Palladium-catalyzed pathways to aryl-substituted indenes: Efficient synthesis of ligands and the respective ansa-zirconocenes

Article abstract of DOI:10.1021/om050937e

Substituted 4-/7-halo-1H/-indenes and 5-methyl-3-bromo-4-/6H-cyclopenta[b] thiophenes were shown to be convenient starting materials for Suzuki-Miyaura, Negishi, and Murahashi protocols to give the corresponding aryl-subsituted indenes and cyclopenta[b]thiophenes of importance for further synthesis of ansa-metallocenes. Alternatively, (2-methyl-1H-inden-4-yl)boronic acid and (1-methoxy-2-methyl-2,3-dihydro-1H-inden-4-yl)boronic acid as well as the respective organozinc and -magnesium reagents can be used for synthesizing aryl-subsituted indenes via the Pd-catalyzed reactions with aryl halides. These synthetic methods were shown to have a very broad scope to afford libraries of aryl-substituted indenes. Finally, synthesis and structure characterization of several representative chiral ansa-zirconocenes, potentially useful as components of highly active and stereoselective olefin polymerization catalysts, have been performed.

Full text of DOI:10.1021/om050937e

Organometallics 2006, 25, 1217-1229
1217
Palladium-Catalyzed Pathways to Aryl-Substituted Indenes:
Efficient Synthesis of Ligands and the Respective ansa-Zirconocenes
Vyatcheslav V. Izmer, Artyom Y. Lebedev, Mikhail V. Nikulin, Alexey N. Ryabov,
Andrei F. Asachenko, Alexander V. Lygin, Denis A. Sorokin, and
Alexander Z. Voskoboynikov*
Department of Chemistry, Moscow State UniVersity, V-234, Moscow, GSP, 119899 Russian Federation
ReceiVed NoVember 1, 2005
Substituted 4-/7-halo-1H-indenes and 5-methyl-3-bromo-4-/6H-cyclopenta[b]thiophenes were shown
to be convenient starting materials for Suzuki-Miyaura, Negishi, and Murahashi protocols to give the
corresponding aryl-subsituted indenes and cyclopenta[b]thiophenes of importance for further synthesis
of ansa-metallocenes. Alternatively, (2-methyl-1H-inden-4-yl)boronic acid and (1-methoxy-2-methyl-
2,3-dihydro-1H-inden-4-yl)boronic acid as well as the respective organozinc and -magnesium reagents
can be used for synthesizing aryl-subsituted indenes via the Pd-catalyzed reactions with aryl halides.
These synthetic methods were shown to have a very broad scope to afford libraries of aryl-substituted
indenes. Finally, synthesis and structure characterization of several representative chiral ansa-zirconocenes,
potentially useful as components of highly active and stereoselective olefin polymerization catalysts,
have been performed.
bilities for changing the coordination environment of zirconium
to enhance activity and/or stereoselectivity of the respective
catalysts remain largely unexplored. First of all, the introduction
of various aryls in position 4 of the indenyl or heteroindenyl
fragments of zirconocenes is of interest. Of analogous impor-
tance would be the study of a similar structural change for
zirconocenes involving, for example, methyls in position 5 or
6 of the indenyls in structure A or without methyl in a position
ortho to sulfur in a metallocene of type B, etc. Another important
problem is the investigation of such metallocene families for
development of polymerization catalysts targeted mostly at the
design of new highly specific catalytic systems for the prepara-
tion of novel brands of special polyolefins with controlled sets
of properties, including morphology, uniform particle size
distribution, physicomechanical parameters, etc., due to highly
stereoselective and stereochemically stable catalysts.
Introduction
The last 15-20 years have witnessed major advances in
R-olefin polymerization catalyst chemistry: in particular, the
stereochemical control of polypropylene synthesis using met-
allocene-based catalysts. A very important contribution came
from Brintzinger et al., who were the first to obtain C2-sym-
metrical ansa-metallocenes.1a These chiral stereorigid complexes
were soon investigated by Ewen1b and Kaminsky and Brintz-
inger et al.1c as precatalysts in propylene polymerization. The
respective zirconium complexes in the presence of a suitable
activator, such as MAO,2 B(C6F5)3, [CPh3]+[B(C6F5)4]-,2b,3 etc.
were found to give new homogeneous, highly stereoselective
catalysts for polymerization of R-olefins.4 Extensive studies of
the relationship between ansa-metallocene structure and activity/
stereoselectivity of the respective propylene polymerization
catalysts showed that, in the general case, the best results are
observed for so-called advanced ansa-zirconocenes of structure
A involving a dimethylsilanediyl-bis(indenyl) chelating ligand
It should be noted that theoretical investigations involving
quantum-chemical calculations on the relationship between
catalyst structure and catalytic activity have recently been
performed for a number of catalytic systems, though satisfactory
results were obtained in only a few cases.7 It is obvious that
reasonable theoretical models for catalytic systems involving
(1) (a) Wild, F. R. W. P.; Zsolnai, I.; Huttner, G.; Brintzinger, H.-H. J.
Organomet. Chem. 1982, 232, 233. (b) Ewen, J. A. J. Am. Chem. Soc. 1984,
106, 6355. (c) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H.-H.; Wild, F. R.
W. P. Angew. Chem., Int. Ed. Engl. 1985, 24, 507. (d) Metallocenes:
Synthesis, ReactiVity, Applications; Togni, A., Halterman, R. L., Eds.; Wiley-
VCH: Weinheim, Germany, 1998, and references therein.
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Int. Ed. Engl. 1980, 19, 390. (b) Chen, E. Y.-X.; Marks, T. J. Chem. ReV.
2000, 100, 1391.
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116, 10015. (b) Bochmann, M.; Lancaster, S. L. Angew. Chem., Int. Ed.
Engl. 1994, 33, 1634.
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100, 1253.
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Antberg, M.; Dolle, M.; Paulus, E. F. Organometallics 1994, 13, 954.
(6) (a) Ewen, J. A.; Jones, R. L.; Elder, M. J.; Rheingold, A. L.; Liable-
Sands, L. M. J. Am. Chem. Soc. 1998, 120, 10786. (b) Ewen, J. A.; Elder,
M. J.; Jones, R. L.; Rheingold, A. L.; Liable-Sands, L. M.; Sommer, R. D.
J. Am. Chem. Soc. 2001, 123, 4763.
bearing methyl in position 2 and aryl in position 4 of the indenyl
fragments.5 The slightly different geometries of analogous ansa-
heterocenes involving cyclopenta[b]thiophene fragments seems
to exert a dramatic effect on the stereoselectivity of the
respective catalysts in propylene polymerization. Thus, an
additional methyl in a position ortho to sulfur is apparently
required to obtain the best results (structure B).6
Though many complexes of this type have been studied so
far at major research centers all over the world, several possi-
10.1021/om050937e CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/25/2006

1218 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
transition metals are still too complex to allow computations at
high levels of theory. Therefore, currently and for at least the
near future, there is no alternative to experimental testing of
various catalysts, conditions, additives, etc.
Thus, this work is aimed at the development of convenient
and high-yield Pd-catalyzed cross-coupling procedures for 4-/
7-halo-1H-indenes and related substrates to obtain the respective
4-/7-aryl-1H-indenes and analogues, including aryl-substituted
heteroindenes, currently available only via multistage proce-
dures.6 First, we analyze general synthetic methods to obtain
starting haloindenes and show how these methods work for the
selected substrates. Next, Pd-catalyzed synthesis of various
arylindenes from haloindenes is described in detail; in particular
the Suzuki-Miyaura, Negishi, and Murahashi protocols for the
key substrates C and D are compared. Finally, the synthesis of
Until recently, in olefin polymerization catalyst studies, high-
throughput methods of research were not applied. The first
reports on such approaches appeared around 5 years ago.8 There
is yet another important incentive for the development of catalyst
screening. Indeed, currently, the major industrial processes are
(i) gas-phase polymerization of ethene and propene, (ii) suspen-
sion polymerization of ethene, and (iii) propene polymerization
in liquid monomer solution. In all of these processes, highly
effective catalysts (e.g., Ziegler-type catalysts) are used. Tech-
nological and economic reasons command the application of
heterogeneous (supported) catalysts, which, however, suffer
from considerable inhomogeneity of active center distribution
and modest net activity. Supported catalysts of the new
generation are expected to overcome these significant draw-
backs. The new generation of supported metallocene catalysts
features active centers of rigorously defined structure uniformly
distributed over the surface. Such catalysts based on metal-
locenes will allow design of fully automated polymerization
processes. On the other hand, any quantitative theoretical
reasoning for supported catalysts is a much more sophisticated
procedure than for homogeneous catalysts, well beyond the
current level of theoretical calculations. Thus, empirical high-
throughput screening is apparently the only way to new
generation catalysts and processes. The sources of potential
catalysts should be manifold: in addition to screening of
available samples and conventional synthesis, high-output
procedures for parallel concurrent synthesis of tens and hundreds
of new compounds employing fast and highly reliable trans-
formations of organometallic compounds. From this point of
view, various metal-catalyzed cross-coupling procedures using,
for example, readily available arylboronic acids and parental
halo-substituted metallocenes would be desirable. Unfortunately,
similar procedures have not been realized so far for several
reasons: in particular, instability of the coordination environ-
ment of zirconium under the conditions for cross-coupling.
Moreover, the chiral ansa-zirconocenes are known to epimerize
readily in the presence of various additives9 or on irradiation
with light.10 Alternatively, high-throughput catalytic cross-
coupling reactions of the respective haloindenes and related
substrates can be used (see also ref 11) to synthesize libraries
of arylindenes and then ansa-zirconocenes of types A and B,
of interest for olefin polymerization. It is desirable to develop
in this way such conditions for Pd-catalyzed cross-coupling
under which a possible side intermolecular Heck reaction with
the olefinic fragment of indenes is suppressed.12
the selected bis(indenyl)dimethylsilanes and the respective ansa-
zirconocenes has been performed to illustrate the approach for
the development of potential olefin polymerization catalysts.
Results and Discussion
Synthesis of 4-/7-Halo-2-methyl-1H-indenes and Ana-
logues. Two general selective methods can be used to synthesize
4-/7-halo-2-methylindan-1-ones and analogous compounds start-
ing from the readily available substrates, i.e. (1) intramolecular
acylation of 3-(2-halophenyl)-2-methylpropanoyl chloride and
related compounds under Friedel-Crafts conditions (eq 1; X
) Cl, Br, I; Y ) Cl, OH, etc.) to afford 4-/7-bromoindan-1-
ones11a,13) and (2) Lewis-acid-catalyzed Nazarov cyclization of
1-(2-halophenyl)-2-methyl-2-propen-1-one and related com-
pounds (eq 2; X ) Cl, Br, I).13j,14
Next, 4-/7-halo-2-methyl-1H-indenes can be obtained via the
reduction of the respective 4-/7-halo-2-methylindan-1-ones
followed by dehydration of the substituted indan-1-oles formed.
(7) (a) Schmid, R.; Ziegler, T. Organometallics 2000, 19, 2756. (b)
Vyboishchikov, S. F.; Musaev, D. G.; Froese, R. D. J.; Morokuma, K.
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Ronca, S.; Budzelaar, P. H. M. Macromolecules 2003, 36, 8171.
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(9) Lin, R. W. U.S. Patent 5,965,759 for Albemarle Corp., 1999.
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H.-H. Organometallics 1997, 16, 1724. (b) Krut’ko, D. P.; Borzov, M. V.;
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1998, 47, 2280.
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ExxonMobil Chemical Co., 2002.
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Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1219
Alternatively, 4-/7-halo-2-methyl-1H-indenes can be obtained
via ortho lithiation of the respective indan-1-oles15 followed by
lithium-halogen exchange with subsequent dehydration. Several
alternative procedures to obtain the desired 4-/7-haloindan-1-
ones or the respective haloindenes can be applied for this pur-
pose also, though their scope is very narrow.16 At the same time,
other reported methods were found to result in undesirable
mixtures of products or include multistage transformations of
low synthetic interest.14d,17 The only example to be mentioned
separately is direct electrophilic halogenation of indan-1-ones
(containing no substituents in position 7) and related substrates
in the presence of Lewis acids.18 This method is very useful
for the preparative synthesis of some 4-/7-halo-1H-indenes19
(see below).
to partial oligomerization of indene formed and, therefore, a
decreased yield of product. The malonate method has been
applied to synthesize many different aryl-/alkyl-substituted
indenes5 and 4-bromo-1H-indene.11a The most important prob-
lems in this case are (1) availability of the desired benzyl halide
and (2) selectivity of the Lewis acid-catalyzed cyclization
reaction (stage b, eq 3) if X1 is hydrogen and X2 * X3. For the
synthesis of 1-4, the selectivity is apparently not an issue.
Indene 1 was obtained as a colorless oil consisting of two
isomers, i.e., 7-bromo-2-methyl-1H-indene (71% by HPLC) and
a minor isomer, 4-bromo-2-methyl-1H-indene (29%). The major
isomer crystallizes slowly at room temperature and, thus, was
isolated in an analytically pure form. The analogous Cl-
substituted indene 2 was obtained as a ca. 1:9 (HPLC) mixture
of 4- and 7-chloro-2-methyl-1H-indenes. The isomeric composi-
tions of 3 and 4 were found to be ca. 7.7:1 and 10:1 (NMR) in
favor of 7-bromo-2,6-dimethyl-1H-indene and 5,7-dibromo-2-
methyl-1H-indene, respectively.
Here, to synthesize 4-/7-bromo-2-methyl-1H-indenes 1-4,
we used the first method mentioned above: i.e., the Lewis acid
catalyzed cyclization of the respective 3-(2-halophenyl)-2-
methylpropanoyl chlorides as shown in eq 3. The starting 3-(2-
Alternatively, 3-(2-bromophenyl)-2-methylpropanoic acid was
synthesized via the reaction of o-bromobenzaldehyde with
triethyl 2-phosphonopropionate20 followed by reduction of the
substituted cinnamic acid formed (eq 4). This procedure gave
the desired saturated acid in 75% total yield. The reduction was
carried out using red phosphorus in aqueous HI at reflux.21 Then,
the substituted propanoic acid was converted into 4-bromo-2-
methylindan-1-one and indene 1 as shown in eq 4.
A very promising synthetic procedure for 4-/7-halo-1H-
indenes is based on the ortho lithiation22 of readily available
1-indanoles. For instance, the reaction of 2-methyl-1-indanole
halophenyl)-2-methylpropanoyl chlorides were obtained via the
standard malonate method, which is based on the reaction of
the respective benzyl halide with sodium diethylmethylmalonate
followed by saponification of ester and then decarboxylation
of the dibasic acid. 3-Aryl-2-methylpropanoic acids formed were
converted into the respective acid chlorides, giving 2-methylin-
dan-1-ones via Lewis acid catalyzed cyclization. The reduction
of 2-methylindan-1-ones with NaBH4 followed by acid-catalyzed
dehydration gave the desired indenes 1-5 as mixtures of
isomers. It should be noted that p-toluenesulfonic acid is a softer
and more selective acidic catalyst than, for example, P4O10 for
dehydration of the alcohol. In some cases, the use of P4O10 leads
n
with BuLi/TMEDA in pentane for 10 h at reflux followed by
treatment with 1,2-dibromoperfluoroethane23 gave 7-bromo-2-
methyl-1-indanol (5) in 83% yield at 93% conversion (HPLC)
of the starting material (eq 5). It should be noted that this
(14) (a) Battacharya, A.; Segmuller, B.; Ybarra, A. Synth. Commun. 1996,
26, 1775. (b) Barnes, R. A.; Kraft, E. R.; Gordon, L. J. Am. Chem. Soc.
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Chow, K.; Garst, M. E. J. Org. Chem. 2003, 68, 10195.
procedure was optimized to achieve a better yield. Further,
4-bromo-2-methyl-1H-indene was obtained from 5 in almost
quantitative yields as shown below.
(15) Panetta, C. A.; Dixit, A. S. Synthesis 1981, 59.
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Bull. Soc. Chim. Belg. 1980, 89, 1043.
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Echavarren, A. M. Eur. J. Org. Chem. 2001, 11, 2107. (b) Cornelius, L. A.
M.; Combs, D. W. Synth. Commun. 1994, 24, 2777.
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Bringmann, G.; Gotz, R.; Keller, P. A.; Walter, R.; Henschel, P.; Schaffer,
M.; Stablein, M.; Kelly, T. R.; Boyd, M. R. Heterocycles 1994, 39, 503.
(21) Gabriel, H. Chem. Ber. 1883, 16, 2037. Stanley, W.; Shih, C. W.;
Priscilla, L. J. Org. Chem. 1950, 15, 593.
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1220 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
The treatment of the ortho-lithiated product with iodine in
an ether/n-pentane mixture resulted in 7-iodo-2-methyl-1-indanol
(6), isolated in as low as 27% yield (eq 6). Side oxidation of
the starting lithium salt with iodine to form some radical
coupling products seems to explain this relatively low yield
observed. 7-Iodo-2-methyl-1H-indene (including ca. 3% of
another isomer) was further synthesized from 7 in almost
quantitative yield, as shown in eq 6.
This straightforward and practical method was shown to work
well for other 1-indanoles studied. Though conditions of these
reactions were not optimized, 7-bromo-2,6-dimethyl-1-indanol
(8) and 4-bromo-2-methyl-2,3,6,7,8,9-hexahydro-1H-cyclopenta-
[a]naphthalen-3-ol (10) were synthesized in this way by starting
from 2,6-dimethyl-1-indanol (eq 7) and 2-methyl-2,3,6,7,8,9-
of 2-bromoisobutyryl bromide and AlCl3 in dichloromethane
resulted in 7-bromo-5-isopropyl-2-methyl-1-indanone in 67%
yield. This reaction is very sensitive to the conditions used; thus,
the yield is shown for the optimized procedure. Finally, the
reduction of the obtained indanone by NaBH4 followed by
dehydration resulted in indene 7 as a pure 4-bromo-substituted
isomer.
Next, 3-bromo-5-methyl-4H-cyclopenta[b]thiophene (16) was
obtained via the reactions shown in eq 10. The key stage of
this synthesis is the regioselective bromination of 5-methyl-
5,6-dihydro-4H-cyclopenta[b]thiophen-4-one (14), giving bro-
moindanone 15 in 94% yield. The observed high regioselectivity
of this reaction seems to result from the concerted directing
effect of the substituents (2-acyl and 3-alkyl) in the thiophene
ring. Though the synthesis of an analogous dibromide, 2,3-
dibromo-4,5-dihydro-6H-cyclopenta[b]thiophen-6-one, via elec-
trophilic dibromination of 4,5-dihydro-6H-cyclopenta[b]thiophen-
6-one was described,25c monobromination has never been used.
In contrast, 2,5-dimethyl-3-bromo-4,5-dihydro-6H-cyclopenta-
[b]thiophen-6-one, a half-product of interest for synthesizing
promising olefin polymerization catalysts, was obtained via
multistage transformations as described by Ewen et al.25d,e It
should be noted that the starting ketone 14 can be obtained from
thiophene and methacrylic acid via a published procedure.25f,g
Thus, the bromination of this ketone followed by its reduction
and then acid-catalyzed dehydration gave thioindene 16 includ-
ing ca. 5% of the other isomer, 3-bromo-5-methyl-6H-cyclo-
penta[b]thiophene.
hexahydro-1H-cyclopenta[a]naphthalen-3-ol (9) (eq 8) in 37 and
41% yields at 57 and 59% conversions (HPLC) of the starting
materials, respectively. Thus, the corresponding bromoindenes
3 and 11 were isolated in 36 and 39% overall yields, respec-
tively.
The other synthetic method used by us is the one-pot acylation
of arene by 2-bromoisobutyryl bromide followed by Nazarov
cyclization.24,25 Thus, 4-bromo-6-isopropyl-2-methyl-1-indanone
(12) and indene 13 were obtained from 4-isopropylaniline as
shown in eq 9. In this way, bromination of N-(4-isopropylphe-
nyl)acetamide followed by deamination of the deprotected
aniline gave 1-bromo-3-isopropylbenzene in 53% total yield.
One-pot acylation-cyclization of this substrate with a mixture
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(23) (a) Wang, W.; Snieckus, V. J. Org. Chem. 1992, 57, 424. (b)
Paquette, L. A.; Ross, R. J.; Shi, Y.-J. J. Org. Chem. 1990, 55, 1589. (c)
Paquette, L. A.; DeRussy, D. T.; Gallucci, J. C. J. Org. Chem. 1989, 54,
2278.
(24) (a) Kizhner, N. Zh. Russ. Fiz.-Khim. O-Va. 1914, 1411. (b) Fabrycy,
A.; Bal, S.; Majewski, E.; Soroka, J. Polish J. Chem. 1978, 52, 2059. (c)
Stehling, U.; Diebold, J.; Kirsten, R.; Ro¨ll, W.; Brintzinger, H.-H.
Organometallics 1994, 13, 964.

Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1221
Synthesis of Arylindenes from Haloindenes and Their
Derivatives via Cross-Coupling Reactions. The palladium-
catalyzed Suzuki-Miyaura coupling reaction has been used for
decades as a powerful tool for synthesizing biaryls.26-29 For
simple aryl bromides, this reaction is known to be carried out
using Pd(OAc)2 as a catalyst and Na2CO3 as a base in acetone
or an acetone-H2O mixture (3/1 v/v). We applied these
conditions to synthesize 4-/7-aryl-2-methyl-1H-indenes from 4-/
7-bromo-2-methyl-1H-indene (1 equiv) and the respective
arylboron derivatives (1 mol for RB(OH)2 and 0.25 mol for
NaBPh4) using 2 mol % of Pd(OAc)2 as a catalyst and 3 equiv
of Na2CO3 (eq 11). This reaction works well for a wide range
for combinatorial applications, our attention turned to a new
generation of catalysts recently introduced into Pd-catalyzed
cross-coupling.27,29 One of the most convenient catalysts of this
type is Pd(PtBu3)2, now commercially available.30 Here, we
performed a comparative study of the Suzuki-Miyaura,26-29
Murahashi,27-29,31 and Negishi27-29,31,32 cross-coupling protocols
using 4-/7-bromo-2-methyl-1H-indene and the representative
series of substrates involving p-tolyl, 1-naphthyl, mesityl, and
2-thienyl fragments (eq 12). It should be noted that conversion
of 1 in all cases was almost quantitative even if the desired
product was obtained in low yield. The studied boronic acids
in Suzuki-Miyaura coupling were found to give 4-/7-aryl-2-
methyl-1H-indenes in high yields. Interestingly, Pd(PtBu3)2
catalyzes well the Suzuki-Miyaura coupling of bulky mesityl-
boronic acid but not the Murahashi and Negishi reactions
applying mesitylmagnesium and mesitylzinc reagents, respec-
tively. However, both Suzuki-Miyaura coupling and the
Murahashi and Negishi reactions gave isomeric 4-/7-p-tolyl-2-
methyl-1H-indenes from 4-/7-bromo-2-methyl-1H-indene in
high yield. On the other hand, 4-/7-chloro-2-methyl-1H-indene
failed to react with p-tolylmagnesium and -zinc reagents (a ca.
1% yield of target material at a ca. 5% conversion of 2) in THF
at 65 °C but reacted readily with p-tolylboronic acid in toluene
at 110 °C. An analogous but less dramatic effect was found in
the case of the synthesis of 20, bearing a 1-naphthyl fragment.
Lower yields were observed for 24, involving the nonbulky
2-thienyl fragment. Probably, thienyl derivatives (products or
byproducts) poison the Pd catalyst, causing these lower yields
of 24 compared with, for example, the yields of 25.
of arylboron substrates and gives, for example, the respective
products involving ortho-substituted aryls (19, 22) and naphthyl
(20) in high yield after 6 h at reflux. However, sterically
hindered mesitylboronic acid failed to react under these condi-
tions. 2-Thienylboronic acid gave a low yield of the respective
(2-thienyl)indene with this protocol.
As soon as we began to seek a protocol working reliably for
as wide a scope of coupling partners as possible that was suitable
(26) (a) Suzuki, A. Pure Appl. Chem. 1985, 57, 1749. (b) Suzuki, A.
Pure Appl. Chem. 1991, 63, 419. (c) Martin, A. R.; Yang, Y. Acta Chem.
Scand. 1993, 47, 221. (d) Suzuki, A. Pure Appl. Chem. 1994, 66, 213. (e)
Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (f) Stanforth, S. P.
Tetrahedron 1998, 54, 263. (g) Miyaura, N. In AdVances in Metal-organic
Chemistry; Liebeskind, L. S., Ed.; JAI: Amsterdam, 1998; Vol. 6, pp 187-
243. (h) Suzuki, A. In Metal-catalyzed Cross-coupling Reactions; Diederich,
F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, Germany, 1998; pp 49-89.
(i) Suzuki, A. J. Organomet. Chem. 1999, 576, 147. (j) Suzuki, A. In
Organoboranes for Synthesis; ACS Symposium Series 783; Ramachandran,
P. V., Brown, H. C., Eds.; American Chemical Society: Washington, DC,
2001; pp 80-93. (k) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002,
58, 9633 and references therein.
(27) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem.
ReV. 2002, 102, 1359 and references therein.
(28) Handbook of Organopalladium Chemistry for Organic Synthesis;
Negishi, E.-I., Ed.; Wiley-VCH: Weinheim, Germany, 2002, and references
therein.
Ligandless Suzuki-Miyaura coupling with NaBPh4 was also
used for bromoindene 3 bearing a substituent in a position ortho
(29) For applications of other bulky, electron-rich phosphines, see: (a)
Guram, A. S.; Rennels, R. A.; Buchwald, S. L. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1348. (b) Louie, J.; Hartwig, J. F. Tetrahedron Lett. 1995,
36, 3609. (c) Zhao, S. H.; Miller, A. K.; Berger, J.; Flippin, L. A.
Tetrahedron Lett. 1996, 37, 4463. (d) Reddy, N. P.; Tanaka, M. Tetrahedron
Lett. 1997, 38, 4807. (e) Hamann, B. C.; Hartwig, J. F. J. Am. Chem. Soc.
1998, 120, 7369. (f) Wolfe, J. P.; Buchwald, S. L. Angew. Chem., Int. Ed.
1999, 38, 2413. (g) Alt, M. H.; Buchwald, S. L. J. Org. Chem. 2001, 66,
2560. (h) Yin, J.; Rainka, M. P.; Zhang, X.-X.; Buchwald, S. L. J. Am.
Chem. Soc. 2002, 124, 1162. (i) Walker, S. D.; Barder, T. E.; Martinelli, J.
R.; Buchwald, S. L. Angew. Chem., Int. Ed. 2004, 43, 1871. For applications
of carbene ligands, see: (j) Huang, J.; Grasa, G.; Nolan, S. P. Org. Lett.
1999, 1, 1307. (k) Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.;
Hartwig, J. F. Org. Lett. 2000, 2, 1423. (l) Caddick, S.; Cloke, F. G. N.;
Clentsmith, G. K. B.; Hitchcock, P. B.; McKerrecher, D.; Titcomb, L. R.;
Williams, M. R. V. J. Organomet. Chem. 2001, 617-618, 635. (m)
Gsto¨ttmayr, C. W. K.; Bo¨hm, V. P. W.; Herdtweck, E.; Grosche, M.;
Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1363.
(30) Applications of PtBu3 are as follows. (a) Negishi reaction: Dai, C.;
Fu, G. C. J. Am. Chem. Soc. 2001, 123, 2719. (b) Gauthier, D. R., Jr.;
Szumigala, R. H., Jr.; Dormer, P. G.; Armstrong, J. D., III; Volante, R. P.;
Reider, P. J. Org. Lett. 2002, 4, 375. (c) Kumada reaction: Walla, P.; Kappe,
C. O. Chem. Commun. 2004, 5, 564. (d) Buchwald-Hartwig amination:
Nishiyama, M.; Yamamoto, T.; Koie, Y. Tetrahedron Lett. 1998, 39, 617.
(e) Yamamoto, T.; Nishiyama, M.; Koie, Y. Tetrahedron Lett. 1998, 39,
2367. (f) Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy, K. H.;
Alcazar-Roman, L. M. J. Org. Chem. 1999, 64, 5575. (g) Lee, S.; Jørgensen,
M.; Hartwig, J. F. Org. Lett. 2001, 3, 2729. (h) Lebedev, A. Y.; Izmer, V.
V.; Kazyul’kin, D. N.; Beletskaya, I. P.; Voskoboynikov, A. Z. Org. Lett.
2002, 4, 623.
(31) Negishi, E.; Liu, F. In Metal-catalyzed Cross-coupling Reactions;
Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, Germany, 1998;
pp 1-47.
(32) Negishi, E. In Organozinc reagents. A Practical Approach; Knochel,
P., Jones, P., Eds.; Oxford University Press: London, 1999; pp 213-243,
and references therein.

1222 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
to bromine (eq 13), as well as for bromoindene 13 (eq 14) and
dibromoindene 4 (eq 15). In all cases studied, the respective
reactions using 1-naphthylzinc chloride gave a ca. 1/2 mix-
ture of 5-methyl-3-(1-naphthyl)-6(4)H-cyclopenta[b]thiophenes
(31) in almost quantitative yields. However, the reaction with
4-tert-butylphenylzinc chloride gave 5-methyl-3-(4-tert-butyl-
phenyl)-6(4)H-cyclopenta[b]thiophenes (32) as the only isomeric
product.
Analogously, hetero-substituted arylindenes 33-35 were
obtained in almost quantitative yields using the Negishi protocol
starting from bromoindenes 1 and 3, respectively, in the presence
of Pd(PtBu3)2 in THF for 5 h at reflux (eqs 18 and 19).
Ph-substituted indenes and diphenylindene 28 were isolated in
high yields and unambiguously characterized.
However, an attempt to obtain the sterically crowded aryl-
indene 29 involving four ortho substituents in the biphenyl
fragment from bromoindene 3 and mesitylboronic acid using
the phosphine-free Pd catalysis failed. Indene 29 was synthesized
in moderate yield (42%) using Pd(PtBu3)2 as a catalyst and an
excess of anhydrous K3PO4 as a base in toluene at 110 °C (eq
16). It is of interest that a mixture of Pd(dba)2 and dicyclohexyl-
The other Pd-catalyzed cross-coupling method involved in
this study is the Stille reaction with aryltin reagents.27-29,33 This
versatile cross-coupling method is known to be tolerant of a
wide range of substituents in aryls. Moreover, while arylboron,
-magnesium, and -zinc reagents involving basic heterocyclic
fragments, e.g. pyridinyl, are either unstable or difficult to
prepare, heteroarylstannanes of this type are readily available
stable reagents. Nevertheless, our attempts to apply this reaction
to obtain 2-thienyl- and 2-pyridyl-substituted indenes from 1
and the respective heteroarylstannanes failed. The reaction of
1 with (2-thienyl)SnnBu3 in the presence of 2 mol % of Pd-
(PPh3)4 in toluene at 120 °C gave the Ph2P-substituted indene
3634 in 6% yield as a result of transfer of the PPh2 group from
PPh3 but did not give the desired product 24. Analogously, 2-(2-
methylinden-4-yl)pyridine was not obtained in the Pd-catalyzed
reaction of 1 with 2-pyridyltin reagent in toluene at reflux. The
only product of this reaction was 2,2′-bipyridine, which was
isolated in 10% yield.
To access the 2-pyridyl-substituted and analogous indenes,
as well as to develop more practical combinatorial procedures
for synthesizing libraries of aryl-substituted indenes, we turned
our attention to a different strategy and attempted to use the
organometallic derivatives of indane as a nucleophilic coupling
partner. We aimed, first, to synthesize such reagents and, then,
to study the scope of their Pd-catalyzed reactions. An isomeric
mixture of indenylboronic acids 38 was obtained in moderate
yield from 4-bromo-1-methoxy-2-methylindane (37)35 (eq 20).
The alternative substrate, 1-methoxy-2-methyl-2,3-dihydroin-
den-4-ylboronic acids (39), was prepared as a mixture of
[2-(9-phenanthryl)phenyl]phosphine ligand especially designed
to catalyze Suzuki-Miyaura coupling of bulky substrates29h
gave 29 in only 24% yield.
Further, the Negishi reaction using 3-bromo-5-methyl-4H-
cyclopenta[b]thiophene (16) was successfully carried out (eq
17). In this way, a mixture of 5-methyl-3-phenyl-6H-cyclopenta-
[b]thiophene and 5-methyl-3-phenyl-4H-cyclopenta[b]thiophene
(30) in a ca. 1/4 ratio was obtained in almost quantitative yield
by starting from 16 and phenylzinc bromide in the presence of
2 mol % of Pd(PtBu3)2 in THF for 10 h at 70 °C. The same
(33) (a) Farina, V.; Krishnamurthy, V.; Scott, W. J. The Stille Reaction;
Wiley-VCH: Weinheim, Germany, 1998. (b) Mitchell, T. N. In Metal-
catalyzed Cross-coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-
VCH: Weinheim, Germany, 1998; pp 167-197, and references therein.

Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1223
Figure 1. Molecular structure of trans-39 with the non-hydrogen
atom labeling scheme. The thermal ellipsoids are drawn at the 50%
probability level.
as the Murahashi and Negishi reactions of Grignard and arylzinc
reagents 27 and 41 (prepared from 37), as shown in eq 22. The
diastereomers in a similar manner, omitting the postreaction
acidification by HCl to avoid the elimination of MeOH. Both
38 and 39 can be used as substrates in Suzuki cross-coupling
with various aryl bromides (and chlorides). If this reaction is
carried out with the MeO derivative 39, treatment by HCl or
TsOH is required to eliminate MeOH and obtain the desired
indenes. Boronic acid 38 was obtained after workup of the
reaction mixture as a pure 7-isomer. The boron-substituted
methoxyindane 39 was isolated in 43% yield as an equimolar
mixture of the respective diastereomers, though the individual
diastereomers could be separated by fractional crystallization
from ethyl acetate. One of themsthe trans isomerswas obtained
in analytically pure form and characterized by X-ray crystal
structure analysis. The molecular structure of trans-39 is shown
in Figure 1. The structure consists of molecules bound together
by strong hydrogen bonds (B-O-H‚‚‚O; see the Supporting
Information for details).
concentration of Grignard reagent 40 in THF solution was
established by the standard titration procedure.36 The concentra-
tion of organozinc reagent 41 was estimated by assuming the
quantitative conversion of 40 into 41, ensured by a 2-fold excess
of ZnCl2 used to obtain the organozinc reagent. A representative
series of various aryl halides was used to study the scope of
the cross-coupling reactions (eq 22). In some cases, the
methoxyindanes initially formed were not isolated but trans-
formed in situ into indenes by acidification with HCl. Like the
Suzuki-Miyaura reaction using 4-/7-bromo-2-methyl-1H-in-
dene (eq 12) discussed above, an alternative version of this
reaction using boronic acid 39 (eq 22) has been found to
give cross-coupling products with p-tolyl, 1-naphthyl, mesityl,
and 2-thienyl fragments in high yields. However, the latter
protocol is advantageous from the combinatorial point of view.
Boronic acids are less readily available than aryl halides;
therefore, a method that cross-couples a single boronic acid to
a series of aryl/heteroaryl indenes is more convenient and
productive than the cross-coupling of a simple halide to a
series of boronic acids. Similar considerations are relevant for
the Murahashi and Negishi reactions of arylmagnesium 40
and -zinc reagents 41 with readily available aryl halides. In
all cases, the Murahashi protocol using 40 gave indenes 20,
Boronic acid 38 was found to react readily with bromoben-
zene in the presence of Pd(OAc)2/2-(di-tert-butylphosphino)-
1,1′-biphenyl29a as a catalyst and K3PO4 as a base to give 17 in
high yield (eq 21).
Next, we performed the comparative study of the Pd(PtBu3)2-
catalyzed Suzuki-Miyaura coupling of boronic acid 39, as well
(34) Mixture of (2-methyl-1H-inden-4-yl)diphenylphosphine and (2-
methyl-1H-inden-7-yl)diphenylphosphine (36). This compound was iso-
lated as a ca. 1/6.5 mixture of 4- and 7-substituted indenes. Anal. Calcd
for C22H19P: C, 84.06; H, 6.09. Found: C, 83.90; H, 6.14. (2-Methyl-1H-
inden-7-yl)diphenylphosphine: 1H NMR (CDCl3) δ 7.29-7.33 (m, 10H,
PPh2), 7.23 (m, 1H, 4-H in indenyl), 7.14 (m, 1H, 5-H), 6.64 (ddd, J ) 7.6
3
Hz, J ) 5.2 Hz, JPH ) 1.1 Hz, 1H, 6-H), 5.47 (m, 1H, 3-H in indenyl),
3.20 (m, 2H, CH2), 2.08 (m, 3H, Me); 13C{1H} NMR (CDCl3) δ 148.0,
147.8, 146.6 (d, JPC ) 1.5 Hz), 145.6 (d, JPC ) 6.6 Hz), 136.1 (d, JPC
)
9.9 Hz), 133.8 (d, JPC ) 19.8 Hz), 128.6 (d, JPC ) 17.6 Hz), 128.4, 127.5
(d, JPC ) 1.8 Hz), 126.8 (d, JPC ) 1.8 Hz), 126.7 (d, JPC ) 1.5 Hz), 120.3,
42.8 (d, JPC ) 10.7 Hz), 16.7; 31P{1H} NMR (CDCl3) δ -14.2. The 4-Ph2P-
substituted indene 36 has been also prepared via an independent route by
starting from Grignard reagent 40 and 1 equiv of Ph2PCl followed by
treatment of the reaction mixture with aqueous HCl. In this way, indene 36
has been obtained in 87% yield.
(35) Successful synthesis and application of an analogous substrates4-
bromo-1-(trimethylsiloxy)-2-methylindaneshas recently been described in
a U.S. patent.11b
(36) Ioffe, S. T.; Nesmeyanov, A. S. Methods of Elementoorganic
Chemistry: Magnesium, Beryllium, Calcium, Strontium, Barium; Acad. Sci.
USSR Publ.: Moscow, 1963.

1224 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
21, 24, and 25 in better yields than the alternative method
using 1 as the starting material (eq 12). The lower yields of
the products in the latter case are likely to be accounted for
by metalation of 4-/7-bromo-2-methyl-1H-indene by Grignard
reagents. The Murahashi reaction using (1-methoxy-2-methyl-
2,3-dihydroinden-4-yl)magnesium bromide was shown to
serve better for the cross-coupling with 2-bromopyridine. The
respective Suzuki-Miyaura and Negishi cross-coupling reac-
tions gave lower yields of 46, probably because of complexa-
tion of organoboron and -zinc reagents with the pyridine
substrate. Thus, the Murahashi protocol gave pyridyl-meth-
oxyindane 46 from 40 in 70% yield. Further, a ca. 1:1.5 mixture
of 7- and 4-(2-pyridyl)indenes was obtained after acidification
of 46 with 12 M HCl and methanol at reflux followed by
treatment of the reaction mixture with aqueous NaOH, as shown
in eq 23.
of 39 by TsOH gave 52 in 32% yield as a ca. 25/1 mixture of
7- and 4-substituted indenes after 1 h at reflux.
It is of interest that the Pd-catalyzed reaction of 39 with C6F5-
Br gave the respective coupling product bearing a C6F5 fragment
in low yield (eq 27). Probably, this can be accounted for by the
Boronic acid 39 was also used to synthesize various het-
eroaryl-substituted indenes, such as 49 and 50, bearing 4-iso-
quinolyl and 3-benzothienyl fragments, respectively (eqs 24 and
25). Under the conditions studied, 2-bromoisoquinoline gave
low reactivity of the intermediate C6F5PdIIBr (formed via the
oxidative addition of C6F5Br to Pd0) under the conditions
studied.37 However, the alternative approach using 37 and
perfluorophenylboronic acid (to exclude the formation of this
unreactive intermediate) also gave the desired coupling product
in low yield. Since 53 was found to give indene 54 (as a ca.
9.5/1 mixture of 7- and 4-isomers) readily after 5 h at reflux in
an aqueous HCl-methanol mixture, the described two-stage
pathways using either 37 or 39 seem to be more useful for
obtaining the target indene 54 than the procedure using the Pd-
catalyzed reaction of 1 with C6F5B(OH)2, giving 54 in as low
as 9% yield.
4-(1-methoxy-2-methyl-2,3-dihydroinden-4-yl)isoquinoline (48)
in 62% yield and then indene 49 in 43% total yield. Whereas
the Suzuki-Miyaura cross-coupling of 4-/7-bromo-2-methyl-
1H-indene and 1-benzothien-3-ylboronic acid in the presence
of 2 mol % of Pd(PtBu3)2 and an excess of K3PO4 gave 50 in
2-3% yield after 15 h in toluene at reflux, the cross-coupling
of the respective organozinc derivative with 41 resulted in 50
in 85% yield.
Next, we studied the synthesis of indenes bearing electron-
withdrawing fluoroaryl fragments in position 4/7. Boronic acid
39 was found to give 4-(2-fluorophenyl)-1-methoxy-2-meth-
ylindane (51) and then indene 52, bearing the electron-
withdrawing 2-fluorophenyl fragment (eq 26). Thus, treatment
Thus, either bromo-substituted indene 1 (or its derivative 37)
or boronic acid 39 (as well as the respective Mg and Zn reagents
40 and 41 or indenylboronic acid 37) can be effectively used
as a starting material, depending on the structure of 4-/7-aryl-
(37) Quite recently C6F5Br has been successfully used as a substrate in
Pd-catalyzed Heck reactions: Albeniz, A. C.; Espinet, P.; Martin-Ruiz, B.;
Milstein, D. J. Am. Chem. Soc. 2001, 123, 11504.

Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1225
2-methyl-1H-indene to be synthesized. Obviously, the methods
described can be successfully applied to synthesize other aryl-
substituted indene ligands.
Finally, an alternative synthesis of aryl-substituted indenes
can be achieved via direct ortho lithiation of 2-methyl-1-indanol
or its analogues (see above) followed by Pd-catalyzed coupling
of the respective arylzinc reagent with aryl halide. This
multistage transformation for 2-methyl-1-indanol was carried
out without purification of half-products and found to give 17
in 71% yield (eq 28). In this way, the only time-consuming
stage is the ortho-lithiation reaction followed by evaporation
of the reaction mixture to replace the hydrocarbon solvent by
THF and remove excess TMEDA.
Regarding NMR data for the compounds under investiga-
tion, the only interesting issue to be discussed is the AB split-
1
ting pattern observed in H NMR spectra of indenes 20 and
49 for 1,1′-protons of the indenyl system involving unsym-
metrical bulky aryls in position 4/7. This inequivalence of
CH2 protons is likely to be explained by hindered rotation of
such ortho-substituted aryls around the indenyl-aryl bond. A
similar phenomenon was observed for methoxyindane 37.
Similarly to methoxyindanes 37, 39, 42, 45, 46, 51, and 53, the
compounds 43 and 48 each consist of a mixture of two
diastereomers. On the other hand, in the 1H NMR spectrum of
methoxyindane 44, bearing a bulky C2-symmetrical mesityl
fragment in position 4, the AB splitting, as expected, is not
developed.
Me2Si-Bridged Ligands and ansa-Zirconocenes. Further,
to synthesize the respective bis(indenyl)dimethylsilanes using
a well-known protocol,1d several of the substituted indenes thus
n
prepared were deprotonated with BuLi and then treated with
0.5 equiv of Me2SiCl2, as shown in eq 29. Ligands 56-60 and
64-66 were isolated as 1/1 mixtures of rac and meso diaster-
eomers using flash chromatography. Ligands 55, 61, and 63
were obtained by low-temperature crystallization as pure
racemates, while ligand 62 was obtained in this way as a ca.
1/1 mixture of rac and meso isomers.
Analogously, the bridging ligands 67 (Ar ) Ph), 68 (Ar )
1-naphthyl), and 69 (Ar ) 4-tBuC6H4) were obtained using
n
MeLi instead of BuLi to metalate the starting cyclopenta[b]-
thiophene 31 (eq 30). rac-67 and rac-68 were isolated in ana-
lytically pure form in 46 and 31% yields, respectively, by crys-
tallization from hexanes. A mixture of rac- and meso-69 was
isolated in 57% yield by flash chromatography on silica gel.
The bridging ligands 57-62 and 64-66 were deprotonated
with 2 equiv of nBuLi, and the resulting dilithium bis(indenyls)
were treated with ZrCl4 in toluene5 to give the respective
zirconocene dichlorides 70-78 (eq 31; yields of analytically
pure isomers are shown here and below). Fractional crystal-
lization from toluene at -30 °C gave pure rac isomer and a ca.
1/1 mixture of rac and meso isomers of 74 in 21 and 9% yields,
respectively. The analogous procedure for 70-72 and 78 gave
pure rac materials and, in the case of 78, several crystals of
meso-zirconocene, which was characterized by an X-ray crystal
structure analysis (see below). On the other hand, only meso-
75 was isolated as an analytically pure material by low-
temperature crystallization from toluene. Additionally, this
synthesis gave a ca. 4:1 mixture of rac- and meso-75 in 20%
yield. The complexes rac-73, rac-76, and rac-77 were obtained

1226 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
by washing the crude products with dichloromethane. rac-77
was additionally recrystallized from toluene to obtain an
analytically pure material.
Next, the deprotonation of 67-69 involving cyclopenta[b]-
thienyl fragments by 2 equiv of MeLi followed by reaction with
ZrCl4(THF)2 in ether gave pure rac-79 (Ar ) Ph; eq 32), rac-
80 (Ar ) 1-naphthyl), and rac-81 (Ar ) 4-tBuC6H4). The
racemates were isolated in analytically pure form in 37, 41, and
24% yields, respectively, by crystallization from dichlo-
romethane (for 79 and 80) or toluene (for 81).
Figure 2. Molecular structure of rac-74 with the non-hydrogen
atom labeling scheme. The minor disordered part of the thophene
cycle is omitted. Thermal ellipsoids correspond to 50% probability.
Alternatively, transmetalation using milder organotin re-
agents38 was applied to synthesize ansa-zirconocenes 82-84
(eq 33). In this way, the bridging ligands 55, 56, and 63 were
Figure 3. Molecular structure of meso-78 with the non-hydrogen
atom labeling scheme. Thermal ellipsoids correspond to 50%
probability.
structures of the complexes are illustrated in Figures 2-4,
respectively, and selected bond distances and angles are given
in Table 1.
The geometry and bonding of these complexes are quite
similar to those of other analogous ansa-zirconocenes reported
in the literature.5,24c,25a,39 In all three complexes the Zr atom
adopts a distorted-pseudotetrahedral coordination. The Zr-Cl
and Zr-Cp(c) distances, as well as the Cp(c)-Zr-Cp(c) and
Cl-Zr-Cl angles, are comparable to those observed for the
first deprotonated with 2 equiv of nBuLi followed by the
treatment with 2 equiv of Et3SnCl to obtain the respective tin-
substituted bis(indenyl)silanes. Finally, these organotin reagents
and ZrCl4 in toluene gave the desired zirconium complexes. In
this case, both rac and meso isomers of 82 could be obtained
by fractional crystallization from toluene. Analogously, analyti-
cally pure meso-84 and a ca. 3:1 mixture of rac and meso
isomers were obtained in 13 and 17% yields, respectively. rac-
83 contaminated with ca. 8% meso complex was obtained from
toluene solution at -30 °C.
(39) (a) Herrmann, W. A.; Rohrmann, J.; Herdtweck, E.; Spaleck, W.;
Winter, A. Angew. Chem., Int. Ed. Engl. 1989, 28, 1511. (b) Spaleck, W.;
Antberg, M.; Rohrmann, J.; Winter, A.; Bachmann, B.; Kiprof, P.; Behm,
J.; Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1992, 31, 1347. (c)
Luttikhedde, H. J. G.; Leino, R. P.; Nasman, J. H.; Ahlgren, M.; Pakkanen,
T. J. Organomet. Chem. 1995, 486, 193. (d) Kaminsky, W.; Rabe, O.;
Schauwienold, A.-M.; Schupfner, G. U.; Hanss, J.; Kopf, J. J. Organomet.
Chem. 1995, 497, 181. (e) Barsties, E.; Schaible, S.; Prosenc, M.-H.; Rief,
U.; Roll, W.; Weyand, O.; Dorer, B.; Brintzinger, H.-H. J. Organomet.
Chem. 1996, 520, 63. (f) Krut’ko, D. P.; Borzov, M. V.; Churakov, A. V.;
Lemenovckii, D. A.; Reutov, O. A. Russ. Chem. Bull. 1998, 2351. (g)
Maciejewski Petoff, J. L.; Agoston, T.; Lal, T. K.; Waymouth, R. M. J.
Am. Chem. Soc. 1998, 120, 11316. (h) Yoon, S. C.; Park, J.-W.; Jung, H.
S.; Song, H.; Park, J. T.; Woo, S. I. J. Organomet. Chem. 1998, 559, 149.
Next, the solid-state structures of rac-74, meso-78, and rac-
81 were investigated by X-ray crystallography. The molecular
(38) (a) Huttenhofer, M.; Prosenc, M.-H.; Rief, U.; Schaper, F.; Brintz-
inger, H.-H. Organometallics 1996, 15, 4816. (b) Nifant’ev, I. E.; Ivchenko,
P. V. Organometallics 1997, 16, 713. (c) Voskoboynikov, A. Z.; Agarkov,
A. Y.; Chernishev, E. A.; Beletskaya, I. P.; Churakov, A. V.; Kuz’mina, L.
G. J. Organomet. Chem. 1997, 530, 75. (d) Agarkov, A. Y.; Izmer, V. V.;
Riabov, A. N.; Kuz’mina, L. G.; Howard, J. A. K.; Beletskaya, I. P.;
Voskoboynikov, A. Z. J. Organomet. Chem. 2001, 619, 280. (e) Izmer, V.
V.; Agarkov, A. Y.; Nosova, V. M.; Kuz’mina, L. G.; Howard, J. A. K.;
Beletskaya, I. P.; Voskoboynikov, A. Z. Dalton Trans. 2001, 1131.

Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1227
in that the two chloride ligands and, hence, the two coordination
sites are nonequivalent (see Zr-Cl distances, Table 1), one of
them being sterically hindered by the benzo units from both
top and bottom, whereas the other is essentially unencumbered.
Conclusion
In this work, we have developed convenient strategies for
the combinatorial synthesis of 4-/7-aryl-substituted indenes,
cyclopenta[b]thiophenes, and related ligands of importance to
obtain libraries of metallocenes. To realize this approach, we
synthesized 4-/7-bromo-substituted indenes using both well-
known and novel (e.g., via ortho lithiation of 1-indanols)
methods and further studied in detail Pd-catalyzed cross-
coupling of these substrates with arylboron, -zinc, and -mag-
nesium reagents. In parallel, a different strategy using organo-
metallic derivatives of indane as nucleophilic coupling partners
has been developed. In this way, 4-boron, -zinc, and -magnesium
derivatives of 1-methoxy-2-methylindane, as well as the respec-
tive indenylboronic acid, were synthesized and unambiguously
characterized. These substrates were tested in Pd-catalyzed
cross-coupling reactions and shown to have wider scope to
access well-designed and not readily available products, such
as 4-heteroaryl- and 4-fluoroaryl-substituted 2-methyl-1H-
indenes. Moreover, the latter protocol is advantageous from the
combinatorial point of view. The organometallic derivatives of
1-methoxy-2-methylindane are less readily available than aryl
halides; therefore, a method that cross-couples a single orga-
nometallic reagent to a series of aryl/heteroaryl halides is more
convenient and productive than the cross-coupling of a simple
halide to a series of organometallic substrates. Finally, to
illustrate the synthetic utility of these protocols, we have reported
the synthesis of selected bis(indenyl)dimethylsilanes and the
respective ansa-zirconocenes of importance for single-site olefin
polymerization catalysis.
Figure 4. Molecular structure of rac-81 with the non-hydrogen
atom labeling scheme. Thermal ellipsoids correspond to 50%
probability.
Table 1. Selected Bond Distances (Å) and Angles (deg) for
rac-74, meso-78, and rac-81
meso-78
rac-81
rac-74a
Zr(1)-Cl(1)
Zr(1)-Cl(2)
Zr(1)-Cp(c)b
Zr(1)-Cp(c)′
2.4275(12)
2.4069(12)
2.246
2.4737(17)
2.4753(16)
2.218
2.4282(9)
2.241
2.243
2.223
c
Si(1)-Cb
1.880(4)
1.887(4)
100.07(4)
95.01(17)
105.8
104.9
105.8
1.869(7)
1.876(7)
98.55(6)
94.7(3)
132.8
106.2
88.6
1.877(3)
Si(1)-Cb′
Cl(1)-Zr(1)-Cl(2)
Cb-Si(1)-Cb′
Cl(1)-Zr(1)-Cp(c)
Cl(1)-Zr(1)-Cp(c)′
Cl(2)-Zr(1)-Cp(c)
Cl(2)-Zr(1)-Cp(c)′
Cp(c)-Zr(1)-Cp(c)′
97.44(5)
94.8(2)
107.7
105.7
128.4
108.2
128.5
107.3
128.4
Experimental Section42
a C2/c space group. b Cp(c) denotes the centroid of the cyclopentadienyl
ring of the indenyl or cyclopenta[b]thienyl ligand. c Cb corresponds to the
bridgehead carbon.
General Procedure. All manipulations with compounds which
are sensitive to both moisture and air were performed either under
an atmosphere of thoroughly purified argon using a standard
Schlenk technique or in a controlled-atmosphere glovebox (VAC).
Analytical and semipreparative liquid chromatography was per-
formed using a Waters Delta 600 HPLC system including a 996
photodiode array detector, Symmetry C18 (Waters, 60 Å, 5 µm,
4.6 × 250 mm) or Chromolith RP-18 (Merck, 4.6 × 100 mm)
columns, and a Nova-Pack C18 column (Waters, 60 Å, 6 µm, 3.9
and 19 × 300 mm), respectively, in a methanol-water mobile
phase. For analytical runs, calculations of yields of the products
were performed under the assumption that extinction coefficients
of isomeric indenes and diastereomeric methoxyindanes are equal.
1H and 13C spectra were recorded with Bruker DPX-300 and
Avance-400 spectrometers for 1-10% solutions in deuterated
solvents. Chemical shifts for 1H and 13C were measured relative to
TMS. In 1H NMR spectra, the assignment was made on the evidence
of double-resonance, NOE, and NOEdif experiments. C and H
microanalyses were done using a Carlo Erba 1106 analyzer.
Typical Procedure for Suzuki-Miyaura Reaction (Method
A). A mixture of 1 mmol of aryl bromide, 1 mmol of arylboronic
acid, 3 mmol of K3PO4, 10.2 mg (0.02 mmol) of Pd(PtBu3)2, and
2 mL of toluene was placed together with a magnetic stirrer bar in
an 8 mL vial under the nitrogen atmosphere of a glovebox. The
reaction was carried out with vigorous stirring at a preset temper-
ature. Then, this mixture was cooled to ambient temperature and
evaporated to dryness. Then, 5 mL of methyl tert-butyl ether was
previously studied dimethylsilyl-bridged zirconocene deriva-
tives.40 Interestingly, the value of the Cp(c)-Zr-Cp(c) angle
in dimethylsilyl-bridged zirconocene complexes practically does
not depend on the bulk of the substituents at Cp ligands (the
range of values is 124.3-128.5° 41). The bending of the Si-C
bonds out of the mean planes of the adjacent C5 rings is 16.3
and 17.5° for meso-78, 17.6 and 18.1° for rac-81, and 8.6° for
rac-74, which has a local 2-fold symmetry. The dihedral angle
between the two C5 fragments is 59.5° for rac-74, 62.4° for
meso-78, and 59.1° for rac-81. The angles between indenyl and
phenyl rings are 34.2, 56.9, 43.3, and 40.4° for meso-78, and
those between the respective phenyl and thiophenyl rings are
29.3 and 46.9°, respectively, for the major and minor disordered
thiophenyl cycles of rac-74 and 40.2 and 44.4° for rac-81. The
phenyl substituents of the opposite indenyl ligands in meso-78
in identical positions are almost perpendicular to each other (the
angles between the respective phenyl planes are 108.4°). The
disposition of the remaining phenyl substituents in meso-78 is
defined by the stacked packing of molecules in the crystal. The
meso-78 complex is similar to the other known meso isomers
(40) Cambridge Crystallographic Database, Release 2003, Cambridge.
(41) (a) Coulson, D. R. Inorg. Synth. 1972, 13, 121. (b) Ukai, T.;
Kawazawa, H.; Ishii, Y.; Bonnett, J. J.; Ibers, J. A. J. Organomet. Chem.
1974, 65, 253.
(42) All experimental details can be found in the Supporting Information.

1228 Organometallics, Vol. 25, No. 5, 2006
Izmer et al.
added to the residue. The resulting mixture was passed through a
short column with silica gel 60 (40-63 µm, diameter 20 mm, length
30 mm). Additionally, this column was washed with 40 mL of
methyl tert-butyl ether. The combined eluate was evaporated to
dryness. The residue was dissolved in 4 mL of acetonitrile; then,
the product was isolated by preparative HPLC.
layer was separated, dried over CaCl2, and evaporated to dryness.
The residue was recrystallized from hexanes-methyl tert-butyl ether
(1/1 v/v). Yield: 8.67 g (37%) of white solid of ca. 1/1 mixture of
rac and meso isomers. Anal. Calcd for C30H28S2Si: C, 74.95; H,
5.87. Found: C, 75.11; H, 5.98. 1H NMR (CDCl3): δ 7.41 (d, J )
7.5 Hz, 1H, 7-H in indenyl of rac compound), 7.37 (d, J ) 7.5 Hz,
1H, 7-H in indenyl of meso compound), 7.32 (dd, J ) 5.1 Hz, J )
1.2 Hz, 2H, 3-H in thienyl of rac and meso compounds), 7.31 (m,
2H, 5-H in indenyl of rac and meso compounds), 7.27 (dd, J )
3.5 Hz, J ) 1.2 Hz, 1H, 5-H in thienyl of meso compound), 7.26
(dd, J ) 3.5 Hz, J ) 1.2 Hz, 1H, 5-H in thienyl of rac compound),
7.12 (t, J ) 7.5 Hz, 1H, 6-H in indenyl of rac compound), 7.11
(dd, J ) 5.1 Hz, J ) 3.5 Hz, 2H, 4-H of thienyl in rac and meso
compounds), 7.10 (t, J ) 7.5 Hz, 1H, 6-H in indenyl of meso
compound), 7.07 (s, 3-H in indenyl of meso compound), 7.01 (s,
3-H in indenyl of rac compound), 3.76 (s, 1-H in indenyl of meso
compound), 3.73 (s, 1-H in indenyl of rac compound), 2.25 (m,
3H, 2-Me in indenyl of meso compound), 2.15 (m, 3H, 2-Me in
indenyl of rac compound), -0.17 (s, 6H, SiMe2 in rac compound),
-0.19 (s, 3H, SiMeMe′ in meso compound), -0.24 (s, 3H, SiMeMe′
in meso compound). 13C{1H} NMR (CDCl3): δ 148.3, 148.1, 145.8,
143.6, 142.6, 142.4, 127.5, 126.6, 126.2, 126.1, 125.54, 125.51,
125.1, 124.7, 123.0, 122.43, 122.38, 47.8, 47.6, 18.1, 17.9, -5.35,
-5.45, -5.51.
Complexes rac- and meso-74. To a solution of 8.67 g (18 mmol)
of 61 in 180 mL of toluene was added 14.4 mL of 2.5 M (36 mmol)
nBuLi in hexanes dropwise at -50 °C. This mixture was stirred
overnight at room temperature, and then 4.40 g (19 mmol) of ZrCl4
was added. The resulting mixture was refluxed for 5 h. The
precipitate was separated and washed with 4 × 70 mL of hot (90
°C) toluene using a funnel with a glass frit (G4). The combined
toluene filtrate was evaporated to dryness. The residue was
recrystallized from 200 mL of toluene at -30 °C. Crystals that
precipitated at this temperature were collected, washed with 2 ×
10 mL of cold toluene, and dried under vacuum. Yield: 2.42 g
(21%) of pure rac-74. Anal. Calcd for C30H26Cl2S2SiZr: C, 56.22;
H, 4.09. Found: C, 56.01; H, 4.16. The mother liquid was
evaporated to ca. 50 mL. Crystals precipitating at -30 °C from
this solution were collected, washed with 2 × 10 mL of cold
toluene, and dried under vacuum. This procedure gave 1.04 g (9%)
of a ca. 1:1 mixture of rac- and meso-74. Found: C, 56.13; H,
4.00. 1H NMR (CD2Cl2): rac-74, δ 7.64 (dd, J ) 8.7 Hz, J ) 0.9
Hz, 2H, 7,7′-H in indenyl), 7.45 (dd, J ) 7.1 Hz, J ) 0.8 Hz, 2H,
5,5′-H in indenyl), 7.36 (dd, J ) 3.6 Hz, J ) 1.2 Hz, 2H, 3,3′-H
in thienyl), 7.32 (dd, J ) 5.1 Hz, 1.2 Hz, 2H, 5,5′-H in thienyl),
7.09 (m, 2H, 3,3′-H in indenyl), 7.08 (dd, J ) 5.1 Hz, J ) 3.6 Hz,
2H, 4,4′-H in thienyl), 7.05 (dd, J ) 8.7 Hz, J ) 7.1 Hz, 2H, 6,6′-H
in indenyl), 2.22 (d, J ) 0.5 Hz, 6H, 2,2′-Me in indenyl), 1.31 (s,
6H, SiMe2); meso-74, δ 7.62 (dt, J ) 8.7 Hz, J ) 0.8 Hz, 7,7′-H
in indenyl), 7.30 (dd, J ) 5.1 Hz, J ) 1.2 Hz, 2H, 5,5′-H in thienyl),
7.28 (dd, J ) 3.6 Hz, J ) 1.2 Hz, 3,3′-H in thienyl), 7.20 (dd, J )
7.1 Hz, J ) 0.8 Hz, 2H, 5,5′-H in indenyl), 7.07 (dd, J ) 3.6 Hz,
J ) 5.1 Hz, 2H, 4,4′-H in thienyl), 6.98 (m, 2H, 3,3′-H in indenyl),
6.79 (dd, J ) 8.7 Hz, J ) 7.1 Hz, 2H, 6,6′-H in indenyl), 2.45 (d,
J ) 0.5 Hz, 6H, 2,2′-Me in indenyl), 1.44 (s, 3H, SiMeMe′), 1.24
(s, 3H, SiMeMe′).
Typical Procedure for Kumada Reaction (Method B). A
mixture of 1 mmol of aryl bromide, 8 mL of a 0.25 M solution of
Grignard reagent in THF, 10.2 mg (0.02 mmol) of Pd(PtBu3)2, and
3 mL of THF was placed together with a magnetic stirrer bar in a
24 mL vial under the nitrogen atmosphere of a glovebox. The
reaction was carried out with vigorous stirring at a preset temper-
ature. Then, this mixture was cooled to ambient temperature and
passed through a short column with silica gel 60 (40-63 µm,
diameter 20 mm, length 30 mm). Additionally, this column was
washed with 30 mL of methyl tert-butyl ether. The combined eluate
was evaporated to dryness. The residue was dissolved in 4 mL of
acetonitrile; then, the product was isolated by preparative HPLC.
Typical Procedure for Negishi Reaction (Method C). A
mixture of 1 mmol of aryl bromide, 8 mL of a 0.25 M solution of
Grignard reagent in THF, 7 mL of a 0.5 M solution of ZnCl2 in
THF, 10.2 mg (0.02 mmol) of Pd(PtBu3)2, and 3 mL of THF was
placed together with a magnetic stirrer bar in a 24 mL vial under
the nitrogen atmosphere of a glovebox. The reaction was carried
out with vigorous stirring at a preset temperature. Then, this mixture
was cooled to ambient temperature and passed through a short
column with silica gel 60 (40-63 µm, diameter 20 mm, length 30
mm). Additionally, this column was washed with 30 mL of methyl
tert-butyl ether. The combined eluate was evaporated to dryness.
The residue was dissolved in 4 mL of acetonitrile; then, the product
was isolated by preparative HPLC.
Mixture of 2-(2-Methyl-1H-inden-4-yl)thiophene and 2-(2-
Methyl-1H-inden-7-yl)thiophene (24). To a mixture of 1.74 g
(3.40 mmol) of Pd(PtBu3)2, 22.0 g (0.17 mol) of 2-thienylboronic
acid, and 108 g (0.51 mol) of K3PO4 was added a solution of 35.8
g (0.17 mol) of 1 in 500 mL of toluene. This mixture was stirred
for 6 h at reflux and then washed with 300 mL of water. The
aqueous layer was separated and washed with 400 mL of methyl
tert-butyl ether. The combined extract was dried over CaCl2 and
evaporated to dryness. Fractional distillation gave a yellow oil, bp
144-147 °C/1 mmHg. Yield: 25.9 g (71%). Anal. Calcd for
1
C14H12S: C, 79.20; H, 5.70. Found: C, 79.09; H, 5.74. H NMR
(CDCl3): 2-(2-methyl-1H-inden-4-yl)thiophene, δ 7.47 (dd, J )
7.5 Hz, J ) 1.1 Hz, 1H, 5-H in indenyl), 7.44 (dd, J ) 3.6 Hz, J
) 1.1 Hz, 1H, 3-H in thienyl), 7.39 (dd, J ) 5.1 Hz, J ) 1.1 Hz,
1H, 5-H in thienyl), 7.35 (t, J ) 7.5 Hz, 1H, 6-H in indenyl), 7.29
(dd, J ) 7.5 Hz, J ) 1.1 Hz, 1H, 7-H in indenyl), 7.19 (dd, J )
5.1 Hz, J ) 3.6 Hz, 1H, 4-H in thienyl), 6.59 (m, 1H, 3-H in
indenyl), 3.57 (m, 2H, CH2), 2.25 (s, 3H, Me); 2-(2-methyl-1H-
inden-7-yl)thiophene, δ 7.47 (d, J ) 7.5 Hz, 1H, 6-H in indenyl),
7.38 (dd, J ) 5.2 Hz, J ) 1.3 Hz, 1H, 5-H in thienyl), 7.35 (t, J )
7.5 Hz, 1H, 5-H in indenyl), 7.32 (dd, J ) 3.6 Hz, J ) 1.3 Hz, 1H,
3-H in thienyl), 7.22 (d, J ) 7.6 Hz, 1H, 4-H in indenyl), 7.19 (dd,
J ) 5.2 Hz, J ) 3.6 Hz, 1H, 4-H in thienyl), 7.02 (m, 1H, 3-H in
indenyl), 3.40 (m, 2H, CH2), 2.25 (s, 3H, Me). 13C{1H} NMR
(CDCl3): 2-(2-methyl-1H-inden-4-yl)thiophene, δ 146.8, 146.1,
143.4, 139.4, 129.6, 127.3, 127.04, 126.99, 124.52, 124.49, 123.0,
119.1, 43.8, 16.6; 2-(2-methyl-1H-inden-7-yl)thiophene, δ 147.0,
146.1, 145.5, 144.2, 143.1, 127.4, 126.5, 126.3, 125.0, 124.6, 123.8,
122.5, 42.9, 16.8.
Crystal Structure Determinations. Data were collected on a
Siemens P3/PC four-circle automated diffractometer (λ(Mo KR)
radiation, graphite monochromator, θ/2θ scan mode) for trans-39
and on a Bruker SMART 1000 CCD diffractometer (λ(Mo KR)
radiation, graphite monochromator, ω and æ scan modes) for rac-
74, meso-78, and rac-81 and corrected for Lorentz and polarization
effects (for trans-39, rac-74, meso-78, and rac-81) and for
absorption (for rac-74, meso-78, and rac-81).43 For details, see
Table 2.
Dimethylbis[2-methyl-4-(2-thienyl)inden-1-yl]silane (61). To
a solution of 21.0 g (99 mmol) of 24 in a mixture of 260 mL of
toluene and 20 mL of THF was added 39.5 mL of 2.5 M (99 mmol)
nBuLi in hexanes dropwise with vigorous stirring at -45 °C. Then
6.0 mL (6.38 g, 49.5 mmol) of dichlorodimethylsilane was added
in one portion. The resulting mixture was stirred overnight at room
temperature, and 200 mL of cold water was added. The organic
(43) Sheldrick G. M. SADABS, V2.01, Bruker/Siemens Area Detector
Absorption Correction Program; Bruker AXS, Madison, WI, 1998.

Pd-Catalyzed Pathways to Substituted Indenes
Organometallics, Vol. 25, No. 5, 2006 1229
Table 2. Crystallographic Data for trans-39, rac-74, meso-78, and rac-81
trans-39
C11H15BO3
rac-74
meso-78‚0.5C7H8
rac-81‚C7H8
empirical formula
fw
C30H26Cl2S2SiZr
640.84
C49.5H42Cl2SiZr
827.04
C45H50Cl2S2SiZr
845.18
206.04
temp (K)
cryst size (mm)
cryst syst
space group
a, Å
b, Å
c, (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
293(2)
120(2)
110(2)
112(2)
0.30 × 0.20 × 0.20
0.40 × 0.20 × 0.20
monoclinic
C2/c
13.299(3)
14.064(3)
14.392(3)
90.0
98.414(5)
90.0
2663(1)
0.30 × 0.30 × 0.10
0.35 × 0.30 × 0.25
monoclinic
P21/n
10.373(2)
22.669(5)
17.646(4)
90.0
97.91(3)
90.0
4110(1)
4
triclinic
triclinic
P1h
P1h
9.961(3)
7.777(2)
8.536(2)
8.748(2)
80.84(3)
72.12(3)
78.97(3)
539.3(2)
2
13.732(4)
16.317(4)
66.730(4)
82.080(5)
74.276(4)
1972.3(9)
2
Z
d
4
calcd (Mg m-3
)
1.269
1.598
1.393
1.366
F(000)
220
0.089
1304
0.835
854
0.480
1760
0.559
µ (mm-1
)
θ range (deg)
index range
2.45-26.06
0 e h e 9
-10 e k e 10
-10 e l e 10
2302
2.12-28.05
-17 e h e 12
-12 e k e 18
-18 e l e 19
7756
2.48-26.37
-11 e h e 12
-16 e k e 17
-20 e l e 20
10 629
1.47-27.03
-8 e h e 13
-14 e k e 28
-22 e l e 22
19 361
no. of rflns collected
no. of unique rflns
2133
3207
7432
8908
no. of rflns with I > 2σ(I)
R1; wR2 (I > 2σ(I))
R1; wR2 (all data)
1607
2196
5133
3902
0.0431; 0.1197
0.0649; 0.1253
2133/0/196
1.045
0.0452; 0.0917
0.0712; 0.1008
3207/6/183
1.023
0.978/-0.385
0.851; 0.813
0.0565; 0.1336
0.0833; 0.1506
7432/2/657
0.979
1.583/-0.656
0.970; 0.850
0.0733; 0.1493
0.1253; 0.1934
8908/0/460
0.888
1.209/-0.748
0.928; 0.884
no. of data/restraints/params
GOF on F2
largest diff peak/hole (e Å-3
abs cor Tmax; Tmin
)
0.248/-0.215
The structures were solved by direct methods and refined by
full-matrix least squares against F2 in anisotropic (for non-hydrogen
atoms) approximation. All the H(C) atom positions were calculated
and refined in isotropic approximation in a riding model with the
Uiso(H) parameters equal to 1.2[Ueq(Ci)] and for methyl groups equal
to 1.5[Ueq(Cii)], where U(Ci) and U(Cii) are respectively the
equivalent thermal parameters of the carbon atoms to which
corresponding H atoms are bonded. The solvate toluene molecule
in the structure meso-78 is disordered over two positions related
by an inversion center. The thiophenyl cycle of the molecule rac-
74 is disordered over two positions related by a 43° rotation around
the C(6)-C(11) bond with the site occupancy factors being equal
to 0.8 and 0.2. All calculations were carried out with the SHELXTL
(PC version 5.10) program package.44 Crystallographic data for
trans-39, rac-74, meso-78, and rac-81 have been deposited with
the Cambridge Crystallographic Data Center, CCDC Nos. 294827-
294830. Copies of this information may be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K. (fax, +44 1223 336033; e-mail, deposit@ccdc.cam.ac.uk; web,
www.ccdc.cam.ac.uk).
Acknowledgment. Financial support from ExxonMobil
Chemical Co. and the International Science and Technology
Center (Grant No. 1036/99) is gratefully acknowledged. We
thank the Crystallography Center of the Institute of Organo-
element Compounds of the Russian Academy of Sciences for
help with the X-ray measurements and refinements. We also
wish to thank Dr. David H. McConville from ExxonMobil
Chemical for fruitful discussions and polymerization experi-
ments performed. Finally, we thank Prof. I. P. Beletskaya.
Supporting Information Available: Text giving all experi-
mental procedures and tables and CIF files giving crystal structure
data for trans-39, rac-74, meso-78, and rac-81. This material is
available free of charge via the Internet at http://pubs.acs.org.
(44) Sheldrick, G. M. SHELXTL, V5.10; Bruker AXS Inc., Madison,
WI, 1997.
OM050937E