Reactivity of permethylzirconocene and permethyltitanocene toward disubstituted 1,3-butadiynes: η4- vs η2-complexation or C-C coupling with the permethyltitanocene

Article abstract of DOI:10.1021/ja991046z

This paper describes the reactivity of permethylzirconocene and permethyltitanocene toward different 1,3-butadiynes. A pointed dependence on the metals and the diyne substituents was found. Unusual, but still stable, five-membered zirconacyclocumulenes (η⁴-diyne complexes, zirconacyclopenta-2,3,4-trienes) Cp*₂Zr-(η⁴-1,2,3,4-RC₄R), R = Ph and SiMe₃, were prepared using two new and effective synthetic routes. One starts with the permethylzirconocene bisacetylides Cp*₂Zr(C=CR)₂, R = Ph (1a), SiMe₃ (1b), which rearrange in sunlight to form the stable five-membered zirconacyclocumulenes Cp*₂Zr(η⁴-1,2,3,4-RC4R), R = Ph (2a), SiMe₃ (2b). The alternative route to 2a and 2b is the reduction of Cp*₂ZrCl₂ with Mg in the presence of the adequate disubstituted butadiynes RC≡C-C≡CR. Both methods failed to produce the analogous titanacyclocumulenes, which seemed extremely unstable. Nevertheless, we were able to obtain distinct products employing the reduction pathway with permethyltitanocene. For R = SiMe₃, the novel titanacyclopropene (η²-complex) Cp*₂Ti(η²-1,2-Me₃SiC ₂C≡CSiMe₃) (3) was isolated. For R = Ph, an activation of both pentamethylcyclopentadienyl ligands was observed resulting in the complex [η⁵-C₅Me₄-(CH ₂)-]Ti[-C-(=CHPh)C(=CHPh)CH₂-η⁵-C ₅Me₄] (4). The reaction of 4 with carbon dioxide led to the Cp*-substituted titanafuranone Cp*Ti[-OC(=O)C(Ph)C(-)C(=CHPh)CH₂-η⁵-C ₅Me₄] (5). The zirconacyclocumulene 2b surprisingly inserted two molecules of CO₂ to give the unprecedented cumulenic dicarboxylate Cp*₂Zr [-OC-(=O)C(SiMe₃)=C=C=C(SiMe₃)C(=O)O-] (6). The η²-complex 3 (titanacyclopropene) took up one molecule of carbon dioxide to afford the titanafuranone Cp*₂Ti[OC(=O)C(SiMe₃)=C(C=CSiMe₃)-] (7).

Full text of DOI:10.1021/ja991046z

J. Am. Chem. Soc. 1999, 121, 8313-8323
8313
Reactivity of Permethylzirconocene and Permethyltitanocene toward
Disubstituted 1,3-Butadiynes: η4- vs η2-Complexation or C-C
Coupling with the Permethyltitanocene
Paul-Michael Pellny, Frank G. Kirchbauer, Vladimir V. Burlakov, Wolfgang Baumann,
Anke Spannenberg, and Uwe Rosenthal*
Contribution from the Institut fu¨r Organische Katalyseforschung an der UniVersita¨t Rostock e.V.,
Buchbinderstr. 5-6, D-18055 Rostock, Germany
ReceiVed April 1, 1999
Abstract: This paper describes the reactivity of permethylzirconocene and permethyltitanocene toward different
1,3-butadiynes. A pointed dependence on the metals and the diyne substituents was found. Unusual, but still
stable, five-membered zirconacyclocumulenes (η4-diyne complexes, zirconacyclopenta-2,3,4-trienes) Cp*2Zr-
(η4-1,2,3,4-RC4R), R ) Ph and SiMe3, were prepared using two new and effective synthetic routes. One starts
with the permethylzirconocene bisacetylides Cp*2Zr(CtCR)2, R ) Ph (1a), SiMe3 (1b), which rearrange in
sunlight to form the stable five-membered zirconacyclocumulenes Cp*2Zr(η4-1,2,3,4-RC4R), R ) Ph (2a),
SiMe3 (2b). The alternative route to 2a and 2b is the reduction of Cp*2ZrCl2 with Mg in the presence of the
adequate disubstituted butadiynes RCtC-CtCR. Both methods failed to produce the analogous titanacy-
clocumulenes, which seemed extremely unstable. Nevertheless, we were able to obtain distinct products
employing the reduction pathway with permethyltitanocene. For R ) SiMe3, the novel titanacyclopropene
(η2-complex) Cp*2Ti(η2-1,2-Me3SiC2CtCSiMe3) (3) was isolated. For R ) Ph, an activation of both
pentamethylcyclopentadienyl ligands was observed resulting in the complex [η5-C5Me4-(CH2)-]Ti[-C-
(dCHPh)C(dCHPh)CH2-η5-C5Me4] (4). The reaction of 4 with carbon dioxide led to the Cp*-substituted
titanafuranone Cp*Ti[-OC(dO)C(Ph)C(-)C(dCHPh)CH2-η5-C5Me4] (5). The zirconacyclocumulene 2b sur-
prisingly inserted two molecules of CO2 to give the unprecedented cumulenic dicarboxylate Cp*2Zr [-OC-
(dO)C(SiMe3)dCdCdC(SiMe3)C(dO)O-] (6). The η2-complex 3 (titanacyclopropene) took up one molecule
of carbon dioxide to afford the titanafuranone Cp*2Ti[OC(dO)C(SiMe3)dC(CtCSiMe3)-] (7).
Introduction
Cp2M(L)(η2-Me3SiC2SiMe3) (M ) Ti, L ) -; M ) Zr, L )
THF, pyridine) as metallocene sources.5k We often found
unexpected results, e.g., different complexations, a C-C single
bond cleavage and various types of coupling reactions. The
generated products proved to be strongly dependent on the
substituents R attached to the diynes, the metals M of the
metallocenes, and the stoichiometries employed.5k
In modern acetylene chemistry,1 synthesis of carbon rich
compounds is an intensively researched area which is also
directed toward organometallic polymers with conjugated π
systems.2 Such compounds often form the basis for high-grade
materials in the field of material science.3 For the synthesis of
various carbon networks,4 it is interesting to understand the
principles of the coupling of polyynes R(CtC)2R. Since these
polyalkyne compounds are difficult to investigate, butadiynes
R(CtC)nR as the smaller homologues were first used as model
compounds, and there are a few relevant publications about
interesting reactions of conjugated as well as of nonconjugated
diynes with titanocene and zirconocene.5 Detailed investigations
have been conducted by the authors into the reactions of
differently substituted 1,3-butadiynes with the complexes
The outstanding result of these studies was the discovery that
the metallocenes “Cp2M” (M ) Ti, Zr)5k react with tBuCtC-
CtCtBu to produce stable five-membered metallacyclocumu-
lenes (η4-complexes, metallayclopenta-2,3,4-trienes) Cp2M(η4-
t
1,2,3,4-tBuC4 Bu), M ) Zr,6 Ti.7 The X-ray diffraction studies
of these complexes have shown the ring system to be planar
and to contain three C-C double bonds from which the central
bond is internally coordinated to the metal center. These
structural features support the description of those compounds
(1) (a) Diederich, F. Oligoacetylenes. In Modern Acetylene Chemistry;
Stang, P. J., Diederich, F., Eds.; VCH: Weinheim, 1995; p 443. (b)
Diederich, F.; Rubin, Y. Angew. Chem., Int. Ed. Engl. 1992, 31, 1101. (c)
Gleiter, R.; Kratz, D. Angew. Chem., Int. Ed. Engl. 1993, 32, 842.
(2) (a) Beck, W.; Niemer, B.; Wieser, M. Angew. Chem. 1993, 105, 969;
Angew. Chem., Int. Ed. Engl. 1993, 32, 923. (b) Altmann, M.; Bunz, U. H.
F. Angew. Chem., Int. Ed. Engl. 1995, 34, 569. (c) Lang, H. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 547. (d) Pirio, N.; Touchard, D.; Dixneuf, P. H.;
Fettouhi, M.; Ouahab, L. Angew. Chem., Int. Ed. Engl. 1992, 31, 651. (e)
Weng, W.; Bartik, T.; Brady, M.; Bartik, B.; Ramsden, A. M. A.; Gladysz,
J. A. J. Am. Chem. Soc. 1995, 117, 7129. (f) Werner, H. Nachr. Chem.
Tech. Lab. 1992, 140, 435.
(5) (a) Nugent, W. A. Taber, D. F. J. Am. Chem. Soc. 1989, 111, 6435
and references therein. (b) Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc.
1995, 117, 5365. (c) Mao, S. S. H.; Tilley, T. D. J. Am. Chem. Soc. 1995,
117, 7031. (d) Mao, S. S. H.; Liu, F.-Q.; Tilley, T. D. J. Am. Chem. Soc.
1998, 120, 1193. (e) Hsu, D. P.; Davis, W. M.; Buchwald, S. L. J. Am.
Chem. Soc. 1993, 115, 10394. (f) Warner, B. P.; Davis, W. M.; Buchwald,
S. L. J. Am. Chem. Soc. 1994, 116, 5471. (g) Du, B.; Farona, M. F.;
McConnville, D. B.; Youngs, W. J. Tetrahedron 1995, 51, 4359. (h)
Takahashi, T.; Aoyagi, K.; Denisov, V.; Suzuki, N.; Choueiry, D.; Negishi,
E. Tetrahedron Lett. 1993, 34, 8301. (i) Takahashi, T.; Kasai, K.; Xi, Z.;
Denisov, V. Chem. Lett. 1995, 347. (j) Takahashi, T.; Xi, Z.; Obora, Y.;
Suzuki, N. J. Am. Chem. Soc. 1995, 117, 2665. (j) Liu, F.-Q.; Harder, G.;
Tilley, T. D. J. Am. Chem. Soc. 1998, 120, 3271. (k) Ohff, A.; Pulst, S.;
Peulecke, N.; Arndt, P.; Burlakov, V. V.; Rosenthal, U. Synlett 1996, 111
and references therein.
(3) Skotheim, T. A. In Handbook of ConductiVe Polymers; M. Dekker:
New York, 1986; Vols. 1 and 2.
(4) Bunz, U. Angew. Chem., Int. Ed. Engl. 1994, 33, 1127.
10.1021/ja991046z CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/31/1999

8314 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Pellny et al.
as distorted cyclocumulenes.5e Despite this evidence, an alterna-
tive bonding description, a diyne-metallocene complex without
a central double bond, has been preferred by others.8 In cal-
culations conducted recently, however, the metallacyclocumu-
lenes were established to be thermodynamically stable, even
more stable than the isomeric bisacetylide complexes.9a This
outcome is noteworthy because the highly strained structure
would have conventionally been thought of as being less stable.
Comparing the complexes to other organic cyclocumulenes6,9b
and certain aspects of their reactions9d,12 provides further
arguments for describing these compounds as metallacyclocu-
mulenes.9c
Investigating the reactivity of the generated five-membered
metallacyclocumulenes we learned that some are just stable as
solids, but in solution dimerize to titanium-substituted radi-
alenes10 and other coupling products.11 We found that the central
double bond of the phenyl-substituted metallacyclocumulenes
Cp2M(η4-1,2,3,4-RC4R), M ) Ti, Zr; R ) Ph, can be externally
complexed with Ni(0).12 In addition, we discerned from the
reactions of the phenyl-substituted titanacyclocumulene Cp2Ti-
(η4-1,2,3,4-PhC4Ph) with acetone and water that an equilibrium
between this species and a η2-butadiyne complex Cp2Ti(η2-1,2-
PhC2-CtCPh) is very likely; the reactions were found to take
place at the complexed triple bond of the proposed isomer.11
Detailed NMR studies revealed that titanacyclocumulenes are
the key intermediates in the C-C single bond cleavage reaction
of butadiynes as well as in the coupling reaction of titanocene
bisacetylides Cp2Ti(CtCR)2 to butadiynes.12 These reactions
are the elemental steps in a novel titanocene-mediated and
-photocatalyzed C-C single bond metathesis in homogeneous
solution.13 The interest in and the value of gaining further insight
into the stability and reactivity of metallacyclocumulenes is
apparent in this context.
Permethylmetallocene compounds are often easier to isolate and
to study because of enhanced oxidative, reductive, and thermal
stability.15 The main problem in employing the Cp* ligand arises
from the C-H activation of the methyl substituents and
subsequent side reactions, which are extensively illustrated in
the literature.16-22 An activation of one or even more methyl
groups of the pentamethylcyclopentadienyl ligands has fre-
quently been observed. For permethyltitanocene, the pioneering
works of Brintzinger16 and Bercaw17 as well as studies by
Teuben18 have shown that a tetramethylfulvene Ti(III) product
Cp*Ti[C5Me4(CH2)]19 is the key intermediate for interesting
C-C coupling reactions, e.g., with ketones18 and isonitriles.18b,20
A second deprotonation to give Cp*Ti[C5Me3(CH2)2] has been
described by Beckhaus.21
To the best of our knowledge, such coupling reactions of
alkynes or diynes with permethylmetallocenes have not been
investigated so far. The only exception we found was described
by Bergman22 in the trapping of the intermediate [Cp*2ZrdO],
formed by heating of Cp*2ZrPh(OH), with RCtC-CtCR to
generate a Cp*-substituted, coordinated enolate.22
This paper reports the interactions of permethyltitanocene and
-zirconocene complexes with 1,3-butadiynes. For zirconium,
five-membered zirconacyclocumulenes (η4-complexes, zircona-
cyclopenta-2,3,4-trienes) are obtained, and for titanium, an
unprecedented η2-complex as well as different C-H activations
of both of the pentamethylcyclopentadienyl ligands with a
subsequent C-C coupling are observed.
Results and Discussion
Syntheses of Five-Membered Metallacyclocumulenes: Two
Synthetic Routes to the Permethylzirconocene Complexes
Cp*2Zr(η4-1,2,3,4-RC4R), R ) Ph, SiMe3. The complexes
Cp2Ti(η2-Me3SiC2SiMe3)23 and Cp2Zr(L)(η2-Me3SiC2SiMe3)24
reacted with butadiynes RCtC-CtCR to afford the five-
membered metallacyclocumulenes Cp2M(η4-1,2,3,4-RC4R) (eq
1).6,7
In investigating the C-C single bond metathesis of 1,3-
butadiynes, we observed that permethyltitanocene and -zir-
conocene complexes would not promote this reaction. The
question arose of whether it is possible to trap intermediates of
the catalytic cycle by extending our investigations to the
interactions of 1,3-butadiynes with the corresponding permeth-
yltitanocene and -zirconocene complexes.
Despite the seemingly strong analogy between the Cp and
the Cp* moieties, these ligands have a large effect on the
reactivity of the (permethyl-)metallocene complexes. The
replacement of hydrogen atoms by methyl substituents changes
the steric and electronic influence of the ligand.14 As a result
of increased steric bulk, higher solubility and the electron donor
characteristics, different reactivities and spectral properties were
found in the Cp* complexes compared to their Cp counterparts.
When using the permethyl analogues Cp*2M(η2-Me3SiC2-
(6) Rosenthal, U.; Ohff, A.; Baumann, W.; Kempe, R.; Tillack, A.;
Burlakov, V. V. Angew. Chem., Int. Ed. Engl. 1994, 33, 1605.
(7) Burlakov, V. V.; Ohff, A.; Lefeber, C.; Tillack, A.; Baumann, W.;
Kempe, R.; Rosenthal, U. Chem. Ber. 1995, 128, 967.
(8) (a) Fro¨mberg, W. Ph.D. Thesis, University of Bochum, 1986. (b)
Temme, B.; Erker, G.; Fro¨hlich, R.; Grehl, M. Angew. Chem., Int. Ed. Engl.
1994, 33, 1480.
(9) (a) Jemmis, E. D.; Giju, K. T. J. Am. Chem. Soc. 1998, 120, 6952.
(b) Jones, M.; Klosin, J. AdV. Organomet. Chem. 1998, 42, 147. (c)
Choukroun, R.; Cassoux, P. Acc. Chem. Res. 1999, 32, 494. (d) Danjoy,
C.; Zhao, J.; Donnadieu, B.; Legros, J.-P.; Valade, L.; Choukroun, R.; Zwick,
A.; Cassoux, P. Chem. Eur. J. 1998, 4, 1100-1105.
(10) Pellny, P.-M.; Burlakov, V. V.; Peulecke, N.; Baumann, W.;
Spannenberg, A.; Kempe, R.; Francke, V.; Rosenthal, U. J. Organomet.
Chem. 1999, 578, 125.
(11) Burlakov, V. V.; Peulecke, N.; Baumann, W.; Spannenberg, A.;
Kempe, R.; Rosenthal, U. J. Organomet. Chem. 1997, 536-537, 293.
(12) Pulst, S.; Arndt, P.; Heller, B.; Baumann, W.; Kempe, R.; Rosenthal,
U. Angew. Chem., Int. Ed. Engl. 1996, 35, 1112.
(13) Pulst, S.; Kirchbauer, F. G.; Heller, B.; Baumann, W.; Rosenthal,
U. Angew. Chem., Int. Ed. Engl. 1998, 37, 1925.
(14) (a) King, R. B. Coord. Chem. ReV. 1976, 20, 15. (b) Maitlis, P. M.
Acc. Chem. Res. 1978, 11, 301. (c) Wolzanski, P. T.; Bercaw, J. E. Acc.
Chem. Res. 1980, 13, 121. (d) Campbell, A. C.; Lichtenberger, D. L. J.
Am. Chem. Soc. 1981, 103, 6389. (e) Pez, G. P.; Armor, J. N. AdV.
Organomet. Chem. 1981, 19, 1. (f) Marks, T. J. Science 1982, 217, 989.
(g) Jutzi, P. Pure Appl. Chem. 1981, 19, 1. (h) Beckhaus, R. In Metallocenes;
Togni, A., Halterman, R. L., Eds.; Wiley-VCH: Weinheim, 1998; p 153
and references therein.
(15) Janiak, Ch.; Schumann, H. AdV. Organomet. Chem. 1991, 33, 290.
(16) (a) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J.
Am. Chem. Soc. 1974, 94, 1219. (b) Bercaw, J. E.; Brintzinger, H. H. J.
Am. Chem. Soc. 1971, 93, 2048.
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Teuben, J. H.; Spek, A. L. J. Am. Chem. Soc. 1985, 107, 7758. (b) Fandos,
R.; Meetsma, A.; Teuben, J. H. Organometallics 1991, 10, 2665.
(19) Fischer, J. M.; Piers, W. E.; Young, V. G. Organometallics 1996,
15, 2410.

Permethylzirconocene and Permethyltitanocene
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8315
SiMe3), M ) Ti,23 Zr,25 in corresponding reactions, a clean
substitution of the acetylene ligand by the diyne was not
observed; the permethyltitanocene complex Cp*2Ti(η2-Me3SiC2-
SiMe3)23 did not react with PhCtC-CtCPh and Me3SiCt
C-CtCSiMe3 in a reaction time of 5 days at room tempera-
ture (eq 2). The same outcome was found in the reaction of
Cp*2Zr(η2-Me3SiC2SiMe3)25 with PhCtC-CtCPh. When
heating a mixture of Cp*2Zr(η2-Me2SiC2SiMe3) and MeCt
C-CtCMe to 60 °C for 24 h, four hitherto unidentified
complexes were indicated, however, next to almost 80% of the
starting material (eq 2).
Cp*2Zr(η4-1,2,3,4-RC4R), R ) Ph (2a), SiMe3 (2b), (eq 4).
Of special note is that the observed rearrangement confirms the
result of theoretical calculations stating that the metallacyclocu-
mulenes are thermodynamically more stable than the bisacetylide
complexes.9a A reaction similar to this rearrangement has
previously been postulated8a and later realized in the Lewis acid-
catalyzed conversion of Cp2Zr(CtCMe)2.8b
As an alternative to the photocatalyzed reaction, the reduction
of Cp*2ZrCl2 in THF with magnesium in the presence of the
butadiynes PhCtC-CtCPh or Me3SiCtC-CtCSiMe3 was
established as an elegant and effective procedure to obtain the
complexes 2a and 2b in a direct way (eq 5).
An explanation for the unsuccessful reactions can be deduced
from the mechanism of the substitution of the bis(trimethylsilyl)-
acetylene by ethylene in Cp2Zr(THF)(η2-Me3SiC2SiMe3). For
this reaction path, an associative mechanism has been described
(commencing addition of ethylene and subsequent elimination
of silylacetylene).26 It is assumed that the steric restrictions re-
sulting from the bulky permethylcyclopentadienyl ligands mini-
mize the likelihood of bimolecular reactions and prevent similar
conversions with the diynes in the examples mentioned above.
The reaction pathway employed for the preparation of the
Cp-coordinated metallacyclocumulenes could not be adapted to
establish metallacyclocumulenes with pentamethylcyclopenta-
dienyl ligands. A new synthetic route to the Cp* analogues had
to be designed. In our studies on the reactions of Cp2Ti(CtC
tBu)2 upon irradiation, we discovered the intermediacy of the
titanacyclocumulene Cp2Ti(η4-1,2,3,4-tBuC4tBu) (as monitored
by NMR measurements). However, we were not able to isolate
this complex, as it readily reacted with free “Cp2Ti” to yield
dimeric complexes.12 The detection of such an intermediate in
that reaction led to the establishment of a procedure to prepare
five-membered permethylzirconacyclocumulenes in significant
quantities. It starts with the new permethylmetallocene bisacetyl-
ides Cp*2Zr(CtCR)2, R ) Ph (1a), SiMe3 (1b). They are
prepared by a salt elimination reaction starting from the complex
Cp*2ZrCl2 and 2 equiv of the corresponding acetylides RCt
CLi (eq 3). Different solvents, e.g., THF, toluene, and diethyl
ether, have been examined in these conversions, and toluene
proved to provide the best yields, although these still have to
be considered poor (22% and 37%).
The second method (eq 5) can be regarded as more general and
starts with simpler substrates, although better yields were
obtained by the rearrangement of the permethylzirconocene
bisacetylides Cp*2Zr(CtCR)2 in sunlight (eq 4).
The new zirconacyclocumulenes with pentamethylcyclopen-
tadienyl ligands Cp*2Zr(η4-1,2,3,4-RC4R), R ) Ph (2a), SiMe3
(2b), show 13C NMR signals [2a: 118.4 (C-â), 179.4 (C-R).
2b: 144.5 (C-â), 188.0 (C-R)] in a typical region also found
for the unsubstituted cyclopentadienyl complexes Cp2M(η4-
1,2,3,4-RC4R) [M ) Ti, R ) Ph: 103.1 (C-â), 176.8 (C-R).11
t
M ) Ti, R ) Bu: 94.7 (C-â), 181.9 (C-R)7 , M ) Zr, R )
tBu: 105.5 (C-â), 186.4 (C-R)6]. As a result of the special
bonding situation,6,7,9a the shifts of the â carbon atoms are
smaller than expected for typical (linear) cumulene systems. A
small influence of the metal and a somewhat stronger effect of
the substituents is noteworthy; zirconium and silyl substituents
cause a low-field shift of the carbon atom in the â position.
This tendency has also been documented for alkyne complexes.
The zirconacyclocumulenes 2a and 2b were investigated by
X-ray crystal structure analyses. The molecular structures are
shown in Figures 1 and 2. The structures of the permethylmet-
allocene complexes 2a and 2b are similar to the formerly
described corresponding five-membered metallacyclocumulenes
of Cp2M (see Table 1), which explicitly differ from metalla-
cyclopentadienes. Table 1 presents the relevant bond distances
and angles. The four carbon atoms of the former butadiyne unit
and the Zr atom form a planar arrangement. The three C-C
The rearrangement of these permethylzirconocene bisacetylides
Cp*2Zr(CtCR)2 1a and 1b in sunlight affords the complexes
(23) Burlakov, V. V.; Polyakov, A. V.; Yanovsky, A. I.; Struchkov, Y.
T.; Shur, V. B.; Vol’pin, M. E.; Rosenthal, U.; Go¨rls, H. J. Organomet.
Chem. 1994, 476, 197.
(20) (a) Strauss, I. Ph.D. Thesis, RWTH Aachen, 1997. (b) Beckhaus,
R.; Strauss, I.; Wagner, T. Unpublished results.
(21) Beckhaus, R.; Sang, J.; Oster, J.; Wagner, T. J. Organomet. Chem.
1994, 484, 179.
(22) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J.
Am. Chem. Soc. 1989, 111, 8751.
(24) Rosenthal, U.; Ohff, A.; Michalik, M.; Go¨rls, H.; Burlakov, V. V.;
Shur, V. B. Angew. Chem., Int. Ed. Engl. 1993, 32, 1193.
(25) Hiller, J.; Thewalt, U.; Polasek, M.; Petrusova, L.; Varga, V.;
Sedmera, P.; Mach, K. Organometallics 1996, 15, 3752.
(26) Mansel, S.; Thomas, D.; Lefeber, C.; Heller, D.; Kempe, R.;
Baumann, W.; Rosenthal, U. Organometallics 1997, 16, 2886.

8316 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Pellny et al.
Table 1. Structural Data of Five-Membered
Metallacyclocumulenes L2M(η4-1,2,3,4-RC4R)
Cp*/Zr/Ph Cp*/Zr/SiMe3
L/M/R
Cp/Ti/tBu3 Cp/Zr/tBu2
distances (Å)
(2a)
(2b)
M-CR
2.252(9)
2.298(10)
2.209(9)
2.213(9)
1.243(13)
1.339(13)
1.276(11)
2.357(5)
2.307(5)
2.303(5)
2.306(5)
1.28(1)
1.31(1)
1.29(1)
2.345(4)
2.357(4)
2.328(4)
2.330(4)
1.296(4)
1.327(4)
1.305(5)
2.422(4)
2.426(5)
2.305(4)
2.307(4)
1.291(6)
1.337(6)
1.293(6)
M-CR′
M-Câ
M-Câ′
CR-Câ
Câ-Câ′
CR′-Câ′
angles (deg)
73.7(3)
71.7(3)
151.3(4)
151.1(4)
M-CR-Câ
M-CR′-Câ′
M-CR-R
70.3(6)
71.6(6)
138.1(9)
139.2(10)
72.8(2)
73.1(2)
152.4(3)
153.2(3)
69.2(3)
69.2(3)
163.1(3)
162.4(3)
152.5(4)
152.3(4)
M-CR′-R
CR-Câ-Câ′- 150.0(10)
150.0(10) 148.5(4)
CR′-Câ′-Câ- 147.8(10)
147.2(5)
97.4(2)
129.7
148.0(4)
97.63(11) 96.85(15)
137.3 135.7/137.1
CR-M-CR′
L-M-L
100.4(4)
129.7
Figure 1. ORTEP diagram (30% probability) of complex 2a. Selected
bond distances (Å) and angles (deg): C1-C10 1.305(5), C1-C2 1.327-
(4), C2-C3 1.296(5), Zr1-C10 2.345(4), Zr1-C1 2.328(4), Zr1-C2
2.330(4), Zr1-C3 2.357(4), C10-Zr-C3 97.63(11), C11-C10-C1
133.0(3), C10-C1-C2 148.0(4), C1-C2-C3 148.5(4), C2-C3-C4
134.3(4).
Figure 3. Perspective view of complex 2a parallel to the plane Zr-
C1-C2-C3-C10.
ligands [deviations of 1.7° and 4.5°] and inclined to the obverse
other one [47.1° and 44.8°] (Figure 3). The angle between the
centroids of the Cp* ligands about the metal is 137.3°.
As a result of the three-dimensional structure of the trimeth-
ylsilyl substituent, a comparatively clear view and quantifying
analysis cannot be presented for 2b. Nevertheless, it is our
conviction that 2b presents us with the more interesting structure.
The large permethylzirconocene unit does not prevent the access
of the demandingly substituted butadiyne. Despite emphasized
steric crowding, the formation of the fairly stable 2b was
successful.
All four metallacyclocumulenes described in Table 1 exhibit
very uniform structural features and thus prove a marginal
influence of the metals, the Cp(*) ligands, and the substituents
of the diynes on the bond distances and angles.
Reduction of Cp*2TiCl2 with Magnesium in the Presence
of 1,3-Butadiynes: Synthesis of a Titanacyclopropene (η2-
Complex) and Two Different C-C Coupling Reactions of
Permethyltitanocene. Both of the described preparative meth-
ods for zirconacyclocumulenes 2a and 2b failed to produce the
corresponding Cp*-substituted titanacyclocumulenes. The ir-
radiation of the permethyltitanocene bis(trimethylsilyl)acety-
lide produced complex 3 (63% yield).27 The reduction of Cp*2-
TiCl2 in the presence of RCtC-CtCR also failed to generate
Figure 2. ORTEP diagram (30% probability) of complex 2b. The
disordered groups (one Cp* ring) have been omitted for clarity. Selected
bond distances (Å) and angles (deg): C1-C2 1.291(6), C2-C3 1.337-
(6), C3-C4 1.293(6), Zr-C1 2.422(4), Zr-C2 2.305(4), Zr-C3 2.307-
(4), Zr-C4 2.426(5), C1-Zr-C4 96.85(15), Si2-C1-C2 163.1(3),
C1-C2-C3 152.5(4), C2-C3-C4 152.3(4), C3-C4-Si1 128.4(3).
bond lengths [2a: 1.296(5), 1.327(4), 1.305(5). 2b: 1.291(6),
1.337(6), 1.293(6) Å] indicate that these bonds are of roughly
similar bond order, displaying double bond character. All four
carbon atoms of the ring have p orbitals perpendicular to the
plane of the cyclocumulene. The sp-hybridized internal C atoms
possess additional p orbitals in that plane. Employing these
orbitals, the central C-C double bond is coordinated to the metal
center, resulting in an elongated C-C double bond. In ac-
cordance with this description the M-(C-â) distances [2a:
2.328(4), 2.330(4). 2b: 2.305(4), 2.307(4)] are shorter than the
M-(C-R) bonds [2a: 2.345(4), 2.357(4); 2b: 2.422(4), 2.426-
(5) Å]. An informative view of 2a is that parallel to the plane
Zr-C1-C2-C3-C10, which shows the phenyl rings in a
minimum of steric interactions; they are tilted slightly out of
that plane [22.9° and 25.3°] displaying an angle of 48.2° between
them. Both are nearly parallel to the plane of one of the Cp*

Permethylzirconocene and Permethyltitanocene
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8317
the cumulene structure, but here we were able to isolate well-
defined products.
The reaction with Me3SiCtC-CtCSiMe3 yielded the ti-
tanacyclopropene (η2-complex) Cp*2Ti(η2-1,2-Me3SiC2Ct
CSiMe3) (3), the first η2-butadiyne-titanocene complex ever
described (eq 6).
This outcome was surprising as it manifested for the first time
a structural type which was previously claimed as an intermedi-
ate in reactions of titanocenes “Cp2M” with butadiynes. The
only isolable products of these conversions of “Cp2Ti” and
butadiynes have been, depending on the stoichiometry, coupled
and cleaved complexes, next to two titanacyclocumulenes.5k,7,11
In this context, it is of special interest what Mach and co-workers
reported in a recent paper: the system of Cp*2TiCl2, Me3SiCt
C-CtCSiMe3, and an excess of magnesium proceeded via a
cleavage of the central C-C single bond of the diyne to afford
a tweezer-like compound [Cp*2Ti(CtCSiMe3)2] [MgCl(THF)].28
The stoichiometric use of Mg in this case led to a very different
product.
Figure 4. ORTEP diagram (30% probability) of complex 3. Selected
bond distances (Å) and angles (deg): C1-C2 1.311(4), Ti-C1 2.123-
(3), Ti-C2 2.085(3), C2-C3 1.401(4), C3-C4 1.215(4), Cl-Ti-C2
36.30(10), Si2-C1-C2 130.0(2), C1-C2-C3 141.9(3), C2-C3-C4
174.7(3), C3-C4-Si1 171.7(3).
Scheme 1
The NMR spectroscopic behavior of Cp*2Ti(η2-Me3SiC2Ct
CSiMe3) (3) is clearly different from that of the η4-butadiyne
complexes (metallacyclocumulenes such as 2a and 2b). At room
temperature, no signals for the quaternary carbon atoms can be
detected. The assumption of a dynamic behavior, deduced from
the broad trimethylsilyl resonance, is confirmed upon cooling
the sample. At 188 K (in toluene-d8), two signals of equal
intensity are found in the silyl region besides four resonances
for quaternary carbon atoms. Two of them appear in the region
characteristic of coordinated C-C triple bonds (205.3 and 227.5
ppm), the other two represent a free silyl-substituted C-C triple
bond (105.1 and 110.7 ppm). The different character of the two
unsaturated functionalities is also obvious from their IR absorp-
tions (1608 and 2092 cm-1, respectively). Consequently, two
29Si NMR signals appear at -12.6 and -20.4 ppm (silicon at
free triple bond, compare -19.3 ppm for Me3SiCtCSiMe3).
The coalescence of the discussed signals (the Cp* resonances
are not affected by the exchange process) is best explained by
an interchanging coordination of the two triple bonds to the
titanium center (Scheme 1). This would account for the apparent
equivalence of the silyl groups at room temperature. The
intermediacy of a metallacyclocumulene in this process is not
proven, but most likely, for only the special combination of
bulky C5Me5 and SiMe3 groups around the small titanium atom
seems to destabilize this species so that an alkyne complex
(metallacyclopropene) is formed instead. A rough estimation
of the activation barrier for this rearrangement (from Tc ) 217
K and ∆ν ) 24 Hz for the proton silyl signals) gives ∆Gq )
(169.1 ppm for the silyl-substituted and 155.2 ppm for the
central C atoms) clearly differ from those determined for
metallacyclocumulenes (e.g., 2b as the closest relative; see
above: 188.0 and 144.5 ppm, respectively) and make clear that
the symmetry found for the latter in solution results from their
true constitution and not from a fast exchange as depicted in
Scheme 1.
The permethyltitanocene η2-complex (metallacyclopropene)
Cp*2Ti(η2-1,2-Me3SiC2CtCSiMe3) (3) was also analyzed by
X-ray crystallography. An ORTEP drawing of 3 is shown in
Figure 4. The structure of 3 represents the first example of a
titanocene η2-complex with a 1,3-butadiyne. This bonding
description is unequivocally proven by the detected bond lengths
and angles. The data of the titanacyclopropene moiety are in
the expected range. The distances [ Ti-C1 2.123(3), Ti-C2
2.085(3), C1-C2 1.311(4) Å] are similar to those found in the
well-known alkyne complexes Cp*2Ti(η2-Me3SiC2SiMe3)23
[2.112(3), 2.126(3), 1.309(4) Å] and Cp*2Ti(η2-PhC2SiMe3)23
[2.098(2), 2.139(2), 1.308(3) Å]. The titanocene is characteristi-
cally bent showing a typical bite angle [141.4°]. The terminal
alkyne’s only weak deviation from linearity [C2-C3-C4 174.7-
(3)°, C3-C4-Si1 171.7(3)°] indicates that there is no interaction
between this triple bond and the metal center. The length of
the triple bond [C3-C4 1.215(4) Å] is as anticipated for
alkynylsilanes.
45 kJ mol-1
.
Unfortunately, the averaged signals of the quaternary carbon
atoms were not detected (decomposition took place before
reaching the region of fast exchange). But the expected values
(27) (a) Kirchbauer, F. G.; Ph.D. Thesis, University of Rostock, 1999.
(b) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Chem. Eur. J. 1999. In press.
(28) Troyanov, S. I.; Varga, V.; Mach, K. Organometallics 1993, 12,
2820.

8318 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Pellny et al.
4
47-H) ) 8 Hz or J(45-H,47-H) ) 1.8 Hz for instance, prove
the coupling of the former butadiyne with the pentamethylcy-
clopentadienyl group.
The 1,3-butadiene system resulting from the two-fold hydro-
gen transfer onto the 1,3-butadiyne exhibits the characteristic
13C NMR shift pattern, although it is strongly distorted from a
planar conformation which is usually preferred. The central
carbon atoms appear low-field shifted from the terminal ones,
with an extreme shift (208.0 ppm) for C13 due to its metalation.
Figure 5 shows the molecular structure of the ligand-to-
substrate coupled complex 4 as determined by an X-ray crystal
structure analysis. The molecular structure of complex 4 proves
the coupling of the butadiyne with one permethylcyclopenta-
dienyl ring under the formation of a functionalized Cp* ligand.
The other Cp* ring shows an activation of a methyl group
resulting in the formation of a tetramethylfulvene ligand.19 The
determined bond lengths are in the expected range for a π-η5:
σ-η1-tetramethylfulvene ligand [4: Ti1-C12 2.271(5), C11-
C12 1.444(6) Å] as shown by a comparison to those found in
the complex Cp*FvTi [2.281(14), 1.437(14) Å].19 The metal-
carbon distance for the functionalized Cp* ligand [4: Ti-C13
2.246(4) Å] is typical for Ti-C(alkyl) bonds. The other bond
distances in the chelating group are those of normal C-C single
bonds [4: C13-C46 1.467(6), C45-C46 1.525(6), C1-C45
1.513(6) Å]. The exocyclic distances [4: C13-C14 1.322(6),
C46-C47 1.357(6) Å] reflect C-C double bonds. This suggests
a description of the substrate as a doubly fused 1,3-butadiene.
The orientation of the phenyl groups minimizes steric repulsion
between the substituents.
Figure 5. ORTEP diagram (30% probability) of complex 4. Selected
bond distances (Å) and angles (deg): C1-C45 1.513(6), C45-C46
1.525(6), C46-C47 1.357(6), C46-C13 1.467(6), C13-C14 1.322-
(6), C13-Ti1 2.246(4), C11-C12 1.444(6), C12-Ti1 2.271(5), C1-
C45-C46 107.6(4), C45-C46-C47 120.4(4), C47-C46-C13 131.1-
(4), C46-C13-C14 123.9(4), C14-C13-Ti1 119.4(3), C11-C12-
Ti1 66.4(3).
Using PhCtC-CtCPh instead the reduction proceeds via
an activation of both pentamethylcyclopentadienyl ligands
leading to a coupling of one Cp* ligand to the substrate and
resulting in the complex [η5-C5Me4-(CH2)-]Ti[-C(dCHPh)C-
(dCHPh)CH2-η5-C5Me4] (4) (eq 7).
Reactions of 2a, 2b, 3, and 4 with Carbon Dioxide. These
reactions with carbon dioxide epitomize the different reactivity
of the obtained complexes.
The reaction of 4 with carbon dioxide in n-hexane generates
the Cp*-substituted titanafuranone Cp*Ti[-OC(dO)C(Ph)-
C(-)C(dCHPh)CH2-η5-C5Me4] (5) (eq 8).
The most prominent feature in the NMR spectra of complex
4 is the presence of eight singlets of equal intensity, representing
eight different Cp* methyl groups. Application of chemical shift
correlation and NOE methods allows complete analysis and
assignment of the 1H and 13C NMR spectra (for the labeling of
the C atoms in 4 see Figures 5 and 9). The NOE cross-peaks
are compatible with the solid-state structure of 4 (see below)
without exception so that there is no doubt it is maintained in
solution. The two-fold C-H activation in the permethylti-
tanocene moiety generates two functionally different cyclopen-
tadienyl systems exhibiting, besides the mentioned methyl
singlets, characteristic NMR properties.
To explain the route by which 5 is formed, it seems reasonable
to invoke the intermediacy of an isomeric η2-alkyne complex
where the CO2 inserts in. The formation of this proposed
intermediate can be rationalized by a simple shift of one proton
(Scheme 2). Such an intermediate would provide a plausible
explanation of why complex 4 reacts with carbon dioxide in a
similar manner as η2-alkyne complexes do.
Scheme 2
C12, one of the methylene groups, is found at 79.5 ppm,
dramatically low-field shifted relative to the other methyl groups.
This shift indicates, together with the coupling constants 1J(C,H)
of 150 Hz and the small geminal coupling of the two protons
(4.4 Hz), an increased s character. Hence, the description of
this Cp* system as a fulvene ligand is justified, even if the
coordination of the exocyclic double bond is of strong metal-
lacyclopropane character. The NMR data for the methylene
group of the other cyclopentadienyl ligand are, however, not
Evidence for the equilibrium proposed in Scheme 2 comes
from the proton NMR spectrum of the starting complex 4. A
small amount (less than 5%) of a species with one intact C5-
Me5 ligand (1.67 ppm, 15H) and one cyclopentadienyl system
1
exceptional, a geminal H,H coupling of 13.5 Hz and J(C,H)
of 130 Hz show that C45 has to be described as an sp3
hybridized carbon atom. Several long-range couplings, 3J(C45,-

Permethylzirconocene and Permethyltitanocene
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8319
linked to another fragment [four singlets, 3H each: 0.98, 1.10,
1.72, 2.00 ppm. CH2 group: 3.52 ppm (d, 1H) and 3.99 ppm
(dd, 1H), olef. CH: 5.55 ppm (br, 1H)] is present which may
be regarded responsible for the formation of 5, which itself
exhibits a very similar shift pattern in its proton resonance
spectrum.
The NMR spectra of 5 were analyzed in the same way as for
complex 4, they also prove that the solid-state structure is
maintained in solution. The chemical shifts (see Experimental
section) take the expected values (for other titanafuranones see
ref 29 and references therein).
The structure of complex 5 (Figure 6) as a result of an
addition of carbon dioxide to complex 4 shows the first Cp*-
substituted titanafuranone. It represents, in contrast to the parent
fulvene complex 4, a characteristically bent metallocene com-
plex. Distances between the metal and the ring centers are 2.115
and 2.073 Å. The bite angle about the titanium center is 140.5°.
These data are in good agreement with those of formerly
described titanocenes. The Cp*-substituted titanafuranone is
characterized by typical bond distances in the metallacycle [5:
Ti-C7 2.158(5), C7-C8 1.351(6), C8-C21 1.493(7), C21-
O1 1.328(6), Ti-O1 1.943(3) Å]. These can be compared to
those of the coupling product of tolane and carbon dioxide at a
titanocene center [2.201(4), 1.340(5), 1.489(5), 1.327(5), 1.965-
(3) Å].29a Two C-C single bonds form the bridge between the
metallacycle and the Cp* ligand as confirmed by the corre-
sponding bond distances [C7-C23 1.477(6), C23-C24 1.541-
(6) Å]. A benzylidene group is attached to C23 [C23-C30
1.342(6) Å], which remains nearly unchanged from the one
found in 4.
Figure 6. ORTEP diagram (30% probability) of complex 5. Selected
bond distances (Å) and angles (deg): Ti-C7 2.158(5), C7-C8 1.351-
(6), C8-C21 1.493(7), C21-O1 1.328(6), Ti-O1 1.943(3), C7-C23
1.477(6), C23-C24 1.541(6), C23-C30 1.342(6), C16-C24 1.508-
(7), C7-Ti-O1 78.2(2), Ti-O1-C21 120.6(3), O1-C21-C8 114.3-
(5), C21-C8-C7 114.0(5), C8-C7-Ti 112.6(4), C8-C7-C23 126.4-
(5), C7-C23-C30 134.2(5), C7-C23-C24 105.7(4), C16-C24-C23
109.0(4), C30-C23-C24 119.5(5).
Surprisingly the five-membered zirconacyclocumulene 2b (η4-
complex, zirconacyclopenta-2,3,4-triene), dissolved in THF,
inserts two molecules of carbon dioxide to give the cumulenic
dicarboxylate Cp*2Zr[OC(dO)C(SiMe3)dCdCdC(SiMe3)-
C(dO)O-] (6) (eq 9).
Figure 7. ORTEP diagram (30% probability) of complex 6. Selected
bond distances (Å) and angles (deg): Zr-O1 2.548(3), O1-C8 1.298-
(3), C8-C7 1.517(4), C7-Si 1.888(3), C7-C14 1.328(4), C14-C14
1.268(6), O1-Zr-O1 102.30(10), Zr-O1-C8 169.6(2), O1-C8-C7
116.6(2), C8-C7-C14 116.8(2), C8-C7-Si 118.4(2), Si-C7-C14
124.7(2), C7-C14-C14 173.1(2).
metal and both ring centers are 2.249 Å, the bite angle is 138.1°.
These data are in good agreement with those of previously
described zirconocenes. The most interesting structural feature
of this nine-membered, monomeric metallacycle is the cumu-
lenic C4 unit. Three double bonds [1.328(4), 1.268(6), 1.328-
(4) Å] are found in an almost linear arrangement [173.1(2)°,
173.1(2)°]. The negligible deviation from linearity is due to the
ring strain which is slightly mitigated by the hinted bending.
The large distances between the metal center and the C4 unit
indicate that there is no coordination of this cumulene to the
metal. The central C-C double bond displays a considerably
shortened distance as compared to the outer bonds of the
cumulene unit. This is an inversion of the ratios found in the
five-membered metallacyclocumulenes where an elongated
central double bond was determined. This can be explained by
the fact that there is a coordination of the central double bond
in the five-membered cumulene species which reduces the bond
order and thus increases the bond length. This effect is missing
in 6, where no coordination was found. Additionally, organic
1,2,3-trienes can be described by two mesomeric structures: the
1,2,3-triene on one hand and a diradical displaying a central
triple bond on the other hand. The relevancy of the second
The 1H NMR spectrum displays only two singlets (0.20 and
1.90 ppm, relative ratio 9:15), indicating a symmetric molecule
with equivalent silyl and cyclopentadienyl groups containing
one butadiyne-derived fragment per zirconium. In the 13C NMR
spectrum, three types of quaternary carbon atoms are found
besides the silyl and cyclopentadienyl signals, the silylated
carbon (134.4 ppm), the carbonyl group (167.8 ppm), and
another low-field signal (185.9 ppm) which is characteristic for
sp carbons in cumulenic hydrocarbons. A coordination of this
butatriene system to zirconium cannot be deduced from these
chemical shift data.
The structure of complex 6 as a result of the insertion of two
molecules of carbon dioxide into complex 2b is shown in Figure
7. It displays the first cumulenic dicarboxylate. The molecular
structure reveals a characteristically bent metallocene arrange-
ment of the ligands around zirconium. Distances between the
(29) (a) Burlakov, V. V.; Yanovsky, A. I.; Struchkov, Y. T.; Rosenthal,
U.; Spannenberg, A.; Kempe, R.; Ellert, O. G.; Shur, V. B. J. Organomet.
Chem. 1997, 542, 105. (b) Thomas, D.; Peulecke, N.; Burlakov, V. V.;
Baumann, W.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Eur. J. Inorg.
Chem. 1998, 1495.

8320 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Pellny et al.
mesomer should manifest itself in 6 in an increased bond order
and a conspicuous shortening of the central C-C bond. The
observation of a shortened central double bond has previously
been made in organic 1,2,3-trienes.30
It is of interest whether the complexes 5 and 6 can be
synthesized in a direct way by reacting the bisacetylides 1a and
1b with CO2 in sunlight without isolating the intermediates 2a
and 2b. Investigations into this question have so far afforded
mixtures of complexes which are currently studied.
The corresponding permethyltitanocene η2-complex 3 (ti-
tanacyclopropene) inserts only one molecule of carbon dioxide
under formation of the titanafuranone Cp*2Ti[OC(dO)-
C(SiMe3)dC(CtCSiMe3)-] (7) (eq 10).
Figure 8. ORTEP diagram (30% probability) of complex 7. Selected
bond distances (Å) and angles (deg): Ti-C7 2.177(2), C7-C17 1.365-
(3), C16-C17 1.503(4), C16-O1 1.317(3), C16-O2 1.227(3), Ti-
O1 1.956(2), C7-C8 1.417(3), C8-C9 1.217(4), C7-Ti-O1 77.75(8),
Ti-C7-C17 112.4(2), C7-C17-C16 113.9(2), C17-C16-O1 114.4-
(2), C16-O1-Ti 121.6(2), C17-C7-C8 124.6(2), C7-C8-C9 174.7-
(3), C8-C9-Si2 176.8(2), C7-C17-Si1 130.5(2).
3
The symmetry of 7 is reduced, compared to 6, because of the
insertion of only one carbon dioxide molecule, and the NMR
spectra exhibit separated resonances for the trimethylsilyl
groups. The shifts of the titanafuranone are similar to those of
complex 5. Two signals at δ(13C) 108.5 and 120.9 ppm prove
the existence of a free carbon-carbon triple bond, although their
shift is found at rather low field. This might be, at least to some
extent, due to the silyl substituents in the â position.
This species can undergo another insertion reaction with CO2
to yield complex 6 (Scheme 3).
Scheme 3
The structure resulting from the insertion of one molecule of
carbon dioxide depicts a second example of a Cp*-substituted
titanafuranone. A characteristically bent metallocene complex
is shown. The angle between the geometrical centers of both
rings and the titanium center is 141.0°. These data are in good
agreement with those of formerly described titanocenes. There
are some similarities to the above-mentioned complex 5 and
the parent metallacycles. The distances in the metallafuranone
[7: Ti-C7 2.177(2), C7-C17 1.365(3), C16-C17 1.503(4),
C16-O1 1.317(3), Ti-O1 1.956(2) Å] (Figure 8) correspond
very well with the data which were presented in the structural
discussion of 5. The distance of the uncoordinated triple bond
[C8-C9 1.217(4) Å] is nearly identical to that found for 3 and
typical for alkynylsilanes.
In support of this view are the reaction courses found for the
coupling of titanocene and zirconocene with 2 equiv of Me3-
SiCtC-CtCSiMe3; titanocene leads to a selective coupling
resulting in the formation of a titanacyclopentadiene displaying
one trimethylsilylalkynyl substituent in the R-position to the
metal center.5k,7
Complex 7 as the result of the reaction of 3 with CO2 is as
expected: One equivalent of carbon dioxide is inserted, display-
ing a definitely favored orientation of the insertion. More
surprising is the insertion of two molecules of CO2 into the
zirconacyclocumulene 2b to form the unprecedented nine-
membered zirconacycle 6. It initially seems obvious that the
observed reactivity is a characteristic feature of the unusual
cyclocumulene structure. A ready insertion of CO2 into both
metal-carbon bonds of the metallacycle would represent a
plausible and very direct mechanism to produce 6. However, it
is possible to explain the formation of 6 starting from a
presumed equilibrium between a η2- and a η4-permethylzir-
conocene complex. Then 2b would start to react in the same
manner as complex 3, forming the zirconium analogue of 7.
While this complex is stable against further carbon dioxide
insertions in the case of the smaller titanium, it seems reasonable
in the case of the larger zirconium to propose a relocation of
the zirconocene unit to form a seven-membered zirconacycle.
Scheme 4
The corresponding reaction of zirconocene affords a different
product, as Buchwald et al. reported;5e the formation of a seven-
membered zirconacyclocumulene is found, which was presumed
to be formed via the intermediacy of the zirconacyclopentadiene
derivative analoguous to the end product of the titanocene
reaction (Scheme 4).
Conclusion
(30) (a) van den Hoek, W. G. M.; Kroon, J.; Kleijn, H.; Westmijze, H.;
Vermeer, P.; Bos, H. J. T. J. Chem. Soc., Perkin Trans. 2 1979, 423. (b)
Higuchi, H.; Asano, K.; Ojima, J.; Yamamoto, K.; Yoshida, T.; Adachi,
T.; Yamamoto, G. J. Chem. Soc., Perkin Trans. 1 1994, 1453.
Due to steric reasons, the complexes Cp*2Ti(η2-Me3SiC2-
SiMe3) and Cp*2Zr(η2-Me3SiC2SiMe3) do not react with

Permethylzirconocene and Permethyltitanocene
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8321
(s, 30H, C5Me5), 7.35 (m, 4H, o-Ph), 7.22 (m, 4H, m-Ph), 7.15 (m,
2H, p-Ph). 13C NMR (THF-d8) δ/ppm: 12.5 (C5Me5), 118.3 ((C-â),
121.0 (C5Me5), 127.1 (i-Ph), 127.2 (p-Ph), 128.7 (m-Ph), 131.8 (o-
Ph), 153.0 (C-R). MS (70 eV) m/z: 562 (M+), 361 (Cp*2Zr+), 204
(PhC2-C2Ph+). IR (Nujol, cm-1): 2073 m, 1593 w, 1493 vs, 1202 s,
1068 w, 1025 m, 785 m, 758 vs, 691 s, 541 s.
1b (R ) SiMe3). Amounts of 432 mg (4.40 mmol) of Me3SiCtCH
and 950 mg (2.20 mmol) of Cp*2ZrCl2 afford 450 mg (37%) of 1b;
mp 162-166 °C (dec under argon). Anal. Calcd for C30H48Si2Zr
(556.1): C, 64.80; H, 8.70. Found: C, 64.82; H, 8.87. 1H NMR (C6D6)
δ/ppm: 0.24 (s, 18H, SiMe3), 2.01 (s, 30H, C5Me5). 13C NMR (C6D6)
δ/ppm: 0.6 (SiMe3), 12.6 (C5Me5), 120.6 (C5Me5), 122.3 (C-â),
175.0 (C-R). MS (70 eV) m/z: 554 (M+), 360 (Cp*2Zr+). IR (Nujol,
cm-1): 2027 m, 1424 s, 1244 vs, 1025 m, 855 vs, 837 vs, 757 m, 683
vs, 604 s.
Cp*2Zr(η4-1,2,3,4-PhC4Ph) (2a). (a) To an amount of 1420 mg
(3.28 mmol) of Cp*2ZrCl2 and 80 mg (3.29 mmol) of Mg turnings
was added a solution of 664 mg (3.28 mmol) of 1,4-diphenylbutadiyne
in 20 mL of THF. The mixture was stirred for 24 h at 55-60 °C, and
the color of the solution changed from light yellow to yellow-red. The
warm solution was filtered, concentrated to 10 mL and allowed to stand
at room temperature to induce the precipitation of red crystals which
were separated, washed with cold n-hexane (-75 °C), and dried in
vacuo to give 834 mg (45%) of 2a. (b) An amount of 150 mg (0.23
mmol) of Cp*2Zr(CtCPh)2 1a was dissolved in 5 mL of toluene. The
solution was allowed to stand in sunlight for 4 days, and the color of
the solution turned from light yellow to red. The solvent was removed
under vacuum, and the red residue was dissolved in 1 mL of n-hexane.
At -78 °C, red crystals appeared which were separated, washed with
cold n-hexane (-75 °C), and dried in vacuo to give 95 mg (74%) of
2a; mp 226-228 °C (dec under argon). Anal. Calcd for C36H40Zr
(563.93): C, 76.67; H, 7.15. Found: C, 76.78; H, 7.15. 1H NMR (THF-
d8) δ/ppm: 1.66 (s, 30H, C5Me5), 7.25 (2H, p-Ph), 7.41 (4H, m-Ph),
7.88 (4H, o-Ph). 13C NMR (THF-d8) δ/ppm: 11.9 (C5Me5), 113.7
(C5Me5), 118.4 (C-â), 128.2 (p-Ph), 129.0 (m-Ph), 134.4 (o-Ph), 136.7
(i-Ph), 179.4 (C-R). MS (70 eV) m/z: 563 (M+), 361 (Cp*2Zr+), 202
(PhC2-C2-Ph+).
butadiynes RCtC-CtCR. Stable five-membered zirconacy-
clocumulenes Cp*2Zr(η4-1,2,3,4-RC4R), R ) Ph (2a) and SiMe3
(2b) (zirconacyclopenta-2,3,4-trienes) can be synthesized by two
new and well-suited methods. The first is the rearrangement of
the permethylmetallocene bisacetylides Cp*2Zr(CtCR)2, R )
Ph (1a), SiMe3 (1b), in sunlight, and the second is the reduction
of Cp*2ZrCl2 with Mg in the presence of disubstituted butadiynes
RCtC-CtCR. The first route realizes preparatively what has
been predicted theoretically.9a
For Cp*2Ti, only titanacyclopropenes Cp*2Ti(η2-1,2-Me3-
SiC2CtCSiMe3) (3) and C-C coupling products were obtained.
It has to be outlined that the zirconacyclocumulene 2b and
the titanacyclopropene 3 are the first examples in which the
underlying substrate Me3SiCtC-CtCSiMe3 is not cleaved by
either our titanocene or zirconocene source (not regarding
coupling reactions 5e,6,7). It has been assumed that the special
electronic effects of the trimethylsilyl group (withdrawing
electron density, especially from the central C-C single bond,
indicated by the extreme resonance structure Me3Si(-))Cd
C(+)-C(+))CdSi(-)Me3, and thus preparing for a further
activation) is responsible for the observation that cumulenes and
other complexed compounds have never been found employing
this substrate. The simple use of the pentamethylcyclopentadi-
enyl ligand instead of the unsubstituted cyclopentadienyl linkage
restricts this reasoning as it obviously does prevent the cleavage
and makes possible the formation of two complexes with intact
C4 backbones. A comparison of 2b and 3 focuses on the
influence of the metals. The larger zirconium generates the η4-
complex, while the smaller titanium evidently is too small to
encompass all four diyne carbons in its coordination sphere.
The existence of a metallacyclocumulene structure (η4-
butadiyne complex) seems to mainly depend on steric factors
resulting from the metals and the substituents of the butadiyne
as well as from the Cp(*) ligands. Compared to Cp2Ti(η4-1,2,3,4-
PhC4Ph), the complex Cp*2Zr(η4-1,2,3,4-PhC4Ph) 2a is much
more stable in solution. The metallacyclocumulene Cp*2Zr(η4-
1,2,3,4-Me3SiC4SiMe3) 2b is stable, whereas all other attempts
failed to prepare metallacyclocumulenes starting from Me3SiCt
C-CtCSiMe3 and “Cp2Ti” or “Cp2Zr”. The conclusion is that
Cp* ligands stabilize such unusual five-membered metallacy-
clocumulenes only for zirconium.
Cp*2Zr(η4-1,2,3,4-Me3SiC4SiMe3) 2b. (a) An amount of 292 mg
(1.50 mmol) of 1,4-bis(trimethylsilyl)butadiyne was dissolved in 10
mL of THF. The solution was added to 650 mg (1.50 mmol) of
Cp*2ZrCl2 and 36 mg (1.50 mmol) of Mg turnings. The mixture was
kept at 55-60 °C and stirred for 48 h. The color of the solution changed
from light yellow to orange-red. The solution was then filtered, and
the solvent was removed in vacuo. The residue was extracted three
times with 5 mL portions of n-hexane. After filtration, concentration
of the clear solution to about 5 mL, and crystallization at -78 °C, an
amount of 669 mg (80%) of 2b formed which was filtered and dried
in vacuo to give orange-red crystals. (b) An amount of 135 mg (0.24
mmol) of Cp*2Zr(CtCSiMe3)2 1b was dissolved in 5 mL of toluene
under argon. After standing for 4 days in sunlight, the color of the
solution turned from light yellow to red. The solvent was removed in
vacuo, and the red residue was redissolved in 1 mL of n-hexane. While
the solution was standing at -78 °C, red crystals appeared which
were separated, washed with cold n-hexane (-75 °C), and dried in
vacuo to give 101 mg (79%) of 2b; mp 195 °C (dec under argon).
Anal. Calcd for C30H48Si2Zr (556.1): C, 64.80; H, 8.70. Found: C,
64.57; H, 8.64. 1H NMR (THF-d8) δ/ppm: 0.45 (s, 18H, SiMe3), 1.61
(s, 30H, C5Me5). 13C NMR (THF-d8) δ/ppm: 3.2 (SiMe3), 12.1 (C5Me5),
113.4 (C5Me5), 144.5 (C-â), 188.0 (C-R). MS (70 eV) m/z: 556 (M+),
360 (Cp*2Zr+).
Experimental Section
All operations were carried out under an inert atmosphere (argon)
using standard Schlenk techniques. Prior to use, solvents were freshly
distilled from sodium tetraethylaluminate under argon. Deuterated
solvents were treated with sodium or sodium tetraethylaluminate,
distilled, and stored under argon. NMR: Bruker ARX 400 at 9.4 T
(chemical shifts given in ppm relative to TMS), recorded at ambient
temperature, unless otherwise noted. Melting points were measured in
sealed capillaries on a Bu¨chi 535 apparatus. Elemental analyses: Leco
CHNS-932 elemental analyzer. Infrared spectra were recorded with a
Nicolet Magna 550 (Nujol mulls using KBr plates). Mass spectrom-
eter: AMD 402.
Cp*2Zr(CtCR)2, R ) Ph (1a), SiMe3 (1b). About 3-5 mmol of
the alkyne HCtCR was dissolved in 5 mL of toluene, cooled to -78
°C, and 1 equiv of n-butyllithium (2.5 M/hexane) was added. After
warming up to room temperature, 0.5 equiv of the complex Cp*2ZrCl2
was added and the solution was stirred for 24 h, the solvents were
then distilled in vacuo, and the residue was suspended in 10 mL of
n-hexane. After filtration and crystallization at -78 °C, the mother
liquor was decanted and the crystals were dried in vacuo.
Cp*2Ti(η2-1,2-Me3SiC2CtCSiMe3) (3). A suspension of 1045 mg
(2.68 mmol) of Cp*2TiCl2, 66 mg (2.71 mmol) of Mg turnings, and
521 mg (2.68 mmol) of 1,4-bis(trimethylsilyl)butadiyne in 15 mL of
THF was stirred for 8 h at 55-60 °C. The resulting green solution
was evaporated to dryness in vacuo, and the residue was extracted with
25 mL of n-hexane. After standing at -78 °C for 2 days, red crystals
appeared which were separated, washed with cold n-hexane (-75 °C),
and dried in vacuo to give 1193 mg (87%) of 3; mp 141-142 °C (dec
under argon). Anal. Calcd for C30H48Si2Ti (512.8): C, 70.27; H, 9.44.
1a (R ) Ph). Amounts of 316 mg (3.10 mmol) of PhCtCH and
650 mg (1.50 mmol) of Cp*2ZrCl2 give 185 mg (22%) of 1a; mp 219-
223 °C (dec under argon). Anal. Calcd for C36H40Zr (563.9): C, 76.67;
1
Found: C, 70.34; H, 9.69. H NMR (toluene-d8, 188 K) δ/ppm: 0.21
1
H, 7.15. Found: C, 76.61; H, 7.28. H NMR (THF-d8) δ/ppm: 2.11
(s, 9H, SiMe3), 0.27 (s, 9H, SiMe3), 1.66 (s, 15H, C5Me5). 13C NMR

8322 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Pellny et al.
The volatile material was removed under vacuum, and the residue was
dissolved in 60 mL of n-hexane at 60 °C. The warm solution was
filtered and evaporated under vacuum to give 1181 mg (76%) of a
green solid. Subsequent recrystallization from n-hexane produced dark-
green crystals; mp 158-160 °C (dec under argon) (Figure 9). Anal.
Calcd for C36H40Ti (520.6): C, 83.06; H, 7.74. Found: C, 82.99; H,
1
7.86. H NMR (C6D6) δ/ppm: 0.96 (s, 3H, C61), 1.13 (s, 3H, C56),
1.26 (s, 3H, C60), 1.37 (s, 3H, C72), 1.49 (s, 3H, C70), 1.66 (d, 1H,
C12), 1.71 (s, 3H, C59), 1.97 (s, 3H, C6), 2.21 (d, 1H, C12), 2.33 (s,
3H, C69), 3.22 (d, 1H, C45), 3.72 (dd, 1H, C45), 4.87 (s, 1H, C14),
5.62 (d, 1H, C47), 6.91 (t, 1H, C51), 6.98 (t, 1H, C18), 7.03 (t, 2H,
C50/52), 7.15 (t, 2H, C17/19), 7.37 (d, 2H, C49/53), 7.63 (d, 2H, C16/
20). 13C NMR (C6D6) δ/ppm: 9.5 (C59), 10.2 (C61), 10.2 (C56), 10.3
(C60), 10.7 (C72), 11.5 (C70), 13.5 (C6), 16.5 (C69), 33.4 (C45), 79.5
(C12), 113.2 (C2), 113.2 (C47), 114.6 (C4), 119.5 (C3), 120.6 (C5),
122.1 (C14), 122.6 (C8), 125.6 (C51), 126.2 (C7), 126.2 (C18), 128.1
(C16/20), 128.2 (C50/52), 128.3 (C11), 128.5 (C49/53), 128.7 (C9),
129.0 (C17/19), 129.4 (C10), 130.5 (C1), 139.0 (C15), 139.8 (C48),
147.5 (C46), 208.0 (C13). MS (70 eV) m/z: 521 (M+).
Figure 9. Molecular structure of 4 labelled according to the labelling
of the respective crystal structure. The labels are used for the assignment
of the NMR signals.
Cp*Ti[-OC(dO)C(Ph)C(-)C(dCHPh)CH2-η5-C5Me4] (5). An
amount of 155 mg (0.298 mmol) of 4 was dissolved in 10 mL of
n-hexane under argon. The resulting green solution was filtered, argon
was carefully removed from the flask under vacuum, and the flask
containing the solution was charged with carbon dioxide. After 3 days
at room temperature, dark red crystals had formed, which were
separated, washed with n-hexane, and dried in vacuo to give 125 mg
(74%); mp 239-241 °C (Figure 10). Anal. Calcd for C37H40O2Ti
(564.60): C, 78.71; H, 7.14. Found: C, 78.95; H, 7.24. 1H NMR (C6D6)
δ/ppm: 1.18 (s, 3H, C20), 1.43 (s, 3H, C29), 1.76 (s, 15H, C6/22/25/
28/37), 1.91 (s, 3H, C27), 2.02 (s, 3H, C26), 2.72 (dd, 1H, C24), 3.90
(dd, 1H, C24), 5.40 (d, 1H, C30), 6.89 (t, 1H, C34), 7.02 (t, 2H, C33/
35), 7.06 (t, 1H, C12), 7.07 (d, 2H, C32/36), 7.32 (t, 2H, C11/13),
8.17 (d, 2H, C10/14). 13C NMR (C6D6) δ/ppm: 10.1 (C29), 10.4 (C20),
11.4 (C27), 11.9 (C6/22/25/28/37), 12.5 (C26), 33.9 (C24), 113.9 (C30),
118.1 (C15), 122.3 (C16), 122.7 (C17), 126.2 (C1/2/3/4/5), 126.4 (C34),
126.6 (C12), 128.1 (C33/35), 128.2 (C11/13), 128.7 (C32/36), 128.8
(C10/14), 129.7 (C18), 133.0 (C19), 138.1 (C9 or C31), 139.8 (C8),
140.4 (C9 or C31), 148.2 (C23), 165.2 (C21), 224.4 (C7). MS (70 eV)
m/z: 564 (M+), 520 (M+ - CO2), 318 (Cp*2Ti+). IR (Nujol, cm-1):
1635 ν(CdO).
Figure 10. Molecular structure of 5 labelled according to the labelling
of the respective crystal structure. The labels are used for the assignment
of the NMR signals.
(toluene-d8, 188 K) δ/ppm: 0.4 (SiMe3), 2.4 (SiMe3), 11.9 (C5Me5),
105.1, 110.7 (CtC), 121.3 (C5Me5), 205.3 (C-â), 227.5 (coord. Ct
C). MS (70 eV) m/z: 512 (M+). IR (Nujol, cm-1): 2092 (ν(CtC)),
1608 (ν(CtC) coord.).
Cp*2Zr[-OC(dO)C(SiMe3)dCdCdC(SiMe3)C(dO)O-] (6). An
amount of 161 mg (0.29 mmol) of 2b was dissolved in 7 mL of THF.
The solution was stirred for 3 h under an atmosphere of CO2 at room
temperature. The solvent was removed, and the residue was extracted
three times with portions of 3 mL of n-hexane. Cooling for 48 h at
-78 °C afforded 97 mg (52%) of yellow crystals which were separated
[η5-C5Me4-(CH2)-]Ti[-C(dCHPh)C(dCHPh)CH2-η5-
C5Me4] (4). A suspension of 1066 mg (2.74 mmol) of Cp*2TiCl2, 67
mg (2.76 mmol) of Mg turnings, and 559 mg (2.76 mmol) of 1,4-
diphenylbutadiyne in 20 mL of THF was stirred for 8 h at 55-60 °C.
Table 2. Crystallographic Data of the Complexes
2a
2b
3
4
5
6
7
cryst. color, habit
cryst. system
space group
lattice constants
a (Å)
b (Å)
c (Å)
orange, prism
monoclinic
C2/c
orange, prism
monoclinic
P21/c
red, prism
triclinic
P-1
green, prism
monoclinic
P21/c
orange, prism
monoclinic
P21/n
yellow, prism
orthorhombic
Fddd
red, prism
triclinic
P-1
27.086(5)
15.533(3)
14.207(3)
10.595(2)
18.220(4)
15.891(3)
11.237(2)
11.534(2)
13.691(3)
76.36(3)
67.09(3)
74.46(3)
2
26.632(5)
8.931(2)
25.953(5)
17.064(3)
8.838(2)
21.308(4)
17.104(3)
17.173(3)
48.170(10)
10.567(2)
12.213(2)
13.991(3)
92.07(3)
100.15(3)
114.87(3)
2
R (deg)
â (deg)
104.31(3)
94.50(3)
109.16(3)
107.70(3)
γ (deg)
Z
8
4
8
4
16
cell volume
5792(2)
1.293
293(2)
0.402
1.99-24.22
12691
4581
2814
334
0.033
0.080
3058.2(11)
1.208
200(2)
0.453
2.23-24.23
8957
4579
3595
288
0.049
0.135
1557.3(5)
1.093
200(2)
0.367
1.85-24.27
4643
4643
3685
298
0.044
5831(2)
1.186
293(2)
0.315
1.59-21.05
11175
6155
3793
667
0.046
0.111
3061.4(10)
1.225
293(2)
0.310
1.83-21.05
5945
3145
1669
361
0.045
0.100
14149(5)
1.209
293(2)
0.409
1.73-24.33
10158
2828
2275
177
0.035
0.093
1600.2(5)
1.156
293(2)
0.366
1.85-24.15
4733
4733
3888
325
0.040
density (g/cm-3
)
temp (Κ)
µ(Μï ΚR) (mm-1
θ range (deg)
)
no. of rflns (measd)
no. of rflns (indep)
no. of rflns (obsd)
no. of parameters
R1 (I > 2σ(I))
wR2 (all data)
0.136
0.127

Permethylzirconocene and Permethyltitanocene
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8323
from the mother liquor by filtration and dried in vacuo; mp 196-198
°C. Anal. Calcd for C32H48O4Si2Zr (644.26): C, 59.67; H, 7.51.
Found: C, 59.54; H, 7.37. H NMR (THF-d8) δ/ppm: 0.20 (s, 18H,
SiMe3), 1.90 (s, 15H, C5Me5). 13C NMR (THF-d8) δ/ppm: -1.2 (SiMe3),
10.9 (C5Me5), 123.3 (C5Me5), 134.4 (CdCSiMe3), 167.8 (CO), 185.9
(CdCSiMe3). MS (70 eV) m/z: 642 (M+), 598 (M+ - CO2), 525 (M+
- CO2 - SiMe3), 360 (Cp*2Zr+). IR (Nujol, cm-1): 2096 w, 1928 w,
1636 m, 1414 s, 1261 s, 1023 s, 841 vs.
cm-1): 2095 m, 2076 m, 1627 vs, 1491 m, 1233 s, 1022 m, 853 vs,
837 vs.
1
X-ray Crystallographic Study of Complexes. Data were collected
with a STOE-IPDS diffractometer using graphite-monochromated Mo
KR radiation. The structures were solved by direct methods (SHELXS-
86)31 and refined by full-matrix least-squares techniques against F2
(SHELXL-93).32 The hydrogen atoms were included at calculated
positions. All other nonhydrogen atoms were refined anisotropically.
Cell constants and other experimental details were collected and
recorded in Table 2. XP (SIEMENS Analytical X-ray Instruments, Inc.)
was used for structure representations and for calculating certain
additional angles and distances in the determined structures.
Cp*2Ti[-OC(dO)C(SiMe3)dC(CtCSiMe3)-] (7). An amount of
100 mg (0.20 mmol) of 3 was dissolved in 5 mL of THF and stirred
for 2 h under an atmosphere of CO2 at room temperature. The solvent
was removed, and the red residue was redissolved in 2 mL of THF.
Cooling for 24 h at -78 °C yielded 90 mg (82%) of a red-brown
crystalline product which was separated from the mother liquor by
filtration and dried in vacuo; mp 208 °C. Anal. Calcd for C31H48O2-
Si2Ti (556.77): C, 66.87; H, 8.68. Found: C, 67.03; H, 8.72. 1H NMR
(C6D6) δ/ppm: 0.18 (s, 9H, SiMe3), 0.70 (s, 9H, SiMe3), 1.76 (s, 15H,
C5Me5). 13C NMR (C6D6) δ/ppm: -0.2 (SiMe3), 1.1 (SiMe3), 12.0
(C5Me5), 108.5, 120.9 (CtC), 125.8 (C5Me5), 167.1, 163.8 (CO, C-â),
221.1 (C-R). MS (70 eV) m/z: 556 (M+); 541 (M+ - Me); 513 (M+
- Me - C2H4), 426 (M+ - C5H9O2Si), 318 (Cp*2Ti+). IR (Nujol,
Supporting Information Available: Tables of crystal data,
structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for 2a,
2b, 3, 4, 5, 6, and 7 (PDF). An X-ray crystallographic file, in
CIF format, is also available. This material is available free of
charge via the Internet at http://pubs.acs.org.
JA991046Z
(31) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(32) Sheldrick, G. M. SHELXL-93; University of Go¨ttingen: Go¨ttingen,
Germany, 1993.