to 1a.
Transition-metal-mediated cyclotrimerization reactions have
been postulated to proceed through the insertion (or the
concerted cycloaddition) of an alkyne to the metallacyclopen-
tadiene.27 However, in our case, the cyclotrimerization is likely
to operate through another mechanistic pathway involving both
zirconium and lanthanide species. Although catalytic couplings
of alkynes under the effect of lanthanide complexes (Ln ) Y,
La, Ce) are known,33 such reactions proceeding through
lanthanide acetylides produce oligomeric (dimeric) rather than
benzene derivatives. In any case, no cyclotrimerization product
was formed when only one of two metals (Zr or La) was present.
The crucial point lies in the absence of benzene derivatives
incorporating both alkynes, when preforming the zirconacyclo-
pentadiene from the first alkyne and subsequently adding a
different second alkyne (Scheme 3 and Table 3). If the
cyclotrimerization product had formed through insertion of the
alkyne into the zirconacyclopentadiene intermediate, a mixed
benzene derivative would have been obtained, in addition to
that formed from the second alkyne. Particularly relevant
examples are those in which very similar alkynes, i.e. pheny-
lacetylene and its deuterated analogue, were used (Table 3,
entries 4 and 5), leading to the separate formation of the
corresponding diene and benzene derivatives. Consequently, the
cyclotrimerization reactions involving a unique alkyne, as
depicted in Scheme 2 and Table 2, would not proceed through
an insertion of the alkyne into the zirconacyclopentadiene
intermediate.
Table 3. Selective Formation of Dienes and Benzene Derivatives
entry
R1
R2
R3
R4
product (yield (%))a
1
2
3
4
5
Ph
Ph
n-C5H11
Ph
Ph
H
H
H
D
Ph
H
H
H
D
H
2c (87b), 4 (75c)
5 (81b), 15 (90c)
14 (80b), 4 (78c)
5 (82b), 4-d3 (87c)
5-d2 (81b), 4 (86c)
4-Me2NC6H4
Ph
Ph
Ph
Ph
a Isolated yields. b Yield related to R1Ct CR2. c Yield related to
R3Ct CR4.
ined. The reaction mixture was analyzed by ESI-MS,30 clearly
indicating formation of the zirconacyclopentadiene intermediate
B (Scheme 3).
Ten equivalents of 3 was added, and the reaction was carried
out as previously detailed. Surprisingly, no benzene derivative
which would result from the insertion of 3 into B was detected.
The only products formed were the diene 1331 and the benzene
derivative 4 (4a:4b ratio 3:2) (Scheme 3, eq a).
Following this intriguing result, we performed a reaction in
which the zirconacyclopentadiene C was first generated from
1a, followed by the addition of 3. Similarly, no insertion product
was observed. The reaction solely afforded the diene 2a and
the benzene derivative 4 (eq b). In the next reactions a catalytic
amount of the first alkyne (and of Cp2ZrCl2) was used (Table
3). Also in these cases, only mixtures of dienes 2 and 5 (or 14)
(related to the first alkyne and the corresponding zirconacyclo-
pentadiene) and benzene derivatives 4 (or 15) (related to the
second alkyne) were obtained. Examples are given in which
terminal alkynes with aryl and alkyl groups were employed.
Among them, the use of phenylacetylene 3 followed by the
addition of (4-(dimethylamino)phenyl)acetylene (4-ethynyl-N,N-
dimethylaniline) led to the exclusive formation of diphenylb-
utadiene 5 (1,3- and 1,4-isomer mixture) and the tris((dimethyl-
amino)phenyl)benzene derivative 15 (entry 2). The same
reaction pattern, i.e. the separate formation of the diene 14 and
the benzene derivative 4, was observed with alkynes bearing
alkyl (C5H11) and aryl (phenyl) groups (entry 3). Similarly,
The described cyclotrimerization appears to take place under
specific conditions, in the presence of zirconocene and lan-
thanide components. The exact structure of the zirconocene
equivalent formed from Cp2ZrCl2 and La as well as that of the
hypothetical cyclotrimerization active (bimetallic?) species
remains unknown. However, the initially formed zirconacycle
appear to be invariably present in the reaction medium, in
stoichiometric or catalytic amount, together with the La species,
to promote the cyclotrimerization reaction. The lanthanide entity
seems to be different from LaCl3 that would be initially formed
from Cp2ZrCl2 and La (according to simple stoichiometry), since
no cyclotrimerization reaction takes place when adding LaCl3
to the Negishi zirconocene equivalent. Possibly, a bimetallic
polarization process through zirconocene-lanthanide chlorine-
bridged assemblies is involved. More detailed mechanistic
studies are needed to provide further insight into this unusual
cyclotrimerization reaction.
(32) Deacon, G. B.; Feng, T.; Nickel, S.; Skelton, B. W.; White, A. H.
J. Chem. Soc., Chem. Commun. 1993, 1328.
(29) No high-yielding and selective general approach to alkyne cyclo-
trimerization has been developed to date.
(30) For a recent review on the uses of electrospray ionization mass
spectrometry for studying intermediates and reaction mechanisms, see: (a)
Santos, L. S. Eur. J. Org. Chem. 2008, 235. (b) For experimental and
calculated HRMS spectra of B, see the Supporting Information.
(31) Fox, M. A.; Chandler, D. A.; Lee, C. J. Org. Chem. 1991, 56, 3246.
(33) (a) Tazelaar, C. G. J.; Bambirra, S.; Van Leusen, D.; Meetsma,
A.; Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936. (b) Nishiura,
M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc.
2003, 125, 1184. (c) Dash, A. K.; Gourevich, I.; Wang, J. Q.; Wang, J.;
Kapon, M.; Eisen, M. S. Organometallics 2001, 20, 5084. (d) Heeres, H. J.;
Teuben, J. H. Organometallics 1991, 10, 1980.

4156 Organometallics, Vol. 27, No. 16, 2008
Joosten et al.
129.4 (CH), 129.2 (2 CH), 128.0 (2 CH), 127.7 (2 CH), 126.5 (CH),
126.1 (CH), 123.2 (CH), 15.7 (CH3), 15.5 (CH3). MS (IE, 70 eV):
m/z 234 (M, 45), 219 (100), 204 (47), 115 (20), 91 (13).
(1E,3E)-1,2,3,4-Tetraphenylbutadiene (2c).35 1,2-Diphenyl-
ethyne (180 µL, 1 mmol) was used. White solid. Mp: 182 °C. Yield:
75%. 1H NMR: δ 6.46 (s, 2 H), 6.81-7.92 (m, 20 H). 13C NMR:
δ 145.6 (2 C), 139.7 (2 C), 137.2 (2 C), 131.6 (2 CH), 130.4 (4
CH), 129.5 (4 CH), 128.8 (4 CH), 127.8 (4 CH), 127.3 (2 CH),
126.6 (2 CH).
In conclusion, we have reported a new reactivity pattern of
a lanthanide-derived zirconocene equivalent. Reactions catalytic
in zirconium, i.e. alkyne dimerization and unusual cyclotrim-
erization in the presence of Zr and La species, have been
described. Further studies of these and other similar reactions
should contribute to the development of catalytic zirconocene
chemistry.
(1E,3Z)-1,3-Diphenyl-2-propylhepta-1,3-diene (2d). Pent-1-
ynylbenzene (160 µL, 1 mmol) was used. Pale yellow oil. Yield:
85%. H NMR: δ 7.32-7.21 (m, 10 H), 6.25 (s, 1 H), 5.96-5.90
(t, J ) 7.3 Hz, 1 H), 2.46-2.40 (m, 2 H), 2.06-1.98 (q, J ) 7.6
Hz, 2 H), 1.64-1.43 (m, 4 H), 1.01-0.90 (m, 6 H). 13C NMR: δ
144.8 (C), 143.4 (C), 140.1 (C), 138.6 (C), 129.7 (2 CH), 129.1
(CH), 128.7 (2 CH), 128.1 (CH), 128.0 (2 CH), 127.9 (2 CH), 126.5
(CH), 126.1 (CH), 31.6 (CH2), 30.5 (CH2), 23.1 (CH2), 22.5 (CH2),
14.2 (CH3), 13.8 (CH3). MS (IE, 70 eV): m/z 290 (M, 9), 247 (57),
205 (100), 91 (28).
Experimental Section
1
All reactions were conducted under an atmosphere of argon using
standard Schlenk techniques. Prior to use, tetrahydrofuran was
distilled under argon from sodium benzophenone ketyl. Zirconocene
dichloride was purchased from Strem Chemicals. Alkynes were
purchased from Aldrich and used as received. Lanthanum and
mischmetall ingots were purchased from Aldrich and Fluka,
respectively, and powdered using a rap under argon. H and 13C
1
NMR spectra were recorded in CDCl3, unless specified, on a Bruker
AC-360 spectrometer. Chemical shifts are reported in delta (δ) units,
expressed in parts per million (ppm). NMR characteristics of all
knowncompoundswereinaccordancewiththeliteraturedata.19,31,34–40
Electrospray Ionization Mass Spectrometry (ESI-MS). All
experiments (MS and HRMS) were performed by using a hybrid
tandem quadrupole/time-of-flight (Q-TOF) instrument, equipped
with a pneumatically assisted electrospray (Z-spray) ion source
(Micromass, Manchester, U.K.) operated in positive mode (EV )
30 V, 80 °C, flow of injection 5 µL/min).
General Procedure for the Preparation of Dienes. A Schlenk
tube was loaded with Cp2ZrCl2 (60 mg, 0.2 mmol), lanthanum or
mischmetall (0.66 mmol), AlCl3 (134 mg, 1 mmol), and THF (5
mL) under an atmosphere of argon. The resulting mixture was
stirred vigorously at 50 °C until a deep red color appeared. At this
stage, the alkyne (2 mmol) was added to the reaction mixture and
the stirring was continued at 50 °C for 2-48 h. An aqueous HCl
solution (0.1 M, 5 mL) was then added at room temperature. The
aqueous layer was extracted with CH2Cl2 (2 × 5 mL), and the
organic phases were combined, dried over MgSO4, and concentrated
under vacuum. The residue was purified by flash column chroma-
tography on silica gel using a mixture of hexane and AcOEt as
eluant to give the diene.
(1E,3E)-2,3-Dimethyl-1,4-bis(trimethylsilanyl)buta-1,3-di-
ene (2′e).34 Ethynyltrimethylsilane (148 µL, 1 mmol) was used.
Colorless oil. Yield: 62%. 1H NMR: δ 5.70 (s, 2 H), 2.00 (s, 6 H),
0.16 (s, 18 H). 13C NMR: δ 153.6 (2 C), 126.0 (2 CH), 19.8 (2
CH3), 0.1 (6 CH3). MS (IE, 70 eV): m/z 226 (19, M), 211 (20),
152 (20), 123 (77), 73 (100).
General Procedure for the Preparation of Trisubstituted
Benzenes. A Schlenk tube was loaded with Cp2ZrCl2 (292 mg, 1
mmol), lanthanum or mischmetall (0.66 mmol), and THF (3 mL)
under an atmosphere of argon. The resulting mixture was vigorously
stirred at 50 °C until a deep red color appeared. At this stage, the
alkyne (10 mmol) was added to the reaction mixture, and the stirring
was continued for 2-48 h at 50 °C. The reaction was then quenched
with an aqueous HCl solution (0.1 M, 5 mL). The aqueous layer
was extracted with CH2Cl2 (2 × 5 mL), and the organic phases
were combined, dried over MgSO4, and concentrated under vacuum.
The residue was purified by flash column chromatography on silica
gel using a mixture of hexane and AcOEt as eluant to give the
corresponding trisubstituted benzene.
Triphenylbenzene (4). Phenylacetylene (1.10 mL) was used.
1
White solid. Yield: 75%. H NMR: 1,3,5-isomer, δ 7.85 (s, 3 H),
7.71-7.23 (m, 15 H); 1,2,4-isomer, δ 7.23-7.71 (m, 18 H). 13C
NMR: 1,3,5-isomer, δ 142.4 (3 C), 141.1 (3 C), 128.3 (6 CH),
127.5 (3 CH), 127.4 (6 CH), 125.3 (3 CH); 1,2,4-isomer δ 142.2
(C), 141.7 (C), 141.2 (C), 140.5 (C), 140.3 (C), 139.5 (C), 130.5
(CH), 130.3 (2 CH), 129.2 (2 CH), 129.1 (CH), 129.0 (2 CH), 128.2
(2 CH), 127.4 (2 CH), 127.3 (CH), 127.2 (2 CH), 127.1 (CH), 126.7
(CH), 125.8 (CH). HRMS (EI, 70 eV): m/z [M]+ calcd for C24H18
306.1403, found 306.1401.
(4E,6E)-5,6-Dipropyldeca-4,6-diene (2a).19 Oct-4-yne (146 µL,
1 mmol) was used. Yellow oil. Yield: 76%. 1H NMR: δ 5.37-5.33
(t, J ) 7.2 Hz, 2H), 2.16-2.02 (m, 8 H), 1.43-1.30 (m, 8 H),
0.93-0.85 (m, 12 H). 13C NMR: δ 141.2 (2 C), 125.9 (2 CH),
30.3 (2 CH2), 30.0 (2 CH2), 23.2 (2 CH2), 22.0 (2 CH2), 14.1 (2
CH3), 13.9 (2 CH3). MS (IE, 70 eV): m/z 222 (88, M), 179 (100),
137 (45), 123 (42), 94 (48), 81(36), 55 (21).
(1E,3Z)-1,3-Diphenyl-2-methylpenta-1,3-diene (2b).34 1-Phe-
nylprop-1-yne (125 µL, 1 mmol) was used. White oil, Yield: 75%.
1H NMR: δ 7.48-7.15 (m, 10 H), 6.15 (s, 1 H), 6.13-6.01 (q, J
Tris(4-methylphenyl)benzene (6).36 1-Ethynyl-4-methylbenzene
(1.26 mL) was used. White solid. Yield: 75%. 1H NMR: 1,3,5-
isomer, δ 7.82 (s, 3 H), 7.12-7.38 (m, 12 H), 2.48 (s, 9 H); 1,2,4-
isomer, δ 7.12-7.38 (m, 15 H), 2.39 (s, 3 H), 2.41 (s, 3 H), 2.47
(s, 3 H). 13C NMR: 1,3,5-isomer, δ 142.1 (3 C), 138.4 (3 C), 137.2
(3 C), 129.5 (6 CH), 127.2 (6 CH), 124.5 (3 CH), 21.2 (3 CH3);
1,2,4-isomer, δ 141.4 (C), 140.7 (C), 140.0 (C), 139.1 (C), 138.7
(C), 138.3 (C), 137.7 (C), 136.1 (C), 135.9 (C), 130.4 (CH), 130.3
(2 CH), 129.8 (2 CH), 129.8 (2 CH), 129.62 (2 CH), 129.6 (2 CH),
127.6 (CH), 126.9 (2 CH), 125.2 (CH), 21.2 (CH3), 21.1 (CH3),
21.0 (CH3). HRMS (EI, 70 eV): m/z [M]+ calcd for C27H24
348.1873, found 348.1867.
) 6.9 Hz, 1H), 2.12 (s, 3 H), 1.66-1.63 (d, J ) 6.9 Hz, 3 H). 13
C
NMR: δ 145.6 (C), 139.8 (C), 138.7 (C), 138.6 (C), 129.9 (2 CH),
(34) Sabade, M. B.; Farona, M. F.; Zarate, E. A.; Yongs, W. J. J.
Organomet. Chem. 1988, 338, 347.
(35) Negishi, E.; Holmes, S. J.; Tour, J. M.; Miller, J. A.; Cederbaum,
F. E.; Swanson, D. R.; Takahashi, T. J. Am. Chem. Soc. 1989, 111, 3336.
(36) Cadierno, V.; Garc´ıa-Garrido, S. E.; Gimemo, J. J. Am. Chem. Soc.
2006, 128, 15094.
(37) Bonvallet, P. A.; Breitkreuz, C. J.; Kim, Y. S.; Todd, E. M.;
Traynor, K.; Fry, C. G.; Ediger, M. D.; McMahon, R. J. J. Org. Chem.
2007, 72, 10051.
(38) Pena, M. A.; Pe´rez, I.; Pe´rez Sestelo, J.; Sarandeses, L. A. Chem.
Commun. 2002, 2248.
(39) (a) Tanaka, K.; Toyoda, K.; Wada, A.; Shirasaka, K.; Hirano, M.
Chem. Eur. J. 2005, 11, 1145. (b) Yong, L.; Butenscho¨n, H. Chem. Commun.
2002, 2852.
(40) Rodr´ıguez, J. G.; Mart´ın-Villamil, R.; Fonseca, I. J. Chem. Soc.,
Perkin Trans. 1 1997, 945.
Tris(4-methoxyphenyl)benzene (7).36 1-Ethynyl-4-methoxy-
1
benzene (1.26 mL) was used. White solid. Yield: 71%. H NMR:
1,3,5-isomer:, δ 7.80 (s, 3 H), 6.78-7.36 (m, 12 H), 3.88 (s, 9 H);
1,2,4-isomer: δ 7.36-6.78 (m, 15 H), 3.88 (s, 3 H), 3.87 (s, 3 H),
3.80 (s, 3 H). 13C NMR: 1,3,5-isomer, δ 159.3 (3 C), 142.6 (3 C),
134.1 (3 C), 129.9 (3 CH), 123.8 (6 CH), 114.2 (6 CH), 55.3 (3
CH3); 1,2,4-isomer δ 159.2 (C), 158.3 (C), 158.2 (C), 140.4 (C),

Multimetallic Zirconocene-Based Catalysis
Organometallics, Vol. 27, No. 16, 2008 4157
139.6 (C), 138.4 (C), 133.9 (C), 133.8 (C), 133.2 (C), 131.0 (CH),
130.8 (2 CH), 128.8 (CH), 128.1 (2 CH), 125.3 (CH), 123.8 (2
CH), 114.4 (2 CH), 113.4 (2 CH), 113.3 (2 CH), 55.30 (CH3), 55.29
(CH3), 55.1 (CH3). HRMS (EI, 70 eV): m/z [M - CH3]+ calcd for
C26H21O3 381.1485, found 381.1485.
(CH2), 29.4 (3 CH2), 29.1 (3 CH2), 22.7 (3 CH2), 22.6 (3 CH2),
14.1 (3 CH3). HRMS (EI, 70 eV): m/z [M - CH3]+ calcd for C25H63
498.5159, found 498.5162.
Tris(1-cyclohexenyl)benzene (11).36 1-Ethynylcyclohex-1-ene
1
(1.17 mL) was used. Yellow liquid. Yield: 67%. H NMR: 1,3,5-
Tris(1-naphthyl)benzene (8).37 1-Ethynyl-1-naphthalene (1.42
mL) was used. White solid. Yield: 80%. 1H NMR: δ 1,3,5-isomer
8.23 (d, J ) 8.0 Hz, 3 H), 7.48-7.96 (m, 21 H); 1,2,4-isomer, δ
7.48-8.15 (m, 24 H). 13C NMR: 1,3,5-isomer, δ 141.4 (3 C), 139.9
(3 C), 133.9 (3 C), 131.6 (3 C), 128.3 (3 CH), 128.0 (3 CH), 127.9
(3 CH), 127.1 (3 CH), 126.2 (3 CH), 125.9 (3 CH), 125.8 (3 CH),
125.4 (3 CH); 1,2,4-isomer:, δ 141.4 (C), 141.3 (C), 141.0 (C),
139.9 (C), 139.8 (C), 138.0 (C), 133.8 (C), 133.7 (C), 133.6 (C),
132.7 (C), 131.6 (C), 131.5 (C), 130.7 (CH), 128.5 (CH), 128.3 (2
CH), 128.2 (CH), 128.1 (CH), 128.0 (CH), 127.9 (2 CH), 127.8
(CH), 127.6 (CH), 127.2 (CH), 127.1 (CH), 126.4 (CH), 126.2 (CH),
126.1 (CH), 126.0 (2 CH), 125.8 (2 CH), 125.7 (CH), 125.5 (CH),
125.4 (2 CH). HRMS (EI, 70 eV): m/z [M]+ calcd for C36H24
456.1873, found 456.1881.
isomer, δ 7.26 (s, 3 H), 6.06-6.14 (m, 3 H), 2.3-2.10 (m, 12 H),
1.64-1.59 (m, 12 H); 1,2,4-isomer, δ 7.19 (dd, J ) 8.1, 2.1 Hz, 1
H), 7.13 (d, J ) 2.1 Hz, 1 H), 7.04 (d, J ) 8.1 Hz, 1 H), 6.06-6.14
(m, 1 H), 5.64-5.72 (m, 2 H), 2.04-2.48 (m, 12 H), 1.15-1.82
(m, 12 H). 13C NMR: 1,3,5-isomer, δ 141.4 (6 C), 125.1 (3 CH),
120.9 (3 CH), 26.6 (3 CH2), 23.5 (3 CH2), 22.4 (3 CH2), 22.1 (3
CH2); 1,2,4-isomer, δ 143.1 (C), 140.2 (2 C), 139.6 (C), 137.7 (C),
136.9 (C), 129.0 (CH), 126.3 (CH), 125.8 (CH), 124.7 (CH), 123.4
(CH), 120.9 (CH), 30.1 (CH2), 30.05 (CH2), 29.5 (CH2), 28.2 (CH2),
26.4 (CH2), 26.3 (CH2), 26.1 (CH2), 23.8 (CH2), 23.6 (CH2), 22.7
(CH2), 22.6 (CH2), 21.9 (CH2). MS (EI 70 eV): m/z 318 (100, M),
237 (33), 179 (39), 165 (62), 141 (50), 81 (76), 79 (67).
Tris(4-(N,N-dimethylamino)phenyl)benzene (15).40 1-Ethynyl-
4-dimethylaniline (1.45 g) was used. Pale yellow oil. Yield: 90%.
1H NMR: 1,3,5-isomer, δ 3.07 (s, 18 H), 6.91 (d, J ) 8.1 Hz, 6
H), 7.69 (d, J ) 8.0 Hz, 6 H), 7.72 (s, 3 H); 1,2,4-isomer, δ 2.97
(s, 6 H), 2.98 (s, 6 H), 3.03 (s, 6 H), 6.69 (d, J ) 7.8 Hz, 2 H),
6.71 (d, J ) 7.7 Hz, 2 H), 6.87 (d, J ) 9.1 Hz, 2 H), 7.17 (d, J )
7.8 Hz, 2 H), 7.20 (d, J ) 7.8 Hz, 2 H), 7.48 (d, J ) 7.9 Hz, 1 H),
7.59 (d, J ) 8.0 Hz, 1 H), 7.63 (s, 1H), 7.66 (m, 2 H). 13C NMR:
1,3,5-isomer, δ 41.6 (6 CH3), 113.7 (3 CH), 123.5 (3 CH), 128.8
(3 CH), 130.7 (3 C), 142.9 (3 C), 150.9 (3 C); 1,2,4-isomer, δ
41.5 (2 CH3), 41.6 (4 CH3), 113.1 (6 CH), 125.4 (CH), 128.6 (2
CH), 129.4 (CH), 130.0 (C), 130.7 (C), 131.45 (2 CH), 131.50 (2
CH), 131.8 (C), 139.0 (C), 140.4 (C), 141.4 (C), 149.7 (C), 149.9
(C), 150.7 (C), 1 C is missing. HR-ESI-MS (positive ion mode):
m/z [M + H]+ calcd for C30H34N3 436.2753, found 436.2747.
Tris(4-biphenyl)benzene (9).38 1-Ethynyl-4-biphenyl (178 mg)
was used. White solid. Yield: 80%. 1H NMR: 1,3,5-isomer, δ 7.91
(s, 3 H), 7.36-7.86 (m, 27 H); 1,2,4-isomer, δ 7.26-7.76 (m, 30
H). 13C NMR: 1,3,5-isomer, δ 142.1 (3 C), 140.6 (3 C), 140.5 (3
C), 140.0 (3 CH), 128.8 (6 CH), 127.7 (6 CH), 127.6 (6 CH), 127.4
(6 CH), 127.1 (6 CH), 125.1 (3 CH); 1,2,4-isomer, δ 142.0 (C),
141.8 (C), 140.7 (C), 140.6 (C), 140.5 (C), 140.3 (C), 140.1 (C),
140.0 (C), 139.9 (C), 139.3 (C), 130.3 (3 C), 130.0 (3 CH), 128.7
(CH), (6 CH), 128.3 (3 CH), 127.7 (6 CH), 127.6 (6 CH), 127.5 (3
CH), 126.6, 125.7 (CH), 124.9 (CH). HRMS (EI, 70 eV): m/z [M]+
calcd for C42H30 534.2342, found 534.2363.
Tris(n-decyl)benzene (10).39 Dodec-1-yne (2.14 mL) was used.
1
Yellow liquid. Yield: 73%. H NMR: 1,3,5-isomer, δ 6.82 (s, 3
H), 2.56 (m, 6 H), 1.52 (m, 6 H), 1.48-1.21 (m, 42 H), 0.88 (t, J
) 6.6 Hz, 9 H); 1,2,4-isomer, δ 7.04 (d, J ) 7.5 Hz, 1 H), 6.94 (s,
1 H), 6.92 (d, J ) 7.5 Hz, 1 H), 2.48-2.61 (m, 6 H), 1.45-1.65
(m, 6 H), 1.20-1.43 (m, 42 H), 0.88 (m, 9 H). 13C NMR: 1,3,5-
isomer, δ 142.5 (3 C), 125.7 (3 CH), 31.6 (3 CH2), 31.5 (3 CH2),
31.3 (3 CH2), 30.1 (3 CH2), 29.1 (9 CH2), 29.0 (3 CH2), 22.5 (3
CH2), 14.1 (3 CH3); 1,2,4-isomer, δ 142.7 (C), 140.3 (C), 140.2
(C), 129.1 (CH), 128.8 (CH), 125.6 (CH), 36.0 (CH2), 35.6 (CH2),
32.8 (CH2), 32.4 (CH2), 31.9 (CH2), 31.6 (CH2), 31.62 (CH2), 31.4
(CH2), 29.9 (CH2), 29.7 (CH2), 29.6 (CH2), 29.56 (3 CH2), 29.5
Acknowledgment. We thank the CNRS and the Ministe`re
de l’Education Nationale et de la Recherche for their financial
support.
Supporting Information Available: Figures giving experimental
and calculated HRMS spectra of the complex B. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM8002703