Synthesis and reactions with carbon dioxide of mono(σ-alkynyl) titanocene(III) complexes Cp*2Ti(C≡CR) (R = Me, t-Bu) and the corresponding "Ate" complexes [Cp*2Ti(C≡CR)2Li(THF)n] (R = SiMe3, t-Bu, Ph)

Article abstract of DOI:10.1021/om010404f

The reactions of the titanium(III) complex Cp*₂TiCl with lithium acetylides RC≡CLi depend strongly on the solvents used. In THF only the lithium tweezer compounds [Cp*_2-Ti(C≡CR)₂Li(THF)_n] (Cp* = η⁵-C<

Full text of DOI:10.1021/om010404f

Organometallics 2001, 20, 5289-5296
5289
Syn th esis a n d Rea ction s w ith Ca r bon Dioxid e of
Mon o(σ-a lk yn yl) Tita n ocen e(III) Com p lexes
Cp *2Ti(CtCR) (R ) Me, t-Bu ) a n d th e Cor r esp on d in g
“Ate” Com p lexes [Cp *2Ti(CtCR)2Li(THF )n ] (R ) SiMe3,
t-Bu , P h )
Frank G. Kirchbauer, Paul-Michael Pellny, Hongsui Sun, Vladimir V. Burlakov,†
Perdita Arndt, Wolfgang Baumann, Anke Spannenberg, and Uwe Rosenthal*
Institut fu¨r Organische Katalyseforschung an der Universita¨t Rostock e.V.,
Buchbinderstrasse 5-6, D-18055 Rostock, Germany
Received May 16, 2001
The reactions of the titanium(III) complex Cp*2TiCl with lithium acetylides RCtCLi
depend strongly on the solvents used. In THF only the lithium tweezer compounds [Cp*2-
Ti(CtCR)2Li(THF)n] (Cp* ) η5-C5Me5; R ) SiMe3, n ) 1 (1); R ) t-Bu, n ) 1 (2); R ) Ph, n
) 2 (3)), not the expected mono(σ-alkynyl) titanocene(III) complexes, were obtained, whereas
in n-hexane these complexes Cp*2Ti(CtCR) were isolated for R ) Me (4), t-Bu (5). The
reaction of the complex [Cp*2Ti(CtCSiMe3)2Li(THF)] (1) with carbon dioxide results in the
titanafuranone 6, which presumably is formed by insertion of carbon dioxide into the η2-
butadiyne complex Cp*2Ti(η2-Me3SiCtCCtCSiMe3). The complex [Cp*2Ti(CtC-t-Bu)2Li-
(THF)] (2) reacts with carbon dioxide to yield the permethyltitanocene carboxylate
Cp*2Ti(O2CCtC-t-Bu) (7) via insertion into the σ-acetylide bond of the in situ formed
titanium(III) intermediate [Cp*2Ti-CtC-t-Bu]. Compound 7 was also obtained in the reaction
of the isolated titanium(III) complex Cp*2Ti-CtC-t-Bu (5) with carbon dioxide. The
interaction of [Cp*2Ti(CtCPh)2Li(THF)2] (3) with carbon dioxide gives the stable bis(σ-
acetylide) permethyltitanocene Cp*2Ti(CtCPh)2 (8) without coupling of the σ-acetylide groups
(as found for 1) and without insertion into the σ-acetylide bond (as found for 2). The syntheses
and reactions of these compounds are compared to those of similar complexes of unsubstituted
titanocene compounds. Complexes 1, 5, and 7 were investigated by X-ray crystal structure
analysis.
In tr od u ction
to butadiynes by, the metallocene cores.4 The course of
reaction can be formulated in such a way that the
titanocene reacts with the diyne to give a dimeric
complex which subsequently dissociates to produce the
extremely unstable monomeric Ti(III) complex [Cp2Ti-
(σ-CtCR)], which then dimerizes to either the respective
starting complex or, in the desired way, to a differently
substituted binuclear complex.4 This view recently also
was supported by dynamic NMR investigations in which
we could show that dinuclear C-C-cleaved complexes,
e.g., [Cp2Ti]2[(µ-CtCSiMe3)(µ-CtC-t-Bu)] very likely are
present in solutions of the uncleaved complexes [Cp2-
Ti]2[µ-η2(1,3):η2(2,4)-t-BuC2-C2SiMe3].5 With regard to
the metal compound Cp2Ti(Me3SiCtCSiMe3) that is
used as the titanocene source, this metathesis could not
be conducted catalytically, because an excess of the
diyne favors, instead of the cleavage, the coupling
reactions of diynes. This makes the complexes with
Do monomeric σ-alkynyl titanocene(III) complexes L2-
Ti(CtCR) really exist? The answer to this question is
of relevance in some catalytic reactions, and such a
compound has never been structurally characterized.
Teuben et al. investigated the reaction of [Cp2TiCl]2 with
NaCtCPh and did not obtain the expected monomeric
complex [Cp2TiCtCPh] but rather a binuclear complex
with a bridging butadiyne ligand, [Cp2Ti]2[µ-η2(1,3):
η2(2,4)-PhC2C2Ph].1 Since then, there has been, to the
best of our knowledge, only one example of such a
monomeric species: Cp*2TiCtCMe, reported as the
product of the reaction of Cp*2TiCl with LiCtCMe, but
without structural characterization.2
We became aware of the question of the synthesis of
monomeric σ-alkynyl titanocene(III) complexes such as
L2Ti(CtCSiMe3) when we considered the mechanism
of our recently described C-C single-bond metathesis
of 1,4-disubstituted 1,3-butadiynes.3 The interaction of
butadiynes with titanocenes and zirconocenes can give,
via metallacyclocumulenes,4 a cleavage of, or a coupling
(3) Kirchbauer, F. G.; Pulst, S.; Heller, B.; Baumann, W.; Rosenthal,
U. Angew. Chem. 1998, 110, 2029; Angew. Chem., Int. Ed. Engl. 1998,
37, 1925.
(4) (a) Ohff, A.; Pulst, S.; Peulecke, N.; Arndt, P.; Burlakov, V. V.;
Rosenthal, U. Synlett 1996, 111. (b) Rosenthal, U.; Pellny, P.-M.;
Kirchbauer, G.; Burlakov, V. V. Acc. Chem. Res. 2000, 33, 119. (c)
Burlakov, V. V.; Ohff, A.; Lefeber, C.; Tillack, A.; Baumann, W.; Kempe,
R.; Rosenthal, U. Chem. Ber. 1995, 128, 967. (d) J emmis, E. D.; Giju,
K. T. J . Am. Chem. Soc. 1998, 120, 6952. (e) J ones, M.; Klosin, J . Adv.
Organomet. Chem. 1998, 42, 147. (f) Choukroun, R.; Cassoux, P. Acc.
Chem. Res. 1999, 32, 494.
† On leave from the A. N. Nesmeyanov Institute of Organoelement
Compounds, Russian Academy of Sciences, Vavilov St. 28, 117813,
Moscow, Russia.
(1) Teuben, J . H.; de Liefde Meijer, H. J . J . Organomet. Chem. 1969,
17, 87.
(2) Luinstra, G. A.; ten Cate, L. C.; Heeres, H. J .; Pattiasina, J . W.;
Meetsma, A.; Teuben, J . H. Organometallics 1991, 10, 3227.
(5) Baumann, W.; Pellny, P.-M.; Rosenthal, U. Magn. Reson. Chem.
2000, 38, 515.
10.1021/om010404f CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/14/2001

5290 Organometallics, Vol. 20, No. 25, 2001
Kirchbauer et al.
coupled diyne, e. g., titanacyclopentadienes, dominant
in the product range. It is well-known that sterically
demanding ligands prevent undesired coupling reactions
of the substrates. We therefore replaced the cyclopen-
tadienyl ligand (Cp) in our starting compounds by the
pentamethylcyclopentadienyl ligand (Cp*).6 Because the
unstable monomeric Ti(III) complexes [Cp2Ti(σ-CtCR)]
are assumed to play such an important role in the
reaction sequence of our metathesis reaction, we were
interested in synthesizing the corresponding permeth-
yltitanocene complexes Cp*2Ti(σ-CtCR).
formation in THF does not depend on the experimental
procedure: adding the Cp*2TiCl to an excess of RCt
CLi or vice versa. Also, warming of the mixtures for
some time gave no different results.
Sch em e 1
Additionally, species such as L2Ti(CtCSiMe3) could
also be important in catalytic oligomerization reactions
of 1-alkynes.7 Cleavage of Me3SiCtCCtCSiMe3 by the
system Cp2TiCl2/magnesium gives the dimeric titanium-
(III) complex [Cp2Ti(CtCSiMe3)]2.8 The system Cp*2-
TiCl2/magnesium/Me3SiCtCCtCSiMe3 under the same
conditions, via cleavage of the central C-C single bond
of the diyne and coupling of the acetylide with another
diyne, yields the complex Cp*2Ti[µ-η2(1,2):η1(3)-Me3-
SiCtCCdC(SiMe3)CtCSiMe3], displaying a hex-3-ene-
1,5-diyn-3-yl ligand.9 The initial formation of the mono-
(alkynyl)titanium(III) complex L2Ti(CtCSiMe3) in both
systems is assumed, which for L ) Cp dimerizes quickly
to [Cp2Ti(CtCSiMe3)]2. Alternatively for R ) Cp*, it can
react with a diyne to yield the complex Cp*2Ti[µ-η2(1,2):
η1(3)-Me3SiCtCCdC(SiMe3)CtCSiMe3]. The Cp* ligands
prevent dimerization of the mono(alkynyl) complexes.
We report here that the expected complexes Cp*2Ti-
(σ-CtCR) (R ) Me, t-Bu) were obtained by the salt eli-
mination reaction of Cp*2TiCl with LiCtCR in n-hex-
ane, whereas in THF with R) Ph, t-Bu, SiMe3 the titan-
ium(III) “ate” complexes [Cp*2Ti(CtCR)2Li(THF)n] were
formed. These complexes are compared with [Cp2Ti(Ct
C-t-Bu)2Li(THF)2] in the reactions with carbon dioxide.
Complexes of the type [L2Ti(CtCR)2MLn], with M )
alkali metal, are very rare in the titanocene system.11
There are only a few examples of partially methylated
analogues such as [(Me4HC5)2Ti(CtCSiMe3)2M(THF)n]
(M ) Li, Na, K, Cs) that were prepared by the reaction
of (Me4HC5)2Ti(CtCR)2 complexes with alkali metals12a,b
and the complex [(Me4HC5)2Ti(CtCCtCSiMe3)2Li-
(THF)2]synthesizedfrom (Me4HC5)2TiClandLiCtCCtCSi-
Me3.12c They were reported also for permethylmetal-
locene systems; e.g., the complex [Cp*2Ti(CtCSiMe3)2-
MgCl(THF)] was prepared by the scission of Me3SiCt
CCtCSiMe3 by the system Cp*2TiCl2 and magnesium.10
Complexes 1-3 are extremely sensitive to air and
moisture. They are readily soluble in n-hexane and more
so in THF and toluene. As titanium(III) complexes they
are paramagnetic. In their IR spectra the absorptions
due to the complexed triple bond are in the same range
(e.g., 1: 1954 cm-1) as those of the partially methylated
analogues that contain the same alkynyl substituent R
) Me3Si, [(Me4HC5)2Ti(CtCSiMe3)2M(THF)n] (M ) Li,
1948 cm-1; M ) Na, 1945 cm-1; M ) K, 1944 cm-1; M
) Cs, 1948 cm-1).12a,b For R ) t-Bu, compared to the
free complex (Cp*2Ti(CtCR)2, 2075 cm-1 6b), the coor-
dination shift for 2 (2030 cm-1) is in the typical range.
The X-ray crystal structure of complex 1 confirmed
the connectivity shown in Scheme 1.
Resu lts a n d Discu ssion
R ea ct ion s of t h e P er m et h ylt it a n ocen e Com -
p lexes. The reactions of the titanium(III) complex Cp*2-
TiCl with lithium acetylides RCtCLi depend strongly
on the solvents used. In THF the expected Cp*2Ti(Ct
CR) complexes could not be prepared by reacting Cp*2-
TiCl with 1 or 2 equiv of RCtCLi. Only the lithium
tweezer compounds [Cp*2Ti(CtCR)2Li(THF)n] (Cp* )
η5-C5Me5; R ) SiMe3, n ) 1 (1), R ) t-Bu, n ) 1 (2); R
) Ph, n ) 2 (3)) were isolated (Scheme 1).
These results are in good agreement with recent
results of Mach et al. in studies of similar systems.10a
Whether the “ate” complexes are thermodynamic or
kinetic products was a question of interest. Their
(6) (a) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann,
W.; Spannenberg, A.; Rosenthal, U. J . Am. Chem. Soc. 1999, 121, 8313.
(b) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Chem. Eur. J . 2000, 6, 81.
(7) (a) Hora´cˇek, M.; C´ısarˇova´, I.; Cˇ ejka, J .; Karban, J .; Petrusova´,
L.; Mach, K. J . Organomet. Chem. 1999, 577, 103. (b) Akita, H.;
Yasuda, H.; Nakamura, A. Bull. Chem. Soc. J pn. 1984, 57, 480. (c)
Varga, V., Petrusova´, L.; Cˇ ejka, J .; Hanusˇ, V.; Mach, K. J . Organomet.
Chem. 1996, 509, 235. (d) Sˇteˇpnicˇka, P.; Gyepes, R.; C´ısarˇova´, I.;
Hora´cˇek, M.; Kubisˇta, J .; Mach, K. Organometallics 1999, 18, 4869.
(8) (a) Wood, G. L.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem.
1989, 28, 382. (b) Rosenthal, U.; Go¨rls, H. J . Organomet. Chem. 1992,
439, C36-C41.
(11) (a) Lang, H.; Rheinwald, G. J . Prakt. Chem. 1999, 341, 1. (b)
Lotz, S.; Van Rooyen, P. H.; Meyer, R. Adv. Organomet. Chem. 1995,
37, 219 and references therein.
(12) (a) Varga, V.; Hiller, J .; Thewalt, U.; Polasek, M.; Mach, K. J .
Organomet. Chem. 1996, 514, 219. (b) Varga, V.; Hiller, J .; Thewalt,
U.; Polasek, M.; Mach, K. J . Organomet. Chem. 1996, 515, 57. (c)
Varga, V.; Mach, K.; Hiller, J .; Thewalt, U.; Mach, K. J . Organomet.
Chem. 1996, 506, 109. (d) Hiller, J .; Varga, V.; Thewalt, U.; Mach, K.
Collect. Czech. Chem. Commun. 1997, 62, 1446.
(9) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Spannenberg,
A.; Mach, K.; Rosenthal, U. Chem. Commun. 1999, 2505.
(10) (a) Varga, V.; Petrusova, L.; Cejka, J .; Mach, K. J . Organomet.
Chem. 1997, 532, 251. (b) Troyanov, S. I.; Varga, V.; Mach, K.
Organometallics 1993, 12, 2820.

Reactions of σ-Alkynyl Titanocene(III) Complexes
Organometallics, Vol. 20, No. 25, 2001 5291
Conducting the reactions of Cp*2TiCl with acetylides
RCtCLi in n-hexane for R ) Ph and SiMe3 gave only
mixtures of complexes, but for R ) Me (4) and t-Bu (5)
the well-defined titanium(III) complexes Cp*2Ti(CtCR)
were isolated (Scheme 2).
Complex 5 was investigated by X-ray diffraction. It
is the first example of the structure of a monomeric
titanocene(III) monoacetylide (see below).
For the formation of the “ate” complexes instead of
the titanium(III) monoacetylides according to Scheme
1, one can assume that the reaction of Cp*2TiCl with 2
equiv of LiCtCR gives the tweezer “ate” complexes
[Cp*2Ti(CtCR)2Li(THF)n] together with unreacted Cp*2-
TiCl. In THF, possibly due to kinetic reasons, the reac-
tion stops here. On the other hand, it seems more likely
that LiCtCR reacts more rapidly with the initially
formed Cp*2Ti(σ-CtCR) than with Cp*2TiCl (Scheme 3).
Starting from complexes 1-3, we were interested in
preparing the monomeric Ti(III) monoacetylides Cp*2-
Ti(σ-CtCR) by dissociation of LiCtCR and in their
subsequent reactions with substrates. Additionally we
tried to prepare the corresponding Ti(IV) diacetylides
Cp*2Ti(σ-CtCR)2 by oxidation with oxygen and elimi-
nation of lithium oxides. These complexes can give by
coupling of the alkynyl units the five-membered titana-
cyclocumulenes Cp*2Ti(η4-1,2,3,4-RC4R).3,4 Such an oxi-
dation by air is a well-established method of preparing
titanium(IV) complexes starting from titanium(III) “ate”
complexes.13
Sch em e 2
However, in all conducted experiments such an alky-
nyl coupling was found only for complex 1 (Scheme 4):
the reaction with an excess of carbon dioxide leads to
the well-known titanafuranone 6,6a,14 which presumably
is formed by insertion of carbon dioxide into the η2-
butadiyne complex [Cp*2Ti(η2-1,2-Me3SiCtCCtCSiMe3)]
(Scheme 4).6a,14
This η2-butadiyne complex was prepared and isolated
before by two different methods, the reduction of Cp*2-
TiCl2 by magnesium in the presence of Me3SiCtCCt
CSiMe3 and, additionally, by irradiation of isolated
Cp*2Ti(CtCSiMe3)2.6a It seems reasonable to assume
an oxidation from Ti(III) to Ti(IV) by carbon dioxide,
similar to what has been found when employing oxygen
from air,13 which was excluded carefully in our experi-
ments described herein. Complex 6 was formed in a
yield of only 40%, in addition to a mixture of unidenti-
fied side products. This can be ascribed to the three
different steps of the formation of 6 (oxidation, coupling,
insertion), not all proceeding quantitatively altogether.
The data of the titanafuranone 6, obtained by reaction
of 1 with carbon dioxide, are identical with those of
samples obtained by reactions of [Cp*2Ti(η2-1,2-Me3-
SiCtCCtCSiMe3)] with carbon dioxide.6a,14
Complexes 4 and 5 are extremely sensitive to air and
moisture. As mentioned above, complex 4 was reported
earlier, but not its structure.2 Both complexes are
soluble in n-hexane and very soluble in THF and
toluene. The paramagnetic titanium(III) complexes
show in their infrared spectra the absorptions due to
the triple bond in the expected range (e.g. 4, 2080 cm-1 2
5, 2071 cm-1).
;
Sch em e 3
The complex [Cp*2Ti(CtC-t-Bu)2Li(THF)] (2) reacts
with carbon dioxide to give the permethyltitanocene
carboxylate Cp*2Ti(O2CCtC-t-Bu) 7 (Scheme 5), via
insertion into the σ-acetylide bond of the assumed
titanium(III) intermediate Cp*2TiCtC-t-Bu, which could
be formed by the dissociation of complex 2.
Complex 7 could be also prepared by reacting the
isolated complex 5 with carbon dioxide (Scheme 6).
A similar compound, Cp*2TiO2CH, was obtained by
Teuben et al.2 in the salt elimination reaction of Cp*2-
TiCl and NaO2CH and, alternatively, by the carbon
dioxide insertion and a subsequent olefin elimination
of Cp*2TiCH2CH2R.15
(13) Seidel, W.; Bu¨rger, I. Z. Chem. 1977, 17, 185.
(14) Kirchbauer, F. G.; Ph.D. Thesis, University of Rostock, 1999.
(15) Pattiasina, J . W.; Heeres, H. J .; van Bolhuis, F.; Meetsma, A.;
Teuben, J . H.; Spek, A. L. Organometallics 1987, 6, 1004.

5292 Organometallics, Vol. 20, No. 25, 2001
Kirchbauer et al.
Sch em e 4
Under an atmosphere of carbon dioxide the titanium-
(III) “ate” complex [Cp*2Ti(CtCPh)2Li(THF)2] 3 reacts,
without any coupling as found for 1 and 2, to the titan-
ium(IV) bis(acetylide) Cp*2Ti(CtCPh)2 (8) (Scheme 7).
The yield of complex 8 was only 32%, the rest being
a mixture of unidentified further products. The titanium
is oxidized during the reaction from Ti(III) to Ti(IV) by
carbon dioxide, as found in the reaction of 1 to 6. Again
air was excluded carefully. The salt elimination reaction
from Cp*2TiCl and LiO2CCtCR, according to Teuben
et al.,17 worked also very well to prepare complex 9 (R
) Ph, Scheme 8), similarly as found for complex 7 (R )
t-Bu), but failed for R ) SiMe3.
reaction of 1. Complex 2 reacts directly, after dissocia-
tion and without being oxidized, with carbon dioxide.
Motivated by these results in the reactions of the “ate”
complexes 1-3 with carbon dioxide, which are strongly
differentiated by the substituents R used, the corre-
sponding reactions of the unsubstituted Cp analogues
and of similar compounds were considered as well.
Rea ction s of Rela ted Tita n ocen e Com p lexes. The
8
Ti(IV) complex Cp2Ti(CtCSiMe3)2 very easily gives,
upon standing under an atmosphere of argon, a reduc-
tion to the diyne Me3SiCtCCtCSiMe3 together with the
well-known dimeric diamagnetic Ti(III) compound [Cp2-
Ti(CtCSiMe3)]2.8 The same reaction is observed under
carbon dioxide. Neither a η2 complex of the formed diyne
nor a compound incorporating carbon dioxide is formed,
as found for the corresponding pentamethylcyclopenta-
dienyl complex.
The comparison of the reactions of 1-3 with carbon
dioxide illustrates the fact that the stability of the bis-
(acetylides) depends on the substituents. Compounds 1
and 3 initially are oxidized followed by an insertion of
carbon dioxide into the intermediates, as shown in the
When using the unsubstituted Cp compound [Cp2Ti-
Sch em e 5

Reactions of σ-Alkynyl Titanocene(III) Complexes
Organometallics, Vol. 20, No. 25, 2001 5293
Sch em e 6
dissociation, the lifetime of the Cp complex is too short
to give a reaction with carbon dioxide. An alternative
reasoning point could be that the Ti-C bond is more
activated in the case of Cp*2Ti(CtC-t-Bu).
In all of these reactions the influence of the substit-
uents on the reactions of the complexes [Cp*2Ti(Ct
CR)2Li(THF)n] (R ) SiMe3 (1), t-Bu (2), Ph (3)) with
carbon dioxide is well documented. Additionally, the
influence of the ligands Cp and Cp*, used in these and
other similar systems, can be compared.
Str u ctu r a l In vestiga tion s. The complex [(Cp*2Ti-
(CtCSiMe3)2Li(THF)] (1) was investigated by X-ray
diffraction.18 However, the poor quality of the crystals
made it impossible to discuss bond lengths and angles
in detail. Nevertheless, connectivity has been estab-
lished. The same applies to the complex [Cp2Ti(CtC-
t-Bu)2Li(THF)2].19 Interestingly, the Cp* compound 1
contains only one THF molecule coordinated to the
lithium, while there are two for the Cp analogue. Steric
interactions between the THF molecules and the Cp*
ligands seem to be obvious reasons for this observation.
Still, the comparable complex [(η5-C5HMe4)2Ti(Ct
CSiMe3)Li(THF)2] contains two THF ligands again.12d
The complexes Cp*2Ti(CtC-t-Bu) (5) and Cp* Ti(O2-
2
CCtC-t-Bu) (7) were also investigated by X-ray diffrac-
tion. Table 1 lists crystallographic data. The molecular
structures are shown in Figures 1 and 2.
The structure of complex 5 consists of a bent metal-
locene in which the titanium atom is coordinated by the
midpoints of the pentamethylcyclopentadienyl rings and
the carbon atom of the acetylide unit. The Ti-C bond
length in the alkynyl complex 5 (2.108(6) Å) is shorter
than that found in the corresponding alkyl compound
Cp*2Ti(CH2-t-Bu) (2.231(5) Å).2
(CtC-t-Bu)2Li(THF)2], which corresponds to the Cp*
complex 2, in the reaction with carbon dioxide at room
temperature, no insertion product such as complex 7
was observed. Instead, a binuclear complex with a
bridging butadiyne, [Cp2Ti]2[µ-η2(1,3):η2(2,4)-t-BuC2C2t-
Bu],16 was obtained (Scheme 9).
Sch em e 7
The structure of complex 7 consists of a bent metal-
locene in which the titanium atom is tetracoordinated
by the midpoints of the pentamethylcyclopentadienyl
rings and the two carboxylate oxygens. The TiO bond
lengths (Ti-O1 ) 2.178(2) Å, Ti-O2 ) 2.185(3) Å) are
longer compared to those in complex Cp*2TiO2COTi-
Cp*2,20 where distances between 2.144(4) and 2.151(4)
Å are found.
The triple bonds are different in both molecules (5,
1.204(6) Å; 7, 1.173(5) Å). The shortening in 7 is very
likely caused by the influence of the carboxylate groups.
The triple bond is, as expected, almost linear in both
(16) (a) Rosenthal, U.; Ohff, A.; Tillack, A.; Baumann, W.; Go¨rls, H.
J . Organomet. Chem. 1994, 468, C4. (b) Sekutowski, D. G.; Stucky, G.
D. J . Am. Chem. Soc. 1976, 98, 1376.
(17) Pulst, S.; Arndt, P.; Heller, B.; Baumann, W.; Kempe, R.;
Rosenthal, U. Angew. Chem. 1996, 108, 1175; Angew. Chem., Int. Ed.
Engl. 1996, 35, 1112.
(18) Crystal data for 1 (crystals were obtained from a solution of
n-hexane/THF): 0.3 × 0.2 × 0.2 mm, dark red prisms, space group
Cmc21, orthorhombic, a ) 12.969(3) Å, b ) 16.121(3) Å, c ) 18.053(4)
Å, V ) 3774(1) Å3, Z ) 4, Fobsd ) 1.041 g cm-3, 5543 reflections
measured, 1653 were independent of symmetry, of which 1034 were
observed (I g 2σ(I)), R1 ) 0.095, wR2(all data) ) 0.310, 131 param-
eters. The Cp* ligands, the SiMe3 groups, and the coordinated THF
molecule are disordered.
This complex previously has been prepared by the
reaction of t-BuCtCCtC-t-Bu with 2 equiv of “Cp2Ti”16a
or by the dimerization of the titanium(III) complex [Cp2-
TiCtC-t-Bu].17 The different reactions of the titanocene
complex [Cp2Ti(CtC-t-Bu)2Li(THF)2] and the above-
mentioned permethyltitanocene complex [Cp*2Ti(CtC-
t-Bu)2Li(THF)] (2) with carbon dioxide may result from
different stabilities and reactivities of the titanium(III)
species Cp2TiCtC-t-Bu and Cp*2TiCtC-t-Bu. After
(19) Crystal data for [Cp2Ti(CtC-t-Bu)2][Li(THF)2] (crystals were
obtained from a solution of n-hexane/THF): 0.2 × 0.1 × 0.1 mm, brown
prisms, space group P21/c, monoclinic, a ) 10.761(1) Å, b ) 17.698(2)
Å, c ) 30.727(3) Å, â ) 92.287(9)°, V ) 5847.2(10) Å3, Z ) 4, Fobsd
)
1.117 g cm-3, 7638 reflections measured, 7174 were independent of
symmetry, of which 4176 were observed (I g 2σ(I)), R1 ) 0.079, wR2-
(all data) ) 0.327, 614 parameters.
(20) Burlakov, V. V.; Dolgushin, F. M.; Yanovsky, A. I.; Struchkov,
Yu. T.; Shur, V. B.; Rosenthal, U.; Thewalt, U. J . Organomet. Chem.
1996, 522, 241.

5294 Organometallics, Vol. 20, No. 25, 2001
Kirchbauer et al.
Sch em e 8
complexes (7, C21-C22-C23 ) 175.5(5)°; 5, Ti-C13-
C14 ) 176.1(5)°, C13-C14-C15 ) 177.8(5)°).
reactivities of the Ti(III) intermediates [Cp2TiCtC-t-
Bu] and Cp*2TiCtC-t-Bu, formed by dissociation of the
starting materials. Only the permethyltitanocene com-
plex Cp*2TiCtC-t-Bu could be isolated in n-hexane, and
it was trapped in THF in the reaction of 2 with carbon
dioxide by isolating Cp*2Ti(O2CCtC-t-Bu) (7). The
lifetime of the corresponding titanocene derivative [Cp2-
TiCtC-t-Bu] is shorter, and it seems to be so unstable
Con clu sion s
The course of the reaction of Cp*2TiCl with lithium
acetylides is governed by the solvents used. The Ti(III)
complexes Cp*2Ti(σ-CtCR) are formed only in n-hex-
ane. In THF the corresponding “ate” complexes [Cp*2-
Ti(CtCR)2Li(THF)n] were obtained.
The reactions of the titanocene complex [Cp2Ti(Ct
C-t-Bu)2Li(THF)2] and the corresponding permethylti-
tanocene complex [Cp*2Ti(CtC-t-Bu)2Li(THF)] (2) with
carbon dioxide epitomize the different stabilities and
Sch em e 9
F igu r e 1. ORTEP view of 5 (30% probability level for the
thermal ellipsoids). For clarity, hydrogen atoms and the second
part of the disordered t-Bu group have been omitted. Selected
bond lengths (Å) and angles (deg): Ti-C13 ) 2.108(6), C13-
C14 ) 1.204(6), C14-C15 ) 1.474(7); Ti-C13-C14 ) 176.1-
(5), C13-C14-C15 ) 177.8(5).
Ta ble 1. Cr ysta llogr a p h ic Da ta of 5 a n d 7
5
7
cryst color, habit
cryst syst
space group
lattice constants
a (Å)
brown, prism
monoclinic
P21/c
green, prism
monoclinic
P21
14.556(3)
12.015(2)
14.685(3)
108.45(3)
4
2436.3(8)
1.089
10.192(2)
9.713(2)
14.011(3)
110.14(3)
2
1302.2(5)
1.131
b (Å)
c (Å)
â (deg)
·
cell vol (Å3)
density (g cm-3
)
F igu r e 2. ORTEP view of 7 (30% probability level for the
thermal ellipsoids). For clarity, hydrogen atoms and the second
part of the disordered t-Bu group have been omitted. Selected
bond lengths (Å) and angles (deg): Ti-O1 ) 2.178(2), Ti-O2
) 2.185(3), C21-C22 ) 1.471(5), C22-C23 ) 1.173(5), C21-
O1 ) 1.257(4), C21-O2 ) 1.256(4); O1-Ti-O2 ) 59.94(9),
O1-C21-O2 ) 120.3(3), Ti-C21-C22 ) 177.8(3), C21-C22-
C23 ) 175.5(5).
temp (Κ)
200(2)
0.358
293(2)
0.347
µ(Μï ΚR) (mm-1
)
no. of rflns (measd)
no. of rflns (indep)
no. of rflns (obsd)
no. of params
7157
7039
3734
4121
1743
3499
241
269
R1(I > 2σ(I))
wR2(all data)
0.066
0.044
0.167
0.113

Reactions of σ-Alkynyl Titanocene(III) Complexes
Organometallics, Vol. 20, No. 25, 2001 5295
warmed to room temperature and 0.477 g (1.35 mmol) of Cp*2-
TiCl was added. The solution was stirred for 24 h, the solvent
was removed in vacuo, and the residue was suspended in 10
mL of n-hexane. After filtration and crystallization at -78 °C,
0.560 g (63%) of blue crystals was obtained, which was filtered
and dried in vacuo: mp >270 °C. Anal. Calcd for C44H56LiO2-
Ti (671.75): C, 78.67; H, 8.40. Found: C, 78.55; H, 8.19. IR
(Nujol; ν (cm-1)): 2013 s, 1591 m, 1585 m, 1038 m, 1025 m,
890 m, 688 m. MS (70 eV; EI m/z (u)): 671 [M]+, 520 [M -
2LiTHF]+, 419 [M - 2LiTHF - C2Ph]+, 318 [Cp*2Ti]+.
P r ep a r a tion of Cp *2Ti(CtCMe) (4). A 0.70 mL amount
(1.74 mmol) of n-butyllithium (2.5 M/n-hexane) was dissolved
in 10 mL of n-hexane under Ar. The argon was carefully
removed in vacuo, and the flask was filled with propyne. The
solution was stirred for 1 h at room temperature, and the
resulting suspension was slowly added to the deep blue
solution of 0.617 g (1.74 mmol) of Cp*2TiCl in 10 mL of
n-hexane. The mixture was stirred for 2.5 h, and the resulting
brown-green solution was concentrated to 7-8 mL. After
filtration and 1 day at -78 °C, 0.411 g (66%) of dark green
complex 4 had formed, which was separated from the mother
liquor, washed with cold n-hexane, and dried in vacuo: mp
163-165 °C. Anal. Calcd for C23H33Ti (357.40): C, 77.30; H,
9.31. Found: C, 77 0.24; H, 8.98. MS (70 eV; EI m/z (u)): 357
[M]+, 318 [Cp*2Ti]+, 317 [Cp*2Ti - H]+. The analytical and
spectroscopic data of the sample are identical with those
described in ref 2.
P r ep a r a tion of Cp *2Ti(CtC-t-Bu ) (5). A solution of 0.21
mL of 3,3-dimethylbutyne (1.7 mmol) in 10 mL of n-hexane
was cooled to -78 °C and treated with 0.68 mL (1.7 mmol) of
n-butyllithium (2.5 M/n-hexane). After 15 min the solution was
warmed to room temperature and the resulting white suspen-
sion was added to the deep blue solution of 0.606 g (1.7 mmol)
of Cp*2TiCl in 10 mL of n-hexane. The mixture rapidly
changed from blue to brown. After filtration and concentration
of the solution to 5 mL, the crystallization at -78 °C gave
greenish brown crystals which were separated from the mother
liquor, washed with cold n-hexane, and dried in vacuo to give
0.430 g (63%) of complex 5: mp 129-131 °C. Anal. Calcd for
that it dimerizes very quickly with formation of [Cp2-
Ti]2[µ-η2(1,3):η2(2,4)-t-BuC2C2t-Bu] before reacting with
carbon dioxide.
An additional observation which supports these con-
clusions comes from the cleavage of Me3SiCtCCt
CSiMe3 in the system Cp2TiCl2/magnesium, which gives
the dimeric titanium(III) complex [Cp2Ti(CtCSiMe3)]2.8
The system Cp*2TiCl2/magnesium/Me3SiCtCCtCSiMe3
yields, via a cleavage of the central C-C single bond of
the diyne and coupling with another diyne, the complex
Cp*2 Ti[µ-η2 (1,2):η1 (3)-Me3 SiCtCCdC(SiMe3 )Ct
CSiMe3].9 In both cases the formation of mono(alkynyl)-
titanium(III) complexes L2Ti(CtCSiMe3) is assumed,
which for L ) Cp dimerizes quickly to [Cp2Ti(Ct
CSiMe3)]2 or alternatively for R ) Cp* can insert an
diyne to yield the complex Cp*2Ti[µ-η2(1,2):η1(3)-Me3-
SiCtCCdC(SiMe3)CtCSiMe3].
In both of the described examples the Cp* ligands
stabilize the mono(alkynyl) complexes and prevent their
dimerization.
Exp er im en ta l Section
All operations were carried out under an inert atmosphere
(argon) using standard Schlenk techniques. Prior to use,
solvents were freshly distilled from sodium tetraethylalumi-
nate under argon. Deuterated solvents were treated with
sodium or sodium tetraethylaluminate, distilled, and stored
under argon. Infrared spectra were recorded with a Nicolet
Magna 550 (Nujol mulls using KBr plates). Mass spectrom-
eter: AMD 402 (EI: electron impact measurements). NMR:
Bruker ARX 400 at 9.4 T (chemical shifts given in ppm relative
to TMS). Melting points were measured in sealed capillaries
on a Bu¨chi 535 apparatus. Elemental analyses: Leco CHNS-
932 elemental analyzer.
P r ep a r a tion of [Cp *2Ti(CtCSiMe3)2Li(THF )] (1). A 0.86
mL amount (6.2 mmol) of trimethysilylacetylene was dissolved
in 5 mL of THF. The colorless solution was cooled to -78 °C,
and 2.48 mL (6.2 mmol) of n-butyllithium (2.5 M/n-hexane)
was added. After the mixture was warmed to room tempera-
ture, 1.1 g (3.1 mmol) of Cp*2TiCl was added and the deep
blue solution was stirred for 24 h. The solvents were distilled
in vacuo, and the brown residue was suspended in 10 mL of
n-hexane. After filtration and crystallization at -78 °C, 0.980
g (54%) of 1 was obtained, which was filtered and dried in
C
26H39Ti (399.48): C, 78.18; H, 9.84. Found: C, 78.24; H, 9.75.
IR (Nujol; ν (cm-1)): 2721 w, 2071 s. MS (70 eV; EI m/z (u)):
399 [M]+, 317 [Cp*2Ti - H]+.
P r ep a r a tion of 6. A 220 mg amount (0.37 mmol) of 1 was
dissolved in 10 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 with 3 mL
portions of n-hexane. Cooling for 48 h at -78 °C afforded 83
mg (40%) of a brown crystalline product, which was separated
from the mother liquor by filtration and dried in vacuo: mp
208 °C. Anal. Calcd for C31H48O2Si2Ti (556.77): C, 66.87; H,
8.69. Found: C, 67.02; H, 8.89. IR (Nujol; ν (cm-1)): 2095 m,
2076 m, 1627 vs, 1491 m, 1233 s, 1022 m, 853 vs, 837 vs. MS
(70 eV; CI, m/z (u)): 556 [M]+, 541 [M - CH3]+, 513 [M - CH3
vacuo: brown crystals; mp >265 °C. Anal. Calcd for C34H56
-
LiOTiSi2 (591.81): C, 69.00; H, 9.54. Found: C, 68.66; H, 9.19.
IR (Nujol; ν (cm-1)): 1954 vs, 1922 sh, 1243 vs, 1036 s, 882
sh, 837 vs, 755 s, 691 s. MS (70 eV; m/z (u)): 519 [M - THF]+,
512 [M - THF]+, 415 [M - LiTHF - C2SiMe3]+, 318 [Cp*2-
Ti]+.
1
- CO]+, 422 [M - Cp* + H]+, 318 [Cp*2Ti]+. H NMR (THF-
P r ep a r a tion of [Cp *2Ti(CtC-t-Bu )2Li(THF )] (2). A solu-
tion of 1.30 mL of 3,3-dimethylbutyne-2 (10.6 mmol) in 15 mL
of THF was cooled to -78 °C and treated with 4.24 mL (10.6
mmol) n-butyllithium (2.5 M/n-hexane). After 15 min the
solution was warmed to room temperature and 1.89 g (5.3
mmol) of Cp*2TiCl was added. The solution was stirred for 24
h, the solvent was removed in vacuo, and the residue was
suspended in 10 mL of n-hexane. After filtration and crystal-
lization at -78 °C, 2.001 g (68%) of green crystals was
obtained, which was filtered and dried in vacuo: mp 178-
179 °C. Anal. Calcd for C36H56LiOTi (559.66): C, 77.26; H,
10.09. Found: C, 77.24; H, 9.85. IR (Nujol; ν (cm-1)): 2030 s,
1237 vs, 1199 m, 1036 s, 883 m. MS: (70 eV; EI m/z (u)): 399
[M - LiTHF - C2-t-Bu]+, 318 [Cp*2Ti]+.
d8, 297 K): δ 0.14 (s, 9 H, SiMe3); 0.24 (s, 9 H, SiMe3), 1.92 (s,
30 H, Cp*). 13C NMR (THF-d8, 297 K): δ -0.3; 0.8 (2 SiMe3);
12.1 (C5Me5); 108.8; 121.6 (CtC); 126.5 (C5Me5); 163.2; 167.1
(C-CO); 221.9 (CTi).
P r ep a r a tion of Cp *2Ti(O2CCtC-t-Bu ) (7). (a ) F r om
Com p lex 2. A 267 mg amount (0.48 mmol) of 2 was dissolved
in 10 mL of THF. The green solution was stirred for 3 h at
room temperature under an atmosphere of CO2. The THF was
evaporated under vacuum, and the residue was extracted three
times with 3 mL portions of n-hexane. Cooling for 48 h at -40
°C afforded 90 mg (42.5%) of green crystals of 7: mp 196-
197 °C.
(b) F r om Com p lex 5. A 176 mg amount (0.44 mmol) of 5
was dissolved in 10 mL of n-hexane under argon, and the
resulting brown solution was filtered. Argon was then carefully
removed in vacuo, and the flask with the solution was filled
with CO2 at room temperature. The color of the solution
P r ep a r a tion of [Cp *2Ti(CtCP h )2Li(THF )2] (3). A solu-
tion of 0.30 mL of phenylacetylene (2.7 mmol) in 15 mL of THF
was cooled to -78 °C and treated with 1.1 mL (2.7 mmol) of
n-butyllithium (2.5 M/n-hexane). After 15 min the solution was

5296 Organometallics, Vol. 20, No. 25, 2001
Kirchbauer et al.
rapidly changed to green. After 1 day greenish blue crystals
had formed which were separated, washed with cold n-hexane,
and dried in vacuo to give 64 mg of complex 7. Subsequent
cooling of the mother liquor to -78 °C gave an additional 110
mg of 7. The total yield is 174 mg (89%): mp 204-205 °C.
(0.98 mmol) of Cp*2TiCl was added. The solution was stirred
for 12 h, the solvent was removed in vacuo, and the residue
was extracted with 10 mL of n-hexane at 60 °C. After filtration
and crystallization at -78 °C, 0.150 g (33%) of dark blue
crystals was formed, which were filtered and dried in vacuo:
mp 128 °C. Anal. Calcd for C29H35O2Ti (463.48): C, 75.15; H,
7.61. Found: C, 74.80; H, 7.44. IR (Nujol; ν (cm-1)): 2721 w,
2213 vs, 1520 s, 1412 vs, 947 m, 691 m, 616 m. MS (70 eV; EI,
m/z (u)): 463 [M]+, 317 [Cp*2Ti - H]+.
Anal. Calcd for
C27H39O2Ti (443.49): C, 73.12; H, 8.86.
Found: C, 72.61; H, 8.82. IR (Nujol; ν (cm-1)): 2720 w, 2267
w, 2218 vs, 1520 s, 1416 vs, 852 s. MS (70 eV; CI, m/z (u)):
443 [M]+, 317 [Cp*2Ti - H]+.
P r ep a r a tion of Cp *2Ti(CtCP h )2 (8). (a ) F r om Com p lex
3. A 140 mg (0.21 mmol) amount of 3 was dissolved in 10 mL
of THF. The green solution was stirred for 3 h at room
temperature under an atmosphere of CO2. The THF was
evaporated under vacuum, and the residue was extracted three
times with 3 mL portions of n-hexane. Cooling for 48 h at -40
°C afforded 35 mg (32%) of red crystals of 8.
Rea ction of [Cp 2Ti(CtC-t-Bu )2Li(THF )2] w ith Ca r bon
Dioxid e. A 150 mg amount (0.31 mmol) of [Cp2Ti(CtC-t-Bu)2]-
[Li(THF)2] was dissolved in 6 mL of THF. The solution was
stirred for 3 h under an atmosphere of CO2 at room temper-
ature. The solvent was removed, and the residue was extracted
three times with 3 mL portions of diethyl ether. Cooling of
the concentrated green solution for 48 h at -78 °C afforded
65 mg (82.0%) of green [Cp2Ti]2[µ-η2(1,3):η2(2,4)-t-BuC2C2t-Bu],
which was separated from the mother liquor by filtration and
dried in vacuo. The analytical and spectroscopic data of the
sample are identical with those described in ref 16a.
X-r a y Cr ysta llogr a p h ic Stu d y of Com p lexes 5 a n d 7.
Data were collected with a STOE-IPDS diffractometer using
graphite-monochromated Mo KR radiation. The structures
were solved by direct methods (SHELXS-86)21 and refined by
full-matrix least-squares techniques against F2 (SHELXL-
93).22 The hydrogen atoms were included at calculated posi-
tions. All other non-hydrogen atoms, except the atoms of the
disordered groups, were refined anisotropically. Cell constants
and other experimental details were collected and recorded
in Table 1. XP (SIEMENS Analytical X-ray Instruments, Inc.)
was used for structure representations.
(b) By Sa lt Elim in a tion . A 0.59 mL (5.6 mmol) solution
of phenylacetylene in 5 mL of THF was cooled to -78 °C and
treated with 2.24 mL (5.6 mmol) of n-butyllithium (2.5 M/n-
hexane). After 10 min the solution was warmed to room
temperature and stirred for 1 h. A 1.09 g amount (2.8 mmol)
of Cp*2TiCl2 was added, the solution was stirred for 12 h, the
solvent was removed in vacuo, and the residue was extracted
with 10 mL of n-hexane at 60 °C. After filtration and
crystallization at -78 °C, 0.685 g (47%) of red crystals was
formed, which was filtered and dried in vacuo: mp 173-177
°C. Anal. Calcd for C36H40Ti (520.59): C, 83.06; H, 7.74.
Found: C, 82.88; H, 7.92. IR (Nujol; ν (cm-1)): 2068 m, 1592
m, 1482 vs, 1261 vs, 1202 m, 758 vs. 1H NMR (THF-d8, 297
K): δ 2.09 (s, 30 H, Cp*), 7.08 (2 H, p-Ph), 7.18 (4 H; m-Ph),
7.26 (4 H, o-Ph). 13C NMR (THF-d8, 297 K): δ 13.3 (C5Me5),
122.1 (i-Ph), 123.9 (C5Me5), 126.4 (p-Ph), 127.9 (CPh), 128.6
(m-Ph), 131.1 (o-Ph), 162.3 (CTi). MS: (70 eV; CI, m/z (u)):
520 [M]+, 505 [M - Me]+, 317 [Cp*2Ti - H]+.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 5 and 7. This material is available
free of charge via the Internet at http://pubs.acs.org.
P r ep a r a tion of Cp *2Ti(O2CCtCP h ) (9). A solution of
0.12 mL of phenylacetylene (1.07 mmol) in 20 mL of THF was
cooled to -78 °C and treated with 0.43 mL (1.07 mmol) of
n-butyllithium (2.5 M/n-hexane). After 10 min the solution was
warmed to room temperature and stirred for 1 h. Carbon
dioxide was bubbled into the solution for 30 min, and 0.346 g
OM010404F
(21) Sheldrick, G. M. Acta Crystallogr. 1990, A 46, 467.
(22) Sheldrick, G. M. SHELXL-93; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.